Determination of Butadiene in Gases HANSTROPSCH AND W. J. MATTOX Research and Development Laboratories, Universal Oil Products Company, Riverside, Ill. HE method g e n e r a l l y adopted for the estimaOf
the
A method f o r the rapid, accurate, routine determination of butadiene in complex gas mixtures is described, in which molten maleic is used as the absorbent, anhydride at 100' the development of this method making possible the analysis of small samples of gas which heretofore could be analyzed only by very tedious and inaccurate methods.
addition of one molecule of the diolefin to one of the maleic anhydride. The cyclic hydrocarbons react instantaneously with evolution of heat, but the addition with straight-chain diolefins is a slower process, butadiene, isoprene, and piperylene all reacting slowly in the cold, although readily a t slightly elevated temperatures. Birch and Scott (1) have made use of this reaction to isolate a number of diolefins from the fractions of a compression-plant gasoline from a high-temperature cracking unit. Martin, Gruse, and Lowy (6) have studied the effect on gum formation of quantitatively removing conjugated dio l e h s from fractions of vapor-phase distillates by treatment with maleic anhydride. The ready formation of these anhydrides having given an excellent method for the quantitative separation and identification of diolefins in liquid hydrocarbon mixtures, the purpose of this investigation was to apply the same reaction to the determination of butadiene in gases.
content of gases has consisted in the addition of bromine followed by the separation of the tetrabromide from admixed dibromides, derived from the olefins, by fractional distillation under reduced pressures and the calculation of the butadiene content of the original gas, as a maximum value from the crude tetrabromide or as a minimum value from either the recrystallized tetrabromide or the regenerated butadiene, the actual quantity being somewhere between these two figures (6). Sorokin and Belikova (8) have determined butadiene by separating it as the tetrachloride. The titrimetric method of Povarnin and Belikova (7) is based on the observation of Bergmann that the dibromide forms within 5 minutes, the tetrabromide after 12 hours. Dobryanskii (4) has also proposed a titrimetric method based on the transformation of the butadiene into the tetrabromide by means of bromine liberated from a weighed quantity of potassium bromate. Markovich and Pigulevski (6) PREPARATION OF 1,3-BUTADIENE found this method to be unreliable for a number of types of The butadiene used in these experiments was isolated from a gases, and good results were obtained only in the analysis cracked refinery gas. A quantity of the cracked gases, containing of highly rectified butene-butadiene distillates. 3 to 5 per cent of butadiene, was passed through a small conA method similar to that of Dobryanskii, and with the densing trap cooled t o -78' 0.by solid carbon dioxide and modifications recommended by Davis, Crandall, and Higbee acetone, a temperature at which all of the C-4 and a part of the C-3 hydrocarbons were co n (2) to eliminate the disturbing densed. These condensed hvdroinfluence of oxygen in these ticarbons were then vapoiized trations, has been tried in this and passed through bromine in laboratory, but the results obcarbon tetrachloride at 0' C. The excess of bromine was retained by this method were inmoved and the carbon tetrachloexact and quite unsatisfactory. ride solution dried over calcium That quinones, azo esters, chloride. An equal volume of and various unsaturated alalcohol was added and the solution cooled in a solid carbon dehydes react with conjugated dioxide-acetone bath, whereu on diolefins to form various ring almost the whole of the higger c o m p o u n d s h a s l o n g been melting form of the butadiene known, and such reactions have tetrabromide crystallized out. For the regeneration of the butarecently been used in identifydiene, equal weights of the careing the diolefins in v a r i o u s fully purified tetrabromide (m. p. gasoline fractions. 118' C.) and zinc d u s t were placed in a flask with ethyl alcoDiels and Alder (3) record hol (approximately2 cc. for each 2 MM I D cdP/u,+mthat the simple open-chain and GLASS T U B / N G gram of the tetrabromide) at 0" cyclic butadienes unite with C. and the whole allowed to warm maleic anhydride to give anslowly u n t i l t h e b u t a d i e n e hydrocyclohexenes in quantitawas liberated. Toward the end of the reaction, the flask was tive yield, the butadiene adheated gently. The yield was dition product being cis-A4almost quantitative and of high tetrahydrophthalic anhydride purity, as shown in the subse(m. p. 103-4' (3.). *; quent distillation on a low-temperature Podbielniak fractionatMost of these addition proding column as a means of further ucts a r e f o r m e d w i t h the purification. greatest e a s e , g e n e r a l l y by allowing the diolefin and maleic APPARATUS.Small amounts S TUB/&G anhydride to react in benzene of molten m a l e i c anhydride s r / O & OF E solution a t ordinary temperaa t 100' C. were found most tures, the reaction involving the suitable as an absorbent for FIGURE1. DIAGRAM OF APPARATUS
