Comparison among Chemical, Thermal, and Electrochemical Regeneration of Phenol-Saturated Activated Carbon

The regeneration of phenol-saturated activated carbon (AC) by chemical, thermal, and electrochemical techniques has been studied and compared in this work. The influence of the solute (NaOH) concentration and the temperature on the conventional chemical and thermal regenerations, respectively, has been analyzed and compared to the optimal results achieved for the electrochemical method. Comparisons are based on the analysis of the remaining products after regeneration, the regeneration efficiency (RE), and the recovery of the textural properties of a commercial phenol-saturated granular AC. Results show that very low-porosity recoveries are achieved by chemical regeneration, independent of the NaOH concentration, and the optimal REs are 20% lower than those obtained by the thermal and electrochemical ones. REs obtained by thermal treatment in an inert atmosphere increase with the temperature up to 750 °C, reaching the highest REs (80−86%) and porosity recoveries at T > 600 °C. The cathodic regeneration in the NaOH medium in an undivided cell, where phenolate desorption is favored and surface blockage is minimized, yields similar RE values (80−85%) and slightly higher porosity than those obtained by thermal treatment. Temperature-programmed desorption (TPD) experiments show that, whereas phenol is almost completely removed electrochemically after 3 h, a temperature of at least 450−600 °C is required to achieve similar results by thermal regeneration.