After performing the experiment i have seen that in some cases iodine no increases with increase in activation time for a constant temperature as well as impregnation ratio but in some combinations the iodine no decreased with increase in time.So what is the reason behind this? Kindly explain
Dear Shilpi,
Iodine Number Definition:
Is defined as the mg of iodine adsorbed by 1 gram of carbon when the concentration of iodine in the residual filtrate is 0.02 normal.The iodine number is a measure of the iodine adsorbed in the pores and, as such, is an indication of the pore volume available in the activated carbon of interest. Generally and commonly, the iodine number is used to determine the degree of exhaustion of a carbon in use. However, this should be viewed with caution as chemical interactions with the adsorbate may affect the iodine uptake giving false results. Thus, the use of iodine number as a measure of the degree of exhaustion of a carbon bed can only be recommended if it has been shown to be free of chemical interactions with adsorbates and if an experimental correlation between iodine number and the degree of exhaustion has been determined for the particular application.
Based on this text, it is reasonable to assume that in some of your experiments there are chemical interactions with the adsorbate that give inconsistent results of the iodine number recorded.
For the iodine number definition, please use the following link:
https://en.wikipedia.org/wiki/Activated_carbon
Hoping this will be helpful,
Rafik
Dear Shilpi,
1. In general, iodine number is used to indicate microporosity, methylene blue number for mesoprosity and molasses number for macroporosity of one adsorbent.
2. Prolong activation time in activated carbon manufacturing may cause pores to rupture, leading to (1) failing intrinsic pore networks that able to block the incoming adsorbate to penetrate deeper into adsorbent matrix and (2) enlargement of the pores - transform the early developed micropores into meso/macropores.
You may correlate the value of the iodine number exhibited by the adsorbent samples prepared at different activation time with the micropore surface area data of the respected adsorbent samples to further confirm your experimental findings.
Further reading: https://www.crcpress.com/Activated-Carbon-Adsorption/Bansal-Goyal/p/book/9780824753443
Thank you.
Azam T
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