US2904406A

US2904406A - Hydrocarbon detection

Info

Publication number: US2904406A
Application number: US582823A
Authority: US
Inventors: Pernell J Moore
Original assignee: Nat Lead Co
Current assignee: NL Industries Inc
Priority date: 1956-05-04
Filing date: 1956-05-04
Publication date: 1959-09-15
Anticipated expiration: 1976-09-15

Description

Sept. 15, 1959 P. J. MOORE HYnRocARBoN DETECTION 2 Sheets-Sheet 1' v Filed May 4, 1956 www Nuts: v

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,Pace/mu J M0065 @AMAA-M nited States Patent Online Patented Sept.` 15, `1959 HYDRCARBON DETECTIN Pernell Moore, Houston, Tex., assignor to National Lead Company, New York, N.Y., a corporation of New Jersey Application May 4, 1956, Serin No. 582,823

4 claims. (C1. 23-232) This invention relates to the selective detection and estimation of hydrocarbons andmore particularly to an improvement in hydrocarbon detectors of the catalytic ilament type.

It has been known for many years that certain metals, particularly platinum, have the ability when suitably heated to` maintain catalytic combusion. aty the metal surface of relatively small amounts of combustible gases such as hydrocarbons when present in air, at temperatures below that corresponding to the self-ignition temperature for the same mixtures in the absence of catalytic agencies. This property has been made use of in the so-called hot-wire filament gas detector, examples of which may be found described in the literature and in numerous patents, such as United States Patent No. 524,361 to Tilghman and United States Patent No. 1,562,243 to Moeller.

In the operation of such detectors, it has likewise been known that methane requires a higher lament temperature for combustion than do higher hydrocarbons,such as ethane, propane, butane, pentane, and indeedhydrocarbons generally having more than one carbon atom permolecule. Where hot-wire gas detectors are used inthe testing of cuttings. andmud returns during the courseof drilling a well for oil or gas, in order to determine if a gas or oil-bearing Zone has been struck, use has been made of this anomalous property of 'methane by making` a determination at` two diherentlament temperatures, e'ected by the use of two different filament voltages, one voltage high enough to combust all of the hydrocarbons present, and the other temperature somewhat lower so that all of the hydrocarbons save methane are combusted. A description of this technique is given, for example, in the article by B. Ottok Pixler appearing in the May 1946 issue of Petroleum Technology' Now there are advantages in selectively detecting those higher hydrocarbons which mayA berpresent, particularly in prospecting and exploration activities connected 'with drilling for petroleum; Indications ofsome importance as to the, nature of the petroleum deposit inA question maybergiven by knowing the relative proportions of `the thereof. Indeed, it has been standard practice,` where a formation encountered 'during drillngis subjected Vto sampling by means of a sofcalled'formation tester, to take a sample of the liquid land gaseoushydrocarbons obtained tol an analytical laboratory and determineV the hydrocarbon composition thereof.v

It would obviously be to a considerable advantage ifi at least Aan approximate idea ofthe distribution of the combust as a group. Thus, differentiation'has.. beenseveral higher hydrocaibons` present, or atleastgroups limited to methane, on the one hand, and all higher hydrocarbons on the other.

An object of the invention is to provide an apparatusA and process for the diierential detection of hydrocarbons, e particularly those in a normally gaseous state or the more volatile liquid hydrocarbons.

Another object of the invention is to provide an apparatus and process for the estimation of the relative amounts of gaseous hydrocarbons in admixture with` air.

Another object of the invention is to provide a method for differentiating between hydrocarbons higher in carbon', chain length than pentane, and those lower.

Another object of the invention is to provide a method of hydrocarbon detection of great usefulness in petroleum prospecting and drilling.

Other objects of the inventionl will become apparent4 as the description thereof proceeds.

In the drawings,

Fig. 1 is a View of an apparatus which can be used` for carrying out the principal objects of the invention.

Fig. 2 is a wiring diagram showing. the electrical.4 connections for a suitable circuit including theapparatus l of Fig. l.

