Fast Liquefaction Of Bamboo Shoot/bamboo Processing Wastes By Polyols With Plasma-assisted Technology

Global energy crisis and environmental problems derived from the massive use of fossil fuels have made seeking for ideal alternatives an imperative issue.As one of the most promising technologies for biomass conversion,biomass liquefaction has been a focus of research over the world.However,economically competitive,fast liquefaction at mild conditions remains a challenge.In this paper,fast liquefaction of bamboo shoot shell(BSS)and bamboo sawdust(BS)at atmospheric pressure was achieved without extra heating,when plasma technology was employed to facilitate the liquefaction.The main investigation contents are described as follow:1.Liquid-phase microplasma technology was employed to facilitate the liquefaction of BSS and BS in polyethylene glycol 400(PEG 400)and ethylene glycol(EG)mixture in the presence of concentrated sulfuric acid.Firstly,effects of liquefaction conditions including liquefaction time,catalyst percentage,solvent/biomass mass ratio and PEG/EG volume ratio on liquefaction were investigated respectively.The liquefaction yield of BSS and BS was 96.73%and 98.02%respectively under the suitable conditions based on the results of single-factor experiments.Secondly,orthogonal test was applied to optimize the liquefaction conditions,and the optimized conditions for BSS and BS respectively were liquefaction time 2.5 min and 6.0 min,catalyst percentage 2.0 wt%and 2.5 wt%,PEG/EG volume ratio 4:1,and solvent/biomass ratio 8:1.After optimization,the yield of BSS and BS reached 97.56%and 98.18%respectively.The greatest effect on BSS liquefaction was catalyst percentage,while solvent/BS ratio was proved to be the dominant influence on BS liquefaction.Lastly,liquefaction product of BSS and BS was analyzed and characterized.After liquefaction,the Higher Heating Value(HHV)of liquid product of BSS and BS was significantly improved to 26.11 and 23.83 MJ/kg respectively,and that product was rich in hydroxyl,methoxyl and carbonyl groups,containing esters,ethers and aromatics.2.Experiments were conducted to study the reasons for fast liquefaction of BSS with plasma-assisted technology when concentrated sulfuric acid was used.First of all,the temperature of the plasma-assisted liquefaction system increased dramatically from room temperature(28.5?)to 107.4? in the first 0.5 min.Then,the temperature kept soaring to 172.1? for the second minute and reached the peak at 195.4? in the third minute.Higher temperature contributes to biomass liquefaction.Secondly,it was found that,the conductivity of the system increased significantly to 600 pS when 2.0 wt%H2SO4 was added.The temperature of the liquefaction system without H2SO4 catalyzed was merely 115.6? after liquefaction for 5.0 min,indicating that the use of H2SO4 can enhance the plasma discharge process and then increase the temperature of the system rapidly.Finally,a spectrometer was applied to detected activated particles generated by plasma discharge and a absorption spectrum at 309 nm,which is much stronger than others,revealed existence of large amount of OH radicals.OH radicals are capable of rapid oxidation of glycosidic bonds and other macromolecular substances,leading to accelerating the liquefaction of BSS.3.Plasma-assisted liquefaction of BSS by polyols was studied without catalyst used,in order to solve the problem of corrosion of equipment owing to the use of strong acid/alkali.Results showed that the liquefaction yield of BSS was 66.33%under the liquefaction conditions of liquefaction time 20 min,PEG/EG volume ratio 3:1,solvent/biomass ratio 6:1.The HHV of liquid product and solid residue of no-catalyst liquefaction was 22.25 and 20.03 MJ/kg,respectively.It was confirmed that plasma-assisted technology is capable of biomass liquefaction with satisfactory yield and producing high value-added products in no-catalyst condition.Then,the solid residue(BSS-SR-N)was employed to simulated wastewater adsorption.Results revealed that BSS-SR-N showed outstanding adsorption capacity for the removal of methylene blue(MB)and Pb(II),with the removal rate of 98.35%and 96.65%,and the maximum adsorption capacity of 192.31 mg/g and 153.85 mg/g,respectively.With the adsorption-regeneration cycle repeated 3 times,the BSS-SR-N regeneration efficiency of MB and Pb(II)still reached 99.02%and 85.44%respectively,indicating that BSS-SR-N is an adsorption material with excellent performance.In conclusion,plasma technology is capable of successfully assisting the biomass liquefaction by polyols to achieve fast liquefaction at atmospheric pressure with less or even no catalyst used,making the liquefaction more moderate,and improving the industrialization potential of biomass liquefaction.