Chemical & Biomolecular Engineering
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Formerly known as the Department of Chemical Engineering.
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Item FUNCTIONAL PARTICLE GENERATION BY AEROSOL-ASSISTED PROCESSES(2018) Liang, Yujia; Ehrman, Sheryl H; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aerosol-assisted processes are continuous with short residence times, simple operating procedures, and facile equipment requirements. They are scalable and promising for fabrication of functional particles as conductive pastes in solar cell metallization and interference packaging, electrode materials in energy storage devices, and photocatalysts in energy conversion. Although aerosol-assisted processes have long been used in manufacturing and their fundamentals have been intensively explored, further investigation is still required to better understand the particle formation mechanisms of different aerosol-assisted processes. In this dissertation, three different aerosol-assisted processes are investigated, spray pyrolysis, colloidal spray pyrolysis (CSP), and spray drying. These processes can be conducted under mild reaction conditions with simple operation procedures. The product particles are controllable. The effects of process variables on the product particles are studied. Furthermore, the prospects of applying these three aerosol-assisted processes in generating functional particles in applications, including solar cell metallization, battery, and photocatalysis are assessed. Part 1) includes Chapters 3-5. I first present Cu-Sn binary particle generation by spray pyrolysis. Through studying the particle oxidation behaviors under different reaction conditions, the Cu-Sn binary particles exhibit high oxidation-resistance. The one-dimensional and two-dimensional structures fabricated by direct printing inks containing Cu-Sn powders display low resistivity. They all suggest that Cu-Sn binary particles produced by spray pyrolysis are promising materials in the inks in printed electronics and in the conductive pastes in solar cell metallization and interference packaging. In Part 2), Chapters 6, a novel aerosol-assisted process, CSP, is developed. This process addresses one restriction of conventional spray pyrolysis which can only be used to fabricate particles from precursor solutions containing high-solubility salts. By applying CSP, tin@carbon (Sn@C) composite particles are produced with controllable interior structures. These composite particles exhibit high-performance as the anode materials for Li-ion and Na-ion batteries. In Part 3), Chapter 7, spray drying is utilized to fabricate photocatalysts from precursor solutions containing SnO2 colloids and edge-oxidized graphene oxide (eo-GO) sheets. The particle morphology, element distribution, and band structures were investigated by various tools. The photocatalytic activity of the composite particles is five times that of commercialized TiO2 (P25) in reducing CO2 into CH4.Item ELECTROCHEMICAL COMPRESSION WITH ION EXCHANGE MEMBRANES FOR AIR CONDITIONING, REFRIGERATION AND OTHER RELATED APPLICATIONS(2017) Tao, Ye; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The refrigeration industry in the US are facing two main challenges. First of all, the phase down of HFCs in the future would require industries to seek alternative refrigerants which do not contribute to global warming. Secondly, the mechanical compressor in the small scale cooling system with a large energy impact is reaching its limitation due to heat transfer and manufacturing tolerances. Therefore there is an urgent need to develop a highly efficient compression process that works with environmentally friendly refrigerants. And the electrochemical compressor is developed to meet these requirement based on the following reasons. First of all, the electrochemical compressor can achieve an isothermal compression efficiency of greater than 90%. It also operates without moving parts, lubrication and noise. Most importantly, the compressor works with environmentally friendly refrigerants. In this thesis, three distinct electrochemical compression processes were studied. The first study is focused on modeling a metal hydride heat pump driven by electrochemical hydrogen compressor. The performance of the cooling-generating desorption reactor, the heating-generating absorption reactor, as well as the whole system were demonstrated. The results showed the superior performance of electrochemical hydrogen compressor over mechanical compressor in the system with optimized operating condition and COP. The second study demonstrated the feasibility of electrochemical ammonia compression with hydrogen as a carrier gas. The reaction mechanisms and the compression principle were verified and the compression efficiency was measured to be greater than 90%. The technology can be applied to ammonia vapor compression refrigeration cycle and ammonia storage. The third study is about developing and studying the electrochemical CO2 compression process with oxygen as a carrier gas. The reaction mechanism was verified and compared for both Pt and CaRuO3 electro-catalysts. And the latter was selected due to better CO2 and O2 absorption. The technology can potentially