Agitating – Stirrer within stationary mixing chamber – Rotatable stirrer
Reexamination Certificate
1998-12-07
2002-02-26
Cooley, Charles E. (Department: 1723)
Agitating
Stirrer within stationary mixing chamber
Rotatable stirrer
C366S329100, C422S135000, C422S226000
Reexamination Certificate
active
06350054
ABSTRACT:
TECHNICAL FIELD
The present invention relates to apparatus for mechanically stirring a quench-cooled subfluidized particulate bed of polymerized monomer during continuous vapor phase polymerization in horizontally disposed cylindrical polymerization reactors. More particularly, the invention is an improved apparatus for stirring polymer particles in reactive gas-filled polymerization reactors incorporating contiguous paddle stations on a coaxial drive shaft within the reactor with a plurality of sub-stations having lengths along the shaft.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 3,639,377 (Trieschmann et al.) describes polymerization of propylene which is carried out in the gas phase. In order that heat of polymerization should be effectively removed, excess monomeric propylene is introduced in liquid or partly liquefied form into the bottom of a vertically disposed cylindrical reaction zone. During polymerization, the fraction of unpolymerized propylene evaporates while absorbing the heat of polymerization. Evaporated propylene is removed from the reaction zone and condensed again outside the reaction zone. While stating that removal of heat according this system of internal cooling also causes intense mixing of the solid polymer powder with the gas phase, Trieschmann et al. state that it is particularly advantageous to use a reactor having a spiral stirrer. Referring to FIGS. 1 and 3 of U.S. Pat. No. 3,639,377, the stirrer appears to be illustrated as having a “U” shape and rotates on a vertical shaft through the bottom of vertical reactor
6
. Catalyst is pumped into the reactor through the top and polymer is discharged from the reactor by means of an external cyclone. Advantageous use of high activity catalysts in a continuous polymerization process requires, however, at least a plurality of the single-stage back-mixing reactor type described in Trieschmann et al.
U.S. Pat. No. 3,944,534 (Sennari et al.) describes gas-phase polymerization of an &agr;-olefin which is carried out in a reaction bed formed by circulation of particulate olefin polymer, caused principally by mechanical agitation to undergo circulation in the up-and-down directions within a substantially vertical-cylinder type reactor. The single-stage back-mixing reactor type described in Sennari et al. likewise is not suitable for use in a continuous polymerization process with high activity catalysts, because age of catalyst carried out of the reactor is substantially the same as the age of catalyst in a back-mixing reactor.
Vapor-phase polymerization of a polymerizable monomer or mixture thereof to produce normally solid polymer substances using a horizontal polymerization reactor containing a subfluidized particulate bed of polymerized monomer has been described in a number of patents including: U.S. Pat. No. 3,957,448 (Shepard et al.), U.S. Pat. No. 3,965,083 (Jezl et al.), U.S. Pat. No. 3,971,768 (Peters et al.), and U.S. Pat. No. 4,627,735 (Rose et al.), the disclosures of which are specifically incorporated herein in their entirety by reference. These U.S. Patents, assigned to the assignee of the present invention, describe polymerization processes and apparatus in which polymer is formed from gaseous monomer in horizontal stirredbed vessels.
In a single reactor, polymerization of monomer or mixture thereof from the vapor state is carried out by an essentially isobaric process typically using a high yield catalyst and cocatalyst. Typically, in operation of such processes and apparatus, particles of polymer are formed around solid catalyst particles.
The horizontally disposed reactor vessel has recycle gas, such as propylene, introduced into the bottom thereof. Typically, quench liquid, such as liquid propylene, is injected into the reactor from the top of the reactor.
Gases and vapors within the reactor vessel are free to circulate and mix together throughout the vapor space. For continuous production of some polymers, particularly copolymers, where it may be necessary to have different gas compositions at subsequent stages of polymerization, a series of two or more reactors is required.
Paddle wheels or other types of stirring vanes inside the vessel sweep through the bed of polymer particles and stir the contents of the vessel. The various types of stirring vanes include staggered paddles, inclined paddles, spiral vanes, or vanes provided with a scraper for scraping the internal wall of the reactor vessel.
Near one end (front end disposed opposite to a take-off end) of the horizontal vessel, a solid transition metal-containing catalyst component is injected at least one point into the top of the vessel, and an aluminum alkyl cocatalyst plus modifiers are injected at an adjacent the point at the top of the vessel.
Solid particles of polymerized monomer are created in the vessel and are withdrawn from the take-off end thereof. Particles of polymerized monomer build up in the stirred reactor and traverse the length of the reactor essentially because of polymerization in the bed and not by the agitator. Advantageously, this condition is ensured by the design of the agitator such as to provide for agitation, but not for significant backward or forward movement of the particles. Since a stirred bed is not in a fluidized condition, back-mixing of the particles of polymerized monomer in the horizontally disposed reactor vessel is limited. In contrast, solid particles in a fluidized bed are very well mixed. Even at commercially useful ratios of length to diameter, horizontal stirred-bed reactor systems can readily achieve a degree of mixing of solids equivalent to two, three, or more theoretical back-mix reactors. Thus, horizontal stirred-bed reactor systems are particularly advantageous, as compared fluidized-bed reactors, for direct production of polymers in a particulate no form.
It is desirable to create polymer particles as quickly as possible, and for this purpose a number of different high activity catalyst systems have been developed.
Use of solid, transition metal-based, olefin polymerization catalyst components is well known in the art including such solid components supported on a metal oxide, halide or other salt such as widely-described magnesium-containing, titanium halidebased catalyst components. Such catalyst components commonly are referred to as “supported.”
As is well known in the art, particulate polymers and copolymers may be sticky, i.e., tend to agglomerate, due to their chemical or mechanical properties or pass through a sticky phase during the production cycle. Sticky polymers also are referred to as non-free flowing polymers because of their tendency to compact into aggregates of much larger size than the original particles and not flow out of the relatively small openings in the bottom of product discharge tanks or purge bins. Polymers of this type show acceptable fluidity in a gas phase fluidized bed reactor, however, once motion ceases, the additional mechanical force provided by the fluidizing gas passing through the distributor plate is insufficient to break up the aggregates which form and the bed will not refluidize.
Although polymers that are sticky can be produced in non-gas phase processes, there are certain difficulties associated with the production of such products in, for example, slurry or bulk monomer polymerization processes. In such processes, the diluent or solvent is present in the resins exiting the reaction system at a high concentration leading to severe resin purging problems particularly if the material in question is a low molecular weight resin or a very low crystallinity resin. Environmental considerations are such that the dissolved monomers and diluent must be removed from the polymer prior to its exposure to air. Safety also dictates the removal of residual hydrocarbons so that closed containers containing the polymers will not exceed safe levels for volatiles in the gas head space over the resin. The safety and environmental concerns are accompanied by a definite economic factor in determining a preference for a quench-cooled, vapor-phase polymerizat
Lee James Hanawalt
Lin Chi-Hung
Wood Barry F.
BP Corporation North America Inc.
Cooley Charles E.
Kim Patrick J.
McDonald Scott P.
Oliver Wallace L.
LandOfFree
Agitator for a horizontal polymerization reactor having... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Agitator for a horizontal polymerization reactor having..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Agitator for a horizontal polymerization reactor having... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2978805