JPH04225822A - Composition for producing cellulose ester membrane for liquid separation - Google Patents

Abstract

PURPOSE: To permit to change a solvent and non-solvent to nonpoisonous material at final usage of a membrane by including a mixture of cellulose ester and a specific solvent to dissolve the cellulose ester at temperature of form a membrane and making the cellulose ester and solvent existent ratio to form a semipermeable membrane. CONSTITUTION: A mixture comprising at least one kind of cellulose esters and at least one kind of solvent selected from glycerol monoacetate, glycerol diacetate, glycerol triacetate or a mixture thereof to dissolve the cellulose esters at temperature to form a membrane, is prepared where the ratio of the cellulose ester and solvent is the one to form a semipermeable membrane. The mixture is heated to the temperature to form a uniform fluid and the uniform fluid is extruded or cast to the semipermeable membrane which is cured and gelatinized by passing through one or more quench zones. The semipermeable membrane obtained in this way is useful for ultra-, micro- or reverse osmotic filtration.

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION This invention relates to novel compositions useful for producing cellulose ester semipermeable membranes for liquid separation. The invention further relates to a method of manufacturing cellulose ester semipermeable membranes for liquid separation using such compositions. The present invention also relates to cellulose ester semipermeable membranes containing certain organic compounds useful for liquid separation.

BACKGROUND OF THE INVENTION Cellulose ester membranes have long been used in membrane liquid separation processes such as microfiltration, ultrafiltration, dialysis, and reverse osmosis. Typically, cellulose ester membranes are made by extrusion, molding, or casting from mixtures containing polymers, solvents, and optional nonsolvents. The solvent is a compound in which the polymer is substantially soluble at the film formation temperature. A nonsolvent is a compound in which the polymer is substantially insoluble at the film formation temperature. Solvents used in the production of cellulose ester membranes include sulfolane, dimethylformamide, N-methylpyrrolidone, and acetone. Nonsolvents that have been used for cellulose esters include methanol, propanol, water, and maleic acid. Polyethylene glycol was used as a non-solvent for cellulose triacetate. Even such residual amounts of solvent and nonsolvent generally cannot remain in the membrane. This is because they cause unacceptable contamination of the fluid being treated. Avoiding such contamination is particularly important in the treatment of serum by dialysis or the desalination of drinking water by reverse osmosis. Solvents and non-solvents are therefore completely removed during membrane production by extensive pouring. Once the solvent and nonsolvent are removed from the membrane, they present extensive repurification problems before disposal or reuse.

After membrane fabrication and removal of solvent and nonsolvent, it is often desirable to dry the water-wet cellulose ester membrane before equipment assembly, storage, or transportation. However, cellulose ester membranes should not be dried directly without pretreatment. This is because direct drying results in adverse structural changes such as cracking or pore collapse that adversely affect membrane performance. Therefore, the pore structure of the membrane is preferably protected during the drying process. This is generally achieved by introducing a non-volatile, water-soluble compound such as glycerol into the pore structure of the membrane before drying. Non-volatile water-soluble substances also preferably serve as surfactants or wetting agents for subsequent rewetting of the membrane. This method is generally referred to as “
This is called "replasticization."

[0004] Such membrane manufacturing methods require complete removal of extrusion, molding or casting solvents and non-solvents, followed by replasticization with non-volatile compounds if the membrane is to be dried. However, it is complicated, time consuming and expensive. The extrusion, molding, or casting solvent must be capable of dissolving the cellulose ester to produce a homogeneous blend that is extrudable, moldable, or castable. However, such compounds can also adversely affect membrane integrity if used as replasticizers. Therefore, to date, the solvents used for extrusion, molding or casting are different from the replasticizers, resulting in multi-step membrane manufacturing methods. Such complex multi-step membrane manufacturing methods can result in considerable variation in membrane performance.

[0005] What is needed is a method for extruding, molding or casting cellulose esters in which the solvent and non-solvent are not hazardous or hazardous or can be converted into substances that are not hazardous or hazardous in the end use of the membrane. The composition is Therefore, such solvents and non-solvents must not be leached from the membrane before use. Additionally, solvents and non-solvents that act as plasticizers during extrusion, molding or casting and also act as replasticizers during drying are highly desirable.

[Means for Solving the Problems] The present invention provides (
A) at least one cellulose ester and (B) glycerol monoacetate, glycerol diacetate, which solubilizes the cellulose ester at the film formation temperature.
glycerol triacetate, or mixtures thereof,
A novel composition useful for producing a cellulose ester semipermeable membrane for liquid separation, characterized in that the cellulose ester and the solvent are present in a ratio that produces a semipermeable membrane. . Optionally, non-solvent glycerol can be included in the mixture.

In another aspect, the invention provides the following steps: (A) (i) at least one cellulose ester and (
ii) producing a mixture comprising at least one solvent of glycerol monoacetate, glycerol diacetate, glycerol triacetate, or a mixture thereof, which solubilizes the cellulose ester at the film formation temperature; (B) the mixture is homogeneous; (C) extruding, forming, or casting the homogeneous fluid into a semipermeable membrane; and (D) passing the membrane through one or more quench zones to gel the membrane. and curing; and the semipermeable membrane thus produced is useful in a membrane-based liquid separation method.

Another aspect of the invention is a cellulose ester membrane useful for liquid separation comprising at least one glycerol monoacetate, glycerol diacetate, glycerol triacetate, or mixtures thereof, and optionally comprising glycerol. Located in an ester semipermeable membrane.

The membrane manufacturing solvent (glycerol monoacetate, glycerol diacetate, glycerol triacetate, or mixtures thereof) and nonsolvent (glycerol) can be converted into materials that are compatible and/or acceptable for the membrane's end use. Because of this, the membrane does not require extensive leaching before use. Moreover, in some cases the solvent and nonsolvent can act as both plasticizers and replasticizers, so that a separate replasticization step is not required.

