Designing high-caliber nonwoven filter mats for coalescence filtration of oil/water emulsions

• Nonwoven filter mats were fabricated and enforced with resin binders.
• Unique roughening treatment was applied to the mats.
• Treated mats showed excellent coalescing separation of 4 oil-in-water emulsions.
• Mats pre-saturated with oils still performed well.
• Good separation was attributed to balanced mat surface wettability.

Oily wastewater is a major problem in industries that can cause severe environmental pollution without proper treatment. In this paper, an easily fabricated, robust and durable nonwoven fibrous filter mat was prepared for coalescence filtration of four kinds of oil-in-water emulsions, namely hexadecane/water, octane/water, soybean oil/water and engine oil/water. An aromatic thermoplastic polyurethane resin (TPU) was selected to bind the fibers together for structure integrity of the mat. Special roughening treatment to the mat was conducted to deliver the required wettability for effective coalescence separation of these emulsions. The filter mat thus prepared reached a tensile strength of 2.99 MPa, 20 times stronger than that of the pristine mat. The mat surface was made both hydrophilic and superoleophilic, allowing it to have separation efficiency as high as 99.61% in a single pass flow. Moreover, even pre-saturated with oil, the mat remained effective in separation and permitted high flow, proving its high caliber for potential industrial applications.