STRUCTURAL ELUCIDATION, MOLECULAR REPRESENTATION AND SOLVENT INTERACTIONS OF VITRINITE-RICH AND INERTINITE-RICH SOUTH AFRICAN COALS
Open Access
- Author:
- Van Niekerk, Daniel
- Graduate Program:
- Energy and Geo-Environmental Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 19, 2008
- Committee Members:
- Jonathan P Mathews, Committee Chair/Co-Chair
Harold Harris Schobert, Committee Member
Caroline Elaine Clifford, Committee Member
Paul C Painter, Committee Member - Keywords:
- coal-to-liquids
solvent extraction
coal
macerals
reflectance
petrography
molecular modeling - Abstract:
- Two Permian-aged South African coals, vitrinite-rich Waterberg and inertinite-rich Highveld coals (similar rank, carbon content and Permian age), were studied to determine the structural differences and similarities of these two coals and how it impacts solvent swelling and extraction. The main differences were that the inertinite-rich Highveld coal was more ordered, more aromatic, and had less hydrogen than the vitrinite-rich Waterberg coal. Analytical data were used to construct advanced molecular representations for vitrinite-rich Waterberg and inertinite-rich Highveld coals. The three-dimensional models were structurally diverse consisting of a molecular weight distribution. The vitrinite-rich coal model consisted of 18,572 atoms and 191 individual molecules and the inertinite-rich coal model consisted of 14,242 atoms and 158 individual molecules. Solvent swelling of coal were conducted using the traditional pack-bed swelling method and a new novel single-particle stop-motion videography swelling method with NMP and CS2/NMP solvents. The single-particle swelling data was used to calculate the kinetic parameters and it was found that the swelling was governed by relaxation of the coal structure (super-Case II swelling). X-ray computed tomography was conducted confirming anisotropic swelling. The petrographic transitions (maceral-group composition and reflectance) with solvent swelling and extraction were also quantified. Random reflectance analysis showed that, for both vitrinite and inertinite, there is a decrease in reflectance values with solvent treatment. Vitrinite reflectograms showed a shift from the dominant reflecting V-types to lower V-types. The inertinite reflectograms exhibited an increase in number of I-types. Molecular simulation and visualization were conducted to study solvent swelling and extraction on proposed molecular models. A theoretical extraction yield was determined using solubility parameters and showed agreement with experimental extraction yield trends. Statistical Associating Fluid Theory (SAFT) modeling was explored to test whether this method could predict swelling extent. The predicted swelling trends of SAFT were comparable to that of the experimental swelling results. Partially solvent swollen structures were constructed by the addition of solvent molecules to the original coal molecules using a amorphous building approach. This method showed that coal-coal non-bonding interaction changes with the introduction of solvent. Changes in hydrogen bond distributions were quantified in the swollen coal models.