FIG. 1 shows the compatibility at room temperature and normal pressure of various compositions of cellulose triacetate, a monoacetate-glycerol mixture (trade name Hallco C-918 monoacetin of The C.P. Hall Company), and glycerol. shows.

The present invention comprises a composition useful for producing cellulose ester membranes comprising at least one cellulose ester and at least one solvent of glycerol monoacetate, glycerol diacetate, glycerol triacetate, or mixtures thereof. . The solvent is present in an amount sufficient to solubilize the cellulose ester at the film formation temperature. A non-solvent can also be present as an optional component. The cellulose ester, solvent, and optional nonsolvent are present in a suitable ratio to create a semipermeable membrane suitable for liquid separation processes.

Embodiments of the Invention Cellulose esters and their synthesis are well known in the art. “Cellulo
``Se Esters, Organic,'' Encyclopedia of Polymer Science and Engineering, 2nd Edition, Volume 3, New York, USA.
Wiley Interscience Publication Office, No. 158-2
See page 26. Preferred cellulose esters useful in the present invention are cellulose acetate, cellulose propionate, cellulose butyrate, cellulose nitrate, cellulose methacrylate, cellulose phthalate, and mixtures thereof. Mixed cellulose esters such as cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate methacrylate are also within the scope of this invention. The term "mixed cellulose ester" refers to cellulose esters in which the polymer backbone contains at least two different ester moieties. Mixed cellulose esters are thus distinctly different from physical mixtures or blends of two or more different cellulose esters. A more preferred cellulose ester for use in the present invention is cellulose acetate, commonly referred to as cellulose acetate, cellulose diacetate, cellulose triacetate, and mixtures thereof. Cellulose acetate has different acetyl contents depending on the degree of substitution. The acetyl content ranges from 11.7% by weight when the degree of substitution is 0.5 to 44.5% by weight when the degree of substitution is 3.
It ranges up to 8% by weight. Cellulose diacetate having an acetyl content of about 32.0 to about 41.0% by weight, and cellulose triacetate having an acetyl content of about 41.0 to about 44.8% by weight, and mixtures thereof, are useful in the present invention. Particularly preferred.

Preferred solvents useful in the present invention are glycerol monoacetate (acetin), glycerol diacetate (diacetin), glycerol triacetate (triacetin), and mixtures thereof. More preferred solvents are glycerol monoacetate, glycerol diacetate, and mixtures thereof. Solvents useful in the present invention may contain small amounts of other compounds that are not deleterious to the membrane or unacceptable for membrane applications. Preferably, these small amounts of impurities in the solvent are less than 15% by weight, more preferably less than 5% by weight. A preferred optional nonsolvent for the present invention is glycerol.

[0014] The concentrations of the components in extrusion, molding or casting compositions may vary. Compatibility of the composition at the extrusion, molding, or casting temperature is one factor to consider when preparing compositions for extrusion, molding, or casting. Compatibility of polymer solutions can be easily determined experimentally by methods well known in the art. The amount of glycerol acetate, glycerol diacetate, or glycerol triacetate used in the compositions of the invention is advantageously sufficient to solubilize the cellulose ester polymer at the extrusion, molding or casting temperature. That is, no other solvent is required to solubilize the cellulose ester. The end use of the membrane is another factor in determining a suitable blend composition. This is because the preferred pore size of the membrane and the rate of migration through the membrane will vary depending on the intended use of the membrane.

For membranes useful for ultrafiltration or microfiltration, the concentration of cellulose ester is preferably at least 10% by weight but less than 80% by weight;
More preferably at least 15% but less than 60% by weight. The concentration of the solvent (glycerol monoacetate, glycerol diacetate, glycerol triacetate or a mixture thereof is preferably 20 to 90% by weight, more preferably 40 to 85% by weight. The concentration of the optional non-solvent (glycerol) is Preferably 0
~80% by weight, more preferably 5~60% by weight.

For membranes useful in dialysis, the concentration of cellulose ester is preferably 10-60% by weight, more preferably 15-55% by weight. The concentration of the solvent (glycerol monoacetate, glycerol diacetate, glycerol triacetate or mixtures thereof) is preferably 40 to 90% by weight, more preferably 45 to 85% by weight. The concentration of the optional non-solvent (glycerol) is preferably 0 to 50% by weight, more preferably 5 to 50% by weight.
It is 40% by weight.

For membranes useful in reverse osmosis, the concentration of cellulose ester is preferably 25-65% by weight, more preferably 35-60% by weight. The concentration of the solvent (glycerol monoacetate, glycerol diacetate, glycerol triacetate, or mixtures thereof) is preferably 15 to 75% by weight, more preferably 35 to 6% by weight.
It is 5% by weight. The concentration of the optional non-solvent (glycerol) is preferably 0 to 30% by weight, more preferably 0 to 20% by weight.

The compositions of the present invention can be used to make membranes useful in liquid membrane separation processes such as microfiltration, ultrafiltration, dialysis, and reverse osmosis. Such membranes can be manufactured by several different methods. In one preferred method, the cellulose ester composition is extruded, molded or casted and then air quenched. In another preferred method, the cellulose ester composition is extruded, molded or casted, then quenched, leached and dried. In yet another preferred method, the cellulose ester composition is extruded, molded or casted, then quenched, soaked, replasticized and dried. The choice of membrane manufacturing method is determined in part by the desired membrane properties.

