Composite deep filtering medium and application thereof

Abstract

The invention relates to the technical field of deep filtration, in particular to a composite deep filtration medium and application thereof. The composite deep filtering medium comprises at least one layer of deep filtering paperboard, one side of the deep filtering paperboard is a liquid inlet surface, and the other side of the deep filtering paperboard is a liquid outlet surface; the deep filtering paperboard comprises filtering fibers; at least one intercepting layer is arranged on the outer side of the liquid inlet surface of the deep filtering paperboard; the deep filtering paperboard is equally divided into a first area, a second area and a third area from the liquid inlet face to the liquid outlet face in the thickness direction of the deep filtering paperboard, the 5-micron particle intercepting efficiency of the first area, the second area, the third area and the intercepting layer is A11, A12, A13 and A2 respectively, A2 is larger than or equal to A11 and smaller than A13, A11 is 60-85%, and A13 is 85-98%; the tightness of the interception layer is smaller than that of the first area. The intercepting layer is arranged on the upstream of the deep filtering paperboard, so that the obtained composite deep filtering medium has better filtering effect and filtering loading capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of deep filtration, and more specifically, to a composite deep filtration medium and its application. Background Art

[0002] In the production process of biopharmaceuticals, cell harvest fluids usually contain a large number of biological components such as intact cells, cell debris, and the target proteins required. In order to separate biological components such as the target proteins required, downstream purification and filtration steps such as clarification filtration, ultrafiltration, and chromatography are required. Among them, clarification filtration is the first step in downstream purification of the biopharmaceutical process to remove impurities such as cell debris, large particle residues, colloids or precipitates, polysaccharides, pigments, and host cell proteins (HCP), biological macromolecule DNA, etc., thereby reducing membrane fouling during subsequent filtration, increasing flux, extending the cleaning cycle and service life, reducing operating costs, and improving production efficiency.

[0003] Among them, the filtration step can be divided into surface filtration and deep filtration according to the mechanism of the filtration medium intercepting solid particles. The main filtration principle of surface filtration is interception, so it can only remove particles with a particle size larger than the pore diameter of the filtration medium. Deep filtration can not only capture and intercept large-sized impurity particles on the surface, but also when the particle size is smaller than the pore diameter of the filtration medium, these small-sized particles can approach the pore wall by means of inertia, diffusion, and adsorption after entering the medium interior, and deposit under the action of static electricity and surface force, thereby separating from the fluid. Since the filter pores are distributed throughout the entire medium thickness of the deep filtration medium, and the filter pores form curved channels in the medium, it has a higher dirt-holding capacity and is widely used in the clarification filtration of cell feed liquids.

[0004] Currently, the deep filtration medium that is more commonly used is deep filtration cardboard, which usually uses cellulose fibers or synthetic fibers as the main components, and modifiers such as filter aids and binders can also be added. For example, the deep filtration cardboard disclosed in the British patent with the application number GB7907310A uses diatomaceous earth and / or perlite as filter aids and cellulose fibers as the main filtration matrix, and the provided deep filtration cardboard can effectively remove fine particle contaminants such as bacteria and viruses, thereby obtaining a filtrate product that meets the quality requirements.

[0005] However, due to the increasing demand for biological products in modern pharmaceutical technology, the pressure of downstream clarification and filtration has also increased simultaneously. The expanded demand for biological products has led to a substantial increase in the titer of upstream biological products, which has also greatly increased the amount of biomass and cell fragments contained in the upstream feed liquid, which has put forward higher requirements for the filter used to clarify the above-mentioned raw material liquid. When facing the clarification and filtration of high-turbidity and high-density feed liquid, the existing deep filter paperboard usually gets blocked earlier, resulting in a rapid increase in the pressure difference, making it difficult to achieve the desired load, which will reduce the utilization rate of the dirt-holding space of the deep filter paperboard and cause a substantial increase in production costs. After research, the inventor found that when filtering cell feed liquid with conventional turbidity, the deep filter paperboard actually undergoes the same clogging process, but because the turbidity of the feed liquid is relatively low, the clogging phenomenon comes relatively slowly, and the load that can be achieved is relatively higher. This load is usually used as the expected load of the deep filter paperboard, which is used to compare its load changes under different feed liquids. However, based on production cost and efficiency considerations, especially when facing large-scale clarification and filtration needs, this expected load is actually still insufficient.

[0006] In order to increase the filtration capacity, EMD Millipore's Chinese patent with authorization announcement number CN105492101B and 3M Innovations' Chinese patent application with publication number CN116887899A each disclose a multi-layer deep filter medium with a reduced pore size gradient, achieving a higher filtration capacity for high turbidity liquids. However, this method does not effectively improve the capacity of a single-layer deep filter medium, and the utilization rate of the filter medium's dirt-holding space is still insufficient.

[0007] Therefore, it is necessary to provide a deep filtration medium with a higher cell feed load capacity for different turbidities and a greater utilization rate of the medium's contamination-holding space. Summary of the invention

[0008] In view of the problems existing in the prior art, the object of the present invention is to provide a composite deep filter medium and application thereof.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] A composite deep filter medium comprises at least one layer of deep filter paperboard, one side of the deep filter paperboard is a liquid inlet surface, and the other side is a liquid outlet surface; the deep filter paperboard comprises filter fibers; at least one interception layer is arranged outside the liquid inlet surface of the deep filter paperboard;

[0011] The deep filter paperboard is divided into a first region, a second region and a third region along its thickness direction from the liquid inlet surface to the liquid outlet surface. The 5 μm particle interception efficiencies of the first region, the second region, the third region and the interception layer are A 11 , A12 , A 13 , A 2 , where A 11 ≤ A 2 < A 13 , A 11 is 60 - 85%, and A 13 is 85 - 98%;

[0012] The tightness of the interception layer is less than that of the first region.

[0013] In the above technical solution, the present invention provides a composite deep - layer filtration medium, including a deep - layer filtration cardboard and an interception layer arranged at its front section. The deep - layer filtration cardboard is formed by the overlapping of filtration fibers to form a framework. During use, the pores between the filtration fibers in the deep - layer filtration cardboard can mechanically intercept and remove biological components with larger diameters such as intact cells or cell debris, while DNA, HCP, etc. can be adsorbed and separated by the deep - layer filtration cardboard through charge adsorption, hydrophobic adsorption, etc., realizing the clarification and purification of target components. The present invention adds an interception layer on the basis of the deep - layer filtration cardboard. As a pre - filtration layer, the interception layer, in addition to its own loading capacity, further improves the loading capacity of the deep - layer filtration cardboard, making the composite deep - layer filtration medium of the present invention have a better loading capacity level and not affecting the flux of the filtration medium.

[0014] In the present invention, as the filtration main body, the deep - layer filtration cardboard adopts an uneven precision design. On the side close to the liquid inlet surface, the filtration precision is lower and the pores are larger, mainly used for removing larger particles; while on the side close to the liquid outlet surface, its filtration precision is higher and the pores are smaller, which can ensure the effective interception of smaller - sized particles, and through the variable precision design, better overall space utilization rate of the filtration medium is achieved, ensuring the effective interception of impurity particles of different sizes.

[0015] Based on this principle, when it is necessary to further increase the loading capacity of the filtration medium, a common method is to add a pre - filtration layer with a lower precision in front of the original filtration medium; however, the inventor found through research that this method has little effect on improving the loading capacity of the deep - layer filtration cardboard under conventional cell broth, and also has limited effect on reducing the loading capacity of the deep - layer filtration cardboard caused by high - turbidity cell broth; on the contrary, the inventor unexpectedly found that when adding a pre - filtration layer with a precision equivalent to or higher than that of the first region but with a lower tightness in front of the deep - layer filtration cardboard, that is, the interception layer of the present invention, it can effectively improve the loading capacity of the deep - layer filtration cardboard itself, essentially improving the loading capacity of the composite deep - layer filtration medium; and after adding the interception layer of the present invention, the turbidity of the filtrate is further reduced.

