Method for synthesizing p-xylene by using h-mww molecular sieve as catalyst
By using H-MWW molecular sieve catalyst, the problems of low activity and easy carbon deposition and deactivation of molecular sieve catalysts were solved, and the high-efficiency catalytic synthesis of p-xylene from 2,5-dimethylfuran was achieved, with high conversion rate and selectivity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHANGZHOU UNIV
- Filing Date
- 2023-08-03
- Publication Date
- 2026-07-31
AI Technical Summary
Existing molecular sieve catalysts exhibit low activity in the synthesis of p-xylene from 2,5-dimethylfuran, are prone to coking and deactivation, have high resistance to mass transfer and diffusion, and are difficult to effectively utilize internal active sites.
Using H-MWW molecular sieve catalysts, H-MCM-22, H-ITQ-2, or H-MCM-36 were prepared from self-made MCM-22(P) without template removal agent. These catalysts have nanosheet structures and high external specific surface areas and were used for the reaction of 2,5-dimethylfuran and acrylic acid at a reaction temperature of 120℃ to 240℃ under nitrogen protection.
It improved catalytic activity and selectivity, reduced coking rate, achieved 99% 2,5-DMF conversion and 97% PX selectivity, with a coking rate of only 2.2%, significantly improving mass transfer and diffusion performance.
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Figure CN117069558B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of chemical catalysis technology, specifically relating to a method for synthesizing p-xylene (PX) from 2,5-dimethylfuran (2,5-DMF) and acrylic acid (AA) using H-MWW molecular sieve as a catalyst. Background Technology
[0002] PX is an important organic raw material and a fundamental raw material in the aromatic hydrocarbon industry chain. Approximately 97% of PX is used to produce purified terephthalic acid, while the remaining 3% is mainly used to prepare dimethyl terephthalate. Terephthalic acid can be further reacted with ethylene glycol to produce polyethylene terephthalate (PET). PET can be used to produce polyester fibers and polyester plastics, which are widely used in textiles, packaging, and other fields.
[0003] Currently, PX production methods both domestically and internationally include aromatics co-production processes, toluene disproportionation, toluene-methanol alkylation, and xylene isomerization. Compared to these methods, the synthetic route using biomass-derived 2,5-dimethylfuran as a raw material offers advantages such as low pollution, high yield, and green sustainability, thus demonstrating strong industrial application prospects.
[0004] Commonly used phosphate catalysts, composite metal oxides, and ionic liquid catalysts suffer from environmental inefficiencies, generally high costs, and difficulties in separating them from products. Molecular sieves are widely used due to their high thermal stability, tunable LiDAR and Beta acid sites, high specific surface area, and large pore volume. However, commonly used molecular sieve catalysts (such as ZSM-5, Y-type, and Beta-type) have small pore sizes, resulting in severe mass transfer and diffusion resistance during reactions. This makes it difficult to effectively utilize the active sites within the catalyst, leading to low catalyst activity and a tendency for carbon deposition and deactivation.
[0005] Therefore, there is an urgent need to develop a highly active molecular sieve catalyst with a low coking rate for use in the synthesis of p-xylene (PX) from 2,5-dimethylfuran. Summary of the Invention
[0006] This invention addresses the problems of low activity and easy coking and deactivation of molecular sieve catalysts in the existing reaction for synthesizing PX from 2,5-dimethylfuran. It provides an H-MWW molecular sieve as a catalyst, which exhibits high catalytic activity and selectivity as well as low coking rate.
[0007] To solve the above-mentioned technical problems, the present invention is carried out according to the following steps:
[0008] A method for synthesizing PX using H-MWW molecular sieve catalysis is characterized by using 2,5-dimethylfuran and acrylic acid as reactants, wherein the molar ratio of 2,5-dimethylfuran to acrylic acid is 1:1 to 1:4 (the amount of 2,5-dimethylfuran is 7.5 mmol); the method uses a self-made H-MWW molecular sieve as a catalyst, with an amount of 0.10 g; the reaction is carried out in a magnetically stirred tank at a reaction temperature of 120℃ to 240℃, with nitrogen as a protective gas.
