US2538710A

US2538710A - Analytical method and apparatus

Info

Publication number: US2538710A
Application number: US667789A
Authority: US
Inventors: Dan E Smith
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1946-05-07
Filing date: 1946-05-07
Publication date: 1951-01-16
Anticipated expiration: 1968-01-16

Description

Jan. 16, 1951 E, s rr 2,538,710

ANALYTICAL METHOD AND APPARATUS Filed May '7, 1946 5 Sheets-Sheet 1 TO VACUUM PUMP SPHERICAL JOINT 310 I COLUMN MANOMETERS POROUS CERAMIC THIMBLE IN VEN TOR.

DAN E. SMITH ATTORNEYS TO AIRLINE Jan. 16, 1951 Filed May 7, 1946 D. E. SMITH 2,538,710

ANALYTICAL METHOD AND APPARATUS Sheets-Sheet 2 PRESSURE MM. H G

FIXED GASES. MOI /o H V FIXE D GAS ES CH4 0 I0 4o so I00 COMPOSITION vs. PRESSURE OF FIXED GASES-METHANE MIXTS. AT -32lF FIG. 3

700 I I I I I I I000 soo- -soo U -7oo I 2 c m, MOL v IN CH4 c m; l l I l l l 0 20 30 4.0 50 60 70 so 90 I00 COMPOSITION OF METHANE-ETHANE MIXT. VS. PRESSURE OF RESIDUE AFTER PUMPING AT 32lF FIG. 4

' INVENTOR. DAN E. SMITH ATTORNEYS Jan. 16, 1951 o. E. SMlTH 2,538,710

ANALYTICAL METHOD AND APPARATUS Filed May 7, 1946 5 Sheets-Sheet 4 50 A CaHmNOL f/o lN ClaHe 1- l-CqHao I 200 0 2 4 6 8 I0 l2 I4 l6 I8 20 PRESSURES OF BINARY MIXTURES AT 32F 280 u- I I l I l l I I I I 0 8 T 240- z LU E5 :20 m m w E 80 PRESS URE, a m. HG AT 238! O l I 1 200 300 400 500 600 700 800 900 I000 IIOO I200 I300 PRESSURES OF ETHANE"PROPANE"ISOBUTANE MIXTG. AT '-|O9F AND 38F FIG. 8

INVENTOR. DAN E. SMITH AT TORNEYS Filed May 7,

D. E. SMITH ANALYTICAL METHOD AND APPARATUS 5 Sheets-Sheet 5 PRESSURE MM He AT 5 I o o PRE SSURE, MM. HG AT 32F 1 PRESSURE MM. H6

900 I000 HOO FIG. 9

I200 PRESSURES OF CHe I-C4HIO-N-C4HIO MIXTS.

I300 I400 AT -38F 8\ 32F MOL /o H2 IN H2 0 IO 4O 5O 6O 7O I00 COMPOSITION VS. PRESSURE OF HYDROGEN METHANE MIXTURES AT -32l F INVENTOR. DAN E. SMITH ATTORNEYS Patented Jan. 16, 1951 ANALYTICAL METHOD AND APPARATUS Dan E. Smith, Bartlesville, kla., assignor to Phillips Petroleum Company, a corporation of Delaware Application May 7, 1946, Serial No. 667 ,7 89

9 Claims.

analysis of normally gaseous hydrocarbon mixtures. By vaporizing liquid nitrogen at atmospheric temperature it is possible to effect a complete condensation of all of the hydrocarbons, including even methane. Utilizing this feature fractional distillation columns have been built wherein any hydrocarbon sample maybe condensed to a liquid, vaporizing liquid nitrogen used to obtain a desired reflux, and hydrocarbons distilled from the mixture in substantially pure fractions and recovered as gases. In some instances, however, particularly when analyzing a hydrocarbon-containing mixture from some commercial process, or from a gas well in any one of various localities, it has been found that the mixtures contained materials other than hydrocarbons, such as nitrogen, oxygen, mixtures of nitrogenand oxygen in various proportions,

and hydrogen. These non-hydrocarbon gases are recovered as mixtures with methane during the course of such fractional distillation.

In ana yzing mixtures which contain only normally gaseous hydrocarbons it is diilicult to make accurate determinations of hydrocarbons which are present in the mixture in small amounts, such as amounts not exceeding about 10 per cent and especially in amounts not exceeding about 5 per cent. In connection with the analysis of products of various conversion processes, it is often desired to know with considerable accuracy the amounts of materials produced, and the characteristics of most apparatus used for such fractional distillations are generally such that a sharp separation is either not readily obtained with the desired accuracy or is obtained on y with the consumption of a considerable amount of time. In the event some non-hydrocarbon gas, such as has just been mentioned, is present rapid methods of determining the amount of such a non-hydrocarbon component have not given satisfactorily accurate results.