[0016] The possible reason is that during the filtration process, the particles in the feed liquid adsorb in the pores of the depth filtration paperboard, which can cause the pore channels to narrow. The more adsorption occurs, the narrower the channels become, and the higher the back pressure. However, an excessively high back pressure is actually not feasible. Therefore, when filtering cell feed liquid, the loading capacity of the depth filtration paperboard usually refers to the feed liquid throughput when the back pressure in the clarification filtration process reaches a set value (such as 1 bar). When the set back pressure value is reached, the utilization rate of the dirt-holding space in the thickness direction of the depth filtration paperboard is not equivalent. This is because during the clarification filtration process, the large-sized particles in the cell feed liquid are mainly intercepted on the side close to the liquid inlet surface, which can cause the pore channels on the liquid inlet surface side to narrow, making it easier for small-sized particles to be adsorbed and intercepted on this side, thus easily causing paperboard blockage. That is to say, when the set back pressure value is reached, it is mainly the side of the depth filtration paperboard closer to the liquid inlet surface that becomes blocked, while the other side far from the liquid inlet surface of the depth filtration paperboard does not actually reach the maximum loading capacity. When the turbidity or density of the cell feed liquid is higher, the above phenomenon is more obvious, the depth filtration paperboard becomes blocked earlier, and the utilization rate of the dirt-holding space is lower.

[0017] For deep filtration cardboard, its accuracy and tightness are usually correlated, that is, in the thickness direction, the accuracy and tightness of deep filtration cardboard usually change synchronously. In the present invention, by presetting an interception layer, the accuracy of the interception layer is equivalent to or higher than that of the first region of the deep filtration cardboard, but the tightness is lower, thereby achieving a higher pore utilization rate of the filter medium, especially achieving a higher pore utilization rate of the deep filtration cardboard, reaching a higher loading capacity and a lower turbidity. When the accuracy of the interception layer is higher, its pores are smaller, and it can intercept large-sized and some small-sized particles in the cell liquid first, so that the amount of cell debris entering the deep filtration cardboard is reduced and the distribution is more dispersed. When small-sized particles enter the deep filtration cardboard, they can smoothly pass through the first region and be intercepted in the region with higher accuracy of the deep filtration cardboard (such as the second region or the third region), thus avoiding the blockage of the cardboard caused by the rapid accumulation of a large amount of cell debris and particles in the first region of the deep filtration cardboard, enabling the overall loading capacity of the deep filtration cardboard to be effectively exerted, that is, greatly improving the actual loading capacity of the application of the deep filtration cardboard, making the composite deep filtration medium of the present invention have a better loading capacity level; and when large particles are intercepted by the interception layer in advance, the deep filtration cardboard is mainly used to intercept smaller particles, the cardboard can exert a higher loading capacity, the interception amount of particles in the liquid is higher, and due to the existence of the interception layer, the filtration pressure of the downstream deep filtration cardboard is relieved, and the intercepted fine particles are retained and will not be "pressed out" of the cardboard, making the turbidity of the liquid in the early stage of filtration lower, so that the overall turbidity of the filtrate can be further reduced. Moreover, the impurity particles intercepted by the interception layer are deposited on the surface and inside of the interception layer, and the particles deposited on the surface of the interception layer form a filter cake layer; since the interception layer has a lower tightness relative to the first region of the deep filtration cardboard at the same time, that is, the structure is relatively loose, there are a large number of pore spaces in the plane direction and the thickness direction of the interception layer. Therefore, with the impact of the liquid, some of the particles intercepted on the upper layer of the interception layer will be continuously washed to the lower layer, so that the impurity particles entering the inside of the interception layer will actually be dispersed in the thickness direction of the entire interception layer, so that the interception layer after intercepting the impurity particles will not be overfilled and blocked in some regions, and can always maintain a certain porosity.As for the filter cake layer formed on the surface of the intercepting layer, it is mainly formed by intercepting particles with larger pore sizes than the intercepting layer itself. On the one hand, the filter cake layer is entirely composed of large particles that have not been intercepted, and the proportion of oversized particles in the slurry is relatively small, so there will not be a problem of excessive accumulation causing blockage of the filter cake layer; on the other hand, unlike cardboard, the filter cake layer is entirely formed by intercepted particles and does not contain fibers that are needed for support and interception, making the structure of the filter cake layer looser. Under the impact of the slurry, the particles in the filter cake layer will move, allowing the slurry to pass through the filter cake layer and enter the intercepting layer; and, when the slurry continues to impact, a fixed channel may be formed on the filter cake layer; furthermore, the filter cake layer does not contain fibers but is composed of large particles, so that the gaps between the particles are larger and no blockage will occur. When the interception layer is as accurate as the first area of ​​the deep filter paperboard, the particles originally intercepted by the first area will be intercepted by the interception layer, and because the interception layer has a lower tightness, that is, it is looser, the particles intercepted by the interception layer can also be dispersed in the thickness direction of the interception layer, and are not easily blocked, so that the feed liquid can smoothly enter the deep filter paperboard for further filtration, and the load capacity of the deep filter paperboard can also be more effectively utilized. Therefore, the composite deep filter medium of the present invention can have both good overall flux and load capacity.

[0018] In the present invention, by controlling the interception accuracy of the interception layer and the deep filtration cardboard within a suitable range and specifying that the interception layer has a lower tightness, better flux, loading capacity and interception effect can be achieved. Among them, the interception accuracy is represented by the interception efficiency of the test material for 5-μm particles. In the present invention, the first region and the third region of the deep filtration cardboard have suitable interception efficiencies for 5-μm particles, so as to ensure qualified filtrate. When the interception efficiencies of the first region and the third region are too high, that is, the accuracy is higher, the pores of the deep filtration cardboard are smaller at this time, resulting in too small flux of the cardboard. And in this case, a large number of large-sized particles directly accumulate outside the deep filtration cardboard to form a relatively thick filter cake layer. When the filter cake layer is too thick, it is not conducive to the flow of the feed liquid into the interior of the cardboard, and the flux of the deep filtration cardboard will be significantly reduced, and the clogging will occur faster. At the same time, the too thick filter cake layer will also cause a greater pressure on the liquid inlet surface of the cardboard, which may affect the strength of the cardboard. When the interception efficiencies of the first region and the third region are too low, some impurities with smaller sizes may not be intercepted by the cardboard and enter the filtrate, resulting in unqualified clarification filtration effect. At the same time, in the present invention, the accuracy of the interception layer is specified to be equal to or higher than that of the first region of the deep filtration cardboard and has a lower accuracy to obtain a higher loading capacity. When the accuracy of the interception layer is lower than that of the first region of the deep filtration cardboard, at this time, the interception layer not only cannot intercept many small particles, but also larger cell debris will pass through the interception layer and enter the deep filtration cardboard. The interception layer cannot play the role of pre-interception and dispersion relative to the first region, that is, there will still be a problem that the first region of the deep filtration cardboard is blocked relatively quickly. When the accuracy of the interception layer is equal to or even higher than that of the third region of the deep filtration cardboard, the pores of the interception layer are too small at this time, which will affect the flux of the feed liquid, and the too high interception accuracy will cause the particles in the feed liquid to clog the interception layer, making the deep filtration cardboard unable to play the filtration role and resulting in a lower loading capacity of the composite deep filtration medium. When the tightness of the interception layer is less than or equal to the tightness of the first region of the deep filtration cardboard, the density of the interception layer is relatively high at this time, and the intercepted particles cannot be further dispersed in the interception layer, so it is easy to be blocked directly in the interception layer earlier, resulting in the feed liquid being unable to enter the deep filtration cardboard further and making the actual loading capacity of the deep filtration cardboard worse.

