(6) Hallsz, I., Schneidw, W., "Gas Chromatography 1961, Lansing,,' 3. Brenner, J. E. Callen, MI. D. Weiss, eds., pp. 287-306, Academ>c Press, Sew Yo&, 1962. (7) Janlk, J., Novlk, J., J . Chromatog. 4, 249-51 (1962). ( 8 ) JanAk, J., Novlk, J., Gas Chroma-
tography Symposium, Brno, Czechoslovakia, June 1962, reported by Janlk, J., J . Chromalog., April 1963, pp. 6, 8. (9) Jentzsch, D., Friedrich, K., z. Anal. Chem. 180, 96-109 (1961). (10) McWilliam, I. G., J . Chromatog. 6 , 110-17 (1961). (11) Nel, W., Pretorius, V., Nature 181, p. 177-8 (1958).
(12) Sternberg, J. C., Galleway, W. S., Jones, D. T. L., "Gas Chromatography 1961, Lansing," N. Brenner, J. E. Callen, M. D. Weiss, eds., pp.231-67, Academic Press, Xew York, 1962.
RECEIVED for review September 5 , 1963. Accepted November 4, 1963.
Separation of Butene Isomers and Butadiene by Gas Liquid Chromatography CECIL E. HlGGlNS and WlLLlS H. BALDWIN Chemistry Division, Ouk Ridge National Laboratory, Oak Ridge, Tenn.
b Retention data are presented for the gas chromotogrophic separation of 1 -butene, trans.2-butene) cis-2butene, and 1,3-butcidiene, using several high boiling liquid substrates at 25" C. The most efFective resolutions were obtained using aryl ethers modified by nitro or aniine groups, aryl aldehydes and ethers, glycerol triacetate, and triethyl phosphate. The butenes produced by pyrolysis of butyl phosphates have been analyzed on a 1 8-foot column OF o-nitrophenetole on Celite. The column characteristics are listed.
G
liquid chromatography is the simplest and most useful method for the analysis of gaseous mixtures. Butene gas m i x t u m are commonly separated by either of two types of substrate. I n one, unstable adducts are formed between the olefin and a complexing agent such as silver nitrate dissolved in a suit2 ble solvent like ethylene glycol (5) or benzyl cyanide (1). The other type ised effectively is a polar organic liquid exemplified by dimethylformamide (6, 14, 20, 22), propylene carbonate I 16), dimethylsulfolane (6, 7 , IO), @$'-oxydipropionitrile (16, 19, 23), or hexamethylphosphoramide (15, 17'). ,Ilthough separation factors arch better a t lower temperatures, providing the substrate remains liquid, some high boiling liquids have given satisfactory separations a t room temperature (5, 6, 8, 13, 16, 17, AS
19).
I n previous work 011 the pyrolysis of tributyl phosphate and related compounds (11) the butene isomers formed were chromatographel-l a t 0' C. using dimethylformamide supported on Celite (22). This highly eRcient liquid must be used a t low temperatures because of its relatively high volatility a t room temperature. .I comparison of several high boiling compounds a t 25" C. shows that several liquids not previously
used can be added to the list of successful partitioning substrates. Although 1-butene, trans-2-butene, and cis-2-butene were the only C4 gaseous products formed from the pyrolysis of the butyl phosphates, 1,3butadiene was included to test the separation of a diolefin from olefins of the same chain length. EXPERIMENTAL
1-Butene a n d cis-2butene were products of T h e Matheson Co., Inc., E a s t Rutherford, N. J., a n d Joliet, Ill. trans-2-Butene and 1,3-butadiene were prepared b y t h e Phillips Petroleum Co., Bartlesville, Okla. The solid support used was 30- to 50-mesh Celite 545 (Johns-Manville Co., New York, N. Y.). Most of the liquids were used as received without further purification. The Hallcomids were supplied by the C. P. Hall Co., Chicago, 111. Other liquids tested included: triethanolamine (Fisher Scientific Co., Fair Lawn, K. J.) ; p,p'-oxydipropionitrile (yepared by the reaction of acrylonitrile with water); 1-naphthonitrile, o - nitroanisole, o - nitrophenetole, ophenetidine, o-nitrotoluene, l-methylnaphthalene, p - aminodiethylaniline (Eastman Kodak Co., Rochester, ?J. Y.); caprylic acid, veratrole, anisaldehyde, m-dimethoxybenzene, pmethylacetophenone, N,N-dimethylformamide, N,N-diethylacetamide, cinnamaldehyde, 1-bromonaphthalene, glycerol triacetate, phenyl ether, dicyclohexylamine (Eastman Organic Chemicals, Distillation Products Industries, Rochester, N. Y.); dibenzylamine, triethyl phosphate (hfatheson Coleman and Bell Division, Natheson Co., Inc., Sorwood, Ohio, and East Rutherford, N. J.); tributyl phosphate (Chemicals and Plastic Division, Food Machinery and Chemical Corp., Xew York, N. Y.); dibutyl butyl phosphinate [prepared and purified in other work ( l a ) ] ;and dibutyl dimethylphosphoramidate (prepared by the reaction of dibutyl phosphite, dimethylamine, and carbon tetrachloride). Materials.
