EDWARD R. ATKINSON', DAVID RUBINSTEIN, and EDWARD R. WINIARCZYK y and Amy Chemical Co., Division of W. R. Grace & Co.
Reaction of
*
Dienes with Cuprous Chloride
Purification af coniugated dienes by the solid cuprous chloride process is improved edly by catalysis with methanol. An analogous process has developed for styrene and other vinyl benzenes
THE
reaction of alkenes or of conjugated dienes with cuprous salts and salts of certain other metals (5)involves a typical dative bonding process (2, 10)' and is the object of continuing study (73). Compounds prepared from cuprous chloride and simple olefins decompose above 0' C. but compounds prepared from butadiene, isoprene, and piperylene are stable to 63', 46', and 68' C . ,respectively. Practical advantage has been taken of this fact in separating conjugated dienes from hydrocarbon streams containing olefin and paraffin hydrocarbons alp weft. All such processes involve the formation of the copper-diene compound at lower temperatures, the separation of unreacted hydrocarbon material, and the subsequent decomposition of the compound by heating to liberate pure diene. The fundamental chemistry involved has been described by Ward and Makin (79). After the early work of Feiler ( 6 ) , Gilliland (7), and Lur'e (9) development work in the United States followed three major courses: The use of aqueous solutions of cupro-ammonia ion or of solutions of cuprous salts in organic amines (77, 77); the use of solid cuprous chloride absorbents for gas- or liquidphase separation of dienes, including fluid-bed technics (72, 76) ; and the use of a solid cuprous chloride absorbent for the absorption of liquid dienes developed during World War 11 at the United Gas Improvement CO. (UGI) (75). An extensive study of this last process has been pursued in this labomtory and is based on private communications from UGI as well as on published information. When the UGI process was applied to separate isoprene from mixtures prepared by blending isoprene with pentane or amylene to contain 50 to 70% isoprene, the reaction of the diene with the cuprous chloride absorbent was so slow that the process was inoperable. When 2 to 3% of methyl alcohol was 1 Present address, Arthur D. Little, Inc., Cambridge 40, Mass.
added to the hydrocarbon mixture, absorption was rapid and quantitative. Using this catalyst, pure isoprene was recovered efficiently from hydrocarbon mixtures containing as little as 20% isoprene and absorption of isoprene or piperylene from commercially available hydrocarbon streams was improved significantly. Water and a few other analogous substances also had a measurable, but less important, effect on the speed of the cuprous chloride-diene reaction. The formation of compounds of styrene with a number of metal salts is known (3) but no reference to a compound with cuprous chloride has been found. During the present work it has been discovered that a styrene-cuprous chloride compound is formed and is stable to 35" C. This reaction has been used to separate styrene-ethylbenzene mixtures Containing as little as 20y0 styrene and analogous procedures have been used to separate other vinylbenzenes from related saturated substances.
Catalysts for Absorptionof isoprene and piperylene Experimental. The separation of high-quality isoprene or piperylene from c b hydrocarbon mixtures was carried' out using the general UGI procedure (75) in a laboratory scale reactor similar to that described by Soday (74). This reactor was designed at UGI and consisted of a horizontal steel cylinder, approximately 6 inches in diameter and 18 inches long, having a total capacity of about 2.5 liters. Agitation was provided by a stout steel perforated paddle revolving at 80 to 90 r.p.m. The paddle was driven by a motor with a suitable gear reduction box. Clearance between the blades of the paddle and the ends a 11s of the reactor was about 1 to 2 o that no appreciable accumulat hard cake occurred at these P T o assist in maintaining the t in a finely divided state 75 steel balls ("4 inch) were used in the reactor. The reactor was surrounded
