CN112279828A

CN112279828A - Method for synthesizing methyl furoate through one-step oxidation esterification of furfural by taking novel nitrogen-doped carbon-supported cobalt as catalyst

Info

Publication number: CN112279828A
Application number: CN202011179102.6A
Authority: CN
Inventors: 赵国明; 高恩远; 万巧巧; 于海滨; 巩玉秀; 孙林; 侯腾; 蒋聪; 潘晟洋; 张朵朵; 王治琦; 杨景茹
Original assignee: Shandong University of Science and Technology
Current assignee: Shandong University of Science and Technology
Priority date: 2020-10-29
Filing date: 2020-10-29
Publication date: 2021-01-29

Abstract

The invention belongs to the field of organic chemistry and catalytic chemistry, and relates to a method for synthesizing methyl furoate by one-step oxidation esterification of furfural by taking Co-N-C-MLM with a symmetrical broken bionic structure as a catalyst. The method takes furfural as a reaction substrate, takes molecular oxygen as an oxygen source, and uses a Co-N-C-MLM catalyst with a symmetrical broken bionic structure to realize the synthesis of methyl furoate by one-step oxidation esterification. The method can ensure that the conversion rate of the furfural reaches more than 90 percent, the selectivity of the methyl furoate reaches 97 percent, and the catalyst can be stably recycled for more than 5 times.

Description

Method for synthesizing methyl furoate through one-step oxidation esterification of furfural by taking novel nitrogen-doped carbon-supported cobalt as catalyst

Technical Field

The invention belongs to the field of organic chemistry and catalytic chemistry, and relates to a method for synthesizing methyl furoate by one-step oxidation esterification of furfural by taking Co-N-C-MLM with a symmetrical broken bionic structure as a catalyst.

Background

Methyl furoate (Methyl 2-furoate) is an important fine chemical product and naturally exists in plants such as peanut, coffee, cocoa and the like. Because the mushroom flavor has strong mushroom flavor at high concentration and fruit flavor at low concentration, the mushroom flavor can be widely applied to industries such as food additives, cosmetic essences and the like as a synthetic spice. At present, the price of furfural is about 1 ten thousand yuan/ton, and the price of methyl furoate is generally more than 10 ten thousand yuan/ton.

Currently, in the industrial synthesis of methyl furoate, furfural is generally used as a raw material and is synthesized by a two-step method, namely furfural is firstly oxidized into furoic acid, and then the furoic acid and methanol are subjected to esterification reaction to finally generate methyl furoate. The oxidation of furfural into furoic acid mostly adopts Cannizzaro reaction, that is, furfural generates intermolecular redox reaction under the action of strong alkali to generate furoic acid and furfuryl alcohol. However, the process uses a large amount of high-concentration alkali, increases the cost and generates a large amount of pollution emission. In the process route of generating the methyl furoate by the esterification of the furoic acid, the used catalyst mainly comprises concentrated hydrochloric acid, concentrated sulfuric acid, solid super acid and the like. When concentrated hydrochloric acid is used as an esterification catalyst, side reaction is easy to occur, so that the problems of low selectivity of methyl furoate, generation of a large amount of wastewater and the like are caused; when concentrated sulfuric acid is used as a catalyst, equipment corrosion is easily caused, and the transportation cost is increased; the solid super acid has the characteristics of easy recovery and low pollution, but the general synthesis method of the catalyst is complex, the preparation process is complicated, and the catalytic stability of the solid super acid is not high.

The literature (Dianthus hai-Zhai-application chemical industry, 2011,40(04):658-₁₃PV₁₂Cr₂O₄₂The yield of final methyl furoate is 89.5% for the esterification catalyst, but heteropolyacid is expensive and has poor catalytic stability. Therefore, the development of a green and efficient synthesis process of the methyl furoate has important research value.

CN109824634A (201711180117.2) takes a silicon dioxide composition as a carrier, and the catalyst prepared by loading cobalt-based composite particles has better catalytic performance in the reaction of synthesizing methyl furoate through one-step oxidation esterification of furfural, wherein the conversion rate of furfural can reach 100% at most, the selectivity of methyl furoate is 99.35%, and the catalyst can be continuously used in a fixed bed reactor for 500 hours without obvious inactivation. However, when synthesizing the catalyst, it is necessary to add a noble metal such as gold, platinum, palladium, or the like to the cobalt-based composite particulate matter, which undoubtedly increases the synthesis cost of the catalyst.

