Dimerization of ethylene catalyzed by a nickel catalyst supported on porous polymers

Reactive Polymers, 13 (1990) 153-160 Elsevier Science Publishers B.V., Amsterdam

153

DIMERIZATION OF ETHYLENE CATALYZED BY A NICKEL CATALYST SUPPORTED ON POROUS POLYMERS JEAN-CLAUDE CARLU and CLAUDE CAZE *

Laboratoire de Chimie MacromolOculaire UA CNRS 351, UniversitO des Sciences et Techniques de Lille Flandres Artois, 59655 Villeneuve D'Ascq Cedex (France) (Received May 1, 1989; accepted in revised form February 10, 1990)

We have tested the possibifity of using polymer-supported catalysts in a heterogeneous way (gas-solid) for the dimerization of ethylene. The catalyst is prepared by complexation of NiCI 2, by a phosphine group supported on a resin followed by reduction with AI(C2Hs)2CI. Good selectivity in butene synthesis has been achieved with a yield up to 80 % of but-l-ene. The formation of oligomers is observed, and these oligomers become embedded in the polymer support, giving rise to decrease of both the specific area and the pore volume. It is proposed that the embedding process causes the deactivation of the catalyst by coverage of the active sites and pore blockage. Correlation between the efficiency of the catalyst and the texture of the different supports is shown.

INTRODUCTION

We have shown for Fischer-Tropsch catalysis the possibility of using polymer-supported catalysts in a heterogeneous way (gas-solid) [1,2]. The catalyst was dispersed in porous polymers and the reaction was performed in a tubular reactor under a flow of C O / H 2. The aim of this paper is to show the same possibility for the dimerization of ethylene; the catalyst system is based on a Ni/Lewis acid combination. The different supports have been obtained by chloromethylation then phosphination of

* To whom correspondence should be addressed. 0923-1137/90/$03.50

porous styrene-divinylbenzene copolymers [3,4], or by phosphination of porous styrenebromostyrene-divinylbenzene terpolymers [5]. The catalytic system has been formed by complexation of NiC12 with the phosphine ligand [6] followed by reduction with AI(C2Hs)2C1. This type of catalyst is known to be active in the homogeneous dimerization and oligomerization of olefins [7], and in the codimerization of olefins and dienes [8]. Some of these catalysts have been tested in homogeneous supported systems [7,9,10] or heterogeneous systems [11] with good results. We have now tried to transpose this type of catalyst, active in both homogeneous and homogeneous supported systems into heterogeneous systems.

© 1990 - Elsevier Science Publishers B.V.

154 EXPERIMENTAL

Polymeric materials Styrene (ST) and bromostyrene (BrST) monomers were commercial products, which were distilled under vacuum prior to use. Divinylbenzene (DVB) was a commercial product containing 35% p-DVB, 15 m-DVB, 35% ethylbenzene and 15% p-ethylbenzene. It was used without purification. The copolymers S T - D V B and the terpolymers S T BrST-DVB were synthesized by suspension radical copolymerization in the presence of a porogenic agent which was hexane or polystyrene ( M , = 193,000. M w / M n = 1.17) [12]. The porogenic agent was extracted in a Soxhlet. Methanol was used in the case of the precipitating porogenic agent hexane, while toluene (12 h), followed by methanol, was used when polystyrene was the porogen [13]. The S T - D V B copolymers were chloromethylated using a well known process [3], then the copolymers and terpolymers were phosphinated with LiP(Ph)2 in T H F [5].

Texture characterization The texture of the beads was characterized in the dry state by pore volume (Vp) and specific area (S) measurements. Pore volumes were obtained using a mercury porosimeter (Carlo Erba 800). Surface areas were obtained from nitrogen adsorption/desorption according to the BET method. The spatial distribution of the catalyst was obtained by electron probe X-ray microanalysis [1].

Preparation of catalysts

vacuum. The (~)-[(P(Ph)2]2 NiC12 complex was reduced by AI(C2Hs)2C1. 1 g of complex was swollen with dichloromethane (20 ml) then the reducing agent was added under nitrogen. After 1 h the dichloromethane was removed by distillation and the catalyst was dried under vacuum for 2 h.

