Membrane filtration method of beer fermentation stock solution and regeneration method of hollow fiber membrane

Abstract

The invention provides a membrane filtration method of a beer fermentation stock solution and a regeneration method of a hollow fiber membrane, and relates to the technical field of beer production. The polyethersulfone with excellent hydrophilicity, thermal stability, chemical stability and biocompatibility is selected as a material of the hollow fiber membrane with the pore diameter of 0.2-0.65 mu m, and the hollow fiber membrane has high flux, high porosity and high filtering efficiency, has a stable beer clarification effect, is used for filtering beer fermentation stock solution, and can be used for filtering beer fermentation stock solution. According to the method, saccharomycetes in the beer fermentation stock solution can be effectively removed, the removal rate of the saccharomycetes is greater than 99.99%, meanwhile, raw material components and flavor substances of beer are reserved to the greatest extent, and a clear and stable beer product is obtained. Moreover, the membrane filtration method provided by the invention has efficient filtration performance, avoids the problems of resource exhaustion and dust pollution of diatomite filtration, is more environment-friendly, provides a green and environment-friendly filtration solution for beer production, and is suitable for industrial production of beer.

Description

Technical Field

[0001] The invention relates to the technical field of beer production, and in particular to a membrane filtration method for beer fermentation stock solution and a hollow fiber membrane regeneration method. Background Art

[0002] Beer filtration is a crucial link in the beer production process. Its purpose is to remove suspended yeast, protein, polyphenols and other substances in beer to achieve clarity, transparency, refreshing taste and stable shelf life. Traditional beer filtration methods mainly use diatomaceous earth as the filtration medium. Diatomaceous earth has good filtration performance, but there are the following problems: First, diatomaceous earth resources are limited, and long-term use will lead to resource depletion; second, diatomaceous earth will produce a lot of dust during the filtration process, which pollutes the environment and also increases the difficulty and cost of operation; third, the filtration efficiency of diatomaceous earth is relatively low, which cannot meet the needs of efficient and large-scale production of beer.

[0003] With the continuous development of membrane separation technology, the application of membrane filtration technology in beer production has gradually attracted attention. Membrane filtration technology uses specially manufactured membranes to separate and purify liquids, and has the advantages of high efficiency, energy saving, and environmental protection. In beer production, membrane filtration technology can replace traditional diatomaceous earth filtration to achieve efficient and environmentally friendly beer filtration, which is of great significance. However, the current membrane filtration method still has the problem of insufficient yeast removal rate. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a membrane filtration method for beer fermentation stock solution and a hollow fiber membrane regeneration method. The present invention uses polyethersulfone to perform membrane filtration on beer fermentation stock solution, and the yeast removal rate is high.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The invention provides a membrane filtration method for beer fermentation stock solution, which uses a hollow fiber membrane to perform membrane filtration on the beer fermentation stock solution to obtain beer filtrate; the hollow fiber membrane is made of polyethersulfone and has a pore size of 0.2-0.65 μm.

[0007] Preferably, the inner diameter of the hollow fiber membrane is 1 to 2 mm.

[0008] Preferably, the outer diameter of the hollow fiber membrane is 1.5 to 3 mm.

[0009] Preferably, the pressure of the membrane filtration is 0.1 to 3 bar.

[0010] The present invention also provides a method for regenerating a hollow fiber membrane, comprising the following steps:

[0011] The hollow fiber membrane used in the membrane filtration method described in the above technical solution is sequentially subjected to water reverse washing, alkaline solution washing, first water washing, acid solution washing and second water washing to obtain a regenerated hollow fiber membrane.

[0012] Preferably, the pressure of the water reverse washing is 0.5-5.0 bar.

[0013] Preferably, the pH value of the alkali solution is ≥12 and the temperature is 30-60°C;

[0014] The alkali solution includes an aqueous solution of sodium hydroxide;

[0015] The alkali solution washing time is 5 to 15 minutes.

[0016] Preferably, the first water washing time is 15 to 75 minutes.

