Methods for determining transition metal compound concentrations in multicomponent liquid systems
Methods for determining the concentration of transition metal compounds in a solution containing more than one transition metal compound are described. Polymerization reactor systems providing real-time monitoring and control of the concentrations of the transition metal components of a multicomponent catalyst system are disclosed, as well as methods for operating such polymerization reactor systems.
1. A process for operating a polymerization reactor system, the process comprising:
(I) contacting a catalyst system comprising a first transition metal compound, a second transition metal compound, an activator, and an optional co-catalyst, with an olefin monomer and an optional olefin comonomer in a reactor within the polymerization reactor system under polymerization reaction conditions to produce an olefin polymer;
wherein the polymerization reactor system comprises a solution reactor, a gas-phase reactor, a slurry reactor, or a combination thereof;
(II) determining a concentration of the first transition metal compound in a solution comprising the first transition metal compound and the second transition metal compound, the concentration determined via the steps of:
(i) submitting a sample of the solution to a sample chamber;
(ii) irradiating the sample in the chamber with a light beam at a wavelength in the UV-visible spectrum; and
(iii) generating a sample absorbance profile of the sample, subtracting a reference absorbance profile of the second transition metal compound in a reference solution from the sample absorbance profile to result in a first transition metal compound absorbance profile, and correlating the first transition metal compound absorbance profile to a standard to determine the concentration of the first transition metal compound in the solution; and
(III) adjusting a flow rate of the first transition metal compound into the reactor when the concentration of the first transition metal compound in the solution has reached a predetermined level.
2. The process of claim 1 , wherein:
the wavelength in step (ii) comprises wavelengths in the 300 nm to 600 nm range;
the sample absorbance profile in step (iii) comprises an absorbance curve over a range of wavelengths;
the reference solution comprises the second transition metal compound and a hydrocarbon solvent; and
the step of correlating is performed at a single wavelength.
3. The process of claim 1 , wherein a weight ratio of the first transition metal compound to the second transition metal compound in the solution is in a range from about 1:20 to about 1:1.
4. The process of claim 3 , wherein:
the catalyst system comprises a first metallocene compound, a second metallocene compound, an activator, and a co-catalyst;
the catalyst system is contacted with ethylene and an olefin comonomer comprising 1-butene, 1-hexene, 1-octene, or a mixture thereof;
the sample absorbance profile, the reference absorbance profile, and the first transition metal compound absorbance profile independently comprise an absorbance curve over a range of wavelengths; and
the standard comprises a calibration curve.
5. The process of claim 1 , wherein:
the olefin polymer comprises an ethylene homopolymer and/or an ethylene ethylene/α-olefin copolymer; and
at least one of the first transition metal compound and the second transition metal compound is a metallocene compound.
6. The process of claim 5 , wherein:
the solution comprising the first transition metal compound and the second transition metal compound is a feed stream to a catalyst preparation vessel; and
the flow rate of the first transition metal compound into the reactor is controlled by adjusting a flow rate of the feed stream to the catalyst preparation vessel, and/or by adjusting a flow rate ratio of the first:second transition metal compound to the catalyst preparation vessel, and/or by adjusting a flow rate of the catalyst system exiting the catalyst preparation vessel and entering the reactor.
7. The process of claim 5 , wherein:
the solution comprising the first transition metal compound and the second transition metal compound is a liquid or homogeneous catalyst system; and
the flow rate of the first transition metal compound into the reactor is controlled by adjusting a flow rate ratio of the first:second transition metal compound to the reactor, and/or by adjusting a flow rate of the liquid or homogeneous catalyst system entering the reactor.
8. The process of claim 5 , wherein:
the solution comprising the first transition metal compound and the second transition metal compound is a solution prepared from a heterogeneous or supported catalyst system; and
the flow rate of the first transition metal compound into the reactor is controlled by adjusting a flow rate ratio of the first:second transition metal compound to the reactor, and/or by adjusting a flow rate of the heterogeneous or supported catalyst system entering the reactor.
