Master of Science / Department of Chemical Engineering / Larry E. Erickson / The damage that can be inflicted by ultraviolet radiation has gained widespread interest. Traditionally sunscreens are made of organic and inorganic components that block two of the three types of ultraviolet radiation, UVA and UVB. This report is a literature review of several articles that have investigated the effects of inorganic UV filters; specifically titanium dioxide and cerium dioxide. There are concerns about absorption of titanium dioxide into the skin and the adverse reactions that could occur, but it was found that there is little to no absorption. Similarly the photostability of titanium dioxide is a concern; this was found to be remedied in part by a surface treatment to the titanium dioxide. The combination of titanium dioxide and carnauba wax was also studied and found to enhance the properties of both the organic and inorganic filters. Ceria was studied as a possible replacement for titanium dioxide. It was found to have similar ultraviolet shielding properties while minimizing the photocatalytic activity and photocytotoxicity seen in titanium dioxide.

Doctor of Philosophy / Department of Chemical Engineering / Keith L. Hohn / Superparamagnetic iron oxide nanoparticle functionalization is an area of intensely active research, with applications across disciplines such as biomedical science and heterogeneous catalysis. This work demonstrates the functionalization of iron oxide nanoparticles with a quasi-monolayer of 11-sulfoundecanoic acid, 10-phosphono-1-decanesulfonic acid, and 11-aminoundecanoic acid. The carboxylic and phosphonic moieties form bonds to the iron oxide particle core, while the sulfonic acid groups face outward where they are available for catalysis. The particles were characterized by thermogravimetric analysis (TGA), transmission electron microscopy (TEM), potentiometric titration, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray photoelectron spectrometry (XPS), and dynamic light scattering (DLS). The sulfonic acid functionalized particles were used to catalyze the hydrolysis of sucrose at 80˚C and starch at 130˚C, showing a higher activity per acid site than the traditional solid acid catalyst Amberlyst-15, and comparing well against results reported in the literature for sulfonic acid functionalized mesoporous silicas. In sucrose catalysis reactions, the phosphonic-sulfonic nanoparticles (PSNPs) were seen to be incompletely recovered by an external magnetic field, while the carboxylic-sulfonic nanoparticles (CSNPs) showed a trend of increasing activity over the first four recycle runs. Between the two sulfonic ligands, the phosphonates produced a more tightly packed monolayer, which corresponded to a higher sulfonic acid loading, lower agglomeration, lower recoverability through application of an external magnetic field, and higher activity per acid site for the hydrolysis of starch. Functionalizations with 11-aminoundecanoic acid resulted in some amine groups binding to the surfaces of iron oxide nanoparticles. This amine binding is commonly ignored in iron oxide nanoparticle syntheses and functionalizations for biomedical and catalytic applications, affecting understandings of surface charge and other material properties.

Master of Science / Department of Chemical Engineering / Mary Rezac / Polymeric membranes have been playing important roles in gas or liquid separations. Polyimide polymers are of interest due to their commercially availability along with good transport, thermal and mechanical properties. In this study, two common commercial polyimide polymers, Matrimid and P84 were blended, to combine the good transport property of Matrimid with the plasticization resistance of P84. Matrimid/P84 blend solutions ranging from 0-100 wt. % Matrimid were prepared to make blend films. Physical properties (density, d-spacing, thickness), transport properties (permeability of H2, N2, CH4, Ar, He, CO2, and gas pairs selectivity), thermal property (mass loss curves of TGA), and liquid solutes (water, methanol, toluene, butanol, 1-propanol, 2-propanol) desorption behavior were measured or characterized. Rules of changing behavior of the properties with mass fraction of Matrimid were investigated, summarized, and interpreted mathematically. As Matrimid mass fraction increases, there are more mobility and space between polymer chains, therefore there are smaller density, larger d-spacing, larger fractional free volume (FFV) and larger permeability. The selectivity-permeability relationship follows the trade-off line. Thermal mass loss curve of the blend films in air have presented intermediate characteristic with rising fraction of Matrimid compared to individual polymers. A partial-miscible behavior has been found from the correlation between permeability and FFV. The desorption behavior was found to be reasonably described by the case III model, where the diffusion rate is similar with relaxation rate of polymers.

