A process for the preparation of coal-based linear alkylbenzene

Abstract

The present application relates to coal chemical and fine chemical technical field, specifically disclose a kind of coal-based straight-chain alkylbenzene preparation method, the preparation method includes the following steps: S1, coal-based fischer-tropsch synthesis oil C9~C13 fraction is mixed with benzene according to 10:1~15:1 mole ratio, nitrogen purging to oxygen content is less than 0.1%, send into fixed bed reactor;S2, at 100~120 ℃, 2.0~3.5 MPa, liquid space velocity 0.5~2.0 h ‑1 The following reaction;Catalyst has gradually enhanced gradient acid center from outside to inside, i.e. outer layer weak acid, middle layer medium acid, inner layer strong acid, and has 150 nm, 40 nm and 6 nm three-stage pore size, acid density 0.95~1.05 mmol / g;S3, product is recovered by flash separation benzene, vacuum rectification product is obtained.The present application is while maintaining 98% or more olefin conversion and straight-chain rate, 2-position substitution rate reaches 65%~70%.

Description

Technical Field

[0001] This invention relates to the fields of coal chemical and fine chemical technology, and more specifically, to a method for preparing coal-based linear alkylbenzenes. Background Technology

[0002] Currently, coal-based linear alkylbenzenes are an important raw material for the production of linear alkylbenzene sulfonates. The quality of these products depends not only on the linearity but also closely on the content of the 2-position substituted isomers. A higher 2-position substitution rate is beneficial for improving the product's biodegradability, detergent performance, and industrial application value; therefore, it has become an important indicator for the production of high-quality linear alkylbenzenes.

[0003] Current research mainly focuses on improving olefin conversion, extending catalyst lifespan, and enhancing catalyst resistance to water and oxygen-containing compounds. However, there is limited research on the formation rules and control methods of the 2-position substitution rate, and an effective selective control system has not yet been established. Due to the high α-olefin content, complex oxygen-containing compound composition, and wide carbon chain distribution of coal-based Fischer-Tropsch synthetic oils, carbocation migration and isomerization reactions easily occur during alkylation, resulting in a 2-position substitution rate that is typically only 40% to 50%, which is insufficient to meet the production requirements of high-end products.

[0004] A search revealed that Chinese patent application CN115043693A discloses a process for preparing coal-based linear alkylbenzenes. This process uses coal-based Fischer-Tropsch synthesis oil and benzene as reactants, and a molecular sieve supported on a strong acid cation exchange resin as a catalyst to carry out an alkylation reaction to prepare coal-based linear alkylbenzenes. The strong acid cation exchange resin used has an acid strength ≥0.9 mmol / g[H2O]. + The coal-based Fischer-Tropsch synthesis oil contains straight-chain olefins with a carbon number distribution of C9 to C13. This existing technology loads a strong acid-type cation exchange resin within the pores of a molecular sieve, exhibiting a certain shape selectivity for alkylbenzene products, a high straight-chain ratio, and maintaining a high olefin conversion rate without dehydrating or deoxygenating the reactants, thus improving catalyst lifetime.

[0005] However, the technology in this existing patent application still has the following shortcomings: First, its catalyst acid centers are provided only by strong acid cation exchange resin, the acid center type is single and the intensity distribution is uniform, and there is a lack of gradient design for the spatial distribution of acid centers. Secondly, after resin is loaded into the molecular sieve channels, the pore structure tends to become homogeneous, failing to form a multi-level gradient pore structure from macropores to micropores. While this catalyst system with uniform acid centers and uniform channels can achieve high olefin conversion and straight-chain ratios, it lacks effective spatial confinement and temporal control over the carbocation migration process. The carbocations generated after α-olefin activation at the acid centers easily undergo repeated migration and skeletal rearrangement between uniformly distributed strong acid sites, leading to a gradual shift in the substitution positions of the benzene ring and alkyl chain from the 2-position to the 3-position, 4-position, and even higher positions. Experimental verification shows that under the optimal process conditions of this existing technology, the 2-position substitution rate is only 48.5% (see Comparative Example 2), far below the requirement for the 2-position isomer content in high-end straight-chain alkylbenzene sulfonate products.

