Method for continuously producing N, N-dimethylaniline

Abstract

The invention relates to the field of synthesis of N, N-dimethylaniline, and discloses a method for continuously producing N, N-dimethylaniline. The invention relates to a method for continuously producing N, N-dimethylaniline, which comprises the following steps: synthesizing N, N-dimethylaniline, regenerating a solvent of a spent catalyst, and returning a regenerated catalyst obtained by regenerating the solvent to the synthesis of N, N-dimethylaniline for recycling, the synthesis of N, N-dimethylaniline comprises the following steps: in the presence of a fresh catalyst, carrying out gas-phase reaction on reaction raw materials methanol and aniline to obtain a spent catalyst; the fresh catalyst comprises a molecular sieve, a carrier and modified components, the modified components are copper and phosphorus, and the amount of medium and strong acids in the fresh catalyst accounts for 35% or more of the total acid amount; the solvent regeneration of the spent catalyst comprises the following steps: sequentially carrying out first-stage solvent regeneration, second-stage hydrogen regeneration and third-stage solvent hydrogen regeneration on the spent catalyst. According to the method, complete regeneration of the deactivated catalyst can be realized, and continuous production of N, N-dimethylaniline in a long period is realized.

Description

Technical Field

[0001] The invention relates to the technical field of synthesizing N,N-dimethylaniline, and in particular to a method for continuously producing N,N-dimethylaniline. Background Art

[0002] The N-alkylation reaction of aniline is an important chemical reaction in commerce. Its product is N,N-dimethylaniline. N,N-dimethylaniline can be used in the production of many important industrial products such as papermaking, textile dyes, medicines, fragrances and explosives. It is an excellent intermediate for chemical products.

[0003] At present, the mainstream production methods of N,N-dimethylaniline are liquid phase method and gas phase method. However, both the liquid phase method and the gas phase method have different defects.

[0004] For example, sulfuric acid is usually used as a catalyst in the liquid phase synthesis of N,N-dimethylaniline, and the process must be carried out under high temperature and high pressure conditions. Therefore, a large amount of acid-soluble oil is produced during the liquid phase production process. A large amount of liquid alkali is required to neutralize the inorganic acid to separate the product, and a large amount of difficult-to-handle inorganic salts are produced, which causes great pollution, high subsequent processing costs, and brings certain safety hazards and greater environmental pressure. In addition, the liquid phase method cannot be produced continuously, and the use of high temperature and high pressure equipment increases investment, which is not conducive to industrial production.

[0005] The gas phase method avoids environmental pollution to a certain extent by using metal oxides, metal salts, molecular sieves, etc. as gas phase catalysts. However, the product selectivity of the gas phase method is about 90%, which is lower than that of the liquid phase method and has not been able to achieve industrial application.

[0006] Based on this, domestic and foreign countries are committed to the research and development of gas phase synthesis, N, N-dimethylaniline, molecular sieves have a regular three-dimensional pore structure, and their suitable acidity and low price are conducive to the diffusion of reactant molecules in the molecular sieve pores and the reaction at the acidic center. Molecular sieve catalysts are widely used in petrochemical and other fields, especially in catalytic cracking, hydrogenation, reforming, isobutane ethylene alkylation, benzene and olefin alkylation and other fields. Therefore, the research on molecular sieve catalysts not only has important academic value, but also has broad application prospects.

[0007] Some research has also been conducted in China. Wu Kerui et al. reported the use of modified ZSM-5 as a catalyst at normal pressure, temperature 300 ° C, and liquid space velocity of 1.0 h -1 When the molar ratio of aniline to methanol is 1:3, the selectivity of dimethylaniline is 88%.

[0008] Li Guotao et al. used β molecular sieve as catalyst, at n(aniline):n(methanol)=1:3, reaction temperature 240-250℃ and space velocity 0.5h -1Under the conditions of , the raw material conversion rate is about 99% and the product selectivity is 85%. The catalyst conversion rate and product selectivity are low, and the conversion rate and selectivity decrease rapidly as the reaction proceeds. How to improve product selectivity and catalyst stability is a problem that molecular sieve catalysts need to solve.

[0009] The coking reaction on the catalyst starts with the alkylation of N,N-dimethylaniline and methanol to form N,N,C-trimethylaniline, and then continues with hydrogen transfer, alkylation and cyclization to form coke deposits with a multi-ring structure that are difficult to volatilize. These carbon deposits are called hard coke, which are generally difficult to remove and require high-temperature oxidative roasting to remove the carbon deposits on the catalyst. High-temperature roasting of general catalysts will destroy the structure of the catalyst, thereby destroying the activity and stability of the catalyst.

[0010] Solid acid catalysts are prone to coking and deactivation, and need to be regenerated frequently. The regeneration methods of deactivated catalysts generally include hydrogenation regeneration, reaction solvent dissolution and cleaning, high-temperature oxidation roasting, oxidant cleaning, etc. Among them, hydrogenation regeneration and reaction solvent dissolution and cleaning regeneration are easier to achieve in industry, but the solvent washing method often cannot completely achieve the complete regeneration of the catalyst, and can only partially regenerate the catalyst. After several washing and regeneration, the catalyst needs to be roasted at high temperature to remove the accumulated hard carbon. The process is cumbersome, the cost is high, and the hard carbon is difficult to remove. Summary of the invention

[0011] The purpose of the present invention is to overcome the problem that the solvent regeneration in the prior art cannot achieve complete regeneration of the catalyst, and to provide a method for continuously producing N,N-dimethylaniline, which can achieve complete regeneration of the deactivated catalyst, improve catalyst stability, and achieve long-term and continuous production of N,N-dimethylaniline.

