The effect of temperature and impregnation ratio on the active carbon porosity

Three active carbons were prepared starting from Algerian date pits by chemical activation with the H3PO4, ZnCl2 and by the method combined in the presence of ZnCl2/CO2. A systematic study of certain parameters (temperature of activation and impregnation ratio) was undertaken. The active carbons obtained were followed by the evaluation of the yield and the physisorption of nitrogen at 77 K. It was shown that the preparation of activated carbon by H3PO4, and ZnCl2 requires relatively moderate temperatures (500-600 degrees C) while the combined method is rather favored at higher temperatures (800 degrees C). The variation of the impregnation ratio revealed that the active carbons obtained have different porosities. Indeed, the prepared carbon by chemical activation with the phosphoric acid is made of mesoporous structure whereas the carbon prepared by ZnCl2, shows a very high ratio of microporosity (90%). This difference in porosity is directly related to the proper activation mechanism of each chemical additive. The study of the evolution on a specific surface of the prepared carbons with various impregnation reports/ratios shows that an increase in the impregnation ratio, improves the specific surface when H3PO4 is used, contrary to the other agents where the surface reaches a certain value then decreases again. In general, a high rate of impregnation led in all cases to a more marked opening of porosity and particularly in presence of H3PO4. This results in the development of a less specific surface, compared with the prepared carbons by ZnCl2 and ZnCl2/CO2. The elaborate active carbons have very interesting textural characteristics and can have various applications.