Fractionation of polyethylene wax by pilot-scale molecular distillation: new insights on process development

Abstract

A falling film molecular distillation (FFMD) process was used in a pilot plant to fractionate a polyethylene wax (PE-Wax) into light paraffin wax (LP-Wax) and super-microcrystalline wax (SM-Wax). The pseudoization technique was applied to represent the molecular distribution of the PE-Wax by pseudo-components (PS1 and PS2). Investigation was made of the influences of the evaporator temperature (EVT), feed flow rate (FF), and condenser temperature (CT) on the percent recovery of distillate (DP), the yield of PS1 in the distillate (YD_PS1), and the distillate flow rate/feed flow rate ratio (DF). The predictive models and the multi-response optimization provided decision criteria about the most suitable operating conditions for fractionating PE-Wax. The best experimental data for DP,YD_PS1, and DF (63.4%, 81.5%, and 0.60, respectively) were obtained with EVT of 184°C, FF of 1.81kg/h, and CT of 28°C, at 0.1Pa. The LP-Wax, recovered mainly in the distillate, exhibited a normal distribution throughout the carbon number range from n-C13 to n-C30. The SM-Wax, recovered in the residue, showed a higher latent heat of storage (>169kJ/kg), according to the phase-change performance of the material. These results offer new insights into processing PE-Wax to obtain value-added products with narrower carbon number distributions.