a mixing device mounted between two catalyst beds in a multi - bed catalytic reactor with a cylindrical shape . the mixing device has a circular outer rim which corresponds to the inner wall of the reactor , and includes a collecting section for collecting fluid from an up - stream catalytic bed , a mixing section for mixing the collected fluid , and a discharging section for discharging the mixed fluid to a down - stream catalytic bed . the collecting section , the mixing section and the discharging section are disposed outside the center of the circular cross - section of the reactor .