Environmental Engineering Reference
In-Depth Information
carbon yield and methylene blue uptake by varying the preparation
parameters of activated carbon. The results indicated that the impregna-
tion ratio had the greatest effect on the methylene blue uptake capacity
followed by the activation temperature. As the activation temperature was
increased, more carbon was gasified by CO 2 and the devolatilization was
enhanced, leading to the development of more pores or widening of the
existing pores, thereby enhancing the dye uptake capacity. Also, as the
activation time and temperature and impregnation ratio were increased,
the burn-off and devolatilization were accelerated, resulting in a decrease
in the carbon yield. Obviously, the goal is to have the highest yield and
adsorption efficiency for the activated carbon. Since the activated carbon
preparation parameters had opposite effects on these two factors, an opti-
mization was carried out in order to find a trade-off to get reasonably high
yield and sufficient adsorption capacity. The optimum condition was
found at the activation time and temperature of 1 h and 862 C, respec-
tively, and the impregnation ratio of 3.1. Applying these conditions to the
activated carbon preparation procedure, methylene blue uptake capacity
of 204 mg.g -1 and carbon yield of 16.5% were predicted. The previous
studies inspired Foo and Hameed to use the same carbonization and
impregnation as Tan et al. [99], but with activation of the char by micro-
wave irradiation with a power of 360W for 5 min [101]. The obtained BET
surface area of 707.8  m 2 .g -1 and pore volume of 0.38 m 3 .g -1 were lower than
the ones obtained for the activated carbon samples with CO 2 -activation
method (1354 m 2 .g -1 and 0.78 m 3 .g -1 , respectively). However, the methy-
lene blue adsorption capacity of the microwave-irradiated carbon was
found to be 312.5 g.g -1 , which is comparatively higher than that of the
CO 2 -activated carbon (276 mg.g -1 ). Figure 5.19 shows the effects of the
activated carbon preparation conditions on the surface area and adsorp-
tion capacity [102]. It was shown that the increase of the impregnation
ratio from 0.25 to 0.75 enhanced both the methylene blue uptake capacity
and the carbon yield, whereas further increase in the impregnation ratio
had an opposite effect. It was proposed that below impregnation ratio of
0.75, the porosities were not completely developed and thus an increase in
the impregnation ratio increased the uptake capacity. However the
increase of the impregnation ratio above 0.75 entailed the catalytic oxida-
tion of the carbon, widening of the mesopores and a decrease in both the
carbon yield and dye uptake capacity. Increase in the microwave power
resulted in continual reduction in the carbon yield due to the severe reac-
tion at higher thermal radiation. Also, as the microwave power increased,
more porous structure was developed and consequently the adsorption
capacity was drastically enhanced. The maximum adsorption capacity
Search WWH ::




Custom Search