Matching Items (3)
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- All Subjects: PFOS
- Genre: Academic theses
- Creators: Lind, Marylaura
- Creators: Boyer, Treavor H.
- Creators: McIntyre, Sean
- Status: Published
Description
The large-scale anthropogenic emission of carbon dioxide into the atmosphere leads to many unintended consequences, from rising sea levels to ocean acidification. While a clean energy infrastructure is growing, mid-term strategies that are compatible with the current infrastructure should be developed. Carbon capture and storage in fossil-fuel power plants is one way to avoid our current gigaton-scale emission of carbon dioxide into the atmosphere. However, for this to be possible, separation techniques are necessary to remove the nitrogen from air before combustion or from the flue gas after combustion. Metal-organic frameworks (MOFs) are a relatively new class of porous material that show great promise for adsorptive separation processes. Here, potential mechanisms of O2/N2 separation and CO2/N2 separation are explored.
First, a logical categorization of potential adsorptive separation mechanisms in MOFs is outlined by comparing existing data with previously studied materials. Size-selective adsorptive separation is investigated for both gas systems using molecular simulations. A correlation between size-selective equilibrium adsorptive separation capabilities and pore diameter is established in materials with complex pore distributions. A method of generating mobile extra-framework cations which drastically increase adsorptive selectivity toward nitrogen over oxygen via electrostatic interactions is explored through experiments and simulations. Finally, deposition of redox-active ferrocene molecules into systematically generated defects is shown to be an effective method of increasing selectivity towards oxygen.
First, a logical categorization of potential adsorptive separation mechanisms in MOFs is outlined by comparing existing data with previously studied materials. Size-selective adsorptive separation is investigated for both gas systems using molecular simulations. A correlation between size-selective equilibrium adsorptive separation capabilities and pore diameter is established in materials with complex pore distributions. A method of generating mobile extra-framework cations which drastically increase adsorptive selectivity toward nitrogen over oxygen via electrostatic interactions is explored through experiments and simulations. Finally, deposition of redox-active ferrocene molecules into systematically generated defects is shown to be an effective method of increasing selectivity towards oxygen.
ContributorsMcIntyre, Sean (Author) / Mu, Bin (Thesis advisor) / Green, Matthew (Committee member) / Lind, Marylaura (Committee member) / Arizona State University (Publisher)
Created2019
Description
Per- and polyfluoroalkyl substances (PFAS) are a group of man-made chemicals that are detected ubiquitously in the aquatic environment, biota, and humans. Human exposure and adverse health of PFAS through consuming impacted drinking water is getting regulatory attention. Adsorption using granular activated carbon (GAC) and ion exchange resin (IX) has proved to be efficient in removing PFAS from water. There is a need to study the effectiveness of commercially available sorbents in PFAS removal at the pilot-scale with real PFAS contaminated water, which would aid in efficient full-scale plant design. Additionally, there is also a need to have validated bench-scale testing techniques to aid municipalities and researchers in selecting or comparing adsorbents to remove PFAS. Rapid Small-Scale Column Tests (RSSCTs) are bench-scale testing to assess media performance and operational life to remove trace organics but have not been validated for PFAS. Different design considerations exist for RSSCTs, which rely upon either proportional diffusivity (PD) or constant diffusivity (CD) dimensionless scaling relationships.
This thesis aims to validate the use of RSSCTs to simulate PFAS breakthrough in pilot columns. First, a pilot-scale study using two GACs and an IX was conducted for five months at a wellsite in central Arizona. PFAS adsorption capacity was greatest for a commercial IX, and then two GAC sources exhibited similar performance. Second, RSSCTs scaled using PD or CD relationships, simulated the pilot columns, were designed and performed. For IX and the two types of GAC, the CD–RSSCTs simulated the PFAS breakthrough concentration, shape, and order of C8 to C4 compounds observed pilot columns better than the PD-RSSCTs. Finally, PFAS breakthrough and adsorption capacities for PD- and CD-RSSCTs were performed on multiple groundwaters (GWs) from across Arizona to assess the treatability of PFAS chain length and functional head-group moieties. PFAS breakthrough in GAC and IX was dictated by chain length (C4>C6>C8) and functional group (PFCAs>PFSAs) of the compound. Shorter-chain PFAS broke through earlier than the longer chain, and removal trends were related to the hydrophobicity of PFAS. Overall, single-use IX performed superior to any of the evaluated GACs across a range of water chemistries in Arizona GWs.
