A method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar

Abstract

This invention provides a method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar. The method includes: reacting low-rank coal pyrolysis volatiles sequentially through a carbon-based catalyst layer and a molecular sieve catalyst layer at a temperature of 500-800℃ under a protective gas atmosphere; the reaction products are then condensed to obtain tar. This method utilizes a series of carbon-based and molecular sieve catalysts for the catalytic cracking of low-rank coal pyrolysis volatiles, fully leveraging the abundant active sites of the carbon-based catalyst and the high selectivity of the molecular sieve. Through the synergistic effect of the carbon-based and molecular sieve catalysts, a significant increase in the content of benzene and naphthalene compounds in the tar obtained from coal pyrolysis is achieved.

Description

Technical Field

[0001] This invention belongs to the field of energy technology, and specifically relates to a method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar. Background Technology

[0002] How to efficiently and cleanly utilize coal resources and increase their added value is a current research hotspot. Traditional coal pyrolysis processes yield tar with high levels of heavy components and complex compositions, which easily clogs and corrodes pipelines, hindering the stable operation of the pyrolysis unit and the deep processing and utilization of the tar. Currently, catalytic pyrolysis technology is commonly used to catalyze the decomposition of volatiles in coal pyrolysis, increasing the content of light aromatics in the tar to some extent. However, existing catalytic pyrolysis technologies have limited effectiveness in increasing the content of light aromatics in the tar obtained from coal pyrolysis, particularly the content of benzene and naphthalene compounds. Since light aromatics such as benzene and naphthalene compounds are basic chemical raw materials for synthesizing numerous chemical products, effectively increasing the content of benzene and naphthalene compounds in the tar obtained from coal pyrolysis can further enhance the added value of coal.

[0003] Catalysts, as a key and breakthrough point in catalytic pyrolysis processes, have attracted widespread attention from researchers, with carbon-based catalysts and molecular sieve catalysts being the most extensively studied. While carbon-based catalysts possess advantages such as large specific surface area, abundant active sites, and well-developed pores, enabling the catalytic cracking of coal pyrolysis volatiles and improving the quality of coal pyrolysis tar, they also suffer from drawbacks such as irregular pore structures and poor selectivity. Current technologies using carbon-based catalysts to catalyze coal pyrolysis volatiles have shown limited increases in benzene and naphthalene compounds in the tar obtained. Although molecular sieve catalysts, with their regular pore structure, abundant and tunable acidic sites, and large specific surface area, are more beneficial than carbon-based catalysts in the catalytic cracking of coal pyrolysis volatiles, different types of molecular sieves exhibit varying selectivity for pyrolysis volatiles due to their different pore structures. Current technologies using molecular sieve catalysts to catalyze coal pyrolysis volatiles have also shown very limited increases in benzene and naphthalene compounds in the tar obtained.

[0004] In summary, how to better increase the content of benzene and naphthalene compounds in the tar obtained from coal pyrolysis is one of the urgent problems to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a method that can effectively increase the content of benzene and naphthalene compounds in the tar obtained from coal pyrolysis by catalytic cracking of volatiles.

[0006] To achieve the above objectives, the present invention provides a method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar, wherein the method includes the following steps:

[0007] At a temperature of 500-800℃ and under a protective atmosphere, the volatiles of low-rank coal pyrolysis are passed sequentially through a carbon-based catalyst layer and a molecular sieve catalyst layer to react, and the products after the reaction are condensed to obtain tar.

[0008] The molecular sieve catalyst includes any one or a combination of two or more of HZSM-5 molecular sieve, HY molecular sieve, Hβ molecular sieve and USY molecular sieve.

[0009] The above-mentioned method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar utilizes a series of carbon-based catalysts and molecular sieve catalysts to catalytically crack low-rank coal pyrolysis volatiles. It makes full use of the abundant active sites of carbon-based catalysts and the high selectivity of molecular sieves, and achieves a significant increase in the content of benzene and naphthalene compounds in the tar obtained from coal pyrolysis under the synergistic effect of carbon-based catalysts and molecular sieve catalysts.