Doctor of Philosophy / Department of Chemical Engineering / Mary E. Rezac / Polyimide membranes have been used extensively in gas separation applications because of their attractive gas transport properties and the ease of processing these materials. Other applications of membranes, such as membrane reactors, which could compete with more traditional packed and slurry bed reactors across a wider range of environments, could benefit from improvements in the thermal and chemical stability of polymeric membranes. This work focuses on blending polyimide and polybenzimidazole polymers to improve the thermal and chemical stability of polyimide membranes while retaining the desirable characteristics of the polyimide. Blended dense films and asymmetric membranes were fabricated and characterized. Dense film properties are useful for studying intrinsic properties of the polymer blends. Transport properties of dense films were characterized from room temperature to 200°C. Properties including miscibility, density, chain packing and thermal stability were investigated. A process for fabricating flat sheet blended integrally skinned asymmetric membranes by phase inversion was developed. The transport properties of membranes were characterized from room temperature to 300°C. A critical characteristic of gas separation membranes is selectivity. Post-treatments including thermal annealing and vapor and liquid surface treatments were investigated to improve the selectivity of blended membranes. Vapor and liquid surface treatments with common, benign solvents including an alkane, an aldehyde and an alcohol resulted in improvements in selectivity.

Doctor of Philosophy / Department of Chemical Engineering / Mary E. Rezac / Reversible organic reactions, such as esterification, transesterification, and acetalisation, have enjoyed numerous laboratory uses and industrial applications since they are convenient means to synthesize esters and ketals. Reversible organic reactions are limited by thermodynamic equilibrium and often do not proceed to completion. High yields for these equilibrium driven reactions can be obtained either by adding a large excess of one of the reactants, which results a reactant(s)/product(s) mixture requiring a separation, or by the selective removal of by-products. Conventional removal techniques including distillation, adsorption, and absorption have drawbacks in terms of efficiency as well as reactor design. Pervaporation membrane reactors are promising systems for these reactions since they have simpler designs, and are more energy efficient compared to conventional downstream separation techniques. This project created a general protocol that can guide one to carry out experiments and collect necessary data for transferring membrane reactor design concepts to the construction of industrial-scale membrane reactors for organic synthesis. Demonstration of this protocol was achieved by (1) experimental evaluation of membrane reactor performance, (2) modeling, and (3) scale-up. The capability of membranes for water/organic separations and organic/organic separations during reversible reactions was investigated. Our results indicated that enhanced membrane reactors selectively removed the by-product water and methanol from reaction mixtures and achieved high conversions for all investigated reactions. Second, modeling and simulation of pervaporation membrane reactor performance for reversible reactions were carried out. The simulated performance agrees well with experimental data. Using the developed model, the effects of permeate pressure and membrane selectivity on membrane reactor yield were examined. Finally, a scale-up on transesterification membrane reactors was carried out. The membrane modules investigated included a bench-scale flat sheet membrane, a bench-scale hollow fiber membrane module, and a pilot-scale hollow fiber membrane module. A 100% conversion was obtained by the selective methanol removal. It is found that with high methanol selectivity membranes, the reaction time to achieve a given conversion continuously decreases with increasing the methanol removal capacity of the reactor system. However, this is a highly nonlinear relationship.

Doctor of Philosophy / Department of Chemical Engineering / Jennifer L. Anthony / Ionic liquids are low melting salts composed of an organic cation and an inorganic or organic anion. Ionic liquids are of interest for their wide range of applications and unique properties, such as the negligible vapor pressure of some types of ionic liquids, and the ability to modify ionic liquid properties by selection of the cation or anion. It has been hypothesized that over one million binary ionic liquids (meaning a single cation/anion pair) are possible. Due to the vast number of potential combinations, it should be possible to design ionic liquids specifically for an application of interest. One potential application is their use as protein solvents. However there is little understanding of how ionic liquids affect proteins. This research examined the solubility and secondary structure of the hydrophobic corn protein zein in seven ionic liquids and three conventional solvents as a function of temperature and solvent properties. Zein’s solubility in the solvents was measured gravimetrically from 30 to 60 degrees Celsius. Solubility was then related to solvent properties to gain an understanding of what solvent properties are important, and how to design an ionic liquid to dissolve zein. It was found that a good solvent for zein has a small molecular volume, a low polarity, and is a weak hydrogen bond acceptor. Infrared spectroscopy with curve fitting was used to examine the secondary structure of zein as a function of both solvent and temperature from 25 to 95 degrees Celsius. It was found that most of the ionic liquids change zein’s secondary structure, but those secondary structure changes were not affected by temperature. Aprotic ionic liquids increase the amount of β-turn secondary structure through non-polar interactions between the mixed aromatic-alkyl imidazolium cations and the non-polar portions of the zein. Strong hydrogen bond accepting molecules were found to increase the amount of β-turn secondary structure. It is hypothesized from this research that suitable solvents for zein will have a small molar volume, low polarity, and be poor hydrogen bond acceptors. This combination of properties will enhance zein’s solubility and limit secondary structure changes that can harm protein properties.

