Studies Of Distillation In A Novel Multi-Stage Counter-Current Rotating Packed Bed

In chemical industry, distillation was often emplyed to separate or purify liquid mixtures in a column. In a traditional distillation column, the liquid flows under the drive of the gravitational force which led to thicker liquid film and lower liquid velocity. Therefore, some disadvantages such as low mass transfer coefficients, small operational flexibility and big volume are existed in traditional distillation column. In some fields, the solvents and crude product are fluctuations in concentration and flowrate, and most of them are batch or semi-continuous effluent. Therefore, the specifications by traditional distillation process are not satisfactory in these fields. As a process intensification device, rotating packed bed(RPB) has small size, high separation efficiency, easily-operated and wide flexiblity, which was supposed to meet the demands in above-mentioned fields.In view of the characteristic of conventional RPB and rotating zigzag bed(RZB), a novel multi-stage counter-current rotating packed bed(MSCC-RPB) was developed. Its structure and principle was described in detail. Continuous'distillation experiments with methanol-water and alcohol-water binary system were carried out in a MSCC-RPB with outside diameter of 365mm, and inside diameter of 145mm at atmospheric pressure. The separation performance of MSCC-RPB was characterized by the number of theoretical trays(NT). Effects of packing, varying rotation speed(N), feedstock concentration(xF), thermal condition of feed(q), reflux ratio(R) and separating binary system on NT of MSCC-RPB were investigated. Experimental results indicated that the separation efficiency with packing in MSCC-RPB increased 30-75% compared with no packing in MSCC-RPB, and the improvement decreased with increasing of N. The optimum value of N for NT was found to be 700-800r·min-1.NT increased with increasing of N at N<700r·min-1, and decreased with increasing of N for N>800r·min-1. The value of NT remained nearly constant with the increase of xF, and increased with increasing values of q and R. The separation efficiency was much higher for alcohol-water binary system than that of methanol-water. For alcohol-water binary system, the height equivalent of a theoretical tray ranged from 19.5 to 31.4mm, which is almost the same as in a conventional RPB. Compare with RZB, the separation efficiency is nearly doubled, and the optimum rotating speed is much lower than that of RZB(its optimun rotating speed is about 1000r·min-1).