Switchable wettability of grain-stacked filter layers from polyurethane plastic waste for oil/water separation

Chengyu Sun; Kun Chen; Bernard Wiafe Biney; Kunyin Wang; He Liu; Aijun Guo; Wei Xia

doi:10.1016/j.jcis.2021.11.158

Switchable wettability of grain-stacked filter layers from polyurethane plastic waste for oil/water separation

J Colloid Interface Sci. 2022 Mar 15:610:970-981. doi: 10.1016/j.jcis.2021.11.158. Epub 2021 Nov 27.

Authors

Chengyu Sun¹, Kun Chen², Bernard Wiafe Biney¹, Kunyin Wang¹, He Liu¹, Aijun Guo¹, Wei Xia¹

Affiliations

¹ State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering, China University of Petroleum (East China), 66 Changjiang West Road, Huangdao District, Qingdao, Shandong 266580, China.
² State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering, China University of Petroleum (East China), 66 Changjiang West Road, Huangdao District, Qingdao, Shandong 266580, China. Electronic address: chenkun@upc.edu.cn.

PMID: 34887059
DOI: 10.1016/j.jcis.2021.11.158

Abstract

Hypothesis: Polyurethane plastic waste (PUPW), a port-abundant solid waste, is difficult to degrade naturally and poses a severe threat to the environment. Hence, the effective recycling of PUPW remains a challenge.

Experiments: Herein, a strategy of converting PUPW into stacked oil/water filtration layer grain through a layer-by-layer (LBL) assembly process is investigated. Notably, such PU-based, grain-stacked, and switchable wettability of the oil/water filter layer is first reported.

Findings: The grain-stacked filter layers are flexible for separating immiscible oil/water mixtures, water-in-oil emulsions (WOE), and oil-in-water emulsions (OWE) under gravity over 10 cycle-usages. They can withstand strong acid/alkali solutions (pH = 1-14) and salt solutions over 12 h. Besides, 100-times scale-up experiments have indicated that the obtained filter layers exhibit an upper to 98.2 % separation efficiency for 10 L real industrial oil/water emulsion in the 24 h continuous operation. The demulsification mechanism for emulsions is that the electrostatic interaction along with adsorption between emulsion droplets and grains leads to the uneven distribution of surfactants on the interface film of the emulsion droplets, increasing the probability of tiny droplets colliding and coalescing into large droplets to achieve oil/water separation. This work proposes an effective and economical method of abundant plastic waste for industrial-scale oil-water separation rather than just on the laboratory-scale.

Keywords: Demulsification mechanism; Oil/water separation; Polyurethane plastic waste; Scale-up experiment; Superhydrophobicity; Underwater superoleophobic.