Patent Application
20100036154
The invention relates to a multistage process for continuous phosgene-free preparation of (cyclo)aliphatic diisocyanates, which comprises the conversion of (cyclo)aliphatic diamines to the corresponding (cyclo)alkylene biscarbamates and the thermal cleavage of the latter to the (cyclo)alkylene diisocyanates and alcohol.
Diisocyanates are valuable chemical compounds which, by the principle of the diisocyanate polyaddition process, allow the controlled formation of polymers which find various industrial uses as polycarbamates or polyureas in foams, elastomers, thermoplastics, fibers, light-stable polycarbamate coatings or adhesives.
The synthetic access route to isocyanates may be via a series of different routes. The oldest variant for industrial scale preparation of isocyanates, which is still prevalent today, is the phosgenation of the corresponding amines using corrosive, very toxic phosgene which contains a high proportion of chlorine, which places particularly high demands on its handling on the industrial scale.
There are several methods for avoiding the use of phosgene for preparation of isocyanates in industrial orders of magnitude. The term “phosgene-free process” is frequently used in connection with the conversion of amines to isocyanates using alternative carbonylating agents, e.g. urea or dialkyl carbonate (EP 18 586, EP 355 443, U.S. Pat. No. 4,268,683, EP 990 644).
The so-called urea route is based on the urea-mediated conversion of diamines to diisocyanates via a two-stage process. In the first process step, a diamine is reacted with alcohol in the presence of urea or urea equivalents (e.g. alkyl carbonates, alkyl carbamates) to give a biscarbamate, which typically passes through an intermediate purification stage and is then cleaved thermally in the second process step to diisocyanate and alcohol (EP 126 299, EP 126 300, EP 355 443, U.S. Pat. No. 4,713,476, U.S. Pat. No. 5,386,053). Alternatively, the actual biscarbamate formation may also be preceded by the separate preparation of a bisurea by controlled reaction of the diamine with urea (EP 568 782). Also conceivable is a two-stage sequence consisting of partial reaction of urea with alcohol in the first step and subsequent metered addition and carbamatization of the diamine in the second step (EP 657 420).
The thermal cleavage of (cyclo)aliphatic biscarbamates can be effected in the gas phase or in the liquid phase, with or without solvent and with or without catalysts. For instance, EP 126 299 and EP 126 300 disclose processes for preparing, respectively, hexamethylene diisocyanate and isophorone diisocyanate by cleaving the corresponding biscarbamates in the gas phase in a tubular reactor in the presence of metallic random packings at 410° C. Apart from the fact that such high temperatures can be established only with complicated technology, the process is afflicted with the disadvantage that partial decomposition of the reaction products already takes place at this temperature, associated with deposits on the random packings and blockage of the tubular reactor, and so the process is not very suitable for industrial production owing to the short service life.
There has therefore been no lack of attempts, by chemical and process technology measures, to achieve yield improvements and restrict undesired by-product formation. For instance, a series of documents describes the use of catalysts which accelerate the cleavage reaction of the biscarbamates (DE 1 022 222, U.S. Pat. No. 3,919,279, DE 2 635 490). Indeed, in the presence of suitable catalysts—these are a variety of basic, acidic and organometallic compounds—it is entirely possible to enhance the isocyanate yield compared to the uncatalyzed variant. However, the formation of undesired by-products cannot be avoided even through the presence of a catalyst. The same applies to the additional use of inert solvents, as likewise recommended in U.S. Pat. No. 3,919,279 and DE 2 635 490, in order to ensure homogeneous distribution of the heat supplied and of the catalyst within the reaction medium. In principle, the use of solvents which boil under reflux, however, results in a reduction in the space-time yield of isocyanates and is, moreover, afflicted with the disadvantage of an additional high energy expenditure.
Examples cited in EP 54 817 for the thermally catalyzed cleavage of monocarbamates describe the partial discharge of the reaction mixture to remove the resinifying by-products which form in the course of the carbamate cleavage. This procedure serves to prevent deposits and blockages in reactors and workup units. There are no indications which point to a yield-increasing utilization of the partial discharge. EP 61 013 describes a similar approach to a solution, the thermolysis in this case being performed in the presence of solvents whose purpose apparently consists in a better absorption of the nonvolatile by-products. Here too, the partial discharge is not utilized in the manner of a yield optimization.
EP 355 443 discloses that a yield increase can be achieved when the high molecular weight utilizable and nonutilizable by-products formed during the cleavage of the biscarbamates in the cleavage reactor, to ensure a disruption-free and selective reaction, are discharged very substantially continuously from the reactor and then converted for the most part in the presence of alcohol and then recycled into the (cyclo)alkylene biscarbamate synthesis. The procedure described is associated with high energy expenditure, since nonutilizable by-products are removed from the discharge of the (cyclo)alkylene biscarbamate synthesis by distillation, it being necessary to evaporate the entire biscarbamate. In contrast to EP 355 443, the biscarbamate discharge in the process of EP 566 925 is divided into two substreams, of which only one is freed by distillation from its high-boiling, nonutilizable by-products, before the contaminated biscarbamate streams are fed to the deblocking reaction in the cleavage reactor. In addition, the continuous cleavage reactor discharge in EP 566 925 is recycled directly, i.e. without a recarbamatization step, into the (cyclo)alkylene biscarbamate synthesis.