I have now found that rapid and accurate analysis of such mixtures may be obtained by the use of the apparatus to be more completely disclosed hereinafter. This'apparatus is used to measure the pressure of a mixture at one or more standard temperatures which can be readily obtained and applied with a high degree of accuracy. This apparatus is usually used in conjunction with any conventional equipment for the low-temperature fractional distillation of hydrocarbon-containing mixtures.

An object of this invention is to analyze hydrocarbon-containing mixtures.

A further object of this invention is to analyze normally gaseous hydrocarbon-containing mixtures.

Still another object of this invention is to provide an apparatus for the analysis of hydrocarbon-containing mixtures.

Other objects and advantages of this invention will become apparent, to one skilled in the art, from the accompanying disclosure and discussion.

Various process modifications of my invention, and a preferred apparatus embodiment of my invention, will now be more specifically described in connection with the accompanying drawings. Figure 1 shows diagrammatically a conventional arrangement of apparatus which is used for the low temperature fractional distillation of hydrocarbon-containing mixtures. Figure 2 illustrates diagrammatically a preferred modification of the ap aratus whichis one embodiment of my invention. Figures 3 to 10, inclusive, are graphs which can be used in conjunction with the apparatus illustrated to make an analysis of hydrocarbon-containing mixtures in accordance with various specific embodiments of my invention. These will be more fully discussed in connection with examples illustrating the practice of my invention.

A preferred manner of practicing the method embodiments of my invention involves the trace tional distillation of a hydrocarbon-containing mixture in the apparatus illustrated in Figure 1 and subsequent analysis in the apparatus of Figure 2 of small portions of the distillate so produced. It is preferrred that the mixtures treated in the apparatus of Figure 2 be substantially free from olefin hydrocarbons and that the hydrocarbon content comprise essentially paraflin hydrocarbons. However, it is to be understood that olefin-containing mixtures may be introduced into the apparatus of Figure 1, olefins removed quantitatively from distillate fractions by means of Orsat absorption apparatus, not shown, as is well known to those skilled in the art, and fractions comprising unabsorbed residual hydrocarbons analyzed in accordance with the present invention. By this modification suitable analysis of olefin-containing mixturesis obtained.

Referring now to Figure 1, a conventional arrangement of apparatus for efiecting low-temperature fractional distillation of hydrocarboncontaining mixtures is shown. This comprises a fractional distillation column H, such as is well known to the art, a kettle ID, a sample inlet line I2, and means l3 at the top for cooling and condensing vapors passing upwardly through the column. This cooling and condensation is effected by indirect heat exchange with vaporizing liquid nitrogen, the liquid nitrogen being introduced through line Hi. The actual temperature is usually determined by means of a thermocouple, but for simplicity is diagrammatically illustrated by thermometer l5. The lowest boiling fraction is removed as a gas through line l and control valve I1 and collected as a gas in one or more receivers 2i and 22. The pressure in the distillation column is indicated by a mercury-filled manometer 23 and the pressure in the receiver into which the gas sample is being passed is indicated by mercury-filled manometer 24. All of the sample receivers and manometers and the distillation column are interconnected by means of a manifold l8. Before an anlysis is started the entire apparatus, including all of the receivers, is evacuated by means of a vacuum pump, not shown, through line 25. Once a sample has been collected in one of the receivers 2| or 22, it can be passed to the apparatus of Figure 2 through

valves

26 and 21 and line 28. Line 28 is connected to line 43 of the apparatus of Figure 2 by any suitable means, such as a spherical joint 30. If desired, of course, the apparatus of Figures 1 and 2 may be permanently joined together. A Toepler pump 3| may be used to effect a suitable mixing of a sample collected in any receiver when the composition of the sample has changed during the period of its collection. It may also be used, in a known manner, to aid in the transfer of a sample from one container to another. As will be readily appreciated, the capacity of each receiver is known and simple calculations based upon the known capacity of any receiver and the pressure indicated by manometer 24 will yield the size of the sample collected in the receiver.

Bulb H), which is the kettle of fractional distillation column II, is evacuated and immersed in a suitable container of liquid nitrogen. A sample to be analyzed is introduced through line l2 and condansed in bulb Ill. If the sample is free from gases which are non-condensible at the temperature of vaporizing liquid nitrogen, such as nitrogen, air, oxygen, or hydrogen, valve i1 is closed during the collection of the sample. However, if such a gas is present it is ofen desirable to cool condenser l3 by introducing liquid nitrogen through line I4 to a temperature sufliciently low to provide adequate reflux of liquid hydrocarbon in the distillation column and to maintain the pressure in the column below atmospheric by passing gases through control valve I! to one of the receivers. In order to insure satisfactory operation, it is desirable to have the sample which is introduced through line I2 free from hydrogen sulfide, water and carbon dioxide. This can be accomplished by simple purification equipment, not shown.

