The invention relates to a process for the synthesis of butylacetate by esterification of acetic acid with butanol by distillation accompanied by chemical reaction utilizing a column in which separation of the reaction products takes place together with the esterification in a catalytically active separation equipment. The invention also relates to a process for the synthesis of isobutylacetate by esterification of acetic acid with isobutyl alcohol by the catalytic distillation method using a column in which separation of the reaction products takes place together with the esterification in a catalytically active separation equipment. The invention also relates to apparatuses for performing said process.
Butylacetate is prepared by the reaction of butanol with acetic acid by which water is produced besides butylacetate. The reaction is reversible and acidic catalysts are utilized to accelerate it. Mineral acids, especially sulfuric acid, or, more recently, ion exchange resins (EP 066059, DE 3636754), or zeolites and so called solid superacids are utilized for this purpose.
According to the state-of-the-art processes (Petrochemia 1985, 25, 99), almost equilibrium composition is achieved in a reactor, the resulting mixture is then distilled by means of a distillation column to separate a mixture, the composition of which is close to the composition of the butanol-butylacetate-water ternary azeotrope. The amount of the reaction water is not sufficient to distill all butylacetate in the mentioned form, therefore additional water must be added. The volume of the waste water to be subsequently treated is thus increased, which is one of the main disadvantages of the processes known in the art. The said steps are very often combined, i.e. the synthesis takes place directly in the distillation column reboiler. Separation of the organic phase from the water phase of the heterogeneous azeotrope prepares conditions for subsequent separation of butylacetate from butanol by distillation of the organic phase in another distillation column from which a mixture containing butanol, traces of dilute water and a small amount of butylacetate is withdrawn as distillate. This overhead product is recycled while butylacetate of purity usually up to 98% mass. is withdrawn as a bottom product. The separation of unreacted butanol from butylacetate is very difficult because of strong nonideality of the mixture. Not only butanol, butylacetate and water create a ternary azeotrope with minimum boiling point but also butanol with butylacetate as well as butanol with water create binary azeotropes. The water phase separated from the first column distillate is further distilled by use of another distillation column, dissolved butanol and butylacetate being separated as distillate, this mixture being recycled to the process. Complex separation of the esterification reaction mixture components is the main disadvantage of the state-of-the-art processes. There are also serious corrosion problems as an additional disadvantage in those processes which utilize mineral acids as catalysts.
Another variant of the butylacetate synthesis takes a possibility to perform the reaction in a column-reactor packed with the ion-exchange catalyst arranged into two zones (CN 1107136A). There is a partial condenser placed into the column head. The vapours are partly condensed in the condenser, the distillate being refluxed to the upper reaction zone without being split into water and organic phases. This has bad impact on the reaction equilibrium, which is a considerable disadvantage of said system. The vapours, non-condensed in the partial condenser, built in the column head, condense in an external condenser, the condensate being refluxed into the column feed after separation of the water from the organic phases, so the problem of accumulation of low boiling impurities in the upper part of the column remains unsolved. The product is withdrawn from the bottom of the reactor. Maximum purity is only 95 to 98 mass % according to said patent (CN 1107136A).
Isobutylacetate is prepared by the reaction of isobutyl alcohol with acetic acid by which water is produced besides isobutylacetate. The reaction is reversible, acidic catalysts are utilized to accelerate it. Mineral acids, especially sulfuric acid or, more recently, solid acidic catalysts are utilized for this purpose as can be seen e.g. from CZ 191357 and CZ 279562. These catalysts can be ion exchange resins, zeolites, so called solid superacids and the like.
