Development Of Thermochemical Conversion Of Lignocellulose From Agricultural Waste For Bio-oil Production

There is a lot of byproducts produced during agricultural products processing which are primarily composed of lignocellulose.Considering that the current technologies for the waste disposal including incineration and landfill could pose a great threat to the environment and water system,converting the waste into value-added fuels or chemicals via pyrolysis is of significance for the environment.On the other hand,the products obtained from pyrolysis can reduce the consumption of fossil fuels,thereby reducing the carbon emission and contributing to the goal of peak carbon emission and carbon neutral in our nation.However,biomass feedstock shows some disadvantages,such as strong hydrophilicity,low energy density,difficulty in storage,and wide distribution,thereby increasing the cost for using as energy source and limiting its further technology development.In order to tackle these issues,this study aims to study the effect of torrefaction on biomass structure and pyrolysis behaviors,produce the value-added chemicals by catalytic pyrolysis of torrefied biomass,and selectively produce aromatics by catalytic co-pyrolysis of torrefied biomass and plastics.The results are as follows.It was found that both microwave and conventional wet torrefaction can change the biomass properties and pyrolysis behaviors significantly.Proximate and elemental analysis show that HHV and oxygen content of biomass treated by microwave wet torrefaction are higher than those treated by conventional wet torrefaction,other than at 150℃.Compared to conventional wet torrefaction,microwave wet torrefaction can remove more acetyl groups in hemicellulose,which could be due to the hot spot effect under microwave irradiation.Experimental results also indicate that HHV and fixed carbon content of treated biomass gradually increase with the torrefaction severity increasing.For 230℃-15min and 210℃-35min,the oxygen content is remarkably decreased.With the reaction time,the crystallinity index shows an upward trend.Different from hydroxyl groups,longer reaction time is more favorable for the acetyl removal than raising temperature.It can be seen from TG curves that TC and DTG curves shift to higher temperatures after wet torrefaction and higher torrefaction severity facilitates this process.Py-GCMS analysis indicates that the acid content in bio-oil decreases and sugar content increases with the microwave wet torrefaction severity increasing.Moreover,microwave wet torrefaction leads to 9.82%higher glucopyranose content at 190℃ and 4.12%lower acid content at 150℃ than conventional wet torrefaction.In order to study the effect of dry torrefaction on physicochemical properties and pyrolysis behaviors of biomass,the physicochemical properties of biomass before and after dry torrefaction were first comprehensively characterized.It was found that torrefaction improves the H/Ceff of corn cob and higher temperature facilitates this process.Torrefaction also decreases the oxygen content,which would enable more hydrocarbon formation during the subsequent pyrolysis.At higher torrefaction temperature,the biomass obtains higher energy density while the mass and energy yields decrease.From this point,240℃ could be the best torrefaction temperature,with a mass yield of 62.36%and an energy yield of 76.04%,in order to maximize the economic benefit.With the temperature increasing,the crystallinity index of biomass is increased to 76.46%at 240℃ and then decreased a little bit.Kinetic analysis indicates that activation energy and pre-exponential factor gradually increase when the temperature goes up.By comparing three models,it was found that calculating activation energy via OFW and calculating pre-exponential factor via KAS and DAEM could be a wiser option.Based on thermodynamic parameter analysis,ΔH,ΔG,andΔS show upward trend with the temperature.Furthermore,we attempt to produce phenols from torrefied corn cob via catalytic microwave-assisted pyrolysis over a Fe _HC@hydrochar catalyst.Carbonaceous catalyst characterization shows that Fe _HC@hydrochar has some advantages compared to other carbonaceous catalysts,such as developed pore structure,uniform metal distribution,and low B/L,which improve the total selectivity and yield of phenols.Stability testing indicates that only a partial loss of catalytic activity can be observed after 7-cycle runs.The potential deactivation mechanism is also studied by characterizing the deactivated catalysts.We also test the catalytic fast pyrolysis of torrefied biomass for aromatic production over a Ni-based hierarchical ZSM-5 catalyst.First,ZSM-5,hierarchical ZSM-5,and Ni-based hierarchical ZSM-5 are characterized and compared,finding that Na OH modification weakens the XRD peak intensity of hierarchical ZSM-5 and Ni addition improves the catalyst framework.Moreover,Na OH modification leads to some macro and meso pores,while Ni addition reduces the BET surface area and micropore volume.Although Ni addition lowers the acid site density a bit,it enhances the selectivity and yield of aromatics.Thermodynamic model shows that Ni-based hierarchical ZSM-5 catalyst reduces the activation energy for catalytic pyrolysis reaction.Finally,by integrating wet torrefaction,co-pyrolysis,and catalysis,the effect of wet torrefaction on aromatic production during catalytic co-pyrolysis of torrefied corn cob and plastics is evaluated.XRD,FTIR,and solid NMR show that wet torrefaction treatment removes most of hemicellulose and partial oxygen in biomass and break down some unstable bonds（acetyl,glycoside bonds and ether bonds in lignin）and change the crystallinity index of biomass.During individual pyrolysis of biomass,wet torrefaction treatment significantly increases the contents of levoglucosan and furans.During co-pyrolysis of torrefied biomass and plastics,wet torrefaction remarkably increases the content of aromatics.It is concluded that aromatic enhancement during co-pyrolysis is primarily caused by several factors.First,wet torrefaction removes most of alkali and alkali earth metals in biomass,promoting the formation of levoglucosan that is the precursor for aromatic generation.Then wet torrefaction removes most hemicellulose in biomass,which destroys its inherent structure to promote aromatic formation.Furthermore,wet torrefaction increases the content of furan,which is an important intermediate for aromatic production.In addition,wet torrefaction improves the H/C_eff of the corn cob.These results indicate that wet torrefaction could be an effective pretreatment method for improving aromatic production during co-pyrolysis.