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Automotive catalytic converters are increasingly used to reduce emissions from internal combustion engines to comply with emission regulations. Maldistributed flow across the catalyst affects its warm up, light off time, ageing, and conversion efficiency. This thesis concerns flow distribution in automotive catalytic converters and methods to improve CFD predictions. Previous studies showed that modelling the monolith flow resistance using the Hagen- Poiseuille’s formulation under predicted flow maldistribution. The predictions were improved by incorporating an additional pressure loss term V2 2 1  , where V is transverse velocity just upstream of a monolith channel, for oblique entry of the flow into the monolith known as the entrance effect. Further improvement was obtained by incorporating the critical angle of attack method. However, there was no experimental evidence to support these oblique entry loss formulations. There also remained the possibility that under prediction of flow maldistribution might be due to the failure to predict flow in the diffuser accurately. A one-dimensional oblique angle flow rig was designed and built to measure the effect of oblique entry flow losses in monoliths. Experiments were performed at different angles of attack (α), using different lengths of substrate and a methodology was developed to obtain the oblique flow entrance losses. The results showed that the pressure loss attributed to the entrance effect increased with the angle of attack. The entrance effect was also found to be dependent on channel Reynolds number and substrate length. The theoretical assumption of V2 2 1  predicts accurately at low Reynolds number but looses its validity at high Reynolds number. From the experimental studies, an improved correlation for the entrance effect has been derived as a function of major controlling variables, i.e., angle of attack, length of the substrates and Reynolds number. A two-dimensional rig was designed to measure the flow field using PIV in a 2-D diffuser placed upstream of two different length substrates. The results showed that the flow in a wide angle diffuser consisted of a central core, free shear layer and recirculation regions. The near-field region was found similar to that of a plane jet. The flow field was found to be independent of Reynolds number. Increasing the substrate length resulted in a flattening of the axial profiles close to the substrate face. A CFD study was undertaken to predict maldistributed flow at the exit of the substrate for an axisymmetric catalyst model by incorporating the measured entrance effect correlation. A fixed critical angle of attack (αc,F) approach was used whereby the entrance effect is assumed constant for α>αc,F. Incorporating the entrance effect with αc,F= 810 improved the prediction of maldistribution in the flow profiles. A 2-D CFD study was undertaken to predict the flow distribution in the diffuser and downstream of the substrate. A comparison of the CFD predictions in the diffuser using different turbulence models showed that all the turbulence models used in this study over predicted the width of the central core region and the V2F turbulence model gave velocity predictions that compared best with PIV. Incorporating the entrance effect improved the predictions close to the diffuser-substrate interface and downstream of the substrate.

Thesis advisor: Kian L. Tan / The acceleration of catalytic asymmetric silylation of syn-diols and triols by use of an azole additive has been developed. By simply adding 7.5-20 mol % of a commercially available small-molecule, 5-ethylthiotetrazole, to a previously reported chiral catalyst, reactions proceed within one hour delivering the desired products with similarly high yields and enantiomeric ratios; there is minimal reaction during the same period when one of the co-catalysts is absent. In an attempt to better understand this silylation mechanism, computational catalyst design and synthetic development were employed. / Thesis (MS) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Experimental and kinetic modeling studies were carried out on the conversion