Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Patent
1996-09-23
1998-12-08
Fortuna, Ana
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
210653, 210496, 21050026, 21050041, 21050029, 21050025, 427343, 427165, 427244, B01D 6100
Patent
active
058464280
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a method for modifying the surface of a membrane and membranes which can be obtained using this method. The method according to the invention enables the surface of a porous organic or inorganic membrane to be modified, so as to control the volume of liquid transported and the diffusion of species through the membrane. The membranes thus modified are useful for the regeneration of photographic solutions, in particular black and white developers, or for the separation of organic compounds from aqueous effluents.
Membranes are widely used in separation techniques. The transport of fluids through membranes takes place by means of different mechanisms, which depend on the structure and nature of the membrane. The most widely used membranes are formed from synthetic or natural organic polymers. Porous membranes contain voids which are large compared with the size of the molecules transported. In these membranes, the pores are interconnected and the solid materials represent only a small percentage of the total volume of the membrane. The porous membranes available commercially have a pore size of between 0.005 .mu.m and 20 .mu.m. They are made from a great variety of polymers so as to obtain a wide range of rigidities and mechanical strengths. Generally, for separation in the aqueous phase, either hydrophilic membranes or hydrophobic membranes are used, according to the experimental conditions (pH, oxidising medium), but also according to the type of molecules to be separated. Thus molecules of the hydrophobic type will tend to be adsorbed more on a hydrophobic support. In order to prevent these molecules from being adsorbed, the surface of the hydrophobic support can be modified by incorporating a hydrophilic group or by means of a fine surface deposition of a hydrophilic polymer.
For pressurised technologies (microfiltration, ultrafiltration, nanofiltration, reverse osmosis), polymers of the hydrophilic type are quite suitable, since they make it possible to have high flows. This is true of cellulose and its derivatives, which have been used in reverse osmosis for a very long time (high flow, good separation selectivity, low cost). However, porous membranes of the hydrophilic type are highly sensitive to the phenomenon of swelling when they come into contact with an aqueous solution (and this behaviour can be more pronounced depending on the pH). Furthermore, these hydrophilic materials have low stability in the presence of certain polar organic solvents, acids or bases, as well as oxidants (chorine, hypochlorite). These materials are also extremely sensitive to bacterial growth, all the more so since they cannot be subjected to base+oxidant or acid+oxidant treatments owing to their low resistance to these chemical agents. For these materials, control of the hydrophilic/hydrophobic balance enables the chemical stability of the support to be increased as a function of the pH and the various aforementioned reagents. It also increases the resistance of these materials to the mechanical stresses arising from the pressure of use.
For systems of the dialysis type, in general what is involved is the separation of the macromolecules and the mineral species (salts) or molecules with a low molecular weight. In this case, hydrophilic materials of the cellulose type and derivatives of cellulose are very well suited to treatment of such environments (high proportion of water). The osmotic forces constitute the "driving" element of this separation process. In this precise case, modification of the hydrophilic/hydrophobic balance will be used to increase the stability of the membrane vis-a-vis the experimental conditions (pH, presence of organic solvents, etc). In general, in the case of dialysis, no attempt is made to control the flow of water; the initial solution is diluted and the small molecules are transported through the membrane. If the solution is to be concentrated, another technology such as ultrafiltration is used in addition to dialysis. On the other hand, in the case of regenerat
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Martin Didier
Poncelet Olivier Jean-Christian
Rigola Jeanine
Eastman Kodak Company
Everett John R.
Fortuna Ana
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