Dehydration of Ethanol by Adsorptive Distillation

Abstract: This The production of anhydrous ethanol is of significant importance in the fuel, pharmaceutical, and chemical industries. However, conventional distillation is restricted by the formation of an ethanol–water azeotrope, which limits ethanol purity to approximately 95.6%. Adsorption-based dehydration techniques have emerged as promising alternatives for overcoming this limitation due to their high selectivity, low energy requirements, and operational simplicity. In the present study, ethanol dehydration was investigated using adsorption and adsorptive distillation techniques employing molecular sieves (3A), coconut shell activated carbon, and silica gel as adsorbents. Four experimental trials were conducted using ethanol–water mixtures containing 90% ethanol and 10% water by volume. In the first two trials, liquid-phase adsorption was performed by initially distilling the feed mixture and subsequently passing the condensate through adsorption columns packed with molecular sieves (3A), coconut shell activated carbon, and silica gel arranged in series. Ethanol purities of 91.10% and 90.63% were obtained for feed compositions of 900 mL ethanol + 100 mL water and 1800 mL ethanol + 200 mL water, respectively. In the third and fourth trials, a vapor-phase adsorptive distillation approach was employed. Ethanol–water vapours generated during distillation were passed directly through adsorption columns containing 50 g molecular sieves (3A) and 50 g silica gel before condensation. Ethanol purities of 93.29% and 97.43% were achieved for feed compositions of 450 mL ethanol + 50 mL water and 90 mL ethanol + 10 mL water, respectively. Ethanol concentration was determined using an Anton Paar analyser.
The results demonstrate that vapor-phase adsorptive distillation provides superior dehydration performance compared to liquid-phase adsorption. Furthermore, the incorporation of silica gel and activated carbon reduced the dependence on costly molecular sieves, thereby improving the economic viability of the process. The highest ethanol purity obtained was 97.43%, indicating that the combined adsorption system is an effective approach for ethanol dehydration. The study highlights the potential of integrating molecular sieves with low-cost adsorbents for the development of efficient and economically sustainable ethanol purification processes.

Keywords: Ethanol dehydration, Adsorptive distillation, Molecular sieves (3A), Silica gel, Activated carbon, Adsorption, Ethanol purification, Bioethanol.