CN1781585B - Inorganic filter media with optimized geometric properties for fluid media - Google Patents

Abstract

The invention relates to a porous support for inorganic elements for separating fluid media for the recovery of filtrates, in the form of elongated rigid elements with a specific volume and cross-section, with a longitudinal central axis, at least two channels, Each channel has a defined hydraulic diameter and flow cross-section and is formed in the carrier parallel to its central axis, the channels together having a filter surface area designed to be covered by at least one separation layer for the fluid medium. According to the present invention: the product of the hydraulic diameter and the filter surface area divided by the volume of the carrier is greater than or equal to 2000; for the carrier, the ratio of its filter surface area to volume is greater than or equal to 340, the sum of the flow sections of the channels on the carrier section The ratio to the hydraulic diameter is greater than or equal to 8m ² /m ² ·mm.

Description

Inorganic filter media with optimized geometric properties for fluid media

technical field

The technical field of the invention is tangential separation by means of separation elements, generally called membranes, made of inorganic materials and comprising a porous support in which is formed a surface on which at least one separation layer is deposited. A series of circulation channels in a fluid medium, the nature and morphology of which are suitable for separating molecules or particles contained in the fluid medium being processed.

Background technique

The object of the invention is more precisely a process for the production of such porous supports.

The invention is aimed at particularly beneficial use in the fields of nanofiltration, ultrafiltration, microfiltration, filtration and reverse osmosis.

Traditionally, a separation membrane or separation element is defined as: a combination of a porous support made of an inorganic material such as ceramics, and one or more separation layers made of an inorganic material deposited on the surface of each flow channel, The separation layers are connected to each other and to the carrier by sintering. Due to the mechanical strength of the support, the function of the support is to make it possible to produce thin separation layers.

In the field of tubular membranes, rigid porous supports assume an elongated shape with polygonal or circular cross-sections. The porous support is arranged to include a series of channels parallel to each other and to the longitudinal axis of the porous support, each channel being cylindrical. These channels communicate at one end with the inlet chamber with the fluid medium to be treated and at the other end with the outlet chamber. The surface of the channel is covered by at least one separation layer which separates molecules or particles present in the fluid medium which flows in the channel in a given direction from one so-called inlet channel end to the other so-called outlet channel end. These membranes separate molecular or particle species in the product to be treated by a sieving effect, provided that all particles or molecules with a diameter larger than the pore size of the membrane are rejected. During separation, fluid movement occurs through the separation layer and then the fluid diffuses into the permeable support towards the outer surface of the porous support. The portion of the treated fluid that has passed through the separation layer and porous support is called the ultrafiltrate and is recovered by a collection chamber surrounding the membrane.

The main performance parameter of a filter carrier is its filter surface area, which corresponds to the product of the inner surface of one channel and the number of channels. The characteristic that best demonstrates the efficiency of a filter medium is the S/V ratio, which indicates the ratio of the filter surface area S to the volume V of the support, since it is obvious that if the filter surface area of the filter medium is large, the outflow of the filter medium is also large. Very big.

Therefore, one way to increase the S/V ratio is to increase the number of channels in the filter carrier. To increase the filter surface area of the filter carrier, a non-circular cross-section was chosen for each channel.

However, another important performance parameter of a filter carrier is its mechanical strength. As the filter surface area increases, the mechanical strength of the filter carrier decreases.

Contents of the invention

Therefore, the object of the present invention is to characterize the porous support so as to optimize its filtration surface area while conferring high performance mechanical strength on it.

To achieve this aim, for the recovery of filtrate, the present invention relates to porous supports for inorganic separation elements of fluid media in the form of elongated rigid elements with a given volume and section, with a longitudinal central axis , at least two passages, wherein each passage has a determined hydraulic diameter (hydraulic diameter) and a flow cross-section (throughcross-section), and is formed in the carrier parallel to its central axis, and these passages have a common filter surface area, which Designed to be covered by at least one separation layer for fluid media.

According to the invention:

- the product of the hydraulic diameter and the filter surface area divided by the volume of the carrier is greater than or equal to 2000,

- For the carrier, the ratio of its filtration surface area to volume is greater than or equal to 340, and the ratio of the sum of the flow cross-sections of the channels on the carrier cross-section to the hydraulic diameter is greater than or equal to 8 (m ² /m ² ·mm).

It was therefore an object of the present invention to determine a porous support comprising the largest possible number of channels. The porous support is considered to have a volume V corresponding to the product of its total cross-section times its length, and to have a filtration surface area St which corresponds to the sum of the internal surface areas of all channels, or, if all channels have the same cross-section, equal to the internal surface area of a single channel and The product of the number of channels. Thus, it has been observed that the ratio of these two properties can be used to define a value from which filtration of the support is efficient if the ratio St/V is increased when the hydraulic diameter of the channel is reduced. Thus, it has been observed that only when the product of the St/V ratio and the hydraulic diameter of the channel is greater than or equal to 2000 does the filter support become truly effective. The units employed are those commonly used by those skilled in the art, in other words the St/V ratio is expressed in m ² /m ³ and the hydraulic diameter of the channels in millimeters. If the channels do not all have the same hydraulic diameter value, the hydraulic diameter of the channels used is the average hydraulic diameter of said channels.

