CN112920187B - A kind of method for removing formaldehyde and synthesizing metal complex simultaneously and its application - Google Patents

Abstract

The invention discloses a method for simultaneously removing formaldehyde and synthesizing metal complexes and application thereof, wherein ammonium salt and soluble metal salt are added into a solution containing formaldehyde; or introducing formaldehyde-containing gas into a mixed solution of ammonium salt and soluble metal salt; the metal complex is obtained after stirring reaction, crystallization and purification. The invention firstly adopts ammonium salt to resource formaldehyde into hexamethylene tetramine, and then utilizes the coordination effect of metal salt and hexamethylene tetramine to promote formaldehyde conversion and simultaneously form stable metal complex for efficiently catalyzing CO₂And (3) performing cycloaddition reaction.

Description

A kind of method for removing formaldehyde and synthesizing metal complex simultaneously and its application

technical field

The invention belongs to the field of environmental protection, and in particular relates to a method for simultaneously removing formaldehyde and synthesizing metal complexes and its application in a CO ₂ cycloaddition reaction.

Background technique

Formaldehyde treatment methods mainly include oxidation method, biological treatment method, stripping method, condensation method, lime method, etc. Among them, technologies such as capturing formaldehyde and converting it into resin [CN201710494960.1], methylal [CN200910032554.9] or urea-formaldehyde resin adhesive [CN201210037079.6] through condensation have attracted widespread attention. However, there is currently no report on the utilization of formaldehyde as a catalyst for catalyzing organic reactions.

In May 2020, scientists monitored the concentration of _CO2 in the atmosphere exceeding 417ppm, a record high. The cycloaddition reaction of CO ₂ in industrial waste gas and epoxide to synthesize cyclic carbonate with high added value turns waste into treasure. From the perspective of replacing the original carbonate synthesis process, it is of great significance for alleviating the greenhouse effect. In addition, this process has the advantages of high atom utilization and few by-products, which conforms to the principles of green chemistry. At present, quaternary ammonium salts and metal salts are mainly used to prepare cyclic carbonates in industry. The reaction conditions are harsh (high temperature and high pressure are required), and the increase in energy consumption leads to indirect emissions of more CO ₂ .

After the metal salt reacts with organic ligands to form metal complexes, the activity is improved, but the complex preparation process, high price, and unsatisfactory stability of metal complexes or organic ligands limit the use of such catalysts in the cyclic carbonate process. application.

SUMMARY OF THE INVENTION

In order to solve the problems existing in the prior art, the object of the present invention is to provide a method for simultaneously removing formaldehyde and synthesizing metal complexes and its application. The coordination of metal salts with hexamethylenetetramine is used to promote the conversion of formaldehyde and form stable metal complexes for efficient catalysis of CO ₂ cycloaddition.

In order to achieve the above object, the present invention adopts the following technical solutions:

A method for simultaneously removing formaldehyde and synthesizing metal complexes, adding ammonium salt and soluble metal salt to a solution containing formaldehyde; or introducing formaldehyde-containing gas into a mixed solution of ammonium salt and soluble metal salt; stirring The metal complex is obtained after reaction, crystallization and purification.

Preferably, the ammonium salt is selected from one or more of ammonium nitrate, ammonium chloride, ammonium bromide, ammonium iodide, ammonium fluoride, ammonium phosphate, ammonium hydrogen phosphate, ammonium dihydrogen phosphate and ammonium acetate.

Preferably, the soluble metal salt is one or more of Zn, Fe, Ca or Mg nitrate, chloride, bromide, iodide, fluoride, phosphate, hydrogen phosphate and dihydrogen phosphate .

Preferably, the molar ratio of the ammonium salt to the soluble metal salt is 4-20:1.

Preferably, in the solution containing formaldehyde, the concentration of formaldehyde is 0.1-10 g/L, and the molar ratio of ammonium salt to formaldehyde is 1-10:1.

Preferably, in the formaldehyde-containing gas, the concentration of formaldehyde is 5-100 mg/L, and the molar ratio of ammonium salt to formaldehyde is 1-10:1.

Preferably, the time for the stirring reaction is 10 min to 6 h.

The present invention also provides the application of the above metal complex for catalyzing the cycloaddition reaction of epoxide and CO ₂ to synthesize cyclic carbonate.

Preferably, the epoxide is one or more of ethylene oxide, epichlorohydrin, propylene oxide, butylene oxide, cyclohexene oxide, cyclopentene oxide and styrene oxide.

Preferably, the molar ratio of the metal complex to the epoxide is (0.005-0.05):1.

Taking zinc bromide hexamethylenetetramine metal complex (ZnBr ₂ ·2Hatm) synthesis as an example, formula (1) is the reaction process of formaldehyde removal and metal complex synthesis of the present invention:

ZnBr ₂ +8NH ₄ Br+12HCHO=ZnBr ₂ ·2Hatm+8HBr+12H ₂ O (1)

It can be seen from formula (1) that due to the introduction of metal salt (ZnBr ₂ ), the hexamethylene tetramine generated by the reaction of formaldehyde and ammonium salt (NH ₄ Br) is converted into a more stable metal complex (ZnBr ₂ ·2Hatm) in time. ), which can not only improve the removal rate of formaldehyde, but also avoid secondary pollution caused by the decomposition of hexamethylenetetramine into formaldehyde.

Compared with the prior art, the technical effect of the present invention is:

(1) The present invention is suitable for both the treatment of formaldehyde waste water and the treatment of formaldehyde waste gas, and the method for removing formaldehyde is simple, the conditions are mild, the cost is low, the efficiency is high, and the speed is fast.

