Maleic anhydride from benzene production

Process Technology Evolution. Maleic anhydride was first commercially produced in the early 1930s by the vapor-phase oxidation of benzene [71-43-2]. The use of benzene as a feedstock for the production of maleic anhydride was dominant in the world market well into the 1980s. Several processes have been used for the production of maleic anhydride from benzene with the most common one from Scientific Design. Small amounts of maleic acid are produced as a by-product in production of phthaHc anhydride [85-44-9]. This can be converted to either maleic anhydride or fumaric acid. Benzene, although easily oxidized to maleic anhydride with high selectivity, is an inherently inefficient feedstock since two excess carbon atoms are present in the raw material. Various compounds have been evaluated as raw material substitutes for benzene in production of maleic anhydride. Fixed- and fluid-bed processes for production of maleic anhydride from the butenes present in mixed streams have been practiced commercially. None of these... 

Supported vanadla used to promote the selective oxidation of hydrocarbons. Is another example. Vanadia with or without promoters, may be supported on silica (naphthalene oxidation [38]), on tltanla o-xylene oxidation [39]) or on a-alumlna (benzene oxidation [ AO]). It was believed that supports should have open porosity (and associated lower surface area) in order to minimise over oxidation to carbon oxides. However, it was shown that reasonably high activities and selectivitles could be obtained over vanadla supported on high surface area material and it was suggested that low selectivity was, in fact, primarily associated with high acidity on the support [AI]. In agreement with this, vanadla supported on 7-alumina shoved zero selectivity for the production of maleic anhydride from benzene If this Is the case, then a high surface area support with minimal acidity would be desired,... 

Maleic Anhydride. The preparation of maleic anhydride from C4 hydrocarbons is given by Bretton (10). The preparation of maleic anhydride from benzene is described in Faith, Keyes, and Clark (31). Maleic anhydride is an important by-product in the phthalic anhydride process. 

Economic data concerning the production of maleic anhydride from benzene, n-butane and olefinic C4 cuts are given in Table 13.4. 

Catalysts which can selectively activate the normally un-reactive paraffins have been developed in recent years. The production of maleic anhydride from butane over vanadium-phosphorous-oxide catalysts has received much attention (Eqn. 5), and is beginning to replace the more wasteful production of maleic anhydride from benzene (Eqn. 6) which is still the major feedstock. Maleic anhydride production from butene or butadiene is also possible (Eqn. 7), but cannot compete with the cheaper butane feed. Maleic anhydride is mainly used in the manufacture of unsaturated polyester resins, fumaric acid manufacture, insecticides, and fungicides (Figure 5). ... 

Maleic anhydride (MA) is an important raw material in the production of alkyd and polyester resins. It was first obtained by Nikolas Louis Vauquelin in 1817, by heating maleic acid to over 140 °C. In 1905, Richard Kempf obtained maleic acid by the oxidation of benzoquinone. The first patents covering the production of maleic anhydride from benzene originate from John M. Weiss and Charles R. Downs in 1918. The oxidation of benzene remains a feasible route to maleic anhydride even today, although since around 1975, n-butane and n-butylene have increasingly replaced benzene as raw materials. n-Butane and n-butylene are available as co-products in steam cracking of naphtha and from natural gas condensates. 

The V-Mo-O oxides are well-known industrial catalysts for the synthesis of acrylic acid from acrolein and maleic anhydride from benzene more recently, V-P-0 systems are being utilized for maleic anhydride production from -butane. The V20s/Ti02 combination was employed for phthalic acid production from o-xylene. V-Fe-O catalyzes oxidation of polycyclic aromatic hydrocarbons to dicarboxylic acids and quinones. Methyl formate is produced by the oxidation of methanol over V-Ti-0 catalysts [58]. For many of these processes, it has been experimentally proved that the catalytic reaction follows a Mars-van Krevelen mechanism. The surface coverage with active oxygen 0 in the steady state of the redox reaction following Mars-van Krevelen mechanism is given by... 

