CA1116159A - Reduction of ticl.sub.4 with reducing agents modified with lewis bases - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Novel TiCl3 catalytic complexes for the stereospecific polymeriza-tion of alpha-olefins and a process for preparation of these catalytic com-plexes which are obtained by reduction of TiCl4 in the presence of a Lewis base which has preferably been complexed with the reducing agent. Further-more, the present invention relates to a process for improved polymerization of alpha-olefins to crystalline polyolefins in high yields and high stereo-specificity using these catalytic complexes.

Description

1 It is kno~n in the ~rt that alpha-olefins can be

2 polymeriz~d in the presence of cataly~ic systems containing

3 solid TiC13 or solid TiC13 m~xed with o~her solid metallic

4 halides7 usually as cocrystalLine eutectics activated by an organic compound of aluminum.
6 These solid compositions containing titanium trl-7 chloride can be prepared by a number of different processes.
8 One of these processes is the reduction of TiG14 by hydrogenO
9 Another process consists of reducing TiC14 with a metal such as aluminum where the cocrystalline material would be alum-11 inum chloride. Another process preferred for several reasons 12 is reduction of TiC14 with alkyl aluminum (halides)0 The 13 TiC13 product which then is normally in ~he brown be~ form 14 contains either aluminum chloride or alkyl aluminum chloride by-products, or both~ associa~ed with the TiC130 For op-16 timum catalytic effects, it is preferred that this brown 17 material be converted to the purple form by either heating 18 or using excess titanium tetrachloride.
19 When alpha-olefins, for example propylene, are polymerized with these ca~alysts, commercially undesirable 21 amounts of amorphous polypropylene are formed along with the 22 desirable isotactic crystalline pol~propylene. It is well 23 known in the ar~ that third components can be added as com-24 plexing agents to titanium trichloride catalysts to improve the isotacticity of the added crystalline polyolefins, al 26 though usually at the eost of reduced efficiency of the 27 polymerization reaction.
28 Thus, Boor & Jordan have descr~bed how titanium 29 trichloride can be imprvved by -the addition of Lewis bases (J.Boor, Jr., "Active Site in Ziegler Catalysts", page 115 31 in "Macromolecular Reviews, Vol. 2"; see also D 0. Jordan, 32 "Ziegler Natta Polymerization" in "The Stereochemistry oE

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1 Macromolecules, Vol. l", edited by A~ Do Ketleyg 1967, 2 Marcel Decker, Inc.).
3 Grignard reagents comprising magnesium compounds 4 complexed with ethers have been used to reduce TiCl4 to TiCl3 for ethylene polymerizations~ See UOS~ 3~801~558O
6 But the ethers are only used to solubili2e the Grignard 7 reagent which is otherwise hydrocarbon-insoluble.
8 That TiCl3 catalysts can be improved by the addi-9 tion of Lewis bases, for example ethers, and/or TiC14 treat ments has been disclosed in German patent DT-2213086~
11 It is demonstrated in that patent how TiCl4 can be reduced 12 with diethyl aluminum chloride to yield a brown reduction 3 product containing titanium trichloride. This brown reduc 4 tion product separated from the reaction medium was subse-quently treated with a special ether, and subsequent to 16 the ether treatment the reaction product was separated and 17 then treated with excess titanium tetrachloride to form a 18 purple catalyst, which when separated from the resction medi-19 um could be activated with diethyl aluminum chloride to yield a catalyst active for the stereospecific polymerization 21 of propylene.
22 Thus, while it is well known that Lewis bases, and 23 specifically ethers, can be used to treat preformed catalysts 24 to improve the stereospecificity and the actîvity of said catalysts, actually carrying out the reduction step for re-26 ducing TiC14 to TiCl3 in the presence of a Lewis base has 27 not been reported nor is it obviousO
28 A highly efficient process to make a catalyst of 29 outstanding quality results from the reduction of TiC14 to TiCl3 in the presence of Lewis bases which complex with 31 the reducing agents.
32 It has been found~ according to ~his inven~ion, ~3.~ 6 ~ ~ ~

