Method for producing N, N-dimethylaniline

Abstract

The invention relates to the field of synthesis of N, N-dimethylaniline, and discloses a method for producing N, N-dimethylaniline. The invention relates to a method for producing N, N-dimethylaniline, which is characterized in that in the presence of a catalyst, reaction raw materials methanol and aniline react, and the reaction is a gas-phase reaction; the preparation method of the catalyst comprises the following steps: (1) mixing a molecular sieve and a carrier to obtain a mixture; and (2) the mixture obtained in the step (1) and a solution containing a copper precursor and a phosphorus-containing compound are mixed and molded, then primary roasting is carried out, the catalyst is obtained, and the amount of medium and strong acids in the catalyst accounts for 35% or above of the total acid amount. According to the method, by controlling the adding sequence of the raw materials in the catalyst preparation process and selecting copper and phosphorus to prepare the catalyst, the stability of the catalyst and the selectivity of a target product can be improved, side reactions can be reduced, the synthesis reaction temperature can be widened, and industrial production is facilitated.

Description

Technical Field

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

[0002] N,N-dimethylaniline is an important chemical product that can be used in the production of many important industrial products such as papermaking, textile dyes, medicines, spices and explosives.

[0003] The main synthesis method of N,N-dimethylaniline is the N-alkylation reaction of aniline. Currently, the main methods for the N-alkylation reaction of aniline include a liquid phase method using sulfuric acid as a catalyst and a gas phase method using aniline and methanol.

[0004] At present, the mainstream synthesis method of N,N-dimethylaniline is a liquid phase method using sulfuric acid as a catalyst, specifically, it is prepared by reacting aniline and methanol at high temperature and high pressure in a high-pressure reactor. The conversion rate of N,N-dimethylaniline prepared by the sulfuric acid method is high. The main disadvantage of this method is that it cannot be produced continuously. The reaction is carried out under high pressure, and corrosion-resistant and high-pressure resistant equipment materials need to be selected, which increases investment. A large amount of acid-soluble oil is produced during the production process. The separation product requires a large amount of liquid alkali to neutralize the inorganic acid and produce a large amount of difficult-to-handle inorganic salts. The subsequent processing cost is high and brings certain safety hazards and greater environmental pressure. This method is highly polluting, and it is urgent to develop a new green production process.

[0005] Since the 1950s, the synthesis of N,N-dimethylaniline from aniline and methanol by vapor phase method has been studied at home and abroad. The catalyst of the vapor phase method is generally metal oxides, metal salts, molecular sieves, etc. The vapor phase method was first successfully developed in India, with a product selectivity of about 90%, which is lower than the liquid phase method, and has not been industrially applied.

[0006] At present, the mainstream production technology in my country is also the liquid phase method with sulfuric acid as the catalyst. In view of the pollution and great safety hazards caused by the sulfuric acid method, my country has also done a lot of research on the green production of N,N-dimethylaniline.

[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] From the reaction mechanism point of view, the alkylation reaction of methanol and aniline to synthesize N,N-dimethylaniline is usually carried out at a high temperature of 300°C, and water molecules are produced during the reaction. Molecular sieves are prone to dealumination under high temperature and water conditions, causing permanent deactivation of the catalyst. Therefore, the conversion rate, selectivity and stability of the catalyst are greatly affected.

[0010] In addition, the coking reaction on the catalyst starts from the alkylation of N,N-dimethylaniline and methanol to form N,N,C-trimethylaniline, and then continues to undergo hydrogen transfer, alkylation and cyclization reactions to form non-volatile coke deposits with a multi-ring structure. 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.

[0011] In order to reduce the occurrence of side reactions, the synthesis reaction needs to be carried out at a lower temperature. The strong acid in the catalyst will cause side reactions. Therefore, in order to increase the life and selectivity of the catalyst and reduce the occurrence of side reactions, it is necessary to increase the proportion of strong acid in the catalyst to reduce the reaction temperature, and reduce the amount of strong acid to reduce side reactions.

[0012] Generally speaking, phosphorus modification of molecular sieve catalysts is mostly concentrated on molecular sieve modification. A small number of literatures have reported phosphorus modification of catalysts after catalyst molding, but this catalyst phosphorus modification method is relatively complicated, and the phosphorus-modified catalyst is calcined again after calcination. Multiple calcinations not only have a great impact on the activity of the catalyst, but also increase the complexity of the catalyst preparation process and have high energy consumption. Summary of the invention

[0013] The purpose of the present invention is to overcome the problems of poor catalyst stability and poor target product selectivity in the N,N-dimethylbenzene synthesis process in the prior art, and to provide a method for producing N,N-dimethylaniline. The method controls the order of adding raw materials in the catalyst preparation process, selects copper and phosphorus to prepare the catalyst, can improve the catalyst stability and target product selectivity, reduce the occurrence of side reactions, and can widen the synthesis reaction temperature, which is suitable for industrial production.

