Upgrading of bio-oil model compounds and a sewage sludge oil via hydrodeoxygenation using non-noble transition metal-based catalysts

Yusuf, Mustapha ORCID: https://orcid.org/0000-0002-6479-1011 (2024). Upgrading of bio-oil model compounds and a sewage sludge oil via hydrodeoxygenation using non-noble transition metal-based catalysts. University of Birmingham. Ph.D.

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Abstract

The realisation of biofuels and chemicals requires the development of highly active and selective catalysts. In this research work, the catalytic hydrodeoxygenation (HDO) of bio-oil model compounds; anisole and benzoic acid, and sewage sludge oil have been investigated. Different catalysts were prepared via the impregnations of Ni and Zn on microporous zeolite (mic-ZSM-5), mesoporous zeolite (hie-ZSM-5), and mesoporous silica (SiO2) supports. The catalysts were characterised, and the reactions were performed over a range of temperatures. The hie-Ni/ZSM-5 catalyst shows the highest acid site concentration, the best metal dispersion, and hence the highest catalytic activity. When treated separately, the HDO of anisole showed a 100% conversion in 2 h at 200 °C, while benzoic acid yields a conversion of 97% in 6 h at 340 °C. However, a decrease in activity was seen during the HDO of a blend of the two model compounds. Conversion was 37% (anisole) and 75% (benzoic acid) in 6 h at 340 ℃. This was attributed to the competitive adsorption of the reactants on the catalytic active sites. Interestingly, both the catalysts from the highly acidic support (ZSM-5) and the nearly neutral support (SiO2) showed a high degree of hydrodeoxygenation. While the Ni/SiO2 produced toluene, the zeolite-base catalysts generated a significant amount of benzene and cyclohexane. This implies a synergy between the support acidity and metal sites in promoting C-C cleavage and hydrodearomatization reactions. A kinetic study carried out with the hie-Ni/ZSM-5 catalyst produced activation energy values of 53.3 kJ mol-1 (anisole) and 137.2 kJ mol-1 (benzoic acid). A comparative analysis of the prepared catalyst with a commercial hydrotreating catalyst in the HDO of sewage sludge oil revealed a promising result. The outstanding performance of the Ni/SiO2 catalyst shows the combined effects of mesoporosity and metal sites. It is obvious that the metal sites, support mesoporosity, and acidity are critical design principles in the development of catalysts for real bio-oil HDO.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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