FI76357B - FOERBAETTRAT KONTINUERLIGT FOERFARANDE FOER FRAMSTAELLNING AV HOMOPOLYMERER OCH KOPOLYMERER AV ETYLEN. - Google Patents

Abstract

1. A continuous process for the manufacture of ethylene homopolymers or copolymers of ethylene with at least one alpha-olefin having from 3 to 8 carbon atoms, successively comprising : a) a first step for (co)polymerizing ethylene at a temperature between 180 and 320 degrees C, under a pressure between 300 and 2 500 bars, in the presence of a catalytic system comprising on the one hand at least one halogenated compound of a transition metal of groups IVa to VIa of the Periodic System and on the other hand at least one activator selected from hydrides and organo-metallic compounds of metals of groups I to III of the Periodic System, the molar ratio of the activator to the transition metal compound being between 1 and 10, b) a second-step for separating the (co)polymer formed from the unreacted monomer(s), under a pressure of between 100 and 500 bars, c) a third step for recycling the unreacted monomer(s), and d) a fourth step for recompression up to the (co)polymerisation pressure, characterized by introducing into the reaction mixture, at the end of the first step, at least one compound selected from monoketones having from 3 to 10 carbons atoms, diketones having from 4 to 11 carbon atoms, monoalcohols having from 1 to 14 carbons atoms, polyalcohols having from 2 to 10 carbon atoms, and water.

Description

1 76357

This invention relates to an improved continuous process for the preparation of homopolymers and copolymers of ethylene. This invention relates to an improved continuous process for the preparation of homopolymers and copolymers of ethylene.

It is known from French patent FR 2 202 899 to homopolymerize and copolymerize ethylene with at least one o-olefin continuously in the presence of a Ziegler-type catalyst system at high temperature and high pressure.

The equipment used comprises at least one reactor with at least one reaction zone, at least one separator, systems for recycling recycled ethylene and, if appropriate, unreacted o <-olefins (hereinafter referred to as monomers) to an auxiliary compressor, which in turn supplies fresh monomers from the main compressor and feeds the selected (mixed) polymerization pressure.

In this type of process, residues of the catalyst system components can be transported away with the gases. On the other hand, this transport may cause continued (mixed) polymerization before and during the separation of the formed (mixed) polymer with the unreacted monomers and a decrease in the average molecular weight of the formed (mixed) polymer recovered in the separator. The continuation of (mixed) polymerization in the tube and separator between the reactor and the separator is very detrimental, as it forces the adjustment of the reactor operating parameters to be changed randomly. The same applies to the separator, where (mixed) polymerization may continue, causing a thermal gradient to occur between its upper and lower parts. Under these conditions, it is, of course, very difficult to obtain a (mixed) polymer with the desired properties. On the other hand, the transport of residues of the catalyst system components 2 76357 may cause the (mixed) polymerization of the monomers recycled in the post-separator recirculation systems. In this way, (mixed) polymers are formed which have a very low molecular weight (less than 2000) and which are oily, greasy or waxy under normal conditions of temperature and pressure. Traps are usually placed in recycling systems to recover these very low molecular weight (mixed) polymers. However, these (mixed) polymers can also deposit on the inner wall of the recirculation channels and their molecular weight may increase as the recycle gases containing residues of the catalyst system components continuously flow past them. While (low) molecular weight (mixed) polymers do little harm as they are easy to eliminate, higher molecular weight (above 2000) (mixed) polymers, on the other hand, are very harmful and can cause pressure losses in equipment and even lead to clogged recirculation channels.

French patent FR 2 302 306 has already described a (mixed) polymerization process in which, at the end of the reaction, at least one substance selected from alkali metal or alkaline earth metal salts of carboxylic acids is injected, the amount injected being sufficient to cause a catalyst, preferably a catalyst metal derivative and activator). The metal salt is preferably sprayed as close as possible to the reactor outlet valve. However, this previously known method is not entirely satisfactory, since the thermal gradient in the separator, although slightly smaller, is still too high. On the other hand, the amount of 2-butene formed by isomerization of 1-butene is too large. 2-Butene is particularly harmful because when it does not copolymerize with ethylene and o <-olefins, it accumulates in recycled gases.

