Lyophilization-induced structural changes in solvent swollen-supercritical carbon sioxide treated- low rank Turkish coals and characterization of their extracts

Official URL: http://dx.doi.org/10.1021/ef049706v

In the present work lyophilization was employed to recover the readily volatile solvent fraction in previously impregnated, solvent-swollen low-rank Turkish coals as well as to potentially remove inherently volatile components of the coal matrix. Experiments were performed subsequently to assess if there existed a correlation between the conformational stability of swollen coal in certain solvents and the magnitude of lyophilization-induced structural changes. Lyophilization-induced alterations in the macroscopic and macromolecular structure of the coal and the effect of lyophilization on the structure of supercritical carbon dioxide extracts of the coal are reported in the present work. Freeze-dried samples were treated with supercritical carbon dioxide in a supercritical system at 50 bar and 80 C. Then the soluble components accessible within raw samples and supercritically treated samples were digestively extracted in tetrahydrofuran, for 24 h at 20 C. Extracts obtained were analyzed using a GC-MS system. Structural changes of the coal particles upon lyophilization were observed by SEM. Lyophilization seemed to increase the BET surface area of the coal samples. Lyophilization did not change the pore size distribution of the coal samples, but it mechanically reduced the particle size of the coal particles. In both types of coal, the amount of material that had extracted into THF after supercritical carbon dioxide treatment was greater in the case of samples that had been previously lyophilized.