Separation of Oil in Water (O/W) Emulsion Using Commercial Microfiltration Membranes and Sand Filters

Crude oil extraction, refinery as well as frequent offshore oil spillage events unavoidably produced large quantity of oily waste water, which exert heavy burden to environment. The treatment of oily wastewater treatment has become one of the most urgent issues for gas/oil/chemical industries [1].

Two kinds of commercial microfiltration membranes (PES and Nitrocellulose) were characterized and tested for oil in water (O/W) emulsion separation, and compared to the performance of the sand filter with different particle size and bed depth. Wettability of the samples were checked through CA and UCA measurements. Surface properties/morphology were characterized with FTIR/SEM (scanning electron microscope). Separation efficiency were evaluated by checking the turbidity of filtrates and confirmed with TOC values. Experimental results revealed that: 1) The commercial membranes show underwater oleophobicity, with average WCA around 145.8º for PES membrane, with average WCA around 137.1º for Nitrocellulose membrane; 2) Two different membranes present separation efficiency higher than 90% for Dodecanese in water Emulsion, higher than 98% for Hexane in water emulsions [2,3].

Sand filters were studied with different bed depth and particle sizes. Preliminary results showed that the slightly hydrophobic surface can effectively separate the O/W emulsion under gravity, which is superior to the commercial membranes. Under the driving force of 0.1 bar, their performance are equivalent or superior to the commercial membrane, suggesting that the sand filter is a low-cost and effective solution for the separation of O/W emulsions. Table 1 lists the experimental results of the 3 samples for O/W separation.

Table 1. The Separation of O/W Emulsion on 3 media

Medium	Depth/Thickness (mm)	Turbidity (NTU)	Flux (L/m2·h)	TOC (ppm)
Stock solution (Dodecane/water)		242		682.8
Sands of 75-150µm （gravity）(C12)	40	0.6	38.4	10.9
Sands of 150-300µm （gravity）(C12)	17	31.7	188.7	54.6
Sands of 300-500µm （gravity）(C12)	27	17.2	194.7	28.5
PES membrane (DP= 0.1 bar）	0.14	2.3	1698.5	56.6
Nitrocellulose membrane （0.1 bar）	0.15	12.1	2239.3	58.4
Stock solution (Dodecane/water)		185		682.8
Sands of 75-150µm （0.1 bar）(C12)	10	73.2	887.2	18.7
Sands of 150-300µm （0.1 bar）(C12)	10	22.6	1596.6	48.2
Stock solution (Hexane)		264		5564.0
Sands of 75-150µm （0.1 bar）(C6)	10	45.3	702.8	12.5
Sands of 150-300µm （0.1 bar）(C6)	10	24.8	1358.8	93.0