Preparation method and process system for preparing chemicals through hydrogenation of medium and low temperature coal tar

Abstract

The invention discloses a preparation method and a process system for preparing chemicals by hydrogenation of medium and low temperature coal tar, and belongs to the technical field of coal chemical industry, the medium and low temperature coal tar is added into a distillation tower for fractionation, the bottom of the distillation tower is fractionated to obtain a heavy fraction HO, the top of the distillation tower is fractionated to obtain a light fraction LO, and the LO is added into a first hydrogenation reactor to obtain LOL; and adding the HO into a second hydrogenation reactor to obtain HOH, adding the LOL and the HOH into a third hydrogenation reactor, and adding the LOL and the HOH into a first rectifying tower and a second rectifying tower for step-by-step rectification after the reaction is completed to respectively obtain cyclohexane, methyl cyclohexane and methylbenzene. According to the mode, the light fraction and the heavy fraction of the medium and low temperature coal tar are subjected to quality-divided and graded conversion, the full components of the medium and low temperature coal tar are fully utilized, and good economic benefits are achieved.

Description

Technical Field

[0001] This invention relates to the field of coal chemical technology, specifically to a method and process system for preparing chemicals by hydrogenation of medium- and low-temperature coal tar. Background Technology

[0002] my country's total production of medium- and low-temperature coal tar is approximately 8 million tons, with production enterprises mainly located in five provinces / autonomous regions: Shaanxi, Xinjiang, Inner Mongolia, Ningxia, and Gansu. Medium- and low-temperature coal tar has a diverse and complex composition, making efficient separation extremely difficult. Due to its rich content of aliphatic hydrocarbons, aromatics, and phenolic compounds, and the presence of petroleum-like components, it is well-suited for hydrogenation to produce fuel oil. After more than a decade of development, the hydrogenation of medium- and low-temperature coal tar to produce fuel oil has reached a considerable scale locally, but the degree of tar classification and utilization is low, and the products are relatively limited. Furthermore, the rapid development of the new energy vehicle industry, driven by policies, technology, and the market, has led to continuous market expansion, impacting the demand for fuel oil. Therefore, the catalytic conversion of medium- and low-temperature coal tar into high-value-added chemicals is an important transformation and will gradually become the main utilization pathway.

[0003] Chinese invention CN116987523A relates to a method for preparing monocyclic aromatic hydrocarbons and naphtha using thermal decarbonization of medium- and low-temperature coal tar. The method involves distilling medium- and low-temperature coal tar at atmospheric and vacuum distillation to extract a >350℃ fraction of pitch; refining the extracted pitch using a solvent to obtain polycyclic aromatic hydrocarbon-rich refined pitch; compounding the polycyclic aromatic hydrocarbon-rich refined pitch with a functional solvent to obtain a compound mixture; and thermally decarbonizing the compound mixture under hydrogen conditions to obtain a product containing monocyclic aromatic hydrocarbons and naphtha. Chinese invention CN106701181B provides a method and apparatus for producing monocyclic aromatic hydrocarbons from a whole fraction of medium- and low-temperature coal tar using fractionation, light phase cracking refining, and heavy phase double cracking followed by refining and cracking of the whole fraction of medium- and low-temperature coal tar.

[0004] Chinese invention CN108641749B relates to a combined hydrogenation process for producing high-quality fuels from medium- and low-temperature coal tar. The medium- and low-temperature coal tar is distilled through a hydrothermal cracking unit, a first atmospheric distillation unit, a hydrorefining unit, a vacuum distillation unit, a diesel and wax oil hydrorefining unit, a wax oil hydrocracking unit, a gasoline and diesel precious metal hydrogenation unit, and a fourth atmospheric distillation unit to obtain the final products naphtha, jet fuel, and diesel fuel.

[0005] Chinese invention CN105694970B relates to a method for producing high-density jet fuel by hydrogenation of medium- and low-temperature coal tar. The method involves mixing and heating medium- and low-temperature coal tar and hydrogen, and then performing a hydrogenation reaction. The hydrogenation products are fractionated to obtain naphtha, crude jet fuel, and tail oil. The crude jet fuel is then refined with clay to obtain high-density No. 6 jet fuel with good oxidation stability, good demulsibility, and good insulation.

[0006] In summary, current technologies for producing fuel oil from medium- and low-temperature coal tar hydrogenation have led to the development of technologies for producing aromatics, naphthenic oils, and aerospace kerosene, thus expanding the product range of medium- and low-temperature coal tar hydrogenation. The products obtained from these technologies are mixtures obtained through fractionation of the hydrogenation products, with further processing of the fractionation products yielding aromatics, naphthenic oils, and aerospace kerosene. Currently, there is a lack of technologies for preparing chemicals from medium- and low-temperature coal tar. Developing such technologies could promote the development of medium- and low-temperature coal tar hydrogenation towards fine chemicals.

[0007] Based on this, the present invention designs a method and process system for preparing chemicals by hydrogenation of medium and low temperature coal tar to solve the above problems. Summary of the Invention

[0008] In view of the above-mentioned shortcomings of the existing technology, the present invention provides a method and process system for preparing chemicals by hydrogenation of medium and low temperature coal tar.