When a sufficient amount of sample has been collected, the valve in line i2 is closed, valve i1 is closed, condenser i3 is cooled, and the kettle is warmed suificiently to allow vaporization of material therefrom to take place at a relatively slow rate. The distillation column is then operated under conditions of total reflux until the temperature indicated by means i5 no longer continues to drop. This indicates that a condition of equilibrium has been reached. The lowest-boiling component is then distilled into one of the receivers at a rate which experience indicates results in efiicient fractional distillation. This lowest-boiling component is distilled until the distillation temperature has increased slightly, but no more than about 1 F. above the boiling point of the material being distilled at the pressure indicated by manometer 23. Such a procedure is well known to those skilled in the art.

When th temperature indicated by means 15 has risen to about 1 F. above the boiling point of the component being distilled, the receiver into which the gas is being passed is out off from the system and a narrow fraction or out between this component and the next higher-boiling component is collected in a smaller receiver, usually one having a capacity of about ml. The overhead iraction is collected in this smaller receiver until the next plateau, or boiling point of the next higher component, has been definitely reached and a sufiicient portion of this higher boiling component has been passed into the small receiver to insure that the material present in distillation column ii is completely free from the lower boiling component. This will generally be the situation when no more than about 20 ml. (gaseous) of a higher boiling component has been passed into the small receiver.

In the event that there is not present a sufficient quantity of the lowest boiling component to efiect adequate collection of a portion of this component by itself, the entire fraction from the start to the plateau of the second component is collected in a small receiver. In either case the material collected in the small receiver is that material which is more accurately analyzed in the apparatus of my invention by the method of my invention. It is to be understood, of course, that during this distillation procedure adequate records are kept of the distillation time, distillation temperature, and pressure, the receiver or rec ivers being used, and the pressures indicated by manometer 24 during the collection of the samples in one or the other of the receivers. Keeping of such records and their subsequent interpretation to give compositions of the materials being distilled is, of course, common to those skilled in the art.

Succeeding components of the sample initially introduced into kettle ID are collected in the manner indicated, with the major portions of the components being collected in large receivers and the transition portions, from one component to the next higher-boiling component, being collected in individual small receivers.

In collecting samples for analyzing in the apparatus of Figure 2 the gas which is present in

manometers

23 and 24 above the mercury level is always included. It is either transferred directly into the apparatus of Figure 2 along with the rest of the sample or, in case only a part of the entire fraction is taken for analysis, suitable mixin to secure uniformity of the sample is accomplished with the aid of Toepler pump 3|, in a manner such as is well known to those skilled in the art.

The small fraction which has been collected in a small receiver is given a, more accurate analysis in the apparatus of Figure 2. This apparatus comprises a sample bulb 40 having a small, accurately known, volume as will be more thoroughly discussed hereinafter. This is joined to a manifold 4| through a spherical joint 42. This manifold comprises two

arms

43 and 44. Arm 43 is connected through valve 45 to the female portion of spherical joint 30. Arm 44 is connected through a spherical joint 46 to one arm of a differential manometer 41. The other arm of differential manometer 41 is connected to a pressureindicating manometer 48, to a source of superatmospheric pressure such as air line 49, and to a source of subatmospheric pressure such as vacuum line 5|. In between manometer 48 and these pressure sources is preferably a surge volume 52. This volume has a capacity such that sudden changes of pressure in the line on the side of the surge volume away from the rest of the apparatus will not cause sudden changes of pressure in

manometers

41 and 48. With the equipment discussed hereinafter, a size of about 500 ml. is satisfactory. Individual valves may be used on

lines

49 and 5|, or a single, two-way valve 53 may be used. The various individual pieces of equipment may be permanently joined together or may be joined together by suitable temporary joints such as

spherical joints

42, 46, 55, 56, and 51. The temperature of bulb 40 may be maintained at any desired level by immersing it in a suitable constant-temperature bath contained in vessel 59.

It is preferred that'each arm of differential manometer 41 be supplied with a check valve 60. Even with experienced operators it is not -uncommon for sudden changes of pressure to occur which will tend to force the mercury, or other liquid contained in differential manometer 41, rapidly up one arm or the other. If this liquid passes out of the manometer, either into bulb 40 or into manometer 46, loss of the sample which has been collected in bulb 40 may result. A suitable check valve, illustrated in Figure 2A, consists very simply of a long porous thimble having a small diameter, the edge of the open end of which is sealed to the inside wall of the arm of the manometer. This thimble should be made so that it is sufficiently porous for gas to pass through it readily, but with pores sufliciently small that themercury, or other liquid, cannot be readily forced through them. It is preferably made of a material not readily wetted by the liquid. Such porous tubes, made of glass or ceramic material, are readily available and are quite satisfactory for use in the manner illustrated as check valves when mercury is the liquid employed in manometer 41.