[0010] In the above-mentioned method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar, preferably, the low-rank coal pyrolysis volatiles are reacted sequentially with a carbon-based catalyst and a molecular sieve catalyst before being condensed into tar;

[0011] In this preferred technical solution, the low-rank coal pyrolysis volatiles are reacted sequentially by a carbon-based catalyst and a molecular sieve catalyst before being condensed into tar, which helps to improve the yield. When the low-rank coal pyrolysis volatiles are condensed into tar and then subjected to catalytic reaction, on the one hand, liquid feed is prone to causing blockage of the feed pipe in the process, and on the other hand, the tar after the low-rank coal pyrolysis volatiles are condensed will also undergo a gasification process during the catalytic reaction. This process is prone to generating carbon deposits, resulting in incomplete gasification of tar and ultimately leading to a decrease in yield.

[0012] More preferably, under a temperature of 500-800℃ and a protective gas atmosphere, the volatiles from the pyrolysis of low-rank coal react sequentially through a carbon-based catalyst layer and a molecular sieve catalyst layer in the following manner:

[0013] A low-rank coal layer, a carbon-based catalyst layer, and a molecular sieve catalyst layer are sequentially arranged in a reactor (for example, preferably arranged from top to bottom in the reactor). The reaction is carried out at 500-800°C under a protective gas atmosphere. During the reaction, a protective gas flow is injected from the outside of the low-rank coal layer (referring to the side of the low-rank coal layer opposite to the side of the adjacent carbon-based catalyst layer), and the reaction products are collected from the outside of the molecular sieve catalyst layer (referring to the side of the molecular sieve catalyst layer opposite to the side of the adjacent carbon-based catalyst layer).

[0014] In this preferred technical solution, a low-rank coal layer, a carbon-based catalyst layer, and a molecular sieve catalyst layer are arranged in a "sandwich" structure in sequence; the low-rank coal undergoes pyrolysis at a temperature of 500-800℃ under a protective gas atmosphere to obtain pyrolysis volatiles, which are then subjected to catalytic cracking reactions by passing through a carbon-based catalyst and a molecular sieve catalyst in sequence at 500-800℃ under a protective gas atmosphere.

[0015] The mass ratio of the total mass of the carbon-based catalyst layer and the molecular sieve catalyst layer to the mass of the low-rank coal seam is preferably 0.05-0.35:1, more preferably 0.1-0.3:1;

[0016] Preferably, the reactor is a fixed-bed reactor;

[0017] Preferably, a partition layer is provided between the low-rank coal seam and the carbon-based catalyst layer; in one specific embodiment, the partition layer is made of quartz wool.

[0018] Preferably, a partition layer is provided on the outside of the molecular sieve catalyst layer; in one specific embodiment, the partition layer is made of quartz wool.

[0019] Preferably, the low-rank coal seam and the carbon-based catalyst layer are placed in baskets with the same inner diameter as the reactor.

[0020] In the aforementioned method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar, preferably, the carbon-based catalyst layer and the molecular sieve catalyst layer are bonded together. The seamless bonding between the carbon-based catalyst layer and the molecular sieve layer helps reduce the residence time of low-rank coal pyrolysis volatiles, allowing the pyrolysis volatiles to undergo catalytic cracking through the two catalyst layers before condensing into tar. In this preferred embodiment, the bonding of the carbon-based catalyst layer and the molecular sieve catalyst layer effectively avoids the excessive residence time of pyrolysis volatiles due to the presence of gaps between the two layers, thus preventing excessive cracking of the pyrolysis volatiles and a decrease in tar yield.

[0021] In the above methods for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar, preferably, the tar obtained by condensing the reaction products is achieved in the following manner:

[0022] The products after the reaction were collected by cooling them in a cold trap at -2°C to -20°C to obtain tar.

