Chloride-free copper catalyst, preparation method and application

Abstract

The invention discloses a chloride-free copper catalyst, a preparation method and application, and belongs to the technical field of catalysts. The invention solves the problem of how to provide a chloride-free copper catalyst with high conversion rate and high space time yield. The invention relates to a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with a copper active component, which is prepared by the following steps: mixing a nitrogen-containing biomass derivative with an additional nitrogen source, adding a proper amount of a pore-forming agent, carbonizing the formed mixture at 500-900 DEG C for 0.5-4 hours, impregnating the loaded copper active component by a wet method, and reducing at high temperature of 200-500 DEG C to obtain the nitrogen-containing three-dimensional interconnected layered porous carbon material. SEM characterization and N2 adsorption and desorption characterization show that the catalyst has a hierarchical porous structure and a high specific surface area; when the finally obtained catalyst is used for catalyzing liquid-phase methanol oxidative carbonylation to synthesize dimethyl carbonate, the conversion rate of methanol can be up to 18.19%, the selectivity of dimethyl carbonate can be up to 97.94%, and the space time yield can be up to 25.69 g. (g.h) <-1 >.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a chlorine-free copper-based catalyst, a preparation method and an application thereof. Background Art

[0002] Dimethyl carbonate (DMC), with the structural formula CH3OCOOCH3, is a non-toxic, biodegradable, green chemical product. Its molecule contains functional groups such as methyl, carbonyl, and methoxy groups, making it a viable alternative to traditional toxic reagents such as dimethyl sulfate, methyl chloroformate, and phosgene. It is widely used in the synthesis of polycarbonates, gasoline additives, and lithium battery electrolytes. In recent years, demand for DMC has steadily increased. The main methods for synthesizing DMC include phosgene, transesterification, urea alcoholysis, direct synthesis from CO2 and methanol, and oxidative carbonylation of methanol. Among these, the liquid-phase oxidative carbonylation of methanol to synthesize DMC avoids the use of toxic substances such as phosgene and NO, offers abundant and readily available raw materials, high atomic utilization, a simple and short process, and is economical and environmentally friendly, making it a popular choice.

[0003] The liquid-phase methanol oxidative carbonylation reaction is mainly based on CuCl catalyst in industry. However, the loss of Cl- in CuCl during the reaction can lead to catalyst deactivation and equipment corrosion.

[0004] The development of a chlorine-free copper-based catalyst can solve the problem of Cl - The corrosion problem is solved, but the product DMC selectivity and methanol conversion rate are greatly reduced. At present, in response to the shortcomings of chlorine-free copper-based catalysts, relevant scholars have studied the relevant modification technologies of copper-based catalysts. It is mainly achieved by preparing supported catalysts to improve the dispersion of copper-based catalysts in order to achieve the purpose of improving methanol conversion rate. For example, U.S. Patent US5391803 uses molecular sieves as carriers and impregnates and loads chlorine-free copper active components to obtain a catalyst with a methanol conversion rate of 15%, but its DMC selectivity is only 60-70%. Patent CN102872879B discloses a chlorine-free bimetallic catalyst with activated carbon as the carrier. The catalyst carrier has a large specific surface area (800-3000m2 / g) and a methanol conversion rate of up to 25%, but the loaded metal content is high (Cu-23.4wt%, La-2.9wt%), and the space-time yield is low (280-500mg·(g·h) -1 Patent CN105293484A discloses a copper nanocrystal catalyst supported by nitrogen-doped graphene. The catalyst has good stability and high product purity, but the raw materials are expensive and the time-space yield is low. Yan Junfen et al. (Yan Junfen, et al., Natural Gas Chemical Industry, 2016, 41(6): 37-43.) prepared a supported copper catalyst using activated carbon as a carrier. The catalyst specific surface area can reach 1658m 2 / g, but the methanol conversion rate of the catalyst is low, only 5.3%. Summary of the Invention

[0005] In response to the problem in the prior art of how to provide a chlorine-free copper-based catalyst with high conversion rate and high space-time yield, the present invention provides a chlorine-free copper-based catalyst, a preparation method and application.

[0006] The technical solution adopted in the present invention is as follows:

[0007] A chlorine-free copper-based catalyst is a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with copper active components.

[0008] Preferably, the copper active component is a copper salt.

[0009] After adopting this technical solution, copper salt can be dissolved in water or organic solvents. The solution can penetrate the pores of the carrier through the impregnation method, allowing copper ions to be evenly adsorbed on the carrier surface, while avoiding local excessive concentration leading to agglomeration. Copper oxide powder is difficult to spread evenly on the surface of the carrier, and it is easy to cause copper particles to agglomerate during the reduction process, so copper salt is selected.

[0010] Preferably, the mass of copper accounts for 3 to 15 wt% of the total weight of the catalyst.

[0011] Preferably, the nitrogen source in the nitrogen-containing three-dimensional interconnected layered porous carbon material comes from one or more of urea, ammonium oxalate and melamine.

[0012] Preferably, the carbon source in the nitrogen-containing three-dimensional interconnected layered porous carbon material comes from one or more of glucosamine hydrochloride, chitin, and chitosan.

[0013] A method for preparing a chlorine-free copper-based catalyst comprises the following steps:

[0014] S1: Preparation of nitrogen-doped biomass-based carbon supports;

[0015] S2: The copper active component is loaded onto a nitrogen-doped biomass-based carbon support to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with the copper active component.

[0016] Preferably, the specific steps of S1 are as follows:

[0017] S101: mixing a nitrogen-containing biomass derivative, a nitrogen source, and a pore-forming agent to obtain a mixture;

[0018] S102: calcining the mixture obtained in S101 at 500-900° C. in a nitrogen atmosphere for 0.5-4 h to obtain a black solid product;

[0019] S103: After the black solid product obtained in S102 is cooled to room temperature, it is washed, filtered, and dried to obtain a nitrogen-doped biomass-based carbon support.

