508
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 15, No. 8
tion potential of the ceric ion is very high, being close t o that of permanganate, thus ensuring a Metals Refining Metals €&fining Powder Metals Powder Metals rapid, complete reaction. Co., 228 Co., 41 and Alloys, 320 and Alloys, 278 DeviaDeviaDeviaDeviaTable V gives analyses of four commercial tion from tion from tion from tion from cuprous oxides, using t’he dichromate and ceric av. av. av. av. % % % % % % % % sulfate methods for determining total reducing 99.31 +0.01 100.14 4-0.06 99.03 -0.04 97.55 0.00 power. I n the case of the dichromate titration, 99.36 +0.06 100.10 f0.02 99.09 f0.02 97.60 +0.05 the copper calculated from metallic copper 99.28 -0.02 100.05 -0.03 99.07 0.00 97.61 +0.06 99.25 -0.05 100.03 -0.05 99.10 +0.03 97.49 -0.06 and cuprous oxide is more than is found by 97.53 -0.02 100.11 +0.03 99 07 0.00 99.35 +0.05 99.23 -0.07 100.05 -0.03 99.04 -0.03 97.50 -0.05 determining total copper electrolytically. The Av. 99 30 0.04 100.08 0.04 99.07 0.02 97.55 0.04 ceric sulfate method shows sufficient copper to allow for the presence of cupric oxide. This is more in accordance with what is to be TABLE VII. TOTALREDUCINGPOWEROF SYNTHETICMIXexpected, since it is doubtful that commercial TURES OF CUPROUS OXIDEA N D CUPRICOXIDE CalcuDichromate Ceric Sulfate cuprous oxides can be manufactured with the total exlated Found Error Found Error clusion of cupric oxide. % 70 % % % Table VI lists the results of 24 determinations of four 91.53 91.96 +0.43 .... 92.71 .... si:& -0.10 commercial cuprous oxide samples for total reducing power 85.45 86:36 +0.91 .... by the ceric sulfate method. A maximum deviation of 83.28 .... 83 : 40 +o. 12 so:i1 +.0.. .4.6 .... 0.1 per cent and an average deviation of 0.04 per cent were 77 79 .,6785 77:60 -0.08 65.59 6 6 : 24 f0.65 .... obtained. Table VI1 shows the results obtained for syn66.32 .... 66:i6 -0.16 thetic cuprous-cupric oxide mixtures by the dichromate and 61.25 6i:65 f0.40 .... 60. OS ... .... 6o:ii -0.03 ceric sulfate methods. TABLEVI. TOTAL REDUCIXG POWER USISG CERICSULFATE
Synthetic mixtures were prepared by weighing varying amounts of cuprous oxide and cupric oxide t o total approximately 0.25 gram and determining t h e total reducing power on t h e entire sample. Cuprous oxide was Rohm & Haas electrolytic grade cuprous oxide C (Table V). Cupric oxide was a reagent grade material with less t h a n 0.1 per cent total reducing power and screened through a 325-mesh screen.
end point \+-ith ceric sulfate. S o additional acids are required. hi^ indicator cannotbe used ,vith dichromate, since the color change from orange to green is obscured by the orange color of the dichromate ion. The cerous ion on the other-hand is colorless. Ceric sulfate is applicable in the determination Of reducing agents in the presence Of high concentrations of hydrochloric acid. The oxidation reduc-
Literature Cited (1)
Am.SOC.Testing Materials, Standard Method of Routine Analy-
sis of Dry Cuprous Oxide, D-283-33. (2) Hurd, L. C., and Clark, .4.R., ISD. EX. CHEM.,ANAL. ED., 8 . 380-2(1936). (3) LeBlanc, M.. and Sachse, H., Ann Phusik, 11, 727 (1931). (4) S c o t t , u’. w., “Standard Methods Of Chemical Analysis”, 5th ed., p. 394, New York, D. Van Kostrand Co., 1939. (5) s. N~~~ Department, specifications 52C4b (1935). . 8, ( 6 ) Zerfass, R.,and Willard, M. L., ISD. ESG CHEX., A s . 4 ~ ED., 303 (1936).
u
THEviews presented in this article are those of t h e writers and are not t o be construed as the official views of t h e S a v y Department.
Determination of Butadiene In the Presence of Other Unsaturated and Saturated Gaseous Hydrocarbons J. F. CUNEO AND R. L. SWITZER Union Oil Company of California, Wilmington, Calif.
