DD300295A7 - METHOD FOR CONTINUOUS PRODUCTION OF ETHYLENEHOMO AND ETHYLENE COPOLYMERS WITH IMPROVED HOMOGENITATION - Google Patents

Abstract

The invention relates to a process for the continuous production of ethylene homo- and ethylene copolymers with improved homogeneity. The goal is to improve the homogeneity of the distribution of comonomers. The dosage of one or more comonomers with significantly higher reactivity than ethylene, especially alkyl esters of alkene monocarboxylic acids, is carried out together with 5 to 100 * based on the alkyl ester, an isolated by molecular sieve extraction from a middle distillate paraffin mixture of the composition 2.5 to 10 * n-paraffins of C number range 11 to 12, 80 to 90 * n paraffins of the C number range 13 to 17 and 0.5 to 10 * n paraffins of the C number range 18 to 20. Preferably comonomers are acrylic acid n-butyl ester or acrylic acid tert-butyl ester used. As a further comonomer vinyl acetate can be used. When organic peroxides are used as polymerization initiators, they can also be dissolved in the mixture of n-paraffins and alkyl esters {ethylene homopolymers; ethylene copolymers; Improve homogeneity; Distribute comonomers; Dosage; alkyl esters; Alkenmonocarbonsaeure; Paraffin mixture; n-paraffin; C number range}

Description

Field of application of the invention

The present invention is applicable to all high-pressure polymerization plants for the production of ethylene copolymers and to the realization of metering devices in plants for the production of polyethylene. Both stirred and tubular reactors are suitable, regardless of the number of reaction zones.

Characteristic of the known state of the art

The preparation of ethylene homo- and ethylene copolymers by the high pressure mass-polymerization process is known, e.g. Ullmann's Encyklopadie der techn. Chemistry, 4th Edition, Vol. 19 (1980), pp. 169-178.

Both stirred reactors, as well as tubular reactors, as well as modifications or combinations are used. The properties of the polymers can be varied within wide limits by the variation of the conditions of synthesis and the type and amount of the comonomers used. Suitable comonomers are compounds which are copolymerizable with ethylene under free-radical conditions, individually or as a mixture, but preferably vinyl esters, ζ. Β.

Vinyl acetate, vinyl propionate, etc., or alkyl esters of alkene monocarboxylic acids, e.g. For example, alkyl acrylates, alkyl methacrylates, etc. To achieve high utility values, a high homogeneity of the distribution of comonomers is required. This is possible only partially or imperfectly for comonomers with much greater reactivity than the other monomers. Thus, the alkyl esters of alkene monocarboxylic acids have significantly higher r values than ethylene. On the notion and meaning of r-values s. e.g. P.Ehrlich and G.A. Mortimer, Adv. Polymer Sci., Vol. 7, (1970), p.432ff.

The copolymerization of ethylene with such comonomers has long been known, for. B. from DE-OS 290116, DE-OS 1520493 or DE-OS 2119047.

However, the products produced by the above processes are not satisfactory in terms of their homogeneity.

This phenomenon is particularly disturbing if the polymers are to meet the highest standards. So you need for the production of hot melt adhesive films very thin films. Irregularities of the hot melt adhesive films (holes, specks, bats) are of considerable disadvantage because they lowered the bond strength at the interface between the material to be bonded (eg polyethylene or metals). At higher stress on the bonding then solve the interconnected materials, for example, at the clip-containing points of the film, again from each other.

Inhomogeneous films of these polymers lead to considerable technical difficulties in the production of laminates. The same applies in general for all other uses.

To solve these problems, various methods have been proposed.

Thus, in a number of patents (DE-OS 2524274,2617411,2617413,2722034) proposed various measures for the treatment of the polymer in the Abscheidezonert, by which one can influence the molecular weight of the copolymer, but not the distribution of the comonomers. Egg has also been tried to improve the distribution by a more favorable dosage of the comonomer.

It is known from US Pat. No. 4,076,919, for the preparation of ethylene polymers or ethylene copolymers, a mixture of ethylene, initiator, regulator and optionally comonomer, which can be an acrylic acid ester, a tubular polymerization system, at its inlet point and at the same time at a second position behind the Intake point where the reaction temperature has reached or exceeded a maximum supply.

