Determination of Metallic Copper and Cuprous Oxide In Commercial Cuprous Oxide Pigments IRVIN BAKER A N D R. STEVENS GIBBS Chemical Laboratory, Norfolk Navy Yard, Portsmouth, \-a.
Cuprous oxide is soluble in cold aqueous ammonia, whereas cupric oxide is but slightly soluble and metallic copper is insoluble. Addition of hydrazine sulfate t o the reagent tends to reduce any divalent copper entering solution and prevents interaction of cupric copper and metal. If the reaction be carried out in a carbon dioxide atmosphere, the metallic copper-cupric oxide mixture may be isolated and the metal determined by direct aolution in acid ferric chloride, follotved by titration with potassium dichromate.
Cuprous oxide is readily soluble in cold, dilute aqueous hydrochloric acid, cupric oxide is slightly sol-
uble, and metallic copper is very slightly soluble. The presence of hydrazine sulfate reduces any divalent copper entering solution and prevents reaction between metallic copper and cupric ion. The addition of potassium chloride 'prevents the precipitation of cuprous chloride from the very dilute hydrochloric acid solution. If the analysis is performed under an inert carbon dioxide atmosphere the metallic copper and cupric oxide may be filtered off, dissolved in acid ferric chloride, and titrated with ceric sulfate. The total reducing power, the sum of the cuprous oxide and copper reducing equivalents, may be determined by direct solution of the sample in acid ferric chloride and subsequent titration under a carbon dioxide atmosphere with ceric sulfate.
C
The precautions required in this method are numerous and are difficult to apply. An extensive investigation of this method was carried out, and the results obtained by slight variations in procedure are outlined in Table I. Difficulties encountered are as follows: 1. The method depends on the ability of the analyst to determine when all the cuprous oxide has dissolved, by observation of the disappearance of red particles from a mixture of brownish red copper and black cupric oxide in a blue solution. Moreover, cuprous oxide may exist in a variety of colors ranging from yellow through red to brown, depending on the particle size. 2. I t is difficult to control the solubility of carbon dioxide in the alkaline extracting solution. A change in rate of introducing carbon dioxide gas over the solution markedly affects the solubility of the cuprous oxide. The pressure over the solution also affects the solubility. Carbon dioxide is a necessary ingredient of the extraction solution and acts as an active solvent, owing to the formation of ammonium carbonate. Therefore, variations in the quantity of carbon dioxide taken up by the solution during extraction alter the results. Replacing carbon dioxide with other inert gases results in very high copper values. 3. The prrsence of a thin film of cupric oxide due to oxidation prevents solution of all cuprous oxide unless vigorous agitation is applied. This results in lower copper values due to the increased solubility of the copper under agitation. 4. The method involves a large personal factor which makes duplicable results difficult to obtain. Results obtained by different operators failed to check. 5 . The time of extraction markedly affects the results.
OMMERCIAL cuprous oxide pigments contain in addition to cuprous oxide various percentages of metallic
copper and cupric oxide. Because of its finely divided state, the metallic copper is soluble or partially soluble in the reagents t h a t dissolve cuprous oxide, rendering its separation difficult. ConsideTable work has been performed t o determine a method of separation of metallic copper-cuprous oxide mixtures.
Determination of Metallic Copper LeBjanc and Sachse (3) determined the percentage of cupric oxide by titrating the iodine liberated by the oxidation of hydrochloric acid solutions of potassium iodide. Rapid oxidation of the copper by the liberated iodine eliminated this method as an analytical procedure. Fitzpatrick (4)attempted to separate the metallic copper from the mixture by boiling the sample with a saturated silver sulfate solution. During the 10-minute boiling extraction period a considerable amount of the cuprous oxide reacts to form metallic copper which is subsequently dissolved, giving high copper values. Zerfass and Willard (6) attempted to analyze the mixture microscopically. Their results were determined on mixtures containing approximately 50 per cent cupric oxide, whereas commercial cuprous oxide contains only a small per cent. The method was not found to be practical in its application to cuprous oxide pigments.
