Long-term operation of heterogeneously catalyzed gas phase partial oxidation of propene to acrylic acid, comprises interrupting gas phase partial oxidation before temperature increase of fixed catalyst bed is permanent

摘要

A heterogeneously catalyzed gas phase partial oxidation of propene to acrylic acid is operated by interrupting gas phase partial oxidation before temperature increase of fixed catalyst bed is permanently 10[deg]C, and at 250-500, preferably 200-450[deg]C, initially conducting a gas mixture consisting of molecular oxygen, inert gas, and optionally steam through intermediate cooler and finally through fixed catalyst bed. The long-term operation of heterogeneously catalyzed gas phase partial oxidation of propene to acrylic acid involves interrupting gas phase partial oxidation before temperature increase of fixed catalyst bed is permanently 10[deg]C, and at 250-500, preferably 200-450[deg]C, initially conducting a gas mixture consisting of molecular oxygen, inert gas, and optionally steam through intermediate cooler and finally through fixed catalyst bed. A starting reaction gas mixture comprising propene, molecular oxygen, and inert gas, and contains the molecular oxygen and propene in a molar ratio of = 1, is conducted in a first reaction stage, at elevated temperature, over a first fixed catalyst bed whose catalysts are such that their active composition is a multilevel oxide containing molybdenum and/or tungsten, and also bismuth, tellurium, antimony, tin, or copper, in such a way that propene conversion in single pass is = 93 mol% and the accompanying selectivity of acrolein formation and of acrylic acid by-production taken together are = 90 mol%, optionally reducing the temperature of the product gas mixture leaving the first reaction stage by direct and/or indirect cooling and optionally adding molecular oxygen and/or inert gas to the product gas mixture, and then conducting the product gas mixture, as starting reaction gas mixture which comprises acrolein, molecular oxygen, and inert gas and contains the molecular oxygen and acrolein in a molar ratio of 0.5, in a second reaction stage, at elevated temperature, over a second fixed catalyst bed whose catalysts are such that their active composition is multilevel oxide containing molybdenum and vanadium, in such a way that acrolein conversion in single pass is =90 mol% and the selectivity of acrylic acid formation assessed over both reaction stages, based in propene converted, is =80 mol%, and by, in order to counteract the deactivation of the fixed catalysts bed, independently increasing the temperature of the particular catalyst bed over time.