According to EP-PS 0096221 a process is claimed in which 0.1 to 2.0 parts by weight of acrylic acid ester are metered in exclusively at the second feed point.

According to EP-PS 99488, an improvement in the distribution of 0.1 to 1.5 parts by weight of acrylic acid ester is achieved if at the inlet point 55 to 75% and at a second Zuführstolle 25 to 45% of the amount of acrylic acid ester are added. The maximum temperature behind the second feed parts is 30 to 40 ° C lower than before the first feed.

According to EP-PS 157108, the amount of comonomer, based on 100 moles of ethylene, ma-. At the inlet point of the polymerization system. 0.3 moles and the remainder are metered in at the two feed point.

According to EP-PS 0175316 it is proposed to meter the comonomer / O separated from the ethylene mixture directly to the polymerization system, or according to EP-PS 101875 and EP-PS 101876 with high-pressure high-speed piston pumps.

It is also known that by the specific choice and the location of the dosage of peroxides (EP-PS 121755, EP-PS101875) or acrylic esters (DE-PS 2657475), the yield or the distribution should be improved.

The distribution of comonomers with respect to ethylene significantly higher reactivity can not be improved by the known methods or only conditionally or with great effort. By varying the deposition conditions, one can not influence the distribution of the comonomers in the molecule. Due to the different dosage of the comonomer or the initiator the ancestor is unfloxible, the number of metering is severely limited or leads to high Aufv / and the effects in terms of homogeneity are limited.

Object of the invention

The object of the invention is the continuous production of ethylene homo- and ethylene copolymers with improved homogeneity, without great technical effort.

Explanation of the essence of the invention

The object of the invention was to develop such measures in the production of ethylene homo- and ethylene copolymers with comonomers with greatly different reactivity ratios, which increase the flexibility of the Hochdruckprozessisationsverfahrons and the homogeneity of the distribution of the comonomers is improved while maintaining the good general polymer properties.

According to a standard international approach are considered ethylene homopolymers in the context of this invention, polyethylenes with comonomer held up to 5Ma understood%.

The object of the invention is achieved by a process for the continuous preparation of ethylene homo- and ethylene copolymers having improved homogeneity and comonomer contents between 1 and 50% by mass in tubular or stirred reactor plants at pressures of 120 to 270 MPa and at temperatures of 443 to 603 K in the presence free radical-forming compounds, optionally molecular weight regulators and other modifiers, and using alkyl esters ν η d alkene monocarboxylic acids, preferably n-butyl acrylate and tert-butyl acrylate, as a comonomer, optionally vinyl acetate as a further comonomer, woboi the dosage of or Comonomers in the intermediate pressure part or directly into the reactor is carried out by the present invention, the dosage of the alkyl ester of Alkenmonocarbonsäure odor dos alkyl esters of Alkonmonocarbonsäure and dos vinylacetate together with 5 to 100 Ma .-%, based on the alkoxy of Alkenmonocarbonsäure, one by molecular sieve extraction from a petroleum middle distillate isolated n-Paraffingemisches the C-number range 11 to 20, wherein the majority of the mixture has a C-number range of 13 to 17 occurs.

Preference is given to using an n-paraffin mixture (also referred to below as parex) which comprises from 2.5 to 10% by mass of n-paraffins of the C-number range 11 to 12.80 to 90% by mass of η-paraffins of the C number range 13 to 17 and 0.5 to 10Ma .-% η-paraffins of the C-number range 18 to 20 consists.

Furthermore, it is possible and advantageous that when using organic peroxides as free radical-forming compounds, these are dissolved in the mixture of η-paraffins and comonomer and dosed together in the Reaktpr. Free-radical-forming compounds can be used in addition to oxygen peroxides and mixtures thereof. Examples of peroxides are: 2-EthylhexylperoxidicarDonat, 3,5,5-Trimothylhexanoylperoxid, tert-Butylpebenzoate, tort-Butylperoxipivalat u.a.

