Patent Application
20240279145
The present invention relates to a process for workup of a methanol/water mixture which is employed in the production of alkali metal methoxides in a reaction column. The mixture is distillatively separated in a rectification column. The vapours obtained at the upper end of the rectification column are compressed in at least two stages and the energy of the vapours compressed in each case is advantageously transferred to bottoms and side streams of the rectification column. This allows particularly energy-efficient use of the energy of the compressed vapours in the process according to the invention.
The process for workup of a methanol/water mixture is employed in the production of alkali metal methoxides in a reaction column, wherein methanol and alkali metal hydroxide solution are reacted with one another in countercurrent in a reaction column. Alkali metal methoxide dissolved in methanol is withdrawn at the lower end and a methanol/water mixture which is worked up with the workup process according to the invention is withdrawn at the upper end. The energy of the compressed vapours may additionally be used for operating the reaction column or for operating a reaction column in which a process for transalcoholization of alkali metal alkoxides is performed.
Alcohol/water mixtures are obtained for example in the production of alkali metal alkoxides from aqueous, optionally alcohol-containing, alkali metal hydroxide solution and alcohol. This process employs in particular methanol and ethanol as the alcohol.
Alkali metal alkoxides are used as strong bases in the synthesis of numerous chemicals, for example in the production of pharmaceutical or agrochemical active ingredients. Alkali metal alkoxides are also used as catalysts in transesterification and amidation reactions.
Alkali metal alkoxides (MOR) are produced by reactive distillation of alkali metal hydroxides (MOH) and alcohols (ROH) in a countercurrent distillation column, wherein the water of reaction formed according to the following reaction <1> is removed with the distillate.
Such a process principle is described, for example, in U.S. Pat. No. 2,877,274 A, wherein aqueous alkali metal hydroxide solution and gaseous methanol are run in countercurrent in a reactive rectification column. This process is described again in generally unchanged form in WO 01/42178 A1.
Similar processes, which, however, additionally employ an entraining agent such as benzene, are described in GB 377,631 A and U.S. Pat. No. 1,910,331 A. This entraining agent is used to separate water and the water-soluble alcohol. In both patent specifications the condensate is subjected to a phase separation to separate off the water of reaction. A further similar process is the reaction of an alkali metal alkoxide with another alcohol in a reaction column (“transalcoholization”) according to DE 27 26 491 A1.
Correspondingly, DE 96 89 03 C describes a process for continuous production of alkali metal alkoxides in a reaction column, wherein the water-alcohol mixture withdrawn at the top of the column is condensed and then subjected to a phase separation. The aqueous phase is discarded and the alcoholic phase is returned to the top of the column together with the fresh alcohol. EP 0 299 577 A2 describes a similar process, wherein the water in the condensate is separated off with the aid of a membrane.
The most industrially important alkali metal alkoxides are those of sodium and potassium, especially the methoxides and ethoxides. Their synthesis is frequently described in the prior art, for example in EP 1 997 794 A1.
The syntheses of alkali metal alkoxides by reactive rectification described in the prior art typically afford vapours comprising the employed alcohol and water. It is advantageous for economic reasons to reuse the alcohol comprised in the vapours as a reactant in the reactive distillation. The vapours are therefore typically supplied to a rectification column and the alcohol present therein is separated off (described for example in GB 737 453 A and U.S. Pat. No. 4,566,947 A). The thus recovered alcohol is then supplied to the reactive distillation as a reactant for example.
Alternatively or in addition a portion of the alcohol vapour may be utilized for heating the rectification column (described in WO 2010/097318 A1). However, this requires that the vapour be compressed in order to achieve the temperature level required for heating the rectification column. Especially a multistage compression of the vapour is thermodynamically advantageous. The vapour is cooled between the compression stages here. The intermediate cooling also ensures that the maximum allowable temperature of the compressor is not exceeded. The disadvantage of this cooling performed in the customary processes is that the energy thus withdrawn dissipates without being utilized.
There is therefore a need for improved processes for workup of an alcohol/water mixture as employable in particular in the context of a process for producing alkali metal alkoxides. This process shall feature a particularly efficient utilization of the energy present in the compressed vapours for operation of the rectification column. The process shall accordingly allow energy-efficient utilization of the heat liberated during compression and cooling of the vapours.
The present invention relates to a process for producing at least one alkali metal alkoxide of formula MAOR, wherein R is methyl, and wherein MA is a metal selected from sodium, potassium, preferably sodium.
In the process according to the invention for producing at least one alkali metal alkoxide a mixture G comprising water and methanol ROH is obtained which is employed in a process for workup of a mixture G comprising water and alcohol ROH, wherein R is methyl, and is worked up using the process for workup of a mixture G. The process for workup of a mixture G is performed in a rectification column and is accordingly a distillative process.
In a further, preferred aspect the present invention relates to a process for transalcoholization of alkali metal alkoxides. In this process the alcohol of an alkali metal alkoxide McOR′ is substituted by another alcohol R″OH by reacting McOR′ with R″OH in a reaction column to afford McOR″, wherein the process utilizes energy from certain vapour streams from the process according to the invention for workup of a mixture G for operation.
Aqueous NaOH SAE2 <102> is reacted in a reaction column RRA <100> with methanol SAE1 <103> to afford the corresponding sodium alkoxide. At the top of the reaction column RRA <100> an aqueous NaOH solution is added as reactant stream SAE2 <102>. It is alternatively also possible to add a methanolic NaOH solution as reactant stream SAE2 <102>. To produce the corresponding potassium methoxide aqueous or methanolic KOH solution is added as reactant stream SAE2 <102>. Above the bottom of the reaction column RRA <100> methanol is added in vapour form as reactant stream SAE1 <103>.
At the bottom of the reaction column RRA <100> a mixture of the corresponding methoxide in the methanol SAP* <104> is withdrawn. The bottoms evaporator VSA <105> and the optional evaporator VSA′<106> at the bottom of the column RRA <100> are used to adjust the concentration of the sodium methoxide solution SAP* <104> to the desired value.
At the top of the reaction column RRA <100> a vapour stream SAB <107> is withdrawn. A portion of the vapour stream SAB <107> is condensed in the condenser KRRA <108> and applied in liquid form to the top of the reaction column RRA <100> as reflux. However, condenser KRRA <108> and the establishment of the reflux are optional.
The obtained vapour SAB <107> is in whole or in part sent to a rectification column, a water/methanol column, RDA <300> as mixture G. The rectification column RDA <300> contains internals <310>. Therein the mixture G is distillatively separated and the methanol is distillatively recovered as vapour SOA <302> overhead.
A reflux may be established at the rectification column RDA <300>. In this case a portion of the vapour SOA <302> is condensed in a condenser KRD <407> and then recycled into the rectification column RDA <300>. In the embodiments where no reflux is established the remaining portion of SOA <302>/the complete vapour stream SOA <302> is precompressed using compressor VDAB2 <303>. A portion of this precompressed vapour is recycled to the reaction column RRA <100> where it is employed as reactant stream SAE1 <103>.
The remaining portion of SOA <302> is passed to the compressor VDx <401> where it is further compressed to afford vapour stream SOA1 <403>, from which energy may be withdrawn in the optional intermediate cooler WTX <402>.
The vapour stream SOA1 <403> is once again compressed using compressor VDx <405> and the resulting vapour SOA2 <404> is then sent to the evaporator VSRD <406> at the bottom of the rectification column RDA <300> for heating, after which fresh methanol <408> is optionally added and it is returned to the rectification column RDA <300> as reflux. If a reflux is established at the rectification column RDA <300>, the stream SOA2 <404> may be mixed with the reflux, i.e. the condensate, from KRD <407> before recycling to RDA <300>, and fed into RDA <300> together therewith. Obtained at the bottom of the rectification column RDA <300> is a water stream SUA <304> which may be at least partially (stream SUA1 <320>) recycled to the rectification column RDA <300>, wherein said stream may be passed through the evaporator VSRD <406> and/or VSRD′ <410>.
This embodiment corresponds to the one described in
The inventive embodiment has the following differences from the aforementioned embodiments:
These differences have the result that the energy of the vapour SOA1 <403> may be more efficiently utilized for heating the rectification column RDA <300> compared to the embodiments according to
At the top of the reaction column RRB <200> an aqueous KOH solution is added as reactant stream SBE2 <202>. It is alternatively possible to also add a methanolic KOH solution as reactant stream SBE2 <202>. Above the bottom of the reaction column RRB <200> methanol is added in vapour form as reactant stream SBE1 <203>.
At the bottom of the reaction column RRB <200> a mixture of the corresponding methoxide in methanol SBP* <204> is withdrawn. The bottoms evaporator VSB <205> and the optional evaporator VSB′ <206> at the bottom of the column RRB <200> are used to adjust the concentration of the potassium methoxide solution SBP* <204> to the desired value.
At the top of the reaction column RRB <200> a vapour stream SBB <207> is withdrawn. A portion of the vapour stream SBB <207> is condensed in the condenser KRRB <208> and applied in liquid form to the top of the reaction column RRB <200> as reflux. However, condenser KRRB <208> and the establishment of the reflux are optional.
The obtained vapour SBB <207> is supplied to the rectification column RDA <300> in admixture with the portion of the vapour SAB <107> not condensed in the condenser KRRA <108>.
A further difference from the embodiment according to
In a departure from
In addition,
Sodium methoxide solution SCE1 <602> is in a reaction column RRC <600> reacted in countercurrent with ethanol SCE2 <603> to afford sodium ethoxide and this is withdrawn as an ethanolic solution.
Withdrawn at the bottom of the reaction column RRC <600> is a bottoms product stream SCP <604> comprising sodium ethoxide.
At the top of the reaction column RRC <600> a vapour stream SCB <607> is withdrawn. At least a portion of the vapour stream SCB <607> is condensed in the condenser KRRC <608> and at least a portion thereof is applied in liquid form to the top of the reaction column RRC <600> as reflux. The vapour stream SCB <607> is withdrawn either in gaseous form upstream of the condenser KRRC <608> (marked by dashed line) and/or in liquid form downstream of the condenser KRRC <608> as stream <609>.
A side stream SZC <610> is preferably withdrawn from the reaction column RRC <600>, wherein energy is transferred to said stream via an intermediate evaporator VZC <611> and SZC <610> may subsequently be recycled to RRC <600>.
As the sodium methoxide solution SCE1 <602> it is preferable to utilize at least a portion of the bottoms streams SAP* <104> and SBP* <204> obtained in the reaction columns RRA <100> and RRB <200>.
The bottoms evaporator VSC′ <606> is heated via a heat transfer medium W1 <502>, in particular water, transported by a pump <501> which absorbs heat from SOA12 <4032> in the intermediate cooler WTX <402> and releases it in the bottoms evaporator VSC <606>.
Alternatively, energy may also be appropriately transferred to the bottoms evaporator VSC <606> or the other bottoms evaporator VSC <605> from another stream selected from SOA2 <404>, SOA11 <4031> and SOA1 <403> before separation into SOA11 and SOA12. Energy may likewise be transferred to the ethanol stream SCE1 <603>, the sodium methoxide solution SCE1 <602> or the side stream SZC <610> from at least one of the streams SOA1 <403>, SOA11 <4031>, SOA12 <4032>, SOA2 <404>.
