A method for continuously producing n-methyldiethanolamine and a catalyst therefor

Abstract

This application discloses a method for the continuous preparation of N-methyldiethanolamine and its catalyst. Formaldehyde aqueous solution and diethanolamine are mixed in a specific ratio and reacted in the presence of hydrogen and a catalyst at a controlled temperature of 80–150°C and a reaction pressure of 2–5 MPa to obtain N-methyldiethanolamine. The catalyst is a supported heterogeneous solid particulate catalyst. This application is the first to employ a continuous catalytic reduction ammoniation method to produce N-methyldiethanolamine using formaldehyde and diethanolamine, both green chemical products, as raw materials. This application overcomes the problems of high toxicity and cost of raw materials, low product yield, and severe pollution in existing N-methyldiethanolamine production processes. Furthermore, the continuous production method improves mass transfer efficiency, enhances the reaction rate, and increases the selectivity of the target product, N-methyldiethanolamine. The method has a simple reaction solution composition, facilitates product separation, and significantly reduces energy consumption and production costs.

Description

Technical Field

[0001] This application relates to a method for the continuous preparation of N-methyldiethanolamine and its catalyst, belonging to the field of chemical synthesis technology of organic amine compounds. Background Technology

[0002] N-Methyldiethanolamine (MDEA) is an organic amine compound containing a tertiary amine group and two hydroxyl groups. It is weakly basic and miscible with solvents such as water and ethanol in any proportion. Since the 1980s, N-methyldiethanolamine has been widely used as a selective desulfurization absorbent in industrial gas purification, particularly for the removal of hydrogen sulfide from natural gas, refinery gas, syngas, and coal gas. In recent years, its application in carbon dioxide capture, storage, and utilization (CCUS) has also become increasingly widespread. Furthermore, this compound can be used as a semi-finished product in pesticides, emulsifiers, and textile auxiliaries, as well as as an intermediate in the antitumor drug nitrogen mustard hydrochloride and a catalyst in carbamate coatings, demonstrating high industrial application value. With the continuous growth in demand for industrial gas purification and carbon capture, the demand for N-methyldiethanolamine is constantly expanding, and its efficient, safe, and low-cost preparation methods have attracted widespread attention.

[0003] Currently, one of the main industrial methods for preparing N-methyldiethanolamine is the reaction of monomethylamine with ethylene oxide. CN 103664650 A discloses a method for preparing N-methyldiethanolamine at room temperature, reacting monomethylamine with ethylene oxide at a temperature of 40℃ to 65℃; CN 101265195 A discloses a method for preparing N-methyldiethanolamine, controlling the reaction temperature between 133℃ and 137℃. In these methods, monomethylamine is a toxic and flammable gas, and ethylene oxide is a highly hazardous flammable and explosive substance, posing significant safety risks during storage, transportation, and use. Furthermore, the byproducts in these processes are complex, and the selectivity of the target product, N-methyldiethanolamine, is relatively low. Obtaining high-purity products requires sophisticated distillation separation methods, increasing production costs and operational complexity.

[0004] Furthermore, CN 111205192 A discloses a method for the continuous preparation of N,N,N′-trimethylbis(aminoethyl) ether in a fixed bed under hydrogen-bearing conditions using 2-[2-(dimethylamino)ethoxy]ethanol and monomethylamine as raw materials and a supported heterogeneous catalyst containing Ni / Co as the main active component. Although this method employs a continuous flow fixed-bed process, monomethylamine, the raw material, is a toxic and flammable gas, and the catalyst system is mainly composed of non-precious metals Ni / Co as the main active component. The target product differs from N-methyldiethanolamine and cannot be directly used for the highly selective preparation of N-methyldiethanolamine; moreover, the catalyst stability needs improvement.

[0005] In addition, there are reports on methods for preparing N-methyldiethanolamine from formaldehyde and diethanolamine via a batch-type catalytic reduction ammoniation reaction. However, batch production methods have inherent limitations such as batch operation and low production efficiency. Furthermore, the reaction process produces a variety of byproducts, resulting in a complex reaction solution composition, which puts significant pressure on subsequent product separation and purification processes, making it difficult to meet the requirements of large-scale continuous industrial production.

