NO131616B - - Google Patents

Description

Catalyst mixture for the polymerization of ethylene.

This invention relates to halogen-free catalyst for use in the polymerization of ethylene, especially catalysts containing organic vanadyl salts and organo-aluminum compounds.

Polymerization of olefins, esp

ethylene, is well known. Numerous agents and substances have been proposed to cause such polymerization to take place or be directed so that one or other desired product is obtained. Many metals, their salts and oxides, peroxy-type compounds which produce free radicals, acids, Friedel-Craft catalysts, ultraviolet light and cathode rays have been proposed with varying degrees of success. The so-called Ziegler catalyst compositions are perhaps the best known, especially a combination of a trialkyl aluminum compound and titanium halide such as, for example titanium tetrachloride.

Although combinations of these compounds cause ethylene polymerization

with very advantageous speed disadvantages arise which cause problems. The most important of these problems is that there are residual chlorine in the polymerized product, which often causes significant corrosion of molds and other devices used in processing the polymer. Various washing methods have been proposed to remove the chlorine from the resin, but these have not proven to be fully satisfactory. It seems that some chlorine may be chemically bound in the polymer molecules and released by heating, and that the washing operations therefore do not give completely good results.

Halogen-free catalysts have been proposed with varying degrees of success to overcome the corrosion problem. It has been proposed to use compounds of metals which in Deming's periodic table are listed in group IV-B to and including VI-B, especially zirconium and thorium compounds and including especially acetyl-acetonates of these two metals. Attempts have also been made to use V+<3->acetylacetonates and hydrated oxides of titanium and zirconium. But all these catalysts give a low polymerization rate and low polymer yield compared to the use of titanium tetrachloride at low pressures. If a working pressure of 50-150 atmospheres is used, the polymerization rate of ethylene is somewhat increased, but is still relatively small, and polymer yields of no more than 5 g per g catalyst, even under these severe conditions.

It has also been shown that vanadium esters of the type (RO),VO, where R is an organic alkyl group, deviate significantly, as far as catalytic activity is concerned, from titanium esters of a similar type, i.e. Ti(OR)-t, or from titanium trialkoxides. Titanium esters such as tetrabutyl titanate in combination with an aluminum alkyl gives a rapid polymerization of ethylene, but the main product is the dimer. If vanadium esters are used, such as triethyl vanadate or tri-n-butyl vanadate, the polymerization is much slower, but the polymer formed has a much higher molecular weight. Significant amounts of low molecular weight wax are also formed, which makes the resin brittle. It is also known to use a catalyst mixture consisting of a trialkyl aluminum compound in combination with vanadium acetylacetonate or vanadium.

However, it has now been found that a very good polymerization catalyst is obtained when a mixture of a halogen-free organoaluminum compound and a vanadyl salt is used, since ethylene polymers are obtained without contamination from halogen, and which are practically free of waxes which are soluble in boiling cyclohexane.

The organo-aluminum compounds, which represent one part of the catalyst composition, can be represented by the general formula AIRs, in which R is a monovalent alkyl or aryl hydrocarbon radical. These compounds are well known when it comes to olefin polymerization, and they are used as one component in the usual Ziegler catalyst. Tri-isobutyl aluminum has proven to be very advantageous for the purposes of the present invention, but also tripropyl, triethyl or any trialkyl or triaryl aluminum can be used with advantage, without the results changing to a significant extent.

The polymerization of ethylene in the presence of an organo-aluminum compound and a metal salt is generally considered to be a two-step reaction, where the first step consists in the addition of ethylene to the organo-aluminum compound so that higher organo-aluminum compounds are formed according to the following equation:

where R,, R, and R,j are the same or different alkyl or aryl groups in the first case and then ethyl groups, and where x, y and z denote whole numbers, the sum of which is equal to n. The second step consists in a cleavage, where the higher organic groups formed according to equation (1) and which are bound to aluminium, are split off and replaced with ethyl groups according to the following equation:

Reactions (1) and (2). represents in combination a true catalytic reaction, the resulting product of which is determined by the relative rate of the addition reaction (1) in relation to the cleavage reaction (2). The addition reaction with A1R;! takes place slowly at low temperatures, but still faster than the cleavage reaction. But. as the temperature rises, the rate of the cleavage reaction becomes greater than the rate of the addition reaction. By raising the temperature to a point where the addition of ethylene to AIR., has a rate that is technically usable, the cleavage reaction has therefore become the predominant factor, and a polymer of low molecular weight is obtained.

For the polymerization reaction to take place quickly, and also a polymer of high

molecular weight is to be formed, an activator or co-catalyst in the form of a metal or metal salt is used in connection with the organo-aluminum catalyst. These activators, depending on their nature and amount, have a strong directing and accelerating effect on the polymerization, and largely determine the effectiveness of the process.

