Browsing by Subject "Adsorption"

Now showing 1 - 11 of 11
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    Adsorption of Freshwater Dissolved Organic Matter to Clay and Polyethylene Particles
    (2019-08) Burrows, Alvin
    Organic matter (OM), especially dissolved organic matter (DOM), plays several integral roles in aquatic systems. OM acts as a short-term sink of carbon and a food source for heterotrophs and shields biota from harmful UV radiation. It also facilitates the transport of nutrients, trace metals and pollutants in the environment. The uptake and transport of these compounds are related to the fate of the DOM to which they are bound. Suspended solids such as clays or microplastics can adsorb DOM into their interlayer spaces or onto their surfaces leading to: 1. Possible physical protection of OM that would have been mineralized or degraded by biota; 2. Increased transport of OM through the water column to the sediments (for sinking particles) or increased time for OM in the surface water (for less-dense microplastic particles); 3. Increased uptake by larger aquatic organisms. Increased particle-associated mobility (either by sinking through the water column or being transported at the surface via wind-driven processes) also increases associated nutrient, trace metal and pollutant transport, which in sufficient quantities, may perturb the aquatic system’s equilibrium and affect its chemistry. Microplastics, a new particle-type in aquatic systems, have been observed and documented in the world’s oceans since the 1970s, but their presence in the Laurentian Great Lakes was first recorded in 2013. The roles that microplastics and other particulates (both naturally occurring and anthropogenically impacted) play in aquatic environments need to be thoroughly studied so that a better understanding of their fate and environmental impact can be gained. The goal of this study was to qualitatively examine and compare the adsorption of open water Lake Superior DOM and DOM from a tributary stream to polyethylene microplastic spheres and to clays (kaolinite and montmorillonite). UV-VIS optical proxies were used to monitor changes in aromaticity (A254, SUVA) and molecular weight (E2:E3, S250-400, SR) within the remaining dissolved phase. Aromaticity proxies suggest that clays preferentially adsorbed aromatic species, while polyethylene had no significant effect on DOM composition. Changes in the amount of carbon remaining in the dissolved phase were measured using dissolved organic carbon (DOC) analysis while the amount adsorbed to the surface of the particulates was measured using elemental analysis (EA). DOC analysis did not show significant changes in the amount of dissolved organic carbon after sorption testing. EA was unable to provide a definitive answer for carbon adsorbed by polyethylene but suggests that kaolinite and montmorillonite adsorb similar amounts of carbon in both environments.
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    Aqueous solution and vapor phase adsorption of oxygenates onto zeolites
    (2012-11) Mallon, Elizabeth Emma
    The ability of zeolites to discriminate between molecules on the basis of size and functionality gives them the potential to be effective adsorbents and membrane materials for purification of biomass-derived chemicals and fuels. Since molecules from biomass are polyfuntional and non-volatile, it is necessary to decouple the interactions that drive aqueous adsorption of oxygenates onto zeolites in order to develop efficient zeolite-based separations for biomass processing. In this dissertation, the roles of adsorbent structural and chemical composition and adsorbate functionality are explored through the systematic development of aqueous and vapor adsorption isotherms of C2-C6 oxygenates on small (FER), medium (MWW, MFI, BEA), and large (MOR, FAU) pore zeolites as well as on hierarchical microporous-mesoporous materials (MCM-36, 3DOm-MFI, and SBA-15). Ambient temperature Henry’s constants (Kads) for aqueous diol and triol adsorption on silicalite-1 (aluminum-free MFI) increase exponentially with carbon number demonstrating that confinement of the adsorbate in the zeolite pores is a primary driving force for adsorption. This conclusion is supported by a monotonic decrease in propylene glycol Kads values with an increase in adsorbent pore size, and by a comparison of propylene glycol Kads values on MWW and MFI and their hierarchical counterparts (MCM-36 and 3DOm-MFI, respectively) that shows that propylene glycol preferentially adsorbs in the micropores of hierarchical materials. A comparison of diol and triol adsorption on silicalite-1 demonstrates that increasing the number of hydroxyl groups causes a decrease in adsorption affinity, and this phenomenon is probed by comparing Henry’s constants for aqueous adsorption of C3 polyfunctional molecules onto zeolites with their octanol-water partition coefficients, Kow, which were calculated using the prevalent ClogP group contribution method. It was found that Kads increases linearly with Kow for these adsorbates on H-ZSM-5 (aluminum-containing MFI), FAU, BEA, and ITQ-1 (MWW) at 278 K regardless of interactions in the bulk phase as measured by the solution activity coefficient. Exceptions to the correlation established between Kads and Kow are the adsorption of 1,2,!