1 that titanium tetrachloride can be reduced with alkyl alum-2 inum (halides) in the presence of Lewis bases to produce 3 highly stereospecific active catalysts.
4 The advantages of the process of the invention are~ (1) the activity of the reducing agent is tempered, 6 thereby allowing greater control of the reduction s~ep 1, 7 (2) the entire process sequence is simplified since the 8 entire reduction and catalyst preparation is performed in 9 only one reactor by simple sequential addition of reagents;
o and (3) by this process highly stereospecific highly acti~e 11 catalysts having properties far superior to those of commer-12 cially available catalysts are formed~
13 The catalysts are preferably fo~med in a novel 14 two-step process, whereby in the first step TiC14 is added to an ether/aluminum alkyl (halide) complex or vice ~ersa 16 at a temperature low enough to control the reduction step, 17 and after the reagents have been mixed the temperature is 18 increased to effect complete reduction maintaining a speci-19 fied stirring speed so as to obtain the catalyst particles in a controlled form. Subsequent to the completed reduction 21 the second phase of the catalyst preparation is enacted by 22 adding TiC14 to the reaction mixture~ and then heating the 23 catalyst and TiC14 at a specified temperature for a time 24 long enough to conver~ the catalyst to the purple form.
Thus, catalysts are prepared by complexing alum-26 inum alkyl halides with the general formula AlRnX3_n where 27 R is a hydrocarbon radical containing from 1 to 8 carbon 28 atoms, preferably 1 to 4 carbon atoms (where the best re-29 sults are obtained when R is selected from ~he group of al-kyl, aryl radicals) and X is a halogen selected from chlor-31 ine, fluorine, bromine, and iodine where the best results 32 are obtained when X is chlorine and n is any number between 0 and 3. Preferably, n is 1.5 to 2.5, with the best results obtained when n is equal to about 1.7. It i5 also understood that the reducing agent can be of the class of aluminum alkyl alkoxides, where in the above general formula X would be OR
instead of halogen; or that the reducing agent is of the class of the organo aluminum polymer compounds whereby two or more of the above-described aluminum alkyl reducing agents are joined by oxygen, nitrogen, sulfur, or methylene bridges.
The Lewis base complexing agent that is complexed to the aluminum alkyl reducing agent can be any compound known in the art which complexes with Lewis acids. Thus those compounds containing one or more atoms or groups having one or more pairs of free electrons capable of effecting coordina-tion with titanium and aluminum alkyl (halides) are generally usable. Specifically among the atoms capable of donating one or more pairs of electrons are those atoms of Groups V and VI
of the Periodic Table for example oxygen, sulfur, nitrogen, phosphorous. As representative examples of compounds contain-ing groups capable of furnishing one or more pairs of electrons, mention rnay be made of ethers, thioethers, phosphines and amines.
It is preferred to use as complexing ayents those compounds having the general formula ROR', RSR', R(R')~R"
where R, R' and R" are hydrocarbon radicals containing from 1 to 15 carbon atoms. The best results are obtained when R, R' and R" are branched hydrocarbon radicals containing from 2 to 8, preferably from 4 to 6, carbon atoms.
The complexing agent is mixed with the reducing agent in the ratio of a molar excess up to 5 to 1 preferably in the ratio of an excess up to 2 to l. And it can be premixed or can be mixed in the reactor and generated ln situ.