[0019] It should be noted that in the present invention, the interception layer is arranged outside the liquid inlet surface of the deep filtration cardboard, and the specific forms of the two are not limited. That is, the composite deep filtration medium of the present invention can be designed as an integral type or a split type, as long as it is ensured that the cell liquid first passes through the interception layer for pre-filtration and then is deeply filtered by the deep filtration cardboard during clarification filtration. For example, the interception layer can be directly integrally formed with the deep filtration cardboard, that is, the interception layer and the deep filtration cardboard are an inseparable whole; or the interception layer and the deep filtration cardboard are independent of each other, the interception layer is stacked above / outside the liquid inlet surface of the deep filtration cardboard, or the interception layer is arranged at intervals above / outside the liquid inlet surface of the deep filtration cardboard, or the interception layer and the deep filtration cardboard in the composite deep filtration medium are separated, that is, the interception layer and the deep filtration cardboard can be used as the filtration media for two treatment processes respectively.

[0020] Further, the 5μm particle interception efficiency A of the first region, the third region and the interception layer 11 , A 13 , A 2 satisfy: A 11 <A 2 <A 13 .

[0021] In the above technical solution, preferably, the precision of the interception layer is between the first region and the third region of the deep filtration cardboard. By controlling the interception layer to have a higher precision than the first region of the deep filtration cardboard, on the basis of ensuring the interception effect on large particles, some smaller particles can be further intercepted, so that the overall particle size of the liquid entering the deep filtration cardboard is smaller, and the size of the large particles that need to be intercepted by the first region of the deep filtration cardboard is also smaller. Therefore, after the first region intercepts the large particles, there are still relatively large pores for the smaller-sized particles to pass through smoothly, so as to better avoid the problem that the first region of the cardboard is blocked prematurely, resulting in insufficient utilization rate of the dirt-holding space of the second and third regions of the deep filtration cardboard, and enabling the actual loading capacity of the deep filtration cardboard to reach a higher level. At the same time, due to the lower tightness of the interception layer and the more porous overall structure, it has a higher dirt-holding capacity. By setting the precision of the interception layer to be slightly higher than that of the first region of the deep filtration cardboard, more particles are intercepted by the interception layer at this time, so that it can match its higher capacity and further improve the overall loading capacity of the composite deep filtration medium.

[0022] Further, the 5μm particle interception efficiency A of the first region, the second region and the third region 11 , A 12 , A 13 satisfy: A 11 <A 12 <A 13 .

[0023] Since different precisions correspond to intercepting target particles of different sizes, preferably, in the above technical solution, the precision gradient of the deep filtration cardboard of the present invention increases from the first region to the third region, so as to achieve step-by-step interception of particles of different sizes; different thickness regions of the deep filtration cardboard can also more specifically intercept particles matching their precision sizes, avoiding a large number of interceptions of larger impurity particles in the region with a higher interception precision of the deep filtration cardboard, resulting in a too rapid attenuation of the flux of the deep filtration cardboard and blockage, thereby being beneficial to improving the filtration load and filtration life of the deep filtration cardboard and reducing the use cost of the deep filtration cardboard.

[0024] Further, the 5μm particle interception efficiency A 11 、A 12 、A 13 、A 2 of the first region, the second region, the third region and the interception layer satisfies: A 11 <A 12 <A 2 <A 13 ,A 11 :A 12 :A 13 :A 2 =1:1.05 - 1.35:1.15 - 1.5:1.1 - 1.4。

[0025] In the above technical solution, in the composite deep filtration medium of the present invention, the precision gradient of the deep filtration cardboard increases from the first region to the third region, so as to achieve step-by-step interception. At this time, the blockage of the deep filtration cardboard will be delayed, which is beneficial to improving the load of the deep filtration cardboard; however, after research by the inventor, it is found that there is still a certain room for improvement in the actual load end point of the deep filtration cardboard with a gradient setting. This is because the load end point is actually due to the blockage of the second region and the first region of the cardboard, resulting in insufficient utilization of the dirt-holding space in the third region. Therefore, the present invention further sets the precision of the interception layer to be between the second region and the third region of the cardboard; the precision of the interception layer is less than that of the first region and the second region. At this time, the interception layer can not only ensure the effective interception of large-size particles, but also further intercept more smaller particles, making the particle size of the liquid material entering the deep filtration cardboard further reduced, thereby avoiding the earlier attenuation of the flux of the deep filtration cardboard and further improving the cardboard load; at the same time, the precision of the interception layer is greater than that of the third region, so that the particles passing through the interception layer and entering the deep filtration cardboard are not too small. At this time, the composite deep filtration medium ensures the interception effect through the third region of the deep filtration cardboard, so it will not affect the interception effect of different precision regions in the thickness direction of the deep filtration cardboard on particles of different sizes, and ensures that the deep filtration cardboard smoothly completes the step-by-step filtration of the liquid material, so as to better exert the load of the deep filtration cardboard.

[0026] In the present invention, the precision ratios among the interception layer, the first region, the second region, and the third region of the deep filtration cardboard are moderate, and there is an appropriate precision difference between the interception layer and each region of the deep filtration cardboard. Thus, it can ensure that the size distribution of the target particles to be intercepted by the interception layer and each region of the deep filtration cardboard is appropriate, making the filtration pressure of each region moderate, and avoiding the problem that due to an excessive precision difference between adjacent interception regions, too many particles to be intercepted are required in the region with relatively high precision and the interception pressure is too high. Therefore, the overall flux of the filtration medium can be better guaranteed. Moreover, since it is very difficult for filtration media with different precisions to achieve a 100% interception effect on the target particles they need to intercept, that is to say, inevitably, some target particles that should be intercepted will enter the next layer of the filtration medium. Therefore, through the above-mentioned appropriate precision gradient setting, reliable interception of their respective target intercepted particles can be better achieved, and there will be no problem that due to too small a precision gradient, too many particles that should be intercepted enter the next region and gradient interception cannot be achieved. Furthermore, a more stable filtration effect is provided, enabling the composite deep filtration medium and the deep filtration cardboard of the present invention to maintain a better loading capacity and a better space utilization rate for biological liquid materials with different turbidities and densities.

[0027] Further, the degrees of tightness of the first region, the second region, the third region, and the interception layer are respectively B 11 、B 12 、B 13 、B 2 , where B 2 <B 11 <B 12 <B 13 , B 11 :B 12 :B 13 :B 2 =1:1.02 - 1.2:1.05 - 1.35:0.2 - 0.7, B 11 is 0.2 - 0.4 g / cm 3 , and the degree of tightness B 2 of the interception layer is 0.1 - 0.25 g / cm 3 .

[0028] In the above technical solution, along the flow direction of the feed liquid, the composite deep filtration medium of the present invention has an overall gradient-increasing tightness. Among them, the tightness of the interception layer is the smallest and the structure is the loosest. After pre-interception, the intercepted particles are not densely distributed upstream of the interception layer but are dispersed throughout the thickness region of the interception layer to ensure that there are sufficient pore channels in the interception layer for the feed liquid to continuously flow through. At the same time, the tightness of the deep filtration cardboard increases sequentially from the first region to the third region, that is, the arrangement of the filtration fibers becomes closer, resulting in a gradual decrease in the porosity. The tightness of the deep filtration cardboard is relatively small on the side close to the liquid inlet surface, that is, the first region, so as to provide more dirt-holding space; while the tightness is relatively large on the side close to the liquid outlet surface, combined with the relatively high precision of the third region, a relatively dense structure is formed to further ensure the reliable interception of small particles and guarantee the interception effect of the composite deep filtration medium.