The membrane is first extruded, molded or casted from the cellulose ester composition as described above. For casting, a homogeneous blend is produced with a viscosity suitable for casting at a given temperature. For casting, the viscosity of the blend is preferably between 2 and
25 poise (0.2 to 2.5 Pa·S). Casting blends can be casted at room temperature or at elevated temperatures depending on the viscosity of the blend. The blend is preferably casted at a temperature of about 25 to about 200C. The membrane is ultrafiltration, fine ▲
In embodiments useful for filtration or dialysis, the casting blend preferably contains 8-50% by weight cellulose ester, more preferably 12-40% by weight cellulose ester. In embodiments where the membrane is useful for reverse osmosis, the blend preferably comprises 10-60% by weight cellulose ester, more preferably 15-50% by weight cellulose ester. The blend may be casted by pouring the blend onto a flat support surface and drawing the blend to the appropriate thickness with a suitable tool such as a doctor blade or casting rod. Alternatively, the blend can be cast in a continuous process by casting the blend on an endless belt or rotating drum. The casting surface is a surface from which the finishing film can subsequently be easily separated from the surface. For example, the membrane can be cast onto a substrate with low surface energy, such as silicone, exposed glass, or metal, or onto a surface to which the membrane will not adhere. The blend can also be cast onto surfaces of liquids with which the polymer is immiscible, such as water or mercury. Alternatively, the blend can be cast onto a support surface, such as a nonwoven web, that is not subsequently dissolved from the finished film. The membrane can also be casted on a permanent support surface that does not substantially impede migration through the membrane. This membrane can then be processed in the same manner as described below for extruded membranes.

In the case of extrusion, the components of the composition for extrusion can be mixed in conventional mixing equipment, such as a Hobart mixer, in a conventional manner prior to extrusion. Alternatively, the extrusion composition can be prepared by extruding the mixture through a twin screw extruder, cooling the extrudate, and grinding or pelletizing the extrudate to a particle size that can be easily fed into a single or twin screw extruder. It can also be homogenized by The components of the extrusion composition can also be mixed directly in a melt pot or twin screw extruder and extruded into a membrane in a single step.

The viscosity of the mixture should not be so high that the mixture is too viscous to be extruded at temperatures that do not adversely affect the polymer. On the other hand, the viscosity must not be so low that the mixture cannot retain its desired shape upon exiting the extrusion die. The membrane can maintain its desired shape by cooling or solidifying during extrusion. In embodiments where the membrane is useful for ultrafiltration, microfiltration or dialysis, the mixture preferably contains 8 to 80% by weight cellulose ester, more preferably 15 to 60% by weight cellulose ester. including. In embodiments where the membrane is useful for reverse osmosis, the mixture preferably contains 10-80% by weight
of cellulose ester, more preferably 15 to 60% by weight of cellulose ester.

The mixture is heated to a temperature that results in a homogeneous fluid with a viscosity suitable for extrusion. The temperature should not be so high that significant decomposition of the cellulose ester occurs. The mixture should not be so low that the fluid is too viscous to be extruded. Extrusion temperature is preferably 20-250
℃, more preferably 25 to 220℃.

The polymer, solvent, and optional nonsolvent are extruded through a sheet, hollow tube, or hollow fiber die (spinneret). Hollow fiber spinnerets are typically porous and therefore produce a large number of hollow fiber irregularities. The hollow fiber spinneret includes a device that supplies fluid to the core of the extrudate. The core fluid is used to prevent the hollow fibers from collapsing as they exit the spinneret. The core fluid can be a gas such as nitrogen, air, carbon dioxide, or other inert gas, or a liquid that is a non-solvent for the polymer, such as water or glycerol. The temperature and composition of the core fluid can affect membrane properties.

The extrudate exiting the die enters one or more quench zones. The environment of the quench zone can be gaseous or liquid. In the quench zone, the extrudate is cooled and gelation and solidification of the film occurs. In a preferred embodiment, the membrane is quenched in air. Within this quenching zone, the membrane gels and solidifies. The temperature of the air zone is preferably 10-100°C, more preferably 20-80°C. The residence time in the air zone is preferably less than 180 seconds, more preferably less than 30 seconds, even more preferably less than 10 seconds. Shrouds can also be used to help regulate air flow rate and air zone temperature.

After or in place of air quenching, the membrane is optionally coated in a liquid that is a substantially non-solvent for the polymer, such as water, or water and glycerol acetate solvent and/or non-solvent glycerol. It can also be rapidly cooled. Some removal of solvent and/or non-solvent from the membrane may occur in the liquid quench zone. The temperature of the quenching zone is preferably at least 0°C to 60°C, more preferably 2°C to 30°C. The residence time in the liquid quench zone at this liquid quench temperature should be sufficient to gel and solidify the membrane. The residence time in the quench liquid zone is preferably less than about 60 seconds, more preferably less than 30 seconds.

[0025] The fiber or film optionally has a godet
Rollers or other conventional equipment can be used to stretch to the appropriate dimensions. Linear velocity is generally not critical;
Can be varied widely. The minimum preferred linear velocity is at least 10 feet/min (for economic reasons of operation).
3 m/min), and more preferably at least 100 ft/min (30.5 m/min). The maximum preferred linear velocity is less than 1000 ft/ft for ease of handling.
minutes (less than 304.8 m/min), and more preferably less than about 500 feet/min (less than 152.4 m/min).

The desired thickness of the membrane will vary depending on the intended end use and other factors. In embodiments where the membrane can be useful for ultrafiltration or fine filtration, the thickness of the film is preferably 10 to 100 microns and the hollow fibers of ultrafiltration or fine filtration are Preferably 100
It has an outer diameter of ~5000 microns, preferably 200-3000 microns, and a wall thickness of preferably 10-500 microns, more preferably 15-200 microns. In embodiments where the membrane can be useful for dialysis, the film preferably has 1
With a thickness of 0 to 75 microns, the hollow fiber for dialysis is 1
00 to 500 microns, more preferably 175 to 300 microns
It has an outer diameter of microns and a wall thickness of preferably 5 to 50 microns and more preferably 10 to 30 microns. In embodiments where the membrane is useful for reverse osmosis, the film preferably contains 1
With a thickness of 0 to 500 microns, the hollow fibers for reverse osmosis preferably have an outer diameter of 100 to 800 microns, more preferably 150 to 500 microns and preferably 1.2
It has an outer diameter to inner diameter ratio of ˜3.5, more preferably 1.8 to 2.5.