Various solvents, reducing agents, and procedures were investigated by this laboratory to find a method that would quantitatively separate the copper in commercial cuprous oxides and eliminate the personal factor of the Hurd and Clark method (1, 2 ) . Various solutions of hydrochloric
TABLE I. METALLIC COPPERBY HURDAND CLARKMETHOD(9) Sample Powder Metals and Alloys, 76
The use of reagents which dissolve cuprous oxide, cupric oxide, or both but have no effect on metallic copper presents many difficulties. Solution of the sample in the reagents invokes a reaction between cupric ions and copper, forming cuprous ion, particularly when the copper is in the finely divided state, as in commercial cuprous oxide pigments. T o decrease the solubility of metallic copper, reducing agents were added which could reduce cupric ions to the cuprous state but not to metallic copper and would not affect the metallic copper. A few such reducing agents are hydrazine sulfate, hydroxylamine hydrochloride, and sodium arsenite. Hurd and Clark ( 1 , 2 )outlined a method for the deterniination of metallic copper and cuprous oxide.
-1.S. T.AI., 1 P o n d e r Metals and Alloys, 79
A. S. T.&I..4
505
cu,
R
8.73 7.01 4.13 20.4 23.1 15.78 4.92 6.49 13.69 14.76 12.93 6.86 L.55 4.04 2.48 3.88 9.19 2.67 7.2
Conditions of Experiment Extracted 5 min. E r.t..r_. a r.t.d 5.~...~~. min. -
Extracted 30 min. Yo COz, o en t o air, extracted 30 min. HBatmospfere, extracted 25 min. H? atmosphere, extracted 10 min. (Extracted t o disappearance of red particles) (Extracted t o disappearance of red particles) (Very little agitation, slow stream of Con) Extracted 3 min. Extracted 5 min. Extracted 10 min. Extracted 15 min. Extracted 30 min. (Extracted t o disappearance of red particles) (Extracted t o disappearance of red particles) (Extracted t o disappearance of red particles) (Extracted to disappearance of red particles) (Extracted to disappearance of red particles)
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 15, No. 8
acid, stirring constantly. Dilute to 1 liter in a volumetric flask. Add a few pieces of mossy aluminum to stabilize the solution. The solution should be restandardized frequently with 0.1 N potassium dichromate or ceric sulfate. Carbon Dioxide-Saturated Distilled Water. Boil distilled water for several minutes and pass a rapid stream of carbon dioxide gas through the solution while cooling. Keep water saturated with carbon dioxide gas. PROCEDURE. Add 10 ml. of c. P. acetone and a few small glass beads to a 250-ml. glass-stoppered, Squibb’s type separatory funnel. Replace air by passing carbon dioxide gas into funnel for a few minutes or adding a lump of carbon dioxide snow. Weigh accurately 1 gram of the well-mixed sample and transfer directly to the separatory funnel. Shake vigorously for 1 minute to dissolve any oil or surface coatings and to disperse and wet the particles thoroughly. Refill funnel with carbon dioxide gas, add 20 ml. of dilute hydrochloric acid solution (1 to 9) and 10 ml. of hydrazine sulfate solution (3 per cent), and shake gently for 1 minute. Remove stopper from funnel, refill with carbon dioxide gas, and add 75 ml. of 10 per cent potassium chloride solution. Shake vigorously for 15 seconds. Filter off the metallic copper-cupric oxide residue in the usual way through a 12.5-cm. 41-H Whatman filter paper and a glass funnel. Allow all of the solution to drain off completely before washing. Wash once with 30 ml. of 10 per cent potassium chloride solution and once with 30 ml. of 5 per REAGENTS REQUIRED. Ferric Chloride Solution. Add 75 cent potassium chloride solution. Keep an atmosphere of carbon grams of ferric chloride hexahydrate and 150 ml. of hydrochloric dioxide over the solution during filtration by adding small pieces acid (specific gravity 1.19) to 400 ml. of distilled water saturated of carbon dioxide snow. Finally, wash with approximately 400 with carbon dioxide. Stir to complete solution. Keep the soluml. of distilled water saturated with ,carbon dioxide, with the tion saturated with carbon dioxide. further addition of small pieces of carbon dioxide snow during Hydrazine Sulfate Solution (3 per cent). Add 3 grams of pure the washing. Place the washed residue and filter paper in a widehydrazine sulfate to 97 ml. of distilled water saturated with carmouthed 