WO2012062469A1

WO2012062469A1 - Ethylene oligomerization catalyst

Info

Publication number: WO2012062469A1
Application number: PCT/EP2011/005650
Authority: WO
Inventors: S. Licciully; K. Albahily; S. Gambarotta; R. Duchateau
Original assignee: Stichting Dutch Polymer Institute
Priority date: 2010-11-10
Filing date: 2011-11-10
Publication date: 2012-05-18

Abstract

The invention relates to An ethylene oligomerization catalyst system comprising an activator and an organometallic complex, wherein the complex comprises a metal chosen from the group consisting of Cr, V and Mo and a ligand defined by the formula (III): wherein R¹ is each independently CH₃ or CH₃CH₂, R² is a straight, branched or cyclic C1-C6 alkyl group or an aryl group and n and m are each independently an integer between 1 and 5. The invention further relates to a process for the oligomerization of ethylene

Description

Ethylene oligomerization catalyst

The present invention relates to an ethylene oligomerization catalyst and a process for making thereof. The present invention also relates to use of such catalyst for making a linear alpha-olefin.

Olefin oligomerization catalysts are known in the art, but sometimes lack selectivity to a desired product and also have a low product yield. Enhancements in preparation methods for oligomerization catalysts to improve productivity and selectivity to the desired product can reduce catalyst cost and improve economics.

US6800702 discloses a catalyst which comprises (a) a source of Chromium, molybdenum or tungsten, (b) a ligand containing at least one phosphorus, arsenic or antimony atom bound to at least one hydrocarbyl or heterohydrocarbyl group having a polar substituent, but excluding the case where all such polar substituents are phPsphane, arsane or stibana groups; and optionally (c) an activator.

US2010/0081777 discloses a P-N-P ligand for ethylene

oligomerizations. The catalyst system comprises i) a source of chromium, (ii) a defined P-N-P ligand and (iii) an activator. It is mentioned that the hexenes and octenes produced with this ligand contain very low levels of internal olefins when produced under preferred reaction conditions. The catalyst components (i), (ii) and (iii) can be unsupported or supported on a support material, for example, silica, alumina, MgCI₂ or zirconia, or on a polymer.

Peulecke et. Al, ChemCatChem Vol. 2, Issue 9, pages 1079-1081 describes a selective homogeneous chromium-based ethene trimerization catalyst heterogenized by immobilization on a functionalized polymer support. The catalyst is based on a new class of aminophosphine ligands with a Ph₂PN(iPr)P(Ph)N(iPr)H (PNPNH) backbone, in conjunction with [CrCI3(thf)3] and Et3AI as a cheap and well- defined aluminum-alkyl activator. This publication also discloses using silica for immobilization of the catalyst (RO)₃Si(CH₂)3NHP(Ph)N(iPr)PPh₂. It is mentioned that after complexation of [CrCI₃(thf)₃] and activation with ΕΐβΑΙ, the oligomerization of ethene resulted in a oligomers/polyethene ratio of only 3:1 and a selectivit within the liquid fraction of up to 70% 1-hexene (after two runs).

While these catalysts have been described in the art, there is still a need for improved catalysts for ethylene oligomerization in terms of selectivity and productivity. An object of the present invention is to provide an ethylene oligomerization catalyst system which has good selectivity towards ethylene oligomer and which has a good ethylene oligomerizing catalysis effect.

According to one aspect of the present invention, an ethylene oligomerization catalyst system is provided comprising an activator and an organometallic complex, wherein the complex comprises a metal chosen from the group consisting of Cr, V and Mo and a ligand defined by the formula (III):

wherein R is each independently CH₃ or CH₃CH_Zl ² is a straight, branched or cyclic C1-C6 alkyl group or an aryl group and n and m are each independently an integer between 1 and 5.

The ethylene oligomerization catalyst system according to the present invention has a very high selectivity towards oligomers and produces no or very small amount of polyethylene.

Preferably, R² is an aryl group, in particular a phenyl group.

Preferably, the metal is Cr. A preferred source of chromium is a chromium halide, especially a chromium chloride. Especially preferred is CrGI₂(THF)₂ or CrCI₃(THF)₃. Other sources of metal include chromium (III) 2-ethylhexanoate; chromium (III) acetylacetonate and Cr(aryl)₃(THF).

Preferably, the metal is Cr and R² is a phenyl group.

