Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 135-147). / As production of shale gas has increased greatly in the United States, the amount of stranded shale gas that is flared as carbon dioxide has become significant enough to be considered an environmental hazard and a wasted resource. The conversion of methane, the primary component of natural gas, into methanol, an easily stored liquid, is of practical interest. However, shale wells are generally inaccessible to reforming facilities, and construction of on-site, conventional methanol synthesis plants is cost prohibitive. Capital costs could be reduced by the direct conversion of methane into methanol at low temperature. Existing strategies for the partial oxidation of methane require harsh solvents, need exotic oxidizing agents, or deactivate easily. Copper-exchanged zeolites have emerged as candidates for methanol production due to high methanol selectivity (> 99%), utilization of oxygen, and low reaction temperature (423-473 K). Despite these advantages, three significant shortcomings exist: 1) the location of surface intermediates on the zeolite is not well understood; 2) methane oxidation is stoichiometric, not catalytic; 3) there are few active sites and methanol yield is low. This work addresses all three shortcomings. First, a new reaction pathway is identified for methane oxidation in copper-exchanged mordenite zeolites using tandem methane oxidation and Koch carbonylation reactions. Methoxy species migrate away from the copper active sites and adsorb onto Bronsted acid sites, signifying spillover on the zeolite surface. Second, a process is developed as the first instance of the catalytic oxidation of methane into methanol at low temperature, in the vapor phase, and using oxygen as the oxidant. A variety of commercially available copper-exchanged zeolites are shown to exhibit stable methanol production with high methanol selectivity. Third, catalytic methanol production rates and methane conversion are further improved 100- fold through the synthetic control of copper speciation in chabazite zeolites. Isolated monocopper species, directed through the one-pot synthesis of copper-exchanged chabazite zeolites, correlates with methane oxidation activity and is likely the precursor to the catalytic site. Together, these synthetic methods provide guidelines for catalyst design and further improvements in catalytic activity. / by Karthik Narsimhan. / Ph. D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1995. / Includes bibliographical references (leaves 223-229). / by Mary Elaine Johnson. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2005. / Includes bibliographical references (p. 209-222). / (cont.) time, while obtaining useful information about the thermodynamic behavior of the system. We show how statistical mechanics can be formulated using the wavelet transform as a coarse-graining technique. For small systems in which exact enumerations of all states is possible, we illustrate how the method recovers reasonably good estimates for physical properties (errors no more than 10%) with several orders of magnitude fewer operations than are required for an exact enumeration. In addition, we illustrate that errors introduced by the wavelet transform vanish in the neighborhood of fixed points of systems as determined by RG theory. Using scaling results from simulations at different length scales, we estimate the thermodynamic behavior of the original system without performing simulations on the full original system. In addition, we make the method adaptive by using fluctuation properties of the system to set criteria under which further coarse graining or refinement of the system is required. We demonstrate our method for the Ising universality class of problems. We also examine the applicability of the WAMC framework to polymer chains. Polymers are quintessential examples of the need for simulations at multiple scales: at one end, we can study short chains using quantum chemistry methods; yet polymers can have relaxation times on the order of seconds or longer, and molecular weights of 10⁶ or more. Even with modern computational resources, simulating behavior at long times or for long chains is still prohibitively expensive ... / Multiscale modeling of physical systems often requires the use of multiple types of simulations to bridge the various length scales that. need to be considered: for example, a density-functional theory at the electronic scale will be combined with a molecular-dynamics simulation at the atomistic level, and with a finite-element method at the macroscopic level. An improvement to this scheme would be a method which is capable of consistently simulating a system at multiple levels of resolution without passing from one simulation type to another, so that different simulations can be studied at a common length scale by appropriate coarse-graining or refinement of a given model. We introduce the wavelet transform as the basis for a new coarse-graining framework. A family of orthonormal basis, the wavelet transform separates data sets, such as spatial coordinates or signal strengths, into subsets representing local averages and local differences. The wavelet transform has several desirable properties for coarse-graining: it is hierarchical, compact, and has natural applications to approximating physical data sets. As a hierarchical method, it can be used to rescale a Hamiltonian to a desired length scale, and at the same time also rescales the particles of the system by creating "blocked" particles in the spirit of renor-malization group (RG) calculations. The wavelet-accelerated Monte Carlo (WAMC) framework performs a Monte Carlo simulations on a small system which will be transformed into a block particle to obtain the probability distribution of the blocked particle; a Monte Carlo simulation is then performed on the resulting system of blocked particles. This method, which can be repeated as needed, can achieve significant speed-ups in computational / by Ahmed E. Ismail. