JPH0356774B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for separating solutes, colloid particles or suspended matter from solutions or suspensions containing the same. More particularly, the present invention relates to a method for pressurized ultrafiltration of various separation products by contacting solutions or suspensions as described above with synthetic semipermeable membranes. Ultrafiltration is a method of separating solutions or suspensions in which the solution or suspension is subjected to pressure such that the solvent is forced through a selected thin membrane. The solvent decomposed therein contains solutes, colloidal particles, or suspended matter of significantly larger size than those in which it was fractionated. Generally, "ultrafiltration method"
refers to a pressurized separation method that includes decomposed molecules, colloid-sized particles, etc. The term is preferably applied to separation operations involving feed streams containing species with molecular weights on the order of approximately 10 times the size of the solvent molecules. Many advantages have been observed in employing this relatively new separation technique, among them the separation of species previously thought to be inseparable from conventional techniques such as evaporation, chemical precipitation, and ultracentrifugation. Compared to the ability to separate, consideration is given to the time to carry out the separation, the efficiency of the separation, the use in generally particularly mild working conditions, and the reduced operating costs. Advantages such as gentle working conditions are particularly important when processing thermally unstable or biologically active substances. When using pressure activated thin film separation methods, the success or failure of this operation depends in large part on the properties of the thin film used. Desirable membrane properties include (a) good hydraulic permeability to solvents with the ability to transport liquid at high rates per unit area of the membrane under acceptable pressure; (b) thermal (c) high fouling resistance; (d) completely free of solutes, suspended solids or colloid particles with molecular weights or sizes exceeding specified values; Or the ability to withhold it almost completely. Membranes commonly used in ultrafiltration techniques currently used in the art can be classified as either (a) homogeneous membranes or (b) anisotropic membranes. Homogeneous thin membranes have limited use in separation processes and are similar to ordinary filters;
and non-retentive to suspended solids or species other than high molecular weight species. Correspondingly, modification of such membranes to retain small molecules results in a corresponding decrease in permeability. Moreover, such thin films are susceptible to internal fouling by retained species. A particularly desirable membrane morphology for the separation of solutes, suspended solids or colloidal particles is a microscopically microporous anisotropic membrane having a thin skin and an underlying supporting spongy backing. The skin surface of the anisotropic thin film is very thin, for example, with a pressure of approximately 0.1μ to approximately 1.0μ, and for example, a pressure of approximately 1μ to approximately 1μ.
It has an average pore diameter in the microμ range of 50 mμ. The equilibrium of the thin film structure further includes a porous polymer structure;
Fluids can pass through this with little or no hydrodynamic resistance. When such a membrane is used as a ``molecular filter'' with its ``skin side'' in contact with a pressurized fluid, virtually all resistance to the fluid flowing through this membrane occurs in the ``skin''; Molecules or particles with a diameter larger than the pores are selectively retained. Because the skin layer has such an unusually thin structure, and the transition from the skin layer to the microporous support layer is so abrupt, the total amount of hydrodynamic resistance to fluid flowing through this membrane is , and the tendency of such thin films to become clogged or fouled by molecules or particulates is greatly reduced. These membranes can take a variety of forms, such as hollow fibers, flat seals, spirally wound sheets or tubular bodies. For the purposes of this invention, it is preferred to use hollow fiber membranes. In currently used ultrafiltration systems, the pressure used to form the tangential flow of the feed stream over the membrane has been limited to low values, and the exact pressure is or depends on the resistance of the thin film to crushing. Generally, the inlet pressure is approximately 15 to
Limited to 100 psig (1.05-7 Kg/m ² g).
Such limitations often cause separation equipment used for solution separation purposes to operate at a lower degree than is entirely economically desirable. Ultrafiltration units or cartridges have a range of approximately 1 ft (0.30 m) to approximately 4 ft (1.22 m) as a result of pressure limitations.
