Study On Aromatics Production From Catalytic Pyrolysis Upgraded Of Lignocellulose

As the fossil resources excessive consumption and environmental pollution,renewable resources to replace fossil resources has become a major problem facing the need to solve the survival and development of human society,biomass energy as a new renewable clean energy was being paid more and more attention,and the catalytic pyrolysis technology was an key way of utilization and energy efficient use of biomass,but because of the relatively lower target production yield and selectivity as well as easily coking of catalyst,so limited its application;so,in this dissertation,using forestry wastes as raw material,we conducted some studies on fundamental and technology research to solve the key scientific and technology problems in producing chemicals such as benzene,toluene and xylene from biomass.The mainly include the biomass feed stocks,hydrogen supplying reagent and modified catalyst to study the mechanism of catalytic pyrolysis and production generation regulation,enhancing methods of the hydrogen to carbon effective ratio and structure change of raw material pretreatment,to improve the yields and selectivity of target products(benzene,toluene and xylene),improve the behavior of bio-oil.The main contents and results of experiments are as follows.The pyrolysis conditions(pyrolysis temperature,catalytic temperature,the biomass to catalyst ratio,adding methods and SAR)of biomass were studied by using Py-GC/MS.The product composition,distribution and mechanisms of biomass were studied.The results show that:The optimal pyrolysis conditions of biomass were pyrolyzed at 450?,catalytic temperature at 550?,SAR25 with a biomass to catalyst of 1:2.The contents of single ring aromatics and residues reached 69%and 28.95%,respectively,and the calorific value reached 31.74 MJ/Kg;in comparison,at a pyrolysis temperature of 450?,the in situ catalytic pyrolysis of biomass only produces 27.51%and 30.01%light aromatic and residues,respectively.And,catalyst can clearly promote the dehydration reaction of the initial stage,which can effectively reduce the activation energy and the steric hindrance effect,accelerate the reaction rate,increase the conversion of wood powder(the conversion rate increased from 70.39%to 94.07%),and reduce the amount of residual carbon;for different catalytic pyrolysis processes,the composition and selectivity of the bio-oil vary:higher permanent gas yields,higher aromatic contents and a higher selectivity to benzene and toluene in the bio-oil were observed from the ex situ catalytic pyrolysis upgrading,and the deoxidation effect was better,however,higher yields of the bio-oil and a higher selectivity to C10+ polycyclic aromatic hydrocarbon were recorded during in situ catalytic pyrolysis;moreover,a higher temperature was conducive to the dealkylation reaction,and it increased the selectivity of non-substituted aromatics,while a lower temperature caused the alkylation reaction,which increased the selectivity of the substituted aromatics.At the same time,with the increase of SRA,the pore volume reduced but average pore diameter of HZSM-5 catalyst increased,the total acidity of the molecular sieve decreased gradually,catalytic activity decreased;meanwhile,the increase in the acidity led to decreased non-condensable gases yield,that were associated with the increase of bio-oil yield,and,calorific value and moisture content were reduced,the ability of deoxygenation enhanced;while,monoaromatic hydrocarbons(BTXE)content decreased,polycyclic aromatic hydrocarbons(2-ring,3-ring)content increased significantly.The selectivity of benzene,toluene and xylene decreased from 69wt%to 6.85wt%,while the selectivity of naphthalene and its derivatives increased significantly,as catalyst acidity increased.Additionally,the acidity increased the selectivity of substituted aromatic,while,and decreased the selectivity to the unsubstituted aromatic.In order to understand the pyrolysis mechanization of biomass and further enable to select suitable agricultural and forestry residues biomass resources for the generation desired products,the pyrolysis and catalytic pyrolysis characteristics of three main components(hemicellulose,cellulose