Process for manufacture of low emission homopolymer or random polypropylene

Abstract

The invention relates to a process for the preparation of a propylene homopolymer or a propylene α-olefin random copolymer comprising the step of a) preparing a propylene homopolymer or a propylene α-olefin random copolymer, wherein the α-olefin is chosen from the group consisting of ethylene, and α-olefins having 4 to 10 carbon atoms, for example 1-butene or 1-hexene by contacting at least the propylene and optionally α-olefin, with a catalyst in a gas-phase reactor at a temperature T1 and a pressure P1, wherein T1 is chosen in the range from 75 to 90° C., for example in the range from 77 to 85° C., for example in the range from 78 to 83° C., wherein P1 is chosen in the range from 22 to 30 bar to prepare a propylene homopolymer (A′) or a propylene α-olefin random copolymer (A′).

Claims

1. A process for the preparation of a propylene homopolymer or a propylene α-olefin random copolymer comprising the steps of: a) preparing a propylene homopolymer or a propylene α-olefin random copolymer, wherein the α-olefin is chosen from the group consisting of ethylene and α-olefins having 4 to 10 carbon atoms, by contacting at least the propylene and optionally α-olefin with a catalyst in a single gas-phase reactor at a temperature T1 and a pressure P1; wherein T1 is chosen in the range from 75 to 83° C.; and wherein P1 is chosen in the range from 22 to 30 bar; to prepare a propylene homopolymer (A′) or a propylene α-olefin random copolymer (A′); and b) visbreaking the propylene homopolymer (A′) or the propylene α-olefin random copolymer (A′) to obtain a propylene homopolymer (A) or a propylene α-olefin random copolymer (A), wherein the propylene homopolymer (A) respectively the propylene α-olefin random copolymer (A) has a melt flow rate that is higher than the melt flow rate of the propylene homopolymer (A′) respectively propylene α-olefin random copolymer (A′) as measured according to ISO1133 (2.16 kg, 230° C.); and wherein the FOG value of the propylene homopolymer (A′) or the propylene α-olefin random copolymer (A′) after the visbreaking and before any subsequent processing step is at most 400 μg/g, as determined by VDA 278.

2. The process according to claim 1, wherein a melt flow rate of the propylene homopolymer (A′) or the propylene a-olefin random copolymer (A′) is in the range from 5.0 to 150 dg/min as measured according to ISO1133 (2.16 kg, 230° C.).

3. The process according to claim 1, wherein in step a) the propylene homopolymer or a propylene α-olefin random copolymer are prepared from propylene, optional α-olefin and a prepolymer, wherein the prepolymer is prepared by contacting propylene and optional α-olefin with a catalyst in a single prepolymerization reactor.

4. The process according to claim 1, wherein the catalyst is a catalyst system which comprises a Ziegler-Natta catalyst and at least one external electron donor.

5. The process according to claim 1, wherein α-olefin in the propylene α-olefin random copolymer is ethylene.

6. The process according to claim 1, wherein a shifting ratio, which is the ratio of the melt flow rate of the propylene homopolymer (A) or the propylene α-olefin random copolymer (A) to the melt flow rate of the propylene homopolymer (A′) or the propylene a-olefin random copolymer (A′) is in the range from 1.5 to 20.

7. The process according to claim 1, wherein the melt flow rate of the propylene homopolymer (A) or propylene α-olefin random copolymer (A) as measured according to ISO1133 (2.16 kg, 230° C.) is in the range from 15 to 250 dg/min.

8. The process according to claim 1, wherein the FOG of the propylene homopolymer (A) or a propylene a-olefin random copolymer (A) is at most 700 μg/g, as determined by VDA 278.

