Experimental and theoretical investigation of purification in a column crystallizer of material with impurities of the eutectic forming type

摘要

A theoretical analysis of the operation of a Schildknecht type of column crystallizer is presented and simplified to three special cases. Experimental determinations were made of concentration profiles established during the purification of benzene with cyclohexane as impurity under steady state, batch conditions of operation. Benzene containing 34 to 500 ppm. cyclohexane was obtained by processing feed material with 5,000 to 30,000 ppm. cyclohexane. It was found that experimental data obtained under conditions of normal operation are well correlated by theoretical expressions if it is assumed that the crystals are not pure but contain cyclohexane at the level of 34 to 100 ppm. It was further established that the resistance to mass transfer between the liquid which adheres to the crystals and the wash liquid is negligible in comparison to backmixing effects as represented in the model by an eddy diffusion term. Smooth operation of the column was obtained at crystal rates below a limiting upper value and at oscillation frequencies above a lower limit.