Design of a dividing wall column for fractionation of biodiesel

Abstract

This study presents an efficient design method for DWC which can fractionate palm methyl esters (PME, biodiesel) into three more valuable product groups: a mixture of methyl laurate and methyl myristate as light-cut, pure methyl palmitate (≥99.5%) as middle cut, and the mixture of the remaining methyl esters (biodiesel), which has good low-temperature operability to such an extent as to come close to cold filter plugging point (CFPP) 0 °C, as heavy cut. The first step of the design was to determine numbers of stages for four sub-sections of DWC, liquid split ratio, and initial reflux ratio by the shortcut design, based on the component net flow model and the method of Fenske, Underwood, and Gilliland (FUG method). Secondly, optimal reflux ratio, vapor split ratio, locations of stages for feed and side product were found out by sensitivity analysis in rigorous simulation. The results from the simulation model developed by the method show that the reboiler duty of a single DWC is about 24% less than that of two simple columns in direct sequence and about 25% less than in indirect sequence. These energy saving ratios are almost close to 30%, which is popularly known as a typical value for energy saving of DWC.