[0020] Preferably, the mass ratio of the nitrogen-containing biomass derivative, the nitrogen source, and the pore-forming agent is 1:(1-2):(1-7).

[0021] Preferably, the pore-forming agent is one or more of sodium bicarbonate, sodium carbonate, and potassium bicarbonate.

[0022] Preferably, the specific steps of S2 are as follows:

[0023] S201: preparing a copper solution;

[0024] S202: mixing the nitrogen-doped biomass-based carbon support obtained in S1 with the copper solution obtained in S201;

[0025] S203: After the mixing is completed, separation and drying are performed, and the obtained solid is calcined in a nitrogen atmosphere at 200-500° C. for 1-5 hours, and after cooling, a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with copper active components is obtained.

[0026] An application of the chlorine-free copper-based catalyst is to catalyze the oxidative carbonylation of liquid-phase methanol to synthesize dimethyl carbonate.

[0027] Preferably, the amount of the chlorine-free copper-based catalyst added is 0.1-0.5 g of catalyst per 10 ml of methanol.

[0028] Preferably, the specific steps for catalyzing the oxidative carbonylation of liquid-phase methanol to synthesize dimethyl carbonate include:

[0029] Methanol and the catalyst are added to an autoclave, and after replacing the air in the reactor with CO, CO and O2 are sequentially introduced, wherein CO:O2=9:1-19:1 (volume ratio), and the total pressure is 2-5 MPa. After reacting at 100-150°C for 0.5-2h, the reaction is cooled in a water bath, and the solid catalyst is separated from the obtained reaction liquid to obtain a clear liquid, thereby achieving reaction synthesis.

[0030] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0031] The present invention provides a heterogeneous solid catalyst, which uses nitrogen-doped biomass-based carbon material as a carrier and Cu as an active component. The catalyst is prepared by an impregnation method, and the nitrogen-doped carbon material containing N atoms and Cu are mixed. + The ion coordination strength is moderate, which ensures that Cu + The stability of Cu +The catalyst has high catalytic activity, improves catalyst stability, and improves the problem of loss of active components of supported catalysts. The catalyst has a high specific surface area, and can reduce the amount of catalyst active metal used, improve the efficiency of the use of catalyst active metal, reduce production costs, and maintain a high contact area with the gas raw materials CO and O2 under the premise of ensuring good dispersibility. In particular, the calcination temperature, calcination time, catalyst loading and dosage of the carrier can be adjusted to improve the catalytic performance of the catalyst, increase the conversion rate of methanol and the selectivity of producing dimethyl carbonate. Ultimately, the conversion rate of methanol in the methanol oxidative carbonylation reaction to synthesize dimethyl carbonate of the present invention can reach a maximum of 18.19%, the selectivity of dimethyl carbonate can reach a maximum of 97.94%, and the space-time yield can reach a maximum of 25.69g·(g·h) -1 . BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 N2 adsorption-desorption isotherms and pore size distribution of the catalyst prepared in Example 1.

[0033] Figure 2 This is the full XPS spectrum of the catalyst prepared in Example 1.

[0034] Figure 3 This is the SEM image of the catalyst prepared in Example 1.

[0035] Figure 4 This is the pore size distribution diagram of the catalyst prepared in Example 1. DETAILED DESCRIPTION

[0036] To make the purpose, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of this application.

[0037] Example 1

[0038] A chlorine-free copper-based catalyst is a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with a copper active component. The preparation method is as follows:

[0039] S1: preparing nitrogen-doped biomass-based carbon support;

[0040] S101: Weigh 7 g of glucosamine hydrochloride powder, 7 g of urea, and 28 g of sodium bicarbonate and mix and grind them evenly;

[0041] S102: The mixture obtained in S101 was transferred to a tube furnace for calcination. During the calcination process, the flow rate of N2 was 100 mL / min, and the temperature was programmed to 800°C at a heating rate of 10°C / min for calcination for 1 hour. After the calcination, the obtained black solid was dispersed in 200 mL of deionized water. After being fully stirred at room temperature for 12 hours, it was washed with anhydrous ethanol and deionized water and filtered until the filtrate was neutral. The obtained black solid material was then placed in a vacuum oven at 100°C and dried for 6 hours. After being taken out, the nitrogen-doped biomass-based carbon support was obtained.

[0042] S2: The copper active component is loaded onto a nitrogen-doped biomass-based carbon support to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with the copper active component:

[0043] S201: Dissolve 0.8632 g of copper nitrate in 60 ml of deionized water and stir evenly to obtain a copper solution:

[0044] S202: 2.0 g of the nitrogen-doped biomass-based carbon support obtained in S1 was mixed with the copper solution obtained in S201 to a Cu mass fraction of 10%, stirred appropriately and ultrasonicated for 1 h, and then the solution was stirred at room temperature for 10 h, and then the mixture was rotary evaporated to obtain a black solid;

[0045] S203: The black solid was dried in a vacuum oven at 80°C for 3 hours. After thorough grinding, it was transferred to a tube furnace for calcination in a N2 atmosphere at a gas flow rate of 100 mL / min. The temperature was programmed to 400°C at a heating rate of 4°C / min and calcined for 4 hours. After the reduction was completed, the original atmosphere was maintained and the solid was cooled to room temperature. The resulting solid product was collected to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with copper active components, thereby obtaining the chlorine-free copper-based catalyst.

[0046] Catalyst Application

[0047] 10 mL of methanol and 0.3 g of catalyst were added to a 100 mL autoclave. After replacing the air in the reactor with CO, 3.6 MPa of CO and 0.4 MPa of O2 were introduced in sequence. After reacting at 120°C for 0.5 h, the reaction mixture was cooled in a water bath. The solid catalyst was separated from the obtained reaction solution to obtain a clear liquid.