by a cooling jacket through which either water or refrigerated methanol was circulated at a rate of about 1.5 gallons per minute. Live steam a t 130' C. was used to heat the reactor when desired. The entire apparatus was encased in cork insulation to facilitate rapid heating or cooling. All connections to the system were maintained in good order so that it was always possible to achieve pressures of less than 10 mm. and with few exceptions the recovery of hydrocarbons in all runs was 95% or better. Because the principal purpose of this work was to acquire operating experience with the process, all variables were examined in some 900 runs. Operating data for selected runs which illustrate the use of absorption catalysts are recorded in Table I and are described in the following text. The absorbents used consisted of a mixture of 957 grams of technical cuprous chloride (assay, 82%), 40 grams of calcium hydroxide, and 2.5 grams of phenyl-B-naphthylamine. They were broken in by carrying out standard runs in the reactor until peak isoprene absorption was reached. This usually required 10 runs, representing about 16 hours of grinding. I n some cases preliminary slush grinding in excess isoprene was used, All comparisons of absorption with or without catalysts are based on runs carried out with a specific absorbent, or with absorbents known to have equivalent diene absorbing capacities. In a typical run the absorbent was cooled to the desired absorption temperature and the precooled hydrocarbon charge added; catalysts when used were dissolved in the hydrocarbons. Simulated isoprene streams were prepared by blending commercial 95% isoprene (Enjay C4., New York) with pentane (Skellysolve A, Skelly Oil Co., Tulsa, Okla.) or amylene (Matheson Co., East Rutherford, N. J.). The mixture was ground for 25 minutes and unabsorbed hydrocarbons removed by allowing the reactor and contents to warm to VOL. 50, NO. 10
OCTOBER 1958
1553
about 20" C. and lowering the pressure in the system to 120 to 130 mm. as rapidly as condenser efficiency permitted. When the rate of distillation fell below 1 drop per 10 seconds the distillate was removed for analysis of this unabsorbed material. To remove absorbed diene the reactor was heated to 70" to 130" C. and the diene allowed to distill a t atmospheric pressure; in the final stages of distillation a pressure of 130 mm. was used. Analytical Procedure. Isoprene assays were carried out by measuring
absorption at 223 ml.c (Beckman Model spectrophotomete;) of solutions containing about 7 X 10-8 grams per liter of hydrocarbon in methanol (purified methyl alcohol, 5. T. Baker Chemical Co., Phillipsburg, N. J.) and using solvent in the reference cell. The method was standardized against pure isoprene (Phillips Chemical Co., Bartlesville, Okla.) and the standardization checked by occasional measurement of samples in spectrograde iso-octane using constants available in the literature
DU
(7).
Table I. Adsorbent
No." 1
Isoprene Concn., Wt. % Wt., g . 300
50
Catalysis of Diene Absorption i4bsorption Temp., Time, O Min. 5 25 18 50 5 25 3 50 25
c.
h'lethanol, M1. None
2
3c 3
150 300 166 300
60 95 50b 75b
50
700
4
41
10
17.5
4
400 700
70 20
17.5 25 10 17
21 400
70
500 328 700 400
55i 38.9 69.2
10 5 12 None 17 None 95% CzHsOH 10 10 Isopropyl alc. 10 Diethylene glycol 10 10 Satd. HzO, 6 days, 25' Satd. HzO, 3 hrs. 25O Satd. H20, 6 days, 25O Satd. HpO, 6 days, 25O Satd. H20,12 hrs. 25O None 10 H2O 15
60
- 10
100
602
7.1
- 25
70
571
5.5
2
25
216 252 246 296 476 245 2 84 180 179 323 380 193 182 256 175 181 166 359 207 335 206 204 211 2 10 384 404 373 338 416
10 47
None 12
8 1O k
600;
15
3 4 3
C. C. C. C. C.
... ... ...
7 3
5
6
7h 7 8
... ... ...
480 466 499 513 494 162 630
10
5f 68
...
... ... ... ...
43.5 44.2 42.3
Unabsorbed Assay, Wt., g % 272 255 299 278 27 95 294 91 63 174 22 205 279 181 191 463 14.7 . I .
4 3
None 10 4d
For piperylene assay a similar procedure was followed, using published absorption data for standardization ( I ) . Although a reliable estimate of both cis- and trans-piperylenes was thus possible, a combined figure was usuallv used for it is known that reaction with cuprous chloride does not separate the isomers (4, 79). Discussion. METHANOL CATALYSIS The first work with isoprene followed some earlier work in which piperylene had been separated from a commerciallv available 50% concentrate by the UGI
... . . a
32.6 8.8
... ... ... ... ... ... ... ... ... ... ...