[0006] In addition, other common molecular sieve catalysts (such as Hβ molecular sieve and HY molecular sieve) can also be used for Fischer-Tropsch alkylation reactions, but their acid center distribution is singular and they lack gradient channel design. They also face the same technical problems of severe carbocation migration and low 2-position substitution rate (only 44% to 46%).

[0007] In summary, current technologies, including the resin-supported molecular sieve composite catalyst disclosed in the aforementioned patent document (CN115043693A), have failed to achieve full-pathway regulation of carbocation generation, migration, and electrophilic substitution reactions from the synergistic perspective of the spatial gradient distribution of acid centers and the pore gradient structure. How to significantly improve the 2-position substitution rate (breaking through to over 65%) while maintaining high olefin conversion (above 98%) and high linear chain ratio (above 98%) remains a pressing technical challenge in this field.

[0008] Therefore, this application proposes a method for preparing coal-based linear alkylbenzenes to solve the above-mentioned problems. Summary of the Invention

[0009] The purpose of this invention is to solve the technical problem of low 2-position substitution rate in existing coal-based linear alkylbenzene preparation methods, and to provide a coal-based linear alkylbenzene preparation method that, through the synergistic regulation of gradient pore structure, gradient acid center distribution, and reaction temperature, benzene ratio and space velocity, suppresses the secondary migration and isomerization of alkyl carbocations, so that the benzene ring preferentially undergoes electrophilic substitution at the 2-position to produce coal-based linear alkylbenzenes.

[0010] The above-mentioned objective of the present invention is achieved as follows: The present invention provides a method for preparing coal-based linear alkylbenzenes, comprising the following steps: S1. The coal-based Fischer-Tropsch synthetic oil is pretreated and the raw material is prepared. The C9 to C13 fraction of the Fischer-Tropsch synthetic oil is selected as the alkylation raw material. Benzene and the Fischer-Tropsch synthetic oil fraction are mixed at a molar ratio of 10:1 to 15:1. Nitrogen gas is used to purge the system so that the oxygen content is less than 0.1%. Then it is continuously transported to the fixed bed reaction system. S2. Continuous alkylation reaction is carried out in a fixed-bed reactor, with the reaction temperature controlled at 100–120℃, the reaction pressure controlled at 2.0–3.5 MPa, and the liquid hourly space velocity controlled at 0.5–2.0 h⁻¹. -1 ; The reactor is filled with a catalyst having a gradient acid center distribution structure that gradually strengthens from the outside to the inside, i.e., the outer layer is a weak acid site, the middle layer is a medium acid site, and the inner layer is a strong acid site; the catalyst has a three-order pore size distribution of 150 nm, 40 nm, and 6 nm; and the acid density of the catalyst is 0.95–1.05 mmol / g. S3. The reaction product is fed into a separation system for post-processing. Unreacted benzene is recovered by flash evaporation, and then light and heavy components are removed by vacuum distillation to obtain the target coal-based linear alkylbenzene product.

[0011] Furthermore, in step S1, the Fischer-Tropsch synthetic oil fraction contains 30%–45% straight-chain α-olefins, 1000–12000 ppm of oxygenated compounds, and 100–600 ppm of water.

[0012] Furthermore, in step S1, the molar ratio of benzene to Fischer-Tropsch synthesis oil fraction is 12:1.

[0013] Furthermore, the catalyst described in step S1 is activated with nitrogen at 120–150°C for 4–6 hours before loading.

[0014] Furthermore, in step S2, the reaction temperature is 110℃, the reaction pressure is 3.0 MPa, and the liquid hourly space velocity is 1.0 h⁻¹. -1 .

[0015] Furthermore, the fixed-bed reactor described in step S2 operates in a top-down flow mode.

[0016] Furthermore, in the three-level pore size distribution described in step S2, the outer layer macropores have a diameter of 150 nm, the middle layer mesopores have a diameter of 40 nm, and the inner layer micropores have a diameter of 6 nm.

[0017] Furthermore, the acid density of the catalyst described in step S2 is 1.00 mmol / g.

[0018] Furthermore, the separation system in step S3 includes a flash tank and a vacuum distillation column, wherein the flash tank is used to recover unreacted benzene and the vacuum distillation column is used to remove light and heavy components.