[0048] Result Analysis

[0049] The product was analyzed by gas chromatography using ethanol as the internal standard. The reaction activity results of the catalyst are shown in Table 1. The N2 adsorption-desorption isotherm and pore size distribution of the catalyst prepared in Example 1 are shown in Table 1. Figure 1 As shown, from Figure 1It can be seen that the catalyst meets the characteristics of the H3 type hysteresis loop in the type IV isotherm. Combined with the pore size distribution diagram, it is found that the catalyst presents a narrow pore size distribution with an average pore size of 4 nm, proving that the prepared catalysts are all hierarchical porous materials with micropores, mesopores and macropores; the full XPS spectrum is shown in Figure 2 As shown, Figure 2 Typical peaks of Cu 2p, O 1s, N 1s, and C 1s can be observed, which further confirms the successful loading of Cu; SEM images are shown in Figure 3 As shown, from Figure 3 It can be seen that the freshly prepared catalysts all have a three-dimensional interconnected hierarchical porous structure (the specific surface area can reach 2535m 2 / g), which is consistent with the conclusion of N2 adsorption-desorption curve. The adsorption pore distribution report of the catalyst obtained in this embodiment is shown in Table 1, and the specific surface area diagram is shown in Table 1. Figure 4 As shown, from Figure 4 As can be seen from Table 1, the specific surface area of ​​the product can reach 2535m 2 / g.

[0050] Table 1

[0051]

[0052] Example 2

[0053] A chlorine-free copper-based catalyst is a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with a copper active component. The preparation method is as follows:

[0054] S1: preparing nitrogen-doped biomass-based carbon support;

[0055] S101: Weigh 7 g of glucosamine hydrochloride powder, 7 g of urea, and 28 g of sodium bicarbonate and mix and grind them evenly;

[0056] S102: The mixture obtained in S101 was transferred to a tube furnace for calcination. During the calcination process, the flow rate of N2 was 100 mL / min, and the temperature was programmed to 800°C at a heating rate of 10°C / min for calcination for 1 hour. After the calcination, the obtained black solid was dispersed in 200 mL of deionized water. After being fully stirred at room temperature for 12 hours, it was washed with anhydrous ethanol and deionized water and filtered until the filtrate was neutral. The obtained black solid material was then placed in a vacuum oven at 100°C and dried for 6 hours. After being taken out, the nitrogen-doped biomass-based carbon support was obtained.

[0057] S2: The copper active component is loaded onto a nitrogen-doped biomass-based carbon support to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with the copper active component:

[0058] S201: Dissolve 0.4316 g of copper nitrate in 60 ml of deionized water and stir evenly to obtain a copper solution:

[0059] S202: 2.0 g of the nitrogen-doped biomass-based carbon support obtained in S1 was mixed with the copper solution obtained in S201 to adjust the mass fraction of Cu to 5%, stirred appropriately and ultrasonicated for 1 h, and then the solution was stirred at room temperature for 10 h, and then the mixture was rotary evaporated to obtain a black solid;

[0060] S203: The black solid was dried in a vacuum oven at 80°C for 3 hours. After thorough grinding, it was transferred to a tube furnace for calcination in a N2 atmosphere at a gas flow rate of 100 mL / min. The temperature was programmed to 400°C at a heating rate of 4°C / min and calcined for 4 hours. After the reduction was completed, the original atmosphere was maintained and the solid was cooled to room temperature. The resulting solid product was collected to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with copper active components, thereby obtaining the chlorine-free copper-based catalyst.

[0061] Catalyst Application

[0062] 10 mL of methanol and 0.3 g of catalyst were added to a 100 mL autoclave. After replacing the air in the reactor with CO, 3.6 MPa of CO and 0.4 MPa of O2 were introduced in sequence. After reacting at 120°C for 0.5 h, the reaction mixture was cooled in a water bath. The solid catalyst was separated from the obtained reaction solution to obtain a clear liquid.

[0063] Result Analysis

[0064] The product was analyzed by gas chromatography using ethanol as the internal standard. The reaction activity results of the catalyst are shown in Table 1.

[0065] Example 3

[0066] A chlorine-free copper-based catalyst is a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with a copper active component. The preparation method is as follows:

[0067] S1: preparing nitrogen-doped biomass-based carbon support;

[0068] S101: Weigh 7 g of glucosamine hydrochloride powder, 7 g of urea, and 28 g of sodium bicarbonate and mix and grind them evenly;

[0069] S102: The mixture obtained in S101 was transferred to a tube furnace for calcination. During the calcination process, the flow rate of N2 was 100 mL / min, and the temperature was programmed to 800°C at a heating rate of 10°C / min for calcination for 0.5 h. After the calcination, the obtained black solid was dispersed in 200 mL of deionized water. After being fully stirred at room temperature for 12 h, it was washed with anhydrous ethanol and deionized water and filtered until the filtrate was neutral. The obtained black solid material was then placed in a vacuum oven at 100°C and dried for 6 h. After being taken out, the nitrogen-doped biomass-based carbon support was obtained.

[0070] S2: The copper active component is loaded onto a nitrogen-doped biomass-based carbon support to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with the copper active component:

[0071] S201: Dissolve 0.8632 g of copper nitrate in 60 ml of deionized water and stir evenly to obtain a copper solution:

[0072] S202: 2.0 g of the nitrogen-doped biomass-based carbon support obtained in S1 was mixed with the copper solution obtained in S201 to a Cu mass fraction of 10%, stirred appropriately and ultrasonicated for 1 h, and then the solution was stirred at room temperature for 10 h, and then the mixture was rotary evaporated to obtain a black solid;

[0073] S203: The black solid was dried in a vacuum oven at 80°C for 3 hours. After thorough grinding, it was transferred to a tube furnace for calcination in a N2 atmosphere at a gas flow rate of 100 mL / min. The temperature was programmed to 400°C at a heating rate of 4°C / min and calcined for 4 hours. After the reduction was completed, the original atmosphere was maintained and the solid was cooled to room temperature. The resulting solid product was collected to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with copper active components, thereby obtaining the chlorine-free copper-based catalyst.

