Benzene oxidation vanadium-promoted catalysts

Oxidation. Benzene can be oxidized to a number of different products. Strong oxidizing agents such as permanganate or dichromate oxidize benzene to carbon dioxide and water under rigorous conditions. Benzene can be selectively oxidized in the vapor phase to maleic anhydride. The reaction occurs in the presence of air with a promoted vanadium pentoxide catalyst (11). Prior to 1986, this process provided most of the world s maleic anhydride [108-31 -6] C4H2O2. Currendy maleic anhydride is manufactured from the air oxidation of / -butane also employing a vanadium pentoxide catalyst. 

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). 

The role of M0O3 as a promoter has been explained as a moderator for benzene oxidation. Bhattacharya and Venkataraman studied a variety of vanadium oxide-based catalysts. They concluded that, under their conditions, the best yields of MA were obtained using the composition V2O5 (1-2.3) Mo03 (1.0), supported on kieselguhr, with 5% cobalt oxide as a promoter. 

The incorporation of vanadium(V) into the framework positions of silicalite-2 has been reported by Hari Prasad Rao and Ramaswamy . With this heterogeneons oxidation catalyst the aromatic hydroxylation of benzene to phenol and to a mixtnre of hydroqninone and catechol conld be promoted. A heterogeneons ZrS-1 catalyst, which has been prepared by incorporation of zirconinm into a silicalite framework and which catalyzes the aromatic oxidation of benzene to phenol with hydrogen peroxide, is known as well in the literature. However, activity and selectivity were lower than observed with the analogous TS-1 catalyst. 

The modified process is based on the oxidation of butane (see Fig. 9.32). A major advantage of C4 over benzene is that no carbon is lost in the reaction. The yield from butane process is 30% greater than that from the benzene process. Also, C4 is much cheaper than benzene. Benzene is a known carcinogen. So, the fixed bed process with n-butane as the raw material has been the only MA route used commercially since 1985 in the United States. In the fixed bed process, a low concentration of butane is passed over the catalyst at 400 80°C and 0.3-0.4MPa. The process generates more water than the benzene process. Unsupported vanadium phosphorus oxide (VPO) catalysts with promoters such as lithium, zinc, and molybdenum are commonly used. 

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