Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
1999-07-26
2002-11-19
Rotman, Alan L. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C560S265000
Reexamination Certificate
active
06482976
ABSTRACT:
BRIEF SUMMARY OF THE INVENTION
1. Technical Field
This invention pertains to processes for producing reaction product through equilibrium-limited reactions, such as esterification and alcoholysis (or transesterification) reactions. The invention is particularly useful in esterification processes such as to make carboxylic acid esters, e.g., butyl acrylate and ethylhexyl acrylate.
2. Background of the Invention
Equilibrium-limited reactions generally involve the reaction of two or more reactants to produce at least one product and, typically, a co-product. In order to achieve a greater conversion to the desired product(s), various techniques have been suggested such as removing the co-product and/or product from the reaction menstruum to maintain a driving force toward the product.
Equilibrium-limited reactions can be conducted in a single reactor with product being selectively removed from the reaction menstruum or in a plurality of reactors in which product is separated from the reaction menstruum in each of the reactor stages. One type of single reactor process is disclosed in U.S. Pat. No. 3,700,726 which discloses a process for making glycol ether acetates in which a reactor operates at a temperature of about 150° C. to 225° C. and a pressure of about 25 psia to about 150 psia to effect the reaction of a lower alkyl acetate with a glycol ether in the presence of catalyst selected from aluminum alkoxides, titanium alkoxides and dialkyl tin oxides. A vapor is withdrawn from the reactor and is distilled to recover the co-product alcohol and a bottoms fraction which is recycled to the reactor. A liquid is withdrawn from the reactor and is flashed in a flash column operating at about 130° C. to 180° C. The overhead from the flash column contains the product ester which is subjected to distillation for purification and the bottoms from the flash column, which contains catalyst, is recycled to the reactor.
Another type of single reactor process is disclosed in U.S. Pat. No. 4,280,010 which discloses a continuous process for making alkyl acrylates free from ether by reacting acrylic acid with a C1 to C4 alkanol in a molar ratio of 1:1 to 1:2 in the liquid phase. The process is conducted at a temperature of 80° C. to 130° C. and a pressure of 100 to 760 mm Hg in the presence of a sulfuric acid or organic sulfonic acid catalyst, and the resulting alkyl acrylate is distillatively purified. As part of the distillation, an azeotropic mixture of alkyl acrylate, reaction water and unreacted alkanol is distilled off near the head of a first distillation zone which is mounted on the reaction zone.
Yet another type of single reactor process is disclosed in European Patent No. 0 733 617 which discloses a process for the continuous esterification of an alkanol with (meth)acrylic acid in the presence of proton-donating catalysts in a homogeneous, liquid, solvent-free phase in which the water generated in the reaction and the produced alkyl esters are continuously separated as an aqueous azeotrope via the head of a rectification zone mounted on the reaction zone and which has a head pressure of 0.1-1 atmospheres, to give a pure (meth)acrylate.
European Patent Application No. 0 779 268 discloses a method for recovering n-butyl acrylate substantially free of acrylic acid from an esterification reaction mixture by distilling from an esterification reactor a vaporized mixture of acrylic acid, n-butyl acrylate, n-butanol and water, and condensing the vaporized mixture to provide a first condensate of an organic phase and an aqueous phase. A portion of the organic phase and aqueous phase is then fed to an acrylic acid separation column. An azeotropic mixture of n-butanol, n-butyl acrylate and water is distilled from the acrylic acid separation column at an aqueous reflux ratio of 8.5:1 to 17:1, and an acrylic acid bottom stream is removed from the distillation column and recycled to the esterification reactor. Refluxing any portion of the organic phase is detrimental to the operation of the acrylic acid separation column (see page 13, line 58 through page 14, line 5). The overhead mixture is condensed to provide a second condensate which is separated into a n-butyl acrylate rich organic phase and an aqueous phase. The n-butyl acrylate rich organic phase is then removed substantially free of acrylic acid. Additional reactants are recovered and recycled after treatment in a separate hydrolytic recovery unit and a cracking reactor.
Frequently, where the reaction is conducted in a single reactor, the residence time to secure the desired conversion results in a large reactor volume per unit volume of product. Moreover, substantial amounts of vapor are typically generated to remove product and co-product, and vaporized reactants are recovered and returned to the reactor, resulting in significant energy costs. Reactant recovery itself may pose difficult problems or require elaborate separation schemes. In some instances, to vaporize the product for its removal, temperatures may be required that result in undesired side reactions and/or subatmospheric pressures are employed that further increase operating costs.
Accordingly, processes for conducting equilibrium-limited reactions are sought that reduce total reactor volumes and number of reactors, minimize reactant recovery problems, and provide sought conversions to the product without the need to resort to significant energy use, e.g., unduly high temperatures or excessive vacuums, in conducting the reactions.
DISCLOSURE OF THE INVENTION
The processes of this invention relate to conducting an equilibrium-limited reaction of at least one carboxylic acid and at least one alcohol to produce at least one ester product in a single reaction zone, wherein the reaction zone temperature and pressure are sufficient to crack heavies, e.g., Michael-Addition heavies, formed in or introduced into said single reaction zone and to vaporize at least a portion of the ester product upon production thereof. An acid separation column containing a rectification zone and a stripping zone provides (in the rectification zone) an overhead fraction comprising the at least one ester product and (in the stripping zone) a bottoms fraction comprising water and the at least one carboxylic acid, in which at least a portion of the bottoms fraction is supplied by controlled means to the single reaction zone sufficient to provide stable and efficient operation of the acid separation column and single reaction zone. While typically only one ester product is ultimately sought, the processes of this invention may make possible the simultaneous formation of two or more ester products. For instance, acrylic acid may be reacted with a mixture of ethanol and butanol to produce the corresponding ethyl and butyl acrylates.
The processes of this invention relate in part to conducting an equilibrium-limited reaction of at least one carboxylic acid and at least one alcohol to produce at least one ester product comprising:
a. reacting at least one carboxylic acid-containing feedstock with at least one alcohol-containing feedstock in the presence of an esterification catalyst in a single reaction zone maintained under reaction conditions sufficient to produce at least one ester product, said reaction conditions comprising a temperature and pressure sufficient to crack heavies formed in or introduced into said single reaction zone and to vaporize at least a portion of said at least one ester product upon production thereof;
b. withdrawing vapor from said single reaction zone, and introducing said withdrawn vapor into the lower portion of an acid separation column, said acid separation column comprising a rectification zone above the point where said withdrawn vapor is introduced into said acid separation column and a stripping zone below the point where said withdrawn vapor is introduced into said acid separation column, to provide (in said rectification zone) an overhead fraction comprising said at least one ester product and (in said stripping zone) a bottoms fraction comprising water and said at least o
Ho Fungau
Patterson Leah Ann
Tellis Cyril B.
Oh Taylor V.
Rotman Alan L.
Union Carbide Chemicals & Plastics Technology Corporation
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