Reverse-phase polymerisation process

Abstract

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, recovering polymer beads, and then cleaning the non-aqueous liquid in which the process comprises providing the non-aqueous liquid in a vessel (1), forming a suspension of monomer beads from the aqueous monomer or monomer blend in the non-aqueous liquid, initiating polymerisation to form polymerising beads, removing a suspension of the polymer beads in non-aqueous liquid from the vessel and recovering, water soluble or water swellable polymer beads from the suspension, in which the non-aqueous liquid contains impurities which comprise particles, and then transferring the non-aqueous liquid from the suspension to a cleaning stage, in which the cleaning stage provides a cleaned non-aqueous liquid suitable for use in a reverse-phase suspension polymerisation process, which cleaning stage comprises removing particles from the non-aqueous liquid in at least one filtration step. The invention also relates to the apparatus suitable for carrying out a reverse-phase suspension polymerisation and polymer beads obtainable by the process or employing the apparatus. The invention further relates to a cleaned non-aqueous liquid obtainable by the process.

Claims

1. A reverse-phase suspension polymerization process for manufacturing polymer beads, comprising: forming a suspension of monomer beads from a water-soluble ethylenically unsaturated monomer or monomer blend in a non-aqueous liquid in a vessel, initiating polymerization to obtain polymer beads, removing a suspension of the polymer beads in the non-aqueous liquid from the vessel and recovering water soluble polymer beads from the suspension, in which the non-aqueous liquid contains impurities which comprise particles, and then transferring the non-aqueous liquid from the suspension to a cleaning stage, in which the cleaning stage provides a cleaned non-aqueous liquid suitable for use in a reverse-phase suspension polymerization process, which cleaning stage comprises removing particles from the non-aqueous liquid in at least one filtration operation, wherein the at least one filtration operation is cross-flow filtration using a membrane or filter formed from a member selected from the group consisting of ceramics, metals, polytetrafluoroethylene, and polyvinylidene fluoride, wherein the membrane or filter used has a pore size of less than 500 nm.

2. The process of claim 1, wherein the cleaned non-aqueous liquid is recycled back into the reverse-phase suspension polymerization process.

3. The process of claim 1, performed continuously.

4. The process of claim 1, wherein the non-aqueous liquid is provided as a volume in the vessel, which volume extends between at least one polymer bead discharge point and at least one monomer feed point, and in which the aqueous monomer or monomer blend is extruded through one or more orifices to form monomer beads which are allowed to flow towards the polymer bead discharge point, and initiating polymerization of the aqueous monomer beads to form polymerizing beads, wherein the polymerizing beads have formed polymer beads when they reach the polymer bead discharge point.

5. The process of claim 4, wherein the polymer beads removed from the vessel at the polymer bead discharge point are subjected to a post polymerization stage.

6. The process of claim 1, wherein the membrane or filter medium has either i) a mean pore diameter of less than 100 nm; or ii) a molecular weight cut off (MWCO) below 150,000 Da.

7. The process of claim 1, wherein the process is conducted in two or more vessels in parallel.

8. The process of claim 1, further comprising grinding the formed polymer beads to produce a polymer powder.

9. The process of claim 1, wherein the cleaning stage comprises a cross-flow filtration operation which provides a stream of clarified non-aqueous liquid and a stream of retentate non-aqueous liquid in which the clarified non-aqueous liquid comprises a lower concentration of particles than the non-aqueous liquid prior to the cross-flow filtration operation, and the retentate non-aqueous liquid comprises a higher concentration of particles than the non-aqueous liquid prior to the cross-flow filtration operation, and in which the stream of retentate non-aqueous liquid is subjected to an evaporation operation and a condensation operation to provide a stream of condensed non-aqueous liquid, wherein the cleaning stage also comprises combining the stream of clarified non-aqueous liquid and the stream of condensed non-aqueous liquid and forming the cleaned non-aqueous liquid.

10. The process of claim 9, wherein the evaporation operation comprises wiped film evaporation.

11. The process of claim 1, wherein the non-aqueous liquid comprises an amphipathic stabilizer.

12. The process of 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 a salt thereof, methacrylic acid or a salt thereof, itaconic acid or a salt thereof, maleic acid or a salt thereof, 2-acrylamido-2-propane sulphonic acid or a salt thereof, vinyl sulphonic acid or a salt thereof, allyl sulphonic acid or a salt thereof, dimethyl amino ethyl acrylate or an acid salt or quaternary ammonium salt thereof, dimethyl amino ethyl methacrylate or an acid salt or quaternary ammonium salt thereof, dimethyl amino propyl acrylamide or an acid salt or quaternary ammonium salt thereof, and dimethyl amino propyl methacrylamide or an acid salt or quaternary ammonium salt thereof.

13. The process of claim 12, wherein at least one monomer is prepared by a chemically catalyzed process, a biologically catalyzed process or a biological process.

14. The process of claim 12, wherein the acrylamide is prepared by a biological catalyzed process or a biological process.

Description

(1) 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 a 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.

(2) 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.

(3) FIG. 3: Schematic representation of the cross-flow testing setup used for the experiments.

EXAMPLE

(4) Inverse suspension polymerisation of an aqueous monomer is carried out in Exxsol D40 as a non-aqueous liquid. Aqueous monomer phase comprised of aqueous monomers, preferably acrylamide, dimethylaminoethyl acrylate methyl chloride quaternary salt. A stabilizer (0.1 wt-% with respect to dispersed phase; a copolymer from methyl methacrylate, stearyl methacrylate, acrylic acid and methacrylic acid) is added to the continuous phase and into the dispersed monomer solution an initiator2,2-Azobis(2-methylpropionamidine)dihydrochlorideis mixed in. After the polymerization, solid polymer is separated from the continuous phase (Exxsol D40) which is subsequently filtered through cross-flow filtration setup.

(5) The Exxsol D40 resulting from the suspension polymerisation process prior to any cleaning contains fine particles (residual polymer product and other materials) and the uncleaned Exxsol D40 is usually turbid due to insolubility of the product in Exxsol D40. Accumulation of these fines leads to process instability, hinders polymerization, and has impact on the product quality. Removal of these impurities is therefore highly desirable.

(6) Cross-flow filtration setup which is used in experiments is shown in FIG. 3. The cross-flow setup consists of a feed vessel and a circulation loop containing the membrane module and a heat exchanger (not shown). The permeate can be recycled to the feed vessel or can be withdrawn and collected in a permeate vessel. The transmembrane pressure, TMP, can be adjusted using valve V1. The TMP was set to values of 0.5 to 1.5 bar. The feed velocity was varied between 1.5 and 4 m/s. Fl and PI are flow rate and pressure indicators. TICtemperature indication and control of the temperature in the feed vessel. V2 valve is allowing to switch from running the concentrate back into the feed vessel to bleeding it out of the circulation loop.

(7) The example describes test performed on a setup in FIG. 3 using Pall Schumacher membrane with a nominal pore size of 10 nm. Membrane had a length of 100 cm and was mounted in a stainless steel tubular module. Experiment was conducted at 30 C.

(8) Solvent flux of a pure Exxsol D40 under TMP of 0.5 bar was 100 kg m.sup.2 h.sup.1. Filtration of Exxsol D40 previously used in polymerizations resulted in stable performanceflux of around 25 kg m.sup.2 h.sup.1 remained constant over the concentration factor of 13. Permeat was of a good quality, transparent, and successfully used in polymerisation reactions again resulting in a product of satisfactory quality.