-triols with carbon number greater than three on H-ZSM-5 and adsorption of all oxygenates studied on FER, which we postulate is due to a shift in the adsorption configuration with adsorbate/zeolite structure which cannot be captured by Kow alone. The effect of zeolite defects on oxygenate adsorption was isolated through the development of vapor and aqueous adsorption isotherms on silicalite-1 materials that vary in structural and surface properties. Silicalite-1 crystals prepared through alkaline-synthesis, alkaline synthesis with steaming post-treatment, and fluoride synthesis routes are confirmed as crystalline MFI by SEM and XRD and are shown to contain ∼8.5 to 0 silanol defects per unit cell by 29Si MAS, 1H MAS, and 1H-29Si CPMAS NMR. A hysteresis in the Ar 87 K adsorption isotherm at 10−3 P/P0 evolves with a decrease in silanol defects, and, through features in the XRD and 29Si MAS NMR spectra, it is postulated that the hysteresis is the result of an orthorhombic-monoclinic symmetry shift with decreasing silanol defect density. Gravimetric and aqueous solution measurements reveal that propylene glycol adsorption at 333 K is promoted by silanol defects, with a maximum 20-fold increase observed for aqueous adsorption in the Henry’s Law regime with an increase from ∼0 to 8.5 silanols per unit cell. A comparison of vapor and aqueous propylene glycol adsorption on defect-free silicalite-1 at 333 K, both of which exhibit the Type V character, indicates that water enhances adsorption by a factor of 2 in the Henry’s Law regime, which is in agreement with simulations reported in the literature. Kads values for aqueous C2-C4 polyol adsorption at 298 K are shown to have a linear dependence on the silanol defect density, which indicates that these molecules preferentially interact with silanol defects. i
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    Data for Fingerprinting diverse nanoporous materials for optimal hydrogen storage conditions using meta-learning
    (2021-05-19) Sun, Yangzesheng; DeJaco, Robert F; Li, Zhao; Tang, Dai; Glante, Stephan; Sholl, David S; Colina, Coray M; Snurr, Randall Q; Thommes, Matthias; Hartmann, Martin; Siepmann, J Ilja; siepmann@umn.edu; Siepmann, J. Ilja; Nanoporous Materials Genome Center; Department of Chemistry; Department of Chemical Engineering and Materials Science; Chemical Theory Center
    Adsorption using nanoporous materials is one of the emerging technologies for hydrogen storage in fuel cell vehicles, and efficiently identifying the optimal storage temperature requires modeling hydrogen loading as a continuous function of pressure and temperature. Using data obtained from high-throughput Monte Carlo simulations for zeolites, metal–organic frameworks, and hyper-cross-linked polymers, we develop a meta-learning model which jointly predicts the adsorption loading for multiple materials over wide ranges of pressure and temperature. Meta-learning gives higher accuracy and improved generalization compared to fitting a model separately to each material. Here, we apply the meta-learning model to identify the optimal hydrogen storage temperature with the highest working capacity for a given pressure difference. Materials with high optimal temperatures are found closer in the fingerprint space and exhibit high isosteric heats of adsorption. Our method and results provide new guidelines toward the design of hydrogen storage materials and a new route to incorporate machine learning into high-throughput materials discovery.
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    Experimental and Economic Assessment of Temperature Swing Adsorption Systems for the purpose of Claus Tail Gas Clean Up
    (2015-01) Al Wahedi, Yasser
    Current regulations of SOx emissions require Sulfur Recovery Units to achieve recoveries in excess of 99.9% which falls beyond the practical limits of a conventional Claus plant. Tail gas treatment unit are commonly added to the Claus unit as to achieve the target recovery. Capital cost of existing commercial Claus Tail gas clean up technologies capable of achieving that recovery can amount to 45% of the total capital cost of the SRU. Adsorption based processes hold significant potential for achieving the targeted recovery at lower costs considering their high selectivity towards removal of ppm level contaminants. This work assesses the potential of such system in competing with commercial alternatives. We begin by identifying and assessing a suitable adsorbent for the target removal. The assessments attempt at understanding the governing mechanism of the adsorption phenomenon by using several material characterization techniques including XRD, TEM, EELS, in addition of traditional breakthrough assessment. Following the adsorption phenomenon is modelled using an appropriate partial differential equations based model which captures the adsorption mechanism and the mass transfer effects. The resulting model is then used in the design and cost optimization of a scaled up unit embedded within the a real industrial plant. A mixed integer nonlinear programing model of the net present worth of costs is formulated and subsequently solved for the minimum possible cost of the entire unit while considering realistic constraints. The resulting figures strongly suggest the potential of an adsorption based process in competing with commercial alternatives.