[0029] In the present invention, each region of the interception layer and the deep filtration cardboard has a suitable tightness range, and the tightness ratio between adjacent filtration regions is moderate. There is a suitable tightness difference between each region of the interception layer and the deep filtration cardboard. Under this tightness range and tightness difference, the entanglement situation between the interception fibers and between the filtration fibers can be controlled to obtain a composite deep filtration medium with a more complex flow channel, a more uniform distribution of the flow channel in the vertical thickness direction of the interception layer and the deep filtration cardboard, and a better flow velocity load. Moreover, by controlling the appropriate tightness of each region of the interception layer and the deep filtration cardboard, the cooperation between each layer of the interception layer and the deep filtration cardboard can be better, so that the intercepted particles can be more dispersed in the corresponding interception region, and the deep filtration medium can maintain a better flux so that each interception region can reach a better load; the present invention provides a more stable and effective filtration effect through specific tightness control, so that the composite deep filtration medium of the present invention can maintain a better load for different biological feed liquids.

[0030] When the tightness of the interception layer and each filtration area of the deep filtration cardboard is too small, the overall structure of the composite deep filtration medium will be too loose, resulting in an increase in thickness, which is not conducive to improving the loading capacity. At the same time, when the tightness is too small, there may also be a problem of insufficient strength, making the structural stability of the medium worse under the impact of the feed liquid. When the tightness of the interception layer and each filtration area of the deep filtration cardboard is too large, the overall structure of the composite deep filtration medium is too dense, resulting in a decrease in flux and easy premature blockage, making the utilization rate of the dirt-holding space of the filtration medium insufficient and the actual loading capacity low. Moreover, in addition to the accuracy, the tightness also affects the interception effect. When the tightness difference between the interception layer and the first area of the deep filtration cardboard is too large, the tightness of the interception layer is too low at this time. Although the lower tightness of the interception layer is conducive to the dispersion of particles, since the interception rate of each filtration area for the target particles cannot reach 100%, the too low tightness weakens the binding of the interception layer to the particles, which may cause more particles that should be intercepted to pass through this filtration area and enter the next area, resulting in blockage and a decrease in the loading capacity of the filtration medium. When the tightness difference between the interception layer and the first area of the deep filtration cardboard is too small, the accuracy of the interception layer is relatively high at this time, and its effect on particle dispersion is limited, resulting in a limited effect on improving the loading capacity of the cardboard, and there is still a problem of low utilization rate of the dirt-holding space.

[0031] Further, the interception layer includes interception fibers, and the SEM average diameters of the filtration fibers and the interception fibers are D 1 , D 2 , D 1 : D 2 = 1:0.3 - 0.8.

[0032] In the above technical solution, the interception layer and the deep filtration cardboard respectively form skeletons through interception fibers and filtration fibers, and the gaps between the fibers are used to intercept impurity particles in the biological feed liquid. Therefore, the structural dimensions of the fibers are the direct factors affecting the accuracy and tightness of the interception layer and the deep filtration cardboard. In the present invention, by controlling the filtration fibers and the interception fibers to have a suitable diameter ratio, specific accuracy and tightness changes of the interception layer and the deep filtration cardboard can be achieved. Among them, the interception fibers have a smaller diameter relative to the filtration fibers, that is, the interception fibers are finer, and the formed interception network is more loose, so that it is easier to obtain a lower tightness to achieve the specific tightness control of the interception layer and the deep filtration cardboard of the present invention. And, the interception fibers are finer, and the pore size of the interception network formed after their mutual overlap can also be adjusted within a wider range, so that an interception layer with higher accuracy and lower tightness of the present invention can be obtained. However, the diameter of the interception fibers cannot be too small, because when the fibers are too fine, the pore size formed between the fibers becomes larger. To ensure the interception effect, more fibers need to be stacked, which will lead to an increase in the density of the medium, thus affecting the flux. Moreover, the too fine fibers have lower strength, which will lead to a worse overall stability of the composite deep filtration medium.

[0033] It can be understood that the measurement methods of various surface morphology parameters (such as thickness, fiber density, fiber diameter, particle size, etc.) of the composite deep filtration medium can be carried out by using a scanning electron microscope to characterize the morphology of the filtration medium structure, and then using computer software (such as Matlab, NIS-Elements, ImageJ, Nano Measure, etc.) or manually measuring and performing corresponding calculations. When actually measuring, for example, when measuring the fiber diameter, the surface (or cross-section) of the composite deep filtration medium can be characterized by an electron microscope first to obtain the corresponding SEM image, and a certain area can be selected, such as 500μm×500μm, 800μm×800μm, 1000μm×1000μm, and the specific area size depends on the actual situation. Then, all the fiber diameters on this area can be measured by using the corresponding computer software or manually (the number of fibers counted should be no less than 20), and then calculated to obtain the average fiber diameter of this area; of course, those skilled in the art can also obtain the above parameters through other measurement means, and the above measurement means are for reference only.

[0034] Further, the SEM average diameter D of the filtration fiber 1 is 10 - 60μm, and the SEM average diameter D of the interception fiber 2 is 5 - 55μm.

[0035] In the above technical solution, on the basis of controlling the diameter ratio of the filtration fiber and the interception fiber, by controlling the fiber diameters of the two within appropriate ranges respectively, it is beneficial to obtain a composite deep filtration medium with better accuracy and tightness distribution and better filtration effect. When the diameters of the filtration fiber and the interception fiber are too large, it may cause the pore diameters of the interception layer and the deep filtration cardboard to be too large, thus affecting the interception effect; while when the diameters of the filtration fiber and the interception fiber are too small, there is a problem of too high density, which affects the flux.

[0036] Further, the density of the interception fibers on the liquid inlet surface of the interception layer is 3 - 15 fibers / 500μm; the density of the interception fibers on the liquid outlet surface of the interception layer is 4 - 30 fibers / 500μm.

[0037] In the above technical solution, the interception layer of the present invention is a gradient structure. On the side close to the liquid inlet surface, the density of the interception fibers is small, the fiber arrangement is looser, and the interception accuracy is lower; on the side close to the liquid outlet surface, the density of the interception fibers is large, the fiber arrangement is denser, and the interception accuracy is higher. By setting the interception layer to have a gradient increase in accuracy and tightness along the direction of the liquid flow, a larger interception load can be obtained while ensuring the interception effect of the interception layer, thereby realizing the improvement of the overall load of the composite deep filtration medium.

[0038] Further, the thicknesses of the deep filtration cardboard and the interception layer are H 1 、H2 ,H 1 : H 2 = 1: 0.3 - 1.2, H 1 is 2 - 6 mm, H 2 is 1 - 5 mm.

