A high hydrophobic low-rank coal and a preparation method thereof

Abstract

The application discloses high-hydrophobic low-rank coal and a preparation method thereof, and belongs to the technical field of surface modification. The specific steps of the preparation method comprise the following steps: adding low-rank coal, an oxidizing agent and an organic solvent I into a three-necked flask, uniformly stirring, carrying out reaction and post-treatment, and obtaining an intermediate product I; adding the intermediate product I, citric acid and DMF into the three-necked flask, uniformly stirring, carrying out reaction and post-treatment, and obtaining an intermediate product II; adding the intermediate product II and an organic solvent II into the three-necked flask, uniformly stirring, adding a catalyst and a hydrophobic modifier, carrying out reaction and post-treatment, and obtaining high-hydrophobic low-rank coal. Through three-step chemical reactions, more hydrophobic chains are introduced on the surface of the low-rank coal, and the hydrophobicity of the surface of the low-rank coal is enhanced. Compared with other surface modification modes, the hydrophobic chains are firmly combined on the surface of the low-rank coal and cannot fall off. The coalification degree of the low-rank coal after hydrophobic modification is improved, and the slurry performance of the modified low-rank coal can be improved.

Description

Technical Field

[0001] This invention belongs to the field of surface modification technology, specifically relating to a highly hydrophobic low-rank coal and its preparation method. Background Technology

[0002] Existing low-rank coal reserves are abundant, accounting for approximately 45.7% of proven coal reserves. Its main characteristics are high internal moisture, low calorific value, and high volatile matter content, leading to low direct combustion efficiency and resource waste. Water-coal slurry gasification can achieve clean and efficient utilization of carbonaceous materials, providing a development direction for the efficient utilization of low-rank coal. However, the surface of low-rank coal contains a large number of hydrophilic oxygen-containing functional groups and abundant pores, resulting in poor slurry-making performance and difficulty in producing high-concentration water-coal slurry, thus limiting its application in water-coal slurry. Therefore, it is necessary to upgrade low-rank coal to improve its slurry-making performance.

[0003] Currently, thermal modification and surface modification can be used to upgrade low-rank coal. Thermal modification involves heating the coal to improve its surface hydrophobicity and coalification by removing hydrophilic oxygen-containing functional groups. However, thermal modification typically requires additional equipment and consumes a large amount of energy, resulting in high costs for industrial applications. Surface modification involves adsorbing surfactants or hydrophobic materials onto the surface of low-rank coal to improve its surface properties. Surface modification is a milder upgrading method compared to thermal modification, but the adsorption between surfactants or hydrophobic materials and low-rank coal is weak and easily desorbed due to environmental influences. Therefore, it is necessary to develop other surface modification methods with stronger binding forces to improve the hydrophobicity of the low-rank coal surface and thus increase its pulp concentration. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention aims to provide a highly hydrophobic low-rank coal and its preparation method, so as to solve the technical problem that the low-rank coal has a large number of oxygen-containing functional groups on its surface, resulting in high viscosity and low slurry concentration in the prepared coal-water slurry, and that the existing surface-modified surfactants or hydrophobic materials have weak adsorption with low-rank coal and are easily desorbed by environmental influences.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] This invention provides a method for preparing highly hydrophobic low-rank coal, comprising the following steps:

[0007] S1: Mix low-rank coal, oxidant and organic solvent I and stir evenly to carry out carboxyl reaction. After the carboxyl reaction is completed, filter, wash and dry to obtain intermediate product I.

[0008] S2: Mix intermediate product I, citric acid and DMF evenly and carry out esterification reaction. After the esterification reaction is completed, filter, wash and dry to obtain intermediate product II.

[0009] S3: Mix intermediate product II and organic solvent II evenly, add catalyst and hydrophobic modifier, carry out epoxy reaction, filter, wash and dry after epoxy reaction to obtain high hydrophobic low-rank coal.

[0010] In a further step of the present invention, in S1, the low-rank coal is one or more of lignite, long-flame coal, non-caking coal, and sub-bituminous coal; the oxidant is one or more of ammonium persulfate and potassium persulfate; and the organic solvent I is one or more of toluene, xylene, and benzene.

