Hydrothermal preparation and characterzation of activated carbon from anthracite powder

Abstract

Supercritical water is used for enhancing porous properties of anthracite powder and three kinds of activated carbon: commercial activated carbon, activated carbon from waste tires and activated anthracite. Distilled water and hydrogen peroxide solution are used as a liquid medium in batch process supercritical water treatment. The experimental variables are treatment time, chemical (NaOH and KOH solution) pre-treatment and concentration of hydrogen peroxide solution. The results show that treatment time and chemical pre-treatment have little effect on the porous properties of the anthracite powder. In case of using distilled water as liquid medium, a slight increase in the surface area and mesopore volume is observed, while the micropore volume decreases. Moreover, the porous properties of activated carbon decrease while the concentration of hydrogen peroxide solution increases. However, it is clear that supercritical water treatment is not effective for improving porous properties of activated carbon. In liquid-phase adsorption and supercritical water regeneration studies, phenol and organic dye Red 31, are selected as the representative adsorbates. The steam activated anthracite powder is compared with a commercial activated carbon. The results indicate that the obtained activated anthracite shows comparable phenol adsorption capacity but much lower dye adsorption capacity than the commercial one. However, supercritical water regeneration efficiency is remarkably high. The first/second regeneration efficiency of commercial activated carbon and activated anthracite exhausted with phenol are 55/98 and 65/99% and in case of RED 31 are 78/100 and 338/93% with losses of activated carbon less than 4% per regeneration. Because of little losses of activated carbon and successive regeneration, this regeneration method is suitable for regenerating exhausted activated carbon.