Textural Development of Activated Carbon Prepared from Recycled PET With Different Chemical Activation Agents

Abstract

In this work a series of microporous activated carbons, with different burn offs, was prepared from recycled PET provided by Selenis (Portalegre-Portugal). These AC were prepared by chemical activation with KOH, NaOH and H3PO4, and carbonised under a N2 flow of 85cm3min-1 between 873 and 1273K. The carbonised samples were then cooled and successively washed until the washable solutions achieved a pH around 7.0, afterwards these were dried at 110ºC. All adsorbents were characterised by the adsorption of N2 at 77K and the pHpcz and the elemental analyse were determined. First, with all activation agents when the carbonization temperature increased up to 723K, the carbonization yield increased. With NaOH, the carbonization yield varied from 8 to 31% and the optimal ratio of NaOH/PET was less than with KOH. The pore size was in all cases larger (between 1.15 and 2.4 nm) when compared with the AC obtained with the other activating agents. On the other hand, the AC prepared with H3PO4 present the narrowest pore size (between 0.76 and 0.83 nm) and the highest micropore volume (0.34 cm3 g-1) was obtained with a ratio of H3PO4/PET =0.75. All samples prepared with H3PO4 present an acidic point of zero charge, between 2.3 and 4.2. AC prepared by chemical activation with KOH, when the carbonisation temperature increased from 873 to 1173 K the yield decreased from 33.5 % to 23%. While at 1273K, the carbonization was too extensive, so this temperature was considered too high, as we only obtained ash. Fig.1 presents the N2 adsorption isotherms on some of the AC activated with KOH at different temperatures, with a ratio of KOH/PET=2. All isotherms are type I typical of microporous carbons. At lower temperatures, the initial steep increase in adsorption is followed by an almost horizontal plateau. However at 1173K the extent of the opening of the knee shows an obvious variation, which generally increases with the pore enlargement.