A humic acid rich in aromatic oxygen and its preparation method

Abstract

The present invention discloses a humic acid rich in aromatic oxygen and a preparation method thereof, belonging to the technical field of general methods in organic chemistry. By using a silica-supported cobalt oxide-manganese oxide-magnesium oxide catalyst in combination with a hydrogen peroxide solution, the present invention can selectively break and destroy the carboxyl structure generated during the oxidation of humic acid, while maximizing the retention of the aromatic ring structure of humic acid. The oxygen atoms exposed after the carboxyl group is broken are connected to the undamaged benzene ring, thereby targeting an increase in the aromatic oxygen content of humic acid. When the humic acid treated with the oxidant in the present invention is mixed with urea, it can effectively reduce the ammonia volatilization loss of urea and enhance the adsorption of soil ammonium nitrogen, thereby retaining more nitrogen in the soil, improving the nitrogen supply intensity of the soil, and reducing urea loss.

Description

Technical Field

[0001] The present invention belongs to the technical field of general methods in organic chemistry, and particularly relates to a humic acid rich in aromatic oxygen and a preparation method thereof. Background Art

[0002] Urea is the most important nitrogen fertilizer variety in China, accounting for about 65% of the total nitrogen fertilizer consumption. After urea is applied to the soil, it will be rapidly hydrolyzed and transformed under the action of urease. In addition to being absorbed by crops and retained by the soil, part of the nitrogen is lost through ammonia volatilization, nitrification, denitrification, runoff and leaching, etc., thus reducing the fertilizer utilization rate.

[0003] Humic acid is a natural organic polymer substance containing various functional groups such as aromatic rings, carboxyl groups, phenolic hydroxyl groups and methoxy groups. It has a macromolecular network structure, has a high cation exchange capacity and strong physical adsorption capacity. Some studies have shown that humic acid rich in aromatic oxygen can further adsorb nutrients and water in the soil, stabilize the activity of soil urease, promote the growth of crop roots and nutrient absorption, improve nutrient utilization rate, and play an important role and significance in the sustainable development of agriculture. At the same time, the presence of aromatic oxygen functional groups can inhibit the activity of microorganisms and slow down the decomposition of humic acid by microorganisms, making the degradation rate of humic acid in the soil relatively slow, so as to maximize the synergistic ability of humic acid.

[0004] To increase the aromatic oxygen content of humic acid, oxidation means are usually used to oxidize humic acid. After traditional oxidation means (such as HNO3, H2SO4, H2O2, etc.), mainly the oxygen content and carboxyl content of humic acid are increased, but there is disorder in the modification direction. During the oxidation process, the oxidant will damage the aromatic ring structure of humic acid, resulting in a significant reduction in its aromaticity, and the increase in aromatic oxygen content is relatively small. It is difficult to significantly increase the aromatic oxygen content of humic acid in a targeted manner. And breaking the carboxyl structure generated during the oxidation process of humic acid while maximizing the retention of the aromatic ring structure of humic acid is the difficulty in targeted improvement of the aromatic oxygen of humic acid. Adding a catalyst with selective catalytic ability during the oxidation process is expected to achieve connecting the oxygen atoms exposed after a large number of carboxyl groups are broken to the undamaged benzene ring, thereby increasing the aromatic oxygen content of humic acid in a targeted manner. Summary of the Invention

[0005] In view of the above-mentioned prior art, the present invention provides a humic acid rich in aromatic oxygen and a preparation method thereof to solve the technical problem of difficult targeted modification of the carboxyl structure of humic acid to increase its aromatic oxygen content.

[0006] To achieve the above object, the technical solution adopted by the present invention is to provide a method for preparing a humic acid rich in aromatic oxygen, comprising the following steps:

[0007] (1) Dissolve humic acid in a sodium hydroxide solution with a concentration of 2 wt%, and prepare a sodium humate solution with a concentration of 0.1 - 0.2 g / mL;

[0008] (2) Under stirring conditions, add the humic acid-modified oxidant to the sodium humate solution, and react at 45 - 55 °C for 90 - 150 min; then cool to room temperature in an ice-water bath; the humic acid-modified oxidant includes a solid catalyst and a hydrogen peroxide solution; the solid catalyst is a cobalt oxide-manganese oxide-magnesium oxide catalyst supported on silica, and its chemical composition is Co3O4-Mn3O4-MgO@SiO2.

[0009] (3) Separate the liquid and freeze-dry to obtain the product.

[0010] Based on the above technical solution, the present invention can also be improved as follows.

[0011] Further, the material ratio of the solid catalyst to the hydrogen peroxide solution in the humic acid-modified oxidant is 1 g: 75 - 85 mL.

