Patent Application
20070241032
This invention relates to a process for the desulfurization of olefinic gasolines comprising a reaction for increasing the weight of sulfur-containing compounds by alkylation with the olefins that are contained in the feedstock by means of an acidic catalyst and comprising a phase for regeneration of said catalyst that can be carried out sequentially or continuously.
This process particularly finds its application in the treatment of conversion gasolines, and in particular gasolines that are produced by catalytic cracking, coking, visbreaking or pyrolysis.
The process that is the object of this invention makes it possible to upgrade a gasoline fraction that optionally comprises hydrocarbons with three or four carbon atoms, by reducing the total sulfur content of said fraction to very low levels, compatible with the current or future specifications, without significant reduction of the output of gasoline and the octane number.
The production of gasolines that meet the new environmental standards requires that their sulfur contents be reduced to values that generally do not exceed 50 ppm and are preferably less than 10 ppm.
Furthermore, it is known that the conversion gasolines, and more particularly those that are obtained from catalytic cracking, have high olefin and sulfur contents and on average represent from 30% to 50% of the gasoline pool.
The sulfur that is present in the gasolines for this reason can be nearly 90% attributed to gasolines that are obtained from catalytic cracking processes that will be called FCC gasoline (FCC designating the abbreviation of fluidized-bed catalytic cracking) below. The FCC gasolines therefore constitute the preferred feedstock of the process for desulfurization of this invention.
More generally, the process for desulfurization according to the invention can be applied to any gasoline fraction that contains a certain proportion of olefins and can also contain several lighter compounds that belong to the C3 and C4 fractions. The gasoline feedstock of said process can also be mixed with methanol-type and ethanol-type alcohols and optionally heavier alcohols.
A first desulfurization method that is very commonly used in refining consists in the hydrodesulfurization of gasolines. To reach the standards currently required by using such processes, it has proven necessary to operate under strict temperature and pressure conditions and in particular to work under high hydrogen pressure.
Such conditions bring about a significant consumption of hydrogen, generally an at least partial hydrogenation of olefins and, consecutively, a significant reduction of the octane number of the desulfurized gasolines that are obtained by said processes.
Another method consists in using processes for desulfurization of gasolines based on a treatment that employs an acidic catalyst. This type of treatment has as its object to increase the weight of thiophenic-type unsaturated sulfur-containing compounds by a reaction for addition (or more specifically for alkylation) on said unsaturated sulfur-containing compounds, olefins that are present in the feedstock, and in parallel, to oligomerize a fraction of said olefins that are contained in the feedstock.
For example, the Patents U.S. Pat. No. 6,059,962 and FR2810671 describe such processes. The thiophenic unsaturated sulfur-containing compounds react with the olefins in the presence of an acidic catalyst, whereby the reaction brings about an increase in weight of said thiophenic compounds. The thiols can also react with the olefins to form sulfides that are themselves increased in weight.
The sulfur-containing compounds that are increased in weight can then be separated by a simple distillation. A gasoline with a low sulfur content is recovered at the top of the distillation column.
The acidic catalysts that are described in the preceding patents are generally solid catalysts that have a Bronstedt acidity, such as the ion exchange resins or the supported sulfuric or phosphoric acids, but also the catalysts based on silica and alumina, such as the amorphous silica-aluminas or the zeolites.
The acidic catalysts that are used for the purpose of reacting the olefins on the sulfur-containing compounds generally have a service life that is limited by depositing deactivating agents on the catalytic surface, a deposit that prevents the reagents from accessing the catalytic sites.
Processes for regenerating or reactivating spent catalysts are described in the literature for processes that use acidic catalysts for the purpose of oligomerizing the olefins or alkylating the aromatic compounds by olefins.
For example, the U.S. Pat. No. 4,062,801 proposes a method for regenerating acidic catalysts by the use of cycles that comprise several stages for immersion of the catalyst in a hot aromatic liquid, then draining the aromatic liquid.
The U.S. Pat. No. 6,025,534 proposes a method for regenerating acidic catalysts used for polymerizing the olefins, without unloading the reactor, consisting in replacing, during the regeneration phase, the olefinic feedstock by a regeneration feedstock that contains aromatic compounds such as the molar ratio between the olefins and the aromatic compounds or between 1 and 10.