[0009] As a limitation of the present invention, the H-MWW molecular sieve catalyst described in the present invention can be any one of H-MCM-22, H-ITQ-2 or H-MCM-36. All three H-MWW molecular sieves are prepared from MCM-22(P) without detemplating agent and have a nanosheet structure. The Si / Al ratio of the H-MWW molecular sieve catalyst is between 10 and 30.
[0010] As a limitation of the present invention, the template-free MCM-22(P) of the present invention is prepared according to the following steps:
[0011] At room temperature, add 0.40g to 2.80g of NaOH (OH) - A solution containing SiO2 (with a molar ratio of 0.05–0.35) was dissolved in deionized water, and 0.83–2.49 g of NaAlO2 was added. The mixture was stirred for 1 hour to obtain a clear and transparent solution. Then, 6.94 g of hexamethyleneimine (HMI) was slowly added dropwise. After the addition was complete, the mixture was stirred for another 0.5 hours. 48.06 g of silica sol (25 wt%) was then slowly added dropwise using a peristaltic pump, followed by 0.12–1.20 g of seed crystals. The mixture was aged in a water bath at 25°C for 24 hours to obtain a pale milky-yellow precursor. The molar ratio of the precursor components was: SiO2∶Al2O3∶NaOH∶HMI∶H2O=0.2∶0.0033–0.01∶0.01–0.07∶0.07∶6. The precursor was transferred to a hydrothermal reactor and crystallized in an oven at 120°C–200°C for 7 days. The precursor in the hydrothermal reactor was filtered, washed, and dried to obtain MCM-22(P) without template removal agent.
[0012] As a further limitation of the present invention, the preparation method of the H-MCM-22 molecular sieve of the present invention is as follows:
[0013] Undetemplated MCM-22(P) was calcined in a muffle furnace at 550 °C for 8 h to obtain Na-type MCM-22 molecular sieve, denoted as Na-MCM-22. After calcination at 1.0 mol·L⁻¹, the sieve was further processed. -1 The NH4Cl aqueous solution was ion-exchanged three times, filtered, washed, dried, and calcined in a muffle furnace for 4 hours at a calcination temperature of 550℃ to obtain H-MCM-22.
[0014] As a further limitation of the present invention, the preparation method of the H-ITQ-2 molecular sieve of the present invention is as follows:
[0015] The undetemplated MCM-22(P) obtained above was mixed with an aqueous solution of hexadecyltrimethylammonium bromide (CTAB) and tetrapropylammonium hydroxide (TPAOH) at a mass ratio of MCM-22(P):CTAB:40% TPAOH:H2O = 1:5.6:6.1:18. The mixture was then refluxed at 80°C for 16 h. The mixture was then placed in an ultrasonic water bath (50 W, 40 kHz) for 2 h to allow the swollen layers to separate. Subsequently, HCl (6.0 mol·L⁻¹) was added dropwise. -1 After adjusting the pH to <2, the product was centrifuged, washed, dried, and then calcined in a muffle furnace at 550℃ for 8 hours to obtain Na-type ITQ-2, denoted as Na-ITQ-2. This was then further processed using 1.0 mol·L⁻¹... -1 The NH4Cl aqueous solution was ion-exchanged three times, filtered, washed, dried, and calcined in a muffle furnace for 4 hours at a calcination temperature of 550℃ to obtain H-ITQ-2.
[0016] As a further limitation of the present invention, the preparation method of the H-MCM-36 molecular sieve of the present invention is as follows:
[0017] The undetempered MCM-22(P) obtained above was mixed with an aqueous solution of hexadecyltrimethylammonium bromide (CTAB) and tetrapropylammonium hydroxide (TPAOH) at a mass ratio of 1:4:1.2 (MCM-22(P) wet filter cake (30 wt%): CTAB (25 wt%): TPAOH (20 wt%). The mixture was stirred uniformly at 80 °C for 3 days, filtered while hot, and then dried in an oven at 60 °C. The dried sample was then mixed with tetraethyl orthosilicate (TEOs) at a mass ratio of 1:5, stirred at 80 °C for 24 hours, filtered while hot, and then dried in an oven at 60 °C. The dried sample was then placed in a muffle furnace and calcined at 550 °C for 5 hours to obtain Na-type MCM-36, denoted as Na-MCM-36. (The last sentence appears to be incomplete and requires further context.) -1 The NH4Cl aqueous solution was ion-exchanged three times, filtered, washed, dried, and calcined in a muffle furnace for 4 hours at a calcination temperature of 550℃ to obtain H-MCM-36.