The present invention relates to a process for producing at least one alkali metal alkoxide of formula MAOR, wherein R is methyl, and wherein MA is a metal selected from sodium, potassium, preferably sodium.
The process according to the invention comprises with steps (a) to (f) a process for workup of a mixture G comprising water and alcohol ROH, wherein R is methyl. ROH is accordingly methanol.
The process according to the invention for workup of a mixture G comprises steps (a) to (f) of the process according to the invention for producing at least one alkali metal alkoxide of formula MAOR.
The mixture G is especially gaseous, in which case it is also referred to as “vapours”. The mixture G is the tops stream from a reaction column in which the alcohol ROH has been reacted with an alkali metal hydroxide NaOH or KOH to afford the corresponding alkali metal alkoxide NaOR or KOR.
According to the invention at least a portion of the vapor stream SAB and, if step (α2) is performed, at least a portion of the vapor stream SBB is employed as the mixture G employed in step (a).
The vapor stream SAB is obtained in step (α1) (described at point 4.2.1).
The vapor stream SBB is obtained in optional step (α2) if this step is performed (described at point 4.2.2).
The vapor stream SBB is only obtained if the optional step (α2) is performed. If the optional step (α2) is performed, SBB is obtained and at least a portion of SBB is employed as mixture G, the at least a portion of SBB is employed as mixture G in admixture with SAB or separately from SAB.
In step (β) of the process at least a portion of the vapor stream SAB and, if step (α2) is performed, at least a portion of the vapor stream SBB is employed in admixture with SAB or separately from SAB as mixture G in step (a) of a process for workup of a mixture G comprising water and alcohol ROH.
According to the invention the mixture G comprising water and alcohol ROH is worked up with the process for workup of a mixture G.
In step (a) of the process according to the invention the mixture G is passed into a rectification column RDA and in RDA separated into at least one vapour stream SOA comprising ROH which is withdrawn at the upper end of RDA and at least one stream SUA comprising water which is withdrawn at the lower end of RDA.
“At least one vapour stream SOA comprising ROH which is withdrawn at the upper end of RDA” is to be understood as meaning that the vapour obtained at the upper end of RDA may be withdrawn there as one or more vapour streams. If said stream is withdrawn there in more than one vapour stream, the m vapour streams are referred to as “vapour stream SOA1”, “vapour stream SOAIII”, [ . . . ], “vapour stream SOAm”, wherein “m” indicates the number of vapour streams withdrawn at the upper end of RDA (in Roman numerals).
“At least one vapour stream SUA comprising water which is withdrawn at the lower end of RDA” is to be understood as meaning that water obtained at the lower end of RDA may be withdrawn there as one or more streams. If said stream is withdrawn there in more than one stream, the n streams are referred to as “stream SUAI”, “stream SUAII”, [ . . . ], “stream SUAn”, wherein “n” is the number of streams withdrawn at the lower end of RDA (in Roman numerals).
The mixture G may be introduced to the rectification column RDA via one or more feed points. It is introduced via two or more feed points for example in the embodiments in which step (α2) is performed in the process according to the preferred aspect of the invention and in step (β) at least a portion of the vapour stream SBB is employed separately from SAB as mixture G in step (a) of the process. In this embodiment the mixture G is thus introduced into the rectification column RDA as two separate streams.
In the embodiments of the present invention in which the mixture G is passed into the rectification column RDA as two or more separate streams it is advantageous when the feed points for the individual streams are at substantially the same height on the rectification column RDA.
In a preferred embodiment of step (a) of the process according to the invention the mixture G is in a rectification column RDA separated into a vapour stream SOA comprising ROH which is withdrawn at the upper end of RDA and a stream SUA comprising water which is withdrawn at the lower end of RDA.
Another term for “upper end of a rectification column” is “head”.
Another term for “lower end of a rectification column” is “bottom” or “foot”.
The pressure of the at least one vapour stream SOA is referred to as “pOA” and its temperature as “TOA”. This relates especially to the pressure and temperature of the at least one vapour stream SOA when it is withdrawn from the rectification column RDA in step (a).
The pressure pOA is especially in the range from 0.5 bar abs. to 8 bar abs., more preferably in the range from 0.6 bar abs. to 7 bar abs., more preferably in the range from 0.7 bar abs. to 6 bar abs., yet more preferably in the range from 1 bar abs. to 5 bar abs., and is most preferably 1 bar abs. to 4 bar abs.
The temperature TOA is especially in the range from 45° C. to 150° C., more preferably in the range from 48° C. to 140° C., more preferably in the range from 50° C. to 130° C., yet more preferably in the range from 60° ° C. to 120° C., most preferably in the range from 60° C. to 110° C.
Any desired rectification column known to those skilled in the art may be employed as rectification column RDA in step (a) of the process. The rectification column RDA preferably contains internals. Suitable internals are, for example, trays, unstructured packings or structured packings. As trays, use is normally made of bubble cap trays, sieve trays, valve trays, tunnel trays or slit trays. Unstructured packings are generally beds of random packing elements. Packing elements normally used are Raschig rings, Pall rings, Berl saddles or Intalox® saddles. Structured packings are for example marketed under the trade name Mellapack® from Sulzer. Apart from the internals mentioned, further suitable internals are known to a person skilled in the art and can likewise be used.
Preferred internals have a low specific pressure drop per theoretical plate. Structured packings and random packing elements have, for example, a significantly lower pressure drop per theoretical plate than trays. This has the advantage that the pressure drop in the rectification column RDA remains as low as possible and the mechanical power of the compressor and the temperature of the alkohol/water mixture to be evaporated therefore remain low.
When the rectification column RDA contains structured packings or unstructured packings these may be divided or in the form of an uninterrupted packing. However, at least two packings are typically provided, one packing above the feed point for the mixture G and one packing below the feed point for the mixture G. It is also possible to provide one packing above the feed point for the mixture G and two or more trays below the feed point of the mixture G. If an unstructured packing is used, for example a random packing, the random packing elements are typically disposed on a suitable support grid (for example sieve tray or mesh tray).
In step (a) of the process according to the invention the at least one vapour stream SOA comprising ROH is then withdrawn at the upper end of the rectification column RDA. The preferred mass fraction of ROH in this vapour stream SOA is ≥99% by weight, more preferably ≥99.6% by weight, yet more preferably ≥99.9% by weight, wherein the remainder is especially water.
Withdrawn at the lower end of RDA is at least one stream SUA comprising water which may preferably comprise <1% by weight, more preferably ≤5000 ppmw, yet more preferably ≤2000 ppmw of alcohol.
The withdrawal of the at least one vapour stream SOA comprising ROH at the top of the rectification column RDA is to be in particular understood as meaning in the context of the present invention that the at least one vapour stream SOA is withdrawn above the internals in the rectification column RDA as a top stream or as a side stream.
The withdrawal of the at least one stream SUA comprising water at the bottom of the rectification column RDA is to be in particular understood as meaning in the context of the present invention that the at least one stream SUA is withdrawn as a bottoms stream or at the lower tray of the rectification column RDA.
The rectification column RDA is operated with or without, preferably with, reflux.
“With reflux” is to be understood as meaning that the vapour stream SOA withdrawn at the upper end of the rectification column RDA is not completely discharged but rather partially condensed and returned to the respective rectification column RDA. In the cases where such a reflux is established the reflux ratio is preferably 0.0001 to 1, more preferably 0.0005 to 0.9, yet more preferably 0.001 to 0.8.
A reflux may be established such that a condenser KRD is attached at the top of the rectification column RDA. In the condenser KRD the respective vapour stream SOA is partially condensed and returned to the rectification column RDA. Generally and in the context of the present invention a reflux ratio is to be understood as meaning the ratio of the proportion of the mass flow withdrawn from the column (kg/h) that is recycled to the respective column in liquid form (reflux) to the proportion of this mass flow (kg/h) that is discharged from the respective column in liquid form or gaseous form.
In step (b) of the process according to the invention at least one side stream SZA is withdrawn from RDA and recycled to RDA.
In a preferred embodiment of step (b) of the process according to the invention a side stream SZA is withdrawn from RDA and recycled to RDA.
“Side stream SZA from RDA” is according to the invention to be understood as meaning that the stream is withdrawn at a withdrawal point EZA below the head and above the bottom of RDA and in particular additionally recycled to RDA at a feed point ZZA (this is the point at which the respective side stream SZA is recycled to the respective rectification column RDA) below the head and above the bottom of RDA.
This is to be understood as meaning in particular that the withdrawal point EZA and preferably also the feed point ZZA of the respective side stream SZA on the rectification column RDA is below the withdrawal points EOA for all vapour streams SOA withdrawn from RDA, preferably at least 1, more preferably at least 5, yet more preferably at least 10, theoretical plates below the withdrawal point EOA for the vapour stream SOA withdrawn from RDA whose withdrawal point EOA is furthest down the rectification column RDA.
This is also to be understood as meaning in particular that the withdrawal point EZA and preferably also the feed point ZZA of the respective side stream SZA on the rectification column RDA is above the withdrawal points EUA for all streams SUA withdrawn from RDA, preferably at least 1, more preferably at least 2, yet more preferably at least 4, theoretical plates above the withdrawal point EUA for the stream SUA whose withdrawal point EUA is furthest up the rectification column RDA.
In the cases in which at least one vapour stream SOA is at least partially recycled into the rectification column RDA (which is the case when a reflux is established at the rectification column RDA for example) the feed point ZOA (i.e. the point at which the at least one vapour stream SOA is at least partially recycled into the rectification column RDA) of the at least one vapour stream SOA is especially also above the withdrawal points EZA and especially also above the feed points ZZA for all side streams SZA withdrawn from RDA, preferably at least 1, more preferably at least 5, yet more preferably at least 10, theoretical plates above the highest point of all withdrawal and feed points for all side streams SZA withdrawn from RDA.
In the cases in which at least one stream SUA is at least partially recycled into the rectification column RDA the feed point ZUA (i.e. the point at which the at least one stream SUA is at least partially recycled into the rectification column RDA) of the at least one stream SUA is especially also below the withdrawal points EZA and especially also below the feed points ZZA for all side streams SZA withdrawn from RDA, preferably at least 1, more preferably at least 2, yet more preferably at least 4, theoretical plates below the lowest point of all withdrawal and feed points for all side streams SZA withdrawn from RDA.
The withdrawal point EZA of the side stream SZA and the feed point ZZA of the side stream SZA on the rectification column RDA may be positioned between the same trays of RDA. However, they may also be at different heights.
In a preferred embodiment of the process according to the invention the withdrawal point EZA and preferably also the feed point ZZA of the at least one side stream SZA on the rectification column RDA are below the feed point ZG, by which the mixture G is passed into the rectification column RDA, and above the bottom of RDA. It is yet more preferable when the withdrawal point EZA and preferably also the feed point ZZA of the at least one side stream SZA on the rectification column RDA are also below the rectification section of RDA.
