Applicability of the Perturbed Hard Chain Equation of State for Simulation of Distillation Processes in the Oleochemical Industry. Part II: Purification of Glycerol

Abstract

Glycerol is a major by-product in the oleochemical industry with extensive end-use markets. Synthetic and natural glycerine fractions are currently purified using steam distillation at subatmospheric pressures. Due to the increasing interest of the pharmaceutical industry in ultrapure glycerol, supercritical fluid extraction followed by appropriate fractionation steps are also employed. It would therefore be convenient to utilize a single thermodynamic model that is capable of predicting all thermodynamic properties needed, and that also covers the whole pressure range which is currently applied in both industries. Different equations of state and activity coefficient models were scanned, and the perturbed hard chain equation of state (PHC-EOS) provided better results than those obtained using activity coefficient models. Pure component parameters were computed using vapor pressure data for glycerol. The fitted parameters were incorporated in the PHC-EOS and resulted in good reproduction of binary vapor—liquid equilibria. Calculations of multicomponent mixtures were performed using these binary parameters. A flow-sheeting program was utilized to simulate a steam distillation process consisting of two integrated columns, operated at subatmospheric pressures, for the purification of different glycerine feedstocks. The simulated flow rate, concentration, and temperature profiles were compared with some operating data obtained from a major oleochemical plant. Analysis of this comparison revealed that the PHC-EOS is very well suited for simulating different distillation processes for the purification of crude glycerine feedstocks.