Study Of Biofuel Production Process Based On Deep Eutectic Solvent Pretreatment Of Lignocellulosic Biomass

Bioethanol was considered an important source of alternative renewable energy.This paper presented a process simulation,techno-economic analysis and life cycle assessment of bioethanol production from lignocellulosic biomass based on deep eutectic solvent pretreatment to provide a relevant theoretical basis for bioethanol development.In the process simulation,the main product bioethanol and the by-product lignin were produced from rice straw（50 ton/h）through a technical route of feed handling,pretreatment,enzymatic hydrolysis and fermentation,wastewater treatment and combined heat and power.The process simulation included a variety of technical methods to ensure subsequent economics,such as pretreatment solvent recovery,detergent recovery,recycled water utilization and waste-to-energy.The simulation results showed that the purity of ethanol was over 95%.The bioethanol yield was 0.21t/t（rice straw）via choline chloride/lactic acid（molar ratio 1:2）pretreatment,which was higher than choline chloride/urea（molar ratio 1:2）.For the deep eutectic solvent pretreatment at different temperatures,the bioethanol yield at 120 ℃ was the highest value in this study.Acidic deep eutectic solvent pretreatment with 20% solid loading showed better results in biomass refining.In addition,combined heat and power,high solid loading and low temperature pretreatment became an important part of the reduction of energy used in the process.In the techno-economic analysis,the investment and operating costs for the production of bioethanol were estimated.The results showed that the investment in pretreatment was over 20% and had a significant impact on costs.Deep eutectic solvent pretreatment process could achieve a profitable period of 10 years or more.Discounted cash flow analysis revealed that the minimum ethanol selling price of choline chloride/lactic acid pretreatment was 2128.1 $/ton,which was over 25.8% lower than the choline chloride/urea pretreatment.This was also competitive with other pretreatment results.In the choline chloride/lactic acid pretreatment,sensitivity analysis showed that minimum ethanol selling price fluctuated by 23.4%,6.25% and 5.31% due to enzymatic hydrolysis cellulose conversion,acetone price and lactic acid price,respectively.This showed that the lower minimum ethanol selling price could be achieved from the aspects of enzyme hydrolysis efficiency,low cost efficient detergent and lactic acid.Combined heat and power and high solid loading pretreatment also had a positive impact on lower minimum ethanol selling price.In the life cycle assessment of bioethanol production processes under choline chloride/urea,choline chloride/lactic acid and sodium hydroxide pretreatment studied.As the net energy values under choline chloride/urea,choline chloride/lactic acid pretreatment were all negative（-4107023 MJ,-643449 MJ）.High solid loading pretreatment could reduce the total net energy input.The net energy ratios and renewability（0.00644 and 0.0412,0.00644 and 0.0414）of two deep pretreatment were lower than the 1.01 and 1.2 of sodium hydroxide pretreatment,while renewability under three pretreatments was increased in the case of predominantly lignin-rich residue supply.The coal consumption of deep eutectic solvent pretreatment was more than 1.93 times alkali pretreatment,resulting in high CO₂ emission.In addition,the use of lignin-rich residue for energy supply also reduced the environmental impact of bioethanol production in the direct environmental release,environmental impact category and relative environmental impact category.Sodium hydroxide pretreatment was associated with a reduction in greenhouse gas emissions of over 33.3% in the results.The coefficients of variation for climate change,ozone depletion and fossil depletion obtained from the three pretreatments were all less than 1%,with a high degree of confidence.The planting and harvesting contributed highly to most impact categories.The improvement of fermentation efficiency and rice straw utilization rate would reduce rice straw input and climate change.Climate change decreased significantly at fermentation efficiencies 85%.