Maleic anhydride operation

Survey of the patent Hterature reveals companies with processes for 1,4-butanediol from maleic anhydride include BASF (94), British Petroleum (95,96), Davy McKee (93,97), Hoechst (98), Huels (99), and Tonen (100,101). Processes for the production of y-butyrolactone have been described for operation in both the gas (102—104) and Hquid (105—108) phases. In the gas phase, direct hydrogenation of maleic anhydride in hydrogen at 245°C and 1.03 MPa gives an 88% yield of y-butyrolactone (104). Du Pont has developed a process for the production of tetrahydrofuran back-integrated to a butane feedstock (109). Slurry reactor catalysts containing palladium and rhenium are used to hydrogenate aqueous maleic acid to tetrahydrofuran (110,111). 

The bulk stmcture of the catalyticaHy active phase is not completely known and is under debate in the Hterature (125,131—133). The central point of controversy is whether (Valone or in combination with other phases is the most catalyticaHy active for the conversion of butane to maleic anhydride. The heart of this issue concerns the role of stmctural disorder in the bulk and how it arises in the catalyst (125,134,135). Most researchers agree that the catalysts with the highest activity and selectivity ate composed mainly of (Vthat exhibits a clustered or distorted platelet morphology (125). It is also generaHy acknowledged that during operation of the catalyst, the bulk oxidation state of the vanadium in the catalyst remains very close to the +4 valence state (125). 

Air is compressed to modest pressures, typically 100 to 200 kPa ( 15-30 psig) with either a centrifugal or radial compressor, and mixed with superheated vaporized butane. Static mixers are normally employed to ensure good mixing. Butane concentrations are often limited to less than 1.7 mol 1 to stay below the lower flammable limit of butane (144). Operation of the reactor at butane concentrations below the flammable limit does not eliminate the requirement for combustion venting, and consequendy most processes use mpture disks on both the inlet and exit reactor heads. A dow diagram of the Huntsman fixed-bed maleic anhydride process is shown in Figure 1. 

Like propane, n-hutane is mainly obtained from natural gas liquids. It is also a hy-product from different refinery operations. Currently, the major use of n-hutane is to control the vapor pressure of product gasoline. Due to new regulations restricting the vapor pressure of gasolines, this use is expected to he substantially reduced. Surplus n-butane could be isomerized to isobutane, which is currently in high demand for producing isobutene. Isobutene is a precursor for methyl and ethyl tertiary butyl ethers, which are important octane number boosters. Another alternative outlet for surplus n-butane is its oxidation to maleic anhydride. Almost all new maleic anhydride processes are based on butane oxidation. 

Luche and coworkers [34] investigated the mechanistic aspects of Diels-Alder reactions of anthracene with either 1,4-benzoquinone or maleic anhydride. The cycloaddition of anthracene with maleic anhydride in DCM is slow under US irradiation in the presence or absence of 5% tris (p-bromophenyl) aminium hexachloroantimonate (the classical Bauld monoelectronic oxidant, TBPA), whereas the Diels Alder reaction of 1,4-benzoquinone with anthracene in DCM under US irradiation at 80 °C is slow in the absence of 5 % TBPA but proceeds very quickly and with high yield at 25 °C in the presence of TBPA. This last cycloaddition is also strongly accelerated when carried out under stirring solely at 0°C with 1% FeCh. The US-promoted Diels Alder reaction in the presence of TBPA has been justified by hypothesizing a mechanism via radical-cation of diene, which is operative if the electronic affinity of dienophile is not too weak. 

The effluent gas from the reactor contains about 50% maleic acid (not maleic anhydride). The balance is some. unreacted feed, CO2, water, and some miscellaneous waste products. A recycle stream is passed through a cooler and recharged to the reactor. The purpose is not only to take another pass at the feed but also to dilute the feed with some already-made maleic acid. That helps to disperse the heat of reaction and to control the operating conditions. 

The gas-phase selective oxidation of o-xylene to phthalic anhydride is performed industrially over vanadia-titania-based catalysts ("7-5). The process operates in the temperature range 620-670 K with 60-70 g/Nm of xylene in air and 0.15 to 0.6 sec. contact times. It allows near 80 % yield in phthalic anhydride. The main by-products are maleic anhydride, that is recovered with yields near 4 %, and carbon oxides. Minor by-products are o-tolualdehyde, o-toluic acid, phthalide, benzoic acid, toluene, benzene, citraconic anhydride. The kinetics and the mechanism of this reaction have been theobjectof a number of studies ( 2-7). Reaction schemes have been proposed for the selective pathways, but much less is known about by-product formation. 

The enzyme acts stereoselectively to produce only the required L-isomer (Figure 4.10). Originally a fermentation process for the production of L-aspartic acid was established. This was modified into an immobilised enzyme process, but since the extracted enzyme is not very stable, an efficient continuous process was not possible. Therefore an immobilised cell system was developed with a very long operational lifetime. Another raw material for L-aspartic acid is maleic anhydride, which is first converted... 

