Cellulose bioethanol production

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. 

Corn stover, a well-known example of lignocellulosic biomass, is a potential renewable feed for bioethanol production. Dilute sulfuric acid pretreatment removes hemicellulose and makes the cellulose more susceptible to bacterial digestion. The rheologic properties of corn stover pretreated in such a manner were studied. The Power Law parameters were sensitive to corn stover suspension concentration becoming more non-Newtonian with slope n, ranging from 0.92 to 0.05 between 5 and 30% solids. The Casson and the Power Law models described the experimental data with correlation coefficients ranging from 0.90 to 0.99 and 0.85 to 0.99, respectively. The yield stress predicted by direct data extrapolation and by the Herschel-Bulkley model was similar for each concentration of corn stover tested. 

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. 

Materials destined for cellulosic ethanol production have been evaluated, and they were found to contain low relative concentrations of fatty acids. Relative to the amount of ethanol produced, the amount of fatty acid byproduct is actually quite significant. Assuming a t q)ical yield of 20% ethanol and 2% fatty acid means that a minimum of 10% of an ethanol producer s high value products could be in the form of fatty acids (59). It has been claimed that microalgal biodiesel is a better alternative than bioethanol from sugarcane (13). 

Jeon YJ, Xnn Z, Rogers PL. (2010). Comparative evaluations of cellulosic raw materials for second generation bioethanol production. Lett Appl Microbiol, 51, 518-524. 

As cellulose only represents 30-40% of the lignocellulosic biomass, the utilization of only glueose in the fermentation would undeniably have an effect on the overall biomass to ethanol conversion yield. Therefore, it is necessary to eonsider the utilization of the hemicellulose hydrolysate in the development of the advanced generation bioethanol production process. ... 

For example, in a (thermochemical) biorefinery, biomass is converted into energy carriers such as transportation fuels (e.g., ethanol), heat, and power and/or chemicals. In terms of energy content, the amount of biomass for (transportation) fuels and CHP (e.g., by combustion) is much higher than the amount used for the production of chemicals. However, in terms of added value, chemicals can provide a significant contribution to the overall cost effeaiveness of the refinery. When the main product of a biorefinery is (hemi) cellulose bioethanol, the lignin ends up in a residue that mostly is used as a fuel to generate heat. The economics of the biorefinery will benefit much from the valorization of this lignin-rich residue to value-added aromatic chemicals. 

An exhaustive economic analysis for the production of cellulose nanowhiskers as a coproduct in an ethanol biorelinery and an ASPEN Plus-based process model (http //www.aspentech.com/core/aspen-plus.cfm) was developed to evaluate ethanol production from wheat straw. All the collected data on cellulose nanocrystals in terms of production, characterization, and application suggest that this nanomaterial could be easily extrapolated to bioethanol production (Duran et al. 2011). 

Du YY, Fang HH, Zheng PW (2013) Porous sepiolite/starch composites Preparation, structure and absorption properties. Adv Mat Res 1937 634-638 Duquesne E, Moins S, Alexandre M, Dubois P (2007) How can nanohybrids enhance polyester/ sepiolite nanocomposite properties Macromol Chem Phys 208 2542-2550 Duran N, Lemes AP, Duran M, Freer J, Baeza J (2011) A mini review of cellulose nanocrystals and its potential integration as co-product in bioethanol production. J Chil Chem Soc 56 672-677... 

Ethanol production by F. oxysporim F3 was considerably affected by pH of both aerated and non-aerated cultures [64], Optimum values were obtained when the pH of the aerated and non-aerated culture of cellulose were 5.5 and 6.0, respectively. It could be due to the changes induced by low pH to systems involved in cellulose hydrolysis, utilization of sugars for bioethanol production, or both [64], At optimum pH, no insoluble cellulose could be detected in the culture medium. On the other hand, low pH of the aerated culture resulted in low ethanol yield. Adjustment of the initial pH in non-aerated growth to an optimal pH was established to be optimal for both P-glucosidase activity and ethanol production, as a consequence the conversion time resulted to about half [65],... 

Fossil energy use This follows similar patterns to the total energy use, that is, for petroleum, coal, and natural gas. Ethanol derived from cellulose (bioethanol) exhibits a high total energy use but ethanol production involves the burning of lignin, a non-fossil energy for heat. 

Hsu,C. L, Chang, K. S.,Lai,M. Z, Chang, T. C., Chang, Y.H., Jang, H.D.Pietreatment and hydrolysis of cellulosic agricultural wastes with a cellulase-producing Streptomyces for bioethanol production. Biomass and Bioenergy 2011, 35,1878-1884. 

Watanabe, T. Potential of cellulosic ethanol. In Lignocellulose conversion Enzymatic and microbial tools for bioethanol production, Faraco, V, Ed., Springer Verlag Berlin, 2013, pp. 1-20. 

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