Optimization of the in situ transesterification of grain sorghum (milo) ddgs to fatty acid methyl esters and fatty acid ethyl esters

Authors: Wyatt, Victor; Johnston, David; Jones, Kerby; Moreau, Robert

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary: To meet the goals of global biofuels production, additional feedstocks are needed. This need has resulted in the search for alternative, low-cost, feedstocks. The economics of many of the processes by which biofuels are made, particularly biodiesel, also need to be improved to make the fuels affordable to the general population. Biodiesel is a renewable fuel that is becoming widely accepted as a replacement or additive for petroleum-based diesel fuel. The in-situ transesterification (IST) method is potentially a cost and energy-saving process by which biodiesel can be produced directly from oil bearing feedstocks rather than from extracted oils. This study was performed to optimize the production of biodiesel from grain sorghum (milo) distillers dried grains and solubles (DDGS). Milo DDGS are a coproduct produced after fermentation of grain sorghum seeds and contains approximately 10% oil. This study demonstrates that the IST process can be successfully modified to produce biodiesel from the oil in milo DDGS. Successful utility of this process will benefit both, the ethanol and biodiesel industries, and grain sorghum farmers.

Technical Abstract: Distillers grains and solubles generated from the ethanol fermentation of grains contain acylglycerols (AG) that can be successfully converted to fatty acid methyl esters (FAME), commonly known as biodiesel. However, when grain sorghum (milo) DDGS were used as a feedstock for in-situ transesterification (IST) under the previously established optimal conditions for other AG-bearing substrates, the yield plateaued at only 32.2 % (corrected in this study to 24.2%). Several IST studies have reported significantly higher conversions of AG-bearing substrates to FAME. Therefore, the goal of this IST study was to improve the conversion of the AG in milo DDGS to FAME by varying the temperature of reaction, the concentrations of the base (sodium methylate, NaOMe), volume of methanol and ethanol, and the amount of moisture in DDGS. Methyl tert-butyl ester was also evaluated as a co-solvent intended to improve miscibility and reaction rate. Among these variables, the most effective change was an increase in temperature from 40°C to 65°C. The most successful reactions used a AG:NaOMe:MeOH molar ratio of 1.0:2.6:168.9. Those reactions used 4.8 mmol of NaOMe dissolved in 12.6 mL MeOH and resulted in a 79.8% conversion of AG to FAME.