Maleic anhydride benzene feed

Although benzene prices have escalated in recent years, a concurrent need for butenes for use in alkylates for motor fuel has also increased and butane prices have also escalated. As a result, a search for alternative feedstocks began and Amoco Chemical Co. commercialized a process in 1977 to produce maleic anhydride from butane. A plant in JoHet came on-stream in 1977 with a capacity of 27,000 t/yr (135,136). No new plants have been built in the United States based on butenes since the commercialization of butane to maleic anhydride technology. In Europe and particularly in Japan, however, where butane is in short supply and needs for butenes as alkylation feed are also much less, butenes may become the dominant feedstock (see Maleic anhydride). 

Similar approaches are applicable in the chemical industry. For example, maleic anhydride is manufactured by partial oxidation of benzene in a fixed catalyst bed tubular reactor. There is a potential for extremely high temperatures due to thermal runaway if feed ratios are not maintained within safe limits. Catalyst geometry, heat capacity, and partial catalyst deactivation have been used to create a self-regulatory mechanism to prevent excessive temperature (Raghaven, 1992). 

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]. 

Catalyst Benzene conversion %) T (°C), T (s), feed comp Selectivity to mucononitrile [%) Selectivity to maleic anhydride (%) Selectivity to maleonitrile [%)... 

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-... 

In normal operation, the butane feed is practically not oxidized, but is burned with the residual gases to produce steam. The operating conditions are closely similar to those used for the oxidation of benzene. BASF (Badische Amlin und Soda Fabrik) uses a fixed bed multi-tube reactor cooled by external molten salt circulation, operating between 360 and 440°C, also producing high-pressure steam. The maleic anhydride selectivity in relation to oxidizable butenes is about 50 molar per cent. 

The same authors 160) reported a process study of ra-butene oxidation to maleic anhydride using an unspecified vanadium catalyst. The catalyst was said to be different from that suitable for benzene oxidation. From the data presented, the reaction appears to be first order in hydrocarbon. A temperature of 430-470° was optimum. On the basis of this study the following conditions for oxidation of w-butenes were recommended butene concentration, 0.9-1.2% by volume temperature, 430-450° gas hourly space velocity, 4000. These conditions give a conversion of butenes of about 80%, a selectivity of 52%, and a yield C X 81100 of 41.6%. This relatively high yield, compared to that reported by others, may in part result from inclusion of about 8% butadiene in the feed. However, Societe d Electrochemie 160a) report C X SjlOO — 49% with butenes over a V-1.2 P catalyst at 470°. 

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). ... 

Given that the available feed stream contains benzene at a concentration of 10 mol/m with a volumetric flow rate, Vq, of 0.0025 mVs (the feed is largely air), a network of isothermal reactors is proposed to maximize the yield of maleic anhydride. 

The process resembles the oxidation of benzene, but the concentration of maleic anhydride in the reaction product is lower. The reaction rate is also lower than for oxidation of benzene, so that a larger reactor (by a factor of 1.2) and bigger compressor with correspondingly higher investment are needed. Some MA plants have recently been revamped for both feedstocks (dual-feed). A disadvantage of butane oxidation is the low yield, which is around 50 to 55 mol %. 

Attempts to use cheaper feed stocks led to the development of new processes. For example, the drive to replace olefins as reactants by parafSns led to the development of processes in which ethane rather ethylene is used to produce vinyl chloride, propane rather than propylene to produce acrylonitrile, and butane rather than benzene to produce maleic anhydride. The drive to produce more-economical synthesis gas from methane has motivated various novel process developments. Moreover, enviromnental regulations and needs caused modifications of many processes in order to minimize the production of pollutants. Most reactors are designed to handle a relatively narrow range of feed concentrations and space velocities. A different design approach has to be used if reactors are to destroy pollutants, as they have to operate at high conversion over a very wide range of feed compositions and feed rates. 

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. 

The first commercial production unit was built by the National Aniline and Chemical Company, part of the Barrett Company, in 1933. However, most of the maleic anhydride used at that time was supphed from phthalic anhydride plants, which produced about 5-10% as a by-product. Demand for maleic anhydride was still low during the 1940s. At that time two typical catalysts were available. One contained 12% vanadium pentoxide/4% molybdenum trioxide supported on a-alumina, while the other contained 10% vanadium pentoxide moderated with less than 1% of lithimn sulfate/sodium sulfate, also supported on a-alumina. The alkali sulfate moderated catalyst was, however, sensitive to sulfur poisons in the benzene feed. 

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