Tuesday, May 3, 2011
Production of bioethanol from renewable sources is one way to meet the demand for alternatives to fossil fuels. Currently, bioethanol is produced from either sugarcane or from starch-containing materials such as corn or wheat. However, further expansion of bioethanol production requires the use of other materials. Second-generation bioethanol (2G) can be produced from, in principle, any cellulose-containing material. There is a wide array of potential raw materials for 2G bioethanol, including forest and agricultural residues, e.g. softwood, straw, corn stover, sugarcane bagasse etc. An advantage is that many of these materials are today considered as waste materials, which instead can be used to add value to the overall bioethanol process. The lignocellulosic materials contain cellulose and hemicellulose, which need to be hydrolyzed to be available for further processing to bioethanol. It is usually necessary to perform some form of pretreatment to access these polymers.
Since lignocellulosic materials is composed of many constituents, with typically about 30–60% cellulose and 15–30% hemicellulose it is necessary to design a process which generates high-enough sugar concentrations to get a reasonable ethanol concentration after fermentation (above 3-5%). A high ethanol concentration prior to distillation is of vital importance for the overall process economics. Therefore, high-solids loadings during hydrolysis are required. In this study, enzymatic hydrolysis of steam-pretreated spruce at high water-insoluble solids (WIS) loadings has been performed. The influence of, e.g., added enzyme activity, WIS content and mixing conditions will be presented.