Adsorption of n-hexane on a low-cost adsorbent obtained from waste tyres and its microwave regeneration

This work investigates adsorption of n-hexane on activated tyre pyrolysis char (ATPC) and granular activated carbon (GAC) as a reference material in a fixed-bed column. Microwave-assisted regeneration is also considered. The adsorbed amount of n-hexane on ATPC is in the range of 37–58 mg/g. Microwave-assisted desorption of ATPC samples enables the recovery of up to 95% of adsorbed n-hexane in this non-optimized microwave setup with the efficiency of microwave energy conversion into heat of only 5–6%. For the 50% breakthrough time, ATPC and GAC are able to purify the n-hexane gas volumes in the ranges of 20–90 and 935–1240 cm3/g, respectively. While adsorption kinetics is not satisfactorily described by pseudo-first and pseudo-second order kinetic models, it is very well reflected by a family of dynamic adsorption models, which are modelled with a single logistic function. Internal diffusion is likely the rate limiting step during adsorption on ATPC, while external and internal diffusion likely plays a role in adsorption to GAC. Although microwave-assisted regeneration is performed in a general purpose microwave reactor, both adsorbents show excellent performance and are very good candidates for the adsorption process. Preliminary results show that magnetite can further reduce microwave energy consumption.