The preparation of (cyclo)aliphatic biscarbamates in a one-pot reaction from diamine, urea and alcohol with simultaneous removal of ammonia is known from EP 18 568. The teaching of EP 18 568 has been developed further and is described in EP 126 299, EP 126 300, EP 355 443, EP 566 925. The disadvantage of the simultaneous reaction of diamine, urea and alcohol undertaken there is the selectivity which is reduced by unavoidable side reactions, as a result of by-products which are inevitably formed in relatively large amounts, which have to be removed before the thermal deblocking of the biscarbamates. EP 568 782 therefore recommends a continuous process for preparing (cyclo)aliphatic diisocyanates, which comprises essentially three main steps, of which the first describes the formation of (cyclo)alkylenebisureas, the second the formation of (cyclo)alkylene biscarbamates from the (cyclo)alkylenebisureas, and the third the cleavage of the (cyclo)alkylene biscarbamates in the liquid phase to the desired (cyclo)aliphatic diisocyanates—i.e. the (cyclo)alkylene biscarbamate is prepared in two separate stages. According to the teaching of EP 568 782, the discharge of the reaction sequence composed of (cyclo)alkylenebisurea formation and subsequent (cyclo)alkylene biscarbamate synthesis is first freed by distillation from low and medium boilers such as alcohols, carbamates and carbonates, and the high boilers in the biscarbamate are removed thereafter by short-path evaporation. The (cyclo)alkylene biscarbamate is deblocked thermally and a portion of the cleavage bottoms is discharged continuously, recarbamatized with alcohol and recycled back into the (cyclo)alkylene biscarbamate synthesis stage.
It is also stated, in EP 1 634 868, that when (cyclo)aliphatic diamines are used, in addition to the one-stage synthesis of (cyclo)aliphatic biscarbamates from (cyclo)aliphatic diamines, alcohol and urea, it is advantageous to prepare the (cyclo)aliphatic biscarbamates by two-stage reaction, which thus proceeds via (cyclo)aliphatic bisurea, of (cyclo)aliphatic diamines with alcohol and urea, to free them of low and medium boilers, to thermally cleave the (cyclo)aliphatic biscarbamates thus purified to release the desired (cyclo)aliphatic diisocyanate, to continuously discharge a portion of the cleavage bottoms from the cleavage apparatus and to recarbamatize it with alcohol, to remove high boiler components therefrom and to recycle the recarbamatized material thus purified into the process, or else to directly remove the high boiler components from the portion of the cleavage bottoms discharged continuously from the cleavage apparatus, to recarbamatize the distillate obtained with alcohol and to recycle the recarbamatized material into the process. It has been found that these process steps firstly achieve a comparatively low steady-state concentration of high boiler components over the entire sequence of biscarbamate synthesis, biscarbamate purification and biscarbamate cleavage, such that deposits which are promoted especially by the high boiler components which are high in viscosity by nature can substantially be prevented, and good plant availability and a good process yield are also ensured over the long term. Secondly, the sequence of recarbamatization and high boiler removal, or high boiler removal with subsequent recarbamatization of the distillate, which follows downstream of the thermal cleavage reaction, has the advantage that, compared to the customary procedure in which the high boilers are removed before the biscarbamate cleavage, the amount of biscarbamate to be converted to the vapor phase is reduced significantly, which allows capital and energy costs to be saved.
In addition, EP 1 582 680 states that, when (cyclo)aliphatic diamines are used, it is advantageous to free the (cyclo)aliphatic biscarbamates of low and medium boilers after they have been synthesized by reacting (cyclo)aliphatic diamines with alcohol and urea and/or urea derivatives, to thermally cleave the (cyclo)aliphatic biscarbamates thus purified to release the desired (cyclo)aliphatic diisocyanate, to continuously discharge a portion of the cleavage bottoms from the cleavage apparatus and to remove high boiler components therefrom, and to recarbamatize the discharge thus purified with alcohol and to recycle it into the process. It has been found that it is possible in this way firstly to achieve a comparatively low steady-state concentration of high boiler components over the overall sequence of biscarbamate synthesis, biscarbamate purification and biscarbamate cleavage, such that deposits which are promoted especially by the high boiler components which are high in viscosity by nature can substantially be prevented, and good plant availability and a good process yield are also ensured over the long term. Secondly, the high boiler removal which follows downstream of the thermal cleavage reaction has the advantage that, compared to the customary procedure in which the high boilers are removed before the biscarbamate cleavage, the amount of biscarbamate to be converted to the vapor phase is reduced significantly, which allows capital and energy costs to be saved.
The currently predominant commercial form of urea prepared on the industrial scale is that of prills, i.e. small pellets with a diameter of 1-3 mm. Even at very low water contents of <0.1%, crystalline urea has such a strong tendency to cake that it is not an option for loose storage in large amounts. Improvement of the storage properties of urea prills, which appears to be necessary, for example, in the case of silo storage of large amounts, is achieved by a subsequent surface treatment of the prills with powders, for example talc, bentonites, kieselguhr, diatoms or other silicatic substances, or by sulfur and also by spray application of small amounts of oil.