9. The process for the preparation of a propylene homopolymer or a propylene a-olefin random copolymer according to claim 1, further comprising step c) reducing the FOG value of the propylene homopolymer (A′) or the propylene a-olefin random copolymer (A′) and/or the propylene homopolymer (A) or the propylene α-olefin random copolymer (A) by maintaining the propylene homopolymer (A′) or the propylene α-olefin random copolymer (A′) and/or the propylene homopolymer (A) or the propylene α-olefin random copolymer (A) at such temperature and for such time as to allow reduction of the FOG value to the desired level to produce a propylene homopolymer (B′) or the propylene α-olefin random copolymer (B′).

10. The process according to claim 1, wherein the single gas-phase reactor is a horizontally stirred single gas-phase reactor.

11. The process according to claim 1, wherein the FOG value of the propylene homopolymer (A′) or the propylene a-olefin random copolymer (A′) is at most 250 μg/g, as determined by VDA 278; wherein a shifting ratio, which is the ratio of a melt flow rate of the propylene homopolymer (A) or the propylene a-olefin random copolymer (A) to a melt flow rate of the propylene homopolymer (A′) or the propylene α-olefin random copolymer (A′), is in the range from 2 to 10; wherein the melt flow rate of the propylene homopolymer (A) or propylene α-olefin random copolymer (A) as measured according to ISO1133 (2.16 kg, 230° C.) is in the range from 25 to 250 dg/min; and wherein the FOG of the propylene homopolymer (A) or a propylene α-olefin random copolymer (A) is at most 400 μg/g, as determined by VDA 278.

12. The process according to claim 1, wherein the catalyst is a catalyst system which comprises a Ziegler-Natta catalyst and at least one external electron donor, which external electron donor is chosen from the group of a compound having a structure according to Formula III (R.sup.90).sub.2N—Si(OR.sup.91).sub.3, a compound having a structure according to Formula IV: (R.sup.92)Si(OR.sup.93).sub.3, or mixtures thereof, wherein each of R.sup.90, R.sup.91, R.sup.92, and R.sup.93, groups are each independently a linear, branched or cyclic, substituted or unsubstituted alkyl having between 1 and 10 carbon atoms.

13. The process according to claim 12, wherein R.sup.90, R.sup.91, R.sup.92, and R.sup.93, groups are each independently ethyl, methyl or n-propyl; and organosilicon compounds having general formula Si(OR.sup.a).sub.4-aR.sub.n, wherein n is from 0 up to 2, and each of R.sup.a and R.sup.b, independently, represents an alkyl or aryl group, containing one or more hetero atoms selected from O, N, S or P, with, 1-20 carbon atoms, and wherein the catalyst system is obtained by a catalyst preparation process comprising the steps of: A) providing a procatalyst obtainable via a process comprising the steps of: i) contacting a compound R.sup.4.sub.zMgX.sup.4.sub.2-z with an alkoxy- or aryloxy-containing silane compound to give a first intermediate reaction product, being a solid Mg(OR.sup.1).sub.xX.sup.1.sub.2-x, wherein: R.sup.4 is the same as R.sup.1 being a linear, branched or cyclic hydrocarbyl group independently selected from alkyl, alkenyl, aryl, aralkyl, alkoxycarbonyl or alkylaryl groups, and one or more combinations thereof; wherein said hydrocarbyl group may be substituted or unsubstituted, may contain one or more heteroatoms; X.sup.4 and X.sup.1 are each independently selected from the group of consisting of fluoride (F—), chloride (Cl—), bromide (Br—) or iodide (I—); z is in a range of larger than 0 and smaller than 2, being 0<z<2; ii) contacting the solid Mg(OR.sup.1).sub.xX.sub.2-x, obtained in step i) with at least one activating compound selected from the group formed of activating electron donors and metal alkoxide compounds of formula M.sup.1(OR.sup.2).sub.v-w(OR.sup.3).sub.w, or M.sup.2(OR.sup.2).sub.v-w(R.sup.3).sub.w, to obtain a second intermediate product; wherein M.sup.1 is a metal selected from the group consisting of Ti, Zr, Hf, Al or Si; M.sup.2 is a metal being Si; v is the valency of M.sup.1 or M.sup.2; R.sup.2 and R.sup.3 are each a linear, branched or cyclic hydrocarbyl group independently selected from alkyl, alkenyl, aryl, aralkyl, alkoxycarbonyl or alkylaryl groups, and one or more combinations thereof; and iii) contacting the first or second intermediate reaction product, obtained respectively in step i) or ii), with a halogen-containing Ti-compound and optionally an internal electron donor to obtain said procatalyst; and B) contacting said procatalyst with a co-catalyst and the at least one external electron donor to form a catalyst.