[0006] In summary, existing methods for preparing N-methyldiethanolamine have varying degrees of technical limitations in terms of raw material safety, target product selectivity, catalytic system stability, and adaptability to continuous production, making it difficult to simultaneously meet the demands of safe, efficient, and low-cost industrial production. Therefore, it is necessary to develop a new method for preparing N-methyldiethanolamine to overcome the shortcomings of the existing technologies. Summary of the Invention

[0007] One of the objectives of this application is to provide a method for the continuous preparation of N-methyldiethanolamine, in order to solve the technical defects of the prior art, such as the high toxicity and danger of the raw materials in the synthesis route using monomethylamine and ethylene oxide, the low selectivity of the target product, the high safety risk of the raw materials in the continuous flow fixed bed process containing the toxic raw material monomethylamine, the target product being non-N-methyldiethanolamine, the need to improve the stability of the catalyst, and the low production efficiency, many by-products, insufficient catalyst stability, and difficulty in achieving large-scale continuous industrial production in the batch-type catalytic reduction ammoniation process.

[0008] To achieve the above objectives, this application adopts the following technical solution: A method for the continuous preparation of N-methyldiethanolamine involves mixing an aqueous formaldehyde solution and diethanolamine to obtain a mixture, which is then continuously fed into a fixed-bed reactor containing a catalyst. In the presence of hydrogen, the reaction temperature is controlled at 80–150°C and the reaction pressure at 2–5 MPa to carry out a catalytic reduction ammoniation reaction to obtain N-methyldiethanolamine. The catalyst is a supported multiphase solid particulate catalyst, comprising a main active component, an auxiliary agent, and a support. The main active component is Pd or Pt, the auxiliary agent is Cu, and the support is at least one of silicon nanotubes or carbon nanotubes. The catalyst is activated by hydrogen reduction before use.

[0009] Preferably, the molar ratio of the formaldehyde aqueous solution to diethanolamine is 1.4:1 to 1.6:1; optionally, the molar ratio is selected from any value of 1.4:1, 1.5:1, 1.6:1 or any range of two of them.

[0010] Preferably, the reaction temperature is 90–140°C, and the reaction pressure is 2–5 MPa; Optionally, the reaction temperature is selected from any value or a range of any two of 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, and 150℃. Optionally, the reaction pressure is selected from any value of 2MPa, 2.5MPa, 3MPa, 3.5MPa, 4MPa, 4.5MPa, 5MPa, or a range of any combination of both.

[0011] Preferably, the liquid hourly space velocity (LHSV) of the diethanolamine is 0.5–2 h⁻¹. -1 The volumetric flow rate ratio of hydrogen to liquid is 80–120:1; Optionally, the liquid volume hourly space velocity is selected from 0.5 h⁻¹. -1 1.0h -1 1.5h -1 2.0h -1 Any value in the range or any combination of both; Optionally, the volumetric flow rate ratio of hydrogen to liquid is selected from any value of 80:1, 90:1, 100:1, 110:1, 120:1, or any range of both.

[0012] Preferably, in the catalyst, based on the total mass of the catalyst, the mass percentage of the main active component is 0.3% to 1.0%, the mass percentage of the auxiliary agent is 0.1% to 0.5%, and the remainder is a carrier; More preferably, the main active component has a mass percentage content of 0.5% to 1.0%, and the auxiliary agent has a mass percentage content of 0.3% to 0.5%. Optionally, the mass percentage of the main active component is selected from any value of 0.3%, 0.5%, 0.8%, 1.0%, or a range of any combination of both. Optionally, the mass percentage of the additive is selected from any value of 0.1%, 0.3%, 0.5%, or a range of any combination of both.

[0013] Preferably, the conditions for activating the catalyst by hydrogen reduction before use are: temperature 100–300°C, pressure 0.05–1.0 MPa, and hydrogen volume hourly space velocity 300–15000 h⁻¹. -1 Time: 1-10 hours; More preferably, the activation treatment temperature is 200–300°C, and the time is 2–5 hours; Optionally, the activation temperature is selected from any value of 100℃, 150℃, 200℃, 250℃, 300℃, or a range of any two. Optionally, the activation treatment pressure is selected from any value or a range of any two of 0.05MPa, 0.1MPa, 0.2MPa, 0.5MPa, and 1.0MPa. Optionally, the hydrogen volume hourly space velocity is selected from 300 h⁻¹. -1 1000h -1 5000h -1 10000h -1 15000h -1 Any value in the range or any combination of both; Optionally, the activation treatment time is selected from any value of 1h, 2h, 5h, 10h, or a range of any combination of both.