In a particularly preferred embodiment of the process according to the invention the withdrawal point EZA and more preferably also the feed point ZZA of the at least one side stream SZA on the rectification column RDA are in the upper ⅘, preferably upper ¾, preferably upper 7/10, more preferably upper ⅔, more preferably upper ½, of the region of the rectification column RDA below the feed point ZG, by which the mixture G is passed into the rectification column RDA, and above the uppermost of all withdrawal and feed points for all streams SUA withdrawn from RDA. It is yet more preferable when the withdrawal point EZA and preferably also the feed point ZZA of the at least one side stream SZA on the rectification column RDA are then also below the rectification section of RDA.
In a further particularly preferred embodiment of the process according to the invention the rectification column RDA contains a rectification section and the withdrawal point EZA and more preferably also the feed point ZZA of the at least one side stream SZA on the rectification column RDA are in the upper ⅘, preferably upper ¾, preferably upper 7/10, more preferably upper ⅔, more preferably upper ½, of the region of the rectification column RDA below the rectification section and above the uppermost of all withdrawal and feed points for all streams SUA withdrawn from RDA.
In step (c) of the process according to the invention at least a portion of the at least one vapour stream SOA (“at least a portion of the at least one vapour stream SOA”=“at least a portion of SOA”) is compressed. This affords a vapour stream SOA1 which is compressed with respect to SOA.
The pressure of the vapour stream SOA1 is referred to as “pOA1” and its temperature as “TOA1”.
The pressure pOA1 is higher than pOA. The precise value of pOA1 may be adjusted by those skilled in the art according to the requirements in step (d) provided that the condition pOA1>pOA is met. The quotient of pOA1/pOA (pressures in bar abs. in each case) is preferably in the range from 1.1 to 10, more preferably 1.2 to 8, more preferably 1.25 to 7, most preferably 1.3 to 6.
The temperature TOA1 is especially higher than the temperature TOA and the quotient of TOA1/TOA (temperature in ° C. in each case) is preferably in the range from 1.03 to 10, more preferably 1.04 to 9, more preferably 1.05 to 8, more preferably 1.06 to 7, more preferably 1.07 to 6, most preferably 1.08 to 5.
The preferred values of pOA1 and TOA1 also apply with preference to SOA11 and SOA12.
The compressing of the at least a portion of the vapour stream SOA in step (c) may be carried out in any desired manner known to those skilled in the art. The compression may therefore be performed for example mechanically and as a single-stage or multi-stage compression, preferably a multi-stage compression. A multi-stage compression may employ a plurality of compressors of the same type or compressors of different types. A multi-stage compression may be carried out with one or more compressors. The use of single-stage compression or multi-stage compression depends on the compression ratio and thus on the pressure to which the vapour SOA is to be compressed.
Any desired compressor, preferably mechanical compressor, known to those skilled in the art and capable of compressing gas streams is suitable as a compressor in the process according to the invention, in particular for compressing the vapour streams SOA to SOA1 or SOA12 to SOA2. Suitable compressors are for example single-stage or multi-stage turbines, piston compressors, screw compressors, centrifugal compressors or axial compressors.
In a multi-stage compression compressors suitable for the respective pressure stages to be overcome are employed.
In step (d) of the process according to the invention energy is transferred from a first portion SOA11 of the compressed vapour stream SOA1 to SZA before SZA is recycled to RDA.
SOA1 is especially in step (d) initially divided into at least two portions SOA11 and SOA12. The ratio of the mass flows (in kg/h) of SOA11 to SOA12 is preferably in the range from 1:99 to 99:1, more preferably in the range from 1:50 to 50:1, yet more preferably in the range from 1:20 to 30:1, yet more preferably in the range from 5:20 to 15:1.
In step (d) of the process according to the invention energy is transferred from the first portion SOA11 to SZA. Step (d) reduces the energy of SOA11 and the stream SOA11 thus especially undergoes at least partial condensation.
According to the invention “transfer of energy” is especially to be understood as meaning “heating”, i.e. transfer of energy in the form of heat.
“Transfer of energy from a first portion SOA11 of the compressed vapour stream SOA1 to SZA” also comprises the cases in which a portion of SOA11 is separated and energy is transferred to SZA only from this portion. This is the case for example in embodiments of the invention in which energy is additionally transferred from SOA11 to the crude product RPA and if step (α2) is performed alternatively or in addition to the crude product RPB (described in section 4.2).
The transfer of energy from SOA11 to SZA, preferably the heating of SZA by SOA11, is preferably effected directly or indirectly.
“Directly” is to be understood as meaning that SOA11 is contacted with SZA without mixing of the two streams, thus transferring energy, in particular heat, from SOA11 to SZA.
This may be performed by passing SOA11 and SZA through an intermediate evaporator VZRD on the rectification column RDA so that SOA11 effects heating of SZA.
The employed heat exchangers, in particular the heat exchangers WTX, WTY, WTZ mentioned hereinbelow, may be heat exchangers known to those skilled in the art, in particular evaporators. In step (d) of the process according to the invention the transfer of energy, preferably heat, from SOA11 to SZA is effected in particular in an intermediate evaporator VZRD.
“Indirectly” is especially to be understood as meaning that SOA11 is contacted with a heat transfer medium W1, preferably via at least one heat exchanger WTX, wherein the heat transfer medium is not SZA, and W1 is thus distinct from SZA, thus transferring energy, preferably heat, from SOA11 to W1 without the two streams mixing, and the heat is then transferred from W1 to SZA by contacting W1 and SZA, wherein SZA and W1 do or do not mix, but preferably do not mix. If W1 and SZA do not mix, the transfer of energy, preferably heat, is effected in particular in a further heat exchanger WTY.
In a further embodiment of the process according to the invention in the case of indirect energy transfer from SOA11 to SZA, in particular heating of SZA by SOA11, energy, preferably heat, may also be initially transferred from SOA11 to W1, preferably by contacting via at least one heat exchanger WTX, and then transferred from W1 to a further heat transfer medium W2 distinct from SZA, preferably by contacting via at least one heat exchanger WTY. The last step then effects transfer of the heat from W2 to SZA, wherein SZA and W2 do or do not mix, but preferably do not mix. If W2 and
SZA do not mix, the transfer of energy, preferably heat, is effected in particular in a further heat exchanger WTZ.
It will be appreciated that still further heat transfer media W3, W4, W5 etc. may accordingly be employed in further embodiments of the present invention.
Utilizable heat transfer media W1 and further heat transfer media W2, W3, W4, W5 include any heat transfer media known to those skilled in the art, preferably selected from the group consisting of water; alcohol-water solutions; salt-water solutions, also including ionic liquids such as for example LiBr solutions, dialkylimidazolium salts such as especially dialkylimidazolium dialkylphosphates; mineral oils, for example diesel oils; thermal oils such as for example silicone oils; biological oils such as for example limonene; aromatic hydrocarbons such as for example dibenzyltoluene. The most preferred heat transfer medium W1 is water.
Salt-water solutions that may be used are also described for example in DE 10 2005 028 451 A1 and WO 2006/134015 A1.
After step (d) SOA11 may then be returned to rectification column RDA, optionally together with fresh alcohol and/or with the reflux for rectification column RDA. In a preferred embodiment further energy is transferred from SOA11, especially after the transfer of energy to SZA.
In a preferred embodiment of the process according to the invention once SOA11 has transferred energy to SZA according to step (d) energy, preferably heat, is transferred from SOA11 to SOA, in particular to the portion of SOA sent to a compression, preferably the compression in step (c), wherein this may be a precompression of SOA or the compression of SOA to SOA1. This is preferably the first compression to which the stream SOA is subjected once it has left the column RDA. This makes it possible to employ a portion of the residual energy/residual heat still stored by SOA11 in the process, in this case for heating of SOA to be compressed. This evaporates any droplets present in SOA and thus prevents entry of droplets into the compressor.
Other, preferred additional sinks for the energy, preferably heat, in SOA11 are described hereinbelow (see paragraph 4.3).
Step (d) of the process according to the invention reflects one aspect of the unexpected effect of the present invention. The excess energy obtained upon compression of the vapour stream SOA to afford the compressed vapour stream SOA1 does not dissipate without being utilized but rather is employed in the rectification. This is effected such that SOA is initially compressed to afford SOA1, thus allowing adjustment to a value optimal for energy transfer from SOA11 to SZA, and then a portion SOA12 that is distinct from SOA11 may be further compressed to afford SOA2. The heat of condensation obtained upon further compression of SOA12 to afford SOA2 is introduced into the column in the bottoms evaporator. The required additional compressor power is less than the heating steam power saved thereby. The process according to the invention requires less energy than those of the prior art, such as are shown in examples 1 and 2. The compression to afford SOA2 allows the pressure and temperature of SOA2 to be adjusted such that optimal energy transfer from SOA2 to SUA1/SUA may be effected.
In step (e) of the process of the invention a portion SOA12 of the compressed vapour stream SOA1 that is distinct from SOA11 is subjected to further compression to afford a vapour stream SOA2 that is compressed relative to SOA11.
It will be appreciated that after performance of step (e) SOA2 is also compressed relative to SOA12 and SOA1.
The pressure of the vapour stream SOA2 is referred to as “pOA2” and its temperature as “TOA2”.
The pressure pOA2 is higher than pOA and the quotient of pOA2/pOA1 (pressures in bar abs. in each case) is preferably in the range from 1.1 to 10, more preferably 1.2 to 8, more preferably 1.25 to 7, most preferably 1.3 to 6.
The temperature TOA2 is especially higher than the temperature TOA1 and the quotient of TOA2/TOA1 (temperature in ° C. in each case) is preferably in the range from 1.03 to 10, more preferably 1.04 to 9, more preferably 1.05 to 8, more preferably 1.06 to 7, more preferably 1.07 to 6, most preferably 1.08 to 5.
The compressing of SOA12 in step (e) may be performed by processes known to those skilled in the art. The compression may therefore be performed for example mechanically and as a single-stage or multi-stage compression, preferably a multi-stage compression. A multi-stage compression may employ a plurality of compressors of the same type or compressors of different types. The use of single-stage compression or multi-stage compression depends on the pressure to which the vapour SOA12 is to be compressed. A precompression described for SOA in the context of step (c) may also be performed for the compression of SOA12 to SOA2 but compression in one stage, i.e. using a compressor VDx, is especially sufficient in step (e).
In step (f) of the process according to the invention energy is transferred from at least a portion of SOA2 to at least a portion SUA1 of the at least one stream SUA before SUA1 is recycled to RDA.
In step (f) of the process energy is preferably transferred from at least a portion of SOA2 to a portion SUA1 of the at least one stream SUA before SUA1 is recycled to RDA.
Step (f) reduces the energy of SOA2 and the stream SOA2 thus especially undergoes at least partial condensation.
Step (f) of the process according to the invention comprises the following preferred embodiments (f1), (f2), (f3):
The transfer of energy from at least a portion of SOA2 to the at least a portion SUA1 of the at least one stream SUA, preferably the heating of the at least a portion SUA1 of the at least one stream SUA by at least a portion of SOA2, is preferably effected directly or indirectly.