Master of Science / Department of Chemical Engineering / Mary E. Rezac / Mary E. Rezac / Energy consumption due to heating, ventilation, and air conditioning amounts to 10-20% of global electrical energy usage. Air conditioning alone uses one trillion kilowatt hours globally. This energy is required for the dehumidification of air in addition to its cooling. New membrane technologies have the potential to decrease air conditioning energy requirements by significant amounts. A membrane acts as a partial heat and mass exchanger in conjunction with a traditional air conditioning system to remove water content and reduce the cooling load. Membranes vary according to their properties and method of mass transport. Liquid membranes have high permeability and selectivity, dense membranes have high selectivity and low permeability, and porous membranes have low selectivity and high permeability. A theoretical model was created to observe how membrane properties affected the potential energy savings of such systems. The most influential properties were flow rate, water permeability and selectivity, membrane area and thickness, and the purge flow temperature. Other properties were determined to be minimally important such as outdoor temperature and humidity. The effect on energy savings in many cases was not a linear relationship but suggested an optimal value beyond which energy savings did not significantly increase. The best simulations showed electrical energy savings of 86-95%.

Doctor of Philosophy / Department of Biological and Agricultural Engineering / Yong Cheng Shi / Donghai Wang / Cellulosic ethanol made from low cost lignocellulosic biomass has been considered as new generation transportation fuel with economic and environmental advantages. Photoperiod-sensitive (PS) sorghum, because of its high biomass yield (2.6 kg dry mass/m2), about 18% of soluble sugar in dry mass, and drought tolerance, is a promising biomass for ethanol production. The overall goals of this study are to develop an efficient approach to convert PS sorghum to ethanol and to understand the structural characteristics of biomass. For increasing the efficiency of biomass conversion, an integrated method, using diluted sulfuric acid pretreatment, has been developed to utilize both the structural polysaccharide (cellulose) and the soluble sugar (sucrose, glucose, and fructose) for fermentation. Response surface methodology was employed to optimize the pretreatment condition for maximizing the cellulose-glucose conversion. Simultaneous enzymatic hydrolysis and yeast fermentation was used for ethanol production. The effects of the buffer concentration, the inoculation dosage and time, and the fermentation temperature were investigated for maximizing ethanol yield. A total conversion efficiency of 77.2% and an ethanol concentration of 2.3% (v/v) were obtained after 72 h fermentation. About 210 kg (~266 Liters) ethanol could be produced from one ton dry mass of PS sorghum under the optimized condition. The structural features of the PS sorghum were studied using techniques including scanning electron microscopy and X-ray diffraction/scattering. Biomass at different botanic locations was investigated. Wide-angle X-ray diffraction (WAXD) study showed that the PS sorghum rind had oriented crystal peaks and the highest degree of crystallinity, whereas the crystalline structures of the inner pith and leaf were less ordered. The results from WAXD suggested that crystalline cellulose was melted at 120 °C before its significant degradation. Both the cellulose crystallinity and the crystal size at the dimension lateral to fiber direction increased as the temperature increased from 120 to 160 °C. The efficiency of enzymatic hydrolysis increased because the protective structure was damaged and most hemicellulose was removed, resulting in the increase in accessible area as suggested by small-angle X-ray scattering result of the increased length of microvoids. The results from WAXD also suggested a simultaneous hydrolysis and crystallization of cellulose by acid.

