Bioethanol Production from Lignocellulosics: Some Process Considerations and Procedures

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.