Electrokinetic phenomena of modified polytetrafluoroethylene membranes in the oily sewage from oil field.1. Introduction
At present, flood development is used primarily in most oilfields all over China. As the water contents of main productive zones have entered the middle or high stage, oily sewage treatment Sewage treatment
Unit processes used to separate, modify, remove, and destroy objectionable, hazardous, and pathogenic substances carried by wastewater in solution or suspension in order to render the water fit and safe for intended uses. problems in nearly every oilfield are getting more and more rigorous. In order to meet the requests of sewage discharge in remote producing field and produced water reinjection in low permeable permeable /per·me·a·ble/ (per´me-ah-b'l) not impassable; pervious; permitting passage of a substance.
That can be permeated or penetrated, especially by liquids or gases. sublayer oilfields, the water quality must be handled more deeply based on the routine sewage disposal Sewage disposal
The ultimate return of used water to the environment. Disposal points distribute the used water either to aquatic bodies such as oceans, rivers, lakes, ponds, or lagoons or to land by absorption systems, groundwater recharge, and irrigation. technology. Membrane separation technology is one of the most important developing tendency in deep treatment [1,2]. The researches on electrokinetic phenomena Electrokinetic phenomena is a family of several different effects that occur in heterogeneous fluids or in porous bodies filled with fluid. The term heterogeneous here means a fluid containing particles. of membranes have attracted extensive attention in membrane science, interface science and other academic circles [3-6]. When electrolyte solution leaking porous membrane vertically(or tangentially tan·gen·tial also tan·gen·tal
1. Of, relating to, or moving along or in the direction of a tangent.
2. Merely touching or slightly connected.
3. ) with definite differential pressure, potential difference will appear accordingly between two sides of the membrane, and valid electric charges on the membrane surface are usually originated from the ion absorption in solution or the liberation of some functional group on membrane micro bore surface. The existence of membrane surface charges influences the ion distribution nearby the contact interface between the membrane and the solution, and results in the formation of so-called ion diffuse electric double layer in neighboring membrane surface [7,8]. Electrokinetic phenomena will appear when the solution and the membrane surface move relatively as a result of pressure difference and other outside forces. However, the reports on electrokinetic phenomena of membranes in oily sewage disposal are few. Experimental investigations on electrokinetic phenomena of modified polytetrafluoroethylene polytetrafluoroethylene
a synthetic material commonly used as a nonstick lining in domestic cooking utensils (frypans); abbreviated PTFE; called also Teflon. Overheating produces toxic fumes that cause an acute hemorrhagic pneumonitis and death in small caged birds, which are membranes (The polytetrafluoroethylene membranes undergo chemical modification In biochemistry, chemical modification is the technique of chemically reacting a protein or nucleic acid with chemical reagents. Chemical modification can have several goals, such as
Intended to counteract or eliminate environmental pollution: antipollution filters; antipollution laws.
an abilities also improved) in handling the oily waste water of oilfields are mainly performed in the paper.
2.1. Experimental Apparatuses and Equipments
Membrane fine filtration equipments. (Figure 1) under the pressure offered by centrifugal pump centrifugal pump
Machine for moving liquids and gases. Its two major parts are the impeller (a wheel with vanes) and the circular pump casing around it. In the most common type, called the volute centrifugal pump, fluid enters the pump at high speed near the centre of the , oily sewage from the stuff fluid tank leak out Verb 1. leak out - be leaked; "The news leaked out despite his secrecy"
get around, get out, break - be released or become known; of news; "News of her death broke in the morning" membrane subassembly sub·as·sem·bly
n. pl. sub·as·sem·blies
An assembled unit forming a component to be incorporated into a larger assembly.
to the permeated fluid storage tank. This flow chart is divided into dead end filtration In the dead-end filtration technique all the fluid passes through the membrane, and all particles larger than the pore size of the Membrane are retained at its surface. This means that the trapped particles start to build up a "filter cake" on the surface of the membrane, which has and mixed current filtration based on the way by which the stuff fluid leak the membrane (The experiments here used mixed current filtration). The membranes used in the tests are modified polytetrafluoroethylene membranes which are supplied by First Petroleum Technology Ltd., whose bore diameters are separately 0.45 and 0.8 [micro]m. In the tests, the pressure differences between both sides of membrane subassembly are measured with EJA EJA Elder Justice Act
EJA East Journal on Approximations
EJA Ergonomic Job Analysis
EJA Environmental Justice Alliance 110A differential pressure transmitter (used at low pressure) and AM1151 capacitive differential pressure transmitter (used at high pressure), the measuring ranges of which are separately 0~40KPa and 0~300KPa, the accuracy figures 0.1% and 0.5%, and the output electric currents are both 4~20mA. Electric signal outputted from differential pressure transmitter are inputted to the computer by HK-PCI812 data acquisition board whose system synthesis error is not more than 0.2%. The flow measurement of membrane assembly used glass rotameter, the main technical descriptions of which are: the measurement range 60~600L/h, the accuracy figure 1.5%. There are agitator ag·i·ta·tor
