US3533747A - Method for determining motor octane number of a hydrocarbon sample - Google Patents

Description

R. E; sun-IERLAND ETAL METHOD Fo Get. 13, 1970 l 3,533,747

R 'DETERMINING MOTOR ocTANE NUMBER 0F A vmfDRocmRoN SAMPLE Filed oct. 51, 1967 ATTORNEYS United States Patent O 3,533,747 METHOD FOR DETERMINING MOTOR OCTANE NUMBER OF A HYDROCARBON SAMPLE Robert Eugene Sutherland, Chicago, Ellsworth R. Fenske, Palatine, Leonard F. Pasik, Mount Prospect, and James H. McLaughlin, Villa Park, lll., assignors to Universal Oil Products Company, Des Plaines, Ill., a corporation of Delaware Filed Oct. 31, 1967, Ser. No. 679,329 Int. Cl. F2311 /00; Gtlln 25/46, 33/22 U.S. Cl. 23-230 3 Claims ABSTRACT 0F THE DISCLOSURE Method for detecting changes in a motor octane number of a gasoline fraction using an analyzer which operates under cool ame generation conditions and which produces an output signal representative of the position of the cool llame within the combustion chamber, said signal being correlatable with the motor octane number of the gasoline fraction.

BACKGROUND OF THE INVENTION The present invention relates to a method for analyzing hydrocarbon compositions. It particularly relates to an improvement in the method for analyzing hydrocarbon mixtures utilizing a stabilized cool flame generator. It specifically relates to an improvement in the method for determining motor octane number of a hydrocarbon composition.

Those skilled in the art are familiar with the phenomena of cool flame generation. Briefly, when a mixture of hydrocarbon vapor and oxygen at a composition within the explosion limit is held at conditions of pressure and temperature below the normal ignition point, partial oxidation reactions occur which generally result in t'he formation of by-products such as aldehydes, carbon monoxide, and other partially oxidized combustion products. These products are apparently produced via `a chain reaction Which also, it is believed, produces ions which then in some manner continue the reaction chain. If such a mixture of hydrocarbon vapor and oxygen is isolated and compressed and/or heated so that these chain reactions proceed at significant reaction rates, then cool flames are observed within the chamber. The cool flames are comprised of light emissions accompanied by the evolution of relatively minor amounts of heat. Implicit in this definition is the fact that the phenomena of cool flame generation is short of total combustion and short of total ignition and explosion. The work of Barush and Paine in Industrial and Engineering Chemistry, volume 43, pages 2329-2332, 1951, describes in detail the results which can be obtained from continuous or stabilized cool flames. Basically, the utilization of this phenomena in the practice of the present invention is one of correlating the distance of the cool ilames from the end of the combustion chamber With a composition parameter of the chamber to be analyzed, such as motor octane number. The essence of the present invention is the discovery of how to modify the operating conditions which are correlatable to Research Octane Number so that a correlation may be obtained with Motor Octane Number.

A more complete explanation and description of the basic apparatus and basic method for detecting composition parameters utilizing cool flames is contained in copending patent application, Ser. No. 471,670, filed July 13, 1965, now U.S. Pat. 3,463,613 issued Aug. 26, 1969. The contents of said copending application are incorporated herein by reference so that additional details thereof need rice not be presented in this application. Those skilled in the art are referred directly to the entire teaching contained in said copending application for additional and specific details as to the construction of the basic apparatus and method of operation thereof. As will be more fully developed hereinafter, the -present invention describes and claims an improvement in the basic method disclosed and claimed in said copending application.

The teachings contained in said copending application relate broadly to the use of the apparatus for detecting changes in octane number, for example, of a gasoline boiling range petroleum fraction. While the information is broadly applicable to the determination of anti-knock characteristics of a motor fuel, it has now been discovered that specific and narrow operating conditions are required before the basic apparatus and method can be commercially used for the determination of Motor Octane Number of a fuel.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide an improved method for analyzing hydrocarbon mixtures.

It is another object of this invention to provide an irnproved method for measuring Motor Octane Number of a hydrocarbon-containing mixture utilizing the cool flame phenomena.