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    High Speed Separations of Complex Mixtures using nano-Liquid Chromatography Coupled with micro Free Flow Electrophoresis
    (2016-03) Geiger, Matthew
    Micro free flow electrophoresis (µFFE) is a separation technique which can be used for unique applications due to its continuous nature. Separations are performed in space, as opposed to time, as laminar flow drives analytes down the separation chamber and are separated laterally by an electric field. This continuous nature makes it an attractive option to be used as a second dimension in multidimensional separations. The major focus of this work will be the development of a 2D separation platform coupling a commercial nano-liquid chromatography (nLC) instrument with an all glass µFFE device followed by investigating factors which could affect the efficiency of the technique. A new µFFE device was designed and fabricated for coupling with nLC. High peak capacity separations of tryptic peptides of BSA demonstrated the power of the technique. Broadening in temporal and spatial dimensions were investigated since peak capacity is calculated using analyte peak width. The observation that the adsorption of analytes only affects broadening in the temporal dimension is critical for maximizing peak capacity. Finally, the effect of using fluorescent labels in 2D nLC × µFFE separations will be demonstrated. The impact of label choice can be seen in the peak capacity and orthogonality of separations of amino acids and peptides.
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    Molecular Simulation of Adsorption in Zeolites
    (2014-08) Bai, Peng
    Zeolites are a class of crystalline nanoporous materials that are widely used as catalysts, sorbents, and ion-exchangers. Zeolites have revolutionized the petroleum industry and have fueled the 20th-century automobile culture, by enabling numerous highly-efficient transformations and separations in oil refineries. They are also posed to play an important role in many processes of biomass conversion. One of the fundamental principles in the field of zeolites involves the understanding and tuning of the selectivity for different guest molecules that results from the wide variety of pore architectures. The primary goal of my dissertation research is to gain such understanding via computer simulations and eventually to reach the level of predictive modeling. The dissertation starts with a brief introduction of the applications of zeolites and computer modeling techniques useful for the study of zeolitic systems. Chapter 2 then describes an effort to improve simulation efficiency, which is essential for many challenging adsorption systems. Chapter 3 studies a model system to demonstrate the applicability and capability of the method used for the majority of this work, configurational-bias Monte Carlo simulations in the Gibbs ensemble (CBMC-GE). After these methodological developments, Chapter 4 and 5 report a systematic parametrization of a new transferable force field for all-silica zeolites, TraPPE-zeo, and a subsequent, relatively ad-hoc extension to cation-exchanged aluminosilicates. The CBMC-GE method and the TraPPE-zeo force field are then combined to investigate some complex adsorption systems, such as linear and branched C6--C9 alkanes in a hierarchical microporous/mesoporous material (Chapter 6), the multi-component adsorption of aqueous alcohol solutions (Chapter 7) and glucose solutions (Chapter 8). Finally, Chapter 9 describes an endeavor to screen a large number of zeolites with the purpose of finding better materials for two energy-related applications, ethanol/water separation and hydrocarbon iso-dewaxing.
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    Role of bank materials as potential source and carrier of phosphorus
    (2013-03) Grundtner, Ashley Lynn
    Lake Pepin is a natural impoundment on the Upper Mississippi River, 80 km south of the Twin Cities, Minnesota. Two major water quality concerns for this lake are the higher rates of sedimentation and elevated eutrophic nutrient conditions. Although the majority of sediments in the Minnesota River and then Lake Pepin are coming from river banks, there is a perception that a significant amount of particulate phosphorus is coming from agricultural lands. The goal of this research was to assess the role of river bank materials as a source and carriers of phosphorus to Lake Pepin. In this study, we characterized the river bank materials in Blue Earth County for equilibrium phosphorus concentration (EPC0), total phosphorus (TP) content, particulate bound P fractions, and the potential of bank materials to adsorb and desorb soluble P. Results showed that bank materials are inherently high in TP content (>400 mg/kg), have low EPC0 (<0.1 mg/L) values, strong P binding ability, and high P adsorption and low P desorption potentials. Since the dissolved P concentrations in river waters contributing to Lake Pepin are >0.1 mg P/L part of the year, low EPC0 values suggest continued P adsorption by bank materials from river waters even under current conditions. Particle enrichment of bank materials during transport explained TP concentrations in Lake Pepin sediments prior to 1850. After 1850, we outlined scenarios using particle enrichment and historical river pollution as potential reasons for higher TP concentrations in Lake Pepin sediments. We conclude that river bank materials are a significant source of TP but not that of dissolved P to either the river system or to Lake Pepin. These materials do act as scavengers of dissolved P from river waters and carry it to downstream locations. The dissolved P in the river could be from the treatment plants, some point sources or agricultural lands. This adsorbed P will be stored in locations where sediments settle and will be a continuous source of dissolved P in the future. One way to prevent sediment from semi-sequestering dissolved P from river waters is to make sure dissolved P concentrations in river water are less than EPC0 values of bank materials.
