Preparation method and application of algal hydrothermal carbon material

Abstract

This invention discloses a method for preparing and applying algal hydrothermal char material. Algae are mixed with a reaction medium at a solid-liquid ratio of 50-100 g / L. After thorough stirring, the mixture is reacted under autogenous pressure and at a temperature of 130-150°C for 3-5 hours. After the reaction, the mixture is filtered, washed, dried, and ground to obtain the algal hydrothermal char material. The reaction medium is a mixed solution of ammonium phosphate and ammonia. The prepared algal hydrothermal char material can be used to improve the saline-alkali geochemical properties, reduce pH and salinity, and ultimately increase crop yield.

Description

Preparation method and application of algal hydrothermal carbon material Technical Field

[0001] This invention belongs to the field of activated carbon technology, specifically relating to a method for preparing and applying algal hydrothermal carbon materials. Background Technology

[0002] By controlling the thermal conversion of biomass under anaerobic or hypoxic conditions, a solid product with extremely rich carbon content—biochar material—is obtained. Due to its high carbon content, well-developed pores, and high stability, it is considered a high-quality raw material for soil improvement, ion adsorption, water purification, and carbon emission mitigation.

[0003] Pyrolysis is a common method for biochar preparation. Compared with high-temperature dry pyrolysis, hydrothermal wet pyrolysis is characterized by its ability to treat waste biomass with high water content, mild reaction conditions, simple processing equipment, convenient operation, and strong adjustability in application scale, making it one of the important directions for the resource utilization of waste biomass.

[0004] Algal cells are high in protein and minerals. After carbonization, the pyrolysis of proteins produces abundant porous structures and carbon-nitrogen and nitrogen-oxygen functional groups, exhibiting good hydrophilicity. They can adsorb various nutrients, which are then slowly released after being applied to the soil, thereby improving soil nutrient utilization.

[0005] Currently, hydrothermal carbonization technology is an economical waste biomass conversion technology that has received increasing attention. However, the reaction medium usually uses strong acids, bases and metal salts. For example, Chinese patent CN 117069103 A uses phosphoric acid to carry out a mixed reaction in a sealed hydrothermal reactor to obtain mixed reactants. The reaction medium uses strong acids, bases or metal salts, which are harmful to the environment and products. Moreover, the synthesis steps are often quite complicated, the hydrothermal temperature is usually above 150℃, and the energy consumption is relatively high.

[0006] In addition, the search revealed few reports on the effects of applying algal hydrothermal carbon to saline-alkali land on soil pH, salinity, physicochemical properties, crop growth, and nutrient utilization efficiency. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing and applying algal hydrothermal carbon materials, so as to overcome the shortcomings of the prior art.

[0008] The present invention adopts the following technical solution:

[0009] A method for preparing an algal hydrothermal carbon material includes the following steps: mixing algae with a reaction medium at a solid-liquid ratio of 50-100 g / L, stirring thoroughly, and reacting under autogenous pressure and at a temperature of 130-150°C for 3-5 hours. After the reaction is completed, the algae are filtered, washed, dried, and ground to obtain the algal hydrothermal carbon material. The reaction medium is a mixed solution of ammonium phosphate and ammonia.

[0010] Furthermore, the algae include cyanobacteria, green algae, algae-water mixtures, or algae sludge.

[0011] Furthermore, the mass ratio of ammonium phosphate to ammonia is 2-4:1.

[0012] Preferably, the mass ratio of ammonium phosphate to ammonia is 3:1.

[0013] Preferably, the solid-liquid ratio of the algae to the reaction medium is 70 g / L.

[0014] Preferably, the algae are mixed with the reaction medium, stirred thoroughly, and then transferred to the inner liner of the reactor. The mixture is then reacted for 4 hours under autogenous pressure and at a temperature of 140°C.

[0015] Further, after filtration and separation, the sample was washed three times with distilled water and dried in a vacuum oven at 60°C for 4 hours.

[0016] Furthermore, the dried algae hydrothermal charcoal is ground into powder with a particle size of 0.5~1 mm using a mortar and passed through a 16-mesh sieve.

[0017] The present invention also provides the application of the algal hydrothermal carbon material prepared by the above preparation method in the improvement of saline-alkali soil.

[0018] This invention also provides the application of the algal hydrothermal carbon material prepared by the above method in corn production in saline-alkali land.

