Study On The Catalytic Pyrolysis Of Typical Municipal Solid Wastes With Alkaline Earth Metal Oxides And HZSM-5

Pyrolysis of municipal solid waste conforms to the concept of low-carbon development,and is an important way to improve domestic energy structure.It is of great significance to reduce environmental risks,achieve global carbon neutrality,and promote the sustainable development of the community of shared future for mankind.However,the unsatisfied quality of pyrolysis oil produced by direct pyrolysis limits the application of municipal solid waste pyrolysis.In order to overcome this problem,suitable catalysts urgently need to be developed.Alkaline earth metal oxides or HZSM-5 have been widely used in the catalytic pyrolysis of municipal solid waste,showing great potential for practical application.However,the catalytic effect and mechanism of their combined catalysis are still unclear.Therefore,here we took the pyrolysis of typical municipal solid waste as an example to evaluate the catalytic effect of alkaline earth metal oxides combined with HZSM-5,and investigated the catalytic mechanism with kinetic method.First,the effect of reaction conditions on the catalytic co-pyrolysis of the waste cotton textiles and polystyrene was assessed.In a fixed bed reactor,reaction conditions included the pyrolysis temperature,the ratio of the raw materials,the ratio of the catalysts and the ratio of catalysts to raw materials on the catalytic co-pyrolysis of the blends were studied,separately.In both CaO/HZSM-5 and MgO/HZSM-5 reaction systems,the yield of pyrolysis oil achieved the highest at 550°C.At the same time,data showed that there was a significant synergistic effect between waste cotton textiles and polystyrene.Besides,the addition of polystyrene improved the quality of pyrolysis oil.When the ratio of polystyrene to waste cotton textile was1:1,the actual content of aromatic C in the pyrolysis oil catalyzed by CaO/HZSM-5 and MgO/HZSM-5 was 23.9%and 23.79%respectively,which were much higher than the theoretical value.The actual content of aliphatic C-O was 22.73%and 22.02%,which were lower than the theoretical value.In addition,compared with the pyrolysis catalyzed by alkaline earth metal oxides or HZSM-5 alone,the coupled catalyst significantly improved the quality of the pyrolysis oil.In the pyrolysis process,alkaline earth metal oxides catalyzed the cracking of macromolecular compounds and reduced oxygen-containing compounds to form hydrocarbon precursors.These hydrocarbon precursors were then converted into aromatic hydrocarbons with HZSM-5.In addition,compared with CaO/HZSM-5,MgO/HZSM-5 exhibited better catalytic performance in improving the quality of pyrolysis oil and the best quality of pyrolysis oil was achieved when the ratio of MgO and HZSM-5 was 1:1 in the study of the ratio of catalysts.Furthermore,the influence of precursor types of alkaline earth metal oxide on the co-pyrolysis process of wood and polystyrene was discussed.For CaO/HZSM-5 reaction system,the quality of pyrolysis oil was the best under the action of CaO prepared by L-calcium lactate（CL-CaO）combined with HZSM-5,where the content of aromatic C-C was 71.17%and the content of oxygen-containing functional group was as low as 13.23%.At the same time,the changes of the types of magnesium oxide precursors have little effect on the composition of pyrolysis oil.In addition,CL-CaO/HZSM-5 was found a better ability of reducing the activation energy,whereas MgO prepared by magnesium carbonate had the lowest activation energy in MgO/HZSM-5 reaction system.Finally,the effects of the SiO₂/Al₂O₃ ratio on the co-pyrolysis process of wood and polystyrene were studied in CaO/HZSM-5 and MgO/HZSM-5 reaction systems.Under the action of HZSM-5 with SiO₂/Al₂O₃ ratio of 18（18-HZSM-5）combined with CaO,the highest content of aromatic C-C in the pyrolysis oil and the lowest content of oxygen-containing functional groups were achieved as 71.34%and 13.07%,respectively.Meanwhile,the lowest content of aromatic C-C and the highest content of oxygen-containing functional groups were achieved as 56.13%and 21.63%,respectively with a SiO₂/Al₂O₃ ratio of 80.In addition,similar results were achieved catalyzed by MgO/HZSM-5.It may be related to the microstructure of HZSM-5 and the distribution of acidic sites on the surface.In addition,the data showed that in the CaO/HZSM-5 reaction system,the highest conversion rate of wood and PS and the lowest apparent activation energy was obtained by CaO/18-HZSM-5.Besides,the activation energy was found lowest with a SiO₂/Al₂O₃ ratio of 200 in MgO/HZSM-5 reaction system.