The tributyl phosphate was purified during work reported elsewhere (3). Triethyl phosphate, caprylic acid, cinnamaldehyde, o-nitroanisole, p,p'-oxydipropionitrile, and dibutyl dimethylphosphoramidate were vacuum-distilled before use. The liquid adduct, (TBP)Z UOZ(SO&,was prepared by equilibrating roughly equal volumes of tributyl phosphate and 2.5M uranyl nitrate hexahydrate and drying the organic phase-on the vacuum pump a t l m m . of HE for 2 hours at 25' to 50" C. The composition was checked by passing a weighed quantity of the dry organic solution in 50% ethyl alcohol through Amberlite 200 (Rohm and Haas, Philadelphia, Pa.) in the hydrogen form (21). The column was washed with 50% ethyl alcohol, and the nitric acid in the effluent was titrated with standard sodium hydroxide. The ratio of 2.2 tributyl phosphate molecules per uranyl nitrate molecule was found. Column Preparation. Column packings were prepared b y dissolving 8 grams of t h e liquid to be tested (Table I) in a 100-ml. round-bottomed flask with just enough ether (or acetone when necessary) to cover t h e 20 grams of 30- to 50-mesh Celite 545 added. T h e ether was removed a t the water p u m p b y use of a rotating evaporator. The dried packing material was rescreened and the 30- to 50-mesh portion was poured into Ushaped 1/4-inch aluminum tubing while the tubing was tapped to settle the packing. Two tubes, each containing 40.5 inches of packed material and plugged a t each end with glass wool, were connected in series in the Fractometer. Chromatography. Separations mere made a t 25' C. using a Perkin-Elmer Model 154 Vapor Fractometer equipped with a thermistor-type thermal conductivity detector. Two '4-inch aluminum U-tubes having a combined packed length of 6.76 feet were connected in series. Flow of the helium carrier gas was maintained a t 60 ml. per minute, measured a t the outlet a t atmospheric pressure and room temperature with a soap-film flow meter. 1-Butene, transVOL. 36, NO. 3, MARCH 1964
* 473
2-butene, cis-2-butene, and 1,3-butadiene (0.5 ml. each) were injected by hypodermic syringe several times separately and as a mixture Of four components. Their behavior was recorded at a chart speed of 1.01 cm. per minute. ~h~ recorder range was 10 mv. and the full-scale pen response time was 4.5 seconds.
The relative retention ratios of the butene isomers and 1,3-butadiene, related to 1-butene as standard, are listed in Table I. Two of the commonly used
polar compounds were included for comparison, dimethylformamide at 0" C. and &p'-oxydipropionitrile at the temperature of the other liquids, 25" C. Most of the liquids tested either suecessfully resolved the butene mixture or would do SO with a column longer than the 6.75-foot test column, but many could not separate the 1,3-butadiene from the butenes. The relative retention ratios closest to those obtained using dimethylformamide at 0' C. were found using triethanolamine, cinnamaldehyde, anis-
25' C.
for Butene Isomers and 1,3-Butadienea
RESULTS
Table I.
