A treatment method for soybean protein processing wastewater

Abstract

The present invention discloses a method for treating soybean protein processing wastewater. In the present invention, magnetic nano-silica is obtained by coating nano-ferroferric oxide with silica. During the subsequent separation process, magnetic separation is adopted, which improves the separation efficiency and features a fast separation speed. First, vinyltrimethoxysilane is used to modify the surface of magnetic nano-silica to obtain magnetic nano-silica particles with double bonds on the surface. Then, through the addition reaction of double bonds, ionic liquid and polyacrylic acid are grafted onto silica, which improves the adsorption performance of silica for proteins. At the same time, polyacrylic acid has good hydrophilic properties and, acting together with the ionic liquid, promotes the efficient adsorption and separation of proteins.

Description

Technical Field

[0001] The present invention relates to the technical field of soybean protein wastewater treatment, and particularly relates to a method for treating soybean protein processing wastewater. Background Art

[0002] Soybean is an important crop rich in protein. Soybean protein isolate processed from it is a refined soybean protein product with high protein purity and deep processing performance, which can be added to food production as an intermediate raw material and has a wide range of uses. Soybean protein isolate can be processed by methods such as alkali dissolution-acid precipitation method, ultrafiltration concentration method, reverse micelle extraction method, and reverse phase high performance liquid chromatography method. Among them, the alkali dissolution-acid precipitation method is a relatively mature and widely used process method for producing soybean protein isolate at present. However, a large amount of soybean whey wastewater will be generated during the production of soybean protein isolate by the alkali dissolution-acid precipitation process, and the wastewater contains rich substances such as protein and sugar, which is extremely easy to cause waste of resources and environmental pollution.

[0003] Generally, the temperature of soybean whey wastewater is between 45 - 50 °C, the pH is 4.5, and the solid content is about 2%. Among them, soybean protein isolate accounts for about 10 - 15%, soybean whey protein accounts for about 10 - 15%, oligosaccharides account for about 40% - 50%, and salt accounts for about 20 - 30%. During the process of obtaining soybean protein isolate by centrifugation, there is still a very small amount of soybean protein isolate remaining in the centrifuged supernatant soybean whey wastewater. The content of this soybean protein isolate in the whey wastewater is extremely low, and the existing technical methods cannot effectively separate this part of soybean protein isolate, let alone realize industrialization.

[0004] Chinese patent document CN 108191950 A discloses a method for recovering soybean protein from soybean whey wastewater, which includes the following steps: adjusting the pH of soybean whey wastewater to alkaline and then concentrating it; adjusting the protein concentration of the concentrated soybean whey concentrate to 12 - 16% and obtaining the soybean protein powder by spray drying. Due to the huge amount of whey wastewater, the existing extraction technology has a high treatment cost and low separation efficiency because of its low content and large treatment volume. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a method for treating soybean protein processing wastewater.

[0006] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0007] A method for treating soybean protein processing wastewater, comprising the following steps:

[0008] (1) Centrifuging the soybean protein processing wastewater to remove large particle impurities, and taking the supernatant as the liquid to be treated;

[0009] (2) Adjust the pH of the liquid to be treated to 5-6, then add an adsorbent thereto, stir for 60-120 min, and after solid-liquid separation, obtain a solid precipitate;

[0010] (3) Add the solid precipitate to an alkali solution for elution, take the supernatant after magnetic separation, and then perform freeze-drying to obtain soy protein powder.

[0011] Preferably, in step (2), the preparation method of the adsorbent is as follows:

[0012] S1. Disperse nano-ferroferric oxide in an aqueous solution of sodium metasilicate, adjust the pH of the solution to 6-7, heat and stir for reaction. After the reaction is completed, perform magnetic separation, washing, and drying to obtain magnetic nano-silica;

[0013] S2. Disperse the magnetic nano-silica in an aqueous ethanol solution, then add vinyltrimethoxysilane thereto, stir for 2-3 h, perform magnetic separation, washing, and drying to obtain magnetic nano-silica particles containing double bonds;

[0014] S3. Add the magnetic nano-silica particles containing double bonds, 1-vinyl-3-octylimidazolium tetrafluoroborate, and acrylic acid to deionized water, ultrasonically disperse evenly, pass nitrogen to remove dissolved oxygen in the reaction system, then add N,N-methylenebisacrylamide and potassium persulfate, and react under a nitrogen atmosphere. After the reaction is completed, perform magnetic separation to obtain a reaction product, and wash and freeze-dry the reaction product to obtain the adsorbent.

