Fuel ethanol production from starchy grain and other crops: An overview on feedstocks, affecting factors, and technical advances

Authors: LI, JUN - HENAN UNIVERSITY OF TECHNOLOGY; ZHAO, RENYONG - HENAN UNIVERSITY OF TECHNOLOGY; XU, YOUJIE - IOWA STATE UNIVERSITY; WU, XIAORONG; Bean, Scott; WANG, DONGHAI - KANSAS STATE UNIVERSITY

Submitted to: Renewable Energy
Publication Type: Review Article
Publication Acceptance Date: 2/8/2022
Publication Date: 2/15/2022
Citation: Li, J., Zhao, R., Xu, Y., Wu, X., Bean, S.R., Wang, D. 2022. Fuel ethanol production from starchy grain and other crops: An overview on feedstocks, affecting factors, and technical advances. Renewable Energy. 188:223-239. https://doi.org/10.1016/j.renene.2022.02.038.
DOI: https://doi.org/10.1016/j.renene.2022.02.038

Interpretive Summary: Fossil fuels currently account for more than 80% of the global energy supply but are considered unsustainable resources because their current depletion rate is a million times faster than their formation rate. This leads to another critical environmental issue: we emit far more carbon dioxide into the environment than the plants on earth can take up through photosynthesis. Developing environmentally friendly, sustainable bioenergy will reduce our reliance on fossil fuels and help with environmental issues. Fuel ethanol production from starchy crops is an important step toward sustainable energy production, which involves multiple steps in the process of converting starch into fuel ethanol. The yield of fuel ethanol from starchy crops is largely affected by those processes as well as the chemical composition and structural characteristics of feedstocks. Many factors such as the supply of starchy crops, market price and availability of the crops, and fluctuating fuel ethanol and petroleum prices, can affect the economics for fuel ethanol production. Some new techniques and value-added products are being developed to valorize the fuel ethanol production. A comprehensive overview on the potentials, challenges, and technical advances in fuel ethanol production from starch-based crops is summarized.

Technical Abstract: Using fuel ethanol to partially substitute petroleum-derived gasoline is commercialized around the world. In this review, an overview on feedstocks, affecting factors, and technical advances in starch ethanol production is systematically presented. The majority of fuel ethanol is produced from starchy crops such as corn, wheat, sorghum, barley, rye, cassava, and triticale, among which corn, wheat, and sorghum are the major contributors. Additional starchy crops have also been studied for fuel ethanol production but have not yet been industrialized. Degerming and decortication can largely improve starch ethanol yield with value-added products produced for fuel ethanol valorization. Starchy crops varieties with high amounts of waxy starch, low amounts of starch-lipid complex formed, and low protein cross-linking after cooking are more productive for fuel ethanol production. Starch and fiber from starchy crops not only can be separated for first- and second-generation ethanol production, respectively, but also combined for 1.5-generation ethanol production, which is technologically and economically feasible. Prehydrolysis of protein during mashing can increase the free amino nitrogen content and thus improve ethanol yield, but its economics need to be assessed. Value-added protein extracted from distiller’s dry grains with solubles for extensive applications can also valorize fuel ethanol production. Recommendations to further improve starch ethanol production and valorize ethanol are included in the review.