1,5=CYCLOOCTADIENE BY T H E CATALYTIC DIMERIZATION OF BUTADIENE G E O R G E B O S M A J I A N , R O B E R T E . B U R K S , J R . ,
A N D C H A R L E S E . F E A Z E L
Southern Research Institute, Birmingham, Ala. J A C K
N EW C0 MB E
,
Columbian Carbon Co., Lake Charles, La.
Process variables in the dimehzation of butadiene to 1,5-~yclooctadienewith bis(tripheny1phosphite)dicarbonylnickel catalyst were studied with a bench-scale, heated-tube reactor. 4-Vinylcyclohe%ene, a higherboiling distillate, and polymer were also formed. The optimum conditions for high selectivity for cyclooctadiene and low selectivities for vinylcyclohexene and polymer were 150" to 170" C. ut 400 to 600 p.s.i.g. and a throughput rate of 0.8 to 3.0 volumes of liquid per reactor volume per hour. A catalyst concentration of 0.75 to 3% was used. The lowei throughput rates gave higher conversions. The presence of benzene as a solvent lowered the cyclooctadiene selectivity.
HE
EIGHT-MEMBERED CYCLIC
HYDROCARBON
cis-cis-I ,5-cy-
Tclooctadiene (COD) is of commercial interest because of its
utility as an intermediate for the production of epoxides, suberic acid, caprylolactam, and related chemicals and polymers. The present work was undertaken in the development of a homogeneous catalytic method for the dimerization of butadiene to cycloocradiene. The purpose of the work was to determine \vhether a continuous reaction system was feasible and to define approximately the effect of temperature. pressure, solvent. throughput rate, and concentration of catalyst on the yield and conversion. The production of small amounts of C O D has been reported in the thermal dimerization of butadiene to 4-vinylcyclohexene (VCH) (3.-fq9 ) . Conditions of butadiene dimerization leading to C O D as the major product were discovered by Reed, who found that the reaction was catalyzed by bis(tripheny1phosphine)dicarbonylnickel, (Ph,P)ZNi(C0)2, or the analogous phosphite compound, [ ( P ~ O ) S P ] ~ N ~ ( C when O ) Z , acetylene was used as an activator and benzene as the solvent (5). The best results were obtained at temperatures below 130' C., where the formation of V C H by thermal dimerization was minimized. The reaction was very sensitive to poisoning. The use of cyclopentadiene and similar compounds as catalyst activators was discovered by Sekul and Sellers ( 6 ) , who also found that ( P h a S b ) 2 N i ( C 0 ) could 2 be used as the catalyst (7). Burks and Sekul showed that isobutylene or diisobutylene could also be used as the catalyst activator (2). Wilke described the use of Ziegler catalysts and related nickel catalysts for the reaction ( 8 ) .
1,5 -cyclooctadiene
/CH=cH2
CH
/I
CH
\
CH
I
CH,
/
C HZ 4-viny lcyclohexene
The present investigation was conducted as the first step in determining optimum conditions for a simplified continuous process with bis(tripheny1phosphite)dicarbonylnickel as the catalyst ( 7 ) . Preliminary experiments indicated that better yields of C O D were obtained and less susceptibility to catalyst poisoning was encountered a t higher temperatures than those used by previous investigators. These experiments also showed that the yields were higher in the absence of benzene, which previously had been used as a solvent for the reaction. A study of the process variables was then undertaken with a bench-scale, heated-tube reactor. This was a simple and inexpensive system with which the feasibility of continuous reaction was quickly established and the process variables were defined within reasonably narrow limits. Experimental Details
Catalyst Preparation. Bis(tripheny1phosphite)dicarbonylnickel was prepared by the displacement of carbon monoxide from nickel carbonyl by triphenyl phosphite (5).