Therefore, the present invention provides an improvement in the method for detecting changes in Research Octane Number of a hydrocarbon-containing fraction using an analyzer which operates under cool flame generation conditions, thereby producing an output signal representative of the position of said cool flame Within a combustion chamber and correlatable to the Research Octane Number of said fraction, said conditions including a relatively high oxygen partial pressure Within said chamber and including a relatively low combustion zone temperature, which improvement comprises detecting changes in Motor Octane Number of a hydrocarbon-containing fraction utilizing said analyzer by adjusting said conditions to include a relatively low oxygen partial pressure in said chamber and to include a relatively high cornbustion zone temperature, thereby producing an output signal correlatable to the Motor Octane Number of said fraction.

Another embodiment of this invention 'includes the improvement hereinabove wherein said adjusted oxygen partial pressure is from 5% to 30% less than said high partial pressure, but suilicient to maintain the generation of said cool flame and wherein said relatively high temperature is from 50 F. to 300 F. higher than said relatively low temperature.

As used herein, the terms Research Octane Number and Motor Octane Number are intended to embody the results obtained in testing the knock characteristics of motor fuels according to standard ASTM methods using the standard CFR engine. Thus, when actane number is referred to herein, it is to be interpreted as being equivalent to the same number as would be obtained on the fuel in question according to the standard ASTM test procedures. As those` skilled in the art know, the Research `Octane Number of motor fuels of octane number and below are tested by ASTM Test No. D-908; for motor fuels above 100 octane number by Test No. D-1656; and for Motor Octane Number,ASTM Test No. D-357-65, as published in ASTM Manual for Rating Motor Fuels and Motor and Research Methods, 5th Edition, 1964 and its 1965 supplement.

Furthermore, as used herein, the term output signal or signal developed by the readout means is to be construed in its meaningful sense and includes analog signals of all types, such as amplitude-modulated, phasemodulated, or frequency-modulated electrical signals or pressure signals by conventional pneumatic transmission media, as well as digital representations of the foregoing. The output signal is further intended to include simple mechanical motion or displacement of a transducer member (whether or not mechanically, electrically, or pneumatically coupled to a physical display means, such as an indicating arm, recorder pin, or digital display board) including by way of illustration, the expansion or contraction of a Bourdon tube, pressure spiral or helix, the displacement of a bellows-dapper, nozzle-diaphragm, or differential transformer-core assembly, the movement of a bimetallic temperature rseponsive element, the motion of a slider of a self-balancing potentiometer, etc. The output signal may be transmitted without physical display directly to reset a final control unit, such as a diaphragm motor valve or a sub-control loop in a cascade system.

Frequently, however, the readout device will comprise or will be coupled to an indicating or recording means, the scale or chart of which may be calibrated in terms of the desired identifying composition parameter of the hydrocarbon sample, such as octane number, initial boiling point, 90% boiling point, vapor pressure, and the like. In the practice of this invention, the location of the cool flame front is, preferably, determined by temperature sensing devices, such as a pair of axially spaced thermocouples fixed at a known distance from one end of the combustion zone in question. As will be more fully developed hereinbelow, the signal developed by the thermocouple means activates appropriate control means by adjusting a combustion zone parameter or condition so as to immobilize the cool flame front at a position generally between the two spaced thermocouples. A most satisfactory combustion condition-which can be used as the control means is the combustion zone pressure.

Test samples which can be continuously analyzed by this invention include those normally gaseous and normally liquid hydrocarbon-containing mixtures comprising either at least one hydrocarbon containing from 1 to about 22 carbon atoms per molecule in admixture with one or more non-hydrocarbons, such as hydrogen, nitrogen, carbon monoxide, carbon dioxide, water, and hydrogen sulfide or at least two different hydrocarbons containing from 1 to about 22 carbon atoms per molecule. The upper limit on carbon number is fixed generally by the preferred operation procedure that the sample (and the reference sample) be vaporized in an air stream under combustion conditions without undergoing any substantial thermal decomposition prior to the oxidation thereof. Therefore, in the context of the present invention, the term hydrocarbon composition is intended to embody all forms of hydrocarbon mixtures in which hydrocarbons predominate, but which may also contain significant amounts of non-hydrocarbon materials and, in particular, may contain such items as tetraethyl lead, tetramethyl lead, and other known anti-knock compounds for use in motor fuel compositions. In the preferred and practical embodiment of this invention, for measurement of Motor Octane Number, the feedstock of test sample or process stream of unknown octane number chargeable to the apparatus of the present invention include those within the gasoline boiling range including such process streams as straight-run gasoline, cracked gasoline, motor alkylate, catalytically reformed gasoline, thermally reformed gasoline, hydrocracker gasoline, etc.

