A method for extracting acid phospholipids from soybean oil processing waste liquid to prepare high bioavailability iron materials

Abstract

The application provides a method for extracting acid phospholipid from soybean oil processing waste liquid to prepare a high-bioavailability iron material. The method uses the soybean oil processing waste liquid as raw material, and prepares Fe chelation material through three steps of selective extraction of acid phospholipid, in-situ pH regulation chelation and green purification, efficiently utilizes the chelation activity, and forms a complex material containing soybean phospholipid, lecithin, amino acid and Fe, and develops the acid phospholipid in the soybean oil processing waste liquid into a high-value fertilizer synergistic material at low cost.

Description

Technical Field

[0001] This invention relates to a method for preparing highly bioavailable iron materials by extracting acidic phospholipids from soybean oil processing wastewater, belonging to the field of comprehensive resource utilization and functional materials technology. Background Technology

[0002] Soybean oil refining wastewater, commonly known as "oil refining wastewater" or "soap residue wastewater," is a high-concentration organic wastewater generated during the refining of crude soybean oil into edible finished oil. It is characterized by its complex composition, high pollution load, and difficulty in treatment, making it one of the major pollution sources in the oil industry. If left untreated and directly released into water bodies, it will not only cause the death of aquatic life but also affect agricultural irrigation and drinking water for residents, resulting in serious environmental pollution.

[0003] Soybean oil refining waste liquid contains a large amount of acidic phospholipids (accounting for 10-30% of the dry basis), which are currently mostly used as low-value feed additives or directly discarded, resulting in not only a waste of resources but also environmental treatment pressure.

[0004] Acidic phospholipids are surfactants with emulsifying, wetting, and dispersing properties. Their hydrolysis products (such as lysophospholipids) and further purified single phospholipid components are even more valuable. Current phospholipid-chelated iron solutions mostly use purified soybean phospholipids (such as PC and PE), which are costly and do not utilize the unique chelating sites (-COOH, -PO4H) of acidic phospholipids in waste liquids. Furthermore, existing chelation technologies require strict pH control (neutral), demanding stringent conditions. Compared to mainstream chelating agents and purified phospholipids on the market, the cost of obtaining acidic phospholipids from waste liquids is far lower than that of purified soybean phospholipids (PC and PE), making it possible to develop low-cost fertilizer synergists. Therefore, how to efficiently utilize the large amounts of acidic phospholipids in soybean oil refining waste liquids remains a challenge. The *Journal of Agricultural and Food Chemistry* (2018) reported on the chelation of iron using neutral phospholipids (PC), but the issues of waste liquid recovery and chelation in acidic environments remain unresolved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing highly bioavailable iron materials by extracting acidic phospholipids from soybean oil processing wastewater.

[0006] This invention uses soybean oil processing waste liquid as raw material and prepares Fe chelate material through a three-step method of selective extraction of acidic phospholipids, in-situ pH-controlled chelation, and green purification. It efficiently utilizes the chelation activity to form an acidic complex material containing soybean phospholipids, lecithin, amino acids, and Fe. This method develops acidic phospholipids from soybean oil processing waste liquid into high-value fertilizer synergistic materials at low cost.

[0007] This invention is achieved through the following technical solution: A method for preparing highly bioavailable iron materials by extracting acidic phospholipids from soybean oil processing wastewater includes the following steps: (1) Waste liquid pretreatment: The soybean oil degumming waste liquid is centrifuged to remove the gum, and acidic phospholipids are enriched by acid precipitation to obtain crude acidic phospholipid extract; (2) Iron chelation reaction: The acidic phospholipid crude extract is mixed with FeSO4 solution, and ascorbic acid-citric acid composite antioxidant is added. The acidic phospholipid crude extract in step (1) is used directly as the chelating agent without purification. The natural carboxyl / phosphate groups are used to achieve efficient chelation of Fe²⁺ in a low-oxygen environment to obtain the chelated product. (3) Green purification: The chelated product is separated by membrane separation to remove free iron ions, and the final product is obtained by freeze drying.

[0008] According to a preferred embodiment of the present invention, in step (1), the centrifugation conditions are a centrifugation speed of 7000-9000 rpm and a centrifugation time of 10-20 min.

[0009] According to a preferred embodiment of the present invention, in step (1), acid precipitation enrichment is achieved by adding acid to the degummed soybean oil waste liquid after centrifugation to adjust the pH to 2.0-3.0, preferably to 2.5.

[0010] According to a preferred embodiment of the present invention, in step (2), the concentration of the FeSO4 solution is 0.05-0.3 mol / L.

[0011] More preferably, in step (2), the concentration of the FeSO4 solution is 0.1 mol / L.

[0012] According to a preferred embodiment of the present invention, in step (2), the molar ratio of the acidic phospholipid crude extract to the FeSO4 solution is 1:(1-3).

[0013] More preferably, in step (2), the molar ratio of the acidic phospholipid crude extract to the FeSO4 solution is 1:1.5.

