Development of Porosity in Bone Char during Decolourization of Sugar Syrup

Abstract

Fresh service bone char was subjected to four column decolourization cycles composed of use for 4 d and re-activation. The adsorption of N₂ by the used and regenerated chars, and the adsorption of methylene blue and iodine by the activated chars, was determined. Specific surface areas of ca. 90 m²/g were recorded up to the end of the third cycle, which then decreased thereafter with appreciable pore widening. Pore size distributions for the fresh and activated char indicated two peaks corresponding to micropores (13–15 Å) and mesopores (35–40 Å). Subsequent to the end of decolourization, the second peak diminished due to deposition of the adsorbed colouring matter inside the mesopores. After regeneration, the mesopores appear again. Use of the Freundlich and Langmuir equations allowed the adsorption data for methylene blue to be linearized properly. The monolayer capacity of the dye appears to be independent of the age of the char. Iodine numbers were generally comparable to the BET surface areas as measured by nitrogen adsorption.