c*
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March 15, 1934
INDUSTRIAL A N D ENGINEERING CHEMISTRY
105
butadiene. The reaction between maleic anhydride and butadiene is rapid a t 100" C., a decided advantage in using the molten anhydride. The gaseous hydrocarbons have an appreciable physical solubility in the molten anhydride, and in order to reduce this physical solubility to a minimum, small amounts of the anhydride must be used. Hence, it was necessary to design a special absorption pipet with which gas absorptions could be made with less than 2 cc. of absorbent, suitable means being provided for maintaining the temperature of the pipet a t 100" C. These conditions have been very successfully met in the pipet shown in Figure 1. Pipets similar to the usual Orsat type, but heated by a steam jacket, requiring large amounts (125 grams) of maleic anhydride were not satisfactory, since the error caused by the physical solubility of the hydrocarbons could not be satisfactorily eliminated. The apparatus, shown diagrammatically in Figure 1, consisted essentially of buret A , in connection with absorber E, through T-stopcock 2, and bulb H with the accompanying leveling bulb I. Leveling bulb G, containing mercury, permitted the displacement of the gas from the absorber. A small flame under J maintained a circulation of boiling water through jacket F and around absorber E , a few small glass beads in the lower bend of J promoting gentle boiling and a regular circulation. Buret A was surrounded by jacket B which contained water and thermometer C, reading to 0.1" C. Saturated salt solution, colored by the addition of a small amount of methyl red in sulfuric acid, was used in the buret, since it was found that maleic anhydride a t 100' C. did not appreciably absorb water vapor from gases saturated with water vapor a t ordinary temperatures.
That the presence of isobutene had no influence on the absorption of butadiene was shown by absorptions from butadiene-isobutene-nitrogen mixtures containing approximately 10 per cent of isobutene. TABLE11. ANALYSISOF BUTADIENE-ISOBUTENE-NITROGEN MIXTURES
PROCEDURE.From 2.0 to 2.5 grams (1.5 t o 2.0 cc.) of fresh1 distilled maleic anhydride were heated to approximately 100" in a shallow dish and drawn into the heated absorber E through stopcock 3. The rubber connection to G was then replaced and mercury introduced into E until all gas was displaced and the molten anhydride stood in the capillaries just above the top of jacket F. B y means of mercury from I , all gas was displaced from H and the capillary connection t o E. A 50- to 100-cc. portion of the gas to be analyzed was taken into the buret, the mercury level in E lowered to the bottom of the U-tube, E, and the gas passed from A, through E, into bulb H , the rate of passage being regulated by adjusting stopcock 4. The gas was then passed back into A , through E, by lowering leveling bottle D and raising I . The gas remaining in E was displaced by raising the molten maleic anhydride into the capillaries just below stopcock 2. The volume was then read and the operation repeated once or twice until no further absorption was observed, the temperature of E being kept at 100" C. This preliminary passage of a portion of the gas was necessary in order to saturate the maleic anhydride with the hydrocarbons, or in case the maleic anhydride had been used in previous analyses, to bring the hydrocarbons already physically dissolved into equilibriumwith those in the sample to be analyzed. A sample of approximately 100 cc., measured t o 0.1 cc., was then taken for the analysis and the absorption carried out as above, correction being made for any change in temperature.
Acetylene (with air) in concentrations greater than 40 per cent was slowly but steadily absorbed. The volume absorbed per pass per 100 cc. of gas for concentrations to 100 per cent is shown in Table IV. TABLEIV. ABSORPTION OF ACETYLENE BY MALEIC ANHYDRIDE
d
ANALYSISOF SYNTHETICMIXTURES
Following the procedure outlined above, analyses were made of a number of synthetic mixtures containing known amounts of butadiene as a means of determining the accuracy of the method. The absorption of butadiene from a butadiene-nitrogen mixture containing 6.7 per cent of butadiene showed that the absorption was rapid and quantitative. TABLEI. ANALYSISOF BUTADIENE-NITROGEN MIXTURES
MIXTURE I Calculated Found 84.5 10.1 5.4 5.3
COMPONENTS Nitrogen Isobutene Butadiene
MIXTURE I1 Calculated Found 85.1 9.6 5.3 5.4
... ...