[0039] In the above technical solution, in the present invention, the setting of the interception layer mainly plays a role of pre - interception. The main filtering body of the composite deep - filtering medium is still the deep - filtering cardboard. The deep - filtering cardboard needs to have a slightly larger volume ratio to obtain a larger filtering load while ensuring the filtering effect, that is, it is necessary to set a larger thickness for the deep - filtering cardboard. When using the deep - filtering cardboard alone, it is mainly due to the premature blockage of the front - end area of the cardboard that the actual load of the cardboard is reduced. That is, in the present invention, the setting of the interception layer is mainly used to relieve the filtering pressure of the first and second areas of the deep - filtering cardboard and avoid premature blockage. Therefore, the thickness of the interception layer cannot be too small, so as to match the higher precision and lower tightness of the interception layer, ensure that the interception layer has a certain interception load, so that the interception layer and the deep - filtering cardboard can maintain a good flux to obtain a larger load and improve the utilization rate of the dirt - holding space of the composite deep - filtering medium. In the present invention, the precision, tightness and load of the interception layer are related. When the precision is higher, more particles are intercepted by the interception layer at this time. In order to ensure the flux, the set tightness of the intercepted particles needs to be smaller so that the intercepted particles can be dispersed in the interception layer. When the tightness is smaller, the interception layer is more fluffy and its thickness is also higher.

[0040] In the present invention, both the interception layer and the deep - filtering cardboard have appropriate thicknesses, and the thicknesses of the two match the actual application to obtain a better filtering effect. When the thicknesses of the deep - filtering cardboard and the interception layer are too large, it is easy to cause the device to be too large in volume and redundant in filtering load; while when the thicknesses of the deep - filtering cardboard and the interception layer are too small, the filtering space is insufficient, resulting in a low load, a short service life of the composite deep - filtering medium, and an increase in filtering cost.

[0041] Furthermore, the filtering fiber is selected from one or more of cellulose fiber, polyacrylonitrile fiber, polyolefin fiber, polyester fiber, and activated carbon fiber.

[0042] In the above technical solution, the cellulose fiber has high hydrophilicity, and the synthetic fiber has a certain degree of hydrophobicity. When the two are used in combination, the deep filtration cardboard can maintain good hydrophilicity, and at the same time, the affinity of the deep filtration cardboard for organic solvents is also improved, which is conducive to the adsorption of impurities dissolved in organic solvents by the cardboard. The activated carbon fiber surface also has many pores. When it is added as a filtration fiber, it can not only serve as the framework of the cardboard to improve the strength of the cardboard, but also improve the adsorption effect of the cardboard. It should be noted that only some optional filtration fiber materials are listed in the present invention. Under the premise of meeting the requirements of interception effect and loading capacity, other materials of filtration fibers can also be selected. In the present invention, the filtration fiber is preferably cellulose fiber.

[0043] Further, the interception fiber is selected from one or more of polypropylene fiber, glass fiber, polyethylene fiber, polyester fiber, and polyacrylonitrile fiber.

[0044] In the above technical solution, the interception fiber constitutes an interception layer for pre-filtration. Only some optional interception fiber materials are listed in the present invention. However, under the premise of meeting the requirements of pre-filtration effect, other materials of interception fibers can also be selected. In the present invention, the interception fiber is preferably glass fiber.

[0045] Further, the deep filtration cardboard further includes a filter aid and / or a binder.

[0046] In the above technical solution, in the present invention, by adding a filter aid to the deep filtration cardboard, the internal micropores of the filter aid are rich and the specific surface area is large, and countless intricate and cross-connected microchannels can be formed in the deep filtration cardboard, which is conducive to providing a more complex flow channel to slow down the attenuation of the flow rate during the filtration process and improve the interception effect of impurities. At the same time, adding a small amount of binder can further improve the bonding strength of the deep filtration medium, improve the burst resistance, bend resistance, etc. of the deep filtration medium; moreover, adding a small amount of binder has little effect on the dissolution of impurities, because the content of the binder itself is low, so the content of the binder fragments that can fall off is also low, and it is easy to control the dissolution of impurity fragments at a low level.

[0047] It should be noted that in the present invention, the deep filtration cardboard mainly removes impurity particles in the biological liquid by physical interception; and when facing a specific biological liquid, the deep filtration cardboard can also be given hydrophobicity and / or electrostatic action by modifying the filtration fiber or selecting a filter aid and a binder with a specific structure and composition, so as to further utilize the hydrophobic interaction and electrostatic adsorption action to better achieve the removal of impurity particles.

[0048] Further, the average particle size d of the SEM of the filter aid is 5-50 μm.

[0049] In the above technical solution, the depth filtration cardboard contains filter aids with appropriate sizes to achieve better interception effects, filtration fluxes, and cardboard strengths. When the particle size of the filter aid particles is too small, there may be a problem of filter aid particle shedding, which affects the filtration effect; while when the particle size of the filter aid particles is too large, the larger filter aid particles may block the pores between the filter fibers, which instead affects the flux.

[0050] Furthermore, the filter aid is selected from one or more of diatomaceous earth particles, silica, perlite, activated carbon, and clay; the binder comprises a water-soluble synthetic polymer based on a urea or melamine-formaldehyde polymer, a polyaminopolyamide-epichlorohydrin polymer, or an acetalated polyacrylamide resin.

[0051] In the above technical solution, the present invention discloses partial selections of the filter aid and the binder. On the premise of meeting the requirements of the filtration effect, other filter aids and binders can also be selected.

[0052] Furthermore, the composite depth filtration medium comprises N layers of depth filtration cardboard arranged continuously, where N is an integer from 2 to 5; along the direction of the feed liquid flow, the overall 5-μm particle interception efficiency and tightness of the N layers of filtration cardboard both increase in a gradient manner.

[0053] In the above technical solution, the composite depth filtration medium of the present invention may also comprise multiple layers of depth filtration cardboard. At this time, the precision and tightness of the multiple layers of depth filtration cardboard are arranged in a gradient. Specifically, for example, the 5-μm particle interception efficiency of the multiple layers of depth filtration cardboard increases in the range of 60-90%, and the tightness increases in the range of 0.2-0.6 g / cm 3 range. The cardboard near the liquid inlet end of the composite depth filtration medium has relatively small precision and tightness, which is mainly used to remove larger particles; the cardboard near the liquid outlet end of the composite depth filtration medium has relatively large precision and tightness, which is used to ensure the interception effect. Through the gradient settings between the multiple layers of depth filtration cardboard and at different thicknesses of a single layer of depth filtration cardboard, the hierarchical interception of particles of different sizes by the depth filtration cardboard is more refined, which is more conducive to the exertion of the cardboard loading capacity and realizes a higher utilization rate of the dirt-holding space of the cardboard. It should be noted that when multiple layers of depth filtration cardboard are provided, the interception layer can be arranged upstream of the multiple layers of depth filtration cardboard or between the multiple layers of depth filtration cardboard. Only the precision and tightness of the interception layer and the downstream depth filtration cardboard adjacent thereto need to be considered. It should be noted that when the interception layer is arranged between the multiple layers of depth filtration cardboard, it is also necessary to control that the overall tightness and precision of the upstream depth filtration cardboard should be less than the tightness and precision of the interception layer.

[0054] Furthermore, the composite depth filtration medium comprises M layers of interception layers arranged continuously, where M is an integer from 2 to 5; along the direction of the feed liquid flow, the overall 5-μm particle interception efficiency and tightness of the M layers of interception layers both increase in a gradient manner.

