The influence of the process conditions on the characteristics of activated carbons obtained from PET de-polymerisation

Abstract

In a previous paper we have reported a procedure to obtain active carbons by carbonisation of the residues obtained from the basic hydrolysis of poly(ethyleneterephthalate) (PET). Now we are getting insight into the relationships between the process parameters and the properties of the active carbons obtained by this procedure. Hydroxide/residue mass ratio, nitrogen flow rate, carbonisation time and carbonisation temperature are the process parameters which have been considered. It is shown that the textural properties of the activated carbons can be tailored by controlling such variables. Thus it is possible to obtain active carbons with a wide range of textural characteristics ranging from a molecular sieve to a sample with heterogeneous pore size but with high adsorption volume (0.8 cm 3/g). This adds value to the procedure of obtaining active carbons from PET wastes. The textural characteristics have been determined by analysing the nitrogen and carbon dioxide adsorption isotherms. Several approaches have been applied to the isotherms, namely BET, Dubinin–Radushkevich, α s-plot and molecular simulation. Our results also show that all the approximations render similar textural characteristics when the micropore network is narrow, uniform and accessible. Nevertheless, it seems the α s-method overestimates micropore volumes in very activated carbons, as DR and molecular simulation render coincident values.