[0019] Furthermore, in step S1, the catalyst loading height accounts for 60% to 80% of the effective volume of the reactor.

[0020] The mechanism of action of this invention is as follows: In traditional catalysts, after olefins generate carbocations, they tend to migrate continuously at strong acid sites, causing the substitution position to gradually shift from the 2-position to the 3-position, 4-position, or even higher, thus reducing the selectivity of the target isomer. This invention achieves mild olefin adsorption at the outer weak acid site, rapid activation at the middle acid site, and promotes rapid electrophilic substitution of the benzene ring at the inner strong acid site. Furthermore, it utilizes gradient channels to achieve rapid product diffusion and desorption, effectively shortening the carbocation residence time, inhibiting skeletal rearrangement and secondary isomerization reactions, and ensuring that the alkyl chain preferentially remains at the 2-position for substitution. This significantly improves the selectivity of the 2-position isomer while maintaining high olefin conversion, straight-chain ratio, and catalyst stability.

[0021] Specifically, the present invention uses C9-C13 straight-chain α-olefins from coal-based Fischer-Tropsch synthesis oil as raw materials to construct a composite catalytic system with a gradient acid center and gradient pore structure working synergistically. This system is optimized and controlled by process parameters such as reaction temperature, benzene-olefin molar ratio, acid density, and space velocity, allowing olefins to preferentially undergo 2-position directional alkylation upon entering the catalyst channels. This effectively suppresses carbocation migration and deep isomerization reactions, thereby significantly improving the selectivity of the 2-position isomer in straight-chain alkylbenzenes while maintaining high olefin conversion and straight-chain ratio. The catalyst acid centers are distributed in a gradually increasing manner from the outside to the inside. The outer weak acid sites first adsorb α-olefins, the middle medium acid sites promote olefin activation, and the inner strong acid sites complete the benzene ring alkylation reaction. The product rapidly desorbs from the channels, reducing secondary rearrangement processes.

[0022] The gradient pore structure in this invention employs a synergistic design of macropores (150 nm), mesopores (40 nm), and micropores (6 nm) to enable hierarchical diffusion of reactants and products within pores of different sizes. The outer macropores reduce diffusion resistance, the mesopores in the middle layer improve the mass transfer efficiency of reactants, and the inner micropores provide shape-selective catalysis, limiting the formation of branched isomers and multi-substituted byproducts, and increasing the probability of 2-position substitution reactions.

[0023] When the number of acid centers is insufficient, the activation efficiency of olefins is low; conversely, excessively high acid density can easily induce continuous migration and isomerization of carbocations, reducing the proportion of isomers at the 2-position. This invention controls the catalyst acid density within the range of 0.95–1.05 mmol / g to achieve the optimal balance between activity and selectivity.

[0024] Since too low a benzene content can easily lead to an increase in polyalkylation reactions, while too high a benzene content will reduce the processing capacity and economy of the equipment, in order to further improve the selectivity of the target product, the present invention controls the benzene molar ratio in the range of 10:1 to 15:1, preferably 12:1, which can take into account both conversion rate and 2-position substitution rate, and obtain the best overall performance.

[0025] Excessive residence time of reactants in the catalyst bed increases the probability of carbocation migration and side reactions, while insufficient residence time reduces the degree of alkylation completion. This invention controls the liquid hourly space velocity (LHSV) to be between 0.5 and 2.0 h⁻¹. -1 Within the range, preferably 1.0 h -1 .

[0026] As temperature increases, the activation capacity of olefins increases, but excessively high temperatures can promote side reactions such as isomerization and cracking, leading to a decrease in selectivity at the 2-position. This invention controls the reaction temperature at 100–120°C, preferably 110°C.

[0027] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention achieves a breakthrough improvement in the 2-position substitution rate of coal-based linear alkylbenzenes. Existing technologies, including those using ordinary Hβ molecular sieves (44.1%) and HY molecular sieves (46.3%), have failed to exceed 50% in this area. Through the synergistic design of gradient acid centers and gradient pore structures, this invention increases the 2-position substitution rate to 68.4% under optimal process conditions. This is 19.9 percentage points higher than the best-performing resin-supported molecular sieve composite catalyst in the prior art, and 24.3 percentage points higher than ordinary Hβ molecular sieves. This improvement is not simply a matter of increased activity, but rather a fundamental optimization of the product isomer distribution achieved through the synergistic regulation of catalyst structure design and reaction process.