14. A process for the preparation of preparing a propylene homopolymer or a propylene a-olefin random copolymer comprising the steps of: a) preparing a propylene homopolymer or a propylene α-olefin random copolymer, wherein the α-olefin is chosen from the group consisting of ethylene and α-olefins having 4 to 10 carbon atoms, by contacting at least the propylene and optionally α-olefin with a catalyst in a single gas-phase reactor at a temperature T1 and a pressure P1, wherein T1 is chosen in the range from 78 to 83° C.; wherein P1 is chosen in the range from 22 to 30 bar; to prepare a propylene homopolymer (A′) or a propylene α-olefin random copolymer (A′); and b) visbreaking the propylene homopolymer (A′) or the propylene α-olefin random copolymer (A′) to obtain a propylene homopolymer (A) or a propylene α-olefin random copolymer (A), wherein the propylene homopolymer (A) respectively the propylene α-olefin random copolymer (A) has a melt flow rate that is higher than the melt flow rate of the propylene homopolymer (A′) respectively propylene α-olefin random copolymer (A′) as measured according to ISO1133 (2.16 kg, 230° C.); wherein the catalyst is a catalyst system comprising a magnesium catalyst and an electron donor; wherein the magnesium catalyst is prepared by reacting titanium tetrachloride, diisobutyl phthalate, and magnesium diethoxide to form a solid material, slurrying the solid material and titanium tetrachloride, and collecting the magnesium catalyst from the slurry; and wherein the electron donor comprises n-propyltriethoxysilane; and wherein the FOG value of the propylene homopolymer (A′) or the propylene α-olefin random copolymer (A′) after the visbreaking and before any subsequent processing step is at most 400 μg/g, as determined by VDA 278.

Description

EXAMPLES

(1) Measurements

(2) Melt Flow Rate

(3) Melt flow rate was determined in accordance with ISO 1133 at 230° C. and 2.16 kg.

(4) FOG

(5) FOG was determined according to VDA 278:2011 from pellets. FOG according to VDA 278 is the sum of all organic compounds of low volatility, which have an elution time greater than or equal to n-tetradecane. FOG is calculated as tetradecane equivalent (TE). FOG according to VDA 278 represents organic compounds in the boiling point range of n-alkanes C.sub.14 to C.sub.32. VDA standards are issued by “Verband der Automobilindustrie”. The VDA standards used herein are available from Dokumentation Kraftfahrwesen (DKF); Ulrichstrasse 14, D-74321 Bietigheim-issingen, Germany or can be downloaded from their website (www.dkf-ev.de). Immediately after peroxide shifting (step II), samples were taken and sealed in Lamigrip aluminium bags from Fisher Scientific. The FOG values were measured within a week from sealing the bags. To allow a direct comparison, all VDA278 measurements were carried out on the same GC equipment.

(6) Experimental

(7) Catalyst I

(8) Catalyst I is prepared according to the method disclosed in U.S. Pat. No. 4,866,022, hereby incorporated by reference. This patent discloses a catalyst component comprising a product obtained by: (a) forming a solution of a magnesium-containing species from a magnesium carbonate or a magnesium carboxylate; (b) precipitating solid particles from such magnesium-containing solution by treatment with a transition metal halide and an organosilane having a formula: R.sub.nSiR′.sub.4-n, wherein n=0 to 4 and wherein R is hydrogen or an alkyl, a haloalkyl or aryl radical containing one to about ten carbon atoms or a halosilyl radical or haloalkylsilyl radical containing one to about eight carbon atoms, and R′ is OR or a halogen; (c) reprecipitating such solid particles from a mixture containing a cyclic ether; and (d) treating the reprecipitated particles with a transition metal compound and an electron donor. This process for preparing a catalyst is incorporated into the present application by reference.

