Lignocellulosic enzymatic hydrolysis

Bioconversion platforms for lignocellulosics-to-ethanol are beginning to become commercially viable, but the effectiveness of the pretreatment stage should still be improved, the cost of the enzymatic hydrolysis stage decreased, and overall process efficiencies improved by better synergies between various process stages. There is also a need to improve process economics by creating co-products that can add revenue to the process. 

NREL (National Renewable Energy Laboratory). Lignocellulosic biomass to ethanol process design and economics utilizing co-current dilute add prehydrolysis and enzymatic hydrolysis for com stover. Golden, CO US (2002). Report available on web http //www.mel.gov/ docs/ fy02osti/32438.pdf... 

Draude, K. M., Kumiawan, C. B., and Duff, S. J. B., 2001, Effect of oxygen delignification on the rate and extend of enzymatic hydrolysis of lignocellulosic material, Biores. Technol.19 113-120. 

Marsden, W. L. and P. P. Gray, "Enzymatic Hydrolysis of Cellulose in Lignocellulosic Materials," CRC Critical Review Biotech. 3 (1986) 235-276. 

The production of fuel ethanol from renewable lignocellulosic material ("bioethanol") has the potential to reduce world dependence on petroleum and to decrease net emissions of carbon dioxide. The lignin-hemicellulose network of biomass retards cellulose biodegradationby cellulolytic enzymes. To remove the protecting shield of lignin-hemicellulose and make the cellulose more readily available for enzymatic hydrolysis, biomass must be pretreated (1). 

Corn stover, like lignocellulosic materials in general, is resistant to enzymatic hydrolysis, because of both the tight network in the lignocellulose complex and the crystalline structure of the native cellulose. These difficulties can be overcome by employing a suitable pretreatment (7). 

A major problem in the commercialization of this potential is the inherent resistance of lignocellulosic materials toward conversion to fermentable sugars (4). To improve the efficiency of enzymatic hydrolysis, a pretreatment step is necessary to make the cellulose fraction accessible to cellulase enzymes. Delignification, removal of hemicellulose, and decreasing the crystallinity of cellulose produce more accessible surface area for cellulase enzymes to react with cellulose (5). 

In this article, we describe the production of xylanase by T. lanuginosus IOC-4145 in semisolid cultivation using corncob as raw material in optimized conditions. Furthermore, we describe the pretreatment effect on corncob and sugarcane bagasse and the enzymatic hydrolysis of these lignocellulosic materials using the produced thermophilic xylanase. 

The enzymatic hydrolysis of soluble birchwood xylan was carried out as follows The substrate (0.5 g) was placed universal or phosphate buffer in 500 mL conical flasks, and 1500 U of crude xylanase was added to start the reaction, for a total volume of 25 mL. The hydrolysis and control reactions were accomplished at the same conditions described for enzymatic hydrolysis of lignocellulosic materials. 

Conversion of lignocellulosic material to ethanol requires hydrolysis of carbohydrate polymers to their constituent sugars. Enzymatic hydrolysis is a common approach to hydrolysis and offers the benefits of mild... 

Harvest the cellulase-containing transgenic plants at the end of the season (dry), grind this material to release enzyme, and subsequently use it in the enzymatic hydrolysis of lignocellulosic biomass for ethanol production. 

Carbohydrates would be the predominant raw materials for future biorefineries. The major polysaccharides found in nature are cellulose, hemicellulose and starch (see Chapter 1). These molecules would be mainly utilised after they are broken down to their respective monomers via enzymatic hydrolysis, thermochemical degradation or a combination of these two. Cellulose and hemicellulose, together with lignin, constitute the main structural components of biomass. Starch is the major constituent of cereal crops. This section would focus on the potential utilisation of carbohydrates and lignocellulosic biomass for chemical production. 

Eriksson, T., Borjesson, J., and Tjerneld, F. 2002. Mechanism of surfactant effect in enzymatic hydrolysis of lignocellulose. Enz. Microbial Technol., 31, 353-364. 

Conversion efficiency and robust fermentation of mixed-sugar lignocellulose-derived hydrolysates are critical for producing ethanol at low cost to realize a commercially viable biorefinery. Biomass sugars are typically released by thermochemical pretreatment followed by enzymatic hydrolysis of chopped or milled biomass. The pretreated soluble fraction of biomass is called the hydrolysate and the hydrolysate containing the insoluble... 

Aden, A., Ruth, M., Ibsen, K., Jechura, J., Neeves, K., et al., Lignocellulosic Biomass to Ethanol Process Design and Economics Utilizing Co-Current Dilute Acid Prehydrolysis and Enzymatic Hydrolysis for Corn Stover NREL Report No. TP-510-32438 available online at URL http //www.nrel.gov/publications/ National Renewable Energy Laboratory Golden, CO, June, 2002, 2002 p. 154. 

The native structure of lignocellulose, which is very complex, renders it resistant to enzymatic hydrolysis. The major component is cellulose, a pi -> 4 polymer of glucose (see Fig. 8.2 a), which accounts for 35-50% of the mass. Lignocellulose also contains 20-35% hemicellulose, a complex polymer of pentoses and hexoses and 10-25% lignin [10, 12]. Techniques to convert lignocellulose into a fermentable sugar mixture have been under development for over 20 years and are now entering use. 

Many factors influence the reactivity and digestibility of the cellulose fractions of lignocellulose materials. These factors include Hgnin and hemicellulose content, crystalhnity of cellulose, and the porosity of the biomass materials. Pretreatment of Hgnocellulosic materials prior to utiHzation is a necessary element in biomass-to-ethanol conversion processes. The objective of the pretreatment is to render biomass materials more accessible to either chemical or enzymatic hydrolysis for efficient product generation. The goals of the pretreatment are ... 

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