According to the state-of-the-art processes relating to isobutylacetate preparation, almost equilibrium composition is achieved in a reactor, the composition being dependent on the starting molar ratio of the reaction components. The resulting mixture is then distilled by means of a distillation column to separate a mixture, the composition of which is close to the composition of the isobutyl alcohol-isobutylacetate-water ternary azeotrope. The amount of reaction water is not sufficient to distill all isobutylacetate in the mentioned form, therefore additional water must be added to the mixture. The volume of the waste water to be subsequently treated is thus increased, which is one of the main disadvantages of the processes known in the art. Said steps are very often combined, i.e. the synthesis takes place directly in the distillation column reboiler. After separating the organic phase from the water phase of the heterogeneous azeotrope it is possible to separate isobutylacetate from isobutyl alcohol by subsequent distillation of the organic phase in another distillation column. The organic phase, separated from the heterogeneous azeotropic mixture contains isobutyl alcohol, isobutylacetate and a certain part of water. Isobutyl alcohol, the rest of water and small part of isobutylacetate are separated from said organic phase by subsequent distillation. The overhead product, obtained this way, is recycled into esterification while pure isobutylacetate is withdrawn as a bottom product. The separation of unreacted isobutyl alcohol from isobutylacetate is very difficult because of strong nonideality of the mixture. Isobutyl alcohol and isobutylacetate create a binary azeotrope, creating also a ternary azeotrope of a minimum boiling point with water. The water phase separated from the distillate of the first column is further distilled by means of another distillation column, dissolved isobutyl alcohol and isobutylacetate being separated overhead, their mixture being recycled to the process. Complex separation of the esterification reaction mixture components is the main disadvantage of these state-of-the-art processes. There are also serious corrosion problems as an additional disadvantage in those processes which utilize mineral acids as catalysts.
Process for the Production of Butylacetate
The process for the production of butylacetate by esterification of acetic acid with butanol in the presence of a solid acidic catalyst consists according to this invention in introducing acetic acid and butanol in a molar ratio 1:1 to 1:10, the overall amount of the feed per volume unit of catalyst being 0.1 to 10 hxe2x88x921, into the system of three zones in which the reaction and distillation take place, the reaction running simultaneously with distillatory separation of the compounds of different boiling points in the reaction zone, while only separation of components by distillation takes place in the upper and lower separation zones, namely of components forming a minimum boiling point ternary azeotrope in the upper separation zone, the volatile mixture of these compounds being split into water and organic phases after being cooled at 5 to 80xc2x0 C., the organic phase being refluxed to the upper separation zone, the ratio of the feed to the refluxed organic phase being 1:1 to 1:20, the reflux representing 60 to 100% of the whole amount of the separated organic phase and butylacetate being withdrawn as a high boiling bottoms product.
According to this process, acetic acid and butanol can be introduced into the reaction zone or into the upper separation zone. Alternatively, acetic acid and butanol are introduced into the system separately, acetic acid being introduced into the reaction zone or into the upper separation zone, butanol being introduced into the reaction zone or into the lower separation zone according to this process. Finally, 1 to 99% of the whole amount of butanol is introduced as a mixture with acetic acid into the reaction zone or into the upper separation zone of the system while 99 to 1% of butanol is introduced separately into the reaction zone or into the lower separation zone at the same time, according to this process.
In a preferred embodiment, the process is performed at a molar ratio of acetic acid vs. butanol in the range of 1:1 to 1:1.3, the feed flow per the catalyst volume unit being 0.5 to 5 hxe2x88x921, the ratio of the feed flow to the organic phase reflux being 1:2 to 1:7 and 90 to 99% of the entire separated organic phase volume being refluxed. The acetic acid or the mixture of acetic acid and butanol fed into the system can contain also butylacetate and/or water. It is thus possible to feed e.g. a product of partial conversion of butanol-acetic acid mixture which contains at maximum the equilibrium concentration of butylacetate and water besides unreacted butanol and acetic acid.
