US2968536A - Colorimetric gas sampler-analyzer - Google Patents

Description

Jan. 17, 1961 F. R. SMITH 2,968,536 Y COLORIMETRIC GAS SAMPLER-ANALYZER Filed Feb. 6, 1957 2 Sheets-Sheet 1 'Ill lill

Jan. 17, 1961 F. R. sMn-H 2,968,536

coLoRIMETRIc GAs SAMPLER-ANALYZER Filed Feb. 6, 1957 2 SheetsSheet 2 w 3o LEU Ouf z R R I 2o AIR sAMr ER-\NA| ZER,cs2 g sET FLow METER To 6.2 o RUN 5 MINUTES E .o

o lo 2o so 4o 5o 6o PARTS PER MILLION CS2 23%, d Patented dan. l?, il

ice

COLORIMETRIC GAS SAMPLER-ANALYZER Frederick R. Smith, Nitro, W. Va., assigner to American Viscose Corporation, Philadelphia, Pa., a corporation of Delaware Filed Feb. 6, 1957, Ser. No. 638,619

4 Claims. (Cl. 23-254) This invention is directed to a novel gas sampleranalyzer. More particularly it is directed to a process and apparatus for rapidly and accurately determining the CS2 concentration in the atmosphere.

In rayon and cellophane mills which employ large quantities of CS2 to form cellulose Xanthates it is necessary to periodically measure the concentration of CS2 in the atmosphere to prevent its reaching a level which is toxic to the workmen.

The usual system for analytical control of CS2 concentrations in rayon mills requires the services of an air sample boy and an analyst. The samples are taken in sets of six to eight, this being about the limiting number one air sample boy can handle. Approximately one half hour is required to prepare absorbing solutions and towers and assemble them into the sample boxes. Each sample taken for CS2 measurement requires 100 ml. of copper diethylamine reagent. Thus, preparation to take samples requires 600-1600 cc. of reagents, and about one half hours time. The sample boxes are then transported to the various sampling locations, a second trip made to assemble tubing and air pumps as necessary, and the samples set up and started. This requires from l to 30 minutes. The sampling is continued for one hour during which time the boxes are rechecked occasionally to maintain their proper functioning. At the end of the hour, the sampling is stopped, the rubber tubing and air pumps returned to their appointed places and the samples transported to the laboratory. They are there disassembled and processed through the necessary analyses. The results are then available two to three hours from the time they are started. Add this to the time needed for solution preparation, cleaning equipment, and replacement of glassware, and it is evident that a considerable effort is expended in the analytical control of gas concentrations. Using this system, special and check samples often have to be scheduled for half to a day later than the original sample. In the meanwhile, it is very likely that the situation will chance, and the source of the high concentration never be known. Use of the sampler-analyzer described in this application would eliminate most of these scheduling diihculties.

Accordingly it is an object of the present invention to provide a method and means for rapidly and accurately determining the concentration of any desired gas in a mixture of gases. A further object is the provision of a gas sampler-analyzer which is adapted for grab-sampling and is simple, compact and portable. A more specific object is the provision of means for collecting small samples of CS2 and analyzing them quantitatively in a matter of minutes.

The invention is best illustrated by reference to the drawings wherein Figure l is a back view showing an assembly embodying the invention in' `as simplified a form as possible.

Figure 2 is a calibration curve which plots the meter reading in micro-amperes against p.p.m. (parts per million) CS2 over a fixed and specified time and flow rate; l

In general, the invention may be described as follows: A sample of gas from any source containing CS2 is pumped at a constant rate through an H2S-scrubber and then into the base of a small bore vertical absorber or diffusion tube lled with an absorber reagent, that is, one which reacts with CS2 to develop a color which may be measured by means of photoelectric cells. As stated above the reagent for CS2 may be copper diethylamine. Por simplicity the invention will be described with respect to CS2 analysis, it being understood that the same basic process may apply to the analysis of other gases. The inner diameter 'of the aforesaid Vertical diffusion tube is small enough so that the gas which is pumped into its base below the liquid level therein is confined into bubbles of the diameter of the tube. As these bubbles rise in the tube they force some liquid to rise ahead of them. Using a short enough tube, the liquid may be pumped from the tube by this action. The discharged liquid is then caught in a funnel, the base of which drains into the absorber tube at a point below that where the sample gas is introduced thereto, so that the liquid is continuously recycled to the absorber. The gas bubbles, however, escape from the top of the funnel and are pumped out of the system. Adjacent the funnel is positioned a column of fresh absorber liquid, i.e., liquid which has not been reacted with CS2-containing gas. Separate beams of light from the same source are passed through both reagent columns and the respective beams then passed onto separate photoelectric cells. The difference in intensity of the light reaching the two photoelectric cells is measured by an electrical system which records the difference upon a potentiometer or similar device.