[0028] 2. While significantly improving the 2-position substitution rate, this invention also maintains excellent overall performance across all indicators. Under optimal process conditions, the olefin conversion rate reaches 99.2%, the linear LAB rate reaches 98.8%, the polyalkylbenzene content is only 1.2%, and the heavy component content is only 0.8%. This indicates that while significantly improving the selectivity of the target isomer, this invention does not sacrifice core indicators such as olefin conversion rate and linear rate, thus resolving the long-standing technical contradiction in existing technologies of "the difficulty in simultaneously achieving high conversion rate and high 2-position selectivity."

[0029] 3. After continuous operation for 1000 h, the olefin conversion rate of the catalyst of this invention remains above 98% (98.3% after 1000 h), and the 2-position substitution rate remains above 67% (67.2% after 1000 h). The activity decay is slow, indicating that the gradient acid center and gradient pore structure have good stability and anti-deactivation ability, and are suitable for long-term industrial operation.

[0030] 4. This invention simplifies the post-processing steps and reduces separation energy consumption. Due to the significant increase in the 2-position substitution rate of the product of this invention, the content of non-target isomers (3-position, 4-position and higher substitution isomers) is reduced accordingly. At the same time, the content of polyalkylbenzene is controlled below 1.5% and the content of heavy components is below 1.0%, which reduces the difficulty of product separation and purification and post-processing energy consumption, and improves the yield of target products and catalyst utilization efficiency.

[0031] In summary, this invention achieves directional control of the 2-position substitution reaction of coal-based straight-chain alkylbenzenes through the synergistic regulation of gradient acid centers, gradient pore structures, and reaction process parameters. It effectively suppresses carbocation migration and continuous isomerization processes, and while maintaining an olefin conversion rate of over 99% and a straight-chain rate of over 98%, it stably increases the 2-position substitution rate to over 68%. This results in significantly superior overall performance compared to existing technologies, and offers advantages such as simple process, stable operation, good economic efficiency, and broad prospects for industrial scale-up applications. Attached Figure Description

[0032] Figure 1 This is a flowchart of the preparation method in an embodiment of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the following description is provided in conjunction with the appendix. Figure 1 The present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0034] This invention provides a method for preparing coal-based linear alkylbenzenes, aiming to solve the technical problem of low 2-position substitution rate in existing coal-based linear alkylbenzene preparation methods. This method, through the synergistic regulation of gradient pore size structure, gradient acid center distribution, and reaction temperature, benzene ratio, and space velocity, suppresses the secondary migration and isomerization of alkyl carbocations, enabling preferential electrophilic substitution of the benzene ring at the 2-position in coal-based linear alkylbenzenes. Specifically, it includes the following steps: S1. Pre-treat and prepare raw materials for coal-based Fischer-Tropsch synthesis oil.

[0035] The C9-C13 fraction of Fischer-Tropsch synthetic oil was selected as the alkylation feedstock, with the straight-chain α-olefin content controlled at 30%-45%, the oxygen-containing compound content controlled at 1000-12000 ppm, and the water content controlled at 100-600 ppm. Benzene and the Fischer-Tropsch oil fraction were mixed at a molar ratio of 10:1 to 15:1, preferably 12:1, and the system was purged with nitrogen to reduce the oxygen content to below 0.1%. The mixture was then continuously pumped to a fixed-bed reaction system. Before loading, the catalyst was activated with nitrogen at 120-150°C for 4-6 hours, and the catalyst loading height occupied 60%-80% of the effective reactor volume.

[0036] S2. Continuous alkylation reaction is carried out in a fixed-bed reactor.