[0018] The beneficial effects achieved by the present invention after adopting the above technical solution are as follows:
[0019] The H-MWW molecular sieve used in this invention has a nanosheet structure with a high external specific surface area and numerous open semi-cage structures on its outer surface, providing abundant and easily accessible active sites. This significantly improves the resistance to mass transfer and diffusion, exhibiting high catalytic activity while reducing catalyst coking. Under reaction conditions of 160℃ and an initial reaction pressure of 1.0 MPa, a 99% conversion of 2,5-DMF and a 97% selectivity for PX can be obtained, with only 2.2% coking after 20 hours of reaction. Attached Figure Description
[0020] Figure 1 The image shows a scanning electron microscope (SEM) image of the molecular sieve catalyst obtained in Example 1. It can be seen from the image that the prepared H-MCM-22 has a nanosheet structure.
[0021] Figure 2 The image shows the XRD pattern of the molecular sieve catalyst obtained in Example 1. As can be seen from the image, the prepared H-MCM-22 exhibits typical H-MWW molecular sieve characteristic diffraction signals.
[0022] Figure 3 The thermogravimetric analysis (TGA) graphs of commercial H-Beta (50) molecular sieve and 0.25H-MCM-22 molecular sieve prepared in Example 10 after reacting for 20 h show that the prepared H-MWW molecular sieve has excellent anti-coking ability. Detailed Implementation
[0023] The present invention will be further described with reference to the following embodiments, but it should be understood that these embodiments are for illustrative purposes only and should not be construed as limiting the implementation of the present invention.
[0024] In this invention, H-MWW molecular sieves were synthesized using different methods. By adjusting the amount of raw materials added and the operating conditions during the synthesis process, different H-MWW molecular sieves can be obtained.
[0025] Examples 1-10
[0026] The following will use undetemplated MCM-22(P) as a base, and modify the reaction conditions to prepare a series of H-MCM-22 molecular sieves for use in the synthesis of p-xylene. The specific methods are as follows; except for the conditions listed in Table 1, the other steps are the same:
[0027] First, dissolve a certain amount of NaOH in 90.10g of deionized water (OH-). -The SiO2 molar ratio was 0.05–0.35, followed by the addition of a certain amount of NaAlO2 and stirring at room temperature for 1 hour. Then, 6.94 g of hexamethyleneimine (HMI) was added, and 48.06 g of silica sol (25 wt%) was slowly added dropwise under vigorous stirring. Finally, 0.12 g–1.20 g of seed crystals were added, and the mixture was aged in a 25°C water bath for 24 hours to obtain a pale milky-yellow precursor. The molar ratio of the synthesized precursor was: SiO2∶Al2O3∶NaOH∶HMI∶H2O=0.2∶0.0033–0.01∶0.01–0.07∶0.07∶6.
[0028] The precursor was transferred to a hydrothermal reactor and crystallized in an oven at 150°C for 7 days. The precursor in the hydrothermal reactor was filtered, washed, and dried to obtain a powder without template removal. This powder was then calcined in a muffle furnace at 550°C for 8 hours to obtain a series of Na-MCM-22 molecular sieves. -1 The NH4Cl aqueous solution was used for ion exchange, followed by drying and calcination in a muffle furnace for 4 hours at 550℃ to obtain H-MCM-22. H-MWW molecular sieves prepared under different conditions are shown in Table 1.
[0029] Example 11
[0030] First, 2.80 g of flake sodium hydroxide was dissolved in 90.10 g of deionized water, then 0.83 g of NaAlO2 was added, and the mixture was stirred at room temperature for 1 h. Next, 6.94 g of hexamethyleneimine (HMI) was added, and 48.06 g of silica sol (25 wt%) was slowly added dropwise under vigorous stirring. Then, 0.60 g of seed crystals was added, and the mixture was aged in a 25°C water bath for 24 h to obtain a pale milky-yellow precursor. The molar ratio of the synthesized precursor was: 0.2SiO2∶0.005Al2O3∶0.05NaOH∶0.07HMI∶6H2O.