Fig. 3 is a graph showing the response of ajpure platinum lament, and also the response of a platinumrhodium alloy filament to various hydrocarbons.,

Fig. 4 is a graph showing the response of a platinum-r copper alloy filament to various hydrocarbons.

Fig. 5 is a graph showing the response of a platinumt filament bearing a thin copper plating in accordance with the invention, to various hydrocarbons.

I have discovered that if, in a heated-filament gas. detector of the general type which has been described, the surface of the catalytic Wire of platinum or palladium has been caused to become impure, and the definite steps 1 are followedof'maintaining,such a lament at a highly elevatedv temperature of about 70D-800 C., or even, higher (but naturally not to the melting pointjof Vthe metal) `for a few seconds and then lowering theiilament,l temperature to the unusually low temperature vof .about 300 C., then for a periodk of time which lasts generally from at least half a minute and occasionally for severall minutes, the lament exhibits selectively' as regards the severalhydrocarbons higher than methane, and more'- over, in such a way that the hydrocarbons of highmolecular weight will combust vand therefore may be detectedt1 at relatively low filament temperatures, approximately 300 C., but the responseV of progressively lighter hydro; carbons is delayed to higher temperatures, but not as high as would be the case ifA the filament had not undergone Athe treatment just described.

The most convenient way of carrying out the differential detection following the treatment as described is, with the filament at the lower temperatureof about; 300 C. following its iiashk heating tothe highertemperature described, to raise the lament temperature slowly, which is conveniently accomplished Vbyraising the voltage across the lament, and then registering the response of the filament as the hydrocarbons which-'may be present are successively combusted in the approximate.- inverse order of molecular weights, care being taken to @accomplish the whole temperature-raising processwithin the time limit set by the duration of the peculiar selective property of the filament, which in a practical Way, is from half .a minute to three or four minutes.

The response of the filament to combustion is generally and most conveniently determined by an electrical circuit designed to respond to uctuations in the electrical resistance of the lament, since the catalytic metals used, particularly platinum, have high temperature coefficientsA of electrical resistance and combustion at theirsurface naturally-raises theA temperature of the ilament somewhat" and accordingly their resistance. A convenient and simple electrical circuit will be described below, in connection with Fig. 2 of the drawings. However, the method of detecting combustion may be accomplished by other means, among which may be the pyrometric observation of the temperature of the filament, and again, the attaching of a thermocouple to the filament at a convenient point, so that a thermoelectric response is obtained when the temperature of the filament rises in response to surface combustion. All of these may be termed means for registering the temperature of the wire or filament.

I have found, in general, that there are two ways of making the surface of the filament impure so that when the process described is carried out, hydrocarbon selectivity is the result. But it is to be understood that I do not mean to be limited to these two general ways of bringing about an impure surface state of the filament, which generally will be of a platinum or palladium base.

The first general method is to coat the filament, which may be platinum or palladium, or others of the platinum group, with a very thin coating of an adherent metal which does not have too high a vapor pressure at 800 C. and is compatible with platinum from an alloying standpoint. Nickel, silver and gold plating have been found to be effective. Copper is also suitable, and all of these may be applied as a coating by electrodeposition. Platinum group metals other than platinum or palladium are also available, such as iridium, rhodium, and ruthenium. These and other suitable metals may also be applied by chemical deposition as used, for example, in the mirror silvering art; or by dipping in the molten metal followed by etching chemically to the desired coating thickness; by sputtering in a vacuum; and by other methods which will give lan adherent coating of the desired thinness, preferably between 0.00005 and 0.0005 inch. All of these coating or allowing metals may be termed heavy metals. Heavy metals other than platinum and palladium are used.

I am aware that coating of platinum filaments has been practiced in this particular art, but such coating, generally of gold, is ordinarily carried out to inactivate a filament completely so that it can be used as a compensator filament in a Wheatstone bridge circuit while still being eX- posed to the combustible vapors. My coating, on the other hand, is much thinner than a deactivating coating, and merely gives a slight contamination of the surface of the catalytic metal, so that its catalytic activity is altered without being destroyed. Moreover, my coating process is used in connection with the particular steps which have been described, which consist of raising the filament to a surface temperature in a relatively high range, lowering it to a relatively low range, and then making the desired detections which may be carried out by gradually increasing the surface temperature of the contaminated filament.

