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

• Synthesis of SAPO-34 catalysts with high purity and small crystal size by employing tri-templating.
• Achieving noticeable light olefin yield (88.7%) in MTO reaction.
• The content of TEA as a template possesses the most significant effect in synthesis gel.
• High purity and crystallinity lead to ameliorate catalytic performance in MTO process.
• The superior yield belongs to the sample with the lowest crystal size and the highest crystalline and surface area.

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 6.5 h−1. Sample prepared with 0.5 MOR:0.5 TEA:1 TEAOH exhibited the highest yield of light olefins (88.7 wt%) owing to its highest crystallinity, smallest crystal size and highest surface area.

Synthesis of SAPO-34 samples using mixture of three templates namely, morpholine, tetraethyl ammonium hydroxide and triethylamine showed tri-templating led to particle size reduction. Performing reactor tests over SAPO-34 catalysts indicated that catalyst with molar ratios of 0.5 MOR:0.5 TEA:1 TEAOH possessed excellent catalytic activity and stability due to its smallest particle size and highest crystallinity.Figure optionsDownload high-quality image (173 K)Download as PowerPoint slide