CN-121986124-A - Method for switching between incompatible catalysts

CN121986124ACN 121986124 ACN121986124 ACN 121986124ACN-121986124-A

Abstract

The present invention relates to a gas phase olefin polymerization process comprising the steps of (a) operating the process in a continuous manner in the presence of a Ziegler-Natta catalyst system (ZN 1), wherein a stream (10) comprising unreacted material and inert material is (partially) recycled back into the reactor, (b) stopping the recycling of stream (10) back into the reactor, (c) gradually stopping the introduction of ZN1 while gradually introducing the Ziegler-Natta catalyst system (ZN 2) into the reactor such that the polymer production rate is maintained at a rate not exceeding 30% lower than the production rate in step (a), and (d) after stopping the introduction of ZN1 and the feed of ZN2 reaches full speed, (partially) resuming the recycling of stream (10) back into the reactor, wherein ZN1 comprises an internal electron donor moiety which reduces the polymerization activity of ZN 2.

Inventors

H. Al Sarmi
Y. Barnett
A. B. Elmad Sea
Z. A. Argosun

Assignees

SABIC环球技术有限责任公司

Dates

Publication Date: 20260505
Application Date: 20240905
Priority Date: 20231009

Claims (14)

1. A process for transitioning from a first Ziegler-Natta catalyst system to a second Ziegler-Natta catalyst system in a gas-phase olefin polymerization unit, Wherein the polymerization unit comprises a polymerization reactor (8) comprising at least one inlet (11) for feeding a reaction mixture (A) to the polymerization reactor, at least one outlet (12) for removing a polymerization product (30) from the reactor and at least one outlet (13) for removing a stream (40) of unreacted material and inert material from the reactor, Wherein the outlet (13) is connected to an inlet (11) through which inlet (11) the stream (10) or a part thereof can be recycled back into the reactor, The method comprises the following steps in this order: (a) Operating the polymerization process in a continuous manner in the presence of a first miller-Natta catalyst system (ZN 1), wherein a stream (10) or a portion thereof is recycled back into the reactor; (b) Stopping the circulation of the stream (10) back into the reactor; (c) Gradually stopping the introduction of ZN1 while gradually introducing a second Ziegler-Natta catalyst system (ZN 2) into the reactor such that the polymer production rate is maintained at a rate which does not drop more than 30% from the production rate in step (a), and (D) After stopping the introduction of ZN1 and the feed of ZN2 reaches full speed, the recirculation of stream (10) or a part thereof back into the reactor is resumed; Wherein ZN1 comprises an internal electron donor moiety that reduces the polymerization activity of ZN 2.
2. The process of claim 1 wherein the polymerization process involves polymerization of ethylene, optionally with one or more comonomers selected from the group consisting of propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and 1-octene.
3. The process of any one of claims 1-2, wherein a trialkylaluminum cocatalyst is added to the reactor in step C to bind the internal electron donor moiety of ZN 1.
4. A method according to claim 3, wherein the molar ratio between the trialkylaluminium and the internal electron donor moiety ranges between 10:1 and 1:1.
5. The method according to any one of claims 1-4, wherein the internal electron donor moiety present in ZN1 is selected from the group consisting of alcohols, organosilicon compounds, polysiloxanes, phenols, ketones, aldehydes, inorganic acid esters, polycarboxylic esters, ethers, amides, anhydrides, nitrogen-containing compounds and acyl halides, preferably wherein the internal electron donor moiety is tetrahydrofuran.
6. The process according to any one of claims 1-5, wherein ZN1 is a supported catalyst system, preferably wherein the support is selected from inorganic oxides such as silica, alumina, magnesia, thoria, zirconia and mixtures of such oxides, more preferably the support is porous silica.
