Depolymerization Of Lignin From Agricultural Waste And Its Catalytic Co-pyrolysis With Waste Cooking Oil

Lignin produced from pulping industry has burdened the environment.The conversion of lignin through depolymerization including sovolysis and pyrolysis which are gaining more and more attention,are prospected methods for the high-value application of lignin.On the other hand,waste cooking oil poses a threat on people's health if returning to be reused as cooking oil,which is often the case by some illegal businesspersons.In this thesis,the effective conversion of lignin and co-pyrolysis of lignin and waste cooking oil were investigated.1.The depolymerization of original lignin existed in the biomass in the ethanol-water solution.In this section,bamboo as an agricultural product was selected as the feedstock,the effects of different extraction conditions?processing temperature and time?on the depolymerization of the original lignin were studied.Also,the change of lignin structure and properties during the solvolysis were characterized.The results showed that the higher temperatures?160-200??and longer processing time?1-3 h?were favorable for the isolation of lignin from the lignocellusic structure.The carbon and oxygen contents of lignin under varied conditions were 60.21-61.18%and 32.36-33.35%,respectively.Moreover,the increase of temperature and reaction time could promote the release of hydrogen radicals,which were conducive to the depolymerization of lignin and produced more phenolic hydroxyl groups and carboxylic groups.The molecular weight of lignin decreased from 5991 g/mol at 160?to 5516 g/mol at 200?,indicating that the decomposition of lignin occurred during the solvolysis.Longer reaction time was contributed to the repolymerization of lignin,resulting in the increase of molecular weight.FT-IR and NMR spectra verified the basic structure and chemical links of lignin.2.Study of lignin pyrolysis with different microwave susceptors.Lignin was pyrolyzed with microwave heating in the presence of different microwave susceptors including silicon carbide?Si C?,activated carbon?AC?,and bio-char?BC?.The temperature profiles of microwave heating with different absorbents were characterized and the three distinct heating stages were proposed,which were believed to correspond to the three main stages of lignin decomposition,including evaporation of moisture,breakage of ether links,and breakage of C-C bonds.The effects of temperature,absorbent loading,and absorbent type on product yield and composition were investigated.Higher pyrolysis temperature favored char removal,conversion of methoxyphenols to other phenols,and H₂ formation while higher Si C loading promoted the production of alkyl phenols and syngas?CO and H₂?.Compared with Si C,both AC and BC helped produce more syngas,accounting for 74.5%and70.1%,respectively.AC was associated with the highest bio-oil and gas production while BC showed the highest selectivity to phenol?58.2%?and alkyl phenols?37.7%?.3.In-situ catalytic pyrolysis of lignin with HZSM-5In this section,in-situ catalytic pyrolysis of lignin during which the lignin was mixed with HZSM-5 was conducted and the effects of catalyst to lignin ratio on the products yields and distribution were investigated.With the increase of catalyst to lignin ratio,the yield of bio-char decreased while the yield of gas increased.In terms of the composition of products,the non-catalytic pyrolysis of lignin mainly produced methoxyphenols,whose chemical selectivity was 73.7%,while the catalytic pyrolysis decreased the selectivity of methoxyphenols to 17.6-19.7%under varied catalytic conditions and the chemical selectivity of alkylphenols and aromatics increased significantly.In addition,HZSM-5 was conducive to the formation of hydrogen and methane but inhibited the production of carbon dioxide.4.Ex-situ catalytic upgrading of vapors from lignin pyrolysisIn this section,ex-situ catalytic pyrolysis of lignin with HZSM-5 was investigated and comparison of in-situ and ex-situ upgrading was studied.The in-situ process produced higher bio-oil and less char than the ex-situ process.The ex-situ process had higher selectivity to aromatics and produced more syngas and less CO₂than the in-situ process.Additional experiments on ex-situ process found that the bio-oil yield and coke deposition decreased while the gas yield increased at higher catalyst-to-lignin ratios and catalytic reforming temperatures.The increased catalyst-to-lignin ratio from 0 to 0.3reduced the selectivity of methoxy phenols from 73.7%to 22.6%while increased that of aromatics from 1.1%to 41.4%.Higher catalytic reforming temperature favored greater conversion of methoxy phenols to alkyl phenols and aromatics.Appropriate catalyst-to-lignin ratio?0.3?together with higher catalytic temperatures were favorable to the syngas formation.5.Catalytic co-pyrolysis of lignin and waste cooking oil with Py-GC/MSThe catalytic co-pyrolysis of lignin and waste cooking oil with HZSM-5 was conducted with Py-GC/MS system.During the process,the pyrolysis temperature was set at 550?,the effects of feedstock to catalyst ratio and lignin to waste oil ratio on the pyrolysis conversion rate and product distribution were investigated.The results showed that the increase in catalyst to feedstock ratio and waste oil to lignin ratio promoted the conversion rate.The addition of catalyst could increase the selectivity of aromatics but decrease the selectivity of phenols.Besides,the synergistic effect between lignin and waste cooking oil existed and promoted the production of aromatics.The highest synergistic effect was obtained when the lignin to waste oil ratio was 1:1and the theoretical value of aromatic selectivity was 86.3%,about 24.8%higher than the experimental value.In addition,catalytic co-pyrolysis of lignin monomeric compounds?phenol and guaiacol?and waste oil was investigated.During the catalytic pyrolysis of only phenol,the conversion rate was almost 0%,but with the addition of waste oil,phenol could be converted to aromatics and alkylphenols.On the other hand,the guaiacol could be converted during the catalytic pyrolysis without waste oil,although the addition of waste oil resulted in more conversion of aromatics and alkylphenols.