At present, the catalyst for the reaction of synthesizing the methyl furoate by oxidative esterification has the defects of high catalyst synthesis cost, poor stability and the like. In order to solve the problems, the catalyst with the Co-N-C-MLM symmetrical breaking bionic structure provided by the patent has the advantages of simple synthesis method and low cost, high activity in the process of catalyzing furfural and methanol to synthesize methyl furoate through oxidative esterification, high selectivity and high catalytic stability of a target product methyl furoate, mild catalytic reaction conditions, high yield of the target product methyl furoate up to 97%, and stable cyclic utilization of the catalyst for more than 5 times.

Disclosure of Invention

The invention provides a method for synthesizing methyl furoate by one-step oxidation esterification of furfural by taking Co-N-C-MLM with a symmetrical broken bionic structure as a catalyst, wherein the method can enable the conversion rate of furfural to reach more than 90%, the selectivity of methyl furoate to reach 97%, and the catalyst can be stably recycled for more than 5 times.

The scheme adopted by the invention is as follows:

a method for synthesizing methyl furoate through one-step oxidation esterification of furfural by taking Co-N-C-MLM with a symmetrical breaking bionic structure as a catalyst comprises the steps of adding a reaction substrate furfural, an auxiliary agent and a Co-N-C-MLM catalyst with a symmetrical breaking bionic structure into methanol, reacting for 0.1-24 hours under the conditions that the temperature is 5-180 ℃, the oxygen pressure is 0.1-6 MPa, and the stirring speed is 100-5000 rpm/min, and synthesizing methyl furoate through one-step oxidation esterification of furfural.

Further, the mass ratio of the methanol to the furfural is (1-100): 1.

Further, the auxiliary agent is one or more of potassium carbonate, sodium methoxide and potassium bicarbonate, and the mass ratio of the auxiliary agent to the furfural is (0.1-10): 1.

Further, the preparation method of the Co-N-C-MLM catalyst with the symmetrical defect bionic structure comprises the following steps: preparing a solution from cobalt salt with the concentration of 0.1-45%, fully dispersing a nitrogen-containing carbon source into the solution according to the mass ratio of the cobalt salt to the nitrogen-containing carbon source of (0.01-30): 1, heating, stirring, refluxing until the cobalt salt and the nitrogen-containing carbon source are fully mixed, and then continuously heating and stirring until the solvent is completely evaporated to dryness; and pyrolyzing the obtained solid in an inert atmosphere, washing and drying to obtain Co-N-C-MLM-P, washing the Co-N-C-MLM-P with alkali, and drying to obtain Co-N-C-MLM-P-B. Treating Co-N-C-MLM-P with acid solution, washing and drying to obtain the Co-N-C-MLM-H catalyst, washing the Co-N-C-MLM-H with alkali and drying to obtain Co-N-C-MLM-B.

Further, in the preparation method of the Co-N-C-MLM catalyst with the symmetrical breaking bionic structure, the adopted cobalt salt comprises one or more of cobalt chloride, cobalt nitrate, cobalt sulfate, cobalt acetate, cobalt-quinoline amine acid and cobalt acetylacetonate; the solvent for dissolving the cobalt salt is one or more of water, methanol and ethanol; the nitrogen-containing carbon source is melamine.

Further, in the preparation method of the Co-N-C-MLM catalyst with the symmetrical broken bionic structure, the heating, stirring and refluxing temperature of the mixed solution is 5-120 ℃, and the refluxing time is 1-48 h; the heating temperature for evaporating the solvent is 5-150 ℃. The inert gas used in the pyrolysis process is one or more of argon, helium and nitrogen; the gas flow rate is 10-120 mL/min; the heating rate is 1-10 ℃/min; the temperature of the pyrolysis process is one or more of 250 ℃, 350 ℃, 550 ℃, 600 ℃ and 900 ℃. The liquid used for washing the catalyst precursor is one or more of methanol, ethanol and water. The acid solution used for treating the pyrolyzed solid is one or more of hydrochloric acid solution, sulfuric acid solution, nitric acid solution, phosphoric acid solution and acetic acid solution; the concentration is 0.01-50%.