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French patent FR 2 075 128 also discloses a process for selectively stopping the polymerization reaction of olefins at low pressure and low temperature, in which an organic compound containing oxygen and / or active hydrogen, or a halogenated hydrogen acid or water, is added to the reactor in an amount less than the stoichiometric amount represented by the sum of the alkyl and hydride groups attached to the aluminum in the activator of the catalyst system. This method is not good when used for polymerization at high pressure and high temperature; namely, the selective destruction of the activator leaves unchanged the transition metal compound which remains active under stringent polymerization conditions.

French patent FR 2 253 764 also discloses a process in which, when polymerizing ethylene at low pressure and low temperature, an alcohol is added after the catalyst in an amount corresponding to 2 to 10 moles / 1 kg of catalyst. This method can control the molecular weight of the polyethylene obtained and does not cause inactivation of the catalyst.

It is an object of the present invention to overcome these disadvantages by proposing a method which causes the growth of the polymers formed to be stopped at the end of the reaction and in gas recirculation systems. In particular, this method makes it possible to better control a separator in which the thermal gradient is considerably smaller, even non-existent. It makes it possible to avoid the formation of high molecular weight polymers in recirculation systems and thus an increase in pressure drop in said systems. It can significantly reduce the isomerization of 1-butene to 2-butene.

The features of the invention appear from the appended claims, wherein the invention relates to a continuous process for the preparation of homopolymers of ethylene or copolymers of ethylene and at least one α-olefin having 3 to 8 carbon atoms, which process comprises in succession: 4 76357 a) a first step , in which ethylene (mixed) is polymerized at a temperature of 180 to 320 ° C, a pressure of 300 to 2500 bar, in the presence of a catalyst system containing at least one transition metal halide compound of groups 4A to 6A of the Periodic Table and at least one activator selected from hydrides and organometallic compounds of metals of groups 1 to 3 of the Periodic Table, the molar ratio of activator to transition metal compound being 1 to 10, b) a second step in which the (mixed) polymer formed is separated from the unreacted monomer or monomers At a pressure of 100 ... 500 bar, c) a third stage with unreacted monomer or the unreacted monomers are recycled and d) a fourth step of re-increasing the pressure to the (mixed) polymerization pressure, the process being characterized by adding to the reaction medium at the end of the first step at least one compound selected from monoketones having 3 to 10 carbon atoms , diketones having 4 to 11 carbon atoms, monoalcohols having 1 to 14 carbon atoms, polyalcohols having 2 to 10 carbon atoms and water.

The α-olefin containing 3 to 8 carbon atoms is selected from propylene, 1-butene, 1-pentene, 1-hexene, methyl-1-pentenes, 1-heptene, 1-octene and mixtures thereof.

Preferably propylene, 1-butene, 1-hexene, mixtures of propylene and 1-butene or 1-butene and 1-hexene are used.

The first, i.e. ethylene (mixed) polymerization step is carried out in at least one reactor with at least one reaction zone. An autoclave reactor or reactors or a tubular reactor or reactors may be used. In order to accurately control the flow rate of the (mixed) polymer formed, it may be advantageous to carry out the (mixed) polymerization in the presence of up to 2 mol% of a chain transfer agent, such as hydrogen.

The catalyst system used contains, on the one hand, at least one halogen compound of a transition metal of side groups 4A to 6A of the Periodic Table, which may be: violet titanium chloride and TiCl3, 1/3 AlCl3 - something of the formula (TiCl3) (MgCl2) y (AlCl3) z ( RMgCl) b, wherein in the formula 2 <a <3, y> 2, 0 £ z £ 1/3 and 0 <b <1, alone or in a mixture of a compound of the formula TiCl3 (AlCl3) w (E, TiCl4) x wherein CKw <1/3 0 <x <0.03 and E is a diisoamyl or di-n-butyl ether ether obtained by reacting a magnesium complex containing at least one compound , selected from magnesium monohalides and magnesium halide hydrides, for contact with a titanium or vanadium halide in which the valence of the metal does not exceed 3 a compound of formula (MXa) (MgX2) b (RMgX) c (HMgX) ^, wherein M is a metal of group 4A or 5A of the Periodic Table, X is a halogen, R is a in a hydrocarbon radical and 2 <a <3.5, l <b_ <30, 1 <c £ 8 and 0 <d_ <10 a compound of formula (TiCl 2, 1/3 AlCl 3) (MCl 3) x (MgX 2) y, wherein in formula M is a transition metal of groups 5A and 6A of the Periodic Table, X is halogen, 0.3 <x <3 and 0 <y <20 a mixed crystalline compound containing TiCl3 (or TiCl2), AlCl3 and other metal chlorides such as PeCl2 * NiCl2 , MOCl 3, MgCl 2 is a compound of formula (MX 3) (SiL 4 -n) b, wherein M is a transition metal of groups 4a to 6A of the Periodic Table, 0 is an optionally substituted aromatic or polyaromatic ring of formula 6. ..15 carbon atoms, L is either a hydrogen atom or a hydroxyl group and l £ n <3, 0.2 <b £ 2, said compound being optionally attached to AlCl 3, MgCl 2 and / or a Group 8 metal halide 6 76357 a compound of formula Xm_n M (OR) n, wherein M is one or more metals of groups IA, 2A, 2B, 3B, and 7A of the Periodic Table, X is a y a divalent inorganic radical, R is a monovalent hydrocarbon radical, m is a valence of M and lj = n <m obtained in the presence of a halogen derivative of a transition metal of groups 4A to 6A.

