Treatment of oil/water emulsion by polyethylene glycol ultrafiltration membrane

Vol.12 No. 5J. CENT. SOUTH UNIV. TECHNOL.Oct. 2005Article ID: 1005 - 9784(2005)05 - 0542 - 04Treatment of oil/ water emulsion bypolyethylene glycol ultrafiltration membraneHE De wen(何德文)，XIAO Yu-tang(肖羽堂)”，LI Xiong(李雄)', JIN Yan(金艳)'(1. School of Metallurgical Science and Engineering,Central South University, Changsha 410083, China;2. School of Environmental Science and Engineering，Nankai University, Tianjing 300071, China)Abstract: Polyethylene glycol ( PEG) membranes with different molecular mass cut-offs were used to treatoil/ water emulsion, and the effects of experimental conditions including pressure, temperature and different opera-ting modes on permeate flux and removal rate of chemical oxygen demand (CODc.) were studied. The results show .that the permeate flux of ultrafiltration membrane is influenced by pressure and temperature; practical pressure ischosen to be0.3-0. 7 MPa for the PEG with molecular mass cut-offs of 8000 and0.7-1.0 MPa for the PEG with .molecular mass cut- offs of 2 500; and the practical temperature is chosen to be 25 - 32 C. Different operating modesof ultrafiltration also influence the permeate flux and removal rate of CODc. The ultrafiltration mermbrane of inter-mittent cross-flow operating mode is easier to be influenced by blocky polarization and contamination than that of se-quential cross- flow operating mode. Rermoval rate of CODcr in intermittent cross- flow and sequential cross- flow con-dition can be maintained at about 93%.Key words: oil/ water emulsion; ultrafiltration membrane; permeate flux; chemical oxygen demandCLC number: X701.3Document code: A1 INTRODUCTIONfor three oil emulsions, and over 90% of chemicaloxygen demand(COD) rejection and 95% of oil re-Oil/ water emulsion employed in the cable andtention can be attained by the UF process. In thiswire manufacturing processes serves the purposespaper polyethylene glycol ( PEG) UF membrane .of lubrication, cooling, surface cleaning and corro-was used, and the optimum operation conditionssion prevention. The oil/ water emulsion consistswere obtained.of up to 97% water, the rest being complex aque-ous mixture w hich comprises different kinds of oils2 EXPERIMENTAL .(mineral, animal， vegetable and synthetic)， alco-hol，sequestrants and surfactants. Because a lot2.1 Materials and methodsof oil/water emulsion needs to be regularly re-The UF experimental apparatus is shown inplaced several times every year and waste oil/ waterFig.1. The system consists of a UF cell and a oil/emulsion is thus generated all over the world everywater emulsion reservoir. The UF cell has an in-year. Currently， there are no effective methods toside diameter of 18 cm and a volume of 2 L and thedeal with waste oil/ water emulsion[2.3].oil/ water emulsion reservoir has a capacity of 5 L.If membrane ultrafiltration(UF) is applied toThe UF cell was equipped with outside thermocou-water purification for public water supply and pol-ple to control the temperature to a desired valuelutant water treatmentlt， it seems to have manyThe UF cell was connected to the waste oil/ wateradvantages such as improvement of water quality,reservoir which was connected to a nitrogen bottlesaving of water purification chemicals and opera-in turn. The pressure in the UF cell was thus con-tion cost，easier operation and maintenance， andstantly maintained indirectly by the bottled nitrosaving of space, time and cost for construction of agen and the UF cell was filled to full capacity withwater purification plant[5.6]. Bansal[7] treated thethe waste oil/ water emulsion during each experi-oily and latex wastewater using membrane ultran-mental run, as fed from the reservoir. To keep thefiltration