Production of 1,3-butadiene from ethanol using zeolite-based catalysts

Kai Gao

Research output: Book/ReportPh.D. thesis

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Abstract

The strategy of Carbon Neutrality was widely accepted by many countries around the world due to contemporary climate change issues including global warming. It is urgent to switch traditional fossil fuels to clean energy as alternatives like wind, solar, and biomass to make the world sustainable. Biomass-derived low carbon resources have a wide range of applications in the production of basic chemicals like ethanol, which can be generated from sugarcane through fermentation. However, the utilization of ethanol to produce downstream value-added chemicals need to develop novel technologies. Therefore, the aim of this thesis focuses on the development of heterogeneous catalysts in the application of ethanol conversion.
Zeolite-supported metal materials were investigated as heterogeneous catalysts in the process of ethanol conversion process due to their high catalytic activity and thermal stability of the structures. The thesis described the research about the conversion of ethanol and the formation of 1,3-butadiene. There are four key consecutive steps in the process of ethanol conversion to 1,3-butadiene: (1) ethanol dehydrogenation to acetaldehyde; (2) aldol condensation to acetaldol, and further dehydration to crotonaldehyde; (3) crotonaldehyde to crotyl alcohol through Meerwein−Ponndorf−Verley (MPV) reaction; (4) crotyl alcohol dehydration to 1,3-butadiene. The zeolite catalysts involved in this thesis were MFI and BEA topologies, in which Zn and/or Y acted as the metallic active sites for the process of the tandem reaction.
Chapter 1 provides fundamental knowledge about catalysis, especially the concept of heterogeneous catalysis. Zeolites are of great importance in the field of heterogeneous catalysis and metal-containing zeolites are described as well.
Chapter 2 introduces characterization techniques related to the zeolite catalysts analysis in this thesis such as N2 physisorption and X-ray analysis to explore the chemical and physical properties of the synthesized zeolite catalysts.
Chapter 3 demonstrates the process of ethanol dehydrogenation to acetaldehyde over Zn-containing zeolites over Zn-containing MFI zeolites such as Zn/Silicalite-1, Zn/Na-ZSM-5, Zn/H-ZSM-5, and Zn incorporation framework MFI zeolite. The catalytic activity and selectivity of acetaldehyde depend on the chemical composition of the Zn metallic sites. The optimum catalyst comprises 5 wt.% Zn supported on the Silicalite-1 zeolite and results in conversion of 65.2% and selectivity of 94.5%.
Chapter 4 investigates the direct conversion of ethanol to 1,3-butadiene over Zn and Y containing zeolite catalysts. The monometallic Zn or Y exhibited very little catalytic activity towards the selectivity of 1,3-butadiene. Several Zn-containing catalysts like Zn/Na-ZSM-5 and Zn/Silicalite-1 demonstrated excellent production of acetaldehyde but terrible selectivity of 1,3-butadiene due to the absence of active sites for aldol condensation reaction. However, the Y containing zeolite catalysts did not show a sufficient yield of 1,3-butadiene due to the lack of acetaldehyde as an intermediate. The bimetallic ZnY/Na-ZSM-5 zeolite catalyst facilitated the production of 1,3-butadiene with a selectivity of 12.4%. The layer by layer arrangement of Zn/Na-ZSM-5 and Y/Na-ZSM-5 zeolites improved the production of 1,3-butadiene with the optimum selectivity of 39%, which indicated the critical role of the distance between Zn and Y active sites.
Chapter 5 describes the conversion of ethanol and acetaldehyde mixtures into the 1,3-butadiene process over Y-supported on ZSM-5 zeolite catalysts. The effects of counter ions in the zeolite on the production of 1,3-butadiene are also investigated. The Y/K-ZSM-5 zeolite was the most effective catalyst and resulted in the production of 1,3-butadiene with the maximum selectivity of 65% at 450°C using a volume ratio of ethanol to acetaldehyde to be 1.5:1. The selectivity of the other catalysts decreased in the order Y/K-ZSM-5 > Y/Na-ZSM-5 ≈ Y/Li-ZSM-5 >> Y/H-ZSM-5. The acidity of zeolite catalyst plays a critical role in the 1,3-butadiene production from ethanol and acetaldehyde mixtures. Furthermore, we show that the ethanol to acetaldehyde ratio has a significant effect on the conversion and selectivity.
Chapter 6 summarizes the major conclusions about all aforementioned projects and gives prospective suggestions to improve the catalytic activity and selectivity regards the 1,3-butadiene production from ethanol and acetaldehyde conversion.
Original languageEnglish
PublisherDTU Chemistry
Number of pages142
Publication statusPublished - 2022

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