Catalysis studies The supported catalyst was introduced under a stream of nitrogen into a tubular reactor, then nitrogen was replaced by ethylene at a given pressure and flow rate and at room temperature. The following reaction parameters are defined: • Tr (turn over rate); mole of ethylene transformed per mole of Ni per second; • S (selectivity); all the selectivities are given in molar units; • the percentage of but-l-ene was calculated using butenes as reference; • 8 (s); the contact time is defined by the ratio volume of catalyst/flow rate of ethylene. All the catalysis experiments were carried out at a pressure of ethylene of 10 bar and for 0.3 < ~ < 3.0. The analysis of the products was performed by gas chromatography under the following conditions: column 4 m × 1 / 8 in, steel, squalane 10% on Porasil C (100-120 mesh); column temp. 20-120 ° C, heating rate 1.5 ° C/min; evaporator temp. 150 ° C; pressure 2 bars N2; FID. Quantitative analysis was performed after calibration with pure products.

R E S U L T S AND D I S C U S S I O N

Morphology of the supports Under nitrogen, a solution of 2 × 10-3 mol of NiC12 • 6H20 in 10 ml of ethanol was added to 3 g of phosphinated support in 20 ml of ethanol and the mixture was heated at 60 ° C for 15 h. The alcohol was then removed by filtration and the beads were dried under

The textures of the functionalized beads are similar to those of the original starting materials (see Table 1), so the morphologies of the functionalized supports are likely to be similar to those of the initial materials.

155 VP

VP cm'/g

cmVg

~

1

I~

/ 0.8

z

/

C5

~ ~

. . . . . . . . . . .

~

/

/ ¢

0.2 f

06

//

C2 O.1

..........

>=-57~..~.~.~

!

0.4

/

i/

/

C6

z/

102

103

10"

.,~ °~

Fig. 1. Integral pore volume distribution of catalysts C1-C4.

102

.. ........................................

: .....................................

103

104

,.~.c~

~t

Fig. 2. Integral pore volume distribution of catalysts C5-C8.

Supports C5 to C8 were obtained using a non-solvating diluent, and these types of polymers could have three different morphologies depending on the percentages of DVB and diluent used in their preparation [12]. The most typical morphology is termed "macroporous". Such polymers are made up of large agglomerates of microspheres, the microspheres themselves being formed from agglomerates of nuclei. In this model there are three families of pores: between the nuclei (5-15 nm), between the microspheres (20-50 nm) and between the agglomerates (50-1000 nm). The surface area is greater than 100 m 2 g-] and the pore volume is 0.1-1 cm3 g - 1 . The morphologies of polymers C6 and C7 conform to this picture.

When the concentration of diluent is high, precipitation can occur on the microspheres and this embedding process causes a decrease in the specific area. This is the case for polymer C5. The morphology of support C8 (obtained at lower diluent and DVB concentration) is on the borderline between a macroporous and a gel-type resin. Supports C1 to C4 were obtained with a polymeric porogen. This type of porogen produces a small surface area (up to 10 m 2 g-a) and large pores. The values of the pore volume obtained for these supports (Table 1) are in good agreement with the literature [14]. The pore volume integral distributions of all these supports are reported in Figs. 1 and 2.

TABLE 1 Chemical characteristics and texture of the different catalysts Sample

C1 C2 C3 C4 C5 C6 C7 C8

a

DVB (%)

Porogen (%)

30 40 40 40 15 30 40 20

10 10 15 20 50 40 35 35

Vp (cm3 g - l )

S (m2 g - l )

Ni (mequiv g-l)

AI/Ni

(2)

p (mequiv g-l)

(1)

(2)

(1)

