Method for reducing molybdenum trioxide content of gases issuing from reactors containing molybdenum-based catalysts

Claim 1

In a process which comprises passing a gas comprising propylene or isobutylene admixed with water vapor, oxygen, and an inert diluent gas through a reaction zone which is maintained at an elevated temperature of about 300° C to 500° C and at a pressure of about 1 to 5 atmospheres absolute and which contains a solid catalyst comprising a molybdenum oxide or a metal molybdate salt which is a source of molybdenum trioxide under the conditions obtaining within said reaction zone, and (b) introducing the gaseous effluent from said reaction zone into a subsequent processing step or zone in which unsaturated aldehydes contained in said effluent are further oxidized with oxygen to the corresponding alkenoic acids at a temperature of approximately 240° to 300° C in the presence of a solid catalyst, the improvement which comprises: cooling said reaction zone effluent gas by approximately 5° C to 200° C, prior to introducing it into said subsequent processing step or zone, by passing said effluent gas through a cooled bed or array of solid bodies which are chemically inert toward said gas, said bed or array having an effective void space greater than about 40%: and condensing varpors of molybdenum trioxide contained in said effluent gas as a result of vaporization of molybdenum trioxide from said reaction zone catalyst upon the surfaces of said solid bodies to diminish the molybdenum trioxide content of said gaseous effluent priot to its entry into said second subsequent processing step or zone.