Study On The Direct Synthesis Of ZSM-5 Molecular Sieve From Waste Molecular Sieve And Fly Ash

The annual discharge of solid waste from coal and chemical industry is huge,which seriously affects the environment,enterprise image and its economic benefit.The value-added utilization of solid waste in coal chemical industry is a challenging but a very important and urgent problem.In this paper,taking the deactivated waste ZSM-5 zeolite and fly ash discharged from gasification section in Ningdong base(Ningxia province)which both contain a large content of silicon and aluminum elements as object of study,we attemped to find a way to synthesize high value-added product of ZSM-5 zeolite,which is a very important material applied in the filed of sorption,seperation and catalysis,with high-efficient and environmental friendly utilization by a quasi-solid phase sythesis.This method not only can save a lot of land for landfill,but also can realize the efficient recycling of these waste resources.The waste ZSM-5 zeolite is from methanol to propylene(MTP)plant.A comprehensive analysis of its properties was carried out first,then the study on structural recovery by recrystallization,such as crystal structure,crystal morphology,pore structure,acid property,and catalytic activity in MTP reaction.The results show that the waste ZSM-5 molecular sieve has very fast crystallization rate.After crystallization for 2 h,the sample has a high crystallinity,even better than the sample for 24 h.After crystallization,the acid sites on the surface was significantly restored,and the pore volume and micropore surface area were significantly increased.It showed 40%propylene and over 80 h lifetime in MTP reaction.Increasing crystallization time can extend the surface acidity,which provides an effective way to regenerate functionally waste ZSM-5.The methods of direct hydrothermal synthesis method,hydrothermal synthesis method with silicon supplementation and quasi-solid phase synthesis method were compared.After the physical and chemical treatment of fly ash,the residue was almost completely converted to ZSM-5 zeolite through a quasi-solid phase crystallization method with segmental heating.The effect of pretreatment of high content impurities of calcium,iron and other elements in fly ash on the synthesis of ZSM-5 molecular sieve was studied with emphasis.The results show that high temperature of acid treatment can reduce the content of heteroatoms.The lower the content of heteroatoms,the more favorable it is to synthesize ZSM-5 zeolite.In addition,the relative crystallinity,surface acidity and olefin selectivity also increase with the reduce of heteroatoms content.The propylene selectivity was close to 40%on the sample PA-H2 obtained on the optimized processing conditions.