Maleic Anhydride A Statistical
Review
JOHN R. 8ΚΙ·:Ι·Λ T h e properties of m a l e i c a n h y d r i d e m a k e it valuable a s a r e s i n f o r m e r and a s a s p e c i a l t y c h e m i c a l for m a n y o t h e r u s e s 1 H E commercial production of maleic anhydride began only 15 years ago al though its synthesis from benzene was dis covered earlic'% almost simultaneously with the introduction of the Gibbs-Conover process for converting naphthalene into phthalic anhydride. As a result of the late beginning and a relatively unfa vorable price differential, production of maleic anhydride has never exceeded 9 % of the output of phthalic anhydride in any year. Nevertheless, the valuable properties ot maleic anhydride have given it an assured position as a resin former, particularly for coatings, and a s a specialty chemical for many other uses. Esters of maleic are similar to the vinyl esters. In addition, upon its successful production depended the commercial existence of such closely related acids a s fumarie, succinic, and malic, certain antiseptics, and wetting agents of the sulfo-succinic type. In war years the demand for maleic anhydride frequently exceeded the amount available by nearly 50%. Relatively few uses were supplied in full and these in cluded oil demulsiflcation, toluene puri fication, rubber, and certain of t h e mixed resins. The demand was further increased when the supply- of tung oil from the East was cut off. T h e use of maleic anhydride with linseed oil imparted fast drying and other valuable properties to t h e latter. While tung oil is again available, the nonyellowing characteristics of maleic anhy dride are still utilized in white enamels. In 1942 the W a r Production Board spon sored the completion of new synthetic capacity and requested greater recovery from other sources. Maximum production continued until recent months when an oversupply developed. Several in the industry regard this as a temporary condi tion and predict that over 15 million pounds annually will be required in the near future. While still uncertain, it ap pears that a capacity of approximately 20 million pounds will be available next year. Should all plans materialize, the total may be significantly greater. Maleic anhydride is obtained from sev eral sources. I t is readily prepared by passing a mixture of benzene vapor and air over a vanadium oxide catalyst at about 450° C. Last year this method ac counted for 8 0 % of the total supply. A second source is the coproduct recovery incident to the synthesis of phthalic an hydride where 5 to 8% of the products 3684
is represented by maleic anhydride. Finally, the butènes and butadiene may be oxidized in the presence of a v a n a d i u m catalyst a t t e m p e r a t u r e s up to 400° C. to give in excess of 2 5 % of t h e theoretical expectancy. This method has not yet proved to be commercially successful. The history of maleic anhydride is inseparably linked with that of phthalic anhydride. Both syntheses are distinctly American developments. Gibbs a n d Conover of the Bureau of Chemistry, Department of Agriculture, announced the phthalic anhydride m e t h o d in 1916. Three years later Weiss and Downs of the Barrett Co.'s research laboratory were granted a patent on the maleic anhydride process. Phthalic anhydride m e t with instant economic success while t h e relatively poor conversion of benzene and the difficulties of recovering the product made t h e cost of producing maleic anhydride competitively prohibitive. Then, too, the premium value in m a k i n g harder a n d more durable resin coatings, alone or in combination with o t h e r materials, was not recognized until the early 1930's. The first production of maleic anhydride on an industrial scale began in 1933 when National Aniline a n d Chemical Co., Inc., installed the benzene process. T h e effluent gases were a t first condensed in a
T a b l e I.
high boiling solvent, but this proved to br both hazardous and expensive. After a few years t h e water process was installed and this procedure with m a n y refinements is employed today. American Cyanamid Co. began recovery from phthalic anhydride operations in 1934 and was soon followed by M o n s a n t o Chemical Co. While Monsanto recovered t h e anhydride, per se, for the most part, Cyanamid produced the acid mainly for consumption as such. In 1940, the Carbide and Carbon Chemicals Corp. produced maleic from the unsaturated h y d r o c a r b o n gases bui subsequently discontinued. Nearly three years ago, Reichhold Chemicals, Inc., installed the benzene process. L a s t year the Koppers Co. began coproduct recovery while Carbide once again began operations employing t h e u n s a t u r a t e s as the raw material. Of the three methods n o w in operation, the benzene process a c c o u n t s for more than two thirds of the m a l e i c a n h y d r i d e produced. Table II. Malcio Anhydride: App r o x i m a t e D i s t r i b u t i o n in 1947 Unit: 1.000 lb. 8,750 Synthetic Rosins Alkvd" 7,250 Other?> 1.500 350 Chemicals'" Other1.090 Abrasives 30 Leather (tannine;) 150 Petroleum'^ 100 Sizing (paper) 00 Miscellaneous ' 750 Maleic resins, tua.leic- jhthalic mixtur ubietic-maleic resins. b Polyvinyl, phenolic, polystyrene, polyacrylic. other polyester resins. c Zinc chromate, diallyltnaleate, carbic anhydride, cliloro maleic a n h y d r i d e , fumaric acid, succinic acid.