It is preferred that bulbs having three different capacities be used as bulb 40. The smallest should have a capacity of 2.0 ml.i0.2 ml. The intermediate bulb should have a capacity of 5.0 ml.i0.5 ml. The largest bulb should have a capacity of 25.0 ml.' .5 ml. When the rest of the apparatus is permanently joined together his preferred that bulb 40 be joined by means of a temporary joint such as spherical joint 42. I have found that spherical joints are particularly satis- 6 factory for this purpose and that bulbs having a suitable capacity can be readily permanently joined to the female portion of commercially available spherical joints with satisfactory seals between each joint andthe male portion which is attached to manifold 4|. With the capacity for each of the .bulbs as indicated, up to joint 42, and with, the capacity for manifold 4| above joint 42, and between the upper level of the liquid in differential manometer 41 and valve 45, not

greater than about 1 ml. satisfactory and accu- Example I The followin procedure is followed in using the apparatus of Figures 1 and 2 to determine the amount of nitrogen, the amount of air, or the amount of nitrogen and air, contained in a mixture of such a component with methane. A sample contained in receiver 22, and having a uniform composition throughout, is passed into receiver 2|, which has a capacity of about 150 ml., until the pressure of the sample in receiver 2| is 500:2 mm. mercury. Bulb 40, having a capacity of 25 ml. (1. e., about /6 the volume of receiver 2|), is completely evacuated, as is the rest of the apparatus between bulb 40 and receiver 2|. Bulb 40 is then immersed in boiling liquid nitrogen (temperature about 321 F.) and the connection is established between receiver 2| and bulb 49. The vaporizing liquid nitrogen extends up to just below spherical joint 42 and the rest of the apparatus is maintained at room temperature, usually about 65 to about F. The pressure of the apparatus on the left hand side of Figure 2 is so adjusted that there is no pressure differential indicated between the two arms of differential manometer 41. The pressure within bulb 40 is then indicated by manometer 48. This pressure is recorded and is used in calculating the composition of the portion.

Referring now to Figure 3, two curves are shown. Curve 63 shows the relationship between the pressure within bulb 40, under the conditions just recited, when the mixture therein and in receiver 2| comprises nitrogen and methane. Curve 64 shows a similar relationship when the mixture comprises air (79 per cent nitrogen, 21 per cent oxygen) and methane. Since this method of analysis includes not only the use of bulb 40 but also the use of receiver 2| and the manifold in between these two units, these curves are somewhat characteristic of the specific apparatus used and must be determined by known mixtures for the specific apparatus with which they are to be used. If it is known that the mixture is composed solely of nitrogen and methane the previously recorded pressure indicates directly, when used together with curve 63, the composition of the mixture. Likewise, if it is known that this mixture comprises air and methane, the indicated pressure, together with curve 64, can be used directly to determine the composition of the mixture. However, when the mixture comprises nitrogen, oxygen and methane (i. e., nitrogen plus air plus methane), a further determination must be made. A further portion of the mixture is analyzed by a conventional Orsat apparatus, not shown, to obtain a determination of its oxygen content. The recorded pressure of bulb 40 and curve 63 are used to obtain an approximation of the nitrogen content of the mixture. The oxygen content obtained from the Orsat analysis is then added to this approximate nitrogen content and the percentage of oxygen in the nitrogen-oxygen portion of the mixture thereby determined. This oxygen percentage is then interpolated, on the line corresponding to the recorded pressure, between

curves

63 and 64 in proportion to the normal content of oxygen in the nitrogen-oxygen mixture, that is, ordinary air (21 per cent). From the resulting point between these two curves the amount of total fixed gases is readily determined from the scale at the bottom. 7

To give a concrete illustration of such an analysis of a nitrogen-air-methane mixture, assume that the pressureindicated by manometer 48 is 200 mm. mercury and that the oxygen content of the total mixture is mol per cent, as determined by a simple Orsat analysis of a portion of the original sample. Using the indicated pressure and curve 63, it is found that the approximate amount of nitrogen is 33 mol per cent. This numerical value is added to the numerical value for the oxygen, giving an approximate composition for the two of 38 mol per cent. The value for the oxygen content divided by this total gives 13.2 mol per cent of oxygen in the fraction which represents the fixed gases alone. tween curves 63 and 64 on the line corresponding to 00 mm. mercury pressure the point corresponding to 13.2 divided by 21 corresponds to 35 mol per cent of fixed gases (nitrogen plus oxygen) in the total mixture.

