Purification of crude glycerol derived from biodiesel production process: Experimental studies and techno-economic analyses

In the present work, crude glycerol was purified by a combined strategy of physicochemical treatment and semi-continuous membrane filtration using a 5 kDa ultrafiltration tubular membrane. Three parameters - temperature, pressure, and flow rate were studied to see the effect of membrane filtration on glycerol purity. A maximum glycerol purity of 93.7% was obtained from crude glycerol of 40% purity after the physicochemical treatment and membrane filtration at the temperature, pressure, and flow rate of 50 °C, 700 kPa, and 50 mL/min, respectively. Most of the purification occurred during physicochemical treatment. Techno-economic analysis based on a scenario where all the purified glycerol is converted to value added chemicals - solketal and glycerol carbonate - showed that the glycerol purification process is economically feasible. In this scenario (scenario 3), the required capital investment was $2.1 million and the net present value of the project were $6 million (with 10% discounting rate) or $3.65 million (with 15% discounting rate), respectively, over 10 years of operation after start-up with capital investment in the initial three-year period with no returns. The unit cost and revenue of crude glycerol purification was $50.85/kg and $80.36/kg, respectively, making it a promising undertaking. The results of the present work can also be useful for the purification or recovery of other valuable biodiesel by-products such as free fatty acids, soaps, and solvents.