Method for extracting protein in ion exchange serous fluid based on pre-coating filtration

Abstract

The invention discloses a method for extracting protein in ion exchange slurry based on pre-coating filtration. The method comprises the following steps: mixing and stirring activated carbon, diatomite, chelating resin and water to prepare pre-coating liquid; the pre-coating liquid is pumped into a pre-coating filter for pre-coating treatment; carrying out vacuum filtration on the ionized slurry in a pre-coating filter coated with a film, and collecting filtrate and filter residues; adding water into the collected filter residues, dispersing, centrifuging the dispersion liquid by a centrifugal machine, and spray-drying the centrifugal supernatant to obtain the compound fertilizer; and carrying out secondary filtration on the filtrate, and carrying out spray drying on the filtrate to obtain the protein. According to the method, impurities and metal ions in the ion exchange slurry can be effectively removed, a main product high-content protein and a byproduct compound fertilizer are prepared, the economic value of the ion exchange slurry is improved, waste liquid and waste residues in the process are fully utilized, and the method is energy-saving and environment-friendly.

Description

Technical Field

[0001] The invention relates to the technical field of protein preparation, and in particular to a method for extracting protein in separation slurry based on pre-coating filtration. Background Art

[0002] Corn soaking water is the organic wastewater generated when corn is wet-processed to produce starch. At present, the development and utilization of corn soaking water mainly uses resin adsorption to recover phytic acid, and then performs subsequent treatment to prepare a series of products. However, a large amount of ion exchange slurry will be generated in the above process. If this part of waste liquid is not treated, it will not only cause secondary pollution to the environment, but also cause waste of resources.

[0003] The slurry from the corn soaking water contains a lot of protein. The corn soaking water protein has physiological activities such as enhancing human immunity and anti-oxidation, and is a protein resource that has not been fully developed and utilized. If the protein in the corn soaking water can be extracted, it can not only improve the economic benefits of the factory and solve the problem of environmental pollution, but also develop new protein resources.

[0004] At present, the method for preparing protein from the slurry of ion exchange mainly removes impurities and metal ions, but it is difficult to filter and cannot be clarified using conventional methods. Although the membrane clarification method has a good clarification effect, it is easy to clog the pipeline, the maintenance cost is high, and the cost of use is high. Therefore, how to effectively recover the protein in the slurry of ion exchange has become a problem that technicians in this field need to solve. Summary of the invention

[0005] The technical problem to be solved by the present invention is: in view of the shortcomings of the prior art, a method for extracting protein from ion-exchanged slurry based on pre-coating filtration is provided, which can effectively remove impurities and metal ions in the ion-exchanged slurry, produce a main product with high protein content and a by-product compound fertilizer, thereby improving the economic value of the ion-exchanged slurry, and the waste liquid and waste residue in the process are fully utilized, which is energy-saving and environmentally friendly.

[0006] In order to solve the above technical problems, the technical solution of the present invention is:

[0007] A method for extracting protein from a separation slurry based on pre-coating filtration, comprising the following steps:

[0008] (1) Preparation of pre-coating liquid: Mixing activated carbon, diatomaceous earth, chelating resin and water to prepare pre-coating liquid;

[0009] (2) Pre-coating treatment: pumping the above-mentioned pre-coating liquid into the pre-coating filter for pre-coating treatment;

[0010] (3) Filtration: The slurry obtained by separation is subjected to vacuum filtration through the pre-coated filter after the coating in step (2), and the filtrate and filter residue are collected;

[0011] (4) Recovering by-products: adding water to the filter residue collected in step (3) to disperse the mixture, centrifuging the dispersion, and spray drying the supernatant to obtain a composite fertilizer;

[0012] (5) Recovering protein: The filtrate from step (3) is filtered twice, and the filtrate is spray-dried to obtain protein.

[0013] Preferably, in step (1), the chelating resin is a mixture of D401 resin and D001×7 resin, and the mass ratio of the D401 resin to the D001×7 resin is 3:(1-5).

[0014] Preferably, in step (1), the mesh sizes of the activated carbon and diatomaceous earth are both 60-150 meshes.

[0015] Preferably, in step (1), the mass ratio of the activated carbon, diatomaceous earth and chelating resin is 1:(0.9-1.2):(0.1-0.2).

[0016] Preferably, in step (1), the volume ratio of the total volume of the activated carbon, diatomaceous earth and chelating resin to water is 1:(1-5).

