Agronomic potential of sorghum as a raw material for ethanol production in Central Ohio

Abstract

The presence of a finite quantity of fossil fuels has prompted the search for new sources of energy which are readily renewable. The Department of Energy completed a report during 1979 in which a scenario was developed that projected the production of over 40 000 million 1 per year of ethanol by the year 2000. Among the assumptions underlying this projected increase in ethanol production was the development of approximately 5.7 million ha of sweet sorghum for commercial production. This area was expected to be distributed evenly between the Corn Belt and the southeastern United States and an average fermentable sugar (combined sucrose, glucose, and fructose) yield was assumed to be 9.5 t ha −1 (approximately 5500 1 ha − of 100% ethanol assuming a 100% conversion efficiency). Sorghum has been recognized for its significant biological potential, but a number of questions must be addressed prior to commercial production on such an extensive scale. Particularly in the midwestern United States, the length of harvesting/processing season would be critical to the cost of the ethanol. The primary objective of this study was to determine the agronomic potential and feasibility of sorghum production for ethanol in central Ohio or other similar temperate production regions. Additional objectives included: (a) determination of total biomass and potential sugar yields for different types of sorghum; and (b) estimation of the harvesting/processing season length under normal conditions in central Ohio. Among the promising lines of sorghum, the dry matter yields produced in the study ranged from 13.0 to 19.0 t ha −1 with fermentable sugar yields ranging from 2.9 to 3.8 t ha −1. If hydrolyzed stalk pith and rind were included, potential fermentable sugars yields exceeded 8.0 t ha −1 plus greater than 2.0 t ha −1 of xylose which now can be fermented to ethanol by Pachysolen tannophilus. Because of the rapid deterioration of sorghum stalks following frost, the effective harvest season length in central Ohio was 40–50 days. Sorghum can become a promising raw material for ethanol production only if technologies can be developed to hydrolyze efficiently and convert all sugars from the stalk fiber to ethanol and to extend the length of the processing season.