In another preferred embodiment, after quenching, the membrane comprises at least one leaching zone comprising a liquid that is substantially non-solvent for the polymer, such as water or a mixture of water and glycerol acetate solvent and/or non-solvent glycerol. Passage removes the solvent and at least a portion of the optional non-solvent. The leaching bath need not remove all of the solvent and optional non-solvent from the membrane. The infusion bath preferably contains up to 75% by weight glycerol in water,
More preferably it contains up to 50% by weight of glycerol in water. The minimum temperature of the leaching bath is the temperature at which removal of solvent and non-solvent from the membrane occurs at a reasonable rate. The minimum temperature of the leaching bath is preferably at least -10°C, more preferably at least 0°C, even more preferably at least 10°C. The maximum temperature of the leaching bath is below the temperature at which membrane integrity is adversely affected. The temperature of the leaching bath is preferably less than about 100°C, more preferably less than about 90°C. The residence time in the brewing bath is preferably less than about 1000 seconds, more preferably less than about 400 seconds. The membrane can be stretched to the desired dimensions before entering the leaching bath, during residence time in the leaching bath, after exiting the leaching bath, or a combination thereof.

[0029] After leaching, the membrane is optionally dried. The membrane can be dried in air or in an inert atmosphere such as nitrogen. The air or inert gas used to dry the membrane should have a sufficiently low water content so that drying of the membrane occurs at a reasonable rate. Room air is a preferred and convenient source of drying the membrane. The membrane can be dried at a temperature at which drying occurs at a reasonable rate and does not adversely affect the membrane. The drying temperature is preferably at least about 60°C, more preferably at least 20°C. Drying temperature is preferably about 120°C
more preferably less than about 90°C. The drying time is preferably at least about 30 seconds, more preferably at least about 60 seconds. The membrane can also be dried under reduced pressure.

In yet another preferred embodiment, the membrane may be leached in a liquid such as water and then subjected to a replasticization step prior to the drying step. The membrane is leached to remove at least a portion of the solvent and non-solvent. A leaching bath does not require removing all of the solvent and non-solvent from the membrane. The minimum temperature of the leaching bath is the temperature at which solvent and nonsolvent removal occurs at a reasonable rate. The minimum temperature of the leaching bath is preferably at least about -
10°C, more preferably at least about 0°C, even more preferably at least about 10°C. The maximum temperature of the leaching bath is below the temperature at which membrane integrity is adversely affected. The maximum temperature of the infusion bath is preferably less than about 100°C, more preferably less than about 90°C. The residence time in the brewing bath is preferably less than about 1000 seconds, more preferably less than about 400 seconds.

The leached membrane can be replasticized by passing the membrane through at least one replasticization zone, such as a glycerol and water bath. In embodiments where the membrane is useful for microfiltration or ultrafiltration, the replasticization bath preferably contains up to about 80% by weight, more preferably about 6% by weight.
Contains up to 0% glycerol by weight. In embodiments where the membrane is useful for dialysis, the replasticization bath preferably contains up to about 70% by weight glycerol, more preferably up to about 60% by weight. In embodiments where the membrane is useful for reverse osmosis, the replasticization bath preferably contains up to about 70% by weight glycerol, more preferably up to about 50% by weight. The minimum temperature of the replasticization bath is the temperature at which replasticization of the membrane occurs at a reasonable rate. The minimum temperature of the glycerol replasticization bath is preferably at least about 10°C, more preferably at least about 20°C.
It is ℃. The maximum temperature of the replasticization bath is below that at which the integrity of the membrane is not adversely affected. The maximum temperature of the replasticization bath is preferably less than about 80°C, more preferably about 60°C.
less than

In one preferred embodiment of the invention, as the concentration of glycerol acetate increases in the leaching and/or replasticizing bath, a portion of the bath is removed and subjected to mild hydrolysis to convert the glycerol acetate to glycerol. After conversion to sodium acetate, the treated portion can then be returned to the leaching and/or replasticizing bath. This recycling eliminates the need to dispose of leaching or replasticizing water-containing solvents, while simultaneously converting the glycerol acetate into a replasticizing agent. The membrane can be stretched to the appropriate dimensions either before, during or after the leaching or replasticizing bath.

Membranes prepared by the above method may contain significant amounts of solvent and optional non-solvent, depending on the quenching, leaching and replasticization conditions used. After manufacture, the membrane can contain up to about 75% by weight of solvent and optional non-solvent. For certain applications, such membranes containing significant amounts of solvent and non-solvent can be stored for long periods of time without adversely impacting the separation properties of the membrane. Additionally, membranes containing significant amounts of solvent and optional non-solvent may be used, since the solvent and optional non-solvent used are or can be converted into materials that are compatible and/or acceptable for the membrane's end use. Depending on the application, it can be used to separate liquids without excessive leaching before use.

Membranes prepared by the above method can be used in liquid separation processes such as microfiltration, ultrafiltration, dialysis and reverse osmosis. Membrane device fabrication methods are generally followed to complete the production membrane device for its particular end use. Such adaptations are readily accomplished by those skilled in the art.

