Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Patent
1978-01-17
1980-01-08
Smith, Edward J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
526 68, C08F 466, C08F 1000
Patent
active
041828011
DESCRIPTION:
BRIEF SUMMARY
THE PROBLEM
In the liquid phase catalytic polymerization under positive pressure of olefins to polyolefins such as polyethylene, polypropylene, polybutylene, etc. in which the reaction mass comprises polyolefin dissolved in liquid monomer which is recovered by flashing it off the polymer as a vapor which is liquified and recycled, the catalysts conventionally used, e.g., Ziegler catalyst, are highly sensitive to the presence of even small amounts of water. Accordingly it is essential that water be removed from the liquid olefin to reduce its water content down to 5-10 ppm or less. This is conventionally done by first stripping water from the liquid olefin feed by means of a stripping tower, e.g., a countercurrent flow packed tower, to reduce the water content to 10 to 20 ppm followed by removing more water down to 5-10 ppm or less by means of a conventional molecular sieve dryer (MSD). The MSD is provided with a plurality (usually two) of beds of granular, water-adsorbing (adsorbing is used herein to mean absorbing and/or adsorbing either physically or chemically) material, such as that sold by Union Carbide Corporation under the trade name 3X. Each bed has heating means (either heating coils using heating fluid or electrical heating elements) therein.
The flow of liquid monomer is cyclically switched by switching valves from one bed to the other. While one of the beds is on-stream, during which water is removed from the liquid monomer and is adsorbed by the granular material of the bed, the other off-stream bed is regenerated by the heating element or elements, which volatilize the water adsorbed thereby during its previous on-stream cycle. Part of the exit flow of dried liquid monomer from the on-stream bed is diverted and volatilized to a gas which is flowed through the off-stream bed to remove the evaporated water therefrom and thereby regenerate the bed to prepare it for the next on-stream cycle. The diverted volatilized liquid monomer is sometimes referred to as the regenerating or carrier or drying gas. The diverted monomer is recovered, i.e., the water is removed therefrom, by special condensation equipment and blended back into the recycle system.
This procedure has serious disadvantages as follows:
1. The capacity of the equipment must be increased to handle the diverted monomer, which increases recycle, thereby requiring increased capacity to handle the increased recycle. This increases the cost.
2. The special condensation equipment and energy required to remove water from the diverted monomer adds to the cost and power requirements of the plant.
3. The cost of compressing the substantial amount of diverted monomer for recycle adds substantially to the cost and power requirements.
BRIEF DESCRIPTION OF THE INVENTION
According to the present invention, these aforesaid problems are eliminated by using as a regenerating gas for the MSD bed, the fuel gas which is required in any event to provide energy elsewhere in the system, such as petroleum gas, propane, butane, heptane, city gas, etc. The MSD bed is not pretreated with steam, or water in any form, since such pretreatment would deleteriously affect the reaction unless such water is removed which would substantially increase the cost. No such pretreatment is necessary when regenerating the MSD bed in accord with the teachings of the present invention.
It has been found that even though the fuel gas is a foreign substance introduced into the system, residual amounts of which may be picked up by the liquid monomer subsequently flowed through the regenerated bed to the reactor, and even though the catalyst is highly sensitive to foreign substances, polymerization of the liquid monomer subsequently flowed through the regenerated bed is not deleteriously affected.
Since the fuel gas leaves the bed being regenerated at an elevated temperature, it is effectively preheated for flow to burners elsewhere in the plant thereby reducing total plant energy requirements.
The flow rate of regenerating fuel gas through the off-stream bed is sufficient to dry
REFERENCES:
patent: 3309350 (1967-03-01), Kelley et al.
patent: 3362940 (1968-01-01), Edwards et al.
patent: 3565873 (1971-02-01), Sutherland, Jr. et al.
patent: 3635931 (1972-01-01), Davison
patent: 4068053 (1978-01-01), Miserlis et al.
patent: 4068060 (1978-01-01), Miserlis et al.
Kirk-Othmer, Encyclopedia of Chemical Technology, vol. 7, pp. 393-394, J. Wiley and Sons, Inc. (New York) 1965.
Lewis Peter J.
Miserlis Constantine D.
Bronstein Sewall P.
Smith Edward J.
The Badger Company, Inc.
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