m), the sum of the positive agglomerate removal pressure and the pressure drop occurring in the cartridge is less than the maximum pressure that the membrane used can withstand. Such suppression of inlet pressure significantly limits the system's ability to efficiently process working solutions. To achieve a given high rate separation effect, multiple ultrafiltration cartridges must be used in parallel configuration. However, such assemblies require significant capital and operating costs. It is an object of the present invention to provide an ultrafiltration device assembly and a method of using the same, in which the range of action within which the thin membrane used for ultrafiltration functions efficiently is greatly increased, and thereby: The equipment and/or energy requirements associated with this system are drastically reduced. Other objects of the invention will be apparent to those skilled in the art from the following description of the invention. According to the invention, the above object is achieved by combining a plurality of ultrafiltration cartridges in a series arrangement and introducing the feed stream to be separated at a pressure exceeding the normal maximum permissible membrane pressure for the particular selected membrane; This is accomplished by simultaneously applying backpressure to the permeate side of the membrane in each cartridge at locations where the inlet pressure exceeds the maximum transmembrane pressure difference normally allowed for the particular membrane used. The advantages gained by this system are:
The explanation below will become clearer. The term "permeate" used in this text refers to flow passing through a thin film surface, and the term "coagulate"
means that the portion of the stream exiting the filter contains stagnant non-permeable species. The action of a cartridge or unit containing an ultrafiltration membrane can generally be described in terms of two pressure differences: the hydrodynamic pressure difference (ΔPHYD) and the transmembrane pressure difference (ΔPTM). . Hydrodynamic pressure differential is the driving force required to move the process fluid as a tangential flow across the membrane, and is calculated as the process side pressure difference at the inlet and outlet of the cartridge: ΔPHYD = P ₁ − P ₂ where P ₁ is the inlet pressure and P ₂ is the pressure at the outlet. This hydrodynamic pressure difference determines the velocity v (ft/sec) of the processing solution across the membrane surface by well-known equations of fluid mechanics. This rate is an important factor in ultrafiltration systems, affecting both the membrane permeation rate and the rate of fouling, if any. For a given thin film and processing fluid, the velocity of the processing fluid is generally expressed as v = f(ΔPHYD,T), where f is a generalized functional representation and T is the temperature of the processing fluid. . Thus, if the temperature T is held constant, the velocity of the process fluid is simply a function of the hydrodynamic pressure difference, rather than the absolute applied pressure. Transmembrane pressure difference (ΔPTM) is the driving force for permeation and is calculated as the difference in pressure across the active membrane surface. This pressure difference varies along the membrane surface according to the hydrodynamic pressure, or if P _x is the process side pressure at a given point and P ₃ is the pressure on the permeate side of the membrane, then the transmembrane pressure The difference is expressed as ΔPTM=P _x −P ₃ . This ensures that the lowest transmembrane pressure difference always occurs at the outlet of the cartridge and the highest transmembrane pressure difference always occurs at the inlet of the cartridge. The performance of all ultrafiltration membranes is generally limited by the maximum transmembrane pressure differential at which the membrane remains resistant to long periods of continuous use without rupture. This does not mean that the membrane cannot be subjected to high pressures briefly or repeatedly. This is unsupported and therefore typically approximately 15 to 50 psig (1.05 to 3.5 Kg/cm ² g)
This is especially true in the case of hollow fiber membranes with a relatively low maximum ΔPTM of the order of . Therefore, in conventionally used thin membranes where the permeability pressure of the membrane is usually zero, the maximum allowable inflow or process side pressure is the maximum allowable thin membrane permeation pressure difference (ΔPTM _nax
= P ₁ ). The present invention will be described below with reference to the accompanying drawings. Figure 1 shows a single membrane cartridge with a maximum membrane permeation pressure difference of 25 psig.
(1.75Kg/cm ² g), inlet pressure 25 psig
(1.75 Kg/cm ² g) and outlet pressure 10 psig (0.7
Kg/cm ² g) or (ΔPHYD−15psig (1.05Kg/cm ²
g), resulting in a flow rate Qgpm and a permeation rate pgpm. Under standard conditions, if a separation operation required a production permeation rate of 2 pgpm, two cartridges in parallel would be required, both operating under the same conditions as the single cartridge of FIG. If two cartridges are placed in series and the first series cartridge (as shown in Figure 3)
If we maintain an inlet pressure of 25 psig (1.75 Kg/cm ² g) at The flow rate is approximately 1/2 that of two cartridges dispensing in parallel for the same ΔP. Also, if the inlet pressure is set to 25 psig (1.75 Kg/cm ² g) or more,
Equal performance is not obtained by this measure since this pressure increase requires that the transmembrane pressure at the cartridge inlet exceed the maximum ΔPTM allowed for the selected membrane. 4 and 5 illustrate the inventive concept of the present invention, i.e. a plurality of cartridges are coupled in series, the inlet pressure into the system significantly exceeds the maximum allowable pressure for the membrane, and the specified maximum ΔPTM
