Bioethanol yields

Figure 9.1 reports the prospective average biofuel yield from different crops in EU-15 over 2005-2010 (GJ ha-1) [3]. Bioethanol yield in EU-15 normally is higher than the biodiesel yield, e.g., a smaller land area will be needed to produce... 

In Brazil, the best bioethanol yield from sugarcane is 7.5 m ha (16). However, bioethanol has only 64% of the energy content of biodiesel. This would require planting sugarcane over a very large area, but may be even not available (17). 

Saccharomyces cerevisiae is the dominant microorganism in the first generation of fuel ethanol production. In recent years, the worldwide bioethanol production reached around 80 billion liters per year. In a typical industrial scale bioethanol fermentation process using Saccharomyces cerevisiae, around 8-14% (v/v) ethanol is produced and the glucose to bioethanol yield is usually over 90% of the theoretical yield. In some processes, simultaneous saccharification and fermentation is applied, in which a-amylase/glucoa-mylase is mixed with Saccharomyces cerevisiae and starchy raw materials. Most of yeast cells harvested in the fermentation are recycled and sent back in order to enhance the cell concentration in the fermenter. Around 5-10% yeast cells end up in Dried Distillers Grains with Solubles (DDGS), which could be sold as animal feed. 

Borines M, De Leon R, McHenry M. Bioethanol production from farming non-food macroalgae in Pacific island nations chemical constituents, bioethanol yields, and prospective species in the Philippines. Renew Sustain Energy Rev 2011 15 4432. 

Wood chips can also be utilized as such to produce bioethanol. The cellulose and hemicellulose material is hydrolyzed in the presence of acids (H2SO4, HCl, or HCOOH) or enzymes to yield glucose and other monosaccharides [16]. Lignin is separated by filtration as a solid residue and the monosaccharides are fermented to ethanol, which, in turn, is separated from water and catalyst by distillation. Ethanol can be used not only as energy source but also as a platform component to make various chemicals, such as ethene and polyethene. Today green acetaldehyde and acetic acid from wood-derived bioethanol is manufactured by SEKAB Ab, at the Ornskoldsvik Biorefinery of the Future industrial park. 

Table 9.2 Yields of bioethanol from the most common crops. (Adapted from [2]).

Notably, however, any comparison of biodiesel vs. bioethanol should be done with great caution, because analysis of an industry such as that related to biofuels is a very complex task and all conclusions are country dependent. It may be interesting, however, to compare the energy balance and environmental impact in producing biodiesel from oilseed rape and bioethanol from wheat crops [4], Table 9.3 reports this comparison. The energy balance for bioethanol is more positive than for biodiesel, in particular when straw is utilized, mainly due to the higher yield... 

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. 

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. 

Lindhauer (2005) recently carried out pilot-plant scale trials of an H202-based alkali extraction process, where a product was separated that had a purity of 70-80% arabinoxylans and a yield of 50% of the initial wheat bran. This process is expected to be commercialised as an integrated plant together with bioethanol production. 

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