US 3305457 A
Description (OCR text may contain errors)
Feb. 21, 1967' E. s. HYMAN 3305,45? HYDROCARBON DETECTION Filed Aug. 9, 1965 RECORDER 127 INVENTOR 3Y6 Z I 19%? 6 mpi ATTORNEYS United States Patent ()filice Cit This is a continuation-in-part of my application Serial No. 151,866, filed November 13, 1961, now abandoned.
The present invention relates to the. detection of hydrocarbons and more particularly to the detection of hydrocarbons by an electrochemical reaction at a treated platinum electrode.
It is an object of this invention to provide for analysis when it is suspected that hydrocarbon is present in a substance the composition of which is at least partially unknown.
It is a further object to provide novel platinum electrodes having sensitivity to hydrocarbons. Hydrocarbons are detected by measuring the electrochemical reaction at these electrodes when these electrodes are exposed to hydrocarbons in an aqueous solution.
The invention may be better understood from the following detailed description of preferred apparatus and procedure and by reference to the drawings in which:
FIGURE 1 shows a probe used in the detection of hydrocarbons according to the present invention;
FIGURE 2 illustrates a potentiometer circuit for practicing the invention; and
FIGURE 3 is another circuit which may be used in carrying out this invention.
In accordance with this invention, I have discovered that certain platinum and related metal electrodes respond to hydrocarbons. In one embodiment, the potential of such an electrode is referred to a standard reference electrode, such as a calomel (mercury-mercury chloride) half cell, in such a manner as to form a galvanic cell. The of the cell is measured, for example, with a potentiometer. The electrode also may be used in a polarographic cell. However, since the reaction taking place at the electrode surface is spontaneous and does not re quire an applied voltage and since the hydrocarbon is uncharged, there is no need for a polarograph.
The phenomenon of detecting the presence of hydrocarbons was first discovered with crude oil and natural gas, in particular by employing the apparatus referred to and claimed in my copending application Serial No. 139,441, filed September 20, 1961, now abandoned, on Hydrogen Detection and Quantitation. It was at first assumed that some minute quantity of hydrogen was present in crude oil or natural gas, though such has never been reported. With further experimentation, however, I observed a clear and unequivocal response to pure methane, ethane and propane and to a petroleum fraction called petroleum ether which has a boiling point range of about 36 C. to 50- C. Though one may speculate that hydrogen was present in the natural gas or crude oil at concentrations not readily detectable, free hydrogen could not have been present in the pure propane, and it is virtually impossible for hydrogen to be present in a fraction that has a minimum boiling point of 36 C. Accordingly, though the apparatus employed to detect the presence of crude oil and natural gas was similar to that used in the detection of molecular hydrogen, the detection of crude oil or natural gas, let alone the methane, ethane, propane and petroleum fraction, was not due to the presence of any hydrogen. These latter hydrocarbons themselves gave a response quantitatively in the same range as the natural oil and gas hydrocarbons. The response in these cases must have been the result of the presence of hydrocarbons since (1) hydrocarbons known to be present would fully explain the response to natural 3,305,457 Patented Feb. 21, 1967 oil and gas and (2) hydrogen is known not to be present.
The platinum type electrodes of this invention may also be termed hydrogen sensitive electrodes, in that they will respond to hydrogen in the same way as ordinary platinum black electrodes. However, they are unique in that they also respond to hydrocarbons.
An essential part of the detection technique comprises dissolving or dispersing a substance, the composition of which is at least partially unknown but is suspected of containing hydrocarbon, in an aqueous solution of an electrolyte or salt solution or perhaps in a nonaqueous conducting medium in contact with the treated platinum type electrode. The aqueous medium may contain any of the standard buffering materials to establish any desired fixed pH and any desired fixed oxidation potential. One quite suitable aqueous medium is human plasma. It inherently contains pH and oxidation potential buffers. A phosphate buffer may also be used, However, the choice of electrolyte is not critical and I have used solutions in water of, e.g., alkali chlorides, phosphates and borates.