and the results from laboratory show thatoil/ water emulsion in the UF cell uniform，a stir-this treatment process is efficient. Bodzek et a1[8]rer中国煤化工speed was provided.studied the performances of polyacrylonitrileTwfines were employed,(PAN) and polyvinyl chloride (PVC) membraneswhidMYHc N M H Gcols(PEGs) with the①Foundation item: Projeet( 50308011) supported by the National Natural Science Foundation of ChinaReceived date: 2004- 12 - 28; Accepted date: 2005-01 - 12Correspotspomdot De wen, PhD; Tel: + 86-731-8830875<0), 13574873151; E -mail: hedewen@ mail. csu. edu. cnHE De-wen.e t al: Treatment of oil/ water emulsion by polyethylene glycol ultrafiltration membranenominal molecular mass cut-offs of 8 000 andoperating pressure is 0 - 0. 7 MPa，the permeate2 500, respectively.flux of PEG with molecular mass cut-offs of 8 000increases rapidly with the increase of the operatingpressure. When the pressure is above 0. 7 MPa,sOOthe permeate flux descends with the increase of op-中era-ting pressure. This is because the gel layerformed by solute on the membrane surface plays afunction of obstruction when the pressure rises tosome extent to bring the blocky polarization[10-On the contrary, the permeate flux of PEG with .molecular mass cut-offs of 2 500 increases withhigh operating pressure because membrane with2smaller diameter and high transfer resistance is notinfluenced by blocky polarizationI1I.Fig.1 UF experimental apparatus1- Nitrogen bottle; 2一Water reservoir; 3- UF cell;4- Stirrer; 5- Temperature controller;30 t6- Thermocouple; 7- Membrane;8一Permeate; 9- Retentate20 FThe oil/ water emulsion UF was obtained froma major copper cable and wire mill in Hunan.First，the oil/ water emulsion from the mill was filtered through a filter bed to remove coarse suspen-0.20.0.81.0ded particles, and then placed in the reservoir andthe UF cell.p/MPaFig.2 Effect of pressure on PEG UF membrance2.2 Influencing factors and indexat 25 C and stirring speed of 450 r/ min .After the system was sealed and connected,1- Molecular mass cut-offs of 8 000;the UF operation began with an appropriate set of2一Molecular mass cut-offs of 2 500operating variables. The influences of pressure,temperature, time and operating modes were stud-Considering permeate efficiency and cost ofied, and so permeate flux and CODcr were chosenequipment and energy consumption， the practicalas important effective indexes which were moni-operating pressure is chosen to be 0. 3 - 0. 7 MPatored regularly[9]for the PEG with molecular mass cut-offs of 8 000and 0. 7- 1.0 MPa for the PEG with molecular3 RESULTS AND DISCUSSIONmass cut-offs of 2 500.3. 1 Pollution of membrane and blocky polarization3.3 Influence of temperature on UF permeate fluxThe pollution of membrane is caused by parti-Fig. 3 shows that temperature greatly influ-cles of colloid and metal ions which lead to wane of .ences the UF permeate flux. The permeate flux ofmembrane aperture or block by adsorption and ag-PEG UF membrane with molecular mass cut-offsgradation on the surface of the membrane. Theof 8 000 rises rapidly in the temperature range of 10pollution of membrance results in the loss of water- 35 "C and decreases sharply at above 35 C. Thepower and the increase of the resistance of waterviscosity of solution decreases with the increase offlow.temperature, as shown in Eqn. (1)， therefore theBlocky polarization is formed by the concen-efficiency of solution transfer is improved.tration of the cycling water (especially oil) to make△p(1)coacervation on the surface of the membrane. TheJ=u(R_+R、)blocky polarization leads to the increase of resist-whe中国煤化工，Tux of UF membrane,ance of the mass transfer and sharply decreases theandto the operating pres-amount of the water in different operation condi-sureMYHCN M H Gsfer resistance of UFtions.membrane，resistance of gel layer and viscosity ofsolution，respectively [12].3.2 Influence of pressure on UF permeate fluxBut in the further permeate process, the effectFig. 