Date of Award
Doctor of Philosophy
Jimmy Mays, Ziling Xue, Robert Counce
The growing evidence and concern over global climate change has presented the relevant nature and urgency for carbon dioxide CO2 emission regulations. With the economical gap between fossil fuel based energy and renewable energy sources’ slowly gradually closing with the technological innovations, the current need exists for a cost-effective solution to CO2 sequestration. This examination of synthesis techniques for activated porous carbon as CO2 adsorbents provides a non-contradictory approach, via “green” synthesis, for selective and energy efficient capture. In this work, the “green” synthesis is approached through the established techniques and activation of monolithic carbon, establishing a templating approach, and using biomass as a carbon precursor.
A soft-templating synthesis is used where phenolic-formaldehyde (PF) resin is polymerized in the presences of an amphiphilic triblock copolymer where, upon calcination, the elimination of the triblock copolymer reveals an inverse carbon replica. For hierarchical mesomacroporous carbon monoliths, dual phase separation of the phloroglucinol-formaldehyde (PF) - triblock copolymer gel in glycolic solvent separates into macroporous domains to form a rod. The porosity of the porous carbon monoliths and the relationship to CO2 capture capacity was examined as a function of the calcination temperature and subsequent activation with potassium hydroxide and CO2.
By using soft-templating, green reactants can be used to further pursue our means-end product. In lieu of the triblock copolymer, using linear poly (ethylene glycol) (PEG) reduces the cost and increases the tunability of the synthesis. Polymerization induced phase separation of the PF-PEG blend occurs through spinodal decomposition and, upon calcination, results in mesoporous carbon. The mesoporosity can be tuned through both the ratio of precursors and the molecular weight of the linear PEG, and activated for microporosity for CO2 adsorption.
Interchanging the phenolic moiety with biomass eliminates the need for further refinement of precursors and accessibility to large-scale synthesis. Chestnut tannin, a hydrolysable polyphenolic, was used and with a triblock copolymer, which resulted in the morphology tunability with weight ratio. Moreover, the tunable structures were only found without the addition of acid. Upon high temperature activation with ammonia, increased microporosity and the addition of nitrogen functionality attributed to increased CO2 uptake capacity.
Nelson, Kimberly Marie, "Synthesis of Mesoporous Carbon for Carbon Dioxide Capture and Sequestration. " PhD diss., University of Tennessee, 2015.