So I have noticed many times that the AC that I get at the end of my CO2 activation has slightly larger diameter than the initial feedstock. I also read that "The products of gas activation mainly occur in granulated form" (Adsorption technology in water treatment : fundamentals, processes, and modeling)
So I am wondering why?
CO2 activation of carbon often increases porosity and hence the particle size. This, of course, is not always the case as it depends on the source carbon.
Muftah El-Naas attached is a photo of my biochar at 500 and AC at 850 °C.
You are right Prof Muftah. Sometimes the CO2 activation route enhances the porosity and particle size. However, it could be advantageous when looking at selective adsorption that requires lower pore sizes for the sorption of low molecular weight sorbates. Also, I have tried it on some biomass but could not get a higher surface area compared to what I got from steam activation route.
Depending on the raw material, the pyrolysis may result in aggregation of the or melting which lead to the change of the starting material into a mass. Thus, the thermal degradation will be done on an intermediate material that is physical different from the starting material being bigger in particle size.
Mahmood M. Barbooti Thank you
Mutiu K. Amosa How increasing pore size will increase the particle size (sauter mean diameter)? I think sintering is the best reason as mentioned by Mahmood M. Barbooti .
Carbon activation by CO2 activation has larger particles where as activated carbon is about .25 mm to .5 mm dia approximately but what is the size before and how by CO2 it becomes large