[0023] In the above-described method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar, preferably, the carbon-based catalyst includes one or more combinations of semi-coke, semi-coke, and commercial activated carbon; more preferably, the carbon-based catalyst is semi-coke; in a specific embodiment, the semi-coke used as the carbon-based catalyst is prepared from low-rank coal of the same type as the low-rank coal (i.e., the low-rank coal that produces the pyrolysis volatiles of the low-rank coal).

[0024] In the above-described method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar, preferably, the carbon-based catalyst has a particle size of less than 0.18 mm. Catalysts with a particle size of less than 0.18 mm can prolong the residence time of pyrolysis volatiles compared to catalysts with a particle size greater than 0.18 mm, providing the necessary time for sufficient contact and reaction between the reactants and the active sites of the catalyst. Furthermore, compared to catalysts with larger particle sizes, catalysts with smaller particle sizes expose more surface active sites for the same mass, which is beneficial for the occurrence of catalytic conversion reactions.

[0025] In the above-mentioned method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar, preferably, the molecular sieve catalyst is HY molecular sieve. When HY molecular sieve is used, under the synergistic effect of carbon-based catalyst and HY molecular sieve catalyst, the content of xylenol in the tar obtained from coal pyrolysis can be significantly reduced, and certain specific types of dimethylphenol and certain specific types of methyl-ethyl-benzene compounds can be removed, which is of great significance for environmental protection and industrial production.

[0026] In the above-described method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar, preferably, the molecular sieve catalyst has a particle size of less than 0.18 mm. Catalysts with a particle size of less than 0.18 mm can prolong the residence time of pyrolysis volatiles compared to catalysts with a particle size greater than 0.18 mm, providing the necessary time for sufficient contact and reaction between the reactants and the active sites of the catalyst. Furthermore, compared to catalysts with larger particle sizes, catalysts with smaller particle sizes expose more surface active sites for the same mass, which is beneficial for the occurrence of catalytic conversion reactions.

[0027] In the above-mentioned method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar, preferably, the mass ratio of the molecular sieve catalyst layer to the carbon-based catalyst layer is greater than 0 and less than or equal to 9, and more preferably 0.25-4:1.

[0028] In the above-mentioned method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar, preferably, the low-rank coal includes one or more combinations of lignite, peat, and bituminous coal; more preferably, the low-rank coal is lignite.

[0029] In one specific embodiment, the molecular sieve catalyst is selected from HY molecular sieve, the carbon-based catalyst is selected from semi-coke, and the low-rank coal is selected from Baiyinhua lignite.

[0030] In the above-mentioned method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar, nitrogen is preferably used as the protective gas.

[0031] In the above-mentioned method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar, preferably, the temperature is 600-750℃.

[0032] In the above-mentioned method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar, preferably, the compounds in the obtained tar mainly include benzene, toluene, xylene, naphthalene, methylnaphthalene, dimethylnaphthalene, phenol, cresol, xylenol and furan.

[0033] The method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar provided by this invention is the first to employ a tandem catalytic system in the tar upgrading process. A carbon-based catalyst and a molecular sieve are connected in series for the catalytic upgrading of volatiles from coal pyrolysis. Through the synergistic effect of the tandem carbon-based catalyst and the molecular sieve catalyst, the catalytic cracking of low-rank coal pyrolysis volatiles is significantly improved, resulting in a substantial increase in the content of benzene and naphthalene compounds in the tar obtained from coal pyrolysis. This solves the problems of high content of heavy components and easy pipe blockage in traditional coal pyrolysis processes, improves the composition of the tar obtained from coal pyrolysis, and increases the added value of the tar. Compared with existing technologies, it has the following superior effects:

[0034] 1. The technical solution provided by this invention fully leverages the characteristics and advantages of carbon-based catalysts and molecular sieve catalysts. In the catalytic cracking process of low-rank coal pyrolysis volatiles, the series-connected carbon-based catalyst-molecular sieve catalyst system produces an excellent "1+1>2" effect. The pyrolysis volatiles are in full contact with the active sites on the pores and surfaces of the series-connected catalysts, promoting the cracking and conversion of volatiles, improving tar composition, and enhancing tar quality. The carbon-based catalyst provides abundant active sites for the catalytic cracking reaction of pyrolysis volatiles. Further, after high-selectivity catalysis by the molecular sieve, the content of high-value-added compounds such as benzene and naphthalene compounds in the tar increases. Under the synergistic effect of the carbon-based catalyst and the molecular sieve catalyst, the content of benzene and naphthalene compounds in the tar obtained from coal pyrolysis is significantly increased, far exceeding the combined increase in benzene and naphthalene compound content that could be achieved by using the carbon-based catalyst alone or the molecular sieve catalyst alone.

[0035] 2. Compared with the existing technology that uses a single catalytic system, the technical solution provided by the present invention uses a series of carbon-based catalyst-molecular sieve catalyst catalytic systems, which can further reduce the content of phenolic compounds and furans in the tar obtained from coal pyrolysis and improve the tar composition. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the fixed-bed reactor in the embodiment.

[0037] Figure 2This is a comparison chart showing the content of benzene and naphthalene compounds in the tar obtained from Examples 1-3 and Comparative Examples 1-4.

[0038] Figure 3 This is a comparison chart of the content of phenolic compounds and furans in the tar obtained from Examples 1-3 and Comparative Examples 1-4.

[0039] Figure 4 This is a comparison chart showing the theoretical and experimental values ​​of the increase in benzene and naphthalene compound content in the tar obtained in Example 3 compared to Comparative Example 1.

[0040] Figure 5 The total ion current spectrum of the tar obtained in Comparative Examples 1, 2, 3 and Example 3 is shown. Detailed Implementation

[0041] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0042] The stainless steel tube fixed bed reactor used in this invention has an inner diameter of 14 mm, a length of 340 mm, and a cylindrical shape. It has a gas inlet at the top and a product outlet at the bottom.

[0043] Unless otherwise specified, the experimental methods used in the embodiments, comparative examples, and experimental examples of this invention are all conventional methods.

[0044] Unless otherwise specified, all reagents and materials used in the embodiments, comparative examples, and experimental examples of this invention are obtained commercially.

[0045] The industrial and elemental analysis data of Baiyinhua lignite involved in the embodiments, comparative examples, and experimental examples of this invention are shown in Table 1.

[0046] Table 1. Industrial and elemental analysis of Baiyinhua lignite.

[0047]

[0048] *: obtained by difference; ad: air-dried basis; d: dry basis; daf: dry ash-free basis.

[0049] Acquisition of the semi-coke catalyst used in the examples and comparative examples:

[0050] 5g of Baiyinhua lignite was added to the isothermal zone of a stainless steel tube fixed-bed reactor. Under N2 atmosphere, the reactor was heated from 20℃ to 800℃ at a rate of 5℃ / min using a programmed heating method and held at 800℃ for 30min. After the Baiyinhua lignite was completely pyrolyzed, it was naturally cooled to room temperature by continuing to purge with N2. The semi-coke obtained from the coal pyrolysis was then removed and stored in a desiccator for later use. The stainless steel tube fixed-bed reactor had an inner diameter of 14 mm and a length of 340 mm. The particle size of the prepared semi-coke was 0.15mm-0.18mm.

[0051] Example 1

[0052] This embodiment provides a method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar, wherein the method includes the following steps:

[0053] In a stainless steel tube fixed-bed reactor, quartz wool, 0.5g of HZSM-5 molecular sieve (particle size 0.15mm-0.18mm), 0.5g of the aforementioned self-made semi-coke catalyst, quartz wool, and 5g of Baiyinhua lignite were loaded sequentially. This completed the arrangement of a low-rank coal layer, quartz wool layer, carbon-based catalyst layer, molecular sieve catalyst layer, and quartz wool layer (e.g., ...) in the stainless steel tube fixed-bed reactor from top to bottom. Figure 1 (as shown); wherein, the low-rank coal seam and the carbon-based catalyst layer are closely bonded; wherein, the low-rank coal seam, the carbon-based catalyst, and the molecular sieve catalyst layer are placed in baskets and then loaded into the stainless steel tube fixed bed reactor;

[0054] N2 is injected through the gas inlet at the top of the stainless steel tube fixed bed reactor to create an N2 atmosphere inside the reactor.