9. The process of claim 5 , wherein:
the solution comprising the first transition metal compound and the second transition metal compound is a solution prepared from a sample mixture from the reactor; and
the flow rate of the first transition metal compound into the reactor is controlled by adjusting a flow rate ratio of the first:second transition metal compound to the reactor, and/or by adjusting a flow rate of the catalyst system entering the reactor.
10. The process of claim 1 , wherein:
the first transition metal compound is an unbridged metallocene compound; and
the second transition metal compound is a bridged metallocene compound.
11. The process of claim 1 , wherein the olefin polymer comprises an oligomerization product of a C 6 -C 24 olefin.
12. A method for determining a concentration of a first transition metal compound in a solution comprising the first transition metal compound and a second transition metal compound, the method comprising:
submitting a sample of the solution to a sample chamber comprising a flow cell;
(ii) irradiating the sample in the chamber with a light beam at a wavelength in the UV-visible spectrum; and
(iii) generating a sample absorbance profile of the sample, subtracting a reference absorbance profile of the second transition metal compound in a reference solution from the sample absorbance profile to result in a first transition metal compound absorbance profile, and correlating the first transition metal compound absorbance profile to a standard to determine the concentration of the first transition metal compound in the solution;
wherein the solution comprises the first transition metal compound, the second transition metal compound, and a hydrocarbon solvent.
13. The method of claim 12 , wherein the wavelength in step (ii) comprises wavelengths in the 300 nm to 600 nm range.
14. The method of claim 12 , wherein:
the sample absorbance profile, the reference absorbance profile, and the first transition metal compound absorbance profile independently comprise an absorbance curve over a range of wavelengths; and
the reference solution comprises the second transition metal compound and the hydrocarbon solvent.
15. A polymerization reactor system comprising:
(A) a reactor configured to contact a catalyst system with ethylene and an optional olefin comonomer under polymerization reaction conditions to produce an ethylene polymer;
(B) a catalyst preparation vessel configured to contact a first transition metal compound, a second transition metal compound, an activator, and an optional co-catalyst to form the catalyst system;
(C) an analytical system configured to determine a concentration of the first transition metal compound in a solution comprising the first transition metal compound and the second transition metal compound present within the polymerization reactor system; and
(D) a controller configured to control a flow rate of the first transition metal compound into the reactor based on the concentration determined by the analytical system.
16. The reactor system of claim 15 , wherein the analytical system comprises an ultraviolet-visible spectrometer.
17. The reactor system of claim 16 , wherein the reactor system comprises:
a single loop slurry reactor; or
two or more reactors, at least one of which is a loop slurry reactor.
18. The reactor system of claim 15 , wherein the analytical system further comprises a filter assembly configured to filter a sample of the solution comprising the first transition metal compound and the second transition metal compound before analysis by the analytical system.
19. The reactor system of claim 15 , wherein:
the reactor system comprises a slurry reactor, a gas-phase reactor, a solution reactor, or a combination thereof;
the ethylene polymer comprises an ethylene homopolymer, an ethylene/1-butene copolymer, an ethylene/1-hexene copolymer, or an ethylene/1-octene copolymer; and
the solution comprises the first transition metal compound, the second transition metal compound, and a hydrocarbon solvent.
20. The reactor system of claim 19 , wherein:
the analytical system comprises an ultraviolet-visible spectrometer; and
the first transition metal compound and the second transition metal compound independently comprise a bridged or unbridged metallocene compound.
21. The reactor system of claim 15 , wherein:
the analytical system comprises an ultraviolet-visible spectrometer with an integrated computer system for measuring a sample absorbance profile of the first transition metal compound in the solution, for subtracting a reference absorbance profile of the second transition metal compound in a reference solution from the sample absorbance profile to result in a first transition metal compound absorbance profile, and for correlating the first transition metal compound absorbance profile to a standard to determine the concentration of the first transition metal compound in the solution;
the solution comprises the first transition metal compound, the second transition metal compound, and a hydrocarbon solvent; and
the solution is a feed stream to the catalyst preparation vessel, and the controller controls the flow rate of the first transition metal compound into the reactor by adjusting a flow rate ratio of the first:second transition metal compound to the catalyst preparation vessel.