“Directly” is to be understood as meaning that at least a portion of SOA2 is contacted with the at least a portion SUA1 of the at least one stream SUA without mixing of the two streams, thus transferring energy, in particular heat, from at least a portion of SOA2 to the at least a portion SUA1 of the at least one stream SUA.
This may be performed by passing the at least a portion of SOA2 and the at least a portion SUA1 of the at least one stream SUA through an bottoms evaporator VSRD on the rectification column RDA SO that SOA11 effects heating of the at least a portion SUA of the at least one stream SUA.
The employed heat exchangers, in particular the heat exchangers WTX, WTY, WTZ mentioned hereinbelow, may be heat exchangers known to those skilled in the art, in particular evaporators. In step (f) of the process according to the invention the transfer of energy, preferably heat, from at least a portion of SOA2 to the at least a portion SUA1 of the at least one stream SUA is in particular effected in a bottoms evaporator VSRD.
“Indirectly” is especially to be understood as meaning that the at least a portion of SOA2 is contacted with at least one heat transfer medium W1 preferably via at least one heat exchanger WTX, wherein the heat transfer medium is not the at least a portion SUA of the at least one stream SUA and W1 is thus distinct therefrom, thus transferring energy, preferably heat, from the at least a portion of SOA2 to the at least one heat transfer medium W1 without the two streams mixing, and the heat is then transferred from W1 to the at least a portion SUA of the at least one stream SUA by contacting W1 with the relevant component, wherein the at least a portion SUA1 of the at least one stream SUA and W1 do or do not mix, but preferably do not mix.
In a further embodiment of the process according to the invention in the case of indirect energy transfer from at least a portion of SOA2 to the at least a portion SUA1 of the at least one stream SUA, in particular heating of the at least a portion SUA1 of the at least one stream SUA by the at least a portion of SOA2, energy, preferably heat, may also be initially transferred from SOA2 to W1, preferably by contacting via at least one heat exchanger WTX, and then transferred from W1 to a further heat transfer medium W2 distinct from the at least a portion SUA1 of the at least one stream SUA, preferably by contacting via at least one heat exchanger WTY. The last step then effects transfer of the heat from W2 to the at least a portion SUA of the at least one stream SUA, wherein the at least a portion SUA1 of the at least one stream SUA and W2 do or do not mix, but preferably do not mix. It will be appreciated that still further heat transfer media W3, W4, W5 etc. may accordingly be employed in further embodiments of the present invention.
Utilizable heat transfer media W1 and further heat transfer media W2, W3, W4, W5 used include any heat transfer media known to those skilled in the art, preferably selected from the group consisting of water; alcohol-water solutions; salt-water solutions, also including ionic liquids such as for example LiBr solutions, dialkylimidazolium salts such as especially dialkylimidazolium dialkylphosphates; mineral oils, for example diesel oils; thermal oils such as for example silicone oils; biological oils such as for example limonene; aromatic hydrocarbons such as for example dibenzyltoluene. The most preferred heat transfer medium W1 is water.
Salt-water solutions that may be used are also described for example in DE 10 2005 028 451 A1 and WO 2006/134015 A1.
After step (f) the at least a portion of SOA2 may then be returned to the rectification column RDA, optionally together with fresh alcohol and/or with the reflux for the rectification column RDA and/or with the stream SOA11 obtained after performance of step (d). In a preferred embodiment further energy is transferred from at least a portion of SOA2, especially after the transfer of energy to the at least a portion SUA1 of SUA.
In a preferred embodiment of the process according to the invention once energy has been transferred from the at least a portion of SOA2 to the at least a portion SUA1 of SUA according to step (f) energy, more preferably heat, is transferred from the at least a portion of SOA2 to SOA, in particular to the portion of SOA which is sent to a compression, preferably the compression in step (c), wherein this may be a precompression of SOA or the compression of SOA to afford SOA1. This is preferably the first compression to which the stream SOA is subjected once it has left the column RDA. This makes it possible to employ a portion of the residual energy/residual heat still stored by the at least a portion of SOA2 in the process, in this case for heating of SOA to be compressed.
Other, preferred additional sinks for the energy, preferably heat, in the at least a portion of SOA2 are described hereinbelow (see paragraph 4.3).
The mixture G employed in the process for workup of a mixture G according to the invention is a water/methanol mixture withdrawn from a reaction column for producing alkali metal alkoxides.
The present invention thus relates to a process for producing at least one alkali metal alkoxide of formula MAOR, wherein R is methyl, and wherein MA is a metal selected from sodium, potassium, preferably sodium.
ROH is accordingly methanol.
In step (α1) of the process according to the invention a reactant stream SAE1 comprising ROH is reacted with a reactant stream SAE2 comprising MAOH in countercurrent in a reactive rectification column RRA to afford a crude product RPA comprising MAOR, water, ROH, MAOH.
According to the invention, a “reactive rectification column” is a rectification column in which the reaction according to step (α1) or step (α2) of the process of the invention proceeds at least in some parts is defined. It may also be abbreviated to “reaction column”.
In step (α1) a bottoms product stream SAP comprising ROH and MAOR is withdrawn at the lower end of RRA. A vapour stream SAB comprising water and ROH is withdrawn at the upper end of RRA.
MA is selected from sodium, potassium, preferably sodium.
The reactant stream SAE1 comprises ROH. In a preferred embodiment the mass fraction of ROH in SAE1 is ≥95% by weight, yet more preferably ≥99% by weight, wherein SAE1 otherwise comprises especially water.
The alcohol ROH employed in step (α1) as reactant stream SAE1 may also be commercially available alcohol having an alcohol mass fraction of more than 99.8% by weight and a mass fraction of water of up to 0.2% by weight.
The reactant stream SAE1 is preferably introduced in vapour form.
The reactant stream SAE2 comprises MAOH. In a preferred embodiment SAE2 comprises not only MAOH but also at least one further compound selected from water, ROH. It is yet more preferable when SAE2 comprises water in addition to MAOH, thus rendering SAE2 an aqueous solution of MAOH.
When the reactant stream SAE2 comprises MAOH and water the mass fraction of MAOH based on the total weight of the aqueous solution forming SAE2 is especially in the range from 10% to 75% by weight, preferably from 15% to 54% by weight, more preferably from 30% to 53% by weight and particularly preferably from 40% to 52% by weight.
When the reactant stream SAE2 comprises MAOH and ROH the mass fraction of MAOH in ROH based on the total weight of the solution forming SAE2 is especially in the range from 10% to 75% by weight, preferably from 15% to 54% by weight, more preferably from 30% to 53% by weight and particularly preferably from 40% to 52% by weight.
In the particular case in which the reactant stream SAE2 comprises both water and ROH in addition to MAOH it is particularly preferable when the mass fraction of MAOH in ROH and water based on the total weight of the solution forming SAE2 is especially in the range from 10% to 575% by weight, preferably from 15% to 54% by weight, more preferably from 30% to 53% by weight and particularly preferably from 40% to 52% by weight.
Step (α1) is performed in a reactive rectification column (or “reaction column”) RRA.
Step (α2), explained further hereinbelow, is performed in a reactive rectification column (or “reaction column”) RRB.
The reaction column RRA/RRB preferably contains internals. Suitable internals are, for example, trays, structured packings or unstructured packings. When the reaction column RRA/RRB contains trays, then bubble cap trays, valve trays, tunnel trays, Thormann trays, cross-slit bubble cap trays or sieve trays are suitable. When the reaction column RRA/RRB contains trays it is preferable to choose trays where not more than 5% by weight, more preferably less than 1% by weight, of the liquid trickles through the respective trays. The constructional measures required to minimize trickle-through of the liquid are familiar to those skilled in the art. In the case of valve trays, particularly tightly closing valve designs are selected for example. Reducing the number of valves also makes it possible to increase the vapour velocity in the tray openings to twice the value typically established. When using sieve trays it is particularly advantageous to reduce the diameter of the tray openings while maintaining or even increasing the number of openings.
When using structured or unstructured packings, structured packings are preferred in terms of uniform distribution of the liquid.
For columns comprising unstructured packings, especially comprising random packings, and for columns comprising structured packings, the desired characteristics of the liquid distribution may be achieved when the liquid trickling density in the edge region of the column cross section adjacent to the column shell, corresponding to about 2% to 5% of the total column cross section, is reduced compared to the other cross-sectional regions by up to 100%, preferably by 5% to 15%. This can easily be achieved by, for example, targeted distributions of the drip points of the liquid distributors or the holes thereof.
The process according to the invention may be performed either continuously or discontinuously. It is preferably performed continuously.
“Reaction of a reactant stream SAE1 comprising ROH with a reactant stream SAE2 comprising MAOH in countercurrent” is according to the invention achieved, in particular, as a result of the feed point for at least a portion of the reactant stream SAE1 comprising ROH in step (α1) being located on the reaction column RRA below the feed point of the reactant stream SAE2 comprising MAOH.
The reaction column RRA preferably comprises at least 2, in particular 15 to 40, theoretical trays between the feed point of the reactant stream SAE1 and the feed point of the reactant stream SAE2.
The reaction column RRA may be operated as a pure stripping column. In this case the reactant stream SAE1 comprising ROH is introduced in vapour form in the lower region of the reaction column RRA.
Step (α1) also encompasses the case where a portion of the reactant stream SAE1 comprising ROH is added in vapour form below the feed point of the reactant stream SAE2 comprising aqueous sodium hydroxide solution MAOH but nevertheless at the upper end or in the region of the upper end of the reaction column RRA. This makes it possible to reduce the dimensions of the lower region of the reaction column RRA. When a portion of the reactant stream SAE1 comprising ROH, in particular methanol, is added especially in vapour form at the upper end or in the region of the upper end of the reaction column RRA only a fraction of 10% to 70% by weight, preferably of 30% to 50% by weight, (in each case based on the total amount of the alcohol ROH employed in step (α1)) is introduced at the lower end of the reaction column RRA and the remaining fraction is added in vapour form in a single stream or divided into a plurality of substreams, preferably 1 to 10 theoretical trays, particularly preferably 1 to 3 theoretical trays, below the feed point of the reactant stream SAE2 comprising MAOH.
In the reaction column RRA, the reactant stream SAE1 comprising ROH is then reacted with the reactant stream SAE2 comprising MAOH according to the reaction <1> described hereinabove to afford MAOR and H2O, where these products are present in admixture with the reactants ROH and MAOH since an equilibrium reaction is concerned. Accordingly, a crude product RPA which comprises ROH and MAOH in addition to the products MAOR and water is obtained in step (α1) in the reaction column RRA.
The bottoms product stream SAP comprising ROH and MAOR is then obtained and withdrawn at the lower end of RRA.
A water-containing alcohol stream, presently described as “vapour stream SAB comprising water and ROH”, is withdrawn at the upper end of RRA, preferably at the column top of RRA.
