JPH0616819B2 - Crossflow Filtration Device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Field of the Invention The present invention relates to a cross-flow filtration device for receiving a feed stock at a feed end face and separating the feed stock into a filtrate and a concentrate.

PRIOR ART Numerous filtration devices exist that separate feedstock into a filtrate and suspended solids that are suspended in the feedstock and too large to pass through the porous structure of the filter. Straight-through filters retain suspended solids on the filter surface or within the filter matrix, allowing only the filtrate to pass through. Crossflow filters operate with a tangential flow across the filter surface, flushing away suspended solids that cannot pass through the pores of the filter surface. Crossflow filters continuously discharge retentate, i.e., concentrated suspended solids, from one location on the filter and filtrate from another location. As is well known in the art, the filtration rate of a crossflow filter is generally limited by the resistance of the filter cake that accumulates on the filter surface. The thickness of this cake, and the associated resistance, is governed by the crossflow rate. This phenomenon of cake thickness being governed by the disproportionate concentration of retained suspended solids, has been widely documented in the technical literature. To achieve maximum filtration rates, crossflow filters are typically constructed from porous materials that offer a lower flow resistance for the filtrate compared to the filter cake. That is, in operation, the pressure drop across the porous filter itself is less than the pressure drop across the filter cake, and the resistance of the filter cake is determined by the hydrodynamic flow conditions across the filter surface.

Cross filters can be constructed using porous monoliths with numerous passages. Such monoliths typically have tens to thousands of parallel, uniformly spaced passages. The feedstock is introduced under pressure into one end of the monolith, flows parallel through these passages, and is withdrawn as a concentrate at the downstream end of the filter. The filtrate flows into the porous monolith walls separating the passages, merges, and flows through the walls toward the monolith's periphery, exiting through a pressure-maintaining outer skin integral with the monolith. Resistance to flow within the tortuous flow paths of the monolith's passage walls severely limits filtration capacity. For this reason, crossflow filters based on porous monoliths with numerous passages and large surface areas are not widely used.

Membrane devices using crossflow filtration as the membrane support use a semipermeable membrane to separate the filtrate (also called the permeate) from the concentrate. There are a variety of membrane devices that separate particles, colloids, macromolecules, and small molecules. Membranes generally require mechanical support.
The support member can be integral with the self-supporting asymmetric membrane, or it can be separate, in which case the membrane is coated onto or simply mechanically supported by a porous support member.

Porous monoliths with numerous passages are particularly useful as membrane supports. In this case, the membrane is attached to the passage walls, which act as both mechanical support and a flow path for the filtrate to drain to a collection area. High flow resistance in the monolith passage walls can, first, hinder proper membrane formation, for example, by dynamic formation. Second, even if the membrane is applied to the monolith passage walls by other methods, the resistance of the passage walls to filtrate flow limits device capacity. This limitation has been clearly recognized in the development of such devices, for example, by Huber and Roberts in U.S. Pat. No. 4,069,157. This patent teaches that this limitation can be overcome by restricting a number of parameters to specific ranges of values. The surface area of the passages per unit volume, the porosity of the support member, and the ratio of the remaining volume of the support member, excluding the passage spaces, to the total volume of the support member are all defined within certain ranges and, in combination, define an acceptable range of permeability coefficients for the support member.

Other monolith-based membrane devices have been developed in the United States, France, and the People's Republic of China.
Experts recognize the permeability limitations of these devices. This limitation is typically overcome by using monoliths with relatively few feed passages of small overall diameter combined with support members having large pore sizes. One such membrane device utilizes multiple small-diameter hexagonal monoliths, each with up to 19 passages, arranged within a cylindrical housing. Filtrate is discharged from all six sides of each monolith, mixed with filtrate discharged from other monoliths, and then collected. The overall packing density of this device, i.e., membrane area per unit volume, is very low.

Monoliths as support members for membrane devices share the common feature of using substantially uniformly spaced passages through the support member. Given these constraints,
Product developers have worked to avoid restricting the flow path of the filtrate using variables such as those detailed by Huber and Roberts in the above-referenced patent.

The flow resistance of the passage walls of porous monoliths has been a limiting factor in the use of monoliths for crossflow filtration or membrane support in membrane systems. Furthermore, this flow resistance becomes increasingly severe as the packing density of the filtration system, i.e., the effective filter or membrane area per unit volume, increases.