[0014] Preferably, the catalyst is prepared by a combination of precipitation and impregnation methods.

[0015] Another objective of this application is to provide a supported heterogeneous solid particle catalyst for the continuous preparation of N-methyldiethanolamine, in order to overcome the technical defects of existing catalysts, such as poor selectivity, insufficient stability, and difficulty in adapting to the requirements of continuous flow industrial production.

[0016] To achieve the above objectives, this application adopts the following technical solution: According to another aspect of this application, a supported heterogeneous solid particle catalyst for the continuous preparation of N-methyldiethanolamine is provided, the catalyst comprising a main active component, an auxiliary agent, and a support; the main active component is Pd or Pt, the auxiliary agent is Cu, and the support is at least one of silicon nanotubes or carbon nanotubes; the catalyst is prepared by a combination of precipitation and impregnation methods.

[0017] Preferably, in the catalyst, based on the total mass of the catalyst, the mass percentage of Pd is 1.0%, the mass percentage of Cu is 0.5%, and the balance is carbon nanotubes.

[0018] Preferably, in the catalyst, based on the total mass of the catalyst, the mass percentage of the main active component is 0.5% to 1.0%, and the mass percentage of the auxiliary agent is 0.3% to 0.5%. Optionally, the mass percentage of the main active component is selected from any value of 0.5%, 0.8%, 1.0%, or a range of any combination of both. Optionally, the mass percentage of the additive is selected from any value of 0.3% or 0.5% or a range of both.

[0019] The beneficial effects that this application can produce include: 1) Replacing highly toxic and dangerous monomethylamine and ethylene oxide with formaldehyde aqueous solution and diethanolamine provides green, safe, inexpensive and readily available raw materials, fundamentally eliminating the safety risks in the storage, transportation and use of raw materials in the existing process route, and significantly reducing raw material costs. 2) A supported heterogeneous solid particle catalyst is used, consisting of Pd or Pt as the main active component, Cu as the promoter, and silicon nanotubes or carbon nanotubes as the support. The active metal is highly dispersed on the nanotube support, and the Cu promoter effectively regulates the electronic structure of the active sites, synergistically improving the selectivity of the catalyst for the reductive ammoniation reaction. Under optimized reaction conditions, the diethanolamine conversion rate can reach 100%, and the N-methyldiethanolamine selectivity is greater than 96%. 3) The supported multiphase solid particle catalyst has excellent long-term operational stability. When the 1.0%Pd-0.5%Cu / carbon nanotube catalyst was continuously operated at 150℃ and 3MPa for 1000 hours, the conversion rate was always maintained at about 99.5%, the average selectivity was greater than 96%, and no deactivation of the catalyst was observed, which fully verified the industrial applicability of the catalytic system. 4) Compared with batch reactor production, the fixed-bed continuous flow catalytic process improves mass transfer efficiency, enhances reaction rate, simplifies and improves the separation of catalyst and reaction products, simplifies the composition of reaction liquid, and makes the product easy to separate and purify, which helps to reduce energy consumption and production costs. 5) Fixed-bed continuous flow process is easy to operate, process parameters are easy to control, suitable for modular expansion, and easy to realize large-scale continuous industrial production. Attached Figure Description

[0020] Figure 1 This is a schematic diagram showing the changes in diethanolamine conversion and N-methyldiethanolamine selectivity over time during 1000 hours of continuous operation of a 1.0%Pd-0.5%Cu / carbon nanotube catalyst. Detailed Implementation

[0021] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0022] Unless otherwise specified, the raw materials and reagents used in the embodiments of this application were all purchased commercially. The products obtained by this invention were analyzed using a Pano GC1949 gas chromatograph with an FFAP capillary column and a flame ionization detector (FID). The diethanolamine conversion and N-methyldiethanolamine selectivity were calculated using the area normalization method.

