Method for product recovery of polyolefins

A method for product recovery method of polyolefins, particularly high-molecular-weight amorphous poly alpha-olefins, wherein the use of water during the method is significantly decreased and wherein the intermediate stage of storing and drying the chunk form of the polyolefin is eliminated. Polyolefins produced in a reactor are heated in a kneader to remove any unreacted monomer(s). The polyolefin material in a liquid form is then transferred directly to an extruder to further remove any unreacted monomer(s) and catalyst(s). Finally, the polyolefin material is pelletized using a pelletizer.

TECHNICAL FIELD 
The present invention relates to methods for product recovery of 
polyolefins, and more specifically to a method of product recovery for 
high-molecular-weight amorphous poly alpha-olefins. 
BACKGROUND OF THE INVENTION 
High-molecular-weight amorphous poly alpha-olefins such as amorphous 
propylene homo- and co-polymers, are important for their use in diverse 
products. The broad utility of these materials is due in large part to the 
unique combination of chemical and physical properties such as chemical 
inertness, softness, flexibility, etc., exhibited by these materials. 
Conventionally, amorphous polyolefins are formed in a reactor and mixed 
with water to deactivate catalysts and remove any monomer(s). Removing the 
catalysts and any monomer(s) renders wet, granular chunks of the product. 
For the material to be shaped into various products, the chunks must be 
dried and then extruded or otherwise shaped. 
Extrusion of the material typically involves feeding the dried chunks from 
a hopper to the feed section of a screw-type extruder. The polyolefin 
material is moved through the extruder by screw flights where it is heated 
and mechanically worked before it is pelletized or otherwise shaped under 
high pressure. Alternatively, such materials are also shaped by other high 
temperature methods such as injection molding, roll milling and 
compression molding. Both lower- and higher-molecular-weight amorphous 
poly alpha-olefins are typically processed as outlined above. 
However, existing methods of product recovery require the introduction of 
water to carry the material through the several stages of recovery. The 
extensive use of water by these methods requires that additional storage 
tanks, delivery and removal lines and other miscellaneous equipment be 
used to introduce, maintain, remove and recycle the necessary volume of 
water. Additionally, existing methods store the material in a chunk form 
prior to extrusion into useable products, thus requiring additional 
storage tanks and associated maintenance equipment for this intermediate 
stage of processing. 
Thus a need has arisen for a product recovery method for polyolefins, 
particularly high-molecular-weight amorphous poly alpha-olefins, wherein 
the use of water during the product recovery is significantly decreased 
and wherein the intermediate stage of storing and drying the chunk form of 
the polyolefin is eliminated. 
SUMMARY OF THE INVENTION 
The present invention overcomes the foregoing and other problems associated 
with the prior art by providing a product recovery method for polyolefins, 
particularly high-molecular-weight amorphous poly alpha-olefins, wherein 
the use of water during the method is significantly decreased, reducing 
the need for additional equipment such as storage tanks, lines and valves, 
and wherein the method operates such that intermediate storage of the 
material is eliminated, thus preventing the need for additional storage 
tanks and associated maintenance equipment. 
According to the present method of product recovery for polyolefins, the 
monomer(s) for the polyolefin are fed into a reactor. The reactor is 
cooled to maintain the appropriate temperature necessary for the 
production of the desired polyolefin. Depending upon the polyolefin 
desired, appropriate catalysts are added to the reactor. 
As the polyolefin material is produced, it is transferred from the reactor 
to a kneader. This transfer is accomplished by a number of methods, but is 
preferably accomplished via a blipper valve. Inside the kneader, the 
polyolefin material is heated to drive off any unreacted monomer(s) 
remaining in the polyolefin material. Sigma blades are used to 
mechanically work the product material to facilitate this removal process. 
The polyolefin material is then transferred via the screw flights of the 
kneader to an extruder for further processing. This step of the method, 
the direct transfer of the polyolefin material in a liquid form, provides 
a distinct advantage over prior methods of storing the polyolefin in wet 
chunk form and drying the chunks at a later date for extrusion. 
In the extruder, the polyolefin material is mixed with small amounts of 
water to deactivate any remaining catalyst(s) in the material and 
antioxidants. Heating the material further drives off any unreacted 
monomer(s), antioxidant solvents and excess steam added during this stage. 
Finally, the polyolefin material is transferred to a pelletizer where it is 
pelletized for storage and/or use. 
High-molecular-weight amorphous poly alpha-olefins exhibit increased 
tackiness and viscosity when compared with lower-molecular-weight poly 
alpha-olefins. Product recovery of these higher-molecular-weight poly 
alpha-olefins has proven especially successful utilizing the present 
method of recovery. 
