CHAMPAIGN, Ill. - Advanced coal-gasification processes are emerging as the most promising technology for converting coal into electricity, but the process generates sizable quantities of hydrogen sulfide, a highly corrosive gas that can destroy pipes and turbines. Chemical engineers at the University of Illinois and the Illinois State Geological Survey are developing materials to remove the hydrogen sulfide and convert it into economically valuable byproducts.
"A typical coal-fired power plant is about 33 percent efficient at generating electricity, while a coal gasifier is up to 50 percent efficient," said Mark Cal, a U. of I. professor of environmental engineering who also is a chemical engineer with the Survey. "Higher efficiency means that fuel can be conserved and greenhouse-gas emissions like carbon dioxide and acid-gas emissions like sulfur dioxide and the nitrogen oxides can be reduced. To achieve maximum performance in coal-gasification plants, an efficient and economical method of removing the hydrogen sulfide from the hot coal gas must be found."
Cal and his colleagues -- environmental engineering professor Mark Rood, Survey scientist Anthony Lizzio and graduate student Brooks Strickler -- are developing carbon-based sorbents that can remove the hydrogen sulfide efficiently.
"While the use of carbon for hot-gas cleanup has had significant potential, previous research has focused mainly on metal-based sorbents such as zinc ferrite, zinc titanate and various copper oxides," Cal said. "But each of these sorbents suffers from at least one major deficiency that prevents its widespread use."
Carbon offers several advantages over metal-based sorbents, Cal said. "Carbon provides excellent resistance to chemical and physical degradation in the harsh coal-gas environment. Carbon adsorbs large quantities of hydrogen sulfide, and can be used as an active support for metals -- such as copper and zinc -- which can enhance the adsorption process. And, carbon is inexpensive."
In their recent study, Cal and his colleagues developed a number of carbon-based sorbents and tested the ability of each sorbent to remove hydrogen-sulfide under different operating conditions. The regenerability of the most promising sorbents also was assessed.
"We've shown that these relatively inexpensive materials can very effectively remove hydrogen sulfide from the hot coal-gas stream," Cal said. "As an added bonus, the hydrogen sulfide that collects on the sorbent can be easily converted into commercially valuable products, such as solid sulfur and sulfuric acid."
Cal presented the team's findings at the September national meeting of the American Chemical Society in Las Vegas.