[0023] The preparation method of the catalyst with a composition of 1.0% Pd-0.5% Cu / CNTs in the embodiments of this application is as follows: Dissolve 0.835 g of PdCl2 in 100 ml of deionized water, adjust the pH to 1 by adding industrial hydrochloric acid (-36%) dropwise, and add 5 g of carbon nanotubes (CNTs) (Zhongke Times Nano, model TNDH) while stirring at 500 rpm. Then, add 0.3 M ammonium carbonate solution dropwise to adjust the pH to 5, and stir at 500 rpm for 5 h at room temperature. After stirring, filter the solution, wash the resulting solid with deionized water until the pH reaches 7, and then dry it at 120 °C for 24 h.

[0024] Weigh 3g of the above sample and immerse it in an aqueous solution containing 0.057g of copper nitrate trihydrate for 24 hours. Then, dry the sample in an oven at 120℃ for 12 hours. The resulting catalyst contains 1.0% Pd and 0.5% Cu / CNTs. Catalysts with other compositions can be prepared similarly.

[0025] Example 1 Weigh 1 g of the above-mentioned 1.0%Pd-0.5%Cu / CNTs catalyst and charge it into a fixed-bed reactor. Before use, the catalyst is activated by hydrogen reduction under the following conditions: temperature 300℃; pressure 0.2 MPa; hydrogen gas hourly space velocity (HHSV) 15000 h⁻¹. -1 The reduction time was 2 hours. After the temperature inside the fixed-bed reactor naturally cooled to 150°C, the pressure was increased to 3 MPa, and the fixed-bed reaction system was allowed to stabilize. A 37% aqueous formaldehyde solution was mixed with diethanolamine at a mass ratio of 1.5:1. After the fixed-bed reaction system stabilized, the mixed liquid was pumped into the reactor using a high-pressure pump, and the liquid hourly space velocity (LHSV) of the diethanolamine was adjusted to 2.0 h⁻¹. -1 The ratio of H2 flow rate to liquid flow rate in the reaction system was 100:1. After a reaction time of 2 hours, samples were taken from the gas-liquid separator for analysis. The reaction evaluation results are shown in Table 1. The diethanolamine conversion rate was 100%, and the selectivity for N-methyldiethanolamine was 98.1%.

[0026] Example 2 Weigh 1 g of 1.0%Pd-0.1%Cu / CNTs catalyst and load it into a fixed-bed reactor. Before use, the catalyst is activated by hydrogen reduction under the following conditions: temperature 300℃; pressure 0.2 MPa; gas hourly space velocity (GHSV) 15000 h⁻¹. -1 The reduction time was 2 hours. After the temperature inside the fixed-bed reactor naturally cooled to 150°C, the pressure was increased to 3 MPa, and the fixed-bed reaction system was allowed to stabilize. A 37% formaldehyde aqueous solution was mixed with diethanolamine at a mass ratio of 1.5:1. After the fixed-bed reaction system stabilized, the mixed liquid was pumped into the reactor using a high-pressure pump, and the liquid hourly space velocity (LHSV) of the diethanolamine was adjusted to 2.0 h⁻¹. -1The ratio of H2 flow rate to liquid flow rate in the reaction system was 100:1. After a reaction time of 2 hours, samples were taken from the gas-liquid separator for analysis. The reaction evaluation results are shown in Table 1. The diethanolamine conversion rate was 100%, and the selectivity for N-methyldiethanolamine was 96.8%.

[0027] Example 3 Weigh 1 g of 1.0% Pd-0.3% Cu / CNTs catalyst and load it into a fixed-bed reactor. Before use, the catalyst is activated by hydrogen reduction under the following conditions: temperature 300℃; pressure 0.2 MPa; gas hourly space velocity (GHSV) 15000 h⁻¹. -1 The reduction time was 2 hours. After the temperature inside the fixed-bed reactor naturally cooled to 150°C, the pressure was increased to 3 MPa, and the fixed-bed reaction system was allowed to stabilize. A 37% formaldehyde aqueous solution was mixed with diethanolamine at a mass ratio of 1.5:1. After the fixed-bed reaction system stabilized, the mixed liquid was pumped into the reactor using a high-pressure pump, and the liquid hourly space velocity (LHSV) of the diethanolamine was adjusted to 2.0 h⁻¹. -1 The ratio of H2 flow rate to liquid flow rate in the reaction system was 100:1. After a reaction time of 2 hours, samples were taken from the gas-liquid separator for analysis. The reaction evaluation results are shown in Table 1. The diethanolamine conversion rate was 100%, and the N-methyldiethanolamine selectivity was 97.5%.