[0019] The beneficial effects of this invention are as follows: This invention uses a mixed solution of ammonium phosphate and ammonia water as the reaction medium, replacing traditional strong acid-base and metal salt media. It utilizes the ammonia gas generated by the hydrothermal reaction at 130-150°C to increase the internal pressure of the reactor. Compared to hydrothermal reactions using other reaction media, which require temperatures of 180°C or even higher, the process of this invention can be carried out at a relatively lower hydrothermal reaction temperature, resulting in milder reaction conditions. Furthermore, this invention achieves carbonization and phosphate group functionalization modification through a one-step hydrothermal reaction, optimizing the preparation process of hydrothermal carbon materials, improving the carbon conversion rate of raw materials, and enhancing the adsorption and ion exchange performance of the hydrothermal carbon product. This allows for the preservation of more nutrients in algal cells. When applied to saline-alkali soils, the acidic hydrothermal carbon effectively reduces soil pH and salinity, significantly improving the soil's physicochemical properties and increasing crop yield. Attached Figure Description

[0020] Figure 1 is an electron microscope image of the algal hydrothermal carbon material prepared according to the present invention. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0022] Example 1: Preparation of algal hydrothermal carbon materials

[0023] The algae used in this invention were collected from the coastal area of ​​Jinmeng Bay Beach in Qinhuangdao. The green algae were harvested by boat, rinsed several times with distilled water, and then naturally air-dried for 2-3 days before being chopped into pieces. First, a mixed solution of ammonium phosphate and ammonia water at a mass ratio of 3:1 was prepared as the reaction medium. Then, the algae raw material was placed in an Erlenmeyer flask, and the reaction medium was added. The solid-liquid ratio of algae to reaction medium was set to 70 g / L. After stirring thoroughly for 1.0 h, the mixture was transferred to the inner liner of a reaction vessel and reacted at autogenous pressure and 140°C for 4 h. After the reaction was completed, the product was collected by vacuum filtration, washed three times with distilled water, dried in a vacuum oven for 4 h, ground, and cooled to room temperature to obtain the hydrothermal carbon material.

[0024] The electron microscope image in Figure 1 shows that the synthesized hydrothermal carbon material is in the form of thin sheets with abundant porous structures. The synthesized hydrothermal carbon material has a moisture content of less than 2%, a particle size of 0.51 mm, a carbon content of 46-50%, a phosphorus content of 6.0-7.5%, and a nitrogen content of 7.5-8.5%.

[0025] Example 2: Yield of Green Algae Hydrothermal Carbon Material

[0026] Same as Example 1, except that different hydrothermal treatment conditions are used, as shown in Table 1.

[0027] Table 1. Yield of hydrothermal carbon under different treatment conditions

[0028] .

[0029] As shown in Table 1, the hydrothermal carbon yield is highest at a hydrothermal temperature of 140℃, and gradually decreases as the hydrothermal temperature increases. Lower temperatures are not conducive to generating higher autogenous pressure, which also reduces the hydrothermal carbon yield. Furthermore, the hydrothermal carbon yield using the mixed solvent as the hydrothermal reaction medium in this embodiment is significantly higher than that using phosphoric acid or ammonia as the reaction medium.

[0030] Example 3: Characteristics of Green Algae Hydrothermal Charcoal

[0031] The hydrothermal carbon prepared in Example 1 was subjected to property testing. The pH of the hydrothermal carbon material was determined according to the standard GB / T12496.7-1999, "Test Methods for pH Value of Wood-based Activated Carbon". The cation exchange capacity (CEC) was determined using the ammonium chloride-ammonium acetate method. The C, H, O, N, and P contents of the composite material were tested using an elemental analyzer, and the specific surface area and pore volume of the hydrothermal carbon were determined using a specific surface area analyzer.

[0032] Table 2 shows that hydrothermal carbon materials have high nitrogen and phosphorus content, large cation exchange capacity, pH 6.1, large specific surface area and pore volume, and can absorb sodium ions in saline-alkali soil and reduce soil pH.

[0033] Table 2. pH, cation exchange capacity and physicochemical properties of hydrothermal charcoal made from green algae

[0034] .

[0035] Example 4: Application of algal hydrothermal carbon in reducing pH of saline-alkali land

[0036] The field trial was conducted at the Huanghua City Saline-Alkali Land Improvement Demonstration Base. One cornfield was selected and divided into two plots: an experimental group and a control group. Each experimental plot had an area of ​​1 mu (667m²). 2 / mu), the corn variety used is Nongda 372.