It is well k~own that such a complexed reagent has different reducing powers and behaves differently from the pure reducing agent by itself. The TiC14 may be added to the complexing agent or vice versa the TiC14 can be added to the complexed aluminum alkyl reducing agent. The several reagents are used in the following ratios expressed by the general formula:
complexing agent(X): aluminum alkyl reducing agent(y):
TiC14(z) where x, y and z can have values from 71 to 5, 1-5, 1-20, respectively, or preferably ~1 to 2, 1, 1-2, as long as x:y is in molar excess and X:y+z is less than 1, or most preferably 1.5, 1, 1, respectively.
While the reduction can be effected at temperatures from -80 to +50C., it is preferred to reduce TiC14 at tempera-ture from -30 to ~15C., or most preferably from -10 to ~5C.
While many solvents can be used for the reduction, it is most preferred that the solvent is a nonreactive solvent such as the paraffinic or alkyl aromatic solvents. Thus, the type of inert solvents that are preferred are those selected ~ from the paraffinic hydrocarbons containing from 5 to 12 carbon atoms. Most preferred solvents are taken from the group of pentane, hexane, heptane or isooctane.
The concentration of reagents and the inert diluent can vary from 0.5 to 4 molar but best results are obtained when the concentration is between 2 and 3 molar.
A wide variety of stirring techniques can be effected during reduction leading in all cases to good catalysts. For better control of the final catalyst product, it is preferred to stir the reaction mixture in a smooth manner during the reduction and warm-up at a rate sufficient to yield catalyst particles having all approximately the same size. Pre~erred stirring rates are from 50 to 600 rpm;

l best results are obtained when the stirring rates are be-2 tween 150 and 400 rpm.
3 The final reaction mixture is warmed up from the 4 reducing temperature to an aging temperature which can be varied from 25 to 90C., with best results obtained when 6 the aging temperature is from 50 to 65Co The rate of warm-7 up can vary from Ool to 3Co per minu~e where the preferred 8 results are obtained when the warm-up rate i5 from 0~5 to 9 1C. per minuteO
The catalyst is held at the aging temperature from ll 1/2 to 6 hours preferably from 105 to 205 hours~
12 Subsequent to the aging, TiC14 is added to the re-13 action mixture in an amount where the TiC14 to TiC13 mole 14 ratio can vary from 005 to 20 or preferably from 1 to 10 or most preferably from 1 to 3-5 The TiC14 can be added in an 16 undiluted form which simplifies the process and the concen-17 trations of reactants and presence of diluent can be varied 18 so as to vary the concentration of the TiC14 in the reaction 19 mixture from 5 to 75 vol. %, preferably from 25 to 50 v310%.
The catalyst after such treatment with TiC14 is 21 heat soak treated from 1/2 to 10 hours, preferably from 1 22 to 2 hours at temperatures which range from ~25 to 90C0, 23 preferably from 50 to 65Co 24 The thus prepared catalyst is separated from the reaction mixture and washed by decantation or filtration 26 with the diluent used in the preparation or with other un-27 reactive hydrocarbonsO
28 It is understood that for simplification also ex-29 cess TiC14 can be trea~ed with the aluminum alkyl ether com-plex so that the subsequent TiC14 treatment described above 3l does not need to be effected 32 It is also understood that the titanium tetra-~ 7.~

chloride can be premixed with othex transition metal ha]ides of Groups IIIB~ IVB, VB before reduction and separation to thereby generate a solid reduction product containing mixtures of transition ~etal halides, where these mi~tures will generate polyolefins having different properties. Finally, it is also understood that the TiC14 reduced as described above can be reduced with and by metal alkyl (halides) other than aluminum alkyl halides. Thus metal alkyl halides of metals of Groups IA, IIA, IIB, IIIA and IVA can be used.
It is known that both ether and TiCl4 must be present in the catalyst to effect activation, and since enough ether must be present to complex at least all of the aluminum compound in the catalyst, it would be preferable to have a slight excess of ether in the reduction mixture; however, the ether should not exceed the molar quantities of aluminum alkyl compound and TiCl4, for then significant reduction would not be expected.
Accordingly, within critical narrow ranges of ether: aluminum alkyl compound TiCl4 mole ratios, highly active, stereo-specific catalysts were obtained.
If in the reduction step, using Et2AlCl, the ratio of ether:AlEt2Cl did not exceed l or if the ether:LTiCl4 -~ AlEt2Cl~
equals l or more, conversion of the brown TiCI3 to the purple form by excess TiCl4 is not possible. See the table following for a summary of the results using different ether ratios during reduction.
Catalyst Color Reducing Agent Ticl4:AlEt2cl:r)IpE After TiCl~Treatment ., . . . .. . __ __ .
AlEt2Cl.2.0 DIPE l:0.5 :l Purple AlEt2Cl.l.3 DIPE l:0.75 :l Purple AlEt2Cl.2.0 DIPE l:l :2 Brown 30 AlEt2Cl.l.0 DIPE l:0.5 : 0.5 Brown AlEt2Cl.l.0 DIPE l:l :l Brown ~.