[0017] Preferably, the pH value of the acid solution is ≤2;

[0018] The acid in the acid solution includes one or more of hydrochloric acid, sulfuric acid, nitric acid and citric acid;

[0019] The acid washing time is 5 to 15 minutes.

[0020] Preferably, the second water washing time is 5 to 15 minutes.

[0021] The present invention selects polyethersulfone with excellent hydrophilicity, thermal stability, chemical stability and biocompatibility as the material of the hollow fiber membrane, and controls the pore size of the hollow fiber membrane to be 0.2-0.65 μm. The hollow fiber membrane has high flux, high porosity and high filtration efficiency, and has a stable beer clarification effect. It is used for filtering beer fermentation stock solution, and can effectively remove yeast in the beer fermentation stock solution, and the yeast removal rate is greater than 99.99%. At the same time, the raw material components and flavor substances of the beer are retained to the greatest extent, and a clear and stable beer product is obtained. Moreover, the membrane filtration method provided by the present invention has high-efficiency filtration performance, and at the same time avoids the resource exhaustion and dust pollution problems of diatomaceous earth filtration, which is more environmentally friendly, provides a green and environmentally friendly filtration solution for beer production, and is suitable for industrial production of beer.

[0022] The present invention sequentially performs water reverse washing, alkali solution washing, first water washing, acid solution washing and second water washing on the used hollow fiber membrane, and adopts the above-mentioned water washing and chemical agent (alkali solution and acid solution) combined cleaning method, which can effectively remove membrane contamination, and the membrane flux recovery rate of the obtained regenerated hollow fiber membrane is above 96%, the filtration performance recovery rate of the hollow fiber membrane is high, and the service life of the hollow fiber membrane is significantly extended. It is suitable for the filtration process of beer production and has high practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention is a membrane filtration device. DETAILED DESCRIPTION

[0024] The invention provides a membrane filtration method for beer fermentation stock solution, which uses a hollow fiber membrane to perform membrane filtration on the beer fermentation stock solution to obtain beer filtrate; the hollow fiber membrane is made of polyethersulfone and has a pore size of 0.2-0.65 μm.

[0025] Unless otherwise specified, the materials and equipment used in the present invention are all commercially available products in the art.

[0026] In the present invention, the pore size of the hollow fiber membrane is 0.2 to 0.65 μm, and in specific embodiments can be 0.2 μm, 0.23 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.52 μm, 0.55 μm, 0.6 μm or 0.65 μm.

[0027] In the present invention, the inner diameter of the hollow fiber membrane is preferably 1-2 mm, and in specific embodiments may be 1 mm, 1.2 mm, 1.5 mm, 1.8 mm or 2 mm.

[0028] In the present invention, the outer diameter of the hollow fiber membrane is preferably 1.5 to 3 mm, and in specific embodiments may be 1.5 mm, 1.8 mm, 2 mm, 2.2 mm, 2.5 mm, 2.8 mm or 3 mm.

[0029] In the present invention, the wall thickness of the hollow fiber membrane (wall thickness = outer diameter - inner diameter) is preferably 0.5-1 mm, and in specific embodiments may be 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm or 1 mm.

[0030] The present invention selects polyethersulfone with excellent hydrophilicity, thermal stability, chemical stability and biocompatibility as the material of the hollow fiber membrane, and controls the pore size of the hollow fiber membrane to be 0.2-0.65 μm. The hollow fiber membrane has high flux, high porosity and high filtration efficiency, has a stable beer clarification effect, is used for filtering beer fermentation stock solution, can effectively remove yeast in the beer fermentation stock solution, and the yeast removal rate is greater than 99.99%. At the same time, the raw material components and flavor substances of the beer are retained to the greatest extent, and a clear and stable beer product is obtained.

[0031] In the present invention, the pressure of the membrane filtration is preferably 0.1 to 3 bar, and in specific embodiments can be 0.1 bar, 0.2 bar, 0.3 bar, 0.4 bar, 0.5 bar, 0.6 bar, 0.7 bar, 0.8 bar, 0.9 bar, 1 bar, 1.2 bar, 1.5 bar, 1.8 bar, 2 bar, 2.2 bar, 2.5 bar, 2.8 bar or 3 bar. The membrane filtration method used in the present invention has efficient filtration performance, while avoiding the resource exhaustion and dust pollution problems of diatomaceous earth filtration, is more environmentally friendly, provides a green and environmentally friendly filtration solution for beer production, and is suitable for industrial production of beer.