Particularly preferred groups of metal complex is represented by formula I) or (II):

In particular preferred embodiments, the metal complex is represented by:

In some embodiments of the present invention, the organometallic complex is supported by an inorganic carrier. The organometallic complex can be supported by for example a Lewis base-Lewis acid interaction between complex and support. An example of a support suitable for this type of interaction is gC(₂.

Preferably the complex is covalently linked to reactive groups on the support. An example of a reactive group is an OH- group. Preferably the support contains vicinal OH groups, which can react with one or more of the Si-OR groups of the ligand of the complex. Examples of carriers that can bind the complex comprise silica, alumina, alumina silicate or clay. Particularly preferred is silica. Vicinal OH groups on a silica carrier are OH groups that are present at adjacent Si-atoms on the surface of the silica carrier.

Surprisingly, the catalyst system comprising the supported organometallic complex according to the present invention was found to have a very high selectivity towards oligomers comparable to the catalyst system according to the present invention used without the inorganic carrier. Particularly advantageously, the catalyst system comprising the supported organometallic complex according to the present invention allows any polyethylene formed to be filtered off. It was found that, due to the presence of the inorganic carrier, any polyethylene produced remains within the catalyst particle. Since polyethylene can be filtered off together with the catalyst particle, reactor fouling can be prevented. In all existing commercial ethylene oligomerization processes, e.g. SHOP (Shell), -S1.H (Chevron-Phillips), a-Sablin (SABIC), the polyethylene produced precipitates and the problem of reactor fouling occurs to a certain extent. Unlike the catalyst systems used in these existing processes, the system according to the present invention allows any produced polyethylene to be easily removed and prevents reactor fouling. Furthermore, leaching tests showed that under the reaction conditions applied, no detectable catalyst leaching occurred.

In the catalyst system according to the present invention where the metal is Cr, Cr may be present in the complex in the form or Cr(lll) such as in the case of complex (I) or in the form of Gr(ll) such as in the calse of complex (II).

The catalyst system according to the present invention where Cr is present in the complex in the form of Cr (II) has an advantage that produces substantially no polymers when used without the support.

The catalyst system according to the present invention where Cr is present in the complex in the form of Cr (III) has an advantage that it has a particularly high selectivity towards certain oligomers, especially at low oligomerization

temperatures. This also allows optimizing the results by tuning the oligomerization temperature.

The activator may be any compound that generates an active catalyst for ethylene oligomerization with the ligand according to the present invention and the source of the metal used. Mixtures of activators may also be used. Suitable

compounds include organoaluminum compounds, organoboron compounds and the like. Suitable organoaluminum compounds include compounds of the formula AIR3, where each R is independently C1-C12 alkyl, oxygen or hali.de; and compounds such as LiAIH4 and the like. Examples include trimethylaluminum (TMA), triethylaluminum (TEA), tri-isobutylaluminium (TIBA), tri-n-octylaluminium and alumoxanes. Alumoxanes are well known in the art as typically oligomeric compounds which can be prepared by the controlled addition of water to an alkylaluminium compound, for example trimethylaluminium. Such compounds can be linear, cyclic, cages or mixtures thereof. Commercially available alumoxanes are generally believed to be mixtures of linear and cyclic compounds. The cyclic alumoxanes can be represented by the formula [R⁶AIO]s and the linear alumoxanes by the formula R⁷(R^BAIO)s wherein s is a number from about 2 to 50, and wherein R⁶, R⁷, and R⁸ represent hydrocarbyl groups, preferably CI to C6 alkyl groups, for example methyl, ethyl or butyl groups. Alkylalumoxanes especially methylalumoxane (MAO) are preferred. (MAO is also referred to as methalumoxane and methylaluminoxane in the literature).

It will be recognized by those skilled in the art that commercially available alkylalumoxanes may contain a proportion of trialkylaluminium. For instance, commercial MAO usually contains approximately 10 wt % trimethylaluminium (TMA), and commercial "modified MAO" (or "MMAG") contains both TMA and TIBA. Quantities of alkylalumoxane are generally quoted herein on a molar basis of aluminium (and include such "free" trialkylaluminium). The alkylalumoxane and/or alkylaluminium may be added to the reaction media (i.e. ethylene and/or diluent and/or solvent) prior to the addition of the catalyst or at the same time as the catalyst is added. Such techniques are known in the art of oligomerization and are disclosed in more detail in for example, U.S. Pat. Nos. 5,491,272; 5,750,817; 5,856,257; 5,910,619; and 5,919,996.