+
+
~ ( C ~ H SPO ) ~Ni(C0)4 + [(CsHb0)~P]2Ni(C0)2 2CO
A typical preparation of the catalyst was as follows. The operation was carried out in an efficient hood where the extremely toxic nickel carbonyl could be safely handled. Nickel carbonyl, 27.2 grams (0.160 mole), was run from a cylinder into a 125-ml. Erlenmeyer flask chilled in ice. The carbonyl was then mixed with 70 ml. of chilled diethyl ether and the mixture was transferred to a 1-liter 3-necked roundbottomed flask in an ice bath. The flask was fitted with a water-cooled reflux condenser, a dropping funnel. and a stirrer. A solution of 35 grams (0.306 mole) of triphenyl phosphite in 100 ml. of ether was added dropwise to the stirred, cooled carbonyl solution. over a period of about one hour, a t a rate sufficient to maintain a gentle evolution of carbon monoxide. The mixture was stirred a t room temperature for an hour and then at 33' C . for another hour. The ether was removed by gentle suction. The product was a white crystalline powder \vith a slight phenolic odor, melting a t 87-89' C. (90-91 C. after recrystallization from absolute ethanol). In the experiments described in this article, the catalyst was used without being recrystallized, as recrystallization did not affect its activity It was stored in a closed container at 5' C . until used. VOL. 3
NO. 2
JUNE 1 9 6 4
117
Apparatus. T h e dimerization apparatus was assembled, with a small amount of welding, from components that are common in laboratories equipped for high-pressure catalytic reactiuns. T h e simplicity of the apparatus made it possible to operate under a variety of reaction conditions, and the small size of the apparatus simplified the work involved in recharging for each experiment. Even so. it was convenient, when desired, to produce a pound of C O D in a working day. .1he apparatus, shown diagrammatically in Figure 1>consisted of a feed reservoir, a reactor, and a product collection system. The feed reservoir was a stainless-steel, high-pressure bomb fitted with a glass liner and with a stainless-steel gas inlet tube connected to a pressure gage and to a cylinder of argon, the pressuring gas. The pressure of argon determined the pressure of the system. T h e feed line from the reservoir was connected to the reactor, which was a coil of l:4-inch I.D. stainless-steel, high-pressure tubing immersed in an oil bath. T h e volume of the heated zone of the reactor was 80 ml. T h e throughput rate was regulated by means of a needle valve on the exit side. Downstream from the exit valve two graduated cylinders cooled with dry ice collected the products. Procedure. All the reactants were placed in the chilled glass iiner of the feed reservoir. Butadiene was released from a cylinder, passed through a column of Drierite, condensed in a tube cooled by dry ice, and measured by volume into the glass liner containing a measured amount of catalyst. T h e reactants were mixed well to ensure homogeneity. Tests conducted earlier in the research had shown that the catalyst was soluble in liquid butadiene and COD. T h e liner was placed in the feed reservoir. and the desired pressure was created and maintained by adding argon. After the temperature of the oil bath became constant, product was withdrawn through the exit needle valve every 5 to 10 minutes. T h e amount withdrawn was measured by volume and the rate of withdrawal a t specific time intervals was governed by the desired rate for each experiment. Each experiment was continued for a few hours under conditions of steady operation. T h e attainment of steady operation was verified by comparative analysis of samples
Tfmp., C. 125 125 125 125 125 125 125 125 135 150 150 150 150 150 165 165 165 165 165 165 165 165 165 165 185
Run 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
16 17 18 19
20 21
22 23
24 25
26 27 COD
118
205 205 = ryrlnortndimr
I&EC
FEED RESERVOIR
REACTOR VENT DRY ICE BATH
U
Figure 1. Apparatus for catalytic dimerization of butadiene