Many metals and metal-containing inorganic compounds, including titanium, zirconium, have been proposed as activators. thorium and vanadium and generally metals in group IV-B to VI-B in Deming's periodic table. Furthermore, many organic compounds of certain metals, especially of vanadium, have been proposed which have different effects on ethylene polymerization. These variations in activity are related to the chemical nature of the organic radicals which are linked to the metal atom, but the exact mechanism by which the activity of the metal atom is affected is not yet fully understood. However, significantly improved polymerization of ethylene can now be achieved by including the vanadyl salts specified in the claim.

The vanadyl compounds are characterized by at least one oxygen atom having a double bond to the vanadium atom and not to any other atom. The expression vanadyl salts, as used in the present claim, denotes organovanadium compounds of the general formula (O = V)RS, where the valence of the (O = V) radical is +2 and R is the residue of a carboxylic acid with one or two carboxyl groups and x is equal to 1 if both carboxyl groups of a dibasic acid are connected to the (O = V)++ group, and is equal to 2 if only one carboxyl group of any R group is connected to (0-V)++ -the radical.

As will be understood, it is only necessary that two carboxyl groups are connected to the (O = V)++ radical. It is not necessary that both carboxyl groups of a dibasic acid are bound to the (O = V)++ group, but instead two different, or identical, dibasic acid groups can be so connected that only one carboxyl group from each enters the bond.

Similarly, where monobasic carboxylic acid ions are concerned, it is not necessary that both ions are identical. A dibasic and a monobasic oxygen ion are attached to the (O = V)++ radical at the same time.

However, this should not be understood to mean that all vanadyl salts which cause polymerization of ethylene in the presence of an aluminum alkyl have the same effect on the polymerization. A particular vanadyl salt can be far more effective as far as the rate of polymerization is concerned, but at the same time give a relatively larger amount of low molecular weight wax than another vanadyl compound gives.

For these reasons, the preferred vanadyl salts are those having the general formula (O = VRX, where R represents an alkyl or alkenyl carboxylic acid ion containing at least two carbon atoms, an alkylenedicarboxylic acid ion having at least one carbon atom separating the carboxyl groups, a phenyl carboxylic acid ion or a phenylenedicarboxylic acid ion, and where x has the value 1 if both carboxyl groups participate in the bond in the (O = V)++ radical and the value 2 if only one carboxyl group in any of the R groups is bound to (O = V )++ radical.

The most preferred vanadyl salts are the vanadyl salts of acetic acid, propionic acid, 2-ethylhexanoic acid, 2-ethylbutyric acid, adipic acid, benzoic acid and maleic acid.

In the chemical literature, many methods for the production of vanadyl salts have been described. However, the salts used in the present invention can generally be prepared by reacting vanadium acetate with the acids described above. Vanadyl acetate can be prepared by reacting V 2 O 5 with acetic acid or with acetic anhydride. Specific reaction conditions for the production of representative vanadyl salts are indicated in the examples below.

The new catalyst compositions are prepared by mixing the selected trialkylaluminium compounds with the selected vanadyl salt compound in an inert organic solvent, e.g. toluene. Preferred molar ratios between aluminum and vanadium are in the range of approx. 1:10 to 10:1, preferably approx. 3 moles of aluminum per 1 mole of vanadium. In polymerizations carried out under pressure, it has proven advantageous to use an excess of trialkylaluminium, in order to counteract contamination in the ethylene monomer. In general, approx. 1 millimol of trialkyl aluminum per liter of solvent, which contains the ethylene monomer, if there are no contaminants in the system.

These contaminants, which consist of water vapour, oxygen and carbon dioxide, react irreversibly with the trialkylaluminium and reduce its effectiveness to a high degree.

The following examples set forth the preparation of typical vanadyl salt activators, complete trialkylaluminum vanadyl salt catalyst compositions, and specific experiments demonstrating the utility of these compositions.

Example 1.

A sample of a vanadyl acetate, which according to analysis contained 27.0 per cent vanadium, for comparison with the calculated 27.54 per cent for

O

II

0 = V(OCCH:1)2 was produced by taking 1 approx. 6 hours, using reflux, heated a mixture of 182 g of V 2 O 5 , 408 g of acetic anhydride and 120 g of acetic acid. Unreacted acetic acid and acetic

acid anhydride was removed by vacuum distillation (0.5 mm Hg) at 100° C. 372 g of a solid vanadyl acetate product was obtained which had a greenish gray color.

Example II.

