Industrial Scale-Up of pH-Controlled Liquid Hot Water Pretreatment of Corn Fiber for Fuel Ethanol Production

Abstract

The pretreatment of cellulose in corn fiber by liquid hot water at 160 degrees C and a pH above 4.0 dissolved 50% of the fiber in 20 min. The pretreatment also enabled the subsequent complete enzymatic hydrolysis of the remaining polysaccharides to monosaccharides. The carbohydrates dissolved by the pretreatment were 80% soluble oligosaccharides and 20% monosaccharides with <1% of the carbohydrates lost to degradation products. Only a minimal amount of protein was dissolved, thus enriching the protein content of the undissolved material. Replication of laboratory results in an industrial trial at 43 gallons per minute (163 L/min) of fiber slurry with a residence time of 20 min illustrates the utility and practicality of this approach for pretreating corn fiber. The added costs owing to pretreatment, fiber, and hydrolysis are equivalent to less than 0.84 dollars/gal of ethanol produced from the fiber. Minimizing monosaccharide formation during pretreatment minimized the formation of degradation products; hence, the resulting sugars were readily fermentable to ethanol by the recombinant hexose and by pentose-fermenting Saccharomyces cerevisiae 424A(LNH-ST) and ethanologenic Escherichia coli at yields >90% of theoretical based on the starting fiber. This cooperative effort and first successful trial opens the door for examining the robustness of the pretreatment system under extended run conditions as well as pretreatment of other cellulose-containing materials using water at controlled pH.