Tri-templates synthesis of SAPO-34 and its performance in MTO reaction by statistical design of experiments

Abstract

The effect of a tri-templating agent [i.e., tetraethyl ammonium hydroxide (TEAOH), triethylamine (TEA) and morpholine (MOR)] on the catalytic performance of SAPO-34 catalyst was investigated in conversion of methanol to olefins (MTO). SAPO-34 catalysts were synthesized hydrothermally with nominal composition as 1 Al2O3:1 P2O5:0.4 SiO2:2y TEAOH:2x TEA:2 (1−(x+y)) MOR:70 H2O. The products were characterized by XRD, SEM, BET, EDX, FT-IR, NH3-TPD techniques. The relative molar ratios were obtained by response surface methodology applying central composite design. Tri-templating led to production of pure SAPO-34 phase with reduced particle sizes. Analysis of Variance (ANOVA) applied for investigating the significance of two independent variables indicated that TEA content was the most significant variable. The catalytic performance of the prepared catalysts was tested in MTO reaction at 410°C and WHSV of 6.5h−1. Sample prepared with 0.5 MOR:0.5 TEA:1 TEAOH exhibited the highest yield of light olefins (88.7wt%) owing to its highest crystallinity, smallest crystal size and highest surface area.