... ... ...
... ... ... ... ... ... ... ... ... . . I
... ...
... ... ...
Isoprene Recovered iissay, Wt., g. % 22 15 3 14 106 95 4 60 94 115 90 74 98
...
... ... . . I
...
...
...
107 107 lSe 229 233 233 201 188 2 10 233 1 59 15e 89 20e 111 189 147 226 12 224 144 100 214 222 66
90 93 736 95
... ... ... ... ... 92 818 90 85e 88 90' 96
... ... 95
... ... ... ... . . I
95
... ... ... ... ... ... ... ...
...
211 182 115 187 175 190 21 204
. I .
... ... ... ...
50 142 155 181 186 92 71 131 164 17e 153
... ...
... ... *..
...
948 101
*
Run 54 55 58 59 61 67 70 91 93 94 95 96 E-14 E-16 E-17 E-27 E-57 E-65 157 457 458 464 128 130 473 491 498 499 500 501 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 502 503 504 538 552
Isoprene blended with a Runs are grouped with respect to the particular batch of absorbent used; composition of absorbent is given in text. Fourteenth run with this absorbent. e Where two figures are given t h e smaller Matheson's Amylene. First run with this absorbent. refers t o t h e first portion of desorbed isoprene distilling. f Seventh run with this absorbent. g Fourteenth run with this absorbent; standPiperySixth run with this absorbent. i Isoprene concentrate from Pennsylvania Industrial Chemicals Go. ardized with 407, isoprene. Absorbent known t o absorb 235 grams of isoprene. lene, Enjay Co., CPS-144.
1554
INDUSTRIAL AND ENGINEERING CHEMISTRY
CONJUGATED DIENES REACTIONS process. Negligible absorption of diene was observed from a mixture of isoprene and pentane containing 50% isoprene (Table I, runs 54, 55, 58). Amylene used in place of pentane had no effect (run 67), nor did doubling the time of absorption (run 59). Absorption of isoprene improved when its initial concentration was raised to 75% (run 70) but the absorption 95% isoprene was much slower than expected (run 61). The addition of small amounts of methanol to the hydrocarbon charge prior to or during the absorption step caused a marked improvement in absorption (runs 91, 93, 95, 96) and its withdrawal caused a low absorption to occur (run 94). This showed that methanol did not remain affixed to the absorbent. The alcohol escaped from the reactor during the distillation and was often isolated as a small lower layer in the distillate. I t was determined that 2.5 ml. of methanol per 100 grams of hydrocarbon charge was adequate and this catalyst was used in the efficient separation of high-quality isoprene from mixtures containing 70% (run 157), 40% (runs E-14, E-16), and 20% (runs 457, 458, 464) isoprene (Table I). The speed of absorption decreased somewhat when less than 2.5 ml. of methanol per 100 grams of hydrocarbon was used (runs 128, 130) although this was not always abrupt (runs E-I6 to E-27; intervening runs same as E-1 7). When a batch of absorbent indicated deterioration (runs E-I4 to E-57) an increase in methanol used caused a partial restoration of absorbent activity (run E-65). Because commercial isoprene streams similar to those used in the original development of UGI process were not available only two runs with such a commercial 50% concentrate were carried out. The use of methanol was found to be essential for good absorption (runs 473, 491). Although absorption of piperylene from a commercially available 50% concentrate occurred (runs 502, 503), a marked increase in absorption took place when methanol was used (runs 504, 538, 552). OTHER CATALYSTS. An absorbent was standardized in a conventional run (run 498) and then used in two subsequent runs in which no methanol catalyst was used; absorption of isoprene decreased markedly (runs 499, 500). USP 95% ethyl alcohol then acted as a catalyst (run 501). I n similar comparisons isopropyl alcohol and diethylene glycol were found to be ineffective (runs 516, 517, 518). A number of small scale experiments were performed which involved a direct comparison of the catalytic activity of many other materials with methanol. n-Propyl alcohol was about as effective
