US2389706A - Apparatus for gas analysis - Google Patents

Description

Nov. 27, 1945. P. s. WILLIAMS ETAL 2,339,706.-

APPARATUS FOR GAS ANALYS IS Filed Jan. '7, 1943 II- V mm mmummazom hm Eo umu 2 553: mm, :5 SEE. 2 mm 5 mm mu Nu muzzommzh. m. mum? u r EEK .vN d S Patented Nov. 27, 1945 APPARATUS FOR GAS ANALYSIS Philip S. Williams and Monroe W. Kriegel, Tulsa, Okla., assignors to Standard Oil Development Company, a corporationot Delaware Application January 7, 1943, Serial No. 471,528

Claims.

The present invention is directed to a readily portable apparatus suitable for analyzing combustible gases. More specifically, the apparatus is particularly suitable for analyzing the amount of hydrocarbons present in soil air.

Apparatus designed for the analysis of soil gas samples is now well known to the art. However, these known arrangements are quite bulky and are usually placed in a centrally located laboratory, requiring the collection of samples in the field andthen transportation of the samples substantial distances to the laboratory. The apparatus of the present invention is a compact unit which may be readily transported so that the samples may be analyzed in the field.

Other objects and advantages of the Present invention may be seen from a reading of the following description taken in conjunction with the drawing, in which the sole figure diagrammatically illustrates a preferred embodiment of the present invention.

Referring specifically to the drawing, numeral II is a connection suitable for attaching pipette 9 containing the sample of soil air to the apparatus. A suitable means of attaching the sample-containing vessel to the apparatus is by rubber tubing l9. Flow of fluid through line II is controlled by suitable cocks, l2 and 3, and a manometer I4 connecting into the line at a point between the two stopcocks. Line l9 connects with scrubber i5 which in turn is in communication with scrubber It. The purpose of scrubber i5 is to remove carbon dioxide from the sample while scrubber I 6 removes water vapor therefrom. It is preferred to employ askerite for the removal of the CO2, and phosphorus pentoxide for the removal of water vapor.

A means for evacuating the apparatus is provided, including a mercury difiusion pump 28 and a mechanicall operated fore pump 29 adapted to back up the mercury diffusion pump.

Between the evacuation means and scrubber it are arranged two branches. One branch comprises only a conduit controlled by stopcock i8. The other branch includes triple trap 19, and a U tube 25 and is arranged for fluid communication with Pirani tube assembly 22, oxygen containing receiver 24 controlled by stopcock 23 and manometer 3|. Flow of fluid through this second branch may be controlled by stopcock i1- and by a mercury valve which will be hereafter described.

The mercury valve includes U tube 25 and a mercury containing reservoir 32 immediately below the U tube and in communication therewith by means of a vertical length of tubing. The upper portion of reservoir 32 above the mercury is provided with an outlet to the atmosphere controlled by stopcock 26. This space above the mercury in the reservoir may also be connected with pump 29 through a two way stopcock 21.

By means of the connections above described,

a single mechanical pump may be employed both,

to operate the mercury valve and to back up the mercury diffusion pump. Any time the pressure in line 25 is below atmospheric the mercury valve may be closed to prevent communication between triple trap I9 and difiusion pump 28 by setting two-way stopcock 21 to prevent communication between reservoir 32 and pump 29 and thereafter opening valve 26. The atmospheric pressure will force mercury from the reservoir upwardly into the U shaped trap 25. When it is desired to open the mercury valve, stopcock 23 may be closed and stopcock 21 set to allow communication between pump 29 and the upper portion of reservoir 32. This allows pump 29 to reduce the pressure above the mercury reservoir and mercury will flow from U tube 25 into the reservoir to allow communication between triple trap l and diffusion pump 28. a

It will be understood that the mercury valve may be operated in a relatively short space of time and that during the interval in which reservoir 32 is in communication with pump, 29 the mercury diffusion pump 28 may continue to operate without being connected to pump 29. When the space above reservoir 32 has been evacuated the stopcock 21 may be-turned to again allow communication between diffusion pump 28 and mechanical pump 29. In this manner, pump 29 serves both to back up mercury diffusion pump 28 and operate the mercury valve without allowing air from the atmosphere to get into-the diffusion pump.

The Pirani tube assembly 22 consists of a pair of Pirani tubes with one connected to the vacuum system as illustrated, and. the other permanently reduced to a very low pressure. The Pirani tube assembly is provided with usual electrical equipment, including filament wires whereby the change in heat conductivity between the filament .wires and the bulbs to the atmosphere is measured to indicate the pressure in the system.

Triple trap I9 is provided with electrodes 20 and 2|. These electrodes are electrically connected to a suitable means for supplying a high voltage current, for example, high voltage transformer 30. When the triple trap has been evacuated to a very low pressure, a high voltage may be impressed across the electrodes tocause combustion of the sample. It is preferable to use a potential of the order of 15,000 volts for-causing this combustion. a

In conducting an analysis with the apparatus described, a pipette 9 of known volume is employed. This allows the weight of soil air in the sample to bedetermined by calculation. The pipette is then attached to the apparatu in the manner shown in the drawing, and triple trap I! then chilled by immersing it in liquid nitrogen. Stopcocks i8 and I3 are then closed and stopcock i2 opened to allow the sample to expand. With evacuating pump 29 in operation, stopcock I3 is then opened slowly and the sample allowed to pass through the ascarite and phosphorus pentoxide into the trap I8, the completeness of the removal 01 the sample from the pipette being noted by observing the reading of manometer it. As the sample passes through trap l9, all hydrocarbons heavier than methane are condensed therein.