The urea industry nowadays preferentially adds formaldehyde at up to 0.6% by weight (Ullmann's Encyclopedia of Industrial Chemistry, Release 2006, 7th Edition) to the urea melt before the prilling in order to increase the stability of the prills. This measure serves to prevent decomposition and caking in the course of transport, and to improve the storage stability.
Urea from a urea melt treated with formaldehyde (including paraformaldehyde) before the prilling or granulation, and urea surface treated with formaldehyde (including paraformaldehyde), likewise an industrially practiced measure for improving the storage properties of the prills, leads to the formation of undesired by-products both in the case of one-stage and two-stage processes and also alternatively after multistage processes for preparing (cyclo)aliphatic biscarbamates, and in the subsequent thermal cleavage of the (cyclo)aliphatic biscarbamates to (cyclo)aliphatic diisocyanates.
The by-products formed in the continuous one-stage or multistage biscarbamate synthesis, after a short run time, not only lead to undesired caking in the apparatus with the consequence of relatively short production periods with subsequent complex cleaning procedures, but are also removable only insufficiently in the known stages, and in the different stages described in detail in the literature, for distillative workup of the crude biscarbamate.
In the units for thermal cleavage of the (cyclo)aliphatic biscarbamate to the (cyclo)aliphatic diisocyanate, both the by-products which have not been removed quantitatively from the biscarbamate stage itself and a by-product spectrum newly generated therefrom lead additionally to caking and hence to reduction of the plant availability as a result of complex cleaning procedures.
It is an object of the invention to provide an improved process for preparing (cyclo)aliphatic diisocyanates, which avoids the abovementioned disadvantages.
The object is achieved, surprisingly, by using, for the continuous preparation of (cyclo)aliphatic diisocyanates by reacting (cyclo)aliphatic diamines with urea and/or urea equivalents (e.g. alkyl carbonates, alkyl carbamates) and alcohols to give (cyclo)aliphatic biscarbamates and subsequent thermal cleavage of the (cyclo)aliphatic biscarbamates to (cyclo)aliphatic diisocyanates to form the (cyclo)aliphatic biscarbamates by one-stage, two-stage and also alternatively by multistage processes, unconditioned urea, irrespective of the administration form (prills, granule, crystals, melt, solution). Unconditioned urea has neither been surface treated nor have additives and/or formaldehyde been added to the melt before the prilling or granulation.
The urea used in accordance with the invention and also the urea employed to prepare urea equivalents (e.g. alkyl carbonates, alkyl carbamates) as a possible precursor to the synthesis of the (cyclo)aliphatic biscarbamates is unconditioned, i.e. it must not have been surface treated with inorganic substances, for example with talc, bentonites, kieselguhr, diatoms, kaolin or other silicatic substances which find use as anticaking agents, and/or originate from a urea melt treated with formaldehyde (including paraformaldehyde) and/or be surface treated with formaldehyde (or paraformaldehyde). In general, the maximum formaldehyde concentration (including paraformaldehyde) of the urea used or of the urea equivalents used is 0.01 to 0.10% by weight, preferably 0.001 to 0.01% by weight and more preferably less than 0.001% by weight.
The process according to the invention has the advantage that a quantitative removal of the by-product spectrum typically generated with the distillation and rectification units described to purify the (cyclo)aliphatic diisocyanates can be omitted, and leads to diisocyanate qualities whose profile of performance properties enables use in further finishing stages without additional workup steps.
The removal of the by-product spectrum generated in the biscarbamate stage from formaldehyde and/or from formaldehyde-containing components of the unconditioned urea used in the reaction with (cyclo)aliphatic diamines in the presence of alcohols is not required, and the use of additional apparatus is unnecessary. Owing to the avoidance of by-products in the biscarbamate stage, in addition, a further by-product spectrum in the thermal cleavage of the (cyclo)aliphatic biscarbamates to (cyclo)aliphatic diisocyanates is subsequently avoided. In this stage of distillative purification of the diisocyanates too, the use of additional apparatus to achieve the desired diisocyanate purities is superfluous.
An additional capital investment associated with a significant reduction in the overall process yield resulting from diamine losses caused by by-product formation, which additionally reduce the plant availability owing to the caking caused in various apparatus parts as a result of complex cleaning procedures, has surprisingly been completely avoided by the inventive use of unconditioned ureas, thus enhancing the economic viability of the process.
The invention provides a process for continuously preparing (cyclo)aliphatic diisocyanates by reacting at least one (cyclo)aliphatic diamine with urea and/or urea equivalents and at least one alcohol to give (cyclo)aliphatic biscarbamates and subsequently thermally cleaving the (cyclo)aliphatic biscarbamates to (cyclo)aliphatic diisocyanates, characterized in that the (cyclo)aliphatic biscarbamates are formed by using unconditioned urea and/or urea equivalents prepared from unconditioned urea.
The invention preferably provides a multistage process for continuously preparing (cyclo)aliphatic diisocyanates by reacting at least one (cyclo)aliphatic diamine with urea and/or urea equivalents, for example alkyl carbonates, alkyl carbamates, and at least one alcohol to give (cyclo)aliphatic biscarbamates and subsequently thermally cleaving the (cyclo)aliphatic biscarbamates to (cyclo)aliphatic diisocyanates, characterized in that the (cyclo)aliphatic biscarbamates are formed by one-stage, two-stage or else alternatively multistage processes by using, irrespective of the administration form (e.g. prills, granule, crystals, melt, solution), unconditioned urea and/or urea equivalents prepared from unconditioned urea (also referred to as carbonic acid derivatives, for example alkyl carbonates, alkyl carbamates).