[0015] Preferably, in step S1, the mass ratio of nano-ferroferric oxide to the aqueous solution of sodium metasilicate is 1-2:100.

[0016] Preferably, in step S1, the mass fraction of the aqueous solution of sodium metasilicate is 10-15%, and the pH value of the aqueous solution of sodium metasilicate is 11-12.

[0017] Preferably, in step S1, the heating and stirring reaction temperature is 70-80 °C, and the heating and stirring reaction time is 3-5 h.

[0018] Preferably, in step S2, the mass ratio of magnetic nano-silica to vinyltrimethoxysilane is 6-10:1-1.5.

[0019] Preferably, in step S3, the mass ratio of the magnetic nano-silica particles containing double bonds, 1-vinyl-3-octylimidazolium tetrafluoroborate, acrylic acid, N,N-methylenebisacrylamide, and potassium persulfate is 10-15:4-8:3-6:0.05-0.1:0.4-0.8.

[0020] Preferably, in step S3, the reaction temperature is 60 - 80 °C and the reaction time is 3 - 5 h.

[0021] Preferably, in step (2), the addition amount of the adsorbent is 15 - 20 g / L.

[0022] Preferably, in step (3), the alkaline solution is a 1 - 1.5 mol / L NaOH solution.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The present invention uses silica-coated nano-ferroferric oxide to obtain magnetic nano-silica. In the subsequent separation process, magnetic separation is used to improve the separation efficiency, which is characterized by a fast separation speed.

[0025] (2) The present invention first uses vinyltrimethoxysilane to modify the surface of magnetic nano-silica to obtain magnetic nano-silica particles with double bonds on the surface, and then through the addition reaction of double bonds, grafts ionic liquid and polyacrylic acid on silica, improving the adsorption performance of silica for proteins. At the same time, polyacrylic acid has good hydrophilic properties, and together with the ionic liquid, it promotes the efficient adsorption and separation of proteins. Specific Embodiments

[0026] The following further elaborates on the present invention through specific preferred embodiments, but the present invention is not limited to the following embodiments.

[0027] It should be noted that unless otherwise specified, the chemical reagents involved in the present invention are all purchased through commercial channels.

[0028] Example 1

[0029] A method for treating soybean protein processing wastewater includes the following steps:

[0030] (1) Centrifuge the soybean protein processing wastewater to remove large particulate impurities, take the supernatant as the liquid to be treated, and use the biuret method to measure the protein content in the liquid to be treated as 4.76 g / L;

[0031] (2) Take 1 L of the liquid to be treated, adjust the pH of the liquid to be treated to 5, then add 15 g of the adsorbent thereto, stir at 25 °C for 60 min, perform solid-liquid separation to obtain a solid precipitate, and measure the protein content in the supernatant as 0.13 g / L; among them, the preparation method of the adsorbent is as follows:

[0032] S1. Disperse 1 g of nano-ferroferric oxide in 100 g of sodium metasilicate aqueous solution with a concentration of 10 wt% and a pH of 11. Adjust the pH of the solution to 7, and heat and stir the reaction at 70 °C for 5 h. After the reaction is completed, perform magnetic separation, washing, and drying to obtain magnetic nano-silica;

[0033] S2. Disperse 6 g of magnetic nano-silica in 100 g of ethanol aqueous solution with a concentration of 80 wt%, then add 1 g of vinyltrimethoxysilane thereto, stir for 2 h, perform magnetic separation, washing, and drying to obtain magnetic nano-silica particles containing double bonds;

[0034] S3. Add 10 g of magnetic nano-silica particles containing double bonds, 4 g of 1-vinyl-3-octylimidazolium tetrafluoroborate, and 3 g of acrylic acid to 150 g of deionized water, ultrasonically disperse evenly, pass nitrogen to remove dissolved oxygen in the reaction system, then add 0.05 g of N,N-methylenebisacrylamide and 0.4 g of potassium persulfate, and react at 60 °C under a nitrogen atmosphere for 5 h. After the reaction is completed, perform magnetic separation to obtain the reaction product, and wash and freeze-dry the reaction product to obtain the adsorbent;

[0035] (3) Add the solid precipitate to 1.5 mol / L NaOH solution for elution, take the supernatant after magnetic separation, and then perform freeze-drying to obtain soy protein powder.

[0036] In this example, the protein recovery rate is 97.27%.