be applied in carbon dioxide transcritical refrigeration cycle and carbon capture. In conclusion, the electrochemical compression is a promising technology with higher compression efficiency and would bring a revolutionary change to the compressor engineering industry and global refrigeration and air conditioning market. It can also be used in fuel storage and separation based on the selective properties of the ion exchange membrane.Item COMPUTATIONAL FLUID DYNAMICS SIMULATIONS OF A PIPELINE ROTOR-STATOR MIXER(2017) Minnick, Benjamin Austin; Calabrese, Richard V; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Rotor-stator mixers provide high deformation rates to a limited volume, resulting in intensive mixing, milling, and/or dispersion/emulsification. CFD simulations of mixers provide flow field information that benefit designers and end users. This thesis focuses on transient three-dimensional simulations of the Greerco pipeline mixer, using ANSYS FLUENT. The modeled unit consists of two conical rotor-stator stages aligned for axial discharge flow. Flow and turbulence quantities are studied on a per stator slot and per rotor stage basis. Comparisons are made between the LES and RANS realizable k-ε model predictions at various mesh resolutions. Both simulations predict similar mean velocity, flow rate, and torque profiles. However, prediction of deformation rates and turbulence quantities, such as turbulent kinetic energy and its production and dissipation rates, show strong dependencies on mesh resolution and simulation method. The effect of operating conditions on power draw, throughput, and other quantities of practical utility are also discussed.Item THE UPGRADING OF METHANE TO AROMATICS OVER TRANSITION METAL LOADED HIERARCHICAL ZEOLITES(2017) WU, YIQING; Liu, Dongxia; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With the boom of shale gas production, the conversion of methane to higher hydrocarbons (MTH) promises a great future as the substituent for hydrocarbon production from crude oil based processes. Among various MTH processes, direct methane aromatization (DMA) is promising since it can achieve one-step methane valorization to aromatics. The molybdenum/zeolite (Mo/MFI or Mo/MWW) has been the most active catalyst for the DMA reaction, which, however, is impeded from industrial practice due to the rapid deactivation by coke deposition. To address this challenge, in this work, transition metal loaded hierarchical 2 dimensional (2D) lamellar MFI and MWW zeolites have been studied as catalysts for the DMA reaction. The effects of micro- and mesoporosity, external and internal Brønsted acid sites, as well as particle size of 2D lamellar zeolites on the DMA reaction have been investigated. Firstly, the spatial distribution of Brønsted acid sites in 2D lamellar MFI and MWW zeolites has been quantified by a combination of organic base titration and methanol dehydration reaction. The unit-cell thick 2D zeolites after Mo loading showed mitigation on deactivation, increase in activity, and comparable aromatics selectivity to the Mo loaded 3D zeolite analogues. A detailed analysis of the DMA reaction over Mo/hierarchical MFI zeolites with variable micro- and mesoporosity (equivalent to variation in particle sizes) showed a balance between dual porosity was essential to modulate the distribution of active sites (Mo and Brønsted acid sites) in the catalysts as well as the consequent reaction and transport events to optimize performance in the DMA reaction. External Brønsted acid sites have been proposed to be the cause of coke deposition on Mo/zeolite catalysts. Deactivation of the external acid sites have been practiced to improve the catalyst performances in the DMA reaction in this work. Atomic layer deposition (ALD) of silica species was conducted on the external surface of 2D lamellar MFI and MWW zeolites to deactivate the external acid sites in Mo/2D lamellar zeolites for the DMA reaction. Another strategy to deactivate external acid sites in Mo/zeolite catalysts was the overgrowth of 2D lamellar silicalite-1 on the microporous zeolites. The as-prepared catalysts showed higher methane conversion and aromatics formation as well as higher selectivity to naphthalene and coke in comparison with Mo loaded microporous analogues.Item Lateral Capsule Migration in Microfluidic Channels(2017) Wang, Yiyang; Dimitrakopoulos, Panagiotis; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A capsule motion inside a microfluidic channel has attracted a lot of attention in recent decades owing to its important applications in industrial, pharmaceutical and physiological systems such as in cell sorting, targeted drug delivery and blood flow. In this dissertation, we computationally investigate an elastic capsule's lateral migration inside a constricted microfluidic device under Stokes flow conditions. We use the Membrane Spectral Boundary Element (MSBE) method to determine the capsule dynamics due to its high computational accuracy and versatility in dealing with complex solid geometries. In the bounded Poiseuille flow of the microfluidic constriction, a capsule, placed initially off-centered will migrate away from the wall and move toward the channel centerline. The capsule's lateral migration behavior