PURIFICATION OF CRUDE GLYCEROL BY A COMBINATION OF PHYSICO-CHEMICAL TREATMENT AND SEMI-CONTINUOUS MEMBRANE FILTRATION PROCESSES

Abstract

Crude glycerol is being increasingly produced in large quantities industrially as a result of increasing biodiesel production and it poses a disposal challenge as it is of little economic value. When purified however it has economic value and a lot of uses including being valorized into fuel additives such as solketal (C6H12O3) and glycerol carbonate (C4H6O4). The purpose of this research therefore was to purify glycerol to technical grade (95 wt%) in the most economically feasible way. In this work, crude glycerol was purified by combined techniques of physico-chemical treatment and semi-continuous membrane filtration using tubular ceramic ultrafiltration and spiral wound polymeric nanofiltration membranes. Three parameters – temperature, pressure, and flow rate - were studied to observe their effects on membrane ultrafiltration of treated glycerol to optimize glycerol purity. A maximum glycerol purity of 93.7 wt% was obtained from purification of crude glycerol of 40 wt% original purity after physico-chemical treatment and membrane filtration using a 5 kDa ultrafiltration membrane at the temperature, pressure, and flow rate of 50°C, 690 kPa g, and 50 mL/min, respectively. Most of the purification occurred during physicochemical treatment. Nanofiltration of a simulated glycerol mixture at varying flow rates and salt contents produced a glycerol purity in the range 96 - 100 wt% up from 94 wt% purity glycerol. Nanofiltration of treated glycerol under various flow rates and relatively constant pressure and salt content at room temperature produced the highest glycerol purities of 97.2 and 94.9 wt% at 80 and 125 mL/min flow rates respectively, both purities of which are of technical grade. Techno-economic analysis of glycerol purified by combined physico-chemical and ultrafiltration techniques based on a scenario where all the purified glycerol was converted to value added chemicals – solketal and glycerol carbonate – has shown that the glycerol purification process is economically feasible with more than 100% return in net present value on capital.