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 178-190). / Drug-eluting stents (DES) are commonly used in coronary angioplasty procedures. A DES elutes drug compounds from a thin polymeric coating into the surrounding coronary artery tissue to reduce in-stent restenosis (a significant lumen loss due to growth of vascular tissue). Biodurable (non-erodible) polymers are often used in the current DES coatings, which stay permanently in the patients. While promising treatment results were obtained, in-stent restenosis remains an issue and late in-stent thrombosis, which is associated with hypersensitivities to the polymer coatings, is also reported. Increasing interests have been raised towards the design of a more biocompatible coating, in particular a poly(lactic acid-co-glycolic acid) (PLGA) coating, for DES applications to improve the drug delivery and reduce adverse outcomes in patients. This dissertation aims to develop a mathematical model for describing the process of drug release from a biodegradable PLGA stent coating, and subsequent drug transport, pharmacokinetics, and distribution in the arterial wall. A model framework is developed in the first part of the dissertation, where a biodurable stent coating is considered, and the intravascular delivery of a hydrophobic drug from an implanted DES in a coronary artery is mathematically modeled. The model integrates drug diffusion in the coating with drug diffusion and reversible drug binding in the arterial wall. The model was solved by the finite volume method. The drug diffusivities in the coating and in the arterial wall were investigated for the impact on the drug release and arterial drug uptake. In particular, anisotropic vascular drug diffusivities result in slightly different average arterial drug levels but can lead to very different spatial drug distributions, and is likely related to the reported non-uniform restenosis thickness distribution in the artery cross-section. The second part of the dissertation focuses on modeling drug transport in a biodegradable poly(D,L-lactic-co-glycolic acid) (PLGA) coating. A mathematical model for the PLGA degradation, erosion, and coupled drug release from PLGA stent coating is developed and validated. An analytical expression is derived for PLGA mass loss. The drug transport model incorporates simultaneous drug diffusion through both the polymer solid and the liquid-filled pores in the coating, where an effective drug diffusivity model is derived taking into account factors including polymer molecular weight change, stent coating porosity change, and drug partitioning between solid and aqueous phases. The model predicted in vitro sirolimus release from PLGA stent coating, and demonstrated the significance of the developed model by comparing with existing drug transport models. An integrated model for intravascular drug delivery from a PLGA-coated DES is developed in the last part of the dissertation. The integrated model describes the processes of drug release in a PLGA coating and subsequent drug delivery, distribution, and drug pharmacokinetics in the arterial wall. Model simulations first compared a biodegradable PLGA coating with a biodurable coating for stent-based drug delivery. The simulations further investigated drug internalization, interstitial fluid flow in the arterial wall, and stent embedment for impact on the drug release and arterial drug distribution of a PLGA-coated stent. These three factors greatly change the average drug concentrations in the arterial wall. Each factor leads to significant and distinguished alterations in the arterial drug distribution that can potentially influence the treatment outcomes. The developed model here provides the basis of a design tool for evaluating and studying a PLGA coating for stent applications. Simulations using the model helped to provide insights into the potential impacts of various factors that can affect the efficacy of drug delivery. With the developed model, optimization of the model parameters can also be performed for future exploration on the design of PLGA-coated drug-eluting stents. / by Xiaoxiang Zhu. / Ph. D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Fossil fuels have powered the transportation industry since the Industrial Revolution. However, rising transportation energy demand and new knowledge about the environmental impact of burning fossil fuels have motivated the development of technologies for sustainable production of renewable, carbon-neutral liquid fuels. To that end, biological systems may be leveraged to fix carbon dioxide and to catalyze the conversion of renewable feed stocks to fuel molecules. Today, the gasoline additive ethanol and biodiesel are produced by yeast fermentation of sugars derived from cornstarch and sucrose and transesterification of vegetable oils, respectively. However ethanol has many drawbacks as a fuel additive, and both biofuels are currently produced from edible feed stocks. For biofuels to contribute significantly to meeting total transportation energy demand, processes for production of fuel molecules from non-food feed stocks must be engineered. Two promising solutions are fermentation of sugars derived from "woody," lignocellulosic biomass and production of fuels from volatile fatty acids (VFAs) such as acetate, which can be produced by fermentation of