GB1567609A - Separating polymers from emulsions thereof - Google Patents

Description

(54) SEPARATING POLYMERS FROM EMULSIONS THEREOF (71) We W BARE, INCORPORATED (also trading as WEK CORPORATION), being a corporation of the state of Florida, and engaged in business at Marianna, Jackson County, Florida, United States of America do hereby declare the invention for which we pray that a Patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to a method of, and an apparatus for, separating polymers from emulsions thereof.

U.S. Patent No. 3,742,093 describes the breaking of an emulsion, to separate polymer from the liquid phase of the emulsion by utilising the conditions of pressure, temperature and shear that exist within an extruder. The emulsion which is used is normally stable at room temperature but unstable under the conditions existing in the extruder. The liquid phase is maintained in the liquid state by establishing a high pressure region in the extruder and maintaining the high pressure by discharging the liquid through a liquid outlet provided with a pressure control valve. This keeps the liquid in liquid form as it is forced out of the extruder, and thereby prevents substantial quantities of the liquid from flashing into vapour during the removal step.

The method described is ideally suited for the manufacture of elastomeric copolymers such as acrylonitrile-butadiene-styrene copolymers. Dispersed particles of polymer in water may be introduced as a latex into a hot, plasticized polymer mixture and the may be mixed in such a manner as to coagulate the latex emulsion, liberating water which is retained in the liquid state and which is removed through a liquid outlet under such conditions of temperature and pressure such that it remains liquid and thereby does not absorb its latent heat of vaporization from the contents of the extruder. However, it has heretofore been considered that it was necessary to introduce the latex emulsion into another polymer such as the aforementioned copolymer, for example, in order to effect the continuous coagulation of the latex. It was apparent that the presence of the polymer or polymer mixture had a significant effect in causing and in maintaining the continuous coagulation of the latex emulsion.

It has now been discovered, surprisingly, that under controlled conditions and without creating a mixture of a latex and a hot, plasticized polymer within the confined housing of an extruder, a latex emulsion may be continuously and reliably coagulated when introduced as the primary and only feed into the extruder.

Suitable means may be provided, such as shear means, which will be described in futher detail hereinafter, to break the emulsion of this main feed within the extruder, thus liberating water and producing a polymer which is forwarded and plasticized within the interfiight spaces between the screw flights of the extruder.

The liberated water may be removed under such conditions of temperature and pressure as to either retain the water in liquid form without substantial volatilization or with a controlled degree of vapourization, which controls the temperature of the polymer.

According to one aspect of the present invention we provide apparatus for separating a polymer from a polymer emulsion which apparatus comprises: a) an elongate housing in which an elongate screw is aranged to be driven in rotation; b) means for injecting a polymer emlusion into said housing; c) a coagulating zone for said emulsion in said housing, said coagulating zone being downstream of said injecting means; d) at least one separator means downstream of said coagulating zone, said at least one separator means defining a first pressure zone within the extruder, said separator means being arranged to permit more readily the flow of polymer than of the liquid of the liquid phase; e) a second pressure zone downstream from said at least one separator means, so that when the apparatus is in use said second pressure zone has a pressure which is less than that of said first pressure zone and sufficient to volatilize liquid components whereby said polymer is separated from said liquid phase; f) liquid phase removal means communicatinug with said second pressure zone to remove said liquid phase from said polymer, and pressure control means operatively associated with said liquid phase removal means for maintaining at least a majority of said separated liquid in the liquid phase; and g) means for continuously extruding coagulated polymer downstream of said liquid phase removal means (f).

According to another aspect of the invention we provide a method of separating a polymer from a polymer emulsion, which method comprises continuously feeding an aqueous polymer emulsion into an apparatus as defined above, continuously coagulating said polymer in said coagulation zone, continuously separating polymer from water, continuously removing water in the liquid state from said means (f) and continuously extruding said polymer through said means (e).

If desired, more than one screw may be provided and, if so, these screws may be interlocking, intermeshing or substantially tangential to one another, depending upon the particular materials that are to be handled.