Ultrafiltration and microfiltration are pressure-driven filtration in which a solution uses a porous membrane to separate solute particles.
It is an excess of law. Separation is achieved on the basis of differences in particle size or molecular weight. Such membranes are characterized by water permeability and sieving coefficient. Water permeability is a measure of the volume of solvent that moves through a membrane under the influence of a pressure gradient. Water permeability ph is expressed as ph=(amount of solvent permeated)/(membrane area)(Δp across the membrane)(time) at a specific temperature. Δp is the differential pressure across the membrane. Water permeability is usually (ml)/(m2)(hour)(cm
expressed in units of Hg). The ultrafiltration and fine filtration membranes of the present invention have at least
It has a hydraulic permeability of approximately 10ml)/(m2)(hour)(cmHg). The sieving coefficient is called φ, and φ=Cf/Cs
It is. Cf is the concentration of a small volume of filtrate at a certain moment, and Cs is the concentration of the filtration solution at the same time. In a closed system, both Cf and Cs increase with time when 0<φ<1.

Ultrafiltration and microfiltration membranes are also characterized by their porosity and porosity. Porosity refers to the volumetric void volume of a membrane. Membranes of the invention useful for ultrafiltration and microfiltration have porosity of about 20 to about 80%. Porosity can be estimated by several techniques including scanning electron microscopy and/or measurements of bubble point, solvent flux, and molecular weight cutoff. Such techniques are well known in the art for characterizing the pore size of microporous membranes and have been described, for example, by Robert
Kösteing's "Symthetic Polyme"
ricMembranes" 2nd edition (published by John Wiley & Sons, New York, USA, 1985), pp. 46-56; "Molecular
and Macromolecular Sie
ving by Asymmetric Ult
rafiltration membranes”,
OWRT report, NTIS No. PB85-15
7766IEAR, published September 1984; and AST
It is described in M trial listening method G316-86. Limit▲ro▼
The average pore size of the particularly useful membranes of the present invention is preferably from about 20 angstroms to about 500 angstroms. The average pore diameter of the microfiltration membrane of the present invention is preferably about 0.0.
5 microns to about 10 microns. The rejection rate of various solutes is determined by filtering a solute-containing solution beyond the limits of a given temperature and pressure.
It can be tested by sequentially feeding one side of a filtration or microfiltration membrane and collecting the permeate from the other side of the membrane to determine the solute rejection rate. Removal rate % is formula 100
Calculated using XX[1-(Cp/CF)]. C
p is the concentration of solute in the permeate and CF is the concentration of solute in the feed solution. A series of different solutes with different nominal molecular weights, such as Blue Dextran 2,
000,000,AP Ferritin 490
,000,Albumin 69,000,Cyto
chrome C 12,400, Vitamin
B-12 1335 and Bethylen
e Blue 320, may be used. The ultrafiltration membrane of the present invention preferably has a molecular weight of about 500 to about 300,000
It has a molecular cutoff of 0.

Dialysis is a process in which solute molecules are exchanged between two liquids by diffusion through a semipermeable membrane under the influence of a chemical potential gradient across the membrane separating the two liquids. The ability of a membrane to perform dialysis separations is characterized by the total diffusive mass transfer coefficient Kov for the solute of interest. In particular, membranes useful for hemodialysis are characterized by the total diffusive mass transfer coefficient for urea, Kov(urea).

Kov (urea) is usually expressed in cm/min. Membranes of the invention useful for hemodialysis have a total diffusive mass transfer coefficient for urea of at least about 20 x 10-3 cm/min at 37°C. Membranes of the invention useful for dialysis have a hydraulic permeability of at least about 10 ml/hr·m 2·cm Hg for blood removal of this water at 37°C.

Reverse osmosis is used for the purification or concentration of solutions containing salts or other low molecular weight solutes, such as the desalination of brine or seawater. In reverse osmosis, a pressure that exceeds the osmotic pressure is applied to the feed solution (high concentration side) to cause the solution to permeate from the high concentration side of the membrane to the low concentration side through a semipermeable membrane. The pressure above the osmotic pressure is the effective pressure and constitutes the driving force that moves the solvent across the membrane. Salts or other solutes are excluded by the membrane. That is, salt does not easily pass through the membrane. The separation performance of a membrane is characterized by the flux of water through the membrane and the salt rejection rate. The rate of water flux through the membrane for a given feed concentration, temperature and pressure is: (amount of water permeated) / (membrane area) (time)
It is expressed as The rate of water flux is usually expressed in GFD or gallons/(ft2 membrane area) (day). 1G
FD is 40.7 l/m2·day. Salt rejection rate % is [1
−(Concentration of permeated water)/(Concentration of supplied water)]×100
It is expressed as

Membranes of the invention useful in domestic reverse osmosis applications at a feed pressure of 50 psi (345 kPa) and a NaCl feed concentration of 0.05 wt.% are preferably at least about 0.05 wt.
It has a water flux of 4 GFD (16.3 l/m2·day) and preferably a salt rejection rate of at least 80%. 25
0 psi (1724 kPa) supply pressure and 0.15%
Membranes of the present invention useful for low pressure reverse osmosis applications at NaCl feed concentrations of preferably have a water flux of 2 GFD (81.4 l/m2·day) and preferably a salt rejection rate of 90%. 400 psi feed pressure and 0.15 wt% NaCl
Membranes of the present invention useful in standard pressure reverse osmosis applications at feed concentrations preferably have a water flux of 2 GFD (81.4 l/m 2 ·day) and a salt rejection rate of at least about 90%. 80
The membrane of the present invention useful for seawater reverse osmosis at a feed pressure of 0 psi (5516 kPa) and a feed concentration of 3.5 wt% NaCl has a water flux of 0.5 GFD (20.4 l/m2·day) and a salt rejection of 97%. has a rate.

[Examples] The following examples are provided to further specifically explain the present invention, and should not be construed as limiting the present invention.