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved cross-flow filtration device which allows for easy drainage of filtrate.

Another object of the present invention is to provide a crossflow filtration device having a large passageway surface area relative to its volume.

It is yet another object of the present invention to provide a crossflow filtration system which utilizes substantially all of the passages in a manner that results in a low pressure drop for filtrate flow, even between the innermost passages and the filtrate collection area associated with the filtration system.

It is yet another object of the present invention to provide a crossflow filtration device in which the passage walls have small pore sizes yet maintain adequate filtrate discharge rates.

(Means for solving the problem) The present invention provides a cross-flow filtration device for receiving a feed stock at a feed end face and separating the feed stock into filtrate and a concentrate, the device comprising a monolith made of a porous material defining a plurality of passages extending longitudinally from the feed end face to a concentrate discharge end face of the monolith, the passages through which the feed stock flows to discharge the concentrate from the cross-flow filtration device, and a filtrate conduit for conveying filtrate toward a filtrate collection area, each filtrate conduit including a plurality of chambers extending longitudinally of the monolith and at least one filtrate slot extending transversely from the chambers to the filtrate collection area, the filtrate conduits being isolated from both end faces of the monolith by blocking members and providing flow paths having a flow resistance less than the flow resistance of the remaining flow paths within the monolith, and at least some of the passages being separated from nearby chambers by the intervening passages.

The present invention has a filtrate conduit for transporting filtrate toward the filtrate collection area, and this filtrate conduit includes a plurality of chambers extending in the longitudinal direction of the monolith and slots extending transversely from these chambers to the filtrate collection area. By providing such a filtrate conduit, filtrate can be efficiently transported from the inside of the monolith toward the filtrate collection area with little flow resistance.

(Effects of the Invention) According to the present invention, the filtrate can be easily discharged,
The pressure drop associated with the flow of filtrate can be reduced, the discharge rate of the filtrate can be maintained appropriately, and the problem of restrictions on filtrate flow due to flow resistance in the passages of the porous monolith can be overcome by adopting a simple configuration.

1, a cross-flow filtration device 10 according to one embodiment of the present invention has a cylindrical monolith and includes a passageway 12 and conduits 16, 18 for the filtrate.
For example, the monolith may be formed by extrusion or other methods during manufacture. In FIG. 1, only the passageway 12 is shown in the center of the cross-flow filtration device 10. Conduits 16, 18 for the filtrate are provided through parallel-oriented slots 18 toward the bottom 20 and top 22 of the cross-flow filtration device 10.
4 and a plurality of chambers (described later in the embodiment of FIG. 2) arranged adjacent to one another and extending in the longitudinal direction of the monolith.

The cross-flow filtration device 10 of the present invention is part of a cross-flow filtration installation 24. A cylindrical ring end fitting 26 is cemented to the outer monolith skin 23 of the cylindrical cross-flow filtration device 10. A threaded end cap 28 is threaded onto a mating threaded portion 30 of a housing 32, compressing the end fitting 26 against a supply connection pipe 34, thereby securing the end fitting 26 to the supply connection pipe 34.
The cylindrical ring 26 seals with an O-ring seal 56. A second O-ring seal 58 is provided between the cylindrical ring 26 and the threaded portion 30 of the housing 32. The filtrate collection area 36 is located between the skin 23 and the housing 32.

In operation of the filter, the feed stock is forced under pressure in the direction indicated by arrow 38. The crossflow filter 10 receives the feed stock at its feed end 40 and allows the fluid to flow longitudinally until it is discharged at its concentrate discharge end (not shown). The feed end 40 reveals the square opening of the passageway 12,
Each opening is surrounded by a wall.
Plugs 44 are also provided for filtrate conduits 16, 18. The plugs 44 at the feed and concentrate discharge ends of the monolith isolate the filtrate conduits 16, 18 from direct contact with the feed stock or concentrate. The walls of the passages 12 prevent filtrate from flowing through the filtrate conduits 16, 18.
These plugs 44 are hardened by curing or baking depending on their composition and are designed to allow flow only into the conduits 16, 18 for the feed stock and retentate and the filtrate.
6, 18. If the plug 44 is made of a porous material, the pores in the plug 44 are preferably no larger than the pores in the walls of the passage 12. The mechanical strength, as well as the chemical and thermal resistance of the plug 44, are selected depending on the characteristics of the feedstock and the pressures and temperatures of intended operation.

