Process for reducing polyolefin die smoke

Polyolefin polymer powder containing active catalyst residues is deactivated by (1) purging with an inert gas containing water vapor and (2) then contacting such powder with a gas mixture containing an inert gas, water vapor, and a third component selected from the group consisting of oxygen, carbon monoxide, carbon dioxide, C.sub.1 -C.sub.4 alcohols and C.sub.2 -C.sub.4 alkeneoxides.

BACKGROUND OF THE INVENTION 
This invention relates to olefin polymerization and more particularly 
relates to deactivating catalyst residues and to removal of the volatiles 
and oligomers from polyolefins, especially polypropylene. 
In production of high molecular weight, solid, polyolefins, typically low 
molecular weight volatile species such as oligomers also are produced. If 
high levels of oligomeric materials remain in the polymer, problems 
typically are encountered when the polymer is used in commercial molding 
machines in that excessive smoke, referred to as "die smoke", is produced. 
Also in the manufacture of polyolefins, especially propylene polymers, 
catalyst residue remains in the polymer after polymerization. This residue 
typically must be deactivated in order to avoid polymer corrosivity. 
The invention described herein presents a method which effectively 
deactivates polymerization catalyst residue, while minimizing die smoke in 
subsequent polymer processing. 
SUMMARY OF THE INVENTION 
Polyolefin polymer powder containing active catalyst residues is 
deactivated by (1) purging with an inert gas containing water vapor and 
(2) then contacting such powder with a gas mixture containing an inert 
gas, water vapor, and a third component selected from the group consisting 
of oxygen, carbon monoxide, carbon dioxide, C.sub.1 -C.sub.4 alcohols and 
C.sub.2 -C.sub.4 alkeneoxides. The resulting polymer exhibits reduced die 
smoke when processed. 
BRIEF DESCRIPTION OF THE INVENTION 
Polymers may be formed in a solution or a slurry in a suitable solvent or 
diluent, typically a liquid hydrocarbon such as hexane or heptane. 
Alternatively polymerization may occur in bulk liquid monomer, for 
example, liquid propylene, or may occur in the vapor phase. It has been 
found that if a polyolefin such as polypropylene is formed in bulk or in 
vapor phase the amount of oligomeric-type material left in the polymer is 
increased over the amount present in solution or slurry-phase products. 
Thus the invention disclosed herein is most suitable to bulk or vapor 
phase polymerization processes. 
Oligomeric-type material present in a polypropylene resin may be attributed 
to several causes. Oligomers may be formed during polymerization as 
non-stereospecific polymers or as a result of fast chain terminations and 
transfers. Also propylene monomer may be trapped inside polymer powder 
which may undergo polymerization during a catalyst deactivation step. 
Further, oligomers may form as degradation products during catalyst 
deactivation or during molten-phase polymer processing. The present 
invention is directed to reducing oligomer production related to trapped 
monomer and polymer degradation. 
Although other methods have been tried to reduce die smoke such as a 
single-stage treatment with an "inert" gas (e.g. nitrogen, water vapor, 
noble gas hydrogen, paraffinic gas) at elevated temperatures below the 
polymer softening point, and incorporation of additives such as Group IA 
and IIA metal oxides, stearates, pelargonates, carbonates, bicarbonates, 
bisulfates and hydroxides, the two-stage method of the present invention 
exhibits advantages in effectiveness of deactivation and oligomer removal. 
In the method of this invention undeactivated polyolefin powder first is 
purged with an inert gas, such as nitrogen, at a temperature ranging from 
about 180.degree. F. to about 10.degree. F. below the polymer softening 
point typically for about 10 to about 90 minutes, then contacted with a 
gas stream containing an inert gas, water vapor and a third component 
selected from the group consisting of oxygen, carbon monoxide, carbon 
dioxide, a C.sub.1 -C.sub.4 alcohol and a C.sub.2 -C.sub.4 alkene oxide at 
a temperature ranging from about 180.degree. F. to about 10.degree. F. 
below the softening point of the polymer for about 10 to about 120 
minutes. 
In more detail our invention is a process of deactivating polymer powder 
containing "live" catalyst residues in a two-stage operation. The first 
stage comprises purging the live polymer powder with a gas inert to the 
conditions used, such as nitrogen, which contains water vapor. Typically, 
the polymer powder is treated with wet nitrogen in a fluidized bed, 
although other batch or continuous contact means can be used. Contact time 
in the first stage typically is about 10 to about 90 minutes and 
preferably about 30 to about 60 minutes at an operating temperature of 
about 180.degree. F. to about 10.degree. F. below the polymer softening 
point with the gas mixture having a maximum dew point about 20.degree. F. 
below the operating temperature. Typically the dew point is about 
40.degree. to about 150.degree. F. which corresponds to about 0.5 to about 
20 wt.% water vapor content. 