[0012] In order to achieve the above object, the present invention provides a method for continuously producing N,N-dimethylaniline, wherein the method comprises: synthesizing N,N-dimethylaniline and regenerating a solvent of a catalyst to be regenerated, and returning the regenerated catalyst obtained by solvent regeneration to the synthesis cycle of N,N-dimethylaniline for reuse;

[0013] The synthesis of N,N-dimethylaniline comprises: in the presence of a fresh catalyst, reacting the reaction raw materials methanol and aniline in a gas phase to obtain a catalyst to be produced; the fresh catalyst comprises a molecular sieve, a carrier and a modified component, the modified component is copper and phosphorus, and the acid content of the medium-strong acid in the fresh catalyst accounts for more than 35% of the total acid content;

[0014] The solvent regeneration of the spent catalyst comprises: sequentially performing a first-stage solvent regeneration, a second-stage hydrogenation regeneration and a third-stage solvent hydrogenation regeneration on the spent catalyst.

[0015] Preferably, the solvent regeneration of the spent catalyst comprises:

[0016] S1, subjecting the catalyst to be regenerated to a solvent regeneration step in the presence of a first solvent;

[0017] S2, subjecting the product obtained in step S1 to a second-stage hydroregeneration under hydrogenation conditions;

[0018] S3, subjecting the product obtained in step S2 to three-stage solvent hydrogenation regeneration under hydrogenation conditions and in the presence of a second solvent to obtain a regenerated catalyst.

[0019] The inventors of the present invention have found in their research that complete regeneration of a deactivated catalyst can be achieved through segmented regeneration. In the present invention, a highly polar solvent is first used to rinse the deactivated catalyst to be regenerated, and the reactants and macromolecular products adsorbed on the acidic sites are rinsed off, thereby restoring part of the activity of the catalyst. The catalyst is then subjected to two-stage hydrogenation regeneration, and the hard carbon on the catalyst is hydrogenated and saturated with hydrogen, so that the carbon deposits on the catalyst are hydrogenolyzed into small molecules, and then solvent washing and regeneration are performed under hydrogenation conditions. After the macromolecular carbon deposit precursors generated during the reaction are saturated with hydrogen, the carbon deposits are dissolved using the similar dissolution mechanism of the solvent, which can effectively remove macromolecular substances such as carbon deposit precursors generated during the reaction, avoid the generation of hard carbon, thereby improving the catalyst stability and achieving continuous production of N,N dimethylaniline. DETAILED DESCRIPTION

[0020] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0021] The present invention provides a method for continuously producing N,N-dimethylaniline, wherein the method comprises: synthesizing N,N-dimethylaniline and regenerating a solvent of a catalyst to be regenerated, and returning the regenerated catalyst obtained by solvent regeneration to the synthesis of N,N-dimethylaniline for recycling;

[0022] The synthesis of N,N-dimethylaniline comprises: in the presence of a fresh catalyst, reacting the reaction raw materials methanol and aniline in a gas phase to obtain a catalyst to be produced; the fresh catalyst comprises a molecular sieve, a carrier and a modified component, the modified component is copper and phosphorus, and the acid content of the medium-strong acid in the fresh catalyst accounts for more than 35% of the total acid content;

[0023] The solvent regeneration of the spent catalyst comprises: sequentially performing a first-stage solvent regeneration, a second-stage hydrogenation regeneration and a third-stage solvent hydrogenation regeneration on the spent catalyst.

[0024] The inventors of the present invention have found in their research that complete regeneration of a deactivated catalyst can be achieved through segmented regeneration. In the present invention, a first solvent with a relatively strong polarity is first used to rinse the deactivated catalyst to be regenerated, and the reactants and macromolecular products adsorbed on the acidic sites are rinsed off, thereby restoring part of the activity of the catalyst. The catalyst is then subjected to two-stage hydrogenation regeneration, and the hard carbon on the catalyst is hydrogenated and saturated with hydrogen, so that the carbon deposits on the catalyst are hydrogenolyzed into small molecules, and then solvent washing and regeneration are performed under hydrogenation conditions. After the macromolecular carbon deposit precursors generated during the reaction are saturated with hydrogen, the carbon deposits are dissolved using the similar dissolution mechanism of the solvent, which can effectively remove macromolecular substances such as carbon deposit precursors generated during the reaction, avoid the generation of hard carbon, thereby improving the catalyst stability and achieving continuous production of N,N dimethylaniline.

[0025] The preparation method provided by the present invention is green, environmentally friendly and pollution-free. The catalyst can be recycled to achieve long-term continuous operation of the catalyst, truly achieving zero pollution and zero emission in the production process, and greatly reducing the energy consumption in the regeneration process, providing an effective method for energy conservation and emission reduction in the catalyst regeneration process, which is beneficial to industrial continuous production and greatly saves production costs.