[0032] In the present invention, the filtration is preferably carried out by a membrane filtration device (see Figure 1 ), according to the flow direction of beer, the membrane filtration device preferably includes a feed liquid pool, a peristaltic pump, a pressure gauge and a membrane assembly connected in sequence; the filter membrane in the membrane assembly is a hollow fiber membrane; the outlet of the membrane assembly is connected to the feed liquid pool and the filtrate storage device respectively. In the present invention, the outlet of the pressure gauge is preferably connected to the inlet of the membrane assembly through the first valve and the second valve respectively. In the filtration mode, the first valve is opened and the second valve is closed, and the beer fermentation stock solution is transported to the inner surface of the hollow fiber membrane by the peristaltic pump, and passes through the membrane under the transmembrane pressure. The beer filtrate is enriched from the outer surface of the hollow fiber membrane into the assembly shell and enters the filtrate storage tank, and the concentrate is circulated back to the feed liquid pool. In the backwash mode, the second valve is opened and the first valve is closed. The cleaning liquid penetrates from the outer surface of the hollow fiber membrane into the inner surface of the hollow fiber membrane under pressure and circulates back to the feed liquid pool.

[0033] The following is a detailed description of the membrane filtration method of beer fermentation stock solution in conjunction with the membrane filtration device. The specific steps are as follows: open the first valve, close the second valve, and the beer fermentation stock solution in the feed liquid pool is transported to the membrane assembly via a peristaltic pump, and filtered through a hollow fiber membrane under transmembrane pressure to obtain beer filtrate, which is enriched in the assembly tube shell from the outer surface of the hollow fiber membrane and enters the filtrate storage tank, and the concentrate flows back to the feed liquid pool. In the present invention, the filtration also obtains a concentrated solution, which flows back to the feed liquid pool. In the present invention, the beer filtrate is preferably transported to the filtrate storage tank. In the present invention, the filtration pressure is preferably controlled by a peristaltic pump and a pressure gauge.

[0034] The present invention also provides a method for regenerating a hollow fiber membrane, comprising the following steps: sequentially subjecting the hollow fiber membrane used in the membrane filtration method described in the above technical solution to water reverse washing, alkaline solution washing, first water washing, acid solution washing and second water washing to obtain a regenerated hollow fiber membrane.

[0035] In the present invention, the regeneration of the hollow fiber membrane is preferably performed in a membrane filtration device.

[0036] In the present invention, the pressure of the water reverse washing is preferably 0.5 to 5.0 bar, and in specific embodiments, it can be 0.5 bar, 1 bar, 1.5 bar, 2 bar, 2.5 bar, 3 bar, 3.5 bar, 4 bar, 4.5 bar or 5 bar; the flow direction of the water during the water reverse washing process is opposite to the flow direction of the beer fermentation stock solution during the aforementioned membrane filtration process; the temperature of the water is preferably room temperature. In the present invention, the water reverse washing is preferably water reverse flushing of the membrane assembly. In the present invention, the water cleaning liquid is preferably discharged after the water reverse washing is completed.

[0037] In the present invention, the pH value of the alkali solution (the solvent is water) is preferably ≥12, and in a specific embodiment, it can be 12, 12.5, 13, 13.5 or 14; the temperature of the alkali solution is preferably 30-60°C, and in a specific embodiment, it can be 30°C, 35°C, 40°C, 45°C, 50°C, 55°C or 60°C; the alkali in the alkali solution includes sodium hydroxide. In the present invention, the time of the alkali solution washing is preferably 5-15min, and in a specific embodiment, it can be 5min, 6min, 7min, 8min, 9min, 10min, 11min, 12min, 13min, 14min or 15min. In the present invention, the alkali solution washing is preferably immersion washing of the alkali solution in a membrane filtration device. In the present invention, the alkali solution enters the membrane assembly for immersion, and the inlet flow direction is opposite to the flow direction of the beer fermentation stock solution in the aforementioned membrane filtration process. In the present invention, the alkali solution cleaning liquid is preferably discharged after the alkali solution washing.

