Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, February 2011. / "September 2010." Cataloged from PDF version of thesis. / Includes bibliographical references (p. 261-265). / Nuclear hydrogen production processes have been proposed as a solution to rising CO 2 emissions and low fuel yields in the production of liquid transportation fuels. In these processes, the heat of a nuclear reactor is used to run the chemical reactions in a hydrogen plant. The resulting system is tightly interconnected and operates at very high temperature and pressure, which can lead to operational disruptions and accidents. For this reason, computational studies validating the safe operation of the system are required by regulatory authorities. In the past, safety studies have been conducted by using legacy codes, such as RELAP and MELCOR, and their focus has been the operation of nuclear power plants. However, traditional legacy codes are not appropriate to simulate nuclear hydrogen production. The simulation of a nuclear reactor itself is already complex because it involves simulating reactor kinetics and transport phenomena. To that complexity, nuclear hydrogen production adds the need to simulate chemical reactions in the hydrogen plant. These chemical reactions cannot be represented easily in legacy codes because these codes lack the flexibility, speed and accuracy required to simulate them. Therefore, only a limited number of studies on the safety of these systems exist. Instead of using legacy codes, this thesis proposes using equation-based simulators developed by the chemical engineering community to model and study the safety of a nuclear hydrogen production plant. Equation-based simulators were designed to be flexible, extensible and fast because they have to simulate a vast range of processes from the chemical industry. Thus, they provide a good platform for the simulation of nuclear hydrogen production systems. This thesis explains the models used for the different parts in the nuclear hydrogen production plant, and then presents the response of this plant model to different accident scenarios. The first contribution of this thesis is a novel equation-based model for the heat transfer loop connecting a nuclear reactor and a hydrogen production plant. This heat transfer loop uses helium as the heat transfer fluid, which makes simulating its behavior difficult because of the need to model gas dynamics. To resolve this, three models for gas dynamics and two set of coupling conditions for boundary variables were tested in JACOBIAN, an equation-based simulator. The three models for gas dynamics in combination with a novel approach to set coupling conditions for boundary variables were able to represent the interesting time scales accurately in transient scenarios. The accuracy and computational speed of these simulations outperformed those produced by a reference model created in RELAP, a legacy code. The second contribution is a model of a nuclear hydrogen production plant using high-temperature steam electrolysis to produce hydrogen. This model was created to study the effect of potential accidents on the nuclear reactor. It included detailed models of the nuclear reactor and heat transfer loop, and a partial model of the electrolysis plant. The nuclear reactor was modeled as a pebble bed modular reactor, which is one of the safest designs available. The reactor was connected to the hydrogen production plant using the heat transfer loop model already developed in this thesis. The hydrogen production plant was partially represented as a steam superheater in the heat transfer loop. The third contribution is the demonstration of the safety characteristics of the nuclear hydrogen production plant by subjecting the plant model to three accident scenarios. The scenarios involved disruptions in the hydrogen plant or in the heat transfer loop, and all of them-directly or indirectly-lead to a loss of heat sink capacity for the nuclear reactor. This resulted in an increase of the nuclear reactor core temperature, which was quickly moderated by the fission power reduction at the fuel pebbles and by the safe design of the nuclear reactor. As a consequence, the maximum temperature reached in the core was always less than the fuel melting point and the reactor was always in a safe condition. The heat transfer loop could suffer the rupture of a pipe in one of the scenarios, and design modifications to address this were suggested. This thesis' results partially prove that nuclear hydrogen production plants could be safe, and simultaneously, that equation-based simulators are good platforms to demonstrate the safety of these plants. Developing these models and tests further will help guarantee the safety of the plant and obtain regulatory and public approval for this new nuclear application. / by Patricio D. Ramírez Muñoz. / Ph.D.