The permeate side of each cartridge with a ΔPTM exceeding ΔPTM is independently back-pressured to the extent necessary to generate a PTM within the cartridge without exceeding the specified maximum Δ for the particular membrane used. As shown in Figure 4, in order to double the flow rate Q in Figure 1, the inlet pressure is 40 psig (28 Kg/cm ² g).
The back pressure regulator increased to 15 psig on the permeate side and used on the permeate side of cartridge B.
Maintain a constant pressure of (1.05Kg/cm ² g). A backpressure of 15 psig (1.05 Kg/cm ² g) on the permeate side of cartridge B is used to reduce the ΔPTM at the inlet to an acceptable 25 psig (1.75 Kg/cm ² g). 15 psig (1.05 psig) across the treated side of the membrane
Given a pressure drop (ΔPHYD) of Kg/cm ² g),
The inlet pressure of cartridge A is 25 psig (1.75
kg/cm ² g) and does not require any back pressure on the permeate side of the membrane. The net effect of such a treatment method is to double the permeation capacity of the system for a given treatment flow rate Q. This improved permeation ability to handle fluid flow rates allows compact system sizes to be obtained, thus reducing capital and making conventional expensive separation techniques economically attractive. Although the use of high pressures initially represents a disadvantage, this disadvantage is more than compensated for by the perceived performance advantages. The horsepower required to carry out the method shown in FIGS. 1-5 is calculated as hp=flow x pressure/1714. In comparing the energy requirements for parallel and series coupled pressurization devices, in this case the permeation yield is
As shown in the figure and Fig. 4, it is 2p. (1) Parallel arrangement hp=2Q×25/1714=0.0292Q (2) Pressurized permeable series arrangement hp=Q×40/1714= 0.0233Q As is clear from the above results, pressurized permeable series arrangement requires a high initial inlet pressure, but
Energy consumption is much lower, representing a 20.2% reduction in energy requirements. In terms of performance, using the permeation rate p as a standard for the hp energy required for this system, the efficiency is compared as follows: (1) Parallel arrangement = capacity / hp = 2p / 0.0292Q = 68.5p / Q (2) Pressurized permeation type Series arrangement = Capacity/hp = 2p/0.0233Q = 85.8p/Q As a result, the pressurized permeable series arrangement form is 25.3%
It works even more efficiently and delivers 25.3% more capacity for a given energy input. As shown in FIG. 5, by applying the pressurized series arrangement concept to more than two cartridges, which independently adjusts the permeate back pressure in each cartridge except the last cartridge in series, two cartridges can be pressurized in series. We obtain higher performance values than those obtained by formula arrangement. In the treatment method shown in Figure 5, 55 psig
(3.85Kg/cm ² g), the initial inlet pressure is 30 psig
(2.1Kg/cm ² g) of back pressure and 15 psig for cartridge B.
(1.05Kg/cm ² g) back pressure is 40 psig (2.8Kg/cm ² g)
applied to the inlet pressure. As will be clear from the following discussion, the efficiency of this system based on 3p output represents a significant advance over the performance of the parallel arrangement of three cartridges. 1 Parallel arrangement hp = 3Q x 25 / 1714 = 0.0438Q Pressurized permeable series arrangement hp = Q x 55 / 1714 = 0.0321Q 2 Parallel arrangement capacity / hp = 3p / 0.0438Q = 68.5p / Q Pressurized permeable series Placement Capacity/hp = 3p/0.0321Q = 93.5p/Q Thus, the three cartridge pressurized permeable series configuration represents a 36.5% increase in efficiency when measured on a capacity/hp basis. The pressurized permeable in-line device of this invention can utilize any of a variety of commonly used membrane cartridges, including hollow fiber, spiral wound, and tubular types. The anisotropic thin film used in the cartridge can be selected from a wide range of synthetic polymeric materials, especially materials with low water adsorption properties. Such polymers that may be used include polycarbonates, polyamides, halogenated polymers such as polyvinylidene fluoride, polychloroethers, polyacetals, polyacrylic acids, polyurethanes, polyimides, polyvinyl acetates, polyethers, and the like. In setting up the pressurized permeate in-line multiple cartridge system of the present invention, the selected membranes are provided with appropriate inflow devices, aggregate removal devices, permeate extraction devices, and a predetermined back pressure on the permeate side of the membranes. and a device for coupling the selected number of cartridges in series. As mentioned above, the last cartridge in the series combination does not require a backpressure generating device. Although serial arrangements containing two to about eight cartridges can be provided, it is generally preferred to limit the number of cartridges in the system to two to three. The economic significance of the pressurized permeate series configuration is demonstrated by the following comparative data obtained by comparing the use of standard manifold diameters used in ultrafiltration processes with a conventional parallel configuration for the same permeate production rate. It is shown by. The cost comparison for the 148 cartridge system is
The surprising economic benefits obtained from a pressurized permeable series arrangement system are demonstrated.