The oxidizing agent utilized in the apparatus of the present invention is preferably an oxygen-containing gas, such as air, substantially pure oxygen, etc. or it may be a synthetic blend of oxygen with an inert or equilibrium effecting diluent, such as nitrogen, carbon dioxide, or steam.

The generation of the stabilized cool flame is effected under combustion conditions generally including superatmospheric pressure and elevated temperature; although,

in some cases, it may be desirable to use atmospheric pressure or sub-atmospheric pressure. For example, the pressure may be in the range from about l2 p.s.i.a. to about p.s.i.a., with a maximum flame front temperature in the range of 600 F. to 1000L7 F. For measuring the composition of a gasoline boiling range fraction it is preferable to employ pressures in the range from 16 p.s.i.a. to 65 p.s.i.a., more preferably, in the range from 16 p.s.i.a. to 50 p.s.i.a. together with induction zone temperature from 550 F. to 850 F. Control of induction zone temperature can be effected by the amount of preheat imparted to the incoming sample stream, including reference sample and air streams and also by supplying heat from an external source to the combustion zones proper. In any case, the permissibel limits within which temperature and pressure may be individually varied without departure from stable operation, even outside of the specific operational limits referred to herein, can be determined by simple experiment for a particular type and quantity of test sample.

As previously mentioned, the detection of the position within the combustion chamber for the test sample and for the reference sample is preferably effected by temperature responsive thermoelectrical means; although, other equivalent means can be used. The thermocouple sensing device may be placed within the combustion chambers as discussed hereinabove or outside of the combustion chamber and may be either fixed or may be movable in such a manner to completely and substantially traverse the lengthwise direction of the combustion chamber in order to locate the position of the stabilized cool flame within each combustion chamber.

The output signal from the thermocouple sensing means is fed through signal means to suitable control means such as a motor activated control valve for regulating, for example, the pressure within the combustion zone. Generally, the output signal from the thermocouple sensing means is lead to a readout device, such as a strip chart or x-y recorder. Preferably, the thermocouple sensing device comprises a pair of axially spaced thermocouple leads which are inserted into thin-walled thermal type pencil wells and may be constructed of any materials known to those skilled in the art, such as for example, iron-constantan. The lead wires from the thermowells are connected to a suitable differential temperature controller. Such controller may be a conventional self-balancing potentiometer in combination with pneumatic control means. A suitable input span for each controller may be from -5 to |5 millivolts and the output signal thereof transmitted may be a conventional 3-15 p.s.i.a. air signal. This control signal is used, for example, to reset the set point on a back pressure controller or can be used to directly control the pressure within the respective combustion zone. The controlled pressure is passed into a standard DP (differential pressure) cell. The output signal from the DP cell iS correlated with a composition parameter, such as Motor Octane Number, in the practice of the preferred embodiment of the invention.

The invention may be more fully understood with reference to the accompanying drawing which is a schematic representation of apparatus for practicing one embodiment of the invention,

DESCRIPTION OF THE DRAWING With reference to the attached drawing, the analyzer comprises, in combination, combustion chamber 14 contained in outer casing or canister 13 having a closed lower end and an open upper end. Canister 13 is provided with a fiuid heating medium inlet conduit 19 and a heating medium outlet conduit 24. Other means may be used to control the temperature within the combustion chamber, such as a confined molten salt bath which is either internally or externally heated. The upper end of canister 13 is enclosed by suitable flange means and gasket means, not shown, those skilled in the art being familiar with appropriate ways of closing a hollow canister of this sort. lf

desired, the exterior of canister 13 may be encased in one or more layers of insulation, again not shown.

Canister 13 contains an elongate thin-wall combustion tube 14 having at its lower extremity a burner nozzle assembly, or other mixing device not shown. Appropriate conduits for the introduction of hydrocarbons to be analyzed and oxygen-containing gas are appropriately shown as conduits and 11, respectively, with the proper fuelair ratio together with added nitrogen from line 29 being injected into combustion chamber 14 via inlet conduit 12. Specific details as to the constrution of the apparatus may be found in said copending application, supra.