Example 1 Compatibility diagram of cellulose triacetate/Hallco C-918 monoacetin/glycerol blend Compatibility diagram of cellulose triacetate/Hallco C-918 monoacetin (trade name of C.P. Hall Company)/glycerol blend is shown in Figure 1. This diagram is constructed by measuring the compatibility of various compositions of these three components at room temperature and pressure. Cellulose triacetate with an acetyl content of about 44% by weight is obtained from Daicel Chemical. H
allco C-918 monoacetin is manufactured by C.P.
Obtained from Whole Company. Hallco C
-918 monoacetin is not a pure compound, but a mixture of glycerol acetates and glycerol. According to gas chromatographic analysis, Hallco C
The composition (area %) of -918 monoacetin is shown in Table 1.

[0043]

[Table I]

[0044] Glycerol is manufactured by J.T. Baker.
Obtained from Chemical Company. Various three-component compositions are prepared in 2,2,2-trifluoroethanol. A few drops of each solution are placed on a microscope slide, the 2,2,2-trifluoroethanol is evaporated and the resulting film is examined microscopically by a polarizing microscope with a phase contrast object and a phase contrast condenser. Films from compositions within the boundaries of the area labeled "1" in the figure exhibited single phase characteristics. Films from compositions within the area labeled "M" exhibited multiphasic properties.

Example 2 Ultrafiltration Application Example 2-1 Cellulose Diacetate Hollow Fiber Cellulose diacetate available from Eastman Chemical under the designation CA394-60, Hallco.
C-918 monoacetin and glycerol as Hob
Mix in an art mixer to obtain a blend consisting of 37% cellulose diacetate, 47% by weight Hallco C-918 monoacetin, and 19% by weight glycerol.

The mixed blend was processed by a single screw extruder with a 16-hole spire nut to about 128 to 14 mm.
Extrude into hollow fibers at 9°C. These fibers are quenched and
Stretch at a speed of 0 ft/min (35.5 m/min). One sample received an additional cold stretch of 10%. Solvent and non-solvent are recovered from the fibers by flushing with water.

The fibers, each containing 160 fibers, are formed into listening cells and the hydraulic permeability and solute rejection rate are measured. To measure the hydraulic permeability of the membrane, the water inside the pores of the hollow fibers at room temperature is subjected to a pressure of about 9 cm Hg. Water penetrating inside the fiber is measured by observing the increase in water volume on the outside of the fiber. To measure the solute rejection rate, solutions of various solutes are pumped into the hollow fiber into a test cell at room temperature. The permeate is collected and analyzed to determine the solute rejection rate. The solute rejection rate % is calculated using the formula 100×[1-(Cp
/CF)]. Cp is the concentration of solute in the permeate and CF is the concentration of solute in the feed solution. The various solutes used and their nominal molecular weights are Blu
e Dextran 2,000,000, Ap
Ferritin 490,000, and Slb
It is umin 69,000. The data are shown in Table II.

[0048]

[Table II]

Example 2-2 A flat sheet of cellulose triacetate is prepared by dissolving about 300 g of cellulose triacetate in about 1700 g of Hallco C-918 monoacetin at about 200° C. with stirring for about 1 1/2 hours. Manufacture a staining solvent. This blend is cooled and stored.

About 50 g of the above blend is heated to about 160° C. with stirring. The viscosity of this solution was approximately 11.25 as measured at 160°C using a Brookfield viscometer.
Poise (1.1 Pa·S). Using a 20 mil (0.5 mm) casting rod, apply this solution to approximately 140 mm.
Hot cast onto a Pyrex glass plate heated to ~150°C. Immediately after casting, the membrane is rapidly cooled in room temperature water. The membrane is leached in room temperature water overnight. The final thickness of the wet membrane is approximately 5.7 mils (0.14 mm).
).

The membrane is cut from the casted film and mounted in an Amicon ultrafiltration cell with an effective surface area of 12 cm 2 . The measured flux of distilled water in the membrane was 8.5 at 8.75 psi (60.3 kPa).
GFD (346 l/m2・day). Blue D
The solution of extran 2,000,000 is 1.0g
2.8/l of dibasic sodium phosphate.
It is made at a temperature of g/l. Blue Dex passing through the membrane
The measured flux of the tran solution was 8.5 psi (
5.4 GFD (219.7 l/m
2 days), and the rejection rate of Blue Dextran is greater than 99.7%.

Example 3 Dialysis Application Hollow fibers are spun from various blend compositions containing cellulose diacetate, glycerol monoacetate, glycerol diacetate, and glycerol. Cellulose diacetate is manufactured by Eastman Chemical Products.
Obtained from Incorporated. The trade name of cellulose diacetate is CA-398-30 in Example 3-5.
but in all other cases CA-39
It is 4-60. Glycerol monoacetate is Hal
lco C-918 Monoacetin
Obtained from Pea Hole. Hallco C-91
8-monoacetin is not a pure compound but has a composition as shown in Example 1. Glycerol diacetate is Ha
llco C-491 Diacetin
Obtained from Pea Hole. Hallco C-49
No. 1 is not a pure compound but a mixture of glycerol acetates and glycerol. According to gas chromatographic analysis, the composition (area %) of Hallco C-491 diacetin is as follows. Glycerol diacetate 52.
5 Glycerol Monoacetate 29.
3 Glycerol Triacetate 14.
9 glycerol
3.3 Glycerol is obtained from The Dow Chemical Company. Glycerol triacetate is obtained from Eastman Namical.

The blend composition can be homogenized by initial compounding extrusion, pelletizing the extrudates, and reextruding the pellets into hollow fibers. Fibers from the various spinning trials are assembled into a test cell and the hydraulic permeability and diffusive mass transfer coefficient for urea is determined. The data are shown in Table III at the end of Example 3.

