Gas phase oxidation of propylene to acrylic acid using ring-shaped multi-metal oxide catalyst of specified geometry to maximize selectivity and space-time yield

摘要

Gas phase oxidation of propylene into acrylic acid in which the mixture of reaction gas is oxidized on a first fixed-bed catalyst and the mixture of product gas which contain acrolein oxidized on a second fixed-bed catalyst. The catalyst shaped bodies comprise an annular geometry in both reaction steps. Gas-phase oxidation of propylene in a one-stage reaction to acrolein and/or acrylic acid or in a two-stage reaction to acrylic acid is such that (i) the initial charge in both cases is /- 160 Nl propylene/l catalyst hour; (ii) the charge to the 2nd stage (if used) includes /- 140 NL acrolein/l catalyst hour ; and (iii) the catalyst or catalysts is/are of ring form with an outer diameter 2-11 mm, length 2-11 mm and a wall-thickness 1-5 mm. The process comprises (A) feeding a mixture of propylene, molecular oxygen and an inert gas with molar ratio O2 : C3H6 /- 1 at high temperature over a solid bed catalyst with characteristics (i) and (iii) above and comprising a multi-metal oxide containing Mo and/or W together with Bi, Te, Sb, Sn and/or Cu such that the propylene conversion and the combined selectivity for acrolein and the acrylic acid by-product are both /- 90 mol.%; and optionally (B) cooling the acrolein-containing gas product and optionally adding molecular O2 and/or inert gas prior to passing it at high temperature and with molar ratio O2 : acrolein /- 0.5 over a Mo- and V-containing multi-metal oxide solid bed catalyst such that the acrolein conversion is /- 90 mol.% and the combined two-stage acrylic acid selectivity (based on propylene conversion) is /- 80 mol.%.