Evaluation of Single-Step Steam Pyrolysis-Activated Carbons from Lesotho Agro-Forestry Residues

Abstract

Activated carbon has been widely used worldwide as an effective filtration or adsorption material for removing biological and chemical contaminants from drinking water. The potential of producing activated carbon (AC) from local agroforestry residues by single-step steam pyrolysis processes was investigated. The research aims to promote innovative use of local raw materials and relatively low-cost techniques in production of activated carbon. Four varieties of activated carbons from four different agroforestry residues, pine (Pinus contorta) cones (PC), Abies (Abies cilicica) seeds (AS), maple (Acer ginnala) seeds (MS) and peach (Prunus persica) stones (PS), were prepared and evaluated. The ACs were evaluated for % carbon yield and their characteristics - iodine number, phenol specific area, ash content, pH, moisture content, and solubility in water and in HCl. The % AC yields for PS, PC, AS and MS were found to be 23.0%, 18.0%, 17.8% and 14.6% respectively, which are generally comparable to the commercially recommend minimum AC yield (20%). The phenol specific areas for the ACs were 399, 388, 381 and 415m2/g, while iodine values were 73.6, 61.4, 52.2 and 100.3g/100g for PSAC, MSAC, ASAC and PCAC, respectively. Phenol and iodine values for a commercial activated carbon (CAC) were 600 m²/g, and 172.9g/100g. Although the adsorption properties for the experimental ACs were generally lower than those of the analyzed CAC, the results still revealed that the experimental ACs possesses high absorptive properties as desired in industrial applications. Other investigated properties namely pH (ranging 8.3 to 9.8), solubility in HCl (2.2 to 4.7%) and solubility in water (2.3 to 5.0%) also showed that single-step steam pyrolysis can produce ACs of close comparison to CAC. Overally, this preliminary investigation has demonstrated potential in application of any of the four materials, coupled with the single-step steam pyrolysis technique, in production of AC.

Tanz. J. Sci. Vol. 37 2011, 120-128