Means may be provided for introducing an initial charge of polymer product within the housing, prior to the start-up, thus providing a suitable base upon which further coagulated polymer particles may be deposited during the emulsifying step.

This is usually not necessary.

The screw flights run less than full of polymer, making the internal pressure inside the screw flights substantially equal to the pressure at the back pressure valve and thus is controllable thereby. The polymer and the water separate from each other in the spaces between the screw flights.

In a preferred embodiment of the invention, means may be provided for countercurrent washing and/or vapor stripping of the coagulated polymer.

Preferably means for introducing a fluid coagulant into the housing is provided upstream of said coagulating zone.

Where countercurrent washing or strife ping is employed it is preferred to employ a high pressure water pump connected into the housing.

The extrusion means comprises preferably a fixed or variable orifice plate comprising a downstream back pressure control means for controlling the amount of water which flows downstream with the polymer. The orifice plate may, if desired, be replaced by a restrictor screw or the equivalent, but should be located downstream of and close to the high pressure pump connection. The countercurrent washing means is discharged via a mechanical filter located downstream of the coagulation zone This serves to release the countercurrently flowing water as well as the water released from the emulsion during coagulation.

Reference is now made to the accompanying drawings in which: Fig. 1 is a vertical sectional view, partly diagrammatic in nature, and shows a typical apparatus embodying the present invention, and Fig. 2 is an enlarged sectional view of a portion of the extruder of Fig. 1 as designated by the arrows 11-11 showing the condition of polymer and water in that portion.

Referring specifically to the drawings, there is shown an extruder (preferably of the twin screw type but optionally single screw) including a housing 11 having a barrel 12 in which a feed screw 13 is driven in rotation by a motor and gears (not shown) in a direction indicated by the arrow at the right hand end of the draw ing, in such a way as to feed material disposed therein toward the left of the apparatus as illustrated.

A plurality of jacket sections 16 are provided, disposed about the barrel 12, for providing heat to material being worked within the barrel 12, such jacket sections being closed from one another by suitable annular ribs 23. It is also contemplated that the jacket sections may be used for providing cooling, when desired.

The extruder screw sections include a coagulation zone 24 having screw sections 37 provided with interflight spaces which provide high pressure regions 39, 39 in the material conveyed by the screw 13.

Three separator means are provided each in the form of a cylindrical restrictor. The cylindrical restrictor 25 is provided at an upstream portion of the screw 13, preferably substantially in line with the emulsion feed line 50. Spaced downstream of restrictor 25 is another restrictor 26, having a function to be described in detail hereinafter, and still further downstream is a third restrictor 40 of the same type. Just downstream of the restrictor 40 a second pressure zone is formed by providing a relatively open flight screw section 41, which produces a sudden reduction of pressure in the polymeric material and the water as they advance beyond the restrictor member 40.

A break is shown in the figure between these screw sections 41 and the downstream portion of the apparatus to indicate that various other mixing, compounding and other sections may also be included, which are unrelated to this invention and which cannot conveniently be shown in this figure. Important details with respect to such arrangements will be described in further detail hereinafter.

Important details with respect to such arrangements will be described in further detail hereinafter.

The housing 11, barrel 12 and screw 13 continue in a downstream direction from the aforementioned break in the drawings, and terminate in extrusion means in the form of an orifice plate 27 which is located at the extreme downstream end of the extruder. It is highly desirable to provide a tapir of concavely arranged orifice plates, adjustable with respect to one another in a manner to restrict the flow of the polymer product, thus regulating its back pressure. One highly advantageous form of such a back pressure device is shown and described in U.S. patent No.

3,874,835. These concavely arranged ori alice plates are highly desirably incorporated into a transversely arranged cutter referred to in the art as a "turbulator" which rapidly and efficiently cuts the polymer product into particles and conveys them efficiently away for further processing, with the aid of a processing fluid which flows in the desired direction to carry the particles quickly away from the area in which the cutters function.

preferring further to the drawings, the number 50 designates a feed pipe for the emulsion, e.g. a latex which is delivered under pressure by a latex pump, which may be of conventional type, as shown in Fig. 1 of the drawings. The latex may be conveniently initially stored in any latex tank, for example. As shown, the latex flow is controlled by a valve 51, and the latex flow impinges directly upon the surface of the cylindrical restrictor 25, at which point initial coagulation takes place, developing a mass of polymeric material in the immediate area of the restrictor 25.

