US3177127A

US3177127A - Gear pump devolatilizing method and apparatus

Info

Publication number: US3177127A
Application number: US183466A
Authority: US
Inventors: Murrey O Longstreth
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1962-03-29
Filing date: 1962-03-29
Publication date: 1965-04-06
Anticipated expiration: 1982-04-06

Description

April 1955 M. o. LONGSTRETH 3,177,127

GEAR PUMP DEVOLATILIZING METHOD AND APPARATUS Filed March 29, 1962 J0 12 W m EXCHANGE/Q 94 h "91 United States Patent Murrey 0.

Midland, Mich., a corpora- Dow Chemical Company, tion of Delaware Filed Mar. 29, 1962, Ser. No. 183,466 4 Claims. (Cl. 202-53) This invention relates to an improvement in a method and apparatus for devolatilizing a partial polymer solution.

The usual practice in devolatilizing a polymer solution, is to pump a heated partial polymer into a vessel by a number of different methods, removing the volatile under reduced atmospheric pressure, and pumping the devolatilized polymer out of the vessel.

The method and apparatus of the present invention represents an improvement over known methods and apparatus of the prior art. Briefly, the device of the invention comprises a gear pump assemblage close coupled to a heat exchanger with means for depositing heated partial polymer directly onto the surface of gears in the pump. A suitable vacuum connection is arranged on top of the pump for removing volatiles.

Among the more important advantages afforded by the device of the invention, is that the problem of low temperature devolatilization of heat sensitive materials is solved. By laying the partial polymer directly upon the moving gears, the inventory, or residence time in the devolatilizer is reduced to a minimum, thus reducing the possibility of discoloration. Allowing the pump to fill substantially independent of temperature considerations, avoids flow of stifi devolatilized material into the pump from a reservoir. By operating at a minimum temperature, thermal degradation is also minimized. The invention is especially well suited for handling polymers of high viscosity.

The main object of this invention is to provide an improvement in a method and a device for devolatilizing a partial polymer solution.

A more specific object is to provide a device adapted for the solution of low temperature devolatilization of heat sensitive materials.

Still another object is to provide a device which reduces the inventory, or residence time of the polymer in the devolatilizer thus reducing the possibility of discoloration.

Another object is to provide a device which fills independently of temperature thus avoiding flow of stiff devolatilized material into the pump forming part of the device.

A further object is to control temperature so as to minimize thermal degradation of a polymer during de'volatilization.

Other objects and features of the invention will become more apparent from the following description and accompanying drawing wherein:

FIG. 1 is a vertical section view of a devolatilizing pump assemblage embodying the principles of the invention; and

FIG. 2 is a section view generally as seen along line 2-2 in FIG. 1.

Numeral 6 identifies a devolatilizing pump assemblage which includes a gear housing 8, and a vacuum chamber housing 10, mounted atop the gear housing and secured thereto by fastening means, such as bolts 12, extending through flange means 14 and 16 provided on the housings 8 and respectively. Polymer moving means in the form of a pair of

herringbone gears

18 and 20, are positioned in the gear housing 8, so that the teeth intermesh, the axis of each gear being located in a given horizontal "ice plane, as best seen in FIG. 1. The gear housing 8 has a centrally arranged inlet opening 22, and an outlet opening 24 in axial alignment with the inlet opening. A threaded opening 26 is formed in a side wall of the gear housing 8, in a generally triangular region 27 defined by a line drawn tangent with the gear teeth extremities and a curved teeth pro-file line of each gear, as illustrated in FIG. 1.

A pipe 28, threaded into the opening 26, is adapted to deliver a partial polymer from a heat exchanger 30, into the gear housing. Power means (not shown) is coupled to the gear 18 via a shaft 32, whereby rotary movement of the

gears

18 and 20, is provided.

A side plate 34 may be removably aifixed to the gear housing 8 for the installation and removal of the

gears

18 and 20. Secured to the lower end of the gear housing 8, by fastening means such as bolts 36, is a discharge pipe 38, the latter being provided with a flange means 40 coextensive with a flange means 42 formed integral with the gear housing 8.

The vacuum chamber housing 10 is formed to provide an axially arranged chamber 44 the lower end of which is coextensive with the gear housing inlet opening 22. A glass plate 46 may be mounted upon the housing 10, which plate serves as a window, or peep-hole for conveniently observing the interior of the pump gear housing 8, and more particularly, the condition of polymer being devolatilized therein. To maintain the glass plate 46 in secure position, a ring-like keeper plate 48 may be mounted atop the plate and held thereupon by fastening means, such as bolts 50, which extend through a flange 52 formed integral with the vacuum chamber housing 10. An opening 54 is formed in a side wall of the housing 10, for receipt of a pipe 56 connected to a source of subatmospheric pressure to produce a vacuum condition in the housing; the volatile drawn off of the polymer being treated, passes through the pipe 56 for condensation by means (not shown), as is well known in the art.

