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N2 explosive decompression pretreatment of biomass for lignocellulosic ethanol production

Raud, M., Olt, J., Kikas, T.
Biomass and bioenergy 2016 v.90 pp. 1-6
barley straw, biomass, catalysts, cell walls, cellulose, enzymatic hydrolysis, ethanol, ethanol production, feedstocks, fermentation, glucose, hemicellulose, hydrolysis, lignin, lignocellulose, nitrogen, surface area, temperature
This paper presents a novel biomass pretreatment method that uses high pressured N2 and temperature to break the hemicellulose and lignin seal around the cellulose macro fibrils in the cell walls of the lignocellulosic biomass in order to open up the biomass structure for more efficient enzymatic hydrolysis. In this method the biomass is exposed to a high pressure using N2 gas, and temperature. Under pressure, cells of the lignocellulosic biomass are filled with a solution saturated with nitrogen. When the pressure is then suddenly released, the feedstock is exposed to an explosive decompression and the dissolved nitrogen is released from the solution. Sudden change in the volume breaks the cell walls and opens the biomass structure resulting in increased surface area of the substrate for enzymatic hydrolysis. No catalysts or chemicals were added in the process thereby, making it economically and environmentally attractive. In this research, a range of different pressures (1–60 bar) and temperatures (25–175 °C) were applied to barley straw to evaluate the efficiency of the pretreatment. The pretreatment was followed by enzymatic hydrolysis and fermentation. Resulting glucose and ethanol concentrations were measured and the yields were considered as an estimate for the most suitable set of pretreatment conditions. The results indicate that the highest glucose yield and hydrolysis efficiency were gained at 150 °C and 10–30 bars. The fermentation efficiency was lower at higher temperatures. Nonetheless, the highest ethanol yield was still gained at the same conditions.