[0026] In the present invention, the catalyst acid distribution is characterized by NH3 programmed temperature desorption method (NH3-TPD). The characterization method is as follows: Instrument: Quantachrome Chemstar TPx Test process: Weigh 0.15g (20-40 mesh) of molecular sieve or catalyst sample, heat it to 550℃, dry it, and then reduce it to 100℃ to make the catalyst saturated with NH3, heat it to 250℃, 350℃, 450℃ and 550℃ respectively to desorb NH3, and use TCD detector to detect NH3 concentration. The adsorption curves obtained at different temperature sections are integrated, and the instrument automatically calculates the acid density distribution at different temperatures. Among them, the acid amount obtained by integration at 250℃ is weak acid, 250℃-450℃ is medium-strong acid, and 450℃-550℃ is strong acid.

[0027] In the present invention, it should be noted that the gas phase reaction refers to that the reaction raw materials methanol and aniline are fed in gaseous form or the reaction conditions during the reaction process make methanol and aniline in gaseous state. The present invention does not specifically limit the gasification method of the raw materials, and the conventional methods defined in the art can be applied to the present invention.

[0028] In the present invention, there is no particular limitation on the amount of the reaction raw materials. Preferably, the molar ratio of methanol to aniline is 1-10:1, preferably 2-8:1.

[0029] In the present invention, the selection range of the synthesis conditions of N,N-dimethylaniline is relatively wide. Preferably, the synthesis conditions of N,N-dimethylaniline include: a reaction temperature of 220-300°C, a mass space velocity of methanol and aniline of 0.1-10h -1 .

[0030] In the present invention, preferably, when the total acid content of the fresh catalyst is reduced to below 20%, the spent catalyst is obtained.

[0031] In the present invention, the solvent regeneration is carried out in three stages. Through the close coordination of each step, the complete regeneration of the catalyst to be regenerated is achieved, thereby increasing the service life of the catalyst. Preferably, the solvent regeneration of the catalyst to be regenerated includes:

[0032] S1, subjecting the catalyst to be regenerated to a solvent regeneration step in the presence of a first solvent;

[0033] S2, subjecting the product obtained in step S1 to a second-stage hydroregeneration under hydrogenation conditions;

[0034] S3, subjecting the product obtained in step S2 to three-stage solvent hydrogenation regeneration under hydrogenation conditions and in the presence of a second solvent to obtain a regenerated catalyst.

[0035] In the present invention, a first solvent with a strong polarity is first used to wash the deactivated catalyst, and the reactants and macromolecular products adsorbed on the acidic sites are washed away to restore part of the activity of the catalyst. Then, the catalyst is saturated with hydrogen, and the hard carbon on the catalyst is hydrogenated and saturated with Cu, so that the carbon deposits on the catalyst are hydrogenolyzed into small molecules, and then the solvent is washed and regenerated under hydrogen conditions. After the macromolecular carbon deposit precursors generated during the reaction are saturated with hydrogen, the carbon deposits are dissolved by the similar dissolution mechanism of the solvent, and the macromolecular substances such as the carbon deposit precursors generated during the reaction are effectively removed, so as to avoid the generation of hard carbon and completely deactivate the catalyst.

[0036] In the present invention, preferably, in step S1, the strong acid content recovery rate of the product obtained in step S1 reaches 80-90%. The advantage of adopting this preferred embodiment is that the method is simple and the acid content of the catalyst can be effectively recovered.

[0037] It should be noted that the recovery rate here refers to the recovery rate of the acid amount of the regenerated catalyst compared to the fresh catalyst after a solvent regeneration, which is calculated by the following formula:

[0038] Recovery rate (%) = the acid amount of the catalyst to be regenerated after a stage of solvent regeneration / the acid amount of the fresh catalyst*100%.

[0039] In the present invention, a first solvent is used to perform a first-stage solvent regeneration on the catalyst to be regenerated, and the present invention has a wide range of choices for the type of the first solvent. Preferably, in step S1, the first solvent is selected from at least one of methanol, ethanol, ethylene glycol and propylene glycol, and methanol is more preferably used. Methanol has a strong polarity, and methanol is used to flush the deactivated catalyst to flush away the reactants and macromolecular products adsorbed on the acidic sites, thereby restoring part of the activity of the catalyst; at the same time, methanol is one of the raw materials for the synthesis reaction, and partial regeneration can be achieved without switching to other solvents during the first-stage solvent regeneration process, saving costs.

[0040] In the present invention, the conditions for regenerating the first stage solvent are selected in a wide range. Preferably, in step S1, the conditions for regenerating the first stage solvent include: a temperature of 200-350°C, a time of 0.5-24h, and a volume space velocity of the first solvent of 0.01-20h -1 Further preferably, in step S1, the conditions for regenerating the first solvent include: temperature of 210-300°C, time of 2-12h, volumetric space velocity of the first solvent of 0.5-15h -1 .

[0041] In the present invention, hydrogen is introduced to saturate the unsaturated hydrocarbons in the catalyst, converting hard carbon into soft carbon, and further realizing complete regeneration of the catalyst. In the present invention, the range of selection of conditions for the second-stage hydroregeneration is relatively wide. Preferably, in step S2, the conditions for the second-stage hydroregeneration include: temperature of 200-350°C, time of 0.5-24h, pressure of 0.01-10MPa, and hydrogen flow rate of 0.001-1000mL / min relative to 1g of fresh catalyst; further preferably, in step S2, the conditions for the second-stage hydroregeneration include: temperature of 220-300°C, time of 2-20h, pressure of 0.1-8MPa, and hydrogen flow rate of 10-1000mL / min relative to 1g of fresh catalyst.

[0042] In the present invention, the second solvent can be selected from a wide range of types. Preferably, the second solvent is selected from at least one of C1-C4 normal alcohols, benzene and aniline, preferably C1-C4 normal alcohols and / or aniline.