This vapour stream SAB comprising water and ROH is employed in step (β) at least partially as mixture G in step (a) of the process according to the invention. A portion of the alcohol obtained in stream SOA in the distillation in step (a) may be supplied to the reaction column RRA as reactant stream SAE1.
In a preferred embodiment of the process according to the invention a portion of SOA is employed as reactant stream SAE1 in step (α1) and if step (α2) is performed alternatively or in addition as reactant stream SBE1 in step (α2).
In a more preferred embodiment of the process according to the invention 5% to 95% by weight, preferably 10% to 90% by weight, more preferably 20% to 80% by weight, yet more preferably 30% to 70% by weight, of the vapour stream SOA is employed as reactant stream SAE1 or if step (α2) is performed alternatively or in addition as reactant stream SBE1 in step (α2).
In this preferred embodiment it is advantageous to compress the portion of the stream SOA employed as reactant stream SAE1/as reactant stream SBE1.
The amount of the alcohol ROH comprised by the reactant stream SAE1 is preferably chosen such that said alcohol also serves as a solvent for the alkali metal alkoxide MAOR obtained in the bottoms product stream SAP. The amount of the alcohol ROH in the reactant stream SAE1 is preferably chosen to achieve in the bottom of the reaction column the desired concentration of the alkali metal alkoxide solution which is withdrawn as a bottoms product stream SAP comprising ROH and MAOR.
In a preferred embodiment of the process according to the invention, and especially in the cases where SAE2 contains water in addition to MAOH, the ratio of the total weight (masses; units: kg) of alcohol employed in step (α1) as reactant stream SAE1 ROH to the total weight (masses; unit: kg) of MAOH employed in step (α1) as reactant stream SAE2 is 4:1 to 50:1, more preferably 8:1 to 48:1, yet more preferably 10:1 to 45:1, yet still more preferably 20:1 to 40:1.
The reaction column RRA is operated with or without, preferably with, reflux.
“With reflux” is to be understood as meaning that the vapour stream SAB/SBB comprising water and ROH withdrawn at the upper end of the respective column, in step (α1) from the reaction column RRA, in step (α2) from the reaction column RRB, is not completely discharged. Thus in step (β) the respective vapour stream SAB/SBB is then not entirely employed as mixture G but rather at least partially, preferably partially, returned to the respective column as reflux, in step (α1) to the reaction column RRA, in step (α2) to the reaction column RRB. In the cases where such a reflux is established the reflux ratio is preferably 0.01 to 1, more preferably 0.02 to 0.9, yet more preferably 0.03 to 0.34, particularly preferably 0.04 to 0.27 and very particularly preferably 0.05 to 0.24.
A reflux may be established by attaching a condenser at the top of the respective column. In step (α1) this is achieved in particular by attaching a condenser KRRA to the reaction column RRA. In step (α2) this is achieved in particular by attaching a condenser KRRB to the reaction column RRB.
In the respective condenser the respective vapour stream SAB/SBB is at least partially condensed and returned to the respective column, in step (α1) to the reaction column RRA/RRB.
In the embodiment in which a reflux is established on the reaction column RRA the MAOH employed in step (α1) as reactant stream SAE2 may also be at least partially mixed with the reflux stream and the resulting mixture thus supplied to step (α1).
Step (α1) is performed especially at a temperature in the range from 45° C. to 150° C., preferably 47° C. to 120° C., more preferably 60° ° C. to 110° C., and at a pressure of 0.5 bar abs. to 40 bar abs., preferably in the range from 0.7 bar abs. to 5 bar abs., more preferably in the range from 0.8 bar abs. to 4 bar abs., more preferably in the range from 0.9 bar abs. to 3.5 bar abs., more preferably at 1.0 bar abs. to 3 bar abs.
The reaction column RRA comprises in a preferred embodiment at least one evaporator which is especially selected from intermediate evaporators VZA and bottoms evaporators VSA. The reaction column RRA particularly preferably comprises at least one bottoms evaporator VSA.
According to the invention “intermediate evaporators” VZ are to be understood as meaning evaporators arranged above the bottom of the respective column, in particular above the bottom of the reaction column RRA/RRB (then referred to as “VZA”/“VZB”) or above the bottom of the rectification column RDA (then referred to as “VZRD”). In the case of RRA/RRB said evaporators especially evaporate crude product RPA/RPB which is withdrawn from the column as side stream SZAA/SZBA.
According to the invention “bottoms evaporators” Vs are to be understood as meaning evaporators which heat the bottom of the respective column, in particular the bottom of the reaction column RRA/RRB or RRC as used in the preferred embodiment and more particularly described hereinbelow (then referred to as “VSA” or “VSA”/“VSB” or “VSB.”/“VSC” or “VSC.”) or the bottom of the rectification column RDA (then referred to as “VSRD” Or “VSRD.”). In the case of RRA/RRB said evaporators especially evaporate at least a portion of the bottoms product stream SAP/SBP. In the case of RRC said evaporators especially evaporate bottoms product stream SCP. In the case of RDA said evaporators especially evaporate bottoms product stream SUA or a portion of SUA, SUA1.
An evaporator is typically arranged outside the respective reaction column or rectification column. Since evaporators transfer energy, in particular heat, from one stream to another they are heat exchangers WT. The mixture to be evaporated is withdrawn via a takeoff from the column and supplied to the at least one evaporator. In the case of the reaction column RRA/RRB intermediate evaporation of the crude product RPA/RPB comprises withdrawal thereof and supply thereof to the at least one intermediate evaporator VZA/VZB.
In the case of the rectification column RDA intermediate evaporation comprises withdrawal of at least one side stream SZA from RDA and supply thereof to the at least one intermediate evaporator VZRD.
In the case of the rectification column RDA bottoms evaporation comprises withdrawal of at least one stream SUA from RDA and supply of at least a portion, preferably a portion, thereof to the at least one bottoms evaporator VSRD.
The evaporated mixture is recycled back into the respective column optionally with a residual proportion of liquid via at least one feed. When the evaporator is an intermediate evaporator, i.e. in particular an intermediate evaporator VZA/VZB/VZRD, the takeoff by means of which the respective mixture is withdrawn and supplied to the evaporator is a side stream takeoff and the feed by means of which the evaporated mixture is returned to the respective column is a side stream feed. When the evaporator is a bottoms evaporator, i.e. heats the column bottoms, i.e. is in particular a bottoms evaporator VSA/VSB/VSRD, at least a portion of the bottoms takeoff stream, in particular SAP/SBP, is supplied to the bottoms evaporator, evaporated and recycled back into the respective column in the region of the column bottom. However it is alternatively also possible to configure suitable tubes, for example on a suitable tray when using an intermediate evaporator or in the bottom of the respective column, traversed by the heat transfer medium, for example the respective compressed vapour stream SOA11/SOA2 (if Vs/VZ are located at the rectification column RDA), or a heating medium W1 In this case, the evaporation occurs on the tray or in the bottom region of the column. However, it is preferable to arrange the evaporator outside the respective column.
Suitable evaporators employable as intermediate evaporators and bottoms evaporators include for example natural circulation evaporators, forced circulation evaporators, forced circulation evaporators with decompression, kettle evaporators, falling film evaporators or thin film evaporators. Heat exchangers for the evaporator typically employed in the case of natural circulation evaporators and forced circulation evaporators are shell and tube or plate apparatuses. When using a shell and tube exchanger the heat transfer medium, for example the compressed vapour stream SOA11/SOA2 in VSRD/VZRD at the rectification column RDA/the heating medium W1, may either flow through the tubes with the mixture to be evaporated flowing around the tubes or else the heat transfer medium, for example the compressed vapour stream SOA11/SOA2 in VSRD/VZRD at the rectification column RDA/the heating medium W1, flows around the tubes with the mixture to be evaporated flowing through the tubes. In the case of a falling-film evaporator, the mixture to be evaporated is typically introduced as a thin film on the inside of a tube and the tube is heated externally. In contrast to a falling-film evaporator, a thin-film evaporator additionally comprises a rotor with wipers which distributes the liquid to be evaporated on the inner wall of the tube to form a thin film.
In addition to the recited evaporator types it is also possible to employ any desired further evaporator type known to those skilled in the art and suitable for use on a rectification column.
When the evaporator operated for example with the compressed vapour stream SOA11/the heating medium W1 as heating vapour is an intermediate evaporator it is preferable when the intermediate evaporator is arranged in the stripping portion of the rectification column RDA in the region between the feed point of the mixture G and above the column bottom or in the case of the reaction columns RRA/RRB below the feed point of the reactant stream SAE2/SBE2. This makes it possible to introduce a predominant proportion of the heat energy via the intermediate evaporator. It is thus possible for example to introduce more than 80% of the energy via the intermediate evaporator. According to the invention the intermediate evaporator is preferably arranged and/or configured such that it is used to introduce more than 10%, in particular more than 20%, of the total energy required for the distillation.
When using an intermediate evaporator it is especially advantageous when the intermediate evaporator is arranged such that the respective rectification column/reaction column has 1 to 50 theoretical trays below the intermediate evaporator and 1 to 200 theoretical trays above the intermediate evaporator. It is especially preferred when the rectification column/reaction column has 2 to 10 theoretical trays below the intermediate evaporator and 20 to 80 theoretical trays above the intermediate evaporator.
The side stream takeoff by means of which the mixture from the rectification column/reaction column is supplied to the intermediate evaporator VZ and the side stream feed by means of which the evaporated mixture from the intermediate evaporator VZ is returned to the respective rectification column/reaction column may be positioned between the same trays of the column. However, it is also possible for the side stream takeoff and side stream feed to be arranged at different heights.
Such an intermediate evaporator VZA can convert liquid crude product RPA present in the reaction column RRA comprising MAOR, water, ROH, MAOH into the gaseous state, thus improving the efficiency of the reaction according to step (α1) of the process according to the invention.
Such an intermediate evaporator VZB can convert liquid crude product RPB present in the reaction column RRB comprising MBOR, water, ROH, MBOH into the gaseous state, thus improving the efficiency of the reaction according to step (α2) of the process according to the invention.
By arranging one or more intermediate evaporators VZA/VZB in the upper region of the reaction column RRA the dimensions in the lower region of the reaction column RRA can be reduced. In the embodiment having at least one, preferably two or more, intermediate evaporators VZA/VZB it is also possible to introduce substreams of the ROH in liquid form in the upper region of the reaction column RRA.
In a further preferred embodiment energy, preferably heat, is transferred from at least a portion of a stream selected from SOA1, SOA2, in particular selected from SOA11, SOA12, SOA2, preferably selected from SOA11, SOA2, to the crude product RPA and if step (α2) is performed alternatively or in addition to the crude product RPB.
“Transfer of energy, preferably heat, from at least a portion of SOA1 to the crude product RPA and if step (α2) is performed alternatively or in addition to the crude product RPB” also comprises the transfer of energy, preferably heat, from at least one stream selected from SOA11, SOA12, or from the stream SOA1 before separation thereof into SOA11, SOA12, to the crude product RPA and if step (α2) is performed alternatively or in addition to the crude product RPB. It also comprises the transfer of energy from a portion of SOA11, SOA12 to the crude product RPA and if step (α2) is performed alternatively or in addition to the crude product RPB.