[0055] The reaction is carried out at a flow rate of 300 mL / min (N2 gas is injected from the gas inlet at the top of the stainless steel tube fixed bed reactor) and a temperature of 600 °C. The product obtained from the reaction is discharged from the product outlet at the bottom of the stainless steel tube fixed bed reactor and collected by cooling in a cold trap at -20 °C to obtain tar.

[0056] Example 2

[0057] This embodiment provides a method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar, wherein the method includes the following steps:

[0058] In a stainless steel tube fixed-bed reactor, quartz wool, 0.5 g of Hβ molecular sieve (particle size 0.15 mm-0.18 mm), 0.5 g of the aforementioned self-made semi-coke catalyst, quartz wool, and 5 g of Baiyinhua lignite were loaded sequentially. This completed the arrangement of a low-rank coal layer, quartz wool layer, carbon-based catalyst layer, molecular sieve catalyst layer, and quartz wool layer (e.g., ...) in the stainless steel tube fixed-bed reactor from top to bottom. Figure 1 (as shown); wherein, the low-rank coal seam and the carbon-based catalyst layer are closely bonded; wherein, the low-rank coal seam, the carbon-based catalyst, and the molecular sieve catalyst layer are placed in baskets and then loaded into the stainless steel tube fixed bed reactor;

[0059] N2 is injected through the gas inlet at the top of the stainless steel tube fixed bed reactor to create an N2 atmosphere inside the reactor.

[0060] The reaction is carried out at a flow rate of 300 mL / min (N2 gas is injected from the gas inlet at the top of the stainless steel tube fixed bed reactor) and a temperature of 600 °C. The product obtained from the reaction is discharged from the product outlet at the bottom of the stainless steel tube fixed bed reactor and collected by cooling in a cold trap at -20 °C to obtain tar.

[0061] Example 3

[0062] This embodiment provides a method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar, wherein the method includes the following steps:

[0063] In a stainless steel tube fixed-bed reactor, quartz wool, 0.5g of HY molecular sieve (particle size 0.15mm-0.18mm), 0.5g of the aforementioned self-made semi-coke catalyst, quartz wool, and 5g of Baiyinhua lignite were loaded sequentially. This completed the arrangement of a low-rank coal layer, quartz wool layer, carbon-based catalyst layer, molecular sieve catalyst layer, and quartz wool layer (e.g., ...) from top to bottom in the stainless steel tube fixed-bed reactor. Figure 1 (as shown); wherein, the low-rank coal seam and the carbon-based catalyst layer are closely bonded; wherein, the low-rank coal seam, the carbon-based catalyst, and the molecular sieve catalyst layer are placed in baskets and then loaded into the stainless steel tube fixed bed reactor;

[0064] N2 is injected through the gas inlet at the top of the stainless steel tube fixed bed reactor to create an N2 atmosphere inside the reactor.

[0065] The reaction is carried out at a flow rate of 300 mL / min (N2 gas is injected from the gas inlet at the top of the stainless steel tube fixed bed reactor) and a temperature of 600 °C. The product obtained from the reaction is discharged from the product outlet at the bottom of the stainless steel tube fixed bed reactor and collected by cooling in a cold trap at -20 °C to obtain tar.

[0066] Comparative Example 1

[0067] This comparative example provides a coal pyrolysis method.

[0068] The only difference between this method and the method provided in Example 3 is that 0.5g of HY molecular sieve (particle size less than 0.18mm) is used instead of 0.5g of quartz sand (particle size of 0.15mm-0.18mm), and 0.5g of the self-made semi-coke catalyst is used instead of 0.5g of quartz sand (particle size of 0.15mm-0.18mm). The other experimental steps are the same as in Example 3.