[0031] The precursor was transferred to a hydrothermal reactor and crystallized in an oven at 150°C for 7 days. After filtration, washing, and drying, the precursor in the hydrothermal reactor yielded a white powder without template removal. MCM-22(P) was mixed with aqueous solutions of CTAB and TPAOH at a mass ratio of 1:5.6:6.1:18 (MCM-22(P):CTAB:40% TPAOH:H2O). The mixture was then refluxed at 80°C for 16 hours. The mixture was then placed in an ultrasonic water bath (50W, 40kHz) for 2 hours to separate the swollen layers. Subsequently, a few drops of HCl (6.0 mol·L⁻¹) were added. -1 Until pH < 2, after centrifugation, washing, and drying, it was calcined in a muffle furnace at 550℃ for 8 h to obtain Na-form ITQ-2, denoted as Na-ITQ-2. After further processing at 1.0 mol·L⁻¹, the final product was further processed. -1The NH4Cl aqueous solution was used for ion exchange, then dried and calcined in a muffle furnace for 4 hours at a calcination temperature of 550℃ to obtain H-ITQ-2.
[0032] Example 12
[0033] First, 2.80 g of flake-shaped NaOH was dissolved in 90.10 g of deionized water, then 0.83 g of NaAlO2 was added, and the mixture was stirred at room temperature for 1 h. Next, 6.94 g of hexamethyleneimine (HMI) was added, and 48.06 g of silica sol (25 wt%) was slowly added dropwise under vigorous stirring. Then, 0.60 g of seed crystals was added, and the mixture was aged in a 25°C water bath for 24 h to obtain a pale milky-yellow precursor. The molar ratio of the synthesized precursor was: 0.2SiO2∶0.005Al2O3∶0.05NaOH∶0.07HMI∶6H2O.
[0034] The precursor was transferred to a hydrothermal reactor and crystallized in an oven at 150°C for 7 days. After filtration and washing, the precursor in the hydrothermal reactor yielded a wet filter cake MCM-22(P) without template removal. A mixture of MCM-22(P) wet filter cake (MCM-22(P) mass percentage approximately 30 wt%), hexadecyltrimethylammonium bromide solution (25 wt%), and tetrapropylammonium hydroxide solution (TPAOH, 20 wt%) was prepared at a mass ratio of 1:4:1.2. The mixture was stirred uniformly at 80°C for 3 days, filtered while hot, and then dried in an oven at 60°C. The dried sample was then mixed with tetraethyl orthosilicate (TEOs) at a mass ratio of 1:5, stirred at 80°C for 24 hours, filtered while hot, and then dried in an oven at 60°C. The dried sample was then placed in a muffle furnace and calcined at 550°C for 5 hours to obtain Na-type MCM-36, denoted as Na-MCM-36. After 1.0 mol·L -1 The NH4Cl aqueous solution was used for ion exchange, then dried and calcined in a muffle furnace for 4 hours at a calcination temperature of 550℃ to obtain H-MCM-36.
[0035] The XRD patterns of the molecular sieves prepared in Examples 1-12 above were analyzed using Origin software, and their crystallinity was calculated.
[0036] Table 1. H-MWW molecular sieves obtained by different preparation methods
[0037]
[0038]
[0039] Examples 13-28
[0040] The H-MWW molecular sieves prepared in Examples 1-12 were used in the synthesis of p-xylene from 2,5-dimethylfuran and acrylic acid, respectively, to obtain Examples 13-28. The specific reaction steps are as follows. Except for the conditions listed in Table 2, the other steps are the same. The catalytic activities obtained are listed in Table 2 below.