Drawings

FIG. 1 is a nitrogen isothermal adsorption desorption curve and a pore size distribution diagram of the catalyst of example 1;

FIG. 2 is an XRD characterization plot of the catalyst of example 1;

FIG. 3 is a Scanning Electron Micrograph (SEM) of the catalyst of example 1.

Detailed Description

The invention is further illustrated by the following examples, which are, however, to be construed as merely illustrative and not limitative of the remainder of the disclosure in any way whatsoever.

Example 1

Reacting melamine with CoCl₂·6H₂O was mixed well in water and then the solvent was evaporated to dryness with stirring. Putting the solid obtained by evaporation into a tubular furnace, and carrying out multi-step pyrolysis at the heating rate of 3 ℃/min under the argon atmosphere to finally obtain the black catalyst precursor. The resulting catalyst was named Co-N-C-MLM-P.

The prepared nitrogen-doped carbon-supported cobalt catalyst is used for the oxidation esterification reaction of furfural, and the operation steps are as follows: adding 0.1g of catalyst, 1mmol of furfural, 1mmol of potassium carbonate as a reaction auxiliary agent, 1mmol of n-dodecane as an internal standard and 10mL of methanol into a 100mL stainless steel high-pressure reaction kettle, introducing 2MPa of oxygen, and reacting at 120 ℃ for 12 hours. After the reaction, the reaction kettle is cooled to room temperature, then the reaction liquid and the catalyst are centrifugally separated, and the reaction liquid is analyzed by gas chromatography. Specific results are shown in table 1.

TABLE 1 Co-N-C-MLM catalyzed reaction of furfural with oxidative esterification to methylfuroate

Examples	Name of catalyst	Conversion Con./%)	Selectivity sel./%)
				1	Co-N-C-MLM-P	83.0	96.9

As can be seen from Table 1, the nitrogen-doped carbon-supported cobalt catalyst synthesized by using melamine as a nitrogen-containing carbon source has high catalytic activity on the oxidative esterification reaction of furfural, the conversion rate reaches 83.0%, and the selectivity reaches 96.9%.

Examples 2 to 6

The Co-N-C-MLM-P catalyst described in example 1 was subjected to stability evaluation. After the reaction is finished, cooling the reaction kettle to room temperature, then centrifugally separating reaction liquid and the catalyst, analyzing the reaction liquid by using gas chromatography, fully washing the catalyst by using methanol and water, and drying the catalyst in an oven at 60 ℃ for 12 hours to obtain the recovered catalyst, and continuing to perform catalytic furfural oxidation esterification reaction experiments. The stability test of the catalyst was performed for 5 times, the operation procedure was the same as the furfural oxidation esterification reaction of the catalyst synthesized in example 1, and the specific results are shown in table 2. (there is a loss in the catalyst recovery process, and the amount of the corresponding reactant is decreased by the mass ratio to the amount of the catalyst)

TABLE 2 Recycling performance results for Co-N-C-MLM catalysts

Examples	Number of cycles	Conversion Con./%)	Selectivity sel./%)
				2	1	82.7	96.7
3	2	82.4	95.9
				4	3	81.9	96.4
5	4	81.2	96.3
				6	5	80.9	96.1

As can be seen from Table 2, the activity of the catalyst remained stable after 5 times of recovery, indicating that the catalyst can be reused without reducing its catalytic activity, and has good effect.

Example 7

The catalyst prepared in example 1 was stirred and refluxed in hydrochloric acid solution, filtered, washed thoroughly with distilled water, and dried at 60 ℃, and the final catalytic material was named Co-N-C-MLM-H (H indicates that the catalyst was washed with hydrochloric acid).

FIG. 1 is a nitrogen isothermal adsorption desorption curve and a pore size distribution diagram of the catalyst of example 2 of the present invention, which shows that Co-N-C-MLM-H has a large specific surface area (234.98 m)²In terms of a/g) and a homogeneous pore structure (average pore diameter of 5.21 nm).