Spaced downstream of the cylindrical restrictot 25 is a cylindrical restrictor 26, past which the coagulum is forced by the operation of the screw flight in the coagulation zone 24. The cylindrical restrictor 26 permits the passage of polymer but resists the flow of water which has ben separated from the polymer. Further, located downstream of the cylindrical re Strictor 26 is another cylindrical restrictor 40, which functions in essentially the same manner as the cylindrical restrictor 26 as heretofore stated.

Located just downstream of the cylindrical restrictor 40 is a vent, shown in the form of a mechanical filter 60 having a pair of rotating screws 61 and 62 driven by motors contained within the housing 63. The mechanical filter 60 is housed in a pipe 64 the lower end of which extends through the barrel 12 and is in open communication with the interflight spaces 41 of the screw 13. At its upper end the housing 64 is provided with a vent line 65 which is connected to a vacuum aspirator line 66.

The number 70 designates an inlet pipe for the introduction of seal weater which may be introduced, at a pressure essentially equal to that of the latex in the area 1t, under the influence of a pump, as shown in Fig. 1. This seal water inlet pipe 70 is located upstream of the pipe 50 through which the latex starting material is introduced.

The number 73 designates a separate inlet line for coagulant, which is introduced as a fluid through a coagulant pump P and a valve V as shown in Fig. 1. This coagulant inlet line 73 is located substantially in line with the latex inlet line 50 and with the restricting cylinder 25.

The number 80 designates a high pressure water inlet line, providing for the introduction of high pressure water from a pump, as indicated in the drawings. This inlet line 80 is located upstream of the orifice plate 27 which is located at the downstream end of the extruder, and is spaced downstream of the mechanical filter 60 and of the restricting cylinders 40, 26 and 25.

The operation of the apparatus in accordance with this invention will now be understood.

With the screw rotating and with the temperatures of the apparatus brought to the desired levels, the valve 51 of the latex inlet pipe 50 is opened, and the latex impinges upon the restricting cylinder 25.

Concurrently, the valve in line 73 is opened, and the associated pump causes the coagulant to flow against the cylindrical restrictor 25 under pressure. The net result is the immediate coagulation of latex around the circumference of the cylindrical restrictor 25, whereupon polymer, liberated water and excess latex flow downstream, from right to left as viewed in Fig. 1 of the drawings. Coagulation continues as the material flows downstream, whereupon it encounters the cylindrical restrictor 26, which functions as a barrier to the flow of at least some of the water but more readily permits the flow of polymer downstream, creating a separation of the water and the polymer. As the material continues to flow donwstream further, it encounters still another cylindrical restrictor 40, which functions in essentially the same manner, and which of course creates a polymer seal around the periphery of the cylindrical restrictor 40.

Concurrently with this, the seal water pump provides seal water through the line 70, at a location slightly upstream of the cylindrical restrictor 25, at a pressure which is essentialy equal to the pressure just downstream of the cylindrical restrictor 25.

This serves to prevent latex or polymer from entering into the packing 69 at the end of the shaft 13.

With respect to the nature of the coagulant, suitable chemical additives for coagulation of latex emulsions are well known in the art, and are not of themselves considered to be part of this invention. Particular individual coagulating solutions and combinations may readily be selected by those skilled in the art for use in conjunction with the particular polymer emulsion, its processing conditions, and concentration, as is well known in the art relating to latex coagulation.

