CA1183647A - Polymerization process and product - Google Patents

Abstract

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ABSTRACT

Improved catalyst productivity rates are obtained in a propylene polymerization process conducted at sufficient pressures to maintain propylene in liquid phase, by carrying out the polymerization in the presence of small amounts of ethylene and or a catalyst system containing trialkylaluminum component and a magn? alide supported catalyst component.
The polymer produced by the process exhibits improved physical and mechanical properties.

Description

BACKGR UND OF THE INVENTION

The CQntinUOUS polymerization of propylene under sufficient pressure to maintain at least a ~ortion of the propylene in the liquid phase ("liquid pool") is well known in the art. In the past the conventional catalyst system used in such polymerization has been an unmodi~ied or an electron donor-modified titanium halide component, acti~ated with an organoaluminum cocatalyst. Typical examples of con-ventional propylene polymerization catalyst systems include cocrystallized titanium trichloride-aluminwm`trichloride ca~alysts of the general formula n~TiC13~AlC13 activated wikh diethyl aluminum chloride or triethylaluminum. The cocrystallized titanium trichloride-aluminum trichloride can have ~een su~jected to a modification treatment with a suitable electron donor compound to increase its activity or stereo-lS specificity. Such compounds include phosphorus compounds,e~ter~ of inorganic and organic acid ethers and numerous other compounds.
Recently new catalysts have been developed which are for more active than the aforementioned co~ventional catalysts in ~he polymerization of alpha-olefins. Briefly described, th~se catalysts are comprised of a titanium halide catalysk component supported on magnesium dihalide and an alkylaluminum compound, which can be present as a complex with an electxon donor compound. These catalyst components have been described in the patent literature, eOg. in U.S. Patents Mo. 3,830,787, No. 3,953,414, NoO 4yO51,313, No. 4,115,319 and No. ~,149,990.
In the polymerization of propylene in the presence of li~uid monomer, it is known that t~e efficiency ~productivity) 6~7 of any of the above catalyst systems is increased by an increase in temperatures up to level in the vicinity of about 155~ or slightly higher, where maximum productivities are obtained. Typically, a raise in temperature from about 125F
to a~out 155F results in almost a doubling of the catalyst efficiency, regardless of the particular selection of catalyst system. Further increases in temperature cause a rapid decline in productivity from the maximum values.
Thus for any catalyst system used in the liquid 10 propylene polymerization there is a maximum productivity level ~hat can be achieved, and this maximum productivity level is achieved at a relatively high temperature and pressure (to assure liquid phase at the temperature). These optimum operating conditions contribuke to the overall cost of the process in the form of utilities needed for increased preheat, cooling and compression requirements.
It is therefore an cbject of the present invention to pro~ide a process for the polymerization of propylene wherein the temperatures (and pressures) can be maintained at lower levels, whIle achieving significantly better catalyst productiv-ities.
~ nother object is to significantly improve catalyst producti-vities at any predeterm;nded pol~merization temperature.
A further object of the present invention is to pxo~ide a novel propylene polymer which exhibits improved processab~lity when extruded or injection molded as compared to conYentional propylene polymers.
Still another object of the present inYention is to pro~ide a novel polypropylene which can be processed at lower extrusion or molding temperatures and~or lower extrusion or molding pressures than con~entional polypropylene resins of the same meltflows~

~ -2-Further object will become apparent from a reading o~ the specification and claims.
DESCRIPTION OF l~E DR:~WING
.
The Figures show by comparison the improved results obta~ned by this in~ention. In Figure l, ~he improvement in catalyst efficiency is shown, while the improvement in polymer impact properties is illustrated in Figure 2.
THE INVENTION
In accordance with the present invention there is 10 provided in a continuous process for t~e catalytic pvlymerization of propylene at elevated temperatu.res and sufficient pressures to maintain propylene in liquid phase in the polymerization zone the improvement of increasing the productivity rate of the catalyst composition to a value higher than the optimum productivity ra~e defined hereinafter. The improvement comprises:
(i) in a pr:ior step determinin~ the optimum productivity rate of the catalyst composition defined below in the homo-poly~erization of propylene;
(ii) introducing ethylene with the propylene feed into the reaction æone in amounts from a~out 0.3 to ab~ut 2 weight percent based on the weight of the propylene feed stream;
(iii) polymer.izing ~he mixture of ethylene and propylene at a temperature in the range from about 115F to about 165F
in the presence of a ca~alys~ composition containing the ~5 components (al. an aluminum trialkyl or an aluminum trialkyl at least partially c~mplexed with an electron donor c~mpound~ and (~) titanium tri- or tetrahalide supported on magnesium dihalide, or a complex of a titanium tri- or tetrahalide with an electron donor compound supported on magnesium dihalide.

