Pretreatment bioethanol

Biocatalytic conversion of lignocellulose into bioethanol, which requires upgrading of existing processes of fermenting sugars by using enzymatic-enhanced pretreatment of (hemi)cellulose. New, improved biocatalysts are needed for this route. 

Currently, cellulosic biomass use is very hmited due to the expensive pretreatment required for breaking the crystalline stractnre of cellnlose. Bioethanol is already an established commodity due to its ongoing non-fuel uses in beverages, and in the manufactnre of pharmaceuticals and cosmetics. In facf ethanol is the oldest synthetic organic chemical used by mankind. Table 3.3 shows ethanol production in different continents (Demirbas, 2008b). 

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 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). 

Index Entries Com stover pretreatment steam explosion hydrolysis bioethanol. 

The use of recombinant microorganisms for cofermentation is one of the most promising approaches in the field of bioethanol production, though their use for large-scale industrial processes still requires fine-tuning of the reliability of the entire process (2). The technical hurdles of cofermentation increase when real biomass hydrolysates have to be fermented. In fact, whatever the biomass pretreatment, the formation of degradation byproducts that could inhibit the fermentation usually requires the addition of a further detoxification step. Therefore, the production of ethanol from hydrolysates should be considered in its entirety, from the optimal pretreatment to the choice of the proper fermentation process. 

Hsu, T.-A. (1996) Pretreatment of Biomass, in Handbook on Bioethanol Production and Utilisation, C.E. Wyman (Ed.), Taylor Francis, London. 

In contrast, the energy gain of ethanol fermentation from a cellulose-based crop was estimated at only 10% [31]. A fife cycle assessment of bioethanol from wood came to a similar conclusion [32]. This unsatisfactory outcome mainly results from the energy-intensive pretreatment with steam explosion, such as is used by Iogen [16]. The replacement of the latter by COz explosion [33] may redress the energetic balance. 

Kejrwords Maize silage Bioethanol Lignocellulose Pretreatment ... 

Bioethanol produced from pretreatment and microbial fermentation of biomass has great potential to become a sustainable transportation fuel in the near future [1]. Brazil and the United States are the largest producers of ethanol for transport, accounting for about 90% of world production. Both coimtries currently produce about 16 billion liters per year with a displacement of 40% of gasoline use in Brazil but only 3% in the United States with... 

In the present study, pretreatment of whole-crop maize silage was studied with the aim of optimizing the bioethanol process. The influence of temperature, time, and pH on sugar recovery and yield after pretreatment and enzymatic hydrolysis was studied as well as the ethanol yield in simultaneous saccharification and fermentation (SSF) with S. cerevisiae. 

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. 

K.P. Yoon, Method for pretreating biomass to produce bioethanol, US Patent 8 278 080, assigned to Industry Academic Cooperation Foundation Keimyung University (Daegu, KR), October 2, 2012. 

Alvira P, Tomas-Pejo E, Ballesteros M, Negro MJ. (2010). Pretreatment technologies for an efficient bioethanol production process based on enzymatic hydrolysis a review. Bioresour Technol, 101,4851 861. 

Chaudhary G, Singh LK, Ghosh S. (2012). AlkaUne pretreatment methods followed by acid hydrolysis of saccharum spontaneum for bioethanol production. Bioresour Technol, 124, 111-118. 

Chen X, Shekiro J, Franden MA, Wang W, Zhang M, Kuhn E, Johnson DK, Tucker MP. (2012). The impacts of deacetylation prior to dilute acid pretreatment on the bioethanol process. Biotechnol Biofuels, 5, 8-22. 

Galbe M, Zacchi G. (2007). Pretreatment of lignocellulosic materials for efficient bioethanol production. Biofuels, 108, 41-65. 

Mirahmadi K, Kabir MM, Jeihanipour A, Karimi K, Tahetzadeh M. (2010). Alkaline pretreatment of spruce and birch to improve bioethanol and biogas production. Bioresources, 5, 928-938. 

The impacts of deacetylation prior to dilute acid pretreatment on the bioethanol process. Biotechnol Biofuels, 5, 8. 

US 0.29/L and US 0.53/L, respectively (Balat, 2011). In 2011, NREL (Colorado, USA) published the detailed report Process Design and Economics for Biochemical Conversion of Lignocellulosic Biomass to Ethanol (Humbird et al.. Mar. 2011). The NREL process design converts corn stover to ethanol by dilute-acid pretreatment, enzymatic saccharification, and co-fermentation, and with a minimum ethanol selling price (MESP) of US 2.15/gal (US 0.57/L calculated) by 2012 conversion targets (Table 7.3). In the report, the biomass amount processed is 2205 dry ton/day at 76% theoretical ethanol yield (79 gal/dry ton). It is expected that this MESP will become the standard for the cost of cellulosic bioethanol. 

Rabelo SC, Filho RM, Costa AC. (2009). Lime pretreatment of sugarcane bagasse for bioethanol production. Appl Biochem Biotechnol, 153, 139-153. 

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