In operating the pump assemblage 6, the partial polymer solution is drawn from the heat exchanger 30 and admitted to the gear housing 8 in the triangular region 27. The rate of flow of the solution, as well as the temperature, are controlled so that the volatiles will be drawn quickly off before the devolatilized polymer is pumped out through the outlet opening 24, by action of the

gears

18 and 20.

It would serve no useful purpose to specify optimum operating pressures and temperatures recommended when operating the device of the invention, since such would depend upon the specific material being processed, and quality of product desired, as will be appreciated. Suffice it to say that for any given material being devolatilized, the pressure and temperature should be such that a polymer of desired purity is produced. In other words, the sub-atmospheric pressure in the chamber housing 10 and the temperature of the polymer stream being layed upon the

gears

18 and 20, should be such as to cause a flash-off of volatiles in the amount and at a rate which will produce a devolatilized polymer having the characteristics desired, especially regarding volatile content.

The foregoing description has been given in detail without thought of limitation since the inventive principles involved are capable of assuming other forms without departing from the spirit of the invention or the scope of the following claims.

What is claimed is:

1. A low temperature method for removing volatiles from a partial polymer solution of high viscosity comprising the steps of feeding a stream of such polymer, after heating, directly onto tandemly arranged intermeshing rotating gear means of a gear pump assemblage in the region of intermesh While providing a sub-atmospheric pressure above said gear means, said feeding being substantially devoid of devolatilization until said stream enters said region of intermesh, the rate of flow of said stream to and said sub-atmospheric pressure above said gear means being regulated to provide for quick removal of the volatiles from the solution, and subsequently conducting the volatiles to a condensing means.

2. A low temperature method for removing volatiles from a partial polymer solution of high viscosity comprising the steps of feeding a stream of such polymer, after heating, directly onto tandemly arranged intermeshing rotating gear means of a gear pump assemblage in the triangular region defined by a line drawn tangent With the gear teeth extremities and the curved teeth profile line of each gear while providing a sub-atmospheric pressure above said gear means, said feeding being substantially devoid of devolatilization until said stream is located within said triangular region, the rate of flow of said stream to and said sub-atmospheric pressure above said gear means being regulated to provide for quick removal of the volatiles from the solution, and subsequently conducting the volatiles to a condensing means.

3. A devolatilizer for removing volatiles from a highly viscous partial polymer product under low temperature conditions comprising, in combination, a gear housing, said housing having a lower polymer outlet opening, a pair of intermeshing rotatable gears forming a gear pump assemblage enclosed in said housing, means to rotate said gears, a vacuum chamber aflixed to and in communication with the upper portion of said gear housing, inlet means independent of said vacuum chamber to admit said polymer solution into said gear housing directly onto said gears, said inlet means opening into the triangular region defined by a line drawn tangent with the gear teeth extremities and the curved teeth profile line of each gear,

4. and outlet means for removing volatiles from said vacuum chamber.

4. .A devolatilizer for removing volatiles from a highly viscous partial polymer product under low temperature conditions comprising, in combination, a gear housing, said housing having a lower polymer outlet opening, a pair of intermeshing rotatable herringbone gears forming a gear pump assemblage enclosed in said housing, means to rotate said gears, a vacuum chamber afiixed to and in communication with the upper portion of said gear housing, inlet means to admit said polymer solution into said gear housing directly onto said gears, said inlet means independent of said vacuum chamber opening into the triangular region defined by a line drawn tangent with the gear teeth extremities and the curved teeth profile line of each gear, and outlet means for removing volatiles from said vacuum chamber.

References Cited by the Examiner UNITED STATES PATENTS 1,156,096 10/15 Price 159-2 1,614,526 1/27 Lambie et al. 2,205,328 6/40 Wills. 2,276,261 3/42 Buzard. 2,298,644 10/42 Hummel. 2,572,063 10/51 Skipper.

FOREIGN PATENTS 324,648 1/30 Great Britain.

369,658 2/23 Germany.

373,676 4/22 Germany.

NORMAN YUDKOFF, Primary Examiner. GEORGE D. MITCHELL, Examiner.