B.5 Production of Maleic Anhydride from Benzene. Unit 600 B.6 Ethylene Oxide Production. Unit 700... 

Table II. Relationship of the Ratio of Areas under a Styrene Peak to the Reference Peak in the Gas Chromatograms of the Pyrolytic Products Obtained from Copolymers of Styrene and Maleic Anhydride in Benzene...

Series reactions also occur in oxidation processes where the required product may oxidize further. An example is the production of maleic anhydride from the oxidation of benzene. In this case, the maleic anhydride can be oxidized further to carbon dioxide and water. Another example of a series reaction occurs in the biochemical reaction in which Pseudomonas ovalis is used to convert glucose to gluconic acid via gluconolactone in batch culture. This first order reaction is represented by... 

Bergman and Frisch [7] disclosed in 1966 that selective oxidation of n-butane was catalyzed by the VPO catalysts, and since 1974 n-butane has been increasingly used instead of benzene as the raw material for maleic anhydride production due to lower price, high availability in many regions and low environmental impact [8]. At present more than 70 % of maleic anhydride is produced from n-butane [6]. However, productivity from n-butane is lower than in the case of benzene due to lower selectivities to maleic anhydride at higher conversions and somewhat lower feed concentrations (< 2 mol. %) used to avoid flammability of a process stream. Under typical industrial conditions (2 mol. % n-butane in air, 673-723K, and space velocities of 1100-2600 h ) the selectivities [9] for fixed-bed production of maleic anhydride from n-butane are 67-75 mol. % at 70-85 % n-butane conversion [10]. Another unique feature of the VPO catalysts is that no support is used in partial oxidation of n-butane.Many studies of n-butane oxidation on the VPO catalysts indicated that crystalline vanadyl(IV) pyrophos-... 

Maleic anhydride reacts with alkylbenzenes in the presence of free radicals to form adducts of Type I and with benzene, chlorobenzene, and alkylbenzenes under photochemical excitation to form adducts of Type II. In this study solutions of maleic anhydride in benzene, toluene, ethylbenzene, and cumene were exposed to high frequency (3.6 and 8.0 kc./ sec.) electric discharge in an atmosphere of N2 or He. Adducts of Type II were isolated in yields ranging from 8 to 23% of the converted maleic anhjydride. The balance was made up of adducts of Type I together with products of higher condensation with maleic anhydride. The product distribution suggests that most of the active species in the present system are excited molecules and not free radicals. 

The reactor effluent, Stream 7—containing small amounts of unreacted benzene, maleic anhydride, quinone, and combustion products—is cooled in E-603 and then sent to an absorber column, T-601, which has both a reboiler and condenser. In T-601, the vapor feed is contacted with recycled heavy organic solvent (dibutyl phthalate). Stream 9. This solvent absorbs the maleic anhydride, quinone, and small amounts of water. Any water in the solvent leaving the bottom of the absorber, T-601, reacts with the maleic anhydride to form maleic acid, which must be removed and purified from the maleic anhydride. The bottoms product from the absorber is sent to a separation tower, T-602, where the dibutyl phthalate is recovered as the bottoms product. Stream 14, and recycled back to the absorber. A small amount of fresh solvent. Stream 10, is added to account for losses. The overhead product from T-602, Stream 13, is sent to the maleic acid column, T-603, where 95 mol% maleic acid is removed as the bottoms product. 

Multicomponent (P04)jf(V205), catalysts are applied in processes to produce maleic anhydride and phthalic anhydride intermediates for polymers. In the classical industrial process, maleic anhydride is the product from benzene and phthalic anhydride the product from naphthalene. Vanadium oxide-based catalysts have a stronger interaction with their substrates than molybdenum oxide-based catalysts. Whereas on M0O3 catalysts the hydrocarbon skeleton remains intact, oxidation on vanadium oxides proceeds with rupture of carbon-carbon bonds and the total number of carbon atoms in the molecule is not maintained in the reaction products. A new development is the use of butane as a reactant in these processes. 

