Start-up process for gas phase production of polybutadiene

Details Start-up process for gas phase production of polybutadiene Start-up process for gas phase production of polybutadiene

1999-11-22

2001-07-03

Teskin, Fred (Department: 1713)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S153000, C526S164000, C526S151000, C526S190000, C526S340400, C526S901000, C526S912000, C526S335000

Reexamination Certificate

active

06255420

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to the production of high cis 1,4-polybutadiene in a gas phase polymerization of 1,3-butadiene. More particularly, the invention relates to a novel process for starting the gas phase polymerization of 1,3-butadiene that reduces or eliminates the induction period for the polymerization, makes the reaction more controllable, and/or reduces overall operation costs.
BACKGROUND OF THE INVENTION
The polymerization of one or more alpha olefins in a gas phase process using Ziegler-Natta catalysts has been practiced commercially for a long time. The polymers produced are considered to be crystalline and are granular, free-flowing and are non-sticky or “dry”.
More recently, the polymerization of ethylene-propylene rubbers (EPRs) such as ethylene-propylene-diene (e.g., ethylidene norbornene, ENB) have been successfully produced commercially in a gas phase process using a vanadium catalyst and an inert particulate material (e.g., carbon black) to maintain the bed of forming polymer in the fluidized state. The so-called “sticky ” polymers produced are amorphous, but otherwise granular, free-flowing, and non-sticky or appear “dry”.
Only most recently, it has been demonstrated that a third class of polymers can be produced by gas phase polymerization processes. However, these polymers have not as yet been produced commercially using a gas phase process. In these gas phase processes, high cis 1,4-polybutadiene can be produced by the gas phase polymerization of 1,3-butadiene using several catalyst systems, preferably in the presence of an inert particulate material such as carbon black and/or silica. See, for example, U.S. Pat. Nos. 4,994,534 and 5,453,471, as well as WO 96/04322 and WO 96/04323. In these processes significant amounts of liquid monomer (butadiene) are present in these gas phase polymerizations. The polymers produced are highly amorphous, granular, free-flowing, appear “wet” (that is they tend to want to clump together over time under certain conditions and develop characteristics of stickiness).
For the gas phase production of polybutadiene on a commercial scale, start-up and passivation procedures presently employed in the production of alpha olefin homo- and copolymers and EPR/EPDMs have not been effective. Such attempts have resulted in an unusually long induction period, difficulty in achieving reactor process control, wasted catalyst and co-catalyst, and an increase in undesirable side-reactions.
Accordingly, there is a need for an improved start-up and passivation process for the gas phase production of polybutadiene.
SUMMARY OF THE INVENTION
There is provided a process for starting a polymerization of butadiene to produce polybutadiene in a gas phase reactor which comprises (i) passivating the reactor and a seed bed by introducing a passivating compound selected from the group consisting of at least one an aluminum alkyl compound a dialkylzinc compound, and mixtures thereof having a concentration ranging from about 2,000 to 20,000 ppm based upon the total amount of polymer employed in the seed bed and (ii) feeding the catalyst and co-catalyst to the reactor before the addition of the butadiene.
DETAILED DESCRIPTION OF THE INVENTION
Commercially, in the gas phase polymerization of homo- and co-polymers of alpha olefins and EPR/EPDMs, a typical start-up for the Unipol™ process and reactor can include in order the following steps: (1) drying the reactor and seed bed; (2) passivating the seed bed; (3) adding the monomer(s); and finally (4) adding the catalyst and co-catalyst with subsequent reaction initiation. During reactor and seed bed preparation, the reactor is typically dried to 10 to 50 ppmv water or less in the reactor. This is followed by the addition of any aluminum alkyl including alkyl aluminum hydrides and chlorides. Preferred aluminum alkyls include, for example, triethylaluminum (TEAL), triisobutyl aluminum, triethylaluminum chloride, dibutylaluminum hydride, and aluminoxane “such as methyl aluminoxane (MAO) and modified methylaluminoxane (MMAO)”. to passivate the seed bed by removing remaining water and other impurities. In a most preferred embodiment, the aluminum alkyl employed as the cocatalyst is employed to passivate the reactor and bed. However, when an aluminoxane is used as the cocatalyst typically a different aluminum alkyl is used for passivation because of cost considerations.
After purging the reactor at least once to remove the byproducts of the passivation step, monomer(s) is added to the reactor and increased gradually to normal operating levels and, when desired, inert particulate material is added. Lastly, the catalyst and co-catalyst is fed into the reactor. The onset of polymerization typically occurs within 1 to 3 hours after addition of the catalyst system and is referred to as the induction period.
However, when the above-described start-up and passivation is employed for the reactor system for the polymerization of 1,3-butadiene to form high cis 1,4-polybutadiene, initiating the reaction under controlled conditions was difficult. An induction period of 4 to 7 hours was observed before reaction commenced, despite the feeding of monomer, catalyst, and co-catalyst. When polymerization did begin, it often progressed at a decelerated rate until the rate of reaction approached the monomer feed rate. This delay or induction period caused reactor process control difficulties such as unwanted side reactions and resulted in wasted catalyst and co-catalyst. For example, the 1,3-butadiene underwent dimerization to form 4-vinylcyclohexane (VCH), which poisoned the catalyst, especially at the temperatures used for polymerization (e.g., 50 to 80° C.). Minimizing the time that 1,3-butadiene spends in the reactor at the reaction temperature decreases the amount of dimerization that can occur.
The start-up process of the present invention reduces the induction period, employs less catalyst and co-catalyst, and minimizes or avoids unwanted dimerization.
In the start-up/passivation process of the invention, butadiene is polymerized to produce polybutadiene in a gas phase reactor after the reactor and seed bed have been passivated. This is accomplished by introducing a passivating agent selected from the group consisting of an aluminum alkyl, a dialkyl zinc compound, or mixture thereof, in a concentration ranging from about 2,000 to 20,000 ppm, preferably about 4000-8000 ppm, based upon the total amount of polymer used in the seed bed (that is, the total polymer in the seed bed prior to start-up). Secondly, the catalyst and co-catalyst are fed to the reactor before the addition of the butadiene.
In a preferred start-up/passivation process, the reactor and seed bed is dried such that there remains only about 10 to 50 ppm water. This is followed by the addition of the 2,000 to 20,000 ppm of the aluminum alkyl, the dialkylzinc compound, or a mixture thereof employed in passivation. Then catalyst and co-catalyst is added in sufficient concentration ranging from 25-70 ppm metal for catalyst, preferably 45-60 ppm metal; and ranging from 15000-25000 ppm for aluminum alkyl, preferably 17000-19000 ppm aluminum alkyl. The catalyst and co-catalyst are pre-fed to the reactor before the monomer. The monomer (butadiene) is introduced last.
By passivating with higher levels of aluminum alkyl or dialkylzinc compound and introducing the monomer last to the reactor, the induction period is reduced to about 30 to 60 minutes. That is, 30 to 60 minutes after the monomer is added to the reactor, polymerization commences. The introduction of the catalyst and cocatalyst before adding the monomer additionally ensures that the undesirable dimerization side-reaction is greatly diminished. And since this side-reaction is no longer taking place, the amount of catalyst and co-catalyst employed in the polymerization is decreased, making the overall process more cost effective.
In the invention, the alkyl aluminum used for passivation can be represented by the formula R
3
Al wherein each R can be the same or different and is an alkyl radical

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