After the live polymer powder is purged with wet inert gas in the first 
stage, the powder is transferred to a second stage and treated, batchwise 
or continuously, with a stream of inert gas (usually nitrogen), water 
vapor, and a third component such as oxygen, carbon monoxide, carbon 
dioxide, C.sub.1 -C.sub.4 alcohol or C.sub.2 -C.sub.4 alkeneoxides. Oxygen 
is preferred. The third component is present in the gas mixture at about 
0.01 to 10 vol.% and preferably about 0.05 to 6 vol.%. The dew point of 
the gas mixture typically is maintained at about 20.degree. F. below 
operating temperature. The operating temperature is maintained between 
about 180.degree. F. to about 10.degree. F. below the softening point of 
the polymer. For polypropylene homopolymer it has been found that the 
preferable temperature is about 240.degree. F. or below. Typical contact 
time in the second stage is about 10 to 120 minutes and preferably is 
about 15 to 30 minutes. The preferable deactivation reactor for the second 
stage is a fluidized bed. 
The polyolefin most useful in this invention is propylene polymer, that is 
propylene homopolymer and copolymers of propylene containing minor amounts 
of ethylene or other copolymerizable alpha-olefins. Other polyolefins in 
which catalyst deactivation and removal of oligomers is necessary also can 
be used. Such polyolefins typically are prepared by contacting an olefin 
monomer with a catalyst comprising a transition metal compound, such as a 
titanium compound, usually a titanium trihalide, and an aluminum alkyl. 
Other substances can be present in minor amounts as catalyst modifiers. 
The catalyst useful in olefin polymerization system from which powder can 
be deactivated according to this invention contains (1) an organoaluminum 
compound and (b) a transition metal compound. 
Useful organoaluminum compounds include trialkylaluminum, dialkylaluminum 
halides, mixtures of trialkylaluminum with dialkylaluminum halides and 
mixtures of trialkylaluminum with alkylaluminum dihalides. Also catalytic 
effective amounts of mixtures of trialkylaluminum and dialkylaluminum 
halides can be used in conjunction with alkyl aluminum dihalides. Useful 
halides include bromides and chlorides and useful alkyl radicals contain 
from two to about six carbon atoms. The preferable halide is chloride and 
the preferable alkyl radical is ethyl. Diethylaluminum chloride (DEAC) is 
most preferable in propylene polymerizations. In a 
trialkylaluminum-dialkylaluminum halide mixture, the preferred amount of 
trialkylaluminum is about 20 to 50 mol percent. In a 
trialkylaluminum-alkylaluminum dihalide mixture, the preferred amount of 
trialkylaluminum is about 30 to 70 mol percent and most preferably about 
40 to 60 mol percent. 
The transition metal compounds useful as a component in the catalyst system 
of this invention are compounds of transition metals of Group IVB, VB and 
VIB of the Periodic Table. Preferably, the transition metal compound is a 
halide of titanium, vanadium, chromium or zirconium. Most preferably, 
titanium trichloride and especially activated titanium trichloride is used 
for propylene polymerizations. Titanium trichloride can be activated to a 
high degree of polymerization activity by chemical and physical means. One 
activated titanium trichloride has an approximate stoichiometric formula 
of TiCl.sub.3.1/3AlCl.sub.3 and has been comminuted. Further, titanium 
trichloride can be activated by forming adducts with Lewis bases such as 
ethers or by supporting the titanium trichloride on a catalytically inert 
substance such as a metal oxide or salt. One suitable titanium trichloride 
is described in U.S. Pat. No. 3,984,350 incorporated by reference herein. 
The molar ratio of transition metal halide to organoaluminum compound in a 
catalyst system can range from about one-tenth to about 10, typically is 
about 1 to 3 and preferably is about 2. The amount of catalyst in a 
polymerization depends on the reactor size and type and on the amount and 
type of olefin monomer and is known to the skilled artisan. 
Catalyst additives can be added in minor amounts such as disclosed in U.S. 
Pat. Nos. 3,950,268 and 4,072,809 incorporated herein by reference. 
Gas phase reactor systems include both stirred bed reactors and fluidized 
bed reactor systems. Examples of such reactor systems are described in 
U.S. Pat. Nos. 3,957,448, 3,965,083, 3,971,768, 3,970,611, 4,129,701, 
4,101,289, 3,652,527, and 4,003,712 all incorporated by reference herein. 
Typical gas phase olefin polymerization reactor systems comprise a reactor 
vessel to which olefin monomer and catalyst components can be added and 
which contain a bed of forming polymer particles. Typically, catalyst 
components are added together or separately through one or more 
valve-controlled ports in the reactor vessel. Olefin monomer, typically, 
is provided to the reactor through a recycle gas system in which unreacted 
monomer removed as off gas and fresh feed monomer are mixed and injected 
into the reactor vessel. A quench liquid can be added to polymerizing 
olefin in order to control temperature. 
If polymer powder is produced in a bulk polymerization process, excess 
monomer should be removed, such as by flash drying, before deactivation 
according to this invention.