[0017] Preferably, in step (2), during the pre-coating treatment, the mesh number of the filter cloth of the pre-coating filter is 60-100 mesh, and the pressure during the pre-coating is -0.04 to -0.1 MPa.

[0018] Preferably, in step (2), after the pre-coating treatment, the thickness of the pre-coating layer is 50-100 mm.

[0019] Preferably, in step (3), the vacuum filtration conditions are: the flow rate of the slurry is 100-150 L / h·m 2 , the pressure is -0.04~-0.1MPa.

[0020] Preferably, in step (4), the volume ratio of the filter residue to water during dispersion is 1:(1-3).

[0021] Preferably, in step (4), the centrifugal speed during centrifugation is 1000-3000 r / min, and the centrifugal time is 3-8 min.

[0022] Preferably, in step (5), a plate and frame filter is used for secondary filtration, the filter cloth mesh number of the plate and frame filter is 60-100 mesh, and the pressure during secondary filtration is -0.04 to -0.1 MPa.

[0023] Preferably, in steps (4) and (5), the precipitate after centrifugation and the filter residue after secondary filtration are used as pre-coating agents in the preparation of the pre-coating liquid in step (1).

[0024] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0025] 1. The present invention provides a method for extracting protein from ion exchange slurry based on pre-coating filtration. The method uses ion exchange slurry except phytic acid as raw material, firstly filters it through a pre-coating filter containing activated carbon, diatomaceous earth and chelating resin as pre-coating layer, and then filters the filtrate for a second time through a plate and frame filter to obtain a high content of protein. The method has high production efficiency and low cost and is suitable for large-scale production.

[0026] 2. The present invention prepares a pre-coat layer by compounding activated carbon, diatomite and chelating resin according to a certain ratio. Activated carbon has a high specific surface area and good adsorption performance, which can not only effectively remove impurities in the slurry, but also effectively adsorb metal ions in the slurry through the active functional groups on its surface; diatomite is a natural mineral material, and its fine pore structure can effectively intercept suspended matter and insoluble impurities, and its porous particle form can provide a larger filtration area and filtration efficiency, thereby improving the flux of the liquid, reducing the clogging of the filter membrane, and ensuring the efficient conduct of the filtration process. The fine particles of diatomite are combined with activated carbon to form a composite structure, which further improves the removal effect of fine impurities. Chelating resin can specifically complex with metal ions in the slurry, effectively remove metal ions while protecting water-soluble proteins, and improve the purity of proteins. In summary, based on the joint action of activated carbon, diatomite and chelating resin, the pre-coat layer optimizes the overall filtration process while removing small particle impurities, and improves the purity and recovery rate of proteins.

[0027] 3. The present invention D401 and D001×7 resins are compounded to form a chelating resin, D001×7 resin is a strongly acidic cation exchange resin with sulfonic acid groups on a styrene divinylbenzene copolymer, D401 resin is a macroporous styrene ion exchange resin containing an iminodiacetic acid chelating group, the active groups on the surface of D401 resin can be complexed with metal ions such as calcium ions and magnesium ions in the ion exchange slurry, thereby achieving the adsorption of metal ions, and the hydroxyl groups in the sulfonic acid groups on the surface of D001×7 resin can be combined with metal ions, thereby adsorbing metal ions in the ion exchange slurry. In summary, the chelating resin composed of the compound of D401 resin and D001×7 resin has a better surface area and effective active sites, and enhances the capture ability of different metal ions; the ion exchange characteristics of D001×7 resin can further optimize the adsorption behavior of the resin, synergistically enhance the removal of multiple metal ions, thereby obtaining a protein with higher purity.

[0028] 4. The present invention adds water to the filter residue after filtration by the pre-coating filter for pulping and dispersion, and then further centrifuges. The centrifugal supernatant contains effective ingredients such as lactic acid, sugars, magnesium salts, calcium salts, etc., which are sold as compound fertilizers, thereby improving the economic benefits of the enterprise.

[0029] 5. The present invention reuses the centrifugal sedimentation in the centrifugal process and the filter residue in the secondary filtration in the preparation of the pre-coating liquid, further reducing energy consumption. DETAILED DESCRIPTION

[0030] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0031] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0032] Among the raw materials in the following examples and comparative examples, D001×7 resin comes from Zhejiang Zhengguang Industrial Co., Ltd. D401 resin comes from Tianjin Yunkai Resin Technology Co., Ltd. Other raw materials are commercially available unless otherwise specified, and the conditions are conventional conditions in the art unless otherwise specified.