A second general method of achieving a suitably impure filament surface is to form the filament of an alloy itself so that the filament contains a foreign metal. I have discovered that such alloys as 5% iridium and 95% platinum; 10% rhodium and 90% platinum; 20% rhodium and 80% platinum, are typical of the alloys which will operate in the manner described when subjected to the process described in yielding selective action. In general, when such an alloy is used, it should consist of about 80 to 95% of the catalytic metal, such as platinum, and the balance the foreign metal chosen. In general, a smaller rather than a larger proportion of the foreign metal is preferable, since its presence tends to reduce the temperature coecient of resistivity of the pure metal, viz., platinum. About a 95:5 Valloy is thus preferable in the general case. Here again, I am aware that such alloys, particularly of metals within the platinum group, have been used, particularly in the hotwire gas detectors in both the compensating and detector structures, but here the purpose was to obtain been used in the fashion described by me, that is, in con-` nection with the process which has been described, which results, even though for a relatively short period of time, in the phenomenon of differential selectivity of the catalytic surface.

Coming now to Figure 1, this shows a mechanical arrangement which I have found to be suitable. In the figure, 10 indicates a metal sleeve into which is fitted a base 11, which should be of insulating material and for which a thermosetting plastic, such as Bakelite is suitable, and into which in turn is embedded a support rod 12, conveniently made of brass. Two shorter support rods 13 are likewise embedded in the base 11, and these three support rods are electrically connected with a threewire cable @14, of which a portion is shown in the figure. Toward the end of support rod 12, a stirrup 15 is attached, as by soldering. This stirrup may likewise be conveniently made of brass, and furnishes a means for suspending two filaments 16 and 17 in spaced relationship to support 13. Of the two filaments, 16 is the detector filament and is prepared for differential selectivity as has been described. In this illustrative embodiment, filament 16 may be a one and one-half inch length of a :10 platinumzrhodium alloy wire which is 0.004 in diameter. Filament 17 is a filament designed to have similar electrical and mechanical properties, except that it lacks catalytic activity altogether. In this illustrative embodiment, filament 17 may consist of a one and onehalf inch length of the same platinum-rhodium alloy. It need not be especially inactivated, since as long as it is not ashed at a high temperature as has been described, it will not respond at all at 300 C. If it is desired, however, to detect propane, ethane and methane with the'same apparatus, filament 17 may be coated with a thin but complete gold plating. mis-match in the filaments as the voltage is raised, which will give a substantial zero shift which however may be cancelled out as described below. A cover 18 is provided which slips over the base 11, and has the major part of its cylindrical portion of a fine wire mesh. For clarity of illustration, cover 18 is shown removed from the filament assembly, but it will be understood that in actual use the protective cover 18 is fitted upon the filament assembly as suggested by the dotted lines in the figure. When thus assembled, the fine wire mesh of the cover 18 permits diffusion and moderate convection of air therethrough, so that the filaments 16 and 17 will be exposed to whatever atmosphere the assembly as a whole is in contact with, and yet lthe mesh prevents the disturbing action of strong drafts. A hole 19 in the end of the protective cover aids in slow convection when the filament assembly is used in a vertical position as distinguished from a horizontal position.

Fig. 2 shows a suitable wiring diagram for connecting the filament assembly of Fig. 1 into an operative electrical circuit. In Fig. 2, 16 and 17 denote the two filaments which have been described in connection with Fig. 1, and 20 and 21 are two resistances, which may be of 10 ohms each, which are connected through a potentiometer 22, conveniently of 2 ohms resistance, and thus form the other two arms of a Wheatstone bridge circuit. This bridge circuit is energized by the application of a voltage which will be described below. Any unbalance in the bridge is shown by a milliameter 23, placed across the bridge, and the voltage across the detector filament 16 is indicated by a voltmeter 24. Suitable types are an ordinary D.C. milliameter of 01 milliampere range, and a 1000-2000 ohms per volt D.C. voltmeter with a scale range of 0-5 volts, respectively. A source of direct current for energizing the bridge circuit is provided, which is most conveniently a 4.5 volt battery 25. For the purpose of switching from an ofi to a detecting and also to a dashing position, a single-pole three-way switchA 26 is provided. Variable resistors 27 and 28, conven- This will cause some seris i'ently of 3 ohms and 10 ohms respectively are provided for adjusting the current under the two conditions of ashing and detecting respectively.