In Figure 1, after entering the feed end 40, the fluid flows along the passage 12. The filtrate is gradually removed as shown by arrow 50, while the non-permeable concentrate continues to flow as shown by arrow 52. The filtrate flows through the conduits 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61,
When it reaches 8, it flows towards skin 23 and
The filtrate is readily passed through the filter 52 and into the filtrate collection area 36 as indicated by arrows 54 .

The crossflow filtration device 10 includes a selectively permeable membrane attached to the surface of the passageway 12. The selectively permeable membrane is suitable for crossflow filtration, ultrafiltration, reverse osmosis, gas separation, and other applications.
Alternatively, it may be selected from a group of membranes suitable for pervaporation.

The surface area of the passage is about 3.28 to ^{1 cm3} per structure.
32.8 ^{cm 2} (approximately 100-1000 ft ² per cubic foot), or approximately 6.56-23.2 ^{cm 2} per cubic ^foot (approximately 2
00 to 800 ^ft2 ).

The crossflow filtration device 10, including the passage walls, can be fabricated from a variety of porous materials such as ceramics, plastics, or resin-filled solids such as sand.
Among ceramics, cordierite, alumina, mullite, silica, zirconia, titania, silicon carbide, spinel, or mixtures thereof are preferred. The porosity of the material can range from 20 to 60%, preferably 30% or greater. The average pore size can be selected over a wide range, but is typically in the range of about 0.1 to 20 microns.

The selection of parameters for the cross-flow filtration device according to the present invention is aided by the application of Kozeny-Carmen to Darcy's law, i.e. where Q/A is the mass flow rate through the porous medium, i.e., volumetric flow rate/unit time/unit cross-sectional area, ε is the porosity,
ΔP is the pressure drop, k' is the Cozeny-Carmen constant (of which there are five values on average), L is the flow length, μ is the viscosity of the fluid, and S is the surface area of the porous medium. The Cozeny-Carmen equation is described, for example, in Journal of Chemical Engineering (Laurent), 10, pp. 1-34 (1999).
75) by Durian, F. A. L., "Single-Phase Flow Through Porous Media and Porous Structures."

The surface area S is related to the pore hydraulic diameter D _H by the following relationship: Therefore, the mass flow rate Q for a given material
/A is related to pore size and other factors as follows: The average pore size is therefore very important in determining the porosity in the walls of the passages. Although it may be considered desirable to use porous materials with the largest pore size available, this is necessarily impossible. In cross-flow filtration,
Since the pore size determines the separation effect, large pore porous materials lack adequate separation efficiency. To use a monolith as a membrane support member, large pore porous materials cannot be used as well. For example, U.S. Pat. No. 3,977,497.
In U.S. Patent No. 7,967, Trulson and Ritz note that with regard to inorganic membranes dynamically formed on microporous support members, when support members are used with materials having pores larger than 2 microns, fines suspended in the particle suspension used to form the membrane penetrate both into the pore structure of the support member and into the pores of the plug, resulting in undesirably low permeation rates. In contrast, Huber and Roberts' dynamic membrane formation method in U.S. Patent No. 4,069,157 allows for preferred pore sizes of 10 to 17 microns. Furthermore,
When inorganic films are formed by slip casting,
Support members with larger pore sizes are available, as described by Alari et al. in U.S. Patent No. 4,562,021. Thus, for monoliths used as membrane support members, the maximum pore size that can be used is determined by the membrane formation technique. However, in general, membranes are easier to form in porous materials with finer pore sizes.

The cross-flow filtration device of the present invention can be configured and constructed from a variety of materials depending on the intended use of the device. Given the structure of the cross-flow filtration device 10, the filtrate flow characteristics can be predicted by examining the cross-section of the monolith. For this purpose, the cross-section is assumed to be capable of handling a filtrate flow rate of 40.7 ^m3 /day/ ^m2 of evenly distributed water within the monolith passages.
Assume a geometric area of 1000 gallons per ^day per square foot (gfd). If this device were used for cross-flow filtration, it would provide typical and desirable filtration rates for many applications.
If the Molinos device is used as the membrane support, the same filtration flow rate level would be appropriate for ultrafiltration and reverse osmosis devices, with such membrane devices having a flow rate of approximately 4.07 ^m³ /s.
This results in a water flux of 1 day/m ² (about 100 gfd) or more, which is not a problem in most applications.