[0038] In the present invention, the time of the first water washing is 15 to 75 minutes, and the first water washing preferably includes washing for 5 to 15 minutes, discharging water washing liquid and washing for 10 to 60 minutes in sequence; in a specific embodiment, the washing for 5 to 15 minutes can be washing for 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes or 15 minutes; in a specific embodiment, the washing for 10 to 60 minutes can be washing for 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes or 60 minutes. In the present invention, the first water washing is preferably water circulating washing in the membrane filtration device. In the present invention, the flow direction of water in the first water washing process is the same as the flow direction of the beer fermentation stock solution in the aforementioned membrane filtration process. In the present invention, the temperature of the water in the first water washing is preferably room temperature.

[0039] In the present invention, the pH value of the acid solution (the solvent is water) is ≤2, and in a specific embodiment, it can be 0.1, 0.5, 0.8, 1, 1.2, 1.5, 1.8 or 2; the acid in the acid solution preferably includes one or more of hydrochloric acid, sulfuric acid, nitric acid and citric acid; the time of the acid solution washing is preferably 5 to 15 minutes, and in a specific embodiment, it can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes or 15 minutes. In the present invention, the acid solution washing is preferably the acid solution circulating washing in the membrane filtration device. In the present invention, the flow direction of the acid solution during the acid solution washing process is the same as the flow direction of the beer fermentation stock solution during the aforementioned membrane filtration process. In the present invention, the acid solution cleaning liquid is preferably discharged after the acid solution washing.

[0040] In the present invention, the time of the second water washing is preferably 5 to 15 minutes, and in a specific embodiment, it can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes or 15 minutes. In the present invention, the second water washing is preferably water circulating washing in the membrane filtration device. In the present invention, the flow direction of water during the second water washing process is the same as the flow direction of the beer fermentation stock solution during the aforementioned membrane filtration process. In the present invention, the temperature of the water for the second water washing is preferably room temperature. In the present invention, it is preferred to discharge water cleaning liquid after the second water washing.

[0041] The present invention sequentially performs water reverse washing, alkali solution washing, first water washing, acid solution washing and second water washing on the used hollow fiber membrane, and adopts the above-mentioned water washing and chemical agent (alkali solution and acid solution) combined cleaning method, which can effectively remove membrane contamination, and the membrane flux recovery rate of the obtained regenerated hollow fiber membrane is above 96%, the filtration performance recovery rate of the hollow fiber membrane is high, and the service life of the hollow fiber membrane is significantly extended. It is suitable for the filtration process of beer production and has high practical application value.

[0042] In order to further illustrate the present invention, the membrane filtration method of beer fermentation stock solution and the regeneration method of hollow fiber membrane provided by the present invention are described in detail below in combination with embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0043] In the following examples and comparative examples, Figure 1 The membrane filtration device shown is used to filter the fermented beer liquid. In the membrane filtration devices used in the embodiment and the comparative example, except for the hollow fiber membrane, the other structural components are the same. The weight average molecular weight of polyethersulfone is 50,000.

[0044] Example 1

[0045] A membrane assembly consisting of a hollow fiber membrane made of polyethersulfone, with a membrane pore size of 0.45 μm and an inner / outer diameter of 1.5 / 2.5 mm was selected, and a membrane filtration device was used to perform membrane filtration on the beer fermentation raw liquid at 0.5 bar to obtain beer filtrate.

[0046] Example 2

[0047] A membrane assembly consisting of a hollow fiber membrane made of polyethersulfone, with a membrane pore size of 0.65 μm and an inner / outer diameter of 1.5 / 2.5 mm was selected, and a membrane filtration device was used to perform membrane filtration on the beer fermentation raw liquid at 0.5 bar to obtain beer filtrate.

