A novel solvothermal approach to synthesize SAPO molecular sieves using organic amines as the solvent and template

A novel solvothermal synthesis route designated as aminothermal synthesis, in which organic amines are used as both the dispersing medium and the template, is developed for the synthesis of SAPO molecular sieves. Three synthetic systems based on triethylamine (TEA), diethylamine (DEA) and TEA-DEA binary mixture were studied. SAPO-34 with good crystallinity and high yield (ca. 90%) was successfully synthesized from TEA and TEA-DEA systems. By adjusting the crystallization temperature, SAPO-18 was for the first time obtained using TEA template. In the case of DEA, a small-pore molecular sieve DNL-6 with RHO topology was synthesized. In an attempt to make the synthetic process environmentally benign and reduce the waste emission, organic liquid was collected after the synthesis of SAPO-34 and reused in next crystallization. It was found that the crystalline product and yield were almost the same as those synthesized with fresh amines. Moreover, CO2 and CH4 were chosen as the probe molecules to investigate the adsorption properties of products. SAPO molecular sieves synthesized by aminothermal method exhibited good adsorption capacities and high CO2/CH4 ratios.