Start up methods for multiple catalyst systems

Details Start up methods for multiple catalyst systems Start up methods for multiple catalyst systems

1999-12-07

2002-04-16

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S078000, C526S079000, C526S090000, C526S119000, C526S348600, C526S348200, C526S348500, C526S901000, C526S905000

Reexamination Certificate

active

06372868

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to methods to introduce multiple catalysts into a gas or slurry phase reactor, particularly for start-up of the reactor.
BACKGROUND OF THE INVENTION
Lately in the art, there have been attempts to produce two polymers together at the same time in the same reactor using two different catalysts. For example, Mobil in PCT patent application WO 99/03899, discloses using a metallocene type catalyst and a Ziegler-Natta type catalyst in the same reactor to produce a bimodal molecular weight distribution (MWD) high-density polyethylene (HDPE). However, running two catalysts at once can be difficult and the start up of a multiple catalyst system can likewise be difficult. Therefore there is a need in the art for start-up procedures for running multiple catalyst systems.
U.S. Ser. No. 09/451,792 entitled
Solution Feed of Multiple Catalysts
, filed Dec. 1, 1999, pending discloses the use of multiple catalysts in gas and slurry phase to produce olefins.
U.S. Ser. No. 09/312,878 filed May 17, 1999 U.S. Pat. No. 6,271,325 filed Aug. 7, 2001 discloses a gas or slurry phase polymerization process using a supported bisamide catalyst.
SUMMARY OF THE INVENTION
This invention relates to methods to introduce multiple catalysts into a gas or slurry phase reactor comprising:
(a) introducing one or more olefins and a first catalyst and an activator into the reactor and allowing the olefins to polymerize,
(b) obtaining a polyolefin,
(c) combining a second catalyst and an optional activator with the first catalyst and activator and thereafter introducing the combination into the reactor and allowing the olefins to polymerize.
In an alternate embodiment step (b) comprises determining whether or not the polyolefin produced in step (a) is a desired polyolefin, and if it is not altering one or more reaction conditions and repeating this step (b).
In another embodiment this invention also relates to a method to introduce multiple catalysts into a gas or slurry phase reactor comprising introducing one or more olefins, a first catalyst and an activator, and a second catalyst and an optional activator into the reactor, wherein the all the catalysts and activators are combined together prior to being introduced into the reactor. In a preferred embodiment, catalysts and activator(s) are introduced into the reactor in a liquid, preferably a solution, slurry or emulsion.
For purposes of this invention a “catalyst” is a metal compound that polymerizes olefins alone or in combination with an activator. A “catalyst system” is the combination of a catalyst and an activator. The term “activator” is used interchangeably with the term “co-catalyst.”
DETAILED DESCRIPTION OF THE INVENTION
In additional embodiments, hydrogen is also introduced into the reactor during step (a). Preferably the hydrogen concentration present in the reactor or gas recycle stream is measured when the desired polyolefin of step (b) is produced and then the hydrogen concentration is not altered during step (c) to be more than 50% more or less than the concentration measured when the desired polyolefin of step (b) is produced. Preferably the hydrogen concentration is not altered during step (c) to be more than 40% preferably not more than 30%, more preferably not more than 20%, more preferably not more than 10% more or less than the concentration measured when the polyolefin of step (b) is produced.
In another preferred embodiment when the polyolefin produced during step (c) is not a desired polyolefin, then the ratio of the first catalyst to the second catalyst introduced into the reactor can be altered.
In another embodiment the method described above further comprises introducing a third catalyst (or more) and, optionally an activator into the reactor. This may optionally be done after determining whether the polyolefin produced in step (c) is a desired polyolefin and if it is not then altering one or more reaction conditions until the desired polyolefin is produced. In an alternate embodiment step (c) further comprises additional catalyst.
Start-Up Methods For Bimodal Systems Utilizing Solution Feed With Two Catalysts
Although the following examples discuss the production of polyethylene (PE) produced with multiple catalysts, preferably solution catalysts, the applicability to any polyolefin produced with more than two catalysts is also recognized. Typically, the polyolefins produced have broad, bimodal or multimodal molecular weight distributions (MWD's). The start-up procedures discussed below are also applicable to all polymerizable monomers and mixtures of such monomers such as propylene, ethylene/propylene, styrene and polar monomers.
In a preferred embodiment a catalyst system that is capable of producing polyethylene (preferably a bi-modal or broad MWD polyethylene) comprises two or more different catalysts where the catalysts have differing, preferably greatly differing, hydrogen and/or comonomer responses. One or more activators are generally also present in the system in order to activate the catalysts. Various activation and feed schemes examples are presented below. In preferred embodiments of the invention, a first catalyst produces a resin with a low molecular weight (this catalyst is referred to as the low molecular weight catalyst), whereas a second catalyst produces a resin with a high molecular weight (this catalyst is referred to as the high molecular weight catalyst). These catalysts coexist in the same reactor to produce a resin with an overall broad or bimodal molecular weight distribution. The multiple catalysts and/or activators are preferably combined together then introduced into the reactor.
The following reactor start-up techniques are described in relation to a solution catalyst feed system, but can be applicable to emulsion, slurry, liquid, powdered, and/or supported catalyst systems. The following start-up techniques are applicable to any of the activation and feed schemes presented below. The following methods are preferably used when the reactor is at a point where catalyst feed is ready to be initiated.
One problem that occurs with the operation of two resin components in the same reactor is that frequently the resin properties of one of the components needs to be fixed. For instance, many times the Melt Index (MI), which is an indirect measurement of the molecular weight, of the low molecular weight (LMW) resin is desired to be within a certain range. With two resin components being simultaneously formed in the same reactor, direct measurement of the LMW resin MI (or HMW resin Flow Index) is difficult. Often times catalyst poisons or analyzer shifts can cause a significant amount of resin to be produced with the wrong LMW or HMW properties.
Additionally one should also consider that when a gas phase reactor is first started, reaction rates come on slowly as an inventory of catalyst is built in the reactor. As may be expected, the residence time changes from start-up to steady state operation. For a bimodal catalyst system, the residence time or STY directly affects the final product properties, such as flow index (I
21
). This is believed to be because, in most cases, the catalyst kinetics are different. Additionally we have noted that catalysts with different kinetic constants and/or half-lives can, in combination with residence time effects, cause a shift in the polymer product made. To compensate, or more preferably control, these variations, on-line control to feed catalysts and/or activators into the reactor at differing rates and/or volumes is preferred.
In a preferred embodiment the multiple catalysts have identical or nearly identical kinetic behavior. In a preferred embodiment, the kinetic profiles or half-lives are within 50% or less of each other, preferably 40% or each other, preferably with 30% of each other, more preferably within 10% of each other.
In preferred embodiments, the following start-up methods may be used.
Method 1
A first start-up method applicable to a solution catalysts involves starting one catalyst and cocatalyst feed prior to s

Affiliated with

Also associated with

Rating

Start up methods for multiple catalyst systems does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Start up methods for multiple catalyst systems, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Start up methods for multiple catalyst systems will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2922324