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The determination set forth in step (i~ is obtained by operating the liquid pool reactor with propylene monomer only, i.e. homopolymerization, at temperatures ~etween 115F
and 165F and measuring the resulting productivity at each S temperature. This esta~lishes the catalyst productivity ~s.
temperature performance which are needed for step (i).
~ t was unexpectedly found that the in~roduction of small amounts of ethylene with the propylene feed and using the above-described ratalyst system caused a dramatic and completely unexpected increase in the catalyst productivity.
It was further found that the increase in productivity was not dependent on the particular level of ethylene concentration in the total feed, but that any level within the range of from about 0.3 to about 2 wt ~, preferably from about 0.5 to about 1.7 wt %, would result in about the same improvement. In addition, and most significant, was the discovery that with ethylene present in the monomer fead, the effect of temperature on catalyst productivity appeared to have been eradicated, i.e., the increased catalyst productivity remained substantially constant over a broad temperature range.
These findings are in direct contradiction to what occurs in the same process, with ethylene additition to the propylene feed but with conventional unsupported titanium catalyst systems. There~ the temperature is the main actor affect~ng the productivity and although at lower than optimum temperatures the presence of ethylene sometimes appears to increase the productivity to a slight degree, e.g. up to 10%
or less r there has been no instance where the presence of ethylene in the propylene feed has resulted in better product-30- I~it~es compared to those o~tained in the absence of ethylene in fe~d and at the optimum polymerization temperature (i.e.

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155-160F) for obtaining maximum productivity. In fact, with some conventional catalysts there is commonly seen a detrimental effect of ethylene feed incorporation at temperatures above about 140F, resulting in producti~;ties that are lower than those obtained in the absence of e~hylene and at the optimum polymerization temperature.
The catalyst components used in the process of the invention can ~e any one of the recently developed, high activity magnesium halide supported catalyst components and organoaluminum cocatalyst components disclosed e.g. in U~S.
Patents No. 3,830,787, No. 3,953,414, No. 4,051,313, No. 4tll5, 319 and No~ 4,149,g90.
Typically, such a catalyst composition is a two component composition where the components are introduced separately into the polymerization reactor. Component (a) of such a composition is advantageously selected from trialkyl aluminums containing from 1 to 8 carbon atoms in the alkyl group, such as triethyl aluminum, trimethyl aluminum, tri-n-butyl aluminum, triisobutyl aluminum, triisohexyl aluminim, tri--n-octyl alum~num and triisooctyl aluminum. Most pxeferably the trialkyl aluminum is complexed with an electron donor prior to introduction into the polymerization reactor. Best results are achieved when esters o~ carboxylic acids or diamines particularly esters o~ aromatic acids are used as the electron donors.
S~me typical ex~mples of such compounds are methyl-and ethyl~enzoate, methyl- and ethyl-p methoxyben~oate, diethyl-carbonate, ethylacetate, dimethylmaleate, triethylborate, ethyl o-chlorobenzoate, ethylnaphthenate, methyl-p-toluate, ethyltoluate, ethyl-p-~utoxy benzoate, ethyl-cyclohexanote, ethylpi~alate, N,M,N',N'-tetramethylendiamine, 1,2,4,-tri-methylpiperazine, 2,5-dimethylpiperazine and the like. The molar ratio of aluminum alkyl to electron donor can range between 1 and 100, prefera~ly between 2 and 5. Solutions of the electron donor and the trialkylaluminum compound in a hydrocarbon such as hexane or heptane are preferably pre-reacted for a certain period of time generally less than 1 hourprior to feeding the mixture into the polymerization reaction zone.
The other component of the catalyst co~position is eithe~ a titanium tri- or tetrahalide supported on magnesium dihalide, or a complex of a titanium tri or tetrahalide with an electron donor compound supported on magnesium dihalide.
The halogen in the respecti~e halid~s can be chlorine, bromine or iodine, the preferred halogen being chlorine. The electron donor, if it is used in forming a complex, is suitably selected from the esters of inorganic and organic oxygenated acids and the polyamines. Examples ~f such compounds are the esters of aromatic carboxylic acids, such as benzoic acid, p-methoxy-~enzoic acid and p-toluic acids and particularly the alkyl esters of sa~d ac~ids; the alkylene diamines, e.g. N',N",N"',N""-tetramethylethylene-diamine. The magnesium to electron donor 20 molar ratio a~e equal to or higher than 1 and preferably between 2 and 10. Generally the titanium content expressed as titanium metal ranges between 0.1 and 20 wt % in the supported catalyst component and prefexably be~n 1 and 3 wt %.
The preparation of such supported catalyst components 25 ha~e been described in the prior art and are commercially availa~le.
The catalyst components (a) and (b~ are fed to the reaction zone in amounts such that the Al/Ti molar ratio is maintained in the broad range between about 1 and about 10,000 30 and prefera~ly between about 10 and 200.

