Next generation solvent contributes to next generation biofuel production from biomass
Kanazawa University
In the present study, researchers of Kanazawa University, Japan, attacked this problem; they succeeded in reducing the toxicity to microorganisms by developing a novel solvent, a carboxylate-type liquid zwitterion*1, for dissolving biomass cellulose (Figure 1). The EC50, the concentration of a substance that reduces the growth of Escherichia coli to 50%, was found to be 158 g/L for the newly developed carboxylate-type liquid zwitterion, whereas the EC50 of ionic liquid*2, one of the conventional solvents of cellulose, was 9 g/L. This indicates that the novel carboxylate-type liquid zwitterion shows 17 fold lower toxicity than the ionic liquid.
With Escherichia coli that can produce ethanol, fermentation ability was examined and revealed to be almost maximal in 0.5 mol/L carboxylate-type liquid zwitterion with a final ethanol concentration of 21 g/L. On the other hand, the same experiment with the ionic liquid produced only 1 g/L ethanol. Thus, fermentation in the presence of the carboxylate-type liquid zwitterion produced 21 times more ethanol than that using the ionic liquid.
In another experiment, bagasse was used as a starting plant biomass for ethanol production without washing/separation processes. Fermentation in the presence of the carboxylate-type liquid zwitterion produced 1.4 g/L ethanol, while no ethanol was obtained with the ionic liquid due to its high toxicity (Figure 2).
With these experimental results, it is shown that, using the carboxylate-type liquid zwitterion, plant biomass could be converted into ethanol in a single reaction pot without washing/separation processes. This should be a big step forward in the production/utilization of second-generation biofuel ethanol through reducing large amounts of energy input.
Besides the first-generation and second-generation biofuel ethanol, a third-generation biofuel, a kind of oil, may be made from some algal species. In order to obtain such a third-generation biofuel from algae, polysaccharides like cellulose, which are main components of cell walls, have to be dissolved. The energy efficiency would be much increased if dissolved polysaccharides could be converted into ethanol. Further development of our current study would significantly contribute to the production of not only second-generation but also third-generation biofuel ethanol.
Furthermore, a lot of attention has been attracted by the unique characteristics of the carboxylate-type liquid zwitterion, and three international collaborations are currently going on, one of which is with Rutgers University, U.S.A.