[0074] Catalyst Application

[0075] 10 mL of methanol and 0.3 g of catalyst were added to a 100 mL autoclave. After replacing the air in the reactor with CO, 3.6 MPa of CO and 0.4 MPa of O2 were introduced in sequence. After reacting at 120°C for 0.5 h, the reaction mixture was cooled in a water bath. The solid catalyst was separated from the obtained reaction solution to obtain a clear liquid.

[0076] Result Analysis

[0077] The product was analyzed by gas chromatography using ethanol as the internal standard. The reaction activity results of the catalyst are shown in Table 1.

[0078] Example 4

[0079] A chlorine-free copper-based catalyst is a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with a copper active component. The preparation method is as follows:

[0080] S1: preparing nitrogen-doped biomass-based carbon support;

[0081] S101: Weigh 7 g of glucosamine hydrochloride powder, 7 g of urea, and 28 g of sodium bicarbonate and mix and grind them evenly;

[0082] S102: The mixture obtained in S101 was transferred to a tube furnace for calcination. During the calcination process, the flow rate of N2 was 100 mL / min, and the temperature was programmed to 800°C at a heating rate of 10°C / min for calcination for 4 hours. After the calcination, the obtained black solid was dispersed in 200 mL of deionized water. After being fully stirred at room temperature for 12 hours, it was washed with anhydrous ethanol and deionized water and filtered until the filtrate was neutral. The obtained black solid material was then placed in a vacuum oven at 100°C and dried for 6 hours. After being taken out, the nitrogen-doped biomass-based carbon support was obtained.

[0083] S2: The copper active component is loaded onto a nitrogen-doped biomass-based carbon support to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with the copper active component:

[0084] S201: Dissolve 0.8632 g of copper nitrate in 60 ml of deionized water and stir evenly to obtain a copper solution:

[0085] S202: 2.0 g of the nitrogen-doped biomass-based carbon support obtained in S1 was mixed with the copper solution obtained in S201 to a Cu mass fraction of 10%, stirred appropriately and ultrasonicated for 1 h, and then the solution was stirred at room temperature for 10 h, and then the mixture was rotary evaporated to obtain a black solid;

[0086] S203: The black solid was dried in a vacuum oven at 80°C for 3 hours. After thorough grinding, it was transferred to a tube furnace for calcination in a N2 atmosphere at a gas flow rate of 100 mL / min. The temperature was programmed to 400°C at a heating rate of 4°C / min and calcined for 4 hours. After the reduction was completed, the original atmosphere was maintained and the solid was cooled to room temperature. The resulting solid product was collected to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with copper active components, thereby obtaining the chlorine-free copper-based catalyst.

[0087] Catalyst Application

[0088] 10 mL of methanol and 0.3 g of catalyst were added to a 100 mL autoclave. After replacing the air in the reactor with CO, 3.6 MPa of CO and 0.4 MPa of O2 were introduced in sequence. After reacting at 120°C for 0.5 h, the reaction mixture was cooled in a water bath. The solid catalyst was separated from the obtained reaction solution to obtain a clear liquid.

[0089] Result Analysis

[0090] The product was analyzed by gas chromatography using ethanol as the internal standard. The reaction activity results of the catalyst are shown in Table 1.

[0091] Example 5

[0092] A chlorine-free copper-based catalyst is a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with a copper active component. The preparation method is as follows:

[0093] S1: preparing nitrogen-doped biomass-based carbon support;

[0094] S101: Weigh 7 g of glucosamine hydrochloride powder, 7 g of urea, and 28 g of sodium bicarbonate and mix and grind them evenly;

[0095] S102: The mixture obtained in S101 was transferred to a tube furnace for calcination. During the calcination process, the flow rate of N2 was 100 mL / min, and the temperature was programmed to 500°C at a heating rate of 10°C / min for calcination for 1 hour. After the calcination, the obtained black solid was dispersed in 200 mL of deionized water. After being fully stirred at room temperature for 12 hours, it was washed with anhydrous ethanol and deionized water and filtered until the filtrate was neutral. The obtained black solid material was then placed in a vacuum oven at 100°C and dried for 6 hours. After being taken out, the nitrogen-doped biomass-based carbon support was obtained.

[0096] S2: The copper active component is loaded onto a nitrogen-doped biomass-based carbon support to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with the copper active component:

[0097] S201: Dissolve 0.8632 g of copper nitrate in 60 ml of deionized water and stir evenly to obtain a copper solution:

[0098] S202: 2.0 g of the nitrogen-doped biomass-based carbon support obtained in S1 was mixed with the copper solution obtained in S201 to a Cu mass fraction of 10%, stirred appropriately and ultrasonicated for 1 h, and then the solution was stirred at room temperature for 10 h, and then the mixture was rotary evaporated to obtain a black solid;

[0099] S203: The black solid was dried in a vacuum oven at 80°C for 3 hours. After thorough grinding, it was transferred to a tube furnace for calcination in a N2 atmosphere at a gas flow rate of 100 mL / min. The temperature was programmed to 400°C at a heating rate of 4°C / min and calcined for 4 hours. After the reduction was completed, the original atmosphere was maintained and the solid was cooled to room temperature. The resulting solid product was collected to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with copper active components, thereby obtaining the chlorine-free copper-based catalyst.

[0100] Catalyst Application

[0101] 10 mL of methanol and 0.3 g of catalyst were added to a 100 mL autoclave. After replacing the air in the reactor with CO, 3.6 MPa of CO and 0.4 MPa of O2 were introduced in sequence. After reacting at 120°C for 0.5 h, the reaction mixture was cooled in a water bath. The solid catalyst was separated from the obtained reaction solution to obtain a clear liquid.

[0102] Result Analysis

[0103] The product was analyzed by gas chromatography using ethanol as the internal standard. The reaction activity results of the catalyst are shown in Table 1.

