CA1102275A

CA1102275A - Breaking oil-in-water emulsion using porous iron electrode

Info

Publication number: CA1102275A
Application number: CA290,685A
Authority: CA
Inventors: Marvin H. Weintraub; Roy L. Gealer; Matthew A. Dzieciuch
Original assignee: Ford Motor Company of Canada Ltd
Current assignee: Ford Motor Company of Canada Ltd
Priority date: 1976-12-27
Filing date: 1977-11-10
Publication date: 1981-06-02
Also published as: DE2757776A1; JPS5382667A; GB1592720A; DE2757776C2

Abstract

ABSTRACT OF THE DISCLOSURE
A method is disclosed for breaking an oil-in-water emulsion. Briefly, the method of this invention includes the following general steps. A porous ferrous ion producing anode is established. A supply of the oil-in-water emulsion is located on one side of the anode and a fixed volume of the emulsion is flowed through a fixed cross sectional area of the anode per unit of time. Less than a passivating current is flowed through each unit area of the anode per unit of time thereby dissolving into the emulsion ferrous ion in sufficient quantity to break the emulsion. The flowing of the fixed volume of the emul-sion through the electrode per unit of time and the dis-solving of sufficient quantity of ferrous ions results in a homogeneous dispersion of the ferrous ions in the fixed volume of the emulsion. There is an in situ generation of hydroxyl ion at the cathode and tiny air bubbles are intro-duced near the electrodes to oxidize the ferrous ions to ferric ions. The ferric ions are then permitted time to break the emulsion and remove the oil therefrom. This oil floats to the top surface in a froth and is removed.

Description

The present invention relates to the breaking of oil-in-water emulsions.
U.S. patent 3,523,891 for "Electrolytic Sewage Trea~ment System and Process" discloses an apparatus ln which a batch treatment process can be carried out i~
which a aissolvable iron electrode is employed to treat sewage waste. The system includes spaced metal electrode plates connected to a power supply for producing multivalent metallic ions and hydroxyl ions during treatm nt of waste waters. The metallic and hydrox~l ions form a flock which floats to the surface of the cell and entraps its suspende~
solids forming a supernatant, frothy sludge.
We have recently been working in the field of electrolytic treatment of waste water containing ~tabilized oil emulsion in an e~fort to decrease the cost and increase the production results of such a treatment syst6m. We have, in particular, been working on a system which is operable on a continuous basis. We also have been inves-kigâting various operational facets of these systems in order to develop a process for treating such oily waste waters which is the most eficient from the standpoint of power consumption per rate of removal of oily materials from waste wa~ers.
Briefly, we have developea a process for breaX-ing an oil-in-water emulsion which may be applied on a continuous basis. We are able to use a porous iron elec-trode in the method as the medium by which ferrous ions are placed uniformly in t:he emulsion to break the same.
Our concept is based on the principle of putting the required ferrous ion concentration necessary ko break the emulsion into the emulsion as rapidly and as uniformly as possible. We obtain this by flowing a ixed amount o~

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~, emulsion through a unit area of a porous ferrous ion pro-ducing anode. A predetermined amount of power is supplied per unit area of the anode. Thus, as a ixed volume of the emulsion flows through a unit area of anode, it receives ,the required amount of ferrous ion necessary to break the emulsion almost in an instantaneous ashion.
Simultaneously, with the dissolving of the anode there is the in situ generation o the hydroxyl ion at the cathode where concentration is fixed by the electrochemical reation. Air is introduced near the electrodes as air is important for effective reaction to occur, that is, the oxidation of ferrous ion to fQr~ic ion which is necessary to break the emulsion~
In accordance with the broad teachings of the method of our invention, an oil-in-water emulsion is broken in the following manner. A porous ferrous ion producing anode is established and a supply of the emulsion is locàted on one side thexeof. A fixed volume of the emul-sion is flowed through the porous anode per unit of time.

2~ Less t~an a passivating current is flowed through each unit area of the anode per unit of time. This current dissolves Lnto the fixed volume of the emulsion passing through the electrode ferrous ion in su~ficient quantity to brealc the fixed volume of the emulsion. The ferrous ions are oxidized to ferric ions which are effective ~or breaking the emulsion. The flowing of a fixed volume of the emulsion through the,porous iron electrode per unit of time and the dissolving of the ferrous ion and oxidizing thereof results in a homogeneous dispersion of ferric ions in the fixed volume of the emulsion.