Inert gas, such as nitrogen, is introduced into the system via line 29 in an amount suflicient to adjust the oxygen partial pressure within combustion chamber 14.'V In the preferred embodiment of this invention, suicient nitrogen is introduced to reduce the oxygen partial pressure from 5% to 30% of the oxygen partialpressure utilized during analysis for Research Octane Number.

Vent gases comprising the partial oxidation products of the stabilized cool flame are removed from combustion tube 14 through line 15 which includes a back pressure regulator or controller 17. Appropriate pressure indicating device, such as a pressure recorder, is indicated at 18.

The front of the stabilized cool flame is relatively narrow, well defined traverse section, spaced a predetermined distance above the inlet assembly. In the present embodiment, the detection of the physical position of the flame is effected by temperature responsive thermoelectric means. As shown with reference to the drawing, the llame position sensing means comprises a pair of axially spaced thermocouples which are inserted into thin-walled, pencil type thermowells, such thermowells preferably having a low heat capacity coupled with a relatively high thermal conductivity in the longitudinal direction. Lead wires 25 and 26 are connected to the inlet terminals of a suitable dilerential temperature of controller 16. The output signal from controller 16. may be transmitted through line 28 to reset the set point of back pressure controller 17 or may directly operate the `pressure control valve.

Additionally, it is to be noted that the heating lluid inlet conduit 19 also passes through heat exchange means 20 having suitable conduit for the passage therethrough of another heating fluid, such -as hot oil, via conduit 21. The amount of heating fluid, eg., molten salt or molten metal (or hot oil), passing through heat exchanger 20 is controlled by control valve 22 which is reset through lead 27 by temperature recorder-controller (TRC) 23 (or simply a temperature controller) which is placed in outlet conduit 24 for the measurement of the temperature of the heating fluid leaving canister 13.

In the operation of the inventive apparatus, when the flame front is exactly positioned between the thermocouples placed in the combustion zone both couples will be about the same temperature, and the voltage appearing at the input of differential temperature of controller 16 will be approximately zero. However, 'another equally satisfactory manner of operation is to operate the apparatus with a small net voltagel dilference,E either positive or negative, corresponding to a temperature differential in the order of 10 F. to 40 F. This means that the ame vfront is then slightly asymmetrical with respect to the front into a fixed predetermined location, the degree of change necessary to reposition the flame front being directly correlatable with the desired composition parameter of the sample charged into the system. For ease of operation, the output from temperature controller 16 is connected by appropriate lead, not shown, to for example, a temperature recorder, not shown, wherein a visual indication of the flame front location may be recorded.

In the practice of the invention utilizing the yapparatus shown in the drawing, a gasoline fraction is introduced via line 10, admixed with air from line 11, and the mixture is introduced together with nitrogen from line 29 into the system via line 12. Typically, combustion chamber 14 is a one-inch diameter tube which is maintained under a pressure from 16 to 50 p.s.i.a. utilizing pressure controller 17, more fully discussed hereinafter. The temperature of the induction zone is about 775 F. (in some cases a higher or lower induction zone temperature in the range of 720-790 F. may be desirable), and is maintained thereat by the introduction of hot molten salt via line 19. In the region of the flame front the temperature climbs rapidly peaking at about 900 F. and then falling off rapidly to about 750 F., although, the level of temperature is limited by the surrounding bath temperature. When the llame front is stabilized, the thermocouple sensing devices will read approximately zero as indicated by the net voltage appearing at the input of differential temperature of controller 16. Temperature controller 16 activates pressure controller 17 so as to move the flame front to a predetermined location within combustion chamber 14. In other words, an increase in pressure will cause the flame front to recede towards the inlet end of the combustion chamber and a decrease in pressure will cause the 4llame front to advance away from the inlet.

Therefore, if the hydrocarbon composition changes in a manner such that the flame front attempts to move back toward the inlet, the thermocouples will reect a temperature change and the differential temperature controller 16 will act through controller 17 to decrease combustion pressure until the front is restored to its predetermined original position. Conversely, if the hydrocarbon composition changes in a manner such that the front attempts to move away from the nozzle, controller 16 activates pressure controller 17 to increase combustion pressure until the front is restored to its original position. In any event, the changing combustion pressure required to immobilize the llame front at its predetermined location, following a composition change, is a correlatable function with such composition change.

