A study of two the sequential displacement of gas and liquid phases in microchannels for eventual application in temperature swing adsorption (TSA) methane purification systems was performed. A model for bulk fluid displacement in 200 m channels was developed and validated using data from an air-water flow visualization study performed on glass microchannel test sections with a hydraulic diameter of 203 m. High-speed video recording was used to observe displacement samples at two separate channel locations for both the displacement of gas by liquid and liquid by gas, and for driving pressure gradients ranging from 19 to 450 kPa m-1. Interface velocities, void fractions, and film thicknesses were determined using image analysis software for each of the 63 sample videos obtained. Coupled 2-D heat and mass transfer models were developed to simulate a TSA gas separation process in which impurities in the gas supply were removed through adsorption into adsorbent coated microchannel walls. These models were used to evaluate the impact of residual liquid films on system mass transfer during the adsorption process. It was determined that for a TSA methane purification system to be effective, it is necessary to purge liquid from the adsorbent channel. This intermediate purge phase will benefit the mass transfer performance of the adsorption system by removing significant amounts of residual liquid from the channel and by causing the onset of rivulet flow in the channel. The existence of the remaining dry wall area, which is characteristic of the rivulet flow regime, improves system mass transfer performance in the presence of residual liquid. The commercial viability of microchannel TSA gas separation systems depends strongly on the ability to mitigate the presence and effects of residual liquid in the adsorbent channels. While the use of liquid heat transfer fluids in the microchannel structure provides rapid heating and cooling of the adsorbent mass, the management of residual liquid remains a significant hurdle. In addition, such systems will require reliable prevention of interaction between the adsorbent and the liquid heat transfer fluid, whether through the development and fabrication of highly selective polymer matrix materials or the use of non-interacting large-molecule liquid heat transfer fluids. If these hurdles can be successfully addressed, microchannel TSA systems may have the potential to become a competitive technology in large-scale gas separation.

The very large number of distinct structures that are known for metal-organic frameworks (MOFs) and zeolites presents both an opportunity and a challenge for identifying materials with useful properties for targeted separations. In this thesis we propose a three-stage computational methodology for addressing this issue and comprehensively screening all available nanoporous materials. We introduce efficient pore size calculations as a way of discarding large number of materials, which are unsuitable for a specific separation. Materials identified as having desired geometric characteristics can be further analyzed for their infinite dilution adsorption and diffusion properties by calculating the Henry's constants and activation energy barriers for diffusion. This enables us to calculate membrane selectivity in an unprecedented scale and use these values to generate a small set of materials for which the membrane selectivity can be calculated in detail and at finite loading using well-established computational tools. We display the results of using these methods for >500 MOFs and >160 silica zeolites for spherical adsorbates at first and for small linear molecules such as CO₂ later on. In addition we also demonstrate the size of the group of materials this procedure can be applied to, by performing these calculations, for simple adsorbate molecules, for an existing library of >250,000 hypothetical silica zeolites. Finally, efficient methods are introduced for assessing the role of framework flexibility on molecular diffusion in MOFs that do not require defining a classical forcefield for the MOF. These methods combine ab initio MD of the MOF with classical transition state theory and molecular dynamics simulations of the diffusing molecules. The effects of flexibility are shown to be large for CH₄, but not for CO₂ and other small spherical adsorbates, in ZIF-8.

Polyimide membranes containing nickel dithiolenes were investigated for the separation of propylene and propane. Permeation and sorption experiments were conducted as well thermal property analyses. Results indicate that the dithiolene has an antiplasticizing effect on the polymers studied. Upon addition of the dithiolene there is a subsequent reduction in the permeability coefficient and the permeability selectivity remains relatively unchanged. There is some evidence of increases in solubility selectivity, but a larger decrease in diffusivity selectivity results in a decrease in the permeability selectivity. Investigation of the thermal and mechanical properties of dithiolene-containing films indicates a reduction in fractional free volume as well as the glass transition temperature when compared to the pure polymer. There is also an increase in the modulus of the films upon addition of the dithiolene. The implications of these results and their correlation with antiplasticization are discussed.

