Process for the Polymerization of Olefins in Solution with Controlled Activity of Catalyst in Reactor Outlet Stream

Abstract

The present invention relates to a polymerisation process, comprising: a) supplying a feed containing ethylene and at least one alpha-olefin having 3 to 12 carbon atoms in a hydrocarbon solvent to a polymerisation reactor, b) contacting the feed of step a) in the reactor with a catalyst to form a reaction mixture containing an ethylene-alpha-olefin co-polymer, whereby the average residence time in the reactor is chosen to be between 0.5 and 30 minutes, c) withdrawing the reaction mixture from the polymerisation reactor as a reactor outlet stream which comprises the ethylene-alpha-olefin co-polymer, unreacted monomer, catalyst, and hydrocarbon solvent, and d) separating hydrocarbon solvent, monomer and comonomer from the reactor outlet stream and recycling it back to the polymerisation reactor without further purification steps, wherein in step c) no more than 5 wt. % of catalyst in an active state is leaving the reactor.

Claims

1. A polymerisation process, comprising: a) supplying a feed containing ethylene and at least one alpha-olefin having 3 to 12 carbon atoms in a hydrocarbon solvent to a polymerisation reactor, b) contacting the feed of step a) in the reactor with a catalyst to form a reaction mixture containing an ethylene-alpha-olefin co-polymer, whereby the average residence time in the reactor is chosen to be between 0.5 and 30 minutes, c) withdrawing the reaction mixture from the polymerisation reactor as a reactor outlet stream which comprises the ethylene-alpha-olefin co-polymer, unreacted monomer and comonomer, catalyst, and hydrocarbon solvent, and d) separating hydrocarbon solvent, monomer and comonomer from the reactor outlet stream and recycling it back to the polymerisation reactor without further purification steps, wherein in step c) no more than 5 wt. % of catalyst in an active state is leaving the reactor.

2. The process according to claim 1 wherein the average residence time of step b) is adjusted to effect that in step c) no more than 5 wt. % of catalyst in an active state is leaving the reactor.

3. The process according to claim 1 wherein adjustment of the average residence time is done by either adapting the solvent feed rate, and/or the catalyst feed rate.

4. The process according to claim 1 wherein the average residence time t.sub.average in the reactor is complying with the relation:
2900/T.sub.reactor−13<t.sub.average<4200/T.sub.reactor−13, wherein T.sub.reactor is the temperature in the polymerization reactor.

5. The process according to claim 1 wherein in step c) no more than 4 wt. % of catalyst in an active state are leaving the reactor.

6. The process according to claim 1 wherein the process is a continuous process.

7. The process according to claim 1 wherein separating hydrocarbon solvent from the reactor outlet stream in step d) is done by feeding the reactor outlet stream to a low pressure separator.

8. The process according to claim 1 wherein no catalyst de-activation agent is added to the reactor outlet stream before entering the low pressure separator.

9. The process according to claim 1 wherein the polymerization catalyst system comprising a metallocene complex and a boron containing cocatalyst and/or an aluminoxane co-catalyst.

10. The process according to claim 9 wherein the metallocene catalyst comprises a hafnocene catalyst.

11. The process according to claim 10 wherein the hafnocene catalyst comprises a hafnocene complex, comprising a cyclopentadienyl (Cp) ligand, a fluorenyl (Flu) ligand and a covalent bridge connecting the two ligands.

12. The process according to claim 1, wherein the polymerization reaction is performed at a temperature of between 120 to 220° C.

13. The process according to claim 1, wherein the polymerization reaction is performed at a pressure of between 50 to 300 bar.

14. The process according to claim 1, wherein polymer mass fraction inside the reactor is between 5.0 wt % to 50.0 wt %.

Description

[0071] In the following the present invention will be illustrated by examples and by referring to the following figures which show:

[0072] FIG. 1: Catalyst 1 fraction of material including active catalyst leaving the reactor at different temperatures, average residence time: 10 min.,

[0073] FIG. 2: Catalyst 2 fraction of material including active catalyst leaving the reactor at different temperatures, average residence time: 10 min.,

[0074] FIG. 3: Catalyst 1 fraction of material including active catalyst leaving the reactor at different temperatures, average residence time: 8 min.,

[0075] FIG. 4: Catalyst 2 fraction of material including active catalyst leaving the reactor at different temperatures, average residence time: 8 min.

[0076] FIG. 5: Catalyst 3 fraction of material including active catalyst leaving the reactor at different temperatures, average residence time: 10 min.,

[0077] FIG. 6: Catalyst 3 fraction of material including active catalyst leaving the reactor at different temperatures, average residence time: 8 min.

