Control of solution catalyst droplets

Details Control of solution catalyst droplets Control of solution catalyst droplets

2000-12-05

2002-05-21

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...

C526S086000, C526S068000

Reexamination Certificate

active

06391986

ABSTRACT:

TECHNICAL FIELD
This invention is concerned with controlling polymerization process parameters through catalyst droplets used in the process.
BACKGROUND INFORMATION
The gas-phase polymerization of olefins in fluidized bed reactors with catalysts in liquid form is well known. In such systems, resin particle size can be controlled by spraying the liquid catalyst in droplet form into a zone which is substantially free of resin (a particle-lean zone). This process allows a brief period of time for the spray droplets to undergo evaporation and solidify before contacting the polymer particles already in the reactor thus reducing the tendency for the droplets to adhere to the already formed particles and form agglomerates. One solution for the problem of agglomerates is described in U.S. Pat. No. 6,075,101 and is accomplished by using a perpendicular spray nozzle together with other process conditions.
Spraying a solution-borne catalyst into a fluidized bed reactor offers significant operational versatility. Because the spray droplets travel at very high speeds, about 150 to 200 feet per second, the droplets must, as noted above, become solid particles within a very short time to avoid the formation of agglomerates. There are a number of factors that influence spray efficiency such as spray nozzle design, shroud design, and liquid and gas flow rates, and most of these factors have been considered. Industry, however, is constantly trying to improve the efficiency of catalyst spray systems and the polymerization processes in which they are used.
DISCLOSURE OF THE INVENTION
An object of this invention, then, is to provide a polymerization process serviced by a more efficient liquid catalyst spray delivery. Other objects and advantages will become apparent hereinafter.
According to the present invention, such a process has been discovered. The process, carried out in the gas phase, comprises contacting one or more olefins with a catalyst system containing a carrier gas and a mixture of solids comprising a transition metal compound or complex and a liquid organic solvent, under polymerization conditions, in a fluidized bed reactor containing resin particles in a fluidized state with the provisos that (a) the mixture of solids and solvent contains at least about 95 percent by weight solids and (b) the mixture is sprayed with the carrier gas into a particle-lean zone, or the fluidized bed, of the reactor.
In a more particular embodiment, the process carried out in the gas phase comprises contacting one or more olefins with a catalyst system containing a carrier gas and a mixture of solids comprising a transition metal compound or complex and a liquid organic solvent, under polymerization conditions, in a fluidized bed reactor containing resin particles in a fluidized state with the following provisos:
(a) the catalyst system is first introduced into one or more nozzles, each having an inlet at one end and an exit tip at the other end, said nozzles being adapted to convert the catalyst system into droplets and spray the droplets into the fluidized bed reactor;
(b) the temperature of the catalyst system, as introduced into each nozzle, is in the range of about minus 20 to about 120 degrees C. (preferably about 0 to about 30 degrees C.);
(c) the weight ratio of the carrier gas to the solvent, as introduced into each nozzle, is in the range of about 0.15:1 to about 20:1;
(d) the weight ratio referred to in proviso (c) is adjusted to provide a temperature in the nozzle and at the tip of each nozzle at about the dew point of the solvent;
(e) the temperature provided in proviso (d) is such that the droplets formed at the tip of the nozzle contain at least about 95 percent by weight solids; and
(f) the droplets are sprayed from the nozzle into a particle-lean zone, or the fluidized bed, of the reactor.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
The term “essentially solids” is defined as the mixture of solids and solvent or the droplet containing at least about 99 percent solids. This mixture can also be referred to as “dry”. It's noted that when an aluminoxane cocatalyst is included, the solids become viscous and appear glassy or gelatinous. The term “at about the dew point of the solvent” is the dew point of the solvent plus or minus about 5 degrees C.; the higher the temperature within the range, the greater the solids content. Thus, at the superheated temperature of dew point plus 5 degrees C., the mixture of solids and solvent is essentially solids or dry. The term “solvent” includes the conventional liquid organic solvents mentioned below and any other organic liquids, e.g., 1-hexene, which are included in the catalyst system, and are introduced into, and can be vaporized in, the nozzle or injection tube.
The “particle-lean zone” is defined as follows: a section of the reactor which normally does not contain the fluidized bed, such as the disengaging section, the gas recirculation system, or the area below the distributor plate; or a section of the reactor which normally would contain the fluidized bed such as a region in which the polymer resin particle density is, for example, at least 2 times lower, preferably about 5 times lower, and most preferably about 10 times lower than that in the fluidized bed. This region is created by deflecting resin away from the catalyst spray with a stream of gas. Methods for creating a particle-free zone and spraying catalyst are described in U.S. Pat. Nos. 5,693,727 and 5,948,871. In a preferred embodiment, the catalyst in a carrier gas such as nitrogen, argon, an alkane, or mixtures thereof is surrounded by a least one gas which serves to move or deflect resin particles in the bed out of the path of the catalyst as it enters the fluidization zone and away from the area of catalyst entry thereby providing a particle lean zone. In a particularly preferred embodiment, the catalyst in the carrier gas is surrounded by at least two gases, the first gas serving primarily to deflect resin particles of the bed out of the path of the liquid catalyst and the second primarily prevents the catalyst injection tube or nozzle tip from getting clogged. The catalyst delivery system comprises a particle-deflecting tube (also known as a plenum) enclosing an optional tip-cleaning tube (also known as a support tube or catalyst support tube) which in turn encloses a catalyst injection tube. Each of these tubes contain a gas, which can act as a particle deflector. The gas in the tip-cleaning tube can, by itself, function as a particle-deflector. When the catalyst in the carrier gas is surrounded by two gases, the catalyst is considered to be shrouded. Preferably, the particle-deflecting plenum gas can be all or a portion of the recycle gas and the tip-cleaning gas can be all or a portion of one or more of the monomers (e.g., ethylene or propylene) employed in the process.
Methods for controlling the temperature of the droplets are numerous and varied ranging from presaturating the carrier gas with the most volatile component of the catalyst solution to passing the entire spray mixture from which the droplets are created through a heat exchanger prior to exiting the spray nozzle. In addition, the temperature of any or all of the components of the spray mixture can be individually controlled prior to mixing. Examples of such components include the activated or unactivated transition metal compound or complex in solution, make-up solvent, and the carrier gas. It is noted that a vaporized solvent could be used as a substitute for the carrier gas.
Another way to control the temperature of the droplets is to control the temperature of the “support tube” or “plenum” gas, i.e., gas flows surrounding the injection nozzle that are typically used to keep resin particles away from the nozzle tip or to help create a particle-lean zone into which the droplets are sprayed. These gases not only change the temperature of the immediate environment of the droplets, but can also affect the temperature of the liquid catalyst system in the nozzle or injection tube if it is in thermal contact wit

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