No solution is described in the prior art for regenerating the acidic catalysts that are used for carrying out the alkylation of the sulfur-containing compounds by the olefins in the olefinic gasolines, however.
This invention relates to a process for the desulfurization of sulfur-containing and olefin-containing gasoline. The principle of desulfurization consists in reacting, by an alkylation reaction, the olefins to the sulfur-containing compounds that are contained in the gasoline to be treated. The sulfur-containing compounds that constitute the effluents of the alkylation reaction are increased in weight relative to the initial sulfur-containing compounds such that the reaction that is used in the process is also described as a reaction for increasing the weight of the sulfur-containing compounds.
The treatment of the olefinic gasolines on acidic catalyst for the purpose of transforming the sulfur-containing compounds by addition of olefins according to the alkylation reaction is generally accompanied by a deactivation phenomenon of the catalyst. This deactivation is reflected by a reduction of the activity of the catalyst and the necessity of increasing the temperature to offset this gradual loss of activity.
The deactivation that is described above represents a major drawback for the process and in the long run requires the replacement of said catalyst.
The replacement of the catalyst assumes that the reactor is shut off during the catalyst unloading and reloading period.
This invention describes in particular a method for regeneration of the catalyst that can be used without unloading the catalyst from the reactor and also optionally without interruption of the reaction for increasing the weight of sulfur-containing compounds. This procedure also makes it possible to keep the catalyst at a high activity level for its entire service life.
The process for desulfurization according to the invention applies to a gasoline fraction that contains olefins, sulfur-containing compounds and optionally molecules that belong to the C3 and C4 fractions.
It comprises at least the following 3 stages:
The agent for regeneration that is used in stage C can be introduced by itself or mixed with the feedstock to be treated. In the case where the regeneration agent is introduced in a mixture with the feedstock to be treated, the reactor continues to operate by producing the effluents of the alkylation reaction at the same time that the catalyst is regenerated.
The molar ratio between the olefinic compounds and the aromatic compounds of the regeneration agent, or of the mixture that results between the regeneration agent and the feedstock to be treated, is generally between 0 and 1, preferably between 0 and 0.5, and even preferably between 0 and 0.25.
The catalyst that is used to carry out the alkylation reaction of the sulfur-containing compounds by the olefins that are contained in the feedstock to be treated is an acidic catalyst that is selected from among the acidic resins, ion exchangers, the catalysts that contain the phosphoric acid mixed with silica, or different types of zeolites that will be described in more detail later.
When the catalyst is selected from among the resins, the acidic resin has an acid capacity of more than 4.7 eq/kg, and preferably more than 5.0 eq/kg.
In general, the acid resin that is used has a pore volume of less than 0.50 ml/g.
When the catalyst that is used contains the phosphoric acid that is mixed with silica, the phosphoric acid content is generally more than 50% by weight.
The catalyst that is used in the alkylation stage can also be an amorphous silica-alumina.
The catalyst that is used in the alkylation stage can also be a zeolite that is selected from the group that consists of Y, beta, ZSM-5, ZSM-3 and ZSM-20, ZSM-57, NU-88, NU-87, NU-86, and EU-1 zeolites.
The process for the desulfurization of a gasoline fraction according to the invention uses operating conditions of which some may depend on the selected catalyst. In general, the operating temperature of the reaction is between 30° C. and 300° C., the operating pressure is encompassed in 0.5 MPa and 6.0 MPa (1 MPa=106 pascals), and the VVH is between 0.1 h−1 and 10 h−1, and preferably between 0.5 h−1 and 5 h−1 per reactor.
The temperature that is used in the regeneration stage is generally greater than or equal to the temperature of the reaction stage, while remaining less than 180° C. when the catalyst that is used is an acid resin, or less than 300° C. when the catalyst that is used is phosphoric acid or a zeolite.
When the feedstock to be treated contains more than 20 ppm of nitrogen and preferably more than 50 ppm of nitrogen, said feedstock can be pretreated in a stage for extraction of the nitrogen-containing compounds.
