Aromatics Production By Catalytic Fast Pyrolysis Of Pine Sawdust Over HZSM-5 Zeolite

The pyrolysis behavior and typical products from sawdust pyrolysis were conducted using thermogravimetry-mass spectroscopy(TG-MS)and pyrolysisgas-chromatography/mass spectrometry(Py-GC/MS).Fast pyrolysis of sawdust was also investigated in a drop tube quartz reactor to understand the effects of temperature and atmosphere(Ar and H2)on the product yields,gas composition,bio-oil characteristics,and the carbon and oxygen conversion.It was found that the H2 atmosphere at high temperature is favorable to the pyrolysis of biomass,which suppresses the polycondensation reaction of macromolecular compounds while promoting the cracking,dehydration,decarbonylation,and decarboxylation reaction.In addition,H2 can promote the formation of phenols and aldehydes.The catalytic reforming of the volatile from sawdust fast pyrolysis was investigated over zeolite(HZSM-5,Si/Al=25/50/80)after obtained the influences of temperature and atmosphere on sawdust fast pyrolysis.The results show that a large amount of olefins and aromatics were obtained after catalytic reforming over zeolite,and their yields and selectivities were affected by Si/Al,experimental temperature,and weight hourly space velocity(WHSV).(25)ZSM-5 is the best catalyst for producing olefins and aromatics,and the maximum aromatic carbon yield of 21.8% was obtained at 500 ?.(25)ZSM-5 produced the most polycyclic aromatic hydrocarbons(PAHs),(50)ZSM-5 produced the most monocyclic aromatic hydrocarbon,and(80)ZSM-5 obtained the maximum monocyclic aromatic hydrocarbon selectivity of 82.9%.The effects of temperature and WHSV on the catalytic effect were investigated over(25)ZSM-5.It was found that the total yield of aromatics increased first and then decreased with the increase of temperature,and the yield of each aromatic hydrocarbon changed with temperature.Among the monocyclic aromatic hydrocarbons,the yield of benzene increased,and the yield of toluene increased first and then decreased,while the yields of other alkylbenzenes decreased with the increase of temperature.The yields of naphthalene,alkylnaphthalene,and PAHs increased first and then decreased with increasing temperature,and all of which reached the maximum at 500 ?.The effect of WHSV on the catalytic effect is very limited,but there is also a certain rule with the increase of WHSV.The yields of benzene,toluene and ethylbenzene increased first and then decreased,the yield of xylene gradually increased,and the yields of naphthalene and PAHs gradually reduced.For further understand the source of aromatics,the three components of lignocellulosic biomass i.e.,lignin,cellulose,and hemicellulose were investigated by catalytic fast pyrolysis experiments at different temperatures.With the increase of temperature,aromatics yields of the three components increased first and then decreased,and the maximum value at 500 ? is 3.3,29.8 and 27.5%,respectively.The abilities of the three components to produce aromatics are reduced in the following order: cellulose > hemicellulose >> lignin.The main pathway for the production of aromatics by lignin is the cracking of oxygen-containing side chains on the benzene ring.The main pathway for the production of aromatics by cellulose and xylan is the aromatization of zeolite.Finally,the carbon deposition on the zeolite was analyzed by TG and DTG curves in air atmosphere.With the increase of temperature,the carbon deposition on zeolite gradually decreased,and the maximum weight loss peak moved toward the high temperature.Cellulose is most easily to form carbon deposition,and the temperature of maximum weight loss peak is higher than that of sawdust.