[0043] In the present invention, preferably, the C1-C4 normal alcohol is selected from at least one of methanol, ethanol, n-propanol and n-butanol.

[0044] In the present invention, preferably, the temperature of the three-stage solvent hydroregeneration is 10-100° C. higher than the temperature of the two-stage hydroregeneration. The advantage of adopting this preferred embodiment is that the method has a low temperature and is simple to operate.

[0045] In the present invention, solvent washing and regeneration are carried out under hydrogen conditions, and the macromolecular carbon precursors generated in the reaction process can be saturated with hydrogen, and then the carbon deposits can be dissolved by utilizing the similar miscibility mechanism of the solvent, which can effectively remove macromolecular substances such as carbon precursors generated in the reaction process, avoid the generation of hard carbon, and completely deactivate the catalyst. In the present invention, the range of selection of conditions for the three-stage solvent hydrogenation regeneration is relatively wide. Preferably, in step S3, the conditions for the three-stage solvent hydrogenation regeneration include: a temperature of 210-450°C, a time of 0.5-50h, a pressure of 0.1-10MPa, and a volume space velocity of the second solvent of 0.01-15h -1 Further preferably, in step S3, the conditions for the three-stage solvent hydrogen regeneration include: temperature of 230-450°C, time of 0.5-48h, pressure of 0.01-8MPa, and volumetric space velocity of the second solvent of 0.01-10h -1 .

[0046] In the present invention, preferably, the amount of strong acid in the fresh catalyst accounts for 40-50% of the total acid, preferably 42-45%.

[0047] In the present invention, there is no particular limitation on the preparation method of the fresh catalyst. Preferably, the preparation method of the fresh catalyst comprises: (1) mixing a molecular sieve and a carrier to obtain a mixture; (2) mixing the mixture obtained in step (1) with a solution containing a copper precursor and a phosphorus-containing compound to form a mixture, and then calcining the mixture once to obtain a fresh catalyst.

[0048] The method provided by the present invention increases the ratio of medium and strong acids in the catalyst by introducing copper, reduces the ratio of strong acids, can reduce the adsorption of methanol with greater polarity at acidic sites, reduce the occurrence of side reactions, and improve the life of the catalyst; further synergizes phosphorus modification to improve the hydrothermal stability of the catalyst under high temperature conditions, does not have a negative impact on the acidity and stability of the catalyst itself, and achieves long-term continuous operation of the catalyst, which is conducive to industrial continuous production and greatly saves production costs. The method provided by the present invention controls the order of adding raw materials during the catalyst preparation process, strictly follows the first mixing of molecular sieves and carriers, and directly mixes and molds the catalyst with a solution containing a copper precursor and a phosphorus-containing compound without roasting, and only needs to be roasted once during the catalyst preparation process, avoiding the multiple roastings of the catalyst after the catalyst is formed and modified in the prior art, reducing the difficulty of the catalyst preparation process and reducing energy consumption.

[0049] In the present invention, the molecular sieve has a wide range of selection. Preferably, in step (1), the molecular sieve is selected from at least one of Y-type molecular sieve, ZSM-5 type molecular sieve, β-type molecular sieve, MCM-22 type molecular sieve and mordenite, preferably at least one of Y-type molecular sieve, ZSM-5 type molecular sieve and β-type molecular sieve, and more preferably β-type molecular sieve.

[0050] In the present invention, preferably, in step (1), the carrier is aluminum oxide and / or silicon oxide.

[0051] In the present invention, preferably, in step (1), the mass ratio of the molecular sieve to the carrier is 95:5-20:80, and more preferably 90:10-25:75.

[0052] In the present invention, the dispersion is improved by regulating the form of the carrier to improve the performance of the catalyst. Preferably, in step (1), the carrier is in a solid state and / or a sol state, and more preferably in a sol state. The advantage of adopting this preferred embodiment is that the molecular sieve and the carrier can be better mixed, more evenly distributed, more strongly interacted, and the catalyst activity is better.

[0053] In the present invention, preferably, when the carrier is in a sol state, the carrier is provided by aluminum sol and / or silica sol.

[0054] In the present invention, there is no particular limitation on the concentration of aluminum sol and silica sol. Preferably, the concentration of aluminum sol and silica sol is independently 10-30 wt%.

[0055] In the present invention, preferably, in step (1), the carrier is alumina.

[0056] In the present invention, there is no particular limitation on the type of aluminum oxide precursor, as long as it can provide aluminum oxide. Preferably, the aluminum oxide is provided by at least one of pseudo-boehmite, aluminum chloride, aluminum hydroxide and aluminum sol.

[0057] In the present invention, there is no particular limitation on the type of copper precursor, as long as it can provide copper element. Preferably, in step (2), the copper precursor is selected from soluble copper compounds, preferably at least one selected from cupric chloride, cuprous chloride, cupric nitrate, cupric sulfate and cuprous sulfate.

[0058] In the present invention, there is no particular limitation on the type of phosphorus-containing compound, as long as it can provide phosphorus. Preferably, in step (2), the phosphorus-containing compound is selected from at least one of phosphoric acid, phosphorous acid, soluble phosphates and phosphites.

[0059] In the present invention, there is no particular limitation on the specific type of the soluble phosphate. Preferably, the soluble phosphate is selected from at least one of ammonium phosphate, diammonium hydrogen phosphate and ammonium dihydrogen phosphate.