[0014] In order to achieve the above object, the present invention provides a method for producing N,N-dimethylaniline, wherein the reaction raw materials methanol and aniline react in the presence of a catalyst, and the reaction is a gas phase reaction;

[0015] Wherein, the preparation method of the catalyst comprises:

[0016] (1) mixing the molecular sieve and the carrier to obtain a mixture;

[0017] (2) The mixture obtained in step (1) is mixed with a solution containing a copper precursor and a phosphorus-containing compound to form a catalyst, and then calcined once to obtain a catalyst, wherein the amount of medium-strong acid in the catalyst accounts for more than 35% of the total acid amount.

[0018] The method provided by the present invention increases the proportion of medium and strong acids in the catalyst and reduces the proportion of strong acids by introducing copper, thereby reducing the adsorption of methanol with greater polarity at acidic sites, reducing the occurrence of side reactions, and increasing the life of the catalyst; further, phosphorus modification is coordinated to improve the hydrothermal stability of the catalyst under high temperature conditions, without having a negative impact on the acidity and stability of the catalyst itself, and long-term continuous operation of the catalyst is achieved, which is beneficial to industrial continuous production and greatly saves production costs.

[0019] The method provided by the present invention controls the order of adding raw materials in the catalyst preparation process, strictly follows the principle of first mixing the molecular sieve and the carrier, and directly mixing them with a solution containing a copper precursor and a phosphorus-containing compound to prepare the catalyst without roasting. Only one roasting is required in the catalyst preparation process, thus avoiding the multiple roastings of the catalyst modification treatment after molding in the prior art, reducing the difficulty of the catalyst preparation process and reducing energy consumption.

[0020] The method provided by the present invention selects copper and phosphorus to prepare the catalyst, which can improve the catalyst stability and target product selectivity, reduce the occurrence of side reactions, make the catalyst run stably to continuously produce N,N-dimethylaniline, and can widen the synthesis reaction temperature, which is applicable to industrial production.

[0021] The method provided by the invention is green, environmentally friendly and pollution-free, and the catalyst can be recycled, thereby achieving zero pollution and zero emission in the production process. DETAILED DESCRIPTION

[0022] 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.

[0023] The present invention provides a method for producing N,N-dimethylaniline, wherein the reaction raw materials methanol and aniline react in the presence of a catalyst, and the reaction is a gas phase reaction;

[0024] Wherein, the preparation method of the catalyst comprises:

[0025] (1) mixing the molecular sieve and the carrier to obtain a mixture;

[0026] (2) The mixture obtained in step (1) is mixed with a solution containing a copper precursor and a phosphorus-containing compound to form a catalyst, and then calcined once to obtain a catalyst, wherein the amount of medium-strong acid in the catalyst accounts for more than 35% of the total acid amount.

[0027] The method provided by the present invention increases the proportion of medium and strong acids in the catalyst and reduces the proportion of strong acids by introducing copper, thereby reducing the adsorption of methanol with greater polarity at acidic sites, reducing the occurrence of side reactions, and increasing the life of the catalyst; further, phosphorus modification is coordinated to improve the hydrothermal stability of the catalyst under high temperature conditions, without having a negative impact on the acidity and stability of the catalyst itself, and long-term continuous operation of the catalyst is achieved, which is beneficial to industrial continuous production and greatly saves production costs.

[0028] The method provided by the present invention controls the order of adding raw materials in the catalyst preparation process, strictly follows the principle of first mixing the molecular sieve and the carrier, and directly mixing them with a solution containing a copper precursor and a phosphorus-containing compound to prepare the catalyst without roasting. Only one roasting is required in the catalyst preparation process, thus avoiding the multiple roastings of the catalyst modification treatment after molding in the prior art, reducing the difficulty of the catalyst preparation process and reducing energy consumption.

[0029] The method provided by the present invention selects copper and phosphorus to prepare the catalyst, which can improve the catalyst stability and target product selectivity, reduce the occurrence of side reactions, make the catalyst run stably to continuously produce N,N-dimethylaniline, and can widen the synthesis reaction temperature, which is applicable to industrial production.