[0033] Protein yield (%) = [(protein yield × protein content) / (dry matter content of the centrifuged slurry × / protein content in the dry matter of the centrifuged slurry)] × 100%.

[0034] Example 1

[0035] A method for extracting protein from a separation slurry based on pre-coating filtration, comprising the following steps:

[0036] (1) Preparation of pre-coating agent:

[0037] Activated carbon (60 mesh), diatomaceous earth (60 mesh), and chelating resin (D401 resin and D001×7 resin are compounded in a mass ratio of 3:2) are mixed in a mass ratio of 1:1:0.15 to obtain a pre-coating agent, and the pre-coating agent and water (the volume ratio of the pre-coating agent to water is 1:3) are mixed and stirred to obtain a pre-coating liquid;

[0038] (2) Pre-coating treatment:

[0039] The pre-coating liquid is pumped into the pre-coating filter (filter cloth mesh number is 100 mesh) for pre-coating treatment, so that the pre-coating layer with a thickness of 50 mm is deposited on the filter cloth surface of the pre-coating filter; during the pre-coating treatment, the pre-coating pressure is -0.075 MPa;

[0040] (3) Filtering:

[0041] 100 L of the centrifugal slurry (the dry matter of the centrifugal slurry accounts for 12%, and the protein accounts for 45% of the dry matter) is vacuum filtered through the pre-coated filter after the coating in step (2), and the filtrate and the filter residue are collected; the vacuum filtration conditions are: the flow rate of the centrifugal slurry is 120 L / h·m 2 , pressure is -0.075Mpa;

[0042] (4) Recycling of by-products:

[0043] The filter residue collected in step (3) is added with water (the volume ratio of the filter residue to water is 1:2) and then dispersed. The dispersion is centrifuged at a speed of 1500 r / min for 5 minutes. The supernatant of the centrifuge is spray-dried (the air inlet temperature is 180° C. and the air outlet temperature is 85° C.) to obtain a composite fertilizer. The centrifugal precipitate is reused for the preparation of the pre-coating solution in step (1);

[0044] (5) Recovering protein:

[0045] The filtrate of step (3) was subjected to secondary filtration using a plate and frame filter (filter cloth mesh number was 80 mesh), the pressure during the secondary filtration was -0.075 MPa, and the filtrate was spray dried (inlet temperature 180°C, outlet temperature 85°C) to obtain 8.47 kg of protein with a protein content of 58 wt% and a protein yield of 91%. The filter residue during the secondary filtration was applied to the preparation of the pre-coating solution in step (1).

[0046] Example 2

[0047] A method for extracting protein from a separation slurry based on pre-coating filtration, comprising the following steps:

[0048] (1) Preparation of pre-coating agent:

[0049] Activated carbon (60 mesh), diatomaceous earth (60 mesh), and chelating resin (D401 resin and D001×7 resin are compounded in a mass ratio of 3:5) are mixed in a mass ratio of 1:1:0.1 to obtain a pre-coating agent, and the pre-coating agent and water (the volume ratio of the pre-coating agent to water is 1:3) are mixed and stirred to obtain a pre-coating liquid;

[0050] (2) Pre-coating treatment:

[0051] The pre-coating liquid is pumped into the pre-coating filter (filter cloth mesh number is 100 mesh) for pre-coating treatment, so that the pre-coating layer with a thickness of 100 mm is deposited on the filter cloth surface of the pre-coating filter; during the pre-coating treatment, the pre-coating pressure is -0.1 MPa;

[0052] (3) Filtering:

[0053] 100 L of the centrifugal slurry (the dry matter of the centrifugal slurry accounts for 12%, and the protein accounts for 45% of the dry matter) is vacuum filtered through the pre-coated filter after the coating in step (2), and the filtrate and the filter residue are collected; the vacuum filtration conditions are: the flow rate of the centrifugal slurry is 150 L / h·m 2 , pressure is -0.1MPa;

[0054] (4) Recycling of by-products:

[0055] The filter residue collected in step (3) is added with water (the volume ratio of the filter residue to water is 1:3) and then dispersed. The dispersion is centrifuged at a speed of 2000 r / min for 6 minutes. The supernatant of the centrifuge is spray-dried (the air inlet temperature is 180° C., and the air outlet temperature is 85° C.) to obtain a composite fertilizer. The centrifugal precipitate is re-used for the preparation of the pre-coating liquid in step (1);

[0056] (5) Recovering protein:

[0057] The filtrate of step (3) was subjected to secondary filtration using a plate and frame filter (filter cloth mesh number 80 mesh), the pressure during the secondary filtration was -0.075 MPa, and the filtrate was spray dried (inlet temperature 180°C, outlet temperature 85°C) to obtain 8.58 kg of protein with a protein content of 57 wt%; the protein yield was 90.6%, and the filter residue during the secondary filtration was applied to the preparation of the pre-coating solution in step (1).

