Horizontal agitator

Abstract

The invention is an improved apparatus for continuously stirring polymer particles in reactive gas-filled polymerization reactors incorporating contiguous paddle stations on a coaxial drive shaft wherein the drive shaft is driven by a hydraulic motor.

Description

BACKGROUND OF THE INVENTION[0001]1. Technical Field[0002]The present invention an improved apparatus for stirring polymer particles in reactive, polymerization reactors incorporating a hydraulic motor on a coaxial drive shaft within the reactor.[0003]2. Description of the Prior Art[0004]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.[0005]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...

AI Technical Summary

Benefits of technology

The invention is a new and improved apparatus for stirring polymer particles in reactive gas-filled polymerization reactors. The apparatus includes a coaxial drive shaft with paddles that sweep through a cylindrical zone within the reactor to mechanically stir the polymer particles. The process also includes using a hydraulic motor to drive the stirring means and providing two or more classes of paddle stations along the drive shaft with sub-stations and sub-station paddles to sweep through a sub-section of the cylindrical zone within the reactor. The technical effect of this invention is an improved process for polymerization in which the polymerization reaction is more efficiently and evenly stirred, resulting in higher quality polymer.

Problems solved by technology

The single-stage back-mixing reactor type described in Sennari et al. 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.

Since this stirred bed is not in a fluidized condition, back-mixing of the particles of polymerized monomer in the horizontally disposed reactor vessel is limited.

The larger the reactor, the more difficult it is to maintain homogeneous fluidization and stirring throughout the entire volume of the fluidized bed.

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.

The low number of moving parts and the relative lack of complexity in a basic subfluidized bed process enhances the operability of the process and typically results in lower costs of production.

Such lumps and strings tend to hang-up or become trapped in transfer equipment and can even plug lines and valves.

One problem with known polymerization processes and apparatus using a vapor-phase polymerization system, is that lumps and strings of resin can form in a quench-cooled subfluidized particulate bed of polymerized monomer without reliable, continuous and accurate methods for mechanical stirring.

Such sticky polymers are difficult to maintain in granular or particulate forms during polymerization, particularly where high rates of production are desired.

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