A method for separating oxygenates from low rank coal

Abstract

This invention discloses a method for separating oxygen-containing compounds from low-rank coal, belonging to the field of clean coal utilization technology. The method involves mixing coal powder with a solvent and then extracting the mixture. A portion of the resulting extract oil is collected as product, while the other portion is used as a circulating solvent, either alone or mixed with the solvent for the next stage of extraction. This process is repeated to increase the number of extraction stages. This method improves coal extraction efficiency, reduces the complexity of the extraction process, and enhances economic benefits by first pretreating the coal and then using a solvent with a high extraction rate for oxygen-containing substances to perform staged extraction of low-rank coal. Simultaneously, the extracted substances are directly used as extractants to extract oxygen-containing substances from the coal.

Description

Technical Field

[0001] This invention belongs to the field of clean coal utilization technology, and particularly relates to a method for separating oxygen-containing compounds from low-rank coal. Background Technology

[0002] Coal is a crucial energy source in my country, occupying a dominant position in the country's energy consumption structure. Achieving efficient and clean utilization of coal can effectively enhance its economic and social value, contributing more significantly to my country's national economy. Low-rank coal possesses good chemical reactivity, high volatile matter and oxygen content, making it easier to convert into liquid fuels or high-value-added chemicals. Therefore, solvent extraction to obtain high-value-added chemicals from low-rank coal is an effective way to achieve clean and efficient coal utilization.

[0003] Patent CN101962560 discloses an extraction method for the fractional extraction of coal liquefaction residue, in which the obtained heavy liquefied oil is moderately hydrogenated with a circulating solvent and used as an extractant. Most other reports focus on improving product yield and studying the mechanism of thermal extraction, with relatively little research on the extraction of specific structures from low-rank coal, including research on the extraction of oxygen-containing substances from low-rank coal. Low-rank coal contains a large number of oxygen-containing structures, making it easily breakable and pulverized during pyrolysis. Extracting oxygen-containing components from low-rank coal can improve its thermal fragility and suppress dust content in pyrolysis oil and gas. Furthermore, it can yield high-value-added oxygen-containing chemicals such as alcohols, phenols, and esters for use in the manufacture of dyes, plastics, pharmaceuticals, pesticides, and textiles. Summary of the Invention

[0004] The purpose of this invention is to provide a method for separating oxygen-containing compounds from low-rank coal. By first performing pretreatment, and then using a solvent with a high extraction rate for oxygen-containing substances to perform fractional extraction on the low-rank coal, the extracted substances are directly used as extractants to extract oxygen-containing substances from the coal. This method improves the coal extraction efficiency, reduces the complexity of the extraction process, and improves economic benefits.

[0005] To achieve the above objectives, the present invention adopts the following specific technical solutions.

[0006] The present invention provides a method for separating oxygen-containing compounds from low-rank coal: coal powder is mixed with a solvent and then extracted. A portion of the resulting extract oil is collected as a product, and the other portion is used as a circulating solvent alone or mixed with the solvent of the next stage of extraction. The raffinate after extraction is then subjected to the next stage of extraction. This process is repeated to increase the number of extraction stages.

[0007] Furthermore, the method may include the following steps:

[0008] S1: Mix coal powder with the solvent and perform primary extraction.

[0009] Preferably, the coal powder is pretreated before being mixed with the solvent.

[0010] Furthermore, the pretreatment involves impregnating the coal powder with an oxidant solution, followed by drying.

[0011] Furthermore, the impregnation time is 8-15 hours, the drying temperature is 110-120°C, and the drying time is 18-30 hours. Pretreatment with an oxidant can effectively increase the oxygen content in the pulverized coal.

[0012] Preferably, the drying is achieved by purging with gas; the gas contains 25-32% oxygen, with the remainder being inert gases. Purging and drying with a gas containing slightly more oxygen than air effectively maintains the oxygen content in the pulverized coal, which is crucial for the effectiveness of pretreatment.

[0013] Further, the primary extraction includes: passing the solvent into a reaction device containing the pretreated coal powder, with a solvent flow rate of 0.4-0.6 ml / min, a hot dissolution temperature of 300-360℃, slowly increasing the pressure to 4-7 MPa, and hot dissolution extraction for 2-6 hours after the temperature and pressure stabilize.

[0014] S2: Of the extract oil obtained from the primary extraction, a portion is collected as product, and the other portion is mixed with the secondary extraction solvent as the first circulating solvent to perform secondary extraction on the raffinate coal after the primary extraction.