[0037] Example 2

[0038] A treatment method for soy protein processing wastewater includes the following steps:

[0039] (1) Centrifuge the soy protein processing wastewater to remove large particle impurities, take the supernatant as the liquid to be treated, and use the biuret method to measure the protein content in the liquid to be treated as 4.76 g / L;

[0040] (2) Take 1 L of the liquid to be treated, adjust the pH of the liquid to be treated to 6, then add 20 g of the adsorbent thereto, stir at 25 °C for 90 min, perform solid-liquid separation to obtain a solid precipitate, and measure the protein content in the supernatant as 0.12 g / L; among them, the preparation method of the adsorbent is as follows:

[0041] S1. Disperse 1.5 g of nano-ferroferric oxide in 100 g of sodium metasilicate aqueous solution with a concentration of 10 wt% and a pH of 12. Adjust the pH of the solution to 7, and heat and stir the reaction at 80 °C for 4 h. After the reaction is completed, perform magnetic separation, washing, and drying to obtain magnetic nano-silica;

[0042] S2. Disperse 8 g of magnetic nano-silica in 100 g of an 80 wt% ethanol aqueous solution, then add 1.5 g of vinyltrimethoxysilane thereto, stir for 2 h, and after magnetic separation, washing, and drying, magnetic nano-silica particles containing double bonds are obtained;

[0043] S3. Add 12 g of magnetic nano-silica particles containing double bonds, 6 g of 1-vinyl-3-octylimidazolium tetrafluoroborate, and 5 g of acrylic acid to 150 g of deionized water, ultrasonically disperse them evenly, pass nitrogen to remove the dissolved oxygen in the reaction system, then add 0.08 g of N,N-methylenebisacrylamide and 0.6 g of potassium persulfate, and carry out the reaction at 60 °C under a nitrogen atmosphere for 5 h. After the reaction ends, magnetic separation is carried out to obtain the reaction product, and the reaction product is washed and freeze-dried to obtain the adsorbent;

[0044] (3) Add the solid precipitate to 1 mol / L NaOH solution for elution, take the supernatant after magnetic separation, and then carry out freeze-drying to obtain soy protein powder.

[0045] In this example, the recovery rate of protein is 98.32%.

[0046] Example 3

[0047] A method for treating soy protein processing wastewater includes the following steps:

[0048] (1) Centrifuge the soy protein processing wastewater to remove large particle impurities, take the supernatant as the liquid to be treated, and use the biuret method to measure the protein content in the liquid to be treated as 4.76 g / L;

[0049] (2) Take 1 L of the liquid to be treated, adjust the pH of the liquid to be treated to 6, then add 18 g of the adsorbent thereto, stir at 25 °C for 90 min, carry out solid-liquid separation to obtain a solid precipitate, and measure the protein content in the supernatant as 0.08 g / L; wherein, the preparation method of the adsorbent is as follows:

[0050] S1. Disperse 2 g of nano-ferroferric oxide in 100 g of a sodium metasilicate aqueous solution with a pH of 12 and a concentration of 15 wt%, adjust the pH of the solution to 7, heat and stir at 80 °C for 3 h. After the reaction is completed, carry out magnetic separation, washing, and drying to obtain magnetic nano-silica;

[0051] S2. Disperse 10 g of magnetic nano-silica in 100 g of an 80 wt% ethanol aqueous solution, then add 1.5 g of vinyltrimethoxysilane thereto, stir for 2 h, and after magnetic separation, washing, and drying, magnetic nano-silica particles containing double bonds are obtained;

[0052] S3. Add 15 g of magnetic nano-silica particles containing double bonds, 8 g of 1-vinyl-3-octylimidazolium tetrafluoroborate, and 6 g of acrylic acid into 150 g of deionized water, ultrasonically disperse them evenly, introduce nitrogen to remove the dissolved oxygen in the reaction system, then add 0.1 g of N,N-methylenebisacrylamide and 0.8 g of potassium persulfate, and carry out the reaction at 80 °C under a nitrogen atmosphere for 4 h. After the reaction ends, obtain the reaction product by magnetic separation, wash the reaction product, and then freeze-dry it to obtain the adsorbent;

[0053] (3) Add the solid precipitate into 1.5 mol / L NaOH solution for elution, take the supernatant after magnetic separation, and then carry out freeze-drying to obtain the soy protein powder.

[0054] In this example, the protein recovery rate is 97.48%.