It is also possible to work to adjust the desired molecular weights of the polymers produced in the presence of polymerization regulators. Suitable regulators are, for example, hydrogen, ketones or aldehydes, preferably propionaldehyde, methyl ethyl ketone, or else hydrocarbons, such as propane or propene. Following polymerization, the polymer-monomer mixture is passed to a high pressure product separator where, at a pressure of 20 to 40 MPj, most of the monomers are separated, purified via cooling and separation equipment, and returned to the process under intermediate pressure conditions. The polymer is freed from residual monomers in a second stage, a low-pressure product separation device, at 0.1 to 1 MPa and granulated by a suitable discharge and transferred into the packaging. The monomer or monomer mixture separated off in the low-pressure product separation device is likewise purified by means of cooling and separating devices and returned to the process under low-pressure conditions.

In the polymers produced according to the invention, the comonomers are homogeneously distributed. The products with comonomer contents below 5% by mass are preferably used for the film insert. The products with the higher comonomer contents are suitable for hot-melt adhesive use, for coatings as well as for coextrusion (multilayer composites).

embodiments Verglelchsbelsplol 1

In a 250-liter continuous two-zone autoclave reactor, ethylene was radically polymerized at a pressure of 140 MPa. The mixture of the reactants was carried out by means of a stirrer at a rotational speed of 1000min ~ The temperature of the Reaktornußenwand was maintained by air circulation to 445 K.

The reaction space is divided by a baffle plate, which is arranged on the reactor shaft, into two successive reaction spaces, in which different reaction bath conditions are set. The upper reaction space comprises 56% and the lower 44% of the total reaction space, Each reaction space is equipped with two Temperaturmeßstellen, each one serves to control their associated initiator pump.

The reactor was fed hourly with 9940kg of ethylene and 60kg of n-butyl acrylate dosed directly into the intermediate pressure reflux gas at a temperature of 308K.

A partial flow of 5000 kg / h went via the above the reaction chamber arranged motor housing to the upper reaction chamber. The second substream was fed together with the initiator for the upper zone.

The initiator in the upper zone was a 20% solution consisting of tert-butyl peroxypivalate and paraffin perliquidum. The amount of initiator for the upper zone is controlled by the thermocouple 1.

The amount of initiator is such that a temperature of 447 Kam thermocouple is kept constant. At the following thermocouple 2 inevitably sets a temperature of 467 K to 47C K a. The mixture of ethylene and polymers of the upper zone passes into the lower reaction zone, with respect to the Temperaturmeßstelle 3 a 1.2% solution of di-tert-butyl peroxide in Paraffinum perliquidum is added as an initiator for further polymerization. The amount of initiator is controlled by means of the thermocouple 4 se, that a temperature of 544 K is kept constant.

The produced polymer is separated from unreacted monomer after pressure reduction to 25 MPa in a two-stage monomer / polymer separation in the intermediate pressure separator (p = 25 MPa, T = 539K) and the low pressure separator (ρ = 0.02 MPa, T = 517K) by means of discharge extruder discharged and granulated. The unreacted monomer is again used in the process via gas purification and cooling.

The produced polymer had a melt index of 0.4 g / 10 min at 463 K and a BelatA mg of 21.19 N and a density of O, 922 g / cni ³ (see Table 1).

example 1

The procedure was carried out according to Comparative Example 1. The difference is that the required 2 wt .-% n-butyl acrylate (36kg / h at 1800kg / h production) in 6kg of an isolated by Molsiebextraktion from a middle distillate cut paraffin mixture of the following composition: 2.5 10% by mass n paraffins of the C number range 11 to 12 80 to 90% by mass η paraffins of the C number range 13 to 17 and 0.5 to 10% by mass η paraffins of the C number range 18 to 20 (Parex) are dissolved and dosed into the intermediate pressure part (see Table 1).

Comparative Example 2

The procedure was analogous to Vergle'chsbeispiel 1 with the difference that 31% by weight of n-butyl acrylate were added in the intermediate pressure part and a lowered melt pressure a higher melt index was achieved (s.Tab. 1).

Example 2

In Example 2, the procedure was analogous to Comparative Example 2, except that the n-butyl acrylate amount of 558 kg (at 1800 kg / h output) was metered dissolved in 33 kg Parex (see Table 1).

