(650b) Adsorption and Diffusion of Bioalcohols in Zeolite SAPO-34 and MOF ZIF-8

Bioalcohols, like biobutanol, form a promising alternative to petroleum-based chemicals and fuels. A major challenge in the economical production of biobutanol is its separation from the aqueous medium in which it is produced by ABE (Acetone-Butanol-Ethanol) fermentation. Given the low concentration of biobutanol in the fermentation broth (typically 20 g/l), the recovery via distillation would be energy- and cost-intensive. Among the alternative methods, adsorption was identified as the most energy-efficient recovery technique.

Adsorptive separation of butanol from aqueous ABE fermentation broth requires adsorbents with high stability, capacity and selectivity towards alcohols and low affinity for water. Additionally, smaller and larger alcohols or other components should be excluded!

From screening and experimental work two suitable materials emerged: SAPO-34 zeolite and ZIF-8 MOF. From the vapor/liquid phase adsorption equilibrium and breakthrough experimentation it could be concluded that, water is not adsorbed at all by ZIF-8, ethanol and acetone (major side products) are adsorbed to a much lower extent as compared to butanol (capacities up to 30 wt%), making ZIF-8 a highly attractive adsorbent for bio-butanol recovery.^[1] Liquid phase adsorption and diffusion measurments showed that, while most zeolites with tubular pores have higher adsorption affinity for longer molecules, SAPO-34 (small cages connected via even smaller windows) exhibits an inverse chain length selectivity^[2] and a nonuniform chain length dependent diffusion,^[3]  allowing removal of short chain alcohols from mixtures with longer ones and hence purification of butanol. A two step process combining ZIF-8 and SAPO-34 offers perspectives for the economical and low energy intensive production of butanol.^[4]

[1] J. Cousin Saint Remi, T. Remy, D. De Vos, G.V. Baron, J.F.M. Denayer, ChemSusChem (2011) 4, 1074-1077.

[2] T. Remy, J. Cousin Saint Remi, R. Singh, P.A. Webley, G.V. Baron, J.F.M. Denayer, J. Phys Chem C (2011) 115, 8117-8125.

[3] J. Cousin Saint Remi, G.V. Baron, J.F.M. Denayer, J. Phys Chem C (2013), DOI: 10.1021/jp312287k

[4] J. Cousin Saint Remi, G.V. Baron, J.F.M. Denayer, Adsorption (2012), 18, 367−373.