Material flowing past the restrictor 40 is suddenly subjected to a drop in pressure just downstream of the restrictor 40 i.e.

in the area beneath the mechanical filter 60. This sudden reduction of pressure results in intertlight spaces 41 running less than full of polymer, thereby liberating water in the liquid state and concurrently liberating polymer which flows further in a downstream direction by the rotation of the screw 13. However, because of the back pressure created by the orifice plate 27 which is located at the downstream end of the extruder, and because the spaces provided by the orifice plate 27 become filled with polymer, the orifice plate 27 forms a pressure seal which blocks off the movement of water downstream beyond the orifice plate 27, thus confining the liberated water within the interflight spaces between the screws 13. This water accordingly flows countercurrently or upstream, and makes its way out through the vent pipe or mechanical filter 60.

The revolving screws 61, 62 of the mechanical filter 60 permit the flow of liquid through the pipe 64 but catch all entrained solid particles and prevent them from leaving the system.

Fig 2 is an enlarged sectional view showing that the polymer and the water separate from each other in the area downstream of the cylindrical restrictor 40, in which downstream section the interflight spaces 41 are running less than full of polymer. It will be observed that the polymer P collects on the driving face of each screw (the surface facing in the downstream direction) whereas the water W collects in the area adjacent the faces of the screws which are facing upstream.

Accordingly, the screws continuously move the polymer in a downstream direction, while the water is permitted to flow countercurrently with respect to the polymer, and to be ejected out through the pipe 64.

Where desired, the high pressure water pump connected to the inlet pipe 80 may additionally be used, thus creating a countercurrent flow of any desired volume of high pressure water. All of such countercurrently flowing water passes out through the pipe 64 or the mechanical filter 60 and mingles with the water that has been liberated from the latex emulsion as heretofore described. Any desired quantity of pre-heated high pressure water can be used, by introduction through the pipe 80, without significantly altering the thermal economy of the apparatus. The water that is recirculated in this manner may be passed through a heat exchanger if desired. Further, any quantities of such high pressure water may be used for countercurrent washing in accordance with this invention, with resulting improvement of the quality of the polymer product, and it may be used in a closed system with high beneficial ecological results.

It is important and advantageous in accordance with this invention that the initial feed is an emulsion which does not require the presence of any other polymeric material fed upstream. Heretofore, it has not been considered possible to coagulate a latex emulsion by direct action within an extruder (see, for example, U.S. patent No. 3,742,093).

It will be appreciated that various modifications may be made in according with this invention. For example, in some instances it may be desirable to preheat that water which is introduced through the line 80, either in the heat exchanger illustrated in the drawings or otherwise. When the water is preheated as indicated herein, the water is initially brought to the same temperature and pressure at which it is intended to be discharged, thus resulting in zero loss of heat in the process due to the introduction and removal of the countercurrently flowing washing water. The quantity of such water may be varied widely without affecting the process, when such water has been preheated to the same temperature as the polymeric material at the discharge or orifice plate 27.

WHAT WE CLAIM IS:- 1. Apparatus for separating a polymer from the liquid phase of a polymer emulsion which comprises: a) an elongate housing in which an elongate screw is arranged to be driven in rotation; b) means for injecting a polymer emulsion into said housing; c) a coagulating zone for said emulsion in said housing, said coagulating zone being downstream of said injecting means; d) at least one separator means downstream of said coagulating zone, said at least one separator means defining a first pressure zone within the extruder, said separator means being arranged to permit more readily the flow of polymer than of the liquid of the liquid phase; e) a second pressure zone downstream from said at least one separator means, so that when the apparatus is in use said second pressure zone has a pressure which is less than that of said first pressure zone and sufficient to volatilize liquid components whereby said polymer is separated from said liquid phase; f) liquid phase removal means communicating with said second pressure zone to remove said liquid phase from said polymer, and pressure control means operatively associated with said liquid phase removal means for maintaining at least a majority of said separated liquid in the liquid phase; and g) means for continuously extruding coagulated polymer downstream of said liquid phase removal means (f).

2. Apparatus according to claim 1, wherein means are provided for introducing washing water, downstream of said coagulating zone (c), for countercurrent washing of coagulated polymer.

3. Apparatus according to claim 1 or claim 2 wherein means are provided for introducing water into said housing at a location upstream of said injecting means (b).

