分批精馏中的持液作用

分批精馏中持液影响塔内的动态过程，因此许多学者一直致力于分批精馏过程中持液作用的研究，但由于研究缺乏系统性，持液的作用一直是学术上争论的热点.本文提出用全过程分离难度系数关联各参数对分离过程的影响，并建立了分批精馏的恒摩尔持液模型，用全过程的分离难度系数研究了分批精馏的持液作用，结果表明：塔顶持液对分离不利，但塔身持液在一定条件下增多可使所需回流比降低；塔内持液量与釜液量之比为一个因子，当q<0.7时，确定的分批精馏塔存在最佳投料量.采用甲苯-乙苯二元物系对最佳投料量进行了实验验证，实验结果与模拟结果吻合较好.

ROLE OF HOLDUP IN BATCH DISTILLATION

Liquid holdup in batch distillation column affects the transfer of mass and heat and thus the whole dynamic response of the system.The role of column holdup on the performance of batch distillation has been studied by researchers in the past,but it is still the focus of debate because none of the studies is systematical.In this paper,the degree of difficulty of separation is proposed to correlate different parameters in batch distillation and the constant holdup model is built.The effect of holdup on batch distillation was studied systematically.It was found that condenser and reflux drum holdup was detrimental to the separation,but increasing column holdup might improve the performance in some cases.Further studies on the dynamic role of column holdup showed that the ratio of column holdup to initial charge acted as a factor.So an optimum initial charge existed for a column when the degree of difficulty of separation q<0.7,which was checked and proved by experiments with toluene-ethyl benzene system.