Spent Catalyst Preparation Process And Characterization Of Zno / Activated Carbon Composites

ZnO/AC composites have become an important research subject in the field of environmental governance for their effectivity of degradation and elimination of harmful pollutants.At present,the widely used methods for preparation of ZnO/AC composites are fixation,latex and sol-gel methods, etc.However,these methods have some disadvantages such as zinc oxide easy separating from activated carbon supported,long process and more waste solution and so on.The spent catalysts after the synthesis of vinyl acetate and mainly composed of ZnO precurors-zinc acetate and activated carbon are the excellent raw material for the preparation of ZnO/AC composites.Compared with traditional processes of regenerating activated carbon and extracting zinc in dealing with the spent catalysts,respectively, the novel process of preparation of ZnO/AC composites can greatly simplify process flow;shorten the process time,reduce secondary pollution,increase economic benefits,and give new path for the better utilization of renewable resources.The pyrolysis characteristics and kinetics of spent catalyst were studied by the thermo-gravimetric analysis method under N₂ atmosphere.The temperature of furnace was increased from 298K to 1473K at 10℃/min.The results showed that the spent catalyst had three fast agravic steps: dehydration,decomposition of zinc acetate,decomposition of organic resins and other complex organic compounds and reaction of ZnO with carbon,the latter two are the main steps of weightlessness.Importantly,the zinc acetate did not decomposed completely until its temperature was up to 1149K.This lag of pyrolysis temperature is due to the wrap of spent catalyst by organic resin.The pyrolysis kinetic equation of spent catalyst followed first-order kinetics model and one dimension(1D)diffuse Parabolic equation.The calculated apparent activation energy was 37.4kJ/mol and 43.1kJ/mol,respectively. On the basis of the analysis of pyrolysis,the ZnO/AC composites were successfully prepared by conventional thermal method.The samples were characterized by X-ray analysis(XRD),N₂-adsorption isotherm(Quanta Autosorb-1),and scanning electron microscopy(SEM).With the increase of pyrolysis temperature,the content of zinc in product increased with the decomposition of zinc acetate at the initial stage of pyrolysis,and then reduced with the overflow of zinc after the reaction of carbon and ZnO.The adsorptive capacity of activated carbon increased with the gradual increase of the specific surface area,but the yield of ZnO/AC composites gradually decreased.It can be found from XRD analysis that the ZnO/AC composites did not show the obvious diffraction peaks of ZnO until the temperature rose to 773K.Both the XRD and SEM analysis proved that the crystal size of the ZnO firstly increased and then decreased with the increase of pyrolysis temperature.This may be related to the reaction of ZnO and carbon.In order to improve the adsorptive properties,the ZnO / AC composites were prepared by using steam as activating agent.The influence of temperature on iodine number,methylene blue adsorption and yield of the ZnO/AC composites were investigated systematically.The samples were also characterized by XRD,Quanta Autosorb-1 and SEM-EDAX.The XRD analysis revealed that the ZnO loaded on activated carbon possesses hexagonal wurtzite structure.It can be found that the varieties of temperature greatly influenced on the morphology of ZnO loaded on activated carbon.With the increase of the temperature,the crystal size of ZnO gradually became larger.When the temperature increased to 1223K, the crystal size of ZnO started to decrease.The pore structures of the samples were characterized by t-plot equation and non-localized density functional theory(NLDFT).It was found that the ZnO / AC composites prepared under various temperatures show high specific surface area,up to l193m²/g.SEM micrographs indicated that the ZnO in the pores of activated carbon was irregular in shape but homogeneously distributed around the pores in stead of blocking them.In summary,this paper using spent catalyst from vinyl acetate synthesis prepared ZnO/AC composite materials,on the one hand industrial waste as raw materials to produce high-value-added,multi-purpose composites.For the purpose of comprehensive utilization of resources;On the other hand,this method has the advantages of low-cost,simple process, easy implementation of industrialization,compared to existing the methods of ZnO/AC composite preparation,and opened up a new avenue to preparation of the ZnO/AC composite material...