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School of Chemical and Biomolecular Engineering

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College of Engineering

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Now showing 1 - 10 of 54

Engineering Porous Organic Cages into Effective Separations Devices: Porous Liquids and Fiber Sorbents

(Georgia Institute of Technology, 2022-09-29) Borne, Isaiah Hilton

Climate change caused by anthropogenic CO2 emissions pose a critical threat to society. The increase in CO2 concentration from the combustion of fossil fuels must be addressed by capturing and sequestering the gas or using it as a feedstock for valuable chemicals. Cleaner energy sources like natural gas and hydrogen must be efficiently and effectively purified from CO2 to be widely used. CO2 capture and storage are typically achieved via the use of physical and chemical solvents, which are mature technologies that have been proven to work on the industrial level. Although these solvent-based gas separation systems are mature, they suffer from various issues like low gas capacities, high regeneration energies, and large operating units/capital costs. There has not been a major innovation in solvent-based gas separations in decades. Porous liquids present an opportunity to revolutionize the gas separations field. Porous liquids imbue liquids with intrinsic microporosity that is typically associated with microporous solids. By dissolving discrete, porous materials in bulky solvents that cannot penetrate the pores, we can develop flowing liquids with intrinsic micropores. This dissertation details the development of porous organic cages engineering those materials into porous liquids. Three main objectives are addressed in this dissertation: 1) use fundamental thermodynamic properties help the characterization and development of Type II porous liquids, 2) determine the potential for porous liquids to be used in large-scale gas separations, and 3) engineer imine-based porous organic cages into materials that can withstand chemically harsh environments or mechanically stressful processes. Work on the first objective showed two main results. First, we show that key thermodynamic experiments can be used to quickly characterize and understand fundamental properties of Type II porous liquids. DSC experiments and partial molar volume measurements are conducted to: 1) prove that porous organic cages can actually dissolve in bulky solvents to create porous solutions and 2) quickly determine if a candidate porous liquid is actually porous without doing expensive and time-intensive PALS experiments. Second, we show that computational tools can be used to accelerate the solvent selection for Type II porous liquids and the computational predictions are validated experimentally In the second objective, a high-level techno-economic analysis is conducted to determine the potential of Type II porous liquids for gas separations. For a case study, we designed a process using a Type II porous liquid to separate concentrated CO2 from CH4. Porous liquids were shown to have lower capital costs and operating costs compared to current industrial physical solvents. The absorption efficiency of these materials were comparable to industrial standards as well. A major issue with the porous liquids is their cost and low selectivity compared to industrial standard solvents. This work presents design goals for future porous organic cages and Type II porous liquids, which should make these materials more effective for gas separations. Lastly in the third objective, a reaction scheme is employed to imbue imine based porous organic cages with acid gas stability. In many situations where CO2 is present, there is also H2S and other acidic gases that can degrade separations materials and pose health threats to those exposed to it. The development of a new, highly soluble and acid gas stable porous organic cage is detailed along with preliminary work on engineering it into a Type II porous liquid. In addition to acid gas stability, we probe the mechanical and chemical stability of imine based porous organic cages by fabricating fiber sorbents embedded with porous organic cages. The porous organic cages are exposed to harsh solvents, high energy input, and mechanical stress to create fiber sorbents which can be used as solid adsorbents for gas separations. The porous organic cages retain their gas separation properties after the fiber spinning process, showing that these materials can withstand harsh conditions and still be useful for gas separations.
Mechanochemical depolymerization of poly(ethylene terephthalate)