250-ml. Erlenmeyer flask from which the air has been bon dioxide. Stir to complete solution. replaced by carbon dioxide gas. Add 15 ml. of the ferric chloride Potassium Chloride Solution (10 per cent). Dissolve 10 grams solution and 15 ml. of (1 to 9) hydrochloric acid solution. Warm of c. P. potassium chloride in 90 ml. of distilled water saturated gently on a steam bath to dissolve the metallic copper-cupric with carbon dioxide. oxide residue, still maintaining a carbon dioxide atmosphere in Acetone, chemically pure reagent grade. the flask. Cool the solution to room temperature in carbon diIndicator, o-phenanthroline ferrous complex (ferroin), manuoxide atmosphere. Add 2 drops of o-phenanthroline (ferrous factured by G. Frederick Smith Company, Columbus, Ohio. complex) indicator and titrate at once with 0.1 N ceric sulfate Ceric Suljate Solution. Weigh 50 grams of anhydrous ceric solution. A sharp, distinct color change from orange to pale sulfate into an 800-ml. beaker and add 26 ml. of concentrated green occurs a t the end point. Back-titrate with 0.03 N ferrous sulfuric acid. Dilute with 30 ml. of water. Heat several hours ammonium sulfate to an orange color. Subtract the ferrous amwith occasional stirring, replacing water lost by evaporation. monium sulfate equivalent from the total titration and calculate Add water in small portions at half-hour intervals until the volthe percentage of metallic copper and report as such. ume reaches about 700 rnl. Cool, transfer to a 1-liter volumetric 1 ml. of 0.1 N ceric sulfate = 0.003179 gram of copper. flask, and dilute to mark. Allow solution to settle several weeks and filter to remove suspended matter. Standardize against PRECAUTIOKS. The analysis must be run entirely in an atmoselectrolytic iron or ferrous ammonium sulfate. phere of carbon dioxide with the exclusion of all air to prevent oxidation of copper. Carbon dioxide snow or dry ice has been Ferrous A m m o n i u m Suljate. Dissolve 12 grams of Mohr’s salt in 200 to 300 ml. of water and add 40 ml. of concentrated sulfuric found a convenient method of replacing air. The sample must be well mixed to obtain a homogeneous mixture; otherwise checks cannot be obtained. TABLE 11. METALLIC COPPER IK COMMERCIAL CUPROUS OXIDE S.4MPLES The solution containing the metallic copper-cupric oxide Hydrazine Sulfate-Potassium Chloride Method residue must be allowed to Rohm & Haas, Metals RefinA . S. T. hl.! 6, Metals RefinPowder Metals Powder Metals drain completely through the Electrolytic Electrolytic ing Co., C-J8 ing Co., 4: and Alloys, 320 and Blloys, 99 DeviaDeviaDevisDeviaDeyiaDeviafilter paper, before the final ation ation ation ation ation ation wash with water, to prevent from from from from from from precipitation of cuprous chloCu av. Cu ai-. Cu av. Cu av. Cu av. Cu av. ride on the filter paper. 7 0 % 7 0 % % % 7 0 % % % % % acid and ammonium hydroxide with such reducing agents as hydroxylamine hydrochloride, mercury, formaldehyde, sugars, sodium arsenite, hydrazine sulfate, and others were tested. None of these methods gave reproducible results for the determination of metallic copper. A series of experiments was conducted, using varying concentrations of hydrochloric acid in conjunction with hydrazine sulfate. When the hydrochloric acid concentration dropped below a certain minimum, the cuprous chloride formed from the reaction precipitated. T o remove this precipitate from the copper residue potassium chloride was added to the extraction mixture. The result was that a very low hydrochloric acid concentration could be employed which was still sufficient to dissolve the cuprous oxide but insufficient to react with the copper, despite the fact that it is finely divided. The hydrazine sulfate was added to prevent interaction of copper and cupric ion. Carbon dioxide had no effect on the solubility of the cuprous oxide in the extracting solution.
0.09 0.09 0.10 0.10
-0.005 -0,005 +0.005 +0.005
0.005 Powder Metals and Alloys, 100 Deviation from Cu av.
Av.0.095
0.32 0.22 0.27
0.27 0.03 Metals Refining Co., C-16 Deviation from Cu av.
%
%
7
6.58
+0.03 -0.11 -0.03
7.36 7.30 7.29 7.34 7.36 7.33 7.37 7.38 7.36 7.35 7.27 7.47 7.35
6.44 6.52 6.63 6.57
Av.6.55
+O.OS
+0.02
0.05
+0.05 -0.05 0.00
0
0.61 0.66 0.73
-0.06 -0.01 +0.07
0.67 0.05 Powder hfetals and Alloys, ,113 Deviation from Cu av.