taken at successive intervals. T h e product was a dark-colored liquid containing no appreciable suspended matter. A portion of each sample was weighed and distilled until the pot temperature reached 170' C. a t 3 mm. of pressure. The amount of nondistillable material was determined by weight. T h e precision of the distillation was the major factor limiting the precision of the analytical methods. After the procedure became carefully standarlized through repetition. the amounts of volatile and nonvolatile material were estimated to be accurate within i5 percentage points. T h e distillate was analyzed by gas chromatography in a Burrell Kromo-Tog, Model K-1, on a 2-meter column. T h e column filling was 30y0 Apiezon N grease on 30-60 mesh firebrick. T h e column temperature was 125' C., and the thermal conductivity detector cell temperature was 150' C. Helium ( 5 5 ml. per minute) was used as the eluting gas. This procedure allowed the separation and determination of COD, V C H , a higher-boiling distillate, and benzene, when present. The weight per cent of each component was calculated from its relative peak area. T h e validity of the weight per cent-peak area relationship was confirmed by analysis of known mixtures. Experimental Program. A series of experiments was planned to obtain information on the optimum process condi-
Table 1. Catalytic Dimerization of Butadiene Throughput Amount of Amount of Selectivities, yea Rate, Pressure, Catalyst, Soluent, ConverMl./Hr. COD VCH HB P.S.I.G. % sion, 9 0 % 1000 20 3 0 15 51 28 1 1000 20 3 30 62 63 21 2 40 3 0 17 40 42 7 1000 80 0 0 0 0 0 0.75 1000 30 2 18 50 0 80 000 1 0 0 0 3 0 0 80 000 3 15 4 80 000 80 3 000 30 8 27 2 80 3 0 4 000 20 000 3 0 78 58 21 3 63 19 7 40 000 3 0 68 0 12 33 20 2 80 0.75 000 80 3 56 22 4 000 0 54 80 3 30 43 41 27 1 000 73 10 2 0.75 200 60 0 10 0.75 64 14 0 86 11 600 60 3 60 60 0 98 21 6 600 21 6 63 120 3 0 71 600 67 18 5 600 240 3 0 50 240 15 17 23 1 58 3 600 33 240 30 7 3 28 0 600 28 2 53 240 800 3 0 13 30 32 7 Trace 52 240 3 1000 54 3 0 13 35 3 240 1000 57 20 2 0 25 240 3 600 25 1 56 240 3 600 0 52 56 30 45 26 0 240 3 600 VCH = vinylcycloh~x~nr;H R = higher-boiling distillatt-; N D = nondistillable product.
PRODUCT RESEARCH A N D DEVELOPMENT
ND 19 14 9 0
28 0
Yield of COD, % 8 39 7 0 1 0 2 1
11
16 9
34 15 22 5 10 13
10 7 15 27 16 13 7 20 18 15
2 45 43 4 30 20 7 55 59 45 33 10 2 7 4 7
14 29 25
tions by a minimum number of experiments. The first experiments were conducted below 150 " C., which is approximately the critical temperature of butadiene, with a pressure of 1000 p.s.i.g. being used in order to be certain that all components were in the liquid phase. The variables were temperature, throughput rate, catalyst concentration, and the amount of solvent present. With three levels of each of four variables, there are 81 possible combinations, but fewer would suffice to define the effect of each variable, if no unpredicted variables are involved. For operation above 150' C., the variables studied were temperature, pressure, throughput rate, catalyst concentration, and amount of solvent present. With three levels of each of five variables, there are 243 possible combinations, but again fewer would show the effect of each variable, provided again that no unpredicted variables are involved. Table I lists the experiments that were performed that gave results necessary for drawing conclusions about the effects of each variable. Results
*
Table I shows, for the different reaction conditions, the per cent conversion of butadiene, the selectivities of COD, higherboiling distillate, and nondistillable product, and the yield of COD. These terms are defined as follows: Conversion =
weight of butadiene consumed weight of butadiene fed
weight of single product Selectivity = weight of butadiene consumed
x
100
x
100
selectivity X conversion 100 The figures shown are averages of three to six analyses of samples obtained successively after the reaction had reached steady-state conditions. The error was estimated to be 1 5 percentage points in the selectivities and slightly more in the conversion of butadiene. Temperature. As the temperature was increased from 125" to 150" C., the conversion of butadiene increased, the selectivity of C O D generally increased, and the selectivity of V C H decreased (compare Runs 1 and 10; 6, 9, and 13; 4 and 12; 8 and 14). When the temperature was increased from 150" to 205" C., in the absence of solvent, the selectivity of C O D decreased slightly and that of V C H increased (Runs 19, 25, and 26). When benzene was used as a solvent above 150" C., these effects were reversed (Runs 21 and 2 7 ) . These results indicate that, in the absence of solvent, the optimum temperature for high C O D selectivity is above 150" C. and probably below about 170" C. Pressure. Since a pressure of 1000 p.s.i.g. was applied in all experiments a t temperatures below 150" C., the effect of pressure was not