[0012] Further, the solid catalyst is prepared through the following steps:

[0013] S1: Dissolve cetyltrimethylammonium bromide in water to prepare a substrate solution with a concentration of 0.02 - 0.05 mol / L;

[0014] S2: Add silicate, cobalt salt, manganese salt, and magnesium salt to the substrate solution, stir for 0.5 - 1 h, then adjust the pH of the system to 8 - 10, and then age at 80 - 100 °C for 1 - 5 h, and then filter to collect the solid to obtain the precursor;

[0015] S3: Dry the precursor at 100 - 120 °C for 10 - 15 h, and then calcine at 280 - 320 °C for 3 - 8 h to obtain the product.

[0016] Further, the molar ratio of silicate, cobalt salt, manganese salt, and magnesium salt is 10:1 - 3:1 - 2:0.5 - 2; the material ratio of silicate to the substrate solution is 1 mol: 10 mL.

[0017] Further, the silicate is sodium silicate; the cobalt salt is cobalt chloride or cobalt nitrate; the manganese salt is manganese sulfate, manganese chloride, or manganese nitrate; the magnesium salt is magnesium sulfate, magnesium chloride, or magnesium nitrate.

[0018] Further, the aging temperature in S2 is 90 °C and the aging time is 3 h; the drying temperature in S3 is 110 °C, the drying time is 12 h, the calcination temperature is 300 °C, and the calcination time is 5 h.

[0019] Further, the mass concentration of the hydrogen peroxide solution is 0.5%.

[0020] Furthermore, the mass ratio of the dosage of the humic acid-modified oxidant to the mass of the humic acid based on the solid catalyst is 1:100.

[0021] Furthermore, in step (2), the reaction temperature is 50 °C and the reaction time is 120 min.

[0022] The present invention also discloses a humic acid rich in aromatic oxygen, which is prepared by the above preparation method.

[0023] The beneficial effects of the present invention are as follows:

[0024] 1. By using the silica-supported cobalt oxide-manganese oxide-magnesium oxide catalyst in combination with the hydrogen peroxide solution, the present invention can selectively break and destroy the carboxyl structure generated during the oxidation of humic acid, while maximizing the retention of the aromatic ring structure of humic acid. The oxygen atoms exposed after the carboxyl group is broken are connected to the undamaged benzene ring, thereby targeting an increase in the aromatic oxygen content of humic acid.

[0025] 2. When the humic acid treated with the oxidant in the present invention is mixed with urea, it can effectively reduce the ammonia volatilization loss of urea and enhance the adsorption of ammonium nitrogen in the soil, thereby retaining more nitrogen in the soil, improving the nitrogen supply intensity of the soil, and reducing urea loss. Description of the Drawings

[0026] Figure 1 It is the XPS C1s peak fitting diagram of HA, OHA and COHA;

[0027] Figure 2 It is the average double bond equivalent minus oxygen value of COHA, OHA and HA;

[0028] Figure 3 It is the average aromaticity index of COHA, OHA and HA;

[0029] Figure 4 It is the influence of COHA, OHA and HA on the urea ammonia volatilization rate;

[0030] Figure 5 It is the influence of COHA, OHA and HA on the cumulative amount of ammonia volatilization;

[0031] Figure 6 It is the influence of COHA, OHA and HA on the content of ammonium nitrogen in the soil during the urea conversion process. Detailed Embodiments

[0032] The following describes the specific embodiments of the present invention in detail with reference to the examples.

[0033] Example 1

[0034] A humic acid-modified oxidant, comprising a solid catalyst and a hydrogen peroxide solution, with the material ratio of the solid catalyst to the hydrogen peroxide solution being 1 g:80 mL; wherein, the mass concentration of the hydrogen peroxide solution is 0.5%; the solid catalyst is a cobalt oxide-manganese oxide-magnesium oxide catalyst supported on silica, with its chemical composition being Co3O4-Mn3O4-MgO@SiO2, and it is prepared through the following steps:

[0035] S1: Dissolve 6 mmol of cetyltrimethylammonium bromide (CTMAB) in 200 mL of distilled water, and ultrasonicate for 15 min to prepare a substrate solution with a concentration of 0.03 mol / L.

[0036] S2: Add 10 mmol of sodium silicate, 2 mmol of cobalt chloride, 1.5 mmol of manganese sulfate, and 1 mmol of magnesium sulfate to the substrate solution, stir for 0.5 h, then adjust the pH of the system to 9, and then age at 90 °C for 3 h. Subsequently, filter, collect the solid, and rinse it 3 times with hot water (90 °C) to obtain a precursor.