As will be appreciated, the ratio between the receiver 2| and bulb 40 may be otherwise than about 6:1; it is preferred that the ratio be between about 4:1 and about 10:1 to about 100:1 or more. The higher limit of this ratio is primarily dependent upon the fixed gas (nitrogen) content of the sample and can be quite high with low proportions of such a fixed gas.

Example II The following procedure is used to determine the amount of methane and ethane in a methane- Interpolating beand valve 45 is opened so that the released gases are removed by the vacuum pump for two minutes more. Valve 45 is again closed,- bulb 40 is warmedto the temperature or melting ice and the residual pressure of the mixture is noted and recorded.

This residual pressure, together with the initial pressure of the mixture at the temperature of melting ice, is used with curve 66 of Figure 4 to determine the amount of ethane present in the original mixture. Thus if the initial pressure was 990 mm., the residual pressure after the preceding manipulation was 325 mm., the corrected residual pressure will be 325 times or 328 mm.

independent of the size of the apparatus so long ethane fraction. A bulb 40 is used having a capacity of ml. Bulb 40 is immersed in boiling liquid nitrogen and, from the appropriate receiver of Figure 1 containing a homogeneous methane-ethane mixture, about to gaseous ml. (normal temperature and pressure) is condensed therein. Stop cook is closed and bulb I0 is warmed to the temperature of melting ice (32 F.). It is desired that under these conditions the pressure of the material contained in bulb 40, as read on manometer 48, should be 1000 i 10 mm. of mercury. In the event that a sample of material has been withdrawn into bulb 40 which is sufliciently large to produce a greater pressure the pressure is relieved through valve 45 until the pressure is within the desired range. This pressure is then recorded. Bulb 40 is again immersed in boiling liquid nitrogen, valve 45 is opened, so that the pressure within the system of Figure 2 may be reduced by means of a vacuum pump operating through line 25. The mixture frozen in bulb 40 by the boiling liquid nitrogen is subjected to the vacuum from this vacuum pump for five minutes. Valve 45 is then closed, bulb 40 warmed again to the temperature of melting ice to release dissolved methane. Bulb 40 is then again cooled with liquid nitrogen as it is within the limitations previously discussed herein.

The preceding procedures may be ,modified somewhat to determine the amount of ethane and heavier material in original samples which contain not more than about 25 per cent of such material. This modified procedure requires no preliminary fractional distillation and is therefore quite rapid, but results in somewhat less accurate analysis. Such a less accurate analysis, however, is often suitable for routine control purposes.

A bulb 40 is used having a volume of 25 ml. About 100 ml. (normal temperature and pressure) of the original gaseous sample is condensed in the bulb. The uncondensed gas is pumped away until the total pressure is not more than 1 mm. of mercury, the material in bulb 40 being at the temperature of boiling liquid nitrogen. The sample is then warmed to approximately the temperature of melting ice, then cooled with liquid nitrogen and uncondensed gases are pumped away for two minutes. The residual pressure is then measured at the temperature of melting ice, and a correction is made for residual methane. Such a correction is 11- lustrated as follows. Assuming the original size of the sample at room temperature to be 102 ml. and the residual pressure on bulb 40 to be 205 mm. of mercury pressure at 32 F., a corrected residual pressure is determined from Figure 4. This is done by determining from curve 86 and the residual pressure the indicated per cent of ethane and assigning a corrected residual pressure of 10 mm. mercury for each per cent of ethane. Thus an actual residual pressure of 205 mm. mercury corresponds to a corrected residual pressure of 193 mm. mercury. Since the volume of the bulb is 25 ml., the corrected volume of the residual hydrocarbon material at 32 F. is

1 25 times or 6.3 ml.

' From this corrected volume the corresponding tion free from fixed gases and. containing, not

more than per cent methane, and for mixtures consisting of ethane and propane containing any proportion of these two constituents.

A bulb 40 is used having a capacity of 2 ml.

Using liquid nitrogen, about 45 to about 55 ml. of the gaseous sample is condensed. The sample should be free, or freed, from air. The bulb is then warmed to the temperature of freely subliming solid carbon dioxide (about 109 F.) This can be readily accomplished by immersing the bulb in a snow of this material. The pressure indicated by manometer 48, when difierentialmanometer 41 is balanced, is then used in connection with curve 61 of Figure 5 when the amount of methane in ethane is to be determined, or in connection with curve 68 of Figure 5 when the amount of ethane in the mixture of ethane and propane is to be determined. The measurement of the pressure may be checked by cooling the bulb with liquid nitrogen and again warming it to the temperature of solid carbon dioxide. Such a check determination should not differ from the original reading by more than :3 mm. mercury.