When the pressure throughout the system has been reduced to approximately 25 millimeters of mercury, valve I1 is closed and the pressure on the trap I9 is further reduced to substantially zero. Trap I9 is then isolated from the evacuating pump by closing the mercury valve, and oxygen is then allowed to enter the trap from reservoir 24 by manipulating valve 23, until the pressure within the trap is about six millimeters as shown by manometer 3|. The hydrocarbon gases within trap iii are then burned by discharging a high voltage through the trap by connecting transformer 30 to a suitable source of electrical power not shown. It has usually been found that an initial discharge voltage of 15,000 is suflicient to pass a discharge through the trap, l9.

It is preferred to remove the liquid nitrogen bath from trap I9 at the same time the electrical discharge between electrodes 20 and 2| is initiated. This allow the trap to be warmed to room temperature while the burning is proceeding. At the same time the discharge is taking place cock I8 is opened to allow the evacuation of reagent traps l and i6.

After the combustion within trap I9 is complete, the circuit is broken and the trap immersed in a bath of liquid nitrogen to condense carbon dioxide and water vapor formed by combustion of the sample. It has been found in usual operations that a discharge of high voltage through the trap for a period of one minute produces satisfactory combustion of the sample. After the carbon dioxide and water vapor have been condensed in the trap l9, excess oxygen is pumped oil by means of the evacuation system through U tube 25. The mercury valve is then closed, and the liquid nitrogen bath adjacent trap I9 is replaced by a bath of dry ice and acetone, which allows the trap to be warmed to -80 C. With the trap maintained at this temperature by the mixture of dry ice and acetone, the pressure of 00: therein is measured by means of the Pirani tube assembly 22. Since the volume of the system in communication with the Pirani tube system has been previously determined, the amount of CO2 present may be determined from a reading of the pressure by means of the Pirani tube assembly. 'The results are preferably expressed on the basis of total combustible carbon in the sample in parts per million parts of initial sample by weight.

Having fully described and illustrated the practice of the present invention, what we desire to claim is:

1. An assembly adapted for analyzing gases comprising in combination a scrubbing means, an evacuating means including a mercury difluslon pump and a mechanical pump, a first conduit and a second conduit each connecting said scrubbing Y means with 'said diflusion pump, a stopcock controlling fiow in each of said conduits adjacent said scrubbing means, a triple trap and U tube inserted in the first conduit, a reservoir, a conduit connecting the reservoir with the first conduit, a pressure gauge assembly, a conduit fluidly connecting the assembly to the first conduit between said triple trap and said U tube, a mercury reservoir arranged adjacent said U tube, a conduit fluidly connecting a lower portion of the U tube with a lower portion of the reservoir, a conduit arranged for connecting said reservoir with said mechanical pump, a stopcock in said conduit, a conduit having a stopcock therein connecting an upper portion of the reservoir with the atmosphere wh'ereby mercury may be forced into and removed from said U tube.

2. A device in accordance with claim 1 in which said triple trap is provided with spaced electrodes therein and a source of high voltage electrical power is electrically connected to said electrodes.

3. An assembly adapted for analyzing gases comprising in combination, a scrubbing means, a mercury diffusion pump, a mechanical pump, a first conduit connecting the scrubbing means with the diiiusion pump, a stopcock in the first conduit, a second conduit connecting the scrubbing means with the diffusion pump, a U tube in the second conduit, a trap in the second conduit between the U tube and the scrubbing means, a stopcock in the second conduit between the trap and the scrubbing means, a mercury reservoir, a third conduit connecting a lower portion of the U tube with a lower portion of the reservoir, a fourth conduit connecting an upper part of the reservoir with the atmosphere, a stopcock in the fourth conduit, a branched conduit defining passages between the diflusion pump and the mechanical pump, and between an upper portion of the mercury reservoir and the mechanical pump, and a stopcock in the branched conduit arranged to connect selectively either the reservoir or the difiusion pump with the mechanical P p.

4. A device in accordance with claim 3 in which the trap is provided with spaced electrodes therein and a source of high voltage electrical power is electrically connected to said electrodes.

5. In an assembly adapted for analyzing gases and including a vessel and a mercury difiusion pump, means defining paths of fluid flow between the vessel and the diffusion pump including a first conduit and a second conduit fluidly connected to form a loop, a stopcock in the first conduit, 9. U tube in the second conduit, a stopcock in the second conduit between the U tube and the vessel, a mercury reservoir adjacent the U tube, a third conduit fluidly connecting a lower portion of the reesrvoir with a lower portion of the U tube, a fourth conduit fluidly connecting an upper portion of the reservoir with the atmosphere, a stopcock in the fourth conduit, a, mechanical pump, a branched conduit defining a path of fiuid communicating between the diffusion pump and the mechanical pump and between an upper portion of the reservoir and the mechanical pump and a valve in the branched conduit arranged to connect selectively either the reservoir with the me-- chanical pump or the diifusion pump with the mechanical pump.

PHILIP S. WILLIAMS. I MONROE W. KRIEGEL.

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