Steam -curing plus ramped -temperature treatment: A novel approach to thermal reactivation.

摘要

Activated carbon as a powder (PAC) and/or as granules (GAC) is employed world-wide to remove volatile, synthetic and taste- and odor-causing compounds from potable water. Furthermore, federal regulations are becoming more stringent every year and therefore employing activated carbon will become even more widespread. However, GAC does have a finite service life and it is therefore thermally reactivated to restore this spent or exhausted GAC back to its virgin capacity. When metals such as calcium accumulate on the GAC surface during its service life, they behave catalytically during the thermal reactivation process. Calcium accumulates to a far greater extent than any other metal and calcium catalysis causes an increase in both mass and volume loss and, more importantly, in the loss of micropore volume. It is these micropores that constitute about 90% of the total surface area and offer an ideal haven for adsorbing small, potentially harmful compounds.;Thermal reactivations were employed with spent GAC to overcome calcium's catalytic behavior. These spent GAC's ranged between 1.6 and 2.4% calcium content. Employing a steam-curing step at 375°C for 60 minutes followed by ramping the temperature from 375°C to 850°C in N2 proved to maintain the micropore volume. In other words, pore size distribution results showed that the carbon reactivated via steam-curing had the same micropore volume as its virgin counterpart. Moreover, the reactivated carbon had more pore volume in widths between 5.4 and 32 A. The 5.4 to 32 A range could be the most important size fraction within GAC for removing organic compounds.;Steam-curing creates a supersaturated environment where some of the steam can condense throughout the entire GAC pore volume. It is believed that this condition facilitates reactions between the steam and the relatively more reactive less organized organic matter. At 375°C, calcium is not catalytic and therefore gasification of the carbon surface will proceed at the normal, uncatalyzed rate which is about 10 to 25 times slower as compared to calcium catalysis. As the temperature increases from 375°C to 850° in N 2, there is the facilitation of un-catalyzed gasification.