A study of the mechanisms associated with CO2 utilisation via the reverse Boudouard reaction

Abstract

• Biochars and hydrochar are significantly more reactive than coal char. • Porosity remained an important indicator of biochar and coal char reactivity. • SP 3 carbon content and chemical functionality were higher in the reactive char. • Demineralisation decreased the strength of CO 2 chemisorption capacity. • Hydrochar kinetics reduced from a RPM to GM model after demineralisation. The main purpose of this work was to investigate the critical mechanisms affecting char reactivity in CO 2 gasification. This research investigated the influence of physical and chemical properties of biochar, hydrochar and coal char samples during CO 2 gasification using a variety of laboratory techniques to measure properties including mineral content, porosity, microcrystalline structure, morphology, surface elements and surface functional groups. These were characterised by inductively coupled plasma (ICP-OES) analysis, nitrogen adsorption analysis, X-ray diffraction (XRD), scanning electron microscopy combined with energy dispersive spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS). Furthermore, this study examined CO 2 -chemisorption measurements of the char samples to measure both organic and inorganic active sites using thermogravimetric analysis. The CO 2 -chemisorption method at low temperatures was implemented to quantify the amount of CO 2 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 CO 2 strong chemisorption capacities and kinetic models, which were used to describe CO 2 gasification by fitting experimental data with these models.

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