7. The method of any one of claims 1-6, wherein ZN2 is prepared in a process comprising the steps of: a) Contacting a dehydrated solid support having hydroxyl groups with a magnesium compound having the general formula MgR 'R ", wherein R' and R" are the same or different and are independently selected from the group comprising alkyl, alkenyl, dienyl, aryl, alkylaryl, alkenylaryl and dienylaryl; b) Contacting the product obtained in step (a) with modified compounds (a), (B) and (C), wherein compound (a) is at least one compound selected from the group consisting of carboxylic acid, carboxylic acid ester, ketone, acyl halide, aldehyde and alcohol, compound (B) is a compound having the general formula R 1 a (R 2 O) b SiY 1 c , wherein a, B and C are each an integer of 0 to 4 and the sum of a, B and C is equal to 4, provided that when C is equal to 4, then modified compound (a) is not alcohol, si is silicon atom, O is oxygen atom, Y 1 is halogen atom, and R 1 and R 2 are the same or different and are independently selected from the group consisting of alkyl, alkenyl, dienyl, aryl, alkaryl and dienylaryl, compound (C) is a compound having the general formula (R 11 O) 4 M 1 ), wherein M 1 is titanium atom, zirconium atom or vanadium atom, O is oxygen atom, and R 11 is selected from the group consisting of alkyl, alkenyl, dienyl, aryl, alkaryl and dienylaryl, and C) is titanium atom, and step (Y) is a titanium atom, wherein the product is obtained in step (Ti) is a titanium atom, and the titanium atom is 4 .
8. The process according to any one of claims 3-7, wherein the trialkylaluminum compound is selected from trimethylaluminum, triethylaluminum, tripropylaluminum, tributylaluminum, triisopropylaluminum, triisobutylaluminum, dimethylaluminum hydride, diethylaluminum hydride, dipropylaluminum hydride, dibutylaluminum hydride, diisopropylaluminum hydride and diisobutylaluminum hydride, preferably from triethylaluminum and triisobutylaluminum hydride.
9. The process according to any one of claims 1-6, wherein ZN2 is a supported catalyst system, preferably wherein the support is selected from inorganic oxides such as silica, alumina, magnesia, thoria, zirconia and mixtures of such oxides, more preferably the support is porous silica.
10. The process according to any one of claims 1-9, wherein during steps (b) and (c) the stream (10) is removed from the polymerization unit.
11. The process according to any one of claims 1 to 10, wherein the stream (10) is subjected to condensation before being recycled back to the polymerization reactor via inlet (11).
12. The process of any of claims 1-11, wherein the polymerization reactor is a fluidized bed gas phase polymerization reactor.
13. The method of claim 12, wherein the polymerization process is conducted in a multi-zone reactor, the polymerization process comprising: -feeding a solid polymerization catalyst to the second zone (2) using a first inlet for receiving a solid polymerization catalyst (20); -feeding a feed (60) comprising olefin monomers to a first connection means (AA) Optionally feeding a feed (70) comprising condensable inert components to a second connection means (BB) -Taking out polyolefin (30) using the first outlet (12) of the second zone (2) and/or third zone (3), and Circulating the fluid from the first outlet (13) of the fourth zone (4) to the first inlet (11) of the first zone (1), Wherein the fluid is circulated by: -compressing the feed (60) and the top recycle stream (40) using a compressor (400) to form a compressed fluid (50) -Subsequently cooling the compressed fluid (50) below the dew point of the compressed fluid using a cooling unit (5) to form a bottom recycle stream (10), and -Feeding the bottom recycle stream (10) to the first zone of the multi-zone reactor (8) via an inlet (11) for receiving the bottom recycle stream of the first zone, and Wherein the superficial gas velocity in the process is in the range of 0.5 to 5 m/s.
14. The process according to any one of claims 1-13, wherein the recovery of the recycle of step (d) is performed when the internal electron donor moiety content in the stream (10) is reduced to 5 ppm by weight or less.