2 shows that the operating pressure hasof blocky polarization constantly increases andgreat inflReh据the UF permeate flux. When theexcesses that of viscosity of solution， so the●544●Journal CSUT Vol. 12 No. 5200520、 208卜1616 F144F12-12 2464860721052503540/hθ/CFig.4 Permeate flux vs time at 0.5 MPa in .Fig.3 Effect of temperature on permeate flux ofintermittent cross- flow conditionPEG UF membrance at 0. 5 MPa andstirring speed of 450 r/ minpermeate water becomes higher, and removal rate1- Molecular mass cut-offs of 8 000 ;of CODcr can be maintained at 93% or so. At the2一Molecular mass cut-offs of 2 500 .same time wastewater in the water reservoir is con-resistance of gel layer plays a more important rolecentrated.with the decrease of the permeate flux. The per-meate flux of PEG UF membrane with molecular1.2-195mass cut- offs of 2 500 increases with the increase of工1.0194生temperature because the membrane with smallerdiameter and high transfer resistance is only influ-enced by the viscosity of solution， not influenced点0.892by blocky polarizationf18]. So the permeate flux of91 &PEG UF membrane rises with the decrease of the .904812 1624viscosity of solution at high temperature.Considering permeate efficiency and tempera-ture endure capability of membrane (UF membraneFig.5 Concentration and removal rate of CODcrcannot be used at above 40 C)，practical tempera-vs time in intermittent cross flow conditionture was chosen to be 25- 32 C for the PEG UF1- CODc, in permeate; 2- -Removal rate of CODcrmembranes with molecular mass cut-offs of 8 0003.4.2 Sequential cross flow operating modeand 2 500.1 ) Permeate flux in sequential cross-flow3.4 Influence of operating modes on UF permeateconditionThe permeate flux of sequential cross-flow op-fluxerating mode at 0. 5 MPa at different times is3.4.1 Intermittent cross- flow operating mode1 ) permeate flux in intermittent cross flowshown in Fig. 6，indicating that the permeate fluxfluctuates in a scope of 13. 5- 18. 5 L/(m2●h).The permeate flux of intermittent cross-flowThe experimental results can be explained as fol-operating mode at 0.5 MPa at different times islows. The sequential cross- flow operating mode ishown in Fig. 4，indicating that the permeate fluxnot influenced by contaminated membrane andof PEG rises during 0 - 6 h, and decreases whenblocky polarization，so the permeate flux does nottime is prolonged, due to blocky polarization andfluctuate because of the balance of transfer resist-contaminated membrane which contains abundantance and the operating pressure.2) Removal rate of CODc, in sequential crossbig particles of organism, colloidal particles and oil .flow_ condition .particlesl4]. Therefore the contaminated mem-中国煤化工emoval rate of CODcrbrane must be cleaned in time in order to keep highpermeate flux-nCNMH Grdition are shown in.MH2) Removal rate of CODcr in intermittentFig.7，Tlulcacllg Lllal lie concentration of CODcrin permeate water can be considered as unchangea-cross-flow conditionThe concentration and removal rate of CODcrble in a scope and removal rate of CODcr keeps atin intermittent cross-flow condition is shown inabout 93%，with permeate water being transparentFig. 5，sA瓦執据that the density of CODcr inand colorless all the time. In practice， cleaningHE De-wen.e t al: Treatment of oil/ water emulsion by polyethylene glycol ultrafiltration membraneoperating mode， and the cleaning time of UF| 8厂membrane can be prolonged in order to save the7Foperating fees in sequential cross- flow operatingE6-mode.5-.REFERENCES!