Improvement of the Catalytic Efficiency of Butene Oligomerization Using Alkali Metal Hydroxide-Modified Hierarchical ZSM-5 Catalysts

Lei Zhang,Chunyu He,Wenbo Shan,Yang Liu,Zhaozheng Song,Qi Wang,Changchun Li,Ming Ke,Chengjie Xia

doi:10.3390/catal8080298

Lei Zhang, Chunyu He + Show 7 more

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https://doi.org/10.3390/catal8080298

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Abstract

Oligomerization of light olefin is an effective method to produce plentiful liquid fuels. However, oligomerization processes using microporous zeolites have severe problems due to steric hindrance. In this paper, oligomerization of butene using a series of new types of hierarchical HZSM-5 zeolite catalysts is studied. To obtain the modified HZSM-5 catalysts, HZSM-5 is treated with the same concentration of LiOH, NaOH, KOH, and CsOH aqueous solutions, respectively. It is demonstrated that the alkali treatment can effectively modify the acidity properties and hierarchical structure of the HZSM-5 catalyst, which is confirmed by X-ray Diffraction (XRD), X-ray Fluorescence (XRF), Nitrogen Adsorption-desorption Measurements, Transmission Electron Microscopy Investigations (TEM), Ammonia Temperature-programmed Desorption Method (NH3-TPD), Pyridine FT-IR, and Thermogravimetric Analysis (TGA). The results show that hierarchical catalysts with interconnected open-mesopores, smaller crystal size, and suitable acidity can better prolong the catalyst lifetime during butene oligomerization. Particularly, the HZSM-5 catalysts treated with CsOH aqueous solution (ATHZ5-Cs) proved to be the most effective catalyst, resulting in approximately 99% conversion of butene and exhibiting C8+ selectivity of 85% within 12 h. Thus, an appropriate hierarchical catalyst can satisfy the oligomerization process and has the potential to be used as a substitute for the commercial ZSM-5 catalyst.

Highlights

Light olefins are generally produced by catalytic cracking or dehydrogenation of light alkanes in the petro-chemical industry [1,2]
The objective of this study is to investigate the effects of different alkali metal hydroxides on ZSM-5 for butene oligomerization, attempting to obtain a best-performing catalyst with adequate hierarchical structure and acidic property for butene oligomerization, and further study its mechanism of mesopores formation through different alkali metals treatment
Hierarchical porous H-ZSM-5 catalysts were prepared by the alkali treatment of HZ5 using aqueous solutions of LiOH, NaOH, KOH, and CsOH in the same concentration (0.2 M), respectively

Summary

Introduction

Light olefins are generally produced by catalytic cracking or dehydrogenation of light alkanes in the petro-chemical industry [1,2]. It is widely known that oligomerization of light olefins is an effective method to produce plentiful liquid fuels (such as gasoline and diesel) and specialty chemical intermediates (such as surfactants, plasticizers and elastomers) [3,4]. Light olefins are generally oligomerized by using homogeneous and heterogeneous catalysts. The use of homogeneous catalysts causes many problems, such as the need for a complex purification process (generally, it is difficult to remove the homogeneous catalysts from products) and pollution [6]. Because of these issues, there is growing interest in the research into heterogeneous catalysts for oligomerization [7]

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