Method for preparing water-soluble lignin chelated calcium fertilizer from concentrated black liquor

Abstract

The application discloses a method for preparing water-soluble lignin chelated calcium fertilizer from concentrated black liquor, and belongs to the technical field of chelated fertilizer preparation.The technical points of the application are as follows: based on the hydrophilicity and chelation of small-molecule lignin in the black liquor, CO2 acid precipitation and calcium chloride chelation are used to prepare a new type of environmentally-friendly calcium fertilizer.The main technical points include: the black liquor is concentrated to a solid content of 30-50%, CO2 gas is introduced for acid precipitation reaction under certain conditions, the precipitate is separated by centrifugation, calcium chloride solid is added to the supernatant under stirring until no precipitate is generated, the precipitate is separated by centrifugation, anhydrous ethanol is added to the supernatant at a volume ratio of 1:1, the mixture is uniformly mixed and then centrifuged, the precipitate is washed with 50% ethanol solution and then dried to obtain the water-soluble lignin chelated calcium fertilizer.The application provides a water-soluble lignin chelated calcium fertilizer preparation technology which is simple, efficient, economical and has great industrialization potential, and opens up a new conversion path for conveniently and effectively converting natural high-molecular material lignin into efficient fertilizer.

Description

Technical Field

[0001] This invention relates to a method for preparing chelated fertilizer, specifically a method for preparing water-soluble lignin chelated calcium fertilizer from concentrated black liquor, belonging to the technical field of preparing chelated fertilizer using black liquor lignin. Background Technology

[0002] Pulp and paper making is one of the pillar industries of my country's national economy. The papermaking process can be divided into three stages: pulping, bleaching, and papermaking, with pulping being the most significant pollutant-generating stage. Statistics show that 1 to 10 tons of waste liquor are generated for every ton of pulp produced. my country's papermaking industry primarily uses alkaline pulping, and the waste liquor, due to its dark brown color, is also known as black liquor. Black liquor is rich in complex components such as lignin and its derivatives, hemicellulose, and cellulose derivatives. If discharged directly into the natural environment without treatment, it will directly lead to darkening of water color and deterioration of odor, resulting in overall water quality deterioration. Furthermore, the high alkalinity of black liquor raises the pH value of water bodies, disrupting the acid-base balance of the ecosystem. Simultaneously, its high biochemical oxygen demand (BOD) consumes large amounts of dissolved oxygen in water bodies, posing a serious threat to aquatic ecosystems. Harmful chemicals in black liquor can also accumulate through the food chain, ultimately causing irreversible damage to animal and human health. Therefore, how to treat black liquor in a clean, efficient, and economical manner has become a key challenge restricting the industry's development. Alkali lignin can be obtained after separating and purifying black liquor from papermaking. Currently, there are various methods for lignin extraction, among which acid precipitation is technically mature. Commonly used acid precipitation agents include sulfuric acid, hydrochloric acid, nitric acid, and carbon dioxide. However, due to the strong corrosiveness of strong acids such as sulfuric acid to equipment, their application is somewhat limited. In contrast, carbon dioxide, with its moderate acidity, reduces equipment corrosion while achieving good acid precipitation results, making it a promising alternative.

[0003] Lignin is an important component of lignocellulose, primarily composed of three structural units: syringylpropane, p-hydroxyphenylpropane, and guaiacolylpropane. The lignin molecule also contains numerous reactive functional groups, such as methoxy, hydroxyl, carboxyl, and carbonyl groups, exhibiting certain reactivity. Currently, in agriculture, lignin serves as a plant growth regulator, fertilizer synergist, soil conditioner, and metal chelator, among other functional materials. Furthermore, lignin-based fertilizers, due to their wide availability of raw materials, low cost, excellent nutrient slow-release properties, and environmentally friendly characteristics, are gradually becoming an important research direction for sustainable agricultural development. However, the highly complex molecular structure and heterogeneous molecular weight distribution of lignin are key factors restricting its large-scale application and high-value-added transformation. These characteristics not only increase the technical difficulty of lignin processing and utilization but also reduce its efficiency and effectiveness in practical applications, thus limiting the widespread promotion and in-depth application of lignin in agriculture.

