Polymer porous structure and process

Details Polymer porous structure and process Polymer porous structure and process

1995-10-11

1997-12-16

Fortuna, Ana

Liquid purification or separation

Processes

Liquid/liquid solvent or colloidal extraction or diffusing...

210654, 210490, 21050041, 21050027, 264 451, 427245, B01D 6100

Patent

active

056981058

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a novel class of polymer membranes, particularly to a structure having high flux and salt rejection, which can be used to advantage in reverse osmosis, and to a process for the construction of such a membrane.
Reverse osmosis membranes, whether integral asymmetric or composite in structure, are known, e.g. those comprising a layer of a sulphonated polysulphone active material, and the latter often have an acceptable performance in terms of water flux and rejection of dissolved salts, the active material providing the good salt rejection and having good chemical stability, e.g. chlorine-, pH- and heat-resistance. However, in general, both the flux and salt rejection of such membranes, represent a compromise level of performance, which is no more than acceptable. Thus, if the water flux of such membranes is at a commercially viable level of performance, the salt rejection is at a level of performance which is merely `average` and vice versa. This means that such membranes can in practice only be used in the reverse osmosis (i.e. in e.g. desalination) of feedwaters with a relatively low salt content, or with the additional cost of recycling any feedwater with a higher salt content.
There is clearly a need for a reverse osmosis membrane with a structure having high flux and an active material having good salt rejection and chemical stability, the performance of which in both aspects is appreciably better than that of known membranes which have good chemical stability, e.g. those comprising a layer of a sulphonated polysulphone.
By `appreciably better` herein we mean that the salt transmission is less than 40% of the value for the corresponding known membrane, whilst the water flux is in excess of 40% of the value for the corresponding known membrane. Preferably, the salt transmission is less than 30%, in particular less than 20%, of the value for the corresponding known membrane, whilst the water flux is preferably in excess of 50%, in particular more than 60%, of the value for the known membrane.
We have now obtained high performance reverse osmosis membranes of this type, in which we have for the first time been able to select a flux level also providing good salt rejection.
Accordingly, the present invention provides a reverse osmosis membrane comprising a support membrane which itself has properties of salt rejection laminated to a layer comprising a cross-linked optionally protected polyol.
Such membranes may be used in the reverse osmosis (i.e. in e.g. desalination) of feedwaters with a relatively high salt content, with minimisation of the cost of recycling any such feedwater with a higher salt content.
The support membrane is one which (in the absence of the layer of cross-linked optionally protected polyol) has salt rejection properties. This support membrane is preferably a reverse osmosis membrane but may be a nanofiltration membrane.
The membranes of the invention may be classed as composite membranes by virtue of their construction which incorporates the support membrane (which itself has salt rejection properties) and the cross-linked polyol layer laminated thereto. The support membrane may, for example, be an integral asymmetric membrane. It is however more preferred that the support membrane is itself a composite membrane (referred to herein as a composite support membrane to distinguish it form the membranes of the invention). The composite support membrane may for example comprise a layer providing a degree of salt rejection laminated to an ultrafiltration support membrane. Membranes in accordance with the invention comprising a composite support membrane and a layer of cross-linked polyol are referred to herein as multi-layer composite membranes.
Preferably the polyol has a weight average molecular weight of 500 to 500,000.
The polyol in any membrane of the present invention will often be cross-linked by means of an active cross-linking agent.
The cross-linking agent may be any species which is capable of reacting with the polyol hydroxyl functions intermolecularly,

REFERENCES:
patent: 4559139 (1985-12-01), Uemura et al.
patent: 4758343 (1988-07-01), Sasaki et al.
patent: 4834886 (1989-05-01), Cadotte
patent: 4895661 (1990-01-01), Cadotte

Affiliated with

Also associated with

Rating

Polymer porous structure and process does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Polymer porous structure and process, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polymer porous structure and process will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-202418