Date of Defense
28-11-2025 5:30 PM
Location
F1-1117
Document Type
Dissertation Defense
Degree Name
Doctor of Philosophy in Civil Engineering
College
COE
Department
Civil and Environmental Engineering
First Advisor
Dr. Ashraf Aly Hassan
Keywords
Greenhouse gases, Circular economy, Waste-utilization, Climate change, CO2 capture and storage, Life cycle assessment, Adsorption
Abstract
Excessive carbon dioxide (CO₂) emissions and large-scale industrial waste generation are the results of rapid industrialization and ever-increasing energy demand. The recent trend of repurposing waste materials for pollution prevention is a promising approach to address both these environmental challenges. One such industrial waste residue generated from acetylene gas production is called carbide slag (CS). Its high Ca(OH)₂ content presents a promising opportunity for its utilization in CO₂ sequestration. However, CS waste is primarily studied as a CaO source for the intensive Ca-looping process. Despite the great potential, the high temperature requirements of the Ca-looping process limit its industrial application. Owing to its highly reactive and readily available Ca(OH)₂ content, this dissertation aims to utilize CS waste for CO₂ sequestration at low temperature and pressure conditions with a minimum energy requirement. The research is carried out through an integrated framework where CS waste is (1) employed directly for dry and wet mineral carbonation for CO₂ capture and conversion, and (2) chemically treated to synthesize a regenerable adsorbent for cyclic CO₂ capture. Dry and wet mineral carbonation were studied under varying process conditions. Further, wet mineral carbonation was modelled using response surface methodology (RSM) and assessed for environmental sustainability and the feasibility of large-scale deployment using life cycle analysis (LCA). Experimental results indicate that dry and wet phase direct mineral carbonation of carbide slag occurs spontaneously at ambient conditions with a carbonation efficiency (CE) of 7% and 37%, respectively. A maximum CO₂ capture capacity (CCC) of 12.2 mol CO₂ kg⁻¹ can be achieved via wet mineral carbonation of CS waste with a liquid to solid (L:S) ratio of 0.2, at ~25 °C temperature, and 10 bar pressure. Quadratic RSM models revealed that CCC was mainly influenced by reaction pressure, followed by the L:S ratio. While initial reaction kinetics were majorly influenced by the CO₂ loading rate and reaction pressure. LCA suggests that utilizing the mineral carbonation end product in cement mixing reduces global warming potential by 300% compared to conventional disposal in landfills. Further, the overall CO₂ reduction potential of the CS waste wet mineral carbonation process ranges from 0.1 to 3.5 kg CO₂ avoided per kg CO₂ captured. Cyclic adsorbent was prepared by functionalizing CS-derived hydroxyapatite (CS-HAp) support with tetraethylenepentamine (TEPA) loading at 10-50% dosage. Prepared adsorbent with 30% TEPA loading (CS-HAp-T-30%) exhibited CO₂ adsorption capacity of 3.41 mmol g⁻¹ at ambient conditions. CO₂ adsorption capacity of CS-HAp-T-30% increased with elevation in pressure. Further, the presence of humidity greatly influenced CO₂ adsorption capacity. CS-HAp-T-30% retained ~70% of performance after over ten cycles. Overall, this study demonstrates the potential of CS waste for CO₂ sequestration as a mineral carbonation feedstock and a precursor of high-value adsorbents for cyclic separation. Therefore, utilizing CS waste for CO₂ sequestration offers dual benefits of waste valorization and decarbonization.
Included in
UPCYCLING CARBIDE SLAG WASTE FOR LOW-TEMPERATURE CO2 SEQUESTRATION: DIRECT APPLICATION AND ADSORPTION AFTER CHEMICAL ALTERATION
F1-1117
Excessive carbon dioxide (CO₂) emissions and large-scale industrial waste generation are the results of rapid industrialization and ever-increasing energy demand. The recent trend of repurposing waste materials for pollution prevention is a promising approach to address both these environmental challenges. One such industrial waste residue generated from acetylene gas production is called carbide slag (CS). Its high Ca(OH)₂ content presents a promising opportunity for its utilization in CO₂ sequestration. However, CS waste is primarily studied as a CaO source for the intensive Ca-looping process. Despite the great potential, the high temperature requirements of the Ca-looping process limit its industrial application. Owing to its highly reactive and readily available Ca(OH)₂ content, this dissertation aims to utilize CS waste for CO₂ sequestration at low temperature and pressure conditions with a minimum energy requirement. The research is carried out through an integrated framework where CS waste is (1) employed directly for dry and wet mineral carbonation for CO₂ capture and conversion, and (2) chemically treated to synthesize a regenerable adsorbent for cyclic CO₂ capture. Dry and wet mineral carbonation were studied under varying process conditions. Further, wet mineral carbonation was modelled using response surface methodology (RSM) and assessed for environmental sustainability and the feasibility of large-scale deployment using life cycle analysis (LCA). Experimental results indicate that dry and wet phase direct mineral carbonation of carbide slag occurs spontaneously at ambient conditions with a carbonation efficiency (CE) of 7% and 37%, respectively. A maximum CO₂ capture capacity (CCC) of 12.2 mol CO₂ kg⁻¹ can be achieved via wet mineral carbonation of CS waste with a liquid to solid (L:S) ratio of 0.2, at ~25 °C temperature, and 10 bar pressure. Quadratic RSM models revealed that CCC was mainly influenced by reaction pressure, followed by the L:S ratio. While initial reaction kinetics were majorly influenced by the CO₂ loading rate and reaction pressure. LCA suggests that utilizing the mineral carbonation end product in cement mixing reduces global warming potential by 300% compared to conventional disposal in landfills. Further, the overall CO₂ reduction potential of the CS waste wet mineral carbonation process ranges from 0.1 to 3.5 kg CO₂ avoided per kg CO₂ captured. Cyclic adsorbent was prepared by functionalizing CS-derived hydroxyapatite (CS-HAp) support with tetraethylenepentamine (TEPA) loading at 10-50% dosage. Prepared adsorbent with 30% TEPA loading (CS-HAp-T-30%) exhibited CO₂ adsorption capacity of 3.41 mmol g⁻¹ at ambient conditions. CO₂ adsorption capacity of CS-HAp-T-30% increased with elevation in pressure. Further, the presence of humidity greatly influenced CO₂ adsorption capacity. CS-HAp-T-30% retained ~70% of performance after over ten cycles. Overall, this study demonstrates the potential of CS waste for CO₂ sequestration as a mineral carbonation feedstock and a precursor of high-value adsorbents for cyclic separation. Therefore, utilizing CS waste for CO₂ sequestration offers dual benefits of waste valorization and decarbonization.