Comparative Example 3

Process technology consists of Comparative Example 1 analogy. The differences are that 5Ma .-% n-butyl acrylate were dosed simultaneously with 5 wt .-% vinyl acetate in the intermediate printing section. In order to achieve a melt index of 2.0 g / 10 min, the reaction pressure was increased to 150 MPa and the temperature at the measuring point 4 (lower zone) was reduced by 20 K by reducing the amount of initiator (see Table 1).

Example 3

In Example 3, the procedure was analogous to Comparative Example 3. Dio required Comonomerendosierung of 80kg n-butyl acrylate and 00 kg of vinyl acetate (based on 1600 kg / h output) was carried out in solution with 80 kg Parex (see Table 1).

Verglolchsbelspiel 4

The procedure in Comparative Example 4 was analogous to Comparative Example 1 (p - 140 MPa, T _ob , _r , _Zon ,: 447 K, T _unliI , zon .: -44 K, melt index: 0.4 g / 10 min).

The difference was in the dosage of n-butyl acrylate (90kg n-butyl acrylate at 1800kg / h output) and the location of the dosage. In Comparative Example 4, n-butyl acrylate was metered directly into the reactor in relation to the temperature measuring point 1 (see FIG.

Example 4

In Example 4, the procedure was analogous to Comparative Example 4. The difference was that the required amount of n-butyl acrylate (90kg) was dissolved in 18kg parex dissolved (see Table 1).

Comparative Example 5

The polymerization was carried out in a high-pressure tube reactor which is subdivided into two reaction zones, through the tempering jacket of which hot water was pumped. The diameter-length ratio of the tubular reactor used is

The reactor was fed 21,900 kg of ethylene per hour. As a chain regulator, 3.2% by volume of propane was added to this feed gas. In addition, 82.0 kg of n-butyl acrylate was fed to the intermediate pressure gas every hour.

For the initiation, the addition of 10.66 kg of 3.5.5.-trimethylhexanoyl peroxide dissolved in paraffin oil (this amount corresponds to a concentration of 2.6 kg of peroxide per tonne of polymerization product) per hour and the addition of 0.234 kg of oxygen per hour were carried out. This set a peak temperature of 588 K in reaction zone 1 and a peak temperature of 585 K in zone 2. The reaction pressure was 226 MPa.

The polymer-monomer mixture was depressurized to 26 MPa via the reactor pressure control valve in the intermediate pressure product separator and separated there. Via a product valve, the deposited polymer melt was decompressed to a pressure of 0.21 MPa in the NiederdruckproduV.tabscheider and discharged from there through an extruder, granulated and the Konfo supplied ¹ x tioning.

The ti. Intermediate pressure and low pressure product separated, unreacted monomers was purified by cooling and separating devices and fed back to the process.

The made-up polymer had a melt index (determined at 463 K) of 2.1 g / 10 min. At a n-butyl acrylate content of 2.0% by mass, a gel content of 2.0% by mass was determined on the polymer (see Table 2).

Belspiel5

The polymerization was carried out analogously to Comparative Example 5, with the difference that the n-butyl acrylate used (82.0 kg / h), based on an output of 4.1 t / h, was metered into 82 kg of Parex dissolved in the intermediate printing part. The gel content in the product could be reduced to 0.27% by weight (see Table 2).

Comparative Example 6

The polymerization is carried out as in Comparative Example 5, but at low reaction pressure, lower peak temperatures and corresponding chain regulator content (see Table 2).

Example β

The procedure is analogous to Comparative Example 6. In contrast, the required 64 kg / h of n-butyl acrylate were dissolved in 35 kg / h of Parex dissolved. The gel content of the product was reduced to 0.22% by mass (see Table 2).

Vergle! Chsbelsplel7

The procedure was analogous to Example 5. The differences exist except in the higher n-butyl acrylate in the simultaneous use of vinyl acetate as an additional comonomer. In this process, 156 kg of vinyl acetate per hour were fed into the feed gas mixture in the intermediate pressure section of the polymerization plant (see Table 2).