[0037] The reactor operates in a top-down flow mode, with the reaction temperature controlled at 100–120 °C, preferably 110 °C, the reaction pressure controlled at 2.0–3.5 MPa, preferably 3.0 MPa, and the liquid hourly space velocity controlled at 0.5–2.0 h⁻¹. -1 Preferably 1.0 h -1 The catalyst employs a gradient acid center structure with an outer weak acid, a middle medium acid, and an inner strong acid, and exhibits a three-tiered pore size distribution of 150 nm, 40 nm, and 6 nm. The α-olefin in the feedstock is first adsorbed and activated at the weak acid sites, then enters the deep pores to complete the benzene ring alkylation reaction. The resulting straight-chain alkylbenzenes are rapidly desorbed, thereby reducing carbocation migration and isomerization reactions. Under continuous operation, the olefin conversion rate can reach 98.5%–99.5%, the straight-chain fraction can reach over 98%, and the 2-position substitution rate can reach 65%–70%.

[0038] S3. The reaction products are then fed into a separation system for post-processing.

[0039] The reaction solution is first subjected to flash evaporation to recover unreacted benzene, with a benzene recovery rate exceeding 98%. Subsequently, light and heavy components are removed by vacuum distillation to obtain the target coal-based straight-chain alkylbenzene product. The polyalkylbenzene content in the product is controlled below 1.5%, and the heavy component content is below 1.0%, achieving a final product purity of over 99%. After continuous catalyst operation for 1000 hours, the olefin conversion rate remains above 98%.

[0040] In this invention, C9-C13 straight-chain α-olefins from coal-based Fischer-Tropsch synthesis oil are used as raw materials to construct a composite catalytic system with a gradient acid center and a gradient pore structure working synergistically. The system is optimized by controlling process parameters such as reaction temperature, benzene-olefin molar ratio, acid density, and space velocity. This allows olefins to preferentially undergo 2-position directional alkylation after entering the catalyst channels, effectively suppressing carbocation migration and deep isomerization reactions. This significantly improves the selectivity of the 2-position isomer in straight-chain alkylbenzenes while maintaining high olefin conversion and straight-chain ratio. The catalyst acid centers are distributed in a gradually increasing manner from the outside to the inside. The outer weak acid sites first adsorb α-olefins, the middle medium acid sites promote olefin activation, and the inner strong acid sites complete the benzene ring alkylation reaction. The product rapidly desorbs from the channels, reducing secondary rearrangement processes.

[0041] The present invention addresses the gradient pore size issue by employing a three-tiered pore structure design comprising macropores, mesopores, and micropores. This design enables hierarchical diffusion of reactants and products within pores of different sizes. The outer macropores reduce diffusion resistance, the mesopores enhance mass transfer efficiency, and the inner micropores provide shape-selective catalysis, limiting the formation of branched isomers and multi-substituted byproducts, and increasing the probability of 2-position substitution reactions. Catalyst performance under different pore size structures is shown in Table 1.

[0042] Table 1. Effect of different pore structures on catalytic performance

[0043] Regarding acid concentration control: When the number of acid centers is insufficient, the olefin activation efficiency is low; when the acid density is too high, it easily induces continuous migration and isomerization of carbocations, reducing the proportion of isomers at the 2-position. This invention controls the catalyst acid density within the range of 0.95–1.05 mmol / g to achieve the optimal balance between activity and selectivity. The experimental results are shown in Table 2.

[0044] Table 2 Effect of different acid densities on the 2-position substitution rate

[0045] Regarding the control of the benzene-olefin ratio: Too low a benzene content can easily lead to an increase in polyalkylation reactions, while too high a benzene content reduces the processing capacity and economic efficiency of the equipment. To further improve the selectivity of the target product, this invention optimizes the molar ratio of benzene to olefin. Experiments show that when the benzene-olefin molar ratio is controlled within the range of 10:1 to 12:1, both conversion rate and 2-position substitution rate can be balanced, achieving the best overall performance. The relevant results are shown in Table 3.

[0046] Table 3. Effect of benzene molar ratio on product composition

[0047] Regarding the control of residence time: Excessive residence time of reactants in the catalyst bed increases the probability of carbocation migration and side reactions, while insufficient residence time reduces the degree of alkylation completion. Therefore, this invention further optimizes the liquid hourly space velocity (LHSV). Experimental results show that when the LHSV is controlled at 1.0 h⁻¹... -1 When the position is around 1 / 2, the highest 2-position substitution rate can be obtained, as detailed in Table 4.