[0028] Example 4 Weigh 1 g of 0.3%Pd-0.5%Cu / CNTs catalyst and load it into a fixed-bed reactor. Before use, the catalyst is activated by hydrogen reduction under the following conditions: temperature 300℃; pressure 0.2 MPa; gas hourly space velocity (GHSV) 15000 h⁻¹. -1 The reduction time was 2 hours. After the temperature inside the fixed-bed reactor naturally cooled to 150°C, the pressure was increased to 3 MPa, and the fixed-bed reaction system was allowed to stabilize. A 37% formaldehyde aqueous solution was mixed with diethanolamine at a mass ratio of 1.5:1. After the fixed-bed reaction system stabilized, the mixed liquid was pumped into the reactor using a high-pressure pump, and the liquid hourly space velocity (LHSV) of the diethanolamine was adjusted to 2.0 h⁻¹. -1 The ratio of H2 flow rate to liquid flow rate in the reaction system was 100:1. After a reaction time of 5 hours, samples were taken from the gas-liquid separator for analysis. The reaction evaluation results are shown in Table 1. The diethanolamine conversion rate was 100%, and the N-methyldiethanolamine selectivity was 96.3%.

[0029] Example 5 Weigh 1 g of 0.5%Pd-0.5%Cu / CNTs catalyst and load it into a fixed-bed reactor. Before use, the catalyst is activated by hydrogen reduction under the following conditions: temperature 300℃; pressure 0.2 MPa; gas hourly space velocity (GHSV) 15000 h⁻¹. -1The reduction time was 2 hours. After the temperature inside the fixed-bed reactor naturally cooled to 150°C, the pressure was increased to 3 MPa, and the fixed-bed reaction system was allowed to stabilize. A 37% formaldehyde aqueous solution was mixed with diethanolamine at a mass ratio of 1.5:1. After the fixed-bed reaction system stabilized, the mixed liquid was pumped into the reactor using a high-pressure pump, and the liquid hourly space velocity (LHSV) of the diethanolamine was adjusted to 2.0 h⁻¹. -1 The ratio of H2 flow rate to liquid flow rate in the reaction system was 100:1. After a reaction time of 5 hours, samples were taken from the gas-liquid separator for analysis. The reaction evaluation results are shown in Table 1. The diethanolamine conversion rate was 99.8%, and the N-methyldiethanolamine selectivity was 96.1%.

[0030] Example 6 Weigh 1 g of 0.8%Pd-0.5%Cu / CNTs catalyst and load it into a fixed-bed reactor. Before use, the catalyst is activated by hydrogen reduction under the following conditions: temperature 300℃; pressure 0.2 MPa; gas hourly space velocity (GHSV) 15000 h⁻¹. -1 The reduction time was 2 hours. After the temperature inside the fixed-bed reactor naturally cooled to 150°C, the pressure was increased to 3 MPa, and the fixed-bed reaction system was allowed to stabilize. A 37% formaldehyde aqueous solution was mixed with diethanolamine at a mass ratio of 1.5:1. After the fixed-bed reaction system stabilized, the mixed liquid was pumped into the reactor using a high-pressure pump, and the liquid hourly space velocity (LHSV) of the diethanolamine was adjusted to 2.0 h⁻¹. -1 The ratio of H2 flow rate to liquid flow rate in the reaction system was 100:1. After a reaction time of 5 hours, samples were taken from the gas-liquid separator for analysis. The reaction evaluation results are shown in Table 1. The diethanolamine conversion rate was 100%, and the selectivity for N-methyldiethanolamine was 97.3%.

