Full Paper Chemical Production of Activated Carbon from Nutshells and Date Stones The effect of chemical reagent (H 3 PO 4 , KOH, and NaOH), temperature (400°C, 475 °C, 550 °C), and impregnation ratio (100 %, 150 %, 200 %) was investigated on the specific surface area and iodine uptake of the carbons produced from al- mond, walnut, and pistachio-nut shells and date stones. The effect of mesh size and holding time was also studied in the case of almond shell. While the alkali ac- tivation of the precursors resulted in such fine powders that purifying them of contaminants was almost impossible, the acid activation of the raw materials produced carbons with high iodine numbers (about 1000 mg I 2 /g carbon). To further characterize their porosity, the almond-based carbons underwent BET measurements, with the results showing comparatively high surface areas (about 1400 m 2 /g). The carbons were rather mesoporous, and thus more suitable for liquid applications, which was confirmed by using the carbons in chromium (VI) uptake in another study [1]. Keywords: Biomass, Characterization Received: October 8, 2005; accepted: April 30, 2006 DOI: 10.1002/ceat.200500325 1 Introduction Due to its special characteristics as an adsorbent, catalyst, or catalyst support, activated carbon has found various applica- tions in the industries dealing with separation or catalytic pro- cesses. Water treatment, decolorizing, and gold recovery are the most important liquid phase applications, while the recov- ery of solvents (such as acetone, pentane, toluene, methylene chloride, methyl ethyl ketone, tetrahydrofuran, bezene, xylene, and toluene), the manufacture of protective filters (like gas masks), general air conditioning, and gas purification (the purification of methane, which can be released in substantial amounts from landfill gas (55 vol.-%) during the anaerobic decay of buried organic municipal waste, and mercury vapor adsorption) may be named as the important gas-phase appli- cations of activated carbon [2]. Activated carbon can also be used as a catalyst in such processes as the synthesis of vinyl chloride, sulfuryl chloride, and terephthalic acid, or as a cata- lyst support in, for example, hydrodesulfurization [2]. Apart from such interesting properties as possessing a very high sur- face area, different pore size distributions, and different func- tional groups which can be modified by changing activation conditions, the availability and abundance, and consequently low price of the raw materials, have lead to the emergence of activated carbon as an economical product in the industries. There are, in general, two methods for producing activated carbons: physical and chemical. The physical method is carried out through the two stages of carbonization and activation. In carbonization, the precursor is heated up to about 500–700 °C under an inert atmosphere such as N 2 or argon, and kept at this temperature for some time. Oxygen and hydrogen are re- leased in the form of CO 2 , CO, H 2 O, aliphatic acids, alcohols, etc. [2] and the material turns into a carbonaceous network of pores, though the pore development is not yet sufficient. In the second stage, the produced char undergoes another heat treatment at about 1000 °C under a moderate oxidizing gas such as CO 2 , CO, H 2 O, or a mixture of them. This helps devel- op the pore network by promoting some reactions between the activating gas and the carbon atoms of the char. In the chemi- cal method, however, the whole production process is per- formed in just one stage that consists of heating the precursor, already impregnated with a chemical reagent like phosphoric acid, at relatively low temperatures of 400–800 °C. The activa- tion temperature is strongly dependent upon the chemical reagent used for impregnation. High surface area, relatively high yield, comparatively low activation temperature, and the variety of functional groups are among the factors rendering the chemical activation ad- vantageous over the physical activation, while the latter, by using no chemicals, profits from fewer environmental prob- © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim http://www.cet-journal.com Cyrus Arjmand 1 Tahereh Kaghazchi 1 Seyed Mahdi Latifi 1 Mansooreh Soleimani 1 1 Chemical Engineering Department, Amirkabir University of Technology, Tehran, Iran. – Correspondence: Prof. T. Kaghazchi (kaghazch@aut.ac.ir), Chemical Engineering Department, Amirkabir University of Technology, Tehran, Iran. 986 Chem. Eng. Technol. 2006, 29, No. 8, 986–991