[0058] Example 3

[0059] A method for extracting protein from a separation slurry based on pre-coating filtration, comprising the following steps:

[0060] (1) Preparation of pre-coating agent:

[0061] Activated carbon (60 mesh), diatomaceous earth (60 mesh), and chelating resin (D401 resin and D001×7 resin are compounded in a mass ratio of 3:3) are mixed in a mass ratio of 1:1:0.15 to obtain a pre-coating agent, and the pre-coating agent and water (the volume ratio of the pre-coating agent to water is 1:3) are mixed and stirred to obtain a pre-coating liquid;

[0062] (2) Pre-coating treatment:

[0063] The pre-coating liquid is pumped into the pre-coating filter (filter cloth mesh number is 100 mesh) for pre-coating treatment, so that the pre-coating layer with a thickness of 90 mm is deposited on the filter cloth surface of the pre-coating filter; during the pre-coating treatment, the pre-coating pressure is -0.8 MPa;

[0064] (3) Filtering:

[0065] 100 L of the centrifugal slurry (the dry matter of the centrifugal slurry accounts for 12%, and the protein accounts for 45% of the dry matter) is vacuum filtered through the pre-coated filter after the coating in step (2), and the filtrate and the filter residue are collected; the vacuum filtration conditions are: the flow rate of the centrifugal slurry is 125 L / h·m 2 , pressure is -0.085MPa;

[0066] (4) Recycling of by-products:

[0067] The filter residue collected in step (3) is added with water (the volume ratio of the filter residue to water is 1:2) and then dispersed. The dispersion is centrifuged at a speed of 2000 r / min for 5 minutes. The supernatant of the centrifuge is spray-dried (the air inlet temperature is 180° C., and the air outlet temperature is 85° C.) to obtain a composite fertilizer. The centrifugal precipitate is reused for the preparation of the pre-coating solution in step (1);

[0068] (5) Recovering protein:

[0069] The filtrate of step (3) was subjected to secondary filtration using a plate and frame filter (filter cloth mesh number was 80 mesh), the pressure during the secondary filtration was -0.075 MPa, and the filtrate was spray dried (inlet temperature 180°C, outlet temperature 85°C) to obtain 8.65 kg of protein with a protein content of 59 wt%; the protein yield was 94.5%, and the filter residue during the secondary filtration was applied to the preparation of the pre-coating solution in step (1).

[0070] Example 4

[0071] A method for extracting protein from a separation slurry based on pre-coating filtration, comprising the following steps:

[0072] (1) Preparation of pre-coating agent:

[0073] Activated carbon (60 mesh), diatomaceous earth (60 mesh), and chelating resin (D401 resin and D001×7 resin are compounded in a mass ratio of 3:2) are mixed in a mass ratio of 1:0.95:0.15 to obtain a pre-coating agent, and the pre-coating agent and water (the volume ratio of the pre-coating agent to water is 1:3) are mixed and stirred to obtain a pre-coating liquid;

[0074] (2) Pre-coating treatment:

[0075] The pre-coating liquid is pumped into the pre-coating filter (filter cloth mesh number is 100 mesh) for pre-coating treatment, so that the pre-coating layer with a thickness of 100 mm is deposited on the filter cloth surface of the pre-coating filter; during the pre-coating treatment, the pre-coating pressure is -0.085 MPa;

[0076] (3) Filtering:

[0077] 100 L of the centrifugal slurry (the dry matter of the centrifugal slurry accounts for 12%, and the protein accounts for 45% of the dry matter) is vacuum filtered through the pre-coated filter after the coating in step (2), and the filtrate and the filter residue are collected; the vacuum filtration conditions are: the flow rate of the centrifugal slurry is 140 L / h·m 2 , pressure is -0.09MPa;

[0078] (4) Recycling of by-products:

[0079] The filter residue collected in step (3) is added with water (the volume ratio of the filter residue to water is 1:1) and then dispersed. The dispersion is centrifuged at a speed of 3000 r / min for 8 min. The supernatant of the centrifuge is spray-dried (the air inlet temperature is 180° C. and the air outlet temperature is 85° C.) to obtain a composite fertilizer. The centrifugal precipitate is reused for the preparation of the pre-coating solution in step (1);