[0048] Example 3

[0049] A hollow fiber membrane assembly made of polyethersulfone, with a membrane pore size of 0.52 μm and a membrane inner / outer diameter of 1.0 / 1.5 mm was selected, and a membrane filtration device was used to perform membrane filtration on the beer fermentation raw liquid at 0.3 bar to obtain beer filtrate.

[0050] Example 4

[0051] A membrane assembly consisting of a hollow fiber membrane made of polyethersulfone, with a membrane pore size of 0.23 μm and an inner / outer diameter of 1.5 / 2.5 mm was selected. The beer fermentation stock solution was filtered using a membrane filtration device at 0.8 bar to obtain beer filtrate.

[0052] Comparative Example 1

[0053] The only difference from Example 1 is that the hollow fiber membrane is made of polyvinylidene fluoride (weight average molecular weight is 68,000) and the inner / outer diameters of the membrane are 1.5 / 2.5 mm.

[0054] Comparative Example 2

[0055] The only difference from Example 1 is that the hollow fiber membrane is made of polyethylene (weight average molecular weight is 58,000) and the inner / outer diameters of the membrane are 1.5 / 2.5 mm.

[0056] Example 5

[0057] The used membrane modules of Examples 1 to 4 and Comparative Examples 1 to 2 were regenerated respectively. The regeneration was carried out in a membrane filtration device. The specific steps are as follows:

[0058] S1: Water reverse flushing:

[0059] (1) Add water to reversely flush the membrane module at a pressure of 1.0 bar;

[0060] (2) Discharge water cleaning fluid;

[0061] S2: Sodium hydroxide aqueous solution immersion cleaning:

[0062] (1) Heat water to 35°C;

[0063] (2) adding sodium hydroxide to a pH value of 12;

[0064] (3) Soaking the sodium hydroxide aqueous solution in the membrane filtration device for 15 minutes; the flow direction of the sodium hydroxide aqueous solution is opposite to the flow direction of the beer fermentation stock solution in the aforementioned membrane filtration process;

[0065] (4) discharging sodium hydroxide cleaning solution;

[0066] S3: Water forward rinsing:

[0067] (1) Add water and circulate it in the membrane filtration device for 15 minutes;

[0068] (2) Discharge water cleaning fluid;

[0069] S4: Acid forward cleaning:

[0070] (1) Add water and circulate it in the membrane filtration device for 40 minutes;

[0071] (2) Slowly add hydrochloric acid to a pH of 2;

[0072] (3) circulating the hydrochloric acid aqueous solution in the membrane filtration device for 15 minutes;

[0073] (4) Discharging hydrochloric acid cleaning solution;

[0074] S5: Water forward rinsing:

[0075] (1) Add water and circulate it in the membrane filtration device for 15 minutes;

[0076] (2) Discharge water cleaning fluid.

[0077] Test Example 1

[0078] Detection of beer filtrate obtained in Examples 1 to 4 and Comparative Examples 1 to 2

[0079] The number of yeast was measured using a Count star TY1100 I-03 yeast counter; the original wort concentration and alcohol content were measured using an Anton Paar / Type III beer automatic analyzer; and the turbidity was measured using a Haffmans / VOS90 / 25 dual-angle turbidity meter. The test results are shown in Table 1.

[0080] The membrane flux test results of the regenerated hollow fiber membrane in Example 5 are shown in Table 1.

[0081] The filtration flux of the hollow fiber membrane was tested using a membrane filtration device, and the permeation flux calculation formula is shown in Formula 1:

[0082]

[0083] Where: J is the membrane water flux, unit is L / m 2 h; V is the permeate volume, in L; A is the effective filtration area of ​​the membrane, in m 2 ; t is the permeation time, unit is h; ΔP is the transmembrane pressure difference, unit is bar.