a wood-oil obtained from high pressure liquefaction of aspen poplar wood to liquid hydrocarbon fuels and useful chemicals in a fixed bed micro-reactor using HZSM-5 catalyst. Similar experiments were conducted using silicalite, H-mordenite, H-Y and amorphous silica-alumina catalysts. <p> Preliminary vacuum distillation studies showed that the wood-oil was made up of volatile and non-volatile fractions. A maximum yield of 62 wt% volatiles at 200 °C, 172 Pa was obtained. The volatile fraction consisted of over 80 compounds. These compounds were comprised of acids, alcohols, aldehydes, ketones, esters, ethers, furans, phenols and some hydrocarbons. The characteristics of the oil showed that it was unstable with time, i.e., its physical properties and chemical composition changed with time probably due to the reaction of free radicals or the oxidative coupling of some of the wood-oil components. However, when the oil was mixed with tetralin, the stability improved. <p> Upgrading studies were first conducted over inert berl saddles in the presence and absence of steam (i. e. non-catalytic treatment/blank runs). Yields of hydrocarbons were between 16 and 25 wt% of the wood-oil. High residue fractions of between 32 to 56 wt% were obtained after processing. Some portions of wood-oil formed a carbonaceous material (char or coke) when exposed to the experimental temperatures. The chars (coke) fraction increased with temperature from 4.7 to 12.5 wt% when processing with steam and 8.0 to 20.4 wt% when processing without steam. <p> Catalytic upgrading studies were first carried out using HZSM-5 catalyst in the presence and absence of steam. The results showed that approximately 40 to 65 wt% of the oil could be converted to a hydrocarbon-rich product (i.e. desired organic liquid product (distillate). This contained about 45 to 70 wt% hydrocarbons with selectivities ranging between 0.47 to 0.88. This fraction was highly aromatic in nature and consisted mainly of benzene, toluene, xylene (BTX compounds) and other alkylated benzenes within the gasoline boiling point range. The yield and selectivities were strong functions of the process time and temperature. A comparison between the two processes, i.e. upgrading in the presence and absence of steam, showed that about 30 to 45 % reduction in coke formation and 5 to 18 wt% increase in organic distillate could be achieved when processing in the presence of steam. These changes were probably due to changes in the rates of cracking, deoxygenation, aromatization and polymerization reactions resulting from the competitive adsorption processes between steam and wood-oil molecules in addition to changes in contact time of molecules. However, the selectivity for hyqrocarbons decreased in the presence of steam. <p> Yields of organic distillate fractions of between 72 to 93 wt% and hydrocarbon yields and selectivities of 44 to 51 wt% and 0.93 to 1.13, respectively, were obtained when wood-oil volatile fraction was upgraded over HZSM-5 after separation from the non-volatile fraction by vacuum distillation. <p> The spent HZSM-5 catalyst could be easily regenerated and reused with little change in its performance. <p> The yields and selectivities for hydrocarbons when upgrading with the other catalysts were between 9 and 22 wt%, and 0.12 and 0.29, respectively for silicalite, 16 and 28 wt%, and 0.22 and 0.28, respectively for H-mordenite, 15.5 and 21 wt%, and 0.17 and 0.21, respectively for H-Y and S.5 and 26.2, and 0.13 and 0.36, resrectively for silica-alumina. Compared to HZSM-5 (yield between 34 and 43 wt%, selectivity of 0.66 to O.SS) these yields and selectivities were much lower. These experiments also showed that the pore size, acidity and shape selectivity of the catalyst influenced the distribution of hydrocarbons in terms of the carbon number. The yield and selectivity of H-mordenite and H-Y (large pore zeolites) were mostly for kerosene range hydrocarbons (C_{<font size=2>9</font>} to C_{<font size=2>15</font>}) and for silicalite and HZSM-5 (medium pore zeolites) for gasoline range hydrocarbons. The hydrocarbon fraction from amorphous silica-alumina did not show any defined distribution. The performance followed the order: HZSM-5> H-mordenite> H-Y> Silicalite, Silica-alumina.