Hydrogen Sulfide Evolution from Colorado Oil Shale

Abstract

The dependence of H/sub 2/S evolution on gas atmosphere was measured in this study. The gas environments used were argon, autogenous (self-generated), and steam-argon mixtures, all at atmospheric pressure. The samples used in these experiments were Green River oil shale from Colorado. In Green River oil shale, sulfur occurs in both inorganic and organic combinations; 70 to 85% of the sulfur is present as pyrite, and most of the remaining sulfur is present as organic sulfur. During pyrolysis, H/sub 2/S could be formed from the reaction of pyrite with hydrocarbons, hydrogen, or water, and from cracking or organosulfur compounds. The objective was to determine the importance of these various reactions and to report the amounts of H/sub 2/S evolved from oil-shale samples obtained from locations in Colorado. Most of the sulfur in oil shale occurs in pyrite and a smaller amount is contained in the kerogen. The major sources of H/sub 2/S during oil shale pyrolysis appears to be the reaction of pyrite with organic matter. In an autogenous atmosphere, most of the H/sub 2/S evolves between 400 and 500/sup 0/C. Addition of finely ground pyrite increases the amount of H/sub 2/S evolved but does not change the evolution profile.more » In an argon atmosphere, however, added pyrite causes a substantial increase in H/sub 2/S evolution only between 475 and 525/sup 0/C. Similar reaction characteristics were observed with large-grained natural pyrite in Tract C-a shale. The argon results demonstrate the importance of intimate contact between the pyrite and organic material. In a steam atmosphere, pyrite is oxidized to iron oxides and the H/sub 2/S evolution increases substantially. In some samples, essentially all the initial sulfur is evolved as H/sub 2/S at temperatures below 800/sup 0/C. However, thermodynamics may limit the amount of H/sub 2/S produced from pyrrhotite under retort conditions.« less