[0037] S3: Place the precursor in an oven at 110 °C and dry for 12 h, then calcine at 300 °C for 5 h to obtain the solid catalyst Co3O4-Mn3O4-MgO@SiO2.

[0038] Example 2

[0039] A humic acid-modified oxidant, comprising a solid catalyst and a hydrogen peroxide solution, with the material ratio of the solid catalyst to the hydrogen peroxide solution being 1 g:75 mL; wherein, the mass concentration of the hydrogen peroxide solution is 0.5%; the solid catalyst is a cobalt oxide-manganese oxide-magnesium oxide catalyst supported on silica, with its chemical composition being Co3O4-Mn3O4-MgO@SiO2, and it is prepared through the following steps:

[0040] S1: Dissolve 4 mmol of cetyltrimethylammonium bromide (CTMAB) in 200 mL of distilled water, and ultrasonicate for 15 min to prepare a substrate solution with a concentration of 0.02 mol / L.

[0041] S2: Add 10 mmol of sodium silicate, 1 mmol of cobalt nitrate, 2 mmol of manganese chloride, and 0.5 mmol of magnesium chloride to the substrate solution, stir for 0.5 h, then adjust the pH of the system to 8, and then age at 80 °C for 5 h. Subsequently, filter, collect the solid, and rinse it 3 times with hot water (80 °C) to obtain a precursor.

[0042] S3: Place the precursor in an oven at 100 °C and dry for 15 h, then calcine at 280 °C for 8 h to obtain the solid catalyst Co3O4-Mn3O4-MgO@SiO2.

[0043] Example 3

[0044] A humic acid modified oxidant, comprising a solid catalyst and a hydrogen peroxide solution, wherein the ratio of the solid catalyst to the hydrogen peroxide solution is 1 g: 85 mL; among them, the mass concentration of the hydrogen peroxide solution is 0.5%; the solid catalyst is a cobalt oxide-manganese oxide-magnesium oxide catalyst supported on silica, and its chemical composition is Co3O4-Mn3O4-MgO@SiO2, which is prepared through the following steps:

[0045] S1: Dissolve 10 mmol of cetyltrimethylammonium bromide (CTMAB) in 200 mL of distilled water, and ultrasonically treat for 15 min to prepare a substrate solution with a concentration of 0.05 mol / L;

[0046] S2: Add 10 mmol of sodium silicate, 3 mmol of cobalt chloride, 1 mmol of manganese nitrate, and 2 mmol of magnesium nitrate to the substrate solution, stir for 0.5 h, then adjust the pH of the system to 10, age at 100 °C for 1 h, then filter, collect the solid, and rinse it 3 times with hot water (100 °C) to obtain a precursor;

[0047] S3: Place the precursor in an oven at 120 °C, dry for 10 h, and then calcine at 320 °C for 3 h to obtain the solid catalyst Co3O4-Mn3O4-MgO@SiO2.

[0048] Experimental Example

[0049] The properties of the humic acid modified oxidants prepared in the three examples of the present invention are similar. Taking the humic acid modified oxidant prepared in Example 1 as an example, the properties of the humic acid modified oxidant are described.

[0050] Use the humic acid modified oxidant to carry out directional catalytic oxidation modification on humic acid to prepare humic acid rich in aromatic oxygen. The specific steps are as follows:

[0051] Dissolve 10 g of humic acid sample in 92 mL of a 2 wt% sodium hydroxide solution. Under continuous stirring, first add the solid catalyst Co3O4-Mn3O4-MgO@SiO2 (0.1 g) in the humic acid modified oxidant to the sodium humate solution, and then add the hydrogen peroxide solution (mass concentration 0.5%, 8 mL) in the humic acid modified oxidant. After mixing evenly, react at 50 °C for 2 h. Immediately after the reaction ends, quickly cool the reaction system in ice water to prevent the reaction from continuing; when it cools to room temperature, perform solid-liquid separation, collect the reaction solution, and freeze-dry the collected solution to obtain humic acid rich in aromatic oxygen, denoted as COHA.

[0052] Meanwhile, humic acid was oxidized with an H2O2 solution as the oxidant, and the specific steps are as follows:

[0053] Dissolve 10 g of humic acid sample in 92 mL of 2 wt% sodium hydroxide solution. While continuously stirring, add 8 mL of 5% H2O2 solution to the humic acid solution. After mixing evenly, react at 50 °C for 2 h. Immediately after the reaction ends, place the reaction system in ice water for rapid cooling to prevent the reaction from continuing. When it cools to room temperature, perform solid-liquid separation, collect the reaction solution, and conduct freeze-drying on the collected solution to obtain oxidized humic acid, denoted as OHA.