The present method minimizes the use of water to carry the product through 
the several stages of recovery processing, thereby minimizing the need for 
storage tanks, delivery and removal lines, valves and other equipment used 
to introduce, maintain, remove and recycle the water. Additionally, the 
present method allows for continuous processing of the polyolefin material 
in a substantially liquid or molten state. This avoids the intermediate 
step associated with existing methods of product recovery wherein the 
material is stored as wet chunks and dried at a later stage for further 
processing. The elimination of this step also precludes the need for 
additional equipment required for the storage, maintenance and drying of 
the product material prior to further processing.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring now to FIG. 1, there is shown the apparatus associated with the 
product recovery method of the present invention. 
The monomer(s) comprising the polyolefin to be produced are continuously 
fed into a reactor 10. The monomer(s) utilized will naturally depend upon 
the polyolefin to be produced. The reactor is cooled and pressurized to 
maintain the desired temperature and pressure for the reaction to occur. 
The resulting polymer is continuously transferred to a kneader 20 via a 
blipper valve 22. The use of a blipper valve 22 allows for convenient 
control of the rate at which the product material is released from the 
reactor 10 to the kneader 20. 
In the kneader 20, the product material is heated to a temperature of from 
about 250.degree.-500.degree. Fahrenheit, depending upon the polyolefin to 
be produced. This increase in temperature drives off unreacted elements 
contained within the product material, such as unreacted propylene, 
ethylene, hydrogen and other monomers. 
A pair of sigma blades (not shown) within the kneader 20 mechanically works 
the product material to facilitate the removal of unreacted monomers and 
other volatiles from the product material. The gases produced by this 
process are vented through a vent line 30 from the kneader 20 to a 
knockout pot 40. From the knockout pot 40, the vented gases are purified 
and returned to the polyolefin plant for reuse via return line 45. To 
prevent carryover of the polyolefin material into the vent line 30, a vent 
valve 47 closes during each blip of material from the reactor 10 to the 
kneader 20. With the vent valve 47 closed, the high gas velocity within 
the relatively small volume kneader does not drive the polyolefin material 
into the vent line 30. The vent valve 47 is operated by a 
microprocessor-based timer (not shown) which controls and coordinates both 
the blipper valve 22 and the vent valve 47. 
Product material is delivered from the sigma blades to a variable speed 
screw (not shown). The screw fights transfer the product material from the 
kneader 20 to an extruder 50. The speed of the screw is adjusted so as to 
maintain a constant inventory of product material in the kneader 20. The 
barrel of the screw is heated to maintain the product material at a 
temperature substantially consistent with the temperature in the kneader 
20. 
In the extruder 50, the product material is mixed with steam to deactivate 
the catalysts and with additives to achieve the desired polyolefin 
material. The steam is added, via a metered water pump (not shown) to 
deactivate the catalyst(s) added to the reactor 10 to facilitate formation 
of the polyolefin. Importantly, this is the only place that water is used 
in the product recovery method of the present invention. 
Additional heating facilitates the removal of any excess water and further 
removes any remaining unreacted monomers or other volatiles from the 
product material. Gases produced within the extruder 50 are vented via an 
extruder vent line 70 from the extruder 50. 
From the extruder 50, the product material is transferred to a pelletizer 
80. The pelletizer 80 includes a die plate and a set of rotating blades 
(not shown) driven by a variable speed motor 90. Heat is provided to the 
die plate to maintain the product material at an extrusion temperature. As 
the product material emerges from the die holes, it is cut into pellets 
sized according to the speed of the rotating blades and is cooled by 
circulating water. The product material rapidly solidifies upon contact 
with the water. 
The pellets are carried by flowing water to a dryer 100, where the pellets 
are recovered from the water and dried with air. The pellets are then 
packaged and stored for later use. 
FIG. 2 is a flow diagram illustrating the steps associated with the product 
recovery method of the present invention. The monomer(s) necessary to 
produce the desired polyolefin are continuously fed into a reactor during 
step 110. The reactor is cooled to facilitate the production of the 
polyolefin material. Polyolefin material is then transferred to a kneader 
where unreacted monomer(s) and volatile(s) are removed 120. The monomer(s) 
and volatile(s) are driven off by heating the polyolefin material in the 
kneader. Mechanical working of the polyolefin material by a pair of sigma 
blades in this step enhances the removal of unreacted elements. Gases 
produced during this step of the process are vented through a knockout pot 
and are purified for reuse 130 and 140. 
In step 150, the polyolefin material is transferred to an extruder where 
water and desired additives such as antioxidants are mixed with the 
polyolefin material 160 and 170. The addition of water deactivates the 
catalysts in the polyolefin material. Gases produced during this step of 
the product recovery method are also vented 180. 
Next, the polyolefin material is transferred from the extruder to a 
pelletizer. In the pelletizer, the polyolefin material is cut via rotating 
blades into pellets and is cooled by circulating water 190. The pellets 
are transferred by the flowing water to a dryer. The pellets are removed 
from the water and dried with air prior to being packaged or used 200. 
Although preferred embodiments of the invention have been illustrated in 
the accompanying drawings and described in the foregoing Detailed 
Description, it will be understood that the invention is not limited to 
the embodiments disclosed, but is capable of numerous rearrangements and 
modifications of parts and elements without departing from the spirit of 
the invention.