The process according to this invention can be performed advantageously in an apparatus comprised of a column consisting of three zones, wherein the reaction zone placed in the middle part of the column contains a solid acidic catalyst immobilized in the reaction zone on distillation trays or by other systems known per se which ensure good contact between the liquid phase and the catalyst particles as well as between the liquid and the vapour phases in the countercurrent flow of these phases, e.g. the catalyst can be embedded in a structural packing with internal channel structure by fixing it between two layers of an inert porous material forming the structure of the packing; the lower and upper separation zones contain inert structural packings, common tower packings or distillation trays, the butanol feed pipe is connected through a closing valve to the acetic acid feed pipe, the joint feed is introduced into the reaction zone or above this zone, a second butanol feed pipe branch is connected to the reaction zone or below this zone being also equipped with a closing valve, a reboiler is connected to the column bottom, the butylacetate withdrawal line being conducted from the reboiler or the bottom, the column head which ends the upper part of the column is connected with the condenser by a vapour pipe, the condensate line leads from the condenser to the separator to the upper part of which a reflux pipe and a withdrawing pipe for the non-refluxed organic phase are connected while the water phase pipe is connected to the lower part of the separator.
In one possible arrangement, the butanol feed closing and control valve is closed, the pipe connection closing and control valve being open, in another arrangement, the butanol feed closing and control valve is open, the pipe connection closing and control valve being closed. Finally, both closing and control valves are open.
Besides feeding butanol and acetic acid independently into different points of the apparatus, the feed pipes configuration described above makes it possible to feed butanol or at least part of it in a mixture with acetic acid to one point in the reaction zone or in the upper separation zone, additional butanol being possibly fed by an independent feed line to the point in the reaction zone or in the lower separation zone placed below the butanol-acetic acid mixture feed point. The same effect can be achieved by preparing the butanol-acetic acid mixture separately, by means of some commonly known mixing device, feeding the mixture to the reaction zone or to the upper separation zone, additional butanol being fed into the reaction zone or into the lower separation zone without connecting both feed lines.
As can be seen from the description, the invention is based on discovery that butylacetate of sufficient quality can be prepared with advantage by the catalytic distillation method utilizing a distillation column consisting of a reaction zone which contains a solid acidic catalyst of common type, whilst there are inert separation zones placed both above and below the reaction zone. These separation zones contribute to establishing optimum concentration profiles of both starting compounds and products along the distillation column. As a result, maximum concentration of reacting compounds in the reaction zone is achieved and, consequently, high productivity of the equipment, optimum utilization of the catalyst as well as high product quality are achieved. Under the optimum conditions according to this invention, the purity of dry butylacetate, which is withdrawn from the reboiler, is above 99% mass.
Process for the Production of Isobutylacetate
Said drawbacks of the well known processes are overcome by the process for the production of isobutylacetate according to this invention, which consists in separately introducing acetic acid and isobutyl alcohol in a molar ratio of from 1:1 to 1:10 and in an amount, expressed as overall feed based on a volume unit of the catalyst, of 0.1 to 10 hxe2x88x921, in the presence of a solid acidic catalyst with simultaneous removing by distillation of the components, into a system where the reaction and the separation by distillation take place in three zones, wherein in the reaction zone the reaction runs simultaneously with the separation by distillation of the components with different boiling points and in the two separation zones only separation of the components by distillation takes place, water, formed as a by-product of the reaction, distilling out of the system in the form of a low-boiling azeotropic mixture, whereafter, the distillate being cooled down to 5 to 80xc2x0 C., said water is separated from the organic portion of the distillate and withdrawn from the system, while the organic components of the distillate are refluxed back, the feeds of acetic acid and isobutyl alcohol being introduced into the system in such a manner that the acetic acid feed is introduced into inside the reaction zone or above this zone, namely into a point located higher than the isobutyl alcohol input, and the isobutyl alcohol feed is introduced into the reaction zone or below it, the ratio between the feed amount of the entering reactants and the refluxed organic phase being from 1:1 to 1:20 and the reflux representing from 50 to 100 per cent of the overall amount of the separated organic phase and isobutylacetate being separated as a higher-boiling bottoms product. Ion exchange resin, e.g. sulfonated styrene-divinylbenzene copolymer (1 to 25% of divinylbenzene) of acidity in the range from 1 to 10 meq H+/g, can be used as the catalyst. Different types of ion exchangers, zeolites or other commonly known acidic catalysts can be used as well.
