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Category: Applied and Industrial Microbiology
Bioethanol Production from Lignocellulosics: Some Process Considerations and Procedures, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555816827/9781555815127_Chap43-1.gif /docserver/preview/fulltext/10.1128/9781555816827/9781555815127_Chap43-2.gifAbstract:
The current emphasis on environmentally friendly liquid transportation fuels has caused a renewed interest in bioethanol and, in particular, lignocellulosic feedstocks for the production of bioethanol. As a result, research into the development of an economic process for the bioconversion of lignocellulosics has accelerated. The primary areas of research crucial to improved process economics consist of feedstock selection, pretreatment, hydrolysis of the pretreated feedstocks, and developing an optimized fermentation process that uses newly engineered ethanologens capable of utilizing various biomass-derived sugars. Various levels of cellulose, hemicellulose, lignin, ash, silica, nitrogen, and moisture will require various pretreatment conditions and chemicals to ensure the most optimum pretreatment for that feedstock. The various pretreatments range from seconds for dilute acid, ammonia fiber explosion (AFEX), and steam explosion to days and weeks for lime pretreatment. Acid pretreatments include both processes featuring the addition of acids and processes without added acids in which the pH is lowered due to release of acetic acid in the course of pretreatment. Pretreatments using bases, such as AFEX, lime pretreatment, and ammonia recycle percolation alone or followed by a successive treatment with hydrogen peroxide, work mainly by swelling the biomass and modifying or solubilizing the hemicellulose and lignin. The enzyme products can be analyzed on silica thin-layer chromatography plates, where sugars are visualized by sulfuric acid charring at high temperature. Lignocellulosic hydrolysate fermentation or bioconversion may be achieved by either solid-state or submerged-liquid fermentation.
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Severity factor impact on solubilization and arabinose release from the corn fiber hull hemicellulose arabinoxylan.
Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of commercially available cellulosic enzymes. Lane 1, molecular mass marker; lanes 2 to 6, commercial xylanases; lanes 7 to 11, commercial cellulases.
Ternary plot for enzyme blend optimization. Three enzymes, each with 10 concentrations, can be tested and plotted in the same experiment. Product (glucose or other sugars) concentration is plotted on the graph, and each line represents a concentration range.
Chromatogram of seven standard sugar mixtures and internal standard showing their retention times (RT) in minutes. RT 12.84 = arabinose; RT 14.18 = xylose; RT 15.92 = fructose; RT 21.41 = mannose; RT 23.27 = galactose; RT 25.79 = glucose; RT 35.17 = inositol (internal standard); RT 37.90 = sucrose; and RT 39.27 = cellobiose. (Courtesy of F. Agblevor from reference 3 .)
Chromatogram of pretreated corn stover liquid fraction showing three regions of unknown compounds (0 to 10 min), monomeric sugars (10 to 30 min), and oligomeric sugars (30 to 45 min). (Courtesy of F. Agblevor from reference 3 .)
Cascade testing: illustration of a continuous setup for testing of ethanologens on a hydrolysate stream derived from a lignocellulosic. Prop, propagation; Enz, enzyme; BW, beer well; F V, fermentation vessel.
Compositions of various biomass feedstocks
Pretreatment selection and impact of pretreatment on lignocellulosics
Some commercial enzyme products available for testing
Properties of leading candidate microorganisms for industrial production of ethanol from xylose
Evaluation scheme for improved ethanologens for scale-up testing