It is essential t~at the polymerization process used ~n this in~ention is one ~herein t~e propylene functions as the i 4 ~

liquid diluent as well as feed to the reac~ion, except for small quantities of inert hydrocarbons, e.g. hexane, mineral oil, petrolatum, etcr, that may be used for the introduction of the catalyst components into the raction zone. The reaction conditions used in the process of this invention generally include polymerization temperatures in the range from about 115F to about 165F and preferably in the range from about 125F to about 155F. The pressure should be sufficiently elevated to maintain at least a portion of the propylene in the liqui~l phase. Suitably pressure of 200 psig and higher are used, e.g. up to about 500 psig. Total solids in the reaction zone, in accordance with this system, are ordinarily in the oxder of ~rom 15 to 50%, although obviously lower or higher, for ex~nple up to 60% polymer solids can be achieved. In order, however, to efficiently handle the slurry, it is p~eferred to keep the polymerization to the present solids above indicated. The reaction is continuous and monomer feed (i.e. propylene and ethylene) and catalyst components are continuously fed to the reactior and a slurry of polymex product and li~uid propylene is withdrawn, preferably through a cyclic discharge valve which simulates continuous operation. I~
desired, various modifiers such as hydrogen may be added to alter the properties of the polymer product. Such modifiers are well known in the art and need not be discussed in any ~5 further detail since they form no part of this invention.
The withdrawn polymer slurry is let down in pressure to, ~or example, 50 psig or less in a low pressure zone (mean~ng a zone maintained at a pressure lower than that ~n the polymer~zation reaction) where due to the drop in pressure 3~ a~d the volatile nature of the polymeriztion ingxedients, there is a flashing of these volatiles from the solid polymer. This flashing, which can be aided by heating, results in a polymer ~ 6~7 powder which is substantially dry and which by this term is to be understood to ~e a polymer containing 5% or less volatiles. The unreacted monomer stream is taken overhead from this low pressure flashing zone and at least a portion thereof is compressed and condensed and returned to the reactor. The polymer is usually passed to a final drying zone to remove residual volatiles.
Alternately the liquid polymerization medium can be filtered or centrifuged under pressure and the li~uid propylene can be returned (after suita~le purge) to the reactor, thus sa~ing energy in the form of recompression. This method has the advantage that certain soluble impurities ~the aluminum alkyls and organic esters) are removed from the polymerD This in turn leads to a polymer product with lower residual residue content~
Because of the generally hugh productivity of the supported catalyst system expressed in terms of pounds of polymer produced per po~d o~ titanium metal, which productivity has been further enhanced by the present invention, there is no 1 20 need to remove catalyst residues rom the polymer in a deashing step as is the case with conventional catalyst~
The polymer products provided in accordance with this invention have a meltflow range ~etween about 0.1 and about 10 g/lOmin., ratio of weight-average molecular weight to ~5 num~er-average molecular weight of above about 6.5, ethylene con~ent ~etween about 0.3 and about 5 wt ~, Ti content not exceeding about 3ppm, Mg content not exceeding about 40ppm, Cl content not exceeding about lOOppm and total ash content not exceeding about 400ppm.
Compared to conventional random copolymers o~ same ethylene contents, the polymers of this invention exhibit about a 20 to 30 percent improvement in impact strength.
Further advantages of the polymers of this invention compared to conventional polymers include wid~r processability range~
lower processing energy requirements, superior ability to fill thin sections and multiple ~a~ity molds, better draw-down, easier drawab~lity and higher processing speed in the continuous filament and staple fiber production.
For example, based on spiral meltflow measurements it was found that polymers of this invention having meltflows lQ (ASTM-1238) in the range of about 2-lOg/lOmin. can be processed at 50-30F lower molding temperatures, or 350-150 psi lower molding pressures than conventional polymers of same meltflows (ASTM-1238).
It is believed that the molecular weight distribution, Mw/Mn is the property that best relates to the improvements in impact strenght as well as polymer rheological properties and processability. Typically, polymerization with a con~entional catalyst system would result in a polymer product having a Mw/Mn ratio of at most 6.5 and generally below 6, while the polymers of this invention ha~e Mw/Mn ratios of at least 6.5 e.g. between about 6.5 and about lO.
Various additivies can, if desired, be incorporated into the polypropylene resin, such as fibers, fillers, anti-oxidants, metal deactivating agents, heat and light stabilizers, dyes, pigments, lubricants and the like.
The polymers can be used with advantage in the manu~acture of fibers, filaments and films by extrusion, of rigid ar~icles by injection molding; and of bottles by blow mold~ng techniques~
The following examples further illustrate the advantages obtained by the invention.

