An investigation of the porosity of carbons prepared by constant rate activation in air

Nutshell carbon was activated in air/N₂ mixtures using controlled rate (CR) methods and the porosity characteristics compared with carbons activated conventionally in CO₂ at 800°C to the same degree of burn off. The advantages of CR activation in air include the use of lower temperatures and the avoidance of thermal runaway. It was also possible to prepare activated carbons with significant microporosity, showing that excessive external burn off was prevented. In the CR experiments, the rate of evolution of CO₂ was controlled and constrained at a set level, either by altering the furnace temperature or the concentration of air in the activating gas. Although the highest micropore volumes (0.4 cm³ g^-1) were obtained at 40% burn off with the conventional method, at 20% burn off, the CR method using air concentration to control CO₂ evolution yielded carbons with similar micropore volumes (0.2 cm³ g^-1) to those activated conventionally.