Referring to Figure l, the analytical elements are housed in a box l0 having sidewalls lll, a floor l2, and a handle i3. Pump 37 draws sample gas through the system and is powered by a motor 3S. Pump 37 may be any type of gas pump such as a diaphragm pump. In one embodiment of the system this pump has a ce.- pacity of 225 cu. in./min. The air containing CS2 is drawn by pump 37 through line Ztl, through owmeter 21, and into the base of H2S-scrubber Z3.

Flowmeter 2l is not illustrated in detail but preferably the owmeter is a glass tube having a tapered bore and calibrations marked along its length. A sapphire ball is placed in the tube and the tube positioned vertically with the narrow end at the bottom.. When air passes into the narrow end, its How upward will cause the ball to float at a point along the tube which is related to the volume of air flowing. Line 2d opens into the base of scrubber chamber 23 through a suitable diffusion means such as a sintered glass filter 22. Scrubber 23 is iilled with any suitable liquid for removing H25 from the gas stream, of which the preferred ones are cadmium acetate and CdCl2, These reagents remove any H23 which would react with diethylamine solution to give a color and a correspondingly higher result for CS2 concentration. Column 23 can be opened for draining and refilling whenever necessary by opening valve 24.

Desulded air is pulled from the top of column 23 through line 25 into diffusion chamber 27. This may take the form of a Vigereaux distillation column having vertical rows of iins 29 projecting from the inner wall of the coltunn so as to describe a tortuous zig-zag opening through the vessel. A delivery tube 3@ connects the top of vessel 27 with a funnel 3l and is sealed into the side of funnel 31. Tube 30 carries the stream of gas bubbles, alternating with globules of reagent solution, from column 27 into the top of funnel 31 wherein the gas bubbles, now stripped of their CS2 content, separate from the liquid and are drawn oii through line 32 to pump 37 where it is vented to the atmosphere through "line 39. Line 32 contains a T-tting l0 in combination with a control valve 41 which can be adjusted to regulate the iiow rate through the system. Delivery tube 30 is bent to the horizontal where it enters funnel 31 to effect more efiicient separation of gas bubbles from the liquid. The liquid reagent drains down through the stern 43 and through optical absorption cell 44 and is recycled to diffusion chamber 27 via return pipe 46. Funnel 31 must be small enough that it does not add excessively to the volume of the unit but deep enough to achieve separation of the gas and liquid delivered to it. While operating there must always be a pool of liquid in the funnel so that no air is carried to absorption cell 44, since this would interfere with the measurement.

The reagent supply 50 is contained in a reagent reservoir 51, which is preferably of polyethylene or other light-weight plastic material. Reservoir 51 is stoppered at 52 and designed to discharge through line 53 to a second absorption cell 54 which serves as the reference cell for the analyzer or colorimeter. Cell 54, in turn, discharges the reagent liquid through line 56 to the intake side of two-way stopcock 57. The outlet orifice of stopcock 57 connects to drain pipe 58, which discharges used reagent from lines 46 and 47 to receptacle 59, preferably of polyethylene or other plastic composition. Receptacle 59 is fitted with a breather tube 601. A new reagent solution is drawn from reservoir 51 into line 53 each time the absorbing unit is recharged, which is effected by turning the handle of stopcock 57 so as to close off drain pipe 58 and provide an open connection between line 56 and line 47. When the stopcock handle is turned to the other position, it will close off line S6 and permit line 47 to drain through line 58. At an intermediate position it disconnects all three lines 56, 47, 58 from each other and permits reagent from line 46 to bypass line 47 and enter the base of absorber 27.

The analyzer means is indicated schematically; being of rather conventional design this feature is not claimed to be patentable per se. Basically the analyzer as referred to from here on and in the claims consists of the two absorption cells 44, 54 and a light source 65 which includes two sets of condensing lenses 66, 66a, one for each photocell 67, 67a of the analyzer. A slot is provided between the absorption cells and photoelectric cells for insertion of a filter and an optical stop (not shown). This is schematic, of course, the filter and shutter units actually being built-in. Leads 68, 68a connect in known manner to an ammeter 70. Knob 71 controls a pair of variable resistors in the light circuit, hence can be set so as to adjust the light output and thus the full scale position of the ammeter 70. A main switch 72 activates the circuit,

Photocells 67, 67a in a preferred embodiment are a matched pair of A selenium self-generating photocells sold by International Rectifier Corp. Ammeter 70 may be an 0-50 micro-ampere panel type meter. The light source 65 need be no more than a 5 cell iiashlight bulb supplied with current from the secondary of a door bell transformer. Lenses 66, 66a are double convex and a typical dimension would be 26 mm. diameter and 28 mm. focal length.

