Patent ID: 7262324

Claim:
In a process of producing unsaturated acids from unsaturated aldehydes by fixed-bed catalytic partial oxidation in a shell-and-tube heat exchanger-type reactor, the reactor comprising one or more catalytic tubes each including a reaction zone of producing the unsaturated acids, the improvement wherein: the reaction zone is divided into two or more shell spaces by at least one partition, each of the divided shell spaces being filled with a heat transfer medium, the heat transfer medium being maintained at isothermal temperature or a temperature difference of 0-5° C., and when the shell spaces divided by the partition in the reaction zone are named, such as zone 1 , zone 2 , zone 3 , . . . and zone N in an axial direction, T h1 -T salt1 is ≦130° C. and T hN -T saltN is ≦110° C., wherein N is an integer of 2 or more, T h1 is the peak temperature of a reaction mixture in a catalyst layer corresponding to the first shell space, T hN is the peak temperature of a reaction mixture in a catalyst layer corresponding to the Nth shell space, T salt1 is the temperature of a heat transfer medium filled in the first shell space, and T saltN is the temperature of a heat transfer medium filled in the Nth shell space.