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~ ~3~47 The experiments were conducted in large scale con~
tinuous pilot plant opexations, wherein monomer and catalyst components were continuously charged to a stirred reactor, the monomer feed rate corresponding to 2 hours residence time in the reactor. The organoaluminum compound of the catalyst system was a hexane solution of triisobutyl aluminum ~TIBA) which had been treated prior to introduction into the reactor with a hexane solution of me.hyl-p-toluate (MPT), an electron donor compound. The solid supported titanium halide catalyst component was a commercially available catalystO The supported catalyst component contained about 1.5 wt % titanium, 20.3 wt ~ magnesium, 60.0 wt % chlorine and 9.6 wt % hydrocarbon volatiles. Ethylbenzoate had been used in the manufacture of the supported catalyst component. The two catalyst components were added ~t r~tes directly proportional to the polymer production rates and in amounts sufficient to maintain a polymer solids concentration in the reactor slurry at a nominal value of about 40~. The catalyst productivity (lB polymer/lb of Ti metal~ was calculated in each case from the polymer slurry withdrawal rate, solids content in the slurry and the titanium catalyst component addition rate. 'rhe pertinent operating conditions and results are shown in Table 1.
In Table 2 the same data are presented in somewhat diffe~ent form. The average productivity of the catalyst at 155F and 0% ethylene addition is ~he base value (100%
ef~iciency~ in the comparison of the data. The average catalyst efficienc;es o~ the experiments at each of the other temperatures have ~sen o~tained by expressing the observed productivities in percent o~ that of the average base p~oductivities.

The data are also depicted in Figure 1.

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Comp. 1 and 4 Cavg.) No 155100 Ex. 2~3 and 5 (avg.) Yes 155119 Comp. 6 No 130 7Q

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( )Catalys~ efficiency low due to low TIBA/MPT ratio (2.1 vs. 2.8 in all other experiments) As seen from the data plotted in Figure 1, the effect of small amounts of ethylene in the propylene feed 15 dra~atically increases the catalyst efficiency (productivity) o~er and above that o~tained at the optimum temperature when no ethylene was added. Also, the effect of temperature appears to have been eradicated, that is~ the improved productivity rate ~s substantially constant over the rather wide temperature 20 range of from 125~F to 155F.
COMPARATIVE EX~PLES 11 - 16 The polymerization procedure described before was followed except that the catalyst systems were two similar per-forming conventional non-supported electron donor promoted tatanium trichloride catalysts with diethyl aluminum chloride as cocatalysts. The pertinent data from the exper~ments are listed in Ta~le 3 and Table 4. As seen from the data, the produc~ ty rates with ethylene present were in all cases in~eriox to that o~ta~nea at about optimum temperature cond~tions U55F~ in khe a~sence of ethylene, and the poly-merizat~on temperature had an appreciable effect upon theproducti~ity r~tes.