The operation of the selective detector unit is as follows. It will be understood that the lament assembly of Fig. 1 is placed in some location where it is desired to detect selectively the presence of hydrocarbons in the gaseous state. Such a place may be, for example, the upper part of a glass jar in which well-cuttings have been Standing for some time; or the upper portion of the jar of a molted milk mixer of the food-homogenizer type Where some cuttings or cores recovered during well drilling operations have been `churned up with a small amount of water or drilling mud; or it might be the flow line of a drilling oil well just above the level of the issuing mud; or it might be the gases recovered from a gas trap of conventional design, as used in the art, or in particular a gas trap as described in the Wilson et al. Patent No. 2,341,169. Again, it might be placed in the exhaust line of an internal combustion engine, or in the stack of an industrial plant, or the like. Accordingly, with the lament assembly of Fig. 1 placed where it is exposed to the gases wherein hydrocarbons are desired to be detected, the switch 26 is turned to its third or flashing position, so that current flows through variable resistor 27 and detector lament 16. Resistor 27 should be adjusted to give a filament temperature of about 700 to 800 C. on filament 16, which may be recognized by a medium-dark red to medium red color. The lament is maintained at this temperature for a few seconds, such as 5 seconds, whereupon the switch is moved to its middle or detecting position, the resistor 28 having been previously adjusted by trial so that a filament temperature of not more than 300 C. results. The position of the slide on resistor 28 is gradually moved to a position of lower resistance, so that the temperature of the filaments 16 and 17 increases. The reaction of the meter 23 is noted or registered as a function of the position of resistor 28, which it will be understood can be calibrated in terms of approximate lament temperature if desired. Naturally, before undertaking such a process of detection, the balancing resistor 22 will have been adjusted so that the bridge will be balanced with no hydrocarbon gases being present. It has been found that a single adjustment of balancing resistor 22 gives suiciently good balance over the range of operating filament temperatures used in detecting the several hydrocarbons from kerosene or heavy crude oil fractions down to ethane. Another switch 29 is shown, which is `connected in tandem with switch 26, and serves to protect the meters from damage when the high dashing voltage is applied.

Fig. 3 shows some results obtained in subjecting various selective hydrocarbons to detection with and without the use of the improvements of this invention. For the results shown, an apparatus corresponding to that of Figs. 1 and 2 was used where the improvement of the invention was utilized, and the detecting filament 16, was a platinum-rhodium wire, of 0.004 diameter, of 90% platinum and rhodium.

In Fig. 3, the abscissae show the voltage of the filament in question, while the ordinates give the meter reading as obtained in the apparatus shown in Fig. 2. The family of curves at the left labeled 0.004 C.P. Pt. shows the response of an ordinary platinum hot wire to higher hydrocarbons. Curves are shown for butane, pentane, hexane, octane and nonane. The family of curves on the left shows that as the lament voltage is raised to slightly in excess of 0.6 volts, all of these hydrocarbons combust as a group, and it is impractical and indeed impossible to dilferentiate among them. On the other hand, the family of curves at the right, labeled 0.004" 10% Rh 90% Pt shows the response obtained when the platinum-rhodium alloy filament described is used. Since the temperature coeiiicient of resistance is lower than for pure platinum, the meter readings are all low- 6 er, ,b'ut this does not prevent a elear distinction to be made between pentane and lower hydrocarbons and butane and higher hydrocarbons. Thus, from Fig. 3 it is seen that when the voltage is raised to about 1.0 volt, octane and nonane are oxidized, and if the filament temperature is progressively raised to about 1.6 to 1.8 volts, hexane pentane and 'butane are oxidized in a fashion making a clear distinction between them possible.