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2~75 In accordance wi~h specific teachings o~ the method of this invention, the amount of electric current passed through the anode per unit area may be calculated by the formula i = (N)f~Co)(10 4~ wherein: N is in the range from 20 to 50; f is flow rate of the emulsion per unit area of electrode in cc/minute; Co is the initial conc~ntration of oil in the water in parts per million; and i is equal to current per unit area of anode in milliamperes.
: The method of this invention may be applied to oil-in~water emulsions of any general type. In particular, an oil-in-~ater emulsion used in machining of metal articles as a coolant and lu~ricant therefor may be treated by this -- , . . .
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process in order to break the emulsion and remove the oil from the water. A typical oil-in~water emulsion for a typical cutting oil lubricant comprises, approximately, hy weight of 79~ mineral oil, 18% of soap emulsifier and 3%
of a mixture of biocidal and stabilizing agents. This soluble oil cutting fluid is prepared by dilu~ing the above-described emulsion with water in a weight ratio of at least a~out 50 to 1. This solution is directed over a metal article upon which a cutting tool is removing material. The cutting fluid cools the article being formed, flushes away the chips being generated in the cutting operation and also lubricates the surface being cut.
After a period of operative life, the cutting oil fluid becomes unsuitable for furthex use and must be discarded~ Being ~n emulslonr the material may not be directly discarded because it contains oil in the water.
Therefore, b~fore the material can be discarded, it is necessary to break the emulsion and thereby separate the oil rom the water, permitting the clean water to be dis-carded and the oil to be recycled or discarded in a manner appropriate for hydrocarbon materials.
A more impor~ant use is for the clean-up of rinse waste waters from the rinsing of machined parts in which the water may contain a dilute concentration o~
emulsified oil generally ranging from 500 to 4000 ppm.
Our process is one which provides an economical ; and efficient method or breaking an oil-in-water emulsion.
The method of our invention will be best understood by considering the contents of the following description '~ .

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while referring to the accompanying drawings, in which:
FIGURE 1 is a drawing which depicts a schematic outline of the system in which the ~nethod of our invention can be practiced. FIGURE 2 is a graphical presentation showing ~he effect of using various amounts of current in the method o our invention.
Oily waste water from a plant, such as discarded waste water from rinsing of parts machined using oil emul-sion coolant is delivered by means of a pump 10 to a storage tank 12. In this tank, heat and air are added hy means of a heater 14 and an air delivery system 1~ ~sche-matically represented by a plurality of arrows). Any ree oil-which flows to the surface in the storage tank may be skimmed of and removed. Also, in the receiving and storage tank, the pH of the oily waste water may be adjusted to a pH in the range of 6 ~o 10 by means of a pH
system 18. The amount of material added from the C~ o I
pH ad~it~on system to achieve the desired pH is calculated in normal pH calculating procedures. A small amount of salt also may have to be added to promote ionic conduc-tivity and prevent passivation of the electrode. The addi-tion of heat and air to the tank is simply to keep the system at set conditions for further treatment.
A second pump 20 continuously withdra~s a portion of the oily waste water héld in the storage tank 12 and delivers that oil-in-water emulsion to an eléctrolytic cell generally indicated by the numeral 22. This cell has a receiving æone 24 into which the ernulsion is initially delivered. The cell also has a ferrous ion producing anode in ~he form of an iron chip anode 26 which can be formed from the metallic chips generated from any steel or iron machining operation. This iron chip anode is slowly dis-~i solved to produce ferrous ions by the passage of alectric -. " ~''~. " ' .

;2Z~ , current therethrough. The rate at which the anode is dissolved is a function of the amount of current passing therethrough. The higher the amount of current, the more iron is dissolved but, of course, the more power that is used. Fresh iron chip additions from time to time to this electrode chamber assure that the chamber contains suffi-cient iron electrode for continuously carrying out the process. When using the electrode we require that less than a passivating current be passed therethrough. By this we mean that a current density is not reached which would result in a discontinuation of iron dissolution and a consumption of power to decompose water instead.
The amount of power passing through the anode controls the amount of iron which is dissolved into the oil-in-water emulsion passing through the anode. If one visualizes the flow of the emulsion through the anode as a slug-type flow in which a unit volume of emulsion moves into the anode is held therein and is treated and then moved therethrough, then it will be easy to understand that on one side of the iron chip anode a slug of emulsion has no iron therein, that the iron is placed in the emul-sion ~o a p~cular conoentra~tion a$ th~t sl~ o~ emulsion passes thro~gh the iron chip anode and khat after passage through the node the slug of emulsion will have a particular level of iron therein which will general~y remain constant.
Thus, the process of iron enterin~ the emulsion is one that occurs almost instantaneously in that the concentra-tion of e1ectric~lly dissolved ferrous ions in the emul~
sion goes from zero on one side of the iron chip anode to r~ .
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1 a certain ~ixed level on the other side of the iron anode, 2 the fixed level belng determined by the amount of power