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Cc>mp. 11 No 155 100 Comp. 12 Yes 150 97 Comp. 13 Yes 1~0 96 Comp. 14 Yes 130 81 Cornp. 15 No 150 88 Comp. 16 Yes 150 96 COMPARATIVE EXA~5PLES 17 - 19 In this set of experiments a conventional unpromoted TiC13 AlC13 catalyst (Stauffex AA) was used under the conditions . shown in Table 5. As seen from rable 6 no improvements over the optimum productivity were obtained in this set of experi-ments.

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C^mp. 17 No 155 100 Comp. 18 ~o 140 70 Comp. 19 Yes 140 80 CO~lPA~ATIVE EXA?lPLES 20 - 22 . The catalyst used in this set of experiments was a phosphorus oxytrichloride modified 3TiC13 AlC13 catalyst with diethylaluminum chloride as cocatalyst. A~ain, no improvement over the optimum productivity rates was obtained with this con.ention catalyst as shown by the data in Tables 7 and 8.

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Comp. 20 No 155 lO0 Comp. 21 and 22 (av~ 'es 130 49 EX~IPLE 23 The polymer product from a continuous polymerization run conducted essentially according to the techni~ue described in Examples l - lO was subjected to a detailed anaylsis. The results are shown in Table 9 together with pertinent operating conditions.
As indicated in Table 9, standard ASTM test methods were used to determine the majority of the properties of the polymer products.
The Mw/Mn ratio was determined by liauid chromatography using o-dichlorobenzene as solvent.
The contents of Ti, Mg and Al were determined by atomic absorption anaylsis of polymer ash dissolved in hydro-chloric acid and the chlorine content by colorimetric determination of combu ed pol~ner sample using a Parr oxygcn bomb.

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EXAMPLE NO. 23 Catalyst PT-l Trialkyl alumin~m Triethyl Trialkyl aluminum/MPT-mol ratio 3.1 Al/Ti-mol ratio 150 Reactor Temperature ~F 130 Reactor Pressure - psig 350 Residence Time - hrs. 1.7 Producti~ity K~/gTi 565 ~dditives:
BHT - ppm 1200 ~5 Irganox 1010 ppm 500 Calc;.um stearate - ppm1000 Hy~rotalcite - ppm 1000 Polymer Propert;es:
Dimer-trimer content-g/kg polymer 3 Isotactic Index - % 69.0 Melt Flow g/lOmin. (1) 2.7 Density gm/cc t2) 0.8971 Mn Mw 329,000 25 . Mw/Mn 7.0 Tensile Strength.
Yield - psi (3) 3270 @ Break - psi (3) ~ 33gO
~lon~ati`on at Break ~ C3~ ~ 577 Flex Modulus-~si x 105 (4~ 1.25 3~

TABI.E 9 (CO~TlNUED) - . _ EXA~IFLE l10 . 2 3 Tensile ~Jod~lus-psi ~ 105 (3) 1.30 HDT - at 66 psl C (5) 72.8 Hardness (Roc~;well) (6) 59.9 LTB-C (7) -9.0 Izod Impact ft lbs/in (8) 2.0 Polymer Impurities:
Ash - ppm 380 Mg - ppm 29 : Ti ~ ppm 2 Cl - ppm 84 Al - ppm 169 (1) ASTM D1238, Cond.L (2) AST~i D1505 (3) ASTM D638~4) AST~I D790 . (5) ASTM D648(6) ~Sl'~l D785 (7) AST~ D746(8) AST~i D256 3~4~

E~ MPLES 24 - 31 _ _~_ _ The follot~ing Table 10 sho~s the substantial improvement in impact strength obtained ~ith the polymers o~ this in~ellt.ion (E~amples 24 - 26) compared to conventional polymers (Comp. E~amples 27 - 31).

