Maleic anhydride operating conditions

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 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]. 

The introduction of rhodium has allowed the development of processes which operate under much milder conditions and lower pressures, are highly selective, and avoid loss of alkene by hydrogenation. Although the catalyst is active at moderate temperature, plants are usually operated at 120°C to give a high n/iso (linear/ branched) ratio. The key to selectivity is the use of triphenylphosphine in large excess which leads to >95% straight chain anti-Markovnikov product. The process is used for the hydroformylation of propene to n-butyraldehyde, allyl alcohol to butanediol, and maleic anhydride to 1,4-butanediol, tetrahydrofuran, and y-butyrolactone. 

The results of the thermal simulation were sufficiently encouraging for us to proceed to the reactor simulation for a number of steady-state operating conditions, but neglecting the maleic anhydride degradation in the fluidized bed. Both the simplified kinetic expression (equation (4)) and the more exact equation (3) were used and the results are shown in Table I as Case 1 and Case 2 respectively. 

The results for a Py-GC/MS analysis of a sample of poly(ethylene-a/f-maleic anhydride) CAS 9006-26-2, with = 100,000-500,000 are shown in Figure 6.9.4. The pyrolysis was done at 600° C in He at a heating rate of 10° C/ms, TAT = 10 s, and the separation was done on a Carbowax column in identical conditions as for other examples previously discussed (see Table 4.2.2). The MS was operated in EI+ mode. The peak identification for the chromatogram shown in Figure 6.9.4 was done using MS spectral library searches only and is given in Table 6.9.3. 

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. 

Ortho-xylene may be oxidized directly by air in vapor phase over vanadium pentoxide catalysts under conditions resembling those used in oxidation of naphthalene to phthalic anhydride. The stability of the cyclic anhydride structure of phthalic anhydride at the temperatures required and in the presence of oxidizing conditions is, of course, the distinctive feature. Since the oxidation of o-xylene to phthalic anhydride requires the theoretical interaction of only six atoms of oxygen relative to the nine required by naphthalene, the amount of heat generated per unit of product is less, and the volume of diluent gases in the product stream may be lower. Because of decreased formation of quinones and color bodies, product purification should be easier. Very little is available by way of information relative to commercial operating conditions. Some laboratory results of early work showed a maximum conversion to total acids of 18.2 per cent when commercial xylene was oxidized in vapor phase over unfused vanadium oxide catalyst. Recent work with o-xylene showed a conversion of 42.7 per cent to phthalic anhydride over unfused vanadium oxide catalyst and conversions up to 61.7 per cent to phthalic anhydride plus fi.6 per cent to maleic... 

A new process to manufacture THF and 1,4 butanediol from maleic anhydride is currently slated for start-up by DuPont in Asturias, Spain in 1996. The process involves the oxidation of n-butane in a transport bed reactor to form maleic anhydride. Recovery of maleic anhydride is accomplished by scrubbing with water which converts the anhydride immediately to maleic acid. The maleic acid is then hydrogenated to tetrahydrofuran in a bubble column reactor. By varying operating conditions in the hydrogenation reactor the alternate or coproduction of 1,4 butanediol can be accomplished. 

The maleic anhydride catalyst is vanadium pentoxide spray coated with porous silica to impart attrition resistance. The catalyst needs to be specially treated for attrition resistance for use in the transport bed reactor. Reactor operating conditions are approximately 500°C (930 F) and 1 atm pressure. 

There is an evident positive linear correlation between both temperature and -butane/oxygen feed concentrations and the production rate of maleic anhydride. The data contains what could be considered outliers, which are not necessarily due to blunders but may be a result of non-standard operating conditions (shut down, start-up, or stand-by) or defects in the analytical system or instrumentation. Although there appears to be an interaction between the n-butane and oxygen concentrations, the two are in fact directly related by stoichiometry ... 

Bulk catalysts comprise mainly active substances, but some binder is often added to aid the forming/shaping operation. This is the case for iron oxide for the water-gas shift (WGS) reaction, iron molybdate for the oxidation of methanol to formaldehyde, and vanadyl pyrophosphate for butane oxidation to maleic anhydride. However, in some cases, bulk catalysts are used as prepared, without the need for addition of the binder. Typically, this involves catalysts prepared by high temperature fusion (eg, the iron-based ammonia synthesis catalyst). The need for the addition of binder, or the requirement for pelleting, solely depends on the strength required for the catalyst under the reaction conditions and the reactor type that is used in. This requires consideration of attrition resistance, and oxide... 

Functionalization of EPDM by grafting with maleic anhydride in a twin screw extruder is possible in a controlled way. Within normal operating limits of the extruder good grafting efficiency could be achieved with Perkadox 14 as initiator. It is shown that at constant process conditions the grafting efficiency is determined only by the initiator/MA ratio, and that the melt viscosity is influenced by the initiator concentration. 

Fixed-bed reactors are much simpler to operate compared to fluidized beds. After charging the catalyst pellets to the tubes and reaching steady state conditions, the reactor may run with little intervention for extended periods of time — even several years. Charging the catalyst and ramping up to steady state are the two most critical stages. It is imperative that all the tubes — in the case of maleic anhydride they may be as many as 35,000 — be loaded with equal amounts of catalyst in order to ensure an even distribution of gases. Several years ago, one tube was left empty in a plant in Europe. As the plant was approaching steady state, the operators realized that the... 

PERA/Nano-ZnO bionanocomposite was synthesized in domestic microwave oven model LG MS 1927C operating at 230V- 50 Hz frequency. MicHERA (0.04 mole) and finely powdered divalent zinc acetate (1 wt%, 3 wt%, 5 wt% and 7 wt% of monomer) were taken in an Erlenmeyer flask and placed in a microwave oven for 2-3 min, thereafter finely powdered maleic anhydride (0.04 mole) was added in the same pot and kept again for 2-3 min under same conditions. The reaction was monitored by TLC and acid value. The synthesized bionanocomposites were translucent light yellow color liquids (98-100% yield), designated as PERA/nano ZnO-1, PERA/ nano ZnO-3, PERA/nano ZnO-5 and PERA/nano ZnO-7 (suffix indicates the % of divalent zinc acetate yield 100%). FTIR (cm 3373- 3367- (-OH), 3057-3051 (t), C=CH- maleic), 3007-3005 (u, C=C-H of fatty acid alkyl chain), 2926.01(1), -CH asym), 2856.58 (i), -CH sym), 1737-1732 (l), >C=0 maleic), 1625-1618(broad, 1), >C=0 amide), 1222-1172 (C-C(=0) -O-C), 1120-1122 (l), C-O secondary hydroxyl), 1068-1066 (i), C-O primary hydroxyl), 657-653(6, surface -OH of nano ZnO), 472-463(1), nano Zn-O). 

Based on the application of severed techniques, the effect of preparation conditions on the activity and selectivity of promoted V-P-O catalysts in the n-butane oxidation to maleic anhydride is described. The type of solvent used, the time of synthesis, conditions of shape-forming operation and composition of the gas mixture for activation are considered. 

Specifically, propylene oxide has reacted directly with maleic and phthalic anhydrides to produce unsaturated polyesters under these milder conditions (15, 16). This would certainly be a major first step toward simplifying the process and lowering the cost. Incidentally, use of propylene oxide in place of propylene glycol would also result in an additional saving of 1 cent per pound in total raw material cost as well (6). After polyesterification, the separate steps of cooling, dilution with styrene, catalysis, impregnation, gelation, and cure are a distinct operational and economic liability. 

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