[0011] In a further step of the present invention, in step S1, the mass ratio of the low-rank coal, the oxidant and the organic solvent I is 1:(0.1-0.3):(2-3).

[0012] In a further step of the present invention, in S1, the reaction temperature of the carboxyl group reaction is 60-70°C, and the reaction time of the carboxyl group reaction is 4-5 hours.

[0013] Furthermore, in step S2, the mass ratio of intermediate product I, citric acid, and DMF is 1:(0.5-0.8):(2-3).

[0014] In a further step of the present invention, in step S2, the reaction temperature of the esterification reaction is 60-70°C, and the reaction time of the esterification reaction is 2-3 hours.

[0015] In a further step of the present invention, in step S3, the organic solvent II is one or more of butyl acetate, methyl acetate, ethyl acetate, and propyl acetate; the catalyst is a mixture of triphenylphosphine and hydroquinone, wherein the mass ratio of triphenylphosphine to hydroquinone is (7-9):1; and the hydrophobic modifier is one or more of neodecanoic acid glycidyl ester, decanoic acid glycidyl ester, stearic acid glycidyl ester, laurate glycidyl ester, and palmitic acid glycidyl ester.

[0016] Furthermore, in step S3, the mass ratio of intermediate product II, organic solvent II, hydrophobic modifier, and catalyst is 1:(7-12):(0.5-1.5):(0.03-0.05).

[0017] In a further step of the present invention, in step S3, the reaction temperature of the epoxy group reaction is 100-110°C, and the reaction time of the epoxy group reaction is 12-16 hours.

[0018] The present invention also provides a highly hydrophobic low-rank coal prepared according to the preparation method of the highly hydrophobic low-rank coal described above.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] This invention discloses a method for preparing highly hydrophobic low-rank coal. First, the low-rank coal is carboxylated using an oxidant, converting surface hydroxyl groups into carboxyl groups. Then, an esterification reaction with citric acid further increases the carboxyl content on the low-rank coal surface. Finally, the carboxyl groups react with the epoxy groups of long-chain glycidyl ethers, introducing more hydrophobic chains onto the low-rank coal surface via covalent bonds, thus enhancing the hydrophobicity of the coal surface. Compared to other surface modification methods, this invention forms covalent bonds through a chemical reaction with the coal surface. These covalent bonds ensure that the hydrophobic chains are firmly bonded to the low-rank coal surface and will not detach. The hydrophobically modified low-rank coal exhibits improved coalification, thereby enhancing its slurry-forming properties. Attached Figure Description

[0021] Figure 1 This is a diagram illustrating the preparation reaction mechanism of Example 1 of the present invention;

[0022] Figure 2 This is a comparison diagram of the water contact angle between the hydrophobically modified lignite obtained in Example 1 of the present invention and the original lignite. Detailed Implementation

[0023] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0024] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0025] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0026] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0027] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0028] This invention provides a highly hydrophobic low-rank coal and its preparation method.

[0029] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0030] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to mass ratio.

[0031] The present invention discloses a highly hydrophobic low-rank coal, which is obtained through a three-step reaction. The first step is the carboxylation of the surface of the low-rank coal, the second step is the esterification reaction of the carboxyl groups on the surface of the low-rank coal with citric acid, and the third step is the reaction of the carboxyl groups of citric acid with the epoxy groups of long-chain glycidyl ether. Hydrophobic chains are introduced on the surface of the low-rank coal in the form of covalent bonds, thereby improving the hydrophobicity of the low-rank coal.

[0032] This invention discloses a method for preparing highly hydrophobic low-rank coal, the specific steps of which are as follows:

[0033] S1: Add low-rank coal, oxidant, and organic solvent I to a three-necked flask and stir until homogeneous. The mass ratio of low-rank coal to oxidant is 1:(0.1-0.3); the mass of organic solvent I is 2-3 times the mass of low-rank coal. Carboxylation reaction of the surface of low-rank coal is carried out at 60-70℃ for 4-5 hours. After filtration, washing with organic solvent I and distilled water, and drying, intermediate product I is obtained.

