DE1954221C3 - Supported catalyst for polymerizing ethylene - Google Patents

Description

a) by neutralizing an aqueous sodium silica solution a silica hydrogel precipitates and a slurry of the same with a SiOr concentration of 5 to 12% and a pH of 3 to 8, whereby the Temperature is kept in the range of 0 to 10 ° C during the precipitation,

b) the Produfo thus obtained at a pH value heated from 3 to 8 and a temperature of 50 to 100 ° C1 for up to 6 hours,

c) the sodium ion concentration in the product thus obtained by washing out less than 20 ppm in the filtrate and

d) the product obtained in this way reduces the size of the hydrogel particles to a diameter of less than 200 microns,

e) a solvent which is immiscible with water and forms an azeotrope with water is added and

f) by distilling off the azeotrope, the water is separated from the gel and the gel is dried.

In recent years there have been new processes and catalysts for stereospecific polymerization received considerable attention. The catalysts with stereospecific effect contain on metal-containing catalytic material deposited on a support, the catalytic system in a heterogeneous phase acts. Known catalysts of this class include, for example, chromium oxide a support made of aluminum or silicon oxide and activated by oxidation with air at 500 "C Silicon oxide.

Using supported chromium oxide catalysts of the above type, polymerizations can be carried out with monomer concentrations of about 2 to 7%. By varying the temperature and the solvent, the conditions can be chosen so that the reaction can be carried out in solution or suspension. Polymerization processes of this type allow the production of polymers with different molecular weights depending on temperature, pressure, solvent and other reaction conditions, including the method for activating the catalyst. For example, in the production of polyethylene, polymers with a high molecular weight (low melt index) can be obtained by the suspension process with a conversion rate of 5000 to 15,000 kg of polyethylene per kg of catalyst. According to the solution process, polymers with a low molecular weight (high melt index) can be obtained, but with a conversion rate of less than 1000 kg of polyethylene per kg of catalyst. To protect the color and appearance of the resin product, the chromium content in the resin must be less than 2 ppm. In solution polymerization

ίο must use the supported chromium oxide catalyst before use of the polymer can be removed.

In contrast, it offers the suspension process, in which no removal of the catalyst is required and that much higher conversion speeds

j5 delivers considerable economic benefits. Suspension process however, they were previously at high degrees of conversion of at least 5000 kg of polyethylene per kg of catalyst limited to the production of polymers with melt indices below 2 Die Use of modifiers, such as hydrogen, lowers and increases the molecular weight the melt index of the polymerization product, the advantages of such modifiers however, limited as they decrease the catalyst activity.

Low molecular weight, high melt index polyolefins have important uses for z. B. Films and Sheets, Extrusion Coating, Injection Molding and Rotary Pressing, which is why a large one There is a need for catalysts with which such polyolefins are produced at high degrees of conversion can be.

Although the variation in the chromium oxide content of the catalyst, the addition of different metal oxide promoters, the combination of different carriers, such as silica, alumina or Zirconium oxide, as well as the application of various Activation temperatures at a given catalyst activity have been widely studied have been, only minor improvements have so far been achieved. Numerous unsuccessful attempts went to the production of polymers with lower molecular weights and higher melt indices at the expense of catalyst activity.

IN-PS 86 925 (reported in Chem. Zentralblatt 1968, No. 41, Rzf. 2974) describes a catalyst for the production of polyolefins with a high melt index, which consists of a porous silica gel with a pore average of 200 to 500 Å and a

so there is a surface of 250 to 350 m ² / g, which has been impregnated with chromium oxide and activated by heating. The silica gel belongs to the class of so-called aerogels, which differ significantly from the xerogels, in particular with regard to the pore size distribution. The IN-PS only gives melt indices measured under high stress, which suggests that the melt indices could not be determined under normal stress. The melt indices achieved according to the IN-PS are therefore also unsatisfactory.

