Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1998-06-16
2001-04-10
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C528S483000
Reexamination Certificate
active
06214903
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a post-reactor process for treating or handling polymers prepared in a gas phase polymerization in the presence of an inert particulate material. More particularly, the invention relates to a process for treating such elastomers so that fines are reduced and the elastomer is more robust during subsequent processing. The invention also relates to a process for treating such elastomers to remove residual monomers and dienes as well as to adequately neutralize and stabilize residual catalyst by-products to prevent product degradation.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,994,534 discloses the polymerization of sticky polymers (also referred to as elastomers) in a gas phase fluidized bed reactor at or above their softening or sticking temperature in the presence of an inert particulate material (carbon black, silica, talc, clay, and the like). U.S. Pat. No. 5,304,588 teaches that the polymer produced using this process produces a unique, non-sticky elastomeric resin particle having an outer shell composed mostly of inert particulate material (e.g., carbon black) and an inner core composed mostly of polymer. In contrast to bale-form sticky polymer produced in solution and slurry polymerizations in the absence of inert particulate material, the gas phase-produced elastomer particles are granular and free-flowing as they exit the reactor and require no post-reactor pulverizing or grinding prior to their introduction into end-use applications. The elastomer is obtained in particle form with an average particle size ranging from about 0.015 to 0.06 inches.
In contrast to other gas phase reactor produced polymers (e.g., homo- and co-polymers of ethylene and/or propylene), it has been discovered that the post-reactor handling of these elastomers is difficult. That is, other non-elastomeric gas phase reactor products require only mild treatment to remove unreacted monomers and other inert hydrocarbons dissolved in the polymer. Their low catalyst residues are readily deactivated by means of additives and do not require an extraction step.
However, gas phase produced elastomers having inert particulate material incorporated in and/or on them are more difficult to treat post-reactor because they can contain one or more dienes and inert particulate materials incorporated in the polymer matrix. For example, a sticky polymer or elastomer produced in the gas phase is much more difficult to treat post-reactor since the diene component (1) has pendant double bond is capable of cross-linking, (2) is a flammable hydrocarbon, (3) can have an unpleasant odor with a very low human detection threshold, (4) is expensive making re-use critical, (5) takes 6 to 10 times longer to desorb than do the other monomers (e.g., C
2
and C
3
) under equivalent processing conditions. Further, post-reactor side-or by-product reactions can cause odor requiring stabilization and/or purging.
Also, it has now been discovered that the elastomeric polymer polymerized using an inert particulate material can produce fines due to inert particulate material not securely or firmly incorporated in the elastomer product. Fines are particles of inert particulate material and/or particles composed of inert particulate material and small quantities of polymer having an average diameter of less than 100 &mgr;m. These fines can foul downstream processing equipment (e.g., pipes, valves, feeders, etc.) resulting in a production shutdown. Accordingly, unlike other polymers produced in the gas phase in the absence of inert particulate material, these elastomers, though rendered granular, non-sticky, and free-flowing by the above-described gas phase polymerization process utilizing inert particulate materials, now require some unique post-reactor processing in order to prevent and/or minimize the presence of fines and/or to improve the robustness of the polymer particle for intact survival during subsequent processing and end-use applications.
Additionally, elastomeric polymers are prone to gel formation due to the existence of residual diene, chloride by-products of the co-catalyst and promoter. Further, elastomeric diene based products can undergo free-radical-initiated degradation, transition-metal-catalyzed degradation, and/or acid-catalyzed degradation or other undesirable post-side reactions. Hence, there is a need to properly treat these elastomeric polymers upon exiting the polymerization reactor to prevent or minimize gel formations and to stabilize and/or prevent post-side reactions prior to packaging the final polymeric product.
Therefore, there is an on-going need for improved materials handling of these polymers upon leaving a gas phase polymerization reactor.
SUMMARY OF THE INVENTION
Accordingly, there is provided an improved post-reactor process for improving the robustness of a polymer particles containing at least 0.3 wt % of an inert particulate material. The process comprises introducing the polymer containing at least 0.3 wt % of the inert particulate material into a fluidized polishing vessel wherein the polymer containing inert particulate material is fluidized using an inert gas; the temperature of the polymer ranges from about 20 to 100 degrees C; the temperature of a fluidizing gas ranges from about 20 to 150 degrees C; the pressure in the polishing vessel ranges from about 2 psi to 50 psi; and the average residence time for the polymer containing inert particulate material ranges from about 15 minutes to 8 hours. Preferably, the superficial gas velocity ranges from about 0.6 to 3 ft/sec and the temperature of the polishing vessel ranges from about 50 to 100 degrees C.
Also, in another preferred embodiment of the invention, the elastomeric material is treated in the fluidized polishing vessel to prevent/minimize gel formation by injecting a gel inhibitor such as an alcohol (C
1
-C
20
alcohol) proportional to the amount of alkyl (i.e., for example, aluminum alkyl from the cocatalyst) used in the polymerization reaction. The molar ratio of alcohol-to-alkyl is about 0.5:1 to 6:1.
In still another preferred embodiment of the invention, the elastomeric material in the fluidized polishing vessel is contacted with a stabilization package.
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Eisinger Ronald Steven
Hussein Fathi David
Jones David Nunn
Raether Ronald Irvin
Rebhan David Merrill
Brown R. C.
Leuzzi P. W.
Michl Paul R.
Union Carbide Chemicals & Plastics Technology Corporation
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