[0034] Wherein, the low-rank coal is one or more of lignite, long-flame coal, non-caking coal, and sub-bituminous coal; the oxidant is one or more of ammonium persulfate and potassium persulfate in any proportion; and the organic solvent I is one or more of toluene, xylene, and benzene in any proportion.

[0035] S2: Add intermediate product I, citric acid and DMF to a three-necked flask and stir until homogeneous. The mass ratio of intermediate product I to citric acid is 1:(0.5-0.8); the mass of DMF is 2-3 times the mass of intermediate product I. The esterification reaction is carried out at 60-70℃ for 2-3 hours. After filtration, washing with DMF and distilled water, and drying, intermediate product II is obtained.

[0036] S3: Add intermediate product II and organic solvent II to a three-necked flask, stir evenly, add catalyst and hydrophobic modifier, and carry out epoxy reaction at 100-110℃ for 12-16h. After filtration, washing with organic solvent II and distilled water, and drying, high hydrophobic low-rank coal is obtained.

[0037] Wherein, the organic solvent II is one or more of butyl acetate, methyl acetate, ethyl acetate, and propyl acetate in any proportion; the catalyst is a mixture of triphenylphosphine and hydroquinone, wherein the mass ratio of triphenylphosphine to hydroquinone is (7-9):1; the hydrophobic modifier is one or more of neodecanoic acid glycidyl ester, decanoic acid glycidyl ester, stearic acid glycidyl ester, laurate glycidyl ester, and palmitic acid glycidyl ester in any proportion.

[0038] The mass ratio of intermediate product II, hydrophobic modifier and catalyst is 1:(0.5-1.5):(0.03-0.05); the mass of organic solvent II is 7-12 times the mass of intermediate product II.

[0039] The highly hydrophobic low-rank coal prepared according to the method is mainly used to prepare coal-water slurry, thereby increasing the slurry concentration of low-rank coal.

[0040] Example 1

[0041] S1: Add 10g of lignite, 1g of ammonium persulfate and 20mL of toluene to a three-necked flask, mix well, stir and react at 60℃ for 4h, filter, wash with toluene and distilled water, and dry to obtain intermediate product I;

[0042] S2: Add 10g of intermediate product I, 5g of citric acid and 20ml of DMF to a three-necked flask, mix well, stir and react at 60℃ for 2h, filter, wash with DMF and distilled water, and dry to obtain intermediate product II.

[0043] S3: Add 10g of intermediate product II and 70mL of butyl acetate to a three-necked flask, mix well, add 0.390g of triphenylphosphine and 0.056g of hydroquinone, and add 5g of neodecanoic acid glycidyl ester using a constant pressure funnel. Stir the reaction at 100℃ for 12h, filter, wash with butyl acetate and distilled water, and dry to obtain highly hydrophobic lignite.

[0044] Example 2

[0045] S1: Add 10g of lignite, 1g of ammonium persulfate and 20mL of toluene to a three-necked flask, mix well, stir and react at 60℃ for 4h, filter, wash with toluene and distilled water, and dry to obtain intermediate product I;

[0046] S2: Add 10g of intermediate product I, 5g of citric acid and 20ml of DMF to a three-necked flask, mix well, stir and react at 60℃ for 2h, filter, wash with DMF and distilled water, and dry to obtain intermediate product II.

[0047] S3: Add 10g of intermediate product II and 80mL of methyl acetate to a three-necked flask, mix well, add 0.473g of triphenylphosphine and 0.068g of hydroquinone, and add 8g of glycidyl decanoate using a constant pressure funnel. Stir the reaction at 105℃ for 13h, filter, wash with methyl acetate and distilled water, and dry to obtain highly hydrophobic lignite.

[0048] Example 3

[0049] S1: Add 10g of long-flame coal, 2g of ammonium persulfate and 25mL of xylene to a three-necked flask, mix well, stir and react at 65℃ for 4h, filter, wash with xylene and distilled water, and dry to obtain intermediate product I;

[0050] S2: Add 10g of intermediate product I, 6g of citric acid and 25ml of DMF to a three-necked flask, mix well, stir and react at 65°C for 2h, filter, wash with DMF and distilled water, and dry to obtain intermediate product II;

[0051] S3: Add 10g of intermediate product II and 90mL of ethyl acetate to a three-necked flask, mix well, add 0.711g of triphenylphosphine and 0.089g of hydroquinone, and add 10g of glycidyl stearate using a constant pressure funnel. Stir and react at 105℃ for 14h, filter, wash with ethyl acetate and distilled water, and dry to obtain highly hydrophobic long-flame coal.

