Research Article pubs.acs.org/journal/ascecg
Butanol Separation from Humid CO2‑Containing Multicomponent Vapor Mixtures by Zeolitic Imidazolate Frameworks Souryadeep Bhattacharyya,† Krishna C. Jayachandrababu,† Yadong Chiang,† David S. Sholl,† and Sankar Nair*,† †
School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive NW, Atlanta, Georgia 30318, United States S Supporting Information *
ABSTRACT: Butanol is a promising renewable fuel and feedstock. A major challenge in fermentative butanol production is to find a cost-effective butanol separation process from dilute aqueous solutions, usually an acetonebutanol-ethanol (ABE) mixture. Nanoporous zeolitic imidazolate frameworks (ZIFs) have shown potential for alcohol separation from dilute solutions. However, little is known about butanol separation from multicomponent mixtures using ZIFs, including the effects of the humid acid gas (CO2) used to sparge the fermenter and generate the vapor product stream. We present a study of butanol separation by ZIF-8, ZIF-90, ZIF-71 and hybrid ZIF-8−90 and ZIF-8−71 adsorbents with binary butanol/water and multicomponent ABE feeds. To obtain reliable structure−property relations for ZIF adsorbents in realistic conditions, we combine multicomponent vapor breakthrough with structural, textural, and stability characterization techniques in humid CO2 environments. In the absence of CO2, more hydrophobic materials such as ZIF-8, ZIF-855-7145, ZIF870-9030, and ZIF-71 are found to be excellent candidates with butanol/water selectivities >10 and butanol capacities >3.5 mmol/ g. However, in the presence of humid CO2, all the materials except ZIF-71 are found to degrade. The mechanistic aspects of this degradation are studied by FTIR spectroscopy and explained based upon acid gas attack of Zn−N coordinate bonds. ZIF-71 emerges as an excellent candidate owing to its acid gas stability, good butanol adsorption capacity, and selectivity. Vapor breakthrough with a model ABE solution demonstrates the high butanol selectivity of ZIF-71 relative to acetone, ethanol, and water and the recovery of a 65 mol % butanol product by desorption at 453 K. This study highlights the importance of determining structure−property relationships of MOF/ZIF materials in realistic multicomponent conditions, and the importance of acid gas stability in their applications. KEYWORDS: Biobutanol, Adsorption, ZIFs, Vapor breakthrough, Separation
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fermentation historically precedes petrobutanol synthesis.2,3 Despite the renewed interest in biobutanol production,2,4,5 several challenges remain in making biobutanol production prevalent in the biofuels market, which is estimated to be worth ∼$250 billion by 2020.1 Presently, the butanol concentration in the aqueous acetone-butanol-ethanol (ABE) fermentation broth is very low (
