Process for the production of aromatics by microwave catalytic dehydrogenation of petroleum naphtha
By using microwave catalysis and platinum-carbon fiber paper with a gradient pore structure, the problems of high-temperature side reactions and catalyst poisoning in naphtha dehydrogenation were solved, achieving low-temperature and efficient dehydrogenation to produce aromatics and improving the stability and selectivity of the catalyst.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- YULIN UNIV
- Filing Date
- 2024-04-19
- Publication Date
- 2026-06-19
AI Technical Summary
In the existing process of naphtha dehydrogenation to produce aromatics, side reactions are prone to occur under high temperature conditions, resulting in reduced selectivity and easy catalyst poisoning. The dynamic reversible process makes it difficult for hydrogen to escape, and the existing catalyst structure is not suitable for efficient dehydrogenation.
A platinum-carbon fiber paper with a gradient pore structure was prepared by oxidizing and etching carbon fibers using a microwave catalytic method. This paper was then used for naphtha dehydrogenation. Microwave-assisted catalysis reduced the reaction temperature and improved the dehydrogenation efficiency. Furthermore, local heating was achieved through microwave conversion of the carbon fibers, thereby reducing side reactions.
This method enables efficient dehydrogenation to produce aromatics at lower temperatures, reducing energy consumption, improving catalyst stability and selectivity, suppressing the enrichment of trace sulfur, and enhancing hydrogen spillover efficiency.
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Figure CN118304882B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalyst preparation technology, and relates to a method for preparing aromatics from naphtha by microwave catalytic dehydrogenation. Background Technology
[0002] Naphtha is an important petrochemical product. Through cracking and reforming, naphtha can yield important monomers such as ethylene, propylene, and dienes. It can also be used for catalytic aromatization to prepare BTX aromatic compounds such as benzene, toluene, and xylene. Typically, precious metals such as phosphorus (Pt) are used as catalytic active centers to catalyze the dehydrogenation of organic alkanes such as cyclohexane, methylcyclohexane, and butane. As a mixture, naphtha contains trace amounts of sulfur, which can easily lead to catalyst poisoning. The dehydrogenation of naphtha to BTX (benzene, toluene, xylene) requires low-pressure, high-temperature conditions, while BTX hydrogenation requires relatively high-pressure, low-temperature conditions. However, naphtha itself is a mixture, and dehydrogenation under high-temperature conditions easily leads to side reactions and reduced selectivity. Furthermore, the naphtha dehydrogenation process involves a dynamic reversible process (dehydrogenation and hydrogenation). Existing dehydrogenation catalysts are generally granular, and their composite packing with quartz sand increases the gas volume, making it difficult for hydrogen to escape. Summary of the Invention
[0003] The purpose of this invention is to provide a method for preparing aromatic catalysts by microwave-catalyzed dehydrogenation of naphtha. This method uses microwave-assisted catalysis to reduce the reaction temperature, achieves local catalytic heating to reduce side reactions, and has high dehydrogenation efficiency.
[0004] The technical solution adopted in this invention is a method for preparing aromatics from naphtha via microwave catalytic dehydrogenation, specifically including the following steps:
[0005] Step 1: Oxidize and etch the surfaces of four different diameter carbon fibers to obtain four modified carbon fibers.
[0006] Step 2: Prepare four platinum-carbon fibers of different diameters based on the four modified carbon fibers obtained in Step 1.
[0007] Step 3: Prepare platinum-carbon fiber paper with gradient pore structure based on the four different diameters of platinum-carbon fiber obtained in Step 2.
[0008] Step 4: Using the platinum-carbon fiber paper with the gradient pore structure obtained in Step 3 to catalyze naphtha, the naphtha is dehydrogenated to obtain aromatics.
[0009] The invention is further characterized by:
[0010] The specific process of step 1 is as follows:
[0011] Step 1.1: Take 1g-3g of carbon fibers with diameters of 50nm-80nm, 100nm-200nm, 500nm-800nm, and 1500nm-2000nm respectively, disperse them in 300mL-900mL of deionized water, and ultrasonically disperse them for 1h-3h with a power of 150W-450W respectively; then add 100mL-300mL of hydrogen peroxide and stir at room temperature for 3h-9h. After the reaction is completed, filter and wash with 200mL-600mL of deionized water three times to obtain four types of oxidized carbon fibers;
[0012] Step 1.2: Add the four types of oxidized carbon fibers obtained in Step 1.1 to 100mL-300mL of 3mol / L-9mol / L H2SO4 solution, stir at room temperature for 20min-60min, then add 1g-3g of NaHCO3 and continue stirring for 2h-6h. After the reaction is complete, filter and wash with 200mL-600mL of deionized water until the washing solution is neutral. Dry at 45℃-60℃ for 24h-48h to obtain the final product.