[0015] Further, the secondary extraction includes: mixing the first circulating solvent and the secondary extraction solvent and passing them into a reaction device containing the raffinate coal that has undergone primary extraction, with a solvent flow rate of 0.4-0.6 ml / min, a hot dissolution temperature of 300-360℃, slowly increasing the pressure to 4-7 MPa, and hot dissolution extraction for 2-6 hours after the temperature and pressure stabilize.

[0016] Preferably, the volume ratio of the first circulating solvent to the secondary extraction solvent is 1:(2-3).

[0017] S3: Of the extract oil obtained from the secondary extraction, a portion is collected as product, and the other portion is mixed with the tertiary extraction solvent as the second circulating solvent to perform tertiary extraction on the raffinate coal after the secondary extraction.

[0018] Furthermore, the three-stage extraction includes: mixing the second circulating solvent and the third-stage extraction solvent and feeding them into a reaction device containing the residual coal after the second-stage extraction, with a solvent flow rate of 0.4-0.6 ml / min, a hot dissolution temperature of 300-360℃, slowly increasing the pressure to 4-7 MPa, and hot dissolution extraction for 2-6 hours after the temperature and pressure stabilize.

[0019] Preferably, the volume ratio of the second circulating solvent to the third-stage extraction solvent is 1:(2-3).

[0020] S4: Of the extracted oil obtained from the three-stage extraction, a portion is collected as product, and the other portion is used as a fourth-stage extractant to perform fourth-stage extraction on the raffinate coal after the three-stage extraction. This step is repeated 3-5 times to obtain the final product.

[0021] Furthermore, the fourth-stage extraction includes: mixing the fourth-stage extractant and passing it into a reaction device containing the residual coal after the third-stage extraction, with a solvent flow rate of 0.4-0.6 ml / min, a hot-melt temperature of 300-360℃, slowly increasing the pressure to 4-7 MPa, and hot-melt extraction for 2-6 hours after the temperature and pressure stabilize.

[0022] Preferably, in steps S1-S4, the solvent, the secondary extraction solvent, and the tertiary extraction solvent are one or more of methanol, ethanol, tetrahydrofuran, or ethyl acetate.

[0023] In this invention, based on the specific structures and properties of different extractants, oxygen-containing substances in low-rank coal can be extracted in a targeted manner. Ethanol, ethyl acetate, tetrahydrofuran, etc., can effectively extract oxygen-containing substances such as phenols, esters, ketones, and alcohols from low-rank coal. Solvents with oxygen-containing structures can effectively extract oxygen-containing substances from low-rank coal. Using solvents with high extraction rates for oxygen-containing substances for staged extraction of low-rank coal achieves targeted extraction of oxygen-containing substances and improves the extraction rate by employing a staged extraction method. Furthermore, the step-by-step extraction under mild conditions, with each stage having a different composition, facilitates subsequent separation and purification.

[0024] The carbon-oxygen bonds in coal are relatively weak, offering the advantage of separation under relatively mild conditions. Steps S1-S4 employ the principle of "like dissolves like," using oxygen-containing substances extracted from low-rank coal as extractants to extract oxygen-containing substances from the coal itself. This can be an effective method for extracting oxygen-containing substances from coal. This extraction method effectively reduces solvent consumption and efficiently extracts oxygen-containing substances from the coal, making the entire extraction system highly efficient and low-consumption. Furthermore, compared to existing technologies that typically separate extracts into different categories and use one category as an extractant to extract coal, increasing technical complexity, this invention uses the extracted substances directly as extractants to extract oxygen-containing substances from coal, reducing the complexity of the extraction process and improving economic efficiency. Attached Figure Description

[0025] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram showing the proportion of various substances in the extracts after each extraction stage in Example 1 of this application;

[0027] Figure 2 This is a schematic diagram showing the proportion of various substances in the extracts after each extraction stage in Example 5 of this application;

[0028] Figure 3 This is a schematic diagram showing the proportion of various substances in the extracts after each extraction stage in Example 8 of this application;

[0029] Figure 4 This is a schematic diagram showing the proportion of various substances in the extracts after each extraction stage of Comparative Example 1 of this application. Detailed Implementation

[0030] The embodiments of the present invention will be described in detail below with reference to specific examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified, specific conditions in the examples are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without a specified manufacturer are all commercially available conventional products. Furthermore, the proportions or contents of components not specified in the present invention can be any proportions or contents, and are not limited to mass ratios, concentration ratios, molar ratios, or volume ratios.

