Recovery of 1-butanol from aqueous solutions using zeolite ZSM-5 with a high Si/Al ratio; suitability of a column process for industrial applications

Commercially available zeolites (CBV28014, CBV901) with a high Si/Al ratio were tested as adsorbents to recover 1-butanol from aqueous solutions such as acetone–butanol–ethanol (ABE) fermentation broth. It was found that these zeolites can quickly and almost completely adsorb 1-butanol from aqueous solutions containing ∼1 wt% of 1-butanol. The binding capacity of the zeolites appeared to be around 0.12 g 1-butanol/g zeolite, and remained constant till equilibrium concentration as low as 0.04 wt% 1-butanol in water. Extrudates were prepared and tested in a column set-up to get an impression of the suitability of these zeolites for industrial applications. Extrudates of 80% zeolite and 20% alumina binder with 16–24 mesh (0.7–1.0 mm) size showed the best adsorption results in a packed bed column with up-flow of ABE broth. The adsorbent loading at 10% breakthrough was calculated to be 0.085 g 1-butanol/g zeolite (9.3 min residence time). A subsequent temperature swing leads to desorption. By choosing the temperature program carefully, it was possible to separate the water/ethanol/acetone and 1-butanol fractions. The resulting 1-butanol concentration in the 1-butanol fraction was 84.3 wt% and thus a concentration factor of 65 was achieved in one step, which is a higher value compared to other isolation techniques. Only 80% of adsorbed 1-butanol could be recovered, the remainder could only be desorbed at higher temperatures as butene. However, this should not be a problem in an industrial process as all stronger binding, catalytic sites will be blocked after the first adsorption/desorption round. A mathematical model was developed to simulate the breakthrough data and a mass transfer coefficient (kpa) of 0.052 min−1 was obtained. Comparison of simulated kpa for different sizes of extrudates clearly indicated that the adsorption rate is determined by solid phase diffusion.