Microporous carbon prepared by microwave pyrolysis of scrap tyres and the effect of K+ in its structure on xylene adsorption

Abstract

This work brings novel information about microwave-assisted pyrolysis of scrap tyres, the industrial realization of which is still an engineering challenge due to both missing fundamental processing issues as well as how to enhance the engineering quality of pyrolytic products, mainly of solid carbon black. One-step microwave pyrolysis of scrap tyres for 50 min at power of 440 W with KOH activation in the mass ratio of 1:3 (scrap tyres:KOH) is successfully applied for the first time to yield micropores-containing carbon black which application potential was verified for xylene adsorption from waste gas. Compared to conventional high-temperature pyrolysis, the microwave pyrolysis requires shorter time and thus significantly reduces input energy. Two-step microwave pyrolysis of scrap tyres at 440 W does not result in more organized graphene-based carbon, but turbostratic carbon is more perturbed. The higher microwave power of 950 W within one-step microwave pyrolysis does not enhance the graphitization of carbon black, but shorten the microwave pyrolysis time to 20 min. The two main physicochemical properties of the novel micro-macroporous carbon black determining its adsorption performance for xylene are the microporosity/large volume of micropores and K+ present in the carbon structure. Micropores <0.52 nm with/without K+ and cavities <0.82 nm with K+ within carbon structure are proved by molecular modeling to be the sites with the highest affinity for xylene adsorption. Higher adsorption capacity of activated carbon blacks compared to non-activated ones correlates with molecular modeling results. More perturbed carbon structure does not affect the xylene adsorption.