... ...
As a further check by means of synthetic mixtures, known amounts of butadiene were added to a cracked refinery gas and the resulting mixtures then analyzed. The small amount of butadiene present in the cracked gas was first removed by passage through maleic anhydride a t 100" C. The cracked gas contained high percentages of ethylene, propene, and butene as well as appreciable amounts of the corresponding paraffins and pentane. The percentages of butadiene added to this gas are given in Table 111, together with the values found by analysis for these mixtures. TABLE111. ANALYSISOF CRACKEDGAS-BUTADIENE MIXTURES BUTADIENE SAMPLE
Calculated % 0.5 0.5 2.4 2.5 5.1 5.1 9.9 9.9 19.0 19.5
1 2 3 4 5 6
7 8 9 10
AT
Found
% 0.5 0.6 2.4 2.5 5.1 5.1 9.8 9.9 18.9 19.5
100" c.
VOLUME DISROLVED
ACETYLENE
%
Cc./lOO cc
30 40 50 100
0.04.05 0.1 0.5
0.0'
Cracked gas-butadiene mixtures were then prepared containing 5 and 15 per cent of acetylene. The analysis of these mixtures, shown in Table V, indicated that acetylene in concentrations up to 15 per cent did not influence the accuracy of the butadiene determination. TABLE V. ANALYSIS OF CRACKED GAS-ACETYLENE-BUTADIENE MIXTURES ANALYSIS
ACETYLENE
1
2
BUTADIENE Calculated Found
%
%
%
5.0 15.0
14.9 5 0
14 9 4 9
The absorption of isoprene vapor (b. p. 35" C.) was found to be quantitative. Isoprene was vaporized in nitrogen to give a mixture containing approximately 10 per cent of isoprene vapor. This mixture was analyzed by absorption in 87 per cent sulfuric acid and by the maleic anhydride absorption. The data are shown in Table VI. TABLEVI. ABSORPTION OF ISOPRENE VAPORBY MALEIC ANHYDRIDE VOLUME PERCENTOF ISOPRENE VAPOR ANALYSIE SAMPLE 87% BY &So4 By anhydride maleic Calcd 1 2 3 4 5
1 1 1 2 3
13 1 13.1
.. ..
..
11.6 11.6 11.7 1.2 1.5
... ... ...
13 1 4
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ANALYTICAL EDITION
The higher values obtained by the sulfuric acid absorption were undoubtedly due to the presence of olefins in the isoprene (from Eastman Kodak Company), most likely pentenes, since pentenes have been found in carefully fractionated isoprene obtained by the distillation of caoutchouc. That low values by the maleic anhydride absorption were not caused by an equilibrium betweeh unreacted isoprene and the isoprene derivative cis-5-methyl-A4-tetrahydrophthalicanhydride (m. p. 64" C.) is shown by the close agreement between the calculated and experimental values in analyses 4 and 5 on samples 2 and 3 which were obtained by diluting sample 1 with known volumes of air.
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Vol. 6, No. 2
Hence, in the analysis of different types of gases, or of gases varying widely in content of hydrocarbons, it was necessary first to pass a portion of the gas through the maleic anhydride so as to saturate the reagent and establish equilibrium between the gas and the physically dissolved portion, thus eliminating errors which might otherwise arise from differences in the amounts of these hydrocarbons held in physical solution with various types of gases.
