Cellulose conversion in dry grind ethanol plants

Dilute-acid pretreatment of distillers' grains and corn fiber

Distillers' grains and corn fiber are the coproducts of the dry grind and wet corn milling industries, respectively. Availability of distillers' grains and corn fiber at the ethanol plant and their high levels of lignocellulosic material make them attractive feedstock for conversion to ethanol. In this study, dilute sulfuric acid hydrolysis for the conversion of distillers' grains and corn fiber to monomeric sugars and the formation of furfural were investigated. The extent of solubilization of biomass beyond monomeric sugars was also monitored. Biomass loadings in the range of 5-20 wt.% at 5% intervals, acid concentrations in the range of 0.5-1.5 vol.% at 0.5% intervals, and temperatures of 120 and 140 degrees C were studied. The highest yields of monomeric sugars were observed when the least amount of biomass loading was pretreated with the highest concentration of sulfuric acid and when the temperature was 140 degrees C. For the majority of the cases under consideration, the most effective period of hydrolysis appeared to be during the initial 20-30 min of the reaction. Formation of furfural during the course of hydrolysis was significantly lower at 120 degrees C and also lower for the distillers' grains samples compared with the corn fiber samples. The total amount of the solubilized matter during the hydrolysis was significantly higher than the amount of the monomeric sugars. Analyses according to standard procedure were performed to quantify moisture, oil, carbohydrates, and ash in distillers' grains and corn fiber samples. The total carbohydrate content of distillers' grains and corn fiber were 57.7+/-2.0 and 77.0+/-1.0 wt.%, respectively. The presented results will provide a foundation for the suitability of the pretreated distillers' grains and corn fiber for enzymatic hydrolysis step.

Extraction of protein from distiller's grain

We have investigated the feasibility of extracting the oil and protein from distiller's grain (DG) to obtain a higher-valued protein-rich product and a carbohydrate-rich residue better suited for conversion to fermentable sugars. Protein extractions based on aqueous ethanol, alkaline-ethanol, and aqueous enzyme treatments were compared. Three of the methods extracted a significant amount of the protein from dried, defatted DG (DDDG). The enzymatic extraction decreased the crude protein content in the solid phase for both milled and unmilled DDDG from 41% (dry weight) to approximately 10% (dry weight) protein in the residual solid; this corresponded to extraction of 90% of the protein in the original DDDG. The alkaline-ethanol extraction was similarly effective for milled but not unmilled DG. Simple extraction with alcohol was not as effective. Amino acid analysis of each protein extract was consistent with it consisting mainly of zeins. For the protease-assisted extractions, 95% the proteins were in the form of peptides smaller than 10kDa.