MEASUREMENT AND DETERMINATION METHODS

[0078] Melt Flow Rate and Flow Rate Ratio

[0079] The melt flow rate (MFR) is determined according to ISO 1133 and is indicated in g/10 min. The MFR is determined at 190° C. for polyethylene and at a loading of 2.16 kg (MFR.sub.2), 5.00 kg (MFR.sub.5), 10.00 kg (MFR.sub.10) or 21.6 kg (MFR.sub.21).

[0080] The quantity FRR (flow rate ratio) is an indication of molecular weight distribution and denotes the ratio of flow rates at different loadings. Thus, for example, FRR.sub.21/10 denotes the value of MFR.sub.21/MFR.sub.10.

[0081] Density

[0082] Density of the polymer is measured according to ISO 1183-1 method A using compression moulded samples. It is indicated in kg/m.sup.3.

[0083] Average Residence Time and Amount of Active Catalyst Leaving Reactor

[0084] The average residence time and the amount of catalyst leaving the reactor in an active state is determined by modelling of the reaction as can routinely be done by the skilled person.

[0085] Catalyst Productivity

[0086] The productivity of the catalyst was determined as the amount of polymer produced divided by the amount of metal in the catalyst (in g-PO/mg-Hf).

Examples

[0087] In the following examples, equations (1), (2) and (3) for three different catalysts (catalyst 1, 2 and 3) were used in order to calculate the catalyst de-activation profile and the amount of active catalyst leaving the reactor with the reactor outlet.

[0088] The parameters used in the equations were:

[0089] Catalyst 1:

C*.sub.cat,0=1mol/m.sup.3

k.sub.d,0=19.3mol.sup.−1s.sup.−1

E.sub.a=26.Math.10.sup.−3J/mol

t.sub.1=0.18.Math.t.sub.total

t.sub.2=0.74.Math.t.sub.total

t.sub.3=0.08.Math.t.sub.total

Catalyst 2:

C*.sub.cat,0=1mol/m.sup.3

k.sub.d,0=26.7mol.sup.−1s.sup.−1

E.sub.a=27.Math.10.sup.−3J/mol

t.sub.1=0.18.Math.t.sub.total

t.sub.2=0.74.Math.t.sub.total

t.sub.3=0.08.Math.total

Catalyst 3:

C*.sub.cat,0=1mol/m.sup.3

k.sub.d,0=9.7Mol.sup.−1s.sup.−1

E.sub.a=26.Math.10.sup.−3J/mol

t.sub.1=0.18.Math.t.sub.total

t.sub.2=0.74.Math.t.sub.total

t.sub.3=0.08.Math.t.sub.total

[0090] The results of the calculations are shown in FIGS. 1 to 6, where the fraction of material leaving the reactor based on the residence time distribution is shown as a function of time.

[0091] The catalyst deactivation constant is calculated for different temperatures (140, 170 and 200° C.) with equation (2) and the deactivation as a function of time with equation (1). The fraction of material, fed to the reactor at time t, leaving the reactor at time t+dt is calculated with equation (3). The calculations are done for two different average residence times: 8 and 10 minutes.

[0092] FIG. 1 and FIG. 3 represent the first catalyst (catalyst 1) with residence times of 10 and 8 minutes, respectively. FIGS. 2 and 4 represent the second catalyst (catalyst 2) with the residence times of 10 and 8 minutes, respectively.

[0093] Looking at FIGS. 1 and 2, the fraction of active catalyst leaving for both catalysts is less than approx. 3 wt. % during all times and temperatures. This indicates that the residence time is long enough in terms of controlling the catalyst activity in the outlet stream to the desired value and well below 5 wt. %.

[0094] Looking at FIGS. 3 and 4 it is seen that the fraction of active catalyst for both catalysts leaving the reactor is less than 5 wt. % for all temperatures 140° C., 170° C. and 200° C. during all times. However, for 140° C. the amount of active catalyst leaving the reactor is about 4.5 wt. % at around 3 minutes. This shows that the residence time of 8 minutes might not be sufficient to ensure having low enough, <4 wt %, concentration of active catalyst leaving the reactor at 140° C.

[0095] Finally, FIGS. 5 and 6 shows that for catalyst 3, which has a k.sub.d,0 which is half of that of catalyst 1, a higher temperature will have to be applied so that at the chosen residence times of 10 min. and 8 min. the catalyst activity in the outlet stream can be controlled to the desired value and well below 5 wt. %.