Example 7

The procedure was carried out analogously to Comparative Example 7. The hourly required 760 kg of n-butyl acrylate are added but in contrast to Comparative Example 7 in 100 kg / h Parex added. The gel content could be reduced from 3.95% by weight in Comparative Example 7 to 0.29% by weight (see Table 2).

Verglelchsbelsplel 8

The polymerization was carried out in the system of Comparative Example 5. 1680 kg / h of n-butyl acrylate were added to the intermediate pressure reflux gas (see Table 2).

Examples

The procedure was carried out analogously to Comparative Example 8. The required 1680 kg / h n-butyl acrylate were dissolved in 150 kg / h Parex and added to the feed gas in the intermediate pressure section of the polymerization. The gel content of the resulting polymer can be determined co.inte with 0.38Ma .-% (see Table 2).

Comparative Example 9

The polymerization unit was used analogously to Vergleichbeispisl 5. As a K controller, 14.3% by volume of hydrogen was used. The initiation was carried out by adding 17.80 kg per hour of a Peroxidgemisches consisting of 8.93 kg 3.5.5.-Trimethylhexanoylperoxid and 8.93 kg tert-butyl perbenzoate, dissolved in paraffin oil, and by dosing of 0.627 kg per hour of oxygen. Polymerization was carried out at a reaction pressure of 160 MPa, peak temperatures of 548 K in reaction zone 1 and 550 K in reaction zone 2 were set. 950 kg / h of n-butyl acrylate were added to the intermediate pressure refluxing gas.

There were obtained 3.8 t / h of a waxy polymer having a n-butyl acrylate content of 25% by mass and a viscosity (determined at 413K) of 350 mm ² / s. This product had a gel content of 3.15 mass% (see Table 2).

example

The procedure was carried out analogously to Vergleichsbeispiet 9. The per hourly metered 950 kg of n-butyl acrylate were dissolved in 350 kg Parex eggs fed to intermediate pressure circuit.

The gel content inr. Product could thus be reduced to 0.25% by mass (see Table 2).

Verglelchsbelsplel 10

The polymerization plant according to Comparative Example 5 was used. The polymerization takes place 6 also analogous to Comparative Example 5 with propane as a chain regulator and using the initiator combination S.S.ö.-trimethylhexanoyl peroxide / Saiierstoff. However, the feed of the n-butyl acrylate was changed, the metering of the acrylate was carried out with 35% by weight of the amount of acrylate to be metered at the beginning of the reaction zone 1 and with the remaining 65% by weight of the amount of acrylate to be metered at the beginning of the reaction zone 2 505 kg of n-butyl acrylate were added every hour. With the reaction conditions listed in Table 2 for Comparative Example 10, 4.2 t / h of a polymer having a melt index of 0.3 g / 10 min (at 463K) and a n-butyl acrylate content of 12 wt% was obtained. The gel content was 4.3% by mass (see Table 2).

Example 10

The procedure was analogous to Comparative Example 10. In contrast, the hourly metered 505 kg of n-butyl acrylate were dissolved in 345kg Parex. The addition of this / / lat / Parex mixture was then again to 35 wt .-%, based on this amount of mixture, at the beginning of the reaction zone. 1

 The product obtained in the polymerization had a low gel fraction of 0.33 mass% (see Table 2).

Table 1: stirred reactor examples

n-butyl acrylate

Peak temperature [K]

upper zone

Reaction pressure IMPa]

melting

ind9x

[G / 10min]

lower

Comparative Example 1 2.1

Example 1 2.1

Comparative Example 2.2

Example 2.2

Comparative Example 3 1.6

Example 3 1.6

Comparative Example 4 2.1

Example 4 2.1

regulators content

Comparative Example 1 2 447 544 140 0.4 0 example 1 2 447 544 140 0.4 0 Comparative Example 2 31 447 544 135 1.5 0 Example 2 31 447 544 135 1.5 0 Comparative Example 3 5 and 5 Vac 449 524 150 2.0 0 Example 3 5 and 5 Vac 449 524 150 2.0 0 Comparative Example 4 5 447 544 140 0.4 0 Example 4 5 447 544 140 0.4 0 Table 1: stirred reactor Examples Specif. initiator solution dosing Gelcehalt consumption agents for location [Times n-butyl acrylate [kg peroxide / t product]

