The Effects Of Templates And Seed On Yield And Crystallization Behavior Of SAPO-34 Synthesis

Owing to good thermal and hydrothermal stability,mild acidity,and special channel structure,SAPO-34 exhibits excellent catalytic properties in methanol to olefins process and selective catalytic reduction of NOx,etc.At present,the main industrial synthesis method of SAPO-34 is hydrothermal method,in which,however,has several serious issues,such as high temperature,high pressure,low product yield and pollution of waste water.In this paper,it mainly studies the synthesis of SAPO-34 by using two different templates(triethylamine(TEA)and diethylamine(DEA)).The effects of templates and seed on yield and crystallization behavior of synthesis of SAPO-34 have been investigated.The following results and conclusions are obtained:1.Taken TEA as template,the yield of SAPO-34 was significantly affected by crystallization time and temperature,while,the amount of template and silicon had little effect on it.As the crystallization time and temperature increased,the yield of SAPO-34 increased.The yield can reach 87.0% and remains stable after crystallization 60 h at 200 ?.Meanwhile,as the crystallization temperature increased,the nucleation and crystallization rate increased with the crystal size decreased.The existence of SAPO-5 hybrid can be inhibited with the amount of template TEA increased.2.Taken DEA as template,with the crystallization time and temperature increasing,the yield of SAPO-34 also increased.However,the yield significantly decreased as the crystallization time increased at the late crystallization period.At 200 ? and crystallization 60 h,the yield can reach 45.3%,then it decreased to 36.2% after 72 h.Meanwhile,with the crystallization temperature decreasing,the nucleation and crystallization rate decreased,but the crystal size became more uniform.With the increase of the amount of DEA template,the existence of SAPO-11 hybrid can be inhibited.3.Compared with DEA system under the same synthesis condition,the synthesis of SAPO-34 by using TEA as template exhibits faster nucleation rate and higher yield,and also obtains more uniform particle size of products.4.Adding seeds in the initial gel can promote nucleation,accelerate the crystallization rate and yield,while reduce the crystal size.By adding seeds in TEA system(180 ?,48 h),the yield of SAPO-34 can be increased from 68.1% to 79.2%,which is at the same yield level of synthesis at 200 ? without seeds.