Simulated moving bed technology for continuous, countercurrent solid-fluid supercritical extraction

Abstract

A model of a countercurrent solid-fluid column (CC) for recovery of natural oils from vegetable seeds by means of supercritical carbon dioxide is developed. The model takes into account seed morphology and mass-transfer limitations. True countercurrent contact may be achieved in practice by applying the Simulated Moving Bed (SMB) technology as developed for adsorption processes. A number of fixed-bed columns are connected in series, and a suitable switching policy for the solvent-feed and product-withdrawal points enables simulation of solids motion. A model of the multi-bed SMB process is developed and calculated performance of the plant is compared with that obtained with the equivalent true countercurrent contact. As a case study, the extraction and fractionation of α-tocopherol from oleic acid is examined. Attractive performances are found for a small number of columns, that is, when a plant with low complexity is considered.