[0037] When sowing on May 4, 2022, apply 100 kg / mu of algal hydrothermal char material as a base fertilizer in combination with organic fertilizer and compound fertilizer (17-17-17). Apply the algal hydrothermal char material in trenches in saline-alkali soil and then cover it with soil (to reduce the erosion of hydrothermal char by sunlight and wind).

[0038] The experimental group was treated with hydrothermal char prepared in Example 1 15 days before corn planting, at a rate of 100 kg / mu, applied simultaneously with the seed fertilizer in furrows. The control group without hydrothermal char was tested at the same time as the experimental group.

[0039] Before applying hydrothermal charcoal, soil samples were collected from multiple locations in the experimental and control groups at a depth of 15 cm to determine the average pH value. After 60 days, soil samples were collected from multiple locations in the experimental and control groups to determine the average pH value. The results are shown in Table 3.

[0040] As shown in Table 3, the average pH value of the experimental group 60 days after corn planting was 0.89 lower than that 15 days before corn planting, which was significantly lower than that of the control group. This indicates that the slightly acidic hydrothermal carbon material can significantly reduce the pH and salinity of the soil.

[0041] Table 3. Effects of algal hydrothermal carbon on pH of saline-alkali land

[0042] .

[0043] Example 5: Application of hydrothermal charcoal in increasing maize crop yield

[0044] The field maize yield test consisted of three treatments: the organic fertilizer treatment used humic acid water-soluble fertilizer, and the hydrothermal charcoal material was from Example 1. The planting process was the same as in Example 4. The results showed that the maize yield after applying hydrothermal charcoal was higher than that of the unfertilized treatment, with an increase rate of over 30.83%. Compared with the humic acid organic fertilizer treatment, the maize yield was also significantly higher, with an increase rate of over 10.74%.

[0045] Table 4. Effects of different treatments on maize yield

[0046] .

[0047] Example 6: Application of hydrothermal carbon materials in improving soil physical and chemical properties

[0048] The large-scale field trial was conducted in saline-alkali land in Huanghua City. One maize experimental field was selected and divided into two smaller plots: an experimental group and a control group. Each experimental plot had an area of ​​2 mu (approximately 0.33 hectares). The maize variety used was Nongda 108. The planting density was 4000 plants / mu (approximately 2000 plants / hectare), and conventional management was implemented.

[0049] The experimental group applied the hydrothermal char prepared in Example 1 1-2 days before corn planting at a rate of 100 kg / mu, applying the fertilizer in furrows and simultaneously with the seed fertilizer.

[0050] Soil samples were collected from the topsoil layer (15 cm) and the content of major elements in the soil was determined, serving as a blank. At the time of corn harvest, the yield was measured and soil samples were collected from multiple locations to determine the soil physicochemical indicators. The results are shown in Table 5.

[0051] Table 5. Effects of hydrothermal carbon on soil physicochemical properties

[0052] .

[0053] Table 5 shows that the application of hydrothermal carbon significantly increased the content of total nitrogen, available phosphorus, and available potassium in the soil, as well as the content of the micronutrients Ca. 2+ Mg 2+ Zn 2+ Mn 2+ The content of all these elements increased significantly. Algal hydrothermal biomass significantly increased the nutrient elements in saline-alkali soils, which can reduce the amount of chemical fertilizers used and effectively promote crop growth.

Claims

1. A method for preparing an algal hydrothermal carbon material, characterized in that, The process includes the following steps: mixing algae with a reaction medium at a solid-liquid ratio of 70 g / L, stirring thoroughly, and reacting at autogenous pressure and 140°C for 3-5 h. After the reaction is completed, the algae are filtered, washed, dried, and ground to obtain algal hydrothermal carbon material. The reaction medium is a mixed solution of ammonium phosphate and ammonia water at a mass ratio of 3:

1.

2. The method for preparing algal hydrothermal carbon material according to claim 1, characterized in that, After the reaction was complete, the sample was washed three times with distilled water and dried in a vacuum oven at 60°C for 4 hours.

3. The method for preparing algal hydrothermal carbon material according to claim 2, characterized in that, The dried algae hydrothermal carbon material is ground into powder with a particle size of 0.5~1 mm using a mortar and pestle, and then passed through a 16-mesh sieve.

4. The application of an algal hydrothermal carbon material prepared by the preparation method according to any one of claims 1 to 3 in improving saline-alkali soil.

5. The application of an algal hydrothermal carbon material prepared by any one of claims 1 to 3 in corn production in saline-alkali land.

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