Efficient demulsification of oil-in-water emulsions using a zeolitic imidazolate framework: Adsorptive removal of oil droplets from water

Kun-Yi Andrew Lin; Yu-Chien Chen; Songkeart Phattarapattamawong

doi:10.1016/j.jcis.2016.05.057

Efficient demulsification of oil-in-water emulsions using a zeolitic imidazolate framework: Adsorptive removal of oil droplets from water

J Colloid Interface Sci. 2016 Sep 15:478:97-106. doi: 10.1016/j.jcis.2016.05.057. Epub 2016 Jun 1.

Authors

Kun-Yi Andrew Lin¹, Yu-Chien Chen², Songkeart Phattarapattamawong³

Affiliations

¹ Department of Environmental Engineering, National Chung Hsing University, 250 Kuo-Kuang Road, Taichung, Taiwan. Electronic address: linky@nchu.edu.tw.
² Department of Environmental Engineering, National Chung Hsing University, 250 Kuo-Kuang Road, Taichung, Taiwan.
³ Department of Environmental Engineering, Faculty of Engineering, King Mongkut's University of Technology Thonburi, Bangkok, Thailand. Electronic address: songkeart.pha@kmutt.ac.th.

PMID: 27288575
DOI: 10.1016/j.jcis.2016.05.057

Abstract

To demulsify oil-in-water (O/W) emulsions, a zinc-based zeolitic imidazolate framework (ZIF-8) was employed for the first time to remove oil droplets from water. ZIF-8 exhibits a high surface area and positive surface charges, making it a suitable adsorbent to adsorb negatively-charged oil droplets. Adsorption behaviors of oil droplets to ZIF-8 were studied by analyzing the adsorption kinetics and isotherm with theoretical models. The activation energy of adsorption of oil droplets to ZIF-8 was determined as 24.1kJmol(-1). The Langmuir-Freundlich (L-F) model was found to be most applicable to interpret the isotherm data and the predicated maximum adsorption capacity of ZIF-8 can reach 6633mgg(-1), revealing a promising capability of ZIF-8 for demulsification. Factors influencing the adsorption of oil droplets to ZIF-8 were investigated including temperature, pH, salt and surfactants. The adsorption capacity of ZIF-8 for oil was improved at elevated temperatures, whereas alkaline condition was unfavorable for the adsorption of oil droplets due to the electrostatic repulsion at high pH. The adsorption capacity of ZIF-8 remained similar in the presence of NaCl but it was reduced in the presence of surfactants. ZIF-8 was regenerated by a simple ethanol-washing method; the regenerated ZIF-8 exhibited more than 85% of regeneration efficiency over six cycles. Its crystalline structure also remained intact after the regeneration. These characteristics indicate that ZIF-8 can be a promising and effective adsorbent to remove oil droplets for demulsification of O/W emulsions.

Keywords: Adsorption; Oil-in-water emulsions; ZIF-8; Zeolitic imidazolate framework.