Study On Synthesis Of SAPO-34 By Mother Liquor Recycling Method And The Effect Of SAPO-34 On Polypropylene

SAPO-34 molecular sieve is an important methanol-to-olefin process catalyst,and the optimization of its synthesis method has attracted people's attention.The traditional hydrothermal synthesis method generally produces a large amount of crystallization mother liquor containing the unreacted raw materials and organic template.If it is directly discharged,it will cause a waste of resources and environmental pollution.Recycling the mother liquor of crystallization to prepare molecular sieves by recycling will help manufacturers reduce the burden of waste liquid treatment,increase the level of raw material utilization,and reduce production costs.Therefore,exploring the method of preparing molecular sieve by recycling mother liquor has great scientific research significance and practical economic value.Polypropylene has become the most widely used polymer material due to its excellent processing and mechanical properties,and it usually needs to be modified and compounded to improve its overall performance.Molecular sieve has a certain porous structure and olefin catalytic properties.Using it as a polypropylene material modification additive can improve the crystallinity of polypropylene,improve the mechanical properties of the material,and reduce the use of compatibilizers.It has certain research significance for studying new methods of comprehensive modification of polypropylene materials and broadening the application fields of molecular sieves.In order to comprehensively utilize the crystallization mother liquor of SAPO-34molecular sieve and explore the performance influence of SAPO-34 molecular sieve-modified polypropylene material,this paper studies the main factors affecting the synthesis such as crystallization time,raw material composition,and crystallization temperature.SAPO-34molecular sieve was successfully prepared by mother liquor recycling method without adding organic template,and Fe/SAPO-34 molecular sieve was synthesized in the crystallization mother liquor environment by using purified iron phosphate.The various typical molecular sieves obtained were characterized by XRD,SEM,FT-IR,NH3-TPD,TG,etc.,and the catalytic effects of different molecular sieves were evaluated through the MTO reaction.Finally,the influence of SAPO-34 molecular sieve on the properties of polypropylene is explored,and the influence of conventional ZSM-5,Na Y,and BETA molecular sieves on polypropylene is compared.The main conclusions of this paper are as follows:(1)The crystallization time plays a key role in the synthesis of SAPO-34 molecular sieve.The traditional hydrothermal method is used to crystallize at 200?.The crystal nucleus is mainly induced to grow before 36h.After multiphase evolution,the best crystal form and microscopic morphology are obtained at 48h.The product remains pure phase and grain within32h.The diameter is about 4?10?m.Too long crystallization time will produce crystal fragments and miscellaneous crystals,which is not conducive to synthesis.When the raw material silicon-aluminum ratio is low,the product tends to form SAPO-11.The increase of the silicon-to-aluminum ratio can speed up the crystal growth.When Si O₂/Al₂O₃=0.6,a perfect cubic crystal product is obtained.Continuing to increase the ratio of silicon to aluminum has little effect on the crystallization of the product,resulting in a waste of raw materials.When the crystallization time is 48h,the lower crystallization temperature will reduce the crystallinity and the yield of the molecular sieve,and the presence of impurity crystals will slow down the reaction process.The increase of the crystallization temperature can accelerate the growth of molecular sieve crystals,and reach the best crystallinity and molecular sieve yield at 200?.(2)The mother liquor recycling method accelerates the synthesis speed of SAPO-34molecular sieve.The best product can be obtained by crystallization at 200?for 36 hours,and the pure phase is maintained within 54 hours.The molecular sieve crystal has a good microscopic morphology,with a particle size of about 2?5?m.The pure phase SAPO-34molecular sieve can be obtained from the crystallization mother liquor in two cycles.As the number of cycles increases,the utilization rate of residual raw materials decreases and impurity crystals are generated.Compared with the traditional hydrothermal method,a single mother liquor cycle can save approximately 45%of aluminum,70%of phosphorus and 15%of silicon.Phosphating slag is hydrothermally purified with phosphoric acid solution to obtain sheet-like Fe PO₄·2H₂O product,which can be prepared by adding a small amount to the crystallization mother liquor to obtain Fe/SAPO-34.Evaluation of the molecular sieves prepared by each method by FT-IR,TG,NH₃-TPD and other means shows that the mother liquor recycling method has significant advantages.The doping of Fe enhances the strong acidity of the molecular sieve,but reduces the structural stability.The performance evaluation of MTO catalytic reaction showed that the mother liquor recycling method to prepare molecular sieves has certain advantages over the traditional hydrothermal method in terms of catalytic life(119min)and diene selectivity(82.5%),and the doping of Fe sacrifices the catalytic life(The price of 70min)enhances the diene selectivity(85.5%).(3)SAPO-34 molecular sieve can significantly improve the mechanical properties of polypropylene materials,and the maximum tensile and impact strength can be achieved when the addition amount is 3%.As the amount of addition increases,too much molecular sieve addition will cause defects in the material,resulting in a gradual decline in mechanical properties.TG analysis shows that SAPO-34 molecular sieve improves the high temperature stability of polypropylene material,and the pyrolysis initiation temperature is increased by 50?compared with pure polypropylene.At the same time,the decomposition rate of polypropylene is accelerated,and the decomposition time is shortened by about 40 minutes,which is helpful for the high temperature and harmless treatment of waste polypropylene materials.At the same time,three conventional molecular sieve modified polypropylenes,ZSM-5,Na Y,and BETA,were tested.XRD tests showed that molecular sieves can strengthen polypropylene?crystals to varying degrees,and SAPO-34 and ZSM-5 can also induce polypropylene production.Produce?crystals with greater strength and improve the overall performance of the material.