ainnionium perchloratc are shov n in Table 111. LITERATURE CITED
(1 j Burns, E. *4., “Analysis of Ammonium
Sitrate. Part 111, Assay,” Jet Propulsion Laboratory, Progress Rept. No. 20-365 (Sept. 2, 1958). ( 2 j Greenberg, -4.L., Walden, G. H., Jr., J. Chem. Phys. 8, 645 (1940). (3) Husken, A., Gaty, F., Chi7n. anal. 30, 12 (1948). (4)Ishihashi, Kiyoshi, Repts. Hiniejz
Tech. CoZZ. 6, 70 (1956). ( 5 ) Knecht, E., Proc. Chem. SOC.25, 229
(1909). (6) Knecht, Edmund, Hibbrrt. Eva, “New Reduction Methods in Volumetric Analysis,” 1st ed., pp. 21, 66-7, Lonymans, Green, London, 1918. ( 7 ) Laniond, J. J., Anal. Chim. Acta 8 , 217 (1953j. (8) Latimer, W. AI., “Oxidation Potentials,” 2nd ed., 11. 268, Prentice-Hall, S e n York, 1952. 19) Pierson, R. XI., Gantz, E. St C., ASAT,.CHEM.26,1809 (1SYA).
(10) Rlbaudo, Charles, “Methods of An-
alyzing Polysulfide-Perchlorate Propellants,” Technical Rept. 2334,SamueI Feltman Ammunition Laboratory, Picatinny Arsenal, Dover, N. J., September 1956. (11) Rosenherg, A., 2. anal. Chem. 90, 103 (1932). (12) Rothmund, V., 2. anorg. u . allgem. Chem. 62, 108-13 (1909). (13) Stahler, A., Chem. Ztg. 33, 759 (1909j. RECEIVED for review February 15, 1960. -4ccepted J u n e 27, 1960.
Titrimetric Determination of Combined Carbon Dioxide in Anhydrous Ammonia A. R. ADAM,’ RAYMOND SYPUTA, and W. E. STEPHENSON Western Operations Inc., Richmond Refinery, Standard Oil Co. o f California, Richmond, Calif.
b A method for determining parts per million of carbon dioxide in anhydrous ammonia has been developed. The carbon dioxide, combined as ammonium carbamate, is separated from the ammonia by weathering, and is determined by acidification and absorption in barium hydroxide. Analysis of known prepared samples in the range of 0 to 50 p.p.m. showed a precision of =t 1.5 p.p.m.
F
ox CERTAIN uses of commercial ammonia, the carbon dioxide content should tie as low as possible. Determination of this impurity is difficult, since the level iiwolved is only a few parts per million. As air contains several hundred parts per million of carbon dioxide, the usual chemical analyses are complicated by difficulty in establishing blanks and by limitations of sample size. Because of the chemical combination of carbon dioxide and ammonia, the usual methods of gas analysis. such as mass spectrometry and gas-liquid chumiatography are not applicahle. The rraction of carbon dioxide with anhydrous ammonia forms ammonium carbamate (1). CO?
+ 29H,
/SHs +
O(”
‘OXHA The method described here is based on the observation that even very small amounts of this mat’erial are quantitatively deposited when the ammonia is weathered off at, or below room temperature. The ammonium carbamate can be deconiposed in a closed system with a 1 Present address, Technical Service Group, Oronite Chemical Co., Belle Chasse, La.
dilute strong acid to liberate the carbon dioxide (1).
“, OC\ \ONH,
barium hydroxide is approximately 0.009N oxalic acid, standardized against a dilute standard sodium hydroxide solution. Water-pumped nitrogen is iised as the flushing gas. PROCEDURE
Several procedures for determining the evolved carbon dioxide were considered. The gravimetric method of Kolthoff and Sandell (9) was tried but was abandoned because of insufficient sensitivity. Of the recent titration procedures ( 3 ) , the one based on the direct titration method of Pieters (4) appeared to be more useful as a control test. A suitable modification of this procedure was developed. APPARATUS A N D REAGENTS
The sample containers are cylinders of Type 316 stainlesh &el of approximately 500-nil. capacity, equipped a t both ends with stainless needle valves and suitable adapters. The acid scrubber is of approximately 250-ml. capacity with a medium frittedglass plate a t the bottom. Three stopcocks are provided a t the top, one to introduce the acid, one to attach an Ascarite tube, and one as the outlet to the absorber. A tower filled with glass wool is placed between the acid scrubber and the absorber to act as a spray trap. The absorber used is specially made with four coarse fritted-glass plates placed 1 inch apart. I n other respects, it is similar to the ASTM lamp qiilfur absorber. A wet-test gas meter is used to measure the throughput of flushing nitrogen. Figure 1 shows the apparatus as assembled for the determination. The solution used to flush the sample cylinder is approximately 2N sulfuric acid. The absorbing solution is approximately 0.01N barium hydroxide. This solution must be protected from carbon dioxide in the atmosphere. The acid solution used to titrate the excess
Prepare the sample cylinder by flushing and filling with a n atmosphere of carbon dioxide-free nitrogen. Attach the tared cylinder to the flushed sample line and draw it nearly full by chilling the exterior of the cylinder sufficiently to keep the sample from vaporizing. Weigh the cylinder to obtain the sample weight. Immerse the cylinder in a water bath maintained below 70” F., leaving the upper valve exposed. Completely weather off the sample a t such a rate that no liquid ammonia is discharged. Close the cylinder valve. Draw approximately 150 ml. of the 2N acid into the acid scrubber and flush the scrubber and trap for 10 minutes with carbon dioxide-free nitrogen through a length of Tygon tubing attached to the inlet side of the scrubber. Close both the inlet tube of the scrubber and the outlet tube of the trap with pinch clamps, and connect the nitrogen supply to the absorber. While flushng with nitrogen, add distilled water and neutralize the abborber to a faint phenolphthaleiii pink. Discard the neutral solution and add a measured volume of the barium hydroxide solution that provides for a t least lOOyo excess of the absorbant. Titrate with the oxalic acid to a faint pink end point. Record the titration as A . Discard the neutral solution and immediately add the same amount of barium hydroxide, discontinue the nitrogen flushing, and place the absorber Ltnd the gas meter in the train. Close the scrubber stopcock leading to the trap and open the one leading to the Ascarite tube. Place a few drops of water in one tip of the cylinder and connect the scrubber inlet to this end with tho Tygon tubing. ReVOL. 32, NO. 10, SEPTEMBER 1960
