Preparation And Catalytic Behaviour Of Nanosized Nickel-Based Catalysts For The Pyrolysis And Gasification Of Municipal Solid Waste To Hydrogen-rich Gas

More and more energy resource especially fossil fuel consumed raising the question ofserious environmental pollution severely threatens the health and survival of human being,and people are aware of the importance of renewable energy,which can gradually replacethe existing fossil fuel in order to relieve the shortage of energy and environmentalpollution.At present,the quantity of Municipal Solid Waste(MSW)has increasedsignificantly in the industrialized and developing countries with the question of itssustainable disposal management.Lots of energy and money was used for transportation,treatment,and final disposal of MSW,thus the disposal of MSW is one of the mostimportant and urgent problems in environmental management in the world.The pyrolysisand gasification of MSW has been considered to be a promising method for future energysystems to meet environmental requirements,and provides one of the mostcost-competitive means of obtaining hydrogen-rich gas from MSW,and have promisingapplication in Waste-To-Energy(WTE)technology.The pyrolysis and gasification ofMSW can not only alleviate the dual-stress of energy and environmental,and reduce thepollution caused by MSW,but also achieve reclamation of MSW.However,during the pyrolysis and gasification process of MSW,much tar and lowgasification efficiency,low hydrogen yield exist.In general,nickel-based catalysts areused to eliminate the tar,increase the yield of hydrogen-rich gas,and to decrease thetemperature of pyrolysis and gasification.Coordination homogeneous precipitation method was used to synthesize nanosizednickel hydroxide powder products with the ammonia and nickel nitrate hexahydrate as theraw materials.Transmission Electron Microscope(TEM),powder X-ray Diffraction(XRD),Thermal Gravimetry and Differential Thermal Analysis(TG/DTA),FourierTransform Infrared spectroscopy(FTIR)and Scanning Electronic Microscope(SEM)wereused to characterize the microstructure and morphology of the synthesized precursor andNano-NiO powder products,the XRD and FTIR patterns showed that the synthesizedprecursor was hexagonalβ-Ni(OH)₂ crystallites,which decompose at 300.3℃,and thenNiO nanocrystal was produced.During the course ofβ-Ni(OH)₂ crystallite preparation,thereaction temperature,reaction time,water volume and mole ratios of Ni(NO₃)₂·6H₂O to ammonia were studied.Compared with Bulk-NiO,δ(OH)peak of the Nano-NiO productsin FTIR pattern gives rise to red-shift.While,v(Ni—O)peak gives rise to blue-shift.XRD and FTIR patterns showed that the NiO powder products are nanosized FCCobtained from the synthesized precursorβ-Ni(OH)₂ crystallite calcined at 400℃.TEMimages showed that spherical Nano-NiO are 20—25 nm in mean particle diameter,NiOnanorods are 5 nm in mean particle diameter,30-50 nm in length and 0.24 nm ininterplanar crystal spacing(111).All NiO nanorods grow in the direction of[111].FTIRpatterns showed that the smaller Nano-NiO powder is,more significant the red-shift ofcharacteristic peak is.Ultrasound chemical precipitation method was used to synthesize the precursor powderswith the ammonium oxalate and nickel nitrate hexahydrate as the raw materials.The XRDpatterns showed that the precursor powders are NiC₂O₄·2H₂O,and FTIR patternsconfirmed the result of XRD pattern.TEM image indicated that Nano-NiO powderproducts agglomerate slightly in a mean particle size of 70 nm.When the mole ratios ofammonium oxalate to nickel nitrate hexahydrate increased,Ni appeared in the powderproducts.The catalytic activity of Nano-NiO and Bulk-NiO powder products used in woodcomponent of MSW pryolysis with TG/DTA method was evaluated,Nano-NiO performedbetter than Bulk-NiO in promoting the decompostion of wood component.The catalyticpyrolysis characteristic was discussed,then dynamics model was proposed according tothe TG/DTA data.Coordination homogeneous precipitation method also was used to synthesize NiOnanosheets on the surface of the support Al₂O₃,the supported coating was 8-500μm inthickness,which consist of NiO nanosheets.XRD,FTIR and SEM were used tocharacterize the microstructure and morphology of the Nano-NiO/Al₂O₃ catalyst.The Nano-NiO/Al₂O₃ catalyst was use in the pyrolysis and gasification process of MSWto evaluate their catalytic activity,experimental results showed that Nano-NiO/Al_O3catalyst performed better than calcined dolomite in eliminating tar and increasinghydrogen yield.Meanwhile,during the MSW pyrolysis with Nano-NiO/Al₂O₃ catalyst orcalcined dolomite,the reactor temperature and heating rate have significant influences on the MSW pyrolysis,higher reactor temperature and heating rate can reduce tar yield andincrease gas yield and hydrogen yield.Furthermore,there was a good agreement between the experimental gas compositionand that corresponding to thermodynamic equilibrium data calculated using GasEq model.Consequently,a kinetic model was proposed for describing the variation of hydrogen yieldand carbon conversion efficiency with S/M(the weight ratio of Steam to MSW)during thecatalytic steam gasification of MSW.The kinetic model revealed a good performancebetween experimental results and the kinetic model.The tar pyrolysis with Nano-NiO and calcined dolomite as catalysts was investigatedusing the TG/DTA method.According to the TG/DTA data,Nano-NiO and calcineddolomite catalysts can lower the activation energy of tar pyrolysis,then a kinetic modelfor tar pyrolysis was developed,and the characteristic of tar pyrolysis with and withoutcatalysts were discussed,then the mechanism of tar pyrolysis was analyzed.