[0013] The specific process of step 2 is as follows:
[0014] Step 2.1: Take 0.5g-1.5g of the four modified carbon fibers respectively, disperse them in 300-900mL of deionized water, and ultrasonically disperse them with 150W-450W high power for 0.5h-1.5h respectively. Add 0.02g-0.06g of platinum nitrate and stir for 8h-24h respectively. After the reaction is completed, filter and wash with 200mL-600mL of deionized water three times. Dry at 45℃-60℃ for 24h-48h to obtain four platinum-supported materials.
[0015] Step 2.2: Four platinum-supported materials are placed in a tube furnace and reduced with hydrogen at 600-800 °C for 6-18 hours under nitrogen protection to obtain four platinum-carbon fibers of different diameters.
[0016] The specific process of step 3 is as follows:
[0017] Four different diameter platinum-carbon fibers, ranging from 0.05g to 0.15g, were dispersed in 20 mL to 60 mL of deionized water and ultrasonically dispersed at 150W to 450W for 0.5h to 1.5h. The platinum-carbon fibers with diameters of 50nm to 80nm were wet-filtered and formed into the first layer of paper. Platinum-carbon fibers with diameters of 100nm to 200nm, 500nm to 800nm, and 1500nm to 2000nm were then filtered and formed into the second, third, and fourth layers of paper, respectively. The resulting four-layer gradient pore structure platinum-carbon fiber paper was dried in a vacuum oven at 45℃ to 80℃ to obtain the final product.
[0018] The specific process of step 4 is as follows:
[0019] Platinum-carbon fiber paper is cut into circular pieces and placed in a fixed-bed catalytic device. Nitrogen is used as the carrier gas at a flow rate of 60 mL / min to 180 mL / min. The gas enters from the first layer of the platinum-carbon fiber paper and overflows from the fourth layer. The reaction pressure is 0.2 MPa to 0.3 MPa. Naphtha is injected through a peristaltic pump at a rate of 3 mL to 9 mL per hour. The microwave catalytic power is 100 to 300 W. The catalytic process is completed instantaneously, yielding the final product.
[0020] The beneficial effects of this invention are as follows: Compared with existing technologies (which use high-temperature dehydrogenation, easily generating carbon deposits, reducing reaction activity, resulting in high energy consumption and deteriorating catalyst stability), this invention uses Pt as the catalytic active center and employs hydrogen peroxide oxidation and sulfuric acid etching on the carbon fiber surface. The hydrogen peroxide oxidation and sulfuric acid etching process inhibits the accumulation of trace sulfur on the support surface during naphtha dehydrogenation. By loading Pt onto carbon fibers and stacking four different diameter Pt-carbon fibers to prepare a gradient structure Pt-carbon fiber paper, hydrogen escapes as the volume of naphtha dehydrogenation gas increases. The reaction is catalyzed using microwave-assisted heating; the use of carbon fiber as the support facilitates the conversion of microwaves into heat, achieving localized catalytic heating, reducing side reactions, and lowering energy consumption. Attached Figure Description
[0021] Figure 1 This is a gradient pore structure catalyst model and carrier gas flow direction in Example 1 of the method for preparing aromatics from naphtha dehydrogenation using microwave catalysis of the present invention.
[0022] Figure 2 Comparison of catalytic stability of Example 1 and Comparative Examples 1 and 4 of the method for preparing aromatic hydrocarbons by microwave catalytic dehydrogenation of naphtha according to the present invention. Detailed Implementation
[0023] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.
[0024] The present invention discloses a method for preparing aromatic hydrocarbon catalysts by microwave-catalyzed dehydrogenation of naphtha, which specifically includes the following steps:
[0025] Step 1 involves surface oxidation and etching treatment of four different diameter carbon fibers, specifically as follows:
[0026] Take 1-3g of carbon fibers (prepared from acrylonitrile) with diameters of 50-80nm, 100-200nm, 500-800nm, and 1500-2000nm respectively, and disperse them in 300mL-900mL of deionized water. Disperse each fiber using high-power ultrasonication at 150W-450W for 1-3 hours. Then add 100mL-300mL of hydrogen peroxide and stir at room temperature for 3-9 hours. After the reaction, filter and wash three times with 200mL-600mL of deionized water. Add the four types of oxidized carbon fibers to 100mL-300mL of 3-9mol / L H2SO4 solution, stir at room temperature for 20-60 minutes, then add 1-3g of NaHCO3 and continue stirring for 2-6 hours. After the reaction is complete, filter the solution and wash it with 200-600 mL of deionized water until the washing solution is neutral. Then dry it at 45℃-60℃ for 24-48 hours.