Hydrogen is a good candidate as a future energy source. Current technologies generate hydrogen from hydrocarbons as mixtures with other species like CO and CO₂. High flux and resistance to contaminants are required for membranes used to separate hydrogen from these mixtures, as well as other requirements such as long operation standard and low cost. Development of new membranes is hampered by the large effort and time required to experimentally develop and test these membranes. I show how first-principles Density Functional Theory (DFT) calculations combined with coarse-grained modeling can be used to predict the performance of metal alloys as H₂ purification membranes. I introduce quantitative modeling methods based on DFT calculations that assess the relative role of surface resistances for metal alloy membranes, the bulk permeation rate through alloy membranes, and the selectivity of metal membranes. In my study, I first examined the importance of surface processes for thin membranes. The possibility of using new materials such as PdCuAg ternary alloys and metal sulfides as hydrogen purification membranes were examined. Finally I predicted the absorption and diffusion of another atomic species, carbon, in the membranes. My methods require no experimental input apart from the knowledge of the bulk crystal structure, so they provide an alternate way to explore new materials as hydrogen purification membranes. My results will be a useful guide for future experimental studies.

The major innovation of this work is an establishment of a novel chiral separation process using preferential crystallization coupled with a membrane barrier. This hybrid process was proved to be promising from a significant increase in product yield and purity compared to existing chiral separation processes. This work sets up a process design platform to extend the use of this hybrid process to a separation of other mixtures. This novel process especially is a promising alternative for chiral separation of pharmaceutical compounds which include more than fifty percent of approved drugs world-wide. A better performance chiral separation technique contributes to cut the operating cost and to reduce the price of chiral drugs.

Metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) have become the focus of intense study over the past decade due to their potential for advancing a variety of applications including air purification, gas storage, adsorption separations, catalysis, gas sensing, drug delivery, and so on. These materials have some distinct advantages over traditional porous materials such as the well-defined structures, uniform pore sizes, chemically functionalized sorption sites, and potential for post-synthetic modification, etc. Thus, synthesis and adsorption studies of porous MOFs have increased substantially in recent years. Among various prospective applications, air purification is one of the most immediate concerns, which has urgent requirements to improve current nuclear, biological, and chemical (NBC) filters involving commercial and military purposes. Thus, the major goal of this funded project is to search, synthesize, and test these novel hybrid porous materials for adsorptive removal of toxic industrial chemicals (TICs) and chemical warfare agents (CWAs), and to install the benchmark for new-generation NBC filters. The objective of this study is three-fold: (i) Advance our understanding of coordination chemistry by synthesizing novel MOFs and characterizing these porous coordination polymers; (ii) Evaluate porous MOF materials for gas-adsorption applications including CO2 capture, CH4 storage, other light gas adsorption and separations, and examine the chemical and physical properties of these solid adsorbents including thermal stability and heat capacity of MOFs; (iii) Evaluate porous MOF materials for next-generation NBC filter media by adsorption breakthrough measurements of TICs on MOFs, and advance our understanding about structure-property relationships of these novel adsorbents.

