Compositions useful for making microporous polyvinylidene fluoride membranes, and process

A composition useful for preparing a microporous polyvinylidene fluoride polymer membrane comprising a mixture of:

• A. at least one polyvinylidene fluoride polymer;
• and
• B. at least one solvent selected from the group consisting essentially of glycerol monoacetate, glycerol diacetate, glycerol triacetate, and mixtures thereof, in an amount itself sufficient to solubilize the polyvinylidene fluoride polymer at the membrane formation temperature;
• wherein the polyvinylidene fluoride polymer and solvent are present in a ratio useful to form a microporous membrane useful for a liquid separation process.

A process for preparing a microporous polyvinylidene fluoride polymer membrane comprising the steps of:

• A. forming a mixture comprising:
• i. at least one polyvinylidene fluoride polymer, and
• ii. at least one solvent selected from the group consisting essentially of glycerol monoacetate, glycerol diacetate, glycerol triacetate, and mixtures thereof, in an amount itself sufficient to solubilize the polyvinylidene fluoride polymer at the membrane formation temperature;
• B. heating the mixture to a temperature at which the mixture forms a homogeneous fluid and possesses sufficient viscosity to be extruded, molded, or cast into a microporous membrane;
• C. extruding, molding, or casting the viscous homogeneous fluid into a microporous membrane;
• and
• D. passing the membrane through one or more quench zones wherein the membrane gels and solidifies;
• wherein the microporous membrane so formed is useful for membrane liquid separation process.

A method for the production of a microporous polyvinylidene fluoride polymer membrane which comprises:

• A. mixing at least one polyvinylidene fluoride polymer with at least one solvent selected from the group consisting essentially of glycerol monoacetate, glycerol diacetate, glycerol triacetate, and mixtures thereof, in a amount itself sufficient to solubilize the polyvinylidene fluoride polymer at the membrane formation temperature;
• B. heating the mixture to a temperature at which the mixture forms a homogeneous fluid and possesses sufficient viscosity to be formed into a membrane of a desired configuration;
• C. forming said homogeneous fluid into a membrane of a desired configuration;
• and
• D. passing the membrane through at least one gaseous quench zone under conditions such that the mixture cools and begins to phase separate while minimizing the loss of solvent(s) from the external surface of the membrane.

A method for the production of a hollow fiber microporous polyvinylidene fluoride polymer membrane which comprises:

• A. mixing at least one polyvinylidene fluoride polymer with at least one solvent selected from the group consisting essentially of glycerol monoacetate, glycerol diacetate, glycerol triacetate, and mixtures thereof, in an amount itself sufficient to solubilize the polyvinylidene fluoride polymer at the membrane formation temperature;
• B. heating the mixture to a temperature at which the mixture forms a homogeneous fluid and possesses a sufficient viscosity at extrusion conditions to permit extrusion of a hollow fiber membrane;
• C. extruding the mixture into a hollow fiber membrane using a core fluid;
• and
• D. passing the hollow fiber membrane through at least one gaseous quench zone under conditions such that the mixture cools and begins to phase separate while minimizing the loss of solvent(s) from the external surface of the hollow fiber membrane.

A method for the production of a sheet microporous polyvinylidene fluoride polymer membrane which comprises:

• A. mixing at least one polyvinylidene fluoride polymer with at least one solvent selected from the group consisting essentially of glycerol monoacetate, glycerol diacetate, glycerol triacetate, and mixtures thereof, in an amount itself sufficient to solubilize the polyvinylidene fluoride polymer at the membrane formation temperature;
• B. heating the mixture to a temperature at which the mixture forms a homogeneous fluid and possesses sufficient viscosity, at extrusion conditions to permit extrusion of a sheet membrane;
• C. extruding the mixture into a sheet membrane;
• and
• D. passing the sheet membrane through at least one gaseous quench zone under conditions such that the mixture cools and begins to phase separate while minimizing the loss of solvent(s) from the external surfaces of the sheet membrane.