Applicability of Composite Silica–Divinylbenzene in Bioethanol Dehydration: Equilibrium, Kinetic, Thermodynamic, and Regeneration Analysis

Abstract

A composite silica–divinylbenzene (SiO2/DVB) adsorbent was prepared for the adsorption of ethanol from the ethanol–water mixture. Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and a Brunauer, Emmett and Teller surface area analyzer were utilized for the characterization analysis of the adsorbents. Batch experiments were executed at different initial ethanol concentrations (10–95 vol %), contact times (1–24 h), and temperatures (10–40 °C). The equilibrium studies indicated a favorable adsorption of ethanol on SiO2/DVB because of a separation factor Rl of 0.18 from the Langmuir model. Moreover, Freundlich parameter constant n was found to be 2.37. This implies that the adsorption is governed by a physical process. Results in the experimental data best-fitted the pseudo-second-order kinetic model (R2 ≥ 0.98 and RMSE ≤ 1.26), which suggests chemisorption as the rate-limiting step of the adsorption system. Based on the Weber–Morris kinetic analysis, intraparticle diffusion occurred after the outer surface of the SiO2/DVB became saturated by ethanol molecules. Approximately 99.2 ± 0.4% (20 °C) and 99.8 ± 0.2% (30 °C) of the ethanol were adsorbed onto the SiO2/DVB adsorbent. Furthermore, thermodynamic parameters indicated a nonspontaneous and exothermic reaction in the adsorption process. It was revealed that the reusability profile of SiO2/DVB showed a 5.3% reduction in terms of the adsorption capacity after the first cycle and 8.3% reduction after four cycles.