[0055] Comparative Example 1

[0056] A method for treating soy protein processing wastewater includes the following steps:

[0057] (1) Centrifuge the soy protein processing wastewater to remove large particle impurities, take the supernatant as the liquid to be treated, and use the biuret method to measure the protein content in the liquid to be treated as 4.76 g / L;

[0058] (2) Take 1 L of the liquid to be treated, adjust the pH of the liquid to be treated to 6, then add 18 g of the adsorbent thereto, stir at 25 °C for 90 min, carry out solid-liquid separation to obtain a solid precipitate, and measure the protein content in the supernatant as 2.24 g / L; among them, the preparation method of the adsorbent is as follows:

[0059] Disperse 2 g of nano-ferroferric oxide in 100 g of sodium metasilicate aqueous solution with 15 wt% and pH of 12, adjust the pH of the solution to 7, heat and stir at 80 °C for 3 h. After the reaction is completed, carry out magnetic separation, washing, and drying to obtain the adsorbent;

[0060] (3) Add the solid precipitate into 1.5 mol / L NaOH solution for elution, take the supernatant after magnetic separation, and then carry out freeze-drying to obtain the soy protein powder.

[0061] In this comparative example, the protein recovery rate is 52.94%.

[0062] Comparative Example 2

[0063] A method for treating soy protein processing wastewater includes the following steps:

[0064] (1) Centrifuge the soybean protein processing wastewater to remove large particulate impurities. Take the supernatant as the liquid to be treated, and use the biuret method to determine that the protein content in the liquid to be treated is 4.76 g / L;

[0065] (2) Take 1 L of the liquid to be treated, adjust the pH of the liquid to be treated to 6, then add 18 g of the adsorbent, stir at 25 °C for 90 min, perform solid-liquid separation to obtain a solid precipitate, and determine that the protein content in the supernatant is 0.95 g / L; Among them, the preparation method of the adsorbent is as follows:

[0066] S1. Disperse 2 g of nano-ferroferric oxide in 100 g of sodium metasilicate aqueous solution with 15 wt% and pH 12, adjust the pH of the solution to 7, heat and stir at 80 °C for 3 h. After the reaction is completed, perform magnetic separation, washing, and drying to obtain magnetic nano-silica;

[0067] S2. Disperse 10 g of magnetic nano-silica in 100 g of ethanol aqueous solution with 80 wt%, then add 1.5 g of vinyltrimethoxysilane, stir for 2 h, perform magnetic separation, washing, and drying to obtain magnetic nano-silica particles containing double bonds;

[0068] S3. Add 15 g of magnetic nano-silica particles containing double bonds and 8 g of 1-vinyl-3-octylimidazolium tetrafluoroborate to 150 g of deionized water, ultrasonically disperse evenly, pass nitrogen to remove dissolved oxygen in the reaction system, then add 0.1 g of N,N'-methylenebisacrylamide and 0.8 g of potassium persulfate, and react at 80 °C under a nitrogen atmosphere for 4 h. After the reaction is completed, perform magnetic separation to obtain the reaction product, and wash and freeze-dry the reaction product to obtain the adsorbent;

[0069] (3) Add the solid precipitate to 1.5 mol / L NaOH solution for elution, take the supernatant after magnetic separation, and then perform freeze-drying to obtain soybean protein powder.

[0070] The protein recovery rate in this comparative example is 80.04%.

[0071] Comparative Example 3

[0072] A method for treating soybean protein processing wastewater includes the following steps:

[0073] (1) Centrifuge the soybean protein processing wastewater to remove large particulate impurities. Take the supernatant as the liquid to be treated, and use the biuret method to determine that the protein content in the liquid to be treated is 4.76 g / L;

[0074] (2) Take 1 L of the liquid to be treated, adjust the pH of the liquid to be treated to 6, then add 18 g of the adsorbent thereto, stir at 25 °C for 90 min, perform solid-liquid separation to obtain a solid precipitate, and measure the protein content in the supernatant to be 1.19 g / L; wherein, the preparation method of the adsorbent is as follows:

[0075] S1. Disperse 2 g of nano-ferroferric oxide in 100 g of a sodium metasilicate aqueous solution with a concentration of 15 wt% and a pH of 12, adjust the pH of the solution to 7, heat and stir the reaction at 80 °C for 3 h. After the reaction is completed, perform magnetic separation, washing, and drying to obtain magnetic nano-silica;

[0076] S2. Disperse 10 g of magnetic nano-silica in 100 g of an ethanol aqueous solution with a concentration of 80 wt%, then add 1.5 g of vinyltrimethoxysilane thereto, stir for 2 h, perform magnetic separation, washing, and drying to obtain magnetic nano-silica particles containing double bonds;

