To avoid competition with food supply and thus avoid food shortage, agricultural wastes called biomass are then used in ethanol production. This second generation biofuel has a limitation though in its conversion efficiency, in terms of energy, time, and raw materials consumed, and yield.
The solvent used to dissolve the cellulosic material in biomass is highly toxic to a specific bacteria, Escherichia coli, which produce ethanol. In order to reduce the toxicity of the solvent-biomass mixture and allow the bacteria to produce ethanol, it has to undergo additional processes – washing and centrifugation or separation. The overall process is inefficient that the energy consumed is more than the energy produced.
To address the process efficiency problem, Japanese researchers developed a new solvent that allows ethanol production even without the washing and separation steps. The new solvent, carboxylate-based zwitterion liquid, is 17 times lower in toxicity to the bacteria than the conventional solvent, enabling the process to produce ethanol in situ.
The conventional solvent is an ionic liquid, that is, it is comprised of molecules that have either a positive charge or a negative charge. The new solvent, on the other hand, is a zwitterion liquid, which is composed of molecules, each having both positive and negative charge, making each molecule’s net charge equal to zero.
Having a much lower toxicity level, the carboxylate-based zwitterion solvent produces 21 times more ethanol than the traditional ionic liquid. Even when the washing and separation steps were removed, it still produced ethanol, while the ionic solvent did not produce any.
With the washing and separation steps removed in the process of ethanol production, that is the biomass-solvent mixture directly undergoes hydrolysis and fermentation, all in one reaction vessel, a significant amount of energy, time, and raw materials are saved, resulting to a more efficient ethanol production.
The newly developed solvent may also be used in producing third-generation biofuel, those are made from algae. It could be used in dissolving the polysaccharides from the algae and convert it into ethanol.