The maximum formaldehyde concentration (including paraformaldehyde) of the urea used or of the urea equivalents used is 0.01 to 0.10% by weight, preferably 0.001 to 0.01% by weight and more preferably less than 0.001% by weight.
The invention provides a process for continuously preparing (cyclo)aliphatic diisocyanates of the formula (I)
OCN—R—NCO
where R is a straight-chain or branched aliphatic hydrocarbon radical having a total of 6 to 12 carbon atoms or an optionally substituted cycloaliphatic hydrocarbon radical having a total of 4 to 18 and preferably 5 to 15 carbon atoms, by reacting (cyclo)aliphatic diamines with unconditioned urea and/or urea equivalents prepared from unconditioned urea and alcohols to give (cyclo)aliphatic biscarbamates and the thermal cleavage thereof, which is characterized by the following individual steps:
H2N—R—NH2
R1—OH
H2N—OC—HN—R—NH—CO—NH2
R1O—OC—HN—R—NH—CO—OR1;
H2N—R—NH2
R1—OH,
R1O—OC—HN—R—NH—CO—OR1
The invention also provides a multistage process for continuously preparing (cyclo)aliphatic diisocyanates of the formula (I)
OCN—R—NCO
where R is a straight-chain or branched aliphatic hydrocarbon radical having a total of 6 to 12 carbon atoms or an optionally substituted cycloaliphatic hydrocarbon radical having a total of 4 to 18 and preferably 5 to 15 carbon atoms, by reacting (cyclo)aliphatic diamines with unconditioned urea and/or urea equivalents prepared from unconditioned urea and alcohols to give (cyclo)aliphatic biscarbamates and the thermal cleavage thereof, wherein a) (cyclo)aliphatic diamines of the formula (II)
H2N—R—NH2
R1—OH
H2N—OC—HN—R—NH—CO—NH2
R1O—OC—HN—R—NH—CO—OR1;
H2N—R—NH2
R1—OH,
R1O—OC—HN—R—NH—CO—OR1
By the process according to the invention, it is possible to prepare (cyclo)aliphatic diisocyanates, i.e. aliphatic and cycloaliphatic, with very good yield and high purities without any problem in continuous operation. What is advantageous in the multistage process according to the invention is especially the fact that, when unconditioned urea and/or urea equivalents prepared from unconditioned urea, also referred to as carbonic acid derivatives, for example alkyl carbonates, alkyl carbamates, with simultaneous use of (cyclo)aliphatic diamines of the formula (II), are used as starting materials for continuous diisocyanate synthesis, caking and deposits which are caused by conditioned urea and are promoted especially by the negative properties of the high-viscosity high boiler components can substantially be prevented. Moreover, the use of unconditioned urea is considered to be advantageous since material wear and erosion up to and including destruction of moving apparatus parts, which occurs as a result of the eroding properties of conditioned urea, for example comprising inorganic anticaking agents, can be avoided, thus also ensuring good plant availability over the long term. Moreover, it is a significant advantage that, in contrast to urea conditioned principally with formaldehyde or formaldehyde-containing components, which causes undesired by-products which are removable only with very great difficulty in the different process stages, the use of unconditioned urea and/or urea equivalents prepared from unconditioned urea allows diisocyanate qualities with high purities to be prepared, whose profile of performance properties does not cause any doubt as to use in further value addition stages.
In the text which follows, the terms diamine, alcohol, bisurea, biscarbamate and diisocyanate are used in the sense of the abovementioned definitions.
The multistage process according to the invention for continuously preparing (cyclo)aliphatic diisocyanates by reacting (cyclo)aliphatic diamines with unconditioned (untreated) urea and/or urea equivalents (e.g. alkyl carbonates, alkyl carbamates) prepared from unconditioned (untreated) urea and alcohols to give (cyclo)aliphatic biscarbamates and subsequent thermal cleavage of the (cyclo)aliphatic biscarbamates to (cyclo)aliphatic diisocyanates makes it possible to produce (cyclo)aliphatic diisocyanates with high purities in reactions which proceed selectively and without disruption. The process according to the invention is suitable especially for preparing aliphatic diisocyanates with a straight-chain or branched aliphatic hydrocarbon radical having a total of 6 to 12 carbon atoms, such as hexamethylene diisocyanate, 2-methylpentane diisocyanate, 2,2,4- and 2,4,4-trimethylhexamethylene diisocyanate or mixtures thereof, octamethylene diisocyanate, decamethylene diisocyanate, 2-methylnonamethylene diisocyanate, dodecamethylene diisocyanate, or an optionally substituted cycloaliphatic hydrocarbon radical having a total of 4 to 18 and preferably 5 to 15 carbon atoms, for example 1,4-diisocyanatocyclohexane, 1,3- or 1,4-cyclohexanedimethane isocyanate, 5-isocyanato-1,3,3-trimethylcyclohexanemethane isocyanate (isophorone diisocyanate), 4,4′-methylenedicyclohexyl diisocyanate (4,4′-H12MDI), 2,2′-methylenedicyclohexyl diisocyanate (2,2′-H12MDI), 2,4′-methylenedicyclohexyl diisocyanate (2,4′-H12MDI), or else mixtures of the aforementioned isomeric methylenedicyclohexyl diisocyanates (H12MDI). Very particular preference is given to preparing 5-isocyanato-1,3,3-trimethylcyclohexanemethane isocyanate (isophorone diisocyanate), 2,2,4- and 2,4,4-trimethylhexamethylene diisocyanate or mixtures thereof, and 4,4′-methylenedicyclohexyl diisocyanate, and also any desired mixtures of 4,4′-H12MDI, 2,4-H12MDI and 2,2′-H12MDI.