[0060] In the present invention, preferably, the phosphorus-containing compound is provided by an aqueous solution of the phosphorus-containing compound. Preferably, the concentration of the phosphorus-containing compound is 0.01-25wt%, preferably 5-25wt%.

[0061] In the present invention, preferably, in step (2), the mass ratio of the copper precursor to the phosphorus-containing compound is 5:95-98:2, and more preferably 30:70-80:20. By controlling the amount of the copper precursor and the phosphorus-containing compound, the acid distribution in the catalyst can be controlled, the proportion of medium and strong acids can be increased, and the hydrothermal stability of the catalyst can be improved, the long-term continuous operation of the catalyst can be achieved, and the reaction temperature of the synthesis reaction can be widened, which is conducive to industrial production.

[0062] In the present invention, preferably, the mass ratio of the carrier in terms of oxide to the copper precursor in terms of element is 80:20-99.9:0.1, and more preferably 95:15-99:1. The advantages of adopting this preferred embodiment are that the preparation method is simple, and Cu 2+ / Cu + More is distributed on the molecular sieve.

[0063] In the present invention, when the carrier alumina exists in a sol state, a peptizing agent needs to be introduced to peptize it. The present invention does not particularly limit the specific operation mode of peptization, and those skilled in the art can select it according to actual needs. Preferably, the preparation method of the catalyst also includes: introducing a peptizing agent into a solution containing a copper precursor and a phosphorus-containing compound and mixing it with the mixture obtained in step (1) to form a mixture.

[0064] In the present invention, there is no particular limitation on the type of peptizing agent, and all peptizing agents conventionally defined in the art are applicable to the present invention. Preferably, the peptizing agent is selected from at least one of nitric acid, hydrochloric acid, sulfuric acid, formic acid and acetic acid.

[0065] In the present invention, there is no particular limitation on the amount of the peptizing agent, as long as it can meet the peptization requirements, and those skilled in the art can select it according to actual needs. Preferably, the amount of the peptizing agent is such that the pH of the solution containing the copper precursor and the phosphorus-containing compound is 1-4. The present invention also does not particularly limit the concentration of the peptizing agent, and those skilled in the art can select it according to actual needs.

[0066] In the present invention, there is no particular limitation on the molding method in step (2), and those skilled in the art can select the method according to actual needs.

[0067] In the present invention, the range of calcination conditions is relatively wide. Preferably, in step (2), the calcination conditions include: a temperature of 450-800°C and a time of 1-10 hours; further preferably, in step (2), the calcination conditions include: a temperature of 500-700°C and a time of 2-8 hours.

[0068] The present invention will be described in detail below by way of examples. In the following examples, all raw materials used are commercially available unless otherwise specified.

[0069] Preparation Examples 1-7 and Comparative Preparation Examples 1-5 are used to illustrate the preparation of fresh catalysts.

[0070] Preparation Example 1

[0071] (1) 90 g HY molecular sieve (silicon to aluminum molar ratio of 5) and 10 g alumina were mixed evenly;

[0072] (2) 3 g of cuprous chloride was added to 100 g of 10 wt% H3PO4 solution, added to the mixed powder in step (1), mixed evenly, and extruded by an extruder, and calcined at 500° C. for 12 h to obtain catalyst Y-1. The acid content of the catalyst is shown in Table 1.

[0073] Preparation Example 2

[0074] (1) 750 g of β molecular sieve (silicon-aluminum molar ratio of 20) and 1250 g of 20 wt% aluminum sol were mixed uniformly;

[0075] (2) 5 g of Cu2SO4 was added to 100 g of a 5 wt% KH2PO4 solution, and then the pH was adjusted to 2.5 with nitric acid and added to the mixture of molecular sieve and aluminum sol, and then mixed and rolled and extruded into small balls, and then calcined at 600°C for 1 hour to obtain catalyst β-1. The acid content of the catalyst is shown in Table 1.

[0076] Preparation Example 3

[0077] (1) 200 g of ZSM-5 molecular sieve (silicon to aluminum molar ratio of 50) and 500 g of 20 wt% silica sol were mixed uniformly;

[0078] (2) 10g of Cu(NO3)2 was added to 100g of 10wt% K3PO4 solution, added to the molecular sieve and silica sol mixture, mixed evenly, extruded and molded by an extruder, and calcined at 800°C for 2h to obtain the catalyst ZSM-1. The acid content of the catalyst is shown in Table 1.

[0079] Preparation Example 4

[0080] The catalyst was prepared according to the method of Preparation Example 2, except that 50 g of Cu2SO4 was added to 200 g of 25 wt% KH2PO4 solution, and then the pH was adjusted to 4 with nitric acid and added to the mixture of molecular sieves and aluminum sol, and calcined at 500°C for 8 h to obtain catalyst β-2.

[0081] The results of the acid content of the catalyst are shown in Table 1.

[0082] Preparation Example 5

[0083] The catalyst was prepared according to the method of Preparation Example 2, except that the amount of Cu2SO4 added was 60 g and other conditions remained unchanged, to obtain catalyst β-3.

[0084] The results of the acid content of the catalyst are shown in Table 1.

[0085] Preparation Example 6

[0086] The catalyst was prepared according to the method of Preparation Example 2, except that 2 g of Cu2SO4 was added to 200 g of a 25 wt% KH2PO4 solution to obtain catalyst β-4.

[0087] The results of the acid content of the catalyst are shown in Table 1.