Capacities of maleic anhydride faciUties worldwide are presented in Table 7. The switch of feedstock from benzene to butane was completed in the United States in 1985, being driven by the lower unit cost and lower usage of butane in addition to the environmental pressures on the use of benzene. Worldwide, the switch to butane is continuing with 58% of the total world maleic anhydride capacity based on butane feedstock in 1992. This capacity percentage for butane has increased from only 6% in 1978. In 1992, 38% of the total world maleic anhydride capacity was based on benzene feedstock and 4% was derived from other sources, primarily phthaUc anhydride by-product streams. 

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. 

The equilibrium between oxepin and benzene oxide created interest in performing Diels-Alder reactions trapping one or both isomeric structures.1 The reaction of maleic anhydride or maleic imide with oxepin and substituted derivatives gives products 1 derived from the addition of the dienophile to the benzene oxide structure.2-l4-126 14 9 156 158 228 231-259... 

Isopropenylbenzofuran (124, Scheme 30) affords good yields of the adducts 123 and 125 on separate reaction with maleic anhydride and tetracyanoethylene. With but-3-en-2-one, 2-isopropenylbenzofuran (124, Scheme 31) affords the adducts 126 and 127 in a combined yield of 29%. When the crude product was dehydrogenated with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone in boiling benzene, the aromatized product 128 (6%) was obtained. It was accompanied by the dicyanodibenzofuran 129, which was found to arise from the excess diene present in the reaction mixture. A speculative mechanism is shown. 

The apparatus shown in Fig. 3, consisting of a 2-1. three-neckcd round-bottomed flask fitted with an efficient stirrer (Note 1), a gas inlet tube, a thermometer, and a reflux condenser is assembled in a ventilated hood. Bubbler tubes containing benzene are attached to the gas inlet tube and the top of the reflux condenser, and 500 ml. of dry benzene and 196 g. (2 moles) of maleic anhydride (Note 2) are placed in the flask. Stirring is begun, the flask is heated with a pan of hot water, and butadiene is introduced (from a commercial cylinder controlled by a needle valve) at a rapid rate (0.6-0.8 1. per minute). When the temperature of the solution has reached 50° (within 3-5 minutes) the pan of water is removed. The exothermic reaction causes the temperature to reach 70-75° in 15-25 minutes. The rapid stream of butadiene is nearly completely absorbed for 30-40 minutes, after which the rate is decreased until the reaction is completed (equal rates of bubbling in the two bubbler tubes) after 2-2.5 hours. The solution is poured into a 1-1. beaker at once to avoid crystallization of the product in the reaction flask. The beaker is covered and the mixture is kept at 0 5° overnight. 

The oxidation of benzene to maleic anhydride is generally described by the simplified reaction scheme (Scheme 1, p. 198). Complete oxidation products (CO, C02) are mainly formed from benzene and not by combustion of maleic anhydride itself. Therefore, the parallel character of the reaction scheme predominates, which implies that a high initial selectivity enables high yields to be obtained. 

A V2Os—K2S04 catalyst was used in a kinetic study by Jaswal et al. [165] with a differential flow reactor at 350—400° C and varying benzene/ oxygen ratio. The overall benzene oxidation rate was adequately described by a simple redox model. Kinetic parameters are given in Table 29. The initial selectivity is not reported by the authors, but a value of 50—60% can be derived from the stoichiometric number n, assuming C02 and maleic anhydride as the main products. 

Process Technology Evolution, Growth in the worldwide maleic anhydride industry is exclusively in the buianc-lo-inaleic anhydride route, often at the expense of benzene-based production. Table 2 shows I 995 and estimated 1996. 1997. and 2000 worldwide maleic production capacity broken down in categories of benzene, butane and phlhalie anhydride coproduct. As can be seen from this table butane routes are expected to grow at the expense of benzene-based processes. 

