Preparation of activated carbons from cherry stones by activation with potassium hydroxide
Introduction
Basically, activated carbon can be prepared by physical and chemical activation methods and, occasionally, by combination of both types of methods. Physical activation consists of reaction of a carbonised product with suitable oxidising gases (i.e. air, steam or carbon dioxide) at temperatures in the 350–550 °C range (air) and between 800 and 1100 °C (steam and carbon dioxide) [1]. Chemical activation is the process where carbonisation and activation of a precursor material occur simultaneously in the presence of dehydrating agents (i.e. H3PO4, ZnCl2, H2SO4, KOH), which influence the course of the pyrolysis, between 400 and 800 °C [2].
Chemical activation using KOH has been reported by many researchers. Several materials such as coals [3], [4], [5], coal-tar pitch [6], resin [7], cork waste [8], and esparto [9] have been used in the preparation of activated carbons by KOH activation. Also, it has been reported that activated carbons with a very large surface area and great micropore volume can be prepared by KOH activation of pre-carbonised carbonaceous materials such as pistachio-nut shells [10], [11], coffee grounds and macadamia nut shells [12], and rice straws [13]. The KOH-activation method has been regarded as a mixed process of physical and chemical processes [14], [15].
Using cherry stones, which is an industrial residue from the manufacture of Kirsch generated abundantly in the Comunidad Autónoma de Extremadura, powder activated carbon is manufactured in the present study by chemical activation with KOH. The influence of carbonisation temperature on textural characteristics and surface functional groups and structures of activated carbon is studied.
Section snippets
Material and experimental methods
Cherry stones (CS, hereafter) were used as the starting material in the preparation of activated carbon. CS, as received from the Asociación de Cooperativas del Valle del Jerte (Cáceres province, Spain), in successive steps were first air-dried, crushed, and sized, the fraction of particle sizes between 1 and 2 mm being chosen. Then, CS were contacted with dilute H2SO4 solution for 24 h (i.e. H2SO4 is a drying agent that also contributes to the removal of inorganic components from lignocellulosic
Results and discussion
Fig. 1 shows the N2 adsorption isotherms measured for the KT samples. Also, Fig. 2 depicts the variation of the cumulative pore volume (mercury porosimetry) against pore radius. From the derived textural data (see Table 1) it follows that the carbonisation temperature greatly influences the development of surface area and porosity in the samples. First, the presence of micropores is highly reduced in K400 and also, although to a somewhat lesser extent, in K500. In contrast, Vmi is 0.69 cm3 g−1 (S
Conclusions
Using cherry stones as precursor and activating chemically with potassium hydroxide, activated carbons with a large surface area and a well developed porosity in the micropore and macropore ranges have been prepared. The product having the best textural properties, including a significant mesopore content, is the one obtained at 900 °C. The products heated at high temperatures seem to be polyaromatic in character and to contain ether type structures.
Acknowledgement
Financial support from MCYT (project BQU2002-03600) is gratefully acknowledged by the authors.
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