Influence of heat treatment in exhaust treatment process on activated carbon regeneration using supercritical carbon dioxide

The effect of heating temperature was examined on the regeneration of activated carbon using supercritical CO₂ (ScCO₂) assumed to be performed in the exhaust facilities of semiconductor production factories. Experiments were carried out with propylene glycol monomethyl ether (PGME) and propylene glycol monomethyl ether acetate (PGMEA) as model VOC components because of their practical importance. Model samples of used activated carbon were prepared by heating at 200‒300°C for 1‒63 h under an argon atmosphere after immersion in liquid PGME or PGMEA solvent. Thermogravimetric analyses (TGA) showed that high boiling point adsorbates (400‒900°C) were not observed after heating at 200°C but were clearly observed after heating at 250°C or above in the activated carbon with PGME. In the activated carbon with PGMEA, high boiling point adsorbates were not observed after heating at 250°C but were observed after heating at 300°C. These high boiling point adsorbates were not removed from activated carbon by ScCO₂ regeneration. This study suggested that high boiling point adsorbates were produced from PGME, PGMEA by heating at higher temperatures, whereas heating at 200°C suppressed their formation and supported the possibility of a high efficiency ScCO₂ process.