This invention is demonstrated, but not limited, by the following Examples. 
EXAMPLES I-III 
Samples of polypropylene powder produced by gas-phase polymerization 
containing active ("live") catalyst residues were deactivated in a 
bench-scale fluid bed apparatus comprising a vertical cylindrical chamber 
four inches in diameter and eight inches high equipped with a gas inlet at 
the bottom and a vent at the top. Nitrogen gas and distilled water were 
blended at metered flow rates to give a desired flow rate and dew point, 
passed through a heater, and then injected into the bottom of the fluid 
bed apparatus. 
Before conducting a deactivation experiment, approximately 350 grams of 
live polypropylene powder was charged to the fluid bed apparatus and flow 
rate, dew point and temperature stabilized at desired levels. Typically, 
polymer powder bed temperature was maintained at 200.degree.-280.degree. 
F. and nitrogen flow rate maintained at 2.5-3.5 SCFM. In conducting a 
deactivation experiment a sample of live powder was charged to the fluid 
bed after which time the bed temperature dropped sharply and then returned 
gradually to the initial temperature. After maintaining the powder at the 
stabilized temperature for about 1 hour, the powder was allowed to cool to 
about 120.degree. F. and then removed and evaluated for die smoke. 
Deactivated polypropylene powder was tested for die smoke by observing die 
smoke while powder and stabilizers were extruded. Deactivated powder 
blended with 0.1 wt.% BHT, 0.1 wt.% Q 328 (trade name for an antioxidant 
and process stabilizer sold by Argus Chemical Company), and 0.05 wt.% 
calcium stearate were extruded in a 11/4 inch Killian single-screw 
extruder maintained at a 425/450/475/500.degree. F. temperature profile at 
a rate of about 10 pounds per hour. Photographs were taken of smoke coming 
from the top of the die head and visually rated as none, very light, 
light, light-moderate, moderate, moderate-heavy, heavy and very heavy. 
A series of experiments was performed to demonstrate the usefulness of our 
invention. In the first experiment (Run A) live polypropylene powder was 
deactivated in the described fluid bed apparatus for 60 minutes with wet 
nitrogen. After testing, the die smoke associated with the resulting 
deactivated product was rated as moderate. In the second and third 
experiments (Examples I and II) live polypropylene powder was treated with 
wet nitrogen in the fluid bed for 30 minutes followed by treatment with a 
mixture of wet nitrogen and 5% oxygen. Die smoke from these products was 
rated light-moderate and light respectively. 
Similarly, in another set of experiments using lower deactivation 
temperatures a product deactivated with only wet nitrogen (Run B) gave a 
die smoke rating of light-moderate, while a product treated with a mixture 
of nitrogen and oxygen (Example III) yielded a smoke rating of light. The 
results of these experiments are summarized in the Table. 
Polypropylene powder used in these experiments was produced in a gas phase 
reactor system similar to that described in U.S. Pat. No. 3,965,083. A 
cylindrical reactor vessel of approximately 8 inches in diameter and 24 
inches in length was equipped with three recycle gas nozzles spaced 
equidistantly along the bottom of reactor and three liquid quench nozzles 
spaced equidistantly along the top of the reactor. The reactor is equipped 
with an off gas port for recycling reactor gas through a condenser and 
back through a recycle gas line to the recycle gas nozzles in the reactor. 
During reactor operation polypropylene powder was produced in the reactor 
bed, flowed over a weir, and discharged through a powder discharge system 
into a secondary closed vessel blanketed with nitrogen. Powder was 
collected from the secondary vessel. Polymerization temperature and 
pressure were maintained at 160.degree. F. and 300 psig respectively. 
Chemically activated titanium trichloride obtained from Solvay & Cie and 
diethylaluminum chloride in hexane solution were introduced into the 
reactor as catalyst components as two streams. 
TABLE 
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Deactivation 
Conditions Run A Ex. I Ex. II 
Run B Ex. III 
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First Stage 
Gas Components 
Nitrogen (wt. %) 
92 92 92 92 92 
Water Vapor (wt. %) 
8 8 8 8 8 
Dew Point (.degree.F.) (1) 
120 120 120 120 120 
Time (minutes) 
60 30 30 60 30 
Temperature (.degree.F.) 
265 265 265 240 240 
Second Stage 
Gas Components 
Nitrogen (wt. %) 
-- 87 87 -- 87 
Oxygen (wt. %) 
-- 5 5 -- 5 
Water Vapor (wt. %) 
-- 8 8 -- 8 
Dew Point (.degree.F.) (1) 
-- 120 120 -- 120 
Time (minutes) 
-- 15 25 -- 20 
Temperature (.degree.F.) 
-- 265 210 -- 240 
Die Smoke Rating (2) 
M L-M L L-M L 
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(1) At a 120.degree. F. dew point, gas contains 8 wt. % water vapor. 
(2) L = light; L-M = light-moderate; M = moderate