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l Since the first step in the reduction yields 2 AlEtC12, and since an AlEtcl2~Base complex might be con 3 sidered too weak to reduce TiC14, one might expect the 4 yield of TiC13 to be limited to 50% of theoretical. See the following equations. TiC14+005 AlEt2Cl R2Q - O.S
6 TiC13~OD5 AlEtC12-R20 + 005 TiC14 0~5 TiC14+0 5 AlEtC12~R20 -7 005 TiC13+0-5 AlC13 R200 8 This concern is reasonable, for while AlEtC12 9 reduces TiC14, the AlEtC12R20 complex with TiC14 yields only a clear green solutionO However, the yield of solid ll catalyst actually obtained indicates that both ethyl groups 12 in AlEt2CloR20 function to reduce TiC13c Possibly TiC13 catalyzes the reduction of the AlEtC12oR~O~TiC14 complex in the same way that TiC13 catalyzes the reduction of TiC13R.
Another possibility is that TiC140R20 complex reduces faster 16 than TiC14, and that therefore in cases where the former 17 can be formed, reduction proceedsO
18 It has been observed that the ethero AlEt2Cl ratio 19 must exceed 1 for beta ~o delta TiC13 co~version to occur, but the reason for this critical ratio is not understoodO
21 At ratios below 1, free aluminum alkyl would be present, 22 but why that should deposit TiC13 in a form less susceptible 23 to rearrangement is difficult to explain, especially since 24 TiC13 catalysts prepared without ether can be converted to the purple delta form by excess TiC140 See the following 26 equations:
1) Heat Brown beta 27 TiC14 + 0.75 AlEt2CloO~5 R20 2~ XS TiC14 TiC13 28 TiC14 ~ 0075 AlEt2cl 2~ XS TiC14 T~C~2 B 29 One reaction that occurs at low R200AlEt2Cl ratios is the disassociation of the AlEtC12 by-productl yielding 31 the AlC13R2o complex.
32 Triethyl aluminum can also in a similar manner be _ g _ l~ S9 complexed with a Lewis base thereby decreasing the reducing 2 power of the more active reducing agentO This lower activ-3 ity is only observed when excess ether is present complexing 4 all the triethyl aluminum.
The lower reduction rate observed with complexed 6 Et2AlCl suggests a process advantage one might expect using 7 AlEt2Cl-R20 rather-than- AlEt2Clo In large scale catalyst 8 preparation, temperature control becomes difficulto The g reduction of TiC14 with complexed aluminum alkyl should be lo gentler and therefore easier to controlO
11 Dimethyl aluminum chloride and trimethyl alumin-12 um reduce TiC14 at a lower rate than the ethyl analogs;
3 however, complexed with ether, days are required for re-14 duction to be effectedO
Lewis bases have been described in many patents 16 and publications, such as U.S0 3,116,274, UOS0 3~825,524 17 and on page 31 of a book entitled SEMIMICRO QUALITATIVE
18 ANALYSIS, by William CO Oelke, publi4hed in 1950 by D.C.
19 Heath & Co.
In addition to the reduction step, the complexes 21 of the invention can also be used as a cocatalyst for either 22 the TiC13 catalysts made by the process of the invention 23 or for TiC13 and other Ziegler transition metal catalysts.
24 The invention is further illustrated by the follow-ing examples:
26 EXA~LE 1 27 To a 250 ml flask is added 24~5 cc (54.6 mm) of 28 a 2.23 molar diethyl aluminum chloride solution in iso 29 octanec Then, 17.8 cc (27.3 mm) of a 1053 molar solution of ethyl aluminum dichloride in hexane is added. The reducing 31 agent mixture is cooled to 0 and 22~4 cc (10902 mm) of di-32 isopentyl ether is added dropwise. 6 cc (5406 mm) of 100%

