Growing Carbon Fibers with Pyritic Coal Fines
David J. Bayless, Andrew Fields, Yongjun Zhou
Ohio University

The focus of this project is to produce vapor grown carbon fibers (VGCF) using waste coal-fines as a feedstock. Coal fines, byproducts of coal mining, contain high concentrations of pyrite, a compound of iron and sulfur. Research is underway to convert the fines into a form usable for growing carbon fibers, which requires carbon, sulfur and an iron catalyst to initiate and continue the reactions. If successful, this research offers the possibility of dramatically reducing the cost of the production process, by making it possible to use unprocessed coal as the main feedstock.

Carbon fibers have been of great practical interest to industry. They are primarily valued for their mechanical properties in aerospace and sports applications. These fibers are found to be stronger than steel, stiffer than titanium and yet lighter than aluminum. Applications for carbon fiber include rubber and cement reinforcements, composites for automobiles, electronics, and aerospace components. For example, an automobile tire made of carbon fiber might never go flat, or asphalt poured with a carbon fiber reinforcing layer might not ever create a pothole.

In the earliest stages of research, laboratory methane, benzene and acetylene were used as the hydrocarbon source for producing VGCF. This was not only extremely costly per unit of fiber produced, the production rate was limited to several grams of fiber per week. The addition of hydrogen sulfide. (H₂S) into the reaction dramatically increased the efficiency of fiber production. But H₂S is expensive, highly corrosive to rubber seals and metal fittings, flammable and as toxic as hydrogen cyanide. As a result, research and development have proven that high sulfur coals are a suitable feedstock for the carbon and sulfur, yet iron pentacarbonyl, which is highly toxic, is still required to generate the iron catalyst. Still, the cost of a unit production is much less with coal as the feedstock, compared with gaseous H₂S and methane.

Even though cost have been lowered, it is clear that a greater reduction in cost must be attained for further commercialization of VGCF. Successful completion of this project will not only make VGCF production safer by eliminating the need for iron pentacarbonyl, it should make it much less expensive by eliminating the need for any processing of the coal. Hence, coal straight from the longwall that contains large quantities of ash and pyrite, as well as carbon, could be directly used as the only VGCF feedstock.