Alternatively, the enzyme can be modified such that it dissolves in a hydrophobic ionic liquid with retention of activity. This approach was demonstrated with cyt c, which, when covalently modified with polyethylene glycol (PEG), dissolved in [EMIm][ Tf2N] with retention of activity. The best results were obtained when the molecular weight of the polymer chain was >2000 [88]. Similarly, a copolymer of PEG and maleic anhydride solubilized subtilisin in [EMIm][NTf2] and a range of similar ionic liquids with good retention of activity and operational stability [89, 90]. 

Reaction between fluorine and maleic anhydride in a mixture of chloroform and fluorotrichloromethane with sodium fluoride gave a significant amount of chlorinated products indicating that radical processes were operating. Even at -25 °C, significant reaction took place by a radical mechanism and at about 0 °C this was the main process [183]. 

Other chemicals present in the resins operation or in other operations on site in the resin company evaluated in the epidemiological study by Blair et al. (1998) include butadiene, styrene, formaldehyde, melamine, maleic anhydride, phosphoric acid and phenol (Zey et al., 1990b). 

MA/EA/VA) (polymer is approx. 80% hydrolyzed maleic anhydride, 10% ethyl acrylate, 10% vinyl acrylate) has been available for many years and exhibits properties similar to those of PMA. It cannot operate at the same extremes of service, but is of lower cost and competes well with other technologies. It has better general dispersion properties than many polyacrylates and is less sensitive to soluble iron. It can often replace polyacrylates as a phosphonate activity enhancer. 

Conversion of maleic acid into maleic anhydride. CAUTION All operations must be conducted in an efficient fume cupboard, owing to the highly toxic nature of the solvent. Mix 100 g of maleic acid with 1,1,2,2-tetrachloroethane (100 ml) in a distillation flask fitted with a Claisen still-head, a thermometer and a condenser set for downward distillation. Heat the mixture on an air bath when the temperature reaches 150°C, 75 ml of 1,1,2,2-tetrachloroethane and between 15 and 15.5 ml of water are present in the receiver. Continue the distillation using an air condenser and change the receiver flask when the temperature reaches 190°C. Collect the maleic anhydride at 195-197°C. Recrystallise the crude anhydride from chloroform. The yield of pure maleic anhydride, m.p. 54 °C, is 70 g (83%). 

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]. 

In addition to the requirements with respect to size, shape, and mechanical stability, the nature of the active phase also has to be adopted when the same catalyst is applied in different reactor concepts mainly due to differing process conditions. Vanadium phosphorous oxide composed of the vanadyl pyrophosphate phase (VO)2P207 is an excellent catalyst for selective oxidation of H-butane to maleic anhydride [44-47]. This type of catalyst has been operated in, for example, fixed-bed reactors and fluidized-bed-riser reactors [48]. In the different reactor types, different feedstock is applied, the feed being more rich in //-butane (i.e. more reducible) in the riser-reactor technology, which requires different catalyst characteristics [49]. 

Similar results have been noted in terpolymerizations involving the p-dioxene-maleic anhydride (49, 51, 52) and vinyl ether-maleic anhydride (45, 49) and vinyl ether-fumaronitrile (49) monomer pairs. Iwatsuki and Yamashita (46) concluded that the molecular complex formed between p-dioxene and maleic anhydride is attacked on the p-dioxene side by a radical to yield the maleic anhydride radical which is considered to be the main growing radical. Thus, a monoradical propagation step is considered operative. 

Recently, attention has been shifted to the oxidative functionalisation of saturated molecules. Reactions such as from ethane —> vinylchloride, propylene — methacrylic acid, or butane -> maleic anhydride, became a target of many research efforts. A catalyst which appeared to be very versatile in such reactions is vanadyl pyrophosphate, (VO)2P20y. The mechanism of oxidative functionalisation is not yet known in all details, but there are many indications that it is in some crucial steps different from the mechanism operating with olefins (see also Chapter 5). 

Description N-butane and air are fed to a fluid-bed catalytic reactor (1) to produce maleic anhydride. The fluid-bed reactor eliminates hot spots and permits operation at close to the stoichiometric reaction mixture. This results in a greatly reduced air rate relative to fixed-bed processes and translates into savings in investment and compressor power, and large increases in steam generation. The fluid-bed system permits online catalyst addition/removal to adjust catalyst activity and reduces downtime for catalyst change out. 

The recovery area uses a patented organic solvent to remove the maleic anhydride from the reactor effluent gas. Aconventional absorption (2)/stripping (3) scheme operates on a continuous basis. Crude maleic anhydride is distilled to separate light (4) and heavy (5) impurities. A slipstream of recycle solvent is treated to eliminate any heavy byproducts that may be formed. The continuous nonaqueous product recovery system results in superior product quality and large savings in steam consumption. It also reduces investment, product degradation loss (and byproduct formation) and wastewater. 

Application Tb produce maleic anhydride from butane using a flu-idized-bed reactor. The reactor is operated at lower butane per-pass conversion to maximize selectivity, and recover and recycle unreacted butane to achieve a higher total process yield. 

Description N-butane and air are normally fed to a fluidized-bed reactor in the presence of a catalyst to produce maleic anhydride. In this process option, the reactor (1) is operated at a lower butane conversion by either reducing the reaction temperature or by increas-... 

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