[0004] Calcium fertilizer is crucial for maintaining cell wall stability and strength, promoting growth and metabolism, improving fruit firmness and quality, and enhancing plant resistance to adverse conditions. Lignin has excellent chelating properties and can complex with Ca ions to form lignin-chelated calcium fertilizer. Lignin-chelated calcium fertilizer overcomes the disadvantage of precipitation when ordinary calcium fertilizer is combined with other fertilizers, thus improving fertilizer efficiency and increasing yield and income. It is also a non-toxic and biodegradable fertilizer, and its production and use do not pollute the environment, meeting the requirements of modern green agricultural development. Given the challenges of reusing black liquor from papermaking and the enormous potential of lignin as a fertilizer, it is essential to design a new method for preparing water-soluble lignin-chelated calcium fertilizer from concentrated black liquor. This method should be simple to operate, low-cost, and easy to scale up for mass production, thus broadening its applications. Summary of the Invention

[0005] To address the problems existing in the background technology, the purpose of this invention is to provide a new method for preparing water-soluble lignin chelated calcium fertilizer from concentrated black liquor that is simple to operate, highly safe, low in energy consumption, and has a high yield. This method prepares an environmentally friendly new type of water-soluble lignin chelated calcium fertilizer through CO2 acid precipitation and calcium chloride chelation, which is conducive to the high-value utilization of lignin from black liquor.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for preparing water-soluble lignin-chelated calcium fertilizer from concentrated black liquor includes the following steps:

[0008] S1: Place concentrated black liquor with a solid content of 30-50% into a reaction vessel, introduce CO2 gas at a certain pressure into it, and react at a certain temperature for a period of time; after the reaction is completed, cool the reaction vessel to room temperature to obtain a dark brown liquid product for later use.

[0009] S2: Centrifuge the product prepared in step S1 to separate the supernatant; add a certain amount of calcium chloride to the supernatant, stir evenly, centrifuge to separate the supernatant, and set aside for later use;

[0010] S3: Add the appropriate amount of anhydrous ethanol to the supernatant prepared in step S2, mix well, centrifuge to separate the light brown precipitate, wash with 50% ethanol solution, and freeze-dry to obtain water-soluble lignin calcium fertilizer.

[0011] Preferably, the black liquor is waste liquid produced by the caustic soda process or sulfate process in the papermaking industry.

[0012] Preferably, the mass ratio of black liquor to CO2 added in step S1 is 1:0.02 to 0.12.

[0013] Preferably, the reaction temperature in step S1 is 30–60°C.

[0014] Preferably, the reaction time in step S1 is 0.5 to 2 hours.

[0015] Preferably, the mass ratio of calcium chloride to supernatant in step S2 is 1:5 to 10.

[0016] Preferably, the volume ratio of the supernatant to anhydrous ethanol in step S3 is 1:1.

[0017] Preferably, the number of cleaning cycles in step S3 is no less than 3.

[0018] Compared with existing detection technologies, the beneficial effects of this invention are reflected in:

[0019] 1. The present invention provides a method for preparing water-soluble lignin chelated calcium fertilizer using concentrated black liquor. Based on the hydrophilicity and chelating properties of small molecule lignin in black liquor, the lignin chelating ability is enhanced by CO2 acid precipitation and calcium chloride chelation, thereby preparing an environmentally friendly water-soluble lignin chelated calcium fertilizer.

[0020] 2. The water-soluble lignin chelated calcium fertilizer prepared by this invention has good water solubility, leaves no residue, and is easy to use. It can better maintain the effectiveness of fertilizer and allow it to be released slowly, which is beneficial to improving the utilization rate of fertilizer nutrients and releasing nutrients fixed in the soil. The chelated fertilizer prepared by using modified lignin as a chelating agent, through the synergistic effect of lignin and trace elements, is conducive to the granulation and disintegration of fertilizer in water, ensuring the rapid and long-lasting effect of fertilizer during use.