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    Simulation data for "Influence of charge sequence on the adsorption of polyelectrolytes to oppositely-charged polyelectrolyte brushes"
    (2019-06-20) Sethuraman, Vaidyanathan; McGovern, Michael; Morse, David C; Dorfman, Kevin D; vsethura@umn.edu; Sethuraman, Vaidyanathan; Dorfman Group
    When a solution of polyanionic chains is placed in contact with a polycationic brush, the polyanions adsorb into the brush. We investigate the influence of the charge sequences of the free and bound species on the thermodynamics of polyelectrolyte adsorption. As model systems, we consider free and brush polyelectrolytes with either block or alternating charge sequences, and study the adsorption process using coarse-grained Langevin dynamics with implicit solvent, explicit counterions, and excess salt. Free energy, internal energy, and entropy of adsorption are computed using umbrella sampling methods. When the number of polyanions exceed the number of polycations, the brush becomes overcharged. Free chains adsorb most strongly when both free and tethered chains have a block charge sequence, and most weakly when both species have an alternating sequence. Adsorption is stronger when the free polyanion has a block sequence and the tethered polycation is alternating than in the reverse case of an alternating free polymer and a tethered block copolymer. Sequence-dependent effects are shown to be largely energetic, rather than entropic, in origin.
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    Soft X-Ray-Assisted Detection Method for Airborne Molecular Contamination (AMC) and its Applications to AMC Filtration Issues
    (2016-07) Kim, Chang Hyuk
    Airborne molecular contamination (AMC) represents a wide range of gas-phase chemical contaminants in cleanrooms. Because AMC can make defects of semiconductor chips by forming undesired nanoparticles and haze under ultra violet lights in the photolithography and change properties of semiconductor chips as dopants, developing methods for monitoring and controlling AMC is highly required in the semiconductor industry. This dissertation focuses on 1) the development of a detection method for AMC and 2) its applications to AMC related issues in the semiconductor industry. The detection method for AMC was developed by converting AMC into nanoparticles under soft X-ray irradiation and measuring them through the aerosol detection instrument, the scanning mobility particle sizer (SMPS). The soft X-ray-assisted detection method for AMC showed high sensitivity, e.g. down to ppt-level SO2. This soft X-ray-assisted detection method was firstly applied to evaluate the filtration efficiency of two AMC filters by measuring the concentration of SO2 downstream of the filters. This AMC detection method was also employed to develop materials, which emit VOCs lower than the conventional materials used in cleanrooms. The process for finding low-VOC replacements can be accelerated by screening candidate materials through this method. In addition, this AMC detection method was applied to measure outgassing from particulate air pollutants (PM2.5), which is a source of AMC. Using this method, a linear relationship was observed between the outgassing and PM2.5 mass loading on the filters. Subsequently, the soft X-ray-assisted detection method was used to study the removal of AMC and nanoparticles simultaneously using a single gas filter, granular activated carbon (GAC). The filtration efficiency of the GAC for 1.5-30 nm particles was investigated at different compositions and face velocities. In the present work, the GAC showed 90% filtration efficiency for sub-3 nm particles, in addition to its original gas adsorption efficiency. Furthermore, the penetration of toluene molecules through the GAC measured by the soft X-ray method was not changed when the GAC was challenged with or without nanoparticles. The results implied that the GACs can be used to remove both AMC and nanoparticles simultaneously.