Fig. 4 shows the invention carried out by means of a platinum-copper -alloy filament having the composition of 98% platinum and 2% copper. The diameter of the Wire was 0.004. It will be seen from the graph that if the filament voltage is raised to :slightly in excess of 1.0 volt, the hydrocarbons Afrom hexane and above are combusted, while it is necessary to increase the voltage in excess of 2.5 volts before pentane and butane are combusted or oxidized. Here `again excellent differentiation may be obtained between these two groups of hydrocarbons. n

Fig. 5 shows ythe invention as carried out with a filament consisting of pure platinum but bearing a thin coating of copper as has been described. The copper plating was a few ten-thousands of` an inch in thickness, and while it varied somewhat on the iilment it was between 0.0001 and 0.0005 thick. Here again, it will be seen that when the filament voltage was raised to approximately 0.7 volts, not only nonane but also 35 A.P.I. gravity crude oil combusted. On the other hand it was necessary to raise the filament voltage to in excess of 1.5 volts before pentane and butane were combusted. Excellent dilferentiation between the groupy of pentane and lower hydrocarbons and a group of higher hydrocarbons was obtained. l

It will be observed that the invention accomplishes its objects, and that results which are not only new but lof considerable commercial importance are obtainable. It is to be understood, therefore, .that the invention is a broad one and although specic embodiments have been described, such modifications as may be made within the broad scope of the invention and appended claims are intended to be included herein.

I claim:

1. In the testing of a plurality of gas samples for hydrocarbon content by -a method involving catalytic cornbustion at the surface of a hot wire, the steps for each sample comprising, irst activating by electrically resistance heating a temperature calibrated wire of a rst metal chosen from the group consisting of platinum and palladium and alloyed with .a minor amount of a second metal compatible with said first metal and chosen from the group consisting of rhodium, iridium, ruthenium, nickel, silver, gold and copper to a temperature of at least 700 C. but below the melting point of the wire for a few seconds, immediately lowering the temperature of the wire to `about 300 C., passing said gas into con-tact with the wire at said lower temperature, maintaining said contact while progressively increasing and noting the wire temperatures, ascertaining the temperatures of the Wire Iand noting excesses in the Wire temperature above that resulting solely from the electrical heating to determine the presence of catalytic combustion at various temperatures indicative of the presence of known components of hydrocarbon gases, the higher molecular weight hydrocarbon `components of said gas beginning to combust lat temperatures not substantially higher 'than 300 C.

2. In the successive testing of gas samples for com-- ponent hydrocarbon gases by a method involving catalytic combustion at the surface of a hot wire, the step-s. for each sample comprising, first activating by electrically resistance heating a Itemperature calibrated wire of a iirst metal chosen from a group consisting of platinum and pal-ladium, presenting a surface containing a minor amount of a second metal impurity compatible with said iirst metal from an alloying standpoint and having a.

relatively low pressure at a temperature of the order of 800 C. to a temperature of at least 700 C. but below the'melting point of the wire for a few seconds, immediately lowering the temperature of the wire to about 300 C., passing said sample into contact with the wire at said lower temperature, maintaining the contact not longer than the duration of activity of :the wire while progressively increasing and noting the calibrated wire temperatures, ascertaining the wire temperatures by known means and noting deviation in the wire temperature above the calibrated .temperature to determine the presence of catalytic combustion at various calibrated temperatures below those necessary for combustion without the wire pretreatment and indicative of the presence of known components of hydrocarbon gases.