[0104] Example 6

[0105] A chlorine-free copper-based catalyst is a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with a copper active component. The preparation method is as follows:

[0106] S1: preparing nitrogen-doped biomass-based carbon support;

[0107] S101: Weigh 7 g of glucosamine hydrochloride powder, 7 g of urea, and 28 g of sodium bicarbonate and mix and grind them evenly;

[0108] S102: The mixture obtained in S101 was transferred to a tube furnace for calcination. During the calcination process, the flow rate of N2 was 100 mL / min, and the temperature was programmed to 900°C at a heating rate of 10°C / min for calcination for 1 hour. After the calcination, the obtained black solid was dispersed in 200 mL of deionized water. After being fully stirred at room temperature for 12 hours, it was washed with anhydrous ethanol and deionized water and filtered until the filtrate was neutral. The obtained black solid material was then placed in a vacuum oven at 100°C and dried for 6 hours. After being taken out, the nitrogen-doped biomass-based carbon support was obtained.

[0109] S2: The copper active component is loaded onto a nitrogen-doped biomass-based carbon support to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with the copper active component:

[0110] S201: Dissolve 0.8632 g of copper nitrate in 60 ml of deionized water and stir evenly to obtain a copper solution:

[0111] S202: 2.0 g of the nitrogen-doped biomass-based carbon support obtained in S1 was mixed with the copper solution obtained in S201 to a Cu mass fraction of 10%, stirred appropriately and ultrasonicated for 1 h, and then the solution was stirred at room temperature for 10 h, and then the mixture was rotary evaporated to obtain a black solid;

[0112] S203: The black solid was dried in a vacuum oven at 80°C for 3 hours. After thorough grinding, it was transferred to a tube furnace for calcination in a N2 atmosphere at a gas flow rate of 100 mL / min. The temperature was programmed to 400°C at a heating rate of 4°C / min and calcined for 4 hours. After the reduction was completed, the original atmosphere was maintained and the solid was cooled to room temperature. The resulting solid product was collected to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with copper active components, thereby obtaining the chlorine-free copper-based catalyst.

[0113] Catalyst Application

[0114] 10 mL of methanol and 0.3 g of catalyst were added to a 100 mL autoclave. After replacing the air in the reactor with CO, 3.6 MPa of CO and 0.4 MPa of O2 were introduced in sequence. After reacting at 120°C for 0.5 h, the reaction mixture was cooled in a water bath. The solid catalyst was separated from the obtained reaction solution to obtain a clear liquid.

[0115] Result Analysis

[0116] The product was analyzed by gas chromatography using ethanol as the internal standard. The reaction activity results of the catalyst are shown in Table 1.

[0117] Example 7

[0118] A chlorine-free copper-based catalyst, the preparation method and the obtained product are the same as those in Example 1;

[0119] Catalyst Application

[0120] 10 mL of methanol and 0.3 g of catalyst were added to a 100 mL autoclave. After replacing the air in the reactor with CO, 3.6 MPa of CO and 0.4 MPa of O2 were introduced in sequence. After reacting at 120°C for 1 hour, the reaction mixture was cooled in a water bath. The solid catalyst was separated from the obtained reaction solution to obtain a clear liquid.

[0121] Result Analysis

[0122] The product was analyzed by gas chromatography using ethanol as the internal standard. The reaction activity results of the catalyst are shown in Table 1.

[0123] Example 8

[0124] A chlorine-free copper-based catalyst, the preparation method and the obtained product are the same as those in Example 1;

[0125] Catalyst Application

[0126] 10 mL of methanol and 0.3 g of catalyst were added to a 100 mL autoclave. After replacing the air in the reactor with CO, 3.6 MPa of CO and 0.4 MPa of O2 were introduced in sequence. After reacting at 110°C for 0.5 h, the reaction mixture was cooled in a water bath. The solid catalyst was separated from the obtained reaction solution to obtain a clear liquid.

[0127] Result Analysis

[0128] The product was analyzed by gas chromatography using ethanol as the internal standard. The reaction activity results of the catalyst are shown in Table 1.

[0129] Example 9

[0130] A chlorine-free copper-based catalyst, the preparation method and the obtained product are the same as those in Example 1;

[0131] Catalyst Application

[0132] 10 mL of methanol and 0.3 g of catalyst were added to a 100 mL autoclave. After replacing the air in the reactor with CO, 3.8 MPa of CO and 0.2 MPa of O2 were introduced in sequence. After reacting at 120°C for 0.5 h, the reaction mixture was cooled in a water bath. The solid catalyst was separated from the obtained reaction solution to obtain a clear liquid.

[0133] Result Analysis

[0134] The product was analyzed by gas chromatography using ethanol as the internal standard. The reaction activity results of the catalyst are shown in Table 1.

[0135] Example 10

[0136] A chlorine-free copper-based catalyst is a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with a copper active component. The preparation method is as follows:

[0137] S1: preparing nitrogen-doped biomass-based carbon support;

[0138] S101: Weigh 7 g of glucosamine hydrochloride powder, 7 g of urea, and 28 g of sodium bicarbonate and mix and grind them evenly;

[0139] S102: The mixture obtained in S101 was transferred to a tube furnace for calcination. During the calcination process, the flow rate of N2 was 100 mL / min, and the temperature was programmed to 800°C at a heating rate of 10°C / min for calcination for 1 hour. After the calcination, the obtained black solid was dispersed in 200 mL of deionized water. After being fully stirred at room temperature for 12 hours, it was washed with anhydrous ethanol and deionized water and filtered until the filtrate was neutral. The obtained black solid material was then placed in a vacuum oven at 100°C and dried for 6 hours. After being taken out, the nitrogen-doped biomass-based carbon support was obtained.

