Maleic anhydride, manufacture

FIGURE 1 Fixed-bed process for maleic anhydride manufacture. 

Maleic Anhydride. Prior to 1975, benzene was the feedstock of choice for maleic anhydride manufacture. By the early 1980s, for economic reasons, many producers had switched to the n-butane process described in the section n-Butane Derivatives . By 1988, all of the maleic anhydride produced in the United States came from that process. However, about half of the maleic anhydride produced abroad still comes from benzene oxidation, with a small amount being recovered as a coproduct in phthalic anhydride manufacture. 

There has been some interest in random copolymers of styrene with small amounts of maleic anhydride. Manufacturers included Monsanto (Cadon), Dow (Resin XP5272) and Dainippon (Ryurex X-15). However, the only current manufacturer of high molecular weight materials appears to be Arco, which markets its products under the trade name Dylarc. The abbreviation SMA is commonly used for these materials. 

Surlyn A n. Ionomer (co-polymer firom ethylene + some acrylic acid or maleic anhydride). Manufactured by DuPont, USA. 

Potential to replace maleic anhydride, manufacture of tetrahydrofuran, polymer... 

The traditional maleic anhydride manufacturing process involves reacting benzene with excess air. A low benzene concentration is used in order not to exceed the flammability limit of the mixture. The reaction gas mixture is passed over a multitubular, fixed bed catalyst reactor at a pressure of 0.15-0.25 MPa. In addition to maleic anhydride, the reaction produces two moles of CO2 and water. The reaction is highly exothermic, causing "hotspots" of 340-500°C. For each ton of benzene that is reacted, 27MJ of heat are generated. Molten eutectic salts circulate outside the reactor tubes to dissipate the heat. Steam is generated when the molten salts are cooled, which is used to drive air compressors (see Fig. 9.31). 

FIGURE 9.31. Maleic anhydride manufacturing process based on benzene. 

CHa CHlCH CHO. Colourless lachrymatory liquid with a pungent odour. B.p. 104 "C. Manufactured by the thermal dehydration of aldol. May be oxidized to crotonic acid and reduced to crolonyl alcohol and 1-butanol oxidized by oxygen in the presence of VjOj to maleic anhydride. It is an intermediate in the production of l-butanol from ethanol. 

Colourless prisms m.p. 130 C. Manufactured by treating maleic anhydride with water. It is converted to the anhydride by heating at By prolonged heating at 150 "C or by heating with water under pressure at 200 C, it is converted to the isomeric (trans) fumaric acid. Reduced by hydrogen to succinic acid. Oxidized by alkaline solutions of potassium permanganate to mesotartaric acid. When heated with solutions of sodium hydroxide at 100 C, sodium( )-malate is formed. Used in the preparation of ( )-malic acid and in some polymer formulations. 

Butyrolactone. y-Butyrolactone [96-48-0] dihydro-2(3H)-furanone, was fkst synthesized in 1884 via internal esterification of 4-hydroxybutyric acid (146). In 1991 the principal commercial source of this material is dehydrogenation of butanediol. Manufacture by hydrogenation of maleic anhydride (147) was discontinued in the early 1980s and resumed in the late 1980s. Physical properties are Hsted in Table 4. 

Uses. Union Carbide consumes its vinyl ether production in the manufacture of glutaraldehyde [111-30-8J. BASF and GAF consume most of their production as monomers (see Vinyl polymers). In addition to the homopolymers, the copolymer of methyl vinyl ether with maleic anhydride is of particular interest. 

Chlorendic Acid. Chlorendic acid [115-28-6] and its anhydride [115-27-5] are widely used flame retardants. Chlorendic acid is synthesized by a Diels-Alder reaction of maleic anhydride and hexachlorocyclopentadiene (see CyclopentadlENE and dicyclopentadiente) in toluene followed by hydrolysis of the anhydride using aqueous base (60). The anhydride can be isolated directly from the reaction mixture or can be prepared in a very pure form by dehydration of the acid. The principal use of chlorendic anhydride and chlorendic acid has been in the manufacture of unsaturated polyester resins. Because the esterification rate of chlorendic anhydride is similar to that of phthalic anhydride, it can be used in place of phthalic anhydride in commercial polyester... 

Maleic anhydride and the two diacid isomers were first prepared in the 1830s (1) but commercial manufacture did not begin until a century later. In 1933 the National Aniline and Chemical Co., Inc., installed a process for maleic anhydride based on benzene oxidation using a vanadium oxide catalyst (2). Maleic acid was available commercially ia 1928 and fumaric acid production began in 1932 by acid-catalyzed isomerization of maleic acid. 