[0069] Comparative Example 2

[0070] This comparative example provides a method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar.

[0071] The only difference between this method and the method provided in Example 3 is that 0.5g of self-made semi-coke catalyst is used instead of 0.5g of HY molecular sieve (particle size less than 0.18mm). The other experimental steps are the same as in Example 3.

[0072] Comparative Example 3

[0073] This comparative example provides a method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar.

[0074] The only difference between this method and the method provided in Example 3 is that 0.5g of HY molecular sieve (particle size 0.15mm-0.18mm) is used instead of 0.5g of the self-made semi-coke catalyst mentioned above. The other experimental steps are the same as in Example 3.

[0075] Comparative Example 4

[0076] This comparative example provides a method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar.

[0077] The only difference between this method and Example 3 is that the order of the molecular sieve catalyst layer and the carbon-based catalyst layer is changed. That is, the position of the carbon-based catalyst layer in Example 3 is replaced by the molecular sieve catalyst layer, and the position of the molecular sieve catalyst layer is replaced by the carbon-based catalyst layer. The other experimental steps are the same as in Example 3.

[0078] Experimental Example

[0079] The composition of the tars prepared in Examples 1-3 and Comparative Examples 1-4 was analyzed using gas chromatography-mass spectrometry (GC / MS). The content of compounds in the tars was calculated using the area normalization method, and the specific data are shown in Table 2.

[0080] The contents of benzene and naphthalene compounds in the tar prepared in Examples 1-3 and Comparative Examples 1-4 are as follows: Figure 2 Table 2 shows the contents of phenolic compounds and furans as follows: Figure 3 As shown in Table 2.

[0081] Table 2. Content (%) of benzene, naphthalene, phenolic compounds, and furans in the tar obtained from the examples and comparative examples.

[0082]

[0083]

[0084] Depend on Figure 2 It can be seen that the content of benzene compounds in the tar prepared in Example 3 is 74.7% higher than that in the tar prepared in Example 2 and 20.2% higher than that in the tar prepared in Example 3. The content of naphthalene compounds in the tar prepared in Example 3 is 140.0% higher than that in the tar prepared in Example 2 and 33.8% higher than that in the tar prepared in Example 3.

[0085] Based on the experimental data from Comparative Examples 1-3, the content of benzene and naphthalene compounds in Example 3 was further analyzed. The theoretical and experimental values ​​of the increase in the content of benzene and naphthalene compounds in Example 3 were compared, and the results are as follows: Figure 4 As shown. Compared with the tar prepared by coal pyrolysis without catalyst (the tar prepared in Comparative Example 1), the theoretical increase in benzene content (half the sum of the increases in benzene content of the tar prepared in Comparative Examples 2 and 3 compared to the tar prepared in Comparative Example 1) was 30.2%, and the theoretical increase in naphthalene content (half the sum of the increases in naphthalene content of the tar prepared in Comparative Examples 2 and 3 compared to the tar prepared in Comparative Example 1) was 57.5%. However, the experimental increases in benzene and naphthalene content of the tar prepared in Example 3 compared to the tar prepared in Comparative Example 1 were 85.4% and 170.7%, respectively, far exceeding the theoretical values; the increase in naphthalene content was particularly significant, with the experimental value being nearly three times the theoretical value. The analysis results indicate that the tandem connection of the semi-coke catalyst and the HY molecular sieve is not a simple linear addition, but rather that these two catalysts have a significant synergistic effect on the catalytic conversion of coal pyrolysis volatiles.

[0086] Depend on Figure 2 , Figure 4 It is evident that the method provided by this invention is more conducive to the formation of light aromatic hydrocarbons such as benzene and naphthalene compounds in tar. The synergistic effect of the carbon-based catalyst and the molecular sieve catalyst produces an excellent "1+1>2" effect, significantly increasing the content of benzene and naphthalene compounds in the tar. Figure 3 It can be seen that, compared with a single catalytic system, the technical solution provided by this invention can further reduce the content of phenolic compounds and furans in tar and improve the tar composition; in particular, the use of a series of semi-coke catalysts and HY molecular sieve catalytic system can achieve a significant reduction in the xylenol content in the tar obtained from coal pyrolysis.