Examples of suitable organoboron compounds are trimethylboron, triethylboron, dimethylphenylammoniumtetra(phenyl)borate, trityltetra(phenyl)borate, triphenylboron, dimethylphenylammonium tetra(pentafluorophenyl)borate, sodium tetrakis[(bis-3,5-trifluoromethyl)phenyl]borate, trityltetra(pentafluorophenyl)borate and tris(pentafluorophenyl) boron.

In the preparation of the catalyst used in the present invention, the quantity of activating compound to be employed is easily determined by simple testing, for example, by the preparation of small test samples which can be used to oligomerize small quantities of ethylene and thus to determine the activity of the produced catalyst. It is generally found that the quantity employed is sufficient to provide 0.5 to 1000 moles of aluminium (or boron) per mole of chromium. MAO is the presently preferred activator. Molar Al/Cr ratios of from 1/1 to 1000/1 are preferred.

According to an yet further aspect of the present invention, a process is provided for preparing the catalyst system according to the present invention. In the first phase, the process comprises the steps of treating PPh₂CI with Br₂ and CH₃CN at a temperature of about 0 °C and adding CI(CH₂)_nSi(R¹0)₃ at a temperature of 60-120 011 005650

°C, preferably 70-90 °C, more preferably around 80 °C. A ligand precursor is obtained. In the subsequent phase, the process comprises the steps of: mixing the ligand precursor with 2.0 equivalents of BuLi and subsequently adding the source of the metal.

According to an yet further aspect of the present invention, a process is provided for preparing the catalyst system wherein the complex is supported by an inorganic carrier. The process comprises the steps of: isolating the organometallic complex, dissolving the complex in toluene and mixing the solution obtained and the inorganic carrier to obtain a supported organometallic compound. Preferably, the carrier is a silica, which is pre-treated at a temperature of 100-900 ^eC, preferably 150- 400 °C, more preferably 200-300 °C, preferably around 250 degrees in vacuo for a period of 1-24 hours, preferably 2-12 hours, more preferably around 6 hours. These temperatures and times are selected to obtain a silica carrier, which contains vicinal OH groups, that are active in binding to the organometallic complex.

The inorganic carrier is preferably silica. Preferably, silica is a porous silica having a BET surface area of at least 100 m²/g, preferably at least 200 m²/g, more preferably 250 m²/g. Preferably, the BET surface area is at most 500 m²/g, more preferably 400 m²/g.

According to an yet further aspect of the present invention, a process is provided for the oligomerization of ethylene comprising contacting the catalyst according to the present invention with ethylene under oligomerization conditions.

Suitable oligomerization conditions are known to the skilled person. The reaction time may e.g. be 10-60 minutes, preferably around 30 minutes. The reaction temperature may e.g. be 30-150 "C, preferably around 90 °C. The reaction pressure may e.g. be 10-60 bar, preferably 40 bar. The temperature may be rapidly reduced after the reaction.

According to a yet further aspect of the present invention, a process is provided for the oligomerization of ethylene comprising mixing the source materials for the catalyst system and ethylene under oligomerization conditions. The source materials may include (R¹0)₃Si(CH2)nN(H)P(Ph)₂N(CH2)mSi(OR^,)₃, a metal precursor such as Cr(Acac)₃, CrCI₃(THF)₃, CrCI₂(THF)₂, Cr (II) 2-ethyl hexanoate or Cr (III) 2- ethyl hexanoate, and the activator such as MAO, AIR_3-XGI_X (x = 0-2). Additionally, the inorganic support may also be added in situ. In a preferred embodiment a ligand precursor which will generate the ligand according to formula (HI) may be mixed with a source of Cr and activator and ethylene under oligomerization conditions. The ligand precursor can be a group 1 , 2 or 13 metal adduct of the ligand (for example the ligand according formula (III) bound to Li or Al), or the H adduct (like for example

(EtO)₃Si(CH₂)₃ NHPBr(Ph)₂NH(CH₂)₃Si(EtO)₃ ).

The present invention will be illustrated with reference to the following non-limiting examples.

