Patent ID: 7164039
Filing Date: 2007-01-16
Classification: 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 comprising propene, molecular oxygen and at least one inert gas in a first reaction stage over a fixed catalyst bed 1 whose active composition is at least one multimetal oxide comprising the elements Mo, Fe and Bi, in such a way that the fixed catalyst bed 1 is arranged in two spatially successive temperature zones A, B, both the temperature of temperature zone A and the temperature of temperature zone B are a temperature in the range from 290 to 380° C., the fixed catalyst bed 1 consists of at least two spatially successive fixed catalyst bed zones, and the volume-specific activity within one fixed catalyst bed zone is substantially constant and increases sharply in the flow direction of the reaction gas mixture 1 at the transition from one fixed catalyst bed zone to another fixed catalyst bed zone, the temperature zone A extends up to a conversion of the propene of from 40 to 80 mol %, on single pass of the starting reaction gas mixture 1 through the entire fixed catalyst bed 1, the propene conversion is ≧90 mol % and the selectivity of acrolein formation and also of acrylic acid by-production taken together and based on converted propene are ≧90 mol %, the sequence in time in which the reaction gas mixture 1 flows through the temperature zones A, B corresponds to the alphabetic sequence of the temperature zones A, B, the hourly space velocity of the propene contained in the starting reaction gas mixture 1 on the fixed catalyst bed 1 is ≧90 l (STP) of propene/l of fixed bed catalyst 1·h the difference T optionally reducing the temperature of the product gas mixture leaving the first reaction stage by cooling and optionally adding molecular oxygen and/or inert gas to the product gas mixture, and afterward conducting the product gas mixture as a starting reaction gas mixture 2 which comprises acrolein, molecular oxygen and at least one inert gas, and contains the molecular oxygen and the acrolein in a molar O the fixed catalyst bed 2 is arranged in two spatially successive temperature zones C, D, both the temperature of temperature zone C and the temperature of temperature zone D are a temperature in the range from 230 to 320° C., the fixed catalyst bed 2 consists of at least two spatially successive fixed catalyst bed zones, and the volume-specific activity within one fixed catalyst bed zone is substantially constant and increases sharply in the flow direction of the reaction gas mixture 2 at the transition from one fixed catalyst bed zone to another fixed catalyst bed zone, the temperature zone C extends up to a conversion of the acrolein of from 45 to 85 mol %, on single pass of the starting reaction gas mixture 2 through the entire fixed catalyst bed, the acrolein conversion is ≧90 mol % and the selectivity of acrylic acid formation, based on propene converted over both reaction stages, is ≧80 mol %, the sequence in time in which the reaction gas mixture flows through the temperature zones C, D corresponds to the alphabetic sequence of the temperature zones C, D, the hourly space velocity of the acrolein contained in the starting reaction gas mixture 2 on the fixed catalyst bed 2 is ≧70 l (STP) of acrolein/l of fixed bed catalyst 2·h the difference T wherein neither the transition from temperature zone A to temperature zone B in fixed catalyst bed 1 nor the transition from temperature zone C to temperature zone D in fixed catalyst bed 2 coincides with a transition from one fixed catalyst bed zone to another fixed catalyst bed zone.