The substance suspected of containing hydrocarbon can be directly exposed or added to the aqueous medium or, as an alternative, indirectly exposed thereto as by using an enclosed probe having a hydrocarbon-permeable membrane and containing the aqueous medium in which the platinum electrode is immersed. The probe may be similar to the arrangement shown in FIGURE 6 of my aforesaid application, and as shown in FIGURE 1 of the present application is a galvanic cell having a cylindrical wall I, a top closure member 2 and a thin hydrocarbonpermeable membrane 3 seling the respective ends of the cylinder. Membrane 3 may be of polyethylene or rubber or any plastic that allows the transit of hydrocarbon, for example, about 0.001 inch thick. A hydrocarbon-sensitive electrode, such as a treated platinum disc 4, is secured parallel to the membrane, separated therefrom by a thin film of aqueous medium. An insulated lead wire 5 extends from the disc through the top closure member to a suitable measuring circuit. The orientation of the platinum disc in close proximity to the membrane and generally parallel thereto is considered a preferred embodiment, since this increases the sensitivity of the probe. Also included in the probe is a reference electrode 6 (the nature of which depends upon the type of measuring circuit used and other considerations obvious to the electrochemist) and an insulated lead wire 7 which connects to it through the top closure member. Besides a calomel half cell, the reference electrode may be silver-silver chloride half cell or a base metal or gold. If the latter is used, the system will not respond to oxidation potential since both electrodes then respond alike, nulling out the signal.
The hydrocarbon-sensitive electrode used is, as aforementioned, of the platinum type, meaning that the base metal is one of the platinum family metals (platinum, rhodium, ruthenium, palladium, osmium, iridium and indium), preferably platinum itself, treated to render it hydrocarbon sensitive. There are two preferred ways of treating the metal electrodes which have been found particularly valuable. They will be described with reference to platinum, but it will be understood that they are useful with the other platinum metals.
(1) The co-precipitation of platinum black and metallic zinc by making the platinum electrode the cathode in a solution of dissolved platinum such as in the form of platinum chloride, e.g., 5%, and dissolved zinc, preferably in the form of an ionized zinc salt, such as zinc sulfate, e.g., five percent (5%), in an electrolyte such as water. The conditions and the anode are not critical. The coprecipitate of zinc and platinum is allowed to form until the surface is covered by a uniform gray coating. Then zinc is dissolved out, e.g., by immersion of the electrode in dilute hydrochloric acid. There remains a gray platinum surface which is sensitive to hydrocarbons, but which must be handled carefully as it can rub off.
(2) A method by which bare shiny platinum is used without any visible coating. The smooth platinum is prepared by being made the anode in a solution of chloride ion in an electrolyte such as a moderate strength aqueous hydrochloric acid (about 5%) or in a strong solution of alkali metal chloride, e.g., NaCl in Water that has been acidified, for example, with a mineral acid. The conditions are not critical other than using sufficient potential to liberate chlorine, e.g., 3 volts, for one minute. The cathode may be any conductor. At this stage of preparation, the electrode has properties which can be explained by assuming that chlorine has formed and dissolved inthe platinum. Specifically, when immersed in an electrolyte solution, its potential is 800 to 900 millivolts positive (at pH 7 assuming saturated calomel electrode to be +0244 volt). Thus, the electrode is at the oxidation potential of chlorine. This shiny platinum electrode is then given a second treatment step, i.e., it is either exposed to molecular hydrogen gas or briefly cathodized in an acid, e.g., an aqueous solution of a mineral acid such as hydrochloric acid. Either of these procedures removes chlorine from the platinum until it is no longer positive with respect to the saturated calomel electrode. This platinum surface is now unique in that it responds more quickly to hydrocarbons than the first preparation and its return from a response is also faster. Moreover, the response is stable with time and, because there is no coating to rub off, it has greater resistance to mechanical abrasion. The conditions of the cathodizing hydrogen treatment are not critical and may be accomplished in dilute (e.g., 5%) hydrochloric acid in a few seconds, using e.g., 2-20 volts DC.
The short treatment, for example a few minutes, with hydrogen gives a transient increase in sensitivity, but continuing the treatment for at least /2 hour to 24 hours gives a more prolonged enhancement of response and this treatment enhances stability for electrodes treated by each of the above methods.