The (cyclo)aliphatic diisocyanates prepared are very suitable for production of polymers containing urethane, isocyanurate, amide and/or urea groups by the polyisocyanate polyaddition process. They additionally find use for preparation of polyisocyanate mixtures modified with urethane, biuret and/or isocyanurate groups. Such polyisocyanate mixtures of (cyclo)aliphatic diisocyanates are used especially to prepare high-value light-stable polyurethane coatings.
The invention also provides formaldehyde-free (cyclo)aliphatic diisocyanates obtainable by processes for continuously preparing (cyclo)aliphatic diisocyanates by reacting at least one (cyclo)aliphatic diamine with urea and/or urea equivalents and at least one alcohol to give (cyclo)aliphatic biscarbamates and then thermally cleaving the (cyclo)aliphatic biscarbamates to (cyclo)aliphatic diisocyanates, characterized in that the (cyclo)aliphatic biscarbamates are formed by using unconditioned urea and/or urea equivalents prepared from unconditioned urea, especially formaldehyde-free (cyclo)aliphatic diisocyanates selected from isophorone diisocyanate, trimethylhexamethylene diisocyanate, H12MDI and hexamethylene diisocyanate (HDI).
“Formaldehyde-free” means that the maximum formaldehyde concentration (including paraformaldehyde) of the urea used or of the urea equivalents used is 0.01 to 0.10% by weight, preferably 0.001 to 0.01% by weight and more preferably less than 0.001% by weight.
The invention is illustrated in detail by the examples which follow.
Examples 1 to 4 describe the preparation of (cyclo)aliphatic diisocyanates using unconditioned urea with a formaldehyde content of <10 ppm. Comparative examples A to D each describe the preparation of (cyclo)aliphatic diisocyanates using commercial urea with a formaldehyde content of 0.55% by weight.
A mixture of 41.0 kg/h of 5-amino-1,3,3-trimethylcyclohexanemethanamine, 29.8 kg/h of unconditioned urea and 107.0 kg/h of n-butanol were pumped via a steam-heated preheater to the first tray of a distillation reactor, and the reaction mixture with continuous removal of the ammonia released at standard pressure.
The mean residence time in the distillation reactor was 7 h. In the bottom of the distillation reactor operated under standard pressure, 12.5 kg/h of butanol from the bottom of an ammonia-butanol separating column were fed into the bottom of the distillation reactor. The amount of energy supplied to the distillation reactor in the reboiler is regulated such that the amount of butanol which is obtained at the top together with the ammonia formed and is condensed in the dephlegmator with warm water at 40° C. corresponds to that introduced in the bottom. The alcohol thus condensed is conducted continuously into an ammonia-butanol separating column. The solution of bisurea in alcohol obtained in the bottom of the distillation reactor was conducted under level control, via a preheater where it was heated to 190 to 200° C., together with 62.0 kg/h of reaction product from the recarbamatization stage, to the uppermost tray of the pressure distillation reactor. The mean residence time in the pressure distillation reactor was 10.5 h. Heating established the following temperature profile: bottom 229° C. and top 200° C. 103.0 kg/h of butanol were introduced into the bottom of the pressure distillation reactor, and the amount of heat carrier oil to the reboiler was regulated such that the amount of butanol drawn off together with the ammonia formed at the top corresponded to that fed in in the bottom.
The butanol/ammonia mixture obtained was subsequently conducted into the ammonia-butanol separating column. The top temperature there was 85° C. The butanol losses which arose through the ammonia discharge and from other losses (low boiler components and residues sent to incineration) were replaced by supplying 4.7 kg/h of fresh butanol into the bottom of the ammonia-butanol separating column. The mixture of 233.2 kg/h obtained in the bottom of the pressure distillation reactor was purified by distillation.
115.5 kg/h of biscarbamate were fed into the falling film evaporator of the combined cleavage and rectification column after addition of 0.2 kg/h of catalyst solution. The energy required for the cleavage and rectification was transferred with heat carrier oil in the falling film evaporator. The carbamate cleavage reaction was undertaken at a bottom pressure of 27 mbar and a bottom temperature of 230° C. The butanol of 40.0 kg/h which was formed during the cleavage and obtained at the top by rectification was drawn off and fed to the recarbamatization stage with the bottoms discharge of 21.7 kg/h from the combined cleavage and rectification column.
The crude diisocyanate of 55.4 kg/h drawn off in a side stream from the combined cleavage and rectification column was fed to a further purifying distillation so as to obtain 52.0 kg/h of purified diisocyanate. The purity of the diisocyanate obtained was determined by gas chromatography to be >99.5% by weight. The overall process yield based on diamine used was 97.2%.