Method I Example 3-1 Approximately 34% by weight of cellulose diacetate (CDA), 4
A blend composition is prepared consisting of 7% by weight Hallco C-918 monoacetin, and 19% by weight glycerol (the resulting composition is about 34% cellulose diacetate, 27.9% glycerol, 23.5% by weight)
% glycerol monoacetate, 13.5% glycerol diacetate, and 0.9% glycerol triacetate. ) This blend at about 162℃
extrude and dry in air. The measured wet fiber dimensions are an inner diameter of 211 microns and a wall thickness of approximately 12 microns.

Example 3-2 Approximately 34% cellulose diacetate (CDA) by weight
), 38% Hallco C-918 monoacetin, and 28% glycerol. (The product composition is approximately 34% cellulose diacetate, 35.3% glycerol, 19% by weight)
．． Corresponds to 0% glycerol monoacetate, 10.9% glycerol diacetate, and 0.7% glycerol triacetate. ) This blend is about 16
Extrude at 7°C, quench in air, and cold stretch 10%. The resulting wet fiber dimensions are approximately 207 microns in inner diameter and approximately 17.5 microns in wall pressure.

Method II Example 3-3 Approximately 35% cellulose diacetate (CDA) by weight
), 53% Hallco C-918 monoacetin, and 12% glycerol. (The product composition is approximately 35% cellulose diacetate, 22.2% glycerol, 26% by weight)
．． This corresponds to 5% glycerol monoacetate, 15.3% glycol diacetate, and 1.0% glycerol triacetate. ) After the initial compounding step, this blend contains, by weight, approximately 39.0% cellulose diacetate, 21.7% glycerol, 24.5% glycerol monoacetate, 14.7% glycerol diacetate, and 1. Contains 0% glycerol triacetate. ) This blend was extruded at about 152°C, quenched in air, and mixed with 50% glycerol and 50% glycerol.
of water at a temperature of approximately 75°C, stretched by 13%,
It is then dried in air at about 50° C. for about 5 minutes. The composition of the final membrane is approximately 57.0% cellulose diacetate, 36.0% glycerol, 3.2% glycerol monoacetate, 3.1% glycerol diacetate, and 1.0% glycerol diacetate, by weight. Glycerol triacetate. The final wet fiber dimensions are approximately 213 microns inside diameter and approximately 15 microns wall thickness.

Example 3-4 Approximately 42% cellulose diacetate (CDA) by weight
), 47.3% Hallco C-918 monoacetin, and 11.7% glycerol. (The product composition is 42% cellulose diacetate, 20.8% glycerol, 23% by weight.
This corresponds to 6% glycerol monoacetate, 13.7% glycerol diacetate, and 0.9% glycerol triacetate. After the initial compounding step, this blend contains approximately 42.0% cellulose diacetate, 2
Contains 0.8% glycerol, 23.2% glycerol monoacetate, 14.0% glycerol diacetate, and 1.0% glycerol triacetate. ) The fibers are treated as in Example 3-3. The composition of the final membrane is approximately 57.0% cellulose diacetate, 34.0% glycerol, 4.6% glycerol monoacetate, 4.0% glycerol diacetate, and 1.0% glycerol diacetate, by weight. Glycerol triacetate. The final wet fiber dimensions are approximately 223 microns inside diameter and approximately 15 microns wall thickness.

Method III Examples 3-5 The initial blend composition was approximately 42% cellulose diacetate (CDA), 47% Hallco C by weight.
-918 monoacetin, and 11% glycerol. (The product composition is about 42.0% cellulose diacetate, 20.0% glycerol, 23.0% by weight).
This corresponds to 5% glycerol monoacetate, 13.5% glycerol diacetate, and 0.9% glycerol triacetate. ) This blend is about 166
°C, quenched in air, passed through an aqueous solution at a temperature of about 75 °C to remove the plasticizer, passed through a room temperature aqueous solution containing about 30-60% by weight glycerol, and extruded in air at about 2 Let dry for a minute. The final wet fiber dimensions are approximately 206 microns inside diameter and approximately 22 microns wall thickness.

EXAMPLE 3-6 The initial blend composition was approximately 34% cellulose diacetate (CDA), 38% Hallco C by weight.
-918 monoacetin, and 28% glycerol. (The product composition is about 34.0% cellulose diacetate by weight) 35.2% glycerol, 19.
Corresponds to 0% glycerol monoacetate, 10.9% glycerol diacetate, and 0.7% glycerol. ) Extrude the fibers as described in Examples 3-5. The wet fiber dimensions measured were approximately 205 microns inside diameter and approximately 12 microns wall thickness.

The total mass transfer rate for urea Kov(urea) is achieved by providing a water pool in the feed volume and pumping it into the fiber lumen. In this dialysis test device, the pool surrounding the fibers is initially a water/urea solution. Measurements are taken at predetermined time intervals to determine the urea concentration in the circulating fluid. The test is conducted at 37°C. During the test, there is no base pressure across the fiber wall.

The total mass transfer rate for urea, Kov(urea), is calculated as N=Kov(urea) as a function of time and fiber area, taking into account the concentration difference of urea in the feed volume and in the dialysis test device outside the fiber. )A(C1-C2). N is the flux across the membrane (moles/min), C1 is the concentration on one side of the membrane in moles/cm3,
C2 is the concentration outside the membrane in moles/cm3, A
is the membrane area in cm2.

2-nitrogen or synthetic ultrafiltration without wall pressure
In the process, the movement of urea across the membrane wall is integrated over a period of time t, yielding Equation 1:

[0063]

V1 is the volume of solution in the feed volume and V2 is the volume of solution in the dialysis beaker.

In these test films, the volumes V1 and V2 and the area A are measured separately and integrated so that the plots of the values on each side of Equation 1 form a straight line. The slope of this straight line makes it possible to calculate the value of Kov (urea) in cm/min. The hydraulic permeability and mass transfer coefficients for urea of the membranes prepared in Example 3 are summarized in Table III.