According to another characteristic of the invention, the mechanical strength of the filter carrier according to the invention is chosen to be optimized so that it has the largest possible number of channels. It should be taken into account that the concept of mechanical strength is related to the quality of the filter carrier. For each filter carrier, the concept of transparency is used to characterize the mass of the filter carrier, which is defined as the ratio of the total cross-section of the fluid passages to the total cross-section of the porous support. For example, for a filter carrier with an outer diameter of 25 mm, comprising 19 individual filter channels with a diameter of 3.5 mm, the transparency is equal to the product of the cross-section of one channel and the number of channels divided by the cross-section of a carrier with a diameter of 25 mm. Therefore, transparency is an indicator of the property of the material in the filter carrier, since it represents the proportion of the surface area of the carrier's total cross-sectional void. This ratio of the surface area of the material times the length corresponds to the volume of the filter carrier material and thus the mass. Thus, good clarity corresponds to a low quality filter medium, and low clarity corresponds to a high quality (mass) filter medium. It has been proved that ^the mechanical properties ^{of the} filter carrier really become efficient. Note that ratios of this magnitude only affect filter supports for which the ratio of filter surface area St to volume V is greater than or equal to 340.

According to the invention, the porous support comprises at least two channels, at least one of which is of circular section when at least one of the channels is of non-circular section. Obviously, the porous support may comprise at least two channels, each of which has a non-circular cross-section. Likewise, the porous support may comprise channels having a circular cross-section centered on the centerline of the support and around which channels having non-circular cross-sections are distributed along one or more circumferences.

Another object of the present invention is to optimize the shape of the channels with non-circular cross-section in the porous support in order to optimize the performance of the filter element. In other words, the performance of the filter element also depends on the thickness of the separation layer that is deposited on the surface of the channels controlled, starting from a suspension or sol-gel.

Thus, according to a characteristic of the invention, each channel having a non-circular cross-section comprises a plurality of fillet radii, the radius of the curvature being always greater than 2 mm. Because of the small value of the fillet radius, the formation of a meniscus was observed when the suspension or sol-gel used to prepare the separation layer deposit was evacuated. For a wall fillet radius of less than 2mm, the meniscus formed during the flow of the suspension or sol-gel is minimal and no defects are formed.

According to another feature of the invention, since each channel has a non-circular cross-section, the shape of the porous support helps to control the thickness of the filter layer. It has to be taken into account that a channel with a non-circular cross-section comprises a planar part and a circular part. By convention, a surface is considered planar if its radius of curvature is greater than or equal to 20 mm; correspondingly, a surface is considered circular if its radius of curvature is less than 20 mm.

It should be taken into account that circular parts should not predominate in the shape of the channels since these surfaces cause the greatest inhomogeneity of the porous volume. Conversely, the thickness of the porous support may be constant between the planes of two adjacent channels, under these conditions the porous volume will not vary. Therefore, according to the invention, the proportion of circular surfaces in the periphery of the non-circular channel should be lower than or equal to 85%, and preferably greater than 30%. Under these conditions, the deposition properties of the filter layer were uniform. Table 1 clearly shows the advantages of this feature. Table 1 shows the mass deposited in the filter layer and the retention ratio of the Dextran 180 KD molecule as a function of the percentage of the circular surface area in the channel when applied to a 300 KD type layer. Thus, when the surface is more circular, the mass of deposition increases due to the large porous reservoir associated with each curved surface. In the case of a perfectly circular surface (100%), this mass becomes so large that cracks appear. As the surface becomes flatter, the sediment thickness of the filter layer decreases in the non-circular part, which explains why the retention decreases together with the percentage of circular surface area.

Table 1 % circular surface area 16 30 61 85 100 Sediment mass (g/m²) 7 8.2 9.1 10.3 15 Retention ratio% 28 48 52 54 32

The invention is not limited to the examples described and depicted, since various changes may be made without departing from the scope of the invention.

Claims (7)

1. porous carrier that is used for the separation of the fluid medium with the inorganic element that reclaims filtrate, this porous carrier is the have volume form of stiffener of elongation of (V) and cross section (S), has vertical central axis, at least two passages, each passage has definite hydraulic diameter and passage section (Si), and is formed in the carrier to be parallel to its central shaft, and passage has filter table area (St) jointly, the separating layer that it is designed to be used for by one deck at least fluid media (medium) covers, and it is characterized in that:

-hydraulic diameter and filter table area (St) divided by the product of the volume (V) of carrier more than or equal to 2000,

-for carrier, the ratio of its filter table area (St) and volume (V) is more than or equal to 340, and the summation of the passage section (Si) of the passage on carrier cross section (S) and the ratio of hydraulic diameter are more than or equal to 8m ²/ m ²Mm.

2. porous carrier according to claim 1 is characterized in that at least one passage has circular cross-section, and simultaneously, at least one passage has noncircular cross section.

3. porous carrier according to claim 1 is characterized in that at least two passages have noncircular cross section.

4. porous carrier according to claim 3 is characterized in that the passage with noncircular cross section has the center around the passage of the circular cross-section of carrier center line around being distributed in.

5. according to each described porous carrier of claim 2-4, it is characterized in that each passage with noncircular cross section comprises: at first, the radius of corner of bending radius is always greater than 2mm, and the second, bending radius is less than or equal to 85% less than surface proportion in the periphery of passage of 20mm.

6. porous carrier according to claim 5 is characterized in that each is had the passage of noncircular cross section, bending radius less than the surface of 20mm in the periphery of passage proportion greater than 30%.

7. inorganic resolution element is characterized in that it comprises each described porous carrier with passage that surface area covered by one deck separating layer at least according to claim 1-6.