<p> With the aid of model compound reactions involving acetic acid methyl ester, propanoic acid, 4-methylcyclohexanol, methylcyclopentanone, 2-methylcyclopentanone, methoxybenzene, ethoxybenzene, phenol, 2-methoxy-4-(2-propenyl) phenol, a synthetic and wood-oil volatile, two reaction pathways were proposed to explain the chemical steps through which the final products of upgrading were obtained. Also, reaction pathways were proposed for each chemical group. These experiments showed that the final products were formed probably through cracking, deoxygenation, olefin formation, oligomerization, hydrogen and hydride transfer, cyclization, isomerization, alkylation and polymerization reactions. <p> Rate models were derived based upon the two reaction pathways and the power law rate model. The rates of formation of products followed the general order: Organic distillate> Hydrocarbons> Residue> Coke> Gas >Aqueous Fraction. Estimates of the values of the kinetic parameters showed that the rate constants ranged between 10^{<font size=2>-6</font>} (aqueous fraction) and 1.81 (volatile fraction), activation energies between 6.7-76.0 x 10^{<font size=2> 3</font>} KJ/Kmol and reaction orders from 0.7 (gas formation) to 2.5 (residue formation). Two mathematical models were derived based on the integral reactor design equation and on the two reaction pathways. This was used to estimate the yield of products. The models predicted the experimental results fairly accurately. Model discrimination showed that the model based on coke and residue formation from both volatile and non­-volatile fractions of the wood-oil best predicted the experimental results.<p> Hydrocarbon selectivity relations which were based on coke, residue and combined coke and residue as undesired products were also derived. Application of these relations showed that lower temperatures and concentrations were most appropriate for higher hydrocarbon selectivity. However, this was at the expense of higher conversions.

Experimental and kinetic modeling studies were carried out on the conversion a wood-oil obtained from high pressure liquefaction of aspen poplar wood to liquid hydrocarbon fuels and useful chemicals in a fixed bed micro-reactor using HZSM-5 catalyst. Similar experiments were conducted using silicalite, H-mordenite, H-Y and amorphous silica-alumina catalysts. <p> Preliminary vacuum distillation studies showed that the wood-oil was made up of volatile and non-volatile fractions. A maximum yield of 62 wt% volatiles at 200 °C, 172 Pa was obtained. The volatile fraction consisted of over 80 compounds. These compounds were comprised of acids, alcohols, aldehydes, ketones, esters, ethers, furans, phenols and some hydrocarbons. The characteristics of the oil showed that it was unstable with time, i.e., its physical properties and chemical composition changed with time probably due to the reaction of free radicals or the oxidative coupling of some of the wood-oil components. However, when the oil was mixed with tetralin, the stability improved. <p> Upgrading studies were first conducted over inert berl saddles in the presence and absence of steam (i. e. non-catalytic treatment/blank runs). Yields of hydrocarbons were between 16 and 25 wt% of the wood-oil. High residue fractions of between 32 to 56 wt% were obtained after processing. Some portions of wood-oil formed a carbonaceous material (char or coke) when exposed to the experimental temperatures. The chars (coke) fraction increased with temperature from 4.7 to 12.5 wt% when processing with steam and 8.0 to 20.4 wt% when processing without steam. <p> Catalytic upgrading studies were first carried out using HZSM-5 catalyst in the presence and absence of steam. The results showed that approximately 40 to 65 wt% of the oil could be converted to a hydrocarbon-rich product (i.e. desired organic liquid product (distillate). This contained about 45 to 70 wt% hydrocarbons with selectivities ranging between 0.47 to 0.88. This fraction was highly aromatic in nature and consisted mainly of benzene, toluene, xylene (BTX compounds) and other alkylated benzenes within the gasoline