The application concerns a process comprising: (A) contacting a gas comprising oxygen, propane and propylene with at least one catalyst under reaction conditions sufficient to at least partially convert the propylene into a final product comprising acrylic acid; (B) feeding said final product to a separation column, in which the final product is split into a liquid stream, which is rich in acrylic acid, and a gaseous by-product stream comprising propane and propylene in a volume ratio of from 99.9:0.1 to 95:5; (C) contacting the gaseous by-product stream with oxygen in the presence of a catalyst under reaction conditions sufficient to at least partially convert propane to acrylic acid.