studied. At temperatures above 150" C., when no solvent was used, the C O D selectivity generally decreased and that of V C H increased when the pressure was increased from 200 to 1000 p.s.i.g. (Runs 19, 22, and 24). When benzene was used as a solvent, the C O D and V C H selectivities both increased with increased pressure (Runs 21 and 23). T h e results indicate that high C O D selectivity is obtained a t low pressures. The maximum yield of C O D is obtained nearer 600 p.s.i.g., probably between 400 and 600. T h r o u g h p u t Rate. When the throughput rate was increased from 20 to 240 ml. per hour (0.25 to 3 volumes of liquid feed per volume of reactor per hour), the C O D selectivity decreased a t 1 2 5 " a n d 150" C. (Runs 1, 3, and 6 ; 10, 11, and 13; 2 and 8) but increased slightly a t 165" C . (Runs 17, 18, and 19). There was little change in the V C H selectivity. Yield =
The conversion decreased with increased throughput rate. Solvent. At temperatures of 150" C. and higher, when benzene was used as a solvent, the selectivity of C O D was lower and that of V C H was generally higher (Runs 1 3 and 14; 19, 20, and 21; 26 and 2 7 ; 23 and 24). The conversion was generally lower when solvent was present, but a t the higher temperatures and pressures, the effect was not as great. At 125" C., the C O D selectivity was higher in the presence of benzene (Runs 1 and 2 ; 6, 7, and 8). These results indicate that for maximum COD selectivity, benzene should not be used as the solvent and that in fact no solvent is necessary for the production of C O D in high yield. Catalyst Concentration, At 150" C., in the absence of solvent, the C O D selectivity was higher and that of V C H was lower when the catalyst concentration was increased from 0.75 to 3Yc (Runs 12 and 13). In the presence of solvent, the C O D selectivity did not change when the catalyst concentration was increased (Runs 5 and 8). Above 150' C . , there was no change in C O D selectivity when the catalyst concentration was varied from 0.75 to 3% (Runs 16 and 17). However, as the catalyst concentration was increased, the selectivities for V C H and nondistillables increased. The optimum catalyst concentration is evidently between 0 . 7 5 and 3%: but it was not determined more closely. Optimum Process Conditions. Although the results contain some anomalies that it would only be speculative to try to explain on the basis of the data available, the optimum conditions for obtaining high selectivity for C O D and low selectivities for V C H and nondistillables probably are 150' to 170' C., a pressure of 400 to 600 p.s.i.g., and a throughput rate of 0.8 to 3.0 volumes of liquid per reactor volume per hour, with no solvent. -4catalyst concentration between 0.75 and 3Yc appears to be satisfactory. The lower throughput rates gave higher conversions. By-products. The data do not allow a conclusion as to the origin of the V C H . It can be formed by thermal, noncatalytic dimerization. T h e nondistillable product was largely a polymer. In most experiments, the amount of the nondistillable product was high if the V C H content was high. The high-boiling distillate could be separated on the gas chromatograph into several components that were not identified ; the principal component in most cases was judged to be 1,5,9cyclododecatriene, on the basis of its chromatographic behavior, Acknowledgment
The assistance of G. S. McCaleb, B. C . Park, and Ruby James in the laboratory work is gratefully acknowledged. This research was conducted a t Southern Research Institute several years ago under the sponsorship of Cities Service Research and Development Co. literature Cited (1) Bosmajian, G. (to Cities Service Research and Development Co.), U. S. Patent 3,004,081(Oct. 10, 1961). (2) Burks, R. E., Jr., Sekul, A. A. (to Cities Service Research and Development Co.), Ibid.,2,972,640 (Feb. 21, 1961). (3) Foster, R. E., Schreiber, R. S., J . A m . Chem. SOC.70, 2303
(1948). (4) Hillyer, J. C., Smith, J. V., Ind. Eng. Chem. 45, 1133 (1953). (5) Reed, H. W. B., J . Chem. SOC.1954, 1931; Reed, H. W. B. (to Imperial Chemical Industries), U. S. Patents 2,686,208 and 2,686,209 (Aug. 10, 1954). (6) Sekul, A. A , , Sellers, H. G. (to Cities Service Research and Development Co.), Ibid., 2,964,575 (Dec. 13, 1960). (7) Sellers, H. G., Sekul, A. A . (to Cities Service Research and
(1950). RECEIVED for review February 25, 1964 ACCEPTED March 26, 1964 VOL. 3
NO. 2
JUNE 1 9 6 4
119