/vWWv[1] Sheng H L, Wen J L. Treatment of waste oil/ wateremulsion by ultrafiltration and ion exchange[J]. WaterResearch，1998. 32(9): 2680 - 2688.816244048[2]LU Shan-zhong， QIAN Kun-min. New method tot/treat waste emulsion[J]. Water and Wastewater Engi-neering, 2000, 26(7): 39-45.Fig.6 Permeate flux vs time at 0. 5 MPa in[3] LU Bin， LU Xiao-qian. Engineering application ofsequential cross- flow conditiontreating technology of oily emulsified wastewater[J].Environmental Engineering. 2001. 19(3): 12- 15. (in .0.9p79Chinese)[4] Kunikane s, Magara Y, Itoh M, et al. A comparative1 94study on the application of membrane technology to the干0.8public water supply[ J]. Journal of Membrane Science,1995，102(5): 149- 154.0.7[5] Wiesner M R，Chelam S. The promise of the mem-g|91brane technology[J]. Environ Sei Technol, 1999， 33(17): 360 - 366.0.6 3691215182124[6] Cortalezzi M M，Rose J, Wells G F, et al. Ceramicmembranes derived from ferroxane nanoparticles:/hnew route for the fabrication of iron oxide ultrafiltra-Fig. 7 Removal rate of CODcr intion membranes [J]. Journal of Membrane Science,2003，227(2): 207 - 217.1- Removal rate of CODc; 2- CODcr[7] Bansal I K. Concentration of oily and latex wastewaterusing ultrafiltration inorganic membranes[J]. Ind Wa-time of UF membrane may be prolonged in order toter Engineering, 1976, 13(10): 6-15.save the operating fees.[8] Bodzek M，Konieczng K. The use of ultrafiltrationmembranes made of various polymers in the treatment4 CONCLUSIONSof oil- emulsion wastewaters[J]. Waste Management,1992，12: 75 - 86.1) Pressure increasing can improve the perme-[9]Lin s H, Lan W J. Waste oil/ water emulsion treat-ment by membrane processes[J]. Journal of Hazard-ate flux and the operating pressure affect more ob-ous Materials， 1998. 59: 189- 199.viously on the PEG UF membrane with larger mo-[10] ZHANG Guo-jun, LIU Zhong zhou. Development oflecular mass cut-offs than on that with smallerthe mechanism and the controlled technique of ultra-one. Considering the blocky polarization and ener-filtration membrane fouling [J ]. Membrane Sciencegy consumption， practical operating pressure isand Technology, 2001，21(4): 39 - 46. (in Chinese) .chosen to be 0.3-0. 7 MPa for the PEG UF mem-[11] KimKJ, Fane AG, FellCJ D, et al. Fouling mecha-brane with molecular mass cut-offs of 8 000 andnisms of membranes during protein ultrafiltration[J ].Journal of Membrane Science, 1992, 68(1): 79- 91.0.7- 1.0MPa for the PEG UF membrane with[12] Ribeiro T H, Rubio J, Smith R W. A dried hydro-molecular mass cut-offs of 2 500. .phobic acquaphyte as an oil filter for oil/ water emul-2) Increasing temperature improves the per-sions[J]. Spill Science and Technology Bulletin,meate flux. Considering permeate efficiency anc2003，8(5): 483 - 489.temperature endure capability ( 40 C) of mem-[13] WANG Xiao-chang， WANG Jin. Kinetic study ofbrane, the practical temperature is chosen to bemembrane fouling under cross flow ultrafiltration op-25- 32 C for the PEG UF membrane with molecu-eration[J]. Environmental Chemistry, 2002, 21(6):552 - 558. (in Chinese) .lar mass cut-offs of 8000 and 2 500.3) Operating mode of UF influences the per-[14]_ CrozesG F, JacangeloJ G, AnselmeC, et al. Impact中国煤化I:onditions on membrane ir-meate flux and removal rate of CODcr. The UF二nal of Membrane Science,membrane of intermittent cross flow operatingMHCNMHGmode is easier to be influenced by blocky polariza-[15] WU Guang xia, ZHANG Dong-hua，QIAN Yan-jun.tion and contamination than that of sequentialThe fouling and cleaning of ultrafiltration membranecross- flow operating mode. So in practice, the con-module[J]. Environmental Chemistry, 2002. 21(4):389 - 3428. (in Chinese)taminated membrane must be cleaned in time tokeep highp厄熬振te flux in intermittent cross flow( Edited by CHEN Wei-ping)