[0027] Step 2, the preparation of four different diameter Pt-carbon fibers, specifically:
[0028] Take 0.5-1.5 g of each of the four modified carbon fibers and disperse them in 300-900 mL of deionized water. Disperse each fiber using high-power ultrasonication at 150 W-450 W for 0.5-1.5 h, and then add 0.02-0.06 g of platinum nitrate and stir for 8-24 h. After the reaction, filter and wash three times with 200-600 mL of deionized water, then dry at 45-60 °C for 24-48 h. Place the four Pt-supported materials in a tube furnace and reduce them with hydrogen at 600-800 °C for 6-18 h under nitrogen protection.
[0029] Step 3, the preparation of Pt-carbon fiber paper with gradient pore structure, specifically involves:
[0030] Four different diameter Pt-carbon fibers (0.05-0.15 g each) were dispersed in 20-60 mL of deionized water and ultrasonically dispersed at 150 W-450 W for 0.5-1.5 h. The Pt-carbon fibers with a diameter of 50-80 nm were wet-filtered and formed into the first layer of paper (10 cm in diameter). Pt-carbon fibers with diameters of 100-200 nm, 500-800 nm, and 1500-2000 nm were then filtered and formed into the second, third, and fourth layers of paper, respectively. The resulting four-layer Pt-carbon fiber paper with a gradient pore structure was dried in a vacuum oven at 45-80 °C for later use.
[0031] Step 4, Pt-carbon fiber paper catalyzes naphtha dehydrogenation to aromatics, specifically as follows:
[0032] Cut Pt-carbon fiber paper into 2cm diameter circular pieces (larger diameter paper is prone to deformation) and place them in a fixed-bed catalytic device (Pt-carbon fiber paper has a four-layer structure, with a 50-80nm Pt-carbon fiber layer as the upper layer and a 1500-2000nm Pt-carbon fiber layer as the lower layer). The reaction carrier gas is nitrogen (nitrogen is introduced before heating and starting the reaction after the carbon paper catalyst is installed) at a flow rate of 60mL / min-180mL / min. The gas enters from the upper layer of the Pt-carbon fiber paper and overflows from the lower layer. The reaction pressure is 0.2-0.3MPa. Naphtha is injected through a peristaltic pump at an injection rate of 3-9mL per hour. The microwave catalytic power is 100-300W, and the catalytic process is completed instantaneously.
[0033] Example 1
[0034] Step 1 involves surface oxidation and etching treatment of four different diameter carbon fibers, specifically as follows:
[0035] 1 g of carbon fibers with diameters of 50 nm, 100 nm, 500 nm, and 1500 nm were taken respectively and dispersed in 300 mL of deionized water. Each dispersion was ultrasonically dispersed at 150 W for 1 h. Then, 100 mL of hydrogen peroxide was added to each dispersion and the mixture was stirred at room temperature for 3 h. After the reaction, the mixture was filtered, and each dispersion was washed three times with 200 mL of deionized water. The four types of oxidized carbon fibers were then added to 100 mL of a 3 mol / L H₂SO₄ solution and stirred at room temperature for 20 min. Then, 1 g of NaHCO₃ was added and stirring continued for 2 h. After the reaction, the mixture was filtered, and each dispersion was washed with 200 mL of deionized water until the washings were neutral. The mixture was then dried at 45 °C for 24 h.
[0036] Step 2, the preparation of four different diameter Pt-carbon fibers, specifically:
[0037] Four types of modified carbon fibers, each weighing 0.5 g, were dispersed in 300 mL of deionized water and ultrasonically dispersed at 150 W for 0.5 h. Then, 0.02 g of platinum nitrate was added and the mixture was stirred for 8 h. After the reaction, the mixture was filtered, washed three times with 200 mL of deionized water, and dried at 45 °C for 24 h. The four Pt-supported materials were then placed in a tube furnace and reduced with hydrogen at 600 °C for 6 h under nitrogen protection.
[0038] Step 3, the preparation of Pt-carbon fiber paper with gradient pore structure, specifically involves:
[0039] Four different diameter Pt-carbon fibers (0.05 g each) were dispersed in 20 mL of deionized water and ultrasonically dispersed at 150 W for 0.5 h. A 50 nm diameter Pt-carbon fiber was wet-filtered and formed into the first layer of paper (10 cm in diameter). Pt-carbon fibers with diameters of 100 nm, 500 nm, and 1500 nm were then filtered and formed into the second, third, and fourth layers of paper, respectively. The resulting four-layer Pt-carbon fiber paper with a gradient pore structure was dried in a vacuum oven at 45 °C for later use.
[0040] Step 4, Pt-carbon fiber paper catalyzes naphtha dehydrogenation to aromatics, specifically as follows:
[0041] Pt-carbon fiber paper was cut into 2cm diameter circular pieces and placed in a catalytic device (the Pt-carbon fiber paper has a four-layer structure, with a 50nm Pt-carbon fiber layer as the upper layer and a 1500nm Pt-carbon fiber layer as the lower layer). The carrier gas was nitrogen with a flow rate of 60mL per minute. The gas entered from the upper layer of the Pt-carbon fiber paper and overflowed from the lower layer. The reaction pressure was 0.2MPa. Naphtha was injected through a peristaltic pump at a rate of 3mL per hour. The microwave catalytic power was 100W.
