Factors affecting CO2 utilisation via the reverse Boudouard reaction and Macro-thermogravimetric development for char conversion

Alsawadi, Ahmed ORCID: https://orcid.org/0009-0006-1770-5287 2025. Factors affecting CO2 utilisation via the reverse Boudouard reaction and Macro-thermogravimetric development for char conversion. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Carbon Capture, Utilisation and Storage (CCUS) is currently known as a key solution to reach net zero emissions, with CO2 utilisation (CCU) via thermochemical gasification technology of renewable materials being a promising pathway. The reverse Boudouard reaction is an interesting option for CCU applications; it is a heterogeneous, endothermic reaction that typically requires temperatures above 700°C to proceed. Therefore, understanding its mechanisms and studying the factors that affect it are beneficial to increase gasification process efficiency and hence reduce risk in process up-scaling. This thesis investigates the critical mechanisms affecting char reactivity in CO2 gasification using biochar, hydrochar and coal char samples by measuring mineral content, porosity, crystalline mineral phases, morphology, surface elements and surface functional groups. CO2-chemisorption measurements of the char samples measured both organic and inorganic active sites using thermogravimetric analysis. The CO2-chemisorption method at low temperatures was implemented to quantify the amount of CO2 adsorbed/desorbed within the char’s surface and to identify its role in char reactivity. Key findings include that while the pore structure of chars is indeed a significant characteristic, porosity alone does not exert the primary influence on gasification reactivity. Gasification reactivity was well correlated with CO2 strong chemisorption capacities. Three kinetic models Volumetric model (VM), Grain model (GM) and Random pore model (RPM) were used to describe CO2 gasification in isothermal and non-isothermal conditions. A novel thermogravimetric fixed bed reactor (Macro-TGA) was designed to examine the effect of using a larger char sample on the gasification reactivity. The reactor was also used to investigate the role of surface area on the reaction performance by comparing the reactivity and produce gas of 12 and 16 mm pellets with the char powder sample. In comparison with Micro-TGA, the reactivity of biochar decreased when using 5 g sample. The kinetic parameters were also lower in the Macro-TGA compared to the Micro-TGA.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Engineering
Uncontrolled Keywords:	1. CCUS 2. Boudouard reaction 3. Char reactivity 4. Demineralisation 5. Char structure 6. CO2 chemisorption 7. Kinetic models 8. Micro-TGA 9. Macro-TGA
Date of First Compliant Deposit:	19 August 2025
Last Modified:	19 Aug 2025 11:38
URI:	https://orca.cardiff.ac.uk/id/eprint/180547

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