[0077] S3. Add 15 g of magnetic nano-silica particles containing double bonds and 6 g of acrylic acid to 150 g of deionized water, ultrasonically disperse evenly, introduce nitrogen to remove the dissolved oxygen in the reaction system, then add 0.1 g of N,N-methylenebisacrylamide and 0.8 g of potassium persulfate, and carry out the reaction at 80 °C under a nitrogen atmosphere for 4 h. After the reaction is completed, perform magnetic separation to obtain the reaction product, and wash and freeze-dry the reaction product to obtain the adsorbent;

[0078] (3) Add the solid precipitate to a 1.5 mol / L NaOH solution for elution, take the supernatant after magnetic separation, and then perform freeze-drying to obtain soy protein powder.

[0079] The protein recovery rate in this comparative example is 75%.

[0080] Finally, it should be noted that the above embodiments do not limit the present invention in any form. For those skilled in the art, based on the present invention, some modifications and improvements can be made. Therefore, any modification or improvement made without departing from the spirit of the present invention falls within the scope of protection required by the present invention.

Claims

1. A method for treating soybean protein processing wastewater, characterized in that It includes the following steps: (1) Centrifuge the soybean protein processing wastewater to remove large particulate impurities, and take the supernatant as the liquid to be treated; (2) Adjust the pH of the liquid to be treated to 5 - 6, then add an adsorbent thereto, stir for 60 - 120 min, and perform solid-liquid separation to obtain a solid precipitate; (3) Add the solid precipitate to an alkali solution for elution, take the supernatant after magnetic separation, and then perform freeze-drying to obtain soybean protein powder; Among them, in step (2), the preparation method of the adsorbent is as follows: S1. Disperse nano-ferroferric oxide in an aqueous solution of sodium metasilicate, adjust the pH of the solution to 6 - 7, heat and stir for reaction. After the reaction is completed, perform magnetic separation, washing, and drying to obtain magnetic nano-silica; S2. Disperse the magnetic nano-silica in an aqueous ethanol solution, then add vinyltrimethoxysilane thereto, stir for 2 - 3 h, perform magnetic separation, washing, and drying to obtain magnetic nano-silica particles containing double bonds; S3. Add the magnetic nano-silica particles containing double bonds, 1-vinyl-3-octylimidazolium tetrafluoroborate, and acrylic acid to deionized water, ultrasonically disperse evenly, pass nitrogen to remove dissolved oxygen in the reaction system, then add N,N-methylenebisacrylamide and potassium persulfate, and perform the reaction under a nitrogen atmosphere. After the reaction ends, perform magnetic separation to obtain the reaction product, and wash and freeze-dry the reaction product to obtain the adsorbent.

2. The treatment method of soybean protein processing wastewater according to claim 1, characterized in that In step S1, the mass ratio of nano-ferroferric oxide to the aqueous solution of sodium metasilicate is 1 - 2:

100.

3. The treatment method of soybean protein processing wastewater according to claim 1, characterized in that, In step S1, the mass fraction of the aqueous solution of sodium metasilicate is 10 - 15%, and the pH value of the aqueous solution of sodium metasilicate is 11 - 12.

4. The treatment method of soybean protein processing wastewater according to claim 1, characterized in that, In step S1, the heating and stirring reaction temperature is 70 - 80 °C, and the heating and stirring reaction time is 3 - 5 h.

5. The treatment method of soybean protein processing wastewater according to claim 1, characterized in that, In step S2, the mass ratio of magnetic nano-silica to vinyltrimethoxysilane is 6 - 10:1 - 1.

5.

6. The treatment method of soybean protein processing wastewater according to claim 1, characterized in that, In step S3, the mass ratio of the magnetic nano-silica particles containing double bonds, 1-vinyl-3-octylimidazolium tetrafluoroborate, acrylic acid, N,N-methylenebisacrylamide, and potassium persulfate is 10 - 15:4 - 8:3 - 6:0.05 - 0.1:0.4 - 0.

8.

7. The treatment method of soybean protein processing wastewater according to claim 1, characterized in that In step S3, the reaction temperature is 60 - 80 °C, and the reaction time is 3 - 5 h.

8. The treatment method of soybean protein processing wastewater according to claim 1, wherein In step (2), the addition amount of the adsorbent is 15 - 20 g / L.

9. The treatment method of soybean protein processing wastewater according to claim 1, characterized in that, In step (3), the alkali solution is a 1 - 1.5 mol / L NaOH solution.