[0009] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing chemicals by hydrogenation of medium- and low-temperature coal tar includes the following steps: Medium- and low-temperature coal tar is added to a distillation column for fractionation. The bottom part of the distillation column yields the heavy fraction HO, and the top part yields the light fraction LO. LO is added to the first hydrogenation reactor to obtain LOL; HO is added to the second hydrogenation reactor to obtain HOH; LOL and HOH were added to the third hydrogenation reactor. After the reaction was completed, the mixture was added to the first and second distillation columns for fractional distillation to obtain cyclohexane, methylcyclohexane and toluene, respectively. The first hydrogenation reactor has a temperature of 240-300℃, a reaction pressure of 6-10 MPa, and a liquid hourly space velocity of 2-8 h⁻¹. -1 Hydrogen-to-oil ratio 500-1000:1; The catalyst support is γ-Al2O3, and the active materials of the catalyst are Ni, Mo and W; The fixed bed is filled as follows: the upper part is filled with NiMoγ-Al2O3, with NiMo active component 10-20% and Ni:Mo ratio 0.8-1.2:0.7-1; the middle part is filled with NiMoWγ-Al2O3, with NiMoW active component 10-20% and Ni:Mo:W ratio 0.5-1:0.5-1:0.5-1; the lower part is filled with NiWγ-Al2O3, with NiW active component 10-20% and Ni:W ratio 0.5-1:0.5-1. The second hydrogenation reactor operates at a temperature of 360-420℃, a reaction pressure of 15-20 MPa, and a liquid hourly space velocity of 0.5-1 h⁻¹. -1Hydrogen-to-oil ratio 800-1700:1; The catalyst supports are β-molecular sieves and γ-Al2O3, and the active materials of the catalyst are Ni, Co, Mo and W; The fixed bed is packed as follows: the upper part is filled with NiMoγ-Al2O3, with 20-30% NiMo active component and a Ni:Mo ratio of 0.8-1.2:0.7-1; the middle part is filled with NiMoWγ-Al2O3, with 10-20% NiMoW active component and a Ni:Mo:W ratio of 0.5-1:0.5-1:0.5-1; and the lower part is filled with CoMoγ-β molecular sieve, with 10-20% CoMo active component and a Ni:W ratio of 0.5-1:0.5-1. The third hydrogenation reactor operates at a temperature of 340-390℃, a reaction pressure of 14-18 MPa, and a liquid hourly space velocity of 0.8-1.2 h⁻¹. -1 Hydrogen-to-oil ratio 500-1200:1; The catalyst support is β molecular sieve and γ-Al2O3, and the active materials of the catalyst are Ni, Mo and W; The fixed bed is filled as follows: upper part NiMoWγ-Al2O3, with 20-30% NiMoW active component and a Ni:Mo:W ratio of 0.5-1:0.5-1:0.5-1; middle part NiMoγ-Al2O3, with 20-30% NiMo active component and a Ni:Mo ratio of 0.5-1:0.5-1; lower part W-β molecular sieve, with 10-20% W active component.

[0010] Furthermore, the specific process of adding LO to the first hydrogenation reactor to obtain LOL is as follows: The top part of the distillation column yields a light fraction LO, which enters the first feed tank. The LO in the first feed tank is added to the first pressurization pump, mixed with hydrogen, pressurized and preheated, and then enters the first hydrogenation reactor. In the first hydrogenation reactor, a demetallization and partial deoxygenation reaction of oxygen-containing compounds is carried out on the catalyst. After the reaction is completed, a light fraction LOL is obtained. The injection method is from bottom to top.

[0011] Furthermore, the specific process of adding HO to the second hydrogenation reactor to obtain HOH is as follows: The bottom part of the distillation column yields a heavy fraction HO, which enters the second feed tank. The HO in the second feed tank is added to the second pressurization pump, mixed with hydrogen, pressurized and preheated, and then enters the second hydrogenation reactor. Hydrogenation cracking reaction is carried out on the catalyst in the second hydrogenation reactor, and the hydrocracked oil HOH is obtained after the reaction. The injection method is from top to bottom.

[0012] Furthermore, the specific process of adding LOL and HOH to the third hydrogenation reactor is as follows: HOH and LOL are pressurized with hydrogen by the third pressurization pump and then enter the third hydrogenation reactor to undergo deoxygenation, saturation, cracking and secondary saturation reactions, respectively, to obtain the fraction LHO. The LHO fraction enters the high-pressure separator for gas-liquid separation. The gas phase enters the third feed tank after heat exchange, and the liquid phase is LHOR. The injection method is from top to bottom.

[0013] Furthermore, the distillation process specifically involves: LHOR is fed into the first distillation column for distillation. Cyclohexane is obtained at the top of the first distillation column, and the bottom material of the first distillation column is fed into the second distillation column for distillation. Methylcyclohexane is obtained at the top of the second distillation column, and toluene is obtained at the bottom of the second distillation column.

[0014] To better achieve the objectives of this invention, this invention also provides a chemical prepared by the above-described preparation method, specifically including cyclohexane, methylcyclohexane, and toluene.