[0031] Example 7 Weigh 1 g of 1.0%Pd-0.5%Cu / SiNTs catalyst and load it into a fixed-bed reactor. Before use, the catalyst is activated by hydrogen reduction under the following conditions: temperature 300℃; pressure 0.2 MPa; gas hourly space velocity (GHSV) 15000 h⁻¹. -1 The reduction time was 2 hours. After the temperature inside the fixed-bed reactor naturally cooled to 150°C, the pressure was increased to 3 MPa, and the fixed-bed reaction system was allowed to stabilize. A 37% formaldehyde aqueous solution was mixed with diethanolamine at a mass ratio of 1.5:1. After the fixed-bed reaction system stabilized, the mixed liquid was pumped into the reactor using a high-pressure pump, and the liquid hourly space velocity (LHSV) of the diethanolamine was adjusted to 2.0 h⁻¹. -1 The ratio of H2 flow rate to liquid flow rate in the reaction system was 100:1. After a reaction time of 5 hours, samples were taken from the gas-liquid separator for analysis. The reaction evaluation results are shown in Table 1. The diethanolamine conversion rate was 100%, and the selectivity for N-methyldiethanolamine was 97.9%.

[0032] Example 8 Weigh 1 g of 1.0%Pt-0.5%Cu / SiNTs catalyst and load it into a fixed-bed reactor. Before use, the catalyst is activated by hydrogen reduction under the following conditions: temperature 300℃; pressure 0.2 MPa; gas hourly space velocity (GHSV) 15000 h⁻¹. -1 The reduction time was 2 hours. After the temperature inside the fixed-bed reactor naturally cooled to 150°C, the pressure was increased to 3 MPa, and the fixed-bed reaction system was allowed to stabilize. A 37% formaldehyde aqueous solution was mixed with diethanolamine at a mass ratio of 1.5:1. After the fixed-bed reaction system stabilized, the mixed liquid was pumped into the reactor using a high-pressure pump, and the liquid hourly space velocity (LHSV) of the diethanolamine was adjusted to 2.0 h⁻¹. -1 The ratio of H2 flow rate to liquid flow rate in the reaction system was 100:1. After a reaction time of 5 hours, samples were taken from the gas-liquid separator for analysis. The reaction evaluation results are shown in Table 1. The diethanolamine conversion rate was 100%, and the N-methyldiethanolamine selectivity was 97.7%.

[0033] Example 9 Weigh 1 g of 1.0%Pd-0.5%Cu / CNTs catalyst and load it into a fixed-bed reactor. The catalyst activation conditions are the same as in Example 1: temperature 300℃, pressure 0.2 MPa, and hydrogen volume hourly space velocity 15000 h⁻¹. -1 The reduction time was 2 hours. After activation, the temperature inside the fixed-bed reactor was lowered to 80°C, and the pressure was increased to 2 MPa until the reaction system stabilized. A 37% formaldehyde aqueous solution and diethanolamine were mixed at a mass ratio of 1.5:1 and continuously pumped into the reactor using a high-pressure metering pump, controlling the liquid hourly space velocity (LHSV) of the diethanolamine at 0.5 h⁻¹. -1 The ratio of H2 volumetric flow rate to liquid volumetric flow rate in the reaction system was 100:1. A continuous flow catalytic reduction ammoniation reaction was carried out at 80℃ and 2MPa. Samples were taken after 5 hours of reaction, and gas chromatography analysis showed a diethanolamine conversion rate of 98.2% and a selectivity of 95.9% for N-methyldiethanolamine.

[0034] Example 10 Weigh 1 g of 1.0%Pd-0.5%Cu / CNTs catalyst and load it into a fixed-bed reactor. The catalyst activation conditions are the same as in Example 1: temperature 300℃, pressure 0.2 MPa, and hydrogen volume hourly space velocity 15000 h⁻¹. -1 The reduction time was 2 hours. After activation, the temperature inside the fixed-bed reactor was lowered to 150°C, and the pressure was increased to 5 MPa until the reaction system stabilized. A 37% formaldehyde aqueous solution and diethanolamine were mixed at a mass ratio of 1.5:1 and continuously pumped into the reactor using a high-pressure metering pump, controlling the liquid hourly space velocity (LHSV) of diethanolamine at 2.0 h⁻¹. -1The ratio of H2 volumetric flow rate to liquid volumetric flow rate in the reaction system was 100:1. A continuous flow catalytic reduction ammoniation reaction was carried out at 150℃ and 5 MPa. Samples were taken after 5 hours of reaction, and gas chromatography analysis showed that the diethanolamine conversion rate was 100%, and the selectivity for N-methyldiethanolamine was 98.0%.