(Georgia Institute of Technology, 2022-08-01) Osibo, Anuoluwatobi Arinola

Efficient chemical recycling of consumer plastics (i.e. depolymerization down to monomers) is a crucial step needed to achieve a circular materials economy. In this work, depolymerization poly(ethylene terephthalate) (PET) via mechanochemical hydrolysis with sodium hydroxide and acid catalyst is studied. When sodium hydroxide is used, complete depolymerization is achieved in 20 min. The stages of the depolymerization are investigated by monitoring monomer yields and the change in the PET molecular weight over the course of the reaction. The monomer yields initially increase linearly with milling time, up to a yield of roughly 40%. However, the molecular weights of the residual PET decrease concomitantly only slightly, suggesting a reaction scheme analogous to a shrinking core model. As the reaction progresses, a physical transition of the PET/NaOH from a powder to a homogenous wax and a simultaneous increase in the depolymerization rate is observed. The influence of ball-to-powder mass ratio (BPR) and milling frequency are studied to derive a kinetic rate expression. The linear relationship between BPR and monomer yield and the known relationship between milling frequency are validated for this system. In the case of acid catalysts, zeolite is observed to perform better and a monomer yield greater than 42% is seen with large pore zeolites. It is hypothesized that the reaction is occurring the pores of the zeolites and the confinement effect of this catalyst provides an advantage as compared to bulk material catalyst.
Engineered Multifunctional Mesoporous Silica Materials for Cooperative and Cascade Catalysis

(Georgia Institute of Technology, 2022-05-05) Cleveland, Jacob William

Cascade catalysis is the process where multiple synthetic transformations are catalyzed in a one-pot procedure. Cooperatively catalyzed reactions are those where multiple catalyst structures work to offer enhanced rates when compared to the use of a single catalyst. The heterogenization of molecular catalysts has enabled a wide breadth of works in the fields of cascade and cooperative catalysis over the past 20 years. This thesis aims seeks novel approaches to develop multicatalytic materials for the purposes for cooperative and cascade reactions by using polymer and silica supported molecular catalysts. In the first work, a modular approach for the compartmentalization of mutually incompatible supported acids and bases is investigated using polymer molecular weight and mesopore size in several composite catalysts. It was found that lower molecular weight composite systems result in the most effective compartmentalization and activity during a deacetalization – Knoevenagel condensation sequence. In the second thesis aim, cooperativity between basic polymer supported benzylamines and weakly acidic silica silanols is engineered during the aldol condensation reaction. Low molecular weight systems outperform higher molecular weight and polymer-free analogues, and copolymer composition plays little to no role during this reaction. In the third project, a novel bifunctional catalyst is developed for a three-step application-based cascade from commodity chemical for the production of a biologically interesting compound. This is accomplished using supported tertiary amine (dimethylaminopropyl) and tetramethylpiperidine nitroxide radical (TEMPO) catalysts. Starting with benzyl alcohol, over 80% yield of the final product (chromene) is accomplished in 26 h.
MULTISCALE COMPUTATIONAL MODELING OF NANOSTRUCTURE AND TRANSPORT IN POLYMER ELECTROLYTE MEMBRANE FUEL CELLS

(Georgia Institute of Technology, 2022-01-04) Lawler, Robin May

Polymer electrolyte membrane fuel cells (PEMFCs) are predicted to revolutionize energy conversion for transportation due to a multitude of advantages over conventional methods. However, due to their lack of resillience to adverse conditions, they are not as widespread as other portable energy technologies. In order to render PEMFCs suitable for extensive use, we must explore methods to enhance their performance such as improving conductivity in extreme conditions and lengthening their lifetime. This thesis aims to address the issue of PEMFC versatility by using multiscale computational simulations to provide fundamental understanding of PEM mechanisms and suggest superior chemistries for PEM components. Specifically, Aim 1 aids in the design of PEMs resistant to hot or dry conditions by offering novel insight into how PEM nanostructure influences proton transport in low-humidity conditions. Aim 2 involves the elucidation of the CeO2 radical scavenging mechanisms in PEMs, as well as the suggestion of an improved CeO2 surface chemistry. Finally, Aim 3 expands upon our first aim by offering an algorithm which accurately predicts pKa (and, consequently, approximates performance) of acids relevant to PEMs, streamlining the design of novel, durable chemistries.
Investigation Of Catalytic Sorbents For Capture And Conversion Of CO2 To Methane