1. One who agitates, especially one who engages in political agitation.
2. An apparatus that shakes or stirs, as in a washing machine.
Noun 1. made by self and temperature control equipment in stuff fluid tank in order to maintain the homogenization homogenization (həmŏj'ənəzā`shən), process in which a mixture is made uniform throughout. Generally this procedure involves reducing the size of the particles of one component of the mixture and dispersing them evenly of the stuff fluid and control its temperature. To keep the sample temperature as it is collected, THD-0515W low temperature thermostatic bath was used to maintain the temperature of sample bottle, and the main technical descriptions of the bath are the measurement range -5~100 [degrees]C, the waveness [+ or -] 0.05 [degrees]C.
HP 34401A digital multimeter (electronics) Digital Multimeter - (DMM) A peice of test equipment used for measuring voltage, current, resistance, and possibly other electircal quantities and displaying the value in number form. is used to measure potential differences between both sides of membrane assembly as oily sewage leaking. WTW WTW Welfare-To-Work
WTW Water Treatment Works
WTW Well-To-Wheels (hybrid electric vehicle)
WTW Watamu Turtle Watch (Kenya)
WTW Woman to Woman (Boston) high accuracy inoLab 740, made in Xiamen Longlide Environment Technique exploitation Co. Ltd., is used to measure electrical conductivities of oily waste water in different temperatures. The dynamic viscosities of the sewage are tested by the concentric cylinder rotary rheometer rhe·om·e·ter
An instrument for measuring the flow of viscous liquids, such as blood. MCR MCR My Chemical Romance (band)
MCR Minimum Capital Requirement
MCR Minimum Cell Rate
MCR Middle Common Room (UK universities)
MCR Multivariate Curve Resolution 301, of which the main technical descriptions are: the minimal torque 0.1 ,[micro]Nm , the maximum torque 200 mNm . Zetasizer3000 Zeta potential zeta potential
see zeta potential. measuring instrument, made by Malvern corporation in England, could detect the electrokinetic potentials of the test solution, and the test temperatures are able to be adjusted within 10~70[degrees]C. The paper test Zeta potentials of suspended particles in oily sewage before and after treatment with this equipment.
[FIGURE 1 OMITTED]
2.2. Test Water Samples
The oily sewages handled in this paper are all from a sewage plant of Shengli Oilfield. In the water, suspended solid content is 10~50mg/L, total mineralization Mineralization
The process by which the body uses minerals to build bone structure.
Mentioned in: Rickets
n the bioprecipitation of an inorganic substance. 48497.1mg/L, oil content 20-100mg/L(measured with 721 light meter), the median diameter of suspended particles around 4 [micro]m (measured with COULTER fully automatic particle size Particle size, also called grain size, refers to the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. analyzer COULTER MULTISIZER 11).
3. Experiment Results and Analysis
3.1. Experiment Basis
According to according to
1. As stated or indicated by; on the authority of: according to historians.
2. In keeping with: according to instructions.
3. the surface and colloid colloid (kŏl`oid) [Gr.,=gluelike], a mixture in which one substance is divided into minute particles (called colloidal particles) and dispersed throughout a second substance. science , potential differences between both sides of capillary pore net or porous bung Bung
experiences modified and extreme levels of want. [Br. Lit.: Sketches by Boz]
See : Poverty made by powder compacting will appear when fluid leaking by force of compression. Millipore filter Millipore filter
trademark for cellulose acetate filters with pore sizes of 8 µm to 10 nm; such membranes are widely used for sterilizing liquid media. can be considered made up from lots of punctuates, and potential differences will also arise during filtering. The streaming potential is then the gradient of potential differences changing with pressure differences when electrostatic current through the membranes is zero, i.e., when solution leaking porous membrane vertically at specified pressure difference [Delta]P, there will be a potential difference [Delta]E between both sides of membrane accordingly, and the streaming potential can be described as:
v =d([Delta]E)/d([Delta]P) (1)
The streaming potentials of membranes can be obtained by tested directly, in which, just connect a voltmeter between the two ends . The streaming potentials can only describe the membrane charged properties qualitatively, but not the quantitative magnitude which can be indicated with Zeta potentials of the membrane surface. The double electrode layer theory considers that there is a "glide surface", on which the solution and surface move relatively, at some distance away from the surface within the membrane surface ion diffuse electric double layer, and the potential difference between "glide surface" and main part of the solution is called Zeta potential. Zeta potential of the membrane surface is an important parameter which determines electrokinetic phenomena of membranes, and depends on membrane material and solution system intently . The micro bore surface Zeta potential ([zeta])  of modified polytetrafluoroethylene membranes can be estimated by outstanding Helmholtz-Smoluchowski equation using membrane streaming potential which has been obtained:
[MATHEMATICAL EXPRESSION A group of characters or symbols representing a quantity or an operation. See arithmetic expression. NOT REPRODUCIBLE IN ASCII ASCII or American Standard Code for Information Interchange, a set of codes used to represent letters, numbers, a few symbols, and control characters. Originally designed for teletype operations, it has found wide application in computers. ] (2)
In which, v is the streaming potential, whose unit is V/Pa; k the electric conductivity of solution, unit S/m(1S = 1c x [s.sup.-] x [V.sup.-1]); [micro] the viscosity, unit Pa x s, [[epsilon].sub.r] and [[epsilon].sub.0] are separately relative dielectric constant dielectric constant
See permittivity. and vacuum dielectric constant, whose units are F/m (1F =1c x [V.sup.-1]).
