(154e) Bio-Ethanol Purification: A Comparison of the Performance of Fluoride-Mediated Silicalite-1 and Zeolitic Imidazolate Frameworks

Renewable energy has received increasing global interest due to rising oil prices. Among various alternatives, biofuels are generally environmentally benign and have the potential to reduce dependence on fossil energy sources. Since the biofuel products, either from corn-based or innovative algae-based technologies, are typically dilute alcohol-in-water solutions, an energy efficient alcohol–water separation technology is required to generate fuel-grade alcohols. Hydrophobic sorbents with high organic adsorption capacities are preferable for the separation of alcohol components while rejecting water molecules. The materials could be prepared as a membrane for a steady-state alcohol–water separation, or be integrated into a packed bed for low-throughput separations, or into a structured fiber sorbent configuration for high-throughput separations. It is therefore discernible that the key issue in this process is the innovation and realization of ideal hydrophobic materials.

We explored the performance of two promising hydrophobic materials, i.e. fluoride-mediated silicalite-1 (F-MFI) and zeolitic imidazolate frameworks (ZIF-8,-71,-90) for vapor phase bio-ethanol purification. For F-MFI, the introduction of mineralizing agent F^- mitigates the formation of internal silanol defects by forming ion-pairs with cationic structure directing agent that remain occluded within zeolite crystals, which results in the synthesis of pure-silica zeolites that are very hydrophobic. For ZIFs, their structures present an inherently hydrophobic nature due to the integral imidazolate linkers. Ethanol and water adsorption isotherms will be discussed in detail and the feasibility of applying these materials to the recovery of bio-ethanol is evaluated in terms of ethanol–water sorption selectivity. A comparison of distinct features for ethanol and water adsorption in F-MFI and ZIFs will be presented. The capability of biofuel purification under vapor mixtures is estimated by the ideal adsorbed solution theory (IAST) and binary breakthrough measurements.