During the production and processing of the oil and gas industry, a large amount of oily sewage will be generated. Existing oily sewage treatment technologies mainly include gravity separation, flotation, coalescence, adsorption, filtration, chemical demulsification, biotechnology, and the combined use of the above technologies. Because these technologies generally have problems such as high processing costs and low operating efficiency, there is an urgent need to develop high-efficiency, energy-saving, and pollution-free oilfield produced water treatment technologies.
Ultrafiltration Membrane Technology to treat oily wastewater has the advantages of low energy consumption, high separation efficiency and good effluent quality. At present, the ultrafiltration membranes used in the treatment of oily wastewater from oil fields at home and abroad mainly include polysulfone (PSF) ultrafiltration membranes, polyethersulfone (PES) ultrafiltration membranes, polyvinylidene fluoride(PVDF) ultrafiltration membranes and composite membranes.
1. PSF Ultrafiltration Membrane
PSF ultrafiltration membrane mainly uses polysulfone as the membrane material, N-methylpyrrolidone as the solvent, and water as the non-solvent. Chakrabarty prepared 4 different types of PSF ultrafiltration membranes and used these 4 types of ultrafiltration membranes to treat oil-water emulsions and oily wastewater from oil fields. The results show that the PSF ultrafiltration membrane cannot reduce the oil content of the effluent to below 10mg/L, and cannot meet the discharge standard of oily wastewater. After ultrafiltration, the effluent must be further processed, such as nanofiltration or reverse osmosis filtration, so that the effluent can meet the discharge standard.
PVDF membrane has the characteristics of corrosion resistance, large membrane flux, high mechanical strength, good hydrophilic performance, and good chemical stability. Under the condition that the transmembrane pressure difference is 0.30-0.35MPa, the membrane surface velocity is 3.0-3.5m/s, and the temperature is 35-40 ℃, the PVDF membrane with a molecular weight of 100Ku interception is used to treat the oil field produced water. The oil content and suspended solids in the effluent are below 1mg/L, and the quality of the effluent meets the oilfield reinjection standard.
3. PES Ultrafiltration Membrane
PES ultrafiltration membrane usually uses polyethersulfone as the membrane material. Using PES ultrafiltration membrane to treat oil field produced water, ultrafiltration of oil in the water, suspended solids and median particle size meet the water quality standards of oilfield reinjection water. Using synthetic PES ultrafiltration membrane to treat oil refinery wastewater, the TOC removal rate can reach more than 96.3%, and the grease removal rate is as high as 99.7%. It can be seen that PES ultrafiltration membrane has a good treatment effect on oil refinery wastewater.
4. Composite Membrane
A single membrane has the disadvantages of complex membrane production process, poor membrane reproducibility, difficulty in preparing small pore membranes, poor quality and flexibility, and high cost. Therefore, two single membranes are combined together to make it have the advantages of two of more single membranes at the same time. Currently, composite membranes are mainly organic-inorganic composite membranes. The polysulfone-Al2O3 composite membrane treats oily wastewater from oilfield, and the oil interception rate can reach 90%, which meets the oilfield reinjection water standard.
Compared with the traditional physical, chemical and biological methods to treat oily wastewater from oil field, ultrafiltration membrane technology does not require the addition of chemicals to treat oily wastewater, does not produce oily sludge, and has low energy consumption, high separation efficiency, and good effluent quality. It open up a new way for the resource utilization of oilfield wastewater.