Browsing by Subject "Calorimetry"
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Item Evaluation of Alternatives for Safer and More Efficient Reactions: A study of the N-oxidation of Alkylpyridines(2012-02-14) Saenz Noval, Lina RocioThe catalytic N-oxidation of alkylpyridines, a reaction which uses hydrogen peroxide as the oxidizing agent and the water soluble phosphotungstic acid as the catalyst, is a reaction employed in the pharmaceutical industry. The safety concerns of this process revolve around the decomposition of hydrogen peroxide and the liquid-liquid phase separation of the reacting mixture. The decomposition of hydrogen peroxide is an undesired reaction parallel to the desired N-oxidation and is responsible for: 1) a high potential for runaway due to the condition sensitivity of the peroxide group, 2) a potential over-pressurization of the reaction vessel during a runaway due to the production of oxygen, and 3) the enrichment with oxygen of the flammable alkylpyridine environment. The presence of an organic phase and an aqueous phase occurs in a wide range of conditions and results in: 1) a dramatic reduction in the reaction selectivity, and consequently in the efficiency, due to the additional mass transfer constrains imposed by the phase separation, and 2) the safety of the process being seriously compromised because most of the catalyst remains in the aqueous phase, excessively promoting the decomposition of hydrogen peroxide over the N-oxidation. With these concerns in mind, this research aimed to determine conditions for an inherently safer and more efficient N-oxidation reaction and focused on three key targets: i) the possibility of reducing the extend of the decomposition of hydrogen peroxide, thus leading to an inherently safer process, ii) the study of phase equilibrium so as to enable the identification of conditions that increase the efficiency of the N-oxidation and reduces the hazards, and iii) the evaluation of safety parameters that will allow for the control of a potential runaway reaction. Two alkylpyridines were considered: 2-methylpyridine which represents the case of a homogeneous reacting mixture and 2,6-dimethylpyridine to study the two-liquid phase separation effects. The methodology employed calorimetric studies to assess the runaway behavior and to determine the conditions that favor the N-oxidation, and for the N-oxidation of 2,6-dimethylpyridine, thermodynamic studies were incorporated to evaluate the conditions for phase separation.Item Mechanisms of Organic-inorganic Interactions in Soils and Aqueous Environments Elucidated using Calorimetric Techniques(2011-08-08) Harvey, Omar R.Organic matter is ubiquitous in the environment and exists in many different forms. Reactions involving organic matter are diverse and many have significant economic and environmental implications. In this research, calorimetric techniques were used to study organic- inorganic reactions in two different systems. The primary objectives were to elucidate potential mechanism(s) by which: (i) natural organic matter (NOM) influences strength development in lime-stabilized soils, and; (ii) plant-derived biochars reacts with cations in aqueous environments. Natural organic matter influenced strength development in lime-stabilized soils through the direct inhibition of the formation of pozzolanic reaction products. The degree of inhibition was dependent mainly on the type of pozzolanic reaction product, and the amount and source of organic matter. The formation of the pozzolanic reaction product, calcium silicate hydrate II (CSH2) was less affected by NOM, than was the formation of CSH1. For a given pozzolanic product, the inhibition increased with NOM content. The effect of organic matter source followed the order fulvic acid> humic acid> lignite. Formation of CSH pozzolanic reaction products decreased by 50-100%, 20-80% and 20-40% in the presence of ?2% fulvic acid, humic acid and lignite, respectively. Cation interactions with plant-derived biochars were complex and depended both on the nature of the cation and biochar surface properties. Reactions involving the alkali cation, K+; occurred via electrostatic ion exchange, on deprotonated functional groups located on the biochar surface and; were exothermic with molar heats of reaction (?Hads) between -3 and -8 kJ mol-1. In contrast, reactions involving the transition metal cation, Cd2+ were endothermic with delta Hads between +10 and +30 kJ mol-1. Reaction mechanism(s) for Cd2+ varied from ion exchange/surface complexation in biochars formed at <350 oC, to an ion exchange/surface complexation/diffusion-controlled mechanism in biochars formed at >/=350 oC. For a given cation, differences in sorption characteristics were attributable to temperature-dependent or plant species dependent variations in the properties of the biochars.Item Metal cation complexation and separation with macrocyclic polyether ligands(Texas Tech University, 2004-12) Vogel, Howard FAt Hanford, Washington, the Department of Energy maintains a site that contains approximately 6x10^7 gallons (2 x l0^8 liters) of waste left over from the development of nuclear weapons after WWII. This volume of material is too great to be stored in Yucca Mountain. Separation of the high-level radionuclides from the bulk of the material will allow the remainder to be treated and disposed of as low-level waste. Once separated, the high-level nuclides are then available for use in commercial applications, such as medical imaging and remote power plants. This study explores the use of crown and lariat ethers for the separation of metal ions. A large number of compounds varying in specific structural aspects are studied using isothermal titration calorimetry (ITC), which directly determines the association constant, stoichiometry, and enthalpy of each metal-ligand system. Augmenting the ITC study is the intense study of a small selection of compounds. These compounds are studied under various conditions using a variety of techniques, such as ion-selective electrodes (ISE) and solvent extraction (SE), allowing for a fuller understanding of their association behavior. The presence of metal ion is our world is ubiquitous. Some of these metals are benign, or even necessary for life. Others are harmful in minute quantities. The ability to selectively remove specific metal ions from waste streams, the environment, and our bodies will be an important process in years to come.Item Spectroscopic and calorimetric studies of aggregated macromolecules(2007) Kitts, Catherine Carter, 1979-; Vanden Bout, David A.Different optical and calorimetric techniques were utilized to gain a better understanding of aggregated macromolecules. This research looked at two different macromolecules: poly(9,9'-dioctylfluorene), a conjugated polymer that forms aggregates in organic solvents; and bovine insulin, which forms amyloid fibrils. Conjugated polymers are of increasing interest due to their thermal stability and ease of solution processing for use in devices. A member of the polyfluorene family, poly(9,9'-dioctylfluorene) (PFO), has been studied due to its blue-emitting spectral properties. However, PFO has been found to form aggregates in solution, which is detected by the presence of a red-shifted absorption peak. This peak is caused when a section of the backbone planarizes forming the [beta]-phase. The [beta]-phase can be removed from the solution upon heating and will not return until the solution is cooled, making it a non-equilibrium process. The dissolution and reformation of the -phase were monitored using absorption spectroscopy and differential scanning calorimetry. Atomic force microscopy (AFM) and near-field scanning optical microscopy (NSOM) were able to probe the aggregates in films. It is important to understand polymer properties in solution in order to understand film morphology. Amyloid fibrils contribute to over 20 different neurodegenerative diseases, in which cures have yet to be found. The fibrils form when a soluble protein misfolds and self-assembles to form insoluble protein aggregates, and the cause of the fibril formation in vivo has still yet to be determined. Spectroscopy studies have been made possible with the use of fluorescent dyes: thioflavin T (ThT), BTA-2, and Congo red (CR). These dyes bind to amyloid fibrils and exhibit changes in their spectral properties. However, the exact mechanism for the binding of these dyes has only recently been studied. Through the use of calorimetry, the forces involved with binding of ThT and CR to amyloid fibrils can be determined. Absorption and fluorescence spectroscopy techniques were employed to study the spectral properties of these dyes. Polarized NSOM was used to determine the ThT or BTA-2's orientation with an individual fibril. Understanding how these dyes bind to fibrils will enable researchers to use spectroscopy to study the early stages of fibril formation.Item The low temperature specific heat and elastic constants of CsI(Texas Tech University, 1970-05) Kunkel, Jeffrey RNot available