without intermediate pressure return gas 2,6

6kg Parex intermediate pressure return gas 0.2

without example 1 3.6

33 kg Parex as Example 1 0.25

without as Example 1 4.0

80 kg Parex as Example 1 0.3

without entrance upper zone 2,7

opposite Mc mstelle 1

18 kg Parex as Example 4 0.25

Table 2: tubular reactor n-butyl Sharpen- Zone 2 reaction enamel * 2.1 regulator example acrylate temporatur 585 print index 2.1 salary salary [K] 585 [MPa] [g / 10 min] 2.3 [VoI.- ⁰ / -! [Wt .-%] Zonei 541 2.3 (P = propane) 2 588 541 226 0.8 3.2 p Comparative Example 5 2 588 589 226 0.8 3.2 p Example 5 2 543 589 185 1.8 1.95 p Comparative Example 6 2 543 569 185 1.8 1.95 p Examples 18u.4Vac 592 569 230 350mm ² / s * 1.8 p Comparative Example 7 18 u. 4 Vac 592 550 230 354mmVs " 1,8P Example 7 42 573 550 210 0.3 2.2 p Comparative Example 8 42 573 574 210 0.3 2.2 p Examples 25 548 574 160 14.3H ₂ Comparative Example 9 25 548 160 14.3H ₂ Example 9 12 576 225 1.75 p Comparative Example 10 12 576 225 1,75P Example 10 * Viscosity at 413 K

Specif. initiator O ₂ solution -6 dosing - 300 295 Table 2: tubular reactor consumption [Kg / t] agents for location example peroxide 0.057 n-butyl gel content Ikg / tl 0.057 acrylate [Wt .-%] 2.6 0,125 without Intermediate pressure return gas 2.6 0,125 82 kg of Parex as example 1 Comparative Example 5 2.95 0.06 without as example 1 2.0 Example 5 2.95 0.06 35 kg of Parex as example 1 0.27 Comparative Example 6 2.75 0,051 without as example 1 2.3 Examples 2.75 0,051 100 kg of Parex as example 1 0.22 Comparative Example 7 2.55 0,165 without as example 1 3.95 Example 7 2.55 0,165 150 kg of Parex as example 1 Ο, ΓΊ Comparative example 4.7 0.059 without as example 1 4.2 Examples 4.7 350 kg of Parex as example 1 0.38 Comparative Example 9 2 / 0.059 without 35% reaction zone 1 3.15 Example 9 65% reaction zone 2 0.25 Comparative Example 10 2.4 345 kg Parex like comparison 4.3 Example 10 Example 10 0.33

Claims (3)

1. A process for the continuous production of ethylene homo- and ethylene copolymers having improved homogeneity and comonomer contents between 1 and 50% by mass in tubular or stirred reactor plants at pressures of 120 to 270 MPa and at temperatures of 443 to 603K in the presence of free-radical-forming compounds, optionally molecular weight regulators and further modifying agents, and using alkyl esters and alkene monocarboxylic acids, preferably n-butyl acrylate and tert-butyl acrylate, as comonomer, optionally vinyl acetate as further comonomerase, wherein the dosage of the comonomer or in the intermediate printing part or directly in the Reactor, characterized in that the dosage of the alkyl ester of Alkenmonocarbonsäure or the alkyl ester of Alkenmonocarbonsäure and vinyl acetate together with 5 to 100Ma .-%, based on the alkyl ester of Alkenmonocarbonsäure, one by Molsiebextraktion from a Erdölmittelde Stillatschnitt isolated n-Paraffingemisches the C-number range 11 to 20, wherein the majority of the mixture has a C-number range of 13 to 17 occurs. 2. The method according to claim 1, characterized in that the n-paraffin mixture used from 2.5 to 10Ma .-% η-paraffins of the C-number range from 11 to 12, 80 to 90 mass% η-paraffins of the C-number range 13 to 17 and 0.5 to 10Ma .-% η-paraffins of the C-number range 18 to 20 consists. 3. The method according to claim 1 and 2, characterized in that when using organic peroxides as free-radical-forming compounds, these are dissolved in the mixture of η-paraffins and comonomer and dosed together in the reactor.