Published by the DTI Oil & Gas Directorate for the reservoir engineering and IOR community in the UK.
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The Separation of Oil Drops from Water Using Micro-Slits

Richard Holdich (R.G.Holdich@lboro.ac.uk) of the Chemical Engineering Department at Loughborough University details the scope of a new EPSRC funded project to investigate the flow of drops through slit like pores and to provide an optimum geometry for micro-slit pores to maximise the rejection of oil drops whilst providing high filtrate flux rate.

The separation of oil drops in water, with diameters greater than a micron, can be achieved by the non-tortuous type of microfilters operating in crossflow. However, all currently available process-scale microfilters are of the tortuous type, which provides an internal surface on which material deposits, thus fouling the microfilter internally and leading to long-term flux decline.

Research at Loughborough University has resulted in a technique that can be used to produce non-tortuous process-scale microfilters. However, non-tortuous microfilters with circular pores may still clog at the surface because drops sit trapped over the holes in the membrane. The force holding the drop in place over the hole is a combination of surface forces and the pressure drop across the membrane. When filtering on micro-slit membranes an oil drop on the slit like pore is not held in place by the pressure drop over the membrane, because the oil drop does not completely block off the water flow through the slit like pore: i.e. the force holding the drop in place is primarily the liquid drag force exerted by the permeate over the drop. This force is much less than the force due to the full pressure field over the membrane. However, careful control of the force on the drop must be exercised to prevent the squeezing of the drop through the slit like pore.

This project investigates the flow of drops through slit like pores and provides an optimum geometry for micro-slit pores to maximise the rejection of oil drops whilst providing high filtrate flux rates. The aim is to develop a technology that can be used to remove oil drops that are too small to be effectively rejected by existing liquid/liquid hydrocyclones and to simultaneously reject suspended solids.

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