as ethyl alcohol. Acetic acid and nitromethane showed some activity although that of acetic acid disappeared when absorbents containing phenyl-P-naphthylamine were used. Diethyl ether, isopropyl alcohol, benzoic acid, and phenol were without effect, the latter two substances being insoluble. Water was a particularly interesting catalyst because it was possible that the commercial hydrocarbon streams used in the original UGI development may have been wet. All UGI patents in this field allude to the need for "dry" reaction conditions. An absorbent was standardized (run 519) and then used to absorb isoprene from mixtures containing small amounts of water (run 521) or mixtures which were thoroughly saturated with water (runs 520, 522, 523, 524). The absorption of isoprene from the latter was good. When water was then omitted from the charge, diene absorption did not occur (run 525) showing that any water remaining in the absorbent did not possess catalytic activity. The addition of water directly to the reactor after adding the hydrocarbon charge was not effective (runs 527, 528, 529; 526 as standard). When water was used there resulted a deterioration of the absorbent which could not be corrected by the return to methanol as a catalyst (runs 530, 531). O n opening the reactor after this sequence of runs, a portion of the absorbent had formed a tough mass which was not broken up by the operation of the reactor. No such agglomeration of absorbent occurred when methanol was used. Hence, of all the catalysts cited above, only methyl, ethyl, and n-propyl alcohols have practical significance. MECHANISM OF CATALYSIS. After this work was completed the catalytic effect of the lower alcohols on the dative bonding of amines to methyl borate was described (8, 78). No mechanism for this catalysis has been suggested in the references cited. Because of the heterogeneous character of the reaction medium methanol and other catalytic agents may have functioned in activating the surface of the cuprous chloride particles. Solid cuprous chloride is known to be a good conductor of electricity. The presence of a n adsorbed polar molecule such as methanol may thus represent a convenient site of attack for the diene molecule, leading to disintegration of the solid particle with consequent formation of fresh surface. An alternate hypothesis suggests that the catalytic agents function in exactly the same way as they do when serving as cocatalysts in the cationic polymerization of olefins by Lewis acids. I n the present case cuprous chloride, while a Lewis acid, is unable to promote extensive polymerization be-
cause of the insolubility of the reasonably stable compound which it forms with the first molecule of olefin reacting. Again, the methanol catalyst was recovered in each run. Its continued use was necessary. I t did not remain affixed to the absorbent.
Reaction of Styrene with Cuprous Chloride
Experimental. Some enrichment of styrene from a 40% styrene and 60% ethylbenzene mixture was obtained using the described apparatus and procedure for the enrichment of acyclic dienes. Temperatures and pressures needed for removing unabsorbed ethylbenzene by distillation decomposed the styrenecuprous chloride compound. The following procedure was then devkloped. When powdered C.P. cuprous chloride (assay 90%) was stirred with excess styrene at room temperature an exothermic reaction occurred accompanied by the swelling of the solid to four times its original volume. It was observed that this compound decomposed reversibly at about 35" C. The formation of the compound from styrene-ethylbenzene mixtures containing 20 to 40% styrene required the use of the lower temperatures (Table 11). In a typical run dilute styrene, cuprous chloride, and methanol were precooled and shaken together. The reaction mixture grew stiff within 2 minutes and heat was evolved. The reaction mixture was then stored at the indicated temperature. The weight of the hydrocarbon mixture was at least four times that of the cuprous chloride in order to preserve some fluidity, even though the styrene present thus exceeded the chemical combining ,capacity of the cuprous chloride. After storage for the desired time the stiff reaction mixture was transferred to a cold Buchner funnel and sucked as dry as possible. The cake was removed from the filter and thoroughly washed by stirring with cold pentane a t -5' to -10' C. using about 300 ml. of solvent for each 100 grams of absorbent. The washed solid was again filtered and washed on the filter with 200 ml. of cold solvent. A mixture of unabsorbed styrene and ethylbenzene wag recovered from the filtrates by distilling off the pentane. High quality styrene was liberated from the washed cuprous chloride-styrene compound by boiling the latter with 300 ml. of pentane. The styrene and pentane were separated by simple distillation after filtering of€ the regenerated cuprous chloride. In an alternate procedure all of these steps were carried out in a refrigerated Buchner funnel equipped with a stout paddle-type stirrer. VOL. 50, NO. 10