[0052] Example 4

[0053] S1: Add 10g of non-sticky coal, 2g of potassium persulfate and 25mL of xylene to a three-necked flask, mix well, stir and react at 70℃ for 5h, filter, wash with xylene and distilled water, and dry to obtain intermediate product I;

[0054] S2: Add 10g of intermediate product I, 7g of citric acid and 25ml of DMF to a three-necked flask, mix well, stir and react at 70°C for 3h, filter, wash with DMF and distilled water, and dry to obtain intermediate product II.

[0055] S3: Add 10g of intermediate product II and 100mL of propyl acetate to a three-necked flask, mix well, add 0.0782g of triphenylphosphine and 0.098g of hydroquinone, and add 12g of glycidyl laurate using a constant pressure funnel. Stir and react at 110℃ for 15h, filter, wash with propyl acetate and distilled water, and dry to obtain highly hydrophobic non-sticky coal.

[0056] Example 5

[0057] S1: Add 10g of bituminous coal, 3g of potassium persulfate and 30mL of benzene to a three-necked flask, mix well, stir and react at 70℃ for 5h, filter, wash with benzene and distilled water, and dry to obtain intermediate product I;

[0058] S2: Add 10g of intermediate product I, 8g of citric acid and 30ml of DMF to a three-necked flask, mix well, stir and react at 70°C for 3h, filter, wash with DMF and distilled water, and dry to obtain intermediate product II;

[0059] S3: Add 10g of intermediate product II and 120mL of butyl acetate to a three-necked flask, mix well, add 1.125g of triphenylphosphine and 0.125g of hydroquinone, and add 15g of glycidyl palmitate using a constant pressure funnel. Stir the reaction at 110℃ for 16h, filter, wash with butyl acetate and distilled water, and dry to obtain highly hydrophobic bituminous coal.

[0060] Application effect test:

[0061] Contact angle:

[0062] 0.5g of raw lignite powder and hydrophobically modified lignite powder (Example 1) were pressed into cylindrical tablets with a diameter of approximately 10mm and a thickness of approximately 2mm using a tablet press. Then, distilled water was dropped onto the coal tablets using a micro-syringe. The shape of the droplets on the coal tablets was observed and photographed using a JC2000D2G contact angle meter, and the contact angle was calculated. The test results are as follows: Figure 2 As shown.

[0063] Depend on Figure 2 It can be seen that the contact angle of distilled water on raw lignite is 65.5°, exhibiting strong hydrophilicity. After hydrophobic modification, the contact angle increases to 104.6°, and the hydrophobicity of the coal surface is significantly improved.

[0064] Preparation and performance testing of coal-water slurry:

[0065] Naphthalenesulfonic acid formaldehyde condensate was used as a dispersant in the slurry preparation, with a fixed addition amount of 0.8% of the coal-based mass. The naphthalenesulfonic acid formaldehyde condensate was stirred evenly with distilled water in a beaker, and then ground coal particles were slowly added at a stirring speed of 1200 r / min. After all the coal particles were added, stirring was continued for 5 min until the coal-water mixture became a homogeneous and stable slurry.

[0066] The apparent viscosity of coal-water slurry (shear rate 100 s⁻¹) was tested using the method specified in GB / T18856.4-2008 and a SMJ-1 type coal-water slurry apparent viscosity meter manufactured by Shanghai Nirun Intelligent Technology Co., Ltd. 1 The maximum pulping concentration was determined by the pulp concentration at an apparent viscosity of 1000 mPa·s.

[0067] At room temperature, pour the prepared coal-water slurry into a beaker, let it stand for 5 minutes, and then slowly pour the coal-water slurry into another container. Visually inspect the flow pattern of the slurry and classify it into four technical index grades: A, B, C, and D. The corresponding judgment criteria are: linear fluid, thick liquid with slightly poor flowability, viscous liquid with poor flowability, and no slurry.