[0031] Example 1

[0032] A method for separating oxygen-containing compounds from low-rank coal:

[0033] (1) Dry the Baiyinhua lignite powder with a mesh size of less than 200 at 80°C under vacuum for 24 hours. Take 10g of the powder and soak it in 25mL of 30% hydrogen peroxide solution for 12 hours. Then dry it at 115°C for 24 hours.

[0034] (2) Take 5g of the coal powder obtained in step (1) and place it in the reaction vessel of the hot-melting device. Use methanol as a solvent to introduce it into the reaction vessel at a flow rate of 0.5ml / min. Set the temperature of the hot-melting device to 350℃ and slowly increase the pressure to 6MPa. After the temperature and pressure stabilize, start timing for the first-stage extraction, which takes 5 hours. After the first-stage extraction is completed, collect the extract oil. Collect a portion of the extract oil and use the other portion as the solvent for the second-stage extraction, which is the first circulating solvent.

[0035] (3) The first circulating solvent obtained in step (2) and ethanol are mixed at a volume ratio of 1:2 as the solvent for secondary extraction. The raffinate obtained in step (2) is placed in the reaction vessel of the hot-melt device. The solvent flow rate is set to 0.5 ml / min, the temperature of the hot-melt device is set to 350°C, and the pressure is slowly increased to 6 MPa. After the temperature and pressure stabilize, the timing is started. The secondary extraction time is 5 hours. After the secondary extraction is completed, the extract oil is collected. A portion of the extract oil is collected, and the other portion is used as the solvent for tertiary extraction, which is the second circulating solvent.

[0036] (4) The extract obtained in step (3) and tetrahydrofuran are mixed at a volume ratio of 1:2 as the solvent for the third-stage extraction. The raffinate obtained in step (3) is placed in the reaction vessel of the hot-melt device. The solvent flow rate is set to 0.5 ml / min, the temperature of the hot-melt device is set to 350°C, and the pressure is slowly increased to 6 MPa. After the temperature and pressure stabilize, the timing is started. The third-stage extraction time is 5 h. After the third-stage extraction is completed, part of the extracted oil is collected, and the other part is used as the solvent for the fourth-stage extraction.

[0037] (5) Place the raffinate obtained in step (4) into the reaction vessel of the hot-melting device, introduce the fourth-stage extraction solvent obtained in step (4), set the solvent flow rate to 0.5 ml / min, set the temperature of the hot-melting device to 350°C, slowly increase the pressure to 6 MPa, and start timing after the temperature and pressure stabilize. The fourth-stage extraction time is 3 hours. Collect a portion of the extracted oil and use the other portion as solvent for repeated extraction.

[0038] (6) Replace the extract oil and raffinate from each extraction stage with the extract oil and raffinate from the previous stage, and repeat step (5) three times to collect the final product. The proportions of various substances in the extracts after each extraction stage are as follows: Figure 1As shown, the extraction effect is better for oxygen-containing substances, and the proportion of oxygen-containing substances in the total extract will increase.

[0039] Example 2

[0040] A method for separating oxygen-containing compounds from low-rank coal differs from Example 1 in that step (1) is as follows: Baiyinhua lignite powder with a mesh size of less than 200 is dried under vacuum at 85°C for 18 hours, 10g of the coal powder is added to 25mL of 31.7% dilute nitric acid solution and soaked for 10 hours, and then dried at 110°C for 20 hours.

[0041] Example 3

[0042] A method for separating oxygen-containing compounds from low-rank coal, which differs from Example 1 in that methanol is replaced with ethanol in step (2), ethanol is replaced with tetrahydrofuran in step (3), and tetrahydrofuran is replaced with ethyl acetate in step (4).

[0043] Example 4

[0044] A method for separating oxygen-containing compounds from low-rank coal, which differs from Example 1 in that tetrahydrofuran is replaced with ethyl acetate in step (4).

[0045] Example 5

[0046] A method for separating oxygen-containing compounds from low-rank coal differs from Example 1 in that, in step (2), methanol is replaced with a mixture of methanol and ethanol at a volume ratio of 1:2 to obtain mixture one; in step (3), ethanol is replaced with a mixture of ethanol and tetrahydrofuran at a volume ratio of 1:2 to obtain mixture two; and in step (4), tetrahydrofuran is replaced with a mixture of tetrahydrofuran and ethyl acetate at a volume ratio of 1:2 to obtain mixture three. The proportions of various substances in the extracts after each extraction stage are as follows: Figure 2 As shown, the extraction effect is better than that of Example 1, and the proportion of oxygen-containing substances in the total extract increases after multi-stage extraction.

