Suchergebnisse

Bioethanol produced from renewable agricultural recourses is currently the most promising biofuel. In a lot of developed countries in Europe and in USA the use of bioethanol as an alternative fuel or a gasoline supplement in the amount of up to 15 % is highly recommended or even required as an ecologically favorable fuel oxygenate. Concerning EU, in November 2001 a new directive was accepted, that requires of members states to establish legislation about utilization of fuels from renewable resources. In 2005. this utilization should cover 2% of the total fuel consumption. This quota is expected to increase to 5.75% in 2010. and furthermore. In our country one of the most suitable agricultural raw material for bioethanol production is corn. Two-steps enzymatic hydrolysis of corn meal by commercially available a-amylase (Termamyl 120 L, Novozymes) and amyloglycosidase (Supersan 240L, Novozymes) and ethanol fermentation of the hydrolyzates by Saccharomyces cerevisiae yeast (culture collection BIB-TMF, Belgrade) was studied in this paper. The conditions of starch hydrolysis such as substrate and enzyme concentration and the duration of time required for enzymatic action were optimized taking into account both the effects of hydrolysis and ethanol fermentation. The results obtained showed that the corn meal hydrolyzates were good substrates for ethanol fermentation by Saccharomyces cerevisiae. The yield of ethanol of more than 80% of theoretical was achieved with a satisfactory volumetric productivity P (g /l ×h). No shortage of fermentable sugars was observed during simultaneous hydrolysis and fermentation. On this way, the savings in time and energy could be realized. By increasing the inoculum size form 1 % to 2 % of Saccharomyces cerevisiae the fermentation time could be reduced from 48 to 32 hours respectively. ; U radu je ispitivan postupak dvojno enzimske hidrolize kukuruznog brašna pomoću komercijalnih enzima a-amilaze (Termamyl 120L, Novozymes) i amiloglukozidaze (Supersan 240L, Novozymes) i fermentacija ...

Processes of bioethanol production currently applied all over the world are reviewed in this paper. Attention is focused on potentially cheap biomass sources, as well as the most important operating factors controlling the progress and result of saccharification and fermentation reactions and affecting the yield of fermentable sugars and ethanol, respectively, such as: the type and concentration of acid, the type of enzyme, the type of working microorganism, operating temperature, duration time and pH. The hydrolysis conditions, namely duration time, temperature and sulfuric acid concentration, were combined in a single parameter, known as the "combined severity" (CS), in order to estimate the efficiency of bioethanol production from biomass. When the CS increases, the yield of fermentable sugars also increases. The decrease in the yield of monosaccharides coincides with the maximum concentrations of by-products, such as furfural and 5-hydroxymethylfurfural, which are well-known as yeast inhibitors. The highest ethanol yields has been obtained using the yeast Saccharomyces cerevisiae. With low oil prices and political reluctance to implement carbon taxes, fuel-ethanol production will remain uncompetitive unless some other form of cost reduction can be made, such as feedstock preparation costs. ; U ovom radu razmotreni su procesi dobijanja etanola iz biomase. Naglasak je stavljen na polazne sirovine, značajne faktore koji kontrolišu tok i efekte reakcija ošećerenja i fermentacije i utiču na prinos fermentabilnih šećera i etanola, respektivno, kao što su: vrste i koncentracije kiselina, vrste enzima, vrsta proizvodnog mikroorganizma, temperatura, pH i vreme trajanja reakcije. Radi sagledavanja perspektive industrijske proizvodnje bioetanola ocenjena je ekonomičnost celokupnog postupka proizvodnje bioetanola iz biomase.