[0054] Using humic acid (HA) and OHA as controls, evaluate the directional modification ability of the catalyst in the present invention.

[0055] 1. Structural characteristics of directionally modified humic acid

[0056] The elemental compositions of different humic acids are shown in Table 1. Compared with HA, the carbon, hydrogen, and nitrogen contents of OHA and COHA decrease, while the oxygen content increases, indicating that the oxidation process reduces the carbon content of humic acid and increases the oxygen content. Compared with HA, the oxygen contents of OHA and COHA increase by 3.4% and 4.8% respectively, and the oxygen content of COHA is further increased compared with OHA, indicating that the introduction of Co3O4-Mn3O4-MgO@SiO2 into the oxidation system can further increase the oxygen content of humic acid. Compared with OHA, the carbon content of COHA increases, indicating that the introduction of Co3O4-Mn3O4-MgO@SiO2 protects the aromatic ring structure of humic acid and prevents the aromatic ring structure from being over-oxidized to generate carbon dioxide and escape.

[0057] Table 1 Elemental compositions of humic acids

[0058]

[0059] Perform C1s peak fitting on COHA, OHA, and HA, and the results are as Figure 1 shown. It can be seen from Figure 1 that compared with HA, the carboxyl group content of OHA increases by 35.56%, while the carboxyl group content of COHA decreases by 20.16%, indicating that the carboxyl group of COHA is directionally damaged. At the same time, it is found that compared with HA, the C-O (aromatic oxygen) contents of OHA and COHA increase by 21.89% and 44.99% respectively, further indicating that the combination of Co3O4-Mn3O4-MgO@SiO2 and H2O2 can directionally break and damage the carboxyl group structure of humic acid, oxidize the carboxyl group structure on the premise of protecting the aromatic carbon structure of humic acid, and connect oxygen atoms to the benzene ring, thereby directionally increasing the aromatic oxygen content of humic acid.

[0060] The average double bond equivalent oxygen reduction values and average aromaticity indices of COHA, OHA, and HA are shown in Figure 2 and Figure 3 respectively. The average double bond equivalent oxygen reduction value reflects the degree of unsaturation of the humic acid carbon skeleton. The higher the value, the lower the carboxyl group content in the molecule. As can be seen from Figure 2 , the carboxyl group content in COHA is the lowest, while the carboxyl group content in OHA oxidized by hydrogen peroxide alone is the highest. The average aromaticity index reflects the number of aromatic ring structures in the humic acid molecular structure. The higher the value, the more aromatic rings are contained in the molecule. As can be seen from Figure 3 , the number of aromatic rings in COHA is similar to that in HA, while the aromatic ring structure in OHA is further damaged and the number of aromatic rings is significantly reduced. The above results indicate that after the combination of Co3O4-Mn3O4-MgO@SiO2 and H2O2, the carboxyl group structure is directionally damaged, while the aromatic ring structure of humic acid is prevented from being significantly damaged, and the aromatic oxygen content of humic acid is directionally increased.

[0061] 2. Effects of Humic Acid on Ammonia Volatilization of Urea and Ammonium Nitrogen Content in Soil during Urea Transformation

[0062] Three kinds of humic acids (HA, OHA, and COHA) were added to molten urea at 130 °C at an addition amount of 0.5% (the mass of humic acid divided by the total mass of humic acid and urea), stirred for 30 s, cooled and crushed, and passed through a 100-mesh sieve to obtain three kinds of humic acid ureas HAU (corresponding to HA), OHAU (corresponding to OHA), and COHAU (corresponding to COHA). Urea without adding humic acid (U) was used as a control.

[0063] 0.068 g of U, HAU, OHAU, and COHAU were respectively mixed with 100 g of soil, added to culture bottles, and at the same time, the treatment without adding fertilizer was used as a control (CK). The soil water content was adjusted to 20%, and the samples were cultured in the dark in a climate chamber at 25 °C. During the culture period, the soil water content was maintained at 20% by the weighing method, and each treatment was repeated 3 times. NH3 was absorbed by the sponge absorption method on the 1st, 2nd, 3rd, 5th, and 7th days after culture, and the ammonium nitrogen content in the soil was measured on the 1st, 2nd, 3rd, 5th, 7th, 14th, and 28th days after culture.

[0064] The effects of humic acid on the ammonia volatilization rate and cumulative ammonia volatilization amount of urea are shown in Figure 4 and 5 respectively. As can be seen from Figure 4 and Figure 5It can be seen that compared with U, humic acid urea can reduce the average ammonia volatilization rate (2.95% - 12.94%) and the cumulative ammonia volatilization amount (2.1% - 16.26%). Compared with HAU, the average ammonia volatilization rate and the cumulative ammonia volatilization amount of OHAU increase by 2.46% and 1.33% respectively, while those of COHAU decrease by 8.22% and 13.41% respectively, indicating that COHA rich in aromatic oxygen can further reduce the ammonia volatilization loss of urea compared with HA.