Helmholtz-Smoluchowski equation is suit for the case when the pipe diameter or capillary tube diameter is far larger than the thickness of double electrode layer. The thicknesses of double electrode layer of membrane borehole bore·hole
A hole that is drilled into the earth, as in exploratory well drilling or in building construction. wall are nanometer degree, while the bore diameters of modified polytetrafluoroethylene membranes used in the experiments are meter degree, in which the latter are far larger than the former, so the equation is fit for the estimate of the membrane surface Zeta potentials here.
3.2. Membrane Surface Zeta Potentials
As the membrane bore diameters, filtering temperatures, filtering flow rates and other elements have obvious effects on filtering effect, and those elements also probably influence the membrane surface Zeta potentials, filtering tests with membranes of different bore diameters were performed under different temperatures and specified flow rates. The potential differences of oily waste water between both sides of the modified PTFE PTFE
polytetrafluoroethylene. filter membrane are measured with HP 34401A digital multimeter at correspondent operating conditions. The streaming potential v of the membrane at different operating conditions could be calculated according to Formula (1) with the potential difference [Delta]E and the pressure difference [Delta]P obtained from experiments. Some results are shown in Table 1.
The table shows that, although there are differences among the membrane bore diameters and operating conditions, the changes of membrane streaming potentials are not obvious: of the 9 tests, the average maximal value is -5.01 mV/KPa, the maximal value -5.3 mV/KPa, the minimum value -4.9 mV/KPa and the standard deviation In statistics, the average amount a number varies from the average number in a series of numbers.
(statistics) standard deviation - (SD) A measure of the range of values in a set of numbers. 0.13642 mV/KPa. In fact, the absolute value of membrane streaming potentials is probably affected by the electrolyte concentration of solution, types and valence states of basic ion and negative ion Negative ion
An atomic or molecular system with an excess of negative charge. Negative ions, also called anions, are formed in attachment processes in which an additional electron is captured by an atom or molecule. and other elements . It is found that the oily waste water investigated here contains Nat with a concentration of 15951.58mg/L and [Mg.sup.2+] of only 261.91 mg/L through water quality analysis, so the effect of [Na.sup.+] is dominating, and as its concentration is far larger than the critical concentration given in reference , the components of the waste water would not change suddenly. Thus the slight alternation alternation /al·ter·na·tion/ (awl?ter-na´shun) the regular succession of two opposing or different events in turn.
alternation of generations metagenesis. of ion concentration caused by sample collection and other reasons would not influence the value of membrane streaming potentials, which is accordant to the experiment results shown in Table 1.
It has been told before that the membrane streaming potentials can not indicate the magnitude of membrane surface electrical properties quantitatively. In order to estimate the membrane surface Zeta potentials and quantitatively describe the electrical properties, Helmholtz-Smoluchowski equation is needed. The correlating parameters in the equation are defined as shown in Table 2 and Table 3 by experiments.
It is thus evident that the Zeta potentials of modified polytetrafluoroethylene membrane surface are between -18.67 - -21.94mV, of which the average value is -20.06mV and the standard deviation 1.3078. In other words Adv. 1. in other words - otherwise stated; "in other words, we are broke"
put differently , during the oil sewage treatment using modified polytetrafluoroethylene membrane, the membrane surface charged negatively and the influences on membrane surface Zeta potentials caused by membrane bore diameters and operating conditions are not obvious. The Zeta potentials of membrane surface are maintained around -20mV.
3.3. Zeta Potentials of the Suspended Particles in Oily Waste Water
In order to profoundly study the electrokinetic phenomena of modified polytetrafluoroethylene membranes, the charging properties of suspended particles should be known. As the electrical properties of general colloidal particles are not expressed with the value of electric charges but the Zeta potential [zeta], the paper measured Zeta potentials of suspended particles under various temperatures by Zetasizer3000 Zeta potential test set, and the results are shown in Table 5.