[0015] To better achieve the objectives of this invention, this invention also provides a process system for chemical preparation, specifically comprising: Distillation column, first raw material storage tank, second raw material storage tank, first pressurizing pump, second pressurizing pump, first preheating furnace, second preheating furnace, first hydrogenation reactor, second hydrogenation reactor, third pressurizing pump, third hydrogenation reactor, high-pressure separator, third raw material storage tank, first distillation column and second distillation column; The top outlet of the distillation column is sequentially connected to the first raw material storage tank, the first pressurizing pump, the first preheating furnace, the first hydrogenation reactor, the third pressurizing pump, the third hydrogenation reactor, the high-pressure separator, the third raw material storage tank, the first distillation column, and the second distillation column via pipelines, and they are interconnected with each other. The bottom outlet of the distillation column is sequentially connected to the second raw material storage tank, the second pressurizing pump, the second preheating furnace, the second hydrogenation reactor, the third pressurizing pump, the third hydrogenation reactor, the high-pressure separator, the third raw material storage tank, the first distillation column, and the second distillation column via pipelines, and they are interconnected with each other. The top outlet of the high-pressure separator is fixedly connected to the third raw material storage tank through a pipeline and they are interconnected. The bottom outlet of the high-pressure separator is fixedly connected to the third pressurizing pump.

[0016] Furthermore, the first hydrogenation reactor is a pre-hydrogenation reactor; The second hydrogenation reactor is a hydrocracking reactor; The third hydrogenation reactor is a hydrogenation refining reactor.

[0017] Compared with the prior art, the beneficial effects of this invention are as follows: 1. The process method adopted in this invention realizes the utilization of the entire fraction of medium- and low-temperature coal tar. The heavy fraction of medium- and low-temperature coal tar is subjected to hydrocracking to lighten it, and further catalytically hydrocracking and saturation are used to obtain the target product. This method performs fractional conversion of the light and heavy fractions of medium- and low-temperature coal tar, making full use of all components of medium- and low-temperature coal tar and achieving good economic benefits.

[0018] 2. The process method adopted in this invention involves cracking and cyclizing aliphatic hydrocarbons in medium- and low-temperature coal tar to obtain aromatic hydrocarbons; hydrogenating and saturating polycyclic aromatic hydrocarbons and opening the ring to obtain light aromatic hydrocarbons; further partially saturating the light aromatic hydrocarbons to obtain cyclohexane, methylcyclohexane and toluene as target products, providing an effective method for the refined utilization of medium- and low-temperature coal tar. 3. The process of this invention is simple. Compared with the existing medium and low temperature coal tar hydrogenation process, it reduces the number of hydrogen reactions by 2-4, the catalyst preparation method is simple, the cost is low, the equipment investment is small, and it is easy to produce on a large scale. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0020] Figure 1 This is a process flow diagram for the preparation of chemicals from medium- and low-temperature coal tar hydrogenation according to the present invention; Figure 2 This is a detailed material composition diagram of the medium- and low-temperature coal tar raw material used in Example 1 of the present invention; Figure 3 This is a detailed material composition spectrum of LO in Example 1 of the present invention; Figure 4 This is a detailed material composition spectrum of HO in Example 1 of the present invention; Figure 5 This is a detailed material composition diagram of LOL in Example 1 of the present invention; Figure 6 This is a detailed material composition diagram of HOH in Example 1 of the present invention; Figure 7 This is a detailed material composition spectrum of LHO in Example 1 of the present invention; Figure 8 This is a detailed material composition diagram of LHOR in Example 1 of the present invention.

[0021] The labels in the diagram represent: 1001. Distillation column; 1002. First raw material storage tank; 1003. Second raw material storage tank; 1004. First pressurizing pump; 1005. Second pressurizing pump; 1006. First preheating furnace; 1007. Second preheating furnace; 1008. First hydrogenation reactor; 1009. Second hydrogenation reactor; 1010. Third pressurizing pump; 1011. Third hydrogenation reactor; 1012. High-pressure separator; 1013. Third raw material storage tank; 1014. First rectification column; 1015. Second rectification column. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] Example 1: The process flow diagram of the present invention is as follows. Figure 1 As shown, the process system of the present invention includes a distillation column 1001, a first raw material storage tank 1002, a second raw material storage tank 1003, a first pressurizing pump 1004, a second pressurizing pump 1005, a first preheating furnace 1006, a second preheating furnace 1007, a first hydrogenation reactor 1008, a second hydrogenation reactor 1009, a third pressurizing pump 1010, a third hydrogenation reactor 1011, a high-pressure separator 1012, a third raw material storage tank 1013, a first rectification column 1014, and a second rectification column 1015. The top outlet of the distillation column 1001 is sequentially connected to the first raw material storage tank 1002, the first pressurizing pump 1004, the first preheating furnace 1006, the first hydrogenation reactor 1008, the third pressurizing pump 1010, the third hydrogenation reactor 1011, the high-pressure separator 1012, the third raw material storage tank 1013, the first rectification column 1014, and the second rectification column 1015 via pipelines, and they are interconnected with each other. The bottom outlet of the distillation column 1001 is sequentially connected to the second raw material storage tank 1003, the second pressurizing pump 1005, the second preheating furnace 1007, the second hydrogenation reactor 1009, the third pressurizing pump 1010, the third hydrogenation reactor 1011, the high-pressure separator 1012, the third raw material storage tank 1013, the first rectification column 1014, and the second rectification column 1015 via pipelines, and they are interconnected with each other. The top outlet of the high-pressure separator 1012 is fixedly connected to the third raw material storage tank 1013 through a pipeline and they are interconnected. The bottom outlet of the high-pressure separator 1012 is fixedly connected to the third pressurizing pump 1010. The first hydrogenation reactor 1008 is a pre-hydrogenation reactor; The second hydrogenation reactor 1009 is a hydrocracking reactor; The third hydrogenation reactor 1011 is a hydrogenation refining reactor.