Improvement of the efficiency of carbon dioxide (CO2) separation from flue gases has been identified as a high-priority research area to reduce the total energy cost of carbon capture and sequestration technologies in coal-fired power plants. Efficient CO2 removal from flue gases by adsorption systems requires the design of novel sorbents capable of capturing, concentrating and recovering CO2 on a cost-effective basis. The preparation of a novel aminosilane-functionalized cellulosic polymer sorbent by grafting of aminosilanes showed promising performance for CO2 separation and capture. A strategy for the introduction of N-(2-aminoethyl)-3-aminoisobutyldimethylmethoxysilane functionalities into cellulose acetate backbone by anhydrous grafting is described in this study. The dry sorption capacity of the aminosilane-functionalized cellulosic polymer reached 27 cc (STP) CO2/ cc sorbent at 1 atm and 39 cc (STP) CO2/ cc sorbent at 5 atm and 308 K. Exposure to water vapor slightly increased the sorption capacity of the sorbent, suggesting its potential for rapid cyclic adsorption processes under humid feed conditions. In addition, a strategy for the preparation of a cellulose acetate-titanium(IV) oxide sorbent by the reaction of cellulose acetate with titanium tetrachloride is presented. The organic-metal hybrid sorbent presented a sorption capacity of 14 cc (STP) CO2/ cc sorbent at 1 atm and 49 cc (STP) CO2/ cc sorbent at 5 atm and 308 K. The novel CO2 sorbents were characterized in terms of chemical composition, density changes, molecular structure, thermal stability, and surface morphology.

Pipeline natural gas is the primary fuel of choice for distributed fuel cell-based applications. The concentration of sulfur in odorized natural gas is about 30 ppm, with acceptable levels being <1 ppm for catalyst stability in such applications. Packed bed technology for desulfurization suffers from several disadvantages including high pressure drop and slow regeneration rates that require large unit sizes. We describe a novel Rapid Temperature Swing Adsorption (RTSA) system utilizing hollow fibers with polymer 'binder', impregnated with high loadings of sulfur selective sorbent 'fillers'. Steam and cooling water can be utilized to thermally swing the sorbent during the regeneration cycles. An impermeable, thin polymer barrier layer on the outside of fiber sorbents allows only thermal interactions with the regeneration media, thereby promoting consistent sorption capacity over repeated cycles. A simplified flow pattern minimizes pressure drop, porous core morphology maximizes sorption efficiencies, while small fiber dimensions allows for rapid thermal cycles.

Compared to the conventional amine adsorption process to separate CO₂ from natural gas, the membrane separation technology has exhibited advantages in easy operation and lower capital cost. However, the high CO₂ partial pressure in natural gas can plasticize the membranes, which can lead to the loss of CH₄ and low CO₂/CH₄ separation efficiency. Crosslinking of polymer membranes have been proven effective to increase the CO₂ induced plasticization resistance by controlling the degree of swelling and segmental chain mobility in the polymer. This thesis focuses on extending the success of crosslinking to more productive asymmetric hollow fibers. In this work, the productivity of asymmetric hollow fibers was optimized by reducing the effective selective skin layer thickness. Thermal crosslinking and catalyst assisted crosslinking were performed on the defect-free thin skin hollow fibers to stabilize the fibers against plasticization. The natural gas separation performance of hollow fibers was evaluated by feeding CO₂/CH₄ gas mixture with high CO₂ content and pressure.

Membrane materials for gas separations span a wide range including polymers, metals, ceramics and composites. Our aim is to create economical hydrothermally stable membranes that can provide high H₂-CO₂ separation at a temperature of 300 degree Celsius, for application in the water-gas shift reactor process. The present work describes the development of novel silica and silica-titania membranes from the controlled oxidative thermolysis of polydimethylsiloxane. The scope of this thesis is fabrication of membranes, material characterization and preliminary gas permeation tests (35-80 degree Celsius) on PDMS derived silica membrane films. The developed membranes can withstand up to 350 degree C in air. High permeabilties of small gas penetrants like He, H₂ and CO₂ have been observed and fairly high separation factors of O₂/N₂=3, H₂/N₂= 14 and H₂/CH₄=11 have been obtained. As the temperature of operation increases, the permeability of hydrogen increases and the separation factor of H₂ from CO₂ increases. The silica membranes exhibit gas separation factors higher than the respective Knudsen values. Additionally, design and construction of a new high temperature gas permeation testing system is described, which will cater to gas permeation tests at temperatures up to 300 degree Celsius for future work. The thesis also includes a detailed plan for future studies on this topic of research.