Dispersing casting of integral skinned highly asymmetric polymer membranes
First Claim
1. A method of making a highly asymmetric integrally skinned polymer membrane with excellent retention properties, a high flow rate, and improved resistance to fouling, said method comprising:
- A. mixing a polymer and a solvent to produce a polymer solution,B. adding a non-solvent in an amount sufficient to produce an unstable dispersion within the binodal or spinodal,C. casting said dispersion on a support,D. quenching said dispersion with a non-solvent quenching liquid in which the solvent is freely soluble but in which the polymer is substantially insoluble, andE. recovering a membrane having a bulk porosity greater than 70%, an integral skin with an mean pore diameter of from about 0.003 to about 3.0 microns and a reticulated integral porous support layer with a gradually increasing mean pore diameter from the skin face to the opposite face, so that at the opposite face the pores have an mean diameter of from at least about 10 to about 20,000 times the average pore diameter of the pores of the skin.
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Abstract
There is disclosed, in one aspect, an improved highly asymmetric membrane comprising a skin and a porous asymmetric support. The skin contains pores which have an mean pore diameter of from about 0.005 to about 3.0 microns and the asymmetric support comprises a reticulated structure which contains pores which have pore diameters of from about 10 to about 20,000 times as large as the pore diameter of the pores of the skin. The membrane has a bulk porosity greater than about 70%. In another aspect, there is disclosed a process for preparing these membranes. This process comprises casting a polymer dope while the dope is in an unstable liquid dispersion condition. The concentration of polymer in the polymer dope should be high enough to produce a coherent membrane yet low enough to form a substantially all-reticulated structure within the asymmetric support. The membranes are characterized by high flow rates, excellent retention properties, and improved resistance to fouling.
174 Citations
11 Claims
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1. A method of making a highly asymmetric integrally skinned polymer membrane with excellent retention properties, a high flow rate, and improved resistance to fouling, said method comprising:
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A. mixing a polymer and a solvent to produce a polymer solution, B. adding a non-solvent in an amount sufficient to produce an unstable dispersion within the binodal or spinodal, C. casting said dispersion on a support, D. quenching said dispersion with a non-solvent quenching liquid in which the solvent is freely soluble but in which the polymer is substantially insoluble, and E. recovering a membrane having a bulk porosity greater than 70%, an integral skin with an mean pore diameter of from about 0.003 to about 3.0 microns and a reticulated integral porous support layer with a gradually increasing mean pore diameter from the skin face to the opposite face, so that at the opposite face the pores have an mean diameter of from at least about 10 to about 20,000 times the average pore diameter of the pores of the skin. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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Specification