Porous structure of activated carbon prepared from cherry stones by chemical activation with phosphoric acid

Cherry stones (CS), a lignocellulosic material abundantly generated by the agrarian industry in the Valle del Jerte (Caceres province, Spain), were used as a precursor in the preparation of granular activated carbon by chemical activation with H3PO4. After previous contact with a dilute H2SO4 solution, CS were first soaked in a H3PO4 solution (i.e., at H3PO4-to-CS ratios ranging between 0.64 and 5.78) at 85 degrees C, and the resultant heterogeneous mixture was oven-dried at 120 degrees C for 24-48 It. Then, acid-impregnated CS were heated from ambient temperature to the carbonization temperature (T-C) either with a single ramp (T-C, in the 350-550 and 600-900 degrees C ranges) or with two ramps: first to 150, 200, or 250 degrees C and then to a higher temperature (T-C, 400 or 500 degrees C. The heating rate was 10 degrees C min(-1). The isothermal time after a heating ramp was 2 h. The heat treatments were carried out in a N-2 atmosphere. The textural characterization of the samples was accomplished by gas adsorption (N-2, -196 degrees C and mercury porosimetry. The uptake of H3PO4 by CS is enhanced when high impregnation ratios are used. The yield of the process of preparation of activated carbon ranges between 30 and 50 wt %. An increase in concentration of the impregnation solution has a stronger beneficial effect on the macroporosity and mesoporosity than on the microporosity. The rise in the carbonization temperature between 350 and 500 degrees C mainly produces mesoporosity development. For the product carbonized at 500 degrees C, the specific surface area (Brunauer-Emmett-Teller) is 1688 m(2) g(-1), the micropore volume is 0.55 cm(3) g(-1), the mesopore volume is 0.78 cm(3) g(-1), and the macropore volume is 0.49 cm(3) g(-1). Carbonization between 700 and 900 degrees C and in two successive steps results in the development of narrow and wide micropores, respectively. The effect on the microporosity is stronger with the rise in temperature in the 700-900 and 150-250 degrees C ranges.