Retention Data a t
1-
B.p., O C. 277-9150mm. 137-91"'"'. 299 259 277 259
228 26 1 252 222 206 300 216 152-4 293 222 216-8 196-21 13rnm.
butene 0.24 0.72 1.83 1.99 2.04 2.05 2.12 2.16 2.20 2.26 2.28 2.40 2.42 2.90 2.92 2.99 3.03 3.62 3.98 4.03 4.23 4.55
Relative retention ratiosb transcis1,322ButaButene Butene diene nd 1.38 1.67 2.29 1.28 1.64 2.75 810 1.41 1.60 1.73 1.29 1.56 2.08 1130 1.35 1.56 2.10 1180 1.30 1.54 1.25 1.48 1.62 810 1.38 1.59 2.01 1350 1.35 1.57 1.98 1380 1.36 1.57 1.41 1.27 1.54 1.85 1370 1.54 1.28 .~ 1 . 7 0 1.41 1.63 i.94 1270 1.37 1.55 1.73 1480 1.28 1.49 2.00 1350 1.29 1.58 1.55 810 1.24 1.47 2.07 1230 ~
1.38 1.33 1.35 1.29 1.29
nntp 125-6lmm, 1.26 4.76 83-93rnm. 1.28 4.83 Hiiiiimid M-6 1.30 147-1633"'m~ 4.90 Hallcomid M-12 1.27 5.19 Tributyl phosphate 180~"'"'~ 5.38 1.31 Caprylic acid 238 5.88 1.27 Dicy clohexylamine 256 Dibutyl dimethylphos85-860.5mm. phoramidate 5.90 1.25 Diethylacetamide 185 5.92 1.27 (9-foot column) Diethylacetamide, 1.31 0' C. (9-foot column) 8.72 Column length, 6.75 feet; loading ratio, 4 grams of solvent carrier gas, helium; flow rate, 50 ml./min. b 1-Butene = 1.00. e Retention time from air peak, minutes. Number of theoretical plates (1-butene).
Table II.
1.66 1.54 1.53 1.48 1.48
3.05 1.41 1.70 1.74 1.39
1270 1430
1.46 1.47 1.48 1.46 1.48 1.50
1.57 1.76 1.47 1.63
880 1150 910 1220
1.13
1150
1.45
1.67
1304
1.48 1.59 t o 10 grams of Celite 545;
o-Nitrophenetole Column Characteristics"
Temp.,
c. tR Wb Q n At R 25 1.32 Air 25 5.95 0.46 12.9 2660 1-Butene trans-2-Butene 25 7.56 0.57 13.3 2830 1.61 3.13 cis-2-Butene 25 8.55 0.65 13.2 2790 0.99 1.62 1,3-Butadiene 25 10.42 0.76 13.7 3000 1.87 2.65 16 1.34 Air 16 7.14 0.56 12.8 2620 1-Butene 16 9.24 0.70 13.2 2790 2.10 3.33 trans-2-Butene 16 10.55 0.80 13.2 2790 1.31 1.75 cis-2-Butene 16 12.99 0.95 13.7 3000 2.44 2.79 1,3-Butadiene a Column length, 13 feet; loading ratio, 4 grams of o-nitrophenetole to 10 grama of Celite 545; carrier gas, helium; flow rate, 50 ml./min.; t ~ retention , time from injection point to peak maximum, minutes; wg, base line intercept cut by tangents to peak inflections; Q = tR/Wb; n, number of theoretical plates = 16Q2; At, retention time between peak maxima; R, peak resolution = At + (Wbl Wb2)/2.
+
474
o
ANALYTICAL CHEMISTRY
-
t
AIR
2 BUTENE-I 3 TRANS-BUTENE-2 4 . CIS-BUTENE-2
5 I,3-BUTADIENE
i:
%4
k
3
I
15
tR"
Liquid Triethanolamine D,P'-Oxydipropionitrile 1-Xaphthonitrile Glycerol triacetate o-Nitroanisole Phenyl ether (TBP)2*UOz(KOa)n Anisaldehyde o-Xtrophenetole I-Bromonaphthalene o-Phenetidine p-Aminodiethylaniline Cinnamaldehy de o-Nitrotoluene Veratrole Dibenz ylamine Triethyl phosphate Dimethylformamide, 0" C. (12-foot column) 1-Methylnaphthalene p-Methylacetophenone m-Dimethoxybenzene Hallcomid M-18 OL Butyl dibutylphosphi-
'
40
5
0
RETENTIGV T I H E , m n.