(Georgia Institute of Technology, 2021-08-26) Park, Sang Jae

The goal of this thesis is to develop dual function materials (DFM), or a catalytic sorbent, that has higher CO2 sorption and CO2 hydrogenation (methanation) capacities than currently existing materials and study fundamentals of CO2 methanation over the synthesized catalytic sorbents. In the first objective, NaNO3 promoted MgO was synthesized and its capability as a sorbent material for integrated capture and conversion application was evaluated. The CO2 sorption mechanism was explored using in-situ XRD and in-situ FTIR measurements, and isothermal regeneration of the sorbent was performed using the new sorbent. In the second objective, integrated capture and conversion was performed using a catalytic sorbent comprised of NaNO3/MgO + Ru/Al2O3. Higher sorption and methane production capacity were obtained, and the CO2 methanation reaction pathway was investigated over the 1% Ru/Al2O3 catalyst and 5% NaNO3/1%Ru/Al2O3 catalyst as well. In the last objective, in depth mechanistic study was performed using operando FTIR and steady state isotopic transient kinetic analysis (SSITKA) to observe the effect of loading of Ru and the presence of NaNO3 on the CO2 methanation reaction mechanism over Ru/Al2O3 catalysts. This research provides more effective catalytic sorbents than previously studied materials in integrated capture and conversion applications, and reveals underlying mechanism(s) of CO2 methanation over the synthesized materials.
UTILIZING PACKED BED REACTORS FOR THE EMPLOYMENT OF C–H FUNCTIONALIZATION IN CONTINUOUS PROCESSING

(Georgia Institute of Technology, 2021-05-04) Hatridge, Taylor A.

Pharmaceutical synthesis typically exhibits low process efficiency and creates large amounts of waste, as complex biologically active molecules are produced through many reaction and purification steps to yield a product with desired stereochemistry and high purity. The past few decades have seen a rise in the development of methods to achieve atom-efficient synthesis via carbon–hydrogen (C–H) functionalization. In particular, dirhodium(II) (Rh2L4) catalysts with donor/acceptor diazo compound precursors enable the insertion of dirhodium carbenes into C–H bonds with high regio- and stereoselectivity. However, the industrialization of this synthesis technique has been limited due to high costs of Rh2L4 catalysts and safety concerns associated with handling large quantities of energetic diazo compounds. This thesis aims to contribute to the resolution of these challenges by demonstrating the application of C–H functionalization to continuous processing via utilization of packed bed reactors. To this end, an immobilized Rh2L4 catalyst was implemented in a packed bed with a process performance commensurate to the homogeneous catalyst employed in batch, although slow catalyst deactivation was observed. Additionally, a three-phase packed bed reactor was employed for the efficient synthesis of diazo compounds via a catalytic, aerobic hydrazone oxidation. Finally, the diazo synthesis was placed upstream of a semi-batch Rh2L4-catalyzed reaction, exhibiting the potential utility of this method in industrially applicable synthetic transformations. The demonstrated flow to semi-batch cascade may enable industrial adoption of C–H functionalization, as the direct utilization of diazo compounds alleviates safety concerns, and low Rh2L4 catalyst loadings may be employed to increase TON for a lower capital cost.
Anti-coking materials and surfaces for hydrocarbon steam crackers

(Georgia Institute of Technology, 2021-04-22) Bukhovko, Maxim P.