[0055] In the above technical solution, the composite deep filtration medium of the present invention may further include multiple interception layers. At this time, the precision and tightness of the multiple deep interception layers are set in a gradient manner. Specifically, for example, the interception efficiency of 5-μm particles of the multiple interception layers increases in the range of 65-95%, and the tightness increases in the range of 0.05-0.4 g / cm 3 range. The interception layer near the liquid inlet end of the composite deep filtration medium has relatively small precision and tightness, mainly used to remove larger particles; the interception layer near the liquid outlet end of the composite deep filtration medium has relatively large precision and tightness, used to ensure the pre-filtration effect of the interception layer. Through the gradient setting between the multiple interception layers and at different thicknesses of a single interception layer, the hierarchical interception of particles of different sizes by the interception layer is more refined, which is more conducive to the performance of the interception layer and the loading capacity of the deep filtration paperboard, and realizes a higher utilization rate of the dirt-holding space of the interception layer and the deep filtration paperboard. It should be noted that when multiple interception layers are set, the multiple interception layers can be set upstream of the deep filtration paperboard or arranged at intervals between multiple deep filtration paperboards. Only the precision and tightness of the deep filtration paperboard and the upstream interception layer adjacent to it need to be considered. It should be noted that when the interception layer is arranged between multiple deep filtration paperboards, it is also necessary to control that the overall tightness and precision of the upstream deep filtration paperboard should be less than the tightness and precision of the interception layer.

[0056] Further, the water flux F of the deep filtration paperboard 1 is 500-6000 L / (min·m 2 @100 kPa), and the water flux F of the interception layer 2 is 5000-23000 L / (min·m 2 @100 kPa).

[0057] In the above technical solution, the interception layer is located upstream of the deep filtration paperboard. Although the precision of the interception layer is slightly higher than that of the first region of the deep filtration paperboard, the tightness of the interception layer is less than the overall tightness of the deep filtration paperboard. Therefore, both the interception layer and the deep filtration paperboard have a relatively high flux, so that the obtained composite deep filtration medium also has a relatively high flux. When applied to clarify and filter biological liquid, the composite deep filtration medium can maintain a relatively optimal flux level, thus ensuring the smooth progress of the filtration process to achieve a higher loading capacity.

[0058] Further, the wet strength S of the deep filtration paperboard 1 is 80-300 kPa, and the wet strength S of the interception layer 2 is 120-800 kPa.

[0059] In the above technical solution, both the deep filtration cardboard and the interception layer have high wet strength, so as to maintain the structural stability during the filtration process, and further ensure the smooth progress of the filtration process to achieve the expected loading capacity.

[0060] Furthermore, the present invention also discloses the application of the above composite deep filtration medium in the clarification filtration of biological liquid materials.

[0061] In the above technical solution, the composite deep filtration medium of the present invention can be used for the clarification filtration of different types of biological liquid materials to achieve a better filtration effect. For example, it can be used for the clarification of fermentation broth or cell culture solution, the clarification of blood and serum products, the filtration of enzyme preparations, etc.

[0062] Furthermore, the turbidity of the biological liquid material is 500 - 5000 NTU, the cell density is 10 - 50 M, and the cell viability is 50 - 100%.

[0063] In the above technical solution, when the composite deep filtration medium of the present invention is used for the clarification filtration of cell culture, it is mainly used to remove impurity particles such as intact cells, cell debris, and other colloidal substances. Among them, turbidity is used to reflect the content of impurity particles in the cell harvest fluid. The greater the turbidity, the higher the content of impurity particles; the cell density and cell viability are used to reflect the proportion of cells in the cell harvest fluid. The greater the cell density and cell viability, the higher the content of intact cells. Through testing, for cell harvest fluids with a wide range of turbidity, cell density, and cell activity, the composite deep filtration medium of the present invention can achieve a greater increase in loading capacity compared to the single deep filtration cardboard, and the utilization rate of the dirt-holding space of the composite deep filtration medium is also greatly improved.

[0064] In summary, the present invention has the following beneficial effects:

[0065] By arranging an interception layer upstream of the deep filtration cardboard and controlling the interception layer to have a precision not lower than that of the first region of the deep filtration cardboard and a tightness lower than that of the first region, the present invention effectively avoids the situation of too rapid attenuation of the flux of the deep filtration cardboard, thereby improving the utilization rate of the dirt-holding space of the deep filtration cardboard and further reducing the turbidity of the filtrate. The composite deep filtration medium of the present invention can take into account relatively better flux, loading capacity, and interception effect, and has a better filtration effect on biological liquid materials with different turbidities, cell densities, and activities. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The following further describes the present invention with reference to the drawings.

[0067] Figure 1 It is a scanning electron microscope (SEM) schematic diagram of the first surface of the deep filtration cardboard in Embodiment 1 of the present invention, with a magnification of 100×;

[0068] Figure 2 Schematic diagram of the scanning electron microscope (SEM) of the liquid inlet surface of the interception layer in Embodiment 1 of the present invention, with a magnification of 100×;

[0069] Figure 3 Schematic diagram of the scanning electron microscope (SEM) of the liquid outlet surface of the interception layer in Embodiment 1 of the present invention, with a magnification of 100×. Detailed implementation manners

[0070] In order to more clearly understand the above objects, features and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation manners. It should be noted that, without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other.

[0071] Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0072] Embodiment 1

[0073] This embodiment provides a composite deep filtration medium, including 1 layer of interception layer and 1 layer of deep filtration cardboard; wherein the interception layer includes interception fibers, and the deep filtration cardboard includes filtration fibers, filter aids and binders; the interception fibers are polypropylene fibers, the filtration fibers are cellulose fibers, the filter aids are diatomaceous earth, and the binders are polyaminopolyamide-epichlorohydrin polymers. The parameters of the interception layer and the deep filtration cardboard are shown in Tables 1 and 2.

[0074] Embodiments 2-12

[0075] The difference between Embodiments 2-12 and Embodiment 1 lies in the different structural parameters of each layer of the interception layer and the deep filtration cardboard, as specifically shown in Tables 1 and 2. Among them, the deep filtration cardboard in Embodiment 6 does not contain filter aids and binders; in Embodiment 7, the interception fibers of the interception layer are glass fibers, the filtration fibers of the deep filtration cardboard are polyacrylonitrile fibers, the filter aids are silica, and the binders are acetaldehyde-acidified polyacrylamide resins.

[0076] Embodiment 13

[0077] Embodiment 13 provides a composite deep filtration medium, including 1 layer of polypropylene fiber interception layer and 2 layers of cellulose fiber deep filtration cardboard located downstream thereof. Among them, the 5μm particle interception efficiencies of the upstream polypropylene fiber interception layer, the middle cellulose fiber deep filtration cardboard and the downstream cellulose fiber deep filtration cardboard are 90%, 85% and 95% respectively, and the overall tightnesses are 0.15 g / cm 3 、0.3 g / cm3 、 0.35 g / cm 3 。

[0078] Comparative Examples 1-4

[0079] The differences between Comparative Examples 1-4 and Example 4 lie in the different structural parameters of the interception layer, as shown in Tables 1 and 2 specifically.

[0080] Comparative Example 5

[0081] The differences between Comparative Example 5 and Example 1 lie in the different structural parameters of the interception layer, as shown in Tables 1 and 2 specifically.

[0082] Comparative Example 6

[0083] The differences between Comparative Example 6 and Example 6 lie in the different structural parameters of the interception layer, as shown in Tables 1 and 2 specifically.

[0084] Comparative Example 7

[0085] The differences between Comparative Example 7 and Example 7 lie in the different structural parameters of the interception layer, as shown in Tables 1 and 2 specifically.

[0086] Comparative Example 8

[0087] The differences between Comparative Example 8 and Example 12 lie in the different structural parameters of the interception layer, as shown in Tables 1 and 2 specifically.

[0088] Testing method:

[0089] Accuracy test: It is represented by testing the interception efficiency of the filter medium for 5-μm particles. The test liquid is a suspension of polystyrene microspheres with a particle size of 5 μm (the suspension of polystyrene microspheres includes 5 wt% of polystyrene microspheres, 0.5 mol / L sodium chloride, and pure water). The turbidity change of the particles in the feed liquid before and after filtration is tested using a turbidimeter, and the interception efficiency of the filter medium, that is, the accuracy, is calculated. The interception efficiency = 1 - turbidity after filtration / turbidity before filtration × 100%. Among them, the deep filtration cardboard is equally divided into a first region, a second region, and a third region along the thickness direction from the liquid inlet surface to the liquid outlet surface, and then the accuracy of each region is tested respectively. The accuracy test results of the examples and comparative examples are shown in Tables 1-2.

