Cross-Flow Microfiltration of Oily Water using a Ceramic Membrane: Flux Decline and Oil Adsorption

Abstract

The microfiltration of oil-water emulsion solutions through a ceramic membrane was investigated in this study. A surfactant-free dispersed oil-water emulsion in the range of 0.2–2% kerosene was fed into a tubular ceramic membrane module as a turbulent flow. The optimal trans-membrane pressure was determined. For oily water containing less than 0.5% kerosene content, the steady-state permeate flux of 3.36 × 10⁻⁵ m³/m² s bar (121 L/m² h bar) could be achieved; the oil retention was as high as 99.5% at a volume concentration factor of 4. The solute diffusion coefficient was 9.765 × 10⁻¹⁰ m²/s and the mass transfer coefficient was 2.687 × 10⁻⁵ m/s in this system. The resistance-in-series model was applied to describe the flux decline and the individual resistance from the membrane, oil adsorption, gel formation, and concentration polarization were calculated. The results indicated that the oil (solute) adsorption on the membrane surface was the major source of resistance. The scanning electron micrograph indicated oil adsorption on the membrane surface. As the oil content in the feed increased, the gel formation and the concentration polarization also played a role, contributing to flow resistance and causing flux decline. Furthermore, increasing the operating temperature enhanced the flux and the activation energy was determined as 2.918 kJ/mol. A reversible model of dispersed oil adsorption into the gel state was used to explain the flux decline during the filtration process.

Keywords:

• Ceramic membrane
• flux decline
• microfiltration
• modeling
• oil-water separation

ACKNOWLEDGEMENT

The authors wish to express their gratitude to Chang Gung University (UERPD 270161) for its financial support. Valuable discussion with the Referees is greatly acknowledged.

Notes

Trans-membrane pressure: 4.14 bar, feed velocity: 0.587 m/s, temperature: 20°C.

Trans-membrane pressure: 4.14 bar, feed velocity: 0.587 m/s, temperature: 20°C.

∗ND: not detectable.

†Oil retention = (1−V_pC_P/V_FC_F) × 100%.

‡VCF = initial feed volume/final volume.

^§Trans-membrane pressure: 4.14 bar, feed velocity: 0.587 m/s, temperature: 20°C.

^a Not available.

^b Almost no water flux at 5000 ppm.