(592d) Effect of Recycling Potassium Hydroxide on Surface Morphology Superactivated Hydrochar Derived from Loblolly Pine

Potassium hydroxide (KOH) is an effective activating agent for the development of substantial surface area and pore volume in activated carbons where more than 200 publications are reported annually (Scopus), most of which utilize KOH for the purpose of chemical activation. Consequently, a considerable fraction of KOH is released into the aqueous environment during the washing process of the activated carbon that promotes eco-toxicity in water. While almost none of the published studies emphasizes on the environmental effect of the released effluent containing residual KOH after activation, our research tapped on the potential of recycling the KOH after subsequent activation so that volume of KOH containing water discharged could be reduced. A novel technique was adopted in our study where the pH of the mixture that constituted the carbon precursor prior to activation (loblolly pine derived hydrochar) and the activating agent solution were every time maintained at pH = 13.5. Summarizing the process, firstly the hydrochar was soaked in the KOH solution of 3.6 mol/l (20 ml) for 2 h at room temperature which was then ultrasonicated for 6 h at room temperature. Afterwards, the solution was evaporated at 80°C overnight (16 h) and the residue was activated at 800 °C for 2 h. Following the activation, the sample was washed with 20 ml of water under vacuum filtration system while the pH of the filtrate was measured repeatedly to determine the volume of KOH solution of 3.6 mol/l required to be added to the filtrate until the pH reached 14. The resulting solution was used for its successive activation cycle following the same process of KOH impregnation as described above for a total of 10 cycles. Surface morphology of the activated carbon produced after each cycle was characterized by nitrogen adsorption isotherms using High-Pressure Volumetric Analyzer. Micropore volume fraction and pore size distribution showed insignificant changes whereas the BET surface area slightly decreased approximately by 5% from 2610 m²/g up to the 10th cycle. To assess the applicability of the activated carbons developed through the recycling KOH process, hydrogen storage was analyzed in the resulting activated carbon of each cycle and substantial hydrogen uptake was found for 10 cycles. Through this study, the applicability of KOH recycling by using the novel technique of maintaining a constant pH of the activating solution is highlighted where the surface morphology insignificantly varied between the cycles and hence the applicability in hydrogen storage capacity of the material demonstrated an inconsequential effect.