Tyre-derived activated carbon – textural propertiesand modelling of adsorption equilibrium ofn-hexane

Abstract

There is general agreement that primary pyrolysis products of end-of-life tyres should be valorised to improve the economics of pyrolysis. In this work, tyre pyrolysis char (TPC) is produced in a pyrolysis pilot plant designed and built at our home university. The produced TPC was upgraded to tyre-derived activated carbon (TDAC) by activation with CO 2 , and then characterised using stereological analysis (SA) and nitrogen adsorption at 77 K. SA showed that the grains of TPC and TDAC were quasi-spherical and slightly elongated with a 25% increase in the mean particle cross-section surface area for TDAC. The textural properties of TDAC demonstrated the BET and micropore surface areas of 259 and 70 m 2 /g, respectively. Micropore volume and micropore surface area were 5.8 and 6.7 times higher for TDAC than TPC at (cid:24) 2 nm, respectively. The n -hexane adsorption was investigated using experiments and modelling. Eight adsorption isotherms along with three error functions were tested to model the adsorption equilibrium. The optimum sets of isotherm parameters were chosen by comparing sum of the normalized errors. The analysis indicated that the Freundlich isotherm gave the best agreement with the equilibrium experiments. In relation to different activated carbons, the adsorption capacity of TDAC for n -hexane is about 16.2 times higher than that of the worst reference material and 4.3 times lower than that of the best reference material. In addition, stereological analysis showed that activation with CO 2 did not change the grain’s shape factors. However, a 25% increase in the mean particle cross-section surface area for TDAC was observed. The results show that the most common particle equivalent diameter, d 2 , is in a range between 10 and 15 (cid:22) m for both compared materials. In addition, a thorough analysis shows a very small difference between the frequencies of the most common particle equivalent diameter in this range (29.6% for TPC against 28.1% for TDAC). No significant difference has been found between the TPC and TDAC samples in terms of shape factors. The shape factors calculated from the d max = d 2 and p = d 2 ratios indicate that the grains of both samples are quasi-spherical and slightly elongated (Wejrzanowski Kurzydlowski, 2003; Wejrzanowski et al., 2008). However, it is worth noting that there is a 25% increase in the mean particle cross-section surface area for the activated sample (TDAC).