Doctor of Philosophy / Department of Chemical Engineering / Peter H. Pfromm / The expanded Renewable Fuel Standard (RFS2), established under the Energy Independence and Security Act (EISA) of 2007, mandates the production of 136.3 GL/year of renewable fuels in the U.S. in 2022: 56.8 GL/year of corn-ethanol, 60.6 GL/year of second generation biofuels such as cellulosic ethanol, and 18.9 GL/year of advanced biofuels such as biomass-based diesel. One of the several challenges when a biochemical conversion technique is used to produce bioethanol from corn and cellulosic feedstock is the high energy demand for recovering and purifying ethanol, which is mainly due to the low concentration of ethanol in the fermentation broth and the challenging water-ethanol vapor liquid equilibrium. Dilute ethanol from the fermentation broth can be separated and concentrated aided by salt extractive distillation to directly produce fuel ethanol leading to significant energy savings. Techniques other than highly energy intensive evaporative salt concentration/crystallization and solids drying for recovering salt, which is used to facilitate distillation, have rarely been considered. In this study, a novel combination of electrodialysis and spray drying was investigated to recover the salt. Salt extractive distillation – with salt recovery enabled by electrodialysis – was conceptually integrated in the fermentation broth-ethanol separation trains of corn and cellulosic ethanol facilities and investigated through process simulation with Aspen Plus® 2006.5 to reduce the recovery and purification energy demand of bioethanol. Experiments for the electrodialytic concentration of calcium chloride from high diluate concentrations, prevalent in the salt recovery process when calcium chloride is used as the salt separating agent in the salt extractive distillation of bioethanol, were carried out to determine the fundamental transport properties of an ion exchange membrane pair comprising commercially available membranes for implementation in the conceptual process designs. The maximum calcium chloride concentration achievable through electrodialytic concentration is 34.6 wt%, which is mainly limited by the water transport number. In case of corn-ethanol, retrofitted salt extractive distillation resulted in an energy demand reduction of about 20% and total annual cost savings on the order of MM$0.5 per year when compared with the state-of-the-art rectification/adsorption process for producing fuel ethanol from the beer column distillate. In case of cellulosic ethanol, salt extractive distillation with direct vapor recompression provided the highest energy savings of about 22% and total annual cost savings on the order of MM$2.4 per year when compared with the base case comprising conventional distillation and adsorption for recovering and purifying ethanol from the fermentation broth. Based on the conceptual process design studies, an overall maximum energy savings potential of 1.5*10[superscript]17 J or about 0.14 Quad (as natural gas higher heating value) per year could be estimated for the targeted 56.8 GL of corn-ethanol and 60.6 GL of cellulosic ethanol to be produced in the U.S in 2022 when salt extractive distillation enabled by electrodialysis is implemented in the fermentation broth-ethanol separation trains of the corn and cellulosic ethanol facilities.

Doctor of Philosophy / Department of Chemical Engineering / James H. Edgar / The exceptional radiation resistance, high melting point, and wide energy bandgap (3.2 eV) of icosahedral boron arsenide, B[subscript]12As[subscript]2, make it an attractive candidate for applications in radiation intense environments, for example, in radioisotope batteries. These devices have potential lifetimes of decades rather than days or weeks that are typical of conventional chemical power cells. Solid state neutron detectors are another potential application of this semiconductor, as the boron-10 isotope has a high thermal neutron capture cross-section, orders of magnitude higher than most elements. To produce high quality crystalline B[subscript]12As[subscript]2 for these applications, this research focused on the epitaxy and electrical properties of B[subscript]12As[subscript]2 thin films. The major findings include the following. Twin-free heteroepitaxial B[subscript]12As[subscript]2 layers were obtained on m-plane 15R-SiC and c-plane 4H-SiC inclined 4° and 7° off-axis in the [1-100] direction. These substrates exposed asymmetric step-terrace surface structures that force B[subscript]12As[subscript]2 layers to adopt a single orientation, thus, twins were eliminated. Consequently, the crystal quality was greatly improved over films on on-axis c-plane 6H-SiC, yielding a maximum hole mobility of 80 cm[superscript]2V[superscript]-1s[superscript]-1, nearly 100 times higher than previously reported values. B[subscript]12As[subscript]2 epilayers grown at 1300°C had the lowest defect densities, smallest residual strains, highest mobility and highest deposition rate. Excess AsH[subscript]3 concentration was advantageous to prevent the loss of arsenic from the epilayer. Undoped B[subscript]12As[subscript]2 exhibited a variable-range-hopping conduction, indicating it was a highly disordered system. All films were p-type with a room temperature hole concentration on the order of 10[superscript]12~10[superscript]15cm[superscript]-3. The thermal activation energy of acceptors varied from 0.15 eV to 0.33 eV. The Hall mobility was dominated by impurity scattering at low temperatures and by polar phonon scattering at high temperatures. H, C, O and Si were the major impurities present in the undoped B[subscript]12As[subscript]2 films with concentrations on the order of 10[superscript]18~10[superscript]19 cm[superscript]-3. Si doping and annealing decreased the resistivity by up to two orders of magnitude. The density of localized states was small in the undoped B[subscript]12As[subscript]2 as the intrinsic acceptor levels (IALs) were compensated by the boron interstitials. However, in Si-doped B[subscript]12As[subscript]2, Si may prevent the interstitial boron atoms from compensating the IALs, yielding a decreased density of localized states. The Hall mobility of B[subscript]12As[subscript]2 epilayer was significantly reduced with increasing silicon concentration.