[0087] The total ion current spectra of the tars prepared in Comparative Example 3, Comparative Examples 1-3 were analyzed, and the results are as follows: Figure 5 As shown. By Figure 5 It can be seen that the total ion current spectra of the tars prepared in Comparative Examples 2 and 3 show a methyl-ethyl-benzene compound at a retention time of approximately 13.4 minutes, while this peak almost disappears at the same retention time in the total ion current spectra of the tar prepared in Example 3, indicating that methyl-ethyl-benzene was not detected at this retention time. Similarly, at a retention time of approximately 20.6 minutes, a distinct dimethylphenol peak appears in the total ion current spectra of the tars prepared in Comparative Examples 2 and 3, while no peak appears in the total ion current spectra of the tar prepared in Example 3 at this time. This demonstrates that using a tandem semi-coke catalyst and HY molecular sieve catalytic system can remove certain types of dimethylphenol and methyl-ethyl-benzene compounds from the tar obtained from coal pyrolysis. These specific types of dimethylphenol and methyl-ethyl-benzene compounds cannot be removed by using either the semi-coke catalyst or the HY molecular sieve catalyst alone, which is of great significance for environmental protection and industrial production. This also indirectly confirms that the tandem catalytic system of the semi-coke catalyst and HY molecular sieve is not a simple linear superposition in the catalytic cracking of pyrolysis volatiles, but rather plays a synergistic role in the cracking and transformation of volatiles.

[0088] From Table 2 and Figure 2 , Figure 3 It can be seen that Example 3 is significantly better than Comparative Example 4 in terms of increasing the content of benzene and naphthalene compounds, and the content of phenolic compounds in Comparative Example 4 is much higher than that in Example 3.

[0089] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for increasing the content of benzene and naphthalene compounds in coal pyrolysis tar, wherein, The method includes the following steps: At a temperature of 500-800℃ and under a protective atmosphere, the volatiles of low-rank coal pyrolysis are passed sequentially through a carbon-based catalyst layer and a molecular sieve catalyst layer to react, and the products after the reaction are condensed to obtain tar. The molecular sieve catalyst is HY molecular sieve; the carbon-based catalyst is semi-coke, and the semi-coke is prepared from low-rank coal of the same type as the low-rank coal; the carbon-based catalyst layer and the molecular sieve catalyst layer are bonded together. The low-rank coal is selected from lignite; The total mass ratio of the carbon-based catalyst layer and the molecular sieve catalyst layer to the low-rank coal seam is 0.05-0.35:1; the mass ratio of the molecular sieve catalyst layer to the carbon-based catalyst layer is 0.25-4:

1.

2. The method according to claim 1, wherein, The low-rank coal pyrolysis volatiles are reacted sequentially with a carbon-based catalyst and a molecular sieve catalyst before being condensed into tar.

3. The method according to claim 2, wherein, Under a protective atmosphere and at a temperature of 500-800℃, the volatiles from the pyrolysis of low-rank coal undergo a reaction by sequentially passing through a carbon-based catalyst layer and a molecular sieve catalyst layer, as follows: A low-rank coal seam, a carbon-based catalyst layer, and a molecular sieve catalyst layer are sequentially arranged in a reactor, and the reaction is carried out at 500-800℃ under a protective gas atmosphere. During the reaction, a protective gas flow is injected from the outside of the low-rank coal seam, and the reaction products are collected from the outside of the molecular sieve catalyst layer.

4. The method according to claim 3, wherein, An interlayer is provided between the low-rank coal seam and the carbon-based catalyst layer.

5. The method according to any one of claims 1-4, wherein, The temperature is 600-750℃.

6. The method according to claim 1, wherein, The carbon-based catalyst has a particle size of less than 0.18 mm.

7. The method according to claim 1, wherein, The molecular sieve catalyst has a particle size of less than 0.18 mm.

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