To this end especially a portion of the relevant stream selected from SOA1, SOA2 or a heat transfer medium W1, to which energy had previously been transferred from the relevant stream selected from SOA1, SOA2, is at least partially passed through an intermediate evaporator VZA/VZB and the energy from the relevant stream selected from SOA1, SOA2/W1 transferred to the crude product stream withdrawn via the side stream takeoff on RRA/RRB, in particular by utilizing the relevant stream selected from SOA1, SOA2/W1 for heating the evaporator VZA/VZB.
According to the invention bottoms evaporators are arranged at the bottom of the respective rectification column RDA/reaction column RRA/RRB/RRC and are then referred to as “VSRD” or “VSRD′”/“VSA” Or “VSA′”/“VSB” Or “VSB′”/“VSC” or “VSC′”. A bottoms product stream (in particular SAP/SBP) present in the respective column (in particular reaction column RRA/RRB) may be passed into such a bottoms evaporator and for example ROH at least partially removed therefrom. In the case of SAP/SBP this may afford a bottoms product stream SAP* having an elevated mass fraction of MAOR compared to SAP or a bottoms product stream SBP* having an elevated mass fraction of MBOR compared to SBP.
In step (α1) of the process according to the invention a bottoms product stream SAP comprising ROH and MAOR is withdrawn at the lower end of the reaction column RRA.
It is preferable when the reaction column RRA comprises at least one bottoms evaporator VSA through which the bottoms product stream SAP is then partially passed to partially remove ROH, thus affording a bottoms product stream SAP* having an elevated mass fraction of MAOR compared to SAP.
In another preferred embodiment transfer of energy, preferably heat, from at least a portion of a stream selected from SOA1, SOA2, in particular selected from SOA11, SOA2, to the crude product RPA and if step (α2) is performed alternatively or in addition to the crude product RPB is therefore undertaken as follows:
Especially a portion of the relevant stream selected from SOA1, SOA2 or a heat transfer medium W1, to which energy had previously been transferred from the relevant stream selected from SOA1, SOA2, is then at least partially passed through a bottoms evaporator VSA/VSB and the energy from the relevant stream selected from SOA1, SOA2/W1 transferred to the bottoms product stream SAP/SBP, in particular by utilizing the relevant stream selected from SOA1, SOA2/W1 for heating the evaporator VSA/VSB.
The mass fraction of MAOR in the bottoms product stream SAP* is in particular elevated compared to the mass fraction of MAOR in the bottoms product stream SAP by at least 0.5%, preferably by ≥ 1%, more preferably by ≥2%, yet more preferably by ≥5%.
It is preferable when SAP or, if at least one bottoms evaporator VSA is used through which the bottoms product stream SAP is at least partially passed to at least partially remove ROH, SAP* has a mass fraction of MAOR in ROH in the range from 1% to 50% by weight, preferably 5% to 35% by weight, more preferably 15% to 35% by weight, most preferably 20% to 35% by weight, in each case based on the total mass of SAP.
The mass fraction of residual water in SAP/SAP* is preferably <1% by weight, preferably <0.8% by weight, more preferably <0.5% by weight, based on the total mass of SAP.
The mass fraction of reactant MAOH in SAP/SAP* is preferably <1% by weight, preferably <0.8% by weight, more preferably <0.5% by weight, based on the total mass of SAP.
Step (α2) is an optional embodiment of the process according to the invention. This is to be understood as meaning that in the context of the preferred embodiment of the process according to the invention step (α2) is or is not performed. In optional step (α2), simultaneously with and spatially separate from step (α1), a reactant stream SBE1 comprising ROH is reacted with a reactant stream SBE2 comprising MBOH in countercurrent in a reactive rectification column RRB to afford a crude product RPB comprising MBOR, water, ROH, MBOH.
In step (α2) of the process according to the invention a bottoms product stream SBP comprising ROH and MBOR is withdrawn at the lower end of RRB. A vapour stream SBB comprising water and ROH is withdrawn at the upper end of RRB.
MB is selected from sodium, potassium, preferably potassium.
The reactant stream SBE1 comprises ROH. In a preferred embodiment the mass fraction of ROH in SBE1 is ≥95% by weight, yet more preferably ≥99% by weight, wherein SBE1 otherwise comprises especially water.
The alcohol ROH employed in step (α2) of the process according to the invention as reactant stream SBE1 may also be commercially available alcohol having an alcohol mass fraction of more than 99.8% by weight and a mass fraction of water of up to 0.2% by weight.
The reactant stream SBE1 is preferably introduced in vapour form.
The reactant stream SBE2 comprises MBOH. In a preferred embodiment SBE2 comprises not only MBOH but also at least one further compound selected from water, ROH. It is yet more preferable when SBE2 comprises water in addition to MBOH, thus rendering SBE2 an aqueous solution of MBOH.
When the reactant stream SBE2 comprises MBOH and water the mass fraction of MBOH based on the total weight of the aqueous solution forming SBE2 is especially in the range from 10% to 75% by weight, preferably from 15% to 54% by weight, more preferably from 30% to 53% by weight and particularly preferably from 40% to 52% by weight.
When the reactant stream SBE2 comprises MBOH and ROH the mass fraction of MBOH in ROH based on the total weight of the solution forming SBE2 is especially in the range from 10% to 75% by weight, preferably from 15% to 54% by weight, more preferably from 30% to 53% by weight and particularly preferably from 40% to 52% by weight.
In the particular case in which the reactant stream SBE2 comprises both water and ROH in addition to MBOH it is particularly preferable when the mass fraction of MBOH in ROH and water based on the total weight of the solution forming SBE2 is especially in the range from 10% to 75% by weight, preferably from 15% to 54% by weight, more preferably from 30% to 53% by weight and particularly preferably from 40% to 52% by weight.
Step (α2) of the process according to the invention is performed in a reactive rectification column (or “reaction column”) RRB. Preferred embodiments of the reaction column RRB are described in section 4.2.1.
“Reaction of a reactant stream SBE1 comprising ROH with a reactant stream SBE2 comprising MBOH in countercurrent” is according to the invention achieved, in particular, as a result of the feed point for at least a portion of the reactant stream SBE1 comprising ROH in step (α2) being located on the reaction column RRB below the feed point of the reactant stream SBE2 comprising MBOH.
The reaction column RRB preferably comprises at least 2, in particular 15 to 40, theoretical trays between the feed point of the reactant stream SBE1 and the feed point of the reactant stream SBE2.
The reaction column RRA may be operated as a pure stripping column. In this case the reactant stream SBE1 comprising ROH is introduced in vapour form in the lower region of the reaction column RRB. Step (α2) of the process according to the invention also encompasses the case where a portion of the reactant stream SBE1 comprising ROH is added in vapour form below the feed point of the reactant stream SBE2 comprising aqueous sodium hydroxide solution MBOH but nevertheless at the upper end or in the region of the upper end of the reaction column RRB. This makes it possible to reduce the dimensions of the lower region of the reaction column RRB. When a portion of the reactant stream SBE1 comprising ROH, in particular methanol, is added especially in vapour form at the upper end or in the region of the upper end of the reaction column RRB only a fraction of 10% to 70% by weight, preferably of 30% to 50% by weight, (in each case based on the total amount of the alcohol ROH employed in step (α2)) is introduced at the lower end of the reaction column RRB and the remaining fraction is added in vapour form in a single stream or divided into a plurality of substreams preferably 1 to 10 theoretical trays, particularly preferably 1 to 3 theoretical trays, below the feed point of the reactant stream SBE2 comprising MBOH.
In the reaction column RRB the reactant stream SBE1 comprising ROH is then reacted with the reactant stream SBE2 comprising MBOH according to the reaction <1> described hereinabove to afford MBOR and H2O, where these products are present in admixture with the reactants ROH and MBOH since an equilibrium reaction is concerned. Accordingly a crude product RPB which contains not only the products MBOR and water but also ROH and MB is obtained in the reaction column RRB in step (α2) of the process according to the invention.
The bottom product stream SBP comprising ROH and MBOR is obtained and withdrawn at the lower end of RRB.
A water-containing alcohol stream, presently described as “vapour stream SBB comprising water and ROH”, is withdrawn at the upper end of RRB, preferably at the column top of RRB.
In step (β) of the process according to the invention at least a portion of this vapour stream SBB comprising water and ROH is employed especially as mixture G in step (a) of the process according to the invention. Said mixture is supplied to the rectification column RDA as mixture G in admixture with SAB or not, i.e. separate from SAB. It is preferable when the vapour streams SBB and SAB are mixed and then the mixture is employed as mixture G in step (a) of the process according to the invention.
The amount of alcohol ROH present in the reactant stream SBE1 is preferably selected so that it simultaneously serves as solvent for the alkali metal alkoxide MBOR present in the bottom product stream SBP. The amount of the alcohol ROH in the reactant stream SBE1 is preferably chosen to achieve in the bottom of the reaction column the desired concentration of the alkali metal alkoxide solution which is withdrawn as a bottoms product stream SBP comprising ROH and MBOR.
In a preferred embodiment of the process according to the invention, and especially in the cases where SBE2 contains water in addition to MBOH, the ratio of the total weight (masses; units: kg) of alcohol employed in step (α2) as reactant stream SBE1 ROH to the total weight (masses; unit: kg) of MBOH employed in step (α2) as reactant stream SBE2 is 4:1 to 50:1, more preferably 8:1 to 48:1, yet more preferably 10:1 to 45:1, yet still more preferably 20:1 to 40:1.
The reaction column RRB is operated with or without, preferably with, reflux.
“With reflux” is to be understood as meaning that the vapour stream SBB withdrawn at the upper end of the respective column, the reaction column RRB in step (α2), comprising water and ROH is not completely discharged, i.e. in step (β) of the process according to the invention not completely employed as mixture G in step (a), i.e. supplied to the rectification column RDA, but rather at least partially, preferably partially, returned to the respective column, the reaction column RRB in step (α2), as reflux. In the cases where such a reflux is established the reflux ratio is preferably 0.01 to 0.99, more preferably 0.02 to 0.9, yet more preferably 0.03 to 0.34, particularly preferably 0.04 to 0.27 and very particularly preferably 0.05 to 0.24.
In the embodiment in which a reflux is established for the reaction column RRB the MBOH employed in step (α2) as reactant stream SBE2 may also be at least partially mixed with the reflux stream and the resulting mixture thus supplied to step (α2).
Optional step (α2) is performed especially at a temperature in the range from 45° C. to 150° C., preferably 47° C. to 120° C., more preferably 60° ° C. to 110° C., and at a pressure of 0.5 bar abs. to 40 bar abs. preferably in the range from 0.7 bar abs. to 5 bar abs., more preferably in the range from 0.8 bar abs. to 4 bar abs., more preferably in the range from 0.9 bar abs. to 3.5 bar abs., yet more preferably at 1.0 bar abs. to 3 bar abs.
