Disclosed is a shell-and-tube reactor that may be used in a method for producing unsaturated aldehydes and/or unsaturated acids from olefins by means of fixed-bed catalytic partial oxidation. The reactor includes at least one reaction zone of a first-step reaction zone for producing unsaturated aldehydes as a main product and a second-step reaction zone for producing unsaturated acids as a main product, and at least one reaction zone of the reaction zones comprises two or more catalytic layers, each of the catalytic layers being packed with a formed product of catalyst as secondary particles, wherein the secondary particles in each catalytic layer are formed of primary particles of a catalytically active component having a different particle size, and the particle size of primary particles of the catalytically active component is controlled so that it decreases from an inlet of the reactor to an outlet of the reactor. A method for producing unsaturated aldehydes and/or unsaturated fatty acids from olefins using the same reactor is also disclosed. According to the present invention, it is possible to control the temperature efficiently at a hot spot, thereby permitting a catalyst to be used stably, and to produce unsaturated aldehydes and/or unsaturated fatty acids with high yield.
Provided is a method of preparing styrene polymers, the method comprising: homogeneously mixing a styrene monomer; a cocatalyst mixture of Group 13 metal-containing organic metal compound cocatalyst and an inert organic solvent; and a catalyst mixture of a metallocene catalyst and the inert organic solvent using a high speed homogenizing mixer to obtain a homogenized mixture; and providing the homogenized mixture to a reactor to initiate polymerization. In this method, catalyst is quickly dispersed among monomers using a high speed homogenizing mixer so that formation of gel, which occurs when a syndiotactic styrene polymer is produced, can be fundamentally prevented. In addition, a styrene polymer prepared using the method has high activity, good stereoregularity, and uniform molecular distribution.