A mixture of 35.7 kg/h of 5-amino-1,3,3-trimethylcyclohexanemethanamine, 25.9 kg/h of conditioned urea with a formaldehyde content of 0.55% by weight and 93.2 kg/h of n-butanol were pumped via a steam-heated preheater to the first tray of a distillation reactor, and the reaction mixture with continuous removal of the ammonia released at standard pressure.
The mean residence time in the distillation reactor was 7 h. In the bottom of the distillation reactor operated under standard pressure, 11.0 kg/h of butanol from the bottom of an ammonia-butanol separating column were fed into the bottom of the distillation reactor. The amount of energy supplied to the distillation reactor in the reboiler is regulated such that the amount of butanol which is obtained at the top together with the ammonia formed and is condensed in the dephlegmator with warm water at 40° C. corresponds to that introduced in the bottom. The alcohol thus condensed is conducted continuously into an ammonia-butanol separating column. The solution of bisurea in alcohol obtained in the bottom of the distillation reactor was conducted under level control, via a preheater where it was heated to 190 to 200° C., together with 51.2 kg/h of reaction product from the recarbamatization stage, to the uppermost tray of the pressure distillation reactor. The mean residence time in the pressure distillation reactor was 10.5 h. Heating established the following temperature profile: bottom 229° C. and top 200° C. 89.0 kg/h of butanol were introduced into the bottom of the pressure distillation reactor, and the amount of heat carrier oil to the reboiler was regulated such that the amount of butanol drawn off together with the ammonia formed at the top corresponded to that fed in in the bottom.
The butanol/ammonia mixture obtained was subsequently conducted into the ammonia-butanol separating column. The top temperature there was 85° C. The butanol losses which arose through the ammonia discharge and from other losses (low boiler components and residues sent to incineration) were replaced by supplying 4.5 kg/h of fresh butanol into the bottom of the ammonia-butanol separating column. The mixture of 212.1 kg/h obtained in the bottom of the pressure distillation reactor was purified by distillation.
94.1 kg/h of biscarbamate were fed into the falling film evaporator of the combined cleavage and rectification column after addition of 0.2 kg/h of catalyst solution. The energy required for the cleavage and rectification was transferred with heat carrier oil in the falling film evaporator. The carbamate cleavage reaction was undertaken at a bottom pressure of 27 mbar and a bottom temperature of 234° C. The butanol of 33.1 kg/h which was formed during the cleavage and obtained at the top by rectification was drawn off and fed to the recarbamatization stage with the bottoms discharge of 17.9 kg/h from the combined cleavage and rectification column.
The crude diisocyanate of 45.82 kg/h drawn off in a side stream from the combined cleavage and rectification column was fed to a further purifying distillation so as to obtain 43.0 kg/h of purified diisocyanate. The purity of the diisocyanate obtained was determined by gas chromatography to be 98.6% by weight. The overall process yield based on diamine used was 92.3%.
A mixture of 38.4 kg/h of 5-amino-1,3,3-trimethylcyclohexanemethanamine, 27.9 kg/h of unconditioned urea, 100.1 kg/h of n-butanol and 57.4 kg/h of reaction product from the recarbamatization stage were pumped via a steam-heated preheater, where it was heated to 190 to 200° C., to the first tray of a pressure distillation reactor.
The mean residence time in the pressure distillation reactor was 10.5 h. Heating established the following temperature profile: bottom 230° C. and top 200° C. 96.7 kg/h of butanol were introduced into the bottom of the pressure distillation reactor, and the amount of heat carrier oil to the reboiler was regulated such that the amount of butanol drawn off at the top together with the ammonia formed corresponded to that fed in in the bottom.
The resulting butanol/ammonia mixture was subsequently conducted into the ammonia-butanol separating column. The top temperature there was 87° C. The butanol losses which arose through the ammonia discharge and from other losses (low boiler components and residues sent to incineration) were replaced by supplying 4.7 kg/h of fresh butanol in the bottom of the ammonia-butanol separating column. The mixture of 220.2 kg/h obtained in the bottom of the pressure distillation reactor was purified by distillation.
105.5 kg/h of biscarbamate were fed into the falling film evaporator of the combined cleavage and rectification column after addition of 0.2 kg/h of catalyst solution. The energy required for the cleavage and rectification was transferred with heat carrier oil in the falling film evaporator. The carbamate cleavage reaction was undertaken at a bottom pressure of 27 mbar and a bottom temperature of 230° C. The butanol of 37.1 kg/h which was formed during the cleavage and obtained by rectification at the top was drawn off and fed to the recarbamatization stage with the bottoms discharge of 20.1 kg/h from the combined cleavage and rectification column.
The crude diisocyanate of 51.4 kg/h drawn off in a side stream from the combined cleavage and rectification column was fed to a further purifying distillation, and 48.2 kg/h of purified diisocyanate were thus obtained. The purity of the diisocyanate obtained was determined by gas chromatography to be >99.5% by weight. The overall process yield based on diamine used was 96.3%.
A mixture of 35.6 kg/h of 5-amino-1,3,3-trimethylcyclohexanemethanamine, 25.9 kg/h of conditioned urea with a formaldehyde content of 0.55% by weight, 93.0 kg/h of n-butanol and 50.9 kg/h of reaction product from the recarbamatization stage were pumped via a steam-heated preheater, where it was heated to 190 to 200° C., to the first tray of a pressure distillation reactor.