[0068] The slurry was sealed and placed in a 100mL graduated cylinder. The breakthrough rate and the presence of sediment were measured after 3 days. Generally, the higher the breakthrough rate of the slurry, the better its stability.

[0069] Table 1 compares the properties of coal-water slurry prepared from the original coal sample and the hydrophobically modified coal sample.

[0070] Table 1 Comparison of the properties of coal-water slurry prepared from the original coal sample and the hydrophobically modified coal sample.

[0071]

[0072] As shown in Table 1, the slurry-making performance of low-rank coal was significantly improved after hydrophobic modification. The maximum slurry concentration of the original lignite was 56.23%, with a flow pattern of D, and a breakthrough rate of only 70.11% after 3 days, exhibiting slight hard sedimentation. After hydrophobic modification, the maximum slurry concentration of the coal-water slurry prepared in Example 1 increased to 64.82%, with a flow pattern of B, and a breakthrough rate of 78.41% after 3 days, exhibiting only slight soft sedimentation.

[0073] This invention introduces a greater number of hydrophobic chains onto the surface of low-rank coal through a three-step chemical reaction, thereby enhancing the hydrophobicity of the coal surface. Compared with other surface modification methods, the hydrophobic chains are firmly bonded to the surface of low-rank coal and will not detach. The degree of coalification of the hydrophobically modified low-rank coal is improved, which can enhance the slurry-forming properties of the modified low-rank coal.

[0074] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing highly hydrophobic low-rank coal, characterized in that, Includes the following steps: S1: Mix low-rank coal, oxidant and organic solvent I and stir evenly to carry out carboxyl reaction. After the carboxyl reaction is completed, filter, wash and dry to obtain intermediate product I. S2: Intermediate product I, citric acid and DMF are stirred evenly and subjected to esterification reaction. After the esterification reaction is completed, the mixture is filtered, washed and dried to obtain intermediate product II; In S2, the mass ratio of intermediate product I, citric acid and DMF is 1:(0.5~0.8):(2~3). S3: Intermediate product II and organic solvent II are stirred evenly, and a catalyst and hydrophobic modifier are added to carry out an epoxy group reaction. After the epoxy group reaction is completed, the mixture is filtered, washed and dried to obtain highly hydrophobic low-rank coal. The catalyst is a mixture of triphenylphosphine and hydroquinone, wherein the mass ratio of triphenylphosphine to hydroquinone is (7~9):

1. The hydrophobic modifier is one or more of the following: glycidyl neodecanoate, glycidyl decanoate, glycidyl stearate, glycidyl laurate, and glycidyl palmitate. In S3, the reaction temperature of the epoxy group reaction is 100~110℃, and the reaction time of the epoxy group reaction is 12~16h; the mass ratio of the intermediate product II, organic solvent II, hydrophobic modifier and catalyst is 1:(7~12):(0.5~1.5):(0.03~0.05).

2. The method for preparing highly hydrophobic low-rank coal according to claim 1, characterized in that, In S1, the low-rank coal is one or more of lignite, long-flame coal, non-caking coal, and sub-bituminous coal; the oxidant is one or more of ammonium persulfate and potassium persulfate; and the organic solvent I is one or more of toluene, xylene, and benzene.

3. The method for preparing highly hydrophobic low-rank coal according to claim 1, characterized in that, In S1, the mass ratio of the low-rank coal, oxidant, and organic solvent I is 1:(0.1~0.3):(2~3).

4. The method for preparing highly hydrophobic low-rank coal according to claim 1, characterized in that, In S1, the reaction temperature of the carboxyl group reaction is 60~70℃, and the reaction time of the carboxyl group reaction is 4~5h.

5. The method for preparing highly hydrophobic low-rank coal according to claim 1, characterized in that, In S2, the esterification reaction temperature is 60~70℃, and the esterification reaction time is 2~3h.

6. The method for preparing highly hydrophobic low-rank coal according to claim 1, characterized in that, In S3, the organic solvent II is one or more of butyl acetate, methyl acetate, ethyl acetate, and propyl acetate.

7. Highly hydrophobic low-rank coal prepared by the method for preparing highly hydrophobic low-rank coal according to any one of claims 1 to 6.

Images