boiling point range. The yield and selectivities were strong functions of the process time and temperature. A comparison between the two processes, i.e. upgrading in the presence and absence of steam, showed that about 30 to 45 % reduction in coke formation and 5 to 18 wt% increase in organic distillate could be achieved when processing in the presence of steam. These changes were probably due to changes in the rates of cracking, deoxygenation, aromatization and polymerization reactions resulting from the competitive adsorption processes between steam and wood-oil molecules in addition to changes in contact time of molecules. However, the selectivity for hyqrocarbons decreased in the presence of steam. <p> Yields of organic distillate fractions of between 72 to 93 wt% and hydrocarbon yields and selectivities of 44 to 51 wt% and 0.93 to 1.13, respectively, were obtained when wood-oil volatile fraction was upgraded over HZSM-5 after separation from the non-volatile fraction by vacuum distillation. <p> The spent HZSM-5 catalyst could be easily regenerated and reused with little change in its performance. <p> The yields and selectivities for hydrocarbons when upgrading with the other catalysts were between 9 and 22 wt%, and 0.12 and 0.29, respectively for silicalite, 16 and 28 wt%, and 0.22 and 0.28, respectively for H-mordenite, 15.5 and 21 wt%, and 0.17 and 0.21, respectively for H-Y and S.5 and 26.2, and 0.13 and 0.36, resrectively for silica-alumina. Compared to HZSM-5 (yield between 34 and 43 wt%, selectivity of 0.66 to O.SS) these yields and selectivities were much lower. These experiments also showed that the pore size, acidity and shape selectivity of the catalyst influenced the distribution of hydrocarbons in terms of the carbon number. The yield and selectivity of H-mordenite and H-Y (large pore zeolites) were mostly for kerosene range hydrocarbons (C_{<font size=2>9</font>} to C_{<font size=2>15</font>}) and for silicalite and HZSM-5 (medium pore zeolites) for gasoline range hydrocarbons. The hydrocarbon fraction from amorphous silica-alumina did not show any defined distribution. The performance followed the order: HZSM-5> H-mordenite> H-Y> Silicalite, Silica-alumina.<p> With the aid of model compound reactions involving acetic acid methyl ester, propanoic acid, 4-methylcyclohexanol, methylcyclopentanone, 2-methylcyclopentanone, methoxybenzene, ethoxybenzene, phenol, 2-methoxy-4-(2-propenyl) phenol, a synthetic and wood-oil volatile, two reaction pathways were proposed to explain the chemical steps through which the final products of upgrading were obtained. Also, reaction pathways were proposed for each chemical group. These experiments showed that the final products were formed probably through cracking, deoxygenation, olefin formation, oligomerization, hydrogen and hydride transfer, cyclization, isomerization, alkylation and polymerization reactions. <p> Rate models were derived based upon the two reaction pathways and the power law rate model. The rates of formation of products followed the general order: Organic distillate> Hydrocarbons> Residue> Coke> Gas >Aqueous Fraction. Estimates of the values of the kinetic parameters showed that the rate constants ranged between 10^{<font size=2>-6</font>} (aqueous fraction) and 1.81 (volatile fraction), activation energies between 6.7-76.0 x 10^{<font size=2> 3</font>} KJ/Kmol and reaction orders from 0.7 (gas formation) to 2.5 (residue formation). Two mathematical models were derived based on the integral reactor design equation and on the two reaction pathways. This was used to estimate the yield of products. The models predicted the experimental results fairly accurately. Model discrimination showed that the model based on coke and residue formation from both volatile and non­-volatile fractions of the wood-oil best predicted the experimental results.<p> Hydrocarbon selectivity relations which were based on coke, residue and combined coke and residue as undesired products were also derived. Application of these relations showed that lower temperatures and concentrations were most appropriate for higher hydrocarbon selectivity. However, this was at the expense of higher conversions.