A vanadyl adipate was prepared by reaction between adipic acid and vanadyl acetate which had been prepared according to Example I. 37 g (0.2 mol) vanadyl acetate was mixed with 29.2 g (0.2 mol) adipic acid in a suitable container which was equipped with a distillation outlet and with such arrangements that a vacuum distillation could be carried out. The mixture of the two components was allowed to react at a temperature of 150-250° C for several hours at atmospheric pressure, until approx. 85 per cent of the calculated acetic acid had distilled off. Vacuum distillation conditions were then established and the remainder of the acetic acid, together with a small amount of adipic acid, was removed. 42.4 g of vanadyl adipate (calculated 42.2 g) was obtained, which according to analysis contained 24.0 percent, which is calculated for

This vanadyl adipate was practically insoluble in a solution of triisobutyl or trimethylaluminum.

Example III.

A vanadyl benzoate was prepared by mixing 18.5 g of dry vanadyl acetate with 50 g of benzoic acid and placing the mixture in a container fitted with a distillation outlet, after which the container containing the contents was heated slowly in an oil bath to 250° C. During the heating, approx. 10.5 g of acetic acid removed. By vacuum distillation, most of the excess benzoic acid was removed. The remaining benzoic acid was removed from the vanadyl benzoate by extraction with boiling ether. 30.5 g of a solid was obtained, which according to analysis contained 16.5 percent vanadium, for comparison with 16.5 percent calculated for

A catalyst composition was prepared from vanadyl acetate and triisobutyl aluminum by the following method: A vanadyl acetate, which had been prepared according to Example I, was ground to a fine suspension in toluene in a vibrating steel ball mill. The suspension was diluted to 0.075 g of vanadyl acetate per ml toluene. Of this suspension, 7.6 ml (0.57 g of vanadyl acetate) was added to a small, dry, argon filled flask containing 7.8 g of triisobutyl aluminum toluene solution. The vanadyl acetate dissolved while developing some heat, and a brown-black solution was obtained. The composition proved to be an effective catalyst for the polymerization of ethylene.

Example V.

A polymerization of ethylene under atmospheric pressure and under isothermal conditions was carried out as follows: In a 1-liter Morton flask, which was equipped with a stirrer, and which contained 500 ml of dry toluene, was added 1.46 g vanadyl acetate and 4.75 g of triisobutylaluminum (in the form of a 20% by volume solution in toluene). The ethylene was bubbled through the toluene for 3 hours at atmospheric pressure, constant stirring and a constant reaction temperature of 35-40° C. During this period approx. 24 g polyethylene, as string-like particles. The polymerization product was separated from the catalyst residues by washing with alcoholic sulfuric acid solution. The product purified in this way had a melt index of zero. When extracted with boiling cyclohexane for 16 hours, the weight loss due to dissolved low molecular weight wax was only 2.2 percent, in contrast to polyethylenes produced using TiCU catalysts

(activators) which showed a content of 7.5-14 wt. wax.

Example VI.

Polymerization of ethylene under pressure was carried out as follows: In a 2 liter autoclave of stainless steel, which contained 1 liter of toluene, 0.73 g of vanadyl acetate and 2.38 g of triisobutylaluminum were added. The ethylene was driven into the autoclave until the total internal pressure was 35 kg/cm<2> at 50° C. The reaction started immediately under heat development, which during approx. 45 minutes raised the temperature to approx. 125° C. When the catalyzed polymerization gave way, the temperature dropped to 115° C, and from now on heat was added from the outside, to keep the temperature between 115° and 145° C. The ram-led reaction time was 3 hours. The polymeric material formed was washed, first with ethanol containing a little sulfuric acid, and then with aqueous ethanol and finally with anhydrous ethanol. 103 g of polyethylene was obtained, which had a melt index of zero and a sp.v. of 0.949 at 25° C. An infrared analysis showed that the product contained no side chains, i.e., that the polymer was practically linear. Extraction with boiling cyclohexane shows that the product contains only 2.0 percent low molecular weight wax.

Example VII.

In a 2 liter autoclave, which contained 1 liter of dry toluene, a suspension of 0.53 g of finely ground vanadyl adipate and 2.85 g of triethylaluminum in 20 ml of toluene was added. Ethylene was then pressed into the autoclave until an internal pressure of 14-21 kg/cm<2> at 40° C was achieved. The ethylene content, measured at this internal pressure in the autoclave, was maintained for approx. 6 hours. In the earliest stages of the reaction, the generation of heat caused a temperature rise to approx. 75 per cent, after which the temperature slowly dropped to approx. 55° C. The yield of 173 g of polyethylene was in the form of almost dry grains, which could easily be washed with alcohol. Extraction with boiling cyclohexane showed a wax content of only 0.8 percent.