PREPARATION OF SOLUTION FOR CALIBRATION gms. OS2 mol. wt. CS2 24.45 is the molecular volume, assuming an average Liters of CS2 vapor= 24.45

Liters of OS2 Liters of sample If time and sampling are constant, then Ammeter reading 1 Concentration l Ammeter reading 2 Concentration 2 To prepare a calibration chart, a series of solutions of known CS2 content are placed in the unit. In each case the absorbing unit is charged with fresh reagent by adjusting two-way stopcock 57 so as to connect line 47 with line 56. The light 65 is turned on, the sample pump 37 is turned on, the sample flow adjusted and the time recorded. At the end of the designated time, the sampling is stopped, reading recorded, and the used reagent drained into lines 47, 58 to receptacle 59. The absorbing unit is rinsed and the sampler-analyzer is ready for the next sample. As shown in Figure 2 the time may be set at 5 minutes and the reading of flowmeter 21 set at 6, `which might correspond to 500 cc./min. Figure2 is a graph obtained from a series of samples of known CS2 concentration.- Other curves of this type could be obtained by changing the variable, as by holding the ammeter reading constant and varying the time of sampling.

For routine control use the instrument is conveniently operated for a set period of time at a constant iiow rate, so that the ammeter reading can be readily translated into p.p.m. CS2 (Fig. 2). It will be readily observed which samples are higher than the desired limit condition and further tests can be made without delay. This will achieve better control of the gas concentrations in an area than is now possible. When a sample is obtained which gives an excessively high reading, using the iixed time method, the samples can be proved by use of a variable time-fixed meter reading calibration.

The invention can be further illustrated by the following example.

Example Fill the reagent reservoir 51 with a freshly prepared solution of copper diethylamine in methyl Cellosolve. Ten cc. of this solution will absorb and react with l litre air sample containing 120 ppm. of CS2. Fill the H28 scrubber 23 half full of 10% cadmium acetate solution. Turn stopcock 57 so as to iill absorber column 27 with reagent, then turn stopcock 57 off. The absorbing unit 27 should be filled so that at the desired flow rate of air, the circulation will be maximum and no entrainment of gas bubbles in absorber liquid is noticed. Turn on pump motor 38. Turn the iiow control valve 41 until the desired flow is indicated by the fiow meter 21. Close the optical stop or shutter control and turn on and adjust analyzer light 65 so as to adjust meter 70 to full scale. Remove the optical stop by opening the shutter control. Time the sample and read the meter at the end of the sampling period. Enter meter reading on calibration chart (Fig. 2) to determine p.p.m. of CS2. Turn sample flow control valve 57 to drain used reagent to waste tank 59, and instrument is ready for refilling and reuse.

The apparatus described should be considered as illustrative of the invention, not limiting, since various modi fications could be made by those skilled in the art Without departing from the basic concept of the invention. Thus, one might analyze for gases other than CS2 by employing the appropriate reagent.` In place of using the acetate or chloride of cadmium to precipitate the H2S one could use other salts such as the sulfate, nitrate, formate, oxalate, halide, etc. Instead of using cadmium as the cation one could use many other metals such as Pb, Hg, Fe, Zn, Cu, Mn, Co, Ni, etc.

I claim:

1. A portable testing device comprising a case, a carrying handle on said case, apparatus mounted within said case for facilitating the batch-wise analysis of the amount of a gaseous impurity in the air, said apparatus comprising a reservoir containing a supply of an indicator liquid which changes color in the presence of the gaseous impurity, said reservoir being mounted in the upper portion of said case so that the liquid may flow therefrom by gravity, a vertical reaction chamber, a iirst liquid transmission line extending parallel to said reaction chamber, said transmission line having an enlarged upper chamber, a small bore tube connecting the upper end of said reaction chamber to the enlarged upper chamber of said transmission line, a lower line interconnecting the lower end of said transmission line and the lower end of said reaction chamber, a second liquid transmission line extending from said reservoir to said lower line, valve means between said second liquid transmission line and said lower line, said valve means being operable to connect said second liquid transmission line to said lower line and to disconnect it therefrom whereby said reaction chamber and said first liquid transmission line may be lled with fresh indicator liquid and then disconnected from the reservoir supply, a conduit opening into the lower end of said reaction chamber for feeding the air to be tested for the gaseous impurity into said reaction chamber wherein the gaseous impurity is reacted with the indicator liquid as the air passes upward through said chamber, said indicator liquid being moved upward in said small bore tube by the air and discharged into the enlarged upper chamber of said first liquid transmission line, means for withdrawing the air from said enlarged upper chamber whereby continued introduction of air into the lower end of said reaction chamber causes the indicator liquid to circulate through the reaction chamber and the first liquid transmission line and gradually change color as it is reacted with more and more of the gaseous impurity, and a photoelectric comparison system mounted in said case, said system including an optical absorption cell in each of said transmission lines and means for comparing the color intensities of the liquid in said cells.