Figure 1. Separation of butenes and 1,3-butadiene at 25" C. Column, 13-fOOt X 0.25-inch coiled copper tubing containing o-nitrophenetole on Celite (loading ratio 4 to 10 by weight) Carrier gas, helium. Flow rate, 50 rnl. per rnin.
aldehyde, o-nitrophenetole, and o-nitroanisole. The retention times using triethanolamine were so short, however, that its use would be extremely impractical. Cinnamaldehyde gave a better relative retention ratio for trans-2-butene at 25" C. than dimethylformamide at 0" C., but the relative retention ratio of cis-2-butene with respect to the trans was not as good. The best cis-trans peak separation (ratio of corrected retention times = cis relative retention ratio t trans relative retention ratio) indicated from Table I was that obtained using the other standard, p,p'-oxydipropionitrile. Peak separation equivalent to that using dimethylformamide was obtained using glycerol triacetate and the amines (0-phenetidine, p-aminodiethylaniline, and dibenaylamine) . Triethyl phosphate was nearly equivalent. Glycerol triacetate, o-phenetidine, and triethyl phosphate also had good relative retention ratios for Il3-butadiene. Increasing the chain length of the amide resulted in less effective separation. Resolution was obtained with dimethylcaproamide (Hallcomid M-6), but better resolution was found with o-nitrophenetole in half the retention time. Since the greater extraction of heavy metals by organic phosphorus compounds having carbon-phosphorus bonds in comparison with tributyl phosphate (2) is due in part to the greater polarity in the phosphoryl group, it was of interest to test this effect on the olefins-diolefin separation reported here. Butyl dibutylphosphinate and tributyl phosphate separated the butene isomers in nearly identical fashion, but the former, a much more polar compound than the tributyl phosphate, had less retaining power for the butadiene than the tri-
Table 111.
Retention Data for Various Substrates
Relative retention ratios“
Solvent AgNO1-ethylene glycol
Ref.
Agh’Oa-glycerol AgNOs-benzylcyanide
Wt. %
Column length, ft.
30 -30 -30 29
6 11 11 11.4
Hexamethylphosphoraniide 1,3-Butylene glycol sulfite o-Xitrophenetole
29 25 29
3 33 13
Dimethylsulfolane
29 33 29 25 25 29 23 26 29
8 15 50
Diethylcyanamide in series with p,p ’-oxydipropionitrile p,p’-Oxydipropionitrile Squalene in series with adiponitrile Glycerol triacetate
;:6.75 : 2.51
;:
Toemp.,
C.
20 50 50 22 30 20 30 25 16 25 28 0 30 25 28 25 0
1-butene, min. Iso(air = 0) butylene 10.6 6.4 3.3 4.1 2.5 10.5 4.6 5.8 3.1 52 14.5
1.06 1.10 1.07
0.7 14.3 3 .O 5.6
23
a
0.45 0.51 0.53 0.65 0.68 1.02 1.04 1.04 1.04
6.3
1.08 1.08 1.09 1.10 1.11 1.11 1.13
trans2-Butene 0.18 0.24 0.22 0.51 0.54 1.23 1.28 1.35 1.36 1.30 1.31 1.36 1.28 1.28 1.31 1.29 1.33 1.27 1.34 1.25 1.27 1.36
1,3cis2-Butene Butadiene 0.86 0.85 0.82 1.15 1.20 1,45 1.50 1.56 1.59 1.52 1.54 1.63 1.50 1.64 1.55 1.55 1.66 1.51 1.63 1.54 1.56 1.61
1.68 4.22 1.23 1.28 2.25 1.76 1.96 2.01 2.23 2.32 2.54 2.20 2.75 1.96 2.07 2.27 2.30 2.50 2.39 2.93
1-Butene = 1.00; :tll retention times measured from air peak to peak maxima. This work.
butyl phosphate had. Evidently the increased polarity of the molecule was more than offset by t be loss of the two oxygens between carbon and phosphorus. Substitution of a dimethylamino group for a bui,oxy group on the phosphorus had very little effect on the relative retention ratios. Tying up the phos)phoryl groups of the tributyl phosphate with uranyl nitrate had surprisingly little effect on the retention ratios. The big effect was the shortening of the retention time, due to the presence of less than half the amount of t:ibutyl phosphate originally used. The number of theoretical plates w s likewise considerably lessened. I n Figure 1 the mesolution of the butenes and l,&butadiene at 25” C. is shown using a 13-foot column of onitrophenetole (29 weight %) on Celite. The relative retention ratios for this separation were 1.00 1.35, 1.56, and 1.96 for 1-butene, traiw-2-butene, cis-2butene, and lJ3-butadiene, respectively, where 1-butene emerged 4.63 minutes after the air peak. Fitting the column with a condenser and cooling to 16” C. further improved the separation. The relative retention ratios were increased to 1.36, 1.59, and 2.131 with 1-butene (1.00) being retained 5.80 minutes after air. The performance of this column is shown in Table 11, in which the symbols are those described b:r Ettre (9). The number of theoretical plates varied from 2600 for 1-butene to 3000 for 1,3-butadiene. The least peak resolution, between trans- and cis-2-butene, was 1.62. A v d u e of 1.5 means resolution is 99.770 complete (9).
