Fuel Alcohol Production from Agricultural Lignocellulosic Feedstocks

Abstract

A two-stage, low-temperature, ambient pressure, acid hydrolysis process that utilizes separate unit operations to convert hemicellulose and cellulose in agricultural residues and crops to fermentable sugars is being developed and tested by the Tennessee Valley Authority and the U.S. Department of Energy (DOE) in Muscle Shoals, Alabama. In laboratory and bench-scale evaluations, the conversion and recovery efficiencies of sugars from hemicellulose and cellulose fractions of corn stover were greater than 90%percnt;. Sugar product concentrations of more than 10%percnt; glucose and 10%percnt; xylose were achieved. In these tests, furfural and hydroxymethyl furfural levels in the sugar solutions never exceeded 0.02gll00 mL, which is far below the levels shown to inhibit fermentation. Based on the results of the bench-scale tests, TVA built a one-of-a-kind acid hydrolysis experimental plant to demonstrate the concepts of low-temperature acid hydrolysis on a much larger scale. The experimental plant was coupled to an existing 10 gal/h fermentation and distillation facility. Plant tests using corn stover have been conducted for more than a year and conversion efficiences have equaled those achieved in the laboratory. Laboratory tests to determine the potential for low-temperature acid hydrolysis of other feedstocks-including red clover, alfalfa, kobe lespedeza, winter rape, and rye grass-are being conducted. Where applicable, process modifications to include extraction before or after hydrolysis also are being studied. This paper describes the experimental plant and process, results obtained in the plant, results of alternative feedstocks testing in the laboratory, and a plan for an integrated system that will produce other fuels, feed, and food from crops grown on marginal land.