[0035] Example 11 Take 1 g of the 1.0%Pd-0.5%Cu / CNTs catalyst prepared in Example 1, and react it under the conditions described in Example 1 (reaction temperature 150℃, reaction pressure 3MPa, diethanolamine liquid hourly space velocity 2.0 h⁻¹). -1 Long-term stability tests were conducted using a hydrogen-to-liquid volumetric flow rate ratio of 100:1. The catalyst underwent the same activation treatment before use (300℃, 0.2MPa, hydrogen volumetric space velocity 15000h⁻¹). -1 (2h). After the reaction started, samples were taken from the gas-liquid separator every 20 hours, and the diethanolamine conversion rate and N-methyldiethanolamine selectivity were analyzed by gas chromatography. The test results after 1000 hours of continuous operation are as follows: Figure 1 As shown, throughout the entire 1000-hour test period, the conversion rate of diethanolamine remained at approximately 99.5%, the average selectivity of N-methyldiethanolamine was greater than 96%, and no catalyst deactivation was observed.

[0036] Table 1 Catalyst composition and reaction evaluation results for each example

[0037] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for the continuous preparation of N-methyldiethanolamine and its catalyst, characterized in that, The formaldehyde aqueous solution and diethanolamine are mixed to obtain a mixture. The mixture is continuously fed into a fixed-bed reactor containing the catalyst. In the presence of hydrogen, the reaction temperature is controlled at 80-150°C and the reaction pressure at 2-5 MPa to carry out a catalytic reduction ammoniation reaction to obtain N-methyldiethanolamine. The catalyst is a supported multiphase solid particle catalyst, comprising a main active component, an auxiliary agent, and a support. The main active component is Pd or Pt, and the auxiliary agent is Cu; The carrier is at least one of silicon nanotubes or carbon nanotubes; The catalyst is activated by hydrogen reduction before use.

2. The method for continuous preparation of N-methyldiethanolamine according to claim 1, characterized in that, The molar ratio of the formaldehyde aqueous solution to diethanolamine is 1.4:1 to 1.6:

1.

3. The method for continuous preparation of N-methyldiethanolamine according to claim 1, characterized in that, The liquid hourly space velocity (LHSV) of the diethanolamine is 0.5–2 h⁻¹. -1 .

4. The method for continuous preparation of N-methyldiethanolamine according to claim 1, characterized in that, The volumetric flow rate ratio of hydrogen to liquid is 80–120:

1.

5. The method for continuous preparation of N-methyldiethanolamine according to claim 1, characterized in that, In the catalyst, based on the total mass of the catalyst, the mass percentage of the main active component is 0.3% to 1.0%, the mass percentage of the auxiliary agent is 0.1% to 0.5%, and the balance is the carrier; Preferably, the main active component has a mass percentage content of 0.5% to 1.0%, and the auxiliary agent has a mass percentage content of 0.3% to 0.5%.

6. The method for continuous preparation of N-methyldiethanolamine according to claim 1, characterized in that, The catalyst was activated by hydrogen reduction before use under the following conditions: temperature 100–300℃, pressure 0.05–1.0 MPa, and hydrogen volume hourly space velocity 300–15000 h⁻¹. -1 Time: 1-10 hours; Preferably, the activation treatment is performed at a temperature of 200–300°C for 2–5 hours.

7. The method for continuous preparation of N-methyldiethanolamine according to claim 1, characterized in that, The catalyst was prepared by a combination of precipitation and impregnation methods.

8. The method for continuous preparation of N-methyldiethanolamine according to claim 1, characterized in that, The reaction is carried out in a fixed-bed reactor.

9. A supported heterogeneous solid particulate catalyst for the continuous preparation of N-methyldiethanolamine, characterized in that, The catalyst includes a main active component, an auxiliary agent, and a support; The main active component is Pd or Pt, and the auxiliary agent is Cu; The support is at least one of silicon nanotubes or carbon nanotubes; based on the total mass of the catalyst, the mass percentage of the main active component is 0.3% to 1.0%, the mass percentage of the auxiliary agent is 0.1% to 0.5%, and the remainder is the support; The catalyst was prepared by a combination of precipitation and impregnation methods.

10. The supported multiphase solid particle catalyst according to claim 9, characterized in that, In the catalyst, based on the total mass of the catalyst, the mass percentage of the main active component is 0.5% to 1.0%, and the mass percentage of the auxiliary agent is 0.3% to 0.5%.

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