[0140] S2: The copper active component is loaded onto a nitrogen-doped biomass-based carbon support to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with the copper active component:

[0141] S201: Dissolve 0.8632 g of copper nitrate in 60 ml of deionized water and stir evenly to obtain a copper solution:

[0142] S202: 2.0 g of the nitrogen-doped biomass-based carbon support obtained in S1 was mixed with the copper solution obtained in S201 to a Cu mass fraction of 10%, stirred appropriately and ultrasonicated for 1 h, and then the solution was stirred at room temperature for 10 h, and then the mixture was rotary evaporated to obtain a black solid;

[0143] S203: The black solid was dried in a vacuum oven at 80°C for 3 hours, thoroughly ground, and then transferred to a tube furnace for calcination. The gas atmosphere was N2, the gas flow rate was 100 mL / min, and the temperature was programmed to 500°C at a heating rate of 4°C / min for 4 hours. After the reduction was completed, the original atmosphere was maintained and the mixture was cooled to room temperature. The resulting solid product was collected to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with copper active components, thereby obtaining the chlorine-free copper-based catalyst.

[0144] Catalyst Application

[0145] 10 mL of methanol and 0.3 g of catalyst were added to a 100 mL autoclave. After replacing the air in the reactor with CO, 3.6 MPa of CO and 0.4 MPa of O2 were introduced in sequence. After reacting at 120°C for 0.5 h, the reaction mixture was cooled in a water bath. The solid catalyst was separated from the obtained reaction solution to obtain a clear liquid.

[0146] Result Analysis

[0147] The product was analyzed by gas chromatography using ethanol as the internal standard. The reaction activity results of the catalyst are shown in Table 1.

[0148] Example 11

[0149] A chlorine-free copper-based catalyst is a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with a copper active component. The preparation method is as follows:

[0150] S1: preparing nitrogen-doped biomass-based carbon support;

[0151] S101: Weigh 7 g of glucosamine hydrochloride powder, 7 g of urea, and 28 g of sodium bicarbonate and mix and grind them evenly;

[0152] S102: The mixture obtained in S101 was transferred to a tube furnace for calcination. During the calcination process, the flow rate of N2 was 100 mL / min, and the temperature was programmed to 800°C at a heating rate of 10°C / min for calcination for 1 hour. After the calcination, the obtained black solid was dispersed in 200 mL of deionized water. After being fully stirred at room temperature for 12 hours, it was washed with anhydrous ethanol and deionized water and filtered until the filtrate was neutral. The obtained black solid material was then placed in a vacuum oven at 100°C and dried for 6 hours. After being taken out, the nitrogen-doped biomass-based carbon support was obtained.

[0153] S2: The copper active component is loaded onto a nitrogen-doped biomass-based carbon support to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with the copper active component:

[0154] S201: Dissolve 0.8632 g of copper nitrate in 60 ml of deionized water and stir evenly to obtain a copper solution:

[0155] S202: 2.0 g of the nitrogen-doped biomass-based carbon support obtained in S1 was mixed with the copper solution obtained in S201 to a Cu mass fraction of 10%, stirred appropriately and ultrasonicated for 1 h, and then the solution was stirred at room temperature for 10 h, and then the mixture was rotary evaporated to obtain a black solid;

[0156] S203: The black solid was dried in a vacuum oven at 80°C for 3 hours. After thorough grinding, it was transferred to a tube furnace and calcined in a nitrogen atmosphere at a gas flow rate of 100 mL / min. The temperature was programmed to 400°C at a heating rate of 4°C / min and calcined for 1 hour. After the reduction was completed, the original atmosphere was maintained and the solid was cooled to room temperature. The resulting solid product was collected to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with copper active components, thereby obtaining the chlorine-free copper-based catalyst.

[0157] Catalyst Application

[0158] 10 mL of methanol and 0.3 g of catalyst were added to a 100 mL autoclave. After replacing the air in the reactor with CO, 3.6 MPa of CO and 0.4 MPa of O2 were introduced in sequence. After reacting at 120°C for 0.5 h, the reaction mixture was cooled in a water bath. The solid catalyst was separated from the obtained reaction solution to obtain a clear liquid.

[0159] Result Analysis

[0160] The product was analyzed by gas chromatography using ethanol as the internal standard. The reaction activity results of the catalyst are shown in Table 1.

[0161] Example 12

[0162] A chlorine-free copper-based catalyst is a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with a copper active component. The preparation method is as follows:

[0163] S1: preparing nitrogen-doped biomass-based carbon support;

[0164] S101: Weigh 7 g of glucosamine hydrochloride powder, 7 g of urea, and 28 g of sodium bicarbonate and mix and grind them evenly;

[0165] S102: The mixture obtained in S101 was transferred to a tube furnace for calcination. During the calcination process, the flow rate of N2 was 100 mL / min, and the temperature was programmed to 800°C at a heating rate of 10°C / min for calcination for 1 hour. After the calcination, the obtained black solid was dispersed in 200 mL of deionized water. After being fully stirred at room temperature for 12 hours, it was washed with anhydrous ethanol and deionized water and filtered until the filtrate was neutral. The obtained black solid material was then placed in a vacuum oven at 100°C and dried for 6 hours. After being taken out, the nitrogen-doped biomass-based carbon support was obtained.

[0166] S2: The copper active component is loaded onto a nitrogen-doped biomass-based carbon support to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with the copper active component:

[0167] S201: Dissolve 0.8632 g of copper nitrate in 60 ml of deionized water and stir evenly to obtain a copper solution:

[0168] S202: 2.0 g of the nitrogen-doped biomass-based carbon support obtained in S1 was mixed with the copper solution obtained in S201 to a Cu mass fraction of 10%, stirred appropriately and ultrasonicated for 1 h, and then the solution was stirred at room temperature for 10 h, and then the mixture was rotary evaporated to obtain a black solid;

[0169] S203: The black solid was dried in a vacuum oven at 80°C for 3 hours. After thorough grinding, it was transferred to a tube furnace for calcination in a N2 atmosphere at a gas flow rate of 100 mL / min. The temperature was programmed to 400°C at a heating rate of 4°C / min and calcined for 4 hours. After the reduction was completed, the original atmosphere was maintained and the solid was cooled to room temperature. The resulting solid product was collected to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with copper active components, thereby obtaining the chlorine-free copper-based catalyst.

