Adsorption of acetone and cyclohexane onto CO2 activated hydrochars.

Abstract

Most of the volatile organic compounds (VOCs) are toxic and harmful to human health and environment. In this study, hydrochars activated with CO2 were applied to remove VOCs. Two typical VOCs, acetone and cyclohexane, were used as the 'model' adsorbates to evaluate hydrochars' performance. Specific surface areas of pristine hydrochars were small (<8m2/g), whereas activated hydrochars showed much higher values (up to 1308m2/g). As a result, the adsorption of VOCs onto the pristine hydrochars (13.24-24.64mg/g) was lower than that of the activated ones (39.42-121.74mg/g). The adsorption of the two VOCs onto the hydrochars was exothermal. In addition, there were significant correlations (R2>0.91) between the VOC removal and hydrochars' specific surface area. These results suggest that the governing mechanism was mainly physical adsorption. Increasing experimental temperature (80-139°C) desorbed the VOCs from the hydrochars. Due to its higher boiling point, cyclohexane desorption required a higher temperature than acetone desorption. The reusability of the activated hydrochars to the two VOCs was confirmed by five continuous adsorption-desorption cycles. The overall results indicated that hydrochars, particularly after CO2 activation, are sufficient for VOC abatement.