Thesis (M.S.) Massachusetts Institute of Technology. Dept. of Chemical Engineering, 1949. / Bibliography: leaves 67-68. / by Raymond Frederick Baddour and Lee Derrickson Carr. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2003. / Includes bibliographical references. / A host of vital, current, and developing technologies, such as pyrolysis, thermal cracking, partial oxidation, and high-efficiency combustion engines, involve complex, gas-phase chemical mechanisms with hundreds of species and thousands of reactions. Building complete, explicit chemical models by-hand for these systems is exceedingly difficult. The bias and intuition of the developers figure strongly in the resultant mechanism, causing important but unanticipated pathways to be ignored, and useless pathways to be included. Thus many chemists and engineers have tried artificial intelligence software tools, or "automated mechanism generators", to build large chemical mechanisms systematically. These tools employ graph-theory algebra, and "rate rules" - estimates of rate constants for classes of reactions - to construct automatically all the possibly important reactions and species for a given set of conditions. All of these tools have been severely hampered by their inability to capture the effects of pressure-dependence and falloff - even though these effects are important in almost every gas-phase system of interest to engineers and designers. Pressure-dependent reactions cannot be included using simple rate rules. Until now they presented an unresolved quandary for automated mechanism generators. This work presents the first automated method for including pressure-dependent reactions generally and systematically, on-the-fly, in computerized mechanism generation. / (cont.) The approach includes in the mechanism only those pressure-dependent pathways important for the conditions of interest, but can find any potentially important pressure-dependent reaction. It works by building partial pressure-dependent reaction networks, step-by-step, in harmony with a rate-based termination criteria which rationally controls overall mechanism size. It uses a fast, approximate method, the Quantum-Rice-Ramsperger-Kassel/Modified-Strong-Collision (QRRK/MSC), to predict rate constants k(T,P) employing only high-pressure-limit rate rules, pressure-dependent network structure, and heat capacity estimates. The error incurred by screening the pressure- dependent networks to include only important sections is small and bounded. Successful applications to various systems, including reactions through cycloalkyl intermediates, are presented. Application of this tool to methane pyrolysis revealed a new, unexpected mechanism. It explained the decades-old mystery of methane autocatalysis at low conversion, a phenomenon which had defied all "by-hand" attempts at mechanism development. Such work hints at the predictive power inherent in the next generation of automated mechanism builders. / by David M. Matheu. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1998. / Includes bibliographical references (leaves 170-181). / by Gokaraju Kanaka Prasad Raju. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Amine functional polymer thin films provide a versatile platform for subsequent functionalization because of their diverse reactivity. Initiated chemical vapor deposition (iCVD) is a polymer chemical vapor deposition technique that utilizes the delivery of vaporphase monomers to form chemically well-defined polymer films with tunable conformality and property. In this thesis work, amine functional iCVD poly(4-aminostyrene) (PAS) thin films were synthesized for the first time. The pendant amine groups enable the formation of a robust nanoadhesive with complementary epoxy functional groups. Bonded devices able to withstand >150 psi were achieved by combining polydimethylsiloxane (PDMS) and a wide variety of polymeric materials. Additionally, the all-iCVD nanoadhesive bonding process displays high resistance against hydrolytic degradation (>2 weeks). In addition to bonding, the iCVD layers remaining in the microfluidic channels provide functional groups for subsequent reaction and also act as diffusion barriers against oxygen permeation into the devices. Two applications utilizing this nanoadhesive bonding technique were introduced, including for growth of E. coli in the iCVD-bonded chips and fabrication of gas impermeable microchannels for microparticle synthesis from organic solvents. Another amine functional conformal coating has been designed, synthesized, and characterized. The novel alternating copolymer thin film synthesized from maleic anhydride and aminostyrene via iCVD extensively self-crosslinks after gentle heating. The annealed copolymer films display an elastic modulus exceeding 20 GPa, far greater than typical polymers (0.5~5 GPa). Moreover, the cross-linked films maintain their flexibility, neither cracking nor delaminating with repeated flexing. This achievement represents a significant advance in the fabrication of tough, durable, conformal, functional coatings. Furthermore, the highly crosslinked coating material has oxygen permeability lower than leading commercially available permeation barrier films, making it an attractive material for electronics or food industries. Also described is the utility of a new initiator, tert-butyl peroxybenzoate (TBPOB), for the iCVD synthesis. Using TBPOB instead of tert-butyl peroxide (TBPO), the rate of iCVD film growth increased by a factor of up to ~8 at comparable conformality and lower the filament temperature from ~250 °C to ~150 °C at a comparable deposition rate. The faster deposition rates improve the economics of the iCVD process and the ability to initiate polymerizations at a much lower filament temperature reduces heat load to substrate, which is advantageous for temperature sensitive polymeric substrates or monomers that decompose at high temperatures. / by Jingjing Xu. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1990. / Vita. / Includes bibliographical references (leaves 323-345). / by Mark Jon Bennett. