Glycerolysis with crude glycerine as an alternative 3 pretreatment for biodiesel production from grease trap 4 waste: Parametric study and energy analysis

Authors: TU, QINGSHI - University Of Cincinnati; LU, MINGMING - University Of Cincinnati; Knothe, Gerhard

Submitted to: Journal of Cleaner Production
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/2017
Publication Date: 6/12/2017
Publication URL: https://handle.nal.usda.gov/10113/5730526
Citation: Tu, Q., Lu, M., Knothe, G.H. 2017. Glycerolysis with crude glycerine as an alternative 3 pretreatment for biodiesel production from grease trap 4 waste: Parametric study and energy analysis. Journal of Cleaner Production. 162:504-511.

Interpretive Summary: Biodiesel, produced from vegetable or other plant oils, is an alternative to diesel fuel derived from petroleum. When biodiesel is produced, a co-product called glycerol is also formed. While glycerol has many uses, increasing biodiesel production has caused excess glycerol to enter the market. Therefore, finding new or expanded uses for glycerol is important to support its market and the economical production of biodiesel as well. In this connection, this work describes the use of crude glycerol from biodiesel production together with an inexpensive but low-quality waste vegetable oil material (trap grease) to assist in the production of biodiesel from this trap grease.

Technical Abstract: This study reports the use of crude glycerine 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 glycerine 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 triacylglycerides (TAG) using crude glycerine after methanol removal. The optimum operating condition was determined as follows: 1:1 M ratio of glycerine 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 the 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).