and lignin)of biomass were investigated using a thermogravimetric analyzer(TGA)with a fixed-bed reactor,respectively,and Fourier transform infrared spectroscopy(FTIR)and elemental analysis were used to characterize,the results showed that:the thermal stability of hemicellulose was the worse,the thermal stability of cellulose is higher,and the range of pyrolysis temperature was narrow,lignin decomposed over a wider range of temperature and generated a higher char yield.After catalytic pyrolysis over HZSM-5 catalyst,the conversion ratio increased,the ratio for the three components in the following order:Lignin<Cellulose<Biomass<Xylan,The Starink method was introduced to analysze the thermal reaction kinetic,the activation energy(Ea)and the correspondence,the addition of HZSM-5 catalyst can improve the reaction activity and decrease the activation energy,the decreased in the the following order:xylan(31.40%)>pine(14.91%)>lignin(7.57%)>cellulose(6.65%);the pyrolysis of cellulose gave the highest yield of bio-oil rich in levoglucosan and other anhydrosugars with minimal coke formation,xylan gave the high gas yield and moderate yield of bio-oil,rich in furfural,lignin gave the highest solid residue and produced a lowest yield of bio-oil that was rich in phenolic compounds;after catalytic pyrolysis,xylan gave the highest the yield of monocyclic aromatic hydrocarbons,that was 76.40%,and preferred to benzene and toluene,and cellulose gave the higher selectivity of xylene and naphthalene,however,lignin could enhance the selectivity of C10+ polycyclic aromatic hydrocarbons,so,catalytic pyrolysis can effectively improve the properties of bio-oil and enhance the fuel performance.The main objective of this work was to study aromatics production via the catalytic pyrolysis upgrading of biomass using metal-loaded(Zn,Ga,Ni,Co,Mg and Cu),alkali solution(0.2mol/L-0.6mol/L)and metal oxides(CaO)were mixed with H-ZSM-5 catalyst to solve the catalyst deactivation.The prepared M-ZSM-5 catalysts were evaluated by X-ray diffraction,thermal desorption spectroscopy and scanning electron microscopy.The properties,composition and production distribution of bio-oil were also analysed.Results showed that the M-ZSM-5 catalysts yielded a higher amount of non-condensable gas at the expense of the liquid yields.The Ga-ZSM-5 catalysts produced the highest yields of bio-oil(25.76 wt%),but the lowest amount of coke(22.08%)compared with the unmodified ZSM-5 catalyst(33.38%).The content of the single-ring aromatics prepared by using the Zn-ZSM-5 catalysts was the highest at 90.28 wt%,whereas that of the polycyclic aromatic hydrocarbon prepared by the Ni-ZSM-5 catalysts was the highest at 31.36 wt%.Moreover,the selectivities of the mono aromatic hydrocarbons,such as C7 and C8,were significantly affected by the use of the M-ZSM-5 catalysts.The Zn-ZSM-5 catalysts were the most selective for toluene and xylenes with contents of 36.52 wt%and 35.32 wt%,respectively,whereas the Co-based catalysts were the most selective for indene.The Ni-based catalysts can obviously improve the selectivities of benzene production and C10+ polycyclic aromatic hydrocarbons.Zn-ZSM-5 is the most effective catalyst that can be used in the production of aromatic hydrocarbons.At the same time,alkali treatment of HZSM-5 can remove the extra-framework Si species to enhance the diffusion property,creation the mesopores,and the pore diameter of mesopores increases with the increase of K2CO3 concentration,however,the total acid amount decreased,the hierarchical HZSM-5 catalyst produced more aromatic hydrocarbons(67.75-82.81%)and less coke(31.26-28.06%)formation in CFP of lignin and lignocellulosic biomass that contained the lignin component than the control HZSM-5(69.25%aromatics and 28.95%coke).The highest aromatic yield(82.81%)and lowest coke yield(28.06%)were obtained in CFP of pine wood with mildly desilicated zeolite treated with 0.5mol/L K2CO3 solution.At last,the pyrolysis characteristics of biomass were changed by the addition of CaO(bond breaking)and ZSM-5(deoxidation)catalyst,which made the carbon residue rate increased significantly,the maximum weight loss rate decreased,biomass conversion rate increased,the activity of catalyst order