The catalytic hydrogenation of an aromatic sulfonyl chloride was investigated in continuous and semi-batch mode processes using a Robinson-Mahoney stationary basket reactor. A complete experimental unit was designed and built. The operating and analytical procedures have been developed and the methodologies to gather the kinetic data have been described. Hydrogenation reactions were conducted at a reaction pressure of 364.7 psia, at three different reaction temperatures: 85 °C, 97 °C and 110 °C, at five different residence times: 0.6 (only at 110 °C), 1.0, 1.5, 2.0, 3.1 hr, with the hydrogen to the aromatic sulfonyl chloride molar ratio: 8.0 mol/mol and hydrogen to argon molar ratio: 3.0 mol/mol. Intrinsic reaction rates of the reacting species were obtained on the surface of a commercial 1 wt% palladium on charcoal catalyst. The conversion and molar yield profiles of the reacting species with respect to process time suggest a deactivation of the 1 wt % palladium on charcoal catalyst. Kinetic data collected in a continuous process mode show that the catalyst is deactivated during an experiment when the process time equal to two to three times the residence time of the liquid within the reactor. XRD analysis shows that the active sites are blocked and an amorphous layer was formed on the surface of the palladium catalyst. Semi-Batch mode experimental data were obtained at 110 °C after 8 hours of reaction time for several aromatic sulfonyl chlorides. A kinetic model has been developed, which includes adsorption of individual components and surface reactions as well as rate equations of the Hougen-Watson type. A hyperbolic deactivation function expressed in term of process time is implemented in the Hougen-Watson equation rates. The mathematical model consists of non-linear and simultaneous differential equations with multiple variables. The kinetic parameters were estimated from the minimization of a multi-response objective function by means of a sequential quadratic program, which includes a quasi-Newton algorithm. The statistical analysis was based on the t- and F-tests and the simulated results were compared to the experimental data.

Whilst there are a large number of C-C bond forming reactions available for the construction of heterocycles a number of these protocols require the use of stoichiometric organometallic reagents. Since heterocycles are present in the vast majority of pharmaceutical agents the ability to forge these structures efficiently with a minimal amount of stoichiometric metallic waste is important. With this in mind we initiated a series of projects that focus on the use of [pi]-unsaturates to serve as surrogates to toxic, air and moisture sensitive nucleophilic organometallic reagents utilized in traditional C-C bond forming reactions. This has allowed us to develop catalytic couplings of vinyl azines to imines to form branched amines, to couplings of dimethylallene to isatin forming a tert-prenyl hydroxy oxindole and this neopentyl alcohol can be substituted with C-nucleophiles forming two contiguous quaternary all-carbon centers in our synthetic studies tert-prenyl indole alkaloid natural products. / text

DExD/H-box proteins are a diverse class of proteins that are implicated in RNA and RNP remodeling. They have sequence homology to DNA helicases and share conserved ATPase domains, suggesting that they use the energy of ATP binding and hydrolysis to mediate conformational rearrangements in RNAs. In the past, the action of DExD/H-box proteins has been characterized primarily on simple model substrates such as small RNA duplexes. It is not known how DExD/H-box proteins manipulate structured RNA, what determines target specificity and what molecular events follow their action. Here, using the well-characterized Tetrahymena group I intron ribozyme, I performed kinetic and thermodynamic studies to understand the mechanism of CYT-19 and related DExD/Hbox proteins. CYT-19 has been shown previously to facilitate the folding of several group I and group II introns. I demonstrated that CYT-19 acts as a chaperone, accelerating the re-folding of a long-lived misfolded species of the Tetrahymena group I ribozyme to its native state. Further characterization of this reaction gave insights into how CYT-19 achieves this action; CYT-19 partially unfolds the misfolded ribozyme and allows it to fold again along the same pathway that exists in the absence of CYT-19. In addition to acting on the misfolded state, CYT-19 also acts on the native state, but this action is largely obscured under stabilizing conditions for the native state because the action is inefficient under such conditions. However, under conditions where the native state is destabilized, the native ribozyme was indeed shown to be partially unfolded by CYT-19. By acting on either species, CYT-19 sets up a steady state of unfolding, and the distribution is shifted from equilibrium to kinetic control, increasing the relative populations of conformations that are kinetically preferred during folding. The efficiency of action seems to correlate with the stability of the ribozyme. These activities are not restricted to CYT-19; the DExD/H-box proteins Mss116p and Ded1 were demonstrated to possess similar activities. Together, these studies give important insights into the mechanisms of action for this ubiquitous class of proteins and have implications for all structured RNAs in cells. / text

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