Obviously, the Zeta potentials are all negative and of the same electrical properties as the surface Zeta potentials. Zeta potential changes apparently as temperature changes, but not show regular patterns of increasing or decreasing monotonously, which is probably relevant with the vergent suspended particles and the fact that sampling sewage could not be absolute uniform.
Seen from the separation behavior, conventional membrane separation filtration is based on a physical sieving rule, that is, the membrane allows the components with smaller bore diameters to go through but entraps those with larger or similar bore diameters. Obviously, with the decrease of the particle diameters, the membrane bore diameters should decreases correspondently, which is bound to cause such problems as decreasing flux and increasing operating costs operating costs npl → gastos mpl operacionales . However, besides physical sieving, the charging membrane has Donnan effect. According to the Dorman balance model, when the solution leak through membrane with charging group, the concentration of counter ions(those ions taking opposite charges to that fixed in the membrane) in the membrane is larger than that in the solution body, while the behavior of ions with same charges is just opposite. Dorman potential difference is thus formed and prevents the ions with same charges in the solution body from diffusing to the membrane. In order to maintain electrically neutral, the membrane also entraps counter ions. So such charging membrane has particular adsorptive separation properties. Additionally, charging groups generate in the membrane, which strengthens the hydrophilicity and increases the permeability of the membrane. Meanwhile, the antipollution competence of the membrane is improved markedly because of the charge effect that charges with the same electric nature reject each other.
Thus the modified polytetrafluoroethylene membranes have strong ability withholding the suspended substance and powerful antipollution competence as a result of the role of the charges on the membranes when used to handle oily waste water, which prolong the backwashing cycle and service life of the filter element. The content about the effectiveness of the modified polytetrafluoroethylene membranes processing oily sewage will be elaborated in other papers.
When dealing with oily waste water, the streaming potentials of the modified polytetrafluoroethylene membranes maintain around -5mV/KPa while the membrane surface Zeta potentials around -20mV, which are slightly dependent on such operating conditions as membrane bore diameters, flow rates, etc. The Zeta potentials of the suspended particles in the sewage being processed are also negative.
The membranes have strong ability withholding the suspended substance and powerful antipollution competence because of the role of the charges on the membranes.
Received December 12, 2008; revised March 30, 2009; accepted April 3, 2009
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Aiguo LIN (1), Yihua YAO (2), Gang LIU (1), Guozhong ZHANG (1), Xiufeng LIN (3)
(1) China University ofPetroleum, Dongying, Shandong, China
(2) Shenli Oilfield Lwning Company, Dongying, Shandong, China
(3) University of Regina History
In direct response to the award of the University of Saskatchewan to Saskatoon rather than Regina, the Methodist Church of Canada established Regina College in 1911 on College Avenue in Regina, Saskatchewan, starting with an enrollment of 27 students; , Saskatchewan, Canada
Table 1. Membrane streaming potentials at different operating conditions. Sequence Bore diameter Temperature Given flow V number of membrane ([degrees]C) rate (L/h) (mV/Kpa) ([micro]m) 1 0.8 30 600 -4.9 2 0.8 50 400 -5.1 3 0.8 70 250 -5.0 4 0.5 30 400 -4.9 5 0.5 50 250 -4.9 6 0.5 70 600 -5.0 7 0.5 30 250 -5.3 8 0.5 50 600 -4.9 9 0.5 70 400 -5.1 Table 2. Conductance ratios and dynamic viscosity of oily waste water under different temperatures. Temperature of water sample ([degrees]C) 30 50 70 Conductance ratio (S/m) 2.5 3.5 4.9 dynamic viscosity (mPa x s) 0.944 0.689 0.544 Note: the conductance ratios shown in the table were measured by inoLab 740, of which the measuring range is LR001 and the accuracy degree is 0.001 [micro]S / cm. Table 3. Dynamic viscosities factors [mu] of oily waste water under different temperatures. Temperature of water sample ([degrees]C) 30 50 70 Dynamic viscosity (mPa x s) 0.944 0.689 0.544 According to the data above, Zeta potentials of modified polytetrafluoroethylene membranes can be calculated through Formula (2). Table 4 shows Zeta potentials of the membrane surface under different experiment conditions. Table 4. Zeta potential on the modified PTFE membrane under different conditions. No. Zeta/mV No. Zeta/mV 1 -18.67 6 -21.52 2 -19.85 7 -20.19 3 -21.52 8 -19.07 4 -18.67 9 -21.94 5 -19.07 Table 5. Zeta potential of suspended particles under different temperatures. Sequence Temperature Zeta potential number ([degrees]C) (mV) 1 30 -14.2 2 40 -1.8 3 50 -4.4 4 60 -8.2 5 70 -12.3