[0024] This embodiment provides a method for preparing chemicals by hydrogenation of medium- and low-temperature coal tar, specifically including the following steps: Step 1: Fractionation of medium- and low-temperature coal tar feedstock Medium- and low-temperature coal tar is fed into distillation tower 1001 for fractionation. Heavy fraction HO is obtained from the bottom of distillation tower 1001, and light fraction LO is obtained from the top of distillation tower 1001. LO enters the first raw material storage tank 1002, and HO enters the second raw material storage tank 1003.

[0025] The basic properties of the medium- and low-temperature coal tar are shown in Table 1.

[0026] Table 1 Basic Properties of Low-Temperature Coal Tar Step 2: First hydrogenation reaction LO from the first raw material storage tank 1002 enters the first pressurizing pump 1004, mixes and pressurizes with hydrogen, and then enters the first preheating furnace 1006. After preheating, it enters the first hydrogenation reactor 1008. The injection method is from bottom to top. The reaction conditions in the first hydrogenation reactor 1008 are: The temperature is 240-300℃, the reaction pressure is 6-10 MPa, and the liquid hourly space velocity is 2-8 h⁻¹. -1 Hydrogen-to-oil ratio 500-1000:1; The catalyst support is γ-Al2O3, and the active materials of the catalyst are Ni, Mo and W; The fixed bed is filled as follows: the upper part is filled with NiMoγ-Al2O3, with NiMo active component 10-20% and Ni:Mo ratio 0.8-1.2:0.7-1; the middle part is filled with NiMoWγ-Al2O3, with NiMoW active component 10-20% and Ni:Mo:W ratio 0.5-1:0.5-1:0.5-1; the lower part is filled with NiWγ-Al2O3, with NiW active component 10-20% and Ni:W ratio 0.5-1:0.5-1. After the reaction is complete, a light distillate is obtained (LOL).

[0027] Step 3: Second hydrogenation reaction The HO in the second raw material storage tank 1003 enters the second pressurizing pump 1005, mixes and pressurizes with hydrogen, and then enters the second preheating furnace 1007. After preheating, it enters the second hydrogenation reactor 1009. The injection method is from top to bottom. The reaction conditions in the second hydrogenation reactor 1009 are as follows: The temperature was 360-420℃, the reaction pressure was 15-20 MPa, and the liquid hourly space velocity was 0.5-1 h⁻¹. -1 Hydrogen-to-oil ratio 800-1700:1; The catalyst supports are β-molecular sieves and γ-Al2O3, and the active materials of the catalyst are Ni, Co, Mo and W; The fixed bed is packed as follows: the upper part is filled with NiMoγ-Al2O3, with 20-30% NiMo active component and a Ni:Mo ratio of 0.8-1.2:0.7-1; the middle part is filled with NiMoWγ-Al2O3, with 10-20% NiMoW active component and a Ni:Mo:W ratio of 0.5-1:0.5-1:0.5-1; and the lower part is filled with CoMoγ-β molecular sieve, with 10-20% CoMo active component and a Ni:W ratio of 0.5-1:0.5-1. After the reaction is complete, hydrocracking oil HOH is obtained.

[0028] Step 4: Third hydrogenation reaction LOL and HOH are pressurized together with hydrogen and then introduced into the third pressurization pump 1010, followed by the third hydrogenation reactor 1011. The injection method is from top to bottom. The reaction conditions in the third hydrogenation reactor 1011 are as follows: The temperature was 340-390℃, the reaction pressure was 14-18 MPa, and the liquid hourly space velocity was 0.8-1.2 h⁻¹. -1 Hydrogen-to-oil ratio 500-1200:1; The catalyst support is β molecular sieve and γ-Al2O3, and the active materials of the catalyst are Ni, Mo and W; The fixed bed packing method is as follows: upper part NiMoWγ-Al2O3, with NiMoW active component 20-30% and Ni:Mo:W ratio of 0.5-1:0.5-1:0.5-1; middle part NiMoγ-Al2O3, with NiMo active component 20-30% and Ni:Mo ratio of 0.5-1:0.5-1; lower part W-β molecular sieve, with W active component 10-20%. After the reaction is complete, the fraction LHO is obtained.

[0029] Step 5: Distillation to obtain chemicals LHO enters the high-pressure separator 1012 for gas-liquid separation. The gas phase enters the third raw material storage tank 1013 after heat exchange, and the liquid phase is LHOR. Part of LHOR (50%) is refluxed into the third pressurization pump 1010, mixed with HOH and LO as described in step four, and then pressurized before entering the third hydrogenation reactor 1011. The remaining LHOR enters the first distillation column 1014, where it is distilled under suitable temperature, pressure, and number of trays. Cyclohexane is obtained at the top of the first distillation column 1014, and toluene is obtained at the bottom.

[0030] like Figures 2-8 The figure shows the detailed material composition of the medium-low temperature coal tar raw material, LO, HO, LOL, HOH, LHO and LHOR in Example 1.