[0065]

[Table III]

Example 4 Application to reverse osmosis Glycerol monoacetate, glycerol diacetate,
Hollow fiber cellulose triacetate (
CTA). These blends are made by mixing the various ingredients to form a viscous powder of plasticized CTA, which is then extruded in a conventional single screw extruder. Extrude the hollow fiber at about 180-190℃,
It is sent into air, quenched in water at about 4-6°C for about 3 seconds, and then leached in water at about 30°C to remove most of the plasticizer. The fibers are then optionally annealed in water at about 65° C. for about 100 seconds. Cellulose Triacetate Fl
It was obtained from Daicel Chemical Industries, Ltd. under the trade name Akes. Glycerol monoacetate is Ha
It was obtained from CP Hall under the trade name llco C-918 monoacetin. Hallco
C-918 monoacetin is not a pure compound, but a mixture of glycerol acetates and glycerol. According to gas chromatographic analysis, Hallco
The composition (area %) of C-918 monoacetin is as follows. glycerol monoacetate
46 glycerol diacetate
29 Glycerol Triacetate
5 glycerol
20

Glycerol diacetate was obtained from CP Hall under the tradename Hallco C-491 diacetin. Hallco C-491 diacetin is not a pure substance, but a mixture of glycerol acetates and glycerol. According to gas chromatographic analysis, the composition (area %) of Hallco C-491 diacetin is as follows. glycerol diacetate
49 Glycerol Monoacetate
24 Glycerol Triacetate
24 glycerol
3 Glycerol is available from The Dow Chemical Company. Glycerol triacetate is available from Eastman Chemical.

The obtained wet hollow fibers are formed into test cells to evaluate their performance. The test cell contains a hollow fiber threaded through stainless steel tubing with a Septa tube plug at the bottom. The Septa plug serves as a barrier to prevent feed fluid from leaking out of the feed shed. A Septa plug is a silicone rubber disc commonly used in gas or liquid chromatography equipment to separate the sample inlet from the outside of the thread.

The water flux and salt rejection rate of the hollow fibers was approximately 25% at an operating pressure of 250 psi (1724 kPa).
It is measured by pumping a 0.15% by weight aqueous NaCl solution into the test cell at a temperature of .degree. The permeate or produced water exiting from the interior or lumen of the fiber is then collected. Next, the NaCl concentration in the produced water column is measured.

Table IVA shows Hallc in the blend composition.
o C-918 monoacetin and Hallco C-
491 diacetin and the effect of various ratios on membrane performance. Table IVB shows the effect of added glycerol in the blend composition on water flux and salt rejection. Table IVC shows the effect of additional glycerol and glycerol triacetate in the blend composition on membrane performance.

[0071]

[Table IVA]

[0072]

[Table IVB]

[0073]

[Table IVC] [Brief explanation of the drawing]

FIG. 1 is a diagram showing the compatibility at room temperature and normal pressure of various compositions of cellulose triacetate/glycol acetates/glycerol according to the present invention.

Claims (12)

[Claims] 1. (A) at least one cellulose ester; and (B) at least one solvent of glycerol monoacetate, glycerol diacetate, glycerol triacetate, or mixtures thereof, which solubilizes the cellulose ester at the film formation temperature. , wherein the cellulose ester and the solvent are present in a ratio that produces a semipermeable membrane. 2. The composition of claim 1, wherein said mixture further comprises a non-solvent glycerol, said glycerol being present in an amount that does not adversely affect the production of membranes from the mixture. 3. The composition of claim 1, wherein said mixture contains 10 to 80% by weight of cellulose ester. 4. The composition of claim 1, wherein the cellulose ester is cellulose acetate, cellulose diacetate, cellulose triacetate, or a mixture thereof. 5. The composition of claim 4, wherein the cellulose ester membrane is useful for ultrafiltration or microfiltration and has a porosity of 20 to 80%. 6. The cellulose ester membrane is useful for dialysis, and is capable of producing at least 10 ml/hr m2 at 37°C.
- The composition of claim 2 having a hydraulic permeability of cmHg and a urea-gold mass transfer coefficient of at least 20 x 10-3 cm/min at 37°C. 7. The cellulose ester membrane is useful for reverse osmosis and has a pressure of 250 pounds per square inch (1724 kPa).
at a feed pressure of at least 2 GFD (81.4 l/m2·
3. The composition of claim 2 having a water flux of 8. The following steps: (A) (i) at least one cellulose ester and (
ii) at least one solvent of glycerol monoacetate, glycerol diacetate, glycerol triacetate, or mixtures thereof, sufficient to solubilize the cellulose ester at the film formation temperature; heating the mixture to a temperature at which the mixture becomes a homogeneous fluid; (C) extruding, forming, or casting the homogeneous fluid onto a semipermeable membrane; and (D) passing the membrane through one or more quench zones. A method for producing a cellulose ester semipermeable membrane, comprising the steps of: gelling and solidifying the membrane by using a membrane, and the semipermeable membrane thus produced is useful in a membrane-based liquid separation method. 9. The method of claim 8, wherein the mixture further comprises non-solvent glycerol, and the glycerol is present in an amount that does not adversely affect the production of membranes from the mixture. 10. The method of claim 9, further comprising the additional step of: (E) passing the membrane through one or more leaching zones to remove at least a portion of the solvent and non-solvent from the membrane. 11. The method of claim 10, further comprising the additional step of: (F) passing the membrane through one or more replasticization zones to replasticize the membrane. [Claim 12] Glycerol monoacetate, glycerol diacetate, glycerol triacetate,
A cellulose ester semipermeable membrane useful for liquid separation, including a cellulose ester semipermeable membrane comprising at least one of the following: or a mixture thereof.