Study On Fast Pyrolysis And Catalytic Pyrolysis Characteristics Of Biomass Under Different Pretreatment

Biomass,as a green and pollution-free renewable resource,has great potential to produce biofuels.Pyrolysis has become one of the most promising biomass utilization technologies due to the resource utilization of gas,liquid and solid products after pyrolysis.In particular,the bio-oil produced by pyrolysis can be used as fuel through upgrading and transformation.It can also be used as raw material for the production of chemicals.However,the effective utilization of biomass is usually limited by high water and oxygen content,low energy density,difficulty in grinding and other factors.The physicochemical properties of biomass itself have a certain influence on the subsequent pyrolysis reaction and product characteristics.Therefore,this topic focuses on the pretreatment of biomass raw materials and the regulation of pyrolysis process,aiming at optimizing the quality of pyrolysis products and increasing the yield of products,especially bio-oil,so as to provide data support for the efficient utilization of biomass.In this study,peanut shell and poplar wood chips were used as raw materials for fast pyrolysis and catalytic pyrolysis in a vertical reactor.The characteristics of pyrolysis products were analyzed,including the yield distribution of the pyrolysis products,the composition analysis of gaseous products and bio-oil.Firstly,the peanut shell and poplar wood chips were washed with deionized water,hydrochloric acid and acetic acid.The untreated raw materials and pretreated samples were pyrolyzed at 550℃.The results showed that the distribution of pyrolysis products changed after washing pretreatment.For peanut shells,the bio-oil yield increased from 38%to 44.75%（hydrochloric acid treatment）and 43.4%（acetic acid treatment）,and the coke yield decreased significantly.After pretreatment,the quality of bio-oil was improved,the acids and ketones mainly composed of acetic acid and 1-hydroxy-2-acetone were decreased,and the content of dehydrated sugars mainly composed of levoglucosan was increased.For poplar wood chips,the yield of pyrolysis gas and bio-oil increased gradually.The variation of bio-oil yield was more prominent,from 43.75%（untreated）to 49.15%（hydrochloric acid treatment）and48.23%（acetic acid treatment）.Secondly,the influence of concentration of acid-washing solution on biomass pyrolysis was explored.The concentration was set as 0.5 mol/L,1.0 mol/L,1.5mol/L and 2.0 mol/L,respectively.The change of concentration had a great influence on the yield of bio-oil and pyrolysis gas.With the increase of concentration,the yield of bio-oil decreased and the yield of pyrolysis gas increased.Considering the subsequent catalytic pyrolysis of the pretreated biomass,the yield of bio-oil was taken as the main index.The optimal pretreatment effect was found when the concentration of the solution was 0.5 mol/L.Then,the biomass treated with 0.5 mol/L hydrochloric acid and 0.5 mol/L acetic acid was catalytic pyrolysis at 550℃with ZSM-5 as catalyst.Compared with the pyrolysis of acid washed biomass,catalytic pyrolysis reduced the yield of bio-oil and improved the yield of pyrolysis gas.The volume fraction of CO and CO₂in pyrolysis gas was further improved in the catalytic pyrolysis process.For the components of bio-oil,the proportion of acids and ketones gradually decreasesd,and the relative content of aromatic hydrocarbons increased greatly.The coupling of acid-washing pretreatment and catalytic pyrolysis can promote the upgrading of pyrolysis products,especially bio-oil.Compared with the catalytic pyrolysis of acid-treated peanut shell and acid-treated poplar sawdust,it was found that the proportion of aromatic hydrocarbons in the pyrolysis oil of acid-treated peanut shell was lower than that of acid-treated poplar wood chips.Finally,the effect of temperature change on the pyrolysis of acid-treatment biomass was studied.Catalytic pyrolysis of biomass pretreated with 0.5 mol/L hydrochloric acid and 0.5 mol/L acetic acid were conducted at the set temperatures（450℃,500℃,550℃,600℃）.In the process of catalytic pyrolysis,temperature had a significant effect on the yield distribution of pyrolysis products.The yield of pyrolysis oil in acid-treated biomass decreased with the increase of temperature,while the yield of pyrolysis gas changed on the contrary,and the coke yield remained unchanged.Higher temperature enhanced the activity of the catalyst and further facilitated the catalytic conversion of oxygen compounds into aromatic hydrocarbons in pyrolysis vapor.The content of aromatic hydrocarbons in the pyrolysis oil treated by acid at 600℃was higher than that at other temperatures.In the catalytic pyrolysis process,acid treatment at low temperature had a certain influence on the pyrolysis reaction process.But overall,the influence of temperature was more important than that of biomass pretreatment.In this study,peanut shell and poplar wood chips were used as raw materials and the synergistic effects of pretreatment and catalytic pyrolysis on the pyrolysis characteristics were considered.The combination of pretreatment technology and catalytic cracking technology can promote the conversion of low-density oxygen-containing biomass into high-quality aromatic hydrocarbons,thus improving the quality of bio-oil.In order to maintain high quality bio-oil and high yield bio-oil at the same time,the pyrolysis process conditions were changed during catalytic pyrolysis.