Vapor-phase transport (VPT) modification of ZSM-5/SiC foam catalyst using TPAOH vapor to improve the methanol-to-propylene (MTP) reaction

Yilai Jiao,Xiaolei Fan,Michal Perdjon,Zhenming Yang,Jinsong Zhang

doi:10.1016/j.apcata.2017.07.036

Yilai Jiao, Xiaolei Fan + Show 3 more

Open Access

https://doi.org/10.1016/j.apcata.2017.07.036

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Abstract

Tetrapropylammonium hydroxide (TPAOH) was introduced in the vapor phase to perform the vapor-phase transport (VPT) modification of the structured ZSM-5 supported on SiC foam (ZSM-5/SiC foam) catalyst. An optimum precursor concentration of 0.5M TPAOH could effectively convert the amorphous aluminosilicate binder to the zeolitic phase with improved intracrystal mesopores, nanosized crystals (ca. 100nm), high concentration of acidity sites (83mmolg−1) as well as a high value of the relative acidity (0.7). Combined with the intrinsic property of macroscopic SiC foams such as the low pressure drop and the high thermal conductivity (14Wm−1K−1 at 773K), TPAOH VPT modified ZSM-5/SiC foam catalyst demonstrated an excellent activity in the catalytic methanol-to-propylene (MTP) reaction, surpassing the state-of-the-art hierarchal ZSM-5 monolith catalyst. The catalyst showed an extended activity for ca. 970h (>95% methanol conversion) with the high selectivity to the propylene (>45%). The coke formation was significantly retarded (ca. 2.1×10−2wt.%h−1) due to the enhanced transport phenomena within the developed structured catalyst.

Highlights

Propylene is a major chemical building block for an array of chemicals and plastics in the modern chemical industry
As demonstrated in our previous work, structured ZSM-5 supported on silicon carbide (SiC) foam catalysts (ZSM-5/SiC foam) have shown improved catalytic performance and stability in methanol to propylene (MTP) reactions in comparison to ZSM-5 pellets [3,5,6,8]
Structured ZSM-5 supported on SiC foam catalysts (ZSM-5/SiC foam) were prepared by dip coating with ZSM-5 in aluminosilcate binder slurry and subsequently modified using the vaporphase transport (VPT) method with the Tetrapropylammonium hydroxide (TPAOH) vapor

Summary

Introduction

Propylene is a major chemical building block for an array of chemicals and plastics in the modern chemical industry. Motivated by the work above, we deduced that VPT modification of ZSM-5/SiC foam using the TPAOH steam could promote the structured catalyst with the improved ZSM-5 coating and the associated catalytic property in the MTP process. TPAOH aqueous solutions were used to generate the vapor to perform the VPT modification of the mixed phase of ZSM-5/aluminosilicate binder on SiC foams. The performance of the developed structured catalysts in the MTP process was evaluated under an industrially relevant velocity and compared with reference catalysts such as steamed ZSM-5/SiC foam catalyst and conventional ZSM-5 pellets. The vapor-phase transport (VPT) modification of ZSM-5 coating on SiC foams was carried out in an autoclave reactor with the inner diameter of 80 mm and the depth of 100 mm, provided a capacity of about 500 cm. The denotation of catalysts of S-F, S-DW, S-TPAOH-0.5 and STPAOH-1 was used to represent the fresh reference ZSM-5/SiC catalyst, the steamed ZSM-5/SiC catalyst, the 0.5 M TPAOH VPT modified ZSM5/SiC catalyst and the 1.0 M TPAOH VPT modified ZSM-5/SiC catalyst, respectively

Characterization of catalysts

Synthesis of ZSM-5 zeolites

Results and discussion

MTP process enhancement by SiC foam supports

Conclusion