Published: March 1982
This report concerns the economics of the fermentation of biomass to produce ethanol for making gasohol.
Biomass, as defined by the United Nations Institute for Training and Research, includes all above-ground, below-ground, and aquatic plant materials. Moreover, secondary products generated from these plant materials, such as paper and municipal solid wastes have also been considered as biomass by many. In this report, biomass is divided into three main classes according to the type of carbohydrates available in them for conversion to ethanol: viz., starch, sugars, and cellulose. One representative feedstock is evaluated for each class. For starch, corn is used because it is one of the common crops in the world, especially in the United States. Although molasses is probably the most frequently used sugar feedstock for ethanol fermentation, sugar beets are used in this report for two reasons: (1) molasses was used for the production of ethanol in Section 5, PEP Report No. 95, Fermentation Processes, and (2) the process economics for using molasses can be approximated from the process economics for using sugar beets by deleting the part of the process in which a sugar solution is produced from the sugar beets and adjusting for the raw material cost. We chose wood as the representative cellulosic feedstock also for two reasons: (1) wood is the only cellulosic feedstock that has been used commercially on a large scale, and (2) an agricultural residue (corn residue) was used for the production of ethanol in Section 7, PEP Report No. 53A, Synthetic Ethanol and Isopropanol.
The report also includes a general review of the properties and performance of gasohol and a preliminary economic evaluation of a novel ethanol recovery process, viz., liquid carbon dioxide extraction.
Technical information for the study was obtained from patents, publications, and non-confidential communications with technology and equipment vendors.