[0048] Table 4 Effect of liquid space velocity on catalytic performance

[0049] Regarding the control of reaction temperature: While increasing temperature enhances olefin activation, excessively high temperatures promote side reactions such as isomerization and cracking, leading to a decrease in 2-position selectivity. Experimental results show that the optimal overall performance is achieved when the reaction temperature is controlled at around 110 °C. This not only maintains an olefin conversion rate of over 99% but also achieves a 2-position substitution rate of 68.4%, approximately 20 percentage points higher than existing technologies. This fully demonstrates the technical advantages of the synergistic optimization of the gradient catalysis system and process parameters.

[0050] Table 5. Changes in product performance at different reaction temperatures

[0051] The implementation of the present invention will be described in detail below with reference to specific embodiments.

[0052] Example 1: Following the above-described scheme of the present invention, the catalyst acid density was controlled at 1.00 mmol / g, with pore sizes of 6 nm, 40 nm, and 150 nm respectively; the reaction temperature was 110 °C; the reaction pressure was 3 MPa; the benzene-to-olefin molar ratio was 12:1; and the liquid hourly space velocity was 1.0 h⁻¹. -1 After 400 hours of continuous operation, the product was analyzed by gas chromatography. The results showed that the catalyst had excellent catalytic performance, as detailed in Table 6.

[0053] Table 6 Reaction results under optimal process conditions

[0054] Example 2: Continuous stability evaluation was conducted using the optimal process conditions of Example 1. The device operated continuously for 1000 hours, and samples were collected every 200 hours to analyze changes in catalyst performance. The results showed that during long-term operation, the olefin conversion rate remained above 98%, the 2-position substitution rate remained above 67%, and the catalyst activity decayed slowly, indicating that the gradient acid center and gradient pore structure have good stability and resistance to deactivation. The experimental results are shown in Table 7.

[0055] Table 7. Results of catalyst stability test during continuous operation

[0056] Comparative Example 1: To verify the technical effect of the present invention, alkylation reactions were carried out under the same reaction conditions using ordinary Hβ molecular sieve catalyst, ordinary HY molecular sieve catalyst, and existing resin-supported molecular sieve composite catalyst. The reaction temperature was 110 °C, the reaction pressure was 3 MPa, the benzene-to-olefin molar ratio was 12:1, and the liquid hourly space velocity was 1.0 h⁻¹. -1 All other process conditions remained the same. Experimental results show that although ordinary molecular sieve catalysts can maintain a high olefin conversion rate, the single distribution of acid centers and severe carbocation migration lead to a significantly low substitution rate at the 2-position. The experimental results are shown in Table 8.

[0057] Table 8 Comparison of the performance of common molecular sieve catalysts

[0058] Comparative Example 2: A comparative experiment was conducted using a resin-supported molecular sieve composite catalyst from the existing technology. This catalyst can improve water and oxygen-containing compound resistance and appropriately increase catalyst lifespan. However, due to the uniform distribution of its acid centers and pore structure, it lacks effective control over the carbocation migration process, thus limiting the improvement in selectivity for the 2-position isomer. The experimental results are shown in Table 9.

[0059] Table 9 Performance of Existing Resin-Supported Molecular Sieves Catalysts

[0060] A comprehensive comparison of this invention with the three catalytic systems mentioned above reveals that, through the synergistic optimization of gradient acid centers, gradient pore structure, and process parameters, this invention maintains a 99.2% olefin conversion rate and a 98.8% straight-chain ratio while increasing the 2-position substitution rate to 68.4%. This represents an improvement of 24.3 percentage points compared to ordinary Hβ molecular sieves, 22.1 percentage points compared to ordinary HY molecular sieves, and 19.9 percentage points compared to existing resin-supported molecular sieve composite catalysts. This fully demonstrates the significant advantages of this invention in improving the selectivity of 2-position isomers.

[0061] Table 10 Comparison of comprehensive performance of different catalytic systems

[0062] The above comparative results show that the present invention does not simply improve catalyst activity, but achieves a significant improvement in the 2-position substitution selectivity through catalyst structure design and synergistic regulation of reaction process. While maintaining high conversion rate and high linear chain rate, it obtains a better product composition, demonstrating significant industrial application value.