[0090] Tightness test: The mass of the filter medium is tested using instruments such as an electronic precision balance, and the thickness of the filter medium is tested using an electric thickness tester. The tightness of the filter medium = mass ÷ (thickness × area). Among them, the deep filtration cardboard is equally divided into a first region, a second region, and a third region along the thickness direction from the liquid inlet surface to the liquid outlet surface, and then the tightness of each region is tested respectively. The tightness test results of the examples and comparative examples are shown in Tables 1-2.

[0091] Morphology parameter test: The morphology of the sample was characterized using a scanning electron microscope, and then measured and corresponding calculations were performed using computer software (such as Matlab, NIS-Elements, Image J, Nano-Measure, etc.) or manually. Among them, when measuring the fiber density on the surface of the interception layer, the fibers in the surface layer (the first three layers of the SEM image) were counted for calculation. The test results of the morphology parameters of the examples and comparative examples are shown in Table 1-2.

[0092] Water flux test: A round filter medium with a diameter of 47 mm was taken and placed in a fixture, and the pure water passing amount when the pressure reached 1 bar at room temperature was measured. Among them, the water flux of the deep filtration cardboard was directly tested for the whole cardboard. The test results of the water flux of the examples and comparative examples are shown in Table 1-2.

[0093] Wet strength test: A round filter medium with a diameter of 90 mm was taken, soaked in pure water for 2 h first, and then its strength was tested using a fully automatic burst strength tester. Among them, the wet strength of the deep filtration cardboard was directly tested for the whole cardboard. The test results of the wet strength of the examples and comparative examples are shown in Table 1-2.

[0094] Filtration effect test: The CHO cell harvest solution A (turbidity 1000 NTU, cell density 15 M, cell viability 90%) and CHO cell harvest solution B (turbidity 2000 NTU, cell density 30 M, cell viability 95%) were respectively supplied to the interception layer, deep filtration cardboard, and composite deep filtration medium of Examples 1-12 and Comparative Examples 1-8 at a rate of 100 L / m 2 / h until the pressure difference reached 1 bar, and the filtration was ended. The turbidity of the filtrate and the filtrate filtration volume (loading capacity) were tested; after the filtration was ended, the deep filtration cardboard in the deep filtration cardboard and the corresponding composite deep filtration medium was dried and weighed respectively, and the loading capacity improvement rate of the deep filtration cardboard after adding the interception layer was calculated. The cardboard loading capacity improvement rate = ((W 1 -W 0 ) / (w 1 -w 0 )-1)×100%, where W 1 is the dry weight of the deep filtration cardboard in the composite deep filtration medium after filtration, W 0 is the dry weight of the deep filtration cardboard in the composite deep filtration medium before filtration, w 1 is the dry weight of the deep filtration cardboard in the composite deep filtration cardboard after filtration, and w 0 is the dry weight of the deep filtration cardboard before filtration. The test results are shown in Table 3.

[0095] Table 1

[0096]

[0097]

[0098] Table 2

[0099]

[0100]

[0101] Table 3

[0102]

[0103] It can be seen from the above experimental data that by arranging an interception layer with specific precision and tightness upstream of the deep filtration cardboard in the present invention, the obtained composite deep filtration medium has a better filtration effect compared with a single interception layer or deep filtration cardboard. Moreover, through individual weighing tests, it is found that the composite deep filtration medium of the present invention effectively avoids the situation of too rapid flux decay of a single deep filtration cardboard, and the loading capacity of the deep filtration cardboard located downstream in the composite deep filtration medium is further increased, that is, the utilization rate of the dirt-holding space of the deep filtration cardboard in the composite deep filtration medium of the present invention is further increased, and the loading capacity is more fully exerted; moreover, when the deep filtration medium of the present invention is used for clarification filtration, the turbidity of the filtrate is further reduced, and the quality of the feed liquid is better.

[0104] It can be seen from comparing the above experimental data that the composite deep filtration medium of the present invention has a good clarification effect on cell feed liquids with different turbidities and densities, and can reach a higher loading capacity compared with a single interception layer or cardboard, which is beneficial to saving process time and reducing production costs. By further comparing the clarification filtration effects of the composite deep filtration media of Examples 1-12 on low-turbidity and low-density cell feed liquids (cell harvest liquid A) and high-turbidity and high-density cell feed liquids (cell harvest liquid B), it can be seen that when the composite deep filtration medium of the present invention is applied to the clarification filtration of high-turbidity and high-density feed liquids, there is a more obvious effect of increasing the loading capacity.

[0105] By comparing Example 4 with Comparative Examples 1-4, Example 1 with Comparative Example 5, Example 6 with Comparative Example 6, Example 7 with Comparative Example 7, and Example 12 with Comparative Example 8, it can be seen that only when the two conditions that the accuracy of the interception layer is between the first region and the third region of the deep filtration cardboard (including being equal to the first region) and the tightness of the interception layer is lower than that of the deep filtration cardboard are simultaneously satisfied, can a composite deep filtration medium with a better filtration effect be obtained. In Comparative Examples 1 and 5-8, the accuracy of the interception layer is less than the first region of the deep filtration cardboard, that is, the interception layer follows the conventional gradient accuracy design scheme. Although it can also bring a certain increase in loading capacity, the effect of increasing the loading capacity is very weak, mainly due to the loading capacity contribution of the interception layer itself, and the improvement effect on the space utilization rate of the deep filtration cardboard is poor. This is mainly because the accuracy of the interception layer is lower, and it can only intercept larger particles. Therefore, it cannot play the role of pre-interception and dispersion relative to the first region of the deep filtration cardboard. At this time, relatively large cell debris and smaller cell particles will still enter the deep filtration and cause early blockage of the cardboard. In Comparative Example 2, the accuracy of the interception layer is higher than the third region of the deep filtration cardboard, that is, the interception accuracy of the interception layer is too high. At this time, the interception is mainly carried out by the interception layer, and most of the loading capacity of the composite deep filtration medium comes from the interception layer, and the loading capacity of the deep filtration cardboard even becomes lower. In Comparative Example 3, the interception layer has a higher accuracy and a higher tightness than the first region of the deep filtration cardboard. During filtration, the interception layer will intercept more particles and the intercepted particles cannot be well dispersed, resulting in earlier blockage of the interception layer and lower loading capacity of the composite deep filtration medium. In Comparative Example 4, the interception layer has a lower accuracy and a higher tightness, and the particles pre-intercepted by the interception layer still cannot be well dispersed in the interception layer, resulting in a lower loading capacity of the composite deep filtration medium.

[0106] By comparing Example 1, Examples 6-7, and Example 12, it can be seen that for deep filtration cardboards with different structures and materials, the composite deep filtration media obtained by adding an interception layer all have a better clarification filtration effect and can achieve a higher filtration loading capacity. Among them, when the deep filtration cardboard includes a filter aid and a binder, and the cardboard adopts a gradient accuracy setting at the same time, the cardboard itself has a higher filtration loading capacity, and the loading capacity of the composite deep filtration medium obtained by adding an interception layer is also higher.