Materials

All reactions were carried out under a dry nitrogen atmosphere in Schlenk line or in a purified nitrogen-filled drybox. Solvents were dried using an aluminum oxide solvent purification system except for anhydrous CH₃CN which was purchased from Sigma-Aldrich and used as received. NH₂(CH₂)₃Si(OEt)₃ (98%) and PPh₂CI (98+%) were purchased from Alfa Aesar and used as it is. Br₂ and BuLi (2.5M in hexane) were purchased from Sigma-Aldrich and used as received. CrCI₃(THF)₃ and CrCI₂(THF)₂ were prepared according to standard procedures. THF. MAO (10% wt in toluene) was purchased from Albemarle. Ethylene was purchased from BOC Gases (polymer grade 3.0) and used as received. GC-MS analysis of the ligands and the oligomers was obtained with a Hewlett-Packard HP 5973 gas chromatograph using an Agilent DB1 column. N R spectra were recorded on Bruker Avance 300 MHz spectrometer; all chemical shifts have been quoted relative to deuterated solvent signals, δ in ppm. Si0₂ was purchased from Grace-Davison (Sylopo 948). Si0₂ had the following properties when calcined at the temperature and time indicated in Table 1 and 2:

Table 1. Gas volumetric titration of silanol content of dried and calcined silica.

Tcalc. m(Si0₂) v_E, T St.

mmolOH/g

(time) 9 mL °c Deviatlon %

120 (3day) 0.605 26.8 20.8 1.83 5.2%

250 (4h) 0.796 27.5 20.4 1.43 0.2%

250 (18h) 0.850 28.6 20.9 1.40 6.1%

600 (4h) 1.094 18.9 20.5 0.72 5.1%

600 (18h) 1.250 20.0 20.3 0.67 11.2%

Table 2. Support properties.

Tcaie '"C, Surface area Pore Pore volume Pore diameter mmolOH

OH/nm

(time) (BET)/(m²/g) surface (BJH)/(cm^J/g) (BETynm /g area

120

296 310 1.82 23.5 1.83 3 7 (3day)

250

293 300 1.71 22.9 1.43 2.9 (6h)

250

283 288 1.63 22.6 1 ,40 3.0 (18h)

600

286 298 1.63 22.4 0.72 1.5 (6h)

600

280 293 1.58 21.6 0.67 1.4 (18 )

Experiment 1

Preparation of the complex

A mixture of 8.0 g of Br₂ and 50 ml of anhydrous CH₃CN cooled at 0°C was added to a mixture of 11.03 g of PPh₂CI and 50 ml of anhydrous CH₃CN cooled at a temperature of 0 °C. The resulting mixture was stirred at 0°C for 1h. 15.18 g of triethylamine followed by 22.14 g of NH₂(CH₂)3Si(OEt)3 was subsequently added at 0°C and the resulting mixture refluxed at a temperature of 80 °C. The temperature was maintained for 5 days to obtain (EtO)₃Si(CH₂)₃ NHPBr(Ph)₂NH(CH₂)₃Si(EtO)₃ (28.8 g, 82% yield). This was mixed with 2.0 eq. of BuLi and at temperature of -80 °C, stirred while slowly heating to room temperature, whereafter 1.0 eq. of CrCI₃(THF)₃ was added to obtain complex 1 after reaction at 25 °C for 24 hours:

complex 1

Oligomerization of ethylene

A Parr reactor was dried in an oven at 115 ^eC overnight prior to the run and then placed under vacuum for 1h at 120 °C. The reactor was then cooled at 95 °C and charged with toluene (90 ml), MAO (1000 eq., 30 mmol of a 10% wt solution in toluene) and 200 psi (about 13.8 bar) of ethylene with stirring. After 15 min the pressure was momentarily released to allow injecting the complex 1 (30 pmol in 10 ml of toluene, prepared in drybox by stirring the complex 1 with toluene for 1h) into the reactor under a stream of ethylene and then the reactor was immediately repressurized with ethylene (600 psi (about 41.4 bar)). The reaction was allowed to run for 30 min while maintaining the temperature at 90 °C. The temperature was then rapidly reduced to 5°C with an ice bath; the reactor was depressurized and a mixture of MeOH/HCI cone. (45ml/5ml) was injected to quench the reaction. The resulting polymeric mass was separated from the organic and aqueous phases by press filtration and dried at 60 °C for 18 h under reduced pressure before the final mass was weighed. The organic phase was separated from the aqueous phase and analysis and yield of oligomers were obtained respectively by GC by using calibrated standard solutions and by ¹H- NMR, integrating the intensity of the olefinic resonances versus the Ph and the Me group of the toluene solvent. Precautions were taken to maintain the temperature as low as possible during the workup to minimize loss of volatiles.

As indicated in Table 1 , 44 mL of oligomers was obtained, showing the activity of the complex 1 to be 2933 mL/mmol Cr/h. 43% of the oligomers obtained were C6 and C8 oligomers. 3.0g of polymer also resulted.

