O/W 에멀젼에서의 전기응집 및 분리

장 우인↕, 이용철

호남석유화학(주)↕, 성균관대학교 섬유·고분자·화학공학부

Electrocoagulation and Separation of Oil-in-Water Emulsion

Woo-In Jang, Yong-Chul Lee

Honam Petrochemical Co., Daejun 305-343, Korea↕

School of Chemical·Polymer and Textile Engineering,

Sungkyunkwan University, Kyunggi 440-746, Korea

Introduction

Recently, the amount of oily wastewater forming emulsion has greatly increased in the machine and tool works and other sources, such as automotive, aerospace, packing and mechanical engineering sectors. Such an emulsion stabilized by surfactant, thermodynamically stable, causes the pollution of lake and river.

Oily wastewater in industries can exist in several forms: free-floating, dispersed and emulsified. Among these, the emulsified oil is the most difficult to treat [1]. Emulsified oil is generated in many diverse industries where metal working operations use water-soluble coolants, cutting & grinding oil and lubricants for machining.

There have been many methods to separate this; chemical and physical methods. However, these conventional methods have some problems. The aim of this study is the removal of oil from metal cutting oily wastes by a electrochemical method. In this study, the effect of various parameters on the demulsification of oil-in-water emulsion was studied on the removal rate and energy consumption. The influence of the different material of the electrode, polarization of reactor, applied potential, electrode size, temperature, initial oil concentration, stirring, and pH were investigated.

Experimental

1. Materials and Experimental

The oil emulsion as a model solution was metal cutting oil produced by Korea Houghton Corporation. This oil contains 80% of mineral oil and 20% of surfactant, cosurfactant and some other additives such as an antifoaming agent, a bactericide and an anticorrosion product.

A beaker of 1L made from two different materials, which are iron and aluminum, was used for the experiment. Experiments were performed with initial oil concentrations of 50, 100, 200 and 400 ppm. Treated solution was collected over a period of 30 minutes with a syringe and analyzed. Experiments were repeated in a range of applied potentials for different electrode material, temperature and initial oil concentration.

2. Analysis

Removal rates were determined from the difference between oil concentrations of the solutions before and after the treatment dividing by initial concentration. The turbidity of an emulsion is related to the concentration of droplets and this parameter can be used to determine the oil concentration in the emulsion. In addition, the light intensity can be measured using U.V. spectrophotometer (model U-3210, Hitachi Co., Japan). Droplet sizes were obtained using a Light Scattering Instrument (model BI-200SM Goniometer, Brookhaven Co., U.S.A.).

Results and Discussion

1. Demulsification studies

These experiments were carried out at 60V and 50℃. In addition, oil-in-water emulsion having initial concentration of 100 ppm and the aluminum or iron electrode material having the size of 3×7, 5×7, and 7×7 cm2 were used. In figure 1, compared to both of aluminum and iron reactor, aluminum reactor has shown better performance than iron one. It needs shorter time to reach the high removal efficiency. During electrolysis in an electrocoagulation procedure, the aluminum or iron anode is oxidized to Al3+ or Fe3+. Probably, aluminum hydroxide destabilizes oil droplets faster than ferric one. Electrode with wide area has better removal rate than the other smaller one because it can produce much more Al3+ to neutralize emulsion droplet charge in the solution. Figure 2 showed the change in energy consumption depending on the material and the polarization of the reactor.

2. Droplet size measurements

As the demulsification proceeded, the particle size increased. The observed increase in droplet size suggests that capability of hybrid system with ultrafiltration process. It isn't desirable for continuous process of practical wastewater treatment due to the limitation of operation time. Therefore, ultrafiltration process can be used to separate oil droplets easily from solution treated for a 30 minutes by electrocoagulation.

3. Applied potential

Removal rate has increased with the increase of applied potential. It can be explained that higher potential gave much more electrons to coalesce. On the other hand, energy consumption has increased with increasing applied potential as expected. As potential increases, the current in the circuit also increases and causes high energy consumption. Therefore, for better performance, either relatively higher removal rate or lower energy consumption should be preferred.

4. Temperature and stirring

In figure 3, removal rate of oil shows a tendency to increase according to the increase of temperature, then decrease over the some point of temperature. The optimum reactor temperature is 50℃. At low temperature, an increase in temperature results in a decrease in emulsion stability, due to an increase the rate of adsorption, the van der Waals forces, and Brownian motion, and decreases the viscosity of the continuous phase film [6]. But, too much high temperature, for example, 70℃, has low removal rate even though it has good removal rate in the beginning. It is presumably due to convection.

It is shown from the figure 4 that stirring does not give good effect to emulsion for demulsification. Stirring disturbs destabilization of oil-in-water emulsion by scattering which destracts electrostatic interaction.

5. Initial oil concentration and pH

In case of high initial oil concentration such as 400 ppm, removal rate of oil was very fast in the beginning and became very slow later. Thus, it can be said that the removal of oil can be carried out effectively applying electrical demulsification without depending on the concentration of oil. Removal rate has increased with the decrease of pH. When the pH was 3, the reaction was so fast that it only took 25 minutes to reach 88% of removal rate. At pH 11, it was slow by 30 min, but it showed good removal rate later.

References

1. C. H. Rhee, P. C. Martyn, and J. G. Kremer, Proceedings of the 42nd Purdue Industrial Waste Conference, West Lafayette, IN, Lewis Publishers, Chelsea, MI, 143 (1987).

2. W. S. W. Ho, and K. K. Sirkar, Membrane Handbook, Van Nostrand Reinhold, New York (1992).

3. M. H. Weintraub, M. A. Dzieciuch, and R. L. Gealer, U.S. Patent, 4194972 (1980).

4. F. G. Oblinger, M. H. Weintraub, R. I. Gealer, and E. J. Blais, Environmental Progress, 3, 1, pp. 1-5 (1984).

5. U. B. Ogutveren, and S. Koparal, J. Environ. Sci. & Health., A32(9&10), pp. 2507-2520 (1997).

6. P. Becher, Encyclopedia of Emulsion Technology, Vol. 2, pp. 1-75, New York, Dekker, (1985)