Spectroscopic studies of chemical kinetics and complexation at high temperatures.

摘要

This thesis consists of two parts: one is the study of chemical kinetics under high temperatures and high pressures, using an IR flow cell; the other is the study of Fe(II)-chloride complexes in aqueous solutions from 10 to {dollar}rm 100spcirc C,{dollar} using UV/Vis/NIR spectrophotometric measurements.; We investigated the use of a new IR on-line high temperature/high pressure solution cell for kinetic studies of chemical reactions up to {dollar}rm 450spcirc C{dollar} and 4,000 psi. These are of importance in many industrial applications, such as coal liquefaction. The hydrolysis of carbon tetrachloride in the presence of trace moisture was investigated to evaluate the cell performance. We found that the predominant reaction mechanism changed around {dollar}rm 200spcirc C,{dollar} with activation energies of {dollar}131pm 12{dollar} kJ/mol (163 to {dollar}rm 200spcirc C){dollar} and {dollar}24pm 3{dollar} kJ/mol (200 to {dollar}rm 262spcirc C).{dollar} The hydrolysis was significantly catalyzed by the presence of iron (present as ferric chloride) below {dollar}rm 200spcirc C.{dollar} Other chemicals, such as trichloroacetic acid, were also investigated. Analyses of the instrument performance and possible improvements are also discussed.; The absorption spectra of ferrous chloride complexes were measured in both the UV and NIR regions at temperatures ranging from 10 to {dollar}rm 100spcirc C{dollar} with chloride concentrations from 0.1 to 16 mol/kg. The stability constants of an complexes were derived from the spectra using a non-negative nonlinear least squares computer program (SQUAD). Earlier work on this system reported in the literature was rigorously reassessed. The activity coefficients of the ionic species were calculated using both the Pitzer model and the Helgeson model. The results obtained with UV and NIR spectra and with different activity coefficient calculation models are in general agreement. Other useful thermodynamic data including the Gibbs energies, enthalpies and entropies for complex formations were also obtained. It was found that the ferrous chloride complexes gradually undergo a transformation from octahedral to tetrahedral coordination when temperature and/or chloride concentration increases. This coordination change is of significant importance as the presence of the tetrahedral complex can increase the solubility of iron in steam generator crevices.