Experiments 2-5

Experiment 1 was repeated except for the temperature at which ethylene was charged to the reactor, as indicated in Table 1. In experiment 5, the catalyst loading was also changed to 15 pmol. The results are indicated in Table 1.

Table 1

Experiments 6-10

Preparation of the complex 1 005650

- 10 -

Preparation of the complex 1 was performed in the same way as in experiment 1.

Preparation of the supported complex 1

0.027g of the complex 1 was isolated and dissolved in 10 mL of toluene. 0.1 g of Silica was pretreated at 250°C under vacuum for a period of 6 hours in order to obtain the so called "activated silica". The solution of the complex 1 and the pretreated silica were mixed and reacted at a temperature of 25(room temperature) °C to obtain a supported organometallic complex.

Oligomerization of ethylene

The same procedure as in experiment 1 was followed for the oligomerization of ethylene using the supported complex 1. The temperature at which ethylene was charged to the reactor and the catalyst loading were as indicated in Table 2. The results are indicated in Table 2.

Table 2

Experiments 1 1-17

Preparation of the complex 2

Complex 2 was prepared. The procedure was the same as in experiment 1, except that {EtO)₃Si(CH₂)₃ NHPBr(Ph)2NH(CH₂)₃Si(EtO)3 was mixed with 2.0 eq. of BuLi and 1.0 eq. of CrCI₂(THF)₂ to obtain complex 2:

complex 2

Oligomerization of ethylene

The same procedure as in experiment 1 was followed for the oligomerization of ethylene using the complex 2. The temperature at which ethylene was charged to the reactor and the catalyst loading were as indicated in Table 3. The results are indicated in Table 3.

Table 3

Experiments 18-24

Preparation of the complex 2

Preparation of the complex 2 was performed in the same way as experiment 11. Preparation of the supported complex 2

Complex 2 supported by Si0₂ was prepared by the same procedure as experiment 6 using complex 2 except in that the amount of silica was 0.2 g.

Oligomerization of ethylene

The same procedure as in experiment 1 was followed for the oligomerization of ethylene using the supported complex 2. The temperature at which ethylene was charged to the reactor and the catalyst loading were as indicated in Table 3. The results are indicated in Table 3. Table 4

Claims

- 13 - Cl-AIMS

1. An ethylene oligomerization catalyst system comprising an activator and an organometailic complex, wherein the complex comprises a metal chosen from the group consisting of Cr, V and Mo and a ligand defined by the formula (III):

wherein R¹ is each independently CH₃ or CH₃CH₂, R² is a straight, branched or cyclic C1-C6 alkyl group or an aryl group and n and m are each independently an integer between 1 and 5.

The catalyst system according to claim 1 , wherein the metal is Cr and R² is a phenyl group.

The catalyst system according to claim 2, wherein the metal complex is represented by formula (I) or (II)

4. The catalyst system according to claim 4, wherein R¹ is Et and n=m=3.

5. The catalyst system according to claim any one of claims 1-5, wherein the activator is MAO. - 14 -

The catalyst system according to any one of claims 1-5, wherein the complex is supported by an inorganic carrier.

The catalyst system according to claim 7, wherein the inorganic carrier comprises silica, alumina, alumina silicate or clay.

A process for preparing the catalyst system according to claim any one of claims 1-6, comprising the steps of treating PPh₂CI with Br₂ and CH₃CN at a temperature of about 0 °C, adding CI(CH₂)_nSi(R¹0)₃ at a temperature of 60- 120 ^eC, preferably 70-90 °C, more preferably around 80 °C, adding 2.0 equivalents of BuLi and subsequently adding the source of the metal to obtain the organometallic complex.

A process for preparing the catalyst system according to 7 or 8, comprising the steps of:

- isolating the organometallic complex,

- dissolving the complex in toluene and

- mixing the solution obtained and the inorganic carrier to obtain a supported organometallic complex, wherein the inorganic carrier is pretreated at a temperature of 100-900 °C, preferably 150-400 °C, more preferably 200- 300 °C, preferably around 250 °C in vacuo for a period of 1-24 hours, preferably 2-12 hours, more preferably around six hours.

A process for the oligomerization of ethylene comprising contacting the catalyst system according to any one of claims 1-6 with ethylene under oligomerization conditions.

A process for oligomerization of ethylene comprising the steps of mixing a ligand precursor which will generate the ligand according to formula (III), a source of Cr, an activator and ethylene under oligomerization conditions.