Restrictions of Bioethanol Production
An attractive feedstock available in large amounts is lignocellulosic biomass, such as herbaceous and woody plants, agricultural and forestry residues, and a large portion of municipal solid waste and industrial waste streams. Cellulosic biomass is a complex mixture of carbohydrate polymers. Therefore, hydrolysates will contain hexoses (C6 sugars) and pentoses (C5 sugars), including glucose, galactose, mannose, D-xylose and L-arabinose. Because the feedstock represents a significant portion of all process costs, an economical fermentation process will require rapid and efficient conversion of all sugars present.
A lack of microorganisms that will efficiently convert hexoses and pentoses to ethanol is a major constraint to the economical conversion of biomass. Most industrial ethanol fermentations use the yeast Saccharomyces cerevisiae (S. cerevisiae) as it exhibits fast sugar consumption, high yields and ethanol tolerance. Although S. cerevisiae is able to ferment hexoses rapidly and efficiently, it is unable to ferment pentose sugars, and to use these sugars for growth.
The pentose sugars D-xylose and L-arabinose are the most abundant hemicellulosic sugars. Prof. Boles has recently constructed industrial yeast strains able to ferment both pentose sugars efficiently to ethanol. These yeast strains and the knowledge derived from his work should greatly enhance the development of an efficient biomass-to-ethanol fermentation process.
Approach of BUTALCO
C5 sugars in bioethanol fermentation are becoming increasingly important as there is pressure on bioethanol margins and the usage of C5 sugars can significantly improve the yield and cost position of existing bioethanol producers using corn, wheat or sugar cane as raw material.
Based on past extensive worldwide research, the patent situation in the field of using C5 sugar for the fermentation is complex and the usage through bioethanol companies difficult. Therefore, BUTALCO is currently developing a new process to use C5 sugars for bioethanol fermentation. The first patent applications have been filed and the aim is to licence this technology to bioethanol producers. |