[0088] Preparation Example 7

[0089] The catalyst was prepared according to the method of Preparation Example 2, except that alumina powder was used instead of aluminum sol, and other conditions remained unchanged to obtain catalyst β-5. The acid content of the catalyst is shown in Table 1.

[0090] Comparative Preparation Example 1

[0091] The catalyst was prepared according to the method of Preparation Example 1, except that no subsequent phosphorus loading was performed. The other conditions were the same as Preparation Example 1, and catalyst DY-1 was obtained.

[0092] The results of the acid content of the catalyst are shown in Table 1.

[0093] Comparative Preparation Example 2

[0094] The catalyst was prepared according to the method of Preparation Example 1, except that only phosphoric acid solution was added during the preparation of the catalyst. The other conditions were the same as Preparation Example 1, and catalyst DY-2 was obtained.

[0095] The results of the acid content of the catalyst are shown in Table 1.

[0096] Comparative Preparation Example 3

[0097] The catalyst was prepared according to the method of Preparation Example 2, except that only copper salt solution was added during the preparation of the catalyst. The other conditions were the same as Preparation Example 2, and catalyst Dβ-1 was obtained.

[0098] The results of the acid content of the catalyst are shown in Table 1.

[0099] Comparative Preparation Example 4

[0100] The catalyst was prepared according to the method of Preparation Example 2, except that only phosphoric acid solution was added during the preparation of the catalyst. The other conditions were the same as Preparation Example 2, and catalyst Dβ-2 was obtained.

[0101] The results of the acid content of the catalyst are shown in Table 1.

[0102] Table 1

[0103]

[0104] The examples and comparative examples are used to illustrate the continuous production of N,N-dimethylaniline

[0105] Examples 1-7

[0106] The catalyst in the above-mentioned Preparation Example 1-7 was selected as a fresh catalyst for the synthesis of N,N-dimethylaniline. The catalyst was loaded into a fixed bed reactor. The reaction temperature was 250°C, the molar ratio of aniline to methanol was 3:1, and the mass space velocity of aniline to methanol was 1h -1 When the acid content of the catalyst is reduced to less than 40% of the fresh catalyst, the catalyst is considered to be deactivated, and the regenerated catalyst is obtained. The reaction feed is stopped and the regenerated catalyst is rinsed with methanol at 250°C for 2 hours. The volume space velocity of methanol is 0.6h -1 .

[0107] After methanol flushing, the feed was stopped and the catalyst was saturated with hydrogen at 230°C for 2 h, with a pressure of 0.1 MPa and a hydrogen flow rate of 10 mL / min relative to 1 g of fresh catalyst.

[0108] After hydrogen saturation, the temperature was raised to 250 °C, and the catalyst was flushed again with n-butanol under hydrogen atmosphere for 0.5 h. The pressure was 0.01 MPa, and the volume space velocity of n-butanol was 0.01 h -1 .

[0109] After washing, the raw material was added again for reaction. The reaction results are shown in Table 2.

[0110] Example 8

[0111] The catalyst in Preparation Example 2 was selected as a fresh catalyst and loaded into a fixed bed reactor. The reaction temperature was 290°C, the molar ratio of methanol to aniline was 9:1, and the mass space velocity of methanol to aniline was 10h -1 When the acid content of the catalyst is reduced to less than 40% of the fresh catalyst, the catalyst is considered to be deactivated, and the catalyst to be regenerated is obtained. The reaction feed is stopped and the catalyst is flushed with methanol at 290°C for 12 hours. The volume space velocity of methanol is 15h -1 .

[0112] After methanol flushing, the feed was stopped and the catalyst was saturated with hydrogen at 290°C for 20 h, with a pressure of 8 MPa and a hydrogen flow rate of 500 mL / min relative to 1 g of fresh catalyst.

[0113] After hydrogen saturation, the temperature was raised to 350 °C, and the catalyst was flushed again with n-butanol under hydrogen atmosphere for 48 h. The pressure was 8 MPa, and the volume space velocity of n-butanol was 10 h -1.

[0114] After washing, the raw material was added again for reaction. The reaction results are shown in Table 2.

[0115] Example 9

[0116] The catalyst in Preparation Example 2 was selected as a fresh catalyst and loaded into a fixed bed reactor. The reaction temperature was 220°C, the molar ratio of methanol to aniline was 1.5:1, and the mass space velocity of methanol to aniline was 0.1 h -1 When the acid content of the catalyst is reduced to less than 40% of the fresh catalyst, the catalyst is considered to be deactivated, and the catalyst to be regenerated is obtained. The reaction feed is stopped and the catalyst is flushed with methanol at 220°C for 6 hours. The volume space velocity of methanol is 5h -1 .

[0117] After methanol flushing, the feed was stopped and the catalyst was saturated with hydrogen at 260°C for 12 h, with a pressure of 4 MPa and a hydrogen flow rate of 10 mL / min relative to 1 g of fresh catalyst.

[0118] After hydrogen saturation, the temperature was raised to 300 °C, and the catalyst was flushed again with n-butanol under hydrogen atmosphere for 20 h. The pressure was 4 MPa, and the volume space velocity of n-butanol was 1 h -1 .

[0119] After washing, the raw material was added again for reaction. The reaction results are shown in Table 2.