[0031] Example 2: This example provides a method for preparing chemicals by hydrogenation of medium- and low-temperature coal tar, specifically including the following steps: The hydrogenation reaction conditions and catalyst parameters for each reactor in Example 2 are shown in Tables 2 and 3.

[0032] Table 2 Hydrogenation reaction conditions in Example 2 Table 3 Catalyst parameters for Example 2 The remaining steps are the same as in Example 1.

[0033] Example 3: This example provides a method for preparing chemicals by hydrogenation of medium- and low-temperature coal tar, specifically including the following steps: The hydrogenation reaction conditions and catalyst parameters for each reactor in Example 3 are shown in Tables 4 and 5.

[0034] Table 4 Hydrogenation reaction conditions in Example 3 Table 5 Catalyst parameters for Example 3 The remaining steps are the same as in Example 1.

[0035] Example 4: This example provides a method for preparing chemicals by hydrogenation of medium- and low-temperature coal tar, specifically including the following steps: The hydrogenation reaction conditions and catalyst parameters for each reactor in Example 4 are shown in Tables 6 and 7.

[0036] Table 6 Hydrogenation reaction conditions for Example 4 Table 7 Catalyst parameters for Example 4 The remaining steps are the same as in Example 1.

[0037] The relevant properties of the materials in Examples 1-4 are shown in Table 8.

[0038] Table 8. Relevant properties of each material (10L / h) Through the implementation of this invention, target light cycloalkanes and aromatics such as cyclohexane, methylcyclohexane and toluene can be successfully produced in a low-temperature coal tar system in the whole fraction, realizing the efficient conversion and cascade utilization of the whole coal tar fraction and achieving the expected process effect.

[0039] As shown in Table 8, Example 1 demonstrates the advanced removal capabilities of the hydrogenation reactors at each stage of the present invention for heteroatom compounds containing oxygen and nitrogen, enabling the heavy components to be fully cracked and converted into lighter products that are easier to separate. This results in the purities of cyclohexane, methylcyclohexane, and toluene reaching 99.2%, 99.6%, and 88.7%, respectively, after distillation. Notably, the total content of the three target products in LHO reached 45.92%, the highest among the four examples.

[0040] In Example 2, without changing the catalyst type and overall system of Example 1, only the active components and their proportions were adjusted. The results showed a significant decrease in the denitrification efficiency of the pre-hydrogenation stage, with the nitrogen-containing compound content in LOL reaching 1.65%, far higher than the 0.16% in Example 1. This increased the denitrification burden on the second and third stage reactors. Although the nitrogen compounds were eventually removed from LHO, it affected the overall reaction equilibrium. Ultimately, the combined content of cyclohexane, methylcyclohexane, and toluene in the LHO stream was 43.72%, a decrease of 2.2% compared to Example 1. Furthermore, the aromatic hydrocarbon content (27.37%) in the intermediate stream HOH was also significantly lower than that in Example 1 (59.14%), indicating changes in cracking depth and aromatization pathway, resulting in a decrease in the lightening efficiency.

[0041] In Example 3, milder reaction conditions were used (lower limits for temperature and space velocity, and higher limits for pressure and hydrogen-to-oil ratio). The denitrification efficiency of the pre-hydrogenation stage was comparable to that of Example 1, demonstrating excellent impurity removal capabilities. However, due to the overall weaker reaction intensity and slightly lower degree of heavy component cracking, the total content of the target product in LHO was 45.05%, slightly lower than in Example 1. The aliphatic hydrocarbon / aromatic hydrocarbon ratio was close to that of Example 1, indicating that the hydrogenation saturation reaction was still sufficient. This example demonstrates that under relatively mild conditions, this process can still maintain high impurity removal efficiency and good product distribution, making it suitable for scenarios with lower requirements for catalyst lifetime and equipment load.

[0042] In Example 4, more stringent reaction conditions were employed (higher limits for temperature and space velocity, lower limits for pressure and hydrogen-to-oil ratio). The denitrification efficiency in the pre-hydrogenation stage was generally better than in Example 2 but worse than in Examples 1 and 3. The high temperature and low hydrogen-to-oil ratio promoted cracking and aromatization reactions, but may have led to some over-cracking; therefore, the total content of the target product in LHO was 43.70%, the lowest among the four examples. The relatively high aromatic content (42.70%) and relatively low aliphatic hydrocarbon content (57.20%) in LHO indicates a shift in the reaction pathway towards aromatization. This example is suitable for applications where higher aromatic yields (such as toluene) are desired.

[0043] The comparison shows that the catalyst and the content of each active component used in Example 1 ensured that the hydrotreating, cracking, and saturation reactions in each reactor section were within a more ideal operating range, exhibiting higher efficiency in the generation of light components. The entire system operated stably under these conditions, with high conversion rates and a reasonable distribution of light products, demonstrating good potential for industrial application and prospects for further scale-up development.

[0044] Comparative Example 1: Compared with Example 1, another medium-low temperature full-fraction coal tar was used as raw material, with other steps unchanged. The results of the LHO stream and distillation products obtained after changing the raw material are shown in Table 9.

[0045] Comparative Example 2: Using another medium-low temperature full-fraction coal tar as raw material, the catalyst, reaction temperature, pressure, space velocity and hydrogen-to-oil ratio conditions were the same as in Example 2. The results of the LHO stream and distillation products obtained after changing the raw material are shown in Table 9.