[0170] Catalyst Application

[0171] 10 mL of methanol and 0.3 g of catalyst were added to a 100 mL autoclave. After replacing the air in the reactor with CO, 1.8 MPa of CO and 0.2 MPa of O2 were introduced in sequence. After reacting at 120°C for 0.5 h, the reaction mixture was cooled in a water bath. The solid catalyst was separated from the obtained reaction solution to obtain a clear liquid.

[0172] Example 13

[0173] A chlorine-free copper-based catalyst is a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with a copper active component. The preparation method is as follows:

[0174] S1: preparing nitrogen-doped biomass-based carbon support;

[0175] S101: Weigh 7g chitosan powder, 7g urea, and 28g sodium bicarbonate and mix and grind them evenly;

[0176] S102: The mixture obtained in S101 was transferred to a tube furnace for calcination. During the calcination process, the flow rate of N2 was 100 mL / min, and the temperature was programmed to 800°C at a heating rate of 10°C / min for calcination for 1 hour. After the calcination, the obtained black solid was dispersed in 200 mL of deionized water. After being fully stirred at room temperature for 12 hours, it was washed with anhydrous ethanol and deionized water and filtered until the filtrate was neutral. The obtained black solid material was then placed in a vacuum oven at 100°C and dried for 6 hours. After being taken out, the nitrogen-doped biomass-based carbon support was obtained.

[0177] S2: The copper active component is loaded onto a nitrogen-doped biomass-based carbon support to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with the copper active component:

[0178] S201: Dissolve 0.8632 g of copper nitrate in 60 ml of deionized water and stir evenly to obtain a copper solution:

[0179] S202: 2.0 g of the nitrogen-doped biomass-based carbon support obtained in S1 was mixed with the copper solution obtained in S201 to a Cu mass fraction of 10%, stirred appropriately and ultrasonicated for 1 h, and then the solution was stirred at room temperature for 10 h, and then the mixture was rotary evaporated to obtain a black solid;

[0180] S203: The black solid was dried in a vacuum oven at 80°C for 3 hours. After thorough grinding, it was transferred to a tube furnace for calcination in a N2 atmosphere at a gas flow rate of 100 mL / min. The temperature was programmed to 400°C at a heating rate of 4°C / min and calcined for 4 hours. After the reduction was completed, the original atmosphere was maintained and the solid was cooled to room temperature. The resulting solid product was collected to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with copper active components, thereby obtaining the chlorine-free copper-based catalyst.

[0181] Catalyst Application

[0182] 10 mL of methanol and 0.3 g of catalyst were added to a 100 mL autoclave. After replacing the air in the reactor with CO, 1.8 MPa of CO and 0.2 MPa of O2 were introduced in sequence. After reacting at 120°C for 0.5 h, the reaction mixture was cooled in a water bath. The solid catalyst was separated from the obtained reaction solution to obtain a clear liquid.

[0183] Example 14

[0184] A chlorine-free copper-based catalyst is a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with a copper active component. The preparation method is as follows:

[0185] S1: preparing nitrogen-doped biomass-based carbon support;

[0186] S101: Weigh 7 g of glucosamine hydrochloride powder, 7 g of urea, and 14 g of sodium bicarbonate and mix and grind them evenly;

[0187] S102: The mixture obtained in S101 was transferred to a tube furnace for calcination. During the calcination process, the flow rate of N2 was 100 mL / min, and the temperature was programmed to 800°C at a heating rate of 10°C / min for calcination for 1 hour. After the calcination, the obtained black solid was dispersed in 200 mL of deionized water. After being fully stirred at room temperature for 12 hours, it was washed with anhydrous ethanol and deionized water and filtered until the filtrate was neutral. The obtained black solid material was then placed in a vacuum oven at 100°C and dried for 6 hours. After being taken out, the nitrogen-doped biomass-based carbon support was obtained.

[0188] S2: The copper active component is loaded onto a nitrogen-doped biomass-based carbon support to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with the copper active component:

[0189] S201: Dissolve 0.8632 g of copper nitrate in 60 ml of deionized water and stir evenly to obtain a copper solution:

[0190] S202: 2.0 g of the nitrogen-doped biomass-based carbon support obtained in S1 was mixed with the copper solution obtained in S201 to a Cu mass fraction of 10%, stirred appropriately and ultrasonicated for 1 h, and then the solution was stirred at room temperature for 10 h, and then the mixture was rotary evaporated to obtain a black solid;

[0191] S203: The black solid was dried in a vacuum oven at 80°C for 3 hours. After thorough grinding, it was transferred to a tube furnace for calcination in a N2 atmosphere at a gas flow rate of 100 mL / min. The temperature was programmed to 400°C at a heating rate of 4°C / min and calcined for 4 hours. After the reduction was completed, the original atmosphere was maintained and the solid was cooled to room temperature. The resulting solid product was collected to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with copper active components, thereby obtaining the chlorine-free copper-based catalyst.

[0192] Catalyst Application

[0193] 10 mL of methanol and 0.3 g of catalyst were added to a 100 mL autoclave. After replacing the air in the reactor with CO, 1.8 MPa of CO and 0.2 MPa of O2 were introduced in sequence. After reacting at 120°C for 0.5 h, the reaction mixture was cooled in a water bath. The solid catalyst was separated from the obtained reaction solution to obtain a clear liquid.