[0120] Example 10

[0121] The catalyst in Preparation Example 2 was selected as a fresh catalyst, and N,N-dimethylaniline was synthesized according to the method of Example 2. The catalyst was loaded into a fixed bed reactor, the reaction temperature was 260°C, the molar ratio of methanol to aniline was 5:1, and the mass space velocity of methanol to aniline was 3h -1 When the acid content of the catalyst is reduced to less than 40% of the fresh catalyst, the catalyst is considered to be deactivated, and the catalyst to be regenerated is obtained. The reaction feed is stopped and the catalyst is flushed with methanol at 260°C for 0.5h. The volume space velocity of methanol is 5h -1 .

[0122] After methanol flushing, the feed was stopped and the catalyst was saturated with hydrogen at 260°C for 12 h, with a pressure of 4 MPa and a hydrogen flow rate of 10 mL / min relative to 1 g of fresh catalyst.

[0123] After hydrogen saturation, the temperature was raised to 300 °C, and the catalyst was flushed again with n-butanol under hydrogen atmosphere for 20 h. The pressure was 4 MPa, and the volume space velocity of n-butanol was 1 h -1 .

[0124] After washing, the raw material was added again for reaction. The reaction results are shown in Table 2.

[0125] Embodiment 11

[0126] The catalyst in Preparation Example 2 was selected as a fresh catalyst. According to the method of Example 2, the catalyst was loaded into a fixed bed reactor. The reaction temperature was 260°C, the molar ratio of methanol to aniline was 5:1, and the mass space velocity of methanol to aniline was 3h -1 When the acid content of the catalyst is reduced to less than 40% of the fresh catalyst, the catalyst is considered to be deactivated, and the catalyst to be regenerated is obtained. The reaction feed is stopped and the catalyst is flushed with methanol at 260°C for 6 hours and the volume space velocity of methanol is 5 hours. -1 .

[0127] After methanol flushing, the feed was stopped and the catalyst was saturated with hydrogen at 260°C for 12 h, with a pressure of 4 MPa and a hydrogen flow rate of 10 ml / min relative to 1 g of fresh catalyst.

[0128] After hydrogen saturation, the temperature was raised to 300 °C, and the catalyst was flushed again with benzene as solvent under hydrogen atmosphere for 20 h. The pressure was 4 MPa, and the volume space velocity of benzene was 1 h -1 .

[0129] After washing, the raw material was added again for reaction. The reaction results are shown in Table 2.

[0130] Comparative Examples 1-4

[0131] The catalysts in the above comparative preparation examples 1-4 and the method in Example 1 were used to carry out the synthesis and washing regeneration reaction of N,N-dimethylaniline. The reaction results are shown in Table 2.

[0132] Comparative Example 5

[0133] The catalyst in Preparation Example 2 was selected as a fresh catalyst and loaded into a fixed bed reactor. The reaction temperature was 260°C, the molar ratio of methanol to aniline was 5:1, and the mass space velocity of methanol to aniline was 3h -1 When the acid content of the catalyst is reduced to less than 40% of the fresh catalyst, the catalyst is considered to be deactivated, and the catalyst to be regenerated is obtained. The reaction feed is stopped and the catalyst is flushed with methanol at 260°C for 6 hours and the volume space velocity of methanol is 5 hours. -1 .

[0134] The temperature was raised to 300°C and the catalyst was flushed again with ethylene glycol for 20 hours at a pressure of 4 MPa and a volume space velocity of 1 h -1 .

[0135] After washing, the raw material was added again for reaction. The reaction results are shown in Table 2.

[0136] Comparative Example 6

[0137] The catalyst in Preparation Example 2 was selected as a fresh catalyst and loaded into a fixed bed reactor. The reaction temperature was 260°C, the molar ratio of methanol to aniline was 5:1, and the mass space velocity of methanol to aniline was 3h -1 When the amount of catalyst acid is reduced to less than 40% of the fresh catalyst, the catalyst is considered to be deactivated, and the spent catalyst is obtained, and the reaction feed is stopped.

[0138] The solvent washing and regeneration are carried out using the method of CN 111589434 A.

[0139] Table 2

[0140]

[0141] As can be seen from the above table, the washing and regeneration using this scheme effectively regenerates the catalyst, and after several reaction-regeneration cycles, the catalyst life does not change significantly, while the control ratio cannot effectively regenerate the catalyst completely, and the catalyst life is significantly reduced after regeneration.

[0142] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for continuously producing N,N-dimethylaniline, characterized in that: The method comprises: synthesizing N,N-dimethylaniline and regenerating a solvent of a catalyst to be regenerated, and returning the regenerated catalyst obtained by solvent regeneration to the synthesis of N,N-dimethylaniline for recycling; The synthesis of N,N-dimethylaniline comprises: in the presence of a fresh catalyst, reacting the reaction raw materials methanol and aniline in a gas phase to obtain a catalyst to be produced; the fresh catalyst comprises a molecular sieve, a carrier and a modified component, the modified component is copper and phosphorus, and the acid content of the medium-strong acid in the fresh catalyst accounts for more than 35% of the total acid content; The solvent regeneration of the spent catalyst comprises: sequentially performing a first-stage solvent regeneration, a second-stage hydrogenation regeneration and a third-stage solvent hydrogenation regeneration on the spent catalyst.

2. The method according to claim 1, wherein: The molar ratio of methanol to aniline is 1-10:1, preferably 1.5-9:1; Preferably, the synthesis conditions of N,N-dimethylaniline include: reaction temperature of 220-300°C, mass space velocity of methanol and aniline of 0.1-10h -1 ; Preferably, when the total acid content of the fresh catalyst decreases to below 40%, a spent catalyst is obtained.

