The Breaking Law Of Chemical Bonds During Lignin Pyrolysis And The Products Regulation

Lignin is an extremely abundant natural resource,it is the only natural macromolecular polymer that provides aromatic rings.In recent years,the biomass refining industry has brought a lot of lignin residue,which needs an effective resource utilization technology.The generation of value-added chemicals or qualitied biofuel from lignin via an effective and selective thermochemical conversion strategy is the key to improve the efficiency of biomass utilization.Pyrolysis is the use of thermal energy to cut off the chemical bonds in the macromolecules of biomass to convert them into low molecular substances in the presence of air or a small amount of air.The breakage and recombination of key chemical bonds,the secondary reaction process of primary pyrolysis products were studied in detail.The relationship between the composition of pyrolysis products and the conditions of pyrolysis conditions,lignin structure,catalyst addition and so on were studied.Those studies would improve the yield and stability of lignin pyrolysis liquid phase products,reduce the content of oligomers,realize their efficient transformation and high value utilization to provide the basis and theoretical guidance.The guaiacol type lignin monomer model was used as the object.The pyrolysis-in situ FTIR was used to detect the functional groups during the pyrolysis process.In combination of the qualitative and semi-quantitative analysis results from the pyrolysis-gas chromatographymass spectrometry(Py-GC-MS),the calculation of the corresponding energy barrier from the main reaction pathway,which proved the key intermediate o-methylenequinone structure during the pyrolysis of guaiacol.And the transition process of o-methylene quinone to pyrolytic coke and oligomer was pointed out.Five kinds of ?-O-4 dimer model compounds were used as the research object.The effects of C?-OH and phenolic hydroxyl groups on pyrolysis process and product distribution were investigated.The results showed that C?-OH was prone to dehydroxymethyl reaction,and the effect on the thermal stability of the model compound is not significant.While the presence of phenolic hydroxyl groups can greatly reduce the fracture temperature of the model compound ?-O-4 ether bond,and the pyrolysis products are more widely distributed.The free radical(m/z=123)was detected by in-situ TG-MS during the pyrolysis of Guaiacylglycerol-betaguaiacyl ether(GG),which proved the free radical homogeneous reaction of the ?-O-4 ether bond in the pyrolysis process.The U—tube closed-type pyrolysis reactor was developed and compared with the distribution of the three lignin raw materials in nitrogen and air atmosphere.It was found that the air had a certain effect on the pyrolysis of lignin,but it should control the reaction time as 60 s.The influence of copper oxide,formate and dihydrate oxalic acid on the pyrolysis process and product distribution of lignin was also studied.It was found that adding 5wt% of copper oxide could significantly improve the yield of liquid product and reduce the fused ring(PAHs)content;calcium formate could significantly improve the yield of guaiacol in pyrolysis bio-oil;dihydrate oxalic acid affects the melting process of lignin before thermal decomposition,and 10wt% addition could obviously reduce the yield of char.The effects of three typical lignin(alkaline lignin AL,enzymatic hydrolysis / mild lignin EMAL,wood lignin MWL)and two modified lignin(based on fir raw materials were studied by hydrochloric acid-formaldehyde method The results showed that the order of the enthalpy of the modified lignin FAL and the lignin-based modified lignin D-AL was found to be MWL> FAL> EMAL> AL>D-AL.The protection of C?-OH and C?-OH can effectively reduce the yield of coke and improve the yield of two high value-added chemicals of pinealdehyde and 4-propenyl-2-methoxyphenol in pyrolysis products.