Reverse-phase polymerization process

Abstract

A reverse-phase suspension polymerization process for the manufacture of polymer beads comprising forming aqueous monomer beads comprising an aqueous solution of water-soluble ethylenically unsaturated monomer or monomer blend and polymerizing the monomer or monomer blend, to form polymer beads while suspended in a non-aqueous liquid, and recovering polymer beads, in which the process comprises providing in a vessel (1) a volume (2) of non-aqueous liquid wherein the volume of non-aqueous liquid extends between at least one polymer bead discharge point (3) and at least one monomer feed point (4), feeding the aqueous monomer or monomer blend through orifices (5) into, or onto, the non-aqueous liquid to form aqueous monomer beads, allowing the aqueous monomer beads to flow towards the polymer bead discharge point initiating polymerization of the aqueous monomer beads to form polymerizing beads, wherein the polymerizing beads form polymer beads when they reach the polymer bead discharge point, removing a suspension of the polymer beads in non-aqueous liquid from the vessel at the polymer bead discharge point and recovering, water soluble or water swellable polymer beads from the suspension, in which the aqueous monomer or monomer blend and/or the orifices is/are vibrated such that the frequency multiplied by the weight average droplet diameter is between 150 and 800 mm/s. The invention also relates to the apparatus suitable for carrying out a reverse-phase suspension polymerization and polymer beads obtainable by the process or employing the apparatus. Furthermore, the invention also relates to polymer beads having a weight mean particle size in the range of 0.05 to 5 mm which are held in a container in an amount of at least 300 kg having a standard deviation of particle size less than 20%. In addition, the invention also provides polymer beads having a weight mean particle size in the range 0.05 to 5 mm having a standard deviation of particle size less than 20% and having an amount of residual acrylamide of less than 500 ppm.

Claims

1. A reverse-phase suspension polymerisation process for the manufacture of polymer beads comprising forming aqueous monomer beads of an aqueous solution comprising water-soluble ethylenically unsaturated monomer or monomer blend and polymerising the monomer or monomer blend, to form polymer beads while suspended in a non-aqueous liquid, and recovering polymer beads, in which the process comprises: providing in a vessel a volume of non-aqueous liquid wherein the volume of non-aqueous liquid extends between at least one polymer bead discharge point and at least one monomer feed point, feeding the aqueous monomer or monomer blend through orifices into, or onto, the non-aqueous liquid to form aqueous monomer beads, allowing the aqueous monomer beads to flow towards the polymer bead discharge point initiating polymerisation of the aqueous monomer beads to form polymerising beads, wherein the polymerising beads have formed polymer beads when they reach the polymer bead discharge point, removing a suspension of the polymer beads in non-aqueous liquid from the vessel at the polymer bead discharge point and recovering, water soluble or water swellable polymer beads from the suspension, in which the aqueous monomer or monomer blend and/or the orifices is/are vibrated such that the frequency multiplied by the weight average droplet diameter is between 150 and 800 mm/s, wherein the non-aqueous liquid flows in a downward direction and co-current with the direction of flow of the monomer beads.

2. The process according to claim 1 in which the polymer beads removed from the vessel at the polymer bead discharge point are subjected to a post polymerisation stage.

3. The process according to claim 1 in which the aqueous monomer or monomer blend and/or the orifices is/are vibrated such that the frequency multiplied by the weight average droplet diameter is between 250 and 500 mm/s.

4. The process according to claim 1 in which the vibration amplitude is between 0.0005 and 0.5 mm.

5. The process according to claim 1 in which the orifices are disposed in at least one plate or at least one grid.

6. The process according to claim 1 in which the orifices comprise a conical part and a cylindrical part.

7. The process according to claim 6 in which the aqueous monomer or monomer blend flows through the conical part and then through the cylindrical part.

8. The process according to claim 1 wherein the process is conducted in two or more vessels in parallel.

9. The process according to claim 1 in which the aqueous monomer or monomer blend and/or the non-aqueous liquid contains a polymerisation initiator.

10. The process according to claim 1 in which the suspension of the polymer beads in the non-aqueous liquid removed at the polymer bead discharge point has a concentration of at least 10% polymer beads on total weight of suspension.

11. The process according to claim 1 in which the aqueous polymer beads are produced at a rate of at least 15 kg/hour.

12. The process according to claim 1 in which an amphipathic stabiliser is included in the non-aqueous liquid.

13. The process according to claim 1 wherein the water-soluble ethylenically unsaturated monomer or monomer blend comprises at least one monomer selected from the group consisting of acrylamide, methacrylamide, N-vinyl pyrrolidone, 2-hydroxy ethyl acrylate, acrylic acid (or salts thereof), methacrylic acid (or salts thereof), itaconic acid (or salts thereof), maleic acid (or salts thereof), 2-acrylamido-2-propane sulphonic acid (or salts thereof), vinyl sulphonic acid (or salts thereof), allyl sulphonic acid (or salts thereof), dimethyl amino ethyl acrylate (or acid salts or quaternary ammonium salts thereof), dimethyl amino ethyl methacrylate (or acid salts or quaternary ammonium salts thereof), dimethyl amino propyl acrylamide (or acid salts or quaternary ammonium salts thereof), dimethyl amino propyl methacrylamide (or acid salts or quaternary ammonium salts thereof), vinyl formamide and combinations of any of the above.

14. The process according to claim 13 in which at least one monomer has been prepared by a chemically catalysed process, a biologically catalysed process or a biological process.