3. The method according to claim 1 or 2, wherein: The solvent regeneration of the catalyst to be regenerated comprises: S1, subjecting the catalyst to be regenerated to a solvent regeneration step in the presence of a first solvent; S2, subjecting the product obtained in step S1 to a second-stage hydroregeneration under hydrogenation conditions; S3, subjecting the product obtained in step S2 to three-stage solvent hydrogenation regeneration under hydrogenation conditions and in the presence of a second solvent to obtain a regenerated catalyst.

4. The method according to claim 3, wherein: In step S1, the medium-strong acid recovery rate of the product obtained in step S1 reaches 80-90%; Preferably, in step S1, the first solvent is selected from at least one of methanol, ethanol, ethylene glycol and glycerol, and is more preferably methanol; Preferably, in step S1, the conditions for regenerating the first solvent include: a temperature of 200-350°C, a time of 0.5-24h, and a volume space velocity of the first solvent of 0.01-20h -1 ; Further preferably, in step S1, the conditions for regenerating the first solvent include: temperature of 210-300°C, time of 2-12h, volumetric space velocity of the first solvent of 0.5-15h -1 .

5. The method according to claim 3, wherein: In step S2, the conditions of the second stage hydrogen regeneration include: temperature of 200-350°C, time of 0.5-24h, pressure of 0.01-10MPa, and hydrogen flow rate of 0.001-10000mL / min relative to 1g of fresh catalyst; Preferably, in step S2, the conditions for the second-stage hydrogen regeneration include: temperature of 220-300°C, time of 2-20h, pressure of 0.1-8MPa, and hydrogen flow rate of 10-1000mL / min relative to 1g of fresh catalyst.

6. The method according to claim 3, wherein: The second solvent is selected from at least one of C1-C4 normal alcohol, benzene and aniline, preferably C1-C4 normal alcohol and / or aniline; Preferably, the C1-C4 normal alcohol is selected from at least one of methanol, ethanol, n-propanol and n-butanol; Preferably, the temperature of the third stage solvent hydroregeneration is 10-100°C higher than the temperature of the second stage solvent hydroregeneration; Preferably, in step S3, the conditions for the three-stage solvent hydrogenation regeneration include: temperature of 210-450°C, time of 0.5-50h, pressure of 0.01-10MPa, and volumetric space velocity of the second solvent of 0.01-15h -1 ; Further preferably, in step S3, the conditions for the three-stage solvent hydrogenation regeneration include: temperature of 230-450°C, time of 0.5-48h, pressure of 0.01-8MPa, and volumetric space velocity of the second solvent of 0.01-10h -1 .

7. The method according to any one of claims 1 to 6, wherein: The amount of strong acid in the fresh catalyst accounts for 40-50% of the total acid, preferably 42-45%; Preferably, the preparation method of the fresh catalyst comprises: (1) mixing a molecular sieve and a carrier to obtain a mixture; (2) mixing the mixture obtained in step (1) with a solution containing a copper precursor and a phosphorus-containing compound to form a mixture, and then calcining the mixture once to obtain a fresh catalyst.

8. The method according to claim 7, wherein: In step (1), the molecular sieve is at least one selected from Y-type molecular sieve, ZSM-5 type molecular sieve, β-type molecular sieve, MCM-22 type molecular sieve and mordenite, preferably at least one selected from Y-type molecular sieve, ZSM-5 type molecular sieve and β-type molecular sieve, and more preferably β-type molecular sieve; Preferably, in step (1), the carrier is aluminum oxide and / or silicon oxide; Preferably, in step (1), the mass ratio of the molecular sieve to the carrier is 95:5-20:80, more preferably 90:10-25:75; Preferably, in step (1), the carrier is in a solid state and / or a sol state, and more preferably in a sol state; Preferably, in step (1), the carrier is alumina.

9. The method according to claim 7, wherein: In step (2), the copper precursor is selected from soluble copper compounds, preferably at least one selected from cupric chloride, cuprous chloride, cupric nitrate, copper sulfate and cuprous sulfate; Preferably, in step (2), the phosphorus-containing compound is selected from at least one of phosphoric acid, phosphorous acid, soluble phosphates and phosphites; Preferably, the soluble phosphate is selected from at least one of ammonium phosphate, diammonium hydrogen phosphate and diammonium dihydrogen phosphate; Preferably, in step (2), the mass ratio of the copper precursor to the phosphorus-containing compound is 5:95-98:2, more preferably 30:70-80:20; Preferably, the mass ratio of the carrier calculated as oxide to the copper precursor calculated as element is 80:20-99.9:0.1, and more preferably 95:15-99:

1.

10. The method according to claim 9, wherein: The method for preparing the fresh catalyst further comprises: introducing a peptizing agent into a solution containing a copper precursor and a phosphorus-containing compound and mixing the mixture obtained in step (1) to form a mixture; Preferably, the peptizing agent is selected from at least one of nitric acid, hydrochloric acid, sulfuric acid, formic acid and acetic acid; Preferably, the amount of the peptizing agent is such that the pH of the solution containing the copper precursor and the phosphorus-containing compound is 1-4; Preferably, in step (2), the calcination conditions include: temperature of 450-800°C and time of 1-10h; Further preferably, in step (2), the calcination conditions include: temperature of 500-700° C. and time of 2-8 h.

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