Higee technology, which has been developed since the late 1970s, is a promising process intensification technology. It promotes equipment size and weight reduction, lowers capital cost, eases the process operation, and saves energy. A rotating packed bed (RPB) is essentially the equipment for Higee technology. In a RPB, a high centrifugal force (5~100 g) is induced by rotating a doughnut shaped packing as shown in the figure on the right. The liquid stream, which is sprayed by the liquid distributor at the center of the RPB, is disintegrated into tiny droplets or thin ligaments, so that vast contact area is generated to enhance the mass transfer. Typically, the mass transfer efficiency per unit volume in a RPB is an order of magnitude higher than that in a conventional packed column. Therefore, for the same capacity, the size of a RPB is dramatically smaller than that of a packed column.
Another unique feature of a RPB is the high micromixing rate, which is 1~3 orders of magnitude higher than that of a stirred tank. Micromixing (i.e., mi
xing at the molecular scale) plays a critical role in the chemical industry when the time scale of the reaction involved is of the same magnitude as, or smaller than the time scale of mixing. In those cases, the reactions may have occurred or completed before the reactants accomplish homogeneous mixing at the molecular. Hence, the reactions proceed at an inhomogeneous state. Consequently, conversion, selectivity, particle size distribution, and molecular weight distribution are significantly influenced by micromixing. Therefore, a RPB, having high micromixing efficiency, is very suitable for fast liquid-liquid reactions