is caused by the combination of the wall effects due to the existence of the channel boundary, the shear gradient generated by the non-linear velocity distribution of the flow, and the lift force created by the capsule deformation. We use a constricted device instead of a straight channel to do the simulations, because the capsule's lateral migration in a straight channel is too slow to be observed easily, while the existence of the converging connection of the constricted device increases the capsule's lateral velocity and thus facilitates its migration. The main goal of our research is to investigate the effects of the capsule's physical properties on its lateral migration behavior. We released various deformable capsules at different initial positions, membrane hardness, viscosity ratios, and capsule volumes inside the constricted channel and computed their deformation behavior and migration trajectories. Our results show that changing a capsule's viscosity ratio or the membrane hardness does not strongly affect the capsule's lateral migration due to the capsule's weak inner circulation. On the other hand, changing the capsule's initial position and capsule volume strongly affect its migration trajectories. Thus soft particles with different sizes can be separated and identified.Item Beyond Li ion: Rechargeable Metal Batteries based on Multivalent Chemistry(2017) Gao, Tao; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The development of advanced battery technology with lower cost and higher energy density is important since various mobile applications are becoming indispensable in our daily life. While Li chemistry has approached its theoretical limit after several decades’ increment improvement, the potential of multivalent chemistry (Mg, Al, etc.) remains unexplored. Compared to Li ion chemistry, multivalent chemistry provides many intriguing benefits in terms of lowering cost and increasing energy density. First of all, minerals containing multivalent element such as Mg, Al, and etc. are much more abundant and cheaper than Li. Second, multivalent metals (Mg, Al etc.) can be directly used as anode materials, ensuring much higher anode capacity than graphite currently used in Li-ion battery. Third, the divalent or trivalent nature of the electroactive cation (Mg2+and Al3+) also promise high capacity for intercalation cathodes because the capacity of these materials are limited by their available ion occupancy sites in the crystal structure instead of its capability to accept electrons. In this dissertation, I detailed our efforts in examining some redox chemistries and materials for the use of rechargeable batteries based on multivalent metal anodes. They include intercalation cathode (TiS2) and conversion cathode (sulfur, iodine). We studied their electrochemical redox behavior in the corresponding chemistry, the thermodynamics, kinetics as well as the reaction reversibility. The reaction mechanism is also investigated with various macroscopic and spectroscopic techniques.Item Organic Anodes and Sulfur/Selenium Cathodes for Advanced Li and Na Batteries(2015) Luo, Chao; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)To address energy crisis and environmental pollution induced by fossil fuels, there is an urgent demand to develop sustainable, renewable, environmental benign, low cost and high capacity energy storage devices to power electric vehicles and enhance clean energy approaches such as solar energy, wind energy and hydroenergy. However, the commercial Li-ion batteries cannot satisfy the critical requirements for next generation rechargeable batteries. The commercial electrode materials (graphite anode and LiCoO2 cathode) are unsustainable, unrenewable and environmental harmful. Organic materials derived from biomasses are promising candidates for next generation rechargeable battery anodes due to their sustainability, renewability, environmental benignity and low cost. Driven by the high potential of organic materials for next generation batteries, I initiated a new research direction on exploring advanced organic compounds for Li-ion and Na-ion battery anodes. In my work, I employed croconic acid disodium salt and 2,5-Dihydroxy-1,4-benzoquinone disodium salt as models to investigate the effects of size and carbon coating on electrochemical performance for Li-ion and Na-ion batteries. The results demonstrate that the minimization of organic particle size into nano-scale and wrapping organic materials with graphene oxide can remarkably enhance the rate capability and cycling stability of organic anodes in both Li-ion and Na-ion batteries. To match with organic anodes, high capacity sulfur and selenium cathodes were also investigated. However, sulfur and selenium cathodes suffer from low electrical conductivity and shuttle reaction, which result in capacity fading and poor lifetime. To circumvent the drawbacks of sulfur and selenium, carbon matrixes such as mesoporous carbon, carbonized polyacrylonitrile and carbonized perylene-3, 4, 9, 10-tetracarboxylic dianhydride are employed to encapsulate sulfur, selenium and selenium sulfide. The resulting composites exhibit exceptional electrochemical performance owing to the high conductivity of carbon and effective restriction of polysulfides