is:ZSM-5>CaO+ZSM-5>CaO,at the same time,characteristic parameter such as activation energy,the activation enthalpy,activation entropy and the steric parameter increased significantly at expensive of reaction ratio;moreover,CaO mixed with ZSM-5 catalyst can improve the gas yield and aromatic hydrocarbon yield significantly,however,the yield of bio-oil decreased slightly,the maximum aromatic yield was 70.45wt%of that pure ZSM-5 catalyst(69wt%),meanwhile,different disposal mode which show different aromatic selectivity,the separated mode of ZSM-5 and biomass mixed with CaO gave the highest yield of BTXE,while,the completely separated mode produced the highest yield of methyl naphthalene in naphthalene and its derivatives.To solve the problem of low hydrocarbon yield in CFP,biomass co-pyrolysis conversion with high H/Ceff ratio feedstocks(rubber seed oil,LDPE and alchohol)were proposed to increase the H/Ceff ratio in biomass conversion process by hydrogen transfer.The reaction pathway of co-catalytic pyrolysis was disclosed and the interaction between biomass and hydrogen supplying reagent were also investigated.aromatic yields and selectivity increased with the H/Ceff ratio,there was a synergistic effect between biomass and hydrogen supplying reagent,RSO,LDPE and methanol can provide hydrogen source to promote biomass catalytic conversion to the target production;furthermore,the oxygenated compounds produced during catalytic pyrolysis,which can also promote the fracture of larger vegetable oil,to occur Diels-Alder reaction,improving the utilization efficiency of hydrogen supplying reagent.RSO and methanol co-pyrolysis with biomass can produce the higher aromatic,however,LDPE was in advance,the highest selectivity of toluene produced by RSO catalytic pyrolysis,and because of the existence of C-C,the selectivity of benzene produced by LDPE was better,and methanol produced more xylene.At the same time,it was found that the products of LDPE were converted from conventional paraffin to light aromatics by catalytic pyrolysis,HZSM-5 catalyst has better deoxidation effect on aldehydes,ketones,acids to produce aromatic,but had a poor deoxidation effect on lignin,so the yield of aromatic was lower,Most of the aromatic hydrocarbons are produced by the break of the side chain in the structure of benzene propane and a smaller parts were throughout deoxidation of phenolic compounds.To improve the high value utilization of biomass,torrefaction pretreatments of biomass were conducted at 210,230,250,270,and 300? with a residence time of 30 min.The pyrolysis of torrefied biomass was also performed on a fixed-bed reactor system at 450 ?.The effect of torrefaction temperature on the yield,energy yield,structure,physical-chemical characteristics,and production composition of bio-oil was studied.The torrefaction pretreatment improved the fuel characteristics of pyrolysis products.When the torrefaction temperature was increased,the-OH and C=O contents decreased,the C=C contents increased,the pyrolysis peak temperature decreased,the residual carbon contents noticeable increased,and the Ea remained in the range of 69 to 129 kJmol-1.The pore volume increased and the crystallinity index decreased due to degradation and recrystallization.The solid yield of pyrolysis biomass decreased sharply in contrast to the liquid yield.When the torrefaction temperature increased,the bio-oil yield decreased from 36.82 wt.%to 20.13 wt.%.The phenol content in the bio-oil markedly increased;however,oxygen containing compounds such as acids,sugars,and furans,significantly decreased,after catalytic pyrolysis,the selectivity of BTXE at the expense of bio-oil yield,when the torrefaction temperature was 230?,the selectivity of BTXE were highest.In brief,catalytic pyrolysis upgrading of biomass and component with modified H-ZSM-5 catalyst can improve the product compositions and distribution,promote the qualities of bio-oil,enhance the yields of target production and reduce the catalyst deactivation,there are significant interactions between biomass and hydrogen supplying reagent,the interaction intensity was related to the H/Ceff ratio,so,achieving the purpose of catalytic conversion of biomass to produce high value-added liquid fuels and chemicals.