The catalyst system, on the other hand, comprises at least one Aktator selected from hydrides and organometallic compounds of metals of groups 1 to 3 of the Periodic Table, which may be: an alkylaluminum such as triethylaluminum, tributylaluminum, triisobutylaluminum, trioctylaluminum a chloroalkylaluminum chlorodiethylaluminum is a dichloroalkylaluminum such as dichloroethylaluminum - one of the RR

^ / 4

R, - Si - 0 - AI

Alkylsiloxalane according to the formula wherein R 1, R 2, R 3, R 4 are hydrocarbon radicals having 1, 10 carbon atoms, and R 5 is either a hydrocarbon radical having 1 to 10 carbon atoms or a type

existing radical, J

an alkylaluminum fluoride-based compound of the formula (AIR2F) (AlR2X) a or (A1R2F) (AlR2H) b (AlR3) c, wherein R is an alkyl group having 1 to 12 carbon atoms, X is a halogen other than fluorine, and 0.1 l <a <0.4, 01, <b <0.4 and 0.05 <c <0.2.

The catalyst system can be precipitated on an inert support comprising, for example, one or more of the following compounds: MgCl 2 »Al 2 O 3, MOO 3, MnCl 2, SiO 2 or MgO.

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For the end of the first stage, the moment when the (mixed) polymerization is completely or almost complete must be considered. Thus, the selected compound may be added to one or more of the last reaction zones (preferably the last) of the reactors, or between the outlet of said last reaction zone and the discharge valve, or between the inlet of said valve and separator.

The addition can optionally be performed at several of these points and can be done by any suitable means, such as with a high pressure pump, and the selected compound is injected neat or dissolved or emulsified in an inert solvent such as a saturated hydrocarbon.

The molecular flux of the added compound is preferably 0.5 to 6 times and more preferably 1 to 4 times the molecular flux of the transition metal or metals of the catalyst system.

The monoketone is selected from the compounds of general formula I2 I4 R1-C-CO-C-R, 1 II 6 hh, the radicals R1, R2, R3, R4 »R5 and R6 being hydrogen or alkyl groups having 1 to 7 carbon atoms , the radicals and Rg can form a single alkylene radical, and the sum of the carbon atoms contained in the monoketone is 3 to 10. For example, methyl ethyl ketone, methyl n-propyl ketone, diethyl ketone, methyl iso-butyl ketone, diisobutyl ketone, cyclohexanone and preferably acetone can be used.

R, ra

The diketone is selected from the general formula jL

R 1 - C - 00 - (O 2) n --CO - C - \

R 1 of R 5 β 76357 ¢ -, j9 - j ay ketones, n being 0, 1 or 2, the radicals R 1, R 2, R 3, R 4, R 5 and R 8 being hydrogen or alkyl groups having 1. ..7 carbon atoms, the radicals R1 and R8 being able to form a single alkylene radical, and the total number of carbon atoms in the dicton being 4 to 11, For example, 2,3-butanedione, acetylacetone, acetonylacetone, 2,3-hexanedione can be used , 3,4-hexanedione, 1,3-cyclohexanedione. The monoalcohol is selected from saturated primary, secondary or tertiary alcohols having 1 to 4 carbon atoms, such as methanol, ethanol or isopropanol. A polyalcohol is a diol or triol having 2 to 10 carbon atoms, such as ethylene glycol. The organic compounds used do not need to be dehydrated.