The reaction column RRB comprises in a preferred embodiment at least one evaporator which is in particular selected from intermediate evaporators VZB and bottoms evaporators VSB. The reaction column RRB particularly preferably comprises at least one bottoms evaporator VSB.
Such an intermediate evaporator VZB can convert liquid crude product RPB present in the reaction column RRB comprising MBOR, water, ROH, MBOH into the gaseous state, thus improving the efficiency of the reaction according to step (α2) of the process according to the invention.
By arranging one or more intermediate evaporators VZB in the upper region of the reaction column RRB the dimensions in the lower region of the reaction column RRB can be reduced. In the embodiment having at least one, preferably two or more, intermediate evaporators VZB it is also possible to introduce substreams of the ROH in liquid form in the upper region of the reaction column RRB.
In step (α2) of the process according to the invention a bottoms product stream SBP comprising ROH and MBOR is withdrawn at the lower end of the reaction column RRB.
It is preferable when the reaction column RRB comprises at least one bottoms evaporator VSB through which the bottoms product stream SBP is then at least partially passed to at least partially remove ROH, thus affording a bottoms product stream SBP* having an elevated mass fraction of MBOR compared to SBP.
The mass fraction of MBOR in the bottoms product stream SBP* is in particular elevated compared to the mass fraction of MBOR in the bottoms product stream SBP by at least 0.5%, preferably by ≥1%, more preferably by ≥2%, yet more preferably by ≥5%.
It is preferable when SBP or, if at least one bottoms evaporator VSB is employed through which the bottoms product stream SBP is at least partially passed to at least partially remove ROH, SBP* has a mass fraction of MBOR in ROH in the range from 1% to 50% by weight, preferably 5% to 35% by weight, more preferably 15% to 35% by weight, most preferably 20% to 35% by weight, in each case based on the total mass of SBP.
The mass fraction of residual water in SBP/SBP* is preferably <1% by weight, preferably <0.8% by weight, more preferably <0.5% by weight, based on the total mass of SBP.
The mass fraction of reactant MBOH in SBP/SBP* is preferably <1% by weight, preferably <0.8% by weight, more preferably <0.5% by weight, based on the total mass of SBP.
In the embodiments of the present process in which step (α2) is also performed it is preferable when the bottoms product stream SAP is at least partially passed through a bottoms evaporator VSA and ROH is at least partially removed from SAP to afford a bottoms product stream SAP* having an elevated mass fraction of MAOR compared to SAP and/or, preferably and, the bottoms product stream SBP is at least partially passed through a bottoms evaporator VSB and ROH is at least partially removed from SBP to afford a bottoms product stream SBP* having an elevated mass fraction of MBOR compared to SBP.
In the embodiments of the present invention in which it is performed step (α2) of the process according to the invention is performed simultaneously with and spatially separate from step (α1). Spatial separation is ensured by performing steps (α1) and (α2) in the two reaction columns RRA and RRB.
In an advantageous embodiment of the invention the reaction columns RRA and RRB are accommodated in one column shell, where the column is at least partially subdivided by at least one dividing wall. Such a column having at least one dividing wall will be referred to as “TRD”. Such dividing wall columns are familiar to those skilled in the art and are described for example in U.S. Pat. No. 2,295,256, EP 0 122 367 A2, EP 0 126 288 A2, WO 2010/097318 A1 and by I. Dejanović, Lj. Matijašević, Ž. Olujić, Chemical Engineering and Processing 2010, 49, 559-580. CN 105218315 A likewise describes dividing wall columns which are used in the rectification of methanol.
In the dividing wall columns suitable for the process according to the invention the dividing walls preferably extend to the column floor and, in particular, preferably span at least a quarter, more preferably at least a third, yet more preferably at least half, yet more preferably at least two thirds, yet still more preferably at least three quarters, of the column by height. They divide the columns into at least two reaction spaces in which spatially separate reactions may be carried out. The reaction spaces provided by the at least one dividing wall may be of identical or different sizes.
In this embodiment the bottoms product streams SAP and SBP may be separately withdrawn in the respective regions separated by the dividing wall and preferably passed through the bottoms evaporator VSA/VSB attached for each reaction space formed by the at least one reaction wall in which ROH is at least partially removed from SAP/SBP to afford SAP*/SBP*.
In a preferred embodiment of the process according to the invention accordingly at least two, more preferably precisely two, of the columns selected from rectification column RDA, reaction column RRA and if step (α2) is performed the reaction column RRB are accommodated in one column shell, wherein the columns are at least partially separated from one another by a dividing wall extending to the bottom of the column.
In the integrated system comprising reaction column RRA (or in the embodiments in which step (α2) is performed reaction column RRA and reaction column RRB) and rectification column RDA in the process according to the invention the rectification column RDA is preferably operated at a pressure selected such that the pressure gradient between the columns is low.
The alcohol ROH is consumed in the process according to the invention and especially in a continuous process mode therefore requires replacement with fresh alcohol ROH.
Supply of the fresh alcohol ROH is thus especially carried out directly as reactant stream SAE1 comprising ROH into the reaction column RRA or in the embodiments in which step (α2) is performed into the reaction columns RRA and RRB.
In the process according to the invention it is further preferable to employ the ROH-comprising vapour stream SOA partially as reactant stream SAE1 in step (α1) and optionally as reactant stream SBE1 in step (α2). The compressed vapour stream SOA1 may alternatively or in addition be employed partially as reactant stream SAE1 in step (α1) and optionally as reactant stream SBE1 in step (α2). In this preferred embodiment it is yet more preferable when the fresh alcohol ROH is added to the rectification column RDA.
When the fresh alcohol ROH is added to the rectification column RDA it is preferably supplied either in the rectifying section of the rectification column RDA or directly at the top of the rectification column RDA. The optimal feed point depends on the water content of the employed fresh alcohol and also on the desired residual water content in the vapour stream SOA. The higher the proportion of water in the employed alcohol and the higher the purity requirements of the vapour stream SOA the more advantageous is a feed a number of theoretical plates below the top of the rectification column RDA. Up to 20 theoretical plates below the top of the rectification column RDA and in particular 1 to 5 theoretical plates are preferred.
When the fresh alcohol ROH is added to the rectification column RDA it is added at the top of the rectification column RDA at temperatures up to boiling point, preferably at room temperature. A dedicated feed may be provided for the fresh alcohol or else when a portion of the alcohol withdrawn at the top of the rectification column RDA is recycled may be mixed therewith after condensation and supplied to the rectification column RDA together. In this case it is particularly preferable when the fresh alcohol is added to a condensate container in which the alcohol condensed from the vapour stream SOA is collected.
As described hereinabove, in an advantageous embodiment of the invention at least two of the columns selected from rectification column RDA, reaction column RRA and if step (α2) is performed the reaction column RRB are accommodated in one column shell, wherein the columns are in each case at least partially separated from one another by a dividing wall extending to the bottom of the column. In the abovedescribed preferred embodiment in which step (α2) is performed these are thus separated from one another by two dividing walls, wherein the two dividing walls extend to the bottom of the column.
In this preferred embodiment the reaction to afford the crude product RPA according to step (α1) or the crude products RPA and RPB according to steps (α1) and (α2) are in particular performed in one part of the TRD, wherein the reactant stream SAE2 and optionally the reactant stream SBE2 are added below but at approximately the height of the upper end of the dividing wall and the reactant stream SAE1 and optionally the reactant stream SBE1 are added in vapour form at the lower end. The alcohol/water mixture formed above the feed point of the reactant stream then becomes distributed above the dividing wall over the entire column region which serves as rectifying section of the rectification column RDA. The second/third lower part of the column which has been separated off by the dividing wall is the stripping section of the rectification column RDA. The energy required for the distillation is then supplied via an evaporator at the lower end of the second portion of the column separated by the dividing wall, wherein this evaporator may be conventionally heated or heated with a portion of the compressed vapour stream SOA2. When the evaporator is conventionally heated an intermediate evaporator heated with a portion of the compressed vapour stream SOA11 may additionally be provided.
In the embodiments in which a portion of SOA is employed as reactant stream SAE1 and/or reactant stream SBE1 SOA is especially compressed with a first compressor VDAB2 (“precompressed”), wherein the difference in the pressures inside the reaction columns RRA and RRB compared to the pressure in RDA may be taken into account.
Instead of the compressor VDAB2 which is arranged downstream of the rectification column RDA and in which SOA is precompressed this preferred embodiment may also employ, alternatively or in addition, a compressor VDAB1 which is arranged upstream of the rectification column RDA and through which the mixture G is passed before it is passed into RDA.
Provided it is not recycled to RDA as reflux the remaining portion of the at least one vapour stream SOA, i.e. especially the portion not employed as reactant stream SAE1 and/or reactant stream SBE1, is in this preferred embodiment then further compressed to afford SOA1. According to the invention SOA becomes SOA1 only in the compressor stage after which SOA1 is divided into SOA11 and SOA12 as are employed in step (d) according to the invention. This compression to compress SOA into SOA1 is in the figures and examples performed with the compressor VD1 (referred to in the figures as <401>).
In step (B) of the process according to the invention at least a portion of the vapour stream SAB, and if step (α2) is performed at least a portion of the vapour stream SBB, in admixture with SAB Or separate from SAB, is employed as mixture G in step (a) of the process according to the invention. If step (α2) is performed it is preferable when the at least a portion of the vapour stream SAB and the at least a portion of the vapour stream SBB are mixed and then employed as mixture G in step (a) of the process according to the invention.
“Employed as mixture G in step (a) of the process according to the invention” is in particular to be understood as meaning that the two streams SAB and SBB are passed into the rectification column RDA and are preferably previously mixed.
However, they may alternatively also be passed into the rectification column RDA at two different feed points.
In an advantageous embodiment of the present invention the energy comprised in at least one of the streams SOA1, SOA2, SOA11, SOA12 is used for operation of other industrial processes. This is advantageous especially in sites hosting integrated systems (chemistry parks, technology parks) where there is always a need for heat for heating. Especially in the case of integrated systems comprising two or more plants for alkali metal alkoxide production this energy may be advantageously utilized. Such integrated systems typically also comprise processes for transalcoholization as described in DE 27 26 491 A1. U.S. Pat. No. 3,418,383 A describes processes for transalcoholization from methoxides to propoxides.
A preferred aspect of the present invention provides that in the process according to the present invention in a reactive rectification column RRC a reactant stream SCE1 comprising McOR′ and optionally R′OH is reacted in countercurrent with a reactant stream SCE2 comprising R″OH to afford a crude product RPC comprising McOR″ and R′OH, wherein a bottoms product stream SCP comprising McOR″ is withdrawn at the lower end of RRC and a vapour stream SCB comprising R′OH is withdrawn at the upper end of RRC,
The process according to the invention according to the preferred aspect of the invention is a process for transalcoholization of a particular alkali metal alkoxide McOR′ to afford another alkali metal alkoxide McOR″ as described for example in DE 27 26 491 A1.
R′ and R″ are two distinct C1 to C6 hydrocarbon radicals, preferably two distinct C1 to C4 hydrocarbon radicals.
