Bioethanol production

In the European Union, ethanol is consumed in Spain, France, Sweden and Germany, especially after conversion into ETBE (ethyl tert-butyl ether), except in Sweden, but its use is increasing in all the other countries. New uses of bioethanol, e.g., in ethanol-direct fuel cells or as raw material for other chemicals, will further expand bioethanol use and production. Table 9.1 summarizes bioethanol production in different countries by 2004 [1], Owing to political decisions (EU directive setting at 5.75% the proportion of biofuels in fuels) and incentive taxation... 

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. 

The expansion of the market, however, will depend considerably on the possibility of an efficient use of other biomass sources, particularly lignocellulosic-based materials, fast growing dedicated crops, and waste resources. Effective integration of bioethanol production into biorefineries will also be a key aspect in decreasing the price by a better use of all the components of biomass. 

Bioethanol production by yeasts is widely used for biodegradation of potato. However, yeasts cannot ferment starch directly, and a two-step enzymatic reaction to glucose is necessary. Different potato wastes such as industrial residues, low-grade potatoes, and spoiled potatoes can be used for acetone/ethanol production (Nimcevic et al., 1998). They used whole potato media... 

Wyman, C E. Handbook on Bioethanol Production and Utilization, Taylor Francis, Inc, Philadelphia, PA. 1996. 

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 simultaneous bioconversion of mixed sugar syrups is one of the most ambitious challenges in the field of bioethanol production. Different productivities and ethanol-tolerance of the yeasts used in the fermentation of glucose and xylose (the most abundant biomass sugars) have led... 

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. 

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. 

Kim, S. and Dale, B.E. 2004. Global Potential Bioethanol Production from Wasted Crops and Crop Residues. Biomass Bioenerg., 26, 361-375. 

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

Table 15.6 Potential of the most common raw materials for bioethanol production.

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