This thesis aims to validate the use of RSSCTs to simulate PFAS breakthrough in pilot columns. First, a pilot-scale study using two GACs and an IX was conducted for five months at a wellsite in central Arizona. PFAS adsorption capacity was greatest for a commercial IX, and then two GAC sources exhibited similar performance. Second, RSSCTs scaled using PD or CD relationships, simulated the pilot columns, were designed and performed. For IX and the two types of GAC, the CD–RSSCTs simulated the PFAS breakthrough concentration, shape, and order of C8 to C4 compounds observed pilot columns better than the PD-RSSCTs. Finally, PFAS breakthrough and adsorption capacities for PD- and CD-RSSCTs were performed on multiple groundwaters (GWs) from across Arizona to assess the treatability of PFAS chain length and functional head-group moieties. PFAS breakthrough in GAC and IX was dictated by chain length (C4>C6>C8) and functional group (PFCAs>PFSAs) of the compound. Shorter-chain PFAS broke through earlier than the longer chain, and removal trends were related to the hydrophobicity of PFAS. Overall, single-use IX performed superior to any of the evaluated GACs across a range of water chemistries in Arizona GWs.
ContributorsVenkatesh, Krishishvar (Author) / Westerhoff, Paul (Thesis advisor) / Sinha, Shahnawaz (Committee member) / Lind, Marylaura (Committee member) / Arizona State University (Publisher)
Created2020
Description
Although anion exchange resins (AERs) have been implemented for a wide range of aqueous contaminants including notorious perfluoroalkyl acids (PFAAs) that are of human health concern, the potential benefits and underlying chemistry of weak-base (WB) AERs are overlooked. To fill these key gaps in the literature, this research evaluated the removal and regeneration efficiency of WB-AER (IRA 67 and IRA 96) with strong-base (SB) AER as the baseline. Batch equilibrium tests were first conducted for the removal of nitrate, sulfate, 3-phenylpropionic acid, and six legacy PFAAs with contrasting properties at different solution pH using polyacrylic and polystyrene chloride-form AERs. In ambient (pH 7) and acidic (pH 4) solutions, the polymer composition was the controlling factor followed by the length of alkyl chain of the resin while AER basicity did not influence the selectivity for the selected contaminants. WB resin had higher capacity than SB analogs based on quantitative analysis using isotherm model parameters. Batch and column adsorption experiments showed significantly greater removal of PFAAs by polystyrene than polyacrylic AERs regardless of resin basicity, with the order of decreasing polyacrylic resin selectivity of PFOS >> PFHxS ≈ PFOA > PFBS > PFHxA ≈ PFBA. The removal performance of WB-AER was reversible, declining drastically at basic conditions and gradually regained once below the pKa of the resin due to the pH-dependent nature of amine groups. This was not the case for IRA 96 (i.e., polystyrene) which exhibited high removal of PFAAs irrelevant of pH because of the nonpolar character of polystyrene matrix. The non-hydrophobic IRA 67 (i.e., polyacrylic) had a satisfactory regeneration using non-toxic salt-only solutions comprising 1% NaOH and 0.5% NaOH + 0.5% NaCl, while IRA 96 was only amenable to brine/methanol regeneration. Important caveats on the validity of isotherm modeling in batch adsorption tests were discussed. Results for batch and column experiments using chloride-form and free-base form WB-AER, respectively, provide insights for industrial applications.
ContributorsKassar, Christian (Author) / Boyer, Treavor H. (Thesis advisor) / Westerhoff, Paul K. (Committee member) / Conroy-Ben, Otakuye (Committee member) / Arizona State University (Publisher)
Created2022