The uniformly distributed filtrate flow rate is 40.7 ^m3 /day/
^m2 (1000 gfd), the pressure drop across the monolith channel walls can be estimated. In the sample calculations below, the monolith parameters are as follows: support material porosity is 45%, channel density is 46.5 square channels/ ^cm2 (300 channels/ ⁱⁿ² ) with a channel size of 1.118 mm diameter (0.044 in), wall thickness is 0.305 mm (0.012 in), and channel surface area is 2
Using equation ( ³ ) and ^a Kozeny-Carmen coefficient of 5, the pressure drop from ^the center of ^the structure to the filtrate conduit is:
The pressure drop is given in kg/cm² (lb/ ^in² ) for different numbers of passages, n , between the filtrate conduits and for different average pore sizes, _DH .
² (psi).

These calculations show that as the number of passages between the conduits increases and the pore size decreases, the pressure drop from the internal passages to the conduit for filtrate increases dramatically. This pressure drop increases with the square of the number of passages, because both the filtrate flow rate (Q/A) and the flow path length (L) increase proportionally with the number of passages.

Similar calculations were performed for monoliths with different passage sizes. The results in Table 2 illustrate this analysis: These calculations were based on the dimensional characteristics of a commercially available monolith (without filtrate channels) with square channels, 45% porosity, 4 micron pore size, and five channels between the channels. For this group of monolithic materials, the pressure drop from the center of the structure increased approximately proportionally to the channel spacing, reflecting the interaction between the variables in Eq. (3).
Thus, for this group of materials, the important parameter is the spacing of the conduits for the filtrate.
It should be noted from Table 1 that for a monolith with fixed passage size, the important parameter is the square of the conduit spacing.

The design chosen for the device of the present invention also depends on the pressure at which the device will be operated. For example, for an ultrafiltration device, the device will typically operate at a pressure between 3.52 and 7.03 gauge.
It is operated under 50-100 psig ( ¹ kg/cm²).
For the monolith materials listed in the table, the preferred monolith substrate has a pore size of 4 microns or greater and five or fewer passages between the filtrate conduits. For reverse osmosis systems, the system should be rated at a gauge pressure of 35.2 to 70.3 kg/ ^cm² (5
These filters operate at lower pressures (00-1000 psig) and use finer pore size materials or a greater number of passages between the conduits for the filtrate.

These values may need to be modified for different porosities, different fluids, different Kozeny-Carmen constant values (material dependent), and other variables.
The above calculation is 40.7 ^m3 /day/ ^m2 (1000 gf
This was based on the assumption that an evenly distributed flow of filtrate (d) flows into the channel walls. This assumption is generally valid for devices with membranes applied to the channel walls, for example, by solution casting or slip casting, and the membrane primarily provides resistance to filtrate discharge. For cross-flow filtration or dynamic membrane applications, the assumption of even filtrate flow is not valid. In these cases, filtrate flow through the porous material is significantly greater close to the filtrate conduit and rapidly decreases with increasing distance from the filtrate conduit. In this case, the spacing between the filtrate conduits must be smaller to allow adequate filtrate flow through the channel walls away from the filtrate conduit. This necessitates the use of porous materials with larger pore size and porosity or thicker channel walls. These considerations dictate different requirements for porous materials used as membrane supports applied by methods other than dynamic membrane application, and for membrane supports formed by cross-flow filters or dynamic membrane applications. However, these typical results highlight the limitations associated with using monoliths without a conduit for the filtrate.
The presence of a conduit for filtrate as detailed herein provides ^a significant advantage as a result of incorporating such ^a conduit.
1000 in ² /in ³ ), preferably 7
This results in the advantageous use of porous materials having passage areas between 8.7 and 315 cm ² /cm ³ (200 and 800 ^{in 2} /in ³ ).

