Cracking characteristics of peanut straw pyrolysis volatiles over Ga-loaded HZSM-5 catalysts
Biomass pyrolysis is an effective method to convert lignocellulosic biomass into bio-oil,but the crude bio-oil has high oxygen content and low calorific value.The catalytic cracking of biomass pyrolysis volatiles using Ga-loaded HZSM-5 catalysts can promote the selective deoxygenation and aromatization of bio-oil,realizing the upgrading of bio-oil.Two Ga-loaded HZSM-5 catalysts(Ga-H5-E and Ga-H5-H)were prepared by ion exchange and hydrothermal methods,respectively.Catalytic cracking experiments of peanut straw pyrolysis volatiles were conducted in a two-stage fixed-bed reactor.The peanut straw was heated from room temperature to 700 ℃ at a heating rate of 10℃/min in the lower part of the reactor,and the evolved volatiles were catalytically cracked by the upper catalyst layer maintained at 600℃.The results show that compared to the unloaded HZSM-5,Ga-H5-E and Ga-H5-H increase the BTX(benzene,toluene and xylene)yield by 77%and 93%,respectively,with a significant increase in the production of toluene and xylene.The catalysts were characterized by thermogravimetric analysis,inductively coupled plasma emission spectrometry,X-ray diffraction,scanning electron microscopy,energy-dispersive X-ray spectroscopy,surface area analyzer,and chemisorption analyzer.The results indicate that the carbon deposition yield on both Ga-loaded catalysts is significantly lower than that on HZSM-5.Ga loading increases the strong acid sites on the catalyst,favoring the catalytic active centers for deoxygenation reactions.Compared to Ga-H5-E,Ga-H5-H has larger mesopores with smaller average pore diameter,and more Ga impregnation into the particle interior,which may promote the aromatization of ethylene and propylene within mesopores,thereby increasing the yield of monocyclic aromatic hydrocarbons.
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