Analytical Pyrolysis - Studies of Sulfur in Coal and Pulp

Sammanfattning: Sulfur in coal and pulp have been characterized using pyrolysis–gas chromatography with a sulfur-selective flame photometric detector (Py–GC/FPD). The samples (50–150 µg) were pyrolyzed at temperatures between 300 and 1400°C usually followed by a combustion in oxygen at high temperature (>1000°C). The main sulfur-containing products were low-molecular compounds such as H2S, COS, SO2, CH3SH and CS2. Multivariate data analysis (principal component analysis, PCA and partial least squares regression, PLS) was used to obtain both qualitative and quantitative information. Fifteen coal samples with very different characteristics were analyzed. The influence of different experimental parameters, such as sample handling, inertness of the system and pyrolysis temperature, on the distribution of the pyrolysis products were studied. Bivariate and multivariate correlations between the pyrolysis products and the sulfur content of coal were found. The thermal degradation of model compounds (polythiophenes) were investigated. The different chemical environments of the thiophenic ring influenced the rate of formation of H2S and the yield of sulfur. Changes in the chemical character of sulfur in wood residues pretreated with different sulfide-containing liquors were studied by fractionated pyrolysis. These changes were followed throughout the cook. Sulfur-containing pyrolysis products were formed at different temperatures and may originate from sulfur forms with different thermal stability. When the alkalinity of the treatment liquor was decreased the amount of sulfur formed at 400 and 600°C was increased. The lignin pyrolysis products correlate well with the amount of absorbed sulfur in the pretreated samples which suggest that the main part of the sulfur becomes covalently linked to the lignin macromolecule.