2. The device of claim 1 wherein a receptacle is mounted in the lower portion of said case and there is means for discharging the reacted indicator liquid from the reaction chamber and the rst transmission line into said receptacle after a test is completed.

3. The device of claim 2 wherein the means for discharging the reacted indicator liquid includes said valve means which is a three-way valve operable to connect said lower line with said receptacle.

4. The device of claim l wherein the means for withdrawing air from the enlarged upper chamber of said rst liquid transmission line comprises a tube connected to said chamber, a pump for pumping the air through said tube, and a control valve in said tube for regulating the rate of flow.

References Cited in the le of this patent UNITED STATES PATENTS 2,328,461 Kienle et al Aug. 31, 1943 2,382,381 Calvert et al Aug. 14, 1945 2,395,489 Major et al. Feb. 26, 1946 2,413,261 Stackhouse Dec. 24, 1946 2,430,895 Tuve et al. Nov. 18, 1947 FOREIGN PATENTS 802,586 France June 13, 1931 OTHER REFERENCES Brady: Anal Chem. 20, 1033-37 (1948). Karasek et al.: Anal. Chem., vol. 28, N0. 2, pp. 233-236, February 1956.

Morehead: Ind. and Eng. Chem, Anal. Ed., vol. 12, No. 6, 1940, Pp- 373-374.

Claims (1)

1. A PORTABLE TESTING DEVICE COMPRISING A CASE, A CARRYING HANDLE ON SAID CASE, APPARATUS MOUNTED WITHIN SAID CASE FOR FACILITATING THE BATCH-WISE ANALYSIS OF THE AMOUNT OF A GASEOUS IMPURITY IN THE AIR, SAID APPARATUS COMPRISING A RESERVOIR CONTAINING A SUPPLY OF AN INDICATOR LIQUID WHICH CHANGES COLOR IN THE PRESENCE OF THE GASEOUS IMPURITY, SAID RESERVOIR BEING MOUNTED IN THE UPPER PORTION OF SAID CASE SO THAT THE LIQUID MAY FLOW THEREFROM BY GRAVITY, A VERTICAL REACTION CHAMBER, A FIRST LIQUID TRANSMISSION LINE EXTENDING PARALLEL TO SAID REACTION CHAMBER, SAID TRANSMISSION LINE HAVING AN ENLARGED UPPER CHAMBER, A SMALL BORE TUBE CONNECTING THE UPPER END OF SAID REACTION CHAMBER TO THE ENLARGED UPPER CHAMBER OF SAID TRANSMISSION LINE, A LOWER LINE INTERCONNECTING THE LOWER END OF SAID TRANSMISSION LINE AND THE LOWER END OF SAID REACTION CHAMBER, A SECOND LIQUID TRANSMISSION LINE EXTENDING FROM SAID RESERVOIR TO SAID LOWER LINE, VALVE MEANS BETWEEN SAID SECOND LIQUID TRANSMISSION LINE AND SAID LOWER LINE, SAID VALVE MEANS BEING OPERABLE TO CONNECT SAID SECOND LIQUID TRANSMISSION LINE TO SAID LOWER LINE AND TO DISCONNECT IT THEREFROM WHEREBY SAID REACTION CHAMBER AND SAID FIRST LIQUID TRANSMISSION LINE MAY BE FILLED WITH FRESH INDICATOR LIQUID AND THEN DISCONNECTED FROM THE RESERVOIR SUPPLY, A CONDUIT OPENING INTO THE LOWER END OF SAID REACTION CHAMBER FOR FEEDING THE AIR TO BE TESTED FOR THE GASEOUS IMPURITY INTO SAID REACTION CHAMBER WHEREIN THE GASEOUS IMPURITY IS REACTED WITH THE INDICATOR LIQUID AS THE AIR PASSES UPWARD THROUGH SAID CHAMBER, SAID INDICATOR LIQUID BEING MOVED UPWARD IN

Images