The formation of block copolymers from styrene-maleic anhydride and acrylic monomers was also indicated by pyrolytic gas chromatography and infrared spectroscopy. A comparison of the pyrograms of the block copolymers in Figure 7 shows peaks comparable with those obtained when mixtures of the acrylate polymers and poly(styrene-co-maleic anhydride) were pyrolyzed. A characteristic infrared spectrum was observed for the product obtained when macroradicals were added to a solution of methyl methacrylate in benzene. The characteristic bands for methyl methacrylate (MM) are noted on this spectogram in Figure 8. 

Ortho photocycloaddition was first reported in a U.S. patent [1] dated September 3, 1957. Irradiation of benzonitrile in the presence of various alkenes resulted in the formation of derivatives of l-cyanobicyclo[4.2.0]octa-2,4-diene. The first ortho photocycloaddition to benzene was reported in 1959 by Angus and Bryce-Smith [2], who discovered that benzene and maleic anhydride react to form a stable adduct at 60°C under the influence of ultraviolet radiation. This 1 2 adduct was formed from one molecule of benzene and two molecules of maleic anhydride. Two years later, Bryce-Smith and Lodge [3] found that acetylenes could also be photoadded to benzene. The isolated products were cyclooctatetraenes, formed by ring opening of the primarily formed bicyclo[4.2.0]octa-2,4,7-trienes. Since those early years, hundreds of examples of ortho photocycloadditions of alkenes to the benzene ring and many mechanistic investigations have been reported and they will be discussed in this chapter. 

The Diels-Alder reaction with /V-phenylmaleimidc has frequently been used for the separation, purification, and structure determination of ortho photocycloadducts [12,47,86,90,108,116,126,132,133,138], Other dienophiles that have been successfully employed in Diels-Alder reactions with ortho adducts are A-(para-bromophenyl)maleimide [116,120], maleimide [116,118,127], maleic anhydride [127,191], tetracyanoethylene [11], and dimethyl acetylenedicarboxy-late [73,127], The Diels-Alder product of A-(para-bromophenyl)maleimide with the exo-ortho adduct formed from 1,4-dioxene and benzene [120] and the Diels-Alder product of maleimide with the endo-ortho adduct from cis-cy-clooctene and benzene [118] were obtained in crystalline form and their structures could be determined by means of x-ray diffraction. 

The oxidation of butane (or butylene or mixtures thereof) to maleic anhydride is a successful example of the replacement of a feedstock (in this case benzene) by a more economical one (Table 1, entry 5). Process conditions are similar to the conventional process starting from aromatics or butylene. Catalysts are based on vanadium and phosphorus oxides [11]. The reaction can be performed in multitubular fixed bed or in fluidized bed reactors. To achieve high selectivity the conversion is limited to <20 % in the fixed bed reactor and the concentration of C4 is limited to values below the explosion limit of approx. 2 mol% in the feed of fixed bed reactors. The fluidized-bed reactor can be operated above the explosion limits but the selectivity is lower than for a fixed bed process. The synthesis of maleic anhydride is also an example of the intensive process development that has occurred in recent decades. In the 1990s DuPont developed and introduced a so called cataloreactant concept on a technical scale. In this process hydrocarbons are oxidized by a catalyst in a high oxidation state and the catalyst is reduced in this first reaction step. In a second reaction step the catalyst is reoxidized separately. DuPont s circulating reactor-regenerator principle thus limits total oxidation of feed and products by the absence of gas phase oxygen in the reaction step of hydrocarbon oxidation [12]. 

A higher atom and mass efficiency is desirable when comparing alternative reaction choices. A clear example of this is the production of maleic anhydride (MA) starting from either benzene or n-butane.72 Benzene or w-butane is partially oxidized in the vapor phase in the presence of air and a solid catalyst at high temperature and pressure. 

EPA 1989d. National Emission Standards for Hazardous Air Pollutants Benzene Emissions from Maleic Anhydride Plants, Ethylbenzene/Styrene Plants, Benzene Storage Vessels, Benzene Equipment Leaks, and Coke By-Products Recovery Plants. U.S. Environmental Protection Agency. 54 FR 38044. 

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