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    Sour Gas Sweetening and Ethane/Ethylene Separation
    (2018-05) Shah, Mansi S
    Chemical separations are responsible for nearly half of the US industrial energy consumption. The next generation of separation processes will rely on smart materials to greatly relieve this energy expense. This thesis research focuses on two very energy-intensive and large-scale industrial separations: sour gas sweetening and ethane/ethylene separation. Traditionally, gas sweetening has been achieved through amine-based absorption processes to selectively remove H2S and CO2 from CH4. Ethane/ethylene is an even harder mixture since the two molecules have very similar sizes, shapes, and self-interaction strengths. Despite their low relative volatility (1.2-3.0), cryogenic distillation is the most commonly used technique for this separation. Compared to absorption and cryogenic distillation, adsorption allows for better performance control by choosing the right adsorbent. Crystalline materials such as zeolites, that have precisely defined pore structure, exhibit excellent molecular sieving properties. Performance is closely linked to structure; identifying top zeolites from a large pool of available structures (~300) is thus crucial for improving the separation. In this thesis research, molecular modeling is used to identify optimal materials for these two separations. Since the accuracy of predictive molecular simulations is governed by the underlying molecular models, the first objective of this thesis research was to develop improved molecular models for H2S, ethane, and ethylene. A wide variety of properties such as vapor-liquid and solid-vapor equilibria, critical and triple points, vapor pressures, mixture properties, relative permittivities, liquid structure, and diffusion coefficients were studied using molecular simulations to parameterize transferable molecular models for these molecules. These models are designed to strike a very good balance between accuracy of predictions and efficiency of simulations. For some of the zeolites for which experimental data existed in the literature, purely predictive adsorption isotherms agreed quantitatively with the available experiments. A computational screening was then performed for over 300 zeolite structures using tailored molecular simulation protocols and high-performance supercomputers. Optimal zeolites for each of the two applications were identified for a wide range of temperatures, pressures, and mixture compositions. Finally, a brief literature survey of the zeolites that have been synthesized in their all-silica form is presented and syntheses for two of the important target framework types is discussed.
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    Value Addition And Nutrient Recovery From Ethanol Coproducts
    (2017-07) Rodrigues Reis, Cristiano
    Grain-to-ethanol production has increased steadily in the United States in the past few decades, which resulted in remarkable records in the availability of co-products. Dry-grind is the most common method of ethanol production worldwide, which concentrates the corn and yeast nutrients in the downstream operations. The industrial corn ethanol process consists of a series of chemical, physical and biological operations. Once the fermented corn mash is produced, it is then processed through a series of distillation and rectification, centrifugation and evaporation processes to generate ethanol and the main co-product, Distillers Dried Grain with Solubles (DDGS). Through a series of condensers, the stillage is dried to produce DDGS. Thus, protein, fat, fiber, and phosphorus concentrations are increased several fold in the DDGS compared with corn. The remaining nutrients from the ethanol distillation are the raw material for producing co-products. They are composed of proteins, fats, sugars, and some other lignocellulosic-derived compounds. In the United States, abundant research has been done in improving the quality of the ethanol co-products which yielded the ethanol industry to have animal feed production to be as relevant as the fuel ethanol production. The liquid fraction produced after the centrifugation of the bottoms of the ethanol rectifying and distilling operations is named thin stillage, produced at volumes several times greater than those of ethanol. A portion of thin stillage is normally recycled as backset water, while the remaining goes through a series of evaporations. Evaporating a large amount of water from thin stillage is an energy-consuming process and recycling the thin stillage may lead to the accumulation of nutrients in co-products in distiller’s grains. There are several other industrial processes to utilize thin stillage, such as oil extraction, anaerobic digestion, and secondary fermentation. Recently, promising results have been reported on the production of important commodity chemicals, extracting high-value products, and energy production from thin stillage. Phytate is the primary storage form of phosphorus and inositol in plants. The bioavailability of phosphorus bound to phytate is low for non-ruminants, and thus the phytate-derived phosphate ingested by these species (e.g. poultry and swine) is largely excreted, resulting in both nutritional deficiencies and environmental pollution. On the other hand, phytate is a widely applied valuable chemical as human nutrition, pharmaceutics, cosmetics, chelating chemical, and the raw material to produce myo-inositol. It is primarily produced from rice bran in Asia and imported to the US market. This creates a great opportunity for the US ethanol industry because extracting phytate as a new product from corn ethanol coproducts, knowing that corn germ has up to 5% phytate in its composition, can create additional revenue while increasing the feeding value of coproducts and decrease the phosphorus excretion in the animal manure. This dissertation also provides an overview on the new processes and products via valorization of thin stillage by innovative technologies that are being currently developed. It also provides the technical development background to develop an ion exchange method to extract phytate from thin stillage, as well as potential environmental benefits and further analyses on the impacts of phytate extraction implementation to ethanol plants. The novel application of thin stillage discussed in this dissertation could open new opportunities for the ethanol plants and ethanol researchers by increasing the revenue and simultaneously potentially reducing negative environmental impacts of ethanol production.