Table The following example illustrates the invention. Example 1 Electrophoretic paint In the device shown in Figure 4, PPG No. 3002H
A flow of approximately 22 gpm of cathodic electrophoretic paint is
Massachusetts 01801, Woburn, Cummings,
2 obtained from Romicon, Inc. located at Park100.
A series of ultrafiltration tests were conducted using a HF26.5-43-CXM cartridge. The results are as follows.

[Table] Example 2 Cheese Whey Whey produced from a cheddar cheese production facility has a protein content of approximately 12% on a dry basis. Romicon HF26.5−43−PM10 hollow fiber ultrafiltration membrane selectively aggregates the protein content of whey and allows low molecular weight sugars and ash to pass through the membrane, reducing the protein content by 35%. The protein content of this whey is easily increased into products. This membrane is capable of processing 120,000 gal of cheddar cheese whey to a 35% protein level in a 20-hour day.
Requires 204 HF26.5-PM10 type cartridges. The capital and energy cost savings achieved by the pressurized permeable series configuration facility over a single factory standard array configuration facility of this capacity size are as follows.

[Table] Example 3 Cheese whey The advantage of the pressurized permeation technology shown in Example 2 is that the 340
For 210,000 gpd systems requiring standard cartridges, it can be obtained in both large and small systems such as:

【table】 [Brief explanation of drawings]

1-5 are diagrams illustrating the differences in performance between a conventional parallel isolation system and a system according to the present invention, and the advantages provided by the present invention. A, B, C...cartridge, V...valve.

Claims (1)

[Scope of Claims] 1. An ultrafiltration method for separating solutes, colloid particles, or suspended substances from solutions or suspensions of these substances by ultrafiltration, comprising: (a) an ultrafiltration method for ultrafiltration; (b) connecting a plurality of separation units comprising thin membranes in a serially arranged flow configuration, thereby comprising at least a first separation unit, a final separation unit and an optional intermediate separation unit; (c) introducing the suspension into the first separation unit at a pressure that exceeds the maximum allowable transmembrane pressure difference across the membrane; (d) repeating steps (b) and (c) for at least each intermediate separation unit; (e) removing permeate from each separation unit; and (f) recovering a concentrate containing solutes, colloid particles or suspended matter from the last separation unit in the series. An ultrafiltration method characterized by: 2. The ultrafiltration method according to claim 1, wherein the thin film is a hollow fiber thin film. 3. The ultrafiltration method according to claim 2, wherein two separation units are connected in series. 4. The ultrafiltration method according to claim 2, wherein three separation units are connected in series. 5. The ultrafiltration method according to claim 1, wherein steps (b) and (c) are repeated in a final separation unit. 6 Approximately 40 to 80 psig (2.8 to 5.6 Kg/cm ²
g) with inlet pressures in the range of approximately 15 to 55 psig
4. The ultrafiltration method of claim 3, wherein a back pressure in the range of 1.05 to 3.85 Kg/cm ² g is applied to the first separation unit of the series arrangement. 7. An inlet pressure of approximately 40 psig (2.8 Kg/cm ² g) and a back pressure of approximately 15 psig (1.05 Kg/cm ² g) are applied to the first separation unit in the series arrangement according to claim 3. ultrafiltration method. 8 Approximately 50 to 120 psig (3.5 to 8.4 Kg/cm ²
g) inlet pressure and approximately 25 to 95 psig (1.75
A backpressure of approximately 40 to 6.65 Kg/cm ² g) is applied to the first separation unit of the series arrangement and
Inlet pressure of 80 psig (2.8 to 5.6 Kg/cm ² g) and approximately 15 to 55 psig (1.05 to 3.85 Kg/cm ² g)
5. The ultrafiltration method of claim 4, wherein a back pressure of . 9 An inlet pressure of approximately 55 psig (3.85 Kg/cm ² g) and a back pressure of approximately 30 psig (2.1 Kg/cm ² g) are applied to the first separation unit in the series arrangement, and approximately
40 psig (2.8 Kg/cm ² g) inlet pressure and approximately 15 psi
5. The ultrafiltration method according to claim 4, wherein a back pressure of 1.05 Kg/cm ² g is applied to the second separation unit in the series arrangement. 10. The ultrafiltration method of claim 1, wherein said membrane has an average porosity in the range of approximately 1 to approximately 50 nm. 11 (a) a plurality of pressure filter cartridges connected in a serially arranged flow configuration and containing membranes for ultrafiltration; (b) inlet means located within each of said pressure filter cartridges; and (c) Provided inside each pressure filter cartridge,
(d) means provided within each pressure filter cartridge;
(e) introducing the solution or suspension to be separated into each pressure filter cartridge except the last pressure filter cartridge at a pressure exceeding the maximum allowable membrane permeation pressure difference across said membrane; (f) for each pressure resistant filter cartridge except said last pressure resistant filter cartridge for producing in each pressure resistant filter cartridge a transmembrane pressure differential not exceeding a maximum allowable transmembrane pressure differential for said membrane; (g) means for coupling said pressure filter cartridges in said series arrangement. 12. The ultrafiltration device according to claim 11, wherein two pressure-resistant filter cartridges are connected in series. 13. The ultrafiltration device according to claim 11, wherein three pressure-resistant filter cartridges are connected in series. 14. The ultrafiltration apparatus according to claim 11, further comprising means for applying back pressure to the last pressure filter cartridge in the series arrangement.