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l TiC14 is added at a rate of 0O15 cc per minuteO At the 2 end of the titanium tetrachloride addition, the reaction 3 mixture is held for 60 minutes and then warmed to 65C. at 4 a rate of 1 per minute~
The reaction mixture is held for 1 hour at 65Co, 6 cooled to 35C., and 60 cc (546 mm) of 100% TiC14 is added 7 at a rate of 2 cc per minuteO The stirring rate is cut 8 back from the 300 rpm used during the reduction to 100 rpm 9 and the solution is warmed to 65C., held there for 2 hoursO
The catalyst examined on the microscope has turned purple ll and has a narrow particle size distribution where the aver 12 age particle diameter is 12 micronsO The catalyst is sepa-3 rated from the reaction medium by filtration and washed 4 three times with 100% heptaneO
To a 1,000 cc flask containing 500 cc of normal 16 heptane at 65Co is added 4~37 cc of a 1~6 molar solution 17 of diethyl aluminum chloride in normal heptaneO Then 0070 18 grams of the catalyst as prepared above is added to the re-19 action mixture which has been saturated with propyleneO
For 2 hours propylene is passed through the 21 stirred solution and polypropylene is generated by the cata-22 lystO At the end of 2 hours addition of propylene is re-23 placed by addition of nitrogen and the polymer slurry is 24 stirred for 12 hours with 1000 cc of isopropyl alcohol and then filteredO The polymer cake is washed with 100 cc of 26 alcohol and the washings added to the filtrateO The fil 27 trate is evaporated to yield 5 o 94 grams of waxy polymer and 28 catalyst residueO
29 The polymer is dried at 65~Co and weighed to yield 87.36 grams of polymer of which 98099% is insoluble 31 in boiling heptaneO After correction for the catalyst 32 residue in the filtrate, the catalyst efficiency is calcu-~ 5 ~

1 lated to be 125.4 grams of polymer per gram of catalyst for 2 a 2 hour polymerization, 0.49% of the polymer is called 3 waxy polymer, that is, polymer soluble in the heptane-iso-4 propyl alcohol slurry and 98.5% of the polymer is insoluble in boiling heptaneO
6 The polymer particles have a narrow particle size 7 distribution, flow well and have an average diameter of 75 8 micronso 9 By comparison, commercial TiC13 M obtained from Stauffer Chemical would have a catalyst efficiency of 42 11 of which 92~5% of the polymer would be insoluble in boiling 12 heptane. Furthermore, the polymer would have a w;de par-13 ticle size distribution.
4 By further comparison, a catalyst prepared by re-duction of TiC14 with diethyl aluminum chloride, and heated 16 to convert the catalyst from the brown to the purple form 17 would have a polymerization catalyst efficiency of 38 and of 18 which ~.5% of the polymer would be insoluble in boiling hep-19 taneO

21 Other catalysts were prepared according to the 22 data illustrated in Table 1 below for Examples 2-4 where 23 the concentration of TiC14 and the etheroaluminum alkyl 24 ratio was varied~

26 Catalysts were prepared by the reduction of TiC14 27 with diethyl aluminum chloride complexed with diisopentyl 28 ether or ethyl ether and as shown in Table 2 below, improved 29 catalysts having high efficiencies and high percent heptane insolubles were obtainedO
31 EXAMPLES 12_14 32 TiC14 was reduced with triethyl aluminum complexed with diisopentyl ether and as ~ tstrated in Table 3 2 below yielded catalysts that had high ca~alys ~ e~ic 3 iency and high percent heptane insolubles~

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1 Although diisopentyl ether is an excellent performer 2 and had been used in many experiments of the invention, 3 it is hereby disclosed that another excellent performing 4 ether is benzyl ether.
It is to be emphasized-that the ether/ethylene

6 aluminum chloride ratio must exceed 1 in order for the

7- TiC14 to be converted to the purple TiC13 after the

8 final TiC14 after-treatment.

