Fast Pyrolysis Of Cotton Straw For Levoglucosan Production And Its Evaluation

There is an urgent need to develop more sustainable energy systems based on renewable lignocellulose due to the ever-increasing rate of energy consumption and environmental issues.The efficient and clean utilization of agricultural and forest waste such as straw has become a new hotspot in the field of energy and environment.Bio-oil is the liquid fuel that can be directly prepared by fast pyrolysis of agricultural and forest waste.Because of its high-water content,high oxygen content and low calorific value,it is difficult to long term storage and transport.Levoglucosan,as the highest sugar content in bio-oil,is one of the vital platform chemicals in the conversion of biofuels and chemicals,which has gained wide attention.In this study,fast pyrolysis of cotton straw was performed under different temperature ranges,particle sizes,holding times and acid concentrations in a fluidized bed reactor to maximize the yield of levoglucosan.What is more,a rapid method for the quantification of levoglucosan in pyrolysis liquids using high-performance liquid chromatography was developed.An improved method?water volume,active carbon weight,and pH?to quickly and easily extract levoglucosan from bio-oil was developed by using flocculation-azeotropic distillation-extraction.The techno-economic analysis and life cycle assessment models were developed based on the experiments from cotton straw convert to levoglucosan,the results showed the feasibility and environmental impact of levoglucosan production.The main conclusion includes:?1?The maximum levoglucosan yield?19.89 wt%?was obtained at the optimal pyrolytic conditions:temperature of 500?,holding time of 1.4 s,particle size of 600–650?m and acid concentration of 8%.This method was with Alltech 2000ES-ELSD,Ultisil?XB-NH₂ column and acetonitrile-water as the mobile phase.The optimal evaporative light scattering detector parameters were achieved at 15?column temperature and by adjusting evaporative light scattering detector setting at 70?drift tube temperature and 3.0?L/min gas flow rate.The calibration curve coefficient of determination on levoglucosan was>0.990determined by an evaporative light scattering detector.Recovery for levoglucosan was in the range of 96.79–99.13%,while LOD was 3.632??g/mL and LOQ was 9.08??g/mL.?2?The extraction of levoglucosan was established by using Design Expert v8.0.6,the optimal combination of these parameters is found as water:bio-oil=1:1?v/v?,active carbon:bio-oil=0.05:1?m/v?and pH at 12.2.The purity and structure of levoglucosan were determined by using chromatographic and spectroscopic techniques,such as HPLC,FT-IR and NMR spectroscopy.The optimal extraction yield of levoglucosan from the bio-oil was78%with the purity of 97%.?3?The levoglucosan production flowsheets were implemented and simulated in the software-SuperPro Designer v 9.5.Four discrete units were employed to simulate the conversion of cotton straw to levoglucosan,these units were biomass pretreatment,fast pyrolysis,bio-oil recovery,and levoglucosan extraction.For the levoglucosan simulated model,the process description,system modeling,and simulation of four processes were carried out,the mass and energy data used for techno-economic analysis and life cycle assessment were from this model.?4?The techno-economic analysis of a plant producing levoglucosan via fast pyrolysis of cotton straw and extraction of levoglucosan from the produced bio-oil was evaluated by modeling a 200,000 t/year feedstock processing plant.The continuous system had lower levoglucosan production price compared with the batch system.For the modeled feedstock handling capacity,the results indicated that levoglucosan production capacity could reach around 18,000 tons/year.The estimated levoglucosan net production cost,including byproduct credits,were$3.0/kg.Additionally,sensitivity analysis showed that the yield of levoglucosan from bio-oil,cotton straw cost,calcium hydroxide cost,hydrochloric acid concentration and days of operation were the main factors in levoglucosan net production cost.In order to achieve a 15%IRR,the minimum levoglucosan selling price was$4.0/kg.The techno-economic analysis results showed that this project was commercially attractive.?5?The life cycle assessment of levoglucosan production was from the cradle to the gate,including six processes,biomass transportation,biomass pretreatment,fast pyrolysis,bio-oil recovery,bio-oil transportation,and levoglucosan extraction.The potential environmental impacts of this LCA model were assessed based on their acidification potential?AP?,eutrophication potential?EP?,global warming potential?GWP?,ecotoxicity potential?ETP?,ozone depletion potential?ODP?and resource depletion?RD?.Among those processes,biomass pretreatment,fast pyrolysis,and bio-oil recovery had high impact factor to the environment.The results showed that the AP,ETP,EP,GWP,ODP,and RD of the production of 1kg levoglucosan were 1.91*10^-2 kg SO₂ eq,24.76 CTUe,1.29*10^-2 kg N eq,4.57 kg CO₂ eq,8.91*10^-7 kg CFC-11eq and 5.52 MJ surplus.The production of levoglucosan was compared with the generation of petroleum-derived chemicals in light of the environmental impact.The environmental burden of bio-based levoglucosan production was much lower than petroleum-derived levoglucosan production.Thus,bio-based levoglucosan production was an environmentally friendly chemical alternative to petroleum-derived levoglucosan production.