(9) Catalyst II

(10) A. Grignard Formation Step

(11) A stirred flask, fitted with a reflux condenser and a funnel, was filled with magnesium powder (24.3 g). The flask was brought under nitrogen. The magnesium was heated at 80° C. for 1 hour, after which dibutyl ether (DBE, 150 ml), iodine (0.03 g) and n-chlorobutane (4 ml) were successively added. After the colour of the iodine had disappeared, the temperature was raised to 80° C. and a mixture of n-chlorobutane (110 ml) and dibutyl ether (750 ml) was slowly added for 2.5 hours. The reaction mixture was stirred for another 3 hours at 80° C. Then the stirring and heating were stopped and the small amount of solid material was allowed to settle for 24 hours. By decanting the colorless solution above the precipitate, a solution of butylmagnesiumchloride (reaction product of step A) with a concentration of 1.0 mol Mg/I was obtained.

(12) B. Preparation of the Intermediate Reaction Product

(13) 250 mL of dibutyl ether was introduced to a 1 L reactor fitted with a propeller stirrer and two baffles. The reactor was thermostated at 35° C. and the stirrer speed was kept at 200 rpm. Then a cooled (to 15° C.) 360 mL solution of the Grignard reaction product as prepared in A and 180 ml of a cooled (to 15° C.) solution of 38 ml of tetraethoxysilane (TES) in 142 ml of DBE were dosed into the reactor for 400 min. with preliminary mixing in a minimixer of 0.15 ml volume, which was cooled to 15° C. by means of cold water circulating in the minimixer jacket. The premixing time was 18 seconds in the minimixer and the connecting tube between the minimixer and the reactor. The stirring speed in the minimixer was 1000 rpm. On the dosing completion, the reaction mixture was kept at 35° C. for 0.5 hours. Then the reactor was heated to 60° C. and kept at this temperature for 1 hour. Then the stirring was stopped and the solid substance was allowed to settle. The supernatant was removed by decanting. The solid substance was washed three times using 300 ml of heptane. As a result, a white solid reaction product was obtained and suspended in 200 ml of heptane.

(14) Under an inert nitrogen atmosphere at 20° C. a 250 ml glass flask equipped with a mechanical agitator is filled with a slurry of 5 g of the reaction product of step B dispersed in 60 ml of heptane. Subsequently, a solution of 0.86 ml methanol (MeOH/Mg=0.5 mol) in 20 ml heptane is dosed under stirring during 1 hour. After keeping the reaction mixture at 200° C. for 30 minutes the slurry was slowly allowed to warm up to 300° C. for 30 min and kept at that temperature for another 2 hours. Finally the supernatant liquid is decanted from the solid reaction product which was washed once with 90 ml of heptane at 300° C.

(15) C. Preparation of the Catalyst

(16) A reactor was brought under nitrogen and 125 ml of titanium tetrachloride was added to it. The reactor was heated to 90° C. and a suspension, containing about 5.5 g of the support obtained in step C in 15 ml of heptane, was added to it under stirring. The reaction mixture was kept at 90° C. for 10 min. Then ethyl benzoate was added (EB/Mg=0.15 molar ratio). The reaction mixture was kept for 60 min. Then the stirring was stopped and the solid substance was allowed to settle. The supernatant was removed by decanting, after which the solid product was washed with chlorobenzene (125 ml) at 90° C. for 20 min. The washing solution was removed by decanting, after which a mixture of titanium tetrachloride (62.5 ml) and chlorobenzene (62.5 ml) was added. The reaction mixture was kept at 90° C. for 30 min. After which the stirring was stopped and the solid substance was allowed to settle. The supernatant was removed by decanting, after which a mixture of titanium tetrachloride (62.5 ml) and chlorobenzene (62.5 ml) was added. Then di-n-butyl phthalate (DBP) (DBP/Mg=0.15 molar ratio) in 3 ml of chlorobenzene was added to reactor and the temperature of reaction mixture was increased to 115° C. The reaction mixture was kept at 115° C. for 30 min. After which the stirring was stopped and the solid substance was allowed to settle. The supernatant was removed by decanting, after which a mixture of titanium tetrachloride (62.5 ml) and chlorobenzene (62.5 ml) was added. The reaction mixture was kept at 115° C. for 30 min, after which the solid substance was allowed to settle. The supernatant was removed by decanting and the solid was washed five times using 150 ml of heptane at 600° C., after which the catalyst III, suspended in heptane, was obtained.