The mean residence time in the pressure distillation reactor was 10.5 h. Heating established the following temperature profile: bottom 232° C. and top 200° C. 88.9 kg/h of butanol were introduced into the bottom of the pressure distillation reactor, and the amount of heat carrier oil to the reboiler was regulated such that the amount of butanol drawn off at the top together with the ammonia formed corresponded to that fed in in the bottom.
The resulting butanol/ammonia mixture was subsequently conducted into the ammonia-butanol separating column. The top temperature there was 88° C. The butanol losses which arose through the ammonia discharge and from other losses (low boiler components and residues sent to incineration) were replaced by supplying 4.6 kg/h of fresh butanol in the bottom of the ammonia-butanol separating column. The mixture of 212.3 kg/h obtained in the bottom of the pressure distillation reactor was purified by distillation.
93.4 kg/h of biscarbamate were fed into the falling film evaporator of the combined cleavage and rectification column after addition of 0.2 kg/h of catalyst solution. The energy required for the cleavage and rectification was transferred with heat carrier oil in the falling film evaporator. The carbamate cleavage reaction was undertaken at a bottom pressure of 27 mbar and a bottom temperature of 234° C. The butanol of 32.8 kg/h which was formed during the cleavage and obtained by rectification at the top was drawn off and fed to the recarbamatization stage with the bottoms discharge of 17.8 kg/h from the combined cleavage and rectification column.
The crude diisocyanate of 45.5 kg/h drawn off in a side stream from the combined cleavage and rectification column was fed to a further purifying distillation, and 42.7 kg/h of purified diisocyanate were thus obtained. The purity of the diisocyanate obtained was determined by gas chromatography to be 98.5% by weight. The overall process yield based on diamine used was 91.9%.
A mixture of 34.7 kg/h of (2,2,4-)2,4,4-trimethylhexamethylenediamine, 27.2 kg/h of unconditioned urea, 97.8 kg/h of n-butanol and 64.0 kg/h of reaction product from the recarbamatization stage were pumped via a steam-heated preheater, where it was heated to 190 to 200° C., to the first tray of a pressure distillation reactor.
The mean residence time in the pressure distillation reactor was 10.5 h. Heating established the following temperature profile: bottom 228° C. and top 200° C. 94.3 kg/h of butanol were introduced into the bottom of the pressure distillation reactor, and the amount of heat carrier oil to the reboiler was regulated such that the amount of butanol drawn off at the top together with the ammonia formed corresponded to that fed in in the bottom.
The resulting butanol/ammonia mixture was subsequently conducted into the ammonia-butanol separating column. The top temperature there was 86° C. The butanol losses which arose through the ammonia discharge and from other losses (low boiler components and residues sent to incineration) were replaced by supplying 4.5 kg/h of fresh butanol in the bottom of the ammonia-butanol separating column. The mixture of 219.0 kg/h obtained in the bottom of the pressure distillation reactor was purified by distillation.
108.4 kg/h of biscarbamate were fed into the falling film evaporator of the combined cleavage and rectification column after addition of 0.2 kg/h of catalyst solution. The energy required for the cleavage and rectification was transferred with heat carrier oil in the falling film evaporator. The carbamate cleavage reaction was undertaken at a bottom pressure of 27 mbar and a bottom temperature of 228° C. The butanol of 38.1 kg/h which was formed during the cleavage and obtained by rectification at the top was drawn off and fed to the recarbamatization stage with the bottoms discharge of 25.7 kg/h from the combined cleavage and rectification column.
The crude diisocyanate of 47.5 kg/h drawn off in a side stream from the combined cleavage and rectification column was fed to a further purifying distillation, and 44.6 kg/h of purified diisocyanate were thus obtained. The purity of the diisocyanate obtained was determined by gas chromatography to be >99.5% by weight. The overall process yield based on diamine used was 96.6%.
A mixture of 34.6 kg/h of (2,2,4-)2,4,4-trimethylhexamethylenediamine, 27.0 kg/h of conditioned urea with a formaldehyde content of 0.55% by weight, 97.3 kg/h of n-butanol and 59.8 kg/h of reaction product from the recarbamatization stage were pumped via a steam-heated preheater, where it was heated to 190 to 200° C., to the first tray of a pressure distillation reactor.
The mean residence time in the pressure distillation reactor was 10.5 h. Heating established the following temperature profile: bottom 231° C. and top 200° C. 93.1 kg/h of butanol were introduced into the bottom of the pressure distillation reactor, and the amount of heat carrier oil to the reboiler was regulated such that the amount of butanol drawn off at the top together with the ammonia formed corresponded to that fed in in the bottom.