0.17 0.22 0.20 0.19 0.98 0.47 0.14 0.16

0.09 0.12 0.12 0.07 1.06 0.37 0.13 0.09

<5 7 7 5 58 204 229 44

< 5 < 5 17 8 86 165 238 38

0.17 0.28 0.18 0.23 0.48 0.28 0.23 0.28

0.070 0.055 0.060 0.051 0.062 0.050 0.056 0.056

150 25 30 25 27 28 26 28

C1 and C2 to C4; polystyrene as porogenic agent; C5 to C8 heptane as porogenic agent. All the terpolymers (C2 to C8) were synthesized with 10% of BrSt in the feed, and the bromide concentration in the bead varied from 0.61 to 0.94 mequiv g 1. (1) Before functionalisation; (2) after functionalisation.

a

156

Another important feature is the distribution of the catalyst in the support. Terpolymers S T - B r S T - D V B obtained with a nonsolvating diluent have an heterogeneous distribution of bromide, in contrast to polymers prepared with a polymeric porogen [13]. For macroporous polymers, the phosphination

process gave also some heterogeneous P distribution [5]. Figure 3 shows typical X-ray microphotographs: of the bromine distribution in macroporous and porous S T - B r S T DVB terpolymers, and of the phosphorus distribution for the same polymers and after the phosphination reaction.

i~"•''~•~I ~ • •~i . . . . . ••:'-•

I

~i°~ ~,~i ~ ~ , i~!~, ~i •~ ~,.~~~•'~ i,• ~L~_,•i.~~ ~~• ~ • • .~'~~' ""~~.~'~,i~,~,'~ ~A~,~' ~ "~~,'-.~i:~ ~ . ~ :~.~~-,~~!' ,: ~~ ~, .~~ i~~ ~,~~. '~:-~i~~ ~,' ~~~; ~. • ~

Fig. 3. Br ( b e f o r e p h o s p h i n a t i o n ) (a) a n d P (b) X - r a y m i c r o p h o t o g r a p h s o f p o l y m e r s C 2 ( A ) a n d C 6 (B).

157 Tr

0.20 ~

I

s-1

0.1.5

O,1

~ 0.10

E

o 0.05

\

/ ~

iI \ . . . . . . . . . . . . . . . . .

0

/I 2R

Fig. 4. Typical quantitative distribution of A1 and Ni in the catalyst (case of C5): ( ) A1; ( - - - - - ) Ni.

10

20

t i m e (h)

Fig. 5. Evolution of Tr vs. time; ( - ) C1; (n) C4.

Complexation of NiC12 by the phosphine ligands and reduction with AI(C2Hs)2C1 give the active catalyst. The distribution of the Ni and AI appears to be independent of the P distribution as can be seen in Fig. 4. This shows a typical quantitative distribution of both Ni and A1 in a bead. We have tried to show the complexation of NiC12 by the phosphine ligand by Raman microprobe analysis [15,161.

Catalysis results All the catalysts studied show the same behaviour with respect to reaction time. Tr is observed to decrease and the selectivity in butene formation and the percentage of but1-ene are constant with time. Whereas support C1 contains diphenylphosphinomethyl groups (~)-C6H4-CHz-P(Ph)2, all the other supports contain triphenylphosphinomethyl groups, (~)-C6H4-P(Ph)z. Comparison between the results obtained with catalysts C1 and C4 (these two supports have approximately the same morphology) reported in Fig. 5 and Table 2 shows that the chemical structure of the ligand plays an important role on the turnover rate. In fact the catalyst C1

shows about 10% of the activity of catalyst C4. The results obtained with polymers C5 to C7 are reported in Table 2 and Fig. 6. The selectivity in butenes and the percentage of but-l-ene decrease from C5 to C7 while the initial Tr increases. For the macroporous supports (C6 and C7) or those derived from a macroporous structure (C5), the results correlate with the specific area. If S increases then there is a more efficient contact between the gas and the catalyst, and this gives rise to an increase in Tr. However, the reaction can be prolonged in an oligomerization process (the selectivity in butenes decreases) and some TABLE 2 Observed selectivities for the different catalysts (average values) Catalysts

Butenes (%)

But-l-ene (%)

C1 C2 C3 C4 C5 C6 C7 C8

84.0 94.0 92.8 87.8 93.6 92.7 90.2 91.2

48.5 81.0 58.8 51.2 75.3 66.5 53.8 46.2

158 Tr s-1

1

""-"t---

0

50

A,~, I"