Figure 2 is an XRD characterization plot of the catalyst of example 2, indicating that the supported is Co nanoparticles.

FIG. 3 is a Scanning Electron Micrograph (SEM) of the catalyst of example 2, which shows that the prepared Co-N-C-MLM-H is a nitrogen-containing carbon nanotube structure.

The prepared nitrogen-doped carbon-supported cobalt catalyst is used for the oxidation esterification reaction of furfural, after the operation steps are the same as the operation steps of the furfural oxidation esterification reaction of the catalyst synthesized in the embodiment 1, the reaction kettle is cooled to room temperature, then the reaction liquid and the catalyst are centrifugally separated, and the reaction liquid is analyzed by gas chromatography. Specific results are shown in table 3.

TABLE 3 Co-N-C-MLM-H catalyzed reaction of furfural with oxidative esterification to synthesize methyl furoate

Examples	Name of catalyst	Conversion Con./%)	Selectivity sel./%)
				7	Co-N-C-MLM-H	90.4	97.0

From table 3, it can be seen that the nitrogen-doped carbon-supported cobalt catalyst washed by the acidic solvent has high catalytic activity for the oxidation esterification reaction of furfural, the conversion rate is as high as 90.4%, and the selectivity is as high as 97.0%.

Examples 8 to 12

The Co-N-C-MLM-H catalyst described in example 13 was subjected to stability evaluation. After the reaction is finished, cooling the reaction kettle to room temperature, then centrifugally separating reaction liquid and the catalyst, analyzing the reaction liquid by using gas chromatography, fully washing the catalyst by using methanol and water, and drying the catalyst in an oven at 60 ℃ for 12 hours to obtain the recovered catalyst, and continuing to perform catalytic furfural oxidation esterification reaction experiments. The stability test of the catalyst was performed for 5 times, the operation procedure was the same as the furfural oxidative esterification reaction of the catalyst synthesized in example 1, and the specific results are shown in table 4. (there is a loss in the catalyst recovery process, and the amount of the corresponding reactant is decreased by the mass ratio to the amount of the catalyst)

TABLE 4 Recycling performance results for Co-N-C-MLM-H catalysts

Examples	Number of cycles	Conversion Con./%)	Selectivity sel./%)
				8	1	87.7	94.4
9	2	86.8	95.2
				10	3	85.9	96.6
11	4	82.5	96.5
				12	5	88.3	96.4

As can be seen from Table 4, the activity of the catalyst is basically stable after 5 times of recycling, which indicates that the catalyst can be reused without reducing the catalytic activity thereof, and has good effect.

Example 13

The catalyst material prepared in example 1 was stirred and refluxed in sodium hydroxide solution, filtered, washed thoroughly with distilled water, and dried at 60 ℃, and the final catalytic material was named Co-N-C-MLM-B (B indicates that the catalyst was washed with an alkaline solution).

The prepared nitrogen-doped carbon-supported cobalt catalyst is used for the oxidation esterification reaction of furfural, and the operation steps are as follows: 0.1g of catalyst, 1mmol of furfural, 1mmol of n-dodecane as an internal standard and 10mL of methanol are added into a 100mL stainless steel high-pressure reaction kettle, and then 2MPa of oxygen is introduced to react for 12 hours at 120 ℃. After the reaction, the reaction kettle is cooled to room temperature, then the reaction liquid and the catalyst are centrifugally separated, and the reaction liquid is analyzed by gas chromatography. Specific results are shown in table 5.

TABLE 5 Co-N-C-MLM-P-B catalyzed reaction of furfural with oxidative esterification to synthesize methyl furoate

Examples	Name of catalyst	Conversion Con./%)	Selectivity sel./%)
				13	Co-N-C-MLM-P-B	95.3	99.4

As can be seen from table 5, the nitrogen-doped carbon-supported cobalt catalyst washed with the alkaline solution still shows high catalytic activity for the oxidation esterification reaction of furfural without the addition of an alkaline auxiliary agent, the conversion rate of the reactant can reach 95.3%, and the selectivity can reach 99.4%.

