An exciting opportunity for Zeolite-A/Bentonite adsorbent design as molecular sieve in fuel grade ethanol production through adsorptive distillation

Dehydration of ethanol using the distillation method is still not optimal, because it will stop at the azeotropic point of 96%. Modification of the distillation method using three processing stages such as distillation, followed by fractionation columns and adsorption using molecular sieve is a new choice in ethanol-water separation above the azeotropic point. Previous studies reported that the use of zeolite powder as molecular sieve requires a complex preparation of equipment and it contaminates ethanol solutions in distillation flasks. In this study, the use of zeolite-A/bentonite (ZAB) adsorbent as molecular sieve to produce fuel grade ethanol through adsorptive distillation has been investigated. ZAB composites were prepared in the form of solid pellets using mixing method. The hydrophilicity properties of ZAB composite was adjusted at pH 10 to obtain zeolite with high hydrophilicity, the alkaline conditions were chosen to prevent a dealumination. ZAB composites were made using a ratio of zeolite-A and bentonite being 6:4 with a thickness of 0.5 mm. Both ZA and ZAB were characterised using X-ray diffraction, Fourier transform infra-red spectroscopy (FTIR), and scanning electron microscopy. The purity of ethanol was analysed using gas chromatography-flame ionization detector. X-ray diffraction patterns of ZA showed sharp peaks of 2θ at 21.63; 24; 27.14; 29.96 and 34.2°, indicating its high crystallinity. FTIR analysis confirmed that ZAB composites were formed. The surface morphology of ZA is in the form of cubic crystals, whereas in ZAB morphology, bentonite coats the cubic surface of ZA. The combination of ZA and bentonite did not significantly change the adsorption properties of ZA and ZAB. By varying the mass of molecular sieve from 10, 20 and 30 g, the optimal condition of adsorptive distillation for ethanol dehydration was obtained at 20 g of ZAB composite with ethanol purity of 98.6%. As for comparison, distillation, distillation fractionation, and adsorption have produced the ethanol purity of 96.2%, 97.3%, and 95.5%, respectively. After the ZAB20 composite is regenerated by heating (120°C), the ethanol purity decreased to 98.3%. Overall, the ZAB20 composite has a potential as molecular sieve to produce fuel grade ethanol in ethanol-water separation through adsorptive distillation.