Experimental Study On Preparation Of Bio-oil By Hydrothermal Liquefaction Of Chinese Herb Residue

Chinese herb residue(CHR)is the waste produced by traditional Chinese medicine,which is usually regarded as biomass waste.Without effective disposal,it will not only cause waste of resources,but also be accompanied by a series of environmental problems.In this thesis,Angelica residue was used as the raw material to carry out an experimental study on the production of bio-oil by hydrothermal liquefaction.The effects of reaction temperature,biomass/water mass ratio(B/W)and reaction time on the yield and quality of bio-oil were investigated by single factor experiments.Then,effects of Fe/ZSM-5,Ni/ZSM-5,and Fe-Ni/ZSM-5 bifunctional catalysts loaded with 5-15 wt% on the deoxygenation and upgrading of bio-oil were discussed.Finally,reaction conditions including reaction temperature,B/W and catalyst dosage were optimized by response surface methodology,which provided data and theoretical support for further pilot scaleup and industrialization of CHR hydrothermal liquefaction technology.The main conclusions are as following:Hydrothermal liquefaction can effectively remove O element in Chinese herb residue to produce C element-enriched bio-oil.Reaction temperature and B/W have significant effects on bio-oil yield and Higher Heating Value(HHV),while reaction time has less effect.When the reaction temperature is 290 ℃,the decomposition of CHR is incomplete,and many unreacted raw materials remain;increasing the temperature can promote the decomposition and conversion of biomass,and improve the yield of bio-oil and conversion of raw materials;when the temperature is too high(350 °C),the intermediates were cracked into gaseous products,and the yield of bio-oil decreased.Higher B/W is not conducive to the heat/mass transfer inside the reactor,on the contrary,it will make more organic matter stay in the water phase and increase the system loss.Appropriate B/W(6.6 wt%)can improve the bio-oil yield and utilization efficiency of CHR.Due to the slow heating rate,most of the CHR were converted when the reaction temperature was raised,and the liquefied products did not change significantly with the increase of time.The parameters optimized by single factor were the reaction temperature of 320 °C,the B/W of 6.6 wt% and the reaction time of 10 min.At this time,the yield and HHV of bio-oil were 24.7 wt% and 29.39 MJ/kg,respectively.The effect of catalyst on the liquefaction process is obvious.The acidic sites of ZSM-5 molecular sieve can promote reactions such as dehydration,hydrogenation and cyclization,and increase the HHV of bio-oil,but reduce its yield.Fe and ZSM-5molecular sieves exhibited a synergistic effect during the liquefaction process,and the yield and HHV of bio-oil were 21.3 wt% and 31.74 MJ/kg,respectively,in catalytic liquefaction of 10 wt% Fe/ZSM-5.The hydrogen generated by Fe redox can stabilize the active reaction intermediate,increase the saturation of bio-oil,and synergistically deoxygenate with molecular sieves,enrich carbon to bio-oil,reduce O/C ratio,and increase H/C and HHV.GC-MS showed that the content of aliphatic compounds in the bio-oil increased to 72.96%,which provided convenience for the directional refining of oil products and reduced the cost of subsequent upgrading.Ni/ZSM-5 has less effect on liquefaction,although Ni can generate H in the reaction,but its C-C bond of cracked organics increases small molecules,resulting in the formation of more gas and water phase products.The effect of Fe-Ni/ZSM-5 catalyst is between that of single metal support,and no synergistic effect is produced.Based on the results of the single factor experiment,firstly,the four factors of reaction temperature,B/W,catalyst dosage and reaction time were analyzed by PlackettBurman design,and the reaction temperature,B/W and catalyst dosage were determined as the main influencing factors.Then,the steepest ascent experiment was designed based on the Plackett-Burman results,with the yield as the target,rapidly approaching the region of maximum response during liquefaction.The center point of each parameter was determined as the reaction temperature of 330 ℃,B/W of 7 wt% and catalyst dosage of11 wt%.Finally,the liquefaction conditions of CHR were optimized by the response surface method,and the experiment of 3 factors and 5 levels was designed by the central composite method.The preparation of bio-oil was carried out according to the experimental plan,and the results were fitted by quadratic polynomial regression using Design Expert software to study the synergistic effect of different variables on the yield of bio-oil.The optimal liquefaction conditions were obtained by solving the response surface model,with a reaction temperature of 342 °C,a B/W of 9 wt%,a catalyst dosage of 7 wt% and a reaction time of 10 min.The bio-oil yield obtained from the confirmatory experiment was 27.38 wt%,which was very close to the theoretical prediction value of the model of 28.15 wt%.