. ~ABLE 10 Polymerized Impact Stren~th, EX. NO C2~ t % inches(l . . _ _ --24 1.7 37 . 25 2.4 33 26 3.6 . 76 Comp. 27 2.2 15 Comp. 28 2.4 27 ; Comp. 29 4.0 62 l Comp. 30 4.0 66 I Comp. 31 4 4 77 ( ) ASTM D2463, bottle drop impact strength at 40F, F50.

The impac-t improvement is depicted graphically in ~igure 2, wh h is based on the data of Table 10.

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Claims (21)

WHAT IS CLAIMED IS:

1. A random propylene ethylene copolymer having a meltflow range between about 0.1 and 10 g/10min., ratio of weight-average molecular weight to number-average molecular weight (Mw/Mn) above about 6.5 polymerized ethylene content between about 0.3 and about 5 wt %, Ti content not exceeding about 3 ppm, Mg content not exceeding about 40ppm, Cl content not exceeding about 100ppm and total ash content not exceeding about 400ppm, said polymer being produced by a process comprising:
continuously feeding catalyst components and a mixture of propylene and ethylene to a polymerization reactor, the mixture containing from about 0.3 to about 2 weight percent ethylene based on the weight of the propylene at a temperature between about 115°F and about 165°F and at a sufficiently elevated pressure to maintain at least a portion of the propylene in liquid phase, withdrawing product in a substantially continuous fashion as a slurry in liquid propy-lene, wherein the catalyst composition is comprised of components:
(a) an aluminum trialkyl or an aluminum trialkyl at least partially complexed with an electron donor compound, and (b) titanium tri- or tetrahalide supported on magnesium dihalide, or a complex of a titanium tri- or tetrahalide with an electron donor compound supported on magnesium dihalide.

2. A polymer according to claim 1, wherein the alkyl group of the aluminum trialkyl catalyst in component (a) contains from 1 to 8 carbon atoms.

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3. A polymer according to claim 1, wherein the aluminum trialkyl catalyst in component (a) is triisobutyl aluminum.

4. A polymer according to claim 1, wherein the aluminum trialkyl catalyst in component (a) is triethyl aluminum.

5. A polymer according to claim 1, where the electron donor compound of component (a) of the catalyst composition is an ester of a carboxylic acid or a diamine.

6. A polymer according to claim 5, wherein said electron donor is an ester of an aromatic acid.

7. A polymer according to claim 6, wherein the ester is methyl-p-toluate.

8. A polymer according to claim 1, wherein the molar ratio of trialkyl aluminum to electron donor ranges between about 1 and about 100.

9. A polymer according to claim 8, wherein said molar ratio is between about 2 and about 5.

10. The polymer of claim 1, wherein component (a) is prepared by prereacting the aluminum trialkyl with the electron donor for less than one hour prior to polymerization.

11. The polymer of claim 1, wherein the titanium tri-ox tetrahalide is a titanium trichloride or titanium tetrachloride.

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12. The polymer of claim 1, wherein the magnesium dihalide is magnesium dichloride.

13. The polymer of claim 1, wherein the electron donor compound of component (b) is a polyamine or an ester of an inorganic or an organic oxygenated acid.

14. The polymer of claim 13, wherein said electron donor is an ester of an aromatic carboxylic acid.

15. The polymer of claim 14, wherein the ester is ethylbenozate.

16. The polymer of claim 1, wherein the magnesium to electron donor molar ratio of component (b) is at least about 1.

17. The polymer of claim 16, wherein said molar ratio is between about 2 and about 10.

18. The polymer of claim 1, wherein the titanium content expressed as titanium metal ranges between about 0.1 and about 20 weight percent in the suppored catalyst component (b) .

19. The polymer of claim 18, wherein the titanium content is between about 1 and about 3 weight percent.

20. The polymer of claim 1, wherein catalyst components (a) and (b) are provided to the reaction zone in a molar ratio of Al/Ti of between about 1 and about 10,000.

21. The polymer of claim 1, wherein said Al/Ti molar ratio is between about 10 and about 200.