Examples 14 to 18

The Co-N-C-MLM-P-B catalyst described in example 1 was subjected to stability evaluation. After the reaction is finished, cooling the reaction kettle to room temperature, then centrifugally separating reaction liquid and the catalyst, analyzing the reaction liquid by using gas chromatography, fully washing the catalyst by using methanol and water, and drying the catalyst in an oven at 60 ℃ for 12 hours to obtain the recovered catalyst, and continuing to perform catalytic furfural oxidation esterification reaction experiments. The stability test of the catalyst was performed for 5 times, the operation procedure was the same as the furfural oxidation esterification reaction of the catalyst synthesized in example 13, and the specific results are shown in table 6. (there is a loss in the catalyst recovery process, and the amount of the corresponding reactant is decreased by the mass ratio to the amount of the catalyst)

TABLE 6 Recycling performance results for Co-N-C-MLM-P-B catalysts

As can be seen from Table 6, the activity of the catalyst did not significantly decrease after 5 cycles of catalyst recycle, indicating that the catalyst could be recycled without decreasing the catalytic activity.

Example 19

The Co-N-C-MLM-H catalyst prepared in example 7 was stirred in sodium hydroxide solution and refluxed, filtered, washed thoroughly with distilled water, and dried at 60 ℃ to obtain the final catalytic material named Co-N-C-MLM-H-B.

The prepared nitrogen-doped carbon-supported cobalt catalyst was used in the oxidative esterification of furfural, and after the same operation steps as those of the furfural oxidative esterification reaction of the catalyst synthesized in example 13 were completed, the reaction kettle was cooled to room temperature, and then the reaction solution and the catalyst were centrifugally separated, and the reaction solution was analyzed by gas chromatography. Specific results are shown in table 7.

TABLE 7 Co-N-C-MLM-H-B catalyzed reaction of furfural with oxidative esterification to synthesize methyl furoate

Examples	Name of catalyst	Conversion Con./%)	Selectivity sel./%)
				19	Co-N-C-MLM-H-B	96.0	99.5

As can be seen from Table 7, the Co-N-C-MLM-H-B catalyst has higher reaction activity for the reaction of oxidizing and esterifying furfural to generate methyl furoate, the conversion rate reaches 96.0%, and the selectivity reaches 99.5%.

Examples 20 to 24

The Co-N-C-MLM-H-B catalyst described in example 19 was subjected to stability evaluation. After the reaction is finished, cooling the reaction kettle to room temperature, then centrifugally separating reaction liquid and the catalyst, analyzing the reaction liquid by using gas chromatography, fully washing the catalyst by using methanol and water, and drying the catalyst in an oven at 60 ℃ for 12 hours to obtain the recovered catalyst, and continuing to perform catalytic furfural oxidation esterification reaction experiments. The stability test of the catalyst was performed 5 times in total, the operation procedure was the same as the furfural oxidative esterification reaction of the catalyst synthesized in example 13, and the specific results are shown in table 8. (there is a loss in the catalyst recovery process, and the amount of the corresponding reactant is decreased by the mass ratio to the amount of the catalyst)

TABLE 8 Recycling performance results for Co-N-C-MLM-B catalysts

Examples	Number of cycles	Conversion Con./%)	Selectivity sel./%)
				20	1	95.6	99.2
21	2	95.3	99.3
				22	3	95.0	99.0
23	4	95.1	99.5
				24	5	94.7	98.9

As can be seen from table 8: during 5 times of recycling, the activity of the catalyst is kept stable. This indicates that the catalyst can be recycled without reducing the activity of the catalyst.

Comparative example 1

Roasting melamine in argon atmosphere, wherein the heating rate is 3 ℃/min, the temperature programming is specifically heating from room temperature to 350 ℃, and keeping for 3h at 350 ℃; then raising the temperature to 600 ℃, and keeping the temperature at 600 ℃ for 3 h; and continuously raising the temperature to 900 ℃, keeping the temperature at 900 ℃ for 2h, and naturally cooling to room temperature to obtain a black solid named as N-C-MLM.

Comparative example 2

Melamine is used directly as catalytic material.

