Maleic anhydride reactor types

Table 4. World Maleic Anhydride Capacity by Reactor Type...

Figure 3.34 Experimental data on selectivity to maleic anhydride vs degree of conversion of 1-butene for different reactor types ( ) channel width 0.08 mm and (A) channel width 0.2 mm micro reactor ( ) fixed-bed reactor [103],...

In industrial practice, the laboratory equipment used in chemical synthesis can influence reaction selection. As issues relating to kinetics, mass transfer, heat transfer, and thermodynamics are addressed, reactor design evolves to commercially viable equipment. Often, more than one type of reactor may be suitable for a given reaction. For example, in the partial oxidation of butane to maleic anhydride over a vanadium pyrophosphate catalyst, heat-transfer considerations dictate reactor selection and choices may include fluidized beds or multitubular reactors. Both types of reactors have been commercialized. Often, experience with a particular type of reactor within the organization can play an important part in selection. 

Among the many mathematical models of fluidized bed reactors found in the literature the model of Werther (J ) has the advantage that the scale-dependent influence of the bed hydrodynamics on the reaction behaviour is taken into account. This model has been tested with industrial type gas distributors by means of RTD-measurements (3)and conversion measurements (4), respectively. In the latter investigation (4) a simple heterogeneous catalytic reaction i.e. the catalytic decomposition of ozone has been used. In the present paper the same modelling approach is applied to complex reaction systems. The reaction system chosen as an example of a complex fluid bed reaction is the synthesis of maleic anhydride (Figure 1). 

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]. 

Type of Reaction and Application. An increased emphasis on gas-solid reactions has been evident for about a decade. Three of the papers in this symposium treat gas-solid reactions, two (13,18) dealing with coal combustion and the other (11) with catalyst regeneration. Of the four papers which consider solid-catalysed gas-phase reactions, one (15) deals with a specific application (production of maleic anhydride), and one (12) treats an unspecified consecutive reaction of the type A B C the other two (14,16) are concerned with unspecified first order irreversible reactions. The final paper (17) considers a relatively recent application, fluidized bed aerosol filtration. Principles of fluid bed reactor modeling are directly applicable to such a case Aerosol particles disappear by adsorption on the collector (fluidized) particles much as a gaseous component disappears by reaction in the case of a solid-catalysed reaction. 

The key to good reactor simulation is undoubtedly a knowledge of the reaction kinetics. The kinetics of the catalytic oxidation of benzene to maleic anhydride has been studied for different catalysts and conditions by many workers (8-13) however only Quach et al ( ) examined a catalyst, FX203, of a type simi-liar to that employed by Kizer et al (FB203-S). Both catalysts are fabricated by Halcon Catalyst Industries, but are of different formulation. 

One of the most industrially important reactions using vanadium pentoxide(V205) catalyst is the partial oxidation of 1-butene to maleic anhydride [1]. Partial oxidation reactions are inherently unselective and often make by-products of little or no value. Oxygen-rich feeds result in low product selectivities and high hydrocarbon conversions [2]. Because partial oxidation and total oxidation always proceed competitively, the selectivity of maleic anhydride from 1-butene is low. Though fixed bed reactors or fludized bed reactors have been used for partial oxidation for the past 30 years, the selectivity of maleic anhydride has not been obtained higher than 69% [3]. Some attempts have been reported on a new type of reactor to overcome the above limit. This is a membrane reactor which offers some advantages. A membrane reactor plays a... 

Typical applications of zeolite membranes in reactors include i) conversion enhancement either by equilibrium displacement (product removal) or by removal of catalyst poisons/ inhibitors and ii) selectivity enhancement either by control of residence time or by control of reactant traffic. A large number of examples are reported and discussed in [49,50,52], Several of them are reported in fable 3. The use of a zeolite membrane as a distributor for a reactant has been attempted for the partial oxidation of alkanes such as propane to propene [137], or n-butane to maleic anhydride [138]. Limited performances were obtained because the back-diffusion of the alkane is hardly controllable with this type of microporous membrane [139]. 

The first and most elementary type of reactor to be considered is the adiabatic. In this case, the reactor is simply a vessel of relatively large diameter. Such a simple solution is not always applicable, however. Indeed, if the reaction is very endothermic, the temperature drop may be such as to extinguish the reaction before the desired conversion is attained—this would be the case with catalytic reforming of naphtha or with ethylbenzene dehydrogenation into styrene. Strongly exothermic reactions lead to a temperature rise that may be prohibitive for several reasons for its unfavorable influence on the equilibrium conversion, as in ammonia, methanol, and SO3 synthesis, or on the selectivity, as in maleic anhydride or... 

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... 

Several industrial processes exist fw the production of maleic anhydride firom n-butane, which differ regarding the type of reactor ai the method employed for maleic anhydride recovery and purification (1-3). All processes onploy the same kind of catalyst, based on a vanadium/phosphorus mixed oxide (4-8). 

Industrial V/P/O-based catalysts can differ in the type of chemistry involved in the different stages, in the nature of the promoters added, and in the type of reactor technology employed for maleic anhydride synthesis. 

A third and final example of problematic scale-up occurs in the production of maleic anhydride by the partial oxidation of butane with air. This was selected to illustrate the pitfalls of scale-up without appropriate reactor-level models. AH of the excellent work in catalyst development and on proper selection of the best reactor type was nuUified by expecting the scale-up to be based on established rules-of-thumb and using empirical models to fit phot-plant performance data. 

The SAN and ABS cxjpolymers aantain approximately 25 wt% of acrylonitrile and polybutadiene rubber in amounts up to 20 wt%. Other styrene copolymers of industrial importance include styrene—maleic anhydride copolymer (SMA), styrene-divinylbenzene copolymer, acrylic—styrene-acrylonitrile terpolymer, and styrene-butadiene copolymer. Recently, metallocene catalysts have been developed to synthesize syndiotactic polystyrene (sPS). The polymerization process and process conditions have major effects on polymer properties and process economy. For styrene homopolymerization and copolymerization, various types of polymerization reactors are used commercially. 

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