A new method of assessing solid state reactivity illustrated by reference to the change in oxidation rate of alkaline and acid washed carbons

Abstract

In this study gasification in air of activated carbons and carbon blacks is investigated using a simultaneous TG-DTA unit. It is found that a final acid or alkaline treatment can substantially alter their reactivity in the gasification reaction in air. To make a proper assessment of their solid state reactivity with respect to their gasification in air a simple method is advanced which has been used recently in assessing solid state reactivity of other materials. In this method a thermogravimetric (TG) plot is obtained on a reference carbon and then similar TG plots are obtained on the other samples of carbon using identical experimental conditions and the same TG unit. The solid state reactivity is assessed from plots of the α_R (the value of α_R, the extent of the gasification of the reference carbon) against the sample carbons values of the α_S (labeled α_S to denote the value of the various carbon samples). The values of appropriate couples of α_R and α_S at temperaturesT ₁,T ₂,T ₃,...T_n allow an α_R-α_S plot to be constructed. If the solid state reactivity of the carbon samples matches exactly that of the reference carbon the result will be a linear plot, showing coincidence of α_S and α_R at all values of α_R. If the solid state reactivity of a carbon sample exceeds that of the reference carbon then the lines plotted will be on one side of the coincidence plot, while if they are less than the carbon reference they will lie on the other side. The results show that treatment of a carbon with alkaline or acid may have a significant effect on the reactivity of the carbon sample which is only partly explained by observable differences in surface area.