[0042] Comparative Example 1 (The carbon fiber surface was not modified, resulting in low catalytic activity and low stability)
[0043] Step 1, the preparation of four different diameter Pt-carbon fibers, specifically:
[0044] Four types of raw carbon fibers, each weighing 0.5 g, were dispersed in 300 mL of deionized water and ultrasonically dispersed at 150 W for 0.5 h. Then, 0.02 g of platinum nitrate was added and the mixture was stirred for 8 h. After the reaction, the mixture was filtered, washed three times with 200 mL of deionized water, and dried at 45 °C for 24 h. The four Pt-supported materials were then placed in a tube furnace and reduced with hydrogen at 600 °C for 6 h under nitrogen protection.
[0045] Step 2, the preparation of Pt-carbon fiber paper with gradient pore structure, specifically involves:
[0046] Four different diameter Pt-carbon fibers (0.05 g each) were dispersed in 20 mL of deionized water and ultrasonically dispersed at 150 W for 0.5 h. A 50 nm diameter Pt-carbon fiber was wet-filtered and formed into the first layer of paper (10 cm in diameter). Pt-carbon fibers with diameters of 100 nm, 500 nm, and 1500 nm were then filtered and formed into the second, third, and fourth layers of paper, respectively. The resulting four-layer Pt-carbon fiber paper with a gradient pore structure was dried in a vacuum oven at 45 °C for later use.
[0047] Step 3, Pt-carbon fiber paper catalyzes naphtha dehydrogenation to aromatics, specifically as follows:
[0048] Pt-carbon fiber paper was cut into 2cm diameter circular pieces and placed in a catalytic device (the Pt-carbon fiber paper has a four-layer structure, with a 50 nm Pt-carbon fiber layer as the upper layer and a 1500 nm Pt-carbon fiber layer as the lower layer). The carrier gas was nitrogen, with a flow rate of 60 mL per minute. The gas entered from the upper layer of the Pt-carbon fiber paper and overflowed from the lower layer. The reaction pressure was 0.2 MPa. Naphtha was injected through a peristaltic pump at a rate of 3 mL per hour. The microwave catalytic power was 100 W.
[0049] Comparative Example 2 (Pt-carbon fiber paper, without gradient pore structure, with uniform porosity, and low hydrogen release rate)
[0050] Step 1, surface oxidation and etching treatment of 100nm carbon fiber, specifically as follows:
[0051] Take 1g of carbon fiber with a diameter of 100nm (acrylonitrile as the precursor), disperse it in 300mL of deionized water, and sonicate it using 150W high-power ultrasonication for 1h. Then add 100mL of hydrogen peroxide and stir at room temperature for 3h. After the reaction is complete, filter and wash with 200mL of deionized water three times. Add the oxidized carbon fiber to 100mL of 3mol / L H2SO4 solution, stir at room temperature for 20min, then add 1g of NaHCO3 and continue stirring for 2h. After the reaction is complete, filter and wash with 200mL of deionized water until the washing solution is neutral, and dry at 45℃ for 24h.
[0052] Step 2, the preparation of Pt-carbon fibers with a diameter of 100 nm, specifically involves:
[0053] 0.5 g of modified 100 nm carbon fiber was dispersed in 300 mL of deionized water and ultrasonically dispersed at 150 W for 0.5 h. Then, 0.02 g of platinum nitrate was added and stirred for 8 h. After the reaction, the mixture was filtered, washed three times with 200 mL of deionized water, and dried at 45 ℃ for 24 h. The Pt-supported material was then placed in a tube furnace and reduced with hydrogen at 600 ℃ for 6 h under nitrogen protection.
[0054] Step 3, the preparation of Pt-carbon fiber paper with gradient pore structure, specifically involves:
[0055] Take 0.2 g of Pt-carbon fiber with a diameter of 100 nm, disperse it in 80 mL of deionized water, and ultrasonically disperse it at 150 W for 0.5 h. Then, directly filter and shape the Pt-carbon fiber paper. Place the obtained Pt-carbon fiber paper in a vacuum oven and dry it at 45 °C for later use.
[0056] Step 4, Pt-carbon fiber paper catalyzes naphtha dehydrogenation to aromatics, specifically as follows:
[0057] Pt-carbon fiber paper was cut into 2cm diameter circular pieces and placed in a fixed-bed catalytic device. The carrier gas was nitrogen with a flow rate of 60 mL per minute. The gas entered from the upper layer of the Pt-carbon fiber paper and overflowed from the lower layer. The reaction pressure was 0.2 MPa. Naphtha was injected through a peristaltic pump at a rate of 3 mL per hour. The microwave catalytic power was 100 W.