Hydrocarbon steam cracking serves as the primary process for ethylene production. A major operating issue within steam cracking furnaces is the formation of solid carbon byproducts (i.e. coke) that deposit within the reactor tubes. The reactor must be periodically shut down to restore acceptable performance and production output. The overall aims of this work focused on exploring catalysts and a coating method that can prevent or limit coke deposition onto surfaces typically found in the cracker furnaces. Mn-Cr-O spinel oxides with varying Mn/Cr content were investigated to determine the differences in their reactivity for gasifying coke with steam and steam-hydrogen mixtures. The kinetics of coke gasification were determined from measured mass changes during thermogravimetric analysis. The Mn1.5Cr1.5O4 catalyst exhibited higher reactivity for coke gasification, and the hypothesized active Mn3+ species were mostly preserved or regenerated within the catalyst structure during simulated steam cracking conditions. Additionally, a Mn/MnO surface coating was successfully formed via electrodeposition on a Fe-Ni-Cr alloy (Incoloy 800H). Mn/MnO coated alloys show a considerable potential improvement compared to pre-oxidized alloy samples by reducing the amount of deposited coke and catalyzing its removal with air. The insights from these studies provide a deeper knowledge of the catalytic activity of various Mn-Cr-O oxides towards radically formed coke, with higher anti-coking performance when more Mn is present. The promising results of using manganese electrodeposition to form an anti-coking surface coating could be used in designing future approaches to optimize steam cracker operations and reduce time/energy expenditures from decoking shutdowns.
Rechargeable Zn-Based Batteries for Large Scale Energy Storage: Operando Imaging, Material Designing and Device Engineering

(Georgia Institute of Technology, 2020-11-19) Wu, Yutong

Energy storage technologies have the potential to change the energy infrastructure from relying heavily on fossil fuels to mostly using temporally intermittent renewable energy sources. Lithium-ion battery is the dominant energy storage solution for portable electronics, but have safety concerns stemming from flammable organic electrolytes, which is more severe when batteries are scaled up for applications in electric vehicles and utilities. And due to the stacked powder-film-on-current-collector geometry, lithium-ion batteries have limitations in scalability and maintainability. Batteries using aqueous electrolyte (e.g. Zn-air) are intrinsically safe, and flow batteries (e.g. Zn-Br) are attractive choice for large scale energy storage. However, these two technologies (Zn-air and Zn-Br) have problems such as rechargeability, self-discharge, and power density. This research identifies the limiting factors of both portable and large-scale batteries, especially zinc-based ones, and innovate at the material and device levels to overcome these limitations. Specifically, Section 1 introduces the background and motivation of this research. Section 2 identifies the root cause for irreversible electrochemical reaction of Zn anode, namely passivation and dissolution, and leverage nanoscale materials design to address these problems. Section 3 develops an in situ visualization platform for studying Br electrochemistry in Zn-Br batteries. Phenomena such as phase separated Br2 formation, self-discharge, and phase change of Br2 product will be imaged, to bridge the gap between electrolyte composition and electrochemical performance. Section 4 uses a hollow fiber based flow battery geometry design to significantly enhance the volumetric power density. The device is universal, scalable, and not limited to electrolyte types. Section 5 provides a conclusion to this research and provides future directions. The outcomes of this research (e.g. in operando imaging platform, design principle of reversible metal anode, high power density electrochemical reactor) provides insights for portable scale and grid scale energy storages and other electrochemical flow devices. To note that the videos in this work is in .avi format.
Synthesis And Applications Of Two-Dimensional Zeolites To Catalysis And Membrane Separations