[0041] 2,5-Dimethylfuran and acrylic acid were mixed at a molar ratio of 1:1 to 1:4, with the concentration of 2,5-dimethylfuran being 0.3 mol·L⁻¹. -1 The concentration of acrylic acid is 0.6 mol·L⁻¹. -1 The solvent was n-heptane, and the total reaction volume was 25 mL. The mixture was transferred to a magnetically stirred reactor, and 0.10 g of molecular sieve catalyst was added. The gas inside the reactor was replaced three times with high-purity N2. The reaction temperature was 120℃~240℃, the initial pressure was 1.0 MPa (N2), and the reaction time was 5 h~20 h. After the reaction was completed, the reactor was placed in an ice-water bath for cooling. The main product was PX, and the byproducts were 2,5-hexanedione and 2,5-dimethylbenzoic acid.
[0042] Comparative Examples 1-5
[0043] Commercially available H-ZSM-5 (Si / Al=50), HY, and H-Beta (Si / Al=50) molecular sieves were used as catalysts for comparative examples.
[0044] 2,5-Dimethylfuran and acrylic acid were mixed at a molar ratio of 1:2, with the concentration of 2,5-dimethylfuran being 0.3 mol·L⁻¹. -1 The concentration of acrylic acid is 0.6 mol·L⁻¹ -1 The solvent was n-heptane, and the total reaction volume was 25 mL. The mixture was transferred to a magnetically stirred reactor, and 0.10 g of catalyst was added. The gas inside the reactor was replaced three times with high-purity N2. The reaction temperature was 160 °C, the initial pressure was 1.0 MPa (N2), and the reaction time was 5 h to 20 h. After the reaction was completed, the reactor was placed in an ice-water bath for cooling. The main product was PX, and the byproducts were 2,5-hexanedione and 2,5-dimethylbenzoic acid.
[0045] The catalytic activity results of Examples 13-28 and Comparative Examples 1-5 in the synthesis of p-xylene from 2,5-dimethylfuran and acrylic acid are shown in Table 2 below.
[0046] Table 2 Comparison of catalytic activity between Examples 13-28 and Comparative Examples 1-5
[0047]
[0048]
[0049] Tables 1 and 2 show that the Si / Al ratio of H-MCM-22, the amount of NaOH used in the synthesis process, and the amount of MCM-22 seed crystals have a significant impact on the crystallinity of H-MCM-22. The higher the crystallinity, the higher the effective content of molecular sieve, and the better the catalytic activity in the synthesis of PX from 2,5-dimethylfuran and acrylic acid.
[0050] Taking Examples 24-26 and Examples 3-5 as examples, as the reaction proceeds, the 0.25H-MCM-22(20) molecular sieve with MWW topology has a lower deactivation rate compared to the H-Beta(50) molecular sieve. This may be because the catalytic reaction is mainly carried out on the acidic sites on the outer surface of the molecular sieve. The H-type MWW molecular sieve has a significant advantage.
[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A process for the synthesis of p-xylene catalyzed by H-MWW molecular sieve, characterized in that The reactants used in this method are 2,5-dimethylfuran and acrylic acid, wherein the molar ratio of 2,5-dimethylfuran to acrylic acid is 1:1 to 1:4; the method uses a self-made H-MWW molecular sieve as a catalyst, and the amount of the catalyst is 0.10 g. The reaction was carried out in a magnetically stirred tank at a temperature of 120℃~240℃, with nitrogen as a protective gas. The H-MWW molecular sieve is either H-MCM-22 or H-ITQ-2, and both H-MWW molecular sieves are prepared from MCM-22 without detemplating agent, exhibiting a nanosheet structure, and the Si / Al ratio in the H-MWW molecular sieve is 10~30. The untempered MCM-22 was prepared according to the following method: (1) Dissolve 0.40 g ~ 2.80 g NaOH in deionized water at room temperature, add 0.83 ~ 2.49 g NaAlO2, and stir for 1 h to obtain a clear and transparent solution; (2) Then slowly add 6.94 g of hexamethyleneimine (HMI) to the solution obtained in step (1). After the addition is complete, continue stirring for 0.5 h. Use a peristaltic pump to slowly add 48.06 g of 25wt% silica sol and add 0.12 g ~ 1.20 g of seed crystals. Aging in a water bath at 25℃ for 24 h yields a pale milky yellow precursor. The molar ratio of each component in the synthesized precursor is SiO2: Al2O3: NaOH: HMI: H2O = 0.2: 0.0033 ~ 0.01: 0.01 ~ 0.07: 0.07:
6. (3) The precursor obtained in step (2) is transferred to a hydrothermal reactor and crystallized in an oven at 120~200℃ for 7 days; (4) The precursor after static crystallization in step (3) is filtered, washed and dried to obtain the MCM-22 without template agent removal; The H-MCM-22 is prepared according to the following method: (1) The undetemplated MCM-22 was calcined in a muffle furnace at 550 °C for 8 h to obtain Na-MCM-22 molecular sieve; (2) The Na-MCM-22 molecular sieve obtained in step (1) is subjected to 1.0 mol·L⁻¹ -1 The H-MCM-22 molecular sieve was obtained by ion exchange with NH4Cl aqueous solution, followed by filtration, washing, drying, and calcination in a muffle furnace at 550 °C for 4 h. The H-ITQ-2 is prepared according to the following method: (1) MCM-22 without template removal agent was mixed with an aqueous solution of hexadecyltrimethylammonium bromide (CTAB) and tetrapropylammonium hydroxide (TPAOH), with a mass ratio of MCM-22:CTAB:40%TPAOH:H2O of 1:5.6:6.1:
18. The mixture was refluxed at 80°C for 16 h to obtain a mixed solution. (2) The mixed solution obtained in step (1) is placed in an ultrasonic water bath for 2 h to separate the swelling layer, and 6.0 mol·L -1 HCl is added to adjust the pH < 2; (3) After centrifugation, washing and drying, the solution obtained in step (2) is calcined in a muffle furnace at 550°C for 8 h to obtain Na-ITQ-2; (4) The Na-ITQ-2 obtained in step (3) was ion exchanged with 1.0 mol·L -1 NH4Cl aqueous solution for 3 times, suction filtered, washed, dried, and calcined at 550 degrees Celsius in a muffle furnace for 4 h to obtain H-ITQ-2.
2. A method for the synthesis of p-xylene catalyzed by H-MWW molecular sieve, wherein the reactants used in this method are 2,5-dimethylfuran and acrylic acid, wherein the molar ratio of 2,5-dimethylfuran to acrylic acid is 1:1 to 1:4; the method uses a self-made H-MWW molecular sieve as a catalyst, with an amount of 0.10 g; the reaction is carried out in a magnetically stirred tank at a reaction temperature of 120℃ to 240℃, with nitrogen as a protective gas; characterized in that The self-made H-MWW molecular sieve is H-MCM-36, and its preparation method is as follows: First, 2.80 g of flake NaOH was dissolved in 90.10 g of deionized water, then 0.83 g of NaAlO2 was added and stirred at room temperature for 1 h. Then, 6.94 g of hexamethyleneimine (HMI) was added, and 48.06 g of 25wt% silica sol was slowly added dropwise under vigorous stirring. Then, 0.60 g of seed crystals were added, and the mixture was aged in a water bath at 25℃ for 24 h to obtain a pale milky yellow precursor. The molar ratio of the synthesized precursor was: 0.2 SiO2 : 0.005 Al2O3 : 0.05 NaOH : 0.07 HMI : 6 H2O. The precursor was transferred to a hydrothermal reactor and crystallized in an oven at 150°C for 7 days. After filtration and washing, the precursor in the hydrothermal reactor yielded a wet filter cake MCM-22 without template removal. This was mixed with a solution of 30wt% MCM-22 : 25wt% hexadecyltrimethylammonium bromide solution : 20wt% tetrapropylammonium hydroxide solution at a mass ratio of 1 : 4 : 1.
2. The mixture was stirred uniformly at 80°C for 3 days, filtered while hot, and then dried in an oven at 60°C. The dried sample was then mixed with tetraethyl orthosilicate at a mass ratio of 1 : 5 and stirred at 80°C for 24 h. The mixture was filtered while hot and then dried in an oven at 60°C. The dried sample was then placed in a muffle furnace and calcined at 550°C for 5 h to obtain Na-type MCM-36, denoted as Na-MCM-36. The sample was then subjected to 1.0 mol·L⁻¹ -1 The NH4Cl aqueous solution was used for ion exchange, followed by drying and calcination in a muffle furnace for 4 h at a calcination temperature of 550℃ to obtain H-MCM-36.