Mechanism Research And Modelling Of Cellulose Fast Pyrolysis Based On The Typical Products

The utilization of biomass energy is an effective contribution to the mitigation of global climate problems and the depletion of fossil resources.At home and abroad,research on thermal conversion of biomass resources is one of the hot problems,for its capability on production of clean fuels and high value-added chemicals.As a major component of lignocellulosic biomass,understanding the pyrolysis behavior of cellulose is fundermental and essential to the whole biomass conversion.However,there is still no consensus on this subject,for example,the insufficient relationship between the reaction mechanism and kinetic model of cellulose pyrolysis.Besides,most of the previous studies are only applicable to specific conditions such as small size particles and low heating rates,and lack of universality.To solve these problems,this paper has carried out which incldes comprehensive experiments and theoretical calculation of the pyrolysis mechanism,cellulose pyrolysis kinetics model,and heat transfer model of large particles.Futhermore,a transition metal@aerogel catalyst was developed on the basis of cellulose pyrolysis charecteristics,and the primary investigation was made.The main results were summarized as follows:Firstly,the weight loss regularity and evolution of characteristic products during cellulose pyrolysis were studied by using TGA-DSC and TGA-FTIR.The relationships between pyrolytic products with temperature,residence time,polymorph,and degree of polymerization?DP?were studied by Py-GC/MS.The interaction mechanism between pyrolytic products was analyzed with experimental methods.It was found that cellulose could undergo decrystallization at 200°C which is a reversible reaction.A few of H₂O?CO₂,and C=O compounds could form at 270°C,and almost all reactions occurred at 290°C.When temperature was 550°C,levoglucosan?LG?reached highest content in 10?20 s.Crystalline structure of cellulose?facilitated the formation of LG.In addition,the actual yield of LG was much lower than the theoretical yield as the DP increase.Secondly,cellobiose and glucose were used as model compounds for the density functional theory calculation.The formation and interaction mechanisms of the three most abundant components,namely LG,hydroxyacetaldehyde?HAA?,and pyruvaldehyde?PA?,were discussed at the molecular level.By combination of experimental analysis and theoretical calculation,a reasonable pyrolysis scheme of cellulose was propsed.It was found that LG is most likely formed via a concerted mechanism.HAA and PA were formed by competitive reaction.HAA is primarily formed from C5-C6,and PA is formed from C1-C2-C3.Furthermore,C2-C3 and C3-C4 dehydration were more likely to occur in pyran ring.Thirdly,on the basis of above research,a more plausible kinetic model of cellulose pyrolysis was proposed.The mechanism function,kinetic parameters,and reaction enthalpy were determined.A comprehensive model of heat transfer in large particle pyrolysis was developed by using the independently developed pyrolysis device.The product distribution under various conditions was predicted and the predicted results were well agreed with the experimental data.The cacluted results indicated that the random scssion model is appreciate for discribing cellulose pyrolysis.Higher heating rate is beneficial to the formation of bio-oil,when the heating rate from 10 to 100°C/min,the calculated bio-oil yield increased from81.7%to 85.3%.During the pyrolysis process,the pores in the sample expanded,and finally changed to char with layered structure.In addition,low porosity and high thickness can also improve the bio-oil yield.This model enables predicting the product distribution of cellulose pyrolysis and in turn can be used to industrial conversion applications.Finally,cellulose-based catalysts were developed and used in cellulose pyrolysis.The specific surface area?SSA?of the catalyst were 300?400 m²/g,and the pores were primarily mesoporous,which is beneficial to the diffusion of products.The diameter of uniformed nanoparticles was less than 20 nm and enenly dispersed.The ratio of feed:catalyst was only10:1,which significantly improved the catalytic efficiency.Iron-based catalysts promoted dehydration and ring opening,and thus promoted the generation of low molecule weight?LMW?products.Nickel-based catalysts have stronger adsorption capacity and catalytic effect on gasification,which can promote the hydrogenation of aldehydes and ketones,and improve the quality of bio-oil.