[0046] Table 9. Results of LHO streams and distillation products obtained after changing raw materials in Comparative Examples 1-2. As shown in Table 9, when only one type of low-temperature full-fraction coal tar was used as the feedstock (Comparative Example 1 and Comparative Example 2), all indicators showed a consistent trend. Firstly, the aliphatic hydrocarbon content in the LHO stream decreased compared to the previous examples, from 58.12% in Example 1 and 56.40% in Example 2 to 55.48% and 54.82%, respectively; while the aromatic hydrocarbon content increased accordingly. This change indicates that the heavy components and hydrogenation cracking characteristics of coal tar from different sources differ, leading to a slight decrease in the generation of light aliphatic hydrocarbons. However, this does not affect the selectivity and separation efficiency of the process for the target product. In summary, the process of this invention can operate stably under different low-temperature full-fraction coal tar feedstock conditions, and the product distribution pattern is clear with high product purity, fully demonstrating the strong adaptability and wide applicability of this invention, and showing good prospects for industrial application.

[0047] Comparative Example 3: Compared with Example 1, the parameters such as temperature, pressure, liquid hourly space velocity and hydrogen-to-oil ratio in the process were changed, while the catalyst used in each reactor was not changed. The specific parameter changes are shown in Table 10.

[0048] Comparative Example 4: Compared with Example 1, the parameters such as temperature, pressure, liquid hourly space velocity and hydrogen-to-oil ratio in the process were changed, while the catalyst used in each reactor was not changed. The specific parameter changes are shown in Table 10.

[0049] Table 10 Reaction conditions for Comparative Examples 3-4 The distillation product results of Comparative Examples 3-4 are shown in Table 11.

[0050] Table 11 Results of distillation products in Comparative Examples 3-4 As shown in Table 11, in Comparative Examples 3 and 4, the component distribution of LHO and the content and purity of the target product after distillation can be affected simply by adjusting the process parameters (temperature, pressure, liquid hourly space velocity and hydrogen-to-oil ratio).

[0051] In Comparative Example 3, the operating conditions of each reactor were at the lower limit of the range described in this invention. Due to the weaker reaction intensity and reduced degree of cracking and aromatization, the content of aliphatic hydrocarbons in LHO was relatively high, while the content of aromatic hydrocarbons decreased slightly. In contrast, Comparative Example 4 adopted the higher limit of the operating conditions of each reactor, and the overall level of hydrogenation cracking and aromatization was improved, resulting in an increase in the proportion of aromatic hydrocarbons and a decrease in the proportion of aliphatic hydrocarbons in LHO. Compared with Comparative Example 3, the toluene content of the three target products obtained by distillation was significantly increased.

[0052] In summary, although the feedstock and catalyst systems of Comparative Examples 3 and 4 remained unchanged, the process parameters affected the reaction depth, product distribution, and distillation efficiency of the hydrogenation process. However, regardless of whether the lower or higher limits of conditions were used, the three-stage hydrogenation process constructed in this invention maintained good reaction continuity and product controllability. Furthermore, the target product could be adjusted by regulating the reaction process conditions.

[0053] Comparative Example 5: Compared with Example 1, the catalyst used in the first hydrogenation reaction was changed: 1) The active ingredient in the upper part of the fixed bed is 10%, and the Ni:Mo ratio is 0.8:1; 2) The active ingredient in the middle of the fixed bed is 15%, and the Ni:Mo:W ratio is 0.5:1:0.5; 3) The active ingredient in the lower part of the fixed bed is 18%, and the Ni:W ratio is 0.5:1.

[0054] The other steps are the same as in Example 1.

[0055] Comparative Example 6: Compared with Example 2, the catalyst used in the first hydrogenation reaction was changed: 1) The active ingredient in the upper part of the fixed bed is 15%, and the Ni:Mo ratio is 1.2:1; 2) The active ingredient in the fixed bed is 18%, and the Ni:Mo:W ratio is 1:0.5:1; 3) The active ingredient in the lower part of the fixed bed is 20%, and the Ni:W ratio is 1:0.5.

[0056] The other steps are the same as in Example 2.

[0057] Comparative Example 7: Compared with Example 1, the catalyst used in the second hydrogenation reaction was changed: 1) The active ingredient in the upper part of the fixed bed is 30%, and the Ni:Mo ratio is 0.8:1.

[0058] 2) The active ingredient in the fixed bed is 25%, and the Ni:Mo:W ratio is 1:0.5:1; 3) The active ingredient in the lower part of the fixed bed is 15%, and the Co:Mo ratio is 0.8:1.

[0059] The other steps are the same as in Example 1.

[0060] Comparative Example 8: Compared with Example 2, the catalyst used in the second hydrogenation reaction was changed: 1) The active ingredient in the upper part of the fixed bed is 25%, and the Ni:Mo ratio is 1:1.

[0061] 2) The active ingredient in the fixed bed is 30%, and the Ni:Mo:W ratio is 0.5:1:0.5; 3) The active ingredient in the lower part of the fixed bed is 18%, and the Co:Mo ratio is 0.5:1.

[0062] The other steps are the same as in Example 2.