[0014] The acidic phospholipid crude extract obtained by this invention contains phosphatidic acid and lysophospholipids, accounting for ≥30% of the dry weight of the crude extract.

[0015] According to a preferred embodiment of the present invention, in step (2), after the ascorbic acid-citric acid composite antioxidant is added, the concentration in the system reaches 0.05-0.2% for ascorbic acid and 0.01-0.1% for citric acid.

[0016] In a further preferred embodiment, in step (2), after the ascorbic acid-citric acid composite antioxidant is added, the concentration in the system reaches 0.1% for ascorbic acid and 0.05% for citric acid.

[0017] According to a preferred embodiment of the present invention, in step (2), the ascorbic acid-citric acid composite antioxidant is a mixture of ascorbic acid and citric acid in a mass ratio of 2:1.

[0018] According to a preferred embodiment of the present invention, in step (2), the low-oxygen environment is a dissolved oxygen ≤0.5 ppm.

[0019] According to a preferred embodiment of the present invention, in step (2), the chelation pH is 3-5.

[0020] According to a preferred embodiment of the present invention, in step (2), the chelation reaction temperature is 40-60°C, and the reaction is carried out for 1-4 hours under nitrogen protection.

[0021] This invention adds an ascorbic acid-citric acid composite antioxidant to achieve efficient chelation of Fe²⁺ (chelation rate ≥95%) under low oxygen conditions (dissolved oxygen).

[0022] According to a preferred embodiment of the present invention, in step (3), membrane separation is performed using a membrane with a molecular weight cutoff of 10 kDa.

[0023] Technical features and advantages of the present invention: 1. This invention is the first to use waste liquid acidic phospholipids (phosphatidic acid, lysophospholipids, etc.) as chelation carriers, which reduces costs by more than 60%, and the chelation ability of acidic phospholipids at low pH is better than that of neutral phospholipids (Comparative Example 1).

[0024] 2. This invention achieves the directional binding of acidic phospholipids and iron through in-situ pH regulation (pH 3-5), avoiding iron hydrolysis under traditional neutral pH conditions. The composite antioxidant system controls the Fe²⁺ oxidation rate to <5%.

[0025] 3. This invention is the first to use acidic phospholipids from waste liquid as a chelation carrier. The acidic phospholipids can still stably chelate at low pH (3-5), making it applicable to a wide range of conditions.

[0026] 4. This invention uses green purification and ion chelation of phospholipid liquid in soybean oil processing wastewater to form an acidic complex material containing soybean phospholipids, lecithin, amino acids, and Fe. Effect tests have shown that it has a significant promoting effect on soil particle formation and stability and increases organic carbon content. It is a potential organic fertilizer enhancement material with potential for industrial development. Attached Figure Description

[0027] Figure 1 This is a graph showing the relationship between the content of complexed iron and the number of large soil aggregates in Example 1. Figure 2 This is a graph showing the relationship between complexed iron content and soil organic carbon accumulation in Example 1. Figure 3 The bar chart shows the iron-bound organic carbon content of Example 1 and the bound organic carbon content of the control group. Detailed Implementation

[0028] The present invention will be further described below with reference to embodiments. It should be understood that the embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0029] Example 1: A method for preparing highly bioavailable iron materials by extracting acidic phospholipids from soybean oil processing wastewater includes the following steps: (1) Take 1 L of soybean oil degumming waste liquid, centrifuge at 8000 rpm for 15 min, then adjust the pH to 2.5, precipitate acidic phospholipids, and obtain crude acidic phospholipid extract (containing 35% phosphatidic acid). (2) Mix the crude acidic phospholipid extract with a 0.1 mol / L FeSO4 solution. 2+ The molar ratio was 1:1.5, and ascorbic acid-citric acid composite antioxidant was added to make the concentration of ascorbic acid 0.1% and citric acid 0.05%; the acidic phospholipid crude extract of step (1) was used directly as a chelating agent without purification. The natural carboxyl / phosphate groups were used to achieve efficient chelation of Fe²⁺ in a low oxygen environment. The reaction was carried out at pH 4.0 and 50℃ under nitrogen protection for 2 hours to obtain the chelated product. (3) The reaction solution was purified by 10 kDa ultrafiltration membrane and freeze-dried to obtain a brownish-red powder (iron content 12.3%, chelation rate 96.5%).

[0030] Example 2: A method for preparing highly bioavailable iron materials by extracting acidic phospholipids from soybean oil processing wastewater includes the following steps: (1) Take 1 L of soybean oil degumming waste liquid, centrifuge at 8000 rpm for 15 min, then adjust the pH to 2, precipitate acidic phospholipids, and obtain crude acidic phospholipid extract (containing 35% phosphatidic acid). (2) Mix the crude acidic phospholipid extract with a 0.1 mol / L FeSO4 solution. 2+ The molar ratio was 1:2. Ascorbic acid-citric acid composite antioxidant was added to make the concentration of ascorbic acid 0.15% and citric acid 0.08%. The acidic phospholipid crude extract from step (1) was used directly as a chelating agent without purification. Its natural carboxyl / phosphate groups were used to achieve efficient chelation of Fe²⁺ in a low-oxygen environment. The reaction was carried out at pH 4.0 and 50℃ under nitrogen protection for 2 hours to obtain the chelated product. (3) The reaction solution was purified by 10 kDa ultrafiltration membrane and freeze-dried to obtain a brownish-red powder (iron content 12.3%, chelation rate 96.5%).

