Study On Preparation Of LaY Molecular Sieve By Liquid-solid Combined Exchange Method

Catalytic cracking(FCC)gasoline is one of the gasoline with the highest sulfur content,and it has a very large proportion in the Chinese market.The FCC catalyst is the key to improving oil products,and the key to achieving this goal lies in the active components of the catalyst.That is,optimizing the production process of rare earth Y-type molecular sieves is necessary to develop low-cost and excellent-performance catalysts.The new generation of optimized performance catalysts should not only inherit the advantages of traditional molecular sieves,but also have problems such as cumbersome modification process,long production cycle,low rare earth utilization rate,and water pollution caused by large amounts of mother liquor to be treated.At the same time,the content of rare earth in the molecular sieve must be precisely controlled,and the rare earth ions should be located in the sodalite cage to enhance the thermal stability of the molecular sieve.In this thesis,NaY molecular sieve is used as the research object,the solid-liquid rare earth ion exchange method is used to modify the selected molecular sieve to obtain LaY molecular sieve with higher exchange degree and better stability.The rare-earth content of LaY molecular sieve prepared by solid-phase exchange method with high-temperature roasting increased significantly,reaching 14.94%.Compared with the traditional liquid phase exchange,the liquid-solid combined exchange method increases the rare earth ion exchange rate by 5.04%and the thermal stability by more than 50?.In this paper,the preparation process of LaY molecular sieve is optimized.By changing the experimental conditions,nearly 100 sets of molecular sieve samples were prepared,and the samples were analyzed by XRF,BET,XRD,DSC-TG,etc.The effects of slurry concentration,exchange time,exchange temperature,and roasting temperature on the rare earth content and molecular sieve performance in the sample were investigated.We finally determined that:the optimal slurry concentration ratio is 15,the optimal exchange time is 2h,and the optimal exchange temperature is 75?,the optimal baking temperature is 500?.Under this condition,the micropore specific surface area of the molecular sieve is above 736.8m2/g,the relative crystallinity is above 76%,and the exchange rate of rare earth is above 75%,which is significantly better than the traditional liquid phase method.The LaY molecular sieve prepared under the optimized process conditions performed well in all aspects:rare earth ions successfully entered the molecular sieve cage,replacing the sodium ions on the original framework,making the modified LaY molecular sieve more stable.Molecular sieve crystals have better internal structural integrity,higher crystallinity,richer pore structure,and larger micropore surface area.After rare earth ions enter the molecular sieve,it effectively suppresses the dealumination of the molecular sieve,improves the silicon-to-aluminum ratio of the molecular sieve,and has better catalytic activity.The new process uses environmentally friendly and pollution-free magnesium hydroxide in the rare earth precipitation process to replace the traditional ammonium salt,avoiding the environmental pollution problems caused by traditional ammonium exchange.It solves the problems of high industrial application cost caused by insufficient exchange,multiple exchanges and roasting,and low rare earth utilization rate.At the same time,it greatly reduces the water treatment process,effectively solves.the environmental protection problems that have always restricted industrial production,and reduced economic costs,thereby effectively increasing revenue,and has certain application prospects.