Once the filtrate reaches the hollow filtrate conduit,
The pressure drop in this conduit to the outer skin of the device must be considered. For the construction described above, a convenient conduit spacing is one passage, or 1.118 mm (0.
The dimensions are 0.044 in. The length of the conduit, i.e., from the center of the monolith to the outer skin of the monolith, is typically 1 to 4 in. In terms of pressure drop in laminar flow, the pressure drop across parallel plates, _ΔPLF , is given by: where V is the fluid velocity, x is the channel length, h is the channel width, μ is the fluid viscosity, and _gc is the gravitational acceleration. For a filtration rate in response to a uniformly distributed water permeability of ^{40.7 m3} /day/ ^m2 (1000 gfd),
The pressure drop in the conduit for the filtrate is small, 7.037 x ^10-4 kg/ ^cm2 (0.01 pF) for conduit lengths up to several inches.
si). Therefore, it is preferable to minimize the thickness of the filtrate conduits, thereby reducing the total conduit volume compared to the total passage volume. This increases the effective surface area per unit volume. A large filter surface area per unit volume allows for increased filtration rates in cross-flow filtration systems.

If it is desired to increase the mechanical support of the walls of the passageway adjacent to the conduit for the filtrate, the conduit can be filled with particulate material in such a way as to form a conduit for the filtrate with less flow resistance than the walls of the passageway.

The crossflow filtration device of the preferred embodiment of the present invention may also be constructed from a conventional monolith having substantially equally spaced passages, such as the monolith of Figure 2. The monolith 150 has spaced rows of passages 152, with rows 156, 157 serving as conduits for the filtrate.
156, 158, 160, and 162 are selected along the length of the monolith. The row indicated by the numeral 154 is omitted for brevity. As shown, rows 156, 158, 160, and 162 are selected along the length of the monolith.
62 are spaced substantially equally apart along the length of the monolith and are generally parallel to one another. These rows are slots 166, 168, 170 and 171, respectively.
2, which are machined into the monolith 150.
170, 172 define channels connecting the longitudinal portions of the filtrate conduits in each row to the filtrate collection area. Each filtrate conduit has a plurality of chambers 176, 178 extending longitudinally of the monolith 150. The filtrate conduit chambers 176, 178 are separated by walls 180 and together define slots 166.
At least some of the passages 152 are separated from nearby chambers 176, 178 by intervening passages 152 therebetween.

Once the slots are cut for each filtrate conduit row, the free and concentrate discharge ends are plugged. As shown in Figure 3, the completed cross-flow filtration device 184 has plugs 186 at the concentrate discharge ends for each slot 188 and mating plugs 190 at the free ends for each filtrate conduit row.

For use as a cross-flow filtration system, monolith 150 is placed in place in an arrangement similar to arrangement 24 of Figure 1. Feedstock flow, indicated by arrow 192, enters the free end of cross-flow filtration system 184. Filtrate flows through the walls of passages 152 into a low-resistance filtrate conduit. The filtrate flows as indicated by arrow 194 until it reaches slot 188, where it flows in the direction indicated by arrow 196.

Furthermore, if desired, the filtrate conduits and channels can be filled with a highly porous material to increase the mechanical support of the passage walls near the filtrate conduits and channels. Note that although the embodiments shown in Figures 2 and 3 have slots at the ends of the monolith, slots may also be provided in the middle of the monolith.

The following example provides a comparison of the permeability for a conventional monolith and a monolith according to the invention having conduits and channels for the filtrate.

EXAMPLE 1 A conventional monolith is assembled into a fixture similar to that of Figure 1. Cylindrical ceramic end rings are bonded to the ends of the monolith using a silicone adhesive. A suitable monolith is obtained from Corning Glass Works, Corning, NY, USA, and is 10.16 cm (4 in) in diameter and 15.24 cm (6 in) long. The passageways are square in shape and have 46.5 cells per square centimeter (300 cells per square inch) evenly spaced. The passageway dimensions are 1.118 mm (0.
0.044 in) and the passage wall thickness is 0.305 mm
(0.012 in). The total passage area through which the filtrate can flow is approximately 1165 ^cm² (28 ^ft² ), with a small passage area near the outer skin of the monolith that is plugged with adhesive. The material of this monolith is cordierite EX-20.
The average pore size is 3 to 4 microns, and the porosity is 33%. After this monolith was installed in the equipment shown in FIG.
The average water infiltration rate based on an estimated area of 68 cm ² (26 in ² ) is 4.48 m ³ /1 at 4.4°C (40°F) and a supply water pressure of 3.52 kg/cm ² (50 psi).
day/m ³ (110 gfd).

