MA from Benzene

Partial oxidation of benzene with air or oxygen in the gas phase produces MA, carbon monoxide, carbon dioxide, and water. Small amounts of other by-products such as phenol, quinone, diphenyl, etc. have been claimed. The majority of studies have employed vanadium oxides or some combination thereof as a catalyst. The reaction is highly exothermic and can maintain itself with proper heat removal. An uncontrolled reaction may give poor selectivities and may even lead to combustion. 

Although there are differences among various schools regarding the nature of reaction intermediates, a simplified generalized scheme appears agreed on without regard to the intermediates. Thus the scheme assumes equilibrium steady state amounts of intermediates. 

Hammar s work suggests some dependence of k on mass-transfer rates. However, other workers, such as Dixon,Mars, Holsen, and Dmuchovsky etalF show no significant dependence. Dixon and Longfield propose that this difference may be due to the catalysts with very low surface areas used by Hammar. 

There are a few common features in the data on benzene oxidation to MA by various workers  

Dmuchovsky et at Monsanto have studied the reaction in detail. 

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The first [] term in the Benzene calculation accounts for the two carbons that are liberated when MA is formed, and the second [] term is for conversion to byproducts, with x/i going to C02 and the other to CO. MA from benzene generates almost four times as much C02 in the reactor than the n-butane route. Additional C02 is generated when unreacted benzene or n-butane and byproduct CO is incinerated in the pollution control equipment from the process. 

In the almost 60 years since the first patent on MA production by Weiss and Downs/ a flood of patent and nonpatent literature has been published. In the benzene oxidation route, vanadium oxide stands out to be the most common feature of all the catalysts. It appears that in the commercial production of MA from benzene, vanadium oxide or cocatalyst promoted vanadium oxide over a support is used (except SAVA process). Typical promoters used are oxides or salts of the following elements Mo, W, Bi, Sn, P, Ag, Cu, Na, B, Ti, and Ni. The V + Mo is most common. Other elements may also act as modifiers (see Ref. 15). 

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