Studies on the Counter Current Liquid-Liquid Extraction Column with Stirrers (Part I)

Abstract

Performance data are presented in this paper for a continuous counter current extraction column which is divided into several compartments by horizontal plates and agitated with paddles fixed on an eccentric common shaft in each compartment. The authors performed the extraction of phenol with benzene from aqueous solution using the laboratory columns, 68mm i.d., and pilot plant column, 300mm i.d., and obtained the following results : One of the most important factors for the efficiency is agitator speed. The stage efficiency has a maximum value at a certain agitator speed. The average effieciency reaches 50〜60% at proper impeller speed. The agitation not only causes an increase in the interfacial area but also decreases the resistance in both individual films of the continuous and dispersed phases, and its effect is rather striking in the dispersed phase. At a higher efficiency condition, the resistance in the extract film would be much smaller than that in the raffinate. In this equipment, the position of ascending pipes, through which the solvent phase is expected to pass, has also an important influence upon efficiency and capacity. If the ascending pipes are arranged at the regular position, the efficiency and capacity are much increased. For the scale-up of this type of column, the impeller speed would be determined by the relation; N3³D2² is equal to constant.