Lashaki, Masoud Jahandar

The atmospheric concentration of CO2 increased from 320 to 425 parts per million by volume (ppmv; 0.0425 vol.%) between 1960 and 2024. Sample CO2 reduction strategies include shifting to renewable energy sources and employing CO2 capture. CO2 capture from the air (also known as direct air capture; DAC) has recently received increased attention. CO2 has the potential to act as an asphyxiant at high concentrations, particularly in enclosed environments (e.g., spacecraft, submarines), requiring air revitalization to remove CO2. Hence, the U.S. Occupational Safety and Health Administration determined a permissible exposure limit of 5,000 ppmv CO2 (0.5 vol.%) throughout an 8-hour work shift. Considering the trace levels of CO2 and the presence of humidity in DAC and air revitalization applications, similar materials can be developed for implementation in both cases. CO2 capture involving amine-functionalized silica materials (“aminosilicas”) can achieve high CO2 uptakes at low concentrations due to high selectivity. Additionally, moisture in CO2-laden gases enhances the CO2 uptake and stability of aminosilicas. Therefore, this research investigated the potential of aminosilicas for removing CO2 from dilute streams, including DAC and air revitalization applications. Aminosilicas were produced using mesoporous silica supports with different particle sizes that were modified with tetraethylenepentamine (TEPA) or branched polyethylenimine (PEI) with different molecular weights (600, 1200, and 1800), or grafted with 3-aminopropyltrimethoxysilane (APTMS). The performance of aminosilicas was assessed to determine equilibrium CO2 adsorption capacity, adsorption kinetics, and cyclic stability.

Deep injection well technology is a reliable and cost-effective technique to manage hazardous wastewater. However, reduced injectivity is an issue for the performance of an injection well which can happen due to the occurrence of biogeochemical clogging. A class 1 deep injection well located at the Solid Waste Authority of Palm Beach County has long suffered similar problems that occurred due to the formation of chemical precipitation and biofilm. In the case of the biofilm, the dominant microorganism detected in previous work was determined to be Entamoeba dispar. The prime source of the protozoan was identified as the local groundwater, which is employed for different purposes within the solid waste facility, such as cooling water and dilution water. Therefore, it is imperative to examine the effectiveness of the commonly used disinfectant chlorine to inactivate the protozoan to eliminate biofilms and clogging. This study conducted a laboratory-based chlorination of the groundwater sample to reveal the required dosages of chlorine needed for 3.0-log inactivation of E. dispar in various temperature (20°C, 25°C, 30°C, and 35°C) and pH (6.5, 7.0, 7.5) conditions.

Amine-grafted silica (i.e., aminosilicas) was investigated for single-stage landfill gas purification via simultaneous removal of CO2, H2S, and water vapor. Aminosilica materials were synthesized by covalent triamine grafting onto mesoporous silica with custom amounts of water and amine. Screening adsorption experiments were completed in dry 30 vol.% CO2 in N2 at 40 °C and assessed using thermogravimetric analysis. Materials with equilibrium CO2 uptakes greater than 1.5 mmol/g were chosen for CO2 adsorption kinetics assessments. The highest-performing aminosilica achieved fast CO2 adsorption by reaching 80% of its equilibrium uptake in one minute. This material also maintained 100% of its initial CO2 uptake when subjected to rigorous 100-cycle testing. It underwent column-breakthrough tests in the presence of different dry and humid gas streams containing CO2, H2S, and water vapor, and achieved concurrent and complete (100%) removal of all target impurities. The results suggest that aminosilicas can purify landfill gas in a single stage.

The potential of plastic waste-derived activated carbon was investigated for the removal of carbon dioxide and hydrogen sulfide from biogas. Activated carbon materials were prepared by carbonizing plastic waste followed by activation via microwave heating after mixing with potassium hydroxide. Samples were tested using thermogravimetric analysis to determine the equilibrium uptake of carbon dioxide. Samples were modified with tetraethylenepentamine and diethanolamine however, sample texture produced was deemed unusable for further testing due to operational concerns. Adsorbent screening was conducted in conditions mimicking that of biogas at a temperature of 40 °C and 30% carbon dioxide in nitrogen. Performant samples were identified as those achieving uptakes greater than 3 wt.%. The best performing sample achieved an uptake of 3.57 wt.% and maintained 99% of its uptake during cycling. Column breakthrough experiments demonstrated that the final candidate achieved complete removal of both carbon dioxide and hydrogen sulfide, suggesting viability for larger scale biogas purification.

The potential of paper waste-derived activated carbon was investigated for the removal of carbon dioxide and hydrogen sulfide from landfill gas. Activated carbon materials were prepared by carbonizing paper waste followed by acid treatment to remove ash, mixing with aqueous phase potassium hydroxide, and activation via microwave heating. Activated samples were tested using thermogravimetric analysis to determine their equilibrium uptake of carbon dioxide. The adsorbent materials were modified with both tetraethylenepentamine and diethanolamine to potentially increase the carbon dioxide uptake, however, all the modified samples had a performance significantly worse than their unmodified counterparts. Adsorbent screening was conducted in conditions mimicking that of landfill gas, namely temperature of 40 °C and 40% carbon dioxide in nitrogen. Performant samples were identified as those achieving uptakes greater than 3 wt.%. The best performing sample achieved an uptake of 5.03 wt.% and maintained 97% of its uptake during 100 successive adsorption-desorption cycles. Column-breakthrough experiments demonstrated that the final candidate achieved complete removal of both carbon dioxide and hydrogen sulfide, suggesting viability for larger scale landfill gas purification.

The potential of amine-grafted silica materials (i.e., aminosilicas) was investigated for single-stage biogas and landfill gas purification via simultaneous removal of CO2, H2S, and water vapor. Custom aminosilicas were synthesized by covalent tethering of primary amines onto commercially available mesoporous silica. Screening adsorption experiments were completed at 40°C in the presence of dry 30 vol.% CO2 in N2, and performance was measured using thermogravimetric analysis. Selected materials with equilibrium CO2 uptakes greater than 6 wt.% were chosen for additional assessments in terms of CO2 adsorption kinetics. The highest-performing aminosilica achieved fast CO2 uptake by reaching 82% of its equilibrium CO2 uptake in one minute. This material was subjected to rigorous 100-cycle testing and retained stable performance as evidenced by maintaining 99% of its initial CO2 uptake throughout cycling. The final candidate also underwent multicomponent column-breakthrough tests and achieved complete (100%) removal of all target impurities. The results suggest promising potential of aminosilicas as a viable method of biogas and landfill gas purification.