After the first, i.e., chlorine treatment step, the electrode (containing chlorine) will respond to hydrocarbons, but in a diiferent manner. On exposure of this electrode to a hydrocarbon in an electrolyte solution the drops quickly. It returns to +800 mv. upon removal to an electrolyte solution free of hydrocarbon. It is believed that chlorine in the platinum combines with the hydrocarbon, that the fall in E.M.F. is the lessening of the concentration of chlorine at the platinum surface during exposure to hydrocarbon, and that the return to +800 mv. when returned to a solution devoid of hydrocarbon is due to replenishment of chlorine to the platinum surface from chlorine stored deeper in the platinum. Indeed this first step electrode could be used todetect hydrocarbons. For example, the electrode may be in the form of a hollow platinum tube with chlorine gas inside. Chlorine would diffuse through the platinum and continuously replenish the surface.
Several other types of measuring circuits may be employed to determine hydrocarbon concentrations when using platinum type electrodes therewith. These include a potentiometer, electronic voltmeter, microammeter, polanograph or any instrument for measuring the electrochemical potential or rate of electrochemical oxidation and reduction including those which measure the forced or spontaneous liberation of electrons from the treated platinum type electrode when exposed to a hydrocarbon or hydrogen.
In potentiometric measurement, illustrated in FIGURE 2, a galvanic cell is formed using the platinum electrode system as a half cell together with any standard reference half cell. The nature of the reference cell is not critical. Any reasonable reference may be used. The basic structure of the potentiometer system includes a closed loop having battery 8, rheostat 9, a calibrated slide wire resistance 10, and means for comparing an unknown E.M.F. to the potential gradient along slide wire 10 including galvanometer 11. The potentiometer is first calibrated against a standard reference battery or cell 12 by setting the slide wire contact to a position corresponding to the known of cell 12, connecting cell 12 to the slide wire through a switch 13 and then adjusting rheostat 9 until no current flows from cell 12, as shown by balance of the galvanometer 11. Switch 13 is then reversed to connect the hydrocarbon measurement cell to the slide wire, and the slide wire contact is adjusted until the galvanometer is balanced so that the position of the slide wire contact indicates E.M.F. in the conventional manner without drawing current from the galvanic cell during balance, thereby eliminating any spontaneous electron ilow caused by liquid junction potential. Of course, a continuously balancing potentiometer or recording potentiometer or electrometer may be substituted.
The hydrocarbon measurement cell of FIGURE 2 is shown using a conventional calomel reference half cell 14 having salt bridge 15 providing a thin film of liquid around the stopper 16 which communicates with the aqueous liquid in vessel 17. A treated platinum electrode 18 of the type previously described is also imrnersed in the aqueous liquid and the lead wires to the calomel half cell and platinum electrode are connected to the potentiometer as shown.
When a hydrocarbon is dissolved or dispersed in the aqueous medium in vessel 17 so as to cause spontaneous liberation of electrons at the platinum electrode 18, the needle of galvanometer 1 1 deflects to indicate an output from the galvanic cell and the presence of a hydrocarbon. The galvanic cell of FIGURE 2 can of course be changed to the probe type shown in FIGURE 1.
Alternatively, the output of the galvanic cell can be measured with an electronic voltmeter, having a high input impedance of 10 or 20 megohrns or more, or any known current measuring device such as a galvanometer.
As previously indicated, another device which can be used for this measurement is disclosed and claimed in my aforesaid application, and shown herein in FIGURE 3. Without any hydrocarbon in the aqueous medium of galvanic cell 32, which may be like FIGURE 1 herein or FIGURE 4 of my above-mentioned application, a stable baseline potential is produced by the overall galvanic cell, across terminals 30 and 31. In order to prevent any current from then flowing in the galvanic cell, a bucking voltage is applied in opposition to the voltage produced by the cell. This is accomplished by appropriately setting the arm of potentiometer 28, the end of which connect across battery 21. This battery is also connected across the emitter 22 and collector 23 electrodes of transistor 24, via resistor 25. With the platinum (black) or analogous electrode of cell 32 being coupled to the base electrode 26 of the transistor, adjustment of the arm of potentiometer 28 prevents current from flowing in the galvanic cell, i.e., takes into account the of the reference half cell, the platinum electrode in that solution and also the of the base of the transistor at no current flow in the base circuit. The proper adjustment can be easily reached without instruments. It is that setting of potentiometer 28 at which there is no shift in current in the emitter-collector circuit or in recorder 27 upon opening and closing the contacts to the electrodes in cell 32. Below this setting, there will be an upward shift, and above it a downward shift. Since no current flows in the galvanic cell when no hydrogen has been introduced thereinto, no polarization of the platinum black electrode occurs, preventing resultant drifts.