I

100

200

150

t i m e (h~

Fig. 6. Evolution of Tr vs time: (,x) C5; ( , ) C6; (D) C7; (e) C8.

isomerization can occur (the percentage of but-l-ene decreases). Figure 7 and Table 2 report results obtained with catalysts C2-C4. These are interesting because an increase is seen in the selectivity of butenes and in the percentage of but-l-ene in changing from C2 to C4, while Tr decreases. Although in general these sys-

terns resemble those described above (i.e. C 5 C7), the differences in reactivity observed for polymers C 2 - C 4 are difficult to explain, and direct correlation of the results with the textural parameters is not so evident. The results obtained using these types of catalyst are of the same order as those obtained using macroporous systems, and this is probably due to

Tr 8-1

0.5

"I ........................... ~--'..~l.'-".,-,..~',.-..,-.,.~-t -" --

25

50

Fig. 7. Evolution of Tr vs. time: (A) C2; (e) C3; (D) C4.

T" . . . . . . .

75

n

I

100

t i m'e

(,r

159 TABLE 3

VP~

cm3/g

Evolution of texture parameters (1) before catalysis; (2) after catalysis Catalyst

C1 C2 C3 C4 C5 C6 C7 C8 0,5

I 5

I 10

i 15

S (m 2 g - 1)

(1)

(2)

(1)

(2)

0.09 0.12 0.12 0.07 1.06 0.37 0.13 0.09

0.05 0.10 0.07 0.03 0.57 0.24 0.09 0.05

< 5 < 5 17 8 86 165 238 38

< 5 < 5 < 5 < 5 14 96 46 < 5

I 20

Fig. 8. Evolution of porous volume vs. time (C5).

the presence of macropores, which can increase the efficiency of the supported catalyst as shown by Guyot [12]. The catalyst C8 gives results similar to those for catalysts C 1 - C 7 for both the selectivity in butenes and Tr, but it gives the worst result for the percentage of but-l-ene (Fig. 6 and Table 2). Comparison of our results (for example Tr and selectivities) with the results obtained in homogeneous catalysis is not really possible, because the two techniques are very different Figs. 8 and 9 show, respectively, the change of the porous volume and the repartition of pores for catalyst C5 vs time. An unchanged VP

cmVg I

Vp (cm 3 g - 1)

repartition of pores is observed but a rapid decrease of the porous volume is obvious. The change of both pore volume and specific area is general, as shown in Table 3. After use in catalysis the beads are embedded with condensed oligomers (after extraction of the beads with xylene, the product obtained shows by microanalysis the presence of only C and H, and the infrared spectra are characteristic only at the absorptions of hydrocarbons). We suggest by analogy with the deactivation process by coke deposition (proposed by Froment and co-workers [17,18]), that deactivation here occurs by active site coverage and pore blockage. This type of deactivation process does not give a direct correlation between the evolution of the kinetic parameters and the evolution of both the specific area and porous volume of the support with time [181.

oh

O.8

CONCLUSIONS 0.6

0.4

0.2

:'2;/

,o, ,o, ,o, (~f Fig. 9. Evolution of integral pore volume distribution vs. time (C5).

We have shown that it is possible to use polymer-supported systems as heterogeneous catalysts for the dimerization of ethylene with good selectivity and turnover rate. The best result gives 90% for the selectivity in butenes and 80% of but-l-ene (in the butenes fraction). Deactivation seems to occur by active

160

site coverage and pore blockage produced by the 10% of oligomers which cannot be removed by the gas flow. The correlation between the catalysis results and the texture parameters of the catalysts (specific area and porous volume, determined in the dry state, which is the state in which we used the catalysts) shows that for macroporous polymers the efficiency increases with the specific area. Such correlation is not possible for supports obtained with polymeric porogen, and we think that a full description of this type of support requires other methods of characterisation. A comparison of the results obtained for these two families of polymers indicates that the texture parameters alone (S and Vp) are not sufficient to explain completely the differences in their efficiency. Additional factors must be involved, e.g. an adsorption process, and for differences in the nature and accessibility of the active sites.