[0080] (5) Recovering protein:

[0081] The filtrate of step (3) was subjected to secondary filtration using a plate and frame filter (filter cloth mesh number was 80 mesh), the pressure during the secondary filtration was -0.075 MPa, and the filtrate was spray dried (inlet temperature 180°C, outlet temperature 85°C) to obtain 8.45 kg of protein with a protein content of 58 wt%; the protein yield was 90.8%; the filter residue during the secondary filtration was applied to the preparation of the pre-coating solution in step (1).

[0082] Example 5

[0083] A method for extracting protein from a separation slurry based on pre-coating filtration, comprising the following steps:

[0084] (1) Preparation of pre-coating agent:

[0085] Activated carbon (60 mesh), diatomaceous earth (60 mesh), and chelating resin (D401 resin and D001×7 resin are compounded in a mass ratio of 3:1) are mixed in a mass ratio of 1:0.95:0.2 to obtain a pre-coating agent, and the pre-coating agent and water (the volume ratio of the pre-coating agent to water is 1:5) are mixed and stirred to obtain a pre-coating liquid;

[0086] (2) Pre-coating treatment:

[0087] The pre-coating liquid is pumped into the pre-coating filter (filter cloth mesh number is 60 mesh) for pre-coating treatment, so that the pre-coating layer with a thickness of 50 mm is deposited on the filter cloth surface of the pre-coating filter; during the pre-coating treatment, the pre-coating pressure is -0.05 MPa;

[0088] (3) Filtering:

[0089] 100 L of the centrifugal slurry (the dry matter of the centrifugal slurry accounts for 12%, and the protein accounts for 45% of the dry matter) is vacuum filtered through the pre-coated filter after the coating in step (2), and the filtrate and the filter residue are collected; the vacuum filtration conditions are: the flow rate of the centrifugal slurry is 100 L / h·m 2 , pressure is -0.06MPa;

[0090] (4) Recycling of by-products:

[0091] The filter residue collected in step (3) is added with water (the volume ratio of the filter residue to water is 1:1.5) and then dispersed. The dispersion is centrifuged at a speed of 1000 r / min for 5 min. The supernatant of the centrifuge is spray-dried (the air inlet temperature is 180° C., and the air outlet temperature is 85° C.) to obtain a composite fertilizer. The centrifugal precipitate is reused for the preparation of the pre-coating solution in step (1);

[0092] (5) Recovering protein:

[0093] The filtrate of step (3) was subjected to secondary filtration using a plate and frame filter (filter cloth mesh number was 80 mesh), the pressure during the secondary filtration was -0.075 MPa, and the filtrate was spray dried (inlet temperature 180°C, outlet temperature 85°C) to obtain 8.35 kg of protein with a protein content of 59 wt%; the protein yield was 91.2%; the filter residue during the secondary filtration was applied to the preparation of the pre-coating solution in step (1).

[0094] In order to better verify the effect of the present invention, the following is further described with reference to Example 1 in combination with a plurality of comparative examples.

[0095] Comparative Example 1

[0096] Compared with Example 1, the difference is that in step (1), only diatomaceous earth is used as the pre-coating agent, and other conditions are the same as those in Example 1. 8.7 kg of protein is obtained, the protein content is 52%, and the protein yield is 83.8%.

[0097] Comparative Example 2

[0098] Compared with Example 1, the difference is that in step (1), only activated carbon is used as the pre-coating agent, and other conditions are the same as those in Example 1. 8.78 kg of protein is obtained, the protein content is 50%, and the protein yield is 81.3%.

[0099] Comparative Example 3

[0100] Compared with Example 1, the difference is that in step (1), the pre-coating agent only uses chelating resin, and other conditions are the same as those in Example 1, and 6445g of protein is obtained, the protein content is 62%, and the protein yield is 74%.

[0101] Comparative Example 4

[0102] Compared with Example 1, the difference is that in step (1), the chelating resin only uses D001×7 resin, and other conditions are the same as in Example 1, obtaining 5981g of protein, with a protein content of 65% and a protein yield of 72%.

[0103] Comparative Example 5

[0104] Compared with Example 1, the difference is that in step (1), the chelating resin only uses D401 resin, and other conditions are the same as in Example 1, and 6750g of protein is obtained, the protein content is 60%, and the protein yield is 75%.