3. In the successive testing of gas samples for component hydrocarbon gases by a method involving catalytic combustion at the surface of a hot wire, the steps for each sample comprising, first activating by electrically resistance heating a temperature calibrated wire of a rst metal chosen yfrom a group consisting of platinum and palladium and alloyed with a minor amount of a second metal impunity compatible with said rst metal from an alloying standpoint and having a relatively low vapor pressure at a `temperature of the order of 800 C. to a temperature of at least 700 C. but below the melting point of the wire for a few seconds, immediately lowering the temperature of the wire to about 300 C., passing said sample into contact with the Wire at said lower temperature, maintaining the contact not Alonger Athan the duration of activity of the wire while progressively increasing and noting the calibrated wire temperatures, asce1-taining the wire temperatures by known means and noting deviation in the wire temperature above the calibrated temperature yto determine the presence of catalytic combustion at various calibrated temperatures indicative of the presence of known components of hydro" carbon gases.

4. A method of testing a plurality of gas samples for hydrocarbon components by catalytic combustion at the surface of a hot wire, comprising the steps for each sample of tirst activating by electrically resistance heating for a few second without melting a temperature calibrated wire -to 4a ytemperature of at least 700 C., said wire composed ofthe order of of a metal from the group consisting of platinum and palladium and of the order of 5% of a metal compatible with said metal from an alloying standpoint and from the group having a relatively low vapor pressure at a temperature ofthe order of 800 C., immediately lowering the wire temperature to the order of 300 C., immediately contacting said wire and gas sample and detecting, if present, the gaseous components of higher molecular weight at temperatures of the order of 300 C., maintaining said contact for not more than the duration of the activity of the wire resulting `from said 700 C. heating while gradually raising the Wire to a temperature less than that necessary without -the aforesaid preliminary treatment for detecting the lower molecular weight components, continuously ascertaining the wire temperature, `and noting the increase in temperature above the calibrated temperature at any time during said temperature raising to indicate the presence of catalytic combustion at that calibrated temperature indicative of the presence of a known component of hydrocarbon gases.

References Cited in the tile of this patent UNITED STATES PATENTS 2,083,520 Miller June 8, 1937 2,152,439 Miller Mar. 28, 1939 2,349,250 Doan May 23, 1944 2,393,220 Jacobson et al. Jan. 15, 1946

Claims

1. IN THE TESTING OF A PLURALITY OF GAS SAMPLES FOR HYDROCARBON CONTENT BY A METHOD INVOLVING CATALYTIC COMBUSTION AT THE SURFACE OF A HOT WIRE, THE STEPS FOR EACH SAMPLE COMPRISING, FIRST ACTIVATING BY ELECTRICALLY RESISTANCE HEATING A TEMPERATURE CALIBRATED WIRE OF A FIRST METAL CHOSEN FROM THE GROUP CONSISTING OF PLATINUM AND PALLADIUM AND ALLOYED WITH A MINOR AMOUNT OF A SECOND METAL COMPATIBLE WITH SAID FIRST METAL AND CHOSEN FROM THE GROUP CONSISTING OF RHODIUM, IRIDIUM, RUTHENIUM, NICKEL, SILVER, GOLD AND COPPER TO A TEMPERATURE OF AT LEAST 700*C. BUT BELOW THE MELTING POINT OF THE WIRE FOR A FEW SECONDS, IMMEDIATELY LOWERING THE TEMPERATURE OF THE WIRE TO ABOUT 300*C., PASSING SAID GAS INTO CONTACT WITH THE WIRE AT SAID LOWER TEMPERATURE, MAINTAINING SAID CONTACT WHILE PROGRESSIVELY INCREASING AND NOTING THE WIRE TEMPERATURES, ASCERTAINING THE TEMPERATURES OF THE WIRE AND NOTING EXCESSES IN THE WIRE TEMPERATURE ABOVE THAT RESULTING SOLELY FROM THE ELECTRICAL HEATING TO DETERMINE THE PRESENCE OF CATALYTIC COMBUSTION AT VARIOUS TEMPERATURES INDICATIVE OF THE PRESENCE OF KNOW COMPONENTS OF HYDROCARBON GASES, THE HIGHER MOLECULAR WEIGHT HYDROCARBON COMPONENTS OF SAID GAS BEGINNING TO COMBUST AT TEMPERATURES NOT SUBSTANTIALLY HIGHER THAN 300*C.