Effect Of Co-pvrolvsis Of Typical Solid Wastes Components On Tar Properties And Its Catalytic Cracking

With the rapid growth in economic of our country and the acceleration of urbanization,the output of municipal solid waste(MSW)also increases sharply.Recently,pyrolysis/gasification of MSW has attracted more and more attention due to incomparable advantages.However,organic pollutants,namely tar will be generated during pyrolysis/gasification.How to control the emission of tar has become a key environmental problem.The diversity of MSW components in our country makes it is necessary to study the effect of interaction during pyrolysis/gasification of complex components on tar characteristics.Based on the previous researches,this dissertation focuses on typical MSW components and researches on the interaction during co-pyrolysis on kinetics as well as the formation,characteristics and catalytic cracking of tar systematically,which is important to obtain a comprehensive understanding of tar characteistics and guide the sorting of MSW as well as the control of tar.Firstly,Py-GC-MS analysis was applied to have an overall understanding of the characteristics of pyrolysis tar derived from MSW.The results were compared with that derived from conventional fossil fuels.Results showed that the pyrolysis products of biomass MSW were rich in oxygenated hydrocarbons while the pyrolysis products of fossil fuel MSW mainly comprised of BTEXs,PAHs,alkanes and alkenes.The pyrolysis products of fossil fuels varied a lot,among which phenols and PAHs were the main composition.Cellulose,starch and soybean protein were chosen as typical biomass MSW components and PVC were chosen as typical fossil fuel MSW components.Thermal analysis was applyied to research on the pyrolytic reaction characteristics.Interaction during the co-pyrolysis of biomass MSW components and PVC on thermal process and kinetic parameters has been paid more attention.Results indicated that interactin had occurred and acceleration had been observed for the pyrolysis of all mixtures.The co-pyrolysis of cellulose/PVC,starch/PVC,soybean protein/PVC reduced the activation energy by 27.58?30.18%,23.34?63.02%and 2.10?12.81%,respectively.On the basis of thermal analysis,fixed-bed pyrolysis experiments were carried out to research on the formation characteristics of tar and interation has also been concerned.When the feeding material contained soybean protein,the possible form of nitrogen of nitrogen-containing tar components had also been analyzed.Results showed that tar derived from cellulose,starch and soybean protein was rich in oxygenated hydrocarbons while tar derived from PVC was not.In addition,the relative content of aromatic compounds in tar derived from cellulose and starch was less than 30%while tar derived from soybean protein and PVC contained much aromatic compounds,which can reach to 50%and 82%,respectively.When cellulose or starch were pyrolyzed with PVC,interaction promoted the cracking and condensation polymerizationof tar.As a result,pyrolysis tar of mixtures contained heavier compounds.When soybean protein and PVC were pyrolyzed together,tar components of class 5 were generated,which will lead to the increase of dew point.Based on the above studies,cellulose and PVC were selected as representative components of MSW.A comprehensive research on tar characteristics as well as interaction during co-pyrolysis has been carried out.It was discoveried that during the co-pyrolysis of cellulose and PVC,PVC had played a dominant role on most tar properties,including the types of H and C bonds,contact angle and so on.What's more,interaction increased the density and particle size of carbon black in tar,even resulted in a wide range of cross-linkage.Meanwhile,interaction enhanced the migration of chlorine to tar.The concentration of chlorine in tar increased by 2 to 9 times,which will lead to corrosion of subsequent equipments easily.In addition,inteactin was observed to improve the surface tension by 26-28%and reduce the kinematic viscosity by 19-30%.Finally,research on effect of interactions on the catalytic cracking of tar was performed with cellulose and PVC chosen as representative MSW components and calcined dolomite as catalyst.Results indicated that calcined dolomite showed excellent catalytic effect for tar derived from individual feeding material and the catalytic efficiency was higher than 90%.However,when cellulose and PVC were mixed together,the catalytic efficiency of pyrolysis tar was about 8-29%lower than expected.The analysis of tar composition showed that the thermal and catalytic decomposition of tar can reduce the diversity of tar components as well as the molecular mass of tar significantly.The analysis of catalyst before and after use indicated that carbon deposition was relatively slight compared with poisioning caused by chlorine.When cellulose and PVC were mixed,the chlorine contents of the used catalyst increased by around 3?15 times than the linear combination of those from the single cases.Therefore,it is the poisoning by chlorine rather than carbon deposition that should be responsible for the low catalytic efficiency of dolomite.To conclude,the interaction between cellulose and PVC promotes the formation of heavier hydrocarbons and improve the concentration of chlorine in tar on one hand and,on the other hand,chlorine in tar is easily to adhere on the surface of catalyst and lead to the poisoning of dolomite.Both contribute to the low cracking efficiency of tar.