Method for preparing unsaturated aldehyde and/or unsaturated fatty acid using fixed-bed catalytic partial oxidation reactor

A method for preparing unsaturated aldehydes, unsaturated fatty acids, or unsaturated aldehydes and unsaturated fatty acids from propane, propylene, isobutylene, t-butylalcohol, or methyl-t-butylether by fixed-bed catalytic partial oxidation in a shell-and-tube heat exchanger reactor comprising a gas inlet and reaction tubes,

• wherein a reaction zone for producing unsaturated aldehydes from propane, propylene, isobutylene, t-butylalcohol, or methyl-t-butylether is divided into two reaction zones fanning sequentially the first reaction zone for producing the unsaturated aldehydes and second reaction zones for producing the unsaturated fatty acids from the gas inlet, each reaction zone being packed with catalysts, and after reaction initiation, temperature of hot spots is controlled to be higher in a catalyst layer of the second reaction zone than in a catalyst layer of the first reaction zone at least during a start-up period.