OCTOBER 1958
1555
Analytical Procedure. Styrene assays were made spectrophotometrically by measuring absorption in methanol a t 290 mp the process being analogous to that described for isoprene. At the wave length chosen ethylbenzene does not absorb. Discussion. In run 27 (Table 11) it was established that when pure styrene was absorbed by cuprous chloride, 2 moles of hydrocarbon was absorbed per mole of cuprous chloride (Cu2C12). This calculation involved an allowance for the purity of the cuprous chloride used and for a loss of 6 to 10 grams of styrene during the final separation from pentane; the latter allowance was established in a separate experiment in which a mixture of styrene and pentane was subjected to the simple distillation used. As the quantity of styrene present in the 40% styrene mixtures exceeded the chemical combining capacity of the absorbent the actual weight of pure styrene recovered was governed by the purity of the cuprous chloride used. Fifty-five to 60 grams of pure styrene was recovered in runs using 100 grams of C.P. cuprous chloride (runs 8, 11, 12, 24, 25, 37). Grinding the chloride prior to use did not increase absorption (run 26). This is reasonable because the solid always disintegrated completely during its reaction with styrene. When C.P. cuprous chloride was purified by washing with dilute sulfuric acid followed by glacial acetic acid, absorption increased as expected (runs 39, 40). Technical cuprous chloride gave inferior results (run 36). When methanol catalyst was omitted from runs involving 40% styrene the time elapsing before the reaction mixture set increased from 2 to 8 minutes. This was of no consequence when absorption times were long, so that the methanol could he omitted entirely (runs 24, 25) or doubled (runs 15,16) without effect. The absorption of styrene from a 20%
mixture with ethylbenzene however did not occur after 16 hours at -15" C. and was negligible after 20 hours at -50" C. By use of the methanol catalyst it was possible to isolate not less than 60% of the available styrene as pure styrene from a 20% solution (run 35). In this work it was necessary to maintain the reaction mixture at - IO" C. or below during the washing out of the unabsorbed hydrocarbons by pentane. OTHERVINYLBEKZEKES. The process described above for styrene was applied with some success to the separation of vinyltoluene from ethyltoluene. Absorption of vinyltoluene from such mixtures containing 40% of the unsaturate did not occur even after storing for 10 days at -17" C. in the presence of methanol. No swelling of the cuprous chloride was observed. When 70% vinyltoluene (Dow Chemical Co., Midland, Mich.) was used absorption occurred and it was possible to prepare 90 to 95% pure material. The procedure used was identical to that described above for styrene except that 800 grams of 70% vinyltoluene was used with 100 grams of cuprous chloride in order to preserve sufficient fluidity. The lower thermal stability of the vinyltoluene-cuprous chloride product required greater attention for maintaining low temperatures during the washing out of unabsorbed hydrocarbons than in the analogous styrene case. I n one run 66 grams of 94.2% pure vinyltoluene was recovered in a run using 100 grams of C.P. cuprous chloride (assay, 90%). When allowance is made for known distillation losses it is apparent that 2 moles of vinyltoluene is absorbed by each mole of cuprous chloride (Cu2C12). ' 4 spectrophotometric assay method at 284 mp was standardized with a freshly distilled sample of vinyltoluene (boiling pointad 77" to 78" C.). It was necessary to distill all ethyltoluene used to remove an impurity which interfered with the assay.
Table II. Absorption of Styrene by Cuprous Chloride at -15"
Cuprous Chloride 100 G., Type
C. AbsorpStyrene tion Styrene Recovered Concn., Methanol, Time, Rt., Assay, Wt., g. wt. % MI. Hr. % Run 300 400 500 400
C.P.
c.P., ground 600
C.P.
400 Tech.
40.5 41.2
41.3 40.0 41.3 99 20.0 40.0
7.5 10 12.5 20
166 3b 20
0
24
16
0
0 10
96 20
c.P., purified
16
c.P., purified and ground a
Blended with ethylbenzene.
