Manufacture of Mixed Oxide Catalysts for Acrolein and Acrylonitrile

Manufacture of Mixed Oxide Catalysts for Acrolein and Acrylonitrile 

The original bismuth molybdate catalyst described in the early patents was supported on silica and prepared by a relatively simple procedure. 

A more active bismuth phosphomolybdate (Table 4.13) was prepared simply by adding an appropriate volume of phosphoric acid to the initial solution. A typical catalyst composition was claimed to be Bi9PMoi2052-55 2Si02. The same catalysts could be used to produce both acrolein and acrylonitrile. 

During full-scale operation it was found that whiskers of molybdenum oxide could form on the catalyst surface in the presence of steam. This led to caking of the particles as well as loss of molybdenum. The problem with catalyst caking is that the fiuid bed ceases to operate correctly and temperature control is severely impaired. This results in significant loss in selectivity. By ensuring that the ratio of bismuth to molybdenum was greater than 2 3 the loss could be controlled. An upper bismuth-tomolybdenum ratio of about 3 4 was fixed because bismuth was expensive. 

The second generation Sohio catalyst, introduced during the inid-l%0s, was an antimony oxide/uranium oxide mixture (U03-2Sb203). A successful iron oxide/antimony oxide catalyst containing some tellurium oxide was subsequently developed by Nitto, a Sohio licensee, in Japan.  

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