Example VIII.

In a 2-litre autoclave, which contains 1 liter of dry toluene, a suspension of 0.53 g of finely ground vanadyl adipate and 2.85 g of triethylaluminum in 20 ml of toluene is added. Ethylene was then added to the autoclave, until an internal pressure of 14-21 kg/cm- at 40° C had been achieved. The ethylene content, measured at this internal pressure in the autoclave, was maintained for approx. 6 hours. In the first stages of the reaction, the generation of heat caused a temperature rise to approx. 75°, after which the temperature slowly dropped to approx. 55° C. The yield of 173 g of polyethylene was obtained in the form of almost dry grains, which could easily be washed with alcohol. Extraction with boiling cyclohexane showed a wax content of only 0.8 percent.

Example IX.

Into a 2-liter autoclave, which contained 1 liter of dry toluene, is added 33 ml of a catalyst composition which has been prepared by dissolving 0.85 g of vanadyl benzoate in 45 ml of a 20% by volume solution of triisobutylaluminum in toluene. Ethylene was then added to the autoclave until an internal pressure of 35 kg/cm - at 35° was achieved. The reaction started immediately and the development of heat raised the temperature to 120-125° C during approx. 1 hour. As the reaction slowed down, the system's temperature dropped to approx. 100—125° C.

The maximum pressure achieved in the autoclave was 44.8 kg/cm-. After the end of 4 hours the pressure had dropped to 21.7 kg/cm-. After the end of 4 hours the pressure had dropped to 21.7 kg/cm- and the reaction was finished. The yield of polyethylene after washing to remove catalyst residues and other impurities was 150 g. Extraction with boiling cyclohexane suggests a wax content of 2.6 percent. A similar experiment was carried out using the same catalyst composition and conditions except that the reaction time was approx. . 20 hours. The dividend was increased by approx.

25 percent

Six further tests were carried out with ethylene under similar conditions and in similar devices as in ex. V, if the reaction takes place at atmospheric pressure, or as in e.g. VI, whose polymerization takes place under pressure. The results are set out in the following Table I.

Polyethylenes, which are produced by ordinary polymerization processes, under atmospheric pressure and using trialkyl aluminum and a vanadyl salt, are completely linear

and has a low wax content, but especially

good properties are found in polyethylenes

which are obtained at relatively high pressures, when they

the same catalyst compositions are used.

For example, gave polyethylene, which has become

produced at 50-145° C at a pressure of approx.

35 kg/cm<2>, and with triisobutyl aluminium

and vanadyl acetate as catalyst material,

no methyl branch chains whatsoever, definitely

by infrared analysis. This suggests a

very strong linearity, actually somewhat better

than in a typical sample of a polymethylene

of high molecular weight. The sp.v. at 25°C

was found to be 0.949 and the melt index

had the value zero.

The given examples are, of course, only

to consider as pure description examples, which

does not limit the invention. The news at

the invention principally lies in the use of

certain vanadyl salts as activators or

co-catalysts along with common ones

organo-aluminium catalysts, where the polymerization conditions can be varied in high

gard, but still within the framework of invention. In particular, the temperature can

is varied from 25 to 145° C and the pressure from 1

to 50 atmospheres, if desired.

In general, the catalyst composition is used dispersed or dissolved in an inert

coal hydrogen liquid. By inert is meant that

this liquid does not contain reactive

groups such as hydroxyl, halogen, amine and

nitro nor such contaminants

such as oxygen and water. Among suitable inerts

coal hydrocarbons are purified heptane, octane,

benzene and toluene.

Claims (6)

1. Catalyst mixture for the polymerization of ethylene consisting of a compound of vanadium and an organo-aluminum compound having the general formula AIR.,, where R is an organic hydro- carbon radical, characterized in that the vanadium compound is a vanadyl salt of a carbonic acid and has the formula where R' is an alkyl, alkenyl or aryl hydrocarbon radical, or that the vanadium compound has the formula: in which n has a value of 1 or greater. 2. Catalyst according to claim 1, characterized in that the molar ratio between aluminum and vanadium is from 1:1 to 10:1. 3. Catalyst according to claim 2, characterized in that the molar ratio between aluminum and vanadium is from 3:1. 4. Catalyst according to claim 1, characterized in that the alkyl hydrocarbon radical R' is a methyl, propyl-2-ethyl-pentyl, 2-ethylbutyl or 2-ethylpropyl radical. 5. Catalyst according to claim 1, characterized in that the vanadyl salt is vanadyl benzoate. 6. Catalyst according to claim 1, characterized in that the vanadyl salt is vanadyl maleate or vanadyl adipate.