Investigation On The Relevance Between Chemical Structure Of Lignin And Properties Of Products Derived From Lignin Torrefaction And Pyrolysis

As the nature's dominant aromatic polymer,lignin isone of the major components in the lignocellulosic biomass,and contributes about 15%-35%weight and 40%energy of the dry lignocellulosic biomass.Lignin is composed of three typical phenylpropane units which are randomly bonded together by the ether bond(?-O-4,?-O-4,and ?-O-4)and the carbon-carbon bond(5-5,?-1,and ?-5).In this study,lignin was used to produce value-added bio-char and bio-chemicals viatorrefaction pretreatment,catalytic fast pyrolysis and carbonization process.(1)Four types of lignin were isolated from palm kernel shell with different severities:milled wood lignin(MWL),alkali lignin(AL),Klason lignin(KL),and organosolv ethanol lignin(OEL).A deep investigation of the relevance of the pyrolysis behaviors and chemical structure was carried out by FTIR,GPC,2D-HSQC-NMR,TGA-FTIR and Py-GC/MS.AL contained highest content of ?-O-4 aryl ether bond(53.9/100 Ar)and highest value of S/G ratio(1.68).MWL showed the widest temperature range(126-536?)of thermal degradation because of its inhomogeneous distribution of molecular weight.Highest content of oxygen-containing non-condensable gas components(H2O,CO2,CO)was observed in AL.The dominant organic components from lignin pyrolysis were S-type phenols,G-type phenols,P-type phenols,and C-type phenols.G-type(9.74-26.01%)was the dominant phenols products in AL,while P-type(44.23-56.01%)for KL,P-type(29.38-56.07%)for OEL,and G-type(9.08-25.81%)and P-type(22.60-29.04%)in MWL.Higher pyrolysis temperature promoted the formation of aromatics.As the conversion rate increased from 0.1 to 0.8,the activation energy estimated from DAEM model of four types of lignin,all gradually increased.(2)In order to reveal the deoxygenation mechanism of lignin torrefaction,the relevance between evolution of chemical structure of torrefied lignin and the properties of torrefied gaseous,liquid,and solid products was established in this study.Results showed that the contents of oxygen element,?-O-4 linkages,oxygen-containing functional groups(aliphatic-OH,aliphatic-COOH,aromatic-OCH3)in lignin decreased with the increase of the torrefaction temperature from 210 to 300?.The oxygen removal eficiency of lignin torrefaction reached the maximum value of 25.53%at 300?.The removed oxygen in the torrefied lignin was transferred into the torrefied gaseous product(E.g.CO2,H2O,and CO)and torrefied liquid product(E.g.G-type and P-type phenols,acids).Among the torrefied gaseous products,CO2 was the dominant oxygen carrier,followed by CO and H2O.Among the torrefied liquid products,G-type phenols were the dominant oxygen carrier,followed by P-type phenols and acids.(3)The effect of lignin source(MWL,AL,KL,and OEL)and lignin/catalyst ratioon the properties of pyrolysis products was investigated by using TGA-FTIR and Py-GC/MS.Results showed that based on the TGA analysis,the residue mass of MWL pyrolysis was lowest in the four types of lignin.The release content of H2O?CH4?CO2and CO gradually increased with the increase of lignin/catalyst ratio.Among the four types of lignin,the content of benzene,xylene,and toluene reached their maximum value of 4.51 × 107,8.58 × 107,and 1.26 × 108,respectively,derived from MWL pyrolysis at the lignin/catalyst ratio of 1:5.(4)First of all,the metal Mg and Ga were selected to modify HZSM-5 to prepare Mg/Ga-HZSM-5 bifunctional catalyst,and secondly,from softwood Chinese fir(CF),hardwood poplar(P)and herbaceous The lignin lignin(MWL)was extracted from corn stalk(CS),and the lignin catalytic pyrolysis experiment was carried out to study the effect of metal modification and lignin species on the yield of triphenylbenzene(BTX).The results showed that P contained the highest ?-O-4 aryl ether bond(53.9/100 Ar),while CS contained the highest S/G ratio(1.68).P is a linear molecular structure with long oxygen-containing branched side chains.CF may have a shorter side chain due to more condensation structures,while CS may have more intermediate cross-linking structures and lignin molecules.The bifunctional catalyst was prepared by Mg,Ga metal modified HZSM-5.It was found that Mg/Ga-HZSM-5 has the largest mesopore volume(0.06 cm3/g)and more weak acid sites(0.55 mmol/g)and the lowest strong acid position(0.29 mmol/g).Mg/Ga-HZSM-5 can effectively improve the selective yield of BTX,which is the best for the catalytic pyrolysis of CS to prepare BTX.Among them,CF(63.01%)increased by 9.95%compared with HZSM-5(53.06%),P(64.47%)increased by 3.4%compared with HZSM-5(61.07%),and CS(63.18%)was higher than HZSM-5(37.77%).improved(25.41%).