A major advantage of adding at least one compound as defined above to the reaction medium is that the (mixed) polymerization reaction is rapidly stopped and that a reduction in the average molecular weight of the (mixed) polymers formed is avoided. In particular, the absence of a thermal gradient or its very strong shrinkage in the separator is noted.

In order to further improve the result obtained and in particular to completely prevent the formation of polymers in the recycle tubes after the separator, the process according to the invention is characterized in that at least one compound is added to the stream of recycled monomer or recycled monomers and, if necessary, is selected from: amides of saturated or unsaturated organic acids having 12 to 22 carbon atoms, polyalkylene polyols having 4 to 500 carbon atoms - compounds having at least 2 reactive epoxy groups.

When the addition is carried out during the second step, care must be taken to add the selected compound either just before or during the separation step, and in any case to the reaction medium at which the separation pressure prevails.

9 76357

When the addition is carried out during the third step, it is clear that the selected compound is added after the separation step and before the repressurization of the gases, preferably before the gases enter the cold traps.

Examples of amides of saturated organic acids which can be used according to the invention are lauramide, myristamide, palmitamide, stearamide, arachidamide. Examples of amides of unsaturated organic acids which can be used according to the invention are oleamide, elaidamide, erucamide, brassidamide. Examples of polyalkylene polyols to be used according to the invention are polyethylene glycols having a molecular weight of 200 to 10,000, polypropylene glycols having a molecular weight of 250 to 4000, encapsulated poly (ethylene propylene) glycols and mixtures thereof. The compounds used according to the invention having at least two reactive epoxy groups are, in particular, epoxidized soybean oil, epoxy derivatives of polyunsaturated organic acid esters, epoxy derivatives of compounds containing several aromatic cores, such as bis-phenol> -Ai's diglycidyl ether.

The amount of compound added during the second or third step is preferably 0.001 to 0.1 mol / ton of recycled monomer or recycled monomers.

The (mixed) polymerization apparatus for carrying out the process according to the invention will now be described in detail, which is shown schematically in the sole attached figure. It shows a polymerization reactor (1), a reactor discharge valve (2), a medium pressure separator (3), a separating funnel (11) with a low pressure, a standard cyclone (4) mounted on the settler (5), a condenser (6), a second settler (7), an auxiliary compressor (8), a main compressor (9) and an inlet line (10) for fresh monomer or monomers.

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Injection sites of compounds added or added to the reaction medium at the end of the first step are indicated by reference numerals (C), (D) and (E).

Optionally, the injection site of the compound or compounds added during step 2 is indicated by the reference mark (E).

The injection sites of the compound or compounds optionally added during step 3 are indicated by reference numerals (A) and (B).

The following non-limiting examples are intended to illustrate the invention.

Example 1 (Comparative Example) The apparatus used is shown schematically in the attached figure (described above). It comprises an autoclave reactor (1) with 3 zones with operating temperatures of 210, 260 and 280 ° C, respectively. In this reactor, a mixture of 60% by weight of ethylene and 40% by weight of 1-butene is copolymerized at a pressure of 800 bar in the presence of a catalyst system (TiCl3, 1/3 AlCl3, VCl3) / 3 (C2H5) 3AI added to the first two reaction zones and 0.1 mol% in the presence of hydrogen to give a copolymer having a flow rate (measured according to ASTM D 1238-7 3) of 1 to 1.5 dg / min. The average residence time of the catalyst system in the reactor is 40 seconds. The separator normally operates at a pressure of 250 bar.

The results obtained are summarized in the attached Table I: is the thermal gradient between the top and the bottom of the separator (3) in ° C.

TB2 is the amount of 2-butene in the recycle gases in% by weight, the gas sampling being carried out at the outlet of the settler (7).

n 76357

It is found that the settler (7) is difficult to empty and that the pressure drop increases very rapidly between the outlet of the separator (3) and the suction of the auxiliary compressor (8).

Examples 2 to 6 The (mixed) polymer intila plant and conditions are the same as in Example 1.

To the injection point mentioned in Table I, the compound mentioned in the table is likewise added in said amount, expressed in moles / gram atom, of titanium + vanadium contained in the catalyst system used. In the case where the selected compound is added in (C), it is found that the temperature of the 3rd reaction zone decreases by 10 to 15 ° C as compared with Example 1.

The settler (7) is easier to empty than in Example 1, and no significant increase in pressure drop is observed even after 200 hours of continuous use.

Example 7 (Comparative Example) The (Mixed) polymerization apparatus and conditions are the same as in Example 1.

