Abstract
Grain sorghum is a potential feedstock for fuel ethanol production due to its high starch content, which is equivalent to that of corn, and has been successfully used in several commercial corn ethanol plants in the United States. Some sorghum grain varieties contain significant levels of surface wax, which may interact with enzymes and make them less efficient toward starch hydrolysis. On the other hand, wax can be recovered as a valuable co-product and as such may help improve the overall process economics. Sorghum grains also contain lignocellulosic materials in the hulls, which can be converted to additional ethanol. An integrated process was developed, consisting of the following steps: 1. Extraction of wax with boiling ethanol, which is the final product of the proposed process; 2. Pretreatment of the dewaxed grains with dilute sulfuric acid; 3. Mashing and fermenting of the pretreated grains to produce ethanol. During the fermentation, commercial cellulase was also added to release fermentable sugars from the hulls, which then were converted to additional ethanol. The advantages of the developed process were illustrated with the following results: (1) Wax extracted (determined by weight loss): ~0.3 wt % of total mass. (2) Final ethanol concentration at 25 wt % solid using raw grains: 86.1 g/L. (3) Final ethanol concentration at 25 wt % solid using dewaxed grains: 106.2 g/L (23.3% improvement). (4) Final ethanol concentration at 25 wt % solid using dewaxed and acid-treated grains (1 wt % H2SO4) plus cellulase (CTec2): 117.8 g/L (36.8% improvement).
Highlights
Ethanol has attracted attention worldwide as a clean and renewable liquid fuel
Each sample was injected twice and the average results are reported. Extraction because it is the final product in an ethanol plant and is readily available
Ethanol was selected as the solvent for wax extraction because it is the final product in an ethanol plant and readily available
Summary
Ethanol has attracted attention worldwide as a clean and renewable liquid fuel. The recent low oil prices encouraged record gasoline consumption, which translated to increased demand for ethanol for use in E10 (10% ethanol, 90% gasoline) as well as higher blends such as E15 and E85. States currently is the largest producer of fuel ethanol in the world. More than 90% of all the ethanol produced in the United States comes from corn. Grain sorghum has attracted strong interest because of high starch contents, which are equivalent to those of corn; low requirements for water and fertilizer; and high heat and drought tolerance. These characteristics allow sorghum to be grown in dry climates and regions where corn cannot thrive [3]. Sorghum is used in at least nine commercial ethanol plants in the United States, mostly as an adjunct feedstock to corn [1]
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