0.97 0.99 0.94 0.96
0.00 +0.02 -0.03 -0.10
0.97 0.02 Powder Metals and Alloys, 111 Deviation from Cu av.
4.25 4.28 4.34 4.32
4.30
-0.05 -0.02 +0.04 CO.02
0.03
Powder hletsls and Alloys, 105 Deviation from Cu av.
%
%
%
%
%
+O.Ol -0.05 -0.06
7.68 7.55 7.50 7.44 7.53 7.52 7.67
+0.12 -0.01
11.74 11.96 11.6 11.74
-0.02 +0.20 -0.16 -0.02
12.56 12.69 12.71 12.63 12.57 12.72 12.77
-0.09 +0.04 +0.06 -0.02 -0.08 f0.07 +0.12
7.56
0.07
11.76
0.10
12.65
0.06
-0.01 +0.01 -0.02 +0.02 +0.03 +O.Ol 0.00 -0.08 +0.12 0.035
-0.06
-0.12 -0.03 -0.04 f0.11
7 0 7 0
6.5 6.25 6.39 6.29 6.39 6.42 6.23 6.33
+0.17 -0.08 f0.06 -0.04 f0.06
fO.09 -0.10 0.09
R E S U L TO F ANALYSES. This method of analysis was used for the determination of metallic copper in eleven samples of commercial cuprous oxides and a number of synthetic mixtures. A total of 79 determinations was run, and the results are outlined in Tables I1 and 111. The method is direct and, with the precautions required, easily carried out. The personal factor required in the Hurd and Clark method (1, 2) for the determination of loss of color, rate of carbon dioxide addition, etc., ha.s been eliminated. With a little prac-
August 15, 1943
ANALYTICAL EDITION
507
centage of cupric oxide in the material by difference, in Hydrazine Sulfate-Potassium Chloride Method nhich the figure for total 2% c u 3.65% C u 6.02% Cu 8.1% Cu 14.27, Cu copper, calculated from the Deviation Deviation Deviation Deviation Deviation cuprous oxide and metallic from from from from from 8 1% 14 20% 2% 3 65% 6 02% copper results, was higher Found Cu Found Cu Found Cu Found Cu Found Cu than the actual total copper % % 7% % % % 70 % 5% 5% determined electrolytically. -0.02 5.92 -0.10 -0.08 14.20 0.00 1.98 -0.02 3.63 8.02 -0.05 -0.04 3.60 5.97 -0.05 +0.07 14.45 +0.25 1.96 6.17 Since it was possible to check $0.02 3.67 -0.02 -0.06 4-0.11 2.02 5,94 6.21 14.46 +0.26 1.96 -0.04 -0.04 5.96 3.61 -0.04 8.05 -0.05 14.10 -0.10 the figure for metallic copper Av. 1.98 0.03 3.63 0.03 5,95 0.06 8.12 0.08 14.31 0.15 accurately, it appears that a Synthetic mixtures were prepared from Rohm & Haas electrolytic grade cuprous oxide C: and 325-mesh metallic the error lies in the fact that copper powder which was extracted with hydrochloric acid-hydrazine sulfate solution, washed, and dried in a vacuum desiccator. Results were corrected for small amount of metallic copper found in analysis of cuprous oxide. the value for total reducing power was too high. An investigation was undertaken t o obtain a n tice the method will give results reproducible within the accurate reproducible method for t'he determination of the limits shown in Tables I1 and 111. A maximum deviation total reducing power of cuprous oxide pigments. Various methods of procedure, oxidizing titrating solutions, indicators, of 0.1 per cent and a n average deviation of 0.05 per cent was obtained with the electrolytic or low copper content and acids were used in the investigation. It was found t h a t varying the quantity of indicator varied the results, whereas cuprous oxides; and a maximum deviation of 0.3 per cent the blank remained the same. Variation in the acids used and an average deviation of 0.15 per cent with cuprous oxides of high copper content. Results determined on the slightly altered the results. The use of ceric sulfate solution as an oxidizing titrating solution produced accurate results. same sample a t different periods of time must not be compared for accuracy, since many samples of cuprous oxide The reagents required are the same as for the det,erminachange considerably from d a y to day. tion of metallic copper. TABLE111. METALLIC COPPER
IN SYNTHETIC MIXTURES'
PROCEDURE. Weigh accurately a 0.2-gram sample and place it
TABLE IV. TOTAL REDUCING POWER USINGPOTASSIUM DICHROMATE Metals Refining Co., 1011
Powder Metals and Alloys, 111