As soon as the arm of potentiometer 28 has been properly adjusted, the aqueous medium in cell 32 may be indirectly exposed to a substance such as gas or liquid suspected of containing hydrocarbon as via the probe in FIGURE '1, or directly exposed thereto by introduction of such into the aqueous medium. Since the input circuit to the transistor is a low impedance path, the electrons liberated from the treated platinum type electrode due to such exposure flow easily and are not restricted by any high impedance such as normally present in other measuring devices, for example a potentiometer (as in FIGURE 2), electrometer, or a vacuum tube voltmeter. In this circuit, the amount of current, rather than the is measured, and the current measured is an indication of the concentration of hydrocarbon exposed to the cell. The transistor is especially ideal for the purpose it serves, since it is a current amplifier which has low input impedance.
Recorder 27 may be a voltmeter or any other suitable device for measuring the voltage variations at collector 23. Sensitivity can be increased by choosing a transistor with a higher beta, using a higher collector load, or using a larger surface of platinum. A wider range can be achieved by reversing any of these procedures, or by increasing the applied voltage.
In the circuit of FIGURE 3, battery 21 may provide 6 volts for a GE 2N508 or 2N190 type PNP transistor, with potentiometer 28 being about 0.1M and resistor 25 approximately 6.8K, While the meter zeroing potentiometer 2 8 may be around 10K. Limitation to these parameters is not intended, however.
The hydrocarbons which can be detected are aliphatic hydrocarbons. Especially good response has been found for saturated aliphatic hydrocarbons, particularly lower saturated aliphatic hydrocarbons having up to six carbon atoms. Examples are methane, ethane, propane, the butanes, the pentanes and the hexanes and mixtures such as petroleum ether. Generally, the response decreases as the molecular weight increases. There is also a response to d-iethyl ether.
The following examples illustrate the practice of the invention.
Example I An electrode was prepared by immersing a small piece of smooth platinum having an area of about 4 square millimeters in 5% aqueous hydrochloric acid and connected to the positive pole of a DC. source. This caused the liberation of chlorine gas at the patinum electrode.
Example 11 A smooth platinum electrode which was anodized as in Example I was then cathodized in the same solution. Hydrogen was liberated at the electrode, and the treatment was continued until the electrode was no longer positive with respect to a saturated calomel half-cell.
Example III The electrode of Example II was employed in the apparatus of FIGURE 3 described above. An ordinary saturated calomel electrode with a fiber type liquid junction was used. The electrolyte was 0.05M Na HPO in water. After the treatment of Example I, the potential was measured with a vacuum tube voltmeter having an 11 megohm input impedance and found to be +800 mv. Methane was bubbled through the electrolyte and there was an immediate response of 400 mv. to +400 mv. The electrode was then placed in fresh electrolyte and the returned to +800 mv.
After the electrode was subjected to the treatment of Example II, it was used in the transistor circuit described. The output of the circuit was adjusted to zero. When propane was bubbled through the electrolyte, the signal was +300 mv. (The treated platinum electrode had become more negative.) The electrode was immersed next in a beaker of the same electrolyte which had been exposed to propane for a longer time and the signal increased to +600 mv. Then the electrode was immersed in a third beaker which contained the same electrolyte already equilibrated with methane; the signal was +600 mv.
Example 1V Another electrode was prepared as in Example II and measurements were made using the same electrolyte and reference electrode and the measuring circuit of FIGURE 3. The circuit was adjusted to zero while the electrode was in hydrocarbon-free electrolyte and then sequentially immersed in a series of beakers of electrolyte. Some of the beakers of electrolyte had been equilibrated with various substances as indicated .below, blank indicating that there was no hydrocarbon;
Mv. Blank 0 Methane +300 Blank 0 Propane +400 Blank 0 Natural oil +250 Benzene O Toluene 0 Diethyl ether +200 Chloroform 0 One important use for the hydrocarbon detection system is prospecting for petroleum and natural gas. If the probe shown in FIGURE 1 is lowered into a borehole, in the usual way, the presence of petroleum or natural gas can be detected. For example, the probe may be positioned behind a drilling device or in a drilling system so that it will indicate the presence or absence of lower hydrocarbons and thus petroleum or natural gas. Similarly, the probe may be used to detect natural gas or the like in a mine or room, or leakage from an underground gas or oil line or the presence of hydrocarbons in a tank or tank car. Other circumstances in which the presence of hydrocarbon must be determined will be obvious.