[0063] Comparative Example 9: Compared with Example 1, the catalyst used in the third hydrogenation reaction was changed: 1) The active ingredient in the upper part of the fixed bed is 25%, and the Ni:Mo:W ratio is 1:0.5:1; 2) The active ingredient in the middle of the fixed bed is 25%, and the Ni:Mo ratio is 1:1; 3) 15% active ingredients in the lower part of the fixed bed.

[0064] The other steps are the same as in Example 1.

[0065] Comparative Example 10: Compared with Example 2, the catalyst used in the third hydrogenation reaction was changed: 1) The active ingredient in the upper part of the fixed bed is 30%, and the Ni:Mo:W ratio is 1:0.5:1; 2) The active ingredient in the middle of the fixed bed is 30%, and the Ni:Mo ratio is 1:1; 3) 20% active ingredients in the lower part of the fixed bed.

[0066] The other steps are the same as in Example 2.

[0067] The results of the LHO stream and distillation products obtained from Comparative Examples 5-10 are shown in Table 12.

[0068] Table 12 Results of LHO streams and distillation products obtained from Comparative Examples 5-10 As shown in Table 12, compared with Examples 1 and 2, the hydrogenation effects of Comparative Examples 5, 7, and 9 all decreased to varying degrees, with the most significant decrease being in the residual nitrogen-containing compounds. 0.21% and 0.11% nitrogen-containing compounds were detected in LHO in Comparative Examples 5 and 7, respectively, while these impurities were completely removed in the examples. This indicates that after adjusting the catalyst composition in the first or second hydrogenation reaction, its hydrodenitrification (HDN) capacity was significantly insufficient. Such residues are usually related to a decrease in the content or dispersion of active metals, reducing the catalyst's efficiency in the hydrogenation cracking and saturation of nitrogen-containing aromatic heterocycles, thus affecting subsequent purification and separation steps. In terms of product distribution, the aromatic hydrocarbon content in Comparative Examples 5, 7, and 9 was slightly higher than in the examples, while the aliphatic hydrocarbon content decreased accordingly. This indicates that the decreased catalyst activity leads to insufficient saturation of heavy components, resulting in incomplete partial cracking and aromatization reactions. Furthermore, the contents of the three types of distillation products (cyclohexane, methylcyclohexane, and toluene) in Comparative Examples 5, 7, and 9 were all lower than those in the Example. The decrease in toluene and cyclohexane content was more pronounced in Comparative Examples 7 and 9, reflecting that insufficient catalyst activity not only reduces conversion rate but also affects the enrichment capacity of the light target product. In contrast, the product properties of Comparative Examples 6, 8, and 10 are closer to those of Example 2, indicating that when the catalyst in the second and third reaction stages maintains a reasonable metal ratio and acidic structure, even with slight adjustments to the first stage, the overall system can still maintain a high hydrogenation efficiency.

[0069] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing chemicals by hydrogenation of medium- and low-temperature coal tar, characterized in that, Includes the following steps: Medium- and low-temperature coal tar is added to a distillation column (1001) for fractionation. The bottom fraction of the distillation column (1001) is a heavy fraction HO, and the top fraction of the distillation column (1001) is a light fraction LO. LO is added to the first hydrogenation reactor (1008) to obtain LOL; HO is added to the second hydrogenation reactor (1009) to obtain HOH; LOL and HOH were added to the third hydrogenation reactor (1011), and after the reaction was completed, they were added to the first distillation column (1014) and the second distillation column (1015) for fractional distillation to obtain cyclohexane, methylcyclohexane and toluene, respectively. The first hydrogenation reactor (1008) has a temperature of 240-300℃, a reaction pressure of 6-10 MPa, and a liquid hourly space velocity of 2-8 h⁻¹. -1 Hydrogen-to-oil ratio 500-1000:1; The catalyst support is γ-Al2O3, and the active materials of the catalyst are Ni, Mo and W; The fixed bed is filled as follows: the upper part is filled with NiMoγ-Al2O3, with NiMo active component 10-20% and Ni:Mo ratio 0.8-1.2:0.7-1; the middle part is filled with NiMoWγ-Al2O3, with NiMoW active component 10-20% and Ni:Mo:W ratio 0.5-1:0.5-1:0.5-1; the lower part is filled with NiWγ-Al2O3, with NiW active component 10-20% and Ni:W ratio 0.5-1:0.5-1. The second hydrogenation reactor (1009) operates at a temperature of 360-420℃, a reaction pressure of 15-20 MPa, and a liquid hourly space velocity of 0.5-1 h⁻¹. -1 Hydrogen-to-oil ratio 800-1700:1; The catalyst supports are β-molecular sieves and γ-Al2O3, and the active materials of the catalyst are Ni, Co, Mo and W; The fixed bed is packed as follows: the upper part is filled with NiMoγ-Al2O3, with 20-30% NiMo active component and a Ni:Mo ratio of 0.8-1.2:0.7-1; the middle part is filled with NiMoWγ-Al2O3, with 10-20% NiMoW active component and a Ni:Mo:W ratio of 0.5-1:0.5-1:0.5-1; and the lower part is filled with CoMoγ-β molecular sieve, with 10-20% CoMo active component and a Ni:W ratio of 0.5-1:0.5-1. The third hydrogenation reactor (1011) operates at a temperature of 340-390℃, a reaction pressure of 14-18 MPa, and a liquid hourly space velocity of 0.8-1.2 h⁻¹. -1 Hydrogen-to-oil ratio 500-1200:1; The catalyst support is β molecular sieve and γ-Al2O3, and the active materials of the catalyst are Ni, Mo and W; The fixed bed is filled as follows: upper part NiMoWγ-Al2O3, with 20-30% NiMoW active component and a Ni:Mo:W ratio of 0.5-1:0.5-1:0.5-1; middle part NiMoγ-Al2O3, with 20-30% NiMo active component and a Ni:Mo ratio of 0.5-1:0.5-1; lower part W-β molecular sieve, with 10-20% W active component.