3 being used at the anode. The particular manner for con-

4 trolling the amount of power used to achieve the best results will be discussed in greater detail hereinbelow.
6 After a slug of emulsion passes through the iron 7 chip anode 26, it passes through a cathode screen 28 at 8 which hydroxyl ions are generated to complete the electro-9 chemical reaction as is known in the art. About this posi-tion, air is added by an air supply system 30. The air ll supplied is in the form of tiny bubbles in order to provide 12 for oxidization of ferrous ions to ferric ions and to 13 develop a mechanism by which the oil coming out of the 14 emulsion may be picked up and floated to the surface. The oil waste, which is an oil-iron hydroxide sludge 32, begins 16 to ~orm on the surface of the emulsion in an emulsion 17 breaking zone 34 of the electrolytic cell 2Z. This zone 18 is sufficiently long to permit substantially full separa-l9 tion of the oily waste from the water.
Near the end of the oil emulsion breaking zone 34 21 of the electrolytic cell 22 is provided a sludge removing 22 system generally identified by the numeral 36. This system 23 includes a conveyor 38 which transports the sludge 32 up-24 wardly from the water and deposits it in a sludge receiving device 40O
26 Clear water is withdrawn from the bottom oE the 27 emulsion breaking zone 34 by means of a pipe 42. The water 28 from this pipe may be pumped to a sewage system or may be 29 recycled depending upon the clarity thereof and the requirements for process water in the plant using this system.
In accordance with the teachings of this inven-tion,- the method of this invention is operated in the following manner. Power is applied at the anode 26 in accordance with the following equation. This equation is based on a unit area of the electrode and each unit area has the same power applied thereto.
The power applied is in accordance with the formula i- (N)f(Co)(10 4) wherein: N is any number in the range from 20 to 50, f is the flow rate of the emulsion per unit area of electrode in cc/minutes; Co is the initial concentration o~ oil in the water in parts per million;
and i is equal to the current per unit area of electrode in milliamperes. This equation, in the form N = i(10+4)/fCo, is shown plotted in ~IGURE 2 versus ~he final concentration in parts per million of oil in the waste water. It should be noted from the graph that when N is in the range rom 30 to 50, the parts per million of oil in the final product 20 i5 very low. It is also important to note that the cur~e flattens out at about the 40 to 50 range and, thus, there is no need o~ exceeding this amount of current. In other words, greater amount of current representative of higher N
values do not produce any significantly greater reduction of oil in the waters being treated. Thus, we teach that it is not desirable to operate at an N value greater than 50 because one simply is wasting power andexperiencing no added benefit therefrom.

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1 In accordance with the preferred teachings o~ the 2 method of this invention, the iron chip anode 26 is 3 operated with the power per unit area being determined in 4 accordance with the formula discussed above in which N is in the range from 20 to 50. Operation of this cell at such 6 a power load has allowed us to process 0.2 gallons per 7 minute of a solution containing 2000 parts per million of 8 oil per square foot of elec~rode. ~enerally, the water 9 delivered through the pipe has a final concentration of oil contained therPin of about 10 parts per million~
11 Having described our method herein, it is 12 apparent that those skilled in the art will ~ind ways of 13 modifying the method which still falls within the true 14 spirit and scope of this invention. It is intended that all such modi~ications be included within the scope o~ the 16 appended claims.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

A method of breaking an oil-in-water emulsion which comprises:
establishing a porous ferrous ion producing electrode;
locating a supply of oil-in-water emulsion on one side of said porous ferrous ion producing electrode;
flowing a fixed volume of the oil-in-water emulsion through said porous ferrous ion pro-ducing electrode per unit of time;
flowing less than a passivating current per unit area of electrode through said porous ferrous ion producing electrode per unit of time, thereby to dissolve into the oil-in-water emulsion ferrous ion in sufficient quantity to break the oil-in-water emulsion;
oxidizing the ferrous ions to ferric ions, the latter ions being effective in breaking the emulsion;
the flowing of a fixed volume of the oil-in-water emulsion through said porous ferrous ion producing electrode per unit of time and the dissolv-ing of said ferrous ions and oxidizing thereof result-ing in a homogeneous dispersion of ferric ions in said fixed volume of the oil-in-water emulsion.

A method of breaking an oil-in-water emulsion which comprises:
establishing a porous ferrous ion producing electrode;
locating a supply of oil-in-water emulsion on one side of said porous ferrous ion producing electrode;
flowing a fixed volume of the oil-in-water emulsion through said porous ferrous ion pro-ducing electrode per unit of time;
flowing electric current through a unit of area of said electrode in accordance with the following equation i = (N)f(Co)10-4 wherein:
N is in the range from 20 to 50, f is the flow rate of oil-in-water emulsion per unit area of electrode in cc/minute, Co is the initial concentration of oil-in-water in parts per million, and i is the current per unit of electrode in milliamps, and oxidizing the ferrous ions to ferric ions, the latter being effective to break the emul-sion.