Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Patent
1986-07-21
1988-11-01
Sever, Frank
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
159DIG27, 203 10, 203DIG17, 210641, 210642, 210648, 2101952, 21032178, B01D 1301
Patent
active
047818379
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to the concentration of a liquid by utilising the difference of osmotic pressure between two liquids, and to apparatus suitable therefore.
BACKGROUND ART
The application of reverse osmosis to the concentration of solutions, for example dilute food products, and to the production of potable water or water of reduced salts content from seawater has in many cases resulted in significant cost benefits when compared with the conventional evaporation and distillation processes respectively. Nevertheless, there is scope for a further substantial cost reduction by eliminating the fouling problem associated with hydrophilic reverse osmosis membranes. The wettability of these membranes provides for close contact with an adherence of foulants such as organic colourants, various inorganic salts, and suspended and colloidal matter. Fouling has in some cases been alleviated by precipitation and filtration pretreatment processes. However, this adds substantially to the cost of the overall process, thus reducing the attractiveness of the reverse osmosis technique.
Hydrophobic porous barriers (e.g. diffusion barriers, such as hydrophobic porous or microporous membranes) of various pore dimensions have been developed for various applications, e.g. for membrane distillation and artificial oxygenation.
Hydrophobic membranes are generally made from an hydrophobic polymer, e.g. polytetrafluoroethylene (TEFLON) or polypropylene, such as membranes produced under the name CELGARD.
Hydrophobic membranes can also be made from hydrophillic polymers which have been specially treated to have reticulation of fluorocarbon radicals at the surface of the polymer.
Hydrophobic membranes are widely used in the medical industry for artificial oxygenation of blood. Such artificial oxygenation units are discarded after use, and are readily available from hospitals after use.
Membrane distillation processes are known which rely on the temperature gradient between two solutions. However, an osmotic distillation process which relies on the difference in osmotic pressure between two solutions has not previously been described.
DISCLOSURE OF THE INVENTION
It is an object of this invention to provide a method of increasing the hydrophobicity of a porous barrier or membrane and to provide membranes prepared by said method.
It is a further object of this invention to provide a method of, and apparatus for, the concentration of a liquid by utilising the difference of osmotic pressure (i.e., osmotic pressure gradient) between two liquids.
It is another object of the present invention to recycle such membrane oxygenation units for use in a membrane separation process using as the driving force the difference of the osmotic pressure between two liquids to achieve a concentration of the liquid having the lower osmotic pressure, or to recover part of the energy available between the two different potential energies of the two different liquids due to the difference in osmotic pressure between the two liquids.
It is yet a further object of this invention to provide a method of, and apparatus for, the concentration of a dilute solution by an osmotic distillation process by the transfer of solvent from the dilute solution in a vapour state through a hydrophobic (non-wettable) porous barrier into a concentrated solution of higher osmotic pressure.
It is yet another object of this invention to provide a process for the fractionation of, or recovery of a solvent from, a solution by a combination of osmotic distillation and reverse osmosis processes.
These and other objects of the invention will be apparent from the following disclosure of the invention.
According to one aspect of the present invention there is provided a porous barrier or diffusion barrier for the concentration of a dilute solution of low osmotic pressure by osmotic distillation comprising an hydrophobic porous or microporous matrix wherein solvent from the dilute solution is transferred through the barrier from one side to the opposite side in a
REFERENCES:
patent: 2984623 (1961-05-01), Lee
patent: 3340186 (1967-09-01), Weyl
patent: 3342729 (1967-09-01), Strand
patent: 3405058 (1968-10-01), Miller
patent: 4476024 (1984-10-01), Cheng
patent: 4545862 (1985-10-01), Gore et al.
patent: 4581236 (1986-04-01), Bandel et al.
Limitinstant Limited
Sever Frank
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