[0105] Comparative Example 6

[0106] Compared with Example 1, the difference is that in step (3), the filtration pressure is -0.2 MPa, and the other conditions are the same as those in Example 1, and 9200 g of protein is obtained, the protein content is 50%, and the protein yield is 85.2%.

[0107] It can be seen from the above examples and comparative examples that the present invention uses activated carbon, diatomaceous earth and chelating resin as pre-coating layer and effectively controls the pre-coating and filtering conditions to obtain high-content protein with a protein yield of more than 90%.

[0108] In Comparative Examples 1-3, only one of diatomite, activated carbon and chelating resin was used as pre-coating agent, and the filtering effect was not good, and the protein purity and yield were all affected. In Comparative Examples 4-5, for the selection of chelating resin type, the present invention selected D001×7 resin and D401 resin composite, which had better effect when recovering protein, because the chelating resin composed of D401 resin and D001×7 resin composite had better surface area and effective active sites, and enhanced the capture ability of different metal ions.

[0109] Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enable any technician in the field to practice the present invention, including making and using any device or system, and implementing any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the literal expression of the claims, or if they include equivalent structural elements that are not substantially different from the literal expression of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A method for extracting protein from a slurry based on pre-coating filtration, characterized in that: The following steps are involved: (1) Preparation of pre-coating liquid: Mixing activated carbon, diatomaceous earth, chelating resin and water to prepare pre-coating liquid; (2) Pre-coating treatment: pumping the above-mentioned pre-coating liquid into the pre-coating filter for pre-coating treatment; (3) Filtration: The slurry obtained by separation is subjected to vacuum filtration through the pre-coated filter after the coating in step (2), and the filtrate and filter residue are collected; (4) Recovering by-products: adding water to the filter residue collected in step (3) to disperse the mixture, centrifuging the dispersion, and spray drying the supernatant to obtain a composite fertilizer; (5) Recovering protein: The filtrate from step (3) is filtered twice, and the filtrate is spray-dried to obtain protein.

2. A method for extracting protein from a separation slurry based on pre-coating filtration according to claim 1, characterized in that: In step (1), the chelating resin is a mixture of D401 resin and D001×7 resin, and the mass ratio of the D401 resin to the D001×7 resin is 3:(1-5).

3. The method for extracting protein from a separation slurry based on pre-coating filtration according to claim 1, characterized in that: In step (1), the mesh sizes of the activated carbon and diatomaceous earth are both 60-150 meshes.

4. The method for extracting protein from a separation slurry based on pre-coating filtration according to claim 1, characterized in that: In step (1), the mass ratio of the activated carbon, diatomaceous earth and chelating resin is 1:(0.9-1.2):(0.1-0.2).

5. The method for extracting protein from separation slurry based on pre-coating filtration according to claim 1, characterized in that: In step (1), the volume ratio of the total volume of the activated carbon, diatomaceous earth and chelating resin to water is 1:(1-5).

6. The method for extracting protein from separation slurry based on pre-coating filtration according to claim 1, characterized in that: In step (2), during the pre-coating treatment, the mesh number of the filter cloth of the pre-coating filter is 60-100 meshes, and the pressure during the pre-coating is -0.04 to -0.1 MPa; and / or after the pre-coating treatment, the thickness of the pre-coating layer is 50-100 mm.

7. The method for extracting protein from separation slurry based on pre-coating filtration according to claim 1, characterized in that: In step (3), the vacuum filtration conditions are: the flow rate of the slurry from the centrifuge is 100-150 L / h·m 2 , the pressure is -0.04~-0.1MPa.

8. The method for extracting protein from separation slurry based on pre-coating filtration according to claim 1, characterized in that: In step (4), the volume ratio of the filter residue to water during dispersion is 1:(1-3); and / or the centrifugal speed during centrifugation is 1000-3000 r / min, and the centrifugal time is 3-8 min.

9. The method for extracting protein from a separation slurry based on pre-coating filtration according to claim 1, characterized in that: In step (5), a plate and frame filter is used for secondary filtration, the filter cloth mesh number of the plate and frame filter is 60-100 mesh, and the pressure during the secondary filtration is -0.04 to -0.1 MPa.

10. The method for extracting protein from separation slurry based on pre-coating filtration according to claim 1, characterized in that: In steps (4) and (5), the precipitate after centrifugation and the filter residue after secondary filtration are used as pre-coating agents in the preparation of the pre-coating liquid in step (1).