organics in municipal solid waste and sewage or syngas. The production of biofuels from lignocellulosic material or VFAs will require metabolic engineering of biocatalysts to improve yields, productivities, and final titers. These metabolic engineering efforts can be facilitated by ¹³C-Metabolic Flux Analysis (MFA), a method for elucidating the otherwise unobservable intracellular metabolic fluxes in biological systems. We first developed protocols for extraction and LC-MS/MS analysis of intracellular metabolites, which provides data that may be used for metabolic flux estimation. We then performed an analysis of both the measurement and modeling errors associated with using these data for flux determination. Finally, we applied ¹³C-MFA to two industrially relevant systems: 1) Fermentation of xylose, a sugar present in lignocellulosic biomass, to ethanol in Saccharomyces cerevisiae, and 2) overproduction of fatty acids that may be transesterified to biodiesel from either glucose or acetate in the oleaginous yeast Yarrowia lipolytica. These experiments identified a potential bottleneck in xylose fermentation in S. cerevisiae and the primary source of NADPH for fatty acid biosynthesis in Y. lipolytica, and also suggested potential strategies for improving lipid yields in Y. lipolytica. / by Thomas M. Wasylenko. / Ph. D.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1959. / Vita. / Includes bibliographical references (leaves B-28-B-32). / by Nai Yuen Chen. / Sc.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1991. / Includes bibliographical references (leaves 87-88). / by David P. Ventola. / M.S.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1961. / MIT copy bound with: Ripple plate efficiencies for an absorption tower / Edward J. Bing. 1961. / Includes bibliographical references (leaf 19). / by Leslie G. Bromwell. / B.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2009. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student submitted PDF version of thesis. / Includes bibliographical references (p. 138-148). / The increasing global focus on alternative energy sources has led to a renewed interest in fuel cells. For low power, portable applications, direct methanol fuel cells (DMFCs) are the most promising type of fuel cell. DMFCs can operate at ambient conditions and only require dilute methanol solutions and air to be input to the devices. At the core of these devices is a proton exchange membrane (PEM) that allows rapid proton transport through the polymer matrix while preventing fuel from permeating across. Additionally, PEMs must have long-term stability in the fuel cell environment, the ability to operate over a wide range of conditions (temperature and humidity), and be cost effective. A promising, robust method for fabricating polymer films with tunable properties is layer-by-layer (LbL) assembly. This technique consists of building a polymer film by sequential dipping into polymer solutions with complementary interactions, such as opposite electrostatic charges. The LbL method allows the formation of thin films that have perm-selective properties and high ionic conductivity values. This work describes the optimization of multilayer systems for use as the PEM in DMFCs. First, LbL assembled films of poly[bis(methoxyethoxyethoxy)-phosphazene] (MEEP) and poly (acrylic acid) (PAA) are demonstrated by utilizing the hydrogen bonding between these two polymers. These films show controlled thickness growth, high ionic conductivity, and excellent hydrolytic stability. The ionic conductivity of these films is optimized by tuning the assembly pH of initial polymer solutions and thereby controlling the hydrogen bonding characteristics. / (cont.) Despite similar film composition, MEEP/PAA LbL films assembled at higher pH values have enhanced water uptake and transport properties, which play a key role in increasing ion transport within the films. At fully humidified conditions, the ionic conductivity of MEEP/PAA is over one order of magnitude higher than previously studied hydrogen bonded LbL systems. The next LbL systems studied consist of a highly sulfonated aromatic polyether (sPPO) paired with amine containing polycations. The best performing sPPO system has ionic conductivity values which are the same order of magnitude as commercially relevant PEMs and has the highest ionic conductivity ever obtained from a LbL assembled film. Additionally, these LbL systems have methanol permeability values over two orders of magnitude lower than traditional PEMs. Incorporating the sPPO systems into DMFCs results in a 53% improvement in power output as compared with DMFCs using traditional PEMs. In-depth structure property studies are performed to understand the nature of the high ionic conductivity of the sPPO LbL systems with respect to film growth, composition, water uptake, and ionic crosslink density. Lastly, the mechanical properties of highly conducting LbL films are improved by forming the LbL matrix on highly tunable electrospun fiber mat (EFM) supports. Free-standing LbL films have moderate mechanical properties when dry, but are mechanically deficient when hydrated. Coating an EFM with the LbL dipping process produces composite membranes with interesting "bridged" morphologies, while still maintaining high ionic conductivity values. / (cont.) The spray LbL assembly is studied as a means for the rapid formation of LbL films on EFMs. At optimized conditions, the LbL materials conformally coat the individual fibers throughout the bulk of the EFM and have uniform surface coatings. The mechanical properties of the spray coated EMFs are shown to be superior to the pristine LbL systems. / by James Nathan Ashcraft. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1999. / Includes bibliographical references. / Supercritical water oxidation (SCWO) typically refers to a waste treatment or remediation process and derives its effectiveness from the unique solvent properties of water above its critical point. When organic compounds and oxygen are brought together in water well above its critical point of 221 bar and 374°C, the oxidation of the organic is rapid and complete to carbon dioxide and water with heteroatoms such as Cl, S and P converted to their corresponding mineral acids which can be neutralized using a suitable base. The research presented in this thesis addresses the general goal of characterizing the mechanisms and kinetics of reactions of model organic chemicals in supercritical water. This goal is achieved through a detailed experimental and theoretical investigation of the oxidation of benzene, a representative model aromatic compound, in supercritical water. Such basic research benefits the field by providing a better understanding of the SCWO process and can lead to better and more efficient designs of commercial waste treatment systems. In preparation for experiments on the SCWO of benzene, an investigation was undertaken to characterize the effects of mixing and oxidant choice on laboratory-scale kinetic measurements. The apparent induction time, previously reported in SCWO kinetics of various model compounds measured in the MIT laboratory-scale tubular reactor system, was found to be influenced by the geometry and flow conditions within the mixing region at the reactor entrance. Redesign of this mixing region led to a reduction in the apparent induction time measured during methanol SCWO from 3.2 to 0.7 seconds. In order to realize higher concentrations of oxygen in the reactor, the use of hydrogen peroxide as an oxidant was explored. The oxidation rate of methanol was found to be the same using hydrogen peroxide or dissolved oxygen, thus demonstrating the use of aqueous hydrogen peroxide solutions as a viable means of introducing molecular oxygen in situ into the laboratory-scale SCWO reactor system. Oxidation and hydrolysis reactions with benzene were thoroughly investigated in supercritical water using a laboratory-scale, plug-flow reactor system. Little to no conversion of benzene occurred in supercritical water at temperatures between 530 and 625°C by a hydrolysis pathway (in the absence of oxygen) for residence times up to 6 s. Oxidation reactions were studied at temperatures ranging from 479 to 587°C, pressures of 139 to 278 bar, reactor residence times from 3 to 7 s, and initial benzene concentrations of 0.4 to 1.2 mmol/L, and oxygen concentrations ranging from 40% of stoichiometric oxygen demand to 100% excess oxygen. The oxidation rate was found to be 0.40±0.06 order in benzene and 0.18±0.05 order in oxygen with an activation energy of 240± 10 kJ/mol. The primary oxidation product at all reaction conditions and levels of benzene conversion was carbon dioxide. Other important oxidation products were carbon monoxide, phenol and methane. Trace levels of additional light hydrocarbon gases and single- and multi-ringed aromatic species were detected as well. Prior to the theoretical investigation of benzene SCWO using an elementary reaction mechanism (ERM), the effects of uncertainty in the input parameters of these ERMs on their predictive capabilities was explored for hydrogen oxidation in supercritical water. Two methods, the Detenninistically Equivalent Modeling Method (DEMM) and Monte Carlo simulations, were applied for this purpose. Analysis revealed the presence of considerable uncertainty in the predicted species concentration profiles arising from the reported uncertainties in the forward rate constants and species enthalpies of fonnation. For example, at the point of maximum uncertainty, the predicted concentrations of hydrogen and oxygen deviated by ±70% from their median values at the upper 97.5% and lower 2.5% probability contours. Model predictions were found to be highly sensitive to two relatively uncertain parameters: the MIJ of H02 radical and the rate constant for H202 dissociation. An elementary reaction mechanism for the supercritical water oxidation of benzene was developed to provide mechanistic insights regarding key reaction pathways. An available, low-pressure combustion mechanism was adapted to the lower temperatures and higher pressures of SCWO through the addition of new reaction pathways and the calculation of the rate constants of pressure dependent reactions using quantum Rice-Ramsperger-Kassel (QRRK) theory. The resulting mechanism, after adjustment, accurately reproduces the exoerimentally measured benzene and phenol concentration profiles at 540°C and 246 bar with stoichiometric oxygen. Additionally, a comparison of the model predictions to benzene SCWO data measured at conditions other than those to which the model WuS fit revealed that the model qualitatively explains the trends of the data and gives good quantitative agreement at many conditions. For example, the model predicts the measured benzene conversion to better than ± 10% conversion at temperatures between 515 and 590°C at 246 bar with stoichiometric oxygen and at pressures from 139 to 278 bar at 540°C with stoichiometric oxygen. The most important difference between this benzene SCWO mechanism and those previously developed for combustion conditions is the inclusion of reactions involving the C6H500 radical. Without their inclusion, the predicted oxidation rate of benzene was too fast and the concentration of carbon monoxide was incorrectly predicted to exceed that of carbon dioxide. / by Joanna L. DiNaro. / Ph.D.