[0058] Comparative Example 3 (In a four-layer gradient porous paper, the first and fourth layers are swapped, resulting in a low hydrogen release rate)
[0059] Step 1 involves surface oxidation and etching treatment of four different diameter carbon fibers, specifically as follows:
[0060] 1 g of carbon fibers with diameters of 50 nm, 100 nm, 500 nm, and 1500 nm (acrylonitrile as the precursor) were taken respectively and dispersed in 300 mL of deionized water. Each fiber was ultrasonically dispersed at 150 W for 1 h. Then, 100 mL of hydrogen peroxide was added and the mixture was stirred at room temperature for 3 h. After the reaction, the mixture was filtered, and each fiber was washed three times with 200 mL of deionized water. The four types of oxidized carbon fibers were then added to 100 mL of a 3 mol / L H₂SO₄ solution and stirred at room temperature for 20 min. Then, 1 g of NaHCO₃ was added and stirring continued for 2 h. After the reaction, the mixture was filtered, and each fiber was washed with 200 mL of deionized water until the washings were neutral. The fibers were then dried at 45 °C for 24 h.
[0061] Step 2, the preparation of four different diameter Pt-carbon fibers, specifically:
[0062] Four types of modified carbon fibers, each weighing 0.5 g, were dispersed in 300 mL of deionized water and ultrasonically dispersed at 150 W for 0.5 h. Then, 0.02 g of platinum nitrate was added and the mixture was stirred for 8 h. After the reaction, the mixture was filtered, washed three times with 200 mL of deionized water, and dried at 45 °C for 24 h. The four Pt-supported materials were then placed in a tube furnace and reduced with hydrogen at 600 °C for 6 h under nitrogen protection.
[0063] Step 3, the preparation of Pt-carbon fiber paper with gradient pore structure, specifically involves:
[0064] Four different diameter Pt-carbon fibers (0.05 g each) were dispersed in 20 mL of deionized water and ultrasonically dispersed at 150 W for 0.5 h. A 1500 nm diameter Pt-carbon fiber was wet-filtered and formed into the first layer of paper (10 cm in diameter). Pt-carbon fibers of 100 nm, 500 nm, and 50 nm were then filtered and formed into the second, third, and fourth layers of paper, respectively. The resulting four-layer Pt-carbon fiber paper with a gradient pore structure was dried in a vacuum oven at 45 °C for later use.
[0065] Step 4, Pt-carbon fiber paper catalyzes naphtha dehydrogenation to aromatics, specifically as follows:
[0066] Pt-carbon fiber paper was cut into 2cm diameter circular pieces and placed in a catalytic device (the Pt-carbon fiber paper has a four-layer structure, with a 50nm Pt-carbon fiber layer as the upper layer and a 1500nm Pt-carbon fiber layer as the lower layer). The carrier gas was nitrogen with a flow rate of 60 mL per minute. The gas entered from the upper layer of the Pt-carbon fiber paper and overflowed from the lower layer. The reaction pressure was 0.2 MPa. Naphtha was injected through a peristaltic pump at a rate of 3 mL per hour. The microwave catalytic power was 100 W.
[0067] Comparative Example 4 (Fixed-bed heating was used to replace microwave-assisted catalysis, resulting in decreased catalytic stability and high energy consumption).
[0068] Step 1 involves surface oxidation and etching treatment of four different diameter carbon fibers, specifically as follows:
[0069] 1 g of carbon fibers with diameters of 50 nm, 100 nm, 500 nm, and 1500 nm (acrylonitrile as the precursor) were taken respectively and dispersed in 300 mL of deionized water. Each fiber was ultrasonically dispersed at 150 W for 1 h. Then, 100 mL of hydrogen peroxide was added and the mixture was stirred at room temperature for 3 h. After the reaction, the mixture was filtered, and each fiber was washed three times with 200 mL of deionized water. The four types of oxidized carbon fibers were then added to 100 mL of a 3 mol / L H₂SO₄ solution and stirred at room temperature for 20 min. Then, 1 g of NaHCO₃ was added and stirring continued for 2 h. After the reaction, the mixture was filtered, and each fiber was washed with 200 mL of deionized water until the washings were neutral. The fibers were then dried at 45 °C for 24 h.
[0070] Step 2, the preparation of four different diameter Pt-carbon fibers, specifically:
[0071] Four types of modified carbon fibers, each weighing 0.5 g, were dispersed in 300 mL of deionized water and ultrasonically dispersed at 150 W for 0.5 h. Then, 0.02 g of platinum nitrate was added and the mixture was stirred for 8 h. After the reaction, the mixture was filtered, washed three times with 200 mL of deionized water, and dried at 45 °C for 24 h. The four Pt-supported materials were then placed in a tube furnace and reduced with hydrogen at 600 °C for 6 h under nitrogen protection.