0
1319
move the pinch clamp from the Tygon tubing. Slowly open the cylinder valve and tap the cylinder until the water enters the tip and causes contraction of the gas volume. Regulate the inflow of acid by pinching the tube and take all of the acid into the cylinder. Close the cylinder valve and the stopcock to thc dscarite tube. Shake the cylinder for 1 minute. Attach a tube from the nitrogen cylinder to the other end of the sample cylinder and, supporting it vertically, slon-ly apply approximately 5 pounds of pressure. Open the stopcock leading t o the trnin and remove the pinch clamp from the trap outlet. Open the lower cylinder valve and gradu:illy pass the acid back into the s:crubher. -idjust the nitrogen flow at the source so t’hat. both cylinder valves can be opened wide, and a flow rat’e through the system is maintained at approximately 0.5 cubic foot per hour. Incline the absorber momentarily to distribute the barium hydroxide solution evenly on the absorber plates. Pass 0.5 cubic foot of nitrogen t,hrough the system. Remove the barium hydroxide absorber from the train and titrate to a faint phenolphthalein pink end point with the oxalic acid solution while flushing with nitrogen. Recortl this titration as
B.
Determine a blank on the system and reagents. Cnlculate the carbon dioxide by : Carbon dioxide, p.p.m. (A
- B - C) ( N ) ( F ) Grams of sample
I. Determination of Carbon Dioxide
in
Deviations
CO*, P.P.M.
from
Calculated Values
“3
Sample -1 B C D E F G H I J I
19, 21 ’?
OJ 6, 5, 6, 7 1, 1, 1 3,4
Diagram of Apparatus
hlaximurn Deviation from hfean, P.P.31. 1
06 1 0 0 5
ANALYTICAL CHEMISTRY
E.
Trap Absorber G. Gas meter
To N2cylinder B. Sample cylinder C. Acid supply D. Scrubber
A = ml. of oxalic acid to titrate a portion of barium hydroxide equal
B = C =
N =
P
=
to that used for the determination ml. of oxalic acid to titrate the excess barium hydroxide in the determination blank, A - B when the entire procedure is carried out nithbut a sample normalitv of the oxalic acid solution 22,000 = equivalent weight of carbon dioside X 1000
DISCUSSION AND RESULTS
=
where
Table
Figure 1. A.
Evaluation of this procedure for accuracy required preparation of samples of known carbon dioxide content. This was done by evacuating the sample cylinders, then flushing into them a portion of carbon dioxide from a calibrated glass tube with a stopcock a t each end. Carhon dioxide-free nitrogen was used as the flushing gas. The cylinders were then filled with anhydrous ammonia and the carbon dioxide was determined as above. Table I lists determinations of a series of prepared samples. The carbon dioxide content of the ammonia used to prepare the known samples was determined by this procedure. The 0-p.p.m. material was obtained from a known carhon dioxide-free source. Because of the relative difficulty of preparing known mixes large enough to be reliably sampled, repeatability of the method was determined only on ammonia plant process streams. The values obtained are summarized in Table 11. As reported by others (S), it was difficult to absorb small amounts of carbon dioxide quantitatively in the weak barium hydroxide solution. ASTM sulfur absorbers with the extra coarse plates first used, but at practical flow rates only about 60% of the carbon dioxide present was retained in one absorber. Under these conditions, four or five absorbers were required to give complete retention. To avoid
F.
the use of a cumbersome train of ahsorbers and still achieve complete absorption, a specially designed absorbei was used. With four coarse fritted plates, this was the equivalent of five ASTM absorbers and effected complete absorption over the range investigated. Several parts of this method could perhaps be varied without impairing its accuracy. The maximum weathering temperature of 70” F. is well below the decomposition temperature of the ammonium carbamate. However, since the authors did not investigate the effect of highrr temperatures, 70’ F. was specified. The volume of flushing nitrogen required to effect complete transfer of the carbon dioxide into the scrubber varies with the total gas volume ot the system ahead of the scrubber. Five tenths cubic foot, as specified above, allowed for an excess of 30 to 40 % over the minimum required by the system used by the authors. The correct volume for different equipment should be established experimentally This flushing rate gave excellent absorption with the equipment described, However, where determination time is important, it is suggested that this rate be substantially increased after approximately 0.1 cubic foot has passed through the system. A low rate is most important during this initial period, when most of the carbon d i o d e is absorbed. LITERATURE CITED
(1) Franklin, E. C., “Kitrogen System of Compounds,” p. 111, Reinhold, Kew
Tork, 1935. (2) I. hf,, Sandell, E. B,, book of Quantitative Inorganic Analysis,” p. 372, hlacmillan, New Yorlr,
1952.
w.,
(3) Loveland, J. Adams, R. 1V.j King, H. H., Jr., Nowak, F. A., Cali, L. J., A N ~ LCHEM. . 31, 1008 (1959). (4)Pieters, H. .4.,Anal. Chim. Acfa 2 , 263 (1948). RECEIVED for review February 29, 1960.
Accepted June 27, 1960.
