Membrane module
The present invention relates to a method for curing adhesives used in the manufacture of membrane modules containing polymeric membranes, particularly polyimide based membranes used for the nanofiltration or ultrafiltration of solutes dissolved in organic solvents using microwaves. To maximise the chemical resistance of the adhesive used in these organic solvent applications, it must be as fully reacted and crosslinked (“cured”) as possible. Typically, thermal processing (heating) of the entire membrane module is used to cure the adhesives. However, the time and temperature required to achieve this high degree of completion of reaction may damage the separation performance of the membrane contained within the membrane module. In one particular aspect, this process utilises microwaves to preferentially promote the curing of epoxy adhesives over the general heating of the membrane module.
1. A process for manufacturing membrane modules comprising a polymeric nanofiltration or ultrafiltration membrane wherein the membrane is substantially unaffected by microwave radiation, a feed spacer, a permeate spacer, a permeate tube, and end caps, the process comprising the steps of:
(a) applying glue lines of an epoxy adhesive containing one or more polarisable bonds to the polymeric nanofiltration or ultrafiltration membrane, wherein the polarisable bonds are capable of being excited by microwave radiation;
(b) positioning the polymeric nanofiltration or ultrafiltration membrane in its desired location within the membrane module and rolling the membrane and spacers to produce a green spiral wound membrane module ensemble with said adhesive not cured to a degree sufficient to guarantee structural integrity of the membrane ensemble; and
(c) applying microwave radiation to the green ensemble to cure the adhesive used to seal the module.
2. A process according to claim 1 wherein the adhesive requires heating at temperatures above 40 deg. C. to fully cure.
3. A process according to claim 1 wherein the adhesive contains epoxy functional groups.
4. A process according to claim 1 wherein the adhesive contains epoxy resins based on the diglycidylether of bis-phenol A (DGEBA) or diglycidylether of bis-phenol F (DGEBF) or glycidyl ether of a phenolic novolac resin (novolac epoxy resins).
5. A process according to claim 1 wherein the adhesive requires a curing agent based on an aliphatic amine or an aromatic amine or a polyamide or an aminoamide or a mercaptan or a polysulphide or a latent curing agent or an anhydride or a catalytic curing agent for the adhesive to cure.
6. A process according to claim 1 wherein the adhesive requires greater than 0.1 hour to fully cure.
7. A process according to claim 1 wherein the membrane material consists of an organic polymer material and optionally contains imide bonds.
8. A process according to claim 7 wherein the organic polymer comprises the following formulation:
9. A process according to claim 1 in which the microwave radiation is in the frequency range 1 to 100 GHz.
10. A process according to claim 1 in which the power of the microwave source is in the range 50 W to 5 kW.
11. A process according to claim 1 in which the microwave radiation is switched so that it is applied in discrete time intervals.
12. A process according to claim 11 , wherein the discrete time interval is from 1 second to 10 minutes.
13. A process according to claim 11 , wherein radiation is applied for a single time interval or is applied in a plurality of pulses.
14. A process according to claim 1 in which the frequency of the microwave radiation is modulated.