[0072] Step 3, the preparation of Pt-carbon fiber paper with gradient pore structure, specifically involves:
[0073] Four different diameter Pt-carbon fibers (0.05 g each) were dispersed in 20 mL of deionized water and ultrasonically dispersed at 150 W for 0.5 h. A 50 nm diameter Pt-carbon fiber was wet-filtered and formed into the first layer of paper (10 cm in diameter). Pt-carbon fibers with diameters of 100 nm, 500 nm, and 1500 nm were then filtered and formed into the second, third, and fourth layers of paper, respectively. The resulting four-layer Pt-carbon fiber paper with a gradient pore structure was dried in a vacuum oven at 45 °C for later use.
[0074] Step 4, Pt-carbon fiber paper catalyzes naphtha dehydrogenation to aromatics, specifically as follows:
[0075] Pt-carbon fiber paper was cut into 2cm diameter circular pieces and placed in a high-temperature, high-pressure catalytic fixed-bed device (the Pt-carbon fiber paper has a four-layer structure, with a 50 nm Pt-carbon fiber layer as the upper layer and a 1500 nm Pt-carbon fiber layer as the lower layer). The carrier gas was nitrogen, with a flow rate of 60 mL per minute. The gas entered from the upper layer of the Pt-carbon fiber paper and overflowed from the lower layer. The reaction pressure was 0.2 MPa. Naphtha was injected through a peristaltic pump at a rate of 3 mL per hour. The reaction temperature was 300-350 ℃, and the heating power was 400 W.
[0076] Analysis and Testing
[0077] like Figure 1 This is a structural model of the catalyst in Example 1, wherein the first layer consists of Pt-carbon fibers with a diameter of 50 nm, and the second, third, and fourth layers are Pt-carbon fiber paper with a gradient structure composed of carbon fibers with diameters of 100, 500, and 1000 nm, respectively, from top to bottom. During catalytic dehydrogenation, the carrier gas flow direction is from the first layer to the fourth layer.
[0078] Table 1: Porosity of each layer in Example 1
[0079]
[0080] Porosity S = 1 - (ρ2 / ρ1), where ρ1 is the inherent density of the carbon fiber, ρ2 is the density of the carbon fiber film, ρ2 = m / (A x h), where m is the mass of the paper, A is the area of the paper, and h is the thickness of the paper. Paper was made from four different Pt-carbon fibers, and their porosities were measured.
[0081] Table 2: Catalytic naphtha performance of Examples 1 and Comparative Examples 1-4
[0082]
[0083] As shown in Table 2, compared with Example 1, the instantaneous hydrogen release rate of Comparative Example 1 showed a significant decrease in the proportion of hydrogen gas. In Comparative Example 1, the carrier was not oxidized or etched.
[0084] Compared with Example 1, the instantaneous hydrogen release rate, hydrogen content, and conversion rate of Comparative Examples 2 and 3 decreased significantly. This is because there is no gradient structure in the Pt-carbon fiber paper, and naphtha dehydrogenation is a reaction in which the gas volume increases, resulting in greater gas resistance and hindering the rapid release of hydrogen.
[0085] Compared with Example 1, the instantaneous hydrogen release rate and selectivity of Comparative Example 4 were reduced. This may be because Comparative Example 4 adopted a fixed-bed reaction with a higher temperature, which led to the generation of side reactions during the dehydrogenation reaction, resulting in a more obvious lower selectivity for BTX.
[0086] The microwave-assisted catalytic reaction used in Example 1 and Comparative Examples 1-3 had a reaction power of 100W, while the fixed-bed heating catalytic reaction used in Comparative Example 4 had a power of 400W, resulting in a significant increase in energy consumption.
[0087] like Figure 2 The figures show the catalytic stability of Example 1 and Comparative Examples 1 and 4 after 11 hours of continuous catalysis. In Example 1, the catalyst activity stability decreased by 1.5% after 11 hours of continuous reaction, while in Comparative Example 1, the catalyst activity stability decreased by 8.5%. This may be because trace amounts of sulfur in the naphtha poisoned the catalyst, resulting in poor stability. In Example 1, oxidation and sulfuric acid etching effectively prevented sulfur accumulation on the support surface. The catalyst activity stability of Comparative Example 4 decreased by 4.5, mainly due to the higher reaction temperature of the fixed-bed heated catalysis, which led to catalyst structural damage.