[0030] The method provided by the invention is green, environmentally friendly and pollution-free, and the catalyst can be recycled, thereby achieving zero pollution and zero emission in the production process.

[0031] 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.

[0032] In the present invention, the catalyst acid distribution adopts NH 3 The characterization was performed by programmed temperature desorption (NH3-TPD). The characterization method is as follows: Instrument: Quantachrome Chemstar TPx Test process: Weigh 0.15g (20-40 mesh) molecular sieve or catalyst sample, heat it to 550℃, dry it, and then cool it to 100℃ to make the catalyst saturated with NH3. 3, respectively, the temperature was raised to 250℃, 350℃, 450℃ and 550℃ to make NH 3 Desorption and detection of NH 3 Concentration. The adsorption curves obtained at different temperature ranges 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.

[0033] In the present invention, the catalyst for the synthesis reaction has a high proportion of medium-strong acid, which can reduce the adsorption of methanol with greater polarity at acidic sites, reduce the occurrence of side reactions, and increase the life of the catalyst. Preferably, the medium-strong acid content of the catalyst accounts for 40-50% of the total acid content, and more preferably 42-45%.

[0034] In the present invention, 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. The advantage of adopting this preferred embodiment is that β-molecular sieve is a commonly used molecular sieve in industry, the preparation technology is mature, and the conversion rate and selectivity in the reaction are good.

[0035] In the present invention, preferably, in step (1), the silicon to aluminum molar ratio of the molecular sieve is 2-1000:1, more preferably 2-100:1.

[0036] In the present invention, the type of carrier can be selected in a wide range. Preferably, in step (1), the carrier is aluminum oxide and / or silicon oxide.

[0037] In the present invention, the amount of the molecular sieve and the carrier can be selected in a wide range. Preferably, in step (1), the mass ratio of the molecular sieve to the carrier in terms of oxide is 95:5-20:80, more preferably 90:10-25:75.

[0038] 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.

[0039] In the present invention, preferably, when the carrier is in a sol state, the carrier is provided by aluminum sol and / or silica sol.

[0040] 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%.

[0041] In the present invention, preferably, in step (1), the carrier is alumina.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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 aqueous solution of the phosphorus-containing compound is 0.01-25wt%, preferably 5-25wt%.

[0047] 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, preferably 30:70-80:20, calculated as the element. 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] In the present invention, the range of selection of calcination conditions is relatively wide. Preferably, in step (2), the calcination conditions include: temperature of 450-800°C, time of 1-15h; further preferably, in step (2), the calcination conditions include: temperature of 500-700°C, time of 2-8h.

[0054] In the present invention, there is no particular limitation on the amount of the reaction raw materials methanol and aniline, as long as they can meet the reaction requirements. Preferably, the molar ratio of methanol to aniline is 1-10:1, preferably 2-8:1.

[0055] In the present invention, the catalyst prepared by the preparation method provided by the present invention can reduce the reaction temperature and expand the application scenarios. Preferably, the reaction conditions include: the reaction temperature is 220-300°C, the mass space velocity of methanol and aniline is 0.1-10h -1 Further preferably, the reaction conditions include: the reaction temperature is 230-290°C, the mass space velocity of methanol and aniline is 0.2-8h -1 .

[0056] The production method of the present invention uses a catalyst prepared by the catalyst preparation method provided by the present invention, which can not only improve the high-temperature hydrothermal stability, but also reduce the reaction temperature, reduce the occurrence of side reactions, improve the conversion rate, selectivity and stability of the catalyst, make the catalyst run stably, and realize the continuous production of N,N-dimethylaniline.

[0057] In the present invention, preferably, the method is carried out in at least one of a fixed bed reactor, a fluidized bed reactor, a moving bed reactor and a slurry bed reactor, and is further preferably carried out in a fixed bed reactor.

[0058] The present invention will be described in detail below by way of examples. In the following examples, unless otherwise specified, all the raw materials used are from commercially available products.

[0059] In the following examples and comparative examples, the conversion of aniline and the selectivity distribution of the obtained products N,N-dimethylaniline and N-methylaniline were determined by anglient-7890 gas chromatography analysis (the chromatographic column is a HP-PONA 50m×0.2mm capillary column) equipped with a high-pressure injector. The detection idea and method for determining the catalyst's one-way life is: when the aniline conversion rate drops to 98%, the catalyst is considered to be deactivated, and the reaction time experienced by the catalyst is the catalyst's one-way life.

