Bioethanol enzyme hydrolysis

Figure 2 An illustration of the various research activities underway to develop the next generation bioethanol plant. The 3 key areas of R D are in pretreatments, enzyme hydrolysis andfermentations. Significant efforts focus on process engineering cmd plant designs with the following at the core SHF -separate hydrolysis and fermentation, SSF - a simultaneous saccharification-fermentation, or SSCF - a simultaneous saccharification-cofermentation.

The compactness and complexity of (ligno)cellulose makes it much more difficult to attack by enzymes with respect to starch. Therefore, the cost of bioethanol production is higher [23], To be cost competitive with grain-derived ethanol, the enzymes used for biomass hydrolysis must become more efficient and far less expensive. In addition, the presence of non-glucose sugars in the feedstock complicates the fermentation process, because conversion of pentose sugars into ethanol is less efficient than conversion of the hexose sugars. 

Bioethanol can be produced from a large variety of carbohydrates with a general formula of (CHjO) . Chemical reaction is composed of enzymatic hydrolysis of sucrose followed by fermentation of simple sugars. Fermentation of sucrose is performed using commercial yeast such as Saccharomyces cerevisiae. First, invertase enzyme in the yeast catalyzes the hydrolysis of sucrose to convert it into glucose and fmctose. 

Glnco-amylase enzyme converts the starch into D-glucose. The enzymatic hydrolysis is then followed by fermentation, distillation and dehydration to yield anhydrous bioethanol. Com (60-70% starch) is the dominant feedstock in the starch-to-bioeth-anol industry worldwide. 

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). 

The cost of enzyme preparations has been decreasing in recent years however, it continues to affect considerably the price of ethanol obtained from cellulosic raw materials. Increased enzymatic hydrolysis efficiency is one way to reduce the enz)me cost in bioethanol production. Another method is enzyme recycle and reuse. Immobilization of biocatalysts allows for their economic reuse and development of continuous bioprocess. Although immobilization poses problems of substrate accessibility and binding for most endo- and exocellulases, P-glucosidase exhibits characteristics amenable to immobilization, such as activity on soluble substrates and the lack of a carbohydrate-binding module. Among the possible approaches, immobilization of (J-glucosidase is one prospective solution to the problem. 

The results presented in this paper were only a very preliminary study of pretreatment of maize silage. Trials should be made at lower temperatures to examine if more energy could be saved in the process. It would also be interesting to determine the content of starch and cellulose separately by enzymatic hydrolysis, instead of total glucan as is the case in this study. Also, enzymatic hydrolysis and SSF using low enzyme loadings (of both cellulases and amylases) should be made to fully see the potential of this promising raw material for bioethanol production. 

The liquefaction and saccharification steps are required for the starchy crops. In these two processes, a-amylase and glucoamyiase are added respectively to convert starch into glucose. These two processes are also collectively known as hydrolysis. It should however be noted that some bioethanol plants use acid instead of enzymes for the hydrolysis process. 

Biological enzymatic conversion of glucose by fermentation also has been extensively studied for the production of many products one of the most important is bioethanol. Many bacteria and fungi could produce enzymes for the hydrolysis of cellulosic material. These microorganisms can be aerobic or anaerobic, mesophillic or thermophillic. ... 

The search for new and cheap substrates for the production of bioenergy and other biotechnological products is continuously demanded. Pal et al. reported that the mustard stalk and straw served as an alternative substrate for the production of lignocellulolytic enzymes and as a source for saccharification. The biomass from halophyte plants such as Retama retam and Juncus maritimus were used as the substrate for bioethanol production. The combined effect of thermochemical pretreatment and enzymatic hydrolysis of kitchen wastes for maximizing the production of fermentable soluble sugars has been described previously. ... 

Another question regards the cost of the enzymes, which are extremely important for the biochemical production of the sugars that will eventually be fermented, thus producing bioethanol. They are indispensable for breaking down the cellulose, a process better known as enzymatic hydrolysis. However, the price of these enzymes is high. Also at the same time, ceUulase and hemiceUulose, which are used in the production of cellulosic ethanol, are more expensive when compared to their first-generation counterparts. For instance, enzymes required for com ethanol production cost US 2.64—5.28 per cubic meter of ethanol produced, while those needed for cellulosic ethanol production are projected to cost US 79.25 (Sainz, 2011). 

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