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2004. / Includes bibliographical references (p. 247-256). / (cont.) on a set composed of the Cartesian product between the parameter bounds and the state bounds. Furthermore, I show that the solution of the differential equations is affine in the parameters. Because the feasible set is convex pointwise in time, the standard result that a convex function composed with an affine function remains convex yields the desired result that the integrand is convex under composition. Additionally, methods are developed using interval arithmetic to derive the exact state bounds for the solution of a linear dynamic system. Given a nonzero tolerance, the method is rigorously shown to converge to the global solution in a finite time. An implementation is developed, and via a collection of case studies, the technique is shown to be very efficient in computing the global solutions. For problems with embedded nonlinear dynamic systems, the analysis requires a more sophisticated composition technique attributed to McCormick. McCormick's composition technique provides a method for computing a convex underestimator for for the integrand given an arbitrary nonlinear dynamic system provided that convex underestimators and concave overestimators can be given for the states. Because the states are known only implicitly via the solution of the nonlinear differential equations, deriving these convex underestimators and concave overestimators is a highly nontrivial task. Based on standard optimization results, outer approximation, the affine solution to linear dynamic systems, and differential inequalities, I present a novel method for constructing convex underestimators and concave overestimators for arbitrary nonlinear dynamic systems ... / My thesis focuses on global optimization of nonconvex integral objective functions subject to parameter dependent ordinary differential equations. In particular, efficient, deterministic algorithms are developed for solving problems with both linear and nonlinear dynamics embedded. The techniques utilized for each problem classification are unified by an underlying composition principle transferring the nonconvexity of the embedded dynamics into the integral objective function. This composition, in conjunction with control parameterization, effectively transforms the problem into a finite dimensional optimization problem where the objective function is given implicitly via the solution of a dynamic system. A standard branch-and-bound algorithm is employed to converge to the global solution by systematically eliminating portions of the feasible space by solving an upper bounding problem and convex lower bounding problem at each node. The novel contributions of this work lie in the derivation and solution of these convex lower bounding relaxations. Separate algorithms exist for deriving convex relaxations for problems with linear dynamic systems embedded and problems with nonlinear dynamic systems embedded. However, the two techniques are unified by the method for relaxing the integral in the objective function. I show that integrating a pointwise in time convex relaxation of the original integrand yields a convex underestimator for the integral. Separate composition techniques, however, are required to derive relaxations for the integrand depending upon the nature of the embedded dynamics; each case is addressed separately. For problems with embedded linear dynamic systems, the nonconvex integrand is relaxed pointwise in time / by Adam Benjamin Singer. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2005. / Includes bibliographical references (p. 123-139). / Zeolites are crystalline, porous aluminosilicates; while a pure silicate structure is charge-neutral, the substitution of A1³⁺ for Si⁴⁺ creates in the framework a negative charge, which can be compensated by a proton that acts as a strong, acid-donating Bronsted site. Zeolites are widely used in industry, most commonly for catalysis and separations. Unfortunately, they have not yet been able to replace all homogeneous catalysts in industrial processes due to the difficulties in reactant and product diffusion to and from the zeolite surface in the absence of a solvent. However, it is believed that if we had a thorough understanding of how solid acids, especially zeolites, catalyze reactions, then we would be able to design heterogeneous catalysts to overcome these difficulties. The nature of the acid sites in zeolites and the factors contributing to enhanced catalytic activity have been the subject of much study in the literature. In particular, the issue of whether all of the acid sites in a particular zeolite are homogeneous or heterogeneous in acid strength requires the development of a systematic way to quantify acidity. To address this, a detailed density functional theory (DFT) investigation of the reactivity of the acid sites in the zeolite chabazite was performed. Energies of adsorption of bases, deprotonation energies, and vibrational frequencies were calculated on a periodic chabazite (SSZ-13) model with various loadings of acid sites per unit cell, and with various structural framework defects. The four acidic oxygens at the aluminum T-site were found to all have roughly the same proton affinity, and the deprotonation energy is not correlated to the O-H bond length or vibrational stretch frequency. Furthermore, the adsorption energy of various bases at / (cont.) each acid site oxygen was found to be roughly the same and correlated only to the gas-phase proton affinity of the base; it does not vary significantly with acid site concentration or framework defects near the acid site. Given the range of local chemical structure that we investigated, these results suggest that the strength of the acid sites in chabazite is not influenced significantly by chemical or structural variations in the framework near the acid site. A comprehensive methodology was also developed and implemented for studying the mechanism for the coupling reaction of two methanol molecules to form ethanol and water in the zeolite chabazite. This test reaction models an initial carbon-carbon bond formation, which is thought to be the rate limiting step in the industrial methanol-to-gasoline and methanol-to-olefins processes. Transition path sampling and constrained molecular dynamics, within the Car-Parrinello approach, were used to study this reaction. A new mechanism was found for the carbon-carbon bond formation, which proceeds at 400⁰C via stable intermediates of water, methane, and protonated formaldehyde. The carbon-carbon bond forms directly and concurrently with a proton transfer from methane to water. This mechanism does not involve the formation of dimethyl ether or surface methoxy groups at the acid site, as previously postulated. Also, the free energy barriers for the reaction in chabazite were compared to the free energy barriers ... / by Cynthia S. Lo. / Ph.D.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1937. / Includes bibliographical references (leaves 63-66). / by Gouq-Jen Su. / Sc.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1988. / Includes bibliographical references. / Ph.D.