In a preferred embodiment the process is performed at a molar ratio of acetic acid vs. isobutyl alcohol in the range of 1:1 to 1:1.5, the feed flow per the catalyst volume unit being 0.5 to 5 hxe2x88x921, the ratio of the feed flow to the organic phase refluxed being 1:2 to 1:7 and 80 to 99% of the entire separated organic phase volume being refluxed. A partially converted mixture of acetic acid and isobutylacohol can be fed instead of pure acetic so the acetic acid containing feed stream can contain also isobutylacetate and/or water and/or a certain part of unreacted isobutylacohol.
The process according to this invention is advantageously performed in an apparatus comprised of a column consisting of three zones, the reaction zone, placed in the middle part of the column, containing a solid acidic catalyst, in a preferred embodiment immobilized in well known types of structural packing with internal channel structure by fixing the catalyst between two layers of an inert porous material forming the structure of the packing; the lower and upper separation zones containing inert structural packings, common tower packings or distillation trays, the acetic acid feed pipe being introduced into the upper part of the reaction zone or above this zone while the isobutyl alcohol feed pipe is connected to the lower part of the reaction zone or below this zone, the column bottom being equipped with a reboiler, the isobutylacetate withdrawing line being conducted either from the reboiler or from the column bottom, the upper part of the column being furnished with a head equipped with a vapour pipe for introducing the distillate vapours into a condenser, from which a condensate line leads to the separator, to the lower part of which a water phase pipe is connected and to the upper part thereof a reflux line and a pipe for withdrawal of the non-refluxed organic portion of the distillate are connected.
It is apparent from the basic features of the invention described above, that it is possible to reach higher than equilibrium, practically up to 100%, conversion of starting compounds to isobutylacetate according to this invention. It is the main function of the separation zones to separate reaction products i.e. isobutylacetate and water from the starting components i.e. acetic acid and isobutyl alcohol and returning the starting components back to the reaction zone, while isobutylacetate is continually separated as a high boiling bottoms product and water is separated as distillate in the form of a volatile ternary heterogeneous azeotrope being withdrawn from the system after being separated from the organic phase of the distillate, which contains mainly isobutyl alcohol and isobutylacetate. The organic phase is entirely or partly refluxed. The amount ratio of starting components fed to the organic phase reflux is 1:1 to 1:20, the reflux representing 50 to 100% of the whole amount of separated organic phase.
Starting components i.e. acetic acid and isobutyl alcohol can be fed either in equimolar ratio, or some excess of isobutyl alcohol can be applied to convert all acetic acid. If the process according to this invention is run under atmospheric pressure, the following temperature profile is established: 110 to 120xc2x0 C. in the reboiler and 87 to 104xc2x0 C. in the head of the column. The process according to the invention can also be performed under reduced pressure. Isobutyl alcohol is introduced below the acetic acid input. Most commonly, isobutyl alcohol is introduced below the reaction zone or into its lower part, while acetic acid is introduced above said zone or into its upper part.
The vapours carried out of the column head condense yielding a mixture which is separated into water and organic phases after being cooled at 80 to 5xc2x0 C. Whole amount, or the major part of the organic phase is refluxed to the column head. The water phase containing dissolved isobutyl alcohol and isobutylacetate is taken off. The alcohol and ester dissolved can be stripped from the water phase and returned to the process. The desired reaction productxe2x80x94dry isobutylacetate is withdrawn from the reboiler at the temperature of 110 to 120xc2x0 C. The product purity depends both on the molar ratio and the amount of starting components introduced to the system and on the catalyst to starting components amount ratio as well as on the catalyst activity. The product obtained is of commercial quality or it is easy to improve its quality to that level by non demanding consequent distillation.