Description

Method for switching between incompatible catalysts The present invention relates to a process for transitioning between incompatible polymerization catalysts. In particular, the present invention relates to a process for transitioning between olefin polymerizations using a first ziegler-natta catalyst to olefin polymerizations using a second ziegler-natta catalyst in a continuous polymerization process. It is often necessary to convert from one type of catalyst that produces polymers with certain characteristics and features to another catalyst that is capable of producing polymers of different chemical and/or physical properties. The transition between similar ziegler-natta catalysts or compatible catalysts is often easy to perform. Compatible catalysts are those catalysts which have similar termination and insertion kinetics of the monomer(s) and comonomer(s) and/or do not interact deleteriously with each other. However, when the catalysts are incompatible or of different types, the process is often complex. For example, when transitioning between two incompatible catalysts (e.g., a first Ziegler-Natta catalyst and a second Ziegler-Natta catalyst), it has been found that some components of the Ziegler-Natta catalyst can act as poisons for the second Ziegler-Natta catalyst. Thus, the components of the first Ziegler-Natta catalyst prevent the second Ziegler-Natta catalyst from promoting polymerization. Furthermore, particularly in continuous conversion processes, the interaction between two incompatible catalysts can result in the production of high levels of particles less than about 120 microns, which are referred to as "fines". Fines may cause operational problems and/or fouling and sheeting events in the reactor (SHEETING INCIDENT). In the past, to accomplish an efficient transition between incompatible catalysts, the first catalytic olefin polymerization process was stopped by various techniques known in the art. The reactor is then emptied, refilled, and a second catalyst is introduced into the reactor. Such catalyst conversions are time consuming and costly due to the need for an extended period of reactor shut down and the creation of off-grade materials during the conversion. There have been many attempts to improve the conversion process between incompatible catalysts. In order to inhibit polymerization of the first incompatible catalyst, the injection of catalyst into the reactor must be discontinued. Stopping the feed of the first catalyst to the reactor does not immediately stop the polymerization occurring within the reactor, as the fluidized bed contains catalyst particles which can still polymerize over an extended period of time. Even if the polymerization in the reactor is allowed to continue for a period of time, the catalyst in the reactor does not deactivate completely for a considerable period of time. Thus, in order to at least partially deactivate the first Ziegler-Natta catalyst, a polymerization inhibitor or catalyst deactivator (killer) is used. There are two general types of catalyst deactivators, reversible catalyst deactivators and irreversible catalyst deactivators. Reversible catalyst deactivators typically initially inhibit catalyst activity and polymerization for a period of time, but do not irreversibly deactivate the catalyst. In fact, after a period of time under normal polymerization conditions, the catalyst will reactivate and the polymerization will continue. These reversible catalyst deactivators may be used in any combination or order of introduction in the process. Irreversible catalyst deactivators irreversibly deactivate the ability of a catalyst to polymerize olefins. The use of catalyst deactivation and/or deactivators is disclosed in U.S. Pat. Nos. 5,442,019, 5,753,786 and 6,949,612B2 to Agapiou, et al, U.S. Pat. No. 5,672,666 to Muhle, et al, and U.S. Pat. No. 6,858,684B2 to Burdett, et al. It would be advantageous to provide a catalyst conversion process that does not require stopping the polymerization, purging the reactor to remove procatalyst and restarting the polymerization with another catalyst. In addition, it would be advantageous if the conversion process could reduce the amount of off-grade material produced during the conversion process, reduce the conversion time, increase the reliability and stability of the conversion process and avoid the need to open the reactor to load the seedbed. It would be further advantageous to provide a catalyst conversion process that prevents reactor fouling. It is an object of the present invention to provide a solution to the above and/or other problems. The present invention relates to a process for transitioning from a first ziegler-natta catalyst system to a second ziegler-natta catalyst system in a gas-phase olefin polymerization unit, Wherein the polymerization unit comprises a polymerization reactor (8) comprising at least one inlet (11) for feeding a reaction mixture (A) to the polymerization reactor, at l