The need for development of sustainable technology that employs locally available sources of energy feedstocks for the production of motor fuels and valuable chemicals is on the rise. This can be attributed to the instability in the global energy and hydrocarbon feedstock markets. Sustainability, low power consumption and minimal carbon gas emission are among the contributing qualities towards this move. Lignocellulosic feedstock sources for biorefineries include energy crops, forestry and agricultural waste and residues which are made up of complex biopolymers such as cellulose, lignin and hemicellulose. Amongst, cellulose is relatively easy to process. Conversely, a flaw in its processing demands the need for the catalyst to be separated from the products and regenerated after the reaction which, however, can be averted by using carbon-based solid-acid catalysts to hydrolyze the cellulose.
Ksenia Sorokina and colleagues at the Boreskov Institute of Catalysis, in Russia, proposed a study to explore the potential of combining catalytic and biotechnological methods in a cellulose biorefinery. They aimed at examining the combination of one pot catalytic cellulose conversion into 5-hydroxymethylfurfura and glucose using a solid-acid catalyst and biotechnological glucose fermentation into ethanol with thermotolerant yeasts. Their goal was to produce 5-hydroxymethylfurfural and Ethanol. Their work is now published in the peer-reviewed journal, ChemSusChem.
The researchers commenced their empirical procedure by hydrolyzing the mechanically activated microcrystalline cellulose in the presence of a solid carbon-based catalyst that had been preliminarily oxidized with wet air. They then recovered the 5-hydroxymethylfurfural by isobutanol extraction from the mixture and the remaining sugar mixture was neutralized and concentrated for subsequent fermentation. The research team then selected the most effective ethanol producers by screening of the isolated thermotolerant yeast strains that were able to grow at 400C.
The authors of this paper observed that hydrolytic dehydration of the mechanically activated microcrystalline cellulose over the carbon-based mesoporous Sibunt-4 catalyst resulted in moderate yields of glucose and 5-hydroxymethylfurfural. The 5-hydroxymethylfurfural was extracted from the resulting mixture with isobutanol and subjected to ethanol fermentation. The team also noted that among the isolated yeast strains, some exhibited high thermotolerance and resistance to inhibitors found in the hydrolysates.
Herein, a comprehensive study on the potential of combining catalytic and biotechnological techniques in cellulose biorefinery with an aim of producing 5-hydroxymethylfurfural and Ethanol has been presented. It has been shown that the use of the strains K. marxianus and O. polymorpha for the fermentation of processed catalytic cellulose hydrolysate has a relatively high efficiency since the strains are resistant to fermentation inhibitors. Therefore, the proposed combination of the catalytic processing of mechanically activated cellulose for the production of 5-hydroxymethylfurfural and subsequent fermentation of the extracted hydrolysate with thermotolerant yeasts is a promising alternative technique for ethanol production by fermentation and can be used to produce other valuable substances, such as bio-acids or bio-alcohols.
Ksenia N. Sorokina, Oxana P. Taran, Tatiana B. Medvedeva, Yuliya V. Samoylova, Alexandr V. Piligaev, and Valentin N. Par. Cellulose Biorefinery Based on a Combined Catalytic and Biotechnological Approach for Production of 5-HMF and Ethanol. ChemSusChem 2017, volume 10, pages 562 – 574.
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