[0047] Example 6

[0048] A method for separating oxygen-containing compounds from low-rank coal, which differs from Example 5 in that in step (3), the ratio of the extract oil obtained as a circulating solvent in step (2) to the second mixture is 1:2.5; and in step (4), the ratio of the extract oil obtained as a circulating solvent in step (3) to the third mixture is 1:2.5.

[0049] Example 7

[0050] A method for separating oxygen-containing compounds from low-rank coal, which differs from Example 5 in that in step (3), the ratio of the extract oil obtained as a circulating solvent in step (2) to the second mixture is 1:3; and in step (4), the ratio of the extract oil obtained as a circulating solvent in step (3) to the third mixture is 1:3.

[0051] Example 8

[0052] A method for separating oxygen-containing compounds from low-rank coal differs from Example 5 in that step (1) is as follows: Baiyinhua lignite powder (below 200 mesh) is dried under vacuum at 80°C for 24 hours. 10g of the powder is then added to 25mL of 30% hydrogen peroxide solution and impregnated for 12 hours. The mixture is then purged with gas at room temperature until dry, with the gas composition being 30% oxygen and 70% nitrogen. The proportions of various substances in the extract after each extraction stage are as follows: Figure 3 As shown, the proportion of oxygen-containing substances is better than that in Example 5. However, the proportion of alcohols and phenols in the oxygen-containing substances is somewhat reduced, while the proportion of ketones and carboxylic acids is increased.

[0053] Example 9

[0054] A method for separating oxygen-containing compounds from low-rank coal, differing from Example 8 in that the gas composition is 32% oxygen and 68% nitrogen.

[0055] Example 10

[0056] A method for separating oxygen-containing compounds from low-rank coal, differing from Example 8 in that the gas composition is 25% oxygen and 75% nitrogen.

[0057] Comparative Example 1

[0058] (1) A method for separating oxygen-containing compounds from low-rank coal: 5g of Baiyinhua lignite powder (below 200 mesh) is placed in a reaction vessel of a hot-melt apparatus. Ethyl acetate is used as the solvent, the solvent flow rate is set to 0.5ml / min, the temperature of the hot-melt apparatus is set to 350℃, and the pressure is slowly increased to 6MPa. After the temperature and pressure stabilize, timing begins, and the hot-melt extraction time is 5h. After extraction is complete, the extracted oil is collected.

[0059] (2) Place the coal residue obtained in step (1) into the reaction vessel of the hot melting device, use tetrahydrofuran as the solvent for secondary extraction, set the solvent flow rate to 0.5 ml / min, set the temperature of the hot melting device to 350°C, slowly increase the pressure to 6 MPa, and start timing after the temperature and pressure stabilize. The extraction time is 5 h. After the extraction is completed, collect the extracted oil.

[0060] (3) Place the coal residue obtained in step (2) into the reaction vessel of the hot melting device, use ethanol as the solvent for the three-stage extraction, set the solvent flow rate to 0.5 ml / min, set the temperature of the hot melting device to 350°C, slowly increase the pressure to 6 MPa, and start timing after the temperature and pressure stabilize. The extraction time is 5 h. After the extraction is completed, collect the extracted oil.

[0061] (4) Repeat the extraction process in step (3) four times, collect the extracted oil, remove the solvent by vacuum rotary evaporation at 70°C, and calculate the extraction rate. The proportions of various substances in the extract after each extraction stage are as follows: Figure 4 As shown, after each extraction stage, the proportion of oxygen-containing substances (carboxylic acids, ketones, esters, phenols, etc.) in the extract increases, while the proportion of aromatics and alkanes decreases relatively. However, the overall extraction effect is significantly different compared to Examples 1, 5, and 8.

[0062] Comparative Example 2

[0063] A method for separating oxygen-containing compounds from low-rank coal, which differs from Comparative Example 1 in that before step (1): Baiyinhua lignite powder with a mesh size of less than 200 is dried under vacuum at 80°C for 24 hours, 10g of the coal powder is added to 25mL of 30% hydrogen peroxide solution for 12 hours, and then dried at 115°C for 24 hours.

[0064] The extraction rates and oxygen-containing substance extraction rates of Examples 1-10 and Comparative Examples 1-2 are shown in Table 1.

[0065] Table 1. Extraction rates and extraction rates of oxygen-containing substances in different implementation methods.