A
RAPID and accurate method of analysis for 1,3-buta-
diene is of considerable importance in the present synthetic rubber program. It is well known that the various methods of preparation of butadiene give products consisting of mixtures of compounds, some of which are of a particularly complex character. Depending upon the method of manufacture butadiene can be associated with any of the following hydrocarbons: n-butane, isobutane, isobutene, 1-butene, cis-2-butene1 trans-2-butene1 methylacetylene, vinylacetylene, and ethylacetylene. The method of analysis for butadiene in gaseous mixtures should be rapid and accurate, regardless of the percentage of the above-mentioned compounds. At the present time the usual method of analysis for butadiene is based on its reaction with molten maleic anhydride a t 100” C. (2, 6). When butadiene exists in the presence of other gases, such as isobutene, butenes, and butanes, a single absorption cannot be used,‘since the gases associated with the
butadiene will be absorbed by the maleic anhydride, giving incorrect results. To overcome this error the molten maleic anhydride must first be treated with a portion of the sample to be tested so that equilibrium with all gases present exclusive of butadiene, particularly isobutene, will be established. When equilibrium is reached, another portion of the gaseous mixture is again absorbed, and the operations are repeated until check values for the butadiene are obtained. I t is desirable to estimate first the amount of butadiene in the gaseous mixture before carrying out the determination, since it has been found necessary by some investigators t o dilute the mixture with nitrogen when the butadiene is present in high percentages. This paper describes a method for the determination of butadiene in gaseous hydrocarbon mixtures free of acetylenes. It has been found possible to remove the acetylenes commonly associated with the butadiene and butenes pro-
August 15, 1943
ANALYTICAL EDITION
duced by cracking petroleum stocks nithout affecting the relative proportion of the remaining gaseous constituents. Details of this method will be published later. The determirlatioll of butadiene consists of two fundamental operations : (1) absorption of the alkenes and alkadienes in a mercuric nitrate solution; ( 2 ) hydrogenation of the alkenes and alkadienes to alkanes. From these data the mole per cent of alkadienes in the hydrocarbon mixture may be calculated by the Colloxing equation: mole yo alkadiene
=
509
TABLE I. BUTADIENE CONTESTOF SYNTHETIC BLENDS 7 -
KO. n-C4HlO % 1 2 3 4 5 6
16.3 15.5 17.8
21.6 18.2 19.6
(mole % unsaturation by hydrogenation) (mole % unsaturation by mercuric nitrate a bsorption)
Apparatus and Material All inorganic chemicals used were of reagent grade, The anhydride was obtained from the Eastman Kodak Company. The apparatus required for the analysis of hydrocarbon gases containing butadiene consists of the following: 1. Any suitable type of analytical hydrogenation apparatus can be used. For this work the apparatus was patterned after the design described in the Universal Oil Products handbook with no essential modification ( 7 ) . 2. An Orsat apparatua, having the gas buret calibrated so that the smallest division is not greater than 0.1 ml. and equipped with at lea.st three bubblers, preferably the Fisher valve bubblertype pipet ( 4 ) is used. 3. The solutions used in the bubbler pipets are 30 per cent potassium hydroxide in one and mercuric nitrate solution in the other two. The second pipet, containing mercuric nitrate solution, is used alternately nith the first one. The most satisfactory composition of the mercuric nitrate reagent is: 600 grams of mercuric nitrate, H g ( X O & 1250 grams of sodium nitrate, NaNOa 383 ml. of 70 per cent nitric acid, HNOa 2100 ml. of distilled water
Procedure The sample is passed through mercuric nitrate solution until the absorption is complete. This operation requires five or six cycles if a fresh solution is in the bubbler at the beginning of the operation. When the solution is partially spent, additional passes may be required to obtain the same result. Samples rich in isobutene will cause a yellow precipitate to form, which at first is redissolved by the reagent. Further additions of isobutene cause a permanent precipitate to form and collect on the surface of the pipet. At this point it is necessary to replace the solution with fresh mercuric nitrate reagent. After complete absorption in the mercuric nitrate pipet, the remaining gas is scrubbed in the caustia bubbler t o remove any traces of nitric acid. Both the alkenes and alkadienes are absorbed by the mercuric salt. If the gas is completely or nearly soluble in the solution, it is necessary to add some inert gas to act as a carrier to enable the ga3 to contact the reagent effectively; air may be used for this. The hydrogenation value of an aliquot portion of the same gas sample is now determined by mixing a known volume of the unknown gas with an excess amount of oxygen-free hydrogen (3). Since the catalyst is poisoned by oxygen, carbon monoxide, or hydrogen sulfide, it is essential that the gas be free of these constituents. The presence of moisture will also lead t o erroneous results, so the gas sample and the hydrogen should be thoroughly dried before they are introduced into the measuring burets. The resulting mixture is then passed through the nickel catalyst until a constant volume is reached. The decrease in volume is calculated in terms of percentage hydrogenation after applying a correction for the deviation of the hydrogen-hydrocarbon mixture from the ideal gas volume (1, 6).
