EDLC from activated carbon derived from black liquor

Abstract

Using black liquor as a porous carbon precursor is considered as an effective approach for value-added us e of black li quor. In additio n, black li quor contains high content of alkali metals (Na, K, etc.), which are effectively used to improve the activation process. Therefbre, preparation of activated carbons (ACs) directly from black liquor may reduce the cost not only fbr lignin-recycling, but also fbr activating agents economizing. Electric double-layer capacitors (EDLCs) are very attractive as a potential energy storage system because of their high power density, quick charge-discharge rate, free maintenance, long-life operation, and environmentally fiTiendly energy technology. EDLCs with activated carbon electrodes are known to have higher capacity fbr energy storage compared with conventional condensers. However, the application of ACs derived from black liquor fbr the preparation of EDLCs has not been reported previously. In chapter 2, high surTface area ACs were prepared by chemical activation of black liquor with potassium hydroxide (KOH), sodium hydroxide (NaOH) and potassium carbonate (K2C03). The influence of carbonization temperature, activation temperature, holding time and impregnation ratio of activating agent to char on the porous characteristics of the ACs was investigate d. The re sults show th at the surTface area and pore volume of AC s, which were estimated by BET methods, were achieved as hi gh as 3 0 89 m2 g'i and 1.76 cm3 g'i fbur times 1arger than a commercial AC from charcoal (944 m2 g'i), under the condition of an carbonization temperature of 600 OC, an activation temperature of 900 OC, a holding time of 2 h and an impregnation ratio (KOH/Char) of 2. In addition, the influence of alkali metals (K and Na) existing in black liquor on activation was also examined. It was found that the alkali metals react as an activating agent in the process of activation, thereby economizing the amount ofactivating agent used in this study to a high degree. In chapter 3, the perTfbrmance of ACs derived fiTom black liquor as EDLCs was characterized. The gravimetric capacitance is fbund to be approximately proportional to the BET surTface area, and the AC with the maximum gravimetric capacitance of41.4 F g'i and the maximum volumetric capacitance of 16.6 F cm'3 was developed under the preparing condition of an carbonization of 600 OC, an activation temperature of 600 OC, a holding time of 2 h and an impregnation ratio (KOH/Char) of 2. In addition, the results obtained in this study confirm that capacitance of ACs from black liquor not only depends on surface area, but also on pore size. This study provides an effective approach to carry out the value-added utiliz ation of black liquor.