Comparing column dynamics in the liquid and vapor phase adsorption of biobutanol on an activated carbon monolith

Adsorbent monoliths are gaining increasing interest in gas phase separation processes, but have rarely been studied for liquid phase separations. In this work, we investigate an activated carbon monolith for the recovery of biobutanol from model liquid mixtures as well as compare the obtained column dynamics with the adsorption of biobutanol from gas mixtures. Single solute adsorption isotherms of acetone, n-butanol and ethanol revealed the carbon’s larger affinity for n-butanol (0.11 g/g adsorbed at 2 wt%), while dynamic separations on a fixed-bed of crushed monolith granules proved its capability to effectively separate an aqueous mixture of these three fermentation products. In contrast, liquid phase breakthrough experiments of n-butanol on the monolith column were marked by almost instantaneous detection of adsorbate at the outlet (< 5 min.) and broad tailing of the concentration curve. Measures to improve inlet flow distribution or increasing temperature to enhance mass transfer were unsuccessful. In contrast, using the same inlet flow distributors, a sharp breakthrough profile could be obtained in vapor phase, while the gas contact time (17 s) was much lower than in liquid phase (1300 s). A comparison of characteristic mass transfer times of the adsorption process highlighted the important role of the external film resistance in liquid compared to vapor phase adsorption.