| Plastic not only brought convenience to people's lives,but also brought serious"white pollution".The disposal of polyolefin plastic,which is widely used today,has become a very urgent social problem.The photocatalytic degradation is relatively a good method,but at present,the catalyst used in the photocatalytic degradation has problems such as high degradation temperature,large amount of coke deposit,low gas-liquid conversion and low liquid yield.In this study,combining the channel advantages of mesoporous and the strong acidity and high hydrothermal stability of microporous on a micro-mesopore composite molecular sieve,the author creates a kind of Ce load of micro-mesoporous composite molecular sieve catalyst,which enjoys the advantages of the two materials,and meet the demand of catalysis and degradation of polyolefin plastic.In the experiment,micro-mesopore composite molecular sieve is produced under microwave heating with the method of microporous mesoporous crystal growth.At the same time,studies were done on the synthesis conditions,surface morphology and pore structure of composite molecular sieve before and after Ce load,acid catalytic activity and chain scission and hydrogenation of open-loop capacity.The effects of composite molecular sieve catalyst degrading polyethylene and polystyrene were examined.The main results of our study are summarized as follows:(1)Y/SBA-15 microporous and mesoporous composite molecular sieve was developed by microwave method,at the same time,rare earth Ce was successfully loaded onto the composite molecular sieve by ion impregnation method.The results show that the optimum synthesis conditions are as follows:the pH value 2-3,silica and P123 molar ratio 58,microwave power 200W,stirring velocity 500r/min,crystallization temperature 100?.(2)Many analysis of testing such as XRD,FT-IR,SEM/EDS,TEM,TG-DTG,N2 adsorption-desorption,XRF,Py-FT-IR and NH3-TPD were used in the characterization analysis of Y/SBA-15 and Ce-Y/SBA-15.The experimental results show that the surface morphology of the Y/SBA-15 and Ce-Y/SBA-15 composite molecular sieve is loose,rough,the overall shape is similar the lotus root,and the overall shape is regular.It can be concluded that SBA-15 mesoporous molecular sieve is along the outer surface of Y type zeolite growth,while SBA-15 growth outside Y which was as the core.The internal of composite molecular sieves has both microporous and mesoporous structure.The mass fraction of Ce in the Ce-Y/SBA-15 was 5.8409%,the majority of cerium was uniformly dispersed into the hole,part of the Ce was into the zeolite framework,thereby cerium doping did not affect the basic structure of composite molecular sieve with no agglomeration,the particle clustouhuiers formed contrast uniformity.In the mesoporous region the results of Y/SBA-15 and Ce-Y/SBA-15 was:mesoporous pore diameter about 6nm,mesoporous wall thickness 1.84,1.88nm,microporous pore diameter about 1.8nm,microporous wall thickness 0.45,0.48nm.The hole wall of Ce-Y/SBA-15 was thicker than Y/SBA-15,the hydrothermal stability of Ce-Y/SBA-15 was more than Y/SBA-15 either.(3)The synthesis mechanism of micro and mesoporous composite material was discussed,and process can be divided into four stages:The first stage is the thforming stage of self-assembly of aggregates,the second stage is to form organic-inorganic compound phase,the third stage is the stage of assembly for rderly complex pore structure,the fourth stage is the orderly composite hole phase.The structure prediction of micro and mesoporous composite material is composed of colloidal particles arranged in disorder to the spherical particles to short rod like particles,and eventually grows into a lotus root tube shaped composite structure.(4)The order of Lewis acidsites strength from large to small is:HY/SBA-15,Ce-HY/SBA-15,HY-SBA-15,NaY/SBA-15,while the order of B acid sites strength from large to small is:Ce-HY/SBA-15,HY/SBA-15,HY-SBA-15,NaY/SBA-15.Ce improved the B acid strength and acid catalytic activity of composite molecular sieves.(5)The synthesis of n-butyl acetate was as the probe reaction,using Ce-HY/SBA-15 as catalyst,when the catalyst mass fraction is 10%,the concentration of cerium nitrate is 0.6mol/L,acid alcohol molar ratio is 1:1.2,reaction time is 2.0h,the rate of esterification was up to 94.4%.Acid catalytic mechanism of rare earth modified molecular sieve was preliminary studied,Ce can improve the acid strength of the composite molecular sieve.Modified acid catalytic composite molecular sieve is composed of B and Lewis acid interaction,and SO42-contributes to the formation of the modified material surface acid sites.(6)Taking n-heptane as the reactant,it is examined the chain breaking ability of the catalyst.The conversion rate of Ce-Y/SBA-15 is higher than Y/SBA-15.Hydrocracking performance of Ce-Y/SBA-15 is better than that of Y/SBA-15,acidic functional and hydrogenation function is well matched in Ce-Y/SBA-15.The cracking reaction of Ce-Y/SBA-15 catalyzing n-heptane is the first-order pyrolysis,while second-order pyrolysis is effectively inhibited.Taking toluene as the reactant,it is examined the ability of open-loop of the catalyst.The open-loop rate of Ce-Y/SBA-15 is more than Y/SBA-15.The hydrogenation products's yield decreases as the temperature increases,the yield of the open-loop products increased with the increase of the acidity of the catalyst.Ce-Y/SBA-15 hydrogenation open-loop ability is better than Y/SBA-15,which shows strong acid quantity increase contributes to the catalyst for hydrogenation of open-loop performance improvement.Ce-Y/SBA-15's acidity and acid strength is higher than Y/SBA-15's,so the chain breaking and open-loop capacity of Ce-Y/SBA-15 is better than Y/SBA-15's.(7)The total acidity of catalysts determines the catalytic degradation of polyethylene effect.High total acid and strong acid distribution of the catalyst can improve the removal rate of polyethylene.Ce-HY/SBA-15 reduces the pyrolysis temperature of 40? of polyethylene,its catalytic degradation of PE obtained the liquid product distribution concentrated,dominated by C7-C14,in which less carbon,more paraffin;while it catalyzed degradation of PE obtained the gas product dominated by C3?C6 fat race.Ce can improve the composite molecular sieve B acid strength and the total acid strength,so in the Ce-HY/SBA-15 catalytic degradation of the PE reaction,the total conversion,gas yield,liquid yield are better than the thermal cracking reaction.The pore structure of catalyst determines the catalytic degradation of polystyrene effect,catalyst which with larger aperture,higher total acid,stronger B acid is helpful for increasing the yield of polystyrene degradation.Ce-HY/SBA-15 reduces the pyrolysis temperature of 60? of polystyrene,its catalytic degradation of PS obtained the liquid product distribution wide,dominated by benzene,toluene,cumene,indene and their derivatives.Ce can improve the composite molecular sieve B acid strength and the total acid strength,so Ce-HY/SBA-15 enhances the catalytic degradation of polystyrene. |
PDF Full Text Request