Patent ID: 6888024
Filing Date: 2005-05-03
Classification: B01J,C07C

Abstract:
1. A process for partially oxidizing propene to acrylic acid in the gas phase under heterogeneous catalysis by conducting a starting reaction gas mixture 1 which comprises propene, molecular oxygen and at least one inert gas, and contains the molecular oxygen and the propene in a molar O 2 :C 3 H 6 ratio of ≧1 in a first reaction stage over a fixed catalyst bed 1 which is arranged in two spatially successive reaction zones A, B, the temperature of reaction zone A being a temperature in the range from 290 to 380° C. and the temperature of reaction zone B likewise being a temperature in the range from 290 to 380° C., and whose active composition is at least one multimetal oxide comprising the elements Mo, Fe and Bi, in such a way that reaction zone A extends to a propene conversion of from 40 to 80 mol % and the propene conversion on single pass through the fixed catalyst bed 1 is ≧90 mol % and the accompanying selectivity of acrolein formation and also of acrylic acid by-production taken together is ≧90 mol %, the temperature of the product gas mixture leaving the first reaction stage is optionally reduced by cooling and molecular oxygen and/or inert gas are optionally added to the product gas mixture, and then the product gas mixture, as a starting reaction gas mixture 2 comprising acrolein, molecular oxygen and at least one inert gas and containing the molecular oxygen and the acrolein in a molar O 2 :C 3 H 4 O ratio of ≧0.5, is conducted in a second reaction stage over a fixed catalyst bed 2 which is arranged in two spatially successive reaction zones C, D, the temperature of reaction zone C being a temperature in the range from 230 to 320° C. and the temperature of reaction zone D likewise being a temperature in the range from 230 to 320° C., and whose active composition is at least one multimetal oxide comprising the elements Mo and V, in such a way that reaction zone C extends to an acrolein conversion of from 45 to 85 mol % and the acrolein conversion on single pass through the fixed catalyst bed 2 is ≧90 mol % and the selectivity of acrylic acid formation assessed over all reaction zones, based on converted propene, is ≧80 mol %, the sequence in time in which the reaction gas mixture flows through the reaction zones corresponding to the alphabetic sequence of the reaction zones, wherein a) the hourly space velocity of the propene contained in the starting reaction gas mixture b) the volume-specific activity of the fixed catalyst bed c) the difference T d) the hourly space velocity of the acrolein contained in the starting reaction gas mixture e) the volume-specific activity of the fixed catalyst bed f) the difference T