This stage can consist of a washing by an aqueous solution, preferably acid, a collection on a solid, or a combination of the two. In the case of the use of a collection mass, it is possible to use, as a collection solid, the same catalyst as the one used for the reaction with a lower degree of activity.
When the catalyst is an acid resin, it can be used in a boiling bed. The technology of the boiling bed is particularly well suited to continuous sampling of the spent catalyst that originates from the reaction medium and to its replacement by fresh catalyst.
The process according to this invention applies in particular to the desulfurization of an FCC gasoline with a boiling point of less than 230° C., preferably less than 160° C., and even preferably less than 130° C.
This invention relates to a catalytic process by acid catalysis, transformation of sulfur-containing compounds that are contained in an olefinic hydrocarbon-containing feedstock, consisting in the addition of olefins that are present in the feedstock to said sulfur-containing compounds.
The process according to the invention is particularly suited for treating gasolines that contain sulfur and olefins. These compounds are present simultaneously in the conversion gasolines and in particular in the gasolines that are obtained from catalytic cracking, fluidized-bed catalytic cracking (FCC), a coking process, a visbreaking process or a pyrolysis process.
The gasolines that originate from one of these units or a combination of said units generally contain at least 30 ppm of sulfur and 10% olefins.
The end point of the feedstocks is generally less than 230° C., but gasolines whose boiling point is less than 160° C. and preferably less than 130° C. will preferably be treated. In addition, these feedstocks can also contain hydrocarbon-containing fractions with 3 or 4 carbon atoms.
They generally contain more than 10% by weight of olefins, and most often more than 20% by weight of olefins. The olefins that are present in these feedstocks are generally olefins that contain 3 to 12 carbon atoms, and most often olefins that contain 4 to 7 carbon atoms.
The feedstocks that are covered by this invention also contain aromatic compounds whose content can vary between 0.5% by weight and 60% by weight, and most often between 1% by weight and 50% by weight. The aromatic compounds are primarily present in the form of benzene, toluene, xylenes and other alkyl benzenes, and optionally in the form of naphthalene and alkylnaphthalenes. The other compounds that are present in the gasoline are paraffin- or naphthene-type compounds that generally do not react within the scope of this process.
The regeneration agent that is used to restore the activity of the catalyst makes it possible to extract the compounds that are deposited on the catalyst and that brought about its deactivation.
The regeneration agent is selected from the group that consists of oxidized compounds or aromatic hydrocarbon-containing fractions.
The oxidized compounds that are the object of this invention are generally alcohols, ethers, or optionally ketones or aldehydes.
The oxidized compounds that are used are preferably selected from the group that consists of methanol, ethanol, propanol, butanol, methyl-tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME) or tert-amyl ethyl ether (TAEE) or a mixture of these oxidized compounds.
The regeneration agent can be used alone or in a mixture with the feedstock to be treated, so as to carry out the regeneration while continuing the alkylation operation.
The regeneration agent can also consist of an aromatic hydrocarbon-containing fraction.
The aromatic hydrocarbon-containing fraction that is used to regenerate the catalyst differs from the feedstock by a significantly higher content of aromatic compounds.
In the text below, this aromatic hydrocarbon-containing fraction will be called an aromatic regeneration fraction.
The content of aromatic compounds of the aromatic regeneration fraction is such that the molar ratio between the olefinic compounds and the aromatic compounds of said fraction is between 0 and 1, preferably between 0 and 0.5, and very preferably between 0 and 0.25.
The aromatic compounds that are contained in the aromatic regeneration fraction include the aromatic compounds that contain between 6 and 20 carbon atoms and that preferably contain between 6 and 12 carbon atoms.
The gasoline that is obtained from catalytic reforming is a preferred source of aromatic compounds and can therefore be used to regenerate the catalyst of the process, which is the object of this invention.
The aromatic regeneration fraction can consist of a mixture of hydrocarbon-containing fractions selected from among the heat-cracking or catalytic-cracking gasolines, the direct distillation gasolines, the gasolines that are obtained from a catalytic reforming unit, the gasolines that are obtained from isomerization units, or any other hydrocarbon-containing fraction.
