SILICA-IMMOBILIZED SULFUR-COMPOUNDS AS SOLID CALIBRANTS FOR TEMPERATURE-PROGRAMMED REDUCTION AND PROBES FOR THE THERMAL-BEHAVIOR OF ORGANICSULFUR FORMS IN FOSSIL-FUELS

For the well-swept fixed-bed reactors used in temperature-programmed r eduction (TPR) to specify the organic sulfur forms present in coals an d kerogens, calibrants must neither melt nor evaporate before the onse t of thermal decomposition. In this respect, nonmelting silica-immobil ized substrates are suitable with the Si-O-C linkage being stable up t o ca. 500 degrees C. Silica-immobilized samples of dibenzothiophene, d iphenyl sulfide, phenyl benzyl sulfide, and thioanisole have been synt hesized and noncatalytic tests have been conducted in atmospheric and high-pressure TPR reactors. The characteristic reduction temperatures of the non-thiophenic compounds investigated are well resolved from th at of dibenzothiophene for both techniques and the results have valida ted previous findings by TPR on coals. The use of high hydrogen pressu re (150 bar) lowered the reduction temperatures substantially. The H2S recoveries from the atmospheric experiments are low suggesting that, for the non-thiophenic compounds, secondary reactions occur yielding r efractory thiophenes which are not detected. Although sulfur recoverie s are greatly improved, such reactions are still evident with 150 bar hydrogen pressure especially in the case of the phenyl benzyl sulfide, possibly as a consequence of the high surface coverages used. Insight s into the retrogressive chemistry occurring for the immobilized pheny l benzyl sulfide have been provided from GC-MS analysis of hydrolyzed TPR residues obtained at different temperatures, and from vacuum pyrol ysis experiments conducted as a function of surface coverage.