EXAMPLE 2 A second monolith of the same material and channel configuration was provided with conduits for filtrate in accordance with the present invention as shown in Figures 2 and 3. These conduits were spaced every fifth row of channels, and the monolith was plugged at both ends with silicone adhesive. Slots were formed in one end of the monolith. Each slot had approximately 12.7 mm of space leading to a filtrate collection area.
(0.5 in) openings in the sides of the monolith. The total passage area through which the filtrate could flow was approximately 1.86 m
² (20 ft ² ), 20% of the area of a conventional monolith due to the conduit for the filtrate and the small area of the passages near the monolith skin plugged by adhesive.
This monolith was inserted into the equipment used in Example 1. The water permeability of this monolith was 4.4°C.
(40°F) and the supply water pressure is 3.52 kg/cm ² (50 ps
i), approximately 97.75 m ³ /day/m ³ (2400 gf
d) was measured.

The monolith of Example 2 exhibited a reduction in passage area of approximately 20%, yet still exhibited a 22-fold increase in monolith permeability over the conventional monolith of Example 1. Subsequent microfiltration tests using a highly turbid suspension of colloidal zirconia with the monolith of Example 2 resulted in a completely clear filtrate, indicating that the high measured permeability was not caused by any leaks or bypasses within the module, but rather was a result of the filtrate conduit provided by the present invention.

While a square array of square channels was used in the above example, it should be recognized that other channel shapes, such as round or triangular, and other arrays, such as hexagonally spaced channels, can be used. Furthermore, while essentially parallel filtrate conduits are described in the above example, it should be recognized that other conduit arrays, such as individual conduits arranged along the radii of a cylindrical monolith, can also be used.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing, with a portion cut away, a cross-flow filtration device according to one embodiment of the present invention.

FIG. 2 is a partial perspective view of an unfinished monolith used in another embodiment of the present invention.

FIG. 3 is a perspective view of a monolith used in yet another embodiment of the present invention.

10: Cross-flow filtration device; 12: Passageway; 14:
...slot, 16, 18...conduit, 20...lower part, 22
...Top, 23...Skin, 24...Cross-flow filtration equipment, 26...End fitting, 30...Threaded portion, 34...Supply connection pipe, 36...Filtrate collection area, 40...Supply end, 44...Plug, 120...
Room, 150... Monolith, 152... Passage, 156, 1
58, 160, 162...column, 166, 168, 17
0,172...slot, 176,178...chamber, 18
0...wall portion, 184...crossflow filtration device, 18
6,190...plug, 188...slot.

Claims (7)

[Claims] 1. A cross-flow filtration device (184) for receiving a feed stock (192) at a feed end face and separating the feed stock into filtrate and a concentrate, the device comprising: a monolith (150) made of a porous material defining a plurality of passages (152) extending longitudinally from the feed end face of the monolith (150) to a concentrate discharge end face thereof, the passages (152) through which the feed stock flows to discharge the concentrate from the cross-flow filtration device; and a filtrate conduit for conveying filtrate toward a filtrate collection area, each filtrate conduit having a plurality of chambers (176, 178) extending longitudinally of the monolith and at least one chamber extending transversely from the chamber to the filtrate collection area.
Slots for filtrate (166, 168, 17
the filtrate conduit is isolated from both end faces of the monolith by blocking members;
and providing flow paths having a flow resistance smaller than the flow resistance of the remaining flow paths within the monolith, wherein at least some of the passages (152) are separated from nearby chambers (176, 178) by intervening passages (152). [Claim 2] A cross-flow filtration device as described in claim 1, characterized in that the slots are formed in at least one of the end faces of the monolith (150) and are sealed to isolate it from the feed stock and the concentrate. 3. The cross-flow filtration device according to claim 1, wherein said porous monolith is made of a ceramic material. 4. The cross-flow filtration device according to claim 1, further comprising a selectively permeable membrane attached to the surface of said passage. 5. The cross-flow filtration device of claim 4, wherein the selectively permeable membrane is selected from the group of membranes suitable for cross-flow filtration, ultrafiltration, reverse osmosis, gas separation, or pervaporation. 6. A crossflow filtration device according to any one of claims 1 to 5, wherein the surface area of said passages is at least 3.28 cm ² /cm ³ (100 ft ² /ft ³ ) of the volume of the monolith. [Claim 7] A crossflow filtration device as described in claim 1, characterized in that the filtrate collection area is arranged along at least one side of the monolith, and the slots are in communication with the filtrate collection area so as to discharge the filtrate to one side of the monolith.