According to a particular method of the invention, it is possible to continue to operate the reactor to carry out the reactions of transformation of the sulfur-containing compounds, while regenerating the spent catalyst, by mixing an aromatic regeneration fraction with the feedstock to be treated, such that the resulting mixture has a molar ratio between the olefinic compounds and the aromatic compounds of said fraction [that] is between 0 and 1, preferably between 0 and 0.5, and very preferably between 0 and 0.25.
For example, it is possible to regenerate the catalyst by mixing, with the feedstock to be desulfurized, a gasoline that is obtained from a catalytic reforming unit in proportions such that the molar ratio between the olefinic compounds and the aromatic compounds of said mixture is between 0 and 1, preferably between 0 and 0.5, and very preferably between 0 and 0.25.
To reactivate the catalyst for alkylation of thiophenes and thiols, an aromatic hydrocarbon-containing fraction whose nitrogen content is less than 100 ppm and very preferably less than 50 ppm will preferably be used.
The catalysts that can be used for the process for transformation of the sulfur-containing compounds by increasing the weight are acidic catalysts such as the ion exchange resins, the supported acids, and the inorganic oxides or mixture thereof.
The resins that are used are preferably acidic sulfonated polystyrene-type resins such as the Amberlyst 15, Amberlyst 35 or Amberlyst 36 resins that are produced by the Rhom & Haas Company, or any other acid resin. A resin that is characterized by an acid capacity of more than 4.7 eq/kg and preferably more than 5.0 eq/kg will preferably be used.
The equivalents per kg correspond to the number of moles of protons per kg of resin.
The pore volume of the resin will generally be between 0.10 ml/g and 0.50 ml/g, preferably between 0.15 ml/g and 0.40 ml/g, and very preferably between 0.16 ml/g and 0.25 ml/g. The mean diameter of the pores is between 10 nm and 40 nm, preferably between 20 nm and 30 nm, and even more preferably between 20 nm and 28 nm.
Furthermore, the supported acids that can be used for this application include, without this being limiting, the Bronstedt acids (for example phosphoric acid, sulfuric acid, and hydrofluoric acid) or the Lewis acids (for example chlorinated alumina, BF3, BC13, and AlC13) that are supported on a solid substrate such as alumina, silica and silica-aluminas.
It will be possible to use the phosphoric acid that is supported on silica, also called SPA and further used in the processes for polymerization of olefins or alkylation of benzene.
This latter type of catalyst is characterized by a phosphoric acid content that is more than 50% by weight and preferably more than 60% by weight.
The inorganic acids with used oxide bases are aluminas, silicas, and preferably amorphous silica-aluminas, or zeolites of the following types: MEL, MFI, ITH, NES, EUO, ERI, FER, CHA, MFS, MWW, MTT, TON, MAZ, MEI, MOR, FAU, BEA, BOG, LTL, and OFF.
Among the MEL-structural-type zeolites, the ZSM-11 zeolite is preferred.
Among the MFI-structural-type zeolites, the ZSM-5 and ZSM-23 zeolites are preferred.
Among the ITH-structural-type zeolites, the ITQ-13 zeolite is preferred.
Among the NES-structural-type zeolites, the NU-87 zeolite is preferred.
Among the EUO-structural-type zeolites, the EU-1 zeolite is preferred.
Among the ERI-structural-type zeolites, the erionite zeolite is preferred.
Among the FER-structural-type zeolites, the ferrierite and ZSM-35 zeolites are preferred.
Among the CHA-structural-type zeolites, the chabazite zeolite is preferred.
Among the MFS-structural-type zeolites, the ZSM-57 zeolite is preferred.
Among the MWW-structural-type zeolites, the MCM-22 zeolite is preferred.
Among the MTT-structural-type zeolites, the ZSM-23 zeolite is preferred.
Among the MAZ-structural-type zeolites, the omega and ZSM-4 zeolites are preferred.
Among the MEI-structural-type zeolites, the ZSM-18 zeolite is preferred.
Among the MOR-structural-type zeolites, the mordenite zeolite is preferred.
Among the FAU-structural-type zeolites, the Y zeolite is preferred.
Among the BEA-structural-type zeolites, the beta zeolite is preferred.
