Halogen treatment of char for the removal of sulfur and mineral matter

Abstract

The purpose of this study was to investigate and apply high temperature halogenation techniques as a means of purifying coal chars, a by-product of mild coal gasification or pyrolysis. These upgraded char compounds have other uses such as anodes, activated carbon, graphite precursor, etc. A research reactor was constructed to conduct the tests required by the program. The reactor is capable of maintaining a temperature in excess of 2000°C and able to withstand corrosive halogen gases. Coal char purification is technically feasible by adopting a gas-thermal process or high temperature process, which is commercially applied in the synthetic graphite industry. Within the scope of the tests completed, larger particles, that is 28 mesh particles, yielded a more purified product than the 200 mesh feedstock. Particle size, the amount of chlorine, and temperature were found to be significant factors. Analysis of the byproducts and study of the data show that the mechanism of char halogenation is largely dependent on temperature and excess chlorine. The reactions between chemical impurities in the char and chlorine appear to occur spontaneously once the proper temperature is achieved. It is difficult to remove impurities because of chemical bonding between elements that occurs during pyrolysis of the parent coal.