In Table I11 we have compiled retention data from the literature pertaining to the solvents recommended for C d olefin separations. Included are values obtained from Figure 1 (and later results for isobutylene retention) and from use of a 10-foot column of glycerol triacetate. The ability to separate isobutylene from 1-butene is shown in column 7 . Phenomenal separations of cis-2-butene from trans-2-butene and of isobutylene from 1-butene are achieved with the silver nitrate solutions ( 1 , 4, 5 ) . Resolution of the isobutylene-1-butene pair using the polar organic liquids is best done by dimethylformamide a t 0” C. (6, 22). Propylene carbonate (16) a t room temperature is also effective. The o-nitrophenetole was found to be ineffective with regard to isobutylene-1-butene separation, but glycerol triacetate compared favorably with most of the polar liquids listed. LITERATURE CITED
(1) Armitage, F., J . Chromatog. 2, 655 (19.591. \ - - - - I
(2) Baldwin, W. H., Higgins, C. E., U. S. Patent 2,864,668 (Dec. 16, 1958). (3) . . Baldwin, W. H.. Hieeins. C. E.. Soldano, B. A., J : Phi;. Chem. 63; 118 11959). (41 Bednas.’M. E. -, J . Chem. 36, 1272 ( l Y 5 8 ) . (5) Bradford, B. W., Harvey, D., Chalkley, D. E., J . Inst. Petrol. 41. \ - ,
~
~~
(6) Craats, F. van de, Anal. Chim. A cta 14, 136 (1956). (7) Csicsery, S. M., Pines H., J . CI;iromatoa. 9. 34 (19621.
(10) Fredericks, E. RI., Brooks, F. R., ANAL.CHEW28. 297 (1956’3. (11) Higgins, C. E . , Baldwin, ITr. H., J . Org. Chem. 26, 846 (1961). (12) Higgins, C. E., Baldwin, W. H., Ruth, J. M., Oak Ridge Natl. Lab., ORNL 1338 (Julv 24. 1952) (declassified March 11. 1967): ’ (13) Hively: R. A.,J . Chem. Eng. Data 5, 237 (1960). (14) Keulemans, -4.I. M., Kwantes, A., Zaal, P., Anal. China. Acta 13, 357 (1958). (15) McEwen, D. J., Chem. Can. 11, KO. 10, 35 (1959). (16) McKenna, T.A,, Jr., Idleman, J. A., AXAL.CHEM.31, 2000 (1959). (17) Morrow, H. S Buckley, K. B., Petrol. Refiner 36, 8. 157 11957). (18) Presto;, S.T.,’Jr., J . Gas Chromatog. 1, S o . 6, 31 (1963). (19) Rohrschneider, L., Z. Anal. Chem. 170, 256 (1959). (20) Rouit, C.;,in “Vapour Phase Chromatography, pp. 291-303, Proc. Sym-
20.
posium Hydrocarbon Res. Group Inst. Petrol., IEE, London, June 1956, D. H. Desty and C. L. A. Harbourn, eds., Academic Press, Yew York, and Butterworths, London, 1957. (21) Samuelson, O., “Ion Exchangers in Analytical Chemistry,” pp. 117-35, Wiley, S e x York, 1953. (22) Taylor, G. W.)Dunlop, 4 . S., in “Gas Chromatography,” pp. 73-85, 1st Intern. Symposium, ISA, August 1957, V. J. Coates, H. J. Soebels, and I. S. Fagerson, eds., Academic Press, Sew York, 1958. (23) Zlatkis, A., Kaufman, H. R .,,,Chap. 30 in “Gas Chromatography, pp. 339-42, Second Intern. Symposium, ISA, June 1959, H. J. Xoebels, R. F. Wall. and N. Brenner. eds.. Academic Press, Sew York, 1961.’ RECEIVED for review September 3, 1963. Accepted December 6, 1963. Oak Ridge National Laboratory is operated for the U. S. Atomic Energy Commission by the Union Carbide Corp. VOL. 36, NO. 3, MARCH 1964
475