[0066] Extraction rate (%) Extraction rate of oxygen-containing substances (%) Example 1 39.06 20.56 Example 2 40.24 22.49 Example 3 37.32 19.38 Example 4 34.81 17.75 Example 5 42.54 24.15 Example 6 41.32 22.19 Example 7 40.61 23.10 Example 8 42.53 26.41 Example 9 42.72 27.65 Example 10 42.94 27.91 Comparative Example 1 30 14.57 Comparative Example 2 30.9 15.45

[0067] As can be seen, compared with Comparative Examples 1 and 2, Examples 1-10 show significantly improved extraction rates and oxygen-containing substance extraction rates. This indicates that the present invention uses a solvent with a high extraction rate for oxygen-containing substances to perform fractional extraction of low-rank coal, and uses the extracted substances directly as extractants to extract oxygen-containing substances from the coal, thus significantly improving the coal extraction efficiency.

[0068] In particular, Examples 8-10 showed significantly better extraction rates and oxygen-containing substance extraction rates than Examples 1-7, indicating that using a gas with a specific oxygen content for purging and drying during the pretreatment process of this invention is significantly superior to ordinary drying.

[0069] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method of separating oxygenates from a low-rank coal, characterized by, Includes the following steps: S1: Coal powder is mixed with a solvent for primary extraction; the coal powder is pretreated before being mixed with the solvent; the pretreatment involves impregnating the coal powder with an oxidant solution, followed by drying; the drying is achieved by purging with gas; the gas contains 25-32% oxygen and the remainder is inert gas; S2: Of the extract oil obtained from the first-stage extraction, a portion is collected as product, and the other portion is mixed with the second-stage extraction solvent as the first circulating solvent to perform a second-stage extraction on the raffinate coal after the first-stage extraction. S3: Of the extract oil obtained from the secondary extraction, a portion is collected as product, and the other portion is mixed with the tertiary extraction solvent as the second circulating solvent to perform tertiary extraction on the raffinate coal after the secondary extraction. S4: Of the extracted oil obtained from the three-stage extraction, a portion is collected as product, and the other portion is used as a fourth-stage extractant to perform fourth-stage extraction on the raffinate coal after the three-stage extraction. This step is repeated 3-5 times to obtain the final product.

2. The method of claim 1, wherein, The soaking time is 8-15 h, the drying temperature is 110-120 ℃, and the drying time is 18-30 h.

3. The method of claim 1, wherein, The solvent, the secondary extraction solvent, and the tertiary extraction solvent are one or more of methanol, ethanol, tetrahydrofuran, or ethyl acetate.

4. The method of claim 1, wherein, The first-stage extraction includes: passing the solvent into a reaction device containing the pretreated coal powder, with a solvent flow rate of 0.4-0.6 ml / min, a hot-melt temperature of 300-360 ℃, slowly increasing the pressure to 4-7 MPa, and hot-melt extraction for 2-6 h after the temperature and pressure stabilize.

5. The method of claim 1, wherein, The secondary extraction includes: mixing the first circulating solvent and the secondary extraction solvent and passing them into a reaction device containing the residual coal after primary extraction, with a solvent flow rate of 0.4-0.6 ml / min, a hot dissolution temperature of 300-360 ℃, slowly increasing the pressure to 4-7 MPa, and hot dissolution extraction for 2-6 hours after the temperature and pressure stabilize.

6. The method of claim 5, wherein, The volume ratio of the first circulating solvent to the secondary extraction solvent is 1:(2-3).

7. The method of claim 1, wherein, The three-stage extraction includes: mixing the second circulating solvent and the third-stage extraction solvent and feeding them into a reaction device containing the residual coal after the second-stage extraction, with a solvent flow rate of 0.4-0.6 ml / min, a hot-melt temperature of 300-360 ℃, and slowly increasing the pressure to 4-7 MPa. After the temperature and pressure stabilize, hot-melt extraction is carried out for 2-6 hours.

8. The method of claim 7, wherein, The volume ratio of the second circulating solvent to the third-stage extraction solvent is 1:(2-3).

9. The method of claim 1, wherein, The four-stage extraction includes: mixing the four-stage extractant and passing it into a reaction device containing coal residue that has undergone three-stage extraction, with a solvent flow rate of 0.4-0.6 ml / min, a hot-melt temperature of 300-360 ℃, slowly increasing the pressure to 4-7 MPa, and hot-melt extraction for 2-6 h after the temperature and pressure stabilize.

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