Therefore, in essence, the present invention is procedurally operated by first determining the proper calibration of the analyzer for Research Octane Number of a desired gasoline boiling range fraction and then adjusting the operating conditions within the analyzer to provide a direct correlation of the output signal at these new conditions for Motor Octane Number. Of course, the reverse procedure could also be used. In other words, the analyzer could be calibrated for the conditions of determining Motor Octane Number and then the operating conditions could be adjusted by lowering the combustion zone temperature and raising the oxygen partial pressure in order to provide a correlation for Research Octone Number.

The following example will illustrate one embodiment of the present invention.

EXAMPLE A hydrocarbon fraction comprising a mixture of C4 alkylate and catalytic reformate (blended to calculate Motor Octane Number) was passed into the inventive system using apparatus as shown in the attached drawing. Various combustion zone conditions were used to demonstrate the inventive method. The results are tabulated in the following table:

(2) therein partially oxidizing the hydrocarbon constituents of said fraction under conditions to generate in said combustion chamber a stabilized cool flame characterized by a relatively narrow well-defined flame front spaced from said one end;

(3) sensing the position of said flame front relative to said one end and developing therefrom a control signal;

(4) varying the pressure of said combustion zone reltrogen r.at.e 1f ally-L50() ,CP/mmm@ l0 sponsive to said control signal in a manner to imame posmon deslred-ZLS from Inlet mobilize said flame front relative t d d Combustion zone pressure-16-30 p.s.i.a. o sal .one en 1 se@ also FIG 1 or said cependant: appncfrrron regardless Offpang 11? COmPQSlUOn 0f sald hydro- 2 4.9 pounds if per pound of feL carbon-containmg fraction;

Heating Nitro- Reactor Motor Ruil fluid gen gas pressure, Octane Number Dcscnption T., F. bleed p.s.i.a. Number' 19.45 84.0 1 RON conditions 670 No gl'gg gig 19. 85.9 26.10 84.0 2 RON conditions plus N21 1ec 1. 070 Ycs. i3 27.50 85.9 21.0 84.0 3 Increase T plus N2 bleed 720 Yes....-{ gig 21.4 85.9 19.5 84.0 4 Further increase T plus N 2 bleed.. 750 Yes.....{ 20.5 85.9 19.4 34.0 5 do 775 Yes.-.-.{ j 20.8 85.0

The above data indicates that Run 1 and Run 2 did not 3; (5) sensing said combustion pressure and developing correlate at all with Motor Octane Number. Runs 3 and 4 therefrom an output signal which is correlated with were generally better, and Run 5 was an excellent correthe research octane number of said fraction; lation providing a significant change in reactor pressure (6) thereafter introducing a stream of inert gas to for each change in Motor Octane Number. In addition, said combustion chamber in suicient amount to the reactor pressure obtained was substantially the same reduce the oxygen partial pressure therein to from as that obtained from the Research Octane Number 5% to 30% less than said high partial pressure, and (RON) run thereby permitting the use of the same readincreasing said combustion zone temperature to from out chart for both types of analysis. It should be noted 50 F. to 300 F. higher than said relatively low that the use of nitrogen bleed did provide a good corretemperature; lation at the bath temperature used for Research Octane (7) repeating steps (1) through (5) inclusive, as modi- Number determination. In short, for determining Motor lied by step (6); and Octane Number, inert gas bleed (i.e. decreased O2 partial (8) sensing saidy combustion pressure and developing pressure) plus increased combustion chamber temperature therefrom an output signal which is correlated with as compared to conditions for Research Octane Number motor octane number of said fraction. are required features of the present invention. 2. Method according to claim 1 wherein said increased PREFERRED EMBODIMENT temperature of step (6) is in the range of 720-790 F.

3. Method according to claim 1 wherein said inert stream comprises nitrogen.

References Cited UNITED STATES PATENTS 2,603,085 7/1962 Cannon. 3,295,585 1/1967 Kovach et al. 3,463,613 8/1969 Fenske et al. 23-230 MORRIS O. WOLK, Primary Examiner R. E. SERWIN, Assistant Examiner U.S. Cl. X.R.

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