15. The process according to claim 13 in which the acrylamide has been prepared by a biological catalysed process or a biological process.

16. The process according to claim 1 in which the so formed polymer beads are ground to produce a polymer powder.

17. The process according to claim 1 in which the process is performed in a continuous mode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Suitable apparatus for carrying out the invention is illustrated diagrammatically in the accompanying drawings.

(2) FIG. 1 shows one type of apparatus, consisting of a cylindrical vessel (1) containing to concentric walls. Monomer beads are formed by extrusion of aqueous monomer employing orifices (5) for feeding or extruding monomer. The monomer beads enter the volume of non-aqueous liquid (2) at the monomer feed point (4) and are initiated and irradiated using the UV source and descend as polymerising beads through a volume of non-aqueous liquid between the concentric walls of the vessel. The suspension of polymer beads is removed through the polymer discharge point (3) situated at the base of the vessel.

(3) FIG. 2 shows another type of apparatus and differs from the apparatus of FIG. 1 in that the vessel (1) has a rectangular horizontal cross-section.

(4) FIG. 3 is a diagrammatic representation of a vertical cross-section of a preferred type of orifice. The upper section of the orifice represents a comical section and the lower section of the orifice represents a cylindrical section.

(5) FIG. 4 is an engineering drawing of a vertical cross-section of a preferred type of orifice. The upper section of the orifice is a conical part with a depth of 1.5 mm and a opening angle of 60 and a lower section which is a cylindrical part with a diameter of 0.275 mm (+/0.002 mm) and a depth of 1.5 mm (+/0.02 mm).

EXAMPLES

Example 1

(6) The preparation of aqueous monomer beads is carried out in vertical vessel (length 10 cm, width 3 cm and height 75 cm) which is filled with Exxsol D40 oil, as a non-aqueous liquid (continuous phase),

(7) An aqueous monomer solution is provided as a dispersed phase, said monomer solution containing of a mixture of acrylamide, dimethylaminoethylacrylate methyl chloride quaternary salt (DMAEAMC), water and adipic acid.

(8) TABLE-US-00001 Water 10.00 kg Acrylamide (50% aqueous solution) 88.60 kg Adipic Acid 3.28 kg DMAEAMC (80% aqueous solution) 77.36 kg

(9) This calculates as acrylamide 24.7%, dimethylaminoethylacrylate methyl chloride quaternary salt 34.5%, water 38.9% and adipic acid 1.8%

(10) A plate providing 80 holes comprising a conical part with a depth of 1.5 mm and an opening angle of 60 as well as a cylindrical part with a diameter of 0.275 mm (+/0.002 mm) and a depth of 1.5 mm (+/0.02 mm) (shown in FIG. 4) is vibrated and submerged into the Exxsol D40.

(11) The aqueous monomer solution is extruded through the holes of the plate in which it is fed with pump without pulsation and a rate of 40 L/h in which the holes are vibrated at different frequencies as set out in Table 1.

(12) The generated droplets are observed via a high speed camera (model: Basler camera scout scA 1600-28 gm) and analyzed via software, giving the size distribution value Span3. Span3 is a relative standard deviation measurement.

(13) This Span3 value is defined as the percentile 90 (90% of the droplets have their weight average diameter below that size) minus 10 (10% of the droplets have their weight average diameter below that size) divided by 50 (the weight average diameter). The meaning of this value is comparable to the relative standard deviation, which is defined as the standard deviation divided by the average diameter.

(14) TABLE-US-00002 TABLE 1 frequency multiplied by X50 the weight average Frequency (weight average) droplet diameter [Hz] [mm] [mm/s] Span3 0 0.71 31% 20 1.00 20 (comparative test) 65% 400 0.61 244 (inventive test) 9% 2000 0.42 840 (comparative test) 52%

Example 2

(15) Example 1 is repeated in an analogous experiments except using a nonvibrating plate but with the monomer solution fed through a membrane chamber in which the membrane is vibrating the monomer. This is shown in Table 2.

(16) TABLE-US-00003 TABLE 2 frequency multiplied by X50 the weight average Frequency (weight average) droplet diameter [Hz] [mm] [mm/s] Span3 390 0.75 292 (inventive test) 14%

Example 3

(17) Example 1 is repeated except that the Exxsol D 40 contains an amphipathic stabiliser and the monomer solution contains an initiator.

(18) Additionally the column is extended to a height of 12 m and the narrow wall (3 cm) of the column is made from borosilicate glass and equipped with 400 UV-LEDs (each side). The UV LEDs (Nichia NCSU099B, 365 nm) irradiate the mixture inside of the column with about 50 mW/cm.sup.2.

(19) The initiator is, 2,2-Azobis(2-methylpropionamidine)dihydrochloride, is added to the monomer solution to give a concentration of 180 ppm.

(20) The amphipathic stabilizer (0.5 wt-% with respect to dispersed phase; e.g. a copolymer from methyl methacrylate, stearyl methacrylate, acrylic acid and methacrylic acid). The Span3 values for the polymer beads generated are shown in Table 3.

(21) TABLE-US-00004 TABLE 3 frequency multiplied by X50 the weight average Frequency (weight average) particle diameter [Hz] [mm] [mm/s] Span3 530 0.53 281 (inventive test) 5.1% 530 0.49 260 (inventive test) 4.5% 530 0.55 291 (inventive test) 5.0%