[0063] In summary, through the above embodiments and comparative examples of this invention, the present invention achieves directional control of the 2-position substitution reaction of coal-based straight-chain alkylbenzenes by synergistic regulation of gradient acid centers, gradient pore structures, and reaction process parameters. This effectively suppresses carbocation migration and continuous isomerization processes, significantly increases the proportion of 2-position isomers, and reduces the formation of non-target isomers such as those at the 3 and 4 positions, as well as polyalkylbenzenes and secondary heavy components. Simultaneously, while maintaining an olefin conversion rate of over 99% and a straight-chain rate of over 98%, the 2-position substitution rate is stably increased to over 68%, reducing the difficulty of product separation and purification and post-processing energy consumption, and improving the yield of the target product and catalyst utilization efficiency. This invention possesses advantages such as simple process, stable operation, good economic efficiency, and broad prospects for industrial scale-up applications.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing coal-based linear alkylbenzenes, characterized in that, Includes the following steps: S1. The coal-based Fischer-Tropsch synthetic oil is pretreated and the raw material is prepared. The C9 to C13 fraction of the Fischer-Tropsch synthetic oil is selected as the alkylation raw material. Benzene and the Fischer-Tropsch synthetic oil fraction are mixed at a molar ratio of 10:1 to 15:

1. Nitrogen gas is used to purge the system so that the oxygen content is less than 0.1%. Then it is continuously transported to the fixed bed reaction system. S2, the continuous alkylation reaction is carried out in the fixed bed reactor, the reaction temperature is controlled at 100-120°C, the reaction pressure is controlled at 2.0-3.5 MPa, the liquid space velocity is controlled at 0.5-2.0 h -1 ; The reactor is filled with a catalyst having a gradient acid center distribution structure that gradually strengthens from the outside to the inside, i.e., the outer layer is a weak acid site, the middle layer is a medium acid site, and the inner layer is a strong acid site; the catalyst has a three-order pore size distribution of 150 nm, 40 nm, and 6 nm; and the acid density of the catalyst is 0.95–1.05 mmol / g. S3. The reaction product is fed into a separation system for post-processing. Unreacted benzene is recovered by flash evaporation, and then light and heavy components are removed by vacuum distillation to obtain the target coal-based linear alkylbenzene product.

2. The method for preparing coal-based linear alkylbenzene according to claim 1, characterized in that, The Fischer-Tropsch synthetic oil fraction in step S1 contains 30%–45% straight-chain α-olefins, 1000–12000 ppm of oxygenated compounds, and 100–600 ppm of water.

3. The method for preparing coal-based linear alkylbenzene according to claim 1, characterized in that, In step S1, the molar ratio of benzene to Fischer-Tropsch synthesis oil fraction is 12:

1.

4. The method for preparing coal-based linear alkylbenzene according to claim 1, characterized in that, The catalyst described in step S1 is activated with nitrogen at 120–150°C for 4–6 h before loading.

5. The method for preparing coal-based linear alkylbenzene according to claim 1, characterized in that, In step S2, the reaction temperature is 110℃, the reaction pressure is 3.0 MPa, and the liquid hourly space velocity is 1.0 h⁻¹. -1 .

6. The method for preparing coal-based linear alkylbenzene according to claim 1, characterized in that, The fixed-bed reactor described in step S2 operates in a top-down flow mode.

7. The method for preparing coal-based linear alkylbenzene according to claim 1, characterized in that, In the three-level pore size distribution described in step S2, the outer layer macropores have a diameter of 150 nm, the middle layer mesopores have a diameter of 40 nm, and the inner layer micropores have a diameter of 6 nm.

8. The method for preparing coal-based linear alkylbenzene according to claim 1, characterized in that, The acid density of the catalyst described in step S2 is 1.00 mmol / g.

9. The method for preparing coal-based linear alkylbenzene according to claim 1, characterized in that, The separation system described in step S3 includes a flash tank and a vacuum distillation column. The flash tank is used to recover unreacted benzene, and the vacuum distillation column is used to remove light and heavy components.

10. The method for preparing coal-based linear alkylbenzene according to claim 1, characterized in that, In step S1, the catalyst loading height accounts for 60% to 80% of the effective volume of the reactor.

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