4. Apparatus according to any of the preceding claims wherein means for introducing a fluid coagulant into said housing is provided upstream of said coagulating zone.

5. Apparatus according to any of the preceding claims wherein means are provided for controlling the flow of said latex into said housing.

6. Apparatus according to any of claims 2 to 5 further comprising backpressure control means located downstream of, and closely adjacent to, said means for introducing washing water.

7. Apparatus according to any of claims 1 to 6 wherein a mechanical filter is connected to said liquid phase removal means.

8. Apparatus for making polymer from a polymer emulsion substantially as described herein with reference to the accompanying drawings.

9. A method of separating a polymer from a polymer emulsion which method comprises continuously feeding an aqueous polymer emulsion into an apparatus as claimed in any of claims 1 to 8, continuously coagulating said polymer in said coagulation zone, continuously separating polymer from water, continuously removing liquid phase in the liquid state from said means (f) and continuously extruding said polymer through said means (g).

10. A method according to claim 9 wherein a coagulant is injected into said coagulation zone.

11. A method of making polymer according to claims 9 or 10, wherein said water includes washing water introduced downstream of said coagulating zone.

12. A method of separating a polymer from a polymer emulsion substantially as described herein with reference to the accomnanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. quantity of such water may be varied widely without affecting the process, when such water has been preheated to the same temperature as the polymeric material at the discharge or orifice plate 27. WHAT WE CLAIM IS:-

1. Apparatus for separating a polymer from the liquid phase of a polymer emulsion which comprises: a) an elongate housing in which an elongate screw is arranged to be driven in rotation; b) means for injecting a polymer emulsion into said housing; c) a coagulating zone for said emulsion in said housing, said coagulating zone being downstream of said injecting means; d) at least one separator means downstream of said coagulating zone, said at least one separator means defining a first pressure zone within the extruder, said separator means being arranged to permit more readily the flow of polymer than of the liquid of the liquid phase; e) a second pressure zone downstream from said at least one separator means, so that when the apparatus is in use said second pressure zone has a pressure which is less than that of said first pressure zone and sufficient to volatilize liquid components whereby said polymer is separated from said liquid phase; f) liquid phase removal means communicating with said second pressure zone to remove said liquid phase from said polymer, and pressure control means operatively associated with said liquid phase removal means for maintaining at least a majority of said separated liquid in the liquid phase; and g) means for continuously extruding coagulated polymer downstream of said liquid phase removal means (f).

2. Apparatus according to claim 1, wherein means are provided for introducing washing water, downstream of said coagulating zone (c), for countercurrent washing of coagulated polymer.

3. Apparatus according to claim 1 or claim 2 wherein means are provided for introducing water into said housing at a location upstream of said injecting means (b).

4. Apparatus according to any of the preceding claims wherein means for introducing a fluid coagulant into said housing is provided upstream of said coagulating zone.

5. Apparatus according to any of the preceding claims wherein means are provided for controlling the flow of said latex into said housing.

6. Apparatus according to any of claims 2 to 5 further comprising backpressure control means located downstream of, and closely adjacent to, said means for introducing washing water.

7. Apparatus according to any of claims 1 to 6 wherein a mechanical filter is connected to said liquid phase removal means.

8. Apparatus for making polymer from a polymer emulsion substantially as described herein with reference to the accompanying drawings.

9. A method of separating a polymer from a polymer emulsion which method comprises continuously feeding an aqueous polymer emulsion into an apparatus as claimed in any of claims 1 to 8, continuously coagulating said polymer in said coagulation zone, continuously separating polymer from water, continuously removing liquid phase in the liquid state from said means (f) and continuously extruding said polymer through said means (g).

10. A method according to claim 9 wherein a coagulant is injected into said coagulation zone.

11. A method of making polymer according to claims 9 or 10, wherein said water includes washing water introduced downstream of said coagulating zone.

12. A method of separating a polymer from a polymer emulsion substantially as described herein with reference to the accomnanying drawings.