Lignin Pyrolysis Liquefaction And Supercritical Methanol Hydrodeoxygenation Of Pyrolytic Bio-oil Mechanism Research

Lignin is an important component of biomass raw materials,which can be converted into liquid fuels through pyrolysis liquefaction.Due to the complexity of the lignin structure and pyrolysis reaction process,the pyrolysis oil has high oxygen content and poor quality,and cannot be directly used for liquid fuels.The supercritical methanol hydrodeoxygenation system can use cheap metal catalysts and methanol hydrogen donors to hydrodeoxidize pyrolysis oil.Aiming at the key issues in the lignin pyrolysis liquefaction and supercritical methanol hydrodeoxygenation of pyrolysis oil,the structure of lignin and the pyrolysis reaction process mechanism,the effect of additives on the pyrolysis characteristics of lignin,and the catalysis of supercritical methanol are studied.The specific research contents are as follows:First,in view of the complexity of lignin structure,the small molecule lignin（β-O-4,NPβ-O-4,5-5 dimer and 5-5 dimer）,macromolecular lignin（DHP and MWL）and native lignin（20 kinds of biomass raw materials）were studied using TGA,Py-GC/MS and in-situ FTIR.The results show that the breaking of C-O bond in small molecule lignin is earlier than the breaking of C-C bond.The increase of the molecular weight in the lignin structure can increase the pyrolysis reactivity of the C-O bond,while reducing the reactivity of the C-C bond.The structure of macromolecular lignin is similar to that of raw lignin.The pyrolysis reaction occurs in a wide temperature range of 200-800℃,the yield of pyrolysis char yield is higher than 40%,and the pyrolysis oil is composed of guaiacol compounds.The correlation coefficient between lignin content in biomass raw materials and phenol products in pyrolysis products is 0.82.Secondly,in view of the complexity of the pyrolysis reaction process,the pyrolysis mechanism of lignin was studied using thermogravimetry,in-situ infrared,Py-GC×GC-TOF/MS and 2D-PCIS.It was found that lignin pyrolysis has an initial reaction stage and a violent reaction stage.The initial stage occurs between 160-330°C and has a weight loss of about 20wt.%,while the violent reaction stage occurs between 330-500°C with about 30wt.%weight loss.In the initial reaction stage,the C-O-C groups decrease,while-OH,C=C,C=O,and CH_n groups increase,and the reaction produces H₂O,CO₂ and CO.At the same time,the lignin softening reaction and polymerization reaction occur,and the microscopic morphology changes,forming lignin fragments with larger molecular weight.The violent stage is mainly the cracking reaction and the secondary reaction of volatile.As the temperature increases（330-500°C）,the C-O-C and C-C bonds of lignin are broken,more light fragments are formed in the volatile,a large number of oxygen-containing functional groups are removed,and the CH_n content in the bio-char increases.Further increasing the pyrolysis temperature,the secondary reaction of the volatile occurred,resulting in the increase of the content of C=O and C=C in the volatile.Thirdly,the effects of Ca-Mg additives on the regulation of lignin pyrolysis softening agglomeration and the formation characteristics of pyrolysis products were studied by fixed bed experiments.The results found that 11 kinds of additives with different base（KOH,Na OH,Mg（OH）₂,Ca（OH）₂,Al（OH）₃,Fe（OH）₃）,metal oxides（Mg O,Al₂O₃）and metal salts（Ca CO₃,Ca（NO₃）₂,Ca Cl₂）.Among these additives,the medium-strong base additives can effectively inhibit the agglomeration to obtain granular lignin bio-char.The Mg（OH）₂additive can promote the generation of CO₂ in the pyrolysis gas and increase the production of catechol in the liquid pyrolysis oil;while the Ca（OH）₂ additive can increase the yield of the pyrolysis gas and increase the content of-OH functional group in the bio-char and reduces the amount of guaiacols in the pyrolysis oil.Fouthly,by introducing a supercritical methanol hydrodeoxygenation reaction（SCM-DHDO）,using Cu Al Mg Ox as a catalyst and methanol as a hydrogen donor,the pyrolysis oil is hydrodeoxygenated and upgraded.The pyrolysis oil is divided into light component and heavy component by water-soluble extraction method.Phenols,alcohols,acids,alcohols,hydrocarbons and ketones in light pyrolysis oil have a higher conversion rate in the SCM-DHDO reaction.Most of the light pyrolysis oil components are converted into C2-C8alcohols,and a small part of the alcohols are further deoxygenated and converted into hydrocarbons.After 4 hours reaction,the aromatic ring structure in the heavy pyrolysis components decreased from 64.3%to 27.3%,and the oxygen content decreased from 26.8%to 9.7%.The hydrogenation rate of Cu Al Mg Ox catalyst（142.0mol/g*h）is about twice that of Ru/C catalyst（78.8mol/g*h）.About 50%of the carbon in the heavy pyrolysis oil is converted into upgraded oil.Some of its fuel properties meet the requirements of high-grade liquid fuels,with an oxygen content of less than 10%,high calorific value 38.2MJ/kg and diesel calorific value 42.6MJ/kg is equivalent.Finally,a 100kg/h pyrolysis coupled SCM-DHDO system model was constructed using Aspen Plus baseing on the experimental research.The system was comprehensively evaluated in terms of material flow,carbon footprint,technical economy,and environmental protection.The effective carbon conversion rate of the system is 33.3%,and it can produce21.6kg of C2-C8 alcohols and 10.8kg of high-grade liquid fuels per hour.In terms of technology and economy,the system has a net present value of 9.9 million yuan,an annual rate of return of 11.3%,and a relatively high rate of return on profit and investment value.In terms of environmental protection indicators,the system’s direct CO₂ emission is 10.8kg/h,and the indirect greenhouse gas emission intensity is 2.5g CO₂-eq/MJ.