Example IV cussed in Example III, except that the temperature of melting mercury (about .-38 F.) is used instead of the temperature of subliming solid carbon dioxide. A small container, such as a test tube, just large enough to fit around the bulb having a capacity of 2 ml., is half filled with clean mercury and then supported around bulb 40 so that the bulb is completely immersed in the mercury. The mercury and the bulb are then cooledto the temperature of liquid nitrogen and a portion of the fraction to be analyzed having a volume of about 45 to 55 ml. is condensed in the bulb. Any traces of air are removed by vacuum pump while maintaining a low temperature. The liquid nitrogen is then removed and the mercury allowed to warm to its melting point. When the mercury has reached its melting point the pressure in bulb 40 becomes constant for about 1 minute. This pressure is then used in connection with one of curves or II of Figure 6, as the case may be, to determine the composition of the original sample. A check determination 'made by again cooling the bulb and mercury with liquid nitrogen and again warming the assembly should agree with the first determination within :3 mm. of mercury.

Example V The following procedure may be used to determine a small amount of propane in admixture with isobutane and for obtaining the composition of any mixture of isobutane and normal About to ml. of the gaseous mixture is condensed in bulb 40 using liquid nitrogen. 11 a smaller quantity of the sample to be analyzed is all that is available, the 2 ml. bulb may be used and half as much material is condensed in it. The bulb is then warmed to the temperature of an intimate mixture of pure ice and distilled water and the resulting pressure is recorded. If the original inixture is one of normal butane and isopentane, this pressure is used together with curve 13 of Figure 7. If the mixture is one of propane inisobutane, curve 12 of Figure 'l is used together with the recorded pressure. If the mixture is one of the other mixtures to which this particular procedure may be applied, the composition may be calculated from the data which has been obtained by the use of the corresponding formula selected from the following group. In each formula X is equal to the difierence between the observed vapor pressure and the vapor pressure of the higherboiling component, at the temperature of melting ice. pressure can either be determined by the use of the apparatus describedherein, using a pure hydrocarbon, or may be determined from any suitable source in the latter.

Isobutane, mol per cent in isobutane plus normal butane =o.24sx Isopentane, mol per cent in isopentane plus normal pentane =1.22x Normal pentane, mol per cent in normal pentane plus diisopropyl =0.95X Normal pentane, mol per cent in

normal pentane plus

2 and 3 me-pentane =0.a5x Normal pentane, mol per cent in normal pentane plus normal hexane =onsx Example VI In some instances it may be desired to use my apparatus for the analysis of ternary fractions which may have been obtained as the light end of a sample introduced through line 12. The following procedure can be used with a mixture containing ethane, propane and isobutane with not more than 10 per cent ethane. It can also be used with a mixture-containing propane, normal butane and isobutane with not more than 10 per.

cent propane.

A bulb 40 is used, having a capacit of 2 ml. Using liquid nitrogen, a portion of the sample having a volume of 45 to 55 ml. is condensed in the bulb. Any air which may be present is removed by evacuation. In case the fraction con-' tains ethane, propane and isobutane, the pressure of the mixture is obtained first by warming the bulb 40 to the temperature of solid carbon dioxide and again by warming the bulb to the temperature of melting mercury. The two pressures so obtained are used together with the diagram shown in Figure 8. In case the fraction contains propane, isobutane and normal butane the pressure is determined first by warming the bulb to the temperature of melting mercury and subsequently to warming the bulb to the temperature of melting ice. These two pressures are then used together with the diagram shown in Figure 9.

In each of Examples II to V1, the pressure in bulb to is always made with valve 45 closed.-

Example V'II When it is desired to determine the amount of hydrogen present in a mixture of hydrogen and methane a rapid method canbe used which is This latter vapor somewhat similar to that employed in Example 11 for determining the amount of methane in a methane-ethane mixture. In this instance a bulb 40 having a capacity of 25 ml. is used. It is immersed in melting ice and the hydrogen-methane sample is passed into it until manometer 48 indicates a pressure of 1000 mm. of mercury. Valve 45 is then closed and bulb 40 is immersed in liquid nitrogen. The resulting pressure, together with curve I of Figure 10, is used to determine the amount of hydrogen present in the mixture.

A similar procedure can be used to make a rapid determination of the amount of nitrogen in the mixture of nitrogen and methane. In this instance the curve to be used is substantially identical with curve 15 of Figure 10, except that the curve has a slight general downward bow in it. Likewise, a similar procedure can be used to determine the amount of air present in a mixture of methane and air. In this instance, however, the curve not only has a slight general downward bow in it, but proceeds directly to the intercept with the ordinate representing 100 per cent air and does not have the peculiar hook to the curve shown in Figure 10.