ANALYTICAL ABSORBING POWER OF MOLTENMALEIC ANHYDRIDE The 2.0 to 2.5 grams of anhydride used in the pipet still actively absorbed butadiene after the absorption of 250 CC. COMPARISON WITH TETRABROMIDE METHOD However, crystals formed in the molten anhydride to such an The analysis of a cracked gas by the maleic anhydride extent after this amount had been absorbed that the anhydride method and by the tetrabromide method gave values in close was usually changed after absorbing approximately 150 cc. agreement, of butadiene. For the average sample, this would be over TABLE VII. ANALYSISOF CRACKED GASBY MALEIC ANHYDRIDE thirty analyses. AND TETRABROMIDE METHODS APPLICATION TO ROUTINE ANALYSIS OF PLANT GASES M~THOD Msleio anhydride Tetrabromide 'ANALYSIS The method is now being used in this laboratory for the 1 3.6 3.8 2 3.4 3.8 routine determination of butadiene in various plant gases. The values by the tetrabromide method were 0.3 per cent Typical analyses are shown in Table 1X. high, as was to be expected, since this method is known TABLEIX. ANALYSISOF PLANT GASES necessarily to give somewhat higher than the correct values. --ANALYSIS A sample of from 20 to 30 liters of gas and 3 or 4 hours' SAMPL~; 1 2 3 1 0.1 0.1 ... time are necessary for an analysis by the tetrabromide 2 0.4 0.4 method, while the analysis can be made by the maleic anhy3 2.6 2.6 i:i dride method in 10 minutes and with samples of 100 cc. or less of gas. The method is proving to be of considerable value in determining the butadiene content of the gases from a number PHYSICAL SOLUBILITY OF HYDROCARBONS of pyrolysis experiments for which until now no method of The gaseous hydrocarbons, other than butadiene, were determination has been available. found to have a very slight physical solubility in molten SUMMARY maleic anhydride a t 100" C. However, the maleic anhydride was rapidly and completely saturated by passing a 1. Molten maleic anhydride at 100" C. has been found small portion of the gas once or twice through the anhydride. a suitable reagent for the quantitative determination of Using fresh maleic anhydride, the analyses in Table VI11 butadiene in complex gas mixtures. were made successively on a cracked refinery gas. 2. Olefins do not react with maleic anhydride and have no influence on the butadiene determination. TABLEVIII. EFFECT OF PHYSICAL SOLUBILITY OF HYDRO3. Acetylene in concentrations up to 15 per cent has no CARBONS ON ANALYSISOF CRACKED GAS BUTADIEINE IN CRACXH~D GASPLUS influence on the butadiene determination. 60 PERCENTAIR BUTADIENE IN 4. Errors which might be introduced by the physical ANALYBIS CRACKEID GAS Calculated Found solution of the hydrocarbons in the molten anhydride have % % % 1 3.6 ... ... been eliminated by using small amounts of the reagent and 2 2.6 ... ... saturating it with the gas before the analysis. 3 4 ' 5. Analyses made on synthetic mixtures containing 6 6 known amounts of butadiene have shown the method to be 7 very exact. 8 6. Approximately 10 minutes and 100 cc. or less of gas In analysis 1 the value 3.6 per cent was too high, being are required for an analysis. caused by the physical solution of the hydrocarbons in the 7. The apparatus and procedure developed and demolten maleic anhydride. The values for analyses 2, 3, and scribed for this analysis are suitable for rapid, routine de4, obtained after the saturation of the maleic anhydride by terminations, the paraffin and olefin hydrocarbons, are correct. The LITERATURE CITED cracked gas contained a high percentage of hydrocarbons, so that more hydrocarbon was in physical solution than in the (1) Birch and Scott, IND. ENG.CHEM.,24, 49 (1932). case of a gas containing a smaller percentage of hydrocarbons. (2) Davis, Crandall, and Higbee, Ibid., Anal. Ed., 3, 108 (1931). This was shown in analyses 5 to 8 in which the hydrocarbon (3) Diels and Alder, Ann., 460, 98 (1928). (4) Dobryanskii, Neftyanoe Khozya'istvo, 9, 574-7 (1925). content was one-half of that in analyses 1 to 4. Analysis (5) Markovich and Pigulevski, Refiner & Natural Gasoline Mfr., 5 gave a value 0.3 per cent low, caused by the release of a 11, NO.4, 307-8 (1932). portion of the dissolved hydrocarbons on the passage of the (6) Martin, Gruse, and Lowy, IND.ENO.CHEM.,25, 381 (1933). gas containing a smaller percentage of hydrocarbon gases. (7) Povarnin and Belikova, J. Russ. Phys. Chem. Soc., 55,226 (1924). The values for analyses 6, 7, and 8 were constant and indi- (8) Sorokin and Belikova, J.Ind. Chem. (Russia),1,28-9 (1925). cated the correct butadiene content. RF,CEW~D October 9, 1933.