The invention relates to a supported catalyst for polymerizing ethylene from an oxide of the Chromium, cobalt, nickel, vanadium, molybdenum or tungsten deposited on a silica xerogel has been, which is characterized in that the Silica xerogel carrier has a surface area in the range from 200 to 500 mVg and the pore volume mainly through pores in the range from 300 to 600 A,

preferably 300 to 500 Å

With the aid of the catalyst according to the invention can Ethylene by the pension process at high levels Conversion degrees are polymerized without the polymer being freed from the catalyst to need. Despite the same activity of the catalyst, the polymers obtained have much lower Molecular weights and higher melt indices than those obtained with the aid of known supported chromium catalysts (including those of IN-PS 86 925) produced polymers. It can e.g. polyethylene with a Melt indexes of 2 to 20 can be obtained at low chromium concentrations (less than 2 ppm).

The silica xerogel carrier used according to the invention is ^{stable at temperatures up to 1100 °} C. when it is calcined in a fluidized bed

The metal oxide deposited on the support is preferably chromium oxide

The proportion of the deposited metal oxides is preferably up to 5% by weight (in particular 1 to 3 Gevy .-%) of the total catalyst.

A preferred method of making the silica xerogel support for the one of the present invention Catalyst (see. Claim 2) is in DE-OS 19 45 422 disclosed.

The aforesaid metal oxides can be deposited on the silica xerogel support in any suitable manner. For example, the carrier can be coated with the metal oxide by mixing the finely ground metal oxide with the carrier at room temperature with the action of shear. The metal oxide and the carrier can also be mixed in a vacuum and / or in a nitrogen atmosphere at 200 ° C. The activation of the catalyst is in air in a fluidized bed at temperatures of 815 ° C to 110o ⁰ C, preferably at 996 ° C is performed. The activation time under these temperature conditions is 2 to 10 hours, preferably 6 hours. Activation is achieved without physically changing the carrier.

The catalyst of the invention is suitable for homo- and copolymerization of ethylene, with as Comonomer at least one 1-olefin with a maximum of 8 carbon atoms in the chain and no branching closer to the double bond than in the 4-pitch

Table I.

(preferably propylene, 1-butene or 1-hexene) can serve.
The following examples illustrate the invention.

Comparative experiment A

Ethylene, isobutane as solvent and the catalyst are continuously fed into a 333 liter loop reactor in such a way that the ethylene saturation is kept at 5% + 1% and the solids content at 15 to 25%. The reactor temperature is kept at 110.4 ° C. and the reactor pressure at 45.7 kg / cm ² . The resulting suspension is circulated at a speed of 4.57 to 7.62 meters

Known catalysts are activated with optimal melt index / synthesis temperature relationships in the air stream in a fluidized bed at 871 to 982 ° C in order to determine the optimal activation temperature for a maximum melt index. The known catalysts are chromium oxide catalysts on commercially available silica gel supports. These catalysts have an average pore volume of 1.6 cmVg, an average surface area of 300 i, i ² / g and a resulting mean pore diameter of 213 Å, determined by nitrogen absorption. They are coated with 2.1% CrOi and have been found to be the optimal catalysts for maximum melt index of the polymer products.

250 g of the respective catalyst are in one

Fluidized bed at (a) 871 ^C C, (b) 926 ° C and (c) 982 ° C using an air flow of 11.3 Lu \ / min. calcined in an activator with a diameter of 10.2 cm. The maximum temperature is maintained in the reactor for 6 hours. The catalysts are then stored in a nitrogen atmosphere until use

Synthesis conditions, catalyst properties after activation and polymer properties are given in Table I below.

The maximum melt index is, as can be seen, with comparable activity values (5000 kg polyethylene /! 'G Catalyst) achieved when the catalyst is activated at 926 ° C. Occurs at higher temperatures severe shrinkage of the catalyst support and the melt index falls

Synthesis conditions catalyst
Type Catalyst-
activation
temperalur average
lich ethylene
saturation Properties of the activated kata
lysators surface middle
Forums
diameter Polymers own
flock ash synthesis
temperature (C) Pores
volume (m ² / g) (Ä) ground,
MI ₂ *) (TpM) (C) Chromium oxide 871 5.1 (cm ³ / g) not
activated not
activated 211 110.0 Chromium oxide 926 5.0 not
activated 226 225 1.3 184 110.4 Chromium oxide 982 4.9 1.44 193 259 1.8 330 110.5 1.6

*) MI ₂ = melt index according to ASTMD-1238-65T (condition E).

example 1

10,800 g of sodium silicate _{solution containing 28.7% SiO 2} and 8.9% Na ₂ O are added to 12,720 g of water with stirring and cooled to 5 ° C. 11,200 g of H ₂ SO ₄ (12.75% by weight) are then added as follows:

(a) 4480 g are added at a constant rate over the course of 1 hour and

(b) the remainder is added over 45 minutes. The final pH of the precipitate is 6.2 and the SiO ₂ content is approximately 8.5%.