Example VIII The identification of the lightest component in a mixture is often difficult when the volume of that component is too small to register a plateau. when the sample is distilled in the apparatus of Figure l. The following procedure may be used to identify ethane and propane specifically, and may be adapted to the identification of other components.

The vapor pressure of the fraction is measured at two temperatures, as described in the preceding procedure. Temperatures of solid carbon dioxide and of melting mercury are used to identify ethane in a mixture possibly containing ethane in propane, while temperatures of melting mercury and ice are used to identify propane in isobutane.

The two vapor pressures just determined are applied to the graphs of Figure 8, or 9, as the case may be, in the same manner as in the preceding procedure. The interpretation of the results are illustrated by the following example.

A binary mixture is suspected of containing a small amount of ethane in propane. If the intercept of the two vapor pressures of this mixture falls on the ethane line originating at the 100 per cent propane point, Figure 8, the presence of ethane is established. If the intercept falls to the left of the line just mentioned, a component having a vapor pressure lower than ethane is present; if the reverse is true, a component having a vapor pressure higher than ethane is indicated.' If the intercept falls at the 100 per cent propane point, the fraction is all propane.

It will be readily appreciated by one skilled in the art that various modifications of my invention may be made, within the limits of the general teaching and disclosure presented hereinbefore. It is to be understood that the numerous specific examples are not to be interpreted as imposing unnecessary limitations upon the claims presented hereinafter.

I claim:

1. An apparatus for analyzing a gaseous hydrocarbon-containing mixture which comprises, in combination, a calibrated bulb wherein a sample to be analyzed is condensed, a valve associated with said bulb through which said sample is introduced, a liquid-filled differential manometer with a first arm directly in communication with said bulb, a check valve in each arm of said manometer adapted to prevent egress of said liquid from said manometer, a pressure-indicating manometer directly connected to the second arm of said differential manometer, and means connected to said indicating manometer and said second arm of said differential manometer for duplicating a pressure within said bulb.

2. An apparatus for analyzing a gaseous hydrocarbon-containing mixture which comprises. in combination, a calibrated bulb wherein a sample to be analyzed is condensed, a valve associated with said bulb through which said sample is introduced, a liquid-filled differential manometer with a first arm directly in communication with said bulb, a check valve in each arm of said manometer adapted to prevent egress of said liquid from said manometer, a pressure-indicating manometer directly connected to the second arm of said differential manometer, and means connected to said indicating manometer and said second arm of said difierential manometer for duplicating a pressure within said bulb, and comprising a source of subatmospheric pressure, a source of superatmospheric pressure, a control valve between each said source and said manometers, and a pressure-surge volume directly connected to said manometers.

3. An apparatus for analyzing a gaseous hydrocarbon-containing mixture which comprises, in combination, a calibrated bulb wherein a sample to be analyzed is condensed, a valve associated with said bulb through which said sample is inuid from said manometer, each said check valve comprising a thimble sealed at its edge to the wall of the manometer arm and composed of a porous material not wetable by the liquid in said manometer, a pressure-indicating manometer directly connected to the second arm of said dlflertial manometer, and means connected to said indicatlng manometer and said second arm of said diiferential manometer for duplicating a pressure within said bulb.

4. An apparatus for analyzing a gaseous hydrocarbon-containing mixture which comprises, in combination, a calibrated bulb wherein a sample to be analyzed is condensed, two arms connected to said bulb, a valve in one of said arms, means to indicate a differential pressure connected to the second of said arms, pressure-indicating means connected to said diflerential pressure means, and means for duplicating the pressure within said bulb connected to said pressure-indieating and said diflerential pressure means.

5. An apparatus for analyzing a gaseous hydrocarbon-containing mixture, which comprises, in' combination, a receiver for a gaseous fraction having a known volume, a calibrated bulb connected thereto having a volume such that the ratio between said volume and the volume of said receiver is between about 1:10 and about 1:4, means for indicating a pressure diflerential connecting on one side with said bulb and receiver, means for indicating an absolute pressure connecting to the second side of pressure diflerential means, and means for establishing and maintaining a desired absolute pressure on said second side of said pressure diil'erential means.

6. A method for analyzing a mixture or known 13. gases which are present 1n unknown proportions in said mixture which comprises at least partially condensing a mixture of said gases in known com position in a vessel maintained at a predetermined low temperature; then measuring the pressure in said vessel; then raising the temperature to a predetermined level and again measuring the pressure in said vessel; repeating the foregoing steps with known mixtures of said gases in different proportions until a sufilcient number of points or pressures have been obtained to plot curves characteristic of the said vessel; then sub-- jecting said mixture of known gases which are present in unknown proportions in said apparatus to said two diiferent temperature levels; recording the pressures at said two difierent temperature levels; and reading from said curves the proportions of the known gases present in said mixture.