Among the BOG-structural-type zeolites, the boggsite zeolite is preferred.
Among the LTL-structural-type zeolites, the L zeolite is preferred.
Among the OFF-structural-type zeolites, the offretite zeolite is preferred.
The ZSM-3 and ZSM-20 zeolites, zeolites of intermediate structural type between EMT and FAU, are also preferably usable. The NU-86 and NU-88 zeolites are also preferably usable. All of the zeolites described above can be used alone or in a mixture.
The catalyst with a zeolite base according to the invention may have undergone one or more treatments that make its acidity change. The preferred treatments are the treatments for dealuminification by any methods that are known to one skilled in the art, the substitutions of protons by metallic and/or alkaline and/or alkaline-earth cations by any of the ion exchange methods or impregnation methods known to one skilled in the art, by a passivation of the outside surface by deposition of a layer of amorphous silica via a gas phase deposition (CVD, chemical vapor deposition, according to the English term meaning: a chemical deposit in vapor phase) or in liquid phase (CLD, or chemical liquid deposition, according to the English term meaning: a chemical deposit in liquid phase) to reduce the acidity of the outside surface of the zeolite.
The process for adding olefins to sulfur-containing compounds contained in the feedstock to be treated, in the presence of an acidic catalyst, is generally used in a reactor that contains the acidic catalyst in a fixed bed.
The catalyst can also just as well be placed in a chamber reactor or in a tubular reactor.
The tubular reactor consists of a set of tubes containing the catalyst in which the feedstock to be treated circulates, the tubes being immersed within a fluid enclosed in a calendar that makes it possible to monitor the temperature. This device makes it possible to monitor the temperature in the catalytic bed and thus to limit the rise in temperature along the bed in the case of exothermic reactions.
According to a particular embodiment of the invention, in the case where the catalyst consists of acid resin, it is possible to use a boiling-bed reactor that makes it possible to limit the hot points in the reactor as well as the rise in temperature along the bed.
This type of reactor makes it possible to carry out a draw-off of spent catalyst and an addition of fresh or regenerated catalyst continuously. In this case, and so as to allow the catalytic bed to be put into motion, it is preferable to use a catalyst whose particle size is less than 2 mm and preferably between 0.2 mm and 1.5 mm.
It is advantageous to use the process in a number of reactors operated in series or in parallel. This type of configuration makes it possible to monitor the temperature of each reactor, but also to regenerate a reactor that contains the spent catalyst while the other reactors are in operation.
The operating conditions of the process are determined based on the feedstock to be treated, the type of catalyst and its activity level, so as to achieve the conversion rates of the desired sulfur-containing compounds.
Work will preferably be done at a temperature of between 30° C. and 300° C.
In the case where the catalyst that is used is acid resin, the temperature is generally between 30° C. and 180° C., and preferably between 40° C. and 170° C., because the crosslinked sulfonic polystyrene resins are degraded at high temperature, which can bring about an irreversible deactivation of the catalyst and corrosion problems.
In the case of acidic catalysts of phosphoric acid type supported on silica, the reactors will be operated at a temperature of generally between 100° C. and 300° C. and preferably between 140° C. and 250° C.
In the case of acidic catalysts of zeolitic type, the reactors are operated at a temperature that is generally between 100° C. and 300° C. and preferably between 120° C. and 270° C.
The operating pressure of the reactors is adjusted so as to maintain the hydrocarbon-containing fraction that is contained in the reactor in liquid phase. Thus, the pressure generally will be between 5 bar and 60 bar, and preferably between 1 MPa and 4 MPa (1 bar=105 pascal=0.1 MPa).
The amount of catalyst used is such that the VVH for each reactor is between 0.1 h−1 and 10 h−1, and preferably between 0.5 h−1 and 5 h−1.
The feedstock that is to be desulfurized can be completely substituted by the regeneration agent or else can be treated in a mixture, continuously or sequentially, with this same agent that is high in aromatic compounds or in oxidized compounds, so as to carry out simultaneously the regeneration of the catalyst and the reaction for increasing the weight by alkylation.
The temperature and pressure conditions of the regeneration are generally identical to the operating conditions of the reaction for increasing weight by alkylation.
