Solvent-free enzymatic esterification of free fatty acids with glycerol for biodiesel application: Optimized using the Taguchi experimental method

Authors: SINGH, RAMKRISHNA - University Of Illinois; Dien, Bruce; SINGH, VIJAY - University Of Illinois

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2022
Publication Date: 7/13/2022
Citation: Singh, R., Dien, B.S., Singh, V. 2022. Solvent-free enzymatic esterification of free fatty acids with glycerol for biodiesel application: Optimized using the Taguchi experimental method. Journal of the American Oil Chemists' Society. 99(9):781-790. https://doi.org/10.1002/aocs.12633.
DOI: https://doi.org/10.1002/aocs.12633

Interpretive Summary: Biodiesel is a diesel substitute manufactured primarily in the Midwest from vegetable oils. It is valued as an ecologically friendly fuel that can be blended with diesel to lower greenhouse gas emissions. It is mostly produced from soybean oil (2.5 billion gals in 2020), but the cost and limited supply of soybean oil constrain its production. Conversion of lower grade oils is technically challenging; in part, because the favored production method responds poorly to the presence of free fatty acids, which are formed from the breakdown of vegetable oils. Herein, a process is described to upgrade low quality oils by eliminating fatty acids. The process uses an enzyme to react the fatty acids with a common chemical called glycerol to form oil. Glycerol is a byproduct of biodiesel production. This study used refined chemicals to better understand the basics and will need to be broaden in the future to include crude feedstocks. Once done, this technology for upgrading oils high in fatty acids may allow for expanding biodiesel production. This will be of interest to the 85 biodiesel plants and processors who produce lower grade oils.

Technical Abstract: Presence of free fatty acids along with glycerides poses a technical difficulty for biodiesel production. This work used a Taguchi L9 design to optimize the solvent-free enzymatic process to result in the esterification of oleic acid with glycerol. Under optimal conditions the esterification reaction temperature of 60°C, enzyme dose of 5 wt%, glycerol: oleic acid molar ratio of 5:1, and reaction time of 3 h, a 75.235'±'2.19% conversion of oleic acid to esters was achieved. With the addition of molecular sieves, the conversion increased to 86.73%'±'1.09%. However, using the parameters predicted by Taguchi design (60°C, 5 wt%, 5:1, and 4.5 h), 88.5%'±'1.11% of oleic acid could be converted to esters derivative. Diglycerides were the major product, and the reaction equilibrium was attained after 4 h. The immobilized enzyme could be used up to seven times with only a 10% reduction in the conversion. Thus, the process can efficiently reduce the free fatty acid content of oil to make it suitable for biodiesel production.