Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid anhydrides
Reexamination Certificate
2000-01-10
2003-07-15
Rotman, Alan L. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid anhydrides
C562S888000, C549S203000, C549S258000, C549S259000, C549S262000
Reexamination Certificate
active
06593495
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the color stabilization of organic acid anhydrides. More particularly, the invention relates to the color stabilization of maleic acid anhydride and other anhydrides which are maintained at elevated temperatures for extended periods of time during the course of their production, storage, and handling. The stabilization method and compositions therefor taught herein provide heretofore-unseen synergistic effects which provide for lessened stabilization treatment levels and greater color stability over compositions and methods of prior art.
BACKGROUND
Anhydrides of carboxylic acids are important as raw materials in various industries and such materials are typically available to end users in either solid or molten form, depending upon the particular anhydride and the intended use. Anhydrides of acrylic acid, acetic acid, succinic acid, phthalic acid, and maleic acid are but five examples of such materials, the entire class of which anhydrides is well-known by those skilled in the chemical art.
Most organic acid anhydrides are colorless in appearance immediately after their initial preparation and purification, but are seen to take on or develop a color after being stored at elevated temperatures for extended, or in some cases moderate, periods of time. While the exact reaction mechanism for the development of coloration in such materials varies with the composition in each case, and the inventor hereof does not wish to be bound by any particular theory, it may be surmised that trace quantities of impurities present undergo oxidation, coupling, polymerization, or otherwise react with either themselves or other impurity molecules present, or with the anhydride itself. It is also possible that the impurities may function as catalysts for the oxidation of the anhydride or its reaction with itself. Regardless of the mechanism, the development of coloration in such materials is generally indicative of impurities, reactions associated therewith, and/or oxidation.
With the advent of strict quality controls in manufacturing processes, greater attention has in general been paid to the presence of minor impurities in chemical raw materials and other physical attributes such as appearance which were often overlooked in the past. Consistency of quality in raw materials provided to a user has become an increasingly important requisite of the raw material supplier. Therefore, any improvement in the stability of a given raw material is viewed as beneficial to the user of the material and products derived therefrom. Accordingly, a distinct advantage would be gained by the provision of a chemical material or system that may be added to a carboxylic acid anhydride which effectively inhibits chemical reactions occurring within the material when it is maintained at temperatures normally experienced during the usual course of its handling and processing, to the extent that changes in color are minimized over extended periods of time.
The art of stabilization of various organic molecules probably dates back to earlier than the discovery in the 1500's that ethanol was stabilized against oxidation catalyzed by impurities present in its aqueous solution by the burning of a candle of sulfur in a barrel prior to its being filled with wine. Since that time, the number and type of known organic molecules has increased dramatically. The increase in the number of known organic molecules has been attended by an increase in the number of stabilizing additives useful in connection with the various materials, the number and type of which are overly voluminous to be treated herein. However, there has in recent years been a number of publications directed at the stabilization of carboxylic acid anhydrides.
One major carboxylic acid anhydride of particular importance in industry is maleic acid anhydride. This material has found widespread use as a raw material for chemical products useful in a variety of industries, including the manufacture of finished fiberglass products, as a graft copolymer with polyisobutylene for use in forming polyisobutylene-succinic anhydride (“PIBSA”) based motor oil and spark-ignition fuel dispersants, and as a comonomer for the manufacture of various multi-functional or highly-engineered copolymers to name but a few.
Maleic acid anhydride may be manufactured starting from a wide variety of raw materials, using processes which have been known for decades. Typically, this material is derived from the catalytic oxidation of a hydrocarbon involving the passing of a gaseous hydrocarbon over a suitable catalyst material in the presence of oxygen. While the number of hydrocarbons from which maleic acid anhydride may be produced is large, most modem production of maleic anhydride is based upon hydrocarbon feedstocks containing four carbon atoms per molecule. The preferred catalyst systems are those which comprise mixed oxides of the elements vanadium and phosphous which are prepared by various proprietary and patented processes wherein the oxidation state of the metal is carefully controlled during catalyst preparation and subsequent annealing or other treatments. Exemplary of processes and catalysts useful in the production of maleic acid anhydride are embodied in the following U.S. Pat. Nos. 3,832,359; 4,111,963; 4,149,992; 4,276,222; 4,253,988; 4,304,723; 4,337,174; 4,359,405; 4,501,907; 4,515,973; 4,528,280; 4,562,268; 4,567,158; 4,632,915; 4,670,415; 4,560,674; 4,855,459; 5,137,860; 5,168,090; 5,185,455; 5,275,996; 5,364,824; 5,617,208; 5,631,387; 5,641,722; 5,734,066; and 5,773,382, the entire contents of which are herein incorporated by reference thereto, as well as patents cited in each as references. As produced from these processes, the maleic anhydride may contain by-products of other organic acids or anhydrides, chromogenic bodies, carbon monoxide, carbon dioxide, and water. Crude maleic anhydride prior to purification can be colored other than water white, and while it can be refined to a substantially color-free material, color generally reappears upon storage as hereinabove described. This is due in part at least to the fact that it is convenient from a manufacturer's standpoint to maintain the temperature at which maleic anhydride is stored in the range of about 60 to 70 degrees centigrade. At such an elevated temperature, many reactions, including colorant-forming reactions between organic molecules occur readily. Therefore, workers have continually sought improved color-stability improvement additive combinations or systems useful in color stabilization of organic acid anhydrides.
In addition to inhibiting reactions which otherwise cause coloration to develop in the anhydride, an additive or system must also not affect the physical properties of the acid anhydride to any extent, and must not in any way interfere with the process(es) or use employed by the end user of the anhydride as a raw material. Therefore, materials or systems which are effective at extremely low concentrations are most desirable.
U.S. Pat. No. 3,975,408 to Boyer et al. discloses and claims an improvement for stabilizing the color of dicarboxylic acids, and especially maleic anhydride, which comprises the addition of a chemical agent selected from halides of transition elements, including titanium, zirconium, cobalt, nickel, ruthenium, vanadium, chromium, manganese, mercury, silicon, phosphorous, bismuth, antimony, lead cerium; and sulfur. The level of treatment is between about 0.01 to 1,000 parts per million by weight, based on the total weight of the anhydride.
U.S. Pat. No. 3,985,776 to Samans et al. teaches the stabilization of maleic anhydride through the use of stannous compounds such as stannous chloride and stannous salts of aliphatic monocarboxylic acids. The level of treatment is between about 1 and 2,000 parts per million based on the weight of the maleic anhydride.
U.S. Pat. No. 3,998,854 to Samans et al. sets forth the use of trithiophosphites as stability additives for use in color-stabilization of maleic anhydride, particularly, the t
Huntsman Petrochemical Corporation
Oh Taylor V.
Rotman Alan L.
Whewell Christopher J.
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