The slurry is then heated to 95 ° C. and held at that temperature for 3 hours. The slurry is then washed with a solution of 1113 g of NH «NO3 in 170 liters of water and then with deionized water until the filtrate has a titer of less than 20 rpm Na ₂ SO ₁ .

The product is reslurried in acetone and washed with water until the water content of the Acetone is less than 1%.

The product is then homogenized and the acetone is distilled off in order to retain the ionic content less than 1% by weight.

The silica gel obtained is calcined in an oven at 538 ° C. for 4 hours before evaluation. the physical properties of the silica xerogel obtained in this way are a pore volume of 2.66 cmVg, a surface of 307 mVg and an average pore diameter of 347 A. You coat the Xerogel with 2.1% CrOs to achieve a chromium concentration similar to that of commercially available Chromium oxide catalysts is comparable.

The coating is then done by adding 813 g drier

Xerogel carrier and 16.45 g of dry powdered chromium oxide are placed in a ribbon blender. A vacuum of 711 mm Hg is applied to the mixer and heat is applied such that a temperature of 250 "C is achieved in 3 hours. The heat is maintained for 2 hours and the > catalyst is then brought to room temperature and in stored in airtight containers.

These catalysts are taking in a fluidized bed

ίο Use air flow rates of 5.65 LtryMinute in an activator with a diameter of 10.2 cm and at temperatures of (a) 954 ° C and (b) Calcined at 996 ° C. The maximum temperature is maintained for 6 hours. Then the Catalysts stored in a nitrogen atmosphere until use. The evaluation of these catalysts in the study is carried out on the same Conditions as in example 1. Synthesis conditions, catalyst properties

20 'after activation and polymer properties are summarized in Table II.

Comparing the results of Table I with the results of Table II, it can be seen that the Reactor conditions are the same, but very much there is a significant increase in the melt index when the, ~ inventionf; em catalysts for the same Activity level are used.

Table II catalyst
Type Catalyst-
activation
temperature average
liche ethy
oil saturation Characteristics of the
Catalyst activated Polymer properties Density,
getem
pert ash Pore upper
volume area middle
Pores
diameter ground,
WED ₂ (TpM) Synthesis conditions example 1 954 = C 5.2 (cmVg) (A) 0.9645 164 Svnthetic
temperature example 1 996 = C 4.8 2.14 252 340 3.2 0.9647 184 CQ 2.23 251 356 4.2 110.4 110.3

Example 2 and Comparative Example B

The present example explains one prepared as in Example 1 and activated at 982 ° C Catalyst. It is evaluated in the loop reactor with hydrogen as a modifier in the Reactor is added. This experiment is compared with the results obtained with an optimal

Table ΠΙ

Chromium oxide catalyst of the prior art (comparative experiment B) can be obtained.

Synthesis conditions, catalyst properties after activation and polymer properties are compared in Table III.

so With the catalyst according to the invention, a lot can be seen at the same level of activity higher melt index achieved.

Synthesis conditions Activation H ₂ conc. Properties of the activated Pol) m erisate properties σρΜ) tion tem- middle Catalyst Synthesis catalyst temperature relationship Pore upper middle MI ₂ density, ash temperature typ H ₂ / Ethya volume area Pore annealed (Q diameter CQ (cmVg) (m ² / g) (A)

111.5 Example 1 982

111.1 chromium oxide 843

(Comparative experiment B)

1X10 ~ ² 1X10 ' ²

253 234

347 260

12.2 0.9668 3.2 0.9699

305 238

Example 3 and Comparative Experiment C

The present example illustrates one (apart from the data in Table IV) according to Example 1 produced catalyst. In the loop reactor, ethylene / 1-hexene copolymers are under

Using this catalyst and the chromium oxide catalyst of the prior art.