Maleic Anhydride. The ACGIH threshold limit value in air for maleic anhydride is 0.25 ppm and the OSHA permissible exposure level (PEL) is also 0.25 ppm (181). Maleic anhydride is a corrosive irritant to eyes, skin, and mucous membranes. Pulmonary edema (collection of fluid in the lungs) can result from airborne exposure. Skin contact should be avoided by the use of mbber gloves. Dust respirators should be used when maleic anhydride dust is present. Maleic anhydride is combustible when exposed to heat or flame and can react vigorously on contact with oxidizers. The material reacts exothermically with water or steam. Violent decompositions of maleic anhydride can be catalyzed at high temperature by strong bases (sodium hydroxide, potassium hydroxide, calcium hydroxide, alkaU metals, and amines). Precaution should be taken during the manufacture and use of maleic anhydride to minimize the presence of basic materials. 

Fumaric acid and malic acid [6915-15-7] are produced from maleic anhydride. The primary use for fumaric acid is in the manufacture of paper siting products (see Papermaking additives). Fumaric acid is also used to acidify food as is malic acid. Malic acid is a particularly desirable acidulant in certain beverage selections, specifically those sweetened with the artificial sweetener aspartame [22839-47-0]. 

Maleic Anhydride, Chemical Safety Data Sheet SD-88, Manufacturing Chemists Association, Washington, D.C., 1974. 

The manufacture of alkyd resins (qv), which are obtained by the reactions of polybasic acids or anhydrides, polyhydric alcohols, and fatty oils and acids, consumes about 17% of the phthahc anhydride demand. While materials such as maleic anhydride, isophthahc acid, and fumaric acid can also be used, phthahc anhydride is the most important. The resin provides a binder for coatings that are apphed for either protection or decoration. Ak quahty concerns have put alkyd resins under pressure from water-based coatings which do not emit organic vapors upon drying. 

Succinic anhydride [108-30-5] (3,4-dihydro-2,5-furandione butanedioic anhydride tetrahydro-2,5-dioxofuran 2,5-diketotetrahydrofuran succinyl oxide), C H O, was first obtained by dehydration of succinic acid. In the 1990s anhydride is produced by hydrogenation of maleic anhydride and the acid by hydration of the anhydride, by hydrogenation of aqueous solutions of maleic acid, or as a by-product in the manufacture of adipic acid (qv) (see Maleic ANHYDRIDE, MALEIC ACID, AND FUMARIC ACID). 

Succinic anhydride is manufactured by catalytic hydrogenation of maleic anhydride [108-31-6]. In the most widely used commercial process this reaction is performed in the Hquid phase, at temperatures of 120—180°C and at moderate pressures, in the range of 500—4000 kPa (72—580 psi). Catalysts mentioned in the patent Hterature include nickel (124), Raney nickel (125,126), palladium on different carriers (127,128), and palladium complexes (129). The hydrogenation of the double bond is exothermic Ai/ = —133.89 kJ/mol (—32 kcal/mol) (130). 

Oxidation. Benzene can be oxidized to a number of different products. Strong oxidizing agents such as permanganate or dichromate oxidize benzene to carbon dioxide and water under rigorous conditions. Benzene can be selectively oxidized in the vapor phase to maleic anhydride. The reaction occurs in the presence of air with a promoted vanadium pentoxide catalyst (11). Prior to 1986, this process provided most of the world s maleic anhydride [108-31 -6] C4H2O2. Currendy maleic anhydride is manufactured from the air oxidation of / -butane also employing a vanadium pentoxide catalyst. 

Polyesters. Unsaturated polyester resins based on DCPD, maleic anhydride, and glycols have been manufactured for many years. At least four ways of incorporating DCPD into these resins have been described (45). The resins are mixed with a cross-linking compound, usually styrene, and final polymerization is accompHshed via a free-radical initiator such as methyl ethyl ketone peroxide. 

Manufacturing. Almost all the THE in the United States is currendy produced by the acid-catalyzed dehydration of 1,4-butanediol [10-63-4]. Only one plant in the United States still makes THE by the hydrogenation of furfural (29). Du Pont recendy claimed a new low cost process for producing THE from / -butane that they plan to commercialize in 1995 (30—32). The new process transport-bed oxidizes / -butane to cmde maleic anhydride, then follows with a hydrogen reduction of aqueous maleic acid to THE (30). 

Fumaric acid may be prepared by heating maleic acid, with or without catalysts. It is also obtained as by-product in the manufacture of phthalic anhydride from naphthalene. The acid is a solid melting at 284°C. Fumaric acid is sometimes preferred to maleic anhydride as it is less corrosive, it tends to give lighter coloured products and the resins have slightly greater heat resistance. 

The major aromatics (organics having at least one ring structure with six carbon atoms) manufactured include benzene, toluene, xylene, and naphthalene. Other aromatics manufactured include phenol, chlorobenzene, styrene, phthalic and maleic anhydride, nitrobenzene, and aniline. Benzene is generally recovered from cracker streams at petrochemical plants and is used for the manufacture of phenol, styrene, aniline, nitrobenzene, sulfonated detergents, pesticides such as hexachlorobenzene, cyclohexane (an important intermediate in synthetic fiber manufacture), and caprolactam, used in the manufacture of nylon. Benzene is also used as a general purpose solvent. 

---