and polyselenides in carbon matrix, which avoids shuttle reaction.Item INVESTIGATING THE INTERACTIONS BETWEEN BIOPOLYMERS AND BLOOD VIA OPTICAL MICROSCOPY(2015) MacIntire, Ian Collins; Raghavan, Srinivasa R; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hydrophobically modified (hm) derivatives of biopolymers such as chitosan have been shown to convert liquid blood into an elastic gel. This interesting material property could make hm-chitosan (hmC) useful as a hemostatic agent in treating severe bleeding. In this work, we attempted to probe the mechanism of action of hmC by studies on mixtures of blood cells and hmC using optical microscopy. Our results show that the presence of hydrophobic tails on hmC induces significant clustering of blood cells. We show that clustering increases as the fraction of hydrophobic tails on hmC increases, length of the hydrophobic tails increases, and as concentration of hmC increases. Finally, clustering due to hmC could be reversed by the addition of the supramolecule a-cyclodextrin, which is known to capture hydrophobes in its binding pocket. The results from this work support the earlier mechanism, with a few important modifications.Item HETEROGENEOUS POLYMERIZATION OF METHYL METHACRYLATE AT LOW TEMPERATURE IN DISPERSED SYSTEMS(2011) EMDADI, LALEH; CHOI, KYU YONG; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)ABSTRACT Title of thesis HETEROGENEOUS POLYMERIZATION OF METHYL METHACRYLATE AT LOW TEMPERATURE IN DISPERSED SYSTEMS Laleh Emdadi, Master of Science, 2011 Directed by: Professor, Dr. Kyu Yong Choi, Chemical and Biomolecular Engineering Department Dispersion polymerization is a unique method to prepare monodisperse polymer particles of 1-10 µm in a single step process. This process is usually carried out at high temperatures that are not cost effective and suitable for special applications such as encapsulation of bio materials. Production of uniform polymer particles at low temperatures via dispersion polymerization has not been studied widely yet. In this research, dispersion polymerization of methyl methacrylate (MMA) in a nonpolar solvent, n-hexane, using N,N-dimethylaniline (DMA) and lauroyl peroxide (LPO) as redox initiators at low temperature has been studied. The evolutions of monomer conversion, polymer molecular weight distribution (MWD), and particle morphology were determined. Under specific reaction conditions, monodisperse micron-sized polymer particles were produced. The same technique was applied in the confined reaction space of a monomer droplet. Using this new process, called micro dispersive suspension polymerization, polymer particles with different internal morphologies produced with various potential applications.Item CFD SIMULATIONS FOR SCALE UP OF WET MILLING IN HIGH SHEAR MIXERS(2011) Yang, Meng; Calabrese, Richard V; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Rotor-stator mixers are widely used in the chemical and pharmaceutical process industries. Up to now, however, few papers discuss the mean flow and turbulence fields generated by them and their influence on final product quality. In this work, CFD results at different scales are used to aid in the scale up of crystal wet milling processes. CFD simulations were performed to simulate different scale mixers. In addition, wet milling studies were conducted at the bench scale to complement the CFD results and predict wet milling performance in larger scale mixers. The flow properties in a batch Silverson L4R rotor-stator mixer at 4000 and 6000 rpm were investigated. A hybrid technique was developed. The new method is computationally efficient compared with the standard sliding mesh method. Macro scale properties are predicted. The turbulent flow field and deformation rate field are compared and analyzed. After obtaining fully converged flow fields, one way coupled particle tracking calculations were performed using an efficient fast particle tracking code. Particles trajectories were recorded, and analyzed. To validate the simulated flow field, particle image velocimetry (PIV) experiments were conducted. CFD simulations of Silverson inline L4R (bench scale), 450LS (pilot scale) and 600LS (plant scale) mixers were conducted at constant tip speed to investigate the scale up effect. The macro scale properties werer predicted. The mean velocity, turbulent and deformation rate fields were investigated. The flow properties of the 450LS and 600LS mixers are quite similar, but they are significantly different from those of the L4R (bench scale) mixer. Therefore, it may be resonable to scale up from pilot scale to plant scale by the general accepted tip speed scale up criterion. However, considering tip speed alone may lead to a significant discrepancy between bench scale and larger scales. Bench scale wet milling experiment were performed at 4000, 6000 and 8000 rpm using sucrose and mannitol in the Silverson L4R inline mixer. The crystal size decreases with rotation rate at both free pumping conditions and constant flow rate conditions. To investigate the effect of flow rate, wet milling of granulated sucrose in the Silverson L4R inline mixer with constant rotor tip speed were performed at different flow rates. It is found that the crystal size increases with the flow rate.