Date of Award

Spring 8-2-2024

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Earth Science

Committee Chair

Richard LaDouceur

First Advisor

Jerome P. (Jerry) Downey

Second Advisor

John Kirtley

Third Advisor

Blaine Berrington

Fourth Advisor

Nicholas P. Stadie

Abstract

Due to the excessive consumption of fossil fuels, which leads to significant greenhouse gas emissions and rapid climate change, it is crucial to develop various Carbon Capture and Sequestration strategies. CO2 sequestration in solid, porous adsorbents like low-cost biochar emerges as a promising method to achieve this goal. However, slow adsorption kinetics are one of the issues that limit the widespread use of biochar. While the characteristics of biochar are important and impact CO2 adsorption, the conditions under which adsorption occurs are equally critical.

In this work, a novel process intensification strategy, namely Low-Frequency High Amplitude resonant vibratory mixing within a mechanochemical environment, is proposed to accelerate the CO2 uptake rate onto biochar. With this approach, the rate of adsorption, characterized by the adsorption rate constant, exhibits an increase of 46.6% and 91.3%, as calculated by two different kinetic models: the Weber and Morris model and the Pseudo-First-Order model. Experimental observations indicate that the kinetics of adsorption follows two rate-limiting steps: external/internal diffusion and physisorption, which occur simultaneously. Numerous physicochemical and morphological characterization analyses are conducted during this study to assess the potential of biochar as a carbon-based solid adsorbent for capturing CO2.

Resonant vibrations increase system energy, promoting collisions between CO2 molecules and carbon surfaces, improving surface/gas interactions and CO2 transport, thus facilitating the kinetic rates. With resonant vibrations, not only are the adsorption kinetics of CO2 onto biochar enhanced, but other requirements of carbon capture and sequestration technologies within adsorption applications—such as adsorption capacity, selective adsorption of CO2 in a gas mixture system, and cyclic adsorption—are also effectively addressed. The collisions caused by resonant vibrations lead to a decrease in particle size, an increase in surface area, and consequently, a 40.15% increase in adsorption capacity. Moreover, the resonant vibrations show a 25.5% improvement in selectively adsorbing CO2 under simulated post-combustion conditions (16% V/V CO2/N2). Lastly, regeneration studies demonstrate improvements in the reusability of biochar in the CO2 adsorption system after 5 cycles with the use of resonant vibrations.

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