[0107] It can be seen by comparing Example 1 with Examples 10 - 11 that for a deep - filtration cardboard with gradient precision, on the basis that the precision of the interception layer is not lower than that of the first region of the deep - filtration cardboard, by further setting its precision between the second region and the third region of the deep - filtration cardboard, it is beneficial to obtain a higher loading capacity and a lower turbidity. At the same time, the utilization rate of the dirt - holding space of the deep - filtration cardboard is also higher. This is because under this precision setting, the interception layer can not only ensure the effective interception of large - sized particles, but also further intercept more smaller particles, making the particle size of the liquid entering the deep - filtration cardboard further decrease. Thus, it can avoid the earlier attenuation of the flux of the deep - filtration cardboard caused by the accumulation of more particles in the first and second regions of the deep - filtration cardboard, so as to further improve the loading capacity of the cardboard. Although the precision of the interception layer in Examples 10 - 11 is also relatively low, it is mainly used to relieve the filtration pressure in the first region of the deep - filtration cardboard, and the improvement effect on the second region is not obvious. Therefore, the effect of increasing the loading capacity is slightly weaker.

[0108] It can be seen by comparing Examples 1 - 3 with Examples 4 - 5 that on the basis of setting the interception layer to have a precision not lower than that of the first region of the deep - filtration cardboard and a tightness lower than that of the first region, by further controlling the precision and tightness ratios between the interception layer and each region of the deep - filtration cardboard, a better effect of increasing the loading capacity of the cardboard can be achieved. In Example 4, the precision ratio between the interception layer and each region of the deep - filtration cardboard is relatively small, resulting in a worse step - by - step filtration effect of the deep - filtration medium. At the same time, the pre - interception effect of the interception layer relative to the first and second regions of the deep - filtration cardboard will also be weakened, and more particles that should be intercepted will pass through the interception layer and enter the deep - filtration cardboard, resulting in a worse effect of increasing the loading capacity of the cardboard. In Example 5, the precision difference and tightness ratio between the interception layer and each region of the deep - filtration cardboard are relatively large, and the upstream interception effect is relatively poor, resulting in too much interception pressure downstream, leading to a worse loading capacity of the composite deep - filtration medium and a worse effect of increasing the loading capacity of the deep - filtration cardboard.

[0109] This specific embodiment is only an interpretation of the present invention, and it is not a limitation of the present invention. After reading this specification, those skilled in the art can make modifications without creative contributions to this embodiment as needed, but as long as it is within the scope of the claims of the present invention, it is protected by the patent law.

Claims

1. A composite deep filter medium, comprising at least one layer of deep filter paperboard, wherein one side of the deep filter paperboard is a liquid inlet surface and the other side is a liquid outlet surface; the deep filter paperboard comprises filter fibers; characterized in that: At least one interception layer is arranged outside the liquid inlet surface of the deep filter paperboard; The deep filter paperboard is divided into a first region, a second region and a third region along its thickness direction from the liquid inlet surface to the liquid outlet surface. The 5 μm particle interception efficiencies of the first region, the second region, the third region and the interception layer are A 11 , A 12 , A 13 , A2, where A 11 ≤A2<A 13 , A 11 60-85%, A 13 85-98%; The compactness of the arresting layer is less than the compactness of the first zone.

2. A composite deep filter medium according to claim 1, characterized in that: The 5 μm particle interception efficiency A of the first region, the third region and the interception layer 11 , A 13 、A2 satisfies: A 11 <A2<A 13 .

3. A composite deep filter medium according to claim 1, characterized in that: The 5 μm particle interception efficiency A of the first area, the second area and the third area 11 , A 12 , A 13 Satisfaction: A 11 <A 12 <A 13 .

4. A composite deep filter medium according to claim 1, characterized in that: The 5 μm particle interception efficiency A of the first region, the second region, the third region and the interception layer 11 , A 12 , A 13 、A2 satisfies: A 11 <A 12 <A2<A 13 , A 11 : A 12 : A 13 :A2=1: 1.05-1.35：1.15-1.5：1.1-1.4。 5. A composite deep filter medium according to claim 1, characterized in that: The tightness of the first area, the second area, the third area and the interception layer are B respectively 11 , B 12 , B 13 , B2, where B2<B 11 <B 12 < B 13 , B 11 :B 12 :B 13 :B2=1:1.02-1.2:1.05-1.35:0.2-0.7, B 11 0.2-0.4g / cm 3 , B2 is 0.1-0.25g / cm 3 .

6. A composite deep filter medium according to claim 1, characterized in that: The interception layer includes interception fibers, and the SEM average diameters of the filter fibers and the interception fibers are D1 and D2, respectively, and D1:D2=1:0.3-0.

8.

7. A composite deep filter medium according to claim 6, characterized in that: The SEM average diameter D1 of the filtering fiber is 10-60 μm, and the SEM average diameter D2 of the intercepting fiber is 5-55 μm.

8. A composite deep filter medium according to claim 6, characterized in that: The density of the intercepting fibers at the liquid inlet surface of the intercepting layer is 3-15 fibers / 500 μm; the density of the intercepting fibers at the liquid outlet surface of the intercepting layer is 4-30 fibers / 500 μm.

9. A composite deep filter medium according to claim 1, characterized in that: The thicknesses of the deep filter paperboard and the interception layer are H1 and H2 respectively, H1:H2=1:0.3-1.2, H1 is 2-6 mm, and H2 is 1-5 mm.

10. A composite deep filter medium according to claim 1, characterized in that: The filter fiber is selected from one or more of cellulose fiber, polyacrylonitrile fiber, polyolefin fiber, polyester fiber, and activated carbon fiber.

11. A composite deep filter medium according to claim 1, characterized in that: The intercepting layer comprises intercepting fibers, and the intercepting fibers are selected from one or more of polypropylene fibers, glass fibers, polyethylene fibers, polyester fibers, and polyacrylonitrile fibers.

12. A composite deep filter medium according to claim 1, characterized in that: The depth filter paperboard may further comprise a filter aid and / or a binder.

13. A composite deep filter medium according to claim 12, characterized in that: The SEM average particle size d of the filter aid is 5-50 μm.

14. A composite deep filter medium according to claim 12, characterized in that: The filter aid is selected from one or more of diatomaceous earth particles, silica, perlite, activated carbon, and clay; the binder comprises a water-soluble synthetic polymer based on urea or melamine-formaldehyde polymer, a polyaminopolyamide-epichlorohydrin polymer, or a glyoxylated polyacrylamide resin.

15. The composite deep filter medium according to claim 1, characterized in that: The deep filter medium comprises N layers of deep filter paperboards arranged continuously, where N is an integer of 2-5; along the flow direction of the feed liquid, the overall 5 μm particle interception efficiency and tightness of the N layers of filter paperboards increase gradually.

16. A composite deep filter medium according to claim 1, characterized in that: The deep filter medium comprises M interception layers which are arranged continuously, where M is an integer of 2-5; along the flow direction of the feed liquid, the overall 5 μm particle interception efficiency and tightness of the M interception layers increase gradually.

17. A composite deep filter medium according to claim 1, characterized in that: The water flux F1 of the deep filter paperboard is 500-6000L / (min·m 2 @100kPa), the water flux F2 of the intercepting layer is 5000-23000L / (min·m 2 @100kPa).

18. The composite deep filter medium according to claim 1, characterized in that: The wet strength S1 of the deep filter paperboard is 80-300 kPa, and the wet strength S2 of the intercepting layer is 120-800 kPa.

19. Use of the composite deep filter medium according to any one of claims 1 to 18 in clarifying and filtering biological fluids.

20. The use according to claim 19, characterized in that The turbidity of the biological liquid is 500-5000 NTU, the cell density is 10-50 M, and the cell viability is 50-100%.

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