Acrylonitrile from propane

Numerous patents have been issued disclosing catalysts and process schemes for manufacture of acrylonitrile from propane. These include the direct heterogeneously cataly2ed ammoxidation of propane to acrylonitrile using mixed metal oxide catalysts (61—64). 

V-Sb-oxide based catalysts show interesting catal)dic properties in the direct synthesis of acrylonitrile from propane [1,2], a new alternative option to the commercial process starting from propylene. However, further improvement of the selectivity to acrylonitrile would strengthen interest in the process. Optimization of the behavior of Sb-V-oxide catalysts requires a thorough analysis of the relationship between structural/surface characteristics and catalytic properties. Various studies have been reported on the analysis of this relationship [3-8] and on the reaction kinetics [9,10], but little attention has been given to the study of the surface reactivity of V-Sb-oxide in the transformation of possible intermediates and on the identification of the sxirface mechanism of reaction. 

PETROX An ammoxidation process for making acrylonitrile from propane or propylene. Developed by BOC Group and partially piloted in New Jersey. 

All catalysts claimed are multifunctional systems. Indeed, the formation of acrylonitrile from propane occurs mainly via the intermediate formation ofpropene the latter is then transformed into acrylonitrile via the allylic intermediate (Figure 9.4). 

H., Asahi-Japan, Process for producing acrylonitrile from propane by ammoxidation, USP 5973186, 1999... 

AH catalysts claimed are multi-functional systems. Indeed, the formation of acrylonitrile from propane occurs mainly via the intermediate formation of propene, which is then transformed to acrylonitrile via the allylic intermediate. It follows that the catalyst possesses different kinds of active site one site that is able to activate the paraffin and oxidehydrogenates it to the olefin, and one site that (amm)oxidizes the adsorbed olefinic intermediate. This second step must be very rapid to limit, as much as possible, the desorption of the olefin. In order to develop an effective cooperation between the two sites, it is necessary to have systems in which they are in close proximity. The muIti-functionaHty is achieved either through the combination of two different compounds (phase-cooperation), or through the presence of different elements inside a single crystaUine structure. In antimonate-based systems, the cooperation between the metal antimonate (having the rutile crystalline structure), responsible for propane oxidative dehydrogenation to propene and propene activation, and antimony oxide, active in allylic ammoxidation, is made more efficient through the dispersion of the latter compound over... 

This review analyzes the properties which are necessary for heterogeneous catalysts to promote the oxyfunctionalization of light paraffins to valuable chemicals. Three catalytic systems are discussed i) vanadium/phosphorus mixed oxide, the industrial catalyst for the oxidation of n-butane to maleic anhydride, which is here also examined for reactions aimed at the transformation of other hydrocarbons ii) Keggin-type heteropolycompounds, which are claimed for the oxidation of propane and isobutane, whose composition can be tuned in order to direct the reaction either to the formation of olefins or to the formation of oxygenated compounds iii) rutile-based mixed oxides, where rutile can act as the matrix for hosting transition metal ions or favour the dispersion of other metal oxides, thus promoting the different role of the various elements in the formation of acrylonitrile from propane. 

The synthesis of acrylonitrile from propane, as an alternative route to the industrial process which employs the olefin as the raw material, is carried out on catalysts which are based on vanadium and antimony mixed oxides. The catalyst contains a large excess of antimony with respect to the stoichiometric requirement for the formation of VSb04, and the... 

Improvements in acrylonitrile yield are also reported with other vapor phase promoters. A patent assigned to Monsanto Co. (125) describes the use of sulfur and sulfur-containing compounds in the feed gas mixture for production of acrylonitrile or methacrylonitrile from propane or isobutane over metal oxide catalysts. Examples of effective sulfur-containing compounds include alkyl or dialkyl sulfides, mercaptans, hydrogen sulfide, ammonium sulfide, and sulfiir dioxide. Best results are apparently achieved using a molar ratio of sulfur (or sulfur compound) to hydrocarbon of 0.0005 1 to 0.01 1. Nitric oxide has also been examined as a gas-phase promoter for propane and isobutane ammoxidation (126). However, it does not appear to be as effective as halogen or sulfur. Selectivities to acrylonitrile from propane are only about 30% over an alumina-supported chromium-nickel oxide catalyst. 

The most effective molybdenum-based oxide catalyst for propane ammoxidation is the Mo-V-Nb-Te-0 catalyst system discovered and patented by Mitsubishi Chemical Corp., Japan, U.S.A. (140). Under single-pass process conditions, acrylonitrile yields of up to 59% are reported, whereas under recycle process feed conditions, the acrylonitrile selectivity is 62% at 25% propane conversion (141). Although the latter results show that the catalyst operates effectively under recycle feed conditions, the catalyst system was originally disclosed for propane ammoxidation under single-pass process conditions. The catalyst was derived from the Mo-V-Nb-0 catalyst developed by Union Carbide Corp. for the selective oxidation of ethane to ethylene and acetic acid (142). The early work by Mitsubishi Chemical Corp. used tellurium as an additive to the Union Carbide catalyst. The yields of acrylonitrile from propane using this catalyst were around 25% with a selectivity to acrylonitrile of 44% (143). The catalyst was also tested for use in a regenerative process mode much like that developed earlier by Monsanto (144) (see above and Fig. 8). Operation under cyclic reduction/reoxidation conditions revealed that the performance of the catalyst improved when it was partially reduced in the reduction cycle of the process. Selectivity to acrylonitrile reached 67%, albeit with propane conversions of less than 10%, since activity in... 

The one-stage synthesis of acrylonitrile from propane is a new chemical oxidation process [1] and commercialization of tiie process is forecast to be possible in a few years [2],... 

Centi, G., TosarelU, T. and Trifiro, F. (1993). Acrylonitrile from Propane on (VO)2P207 with Preadsorbed Ammonia. 1. Role of Competitive Adsorption Phenomena in Determining Selectivity, J. Catal., 142, pp. 70-83. 

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