[0088] Example 2
[0089] Step 1 involves surface oxidation and etching treatment of four different diameter carbon fibers, specifically as follows:
[0090] 3g of carbon fibers with diameters of 80nm, 200nm, 800nm, and 2000nm were taken respectively and dispersed in 900mL of deionized water. Each dispersion was ultrasonically dispersed at 450W for 3 hours. Then, 300mL of hydrogen peroxide was added to each dispersion and the mixture was stirred at room temperature for 9 hours. After the reaction, the mixture was filtered, and each dispersion was washed three times with 600mL of deionized water. The four types of oxidized carbon fibers were then added to 300mL of 9mol / L H₂SO₄ solution and stirred at room temperature for 60 minutes. Then, 3g of NaHCO₃ was added and stirring continued for 6 hours. After the reaction, the mixture was filtered, and each dispersion was washed with 600mL of deionized water until the washings were neutral. The mixtures were then dried at 60℃ for 48 hours.
[0091] Step 2, the preparation of four different diameter Pt-carbon fibers, specifically:
[0092] 1.5 g of each of the four modified carbon fibers were dispersed in 900 mL of deionized water and ultrasonically dispersed at 450 W for 1.5 h. Then, 0.06 g of platinum nitrate was added and the mixture was stirred for 24 h. After the reaction, the mixture was filtered and washed three times with 600 mL of deionized water, and dried at 60 °C for 48 h. The four Pt-supported materials were then placed in a tube furnace and reduced with hydrogen at 800 °C for 18 h under nitrogen protection.
[0093] Step 3, the preparation of Pt-carbon fiber paper with gradient pore structure, specifically involves:
[0094] Four different diameter Pt-carbon fibers (0.15 g each) were dispersed in 60 mL of deionized water and ultrasonically dispersed at 450 W for 1.5 h. The 80 nm diameter Pt-carbon fiber was wet-filtered and formed into the first layer of paper (10 cm in diameter). Pt-carbon fibers with diameters of 200 nm, 800 nm, and 2000 nm were then filtered and formed into the second, third, and fourth layers of paper, respectively. The resulting four-layer Pt-carbon fiber paper with a gradient pore structure was dried in a vacuum oven at 80 °C for later use.
[0095] Step 4, Pt-carbon fiber paper catalyzes naphtha dehydrogenation to aromatics, specifically as follows:
[0096] Pt-carbon fiber paper was cut into 2cm diameter circular pieces and placed in a catalytic device (the Pt-carbon fiber paper has a four-layer structure, with an 80nm Pt-carbon fiber layer as the upper layer and a 2000nm Pt-carbon fiber layer as the lower layer). The carrier gas was nitrogen with a flow rate of 180mL per minute. The gas entered from the upper layer of the Pt-carbon fiber paper and overflowed from the lower layer. The reaction pressure was 0.3MPa. Naphtha was injected through a peristaltic pump at a rate of 9mL per hour. The microwave catalytic power was 300W.
[0097] Example 3
[0098] Step 1 involves surface oxidation and etching treatment of four different diameter carbon fibers, specifically as follows:
[0099] Two g of carbon fibers with diameters of 60 nm, 150 nm, 700 nm, and 1800 nm were taken respectively and dispersed in 800 mL of deionized water. Each dispersion was ultrasonically dispersed at 300 W for 2 h. Then, 200 mL of hydrogen peroxide was added to each dispersion and the mixture was stirred at room temperature for 7 h. After the reaction, the mixture was filtered, and each dispersion was washed three times with 400 mL of deionized water. The four types of oxidized carbon fibers were then added to 200 mL of 6 mol / L H₂SO₄ solution and stirred at room temperature for 40 min. Then, 2 g of NaHCO₃ was added and stirring continued for 4 h. After the reaction, the mixture was filtered, and each dispersion was washed with 400 mL of deionized water until the washings were neutral. The mixture was then dried at 50 °C for 36 h.
[0100] Step 2, the preparation of four different diameter Pt-carbon fibers, specifically:
[0101] 1.0 g of each of the four modified carbon fibers was dispersed in 600 mL of deionized water and ultrasonically dispersed at 300 W for 0.8 h. Then, 0.04 g of platinum nitrate was added and stirred for 12 h. After the reaction, the mixture was filtered, washed three times with 400 mL of deionized water, and dried at 50 °C for 36 h. The four Pt-supported materials were then placed in a tube furnace and reduced with hydrogen at 700 °C for 12 h under nitrogen protection.
[0102] Step 3, the preparation of Pt-carbon fiber paper with gradient pore structure, specifically involves:
[0103] Four different diameter Pt-carbon fibers (0.10 g each) were dispersed in 40 mL of deionized water and ultrasonically dispersed at 300 W for 1.0 h. A 70 nm diameter Pt-carbon fiber was wet-filtered and formed into the first layer of paper (10 cm in diameter). Pt-carbon fibers with diameters of 150 nm, 700 nm, and 1800 nm were then filtered and formed into the second, third, and fourth layers of paper, respectively. The resulting four-layer Pt-carbon fiber paper with a gradient pore structure was dried in a vacuum oven at 70 °C for later use.