(17) Catalyst III

(18) Catalyst Ill is prepared according to the method described in U.S. Pat. No. 5,093,415 of Dow, hereby incorporated by reference. This patent discloses an improved process to prepare a catalyst including a reaction between titanium tetrachloride, diisobutyl phthalate, and magnesium diethoxide to obtain a solid material. This solid material is then slurried with titanium tetrachloride in a solvent and phthaloyl chloride is added. The reaction mixture is heated to obtain a solid material which is reslurried in a solvent with titanium tetrachloride. Again this was heated and a solid collected. Once again the solid was reslurried once again in a solution of titanium tetrachloride to obtain a catalyst.

(19) Propylene Homopolymer Polymerization Experiments

(20) Step I)

(21) Polymerization experiments of propylene homopolymers (Table 1) were performed on a bench-scale gas-phase reactor using catalysts I, II and III described above at different reaction temperatures (50, 60, 70 and 80° C.) as well as with different external electron donors in order to determine the effect of the reaction temperature on the FOG emission values of the propylene homopolymers. The pressure used was 22 bar. Triethylaluminium was used as co-catalyst, and two external electron donors were employed; di(iso-propyl) dimethoxysilane (DiPDMS) and n-propyltriethoxysilane (nPTES). Homopolymers produced at a temperature of 50, 60 and 70° C. are denoted with CE as comparative experiments. Homopolymers produced at 80° C. are denoted with RE as reference experiments of the present invention. RE and CE are together show the effects of the reaction temperature on the FOG emission values of polypropylene. At a given reaction temperature (T.sub.R1, also referred in the present invention as the reactor temperature), propylene homopolymers of melt flow rate 50 dg/min were produced at different H2/C3 molar ratios, due to the different hydrogen sensitivity of the external donors. H2/C3 is the molar ratio of hydrogen to propylene in the gas cap of the reactor, measured by on-line gas chromatography.

(22) TABLE-US-00001 TABLE 1 Polymerization and FOG data of propylene homopolymers of melt flow rate 50 dg/min T.sub.R1 H.sub.2/C.sub.3 FOG Exp # Catalyst External Donor ° C. mol/mol μg/g CE1 I nPTES 60 0.029 710 RE1 I nPTES 80 0.0157 490 CE2 II DiPDMS 60 0.061 665 RE2 II DiPDMS 80 0.049 585 CE3 III DiPDMS 60 0.048 590 RE3 III DiPDMS 80 0.029 510 CE41 III nPTES 50 0.026 410 CE42 III nPTES 60 0.022 290 CE43 III nPTES 70 0.013 250 RE4 III nPTES 80 0.0054 190

(23) From Table 1, it is clear that for a given melt flow of the propylene homopolymer, the increase in T.sub.R1 reduces the FOG value, and this effect is independent of the catalyst/external donor system.

(24) From Table 1, it is also clear that the use of nPTES compared to other external electron donors results in lower FOG emission values. Same examples can be used as illustrations.

(25) Moreover, it is shown in Table 1 that the combination of catalyst III and nPTES leads to the lowest FOG values at given MFR and given T.sub.R1. This can be for example illustrated by comparing CE1/RE1 (catalyst I and nPTES) or CE3/RE3 (catalyst III and DiPDMS) with CE42/RE4 (catalyst III and nPTES).