Powder Metals a n d Alloys, 99
Powder Metals and .4lloys, 105
%
70
70
%
101.8 102.1 103.4 102.6
106.1 107.0
98.2 99.3
106.0 109.5
106.4
98.4
106.5 109.2
Determination of Total Reducing Power
in a 250-ml. vent,ed, glass-stoppered Erlenmeyer flask previouslv
filled with carbon dioxide gas. Add a few small glass beads and 10 ml. of ferric chloride solution. Heat gently for 15 minutes, stirring occasionally and maintaining a carbon dioxide atmosphere a t all times. After the sample has dissolved, cool and titrate a t once with 0.1 N ceric sulfate solution by the procedure given for the determination of metallic copper. Calculate the total reducing power as cuprous oxide and report as such. 1 ml. of 0.01 N ceric sulfate = 0.007157 gram of cuprous oxide. To determine the percentage of cuprous oxide multiply the per cent of metallic copper by 2.252 and subtract from the per cent of total reducing power as cuprous oxide. The difference is percentage of cuprous oxide. To determine percentage of cupric oxide, use the following formula:
Determining total reducing power of cuprous oxide piga = Cu20 X 0.888 = metallic copper equivalent of Cu20 b = metallic copper as determined ments b y solution of the sample in hydrochloric acid-ferric c = total copper determined electrolytically chloride solution, followed b y titration of the resulting ferrous c - (a b ) = d = per cent of copper as CuO iron with potassium dichromate, using barium diphenylamine d X 1.252 = per cent of CuO sulfonate indicator, was found t o be unsatisfactory. Results obtained differed in some cases by as much as 1.5 per cent, Ceric sulfate, in the determination of total reducing although the procedure was identical in each case ( 5 ) . Table power and metallic copper, has a number of advantages over potassium dichromate. I n the case of the dichromate with IV lists the values obtained on a number of commercial diphenylamine sulfonate as indicator, a considerable quantity samples. of indicator is necessary to give a visible color change a t the In a report made b y the National Bureau of Standards in March, 1942, on the analysis of samples of cuprous oxide, a end point. Often the change from deep green to purple is difficult t o obtain sharply, even though a n excess of phosvalue of 98.0 per cent was obtained for total reducing power on sample C-16 and 10 days later a value of 99.0 per cent phoric and sulfuric acid is present. With o-phenanthroline, was obtained. As samples of cuprous oxide lose reducing 2 drops of indicator give a sharp, distinct color change a t t h e power during storage, this is not consistent with other results obtained on similar samples, which showed a loss TABLE v. ANALYSESO F C0,ZIlfERCIAL CUPROUS OXIDE PIG4IEXTS in reducing power. The reMetals Refining Metals Refining sults obtained b y two operaSample Rohm & Haas C Rohm & Haas F Co., 113 c o . , 1011 tors on samples C-17, C-18, 7 0 % 7 0 % % % % % Metallic Cu 0.33 0.33 0.83 0.83 1.4 1.4 3.6 3.6 and C-19 varied as much as Total Cu (electrolytic) 66.07 66.07 66.70 66.70 88.10 68.10 66.01 68.01 0.5 per cent when run at the Total 'poddwueclinp { potassium dichromate 97.80 96.92 100.80 103.5 .... same time, which is conceric sulfate 97:oo 98: 20 99:io . . . . 102.1 CulO (calcd.) 97:i5 96.34 9+:05 96.50 96.5, 95.40 94.00 sidered too large an error for Total Cu calcd. from metallic Cu the determination of total and CuzO 86;60 85.67 87;03 86.25 88;14 67.15 86;34 87.10 CuO, by difference 0.25 0.38 1.20 1.13 reducing power. Numerous instances were a iiegative figure. found in determining the per-
+
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 79,75 so:i1 +.0.. .4.6 .... 0.1 per cent and an average deviation of 0.04 per cent were 77.68 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 CERIC SULFATE
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-
