Patent ID: 7667073

Claim:
A process for making acrylic acid, comprising partially oxidizing acrolein in the presence of a catalytically active multimetal oxide comprising material which comprises at least one of the elements Nb and W, and the elements Mo, V and Cu, wherein the molar fraction of the element Mo, based on the total amount of all elements other than oxygen in the catalytically active multimetal oxide comprising material, is from 20 to 80 mol %, wherein the molar ratio of Mo to V, Mo/V, is from 15:1 to 1:1, wherein the corresponding molar ratio Mo/Cu is from 30:1 to 1:3 and the corresponding molar ratio Mo/(total amount of W and Nb) is from 80:1 to 1:4, said catalytically active multimetal oxide obtained by a process comprising preparing an intimate dry blend comprising ammonium ions from starting compounds that comprise the elemental constituents of the multimetal oxide comprising material, other than oxygen, as components; and thermally treating the intimate dry blend at elevated temperatures in an atmosphere A having a low content of molecular oxygen, so that at least a portion of the ammonium ions contained in the intimate dry blend are decomposed at ≧160° C. with liberation of ammonia, wherein the thermal treating comprises: heating the intimate dry blend at a heating rate of ≦10° C./min to a decomposition temperature in a decomposition temperature range of from 240° C. to 360° C., and then keeping the temperature in the decomposition range until at least 90 mol % of the total amount M A of ammonia liberated altogether in the entire course of the thermal treatment of the intimate dry blend from the intimate dry blend at above 160° C. has been liberated; reducing, to ≦0.5% by volume, the content of molecular oxygen in the atmosphere A in which the thermal treatment of the intimate dry blend takes place no later than when the intimate dry blend has reached 230° C., and maintaining the reduced oxygen content until at least 20 mol % of the total amount M A of ammonia liberated altogether in the entire course of the thermal treatment has been liberated; taking the intimate blend out of the decomposition temperature range, at a rate of ≦10° C./min, and into a calcination temperature range of from 380 to 450° C. no earlier than when ≧70 mol % of the total amount of M A of ammonia liberated altogether in the entire course of the thermal treatment has been liberated; increasing the content of molecular oxygen in the atmosphere A to >0.5 to 4% by volume no later than when 98 mol % of the total amount M A of ammonia liberated altogether in the entire course of the thermal treatment has been liberated; and calcining the intimate dry blend at this increased oxygen content of the atmosphere A in the calcination temperature range.