2. The method for preparing chemicals by hydrogenation of medium- and low-temperature coal tar according to claim 1, characterized in that, The specific process of adding LO to the first hydrogenation reactor (1008) to obtain LOL is as follows: The top fraction of the distillation column (1001) is distilled to obtain light fraction LO. LO enters the first raw material storage tank (1002). LO in the first raw material storage tank (1002) is added to the first pressurization pump (1004), mixed with hydrogen, pressurized and preheated, and then enters the first hydrogenation reactor (1008). In the first hydrogenation reactor (1008), a demetallization reaction and partial deoxygenation reaction of oxygen-containing compounds are carried out on the catalyst. After the reaction is completed, light fraction LOL is obtained. The injection method is from bottom to top.

3. The method for preparing chemicals by hydrogenation of medium- and low-temperature coal tar according to claim 1, characterized in that, The specific process of adding HO to the second hydrogenation reactor (1009) to obtain HOH is as follows: The bottom fraction of the distillation column (1001) is a heavy fraction HO, which enters the second feed tank (1003). The HO in the second feed tank (1003) is added to the second pressurization pump (1005), mixed with hydrogen, pressurized and preheated, and then enters the second hydrogenation reactor (1009). Hydrogenation cracking reaction is carried out on the catalyst in the second hydrogenation reactor (1009), and the hydrocracking oil HOH is obtained after the reaction. The injection method is from top to bottom.

4. The method for preparing chemicals by hydrogenation of medium- and low-temperature coal tar according to claim 1, characterized in that, The specific process of adding LOL and HOH to the third hydrogenation reactor (1011) is as follows: HOH and LOL are pressurized with hydrogen through the third pressurization pump (1010) and then enter the third hydrogenation reactor (1011) to undergo deoxygenation, saturation, cracking and secondary saturation reactions, respectively, to obtain the fraction LHO. The LHO fraction enters the high-pressure separator (1012) for gas-liquid separation. The gas phase enters the third raw material storage tank (1013) after heat exchange, and the liquid phase is LHOR. The injection method is from top to bottom.

5. The method for preparing chemicals by hydrogenation of medium- and low-temperature coal tar according to claim 1, characterized in that, The specific process of distillation is as follows: LHOR is fed into the first distillation column (1014) for distillation. Cyclohexane is obtained at the top of the first distillation column (1014). The bottom material of the first distillation column (1014) is fed into the second distillation column (1015) for distillation. Methylcyclohexane is obtained at the top of the second distillation column (1015). Toluene is obtained at the bottom of the second distillation column (1015).

6. A chemical substance prepared by the preparation method according to any one of claims 1-5, characterized in that, Specifically, it includes cyclohexane, methylcyclohexane, and toluene.

7. A process system for preparing chemicals according to claim 6, characterized in that, Specifically, it includes: Distillation column (1001), first raw material storage tank (1002), second raw material storage tank (1003), first pressurizing pump (1004), second pressurizing pump (1005), first preheating furnace (1006), second preheating furnace (1007), first hydrogenation reactor (1008), second hydrogenation reactor (1009), third pressurizing pump (1010), third hydrogenation reactor (1011), high pressure separator (1012), third raw material storage tank (1013), first rectification column (1014), and second rectification column (1015); The top outlet of the distillation column (1001) is sequentially connected to the first raw material storage tank (1002), the first pressurizing pump (1004), the first preheating furnace (1006), the first hydrogenation reactor (1008), the third pressurizing pump (1010), the third hydrogenation reactor (1011), the high-pressure separator (1012), the third raw material storage tank (1013), the first rectification column (1014), and the second rectification column (1015) via pipelines, and they are interconnected with each other; The bottom outlet of the distillation column (1001) is sequentially connected to the second raw material storage tank (1003), the second pressurizing pump (1005), the second preheating furnace (1007), the second hydrogenation reactor (1009), the third pressurizing pump (1010), the third hydrogenation reactor (1011), the high-pressure separator (1012), the third raw material storage tank (1013), the first distillation column (1014), and the second distillation column (1015) via pipelines and is interconnected with each other; The top outlet of the high-pressure separator (1012) is fixedly connected to the third raw material storage tank (1013) through a pipeline and they are interconnected. The bottom outlet of the high-pressure separator (1012) is fixedly connected to the third pressurizing pump (1010).

8. The process system for preparing chemicals according to claim 7, characterized in that: The first hydrogenation reactor (1008) is a pre-hydrogenation reactor; The second hydrogenation reactor (1009) is a hydrocracking reactor; The third hydrogenation reactor (1011) is a hydrogenation refining reactor.

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