(395ba) Supercritical Carbon Dioxide Regeneration of Activated Carbon for Industrial Re-Use

Activated carbon is widely used to remove hazardous substances such as volatile organic compounds (VOCs) by its high adsorption ability. Recently, regeneration processes of the used activated carbon are strongly demanded from the viewpoints of sustainability and reducing running cost. Supercritical carbon dioxide (ScCO₂) technology is regarded as a promising regeneration method because of its high diffusivity into microstructure of activated carbon and the operation capability at mild temperature (Critical point: 304 K).  In this study, we have investigated the scCO₂ regeneration of activated carbon used at an industrial process.

We selected about 20 activated carbon samples used at an exhaust gas purification process of an electronic device factory in Japan. In experiment, scCO₂ was introduced to a regeneration column for 6h at 2.0L (SATP)/min, 20.0 MPa and 353 K.  Regeneration ratio was defined as the recovering of specific surface area with a nitrogen adsorption method.  The amounts of contaminants before and after regeneration were measured by a thermo gravimetric analysis (TGA). DTG (derivative TG) curve clearly showed bimodal shape corresponded to low (< 673 K) and high-boiling (> 673 K) components on the activated carbon.

The results showed higher regeneration ratio more than 90 % was achieved by scCO₂ cleaning in the cases of used activate carbon containing almost only low-boiling components. Furthermore, the regeneration efficiency linearly and dramatically decreased with increasing high-boiling components.  This dependence indicated a predictive possibility of the regeneration ratio of the used activated carbon by means of the amounts of high-boiling contaminant.