Browsing by Author "Arnold, Ross A."

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    CO2 Gasification of Sugarcane Bagasse Char: Consideration of Pyrolysis Temperature, Silicon and Aluminum Contents, and Potassium Addition for Recirculation of Char
    (2020-11-24) Motta, Ingrid Lopes; Arnold, Ross A.; Lopez-Tenllado, Francisco Javier; Filho, Rubens Maciel; Wolf Maciel, Maria Regina; Hill, Josephine M.
    In sugarcane bagasse gasification, char recirculation to the gasifier improves the syngas quality and process efficiency. To determine the effect of char properties on the reaction kinetics, in this work, the pregasification pyrolysis temperature, particle size, and catalyst (potassium) loading were varied. Char samples were prepared at 750–900 °C via pyrolysis and gasified isothermally in a thermogravimetric analysis unit at 850 °C with CO2, and gasification data were modeled using the random pore and extended random pore models. Increasing pyrolysis temperatures did not affect the char morphology and surface composition but did reduce the surface area, as determined by N2 adsorption, decreasing initial gasification rates, and the overall fitted rate constants. Reduction of the particle size via ball milling decreased the time required for complete conversion and changed the shape of the rate versus conversion curves from monotonically decreasing to concave down. The char sample prepared via pyrolysis at 900 °C was an exception, having a maximum rate at ∼10% conversion without ball milling. After ball milling of the char sample prepared at 750 °C, there was an accumulation of ash (Al and Si) on the surface of the particles and a reduction in the surface area, consistent with the ash blocking pores—the porosity in these samples increased during the initial stages (up to ∼20% conversion) of gasification. The gasification behavior was generally well modeled by the extended random pore model. Although the addition of KOH (K/Al mass ratio ∼ 0.2–1.25) enhanced the gasification rates, too much K—from the addition of KOH or after 90% conversion—created mass-transfer limitations resulting in lower gasification rates.
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    Effect of calcium and barium on potassium-catalyzed gasification of ash-free carbon black
    (2019-06-15) Arnold, Ross A.; Hill, Josephine M.
    Gasification of carbon black, an ash-free carbon feed, was performed with K2CO3 and either CaCO3 or BaCO3 as catalysts to examine their interaction. Mixtures were prepared by low-energy ball-milling, and then gasified with CO2 at 750–850 °C in a thermogravimetric analyzer. At temperatures below 800 °C, the presence of calcium had little impact on the potassium-catalyzed gasification of carbon black. At higher temperatures, calcium promoted the activity of potassium up to ∼50% conversion through the formation of a eutectic phase that increased the diffusivity of the potassium. At higher conversions, the tendency of CaCO3 to sinter and limit diffusion of CO2 to the carbon inhibited the reaction. BaCO3 also formed a eutectic phase with K2CO3 confirming that the phase change was beneficial. In contrast to CaCO3, however, BaCO3 does not sinter at 850 °C, such that gasification was promoted to complete conversion.
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    Impact of particle size and catalyst dispersion on gasification rates measured in a thermogravimetric analysis unit: Case study of carbon black catalyzed by potassium or calcium
    (2020-11-19) Arnold, Ross A.; Motta, Ingrid L.; Hill, Josephine M.
    Gasification is often studied in the laboratory using a thermogravimetric analysis (TGA) unit with less than 1 g of sample in order to obtain intrinsic rates. Many studies, however, neglect to consider the impact of particle size, of both the gasification feed and the catalyst, and catalyst dispersion on the measured rates. The impact of these factors was demonstrated using catalytic gasification of carbon black, an ash-free feed, as a case study, with K2CO3 or CaCO3 as catalysts at 850 °C in a CO2 atmosphere. Hand-mixing and ball-milling were used to alter the initial parameters. Ball-milling reduced both the particle size of both species and increased the catalyst dispersion, resulting in higher interfacial areas and gasification rates than hand-mixing. The changes in gasification kinetics were estimated by modeling the rates using the random pore and extended random pore models (RPM and eRPM, respectively). The impact of the interfacial contact area between carbon and catalysts (varied by particle size and mixing method) was dependent on the activity of the catalyst with the more active (potassium) catalyst being less affected. CaCO3 was found to sinter at 850 °C, reducing available catalytic surface area and blocking CO2 access to the carbon feed. It is recommended to consider these factors in future studies and to always report the particle sizes used.