Asymmetric membranes for use in nanofiltration

a technology of asymmetric membranes and nanofiltration, applied in the direction of membranes, filtration separation, separation processes, etc., can solve the problems of not being widely applied to the separation of organic solvent solutes, no reports to date describing the application of osn in strongly basic or acidic organic solvent environments, and integrally skinned polyimide membranes formed by phase inversion are not stable in all solvents, so as to achieve low or no flux and high flux

Inactive Publication Date: 2013-05-16
IMPERIAL INNOVATIONS LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0017]Membranes of the invention can be used for nanofiltration operations in organic solvents. In particular, they can be used for nanofiltration operations in solvents in which the base polybenzimidazole is soluble. This is advantageous with respect to many of the prior art asymmetric solvent nanofiltration membranes, which lose structure and dissolve in typical dope solvents such as dimethylacetimide (DMAc), and exhibit low or no flux in some chlorinated solvents such as dichloromethane. Further, membranes of the present invention can be employed in a feed stream for nanofiltration in which the solvent is strongly acidic or basic, or in which the feed stream contains components which are strongly acidic or basic. This is advantageous with respect to the prior art asymmetric solvent nanofiltration membranes, which lose structure and dissolve under strongly acidic or basic conditions. Membranes of the present invention however are stable in these solvents, offering acceptable flux and rejections. Yet a further advantage of the membranes of the present invention is that they may exhibit higher fluxes than known membranes when mixtures of water and organic solvent are being processed.

Problems solved by technology

Nanofiltration has been widely applied to filtration of aqueous fluids, but due to a lack of suitable solvent stable membranes has not been widely applied to the separation of solutes in organic solvents.
However, there are no reports to date describing the application of OSN in strongly basic or acidic organic solvent environments.
However integrally skinned polyimide membranes formed by phase inversion are not stable in all solvents, even when crosslinked according to GB 2,437,519.
In particular, they are not stable in strongly basic or acidic organic environments.
However, these methods are known to lead to a dramatic increase in the brittleness of the membranes, making them difficult to manufacture and use.

Method used

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  • Asymmetric membranes for use in nanofiltration
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  • Asymmetric membranes for use in nanofiltration

Examples

Experimental program
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example 1

[0082]Polybenzimidazole polymer was synthesised as follows.

[0083]625 gm of Polyphosporic acid (PPA) was weighted in a 1 liter 3 neck round bottom flask at room temperature followed by the fixing of flask to the overhead stirring assembly equipped with oil bath. The oil was heated to 155° C., at around 125° C. the addition of tetra-amine was started under the constant flow of dry nitrogen. The addition was very slow in such a way that it lasted for more than 15 minutes. After the completion of tetraamine addition the temperature was further raised to 170° C. and kept constant for 45 minutes flowed by diacid addition. The reaction was further kept stiffing for next 4 hrs at 170° C. After 4 hrs the reaction temperature was further raised to 210° C. for next 2.5 hrs followed by 230° C. for 2 hrs. At the end of reaction the viscous polymer solution was poured in large excess of water in the form of fine continuous fiber.

[0084]The crude PBI fibers were crushed in to fine pieces and furthe...

example 2

[0092]Membranes were formed as in Example 1 above and then crosslinked as follows.

[0093]The membranes were immersed into a bath of methyl isobutyl ketone and crosslinker (dibromobutane) for 12 hrs. at 60° C. temperature. The membrane was then removed from the crosslinking bath and washed with IPA to remove any residual crosslinker. Following this, the membrane was immersed into a bath of IPA / polyethylene glycol 400 (40 / 60, v / v %) to prevent drying out. The membranes were then air dried to remove excess solvent. The dried membrane was fixed to the glass plate with the help of PVC tape and heated in oven at 100° C. for 1 hr.

[0094]These crosslinked membranes were then tested for flux and rejection as described above. The data from these tests is shown in FIGS. 9 and 10.

example 3

[0095]Crosslinked polybenzimidazole membranes were prepared as per Example 3 and were immersed into undiluted solutions of monoethanolamine and trifluoroacetic acid and held at 30° C. The membranes were monitored for stability over 4 weeks. No change in the membranes appearance or properties was observed.

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Abstract

Improved integrally skinned asymmetric membranes for organic solvent nanofiltration, and their methods of preparation and use are disclosed. Membranes are formed from polybenzimidazoles by phase inversion and are then crosslinked by addition of crosslinking agents. These stabilise the membranes and allow solvent nanofiltration to be maintained even in the solvents from which the membranes were formed by phase inversion, and in strongly acidic and strongly basic solvents.

Description

FIELD OF THE INVENTION [0001]The present invention relates to asymmetric membranes for nanofiltration, particularly nanofiltration of solutes dissolved in organic solvents, and particularly the nanofiltration of solutes dissolved in strongly basic and acidic organic solvent environments.BACKGROUND TO THE INVENTION [0002]Membrane processes are well known in the art of separation science, and can be applied to a range of separations of species of varying molecular weights in liquid and gas phases (see for example “Membrane Technology and Applications” 2nd Edition, R. W. Baker, John Wiley and Sons Ltd, ISBN 0-470-85445-6).[0003]Nanofiltration is a membrane process utilising membranes whose pores are generally in the range 0.5-5 nm, and which have molecular weight cut-offs in the region of 200-2,000 Daltons. Molecular weight cut-off of a membrane is generally defined as the molecular weight of a molecule that would exhibit a rejection of 90% when subjected to nanofiltration by the membr...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): B01D71/62
CPCB01D61/027B01D67/0011B01D67/0079B01D67/0097B01D2325/022B01D69/141B01D71/62B01D2323/30B01D69/02B01D69/125
Inventor LIVINGSTON, ANDREW GUYBHOLE, YOGESH SURESH
Owner IMPERIAL INNOVATIONS LTD
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