[0065] The effect of humic acid on the content of ammonium nitrogen in soil during the urea conversion process is as Figure 6 shown. It can be seen from the figure that compared with U, the content of ammonium nitrogen in soil decreases on the 1st day of cultivation for humic acid urea, and the content of ammonium nitrogen in soil of COHAU further decreases compared with HAU. At the peak of ammonia volatilization on the 2nd day of cultivation, the content of ammonium nitrogen in HAU is lower, which is consistent with the result of the increased ammonia volatilization of HAU on the 2nd day. Compared with HAU, the content of ammonium nitrogen in soil of COHAU increases by 5.60%, indicating that COHA rich in aromatic oxygen can further improve the adsorption of ammonium nitrogen in soil compared with HA, retain more nitrogen in the soil, improve the nitrogen supply intensity of the soil, and reduce urea loss.

[0066] Although the specific implementation manners of the present invention have been described in detail with reference to the embodiments, it should not be construed as a limitation on the protection scope of this patent. Within the scope described in the claims, various modifications and deformations that can be made by those skilled in the art without creative efforts still fall within the protection scope of this patent.

Claims

1. A method for preparing humic acid rich in aromatic oxygen, characterized in that, It includes the following steps: (1) Dissolve humic acid in a sodium hydroxide solution with a concentration of 2 wt%, and prepare a sodium humate solution with a concentration of 0.1 - 0.2 g / mL; (2) Under stirring conditions, add the humic acid-modified oxidant to the sodium humate solution, and react at 45 - 55 °C for 90 - 150 min; then cool it to room temperature in an ice-water bath; the humic acid-modified oxidant includes a solid catalyst and a hydrogen peroxide solution, and the material ratio of the solid catalyst to the hydrogen peroxide solution is 1 g: 75 - 85 mL; the dosage of the humic acid-modified oxidant calculated by the solid catalyst and the mass ratio of humic acid is 1:100; the solid catalyst is a cobalt oxide-manganese oxide-magnesium oxide catalyst supported on silica, and its chemical composition is Co3O4-Mn3O4-MgO@SiO2; (3) Separate the liquid and freeze-dry it to obtain the product.

2. The method for preparing humic acid rich in aromatic oxygen according to claim 1, characterized in that, The solid catalyst is prepared through the following steps: S1: Dissolve cetyltrimethylammonium bromide in water to prepare a substrate solution with a concentration of 0.02 - 0.05 mol / L; S2: Add silicate, cobalt salt, manganese salt and magnesium salt to the substrate solution, stir for 0.5 - 1 h, then adjust the pH of the system to 8 - 10, and then age at 80 - 100 °C for 1 - 5 h, and then filter to collect the solid to obtain the precursor; S3: Dry the precursor at 100 - 120 °C for 10 - 15 h, and then calcine at 280 - 320 °C for 3 - 8 h to obtain the product.

3. The method for preparing humic acid rich in aromatic oxygen according to claim 2, characterized in that: The molar ratio of the silicate, cobalt salt, manganese salt and magnesium salt is 10:1 - 3:1 - 2:0.5 - 2; the material ratio of the silicate to the substrate solution is 1 mol:10 mL.

4. The method for preparing humic acid rich in aromatic oxygen according to claim 3, characterized in that: The silicate is sodium silicate; the cobalt salt is cobalt chloride or cobalt nitrate; the manganese salt is manganese sulfate, manganese chloride or manganese nitrate; the magnesium salt is magnesium sulfate, magnesium chloride or magnesium nitrate.

5. The method for preparing humic acid rich in aromatic oxygen according to claim 2, characterized in that: In S2, the aging temperature is 90 °C and the aging time is 3 h; in S3, the drying temperature is 110 °C, the drying time is 12 h, the calcination temperature is 300 °C, and the calcination time is 5 h.

6. The method for preparing humic acid rich in aromatic oxygen according to claim 1, characterized in that: The mass concentration of the hydrogen peroxide solution is 0.5%.

7. The method for preparing humic acid rich in aromatic oxygen according to claim 1, characterized in that: In step (2), the reaction temperature is 50 °C and the reaction time is 120 min.

8. A humic acid rich in aromatic oxygen, characterized in that: It is prepared by using the method for preparing humic acid rich in aromatic oxygen described in any one of claims 1 - 7.

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