Effect of the nature of a support on the catalytic activity of a palladium catalyst in the synthesis of vinyl acetate by gas-phase ethylene acetoxylation

Abstract

The effect of the nature and texture of a support on the activity, selectivity, and stability of modified palladium catalysts in the synthesis of vinyl acetate (VA) by gas-phase ethylene acetoxylation is studied. Industrial and pilot supports based on A1 and ShN-2 alumina and KSK and KSS-3 silica gel, both original and thermally treated, are used to prepare the catalysts. As the result of catalytic tests (48 and 200 h in duration), KSS-3(1) silica gel support preliminarily subjected to hydrothermal treatment is chosen as our base carrier for palladium catalysts in VA synthesis. By varying the temperature (and thus the water vapor pressure) as well as the duration of KSS-3 silica gel treatment, we obtain the optimum parameters for the support that ensure the stable operation of a catalyst for VA synthesis: a bulk density of 0.54 g/cm3, a surface area of 150 ± 10 m2/L, a pore volume of 0.80–0.83 cm3/g, and a pore radius of 1100–1200 nm. It is shown that during the operation of catalyst containing 1.5% Pd, 0.75% Au, and 5.0% potassium acetate on a KSS-3(1) support over 6 months in an industrial reactor for VA synthesis, the values of the activity and selectivity indices are 20–25% higher than those of any industrial catalyst. The findings of the study enable us to recommend the support for industrial applications with a predicted service life of the catalyst of at least three years. A procedure for predicting the effectiveness of catalyst operation for long periods (up to ∼1000 h) on the basis of short (48 h) tests is developed and experimentally verified. The practical importance of the procedure is that its use in selecting a support for mixed supported catalysts for synthesizing VA from ethylene will considerably reduce the number and duration of experiments.