7. A method for the analysis of a mixture of methane, nitrogen and oxygen present in unknown proportions which comprises collecting a known volume of methane and nitrogen in a first container, connecting to said container 9. second container having a known volume substantially smaller than that of said first container, maintaining said second container at a fixed low temperature for a time sufficient to establish an equilibrium and recording thepressure in said connected containers; repeating the foregoing steps a number of times and with difierent mix- L tures of methane and nitrogen in known proportions until a suflicient number of pressures have been recorded to establish a curve characteristic of said containers in equilibrium for any mixture of methane and nitrogen; then repeating the foregoing steps a number of times with difierent mixtures of methane and air in known proportions to establish a curve characteristic of said con-' tainers in equilibrium for any mixture of methane and air; then determining as before the pressure in said connected containers for said mixture of methane, nitrogen and oxygen present in unknown proportions; determining a numerical value for the oxygen content of said gas by conventional means; approximating a numerical value for the nitrogen content of the mixture of unknown proportions employing said curve characteristic of said containers in equilibrium for any mixture of methane and nitrogen; addin said numerical value for nitrogen to that for the oxygen to obtain an approximate value for the nitrogen and oxygen in said mixture; then dividing the numerical value of the oxygen content by said sum thus obtained to obtain the percentage of oxygen in the fraction which represents the nitrogen and oxygen (fixed gases) alone; interpolating between said curves on the ling/corresponding to the pressure determined with said mixture of methane, nitrogen and oxygen in unknown pro-portions, at a point in the direction of said curve characteristicfor methane and air. the distance of said point along said line being deter'mined'by' dividing the percentage of oxygen by 21; and then reading off the percentage of fixed gases in the mixture.

8. A method for analyzing a mixture of known gases which are present in unknown proportions in said mixture which comprises collecting a known volume of a mixture of said gases in known composition in'a first vessel maintained at a predetermined temperature; passing a portion of said gases in known composition into a second vessel maintained at another predetermined lower temperature until equilibrium between the two vessels is accomplished and then measuring the pressure in said vessels; repeating the aforesaid steps until a suificient number of pressures have been measured at equilibrium to plot a curve of pressure versus composition characteristic for the ap paratus; then subjecting said mixture of known gases which are present in unknown pro-portions to the aforesaid steps which determine the pressure at equilibrium and reading from said curve the proportions of the known gases in said mixture.

9. A method for analyzing a mixture of known gases which are present in unknown proportions in said mixture which comprises condensing a known volume of a mixture of said gases in known composition in a vessel maintained at a predetermined temperature, sealing said vessel; then warming said vessel to another predetermined temperature; then measuring the pressure therein; then repeating the aforesaid steps until a sufficient number of pressures have been measured as before to plot a curve of pressure versus composition characteristic for said vessel; then subjecting said mixture of known gases which are present in unknown proportion to the aforesaid steps to determine its'pressure, warming as before and reading from said curve the proportions of the known gases in said mixture.

' DAN E. SMITH.

REFERENCES CITED The following references are of record in the file of this patent:

UITED STATES PATENTS Number Name Date 1,880,720 a Blackwood et a1. Oct. 4, 1932 2,009,814 Podbielniak July 30, 1935 2,212,681 Dunn Aug. 2'7, 1940 2,257,577 Rosenberger Sept. 30, 1941 2,286,384 Sanderson June 16, 1942 2,287,101 Horvitz June 23, 1942

Claims

1. AN APPARATUS FOR ANALYZING A GASEOUS HYDROCARBON-CONTAINING MIXTURE WHICH COMPRISES, IN COMBINATION, A CALIBRATED BULB WHEREIN A SAMPLE TO BE ANALYZED IS CONDENSED, A VALVE ASSOCIATED WITH SAID BULB THROUHG WHICH SAID SAMPLE IS INTRODUCED, A LIQUID-FILLED DIFFERENTIAL MANOMETER WITH A FIRST ARM DIRECTLY IN COMMUNICATION WITH SAID BULB, A CHECK VALVE IN EACH ARM OF SAID MANOMETER ADAPTED TO PREVENT EGRESS OF SAID LIQUID FROM SAID MANOMETER, A PRESSURE-INDICATING MANOMETER DIRECTLY CONNECTED TO THE SECOND ARM OF SAID DIFFERENTIAL MANOMETER, AND MEANS CONNECTED TO SAID INDICATING MANOMETER AND SAID SECOND ARM OF SAID DIFFERENTIAL MANOMETER FOR DUPLICATING A PRESSURE WITHIN SAID BULB.