[0104] Step 4, Pt-carbon fiber paper catalyzes naphtha dehydrogenation to aromatics, specifically as follows:
[0105] Pt-carbon fiber paper was cut into 2cm diameter circular pieces and placed in a catalytic device (the Pt-carbon fiber paper has a four-layer structure, with a 70nm Pt-carbon fiber layer as the upper layer and an 1800nm Pt-carbon fiber layer as the lower layer). The carrier gas was nitrogen with a flow rate of 120mL per minute. The gas entered from the upper layer of the Pt-carbon fiber paper and overflowed from the lower layer. The reaction pressure was 0.25MPa. Naphtha was injected through a peristaltic pump at a rate of 7mL per hour. The microwave catalytic power was 200W.
Claims
1. A process for the dehydrogenation of naphtha catalytically using microwaves to produce aromatics, characterized in that: Specifically, the steps include the following: Step 1 involves oxidizing and etching the surfaces of four different diameter carbon fibers to obtain four modified carbon fibers; the specific process of Step 1 is as follows: Step 1.1: Take 1g-3g of carbon fibers with diameters of 50nm-80nm, 100nm-200nm, 500nm-800nm, and 1500nm-2000nm respectively, disperse them in 300mL-900mL of deionized water, and ultrasonically disperse them for 1h-3h at a power of 150W-450W respectively; then add 100mL-300mL of hydrogen peroxide and stir at room temperature for 3h-9h. After the reaction is completed, filter and wash with 200mL-600mL of deionized water three times to obtain four types of oxidized carbon fibers; Step 1.2: Add the four types of oxidized carbon fibers obtained in Step 1.1 to 100mL-300mL of 3mol / L-9mol / L H2SO4 solution, stir at room temperature for 20min-60min, then add 1g-3g of NaHCO3 and continue stirring for 2h-6h. After the reaction is complete, filter and wash with 200mL-600mL of deionized water until the washing solution is neutral. Dry at 45℃-60℃ for 24h-48h to obtain the final product. Step 2: Prepare four platinum-carbon fibers of different diameters based on the four modified carbon fibers obtained in Step 1. Step 3: Prepare platinum-carbon fiber paper with gradient pore structure based on the four different diameters of platinum-carbon fiber obtained in Step 2. Step 4: Using the platinum-carbon fiber paper with the gradient pore structure obtained in Step 3 to catalyze naphtha, the naphtha is dehydrogenated to obtain aromatics.
2. The process for the dehydrogenation of catalytic naphtha to aromatics by microwave according to claim 1, characterized in that: The specific process of step 2 is as follows: Step 2.1: Take 0.5g-1.5g of the four modified carbon fibers respectively, disperse them in 300-900mL of deionized water, and ultrasonically disperse them with 150W-450W high power for 0.5h-1.5h respectively. Add 0.02g-0.06g of platinum nitrate and stir for 8h-24h respectively. After the reaction is completed, filter and wash with 200mL-600mL of deionized water three times. Dry at 45℃-60℃ for 24h-48h to obtain four platinum-supported materials. Step 2.2: Four platinum-supported materials are placed in a tube furnace and reduced with hydrogen at 600-800 °C for 6-18 hours under nitrogen protection to obtain four platinum-carbon fibers of different diameters.
3. The process for the dehydrogenation of catalytic naphtha to aromatics by microwave according to claim 2, characterized in that: The specific process of step 3 is as follows: Four different diameter platinum-carbon fibers, ranging from 0.05g to 0.15g, were dispersed in 20 mL to 60 mL of deionized water and ultrasonically dispersed at 150W to 450W for 0.5h to 1.5h. The platinum-carbon fibers with diameters of 50nm to 80nm were wet-filtered and formed into the first layer of paper. Platinum-carbon fibers with diameters of 100nm to 200nm, 500nm to 800nm, and 1500nm to 2000nm were then filtered and formed into the second, third, and fourth layers of paper, respectively. The resulting four-layer gradient pore structure platinum-carbon fiber paper was dried in a vacuum oven at 45℃ to 80℃ to obtain the final product.
4. The process for the dehydrogenation of catalytic naphtha to aromatics by microwave according to claim 3, characterized in that: The specific process of step 4 is as follows: Platinum-carbon fiber paper is cut into circular pieces and placed in a fixed-bed catalytic device. Nitrogen is used as the carrier gas at a flow rate of 60 mL / min to 180 mL / min. The gas enters from the first layer of the platinum-carbon fiber paper and overflows from the fourth layer. The reaction pressure is 0.2 MPa to 0.3 MPa. Naphtha is injected through a peristaltic pump at a rate of 3 mL to 9 mL per hour. The microwave catalytic power is 100 to 300 W. The catalytic process is completed instantaneously, yielding the final product.