Experimental Results The method was applied to synthetic blends of n-butane, isobutene, and butadiene. These known mixtures were prepared by weighing definite amounts of each hydrocarbon gas into a stainless steel bomb. A comparison of the butadiene
Blendi-C&
% 0
19.3
29.9 45.6 53.4 65.1
-
C4Ha
Unsaturation B Y hydroB y Hg(N0s)z genation solution
CiHa Determined B y hydrogenation By maleic Hg(N0a)z anhydride
%
%
%
%
%
83.7 95.2 02.3 32.8 28.4 15.3
167.4 149.9
83.7 84.7
83.7 65.2 52.2 32.5
83.6
134.6 113.6 110.1 95.7
82.4 81.7 81.1
80.6
28.4
15.1
64.0 51.8 31.8 28.6 15.0
content by the maleic anhydride method for known blends is given in Table I.
Discussion The results obtained by maleic anhydride absorption, though fairly close in most cases, fail to agree with the known values as well as the results obtained by this method. I n carrying out the maleic anhydride method the pressure above the molten anhydride must be kept as close to atmospheric as possible. Substantial variations in the pressure cause a considerable difference in the amount of nonreactive gases nhich will dissolve in maleic anhydride. It must also be assumed that the solubility of the gaseq, other than the butadiene in the tetrahydrophthalic anhydride, is the same as it is in the maleic anhydride. It has been observed that, before an operator can obtain reproducible results by the maleic anhydride method, a certain amount of manipulative skill must be acquired, whereas the method described requires little experience to give sntiafactory results. Isobutene was used in the blends (see Table I) in place of some other butene, because there has been some question a4 to vhether the mercuric nitrate unsaturation value could be depended upon when the sample contained isobutene. The tabulated results show that quantitative absorption of isobutene, as well as butadiene, can be easily accomplished, provided the mercuric nitrate reagent is replaced as soon as a n y appreciable crystallization of the hydrocarbon-mercuric salt occurs in the solution. The recovery of mercury from the spent solutions is accomplished by collecting the spent reagent in a jar and suspending a strip of lead in the liquid. The solution should be made acid with concentrated nitric acid. Lead will replace the mercury in solution, and metallic mercury will collect in the bottom of the jar. This helps to eliminate the cost involved by the use of mercury salts.
Acknowledgment The authors wish to thank R. S.Crog for suggesting the extension of the hydrogenation method to include butadiene, and Margaret Jean Saltsman for her assistance.
Literature Cited (1) Dolgoplosk. B. A . , and Korneev, Sintet. Kauchuk, KO.4, 15-18, (1936). (2) Korotkov, A. 4., I b i d . , KO.4, 23-31, (1933). (3) McMillan, IT. 4..Cole, H. A., and Ritchie, A . V., IWD.ENG. CHEY..AWLL. ED..8. 105 (1936). (4) Matuszak, hi. P., “Fischer Gas Analysis Manual”, p. 61, Pittsburgh, Fischer Scientific Co., 1934. (5) Robey, R. F., and hlorrell, C. E., IND.ENG.CHEM.,AXAL.ED., 14,880 (1942). (6) Tropsch, H., and Mattox, W. J., Ibid., 6 , 104 (1934). (7) Universal Oil Products Co., “U. 0. P. Laboratory Test Methods for Petroleum and Its Products”, p. G. 70, Chicago, Ill, 1940. PRESESTED before t h e Division of Rubber Chemistry a t she 105th Meeting of t h e AMERICAN CHEMICAL SOCIETY, Detroit, Mich.