[0194] Example 12

[0195] A chlorine-free copper-based catalyst is a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with a copper active component. The preparation method is as follows:

[0196] S1: preparing nitrogen-doped biomass-based carbon support;

[0197] S101: Weigh 7 g of glucosamine hydrochloride powder, 7 g of urea, and 28 g of sodium bicarbonate and mix and grind them evenly;

[0198] S102: The mixture obtained in S101 was transferred to a tube furnace for calcination. During the calcination process, the flow rate of N2 was 100 mL / min, and the temperature was programmed to 800°C at a heating rate of 10°C / min for calcination for 1 hour. After the calcination, the obtained black solid was dispersed in 200 mL of deionized water. After being fully stirred at room temperature for 12 hours, it was washed with anhydrous ethanol and deionized water and filtered until the filtrate was neutral. The obtained black solid material was then placed in a vacuum oven at 100°C and dried for 6 hours. After being taken out, the nitrogen-doped biomass-based carbon support was obtained.

[0199] S2: The copper active component is loaded onto a nitrogen-doped biomass-based carbon support to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with the copper active component:

[0200] S201: Dissolve 0.8632 g of copper nitrate in 60 ml of deionized water and stir evenly to obtain a copper solution:

[0201] S202: 2.0 g of the nitrogen-doped biomass-based carbon support obtained in S1 was mixed with the copper solution obtained in S201 to a Cu mass fraction of 10%, stirred appropriately and ultrasonicated for 1 h, and then the solution was stirred at room temperature for 10 h, and then the mixture was rotary evaporated to obtain a black solid;

[0202] S203: The black solid was dried in a vacuum oven at 80°C for 3 hours. After thorough grinding, it was transferred to a tube furnace for calcination in a N2 atmosphere at a gas flow rate of 100 mL / min. The temperature was programmed to 400°C at a heating rate of 4°C / min and calcined for 4 hours. After the reduction was completed, the original atmosphere was maintained and the solid was cooled to room temperature. The resulting solid product was collected to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with copper active components, thereby obtaining the chlorine-free copper-based catalyst.

[0203] Catalyst Application

[0204] 10 mL of methanol and 0.3 g of catalyst were added to a 100 mL autoclave. After replacing the air in the reactor with CO, 1.8 MPa of CO and 0.2 MPa of O2 were introduced in sequence. After reacting at 120°C for 0.5 h, the reaction mixture was cooled in a water bath. The solid catalyst was separated from the obtained reaction solution to obtain a clear liquid.

[0205] Result Analysis

[0206] The product was analyzed by gas chromatography using ethanol as an internal standard. The reaction activity results of the catalyst are shown in Table 2. Specifically, the specific parameter changes and catalyst reaction activity results of Examples 1-15 are shown in Table 2 (the meanings of the letter codes in Table 1 are: DMC: dimethyl carbonate, DMM: methylal, MF: methyl formate; DMM and MF are the main by-products):

[0207] Table 2

[0208]

[0209]

[0210]

[0211] From the results in the above examples, it can be concluded that the space-time yield of the nitrogen-doped biomass-based carbon support-supported copper-based catalyst provided by the present invention for the oxidative carbonylation of methanol to dimethyl carbonate in liquid phase can be as high as 25.69 g·(g·h) -1 In the present invention, the methanol conversion rate and dimethyl carbonate selectivity can be adjusted by adjusting the calcination time and temperature of the carbon support, the calcination time and temperature of the catalyst, the loading amount of the active component, and the temperature and time of the reaction. The catalyst prepared by the present invention can be separated from dimethyl carbonate by a simple separation method (standing and removing the supernatant, and the remaining portion can be centrifuged to achieve solid-liquid separation).

[0212] The above-described embodiments merely represent specific implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of protection of the present application. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the technical concept of the present application, and all such variations and improvements fall within the scope of protection of the present application.

Claims

1. A chlorine-free copper-based catalyst, characterized in that: It is a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with copper active components.

2. A chlorine-free copper-based catalyst according to claim 1, characterized in that: The mass of copper accounts for 3 to 15 wt% of the total weight of the catalyst.

3. A chlorine-free copper-based catalyst according to claim 1, characterized in that: The copper active component is a copper salt.

4. A chlorine-free copper-based catalyst according to claim 1, characterized in that: The nitrogen source in the nitrogen-containing three-dimensional interconnected layered porous carbon material comes from one or more of urea, ammonium oxalate and melamine.

5. The chlorine-free copper-based catalyst according to claim 1, wherein: The carbon source in the nitrogen-containing three-dimensional interconnected layered porous carbon material comes from one or more of glucosamine hydrochloride, chitin, and chitosan.

6. A method for preparing the chlorine-free copper-based catalyst according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1: Preparation of nitrogen-doped biomass-based carbon supports; S2: The copper active component is loaded onto a nitrogen-doped biomass-based carbon support to obtain a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with the copper active component.

7. The method for preparing a chlorine-free copper-based catalyst according to claim 6, wherein: The specific steps of S1 are as follows: S101: mixing a nitrogen-containing biomass derivative, a nitrogen source, and a pore-forming agent to obtain a mixture; S102: calcining the mixture obtained in S101 at 500-900° C. in a nitrogen atmosphere for 0.5-4 h to obtain a black solid product; S103: After the black solid product obtained in S102 is cooled to room temperature, it is washed, filtered, and dried to obtain a nitrogen-doped biomass-based carbon support.

8. The method for preparing a chlorine-free copper-based catalyst according to claim 6, wherein: The specific steps of S2 are as follows: S201: preparing a copper solution; S202: mixing the nitrogen-doped biomass-based carbon support obtained in S1 with the copper solution obtained in S201; S203: After the mixing is completed, separation and drying are performed, and the obtained solid is calcined in a nitrogen atmosphere at 200-500° C. for 1-5 hours, and after cooling, a nitrogen-containing three-dimensional interconnected layered porous carbon material loaded with copper active components is obtained.

9. Use of the chlorine-free copper-based catalyst according to any one of claims 1 to 5, characterized in that: Used to catalyze the liquid-phase oxidative carbonylation of methanol to synthesize dimethyl carbonate.

10. The use of a chlorine-free copper-based catalyst according to claim 6, characterized in that: The amount of chlorine-free copper-based catalyst added is 0.1-0.5 g of catalyst per 10 ml of methanol.

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