(26) Additional Examples are presented in Table 2 with the combination of catalyst III and nPTES for a series of propylene homopolymers produced at four different T.sub.R1 (50, 60, 70 and 80° C.) with a melt flow rate of 30 dg/min.

(27) TABLE-US-00002 TABLE 2 Polymerization and FOG data of propylene homopolymers of MFR 30 dg/min T.sub.R1 H.sub.2/C.sub.3 FOG Exp # Catalyst External Donor ° C. mol/mol μg/g CE51 III nPTES 50 0.016 360 CE52 III nPTES 60 0.0149 280 CE53 III nPTES 70 0.008 220 RE5 III nPTES 80 0.0037 180

(28) Same observations are made from Table 2 with respect to the positive effect of higher T.sub.R1 on lowering the H2/C3 molar ratio and hence on decreasing the FOG emission value of the propylene homopolymers.

(29) Step II)

(30) For achieving high flow propylene homopolymers, these reactor powders (the intermediate propylene homopolymer powders) were melt-processed by peroxide shifting (i.e. visbreaking) to higher melt flow rates to obtain the final propylene homopolymer. This was done by feeding the powder to an extruder and adding Luperco 802PP40 as a peroxide (1,4-bis(2-tert-butylperoxypropan-2-yl)benzene, CAS Registry Number: 2781-00-2) in different concentrations. Table 3 lists details of the visbreaking experiments for reactor powders CE53 and RE5 including starting MFR (intermediate MFR) and final MFR (target MFR), the amount of peroxide in weight percentage and FOG values. Besides the peroxide, some additives common in the art were also added (0.25 weight percentage). The additive package was the same for all experiments.

(31) TABLE-US-00003 TABLE 3 FOG data of polypropylene homopolymer powders (the intermediate propylene homopolymer) and the peroxide shifted products (the final propylene homopolymer) Intermediate MFR Target MFR $\frac{\mathrm{Target}\mathrm{MFR}}{\mathrm{Intermediate}\mathrm{MFR}}$   Peroxide   FOG Exp # dg/min dg/min — wt. % μg/g CE53 30 30 1 0 220 CE53-S1 30 92 3.07 0.041 350 RE5 30 30 1 0 180 RE5-S1 30 89 2.97 0.04 285 *CE53-S1 is peroxide shifted propylene homopolymer from experiment CE53, RE5-S1 is peroxide shifted propylene homopolymer from experiment RE5. *intermediate MFR is the MFR of the intermediate propylene homopolymer *target MFR is the MFR of the final propylene homopolymer *shifting ratio is the target MFR divided by the intermediate MFR

(32) Table 3 shows that the visbreaking of an intermediate propylene homopolymer to higher melt flow rates to obtain the final propylene homopolymer commonly results in increased FOG values. This can be for example illustrated by comparing CE53-S1 with CE53, or also by comparing RE5-S1 with RE5.

(33) However, it is also clear from Table 3 that the positive effect of increasing T.sub.R1 during the polymerization process of the intermediate propylene homopolymer on lowering its FOG value is preserved when peroxide shifting the powder to higher melt flow rates to obtain the final propylene homopolymer. For instance, Example RE5-S1 has lower FOG value than Example CE53-S1, although both propylene homopolymers are peroxide shifted from a melt flow 30 to about 90 dg/min; the only difference between the two examples is the temperature in the reactor (T.sub.R1) during the polymerization process of their respective intermediate propylene homopolymer; the higher T.sub.R1, the lower the FOG value of the final propylene homopolymer.

(34) The person skilled in the art knows how to vary the MFR value of the intermediate propylene homopolymer. The MFR value of the intermediate propylene homopolymer influences the FOG values for the desired MFR of the final propylene homopolymer.

(35) Therefore, the present invention demonstrates that propylene homopolymers combining high melt flow and low FOG emissions can be produced in the process of the invention.