Extraction of Caprolactam with Toluene in a Pulsed Disc and Doughnut Column—Part I: Recommendation of a Model for Hydraulic Characteristics

Abstract

Caprolactam, the monomer for Nylon‐6, is industrially recovered from an aqueous feed containing ammonium sulphate by extraction with organic solvents like benzene, toluene, or chlorinated hydrocarbons followed by back‐extraction with water. Extraction columns like the Rotating Disk Contactor and Pulsed Packed Column are industrially applied. In this paper a model is recommended for the description of the hydraulic characteristics of a pulsed disc and doughnut column for caprolactam extraction with toluene. In Part II and III the hydraulic and mass transfer characteristics, respectively, are determined and described with the developed models. The hydraulic characteristics are correlated as a function of the operating conditions for the experimental conditions covering the industrial operating range. The model is derived for equilibrium conditions in order to avoid the influence of mass transfer. The final model describes the operational window via equations describing flooding due to insufficient pulsation, and flooding due to a too small relative velocity between both phases and phase inversion. In the operational window several operational regimes can be distinguished, being mixer‐settler, dispersion, and emulsion type operation. Finally, two equations are presented for the description of the Sauter drop diameter and hold‐up at each operational point. The hydraulic characteristics are correlated using physical properties, operational parameters, and geometrical characteristics of the column.