Molecular sieving behavior of carbonized wood: Selective adsorption of toluene from a gas mixture containing alpha-pinene
2009
Yamashita, R., Shizuoka-ken. Industrial Research Inst. (Japan) | Saito, Y. | Sakuragawa, S.
The adsorption properties of wood carbonized at various temperatures were investigated using a mixed gas containing toluene and alpha-pinene. Hinoki (Chamaecyparis obtusa) samples carbonized at 500deg - 1100degC were exposed to gas mixtures of toluene and alpha-pinene at 20degC. The samples carbonized at 500deg - 700degC only adsorbed toluene, whereas those carbonized at 800deg - 1100degC adsorbed both toluene and alpha-pinene. Analysis of the surface structure of the carbonized wood by nitrogen adsorption at liquid nitrogen temperature indicated that the sample carbonized at 700degC had micropores mainly 0.6 nm in diameter and few mesopores, whereas the samples carbonized at 900degC and 1100degC had mesopores and micropores larger than 0.8 nm in diameter. With the sample carbonized at 700degC, the flat-shaped toluene molecules could probably penetrate into the narrower pores, 0.8 nm in diameter, whereas the bulky globular-shaped alpha-pinene molecules could not. Carbonization at temperatures higher than 900degC probably enlarged the pore size and thereby reduced the selectivity of adsorption. The results revealed that wood carbonized below activation temperature has a unique flat-pore structure that seems to work as a kind of molecular sieving carbon, successfully removing only the harmful volatile organic compound (VOC), toluene, and leaving behind a pleasant aroma of alpha-pinene in the atmosphere.
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