| Bio-oil from biomass pyrolysis is a complex mixture.Due to its many components and poor quality,the development of biomass pyrolysis technology and its industrial application are severely restricted.Upgrading bio-oil is a necessary means to improve the quality of bio-oil.Distillation,as one of the most effective technical methods for the separation and upgrading of liquid mixtures,is widely used for preliminary upgrading of bio-oil.However,during the distillation of bio-oil,a kind of residue that is difficult to be directly used is generated at the bottom of the equipment.If it is not effectively used,it will not only affect the comprehensive efficiency of bio-oil distillation but also cause serious environmental pollution.Therefore,based on the physicochemical properties of bio-oil distillation residue,a series of studies on co-pyrolysis of bio-oil distillation residue with bituminous coal and walnut shells to produce high value-added liquid products and biochar were conducted to explore the synergistic effects and co-pyrolysis mechanism.The distribution and properties of co-pyrolysis products were studied,and the effects of fractional condensation and torrefaction pretreatment on the enrichment and upgrading of high value-added products were revealed.The mechanism of multi-factor coupling of co-pyrolysis raw material ratio,pyrolysis conditions,fractional condensation and torrefaction pretreatment on co-pyrolysis products was clarified.1.Study on physicochemical properties and pyrolysis characteristics of bio-oil distillation residueThe physicochemical properties and composition of bio-oil distillation residue were analyzed in detail through basic analysis methods and ethanol dissolution experiments.The results showed that the bio-oil distillation residue were a complex mixture mainly composed of pyrolytic lignin,phenols,hydrocarbons,furans and so on.Among them,the pyrolysis lignin reached about 60%.Bio-oil distillation residue had a large amount of carbon and rich functional groups,and its volatile content and calorific value were as high as 71.95%and 29.12 MJ/kg,respectively.The pyrolysis characteristics and kinetics of bio-oil distillation residue were studied by thermogravimetric analyzer coupled with infrared spectrophotometer.The results showed that the pyrolysis of bio-oil distillation residue could be divided into three stages.The main pyrolysis reaction was a secondary chemical reaction with an apparent activation energy of 72.52 kJ/mol.The pyrolysis characteristics of bio-oil distillation residue were the most similar to lignin,and there was a difference compared with cellulose and hemicellulose.Biochar was produced from bio-oil distillation residue through a tube furnace under different induction conditions.The physicochemical properties and evolution of biochar under different induction conditions were systematically analyzed.It was found that with the increase of induction temperature,the yield of biochar was gradually reduced,but the calorific value was not changed.Moreover,the carbon content of biochar was gradually increased with increasing the induction temperature,while the hydrogen element and oxygen element were gradually decreased.In addition,the functional groups were gradually weakened with the increase of induction temperature,and the thermal stability was gradually increased.Compared with the nitrogen atmosphere,the yield and calorific value of biochar were higher in the carbon dioxide atmosphere at low and medium temperature,and the opposite phenomenon occurred at high temperature.The carbon content of biochar in the carbon dioxide atmosphere was higher,the oxygen content was lower,and the hydrogen content was similar.In addition,the degree of graphitization of biochar in a carbon dioxide atmosphere was higher,and the thermal stability was slightly worse.2.Study on co-pyrolysis characteristics and product distribution of bio-oil distillation residue and bituminous coal.Co-pyrolysis experiments of bio-oil distillation residue and bituminous coal were carried out using thermogravimetric analyzer coupled with infrared spectrophotometer.The effects of the addition of bituminous coal on the pyrolysis characteristics of bio-oil distillation residue were studied.Additionally,the C-R(Coast-Redfern)method and FWO(Flynn-Wall-Ozawa)method were used to analyze the kinetics of co-pyrolysis of bio-oil distillation residue and bituminous coal.Moreover,the synergistic effect of co-pyrolysis and the effect of bituminous coal on the pyrolysis volatile content of the distillation residue of bio-oil were found.The results showed that as the percentage of bituminous coal increased,the temperature of the main mass loss peak of co-pyrolysis gradually moved to the high temperature region,while the reactivity gradually decreased,the apparent activation energy decreased first and then increased,and the number of reaction order in the main reaction stage gradually increased.There were obvious synergy effects in the co-pyrolysis process,and the synergy effects were more obvious in the low temperature.The addition of bituminous coal did not change the type of gaseous products,but can change the relative concentration of gaseous products.Combined with fractional condensation,the co-pyrolysis of bio-oil distillation residue and bituminous coal was carried out based on the central composite design method.The effects of co-pyrolysis conditions(the percentage of bio-oil distillation residue,pyrolysis temperature,gas flow)on the distribution and physicochemical properties of solid,liquid and gas products were systematically analyzed.The synergistic effects and mechanisms of co-pyrolysis were explored.The results showed that the best fit models for the product yields of solid and liquid from co-pyrolysis were quadratic models,while the best fit models for carbon content,hydrogen content,and oxygen content of the solid product were all linear models.In addition,the best fit model for the fractional yield of liquid products was a linear model.The addition of bituminous coal can significantly change the component distribution of co-pyrolysis liquid products,and promote the separation and enrichment of compounds in liquid products.Phenols,furans,and nitrogen-containing compounds tended to be enriched at higher condensation temperatures,while hydrocarbons tended to be enriched at lower condensation temperatures.The non-condensable gas of co-pyrolysis mainly contained H2,CO,CO2,and CH4,and the best fitting model for the concentration of non-condensable gas was a quadratic model.When the concentration of CH4 was the largest,the calorific value was up to 16.78 MJ/Nm3.3.Study on co-pyrolysis characteristics and co-pyrolysis coupled torrefaction pretreatment of bio-oil distillation residue and walnut shellsCo-pyrolysis experiments of bio-oil distillation residue and walnut shells were performed by thermogravimetric analyzer coupled with infrared spectrophotometer.The effects of the addition of bio-oil distillation residue on the pyrolysis characteristics of walnut shells were studied.A multi-component fitting model was used to analysis the co-pyrolysis of bio-oil distillation residue and walnut shells.The results showed that the addition of bio-oil distillation residue had a small effect on the position of the main mass loss peak of co-pyrolysis,and significantly reduced the maximum mass loss rate of co-pyrolysis.The co-pyrolysis synergy had a positive effect on the co-pyrolysis conversion rate and a negative effect on the mass loss rate,and the synergy effect was more pronounced at low temperatures.Moreover,the effect of the synergistic effect on the co-pyrolysis conversion rate and mass loss rate increased with the increase of walnut shells.The best fitting reaction model for co-pyrolysis was a five-component reaction model,and the fitting correlation coefficients under different mixing ratios were all higher than 0.9990.A tubular furnace and a small fixed-bed pyrolysis device equipped with a three-stage condensation system were used for the co-pyrolysis coupled torrefaction pretreatment of bio-oil distillation residue and walnut shells.The physicochemical properties and components of torrefied solid products and co-pyrolysis products were systematically analyzed,and the influence of torrefaction pretreatment coupled with co-pyrolysis on pyrolysis products was studied.It was found that there were obvious synergistic effects in the torrefaction and co-pyrolysis process.As the proportion of bio-oil distillation residue increased,the synergistic effect became more obvious,and the biochar yield gradually increased,while the total yield of liquid products decreased first and then increased.The total liquid product yield was lowest when the percentage of bio-oil distillation residue was 50%.With the increase of torrefaction temperature,the yield of biochar increased gradually,and the yield of liquid product gradually decreased;the torrefaction pretreatment was benifical to the enrichment of phenols in the liquid product of co-pyrolysis,and the phenols tended to enrich in the second condensation stage. |
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