It is advantageous, however, to carry out the regeneration in the high range of admissible temperatures, both for the protection of the catalyst and for the good operation of the installations. The regeneration period should be sufficient for restoring a significant portion of the activity of the catalyst. Generally, the regeneration is carried out over a period of a duration of between 1 hour and 250 hours, and preferably between 2 hours and 200 hours, and even between 10 hours and 100 hours.
The regeneration can be carried out several times during the life of the catalyst by linking several successive cycles for deactivation and regeneration so as to maximize the service life of the catalyst.
The following Example 1 shows the possibility of regenerating the catalyst that is used, here Amberlyst 15, by means of an aromatic regeneration fraction that consists of toluene.
A gasoline A that is sampled on a catalytic cracking unit is characterized by:
A reactor with a 50 ml volume is loaded with an acid resin that is marketed by the Rhom & Haas Company under the name of Amberlyst 15.
The initial temperature is 90° C. for a conversion of the thiophene of 99%. Then, the temperature is adjusted so as to carry out a conversion of thiophene that is always between 90% and 99%. The term adjustment means that when the conversion that decreases over time pursuant to the continuous deactivation of the catalyst reaches 90%, the reaction temperature is increased by an increment of 10° C., which has the effect of raising the conversion to a value that is close to 99%. After each increment of 10° C., the conversion of the thiophene was measured by returning to 90° C. (return point) so as to follow the deactivation of the catalyst at this temperature.
The conversion rate of the thiophene is calculated from the measurement of the thiophene content carried out by gas phase chromatography provided with a specific sulfur detector.
At the end of 24 hours, the injection of toluene is halted, which marks the end of the second part of the experiment.
A sample of the reaction effluents is taken at the end of 12 hours after the beginning of the third part of the experiment, i.e., after the injection of feedstock A. This sample is analyzed so as to obtain a measurement of the activity of the catalyst.
The thiophene content that is measured in the sample is 2.1 ppm, which corresponds to a thiophene conversion rate of 98% at 90° C., or a conversion on the same level as the one obtained in the first part of the experiment.
The regeneration procedure by using toluene as a regeneration agent therefore makes it possible to restore the activity of the catalyst.
The Examples 2 and 3 that follow illustrate the possibility of restoring the activity of the catalyst while continuing to convert the thiophenic compounds.
A feedstock B that consists of the gasoline A to which ethanol is added at a rate of 5% by weight is prepared. The gasoline A is treated under conditions that are identical to Example 1, with a new loading of Amberlyst 15 resin.
At the end of 24 hours from the beginning of the second part of the experiment, a sample of the reaction effluents is taken, and the measured thiophene content is 15 ppm, which corresponds to a thiophene conversion rate of 86%. This conversion rate is certainly less than the one of the first part of the experiment, but it nevertheless makes it possible to continue to carry out the reaction for increasing in weight by alkylation, while regenerating the catalyst.
The thiophene content that is measured at the end of 12 hours from the beginning of the third part of the experiment is 5.4 ppm, which corresponds to a conversion rate of 95%, very close to the conversion rate obtained in the first part of the experiment.
A feedstock C that consists of the gasoline A that is supplemented with toluene at a rate of 50% by weight is prepared. The gasoline A is treated under conditions that are identical to Example 1 with a new loading of Amberlyst 15 resin.
The gasoline B is injected under the same conditions of flow rate, pressure and temperature.
At the end of 24 hours from the beginning of the second part of the experiment, a sample of the reaction effluents is taken, and the measured thiophene content is 3 ppm, which corresponds to a thiophene conversion rate of 94%. This conversion rate makes it possible to continue to carry out the reaction of increasing in weight by alkylation, while regenerating the catalyst.
The thiophene content that is measured at the end of 12 hours from the beginning of the third part of the experiment is 3.6 ppm, which corresponds to a conversion rate of 96%, very close to the conversion rate obtained in the first part of the experiment.
| Number | Date | Country | Kind |
|---|---|---|---|
| 05/08.844 | Aug 2005 | FR | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/FR06/01927 | Aug 2006 | US |
| Child | 11819054 | Jun 2007 | US |
