Synthesis of SAPO-34 Molecular Sieves via Novel Intermittent Hydrothermal Treatment and Its Effect on the Crystallization and Product Properties

Zhihui Guo,Ping Miao,Lei Guo,Yunpeng Xue,Fei Li,Weiping Zhu,Qi Yin,Ruixue Yuan,Lianbin Xu

doi:10.3390/catal7050150

Abstract

Intermittent hydrothermal treatment was introduced into the synthesis of SAPO-34 molecular sieves to control the nucleation and the growth in the crystallization. The effect of the crystallization time, the order of long-time and short-time crystallization in two-stage crystallization, and frequency in multi-stage crystallization on synthesis, physicochemical properties and catalytic performance for conversion of methanol to light olefins (MTO) has been studied. The results show that pure SAPO-34 can be obtained with increasing crystallization time. The interruption of the initial crystallization is more beneficial for improving the Si distribution and the MTO catalytic performance of SAPO-34 molecular sieves. The sample obtained by repeatedly alternating heating and cooling during crystallization shows smaller particle size, higher acidity, longer lifetimes and higher yields of ethylene than that obtained by the conventional continuous crystallization at high temperature.

Highlights

The methanol-to-olefins (MTO) process has attracted much attention because of the increasing demand for light olefins in petrochemical industries [1]
The results show that the crystallinity, morphology, particle size, surface area, purity and textural properties are affected apparently by crystallization time and temperature
Various SAPO-34 molecular sieves were synthesized via intermittent crystallization in the hydrothermal treatment

Summary

Introduction

The methanol-to-olefins (MTO) process has attracted much attention because of the increasing demand for light olefins in petrochemical industries [1]. In the MTO reaction, the SAPO-34 molecular sieve has been considered to be a uniquely effective catalyst for the conversion of methanol to olefins with high catalytic activity and selectivity, due to its appropriate small pores (0.38–0.43 nm), mild acidity, and high hydrothermal stability [2,3]. As reported by Xing et al [4], certain content of carbon buildup can constrict the pores of SAPO-34 and benefit the product selectivity to smaller olefins. If the lifetime of SAPO-34 in a single MTO process can be increased, the residence time of SAPO-34 molecular sieve catalysts in the industrial reactor will be increased, the content of carbon buildup will be able to be controlled, and the selectivity of ethylene and propylene in industry will be increased. There are various pieces of research about increasing the SAPO-34 molecular sieve lifetime in the MTO process [2,3,5,6,7]

Methods

Results

Conclusion