[0084] Table 1 Beer quality indicators before and after filtration and membrane flux test results of the regenerated hollow fiber membrane

[0085] Liquid index Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Beer fermentation liquid Yeast count (10,000 / mL) 0 0.01 0 0 0.02 0.02 120 Yeast removal rate (%) 100 ＞99.99 100 100 99.98 99.98 - Original wort concentration (°P) 14.55 14.53 14.54 14.36 13.53 12.61 14.63 Turbidity (90°) 0.36 0.46 0.47 0.3 0.5 0.65 12.7 Membrane flux recovery rate after regeneration (%) 98％ 96％ 98％ 99％ 82％ 60％ -

[0086] As can be seen from Table 1, after the present invention uses polyethersulfone as the material of the hollow fiber membrane for membrane filtration, the number of yeast in the beer filtrate is ≤0.01 ten thousand / mL, the yeast number removal rate is >99.99%, and the yeast removal rate is high; the original wort concentration is above 14.36°P, and the raw material components and flavor substances of the beer are retained to the greatest extent; the turbidity is ≤0.47 (90°), and the clarity is high.

[0087] The regenerated hollow fiber membrane obtained by the regeneration method provided by the invention has a membrane flux recovery rate of 96-99%, and the membrane flux recovery rate is above 96%. The filtration performance recovery rate of the hollow fiber membrane is high.

[0088] In summary, the present invention selects polyethersulfone with excellent hydrophilicity, thermal stability, chemical stability and biocompatibility as the material of the hollow fiber membrane. The hollow fiber membrane has high flux, high porosity and high filtration efficiency, has a stable beer clarification effect, and is used for filtering beer fermentation stock solution. It can effectively remove yeast in the beer fermentation stock solution, and the yeast removal rate is greater than 99.99%. At the same time, the raw material components and flavor substances of the beer are retained to the greatest extent, and a clear and stable beer product is obtained. Moreover, the membrane filtration method provided by the present invention has efficient filtration performance, while avoiding the resource exhaustion and dust pollution problems of diatomaceous earth filtration, which is more environmentally friendly, and provides a green and environmentally friendly filtration solution for beer production, and is suitable for industrial production of beer.

[0089] Moreover, the present invention sequentially performs water reverse washing, alkali solution washing, first water washing, acid solution washing and second water washing on the used hollow fiber membrane, and adopts the above-mentioned water washing and chemical agent (alkali solution and acid solution) combined cleaning method, which can effectively remove membrane contamination, and the filtration performance recovery rate of the hollow fiber membrane is high, which significantly extends the service life of the hollow fiber membrane, is suitable for the filtration process of beer production, and has high practical application value.

[0090] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A membrane filtration method for beer fermentation stock solution, characterized in that: The beer fermentation stock solution is filtered by a hollow fiber membrane to obtain a beer filtrate; the hollow fiber membrane is made of polyethersulfone and has a pore size of 0.2 to 0.65 μm.

2. The membrane filtration method according to claim 1, characterized in that The inner diameter of the hollow fiber membrane is 1 to 2 mm.

3. The membrane filtration method according to claim 1 or 2, characterized in that: The outer diameter of the hollow fiber membrane is 1.5 to 3 mm.

4. The membrane filtration method according to claim 1 or 2, characterized in that: The pressure of the membrane filtration is 0.1 to 3 bar.

5. A method for regenerating a hollow fiber membrane, characterized in that: The following steps are involved: The hollow fiber membrane used in the membrane filtration method according to any one of claims 1 to 4 is sequentially subjected to water reverse washing, alkaline solution washing, first water washing, acid solution washing and second water washing to obtain a regenerated hollow fiber membrane.

6. The regeneration method according to claim 5, characterized in that: The pressure of the water reverse washing is 0.5-5.0 bar.

7. The regeneration method according to claim 5, characterized in that: The pH value of the alkali solution is ≥12, and the temperature is 30-60°C; The alkali in the lye includes sodium hydroxide; The alkali solution washing time is 5 to 15 minutes.

8. The regeneration method according to claim 5, characterized in that: The first water washing time is 15 to 75 minutes.

9. The regeneration method according to claim 5, characterized in that: The pH value of the acid solution is ≤2; The acid in the acid solution includes one or more of hydrochloric acid, sulfuric acid, nitric acid and citric acid; The acid washing time is 5 to 15 minutes.

10. The regeneration method according to claim 5, characterized in that: The second water washing time is 5 to 15 minutes.

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