Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-01-19
2001-10-16
Padmanabhan, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S410000
Reexamination Certificate
active
06303826
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for purification of acetone containing at least one oxidizable impurity by contacting the acetone with a heterogeneous oxidation catalyst in the presence of oxygen.
2. Related Background Art
The commercial process for purifying acetone employs a distillation column which separates water and other higher-boiling impurities from the acetone. Traditionally, removal of light aldehyde impurities is accomplished by reactive distillation in which an aqueous solution of sodium hydroxide is injected into the distillation column to promote condensation of aldehydes to form higher-boiling compounds. See, e.g., U.S. Pat. Nos. 5,788,818; 5,567,853; 4,329,510; 3,668,256; 2,906,676; 2,906,675; and 2,624,699. Use of this process requires introduction of water to the distillation column to aid in removing salts and other by-products of the sodium hydroxide reaction. The presence of water, salts, and high-boiling by-products reduces the efficiency of the distillation column.
In particular, crude acetone resulting from the production of phenol from cumene typically contains about 200-700 ppm aldehydes and 200-500 ppm methanol. Treatment of acetone with aqueous sodium hydroxide during distillation leads to production of distillation bottoms containing large amounts of polymers and salts, thereby decreasing the efficiency of conventional reboilers. Moreover, base-catalyzed self-condensation of acetone reduces the yield of purified acetone. Impurity levels in commercial acetone purified by this method are still about 30-50 ppm for acetaldehyde and about 200-300 ppm for methanol. A method for purification of acetone that overcomes the aforementioned difficulties is disclosed herein.
Oxidation of aldehydes and alcohols in the presence of oxidation catalysts is well known in the art. However, applicants are not aware of any attempt to use such a method to purify acetone containing aldehyde and alcohol impurities. The mechanism of oxidation of acetaldehyde, present at high concentrations in various solvents, including acetone, by soluble palladium clusters has been studied by Starchevskiy et al., as reported in
Dokl. Akad. Nauk
, volume 342, page 772 (1995). However, this study clearly was not directed to a purification method for acetone. Indeed, this reference provides no indication as to whether the soluble palladium catalyst reduced acetaldehyde to ppm levels in acetone, or the extent of acetone decomposition encountered during the oxidation. For these reasons, Starchevskiy et al. do not provide a method that would allow efficient purification of acetone by selective oxidation of impurities.
Applicants are not aware of any use of oxidation catalysts in purification of acetone, despite the commercial quantities of acetone produced worldwide by a variety of processes. An efficient process for purification of acetone would be highly desirable.
SUMMARY OF THE INVENTION
The present invention is directed to a method for purification of acetone containing at least one oxidizable impurity. The method comprises the steps of: (a) contacting acetone containing at least one oxidizable impurity with a heterogeneous oxidation catalyst in the presence of oxygen for a time and at a temperature sufficient to oxidize at least a portion of at least one of the oxidizable impurities; and (b) substantially separating purified acetone from the resulting mixture obtained from step (a).
DETAILED DESCRIPTION OF THE INVENTION
In the method of the present invention, impure acetone is contacted with a heterogeneous oxidation catalyst in the presence of oxygen. The impure acetone contains at least one oxidizable impurity, i.e., an impurity readily susceptible to oxidation. Such impurities include without limitation aldehydes, alcohols, benzylic compounds and alkenes. The method of the present invention successfully reduces or removes oxidizable impurities from acetone without oxidizing a substantial portion of the acetone. Suitable oxidation catalysts are those capable of oxidizing alcohols, aldehydes, benzylic compounds and alkenes. Typically, commercial crude acetone is obtained from the cumene oxidation process, and contains acetaldehyde, methanol, and smaller amounts of propionaldehyde and cumene, among other impurities. Typically, commercial crude acetone contains no more than about 700 ppm of aldehyde impurities and no more than about 300 ppm of methanol. Preferably, the method of this invention is practiced on an acetone stream containing less than about 1000 ppm of aldehyde impurities and less than about 500 ppm methanol. Preferred oxidation catalysts are those capable of oxidizing alcohols and aldehydes.
Suitable oxidation catalysts for use in the method of this invention include without limitation precious metals or other transition metals supported on carbon or inorganic materials (i.e., supported catalysts) and precious metals or other transition metals in substantially pure form. Preferred catalysts are precious metals supported on carbon, or on inorganic supports. Inorganic supports include without limitation alumina, silica, clay, titania/zirconia, and magnesia. Alumina and silica supports are preferred. Palladium is the most preferred of the precious metals. The most preferred catalyst is palladium on &agr;-alumina.
The Examples presented hereinafter demonstrate that there is considerable variation in the efficiencies of various metals and supports. Either palladium on carbon or palladium on silica provides a high percentage conversion of aldehydes and alcohols to their oxidized forms, as shown in Examples 1, 2, 4 and 7. However, the consumption of acetone (“acetone burn”) is higher for the silica support. Palladium on alumina gives variable results depending on the type of alumina used. When the support is a relatively low-surface-area &agr;-alumina, as in Example 8, high percentage conversions of aldehydes and methanol are obtained with very low consumption of acetone and with relatively low levels of byproducts. However, when the support is a relatively high-surface-area &ggr;-alumina, although percent conversions for both acetaldehyde and methanol are roughly comparable to those obtained with an &agr;-alumina or silica support, initially increased consumption of acetone and formation of byproducts are observed, as shown in Example 9. The Pd/&ggr;-alumina catalyst produces high initial levels of byproducts, with little of the expected acetic acid oxidation product, but appears to stabilize at longer times, producing lower levels of byproducts. Platinum on carbon, ruthenium on carbon, and manganese nodules provide lower conversions, especially for acetaldehyde, as shown in Examples 3, 5 and 6, respectively. Manganese nodules also appear actually to promote the formation of methanol at higher temperatures.
Oxygen is introduced into the reaction vessel as air, as pure oxygen, as a mixture of oxygen or air with one or more non-oxidizable gases, including without limitation nitrogen, and the noble gases, or from a compound which serves as an oxygen source, including without limitation nitrous oxide, hydrogen peroxide, and organic peroxides and hydroperoxides.
After at least a portion of at least one of the oxidizable impurities is oxidized, purified acetone is separated from the mixture, either as a vapor, or as a liquid. The heterogeneous catalyst typically is removed from the vapor or liquid components by filtration. This may be achieved by using the catalyst in the form of a fixed or fluidized bed from which the liquid components are separated by filtration as part of the normal operation of the catalyst bed, or by a separate filtration operation designed to remove an insoluble catalyst from a vapor or liquid product. Purified acetone typically is separated from the oxidized impurities by distillation of the lower boiling acetone. Typically, purified acetone containing less than about 10 ppm acetaldehyde and less than about 100 ppm methanol is obtained from a commercial acetone stream using the method of this inven
Bhinde Manoj V.
Keenan Scott R.
Koons, Jr. Robert A.
McWilliams Matthew P.
Padmanabhan Sreeni
Pepper Hamilton LLP
Sunoco Inc. (R&M)
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