(739f) Butanol Separation from Multicomponent Vapor Mixtures Using Zeolitic Imidazolate Frameworks | AIChE

(739f) Butanol Separation from Multicomponent Vapor Mixtures Using Zeolitic Imidazolate Frameworks


Bhattacharyya, S. - Presenter, Georgia Institute of Technology
Jayachandrababu, K. C., Georgia Institute of Technology
Sholl, D. S., Georgia Institute of Technology
Nair, S., Georgia Institute of Technology
Biobutanol is a promising renewable alternative to conventional petroleum-derived liquid fuels, and can be used as either as an additive or as a direct gasoline replacement. It also has many industrial applications, e.g., in the production of paints and polymers. A major challenge in fermentative biobutanol production is to find a cost-effective butanol separation process from the extremely dilute aqueous butanol solution (which is usually in the form of an acetone-butanol-ethanol mixture). Vapor-phase adsorption after gas stripping of the butanol solution can be an effective option to separate butanol from water due to the favorable nature of butanol-water vapor liquid equilibrium. Zeolitic Imidazolate Frameworks (ZIFs), a set of nanoporous metal-organic frameworks (MOFs) with tunable porosity and functionality are possible candidates for this purpose. In previous work by some of the present authors on ZIF-8, ZIF-90 and ZIF-71 adsorbents, it was found from single-component adsorption isotherms and IAST predictions that ZIF-8 and ZIF-71 may be useful for this separation.1 Previous work from our group has also demonstrated that the effective pore size, hydrophobicity, and organophilicity of ZIFs can be tuned using mixed-linker ZIFs.2

However, very little is known about separation of butanol from multicomponent vapor mixtures. In particular, an important issue is the presence of humidified acid gas (CO2) in differing amounts in the vapor mixture, which may cause degradation of ZIF materials by attacking the Zn-N coordination bonds. To understand these effects and their impact on butanol separation, here we evaluate the separation performance of ZIF-8, ZIF-90, ZIF-71, hybrid ZIF-8x-90100-x and ZIF-8x71100-x adsorbents with a 1 mole % butanol-in-water system through vapor phase breakthrough experiments at 35 °C and 1 bar. For simplicity, acetone and ethanol were not included in the mixture. We conducted long-term stability studies of the adsorbents in humid air and CO2 in addition to vapor breakthrough studies. The separation properties are presented in detail and qualitatively explained based upon the textural properties, hydrophobicity, and organophilicity of the ZIF frameworks. ZIF-8 and ZIF-71 are found to be best materials (in terms of butanol selectivities ~15 and capacities ~4.3 mmol/g) for this separation in the absence of humid CO2 in the feed stream. However, in the presence of humid CO2, ZIF-8, ZIF-90 and ZIF-8x-90100-x hybrids are found to be unstable upon long-term operation. The mechanistic aspects of this degradation are studied by several techniques including FTIR spectroscopy and explained. From a practical viewpoint, ZIF-71 appears to be an excellent candidate for butanol separation owing to its acid gas stability as well as good butanol adsorption capacity and selectivity.


1. Zhang, K.; Lively, R. P.; Dose, M. E.; Brown, A. J.; Zhang, C.; Chung, J.; Nair, S.; Koros, W. J.; Chance, R. R., Alcohol and Water Adsorption in Zeolitic Imidazolate Frameworks. Chem. Commun. 2013, 49, 3245-3247.

2. Eum, K., et al., Highly Tunable Molecular Sieving and Adsorption Properties of Mixed-Linker Zeolitic Imidazolate Frameworks. J. Am. Chem. Soc. 2015, 137, 4191-4197.