1556
At
- 10'
97.5 99.5 105 97.5 100.5 101
55 60 26 33 56 66 69
103
0
C.P.
of just 7.5% styrene.
58 55 57 65 63 60
C.
...
99c 101 100.5 101.7 102.2
8
11 12 15 16 24 25 26 27 35 36
37 39 40
Unabsorbed fraction of this run had an assay
INDUSTRIAL AND ENGINEERING CHEMISTRY
Dow's divinylbenzene stated to contain 20 to 25% of divinylbenzenes and 75 to 80% ethylvinylbenzene reacted rapidly at room temperature with solid cuprous chloride and the resulting paste appeared stable to 75" C. I t is obvious that an analogous separation process could be developed for this substance. N o reaction between cuprous chloride and a-methylstyrene was observed even after 4 days at -12' C. with or without the use of methanol catalyst. This failure to react is reasonable because of the steric factor involved. Acknowledgment
The authors wish to thank this company for permission to publish this material and V. S. Frank, H. S. Stidham, and E. C. Stivers for valued assistance in the development of the spectrophotometric assay procedures. Literature Cited (1) American Petroleum Institute, Pittsburgh, Pa., Project 44. NBS Catalog of
Hydrocarbon Spectra, 1953. (2) Andrews, L. J., Chcm. Revs. 54, 713 (1954). (3) Boundy, R. H., Boyer, R. F., "Styrene," p. 87, Reinhold, Kew York, 1954. (4) Craig, D., J . Am. Chcm. SOC. 65, 1006 (1943). (5) Douglas, B. E., "Chemistry of Coordination Compounds" (J. C. Bailar, editor), p. 487, Reinhold, New York, 1956. (6) Feiler, P. (to I. G. Farbcn.), U. S . Patent, 1,795,549 (March 10, 1931). (7) Gilliland, E. R. (to Standard Oil Development Co.), Ibid.,2,209,452 (July 30. 1940). (8) Horn, 'H., Gould, E. S., J . Am. Chem. SOC. 78, 5172 (1956). (9) Lur'e, M. A., others, Sintet. Kauchuk 3, NO.6, 13-29 (1934). (IO) Mulliken, R. S., J . Am. Chcm. SOC. 74. 811 (1952): J . Phw. Chem. 56. 801 (1952). ' (11) Phillips Petroleum Co., Bartlesville, Okla., U. S . Patents 2,526,971 (Oct. 24, 1950), 2,557,923 (June 26, 1951), 2,589,960 (March 18, 1952). (12) Ibid.,2,386,272, 2,386,274, 2,386,300, 2,386,390-2,386,358, 2,386,360, 2,386,366, 2,386,379, 2,386,734 (Oct. 9, 1945), 2,527,964 (Oct. 31, 1950), 2,606,938 (24ug. 12, 1952), 2,756,267 (13) (July Slade, 24, P. 1956). E., Jonassen, H. B., J . Am.
Chem. SOC. 79, 1277 (1957). (14) Soday, F. J. (to United Gas Improvement Co.), U. s. Patent 2,395,955 March 5, 1946. (15) Soday, F. J., Chaney, N. K., Breuer, F. W. (to United Gas Improvement Co.), Ibid., 2,389,647 (Nov. 27, 19451, 2,395,954-2,395,959 (March 5, 1946). (16) Standard Oil Development Co., Ibid.,2,515,134 (July 11, 1950). (17) Ibid., 2,388,913 (Nov. 13, 1945), 2,397,996 (April 9, 19461, 2,430,972 (Nov. 18, 1947), 2,436,471, 2,436,472 (Feb. 24, 1948), 2,438,437 (March 28, 1948), 2,463,846, 2,463,902 (March 8, 1949), 2,497,150 (Feb. 14, 1950). (18) Urs, S. V., Gould, E. S., J . Am. Chem. SOC.74, 2948 (1952). (19) Ward, .4. L., Makin, E. C., Ibid., 69, 657 (1947).
RECEIVED for review December 6, 1957 ACCEPTED July 7, 1958