According to French patent FR 2 302 305, calcium stearate is added in (C) in Table I, which also contains the results obtained, the amount of moles / gram atom of titanium + vanadium. The temperature of reaction zone 3 is observed to decrease by 10 ° C compared to Example 1.

Examples 8 to 15 (Mixed) polymerization equipment and conditions are the same as in Example 1.

12 7635 7

To the injection point (D) is added 1 mole of acetone / gram atom of titanium + vanadium contained in the catalyst system. The amounts of compound added in step 2 (injection point E) and step 3 are expressed in moles / tonne of recycled monomers.

In the third step, said compound is injected according to the amount mentioned in both (A) and (B). The total amount added in (A) and (B) is thus equal to twice the amount mentioned in Table II.

In addition to the above information, Table II also mentions; TB2 (already defined), trapped IF (measured according to ASTM D 1238-73 and expressed in dg / min) and pressure drop PC (expressed in bars) at the outlet of the separator (3) trapped in the cyclone (4) and settler (7), respectively and between the suction of the auxiliary compressor (8) after 0.50, 100 and 200 hours of continuous operation. The thermal gradient observed between the upper and lower part of the separator (3) is zero in all examples 8 ... 15.

For comparison, the values obtained in the comparative experiment (Example 1) are entered in Table II.

Table I

Pre- Spray mark Compound item amount ΔΤ TB2 1 2 3 4 5 6 7 - 25 6 2 acetone C 101 3 acetone D 152 4 methanol C 103 5 water C 4 0 2 6 water C 14 2 7 calcium stearate C 1 18 5 13 763 57 .1., .., -, I ". <>.> .....— x: O 1.-. ΙΛ ΙΛ CC ΙΛ cc O o ^^ r - ^ - LT, otnocc O (si

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Ο ΤΓ Κι ks ΙΛ - _C ιΛ C O in O lt. O f. Ui (O k; Ki ^ ro ^ k *, rn

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(0 I g g Ό _ g «M

^. ί aa * h ® o jj I 1 I (JU g OC «<IO U2 • (Oi a H (3 TT o L_- t £ n (0 .p jj, ¾ UO u:“ H nao tj ui vj &. a. = * * <- <n-- *

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Claims (8)

14 76357 A continuous process for the preparation of homopolymers of ethylene or copolymers of ethylene and at least one ol-olefin having 3 to 8 carbon atoms, which process comprises successively: a) a first step in which ethylene (mixed) is polymerized at 180 to 320 ° C at a temperature of 300 to 2500 bar, in the presence of a catalyst system containing at least one transition metal halide compound of groups 4A to 6A of the Periodic Table and at least one activator selected from hydrides of the metals of groups 1 to 3 of the Periodic Table. and organometallic compounds, the molar ratio of activator to transition metal compound being 1 to 10, b) a second step of separating the (mixed) polymer formed from the unreacted monomer or monomers at a pressure of 100 to 500 bar, c) a third step in which the unreacted monomer or unreacted monomers are recycled, and (d) a fourth step in which the pressure is increased up to the (mixed) polymerization pressure, characterized in that at the end of the first step at least one compound selected from ketones, such as acetone, alcohols, such as methanol, and water is added to the reaction medium. Process according to Claim 1, characterized in that the molecular flux of said compound is 0.5 to 6 times the molecular flux of the transition metal or metals of the catalyst system. Process according to Claim 1 or 2, characterized in that the molecular flux of said compound is 1 to 4 times the molecular flux of the transition metal or metals of the catalyst system. 15 76357 Process according to one of Claims 1 to 3, characterized in that at least one further compound selected from the following is added to the stream of recycled monomer or recycled monomers and, if appropriate, the (mixed) polymers formed: - amides of saturated or unsaturated organic acids having from 12 to 22 carbon atoms from polyalkylene polyols having from 4 to 500 carbon atoms - from compounds having at least 2 reactive epoxy groups. Process according to Claim 4, characterized in that the amount of said compound is 0.001 to 0.1 mol / ton of recycled monomer or recycled monomers. Process according to Claim 4, characterized in that the amide is chosen from erucamide, oleamide and stearamide. Process according to Claim 4, characterized in that the polyalkylene polyol is a polyethylene glycol having a molecular weight of 200 to 10,000. Process according to Claim 4, characterized in that the compound containing at least 2 reactive epoxy groups is epoxidized soybean oil. ie 763 5 7