Glycerolysis with crude glycerin as an alternative pretreatment for biodiesel production from grease trap waste: Parametric study and energy analysis

This study reports the use of crude glycerin from biodiesel production in the glycerolysis process and presents the associated parametric and energy analyses. The potential of glycerolysis as an alternative pretreatment method for high free fatty acid (FFA) containing fats, oils and greases (FOGs) is also assessed. Crude glycerin has been produced in substantial excess as a byproduct of the alkaline transesterification process to make biodiesel. Utilization of crude glycerin with minimum processing can significantly benefit the biodiesel industry. A grease trap waste derived low quality grease (30% FFA) was converted to monoacylglycerols (MAG), diacylglycerols (DAG) and triacylglycerols (TAG), using crude glycerin after methanol removal. The optimum operating condition was determined as follows: 1:1 M ratio of glycerin and FFA, 230 °C and 150 min, which effectively reduced the FFA% below 1 wt%. The change of grease composition, i.e., MAG, DAG, TAG, glycerin and FFA, during glycerolysis process was measured to better understand process kinetics. As compared with acid-catalyzed esterification, glycerolysis has the potential advantages of utilizing crude glycerin, while eliminating the use of hazardous chemicals, such as H2SO4 and methanol. Process simulation results showed that biodiesel production from glycerolysis-treated oil was less energy intensive (0.251 MJ/kg biodiesel produced) than that from the conventional “esterification and transesterification” route (0.534 MJ/kg biodiesel produced). Glycerolysis with crude glycerin can be an effective alternative pretreatment technology to acid-catalyzed esterification, especially for brown grease (FOGs with greater than 15% FFA).