[0031] Example 3: A method for preparing highly bioavailable iron materials by extracting acidic phospholipids from soybean oil processing wastewater includes the following steps: (1) Take 1 L of soybean oil degumming waste liquid, centrifuge at 8000 rpm for 15 min, then adjust the pH to 2.5, precipitate acidic phospholipids, and obtain crude acidic phospholipid extract (containing 35% phosphatidic acid). (2) Mix the crude acidic phospholipid extract with a 0.2 mol / L FeSO4 solution. 2+ The molar ratio was 1:2, and ascorbic acid-citric acid composite antioxidant was added to make the concentration of ascorbic acid 0.2% and citric acid 0.1%; the acidic phospholipid crude extract of step (1) was used directly as a chelating agent without purification. The natural carboxyl / phosphate groups were used to achieve efficient chelation of Fe²⁺ in a low oxygen environment. The reaction was carried out at pH 4.0 and 50℃ under nitrogen protection for 2 hours to obtain the chelated product. (3) The reaction solution was purified by 10 kDa ultrafiltration membrane and freeze-dried to obtain a brownish-red powder (iron content 12.3%, chelation rate 96.5%).

[0032] Comparative Example 1: Neutral phospholipid chelated iron When purified soybean phospholipids (PC≥80%) were used to replace the crude extract of waste liquid, the chelation rate was only 82% under the same conditions (dropped to 70% when pH>6), demonstrating the advantage of acidic phospholipids at low pH.

[0033] Experimental Example 1 The high bioavailability iron material prepared in Example 1 was applied to the soil. Test results showed that the content of complexed iron was significantly positively correlated with the number of soil macroaggregates (p < 0.01). Figure 1 The content of chelated iron showed a significant positive correlation with the accumulation of soil organic carbon (p < 0.01), see [reference needed]. Figure 2 Furthermore, the content of iron-bound organic carbon was significantly higher than that of the control group (without the application of high bioavailability iron material), indicating that the present invention, through green purification and ion chelation of phospholipid liquid in soybean oil processing wastewater, forms an acidic complex material containing soybean phospholipids, lecithin, amino acids, and Fe. This material has a significant promoting effect on soil particle formation and stability and increases organic carbon content, and is a potential organic fertilizer enhancement material with industrial development potential.

Claims

1. A method for preparing highly bioavailable iron materials by extracting acidic phospholipids from soybean oil processing wastewater, comprising the following steps: (1) Waste liquid pretreatment: The soybean oil degumming waste liquid is centrifuged to remove the gum, and acidic phospholipids are enriched by acid precipitation to obtain crude acidic phospholipid extract; (2) Iron chelation reaction: The acidic crude phospholipid extract was mixed with FeSO4 solution, and ascorbic acid-citric acid composite antioxidant was added. The acidic crude phospholipid extract from step (1) was used directly as the chelating agent without purification. The natural carboxyl / phosphate groups were used to achieve Fe chelation under low oxygen conditions. 2+ The efficient chelation yields chelated products; (3) Green purification: The chelated product is separated by membrane separation to remove free iron ions, and the final product is obtained by freeze drying.

2. The method according to claim 1, characterized in that, In step (1), the centrifugation conditions are a centrifugation speed of 7000-9000 rpm and a centrifugation time of 10-20 min.

3. The method according to claim 1, characterized in that, In step (1), acid precipitation enrichment involves adding acid to the degummed soybean oil waste liquid after centrifugation to adjust the pH to 2.0-3.

0.

4. The method according to claim 1, characterized in that, In step (2), the concentration of FeSO4 solution is 0.05-0.3 mol / L.

5. The method according to claim 1, characterized in that, In step (2), the molar ratio of the crude acidic phospholipid extract to the FeSO4 solution is 1:(1-3).

6. The method according to claim 1, characterized in that, In step (2), after the ascorbic acid-citric acid composite antioxidant is added, the mass percentage concentration of ascorbic acid in the system is 0.05-0.2%, and the mass percentage concentration of citric acid is 0.01-0.1%.

7. The method according to claim 1, characterized in that, In step (2), the ascorbic acid-citric acid composite antioxidant is a mixture of ascorbic acid and citric acid in a mass ratio of 2:

1.

8. The method according to claim 1, characterized in that, In step (2), the low-oxygen environment is defined as dissolved oxygen ≤0.5 ppm.

9. The method according to claim 1, characterized in that, In step (2), the chelation pH is 3-5, the chelation reaction temperature is 40-60℃, and the reaction is carried out for 1-4 hours under nitrogen protection.

10. The method according to claim 1, characterized in that, In step (3), membrane separation is performed using a membrane with a molecular weight cutoff of 10 kDa.

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