Comparative example 3

Adding CoCl₂·6H₂Drying O at 110 ℃ for 5h, and naturally cooling to room temperature to obtain CoCl₂。

The catalyst synthesized in the comparative examples 1 to 3 is used for furfural oxidation esterification reaction, and the operation steps are the same as those of the furfural oxidation esterification reaction of the catalyst synthesized in the example 1. Specific results are shown in table 3.

TABLE 3 reaction of N-C-MLM with Melamine catalyzed Furfural oxidative esterification to methyl Furfurate

Comparative example	Name of catalyst	Conversion Con./%)	Selectivity sel./%)
				1	N-C-MLM	0.3	TRACE
2	MLM	0.2	TRACE
				3	CoCl₂	9.0	76.8

As can be seen from examples and comparative examples 1 to 3, the nitrogen-doped carbon material not supporting cobalt has no catalytic activity for the oxidative esterification of furfural, while CoCl₂Has only low catalytic activity.

The present invention is not limited to the above embodiments, and various changes and modifications may be made in accordance with the present invention without departing from the spirit thereof, and shall fall within the scope of the present invention.

Claims

1. A method for synthesizing methyl furoate through one-step oxidation esterification of furfural by taking Co-N-C-MLM with a symmetrical broken bionic structure as a catalyst is characterized in that a reaction substrate furfural, an auxiliary agent and a Co-N-C-MLM catalyst with a symmetrical broken bionic structure are added into methanol, the mixture reacts for 0.1-24 hours under the conditions that the temperature is 5-180 ℃, the oxygen pressure is 0.1-6 MPa, and the stirring speed is 100-5000 rpm/min, and the methyl furoate is synthesized through one-step oxidation esterification of furfural.

2. The method according to claim 1, wherein the mass ratio of methanol to furfural is (1-100): 1.

3. The method according to claim 1, wherein the auxiliary agent is one or more of potassium carbonate, sodium methoxide and potassium bicarbonate, and the mass ratio of the auxiliary agent to the furfural is (0.1-10): 1.

4. The method as claimed in claim 1, wherein the preparation method of the Co-N-C-MLM catalyst with the symmetrical defect bionic structure comprises the following steps:

preparing a solution from 0.1-45% of cobalt salt, fully dispersing a nitrogen-containing carbon source into the solution according to the mass ratio of the cobalt salt to the nitrogen-containing carbon source of (0.01-30) to 1, heating, stirring, refluxing until the cobalt salt and the nitrogen-containing carbon source are fully mixed, and then continuously heating and stirring until the solvent is completely evaporated to dryness.

5. And pyrolyzing the obtained solid in an inert atmosphere, washing and drying to obtain Co-N-C-MLM-P, washing the Co-N-C-MLM-P with alkali, and drying to obtain Co-N-C-MLM-P-B.

6. Treating Co-N-C-MLM-P with acid solution, washing and drying to obtain the Co-N-C-MLM-H catalyst, washing the Co-N-C-MLM-H with alkali and drying to obtain Co-N-C-MLM-B.

7. The method according to claim 4, wherein the cobalt salt is one or more selected from the group consisting of cobalt chloride, cobalt nitrate, cobalt sulfate, cobalt acetate, cobalaminic acid and cobalt acetylacetonate; the solvent for dissolving the cobalt salt is one or more of water, methanol and ethanol; the nitrogen-containing carbon source is Melamine (MLM).

8. The preparation method according to claim 4, wherein the heating, stirring and refluxing temperature of the mixed solution is 5-120 ℃, and the refluxing time is 1-48 h; the heating temperature for evaporating the solvent is 5-150 ℃.

9. The inert gas used in the pyrolysis process is one or more of argon, helium and nitrogen; the gas flow rate is 10-120 mL/min; the heating rate is 1-10 ℃/min; the temperature of the pyrolysis process is one or more of 250 ℃, 350 ℃, 550 ℃, 600 ℃ and 900 ℃.

10. The liquid used for washing the catalyst precursor is one or more of methanol, ethanol and water.

11. The acid solution used for treating the pyrolyzed solid is one or more of hydrochloric acid solution, sulfuric acid solution, nitric acid solution, phosphoric acid solution and acetic acid solution; the concentration is 0.01-50%.