Synthesis Of Kaolin/SAPO-34 Composites By In-situ Crystallization

SAPO-34 showed excellent catalytic performance in the methanol-to-olefins（MTO）process due to its high selectivity,moderate acidity and high hydrothermal stability.However,the traditional MTO catalysts were prepared from SAPO-34 and carrier by adherent agents,resulting in the diffusion limitation of reactants and short life.In this paper,the Kaolin/SAPO-34 composites were synthesized by in-situ crystallization used metakaolin as raw materials.This procedure was characterized with SAPO-34 molecular sieve supported on the kaolin,which greatly improved the catalytic peroperties and antiabrasion.SAPO-34 were synthesized used diethylamine（DEA）,triethylamine（TEA）and morpholine（MOR）as template,respectively.The samples were characterized by XRD,SEM,BET and FT-IR.The results showed that the samples synthesized by TEA possessed an irregular shape in morphology with crystal size of 2-6 μm,and had a BET surface area of 251.5 m²,g^-1.The samples synthesized by MOR possessed larger particle size（7 μm）than that of samples obtained by TEA.The samples synthesized by DEA possessed regular shape in morphology with homogeneous crystal size of 2 μm,and had a BET surface area of 309.3 m²,g^-1.As a comparison,the sample prepared by DEA exhibited more regular structure and larger surface area.Therefore,the influence of starting gel ratio on the crystallinity of SAPO-34 was investigated used DEA as template,resulting that optimal molar ratio of n（Al2O3）:n（P2O5）:n（SiO2）:n（DEA）:n（H20）was 1.0:0.8:0.6:2.0:50.Kaolin/SAPO-34 composites were synthesized by in-situ crystallization used diethylamine,triethylamine and morpholine as templates.The samples were characterized by XRD,SEM,BET and FT-IR.The results showed that the samples synthesized by DEA possessed an irregular shape in morphology,and had a BET surface area of 266.0 m²,g^-1.The samples synthesized by TEA possessed uniform particle size distribution,and had a BET surface area of 354.6 m²,g^-1.The samples synthesized by MOR possessed regular crystal morphology with particle size of 1.5 μm,and had a BET surface area of 385.4 m²,g^-1.The results showed that the samples prepared by MOR possessed more uniform structure and particle size and larger surface area,so optimal molar ratio of n（Al2O3）:n（P2O5）:n（SiO2）:n（MOR）:n（H20）was 1.0:1.0:0.75:4.0:50.The scale-up synthesis of SAPO-34 and Kaolin/SAPO-34 composites was carried out.The BET surface area of SAPO-34 were 320.1 m²,g^-1 and Kaolin/SAPO-34 composites were 290.3 m²,g^-1,respectively.