Preparation And Study On Active Carbon Based On Coal-tar Pitch

The research is about the active carbon prepared by chemical activation, the medium temperature coal-tar pitch was oxidized in atmospheric before chemical activation, then the specific surface area of the active carbons beyond 1800m2/g. The result shows coal-tar pitch can be used to prepare high specific surface area active carbon too. It not only resolves the problem of material source, but also finds an economical and reasonable route for massive coke by-products. Coal-tar pitch has special chemical property, such as low softening point, high volatile matter, unsteadiness behavior etc, so the active carbon prepared form coal-tar pitch directly has low specific surface area. In order to getting high specific surface area active carbon, the research select stabilizing pretreatment of coal-tar pitch by atmospheric oxidation thermal polymerization process based on many documents. The specific surface area of active carbon prepared from precursor is higher than active carbon prepared from coal-tar pitch. It can be found that the optimal pretreatment process is that heats the coal-tar pitch at rate of 2℃/min to 420℃, then constant temperature for 2 hours. Under this condition, the precursor has the best property by testing of volatile matter content, methylbenzene non-dissolve matter (TI) content, elemental analysis, FTIR, XRD, polarizing microscope and SEM, and the active carbon prepared from this precursor has the best property. There are many factors affect the specific surface area, pore structure and adsorptive capacity of active carbon in the process, so the influence of precursor's particle size, alkali/carbon and wetting agent (absolute alcohol) addictive level on active carbon was considered in this paper. At the same time, carbonization temperature, carbonization time, activation temperature and activation time in the process were taken into account by orthogonal design method. The result shows that precursor's particle size affect property of active carbon directly, but there is not obvious rule; specific surface area and iodonium adsorbance of active carbon increase with alkali/carbon increasing, but high alkali/carbon leads to mesopore proportion increasing; the absolute alcohol make the specific surface area and iodonium adsorbance of active carbon decreased, but it is available to the growing of micropore. It also can be found that the process of conditions have influence on specific surface area as following during the process, carbonization time>activation time> carbonization temperature >activation temperature. So the optimum conditions are the carbonization temperature 450℃, carbonization time 30min, activation temperature 800℃and activation time 100min respectively. While the influences on iodonium adsorbance are activation time>carbonization time>activation temperature> carbonization temperature, and the optimum conditions are carbonization temperature 350℃, carbonization time 30min, activation temperature 800℃and activation time 80min. According to KOH activation mechanism, developed pore structure and high specific surface area are mostly produced from activation phase, so proper activation temperature and activation time are important conditions for sufficient reaction. Short activation time is not enough for sufficient reaction, for it can not produce developed pore structure and high specific surface area. While long activation time and high activation temperature can lead to deep activation reaction and excess micropore agglutination, then lead to specific surface area decreased. However, the influence of carbonization phase on specific surface area is greater than activation phase. There are three reasons: firstly, precursor has high graphitizing degree after carbonization phase, which is a disadvantage to high specific surface area active carbon; secondly, KOH dehydration in carbonization phase offer activation (K2O and CO2 composed to K2CO3 and K2O reduce to K) integrant K2O, which is important premise step; thirdly, carbonization phase not only produce carbonization, but also company with activation, even to rather degree, which effect the following phase, that is activation.