Recycling of crude oil from oily wastewater via a novel hydrogel coalescer

•A hydrogel coated tube coalescer was prepared via polymerization of acrylamide.•The coalescer allowed fast separation of oil droplet from water within seconds.•The reagent-free method allowed recycle of crude oil without formation of oil sludge. Oily wastewater is a potential resource for recycled crude oil; however, the formation of oil sludge during water disposal makes the oil unrecyclable. In this study, a hydrogel coalescer was prepared by polymerization grafting of acrylamide on a metal tube filter, which separated the emulsion into layers of water and oil when the oily water permeated the 1-mm-thick wall. The oil was easily recycled without any oil sludge formation. The material had an oil removal efficiency of 98% at a high flux up to 5000 L/(m2·h) up to an inlet pressure of 3 bar. The oil exhibited weak adhesion to the coalescer and could be easily flushed away. The fouling analysis showed bubbles, and the formation of the water-in-oil (W/O) emulsion led to the blocking of the pore. After the addition of a demulsifier into the hydrogel, the formation of the W/O emulsion was strongly suppressed, and the material showed an enhanced anti-blocking performance and higher flux. Hence, we developed a potential reagent-free solution for the disposal of oily wastewater and a recycling technique for obtaining crude oil from it.