Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
2000-04-27
2002-06-04
Geist, Gary (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C560S231000, C560S248000
Reexamination Certificate
active
06399812
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
Not applicable.
BACKGROUND
1. Field of Invention
This invention relates to a process for production of aliphatic esters by catalytic conversion of the corresponding alcohols having carbon numbers between 1 and 10. In particular, the process can be used advantageously for production of ethyl acetate by conversion of ethyl alcohol.
2. Description of Prior Art
Ethyl acetate is a commercially important chemical. It is especially suitable as a solvent for extraction processes in the food industry. It finds applications as a high-grade defatting detergent. It is used for preparation of cosmetics, glues, lacquers, paint as well as polymer solution in paper industry. High purity ethyl acetate is used as an anhydrous medium and also as an intermediate in chemical syntheses.
Commercially, ethyl acetate is recovered as a by-product or produced through chemical synthesis. In 1988, 65 and 35% of ethyl acetate produced in the US were from by-product recovery and chemical synthesis, respectively.
Ethyl acetate is recovered as a by-product from n-butane liquid phase oxidation and as a co-product in polyvinyl butyral production process.
As the demand for ethyl acetate increases due to environmental concerns, more ethyl acetate has to be produced through chemical syntheses. Currently, there are two commercial processes for synthesizing ethyl acetate, namely, the Hoechst process based on the Tischenko reaction and the esterification process based on direct reaction of acetic acid with ethanol. In the Tischenko reaction, acetaldehyde is dimerized to ethyl acetate in the presence of aluminum ethoxide. In the direct esterification process, ethanol is reacted with acetic acid in the presence of acidic catalyst.
In the Hoechst process, a catalyst solution of aluminum ethoxide is first prepared by dissolving granular aluminum in an ethanol-ethyl acetate mixture in the presence of aluminum chloride and a small amount of zinc chloride. The reaction evolves hydrogen and is exothermic. Intensive cooling is required to prevent the loss of organic matter. The final solution contains about 2% aluminum. The next step in the process is to introduce the catalyst solution along with acetaldehyde simultaneously into a reactor. The reaction varies according to the temperature and the catalyst quantity. These parameters are adjusted to accomplish about 98% conversion in one pass through the reactor. A further 1.5% transformation is obtained in the stirring vessels where a residue is separated from the product. The reactor is kept cooled to about 0° C. by the use of a chilled brine. The residence time in the reactor is about one hour. The distillable products are removed in the residue separation vessel by evaporation. The residue is treated with water to convert as much as possible to ethanol. The remainder can either be treated in a biological degradation plant or incinerated. The combined distillable products are then separated in a series of distillation steps to give ethyl acetate, the product; unconverted acetaldehyde for recycle: light ends which can be used for fuel; a mixture of ethyl acetate and ethanol, which can be used in the catalyst preparation step; and a by-product, acetaldehyde diethyl acetal, which can be recovered for sale or hydrolyzed for recovery of acetaldehyde and ethanol. This process is complicated in operation procedures and equipment in the processing steps. It employs expensive and dangerous catalyst systems.
In the esterification process, ethanol and acetic acid are combined with a recycle of crude ethyl acetate in a reactor, which is also an azeotropic distillation column. The reaction produces water as a waste product. The water impedes the reaction, and the reaction column removes the water as an azeotrope as it is generated. The overhead condensate is collected in a decanter where the product separates into two phases. The organic phase is partially recycled to the reaction column and the balance is fed to a second distillation column, which produces a bottom product of ethyl acetate and an overhead product of an azeotrope of ethyl acetate, water and ethanol. The overhead condensate is collected in a second decanter, where it separates into two phases as before. The organic phase is recycled to the column while the aqueous phase is combined with the aqueous phase from the first column and fed to a third column to produce a waste stream from the bottom and the azeotrope from the top. The azeotrope is recycled to the reaction column. Since esterification is a reversible reaction, the conversion per pass is theoretically limited by the equilibrium constant K which is defined as follows: K=[ETOAC]×[H
2
O]/[ETOH]×[HOAC], where [ETOAC], [H
2
O], [ETOH] and [HOAC] are mole % of ethyl acetate, water, ethanol and acetic acid in the reactor, respectively. In order to overcome this problem, several azeotropic distillation columns with recycle as well as catalytic distillation can be used, leading to complicated and expensive operation. Furthermore, water in the ethanol feed impedes the reaction and limits conversion level of the esterification so that an expensive ethanol of low water content has to be used.
Ethyl acetate is synthesized from ethylene and acetic acid. U.S. Pat. No. 4,275,228 disclosed that ethyl acetate is prepared by vapor phase reaction of ethylene and acetic acid in the presence of a catalytic amount of a solid, ion-exchange fluoropolymer comprising sulfonic acid moieties. Conversions of acetic acid vary from 30% at 126° C. with a residence time of 55 hours to 60% at 150° C. with a residence time of 30 hours. Obviously, the reaction rate is too low to be commercially viable. In addition, the ion-exchange resin catalyst in the high temperature, oxidative reaction condition would itself be oxidized leading to rapid aging and crumbling. For the similar process, U.S. Pat. No. 5,241,106 reveals a variation whereby the catalyst comprises tungstophosphoric acid of which 10-90% of the total amount of proton is replaced with a member selected from the group consisting of (a) cesium metal ion, (b) a combination of cesium metal cation and at least one cation selected from alkali metal cations other than cesium cation, and (c) a combination of cesium metal cation and at least one cation of iron group metal cations. The process is flexible and can be carried out in either vapor or liquid phase. In addition, the reaction rate can be improved by adding control amount of water in the feed. However, the reaction rate and the yield of ethyl acetate remain too low for commercial application.
Ethyl acetate is produced by hydrogenation of acetic anhydride. U.S. Pat. No. 4,886,905 disclosed a process for preparation of ethylene diacetate and/or ethyl acetate by hydrogenating acetic anhydride in the presence of a homogeneous ruthenium catalyst, methyl iodide and, optionally, lithium iodide. The process can also be utilized to hydrogenate mixtures of acetic anhydride and ethylene diacetate to produce ethyl acetate alone. This process is complex to operate. It requires the use of homogeneous complex catalyst. The co-product, acetic acid, must be separated and converted back to acetic anhydride for reuse. In addition, the catalyst and iodides must be separated from the reaction products and recycled.
Another approach is to produce ethyl acetate from methyl acetate. In U.S. Pat. No. 4,780,566, a process is described for producing ethyl acetate either alone or in mixture with acetic acid, by homologation of methyl acetate with CO and H
2
in the presence of a catalyst in the form of a Ru compound and catalysis promoter of hard acid type in an atmosphere of hydrogen and carbon dioxide. This process is not only complex but also poor in selectivity for ethyl acetate. It produces significant amount of by-product, acetic acid, alcohols, ethers, propionates, methane and ethane.
Ethyl acetate is produced by catalytic oxidation of ethanol. U.S. Pat. No. 5,334,751 disclosed
Chang Jen-Ray
Yan Tsoung Y.
Forohar Farhad
Geist Gary
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