(Georgia Institute of Technology, 2020-05-14) Korde, Akshay

Zeolites have proven themselves as attractive materials for catalysis and separation applications due to their ordered microporous structure and presence of strong acid sites. These materials can crystallize in several topologies and compositions that can be used to tune their properties to suit a particular application. However, due to their microporous nature, these materials impose mass transfer limitations, especially on large molecules, that reduce their catalytic activity. Two-dimensional zeolite nanosheets with single unit-cell thickness and high aspect ratio help to overcome this limitation by reducing the diffusion path length and increasing the external surface area that provides better access to catalytic sites in when using large molecules. These nanosheets can also be exfoliated and processed into highly oriented, ultra-thin membranes that can retain the molecular sieving ability of the corresponding bulk 3D zeolite. However, only 10 or so frameworks have been synthesized so far in the 2D morphology and even for the existing 2D zeolite nanosheets, the structure-property relationships have not been fully studied. The work described here aims to develop structure-property relationships for some of the existing zeolite nanosheets by using them in catalytic and membrane separation applications while developing generalized synthesis methodologies to expand the library of zeolites crystallized with a single unit-cell thickness. The first objective of the thesis was to study the effect of Si/Al ratio on the catalytic activity of 2D MFI nanosheets. The nanosheets with varying Si/Al ratios were characterized in detail and their catalytic performance was compared using the liquid phase Friedel-Crafts alkylation of mesitylene with benzyl alcohol & the self-etherification of xvi benzyl alcohol that occurs in parallel, both of which are catalyzed by Brønsted acid sites. The turnover frequency (TOF) of the catalysts is found to decrease with decreasing Si/Al ratio, with the etherification reaction being the main contributor to this trend. When the same reaction is carried out in the presence of a bulky poison, 2,6 di-tert-butylpyridine (DTBP), to selectively deactivate the external acid sites, only the etherification reaction of benzyl alcohol takes place in the micropores of the 2D MFI catalyst and the effectiveness factor is found to decrease with decreasing Si/Al ratio. Thus, increasing the density of acid sites in the micropores by decreasing the Si/Al ratio makes it more difficult for the reactant molecules to access them, as demonstrated by the decrease in TOF and the effectiveness factor. In the next objective, exfoliated AEL nanosheets, with one-dimensional pores running through the plane of the nanosheets, were used to form an intermediate layer on the shell side of α-alumina hollow fiber for forming a poly(amide) (PA) film via interfacial polymerization (IP) between a diamine in an aqueous phase and an acid chloride in an organic phase. PA membranes have been widely used for the desalination of brackish water and seawater. The thin AEL molecular sieve nanosheet layer likely acts as a reservoir to store the diamine molecules, while allowing for its controlled release during the IP reaction. The composite AEL nanosheet-poly(amide) membrane exhibited a high water flux and NaCl rejection as well as displayed long-term stability in pervaporative desalination. Lastly, new organic structure directing agents (OSDAs) were synthesized and screened to crystallize new zeolites with single unit-cell crystal thickness in a one-pot, bottom-up manner. This has resulted in the crystallization of a novel microporous zeolitic nanotube, using a bolaform OSDA with a biphenyl group in the hydrophobic center and xvii hydrophilic quinuclidinium groups at the ends, separated by a C10 carbon chain. The growth mechanism of the nanotubes was studied through time-resolved crystallization of the material that revealed the formation of a mesostructure very early on in the synthesis due to the micellar assembly of the OSDA. The SDA most likely forms a cylindrical or rod-like micellar assembly, with the biphenyl groups of the SDA molecules interacting with each through π-π interactions, while the quinuclidinum groups direct the crystallization of the microporous zeolitic walls of the nanotube. In summary, this thesis will help to advance the field of separations and catalysis by uncovering structure property relations of existing 2D zeolites while developing a new zeolite morphology. All these materials may be advantageous over their conventional 3D zeolite counterparts.
MFI ZEOLITE MEMBRANES ON CERAMIC HOLLOW FIBERS: SCALABLE FABRICATION PROCESSES AND HYDROCARBON SEPARATION PROPERTIES

(Georgia Institute of Technology, 2020-05-14) Min, Byunghyun

MFI zeolite membranes are attractive for the separation of industrially important hydrocarbon gas mixtures such as xylene isomers, butane isomers and natural gas components, based on the differences in the chemical and physical properties. However, zeolite membranes including MFI membranes have been unsuccessful in achieving economic viability for industrial-scale gas separation applications. The large-scale industrial application of zeolite membrane systems can be realized by overcoming the following barriers: firstly, develop scalable and reliable membrane fabrication strategies to produce the high-performance membrane; secondly, reduce the cost and achieve performance intensification of the membrane system by employing hollow fiber modules with high membrane area per unit volume; and thirdly, obtain a thorough understanding of multicomponent separation behavior in zeolite membranes at industrially interesting conditions. In the above context, the overall focus of this thesis is to develop novel, technologically scalable fabrication strategies to make thin and highly selective MFI zeolite membranes and to understand their synthesis-structure-permeation property relations by a combination of experiment and modeling. This thesis has focused on the MFI zeolite type, because of its particularly attractive properties for a wide range of hydrocarbon separations.