[0060] In the present invention, the catalyst acid distribution adopts NH 3 Programmed temperature desorption method (NH 3 -TPD) was used for characterization. The characterization method is as follows: Instrument: Quantachrome Chemstar TPx Test process: Weigh 0.15g (2040 mesh) molecular sieve or catalyst sample, heat it to 550℃ and dry it, then cool it down to 100℃ to make the catalyst saturated with NH 3 , respectively, the temperature was raised to 250℃, 350℃, 450℃ and 550℃ to make NH 3 Desorption and detection of NH 3 Concentration. The adsorption curves obtained at different temperature ranges 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.

[0061] Example 1

[0062] (1) 90 g HY molecular sieve (silicon to aluminum molar ratio of 5) and 10 g alumina were mixed evenly;

[0063] (2) Take 3g of cuprous chloride and add 100g of 10wt% H 3 PO 4 The solution was added to the mixed powder in step (1) and mixed evenly, and then extruded by an extruder, and calcined at 500°C for 12h to obtain catalyst Y-1. The acid content of the catalyst is shown in Table 1.

[0064] The catalyst was reacted in a fixed bed reactor, the molar ratio of methanol to aniline was 3:1, and the mass space velocity of methanol and aniline was 1h -1 The reaction temperature was 250°C, and the raw materials were pumped into the reactor by a raw material pump. Aniline and methanol were gasified in the reactor and reacted after contacting the catalyst bed. The reaction results are shown in Table 2.

[0065] Example 2

[0066] (1) 750 g of β molecular sieve (silicon-aluminum molar ratio of 20) and 1250 g of 20 wt% aluminum sol were mixed uniformly;

[0067] (2) Take 5g Cu 2 SO 4 Add 100g of 5wt% KH 2 PO 4 The solution was then added to the mixture of molecular sieve and aluminum sol after adjusting the pH to 2.5 with nitric acid, mixed and rolled, 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.

[0068] The reaction was carried out according to the method and reaction conditions of Example 1. The reaction results are shown in Table 2.

[0069] Example 3

[0070] (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;

[0071] (2) Take 10g Cu(NO 3 ) 2 Add to 100g of 10wt% K 3 PO 4 The molecular sieve and silica sol were added to the solution, 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.

[0072] The reaction was carried out according to the method and reaction conditions of Example 1. The reaction results are shown in Table 2.

[0073] Example 4

[0074] The catalyst was prepared according to the method of Example 2, except that 50 g Cu 2 SO 4 Add 200g of 25wt% KH 2 PO 4The solution was then added to a mixture of molecular sieves and aluminum sol after adjusting the pH to 4 with nitric acid, and calcined at 500°C for 8h to obtain catalyst β-2.

[0075] The results of the acid content of the catalyst are shown in Table 1.

[0076] The reaction was carried out according to the method and reaction conditions of Example 1. The reaction results are shown in Table 2.

[0077] Example 5

[0078] The catalyst was prepared according to the method of Example 2, except that Cu 2 SO 4 The added amount is 60 g, and other conditions remain unchanged to obtain catalyst β-3.

[0079] The results of the acid content of the catalyst are shown in Table 1.

[0080] The reaction was carried out according to the method and reaction conditions of Example 1. The reaction results are shown in Table 2.

[0081] Example 6

[0082] The catalyst was prepared according to the method of Example 2, except that 2 g Cu 2 SO 4 Add 200g of 25wt% KH 2 PO 4 Catalyst β-4 is obtained in the solution.

[0083] The results of the acid content of the catalyst are shown in Table 1.

[0084] The reaction was carried out according to the method and reaction conditions of Example 1. The reaction results are shown in Table 2.

[0085] Example 7

[0086] The catalyst was prepared according to the method of Example 2, except that alumina powder was used instead of aluminum sol. Other conditions remained unchanged, and catalyst β-5 was obtained.

[0087] The reaction was carried out according to the method and reaction conditions of Example 1. The reaction results are shown in Table 2.

[0088] Comparative Example 1

[0089] The catalyst was prepared according to the method of Example 1, except that the subsequent phosphorus loading was not performed, and the other conditions were the same as Example 1 to obtain catalyst DY-1. The acid content of the catalyst is shown in Table 1.

[0090] The reaction was carried out according to the method and reaction conditions of Example 1. The reaction results are shown in Table 2.

[0091] Comparative Example 2

[0092] The catalyst was prepared according to the method of Example 1, except that only phosphoric acid solution was added during the catalyst preparation, and the other conditions were the same as Example 1, to obtain catalyst DY-2. The acid content of the catalyst is shown in Table 1.