[0021] 3. The method of preparing water-soluble lignin chelated calcium fertilizer using concentrated black liquor of the present invention utilizes waste liquor generated from the caustic soda process or sulfate process in the papermaking industry as raw material. This raw material is widely available, renewable, and environmentally friendly. The preparation method is simple to operate, low in cost, and suitable for large-scale industrial application and promotion. Attached Figure Description

[0022] Figure 1 This is a product diagram showing the solid-liquid state of the water-soluble lignin calcium fertilizer of the present invention;

[0023] Figure 2 This is a scanning electron microscope image of the water-soluble lignin calcium fertilizer of the present invention;

[0024] Figure 3 The infrared spectrum of the water-soluble lignin calcium fertilizer of the present invention is shown below.

[0025] Figure 4 This is a comparison of the stem and root growth of rice plants 10 days after spraying different concentrations of water-soluble lignin calcium fertilizer in Example 5 of the present invention.

[0026] Figure 5 This is a bar chart showing the stem and root length growth indicators of rice plants 10 days after spraying different concentrations of water-soluble lignin calcium fertilizer in Example 5 of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] 100L of concentrated black liquor with a solid content of 30% was placed in a 200L reactor. CO2 gas at 0.5MPa was introduced, and the reaction was carried out at 30℃ for 0.5h. After the reaction, the reactor was cooled to room temperature, the product was removed, and the supernatant was separated by centrifugation. 800g of calcium chloride was added in batches, stirred thoroughly until no more precipitate formed. The supernatant was then separated by centrifugation, and anhydrous ethanol was added to it at a 1:1 volume ratio. After mixing thoroughly, a light brown precipitate was separated by centrifugation, washed three times with a 50% ethanol solution, and freeze-dried to obtain water-soluble lignin calcium fertilizer. The Ca content in the solid was determined to be 18.96%.

[0030] When applied to hydroponically grown bok choy, compared to untreated black liquor alkali lignin chelated calcium fertilizer, the root length of bok choy increased from 8.8±0.3cm to 12.2±0.4cm, with no dry heart phenomenon occurring.

[0031] Example 2

[0032] 100L of concentrated black liquor with a solid content of 40% was placed in a 200L reactor. CO2 gas at 1.0 MPa was introduced, and the reaction was carried out at 40℃ for 1 hour. After the reaction, the reactor was cooled to room temperature, the product was removed, and the supernatant was separated by centrifugation. 850g of calcium chloride was added in batches, stirred thoroughly until no more precipitate formed. The supernatant was then separated by centrifugation, and anhydrous ethanol was added to it at a 1:1 volume ratio. After mixing thoroughly, a light brown precipitate was separated by centrifugation, washed three times with a 50% ethanol solution, and freeze-dried to obtain water-soluble lignin calcium fertilizer. The Ca content in the solid was determined to be 19.84%.

[0033] Example 3

[0034] 100L of concentrated black liquor with a solid content of 45% was placed in a 200L reactor. CO2 gas at 1.5MPa was introduced, and the reaction was carried out at 50℃ for 1.5 hours. After the reaction, the reactor was cooled to room temperature, the product was removed, and the supernatant was separated by centrifugation. 900g of calcium chloride was added in batches, stirred thoroughly until no more precipitate formed. The supernatant was then separated by centrifugation, and anhydrous ethanol was added to it at a 1:1 volume ratio. After mixing thoroughly, a light brown precipitate was separated by centrifugation, washed three times with a 50% ethanol solution, and freeze-dried to obtain water-soluble lignin calcium fertilizer. The Ca content in the solid was determined to be 20.02%.

[0035] Example 4

[0036] 100L of concentrated black liquor with a solid content of 50% was placed in a 200L reactor. CO2 gas at 2.0 MPa was introduced, and the reaction was carried out at 60℃ for 2 hours. After the reaction, the reactor was cooled to room temperature, the product was removed, and the supernatant was separated by centrifugation. 1000g of calcium chloride was added in batches, stirred thoroughly until no more precipitate formed. The supernatant was then separated by centrifugation, and anhydrous ethanol was added to it at a 1:1 volume ratio. After mixing thoroughly, a light brown precipitate was separated by centrifugation, washed three times with a 50% ethanol solution, and freeze-dried to obtain water-soluble lignin calcium fertilizer. The Ca content in the solid was determined to be 21.05%.

