Year: 2018
Type: article
Abstract: In this study we characterized the major volatile sulfur compounds produced during pyrolysis of chars under different atmospheres and temperatures.To investigate the effects of pyrolysis atmosphere on the evolution of vola- tile sulfur compounds, an acid-leached char made from high-sulfur Illinois coal was pyrolyzed at 800° C in a hydrogen and in a nitrogen atmosphere.Thiophenic organic compounds were the major products of pyrolysis of the acid-leached char in a hydrogen atmosphere.We then used online pyroprobe-pyrolysis-gas chromatography (PY-GC) to characterize the volatile products evolving at different temperatures from an untreated char, an acid-leached char, and three model chars (a demineralized char and two demineralized chars into which additional sulfur had been incorporated).Hydrogen sulfide gas evolution from the first two chars was measured at progressively increasing temperatures and was found to peak in three temperature regions.Overall, more sulfur gas evolved from the acid-leached char than from the untreated char.Forms of nonmineral sulfur in the char were classified into three types on the basis of the temperatures at which maximum hydrogen sulfide evolution occurred: Type I, elemental sulfur, at 500°C; Type II, weakly-bound sulfur, between 700 and 800°C; and Type III, strongly bound sulfur, at greater than 1000°C.Study results indicate that elemental sulfur was produced during hydrochloric acid leaching and suggest that the improved rate of sulfur removal observed when char was acid-leached before hydropyrolysis is probably partly due to the conversion of strongly bound mineral sulfur forms to elemental sulfur or weakly bound sulfur forms that can be more easily removed by hydrogen during subsequent hydropyrolysis.The chemical reaction with hydrogen, in addition to heat, was necessary to prevent the elemental sulfur produced during acid leaching and retained in the char from becoming refixed into the char matrix during pyrolysis.Information provided by this study on the retention of sulfur in char and the reactions involved in its removal may have important implications for the development of coal desulfurization processes using a low-sulfur char made from high-sulfur coal.
Authors: Mei-In Melissa Chou, Robert A. Griffin
Language: English
Subfield: Fuel Technology
Field: Energy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2590467974