Even at a lower synthesis temperature, there is evidently a very significant increase in the melt index when the catalyst according to the invention is used the same level of activity is used.

Tabf''e IV

Synthesis conditions Properties of the activated Mixed polymer properties

Catalyst-
Type catalyst
activation
temperature Witches Catalyst Upper
area Synthesis-
temperature (C) (Weight- · /.) Pores
volume (no / g) CO Chromium oxide 926 0.5 (cm ³ / g) 226 106 attempt C) 1.44 example 1 982 0.5 305 105.2 2.48

medium ground, density, ash

Pore MI2 tempered

diameter pert

(A) (TpM)

225

330

1.0

4.0

0.956 150

0.956 250

Example 4 and Comparative Experiment D

The present example also illustrates a catalyst prepared according to Example 1 (apart from the data in Table V). In the loop reactor ethylene are / 1-butene copolymers with ^U SE this catalyst and the chromium oxide catalyst of the prior art prepared.

30th Synthesis conditions, catalyst properties and copolymer properties are given in Table V. compared.

Again, using the catalyst of the present invention at the same level of activity (14,000 kg of polyethylene per kg of catalyst) a product with a considerably higher melt index (2.50 versus 0.14).

Table V

Synhesion conditions catalyst ! -But, Catalyst properties Upper Pores Mixed polymer properties (TpM) Synthesis catalyst activation Pores area diameter ground, density, ash temperature typ temperature volume MI2 getem (C) (Wt .-%) (m ² / g) (A) pert (C) (cnrVg)

101 Chromium oxide 843 1.7 1.60 300 213 0.14 0.9425 70 (comparative test D)

102 Example 1 982 1.6 2.12 242 335 2.50 0.9430 72

Comparative experiments E

(Comparison of the supported catalyst according to the invention with the supported catalyst
the IN-PS 86 925)

A determination of the properties of the catalyst carrier used in accordance with IN-PS 86 925 Aerogels gave the following result:

Calculated

middle

Pore diameter

55 (A)

Average Particle size

(μΐη)

surface
(mVg)

Pore volume
(cmVg)

318 - measured after the
Standard B.ET. method
(31OmVg)

1.65 - N ₂ - P / Po 0.967
1.84 - H ₂ O, method according to
Innes (l, 55)

208 to 231 (200)
3-4 (4)

Values in parentheses are from a Grace Company prospectus on aerogels »Syloid«, to which the catalyst supports according to the above IN-PS belong. Between the measured and based on the values taken from the prospectus good match.

In FIG. 1 is the distribution of pore diameter versus cumulative pore volume for one catalyst support used according to the invention

carried.

In FIG. 2 is the pore diameter distribution versus cumulative pore volume for the airgel in accordance with IN-PS above. The F i g. 3 illustrates the distribution of pore diameters for a catalyst support according to the invention in an ancier manner of application. Comparison to the aerosol according to the above IN-PS. From Fig. 3 it can be seen particularly clearly that the materials compared are very considerable Differences in the pore diameter distribution

10

The pore volume in the silica xerogel used according to the invention is mainly due to pores in the range from 300 to 600 Å is formed.

Specifically, this different pore diameter distribution is responsible for the fact that with the aid of the catalyst according to the invention polymers are obtained, their Melt indices under normal stress are higher than the melt indices measured under high stress the polymers prepared according to the above IN-PS.

For this purpose 2 sheets of drawings

Claims (2)

Patent claims: 1. Supported catalyst for polymerizing ethylene from an oxide of chromium, cobalt, nickel, vanadium, molybdenum or tungsten, which has been deposited on a silica xerogel, characterized in that the support made from silica xerogel has a surface area in the range from 200 to 500m ² / g has "and the pore volume is mainly formed by pores in the range from 300 to 600 Å. 2. Supported catalyst according to claim 1, characterized in that the silica xerogel is prepared has become through the fact that one