[0037] Example 5

[0038] Rice Fertilizer Effect Experiment: Plump and uniform rice seeds were selected, disinfected by soaking in 3% H2O2 for 15 minutes, then repeatedly rinsed with distilled water. After soaking in distilled water for 24 hours, the seeds were placed in germination boxes lined with germination paper and incubated in a dark incubator at 30℃ for germination treatment. Seeds with uniform growth were transplanted into 6-well hydroponic boxes and cultured with Hoagland's nutrient solution. They were placed in a light incubator (culture temperature: daytime 25℃ / nighttime 20℃, light intensity: 14-10h, light intensity 10000lx, relative humidity 60-80%), with the nutrient solution changed every 4 days. After the rice plants adapted to the hydroponic environment for 3 days after transplanting, different rice treatment groups were set up: CK, 0.1% lignin chelated calcium, 0.2% lignin chelated calcium, and 0.3% lignin chelated calcium. After 10 days of culture, rice plants were collected, and physiological indicators such as stem length and root length were measured. A comparison of stem and root length growth of rice plants 10 days after spraying with different concentrations of water-soluble calcium lignin fertilizer is shown in the attached image. Figure 2 Figure 2 The images shown in this example are illustrated in Table 1 below, and the actual measurement data is shown in Table 1.

[0039] Table 1 Comparison of rice plant growth 10 days after spraying with different concentrations of water-soluble lignin calcium fertilizer.

[0040] project CK 0.1% lignin-chelated calcium 0.2% lignin-chelated calcium 0.3% lignin-chelated calcium Stem length (cm) 10.06 13.7 22.83 12.28 Root length (cm) 5.07 8.51 9.68 8.91

[0041] Experimental analysis showed that, compared to the control group (CK) without calcium fertilizer, the stem length of all three treatment groups treated with lignin-chelated calcium fertilizer increased, with the 0.2% treatment group showing the most significant increase, reaching a stem length of 22.83 cm. Root length also increased in all three groups, with the 0.2% treatment group reaching a root length of 9.68 cm. The bar charts showing the stem and root length growth indicators of rice plants 10 days after spraying different concentrations of water-soluble lignin-calcium fertilizer are attached. Figure 3 .

[0042] In summary, the water-soluble lignin-calcium fertilizer prepared by this invention exhibits high lignin calcium ion chelation, effectively promoting crop growth and development and enhancing nutrient conversion and utilization. The preparation method is environmentally friendly, simple to operate, and low-cost, making it suitable for large-scale industrial application and promotion. It opens up a convenient and effective conversion pathway for transforming the natural polymer material lignin into a high-efficiency fertilizer.

[0043] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing water-soluble lignin-chelated calcium fertilizer from concentrated black liquor, characterized in that... Includes the following steps: S1: Place concentrated black liquor with a solid content of 30-50% into a reaction vessel, introduce CO2 gas at a certain pressure into it, and react at a certain temperature for a period of time; after the reaction is completed, cool the reaction vessel to room temperature to obtain a dark brown liquid product for later use. S2: Centrifuge the product prepared in step S1 to separate the supernatant, add a certain amount of calcium chloride and stir evenly, centrifuge to separate the supernatant, and set aside for later use; S3: Add the appropriate amount of anhydrous ethanol to the supernatant prepared in step S2, mix well, centrifuge to separate the light brown precipitate, wash with 50% ethanol solution, and freeze-dry to obtain water-soluble lignin calcium fertilizer. The concentrated black liquor mentioned above is a concentrated liquid of waste liquor produced by the caustic soda process or sulfate process in the papermaking industry. The mass ratio of black liquor to CO2 added in step S1 is 1:0.02~0.12; The mass ratio of calcium chloride to supernatant in step S2 is 1:5~10; The pressure of CO2 introduced in step S1 is 0.5–2 MPa; The reaction time in step S1 is 0.5 to 2 hours.

2. The method for preparing water-soluble lignin-chelated calcium fertilizer from concentrated black liquor according to claim 1, characterized in that: The reaction temperature in step S1 is 30~60 ℃.

3. The method for preparing water-soluble lignin-chelated calcium fertilizer from concentrated black liquor according to claim 1, characterized in that: The volume ratio of the supernatant to anhydrous ethanol in step S3 is 1:

1.

4. The method for preparing water-soluble lignin-chelated calcium fertilizer from concentrated black liquor according to claim 1, characterized in that: The number of cleaning cycles described in step S3 shall not be less than 3.

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