Regeneration of Granular Activated Carbon Using Non-conventional Technologies

Abstract

Most engineers and scientists know that activated carbon will adsorb many organic compounds from aqueous and vapor streams. They also know that the operating costs are high. This costly misconception arises out of the predominant industrial practice, once the adsorption capacity is consumed and the carbon is "spent", of using the activated carbon once and land filling or thermally regenerating the activated carbon. However, other alternatives exist for the regeneration of activated carbon and the practicing technologist has to be able to recognize the appropriate applications for each technology. Solvent extraction is a method of regenerating granular activated carbon that has become "spent" in the treatment of either air or water pollution. Non-toxic solvents dissolve adsorbed material out of the pores of the carbon. Subsequently, the residual solvent is removed from the carbon by steaming. The material desorbed is separated from the regeneration solvent by distillation. The solvent is recycled and the desorbed material is recovered in a concentrated form for recycling or disposal. The method can be used to regenerate carbon used for either wastewater treatment or air pollution abatement. According to Waste Min Incorporated, USA, seventy to ninety percent of the capacity virgin carbon is recovered using solvent regeneration. The cost and energy requirements are less than one third of the requirements of thermal regeneration or replacement. After solvent extraction, the carbon is returned to adsorption service and the solvent is recovered for reuse. The equipment is a combination of commercial equipment used for granular carbon adsorption and chemical plant used to recover the solvent for reuse. Solvent extraction can be applied wherever virgin or thermally regenerated granular activated carbon are utilized. The adsorption is done in commercial adsorption vessels for granular activated carbon. The solvent extraction is done either in the adsorption vessels or a separate desorption vessel. The solvent recovery is done in commercial distillation equipment. The specifics of the operation are proprietary. The cost of replacing or regenerating the spent granular activated carbon is high and limits the commercial applications. Solvent extraction allows cost-effective and energy-lean regeneration of the spent granular activated carbon. The desorbed organics are recovered intact and can be recovered or utilized as fuel. The activated carbon pore structure us not degraded by the solvent extraction process and can be reused indefinitely.