[0093] The reaction was carried out according to the method and reaction conditions of Example 1. The reaction results are shown in Table 2.

[0094] Comparative Example 3

[0095] The catalyst was prepared according to the method of Example 2, except that only copper salt solution was added during the catalyst preparation, and the other conditions were the same as Example 2 to obtain catalyst Dβ-1. The acid content of the catalyst is shown in Table 1.

[0096] The reaction was carried out according to the method and reaction conditions of Example 1. The reaction results are shown in Table 2.

[0097] Comparative Example 4

[0098] The catalyst was prepared according to the method of Example 2, except that only phosphoric acid solution was added during the preparation of the catalyst, and the other conditions were the same as Example 2 to obtain catalyst Dβ-2. The acid content of the catalyst is shown in Table 1.

[0099] The reaction was carried out according to the method and reaction conditions of Example 1. The reaction results are shown in Table 2.

[0100] Table 1

[0101]

[0102] From the results in the above table, it can be seen that the combined modification of phosphate and Cu ions can increase the total acid content and acid strength of the catalyst, especially the proportion of medium-strong acid, effectively reduce the proportion of strong acid in the catalyst, and reduce the occurrence of side reactions.

[0103] Table 2

[0104]

[0105] It can be seen from the above table that the catalyst prepared by loading copper and phosphorus using the preparation method provided by the present invention can effectively reduce the selectivity of the main by-products N-methylaniline and N,N,C-trimethylaniline, and effectively increase the life of the catalyst.

[0106] Example 8

[0107] The method of Example 2 was followed, except that the reaction temperature was 230° C. The reaction results are shown in Table 3.

[0108] Comparative Example 5

[0109] The method of Comparative Example 3 was followed, except that the reaction temperature was 230° C. The reaction results are shown in Table 3.

[0110] Comparative Example 6

[0111] The method of Comparative Example 4 was followed, except that the reaction temperature was 230° C. The reaction results are shown in Table 3.

[0112] Table 3

[0113]

[0114] From the results in the above table, it can be seen that increasing the amount of medium-strong acid can reduce the reaction temperature, inhibit the occurrence of side reactions at high temperatures, reduce carbon deposits, and extend the life of the catalyst.

[0115] 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 producing N,N-dimethylaniline, characterized in that: In the presence of a catalyst, the reaction raw materials methanol and aniline react, and the reaction is a gas phase reaction; Wherein, the preparation method of the catalyst comprises: (1) mixing the molecular sieve and the carrier to obtain a mixture; (2) The mixture obtained in step (1) is mixed with a solution containing a copper precursor and a phosphorus-containing compound to form a catalyst, and then calcined once to obtain a catalyst, wherein the amount of medium-strong acid in the catalyst accounts for more than 35% of the total acid amount.

2. The method according to claim 1, wherein: The amount of the medium-strong acid in the catalyst accounts for 40-50% of the total acid, preferably 42-45%.

3. The method according to claim 1 or 2, 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 calculated as oxide is 95:5-20:80, more preferably 90:10-25:

75.

4. The method according to claim 3, wherein: 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.

5. The method according to any one of claims 1 to 4, 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 ammonium dihydrogen phosphate.

6. The method according to any one of claims 1 to 5, wherein: In step (2), the mass ratio of the copper precursor to the phosphorus-containing compound is 5:95-98:2, preferably 30:70-80:20, calculated on an element basis; 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 85:15-99:

1.

7. The method according to claim 4, wherein: The preparation method of the 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, phosphoric acid, formic acid and acetic acid; Preferably, the amount of the peptizing agent used is such that the pH of the solution containing the copper precursor and the phosphorus-containing compound is 1-4.

8. The method according to any one of claims 1 to 7, wherein: In step (2), the calcination conditions include: temperature of 450-800° C. and time of 1-15 h; Preferably, in step (2), the calcination conditions include: temperature of 500-700° C. and time of 2-8 h.

9. The method according to any one of claims 1 to 8, wherein: The molar ratio of methanol to aniline is 1-10:1, preferably 2-8:

1.

10. The method according to any one of claims 1 to 9, wherein: The reaction conditions include: the reaction temperature is 220-300°C, the mass space velocity of methanol and aniline is 0.1-10h -1 ; Preferably, the reaction conditions include: reaction temperature of 230-290°C, mass space velocity of methanol and aniline of 0.2-8h -1 .

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