Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2001-12-06
2004-03-02
Shah, Mukund J. (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
Reexamination Certificate
active
06700016
ABSTRACT:
This Application was filed under 35 U.S.C. 371 and is the U.S. National Stage of PCT/EP00/05004, filed May 31, 2000.
The present invention relates to a process for the purification of acrylic acid or methacrylic acid. The present invention furthermore relates to a process for the preparation of acrylic acid or methacrylic acid using the purification process.
Acrylic acid and methacrylic acid are key chemicals. Owing to their very reactive double bond and the acid function, acrylic acid is particularly suitable as a monomer for the preparation of polymers, for example for adhesives, dispersions, coating materials or superabsorbers.
WO-A-9 801 415 discloses a process for the preparation of acrylic acid or methacrylic acid, in which first a product mixture containing the acid is prepared, said mixture is condensed and the acid is then crystallized from the solution obtained in the condensation.
It is an object of the present invention to increase the purity of acrylic acid or methacrylic acid.
We have found that this object is achieved if the crystals of acrylic acid or methacrylic acid are washed with a wash or purification liquid containing the corresponding acid and having a temperature of from 15 to 40° C. Surprisingly, it has been found that a very good purification effect is achieved in a very simple manner by this measure.
The present invention therefore relates to a process for the purification of acrylic acid or methacrylic acid by crystallization to obtain crystals and a mother liquor, wherein the crystals are washed with a wash liquid containing acrylic acid or methacrylic acid and having a temperature of from 15 to 40° C.
In one embodiment, the present invention;relates to a process for the preparation of acrylic acid, which comprises the following stages:
(a) preparation of a gaseous product mixture which essentially has the composition of a reaction mixture of the catalytic gas-phase oxidation of C3- or C4-alkanes, C3- or C4-alkenes, C3- or C4-alkanols and/or C3- or C4-alkanals and/or precursors thereof to acrylic acid or methacrylic acid,
(b) condensation of the gaseous product mixture,
(c) crystallization of the acrylic acid or methacrylic acid from the solution obtained in stage (b) and
(d) purification of the acrylic acid or methacrylic acid from the crystals of the preceding stage according to the purification process of the invention described above.
Preferred embodiments of the invention are defined in the following description, the example and the subclaims.
According to the invention, the acrylic acid or methacrylic acid crystals are washed with a wash liquid or purification liquid containing the corresponding acid and having a temperature of from 15 to 40° C., preferably from 20 to 35° C., in particular from 20 to 30° C., most preferably from 20 to 25° C.
A wash liquid which has a higher purity than the mother liquor from the crystallization with respect to the acrylic acid or methacrylic acid to be crystallized is expediently used. Preferably, the wash liquid contains from 90 to 99.99, in particular from 97.0 to 99.9, most preferably from 99.0 to 99.8, % by weight, based in each case on 100% by weight of wash liquid, of acid. Pure acid, i.e. a pure product comprising from 99.3 to 99.8% by weight of acrylic acid or methacrylic acid, or the acid solution to be purified by crystallization, i.e. the feed of the crystallization or the solution obtained from the condensation of the gaseous product mixture according to stage (b), is advantageously used as wash liquid. The impurities in the wash liquid are generally impurities/byproducts from the preparation and/or purification process of the acid. The wash liquid is preferably used in an amount of from 3 to 80, in particular from 5 to 50, more preferably from 10 to 25, g of wash liquid/100 g of crystals.
The procedure for the wash process is not subject to any restriction. The washing can be carried out in one stage or in a plurality of stages. It is preferably carried out in a plurality of stages, in particular two stages. The washing can be effected continuously or batchwise in apparatuses customary for this purpose. Centrifuges, suction filters or belt filters are advantageously used. Expediently, washing is effected continuously with the use of continuous apparatuses for solid-liquid separation, such as centrifuges, decanters or belt filters, and batchwise with the use of batchwise apparatuses for solid-liquid separation, e.g. suction filters. The washing can be carried out on centrifuges or belt filters in one stage or a plurality of stages. Here, the wash liquid can also be fed countercurrently to the crystal cake.
In general, mixtures which preferably contain from 65 to 99.9, in particular from 75 to 99,8, most preferably from 85 to 99,5, % by weight, based in each case on 100% by weight of mixture, of acrylic acid or methacrylic acid, the remainder comprising impurities/byproducts of any type, in particular impurities or byproducts from the preparation process of the acid, for example of the catalytic gas-phase oxidation, are suitable for the crystallization of the acrylic acid or methacrylic acid, from which the crystals to be purified according to the invention are then obtained. The crystallization is advantageously carried out as a suspension crystallization.
The crystallization process used is not subject to any restriction. The crystallization can be carried out continuously or batchwise, in one stage or a plurality of stages. The crystallization is preferably effected in one stage. In another preferred embodiment of the invention, the crystallization is carried out as a fractional crystallization. In fractional crystallization, all stages which produce crystals which are purer than the acid solution fed in are usually referred to as purification stages and all other stages are usually referred to as stripping stages. Multistage processes are expediently operated here according to the countercurrent principle, in which, after the crystallization in each stage, the crystals are separated from the mother liquor and these crystals are fed to the respective stage having the next highest purity, while the crystallization residue is fed to the respective stage having the next lowest purity.
The temperature of the solution during the crystallization is advantageously from 14 to −30° C., in particular from 14 to −5° C. The solids content in the crystallizer is advantageously between 0 and 90, preferably between 10 and 80, more preferably between 15 and 50, g of solid/100 g of suspension.
In an advantageous embodiment of the invention, the crystallization is effected by cooling the apparatus walls or by evaporating the solution under reduced pressure. In the crystallization by cooling of apparatus walls, the heat is removed by means of scraped-wall heat exchangers which are connected to a stirred kettle or a container without a stirrer. The circulation of the crystal suspension is ensured here by a pump. In addition, it is also possible to remove the heat via the wall of a stirred kettle having a stirrer passing close to the wall. A further preferred embodiment in the case of the cooling crystallization comprises the use of cooling disk crystallizers, as produced, for example, by Gouda (the Netherlands). In a further variant of the crystallization by cooling, the heat is removed by means of conventional heat exchangers (preferably tube-bundle or plate-type heat exchangers). In contrast to scraped-wall heat exchangers, stirred kettles having stirrers passing close to the wall or cooling disk crystallizers, these apparatuses have no means for avoiding crystal layers on the heat-transfer surfaces. If a state in which the thermal resistance assumes too high a value owing to the formation of a crystal layer is reached during operation, switching to a second apparatus takes place. During the operating time of the second apparatus, the first apparatus is regenerated (preferably by melting off the crystal layer or flushing the apparatus with unsaturated solution). If too high a thermal resistance is re
Baumann Dieter
Eck Bernd
Heilek Jörg
Schliephake Volker
BASF - Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Shah Mukund J.
Tucker Zachary C.
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