While preferred embodiments of apparatus and procedure have been described, it will be obvious that modifications and improvements thereof may be made without departing from the scope of the invention, as set forth in the claims.
1. A method of manufacturing an electrode which is sensitive to hydrocarbons which comprises electrolytically coprecipitating zinc and a platinum metal on the surface of a platinum metal electrode by passing an electric current through said platinum metal electrode while in contact with an electrolyte containing dissolved cationic zinc and platinum in such manner that said platinum metal electrode is the cathode and removing zinc from said electrode.
2. A method of manufacturing a bare, shiny platinum metal electrode which is sensitive to hydrocarbons which comprises passing electric current through a bare, shiny platinum metal electrode in such manner that the electrode is the anode, while said electrode is in contact with a chloride ion-containing electrolyte and without deposition of visible coating, the potential at said electrode being sufficient to liberate chlorine, until said electrode, when immersed in an electrolyte, has the oxidation potential of chlorine, and thereafter treating said electrode with hydrogen until it no longer has a substantially positive potential with respect to a saturated calomel electrode.
3. A method of manufacturing an electrode as set forth in claim 1 in which said electrolyte containing zinc and platinum is an aqueous solution of zinc sulfate and platinum chloride.
4. A method of manufacturing an electrode as set forth in claim 1 in which zinc is removed by contact with dilute hydrochloric acid.
5. A method of manufacturing an electrode as set forth in claim 1 in which said metal electrode is platinum and the platinum metal which is coprecipitated is platinum.
6. An electrode sensitive to hydrocarbons comprising a platinum metal having a surface precipitate of platinum manufactured by the method of claim 1.
7. A method of detecting the presence of hydrocarbon comprising exposing an electrolyte in which is immersed the electrode set forth in claim 6 to a substance of composition unknown but suspected of containing hydrocarbon and detecting any electro-chemical reaction at the surface of said electrode owing to said exposing.
8. A method of manufacturing an electrode as set forth in claim 2 in which said chloride ion-containing electrolyte is an aqueous solution of hydrogen chloride.
9. A method of manufacturing an electrode as set fourth in claim 2 in which said chloride ion-containing electrolyte is an aqueous solution of an alkali metal chloride that has been acidified.
10. A method of manufacturing an electrode as set forth in claim 2 in which the further treatment comprises contacting said electrode with molecular hydrogen.
11. A method of manufacturing an electrode as set forth in claim 2 in which the further treatment comprises passing electric current through said electrode in such manner that it is the cathode, while in contact with an acid.
12. A method of manufacturing an electrode as set forth in claim 11 in which said acid is an aqueous solution of a mineral acid.
13. A method of manufacturing an electrode as set forth in claim 12 in which said acid is hydrochloric acid.
14. A method of manufacturing an electrode as set forth in claim 2 in which said platinum metal is platinum.
15. An electrode sensitive to hydrocarbons comprising a bare, shiny platinum metal which has been treated by the method of claim 2.
16. A method of detecting the presence of hydrocarbon comprising exposing an electrolyte in which is immersed the electrode of claim 15 to a substance of composition unknown but suspected of containing hydrocarbons, and detecting any electrochemical reaction at the surface of said electrode owing to said exposing.
References Cited by the Examiner UNITED STATES PATENTS 2,442,476 6/1948 Taggert 2011.1 2,792,341 5/1957 Atkinson 20447 2,954,333 9/1960 Heiskell 204-128 3,055,811 9/1962 Ruff 20498 3,102,085 8/1963 Edwards et a1 204290 OTHER REFERENCES Bowden et al., Royal Society of London, Proceedings, Series A, vol. 125, pages 446462, August- November 1929.
Potter, Electrochemistry, 1956, London, Clever- Hume Press Ltd., pages 101-104, 340 and 341.
JOHN H. MACK, Primary Examiner.
T. H. TUNG, Assistant Examiner.