The resulting butanol/ammonia mixture was subsequently conducted into the ammonia-butanol separating column. The top temperature there was 89° C. The butanol losses which arose through the ammonia discharge and from other losses (low boiler components and residues sent to incineration) were replaced by supplying 5.1 kg/h of fresh butanol in the bottom of the ammonia-butanol separating column. The mixture of 228.1 kg/h obtained in the bottom of the pressure distillation reactor was purified by distillation. 101.3 kg/h of biscarbamate were fed into the falling film evaporator of the combined cleavage and rectification column after addition of 0.2 kg/h of catalyst solution. The energy required for the cleavage and rectification was transferred with heat carrier oil in the falling film evaporator. The carbamate cleavage reaction was undertaken at a bottom pressure of 27 mbar and a bottom temperature of 233° C. The butanol of 35.6 kg/h which was formed during the cleavage and obtained by rectification at the top was drawn off and fed to the recarbamatization stage with the bottoms discharge of 24.0 kg/h from the combined cleavage and rectification column. The crude diisocyanate of 44.4 kg/h drawn off in a side stream from the combined cleavage and rectification column was fed to a further purifying distillation, and 41.7 kg/h of purified diisocyanate were thus obtained. The purity of the diisocyanate obtained was determined by gas chromatography to be 98.2% by weight. The overall process yield based on diamine used was 90.8%.
The uppermost tray of a pressure distillation reactor was charged with 31.9 kg/h of H12MDA, 18.7 kg/h of unconditioned urea and 67.4 kg/h of n-butanol, and the reaction mixture was converted with continuous removal of the ammonia released at 10 bar, 220° C. and with a mean residence time of 10.5 h. In the bottom of the pressure distillation reactor, 66.1 kg/h of butanol were fed in, and the amount of alcohol drawn off at the top together with the ammonia released was selected such that it corresponded to the alcohol input in the bottom. The resulting butanol/ammonia mixture was subsequently conducted into the ammonia-butanol separating column. The top temperature there was 86° C. The butanol losses which arose through the ammonia discharge and from other losses (low boiler components and residues sent to incineration) were replaced by supply of fresh butanol in the bottom of the ammonia-butanol separating column. The reactor discharge, together with the material of value stream from the high boiler removal, was freed by distillation of excess butanol and low and medium boilers, and the remaining 89.9 kg/h of bis(4-butoxycarbonylaminocyclohexyl)methane (H12MDU) were conducted as a melt (140° C.) into the circulation system of the falling film evaporator of the cleavage and rectification column, and the deblocking reaction was performed at a temperature of 234° C. and a bottom pressure of 8 mbar in the presence of a catalyst. The crude H12MDI obtained was fed to a purifying distillation to obtain 37.3 kg/h of pure H12MDI. 26.3 kg/h of crude butanol were obtained as the top product of the cleavage and rectification column. To maintain constant mass within the cleavage and rectification column, and prevent deposits and blockages of the cleavage apparatus, a substream was discharged continuously from the circulation system and combined with 2.2 kg/h of bottoms discharge from the H12MDI purifying distillation and the top product from the cleavage and rectification column and reurethanized. The reurethanized stream was freed of excess butanol and separated by distillation into a waste stream rich in high boilers and a material of value stream. The 28.8 kg/h of material of value stream were fed together with the reactor effluent of the diurethane preparation to the flash stage. The purity of the diisocyanate obtained was determined by gas chromatography to be >99.5% by weight. The overall process yield based on diamine used was 93.8%.
The uppermost tray of a pressure distillation reactor was charged with 29.9 kg/h of H12MDA, 17.6 kg/h of conditioned urea with a formaldehyde content of 0.55% by weight and 63.3 kg/h of n-butanol, and the reaction mixture was converted with continuous removal of the ammonia released at 10 bar, 220° C. and with a mean residence time of 10.5 h. In the bottom of the pressure distillation reactor, 63.2 kg/h of butanol were fed in, and the amount of alcohol drawn off at the top together with the ammonia released was selected such that it corresponded to the alcohol input in the bottom. The resulting butanol/ammonia mixture was subsequently conducted into the ammonia-butanol separating column. The top temperature there was 88° C. The butanol losses which arose through the ammonia discharge and from other losses (low boiler components and residues sent to incineration) were replaced by supply of fresh butanol in the bottom of the ammonia-butanol separating column. The reactor discharge, together with the material of value stream from the high boiler removal, was freed by distillation of excess butanol and low and medium boilers, and the remaining 78.6 kg/h of bis(4-butoxycarbonylaminocyclohexyl)methane (H12MDU) were conducted as a melt (140° C.) into the circulation system of the falling film evaporator of the cleavage and rectification column, and the deblocking reaction was performed at a temperature of 240° C. and a bottom pressure of 11 mbar in the presence of a catalyst. The crude H12MDI obtained was fed to a purifying distillation to obtain 32.6 kg/h of pure H12MDI. 23.0 kg/h of crude butanol were obtained as the top product of the cleavage and rectification column. To maintain constant mass within the cleavage and rectification column, and prevent deposits and blockages of the cleavage apparatus, a substream was discharged continuously from the circulation system and combined with 2.0 kg/h of bottoms discharge from the H12MDI purifying distillation and the top product from the cleavage and rectification column and reurethanized. The reurethanized stream was freed of excess butanol and separated by distillation into a waste stream rich in high boilers and a material of value stream. The 21.1 kg/h of material of value stream were fed together with the reactor effluent of the diurethane preparation to the flash stage. The purity of the diisocyanate obtained was determined by gas chromatography to be 98.0% by weight. The overall process yield based on diamine used was 87.3%.
Table 1 which follows shows once again, in summary, the essential features of examples 1 to 8 with the significant differences in the diisocyanate purities and the process yields depending on the urea quality used.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102006061475.5 | Dec 2006 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2007/061870 | 11/5/2007 | WO | 00 | 6/18/2009 |
