We report the use of 3D-printed ZIF-8 adsorbent monoliths for the recovery of biobutanol from model fermentation mixtures. Two ZIF-8 monoliths, obtained by layer-by-layer printing, with different fiber thickness (250 and 600 μm), front channel size (350 μm × 350 μm and 760 μm × 760 μm), and side channel size (<60 and 260 μm) were studied. Equilibrium isotherms of acetone−butanol−ethanol (ABE) fermentation products showed that both monoliths retained a high saturation capacity (0.2 g/g) for n-butanol and a low saturation capacity for water (0.04 g/g). Mixture breakthrough experiments demonstrate that a high amount of butanol is adsorbed (0.2 g/g) in dynamic conditions, close to the pure component capacity. When increasing the carrier gas flow rate, broadening of the n-butanol breakthrough profile was observed for the 250 μm fiber monolith, while no broadening of the profile was observed for the 600 μm fiber monolith. Computational fluid dynamics (CFD) simulations show that the small side channels of the 250 μm monolith (<60 μm) leads to maldistribution of the flow at the inlet. Finally, the thermal regeneration of the monoliths was investigated, showing the capacity of the ZIF-8 monoliths could be fully restored for different adsorption−desorption cycles.

While in most adsorptive separations different mixture components tend to compete for different adsorption sites, we report the existence of cooperative effects in the adsorption of alcohols (ethanol and 1-butanol) from the vapor phase on ZIF-8. The presence of these molecules in binary mixtures leads to an increase in their equilibrium capacities, compared to the pure component isotherms. These effects were first observed when predicting the mixture equilibrium capacities using the ideal adsorbed solution theory (IAST) and were also observed via grand canonical Monte Carlo (GC MC) simulations. GC MC simulations showed that the interaction between adsorbate molecules leads to the cooperative effect predicted by IAST. The predicted cooperative adsorption could be confirmed via breakthrough experiments. In these experiments, a "roll-up" of 1-butanol was observed during the regeneration of a ZIF-8 packed column. A dynamic breakthrough model employing IAST was developed and used to explain the effect of the adsorption equilibrium on the dynamic breakthrough profiles.

No abstract

This paper was prepared for presentation at the 1999 SPE International Symposium on Oilfield Chemistry held in Houston, Texas, 16-19 February 1999.