REFERENCES 1 J.C. Carlu, D. Le Maguer, C. Caze and F. Petit, Fischer-Tropsch synthesis catalyzed by iron catalyst supported on porous polymers. 1. Synthesis of the supported catalyst and study of the repartition of the catalyst in the polymeric support, Reactive Polym., 8 (1988) 119. 2 J.C. Carlu, C. Caze and F. Petit, Fischer-Tropsch synthesis catalyzed by iron catalyst supported on porous polymers. 2. Catalytic results, Reactive Polym., 12 (1990) 187. 3 S. Wali Alami, D. Le Maguer and C. Caze, Influence of the preparation methods on the functional group distribution of chloromethylated copolymers, Reactive Polym., 6 (1987) 213. 4 Grubbs and L.C. Kroll, Catalytic reduction of olefins with a polymer supported rhodium(l) catalyst, J. Am. Chem. Soc., 73 (1971) 3062. 5 M. Bacquet, D. Le Maguer and C. Caze, Chemical modification of polymeric supports: 1. Phosphination of porous styrene/bromostyrene/divinylbenzene terpolymers, Angew. Makromol. Chem., submitted. 6 L.M. Venanzi, Tetrahedral nickel(II) complexes and the factors determining their formation. Part 1: Bi-

7

8

9

10

11

12

13

14

15

16

17

18

striphenyl phosphine nickel(II) compounds, J. Chem. Soc., (1958) 719. C.U. Pittman, Jr., and L.R. Smith, Selective, highyield linear dimerisation of 1,3-butadiene catalyzed by (PPh3)zNiBr 2 and NaBH 4 and its polymerbound Ni(0) analog, J. Am. Chem. Soc., 97 (1975) 341. R.G. Miller, T.J. Kealy and A.L. Barney, Codimerization of a-olefins and conjugated dienes by a nickel based coordination catalyst, J. Am. Chem. Soc., (1967) 3756. F.R. Hartley, Dimerisation, oligomerisation, polymerisation, disproportionation and isomerisation of olefins and acetylenes, in: Supported Metal Complexes, D. Reidel, Dordrecht (1985). T. Mizoroki, N. Kawaka, S. Hinata, K. Maruya and A. Ozaki, Nickel complex catalyst bound to halogenated polystyrene with a nickel-carbon tT bond, Catal., Proc. Int. Symp., (1974) 319. E. Angelscu, A. Angelescu, S. Nenciulescu and I.V. Nicolescu, Ethylene dimerization by heterogeneous coordinated catalysis. III. Rev. Chim. (Bucharest), 32 (1981) 559. A. Guyot, Synthesis and structure of polymer supports, in: D.C. Sherrington and P. Hodge (Eds.), Synthesis and separation using functional polymers, J. Wiley, New York, NY, 1988. M. Bacquet, D. Le Maguer and C. Caze, Porous texture and bromide distribution in porous styrene-bromostyrene-divinylbenzene terpolymers, Eur. Polym. J., 24 (1988) 533. J. Seidl, J. Malinsky, K. Dusek and W. Heitz, Makroporose Styro-Divinylbenzol-Copolymereund ihre Verwendung in der Chromatographic und zur Darstellung von Ionenaustauschem, Adv. Polym. Sci., 5 (1967) 113. M. Bacquet, C. Caze, J. Laureyns and C. Bremard, Spatial distribution of pendent vinyl groups during chloromethylation of macroporous styrene-divinylbenzene copolymers, Reactive Polym., 9 (1988) 147. J. Laureyns, C. Bremard, M. Bacquet and C. Caze, Identification and spatial repartition of functional groups grafted onto macroporous copolymers, Proc. llth International Conference on Raman Spectroscopy, London, 1988. G.B. Marin, J.W. Beeckman and G.F. Froment, Rigorous kinetic models for catalyst deactivation by coke deposition: application to butene dehydrogenation, J. Catal., 97 (1986) 416. In-Sik Nam and G.F. Froment, Catalyst deactivation by site coverage through multi-site reaction mechanisms, J. Catal., 108 (1987) 271.