Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2000-04-18
2002-02-12
Killos, Paul J. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S519000, C562S608000
Reexamination Certificate
active
06346645
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel method for treating an oxygenated organic liquid stream contaminated with a carbonyl impurity such as acetaldehye or acetone. Contacting the organic liquid with a resin having an amine functional group effectively removes the undesired carbonyl compounds.
BACKGROUND OF THE INVENTION
Adsorptive techniques to remove carbonyl compound impurities have been applied for different reasons to a variety of industrial product streams. For example, Japanese patent 2737290 discloses the use of mineral acid salts of hydrazine-group containing ion exchange resins for the removal of aldehydes from waste water. The adsorptive separation reduces the odor of contaminated water. Canadian patent application 2052435describes the use of a solid nonionic polystyrene adsorbent to remove unsaturated aldehydes, thereby improving beverage (e.g. beer) stability and taste. U.S. Pat. No. 5,132,456 sets forth a process for separating carboxylic acids from aqueous feedstocks by contact with an acid-sorbing phase that can include a weakly to moderately basic anion exchange resin.
The adsorption of carbonyl compounds from hydrocarbon streams, particularly olefinic liquids, has proven beneficial in terms of facilitating downstream processing operations. In German patent 3512352, for example, the adsorptive removal of carbonyl sulfide from a propene stream is carried out to improve its quality as a feedstock for subsequent polymerization in the presence of a Ziegler catalyst. The adsorbent material in this case is an anion exchange resin having an amine function. Soviet Union patent application 695996 discloses several types of resins effective for the removal of carbonyl compounds from isobutylene. The purification of this feed is taught to improve the quality of the butyl rubber end product, resulting from the copolymerization of the purified isobutylene with isoprene.
In addition to carbonyl compound removal from liquid aqueous and hydrocarbon streams, the prior art has also addressed the need to free oxygenated organic liquids of these reactive impurities. Of particular concern is the purification of carboxylic acids, (which are themselves carbonyl compounds) containing trace amounts of carbonyl impurities such as aldehydes and ketones. It is well documented that these impurities invariably contaminate commercial acetic acid products resulting from the catalytic carbonylation of methanol with carbon monoxide, a process that serves as the basis for virtually all new acetic acid capacity. Acetic acid is industrially significant, mainly due to its use in the production of purified terephthalic acid and vinyl acetate monomer.
Methods for manufacturing acetic acid by methanol carbonylation that have proven commercially successful are described in U.S. Pat. No. 3,769,329, and more recently in U.S. Pat. No. 5,001,259. The '259 patent discloses a method for maintaining high catalyst activity and stability in the methanol carbonylation environment by using a specified amount of iodide ions above that which is normally present as methyl iodide or other organic iodide promoter. A distinguishing characteristic of this process, compared to that described in the earlier '329 patent, is the ability to achieve competitive reaction rates and prevent catalyst precipitation at reactor water levels of only 4 wt-% or less. In U.S. Pat. No. 5,344,755, another type of low water process is described, where a supported rhodium (i.e. heterogeneous) catalyst is used in place of the homogeneous catalysts set forth in the former '329 and '259 references.
It is recognized in the art that acetic acid produced by methanol carbonylation, and particularly using the low water processes of the aforementioned '259 and '755 patents, contains a considerable amount of byproduct impurities which can be detected based on their reducing action on permanganate solution. Furthermore, these impurities are not easily separable using the conventional distillation schemes downstream of the carbonylation reactor section designed to purify the product acetic acid from catalyst, methyl iodide promoter, water, and methyl acetate. The presence of such impurities is highly undesirable because they adversely affect the product permanganate time, an important commercial test (STM.170) of the acetic acid quality. Even small amounts of reducing impurities can degrade the stability, usefulness, and overall salability of the acetic acid product. Reducing impurities that have been found to significantly impact permanganate time include, but are not limited to, saturated and unsaturated aldehydes, namely acetaldehyde, butyraldehyde, crotonaldehyde, 2-ethyl crotonaldehyde, 2-methyl 2-pentanal, and 2-ethyl butyraldehyde. Additionally, other undesired carbonyl species such as the ketones acetone and methyl ethyl ketone normally exist to some extent in the final acetic acid. Although such carbonyl compounds may have little or no effect on the permanganate time, their removal is desired in order to improve the overall purity of the product.
The importance of purifying commercial acetic acid streams of various carbonyl contaminants (and especially reducing impurities) is apparent from the prior art references dealing with this problem. For example, U.S. Pat. No. 5,155,265 proposes reacting the carbonyl impurities with ozone to form a reactive oxygenated species or complex that can thereafter be more easily separated. This removal is carried out by passing the ozone-treated acetic acid through a carbonaceous material. Additionally, the effluent from this removal step is optionally contacted with a macroreticulated strong acid cation exchange resin which is stable in the acetic acid and has at least one percent of its active sites converted to the silver or mercury ion-exchange form.
U.S. Pat. No. 5,371,286, herein incorporated by reference, identifies particular intermediate streams in commercial acetic acid processing that contain relatively high concentrations of carbonyl impurities. Specifically, the overhead liquid stream from a commonly employed fractionator to separate primarily methyl iodide and acetic acid (referred to as the “splitter” column) tends to accumulate substantial quantities of carbonyl compounds, particularly acetaldehyde. If sufficient water is present, this stream will phase separate, with the carbonyl impurities partitioning preferentially into a heavy phase. In either case, the splitter column overhead or some portion thereof can be routed to another column for further processing by distillation and phase separation
European patent 0487284 B1 proposes an alternate treatment of the splitter column overhead stream, which, as mentioned previously, has a significant content of carbonyl compounds compared to other intermediate process streams. Specifically, the splitter column overhead can be contacted with a solution of a compound that reacts with the carbonyls to facilitate subsequent separation by distillation. The reactive compound in this case is an amino compound such hydroxylamine in aqueous solution. The reaction of hydroxylamine and the carbonyl impurities in an oximation reactor produces oximes. The oximes in the reactor effluent are first phase separated in an aqueous phase and then distilled for removal of the oximation products.
In U.S. Pat. No. 5,625,095, the benefits associated with maintaining an acetaldehyde concentration in the reactor of 400 ppm or less are disclosed, particularly in terms of reducing the amounts of carbonyl impurities and organic iodides in the acetic acid product. Process conditions to reduce the acetaldehyde concentration are described, which may be used alone or in combination with specific extraction and distillation procedures. U.S. Pat. No. 5,783,731 discloses the treatment of the vent gas stream of the splitter column overhead stream to remove relatively high levels of acetaldehyde contained therein. The treatment involves condensing the vent gas stream and further contacting it with an aqueous amino compound to allow th
House David W.
Kulprathipanja Santi
Pujado Peter R.
Forohar Farhad
Killos Paul J.
Spears, Jr. John F.
Tolomei John G.
UOP LLC
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