Purification of industrial toluene from technical to reagent grade using Diahope activated carbon in a pilot-scale fixed-bed column

Abstract

The removing organic impurities from technical-grade toluene (99.1 %) to produce reagent-grade toluene (99.9 %) has been addressed by assessing the mono- and multi-component adsorption of methylbenzothiophene (MBT), ethylcyclopentane (ECP), and xylene (XYL), which represent sulfur, non-aromatic, and aromatic impurities, respectively. Laboratory-scale static-experiments conducted between 10 and 30 °C showed that although toluene sorption on granulated activated carbon (GAC) is exothermic, the sorption capacity for each impurity increased with temperature, indicating endothermic sorption for the impurities. The sorption behavior for MBT and ECP followed the Langmuir model while for XYL followed the Freundlich model with the order of sorption affinity as MBT > ECP > XYL. In pilot-scale dynamic-experiments, the breakthrough curves (BTCs) were evaluated under various bed heights (60 and 120 cm), flow rates (1–3 L min−1), sorbate inlet concentrations (200–400 mg L−1), and optimal temperature (30 °C) obtained in static experiments. In mono-component sorption, the highest sorption capacities for MBT, ECP, and XYL were 97.1, 70.7, and 65.4 mg g−1, respectively, while the corresponding values were 46.0, 43.0, and 22.9 mg g−1 respectively, in multi-component sorption under the same operating conditions. A CFD simulation in COMSOL (v.6.2) revealed sharper BTCs with time delay compared to the experimental data while a good correlation (R2 > 0.99) was observed for BT models. The narrower mass transfer zone for MBT and ECP compared to XYL indicated more effective sorption of these sorbates, respectively. Regenerating GAC up to four cycles with hot N2 (80 °C) showed a satisfactory sorption capacity for industrial toluene impurities, indicating a reversible sorption–desorption process with a cumulative sorption usage rate of 5.5 g L−1. The pilot-scale set-up used in this study successfully purified a large volume (∼475 L) of industrial toluene.