9 It is also apparent that the ether aluminum ethyl chloride complex actually;changes the mechanism of 11 reduction and`the properties of the final catalyst 12 product.
13 Another important observation regarding the complex 14 of the invention is that the various aluminum alkyl or aluminum alkyl chloride complexes are quite different 16 depending on the Lewis acid strength of the aluminum 17 alkyl. Thus, the strongest reducing agents go in the 18 order of aluminum triethyl, followed by aluminum diethyl 19 chloride, followed by ethyl aluminum dlchloride. But the Lewis acidity strength of these reducing agents proceeds 21 from strong to weak, e.g., from ethyl aluminum dichloride, 22 which is stronger than diethyl aluminum chloride, which 23 , is stronger than triethyl aluminum.
24 The ethyl aluminum dichloride complex with diisopentyl ether is the least effective reducing agent.
26 The best catalyst results are obtained when using a 27 mixture of ethyl aluminum dichloride and diethyl aluminum 28 dichloride with diisopentyl ether.
29 When diethyl aluminum chloride is used by itself, as pointed out above, the ether diethyl aluminum chloride 31 ratio must exceed 1 in order to obtain the desired 32 purple delta TiC13.

s9 1 Tri~.thyl alllminum complexed ~ith dii.sopentyl ether 2 was observed to be the most active reducing agent yielding .
3 very high percentage yields at temperatures around 0C., 4 but suffering from a very broad particle size distr1bution.

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Claims (12)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a process for preparing a TiCl3 catalyst complex for stereo-regular polymerization of alpha-olefins wherein said catalyst complex is prepared by reducing TiCl4 in a non reactive solvent with an aluminum alkyl to obtain a brown reduced TiCl3 solid compound and activating the brown reduced TiCl3 solid compound by conversion to the purple form, the improvements comprising:
(a) in said reduction step (i) contacting TiCl4 with a dihydrocarbon ether/aluminum alkyl complex at a temperature within the range of about -80 to +50 C, wherein said aluminum alkyl compound is selected from aluminum triethyl, diethyl aluminum chloride and mixtures of diethyl aluminum chloride and ethyl aluminum dichloride and said complex being obtained by complexing said aluminum alkyl with a molar excess of said ether, and wherein the mole quantity of dihydrocarbon ether as compared to the totality of TiCl4 and aluminum alkyl compound is less than 1; and (ii) warming the resulting reaction mixture of (i) to about 25-90° C and maintaining said temperature for about 1/2 to about 6 hours to obtain a brown reduced solid TiCl3 complex; and (b) in said activating step contacting said brown reduced solid TiC13 compound with TiCl4 at an elevated temperature of about 25-90°C for about 1/2 to about 10 hours until said TiCl3 compound is converted to purple form.

2. A process according to claim 1, wherein the reagents in said reducing step are employed at a mole ratio of ether : aluminum alkyl compound : TiCl4 of 1.5 : 1 : 1.

3. A process according to claim 1, wherein said ether has the formula ROR', where R and R' are hydrocarbon radicals containing from 2 to 8 carbon atoms.

4. A process according to claim 1, wherein the ether/aluminum alkyl complex consists essentially of a mixture of diethyl aluminum chloride and ethyl aluminum dichloride complexed with diisopentyl ether.

5. A process according to claim 1, wherein in said activating step the TiCl4 is added directly to the reaction mixture of the reducing step (a).

6. The process according to claim 1, wherein the dihydrocarbon ether is mixed with the aluminum alkyl in the ratio of an excess up to 5 moles.

7. A process for polymerizing an alpha-olefin utilizing the after-treated catalyst of claim 1 in a standard Ziegler polymerization.

8. A process for polymerizing an alpha-olefin utilizing the after-treated catalyst of claim 2 in a standard Ziegler polymerization.

9. A process for polymerizing an alpha-olefin utilizing the after-treated catalyst of claim 3 in a standard Ziegler polymerization.

10. A process for polymerizing an alpha-olefin utilizing the after-treated catalyst of claim 4 in a standard Ziegler polymerization.

11. A process for polymerizing an alpha-olefin utilizing the after-treated catalyst of claim 5 in a standard Ziegler polymerization.

12. A process for polymerizing an alpha-olefin utilizing the after-treated catalyst of claim 6 in a standard Ziegler polymerization.