More preferably R′ is methyl and R″ is a C2 to C4 hydrocarbon radical, yet more preferably R′=methyl and R″=ethyl.
The process according to the preferred aspect of the invention (hereinbelow also referred to as “transalcoholization”) is performed in a reactive rectification column RRC. Suitable reactive rectification columns include columns described for RRA at point 4.2.1 in the context of step (α1).
The reaction column RRC is operated with or without, preferably with, reflux. If a reflux is established in particular the vapour SCB is partially or completely passed through a condenser KRRC and the condensed vapour may then be returned to the reaction column RRC or employed as reactant stream SAE1 Or SBE1. It may also be employed as the fresh alcohol stream in RDA.
In the transalcoholization a bottoms product stream SCP comprising McOR″ is withdrawn at the lower end of RRC. A vapour stream SCB comprising R′OH is withdrawn at the upper end of RRC.
Preferably, in the embodiments of the transalcoholization which also comprise performing the process for producing an alkali metal alkoxide according to the invention the employed reactant stream SCE1 comprising McOR′ and optionally R′OH preferably comprises at least a portion of SAP, in particular since R=methyl and thus also R′=methyl. It is then particularly preferable when R″=ethyl. A transalcoholization of alkali metal methoxide to the corresponding alkali metal ethoxide is accordingly carried out.
In a preferred alternative in the embodiments of the transalcoholization which also comprise performing the process for producing an alkali metal alkoxide including step (α2) according to the invention the employed reactant stream SCE1 comprising McOR′ and optionally R′OH preferably comprises at least a portion of SBP, in particular since R=methyl and thus also R′=methyl. It is then particularly preferable when R″=ethyl. A transalcoholization of alkali metal methoxide to the corresponding alkali metal ethoxide is accordingly carried out.
When SBP and SAP comprise the same alkali metal alkoxide and the same alcohol ROH these two streams may also be employed separately or in admixture as SCE1, i.e. in particular first mixed and then supplied to the column RRC as reactant stream SCE1 or supplied to the column RRC separately as two reactant streams SCE1.
The reactant stream SCE2 comprises R″OH. In a preferred embodiment the mass fraction of R″OH in SCE2 is ≥85% by weight, more preferably ≥90% by weight, wherein SCE2 otherwise comprises in particular McOR″ or another denaturant. The alcohol R″OH employed as reactant stream SCE2 may also be commercially available alcohol having an alcohol mass fraction of more than 99.8% by weight and a mass fraction of water of up to 0.2% by weight.
“Reaction of a reactant stream SCE1 comprising McOR′ and optionally R′OH with a reactant stream SCE2 comprising R″OH in countercurrent” is according to the invention ensured, in particular, as a result of the feed point for at least a portion of the reactant stream SCE1 comprising McOR′ being located on the reaction column RRC above the feed point of the reactant stream SCE2 comprising R″OH.
The reaction column RRC is operated with or without, preferably with, reflux.
In a preferred embodiment the reaction column RRC comprises at least one evaporator which is in particular selected from intermediate evaporators VZC and bottoms evaporators VSC. The reaction column RRC particularly preferably comprises at least one bottoms evaporator VSC.
In the case of the reaction column RRC intermediate evaporation comprises withdrawal of at least one side stream SZC from RRC and supply thereof to the at least one intermediate evaporator VZC.
In the case of the reaction column RRC bottoms evaporation comprises withdrawal of at least one stream, for example SCP from RRC and supply of at least a portion, in the case of SCP preferably a portion, to the at least one bottoms evaporator VSC.
Suitable evaporators employable as intermediate evaporators and bottoms evaporators are described in section 4.2.1.
In the transalcoholization, energy, preferably heat, is transferred from at least a portion of a stream selected from SOA1, SOA2 to the crude product RPC. This is preferably effected by transfer of energy from at least a portion of a stream selected from SOA1, SOA2 to SCE1 or SCE2 before passage thereof into RRC followed by transfer of energy from SCE1/SCE2 to the crude product RPC present in RRC, with which they mix together.
Accordingly energy, preferably heat, from at least a portion of a stream selected from SOA1, SOA2, in particular from at least one stream selected from SOA11, SOA12, SOA2, preferably from at least one stream selected from SOA11, a portion of SOA2, is transferred to the crude product RPC.
“Transfer of energy, preferably heat, from at least a portion of SOA1 to the crude product RPC″ also comprises the transfer of energy, preferably heat, from at least one stream selected from SOA11, SOA12, stream SOA1 before separation thereof into SOA11, SOA12 to the crude product RPC.
In addition crude product RPC may also be passed through an intermediate evaporator VZC or a bottoms evaporator VSC and in VZC/VSC energy, preferably heat, may be transferred from at least a portion of a stream selected from SOA1, SOA2 to the crude product RPC.
In addition the bottoms product stream SCP may also be partially passed through an intermediate evaporator VSC and then partially recycled to RRC, wherein in VSC energy, preferably heat, is transferred from at least a portion of a stream selected from SOA1, SOA2 to the recycled portion of SCP and then in the column RRC transferred from SCP to the crude product RPC present in the column.
The transfer of energy from at least a portion of a stream selected from SOA1, SOA2 to the recited streams is effected directly or indirectly, i.e. without or with heat transfer medium W1, as described accordingly in section 4.1.4.
The preferred embodiment of the process according to the invention makes it possible to efficiently employ the energy from SOA1, SOA2, in particular from SOA2, SOA11, SOA12. This reduces the total energy demand.
A stream of aqueous NaOH (50% by weight) SAE2 <102> of 100 kg/h is supplied at 30° C. to the top of a reaction column RRA <100>. A vaporous methanol stream SAE1 <103> of 1034.9 kg/h is supplied in countercurrent at the bottom of the reaction column RRA <100>. The reaction column RRA <100> is operated at a head pressure of 2.15 bar abs. At the bottom of the column RRA <100> a virtually water-free product stream SAP* <104> of 219.7 kg/h is withdrawn (30% by weight sodium methoxide in methanol). The evaporator VSA <105> of the reaction column RRA <100> introduces about 24 KW of heating power using low pressure steam. A vaporous methanol-water stream SAB <107> is withdrawn at the top of the reaction column RRA <100> and 80 kg/h thereof are condensed in the condenser KRRA <108> and returned to the reaction column RRA <100> as reflux while the remaining stream of 915.2 kg/h is supplied to a rectification column RDA <300>. The rectification column RDA <300> is operated at a head pressure of 2.0 bar abs. At the bottom of the rectification column RDA <300> a liquid water stream SUA <304> of 72.2 kg/h is discharged (500 ppmw of methanol). At the top of the rectification column RDA <300> a vaporous methanol stream SOA <302> (2 bar, 83° ° C.; 200 ppmw of water) of 1903.6 kg/h is withdrawn and 63.9 kg/h thereof are condensed in a condenser KRD <407> while the remaining stream is supplied to a first compressor VDAB2 <303> and therein compressed to 2.6 bar abs. The stream is subsequently divided and a stream of 1034.9 kg/h is recycled to the reaction column RRA <100>. The remainder of 804.8 kg/h is supplied to a multi-stage compression with intermediate cooling. In the compressor VD1 <401> the stream is compressed to pOA1=4.8 bar abs. and TOA1=156° C. to obtain stream <403>. In the subsequent intermediate cooling in the intermediate cooler WTX <402> the stream is cooled to 145° C. and about 4.4 KW of heat are removed using cooling water. In the compressor VDx <405> the stream is finally compressed again to 9.0 bar and 200° C. to obtain stream <404>. The subsequent condenser which is simultaneously the bottoms evaporator VSRD <406> of the rectification column RDA <300> provides the approximately 238 KW of heating power for the rectification column RDA <300>. The thus condensing methanol stream <404> is mixed together with 191.9 kg/h of fresh methanol (1000 ppmw of water) <408> and the 63.9 kg/h of previously condensed vapours and recycled to the top of the rectification column RDA <300>.
The compressor power sums to about 55 kW.
Together with the 24 KW for the heating steam this results in a compressor and heating steam power demand of about 79 kW.
The arrangement in noninventive example 2 corresponds to that of example 1 with the following differences:
The rectification column RDA <300> comprises an intermediate evaporator VZRD <409>. A liquid stream SZA <305> is withdrawn from the rectification column RDA <300> at 94° C. and about 230 KW of heat are transferred thereto in the intermediate evaporator VZRD <409>, wherein the stream is partially evaporated and subsequently returned to the rectification column RDA <300>. A vaporous methanol stream SOA <302> (200 ppmw of water) of 1887.1 kg/h is withdrawn at the top of the rectification column RDA <300> and 89.4 kg/h thereof are condensed in a condenser KRD <407>. The remaining stream is compressed to 2.6 bar abs. in a first compressor VDAB2 <303> as in example 1. A substream of 1034.9 kg/h is then recycled to the reaction column RRA <100>. The remainder of 762.8 kg/h is compressed to 5.6 bar abs. and 168° C. to obtain stream <403>. The subsequent condenser which is simultaneously the intermediate evaporator VSRD <409> of the rectification column RDA <300> provides the approximately 230 KW of heating power for the rectification column RDA <300>. The thus condensed methanol stream <403> is mixed with 191.9 kg/h of fresh methanol <408> and the 89.4 kg/h of previously condensed vapours and returned to the top of the rectification column RDA <300>. The bottoms evaporator VSRD <406> of the reaction column RDA <300> introduces about 20 KW of heating power using low pressure steam. Compared to example 1 the vapour stream need be compressed only to 5.6 bar abs. instead of 9 bar abs. to be able to transmit its heat to the evaporator VZRD <409> since the boiling temperature in the intermediate evaporator VZRD <409> is lower than in the bottoms evaporator VSRD <406>. The compressor power thus sums to only about 38 KW (instead of 55 KW) while the heating steam demand increases relative to example 1 to about 44 KW since the bottoms evaporator VSRD <406> requires a heating power of 20 KW and this introduced with the heat of low pressure steam. The compressor and heating steam power demands thus sum to about 82 kW.
The arrangement in inventive example 3 corresponds to that of example 1 and 2 with the following differences:
The compressor power sums to about 42 KW (instead of 55 KW in example 1). Since no low pressure steam is required for the bottoms evaporator VSRD <406> only about 24 KW need be provided using heating steam as in example 1. The sum of the compressor and heating steam power demands thus falls to about 66 kW.
Compared to example 1 only a lower vapour stream need be compressed to 9 bar abs., a large part of the vapour stream need only be compressed to 5.6 bar abs. as in example 2, thus reducing the total compressor power. However, compared to example 2 steady state operation does not require any low pressure steam in the bottoms evaporator VSRD <406>, thus reducing the heating steam demand compared to example 2.
The total energy to be supplied is minimized by the process according to example 3.
The proportion of heating power provided by low pressure steam and compressor power in each case is shown in
Result: The inventive procedure of effecting staged compression of the vapour stream and thus operating the intermediate evaporator and the bottoms evaporator with the vapours compressed to different extents surprisingly achieves energy savings.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21179722.0 | Jun 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/057591 | 3/23/2022 | WO |