(2) The present invention adopts a coupling strategy to remove formaldehyde and at the same time utilize resources to obtain an efficient CO ₂ cycloaddition catalyst, thereby saving resources and avoiding secondary pollution of formaldehyde.

(3) The hexamethylenetetramine metal complex prepared by the present invention is rich in basic sites (4 mol of tertiary amine in 1 mol molecule), has a cage-like structure, is stable to water, and can be highly selective under mild conditions. Catalytic and high-yield cycloaddition of _CO and epoxides for the synthesis of cyclic carbonates.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Example 1

Take 323g (3.3mol) of ammonium bromide and 1.12g (0.825mol) of zinc bromide respectively and add them to 10L of water with a formaldehyde concentration of (3.3mmol) 10g/L. After stirring for 6h, the formaldehyde concentration is reduced to 1.4mg/L. Evaporation and crystallization, suction filtration to obtain a crude product, washing with ethanol, adding 95 wt.% ethanol for recrystallization to obtain zinc bromide hexamethylenetetramine metal complex-1.

Example 2

Take 177g (3.3mol) of ammonium chloride and 61g (0.55mol) of calcium chloride and add them to 100L of water with a formaldehyde (1.65mol) concentration of 0.5g/L. After stirring for 10min, the formaldehyde concentration is reduced to 0.8mg/L. Evaporation and crystallization, suction filtration to obtain a crude product, washing with ethanol, adding 95 wt.% ethanol for recrystallization to obtain calcium chloride hexamethylenetetramine metal complex.

Example 3

Take 32.3g (0.33mol) of ammonium bromide and 2.72g (20mmol) of zinc bromide respectively and add them to 1L of water to dissolve, and feed 30L of 100mg/L formaldehyde gas under stirring (the gas flow rate is 100mL/min), the formaldehyde concentration in the gas decreases After stirring for 6 hours, the formaldehyde concentration in the solution was 0.6 mg/L, then evaporated and crystallized, and suction filtered to obtain the crude product. After washing with ethanol, 95 wt.% ethanol was added for recrystallization to obtain zinc bromide hexamethylene. tetramine metal complex-2.

Example 4

Take 17.7g (0.33mol) of ammonium chloride and 1.36g (10mmol) of zinc chloride respectively and add them to 100mL of water to dissolve, and feed 50L of 5mg/L formaldehyde gas under stirring (the gas flow rate is 100mL/min), the formaldehyde concentration in the gas decreases After stirring for 2 hours, the formaldehyde concentration in the solution was 0.3 mg/L, then evaporated and crystallized, and suction filtered to obtain the crude product. After washing with ethanol, 95wt.% ethanol was added for recrystallization to obtain zinc chloride hexamethylene chloride. base tetraamine metal complexes.

Comparative Example 1

Take 177g (3.3mol) of ammonium chloride and add it to 100L of water with a formaldehyde (1.65mol) concentration of 0.5g/L. After stirring for 10min, the formaldehyde concentration is reduced to 0.1g/L.

Comparative Example 2

17.7g (0.33mol) of ammonium chloride was added to 100mL of water to dissolve, and 50L of 5mg/L formaldehyde gas was introduced under stirring (the gas flow rate was 100mL/min), and the formaldehyde concentration in the gas was reduced to 3.2mg/L.

Application example 1

At room temperature, 0.6mmol of zinc bromide hexamethylenetetramine metal complex-1 prepared in Example 1, 0.15g of internal standard biphenyl, 30mmol of epichlorohydrin, and 30mmol of epichlorohydrin were successively added to the 30mL autoclave, and stirred at room temperature. 2MPa CO ₂ was introduced into the reactor, then the reaction kettle was put into an oil bath reactor with magnetic stirring and reacted at 80 °C for 5 h. After the reaction was completed, the reaction kettle was placed in cold water to cool, and then CO ₂ was released. After centrifugation, the supernatant was taken for GC analysis: the yield of cyclic carbonate was 92.8%, and the selectivity was 99.8%.

Application example 2

At room temperature, in a 30mL autoclave, successively added calcium chloride hexamethylenetetramine metal complex 0.3mmol obtained in Example 2, internal standard biphenyl 0.15g, propylene oxide 30mmol, and passed into under stirring at room temperature. 1.5MPa CO ₂ , then put the reaction kettle into an oil bath reactor with magnetic stirring and react at 80 °C for 10 hours. After the reaction, the reaction kettle was cooled in cold water, and then CO ₂ was released. The reactants were taken out and centrifuged. The supernatant was taken for GC analysis: the yield of propylene carbonate was 96.3%, and the selectivity was 99.7%.

Application example 3

At room temperature, 1.5 mmol of zinc bromide hexamethylenetetramine metal complex-2 prepared in Example 3, 0.15 g of internal standard biphenyl, and 30 mmol of propylene oxide were successively added to a 10 mL reaction tube, and the reaction tube was mixed with Connect a 1L CO ₂ air bag, then put the reaction tube into an oil bath reactor with magnetic stirring for 24 hours at 30 °C, release CO ₂ after the reaction, take out the reactant, and after centrifugation, take the supernatant for GC Analysis: The yield of propylene carbonate was 82.5% and the selectivity was 99.8%.

Application example 4

At room temperature, 0.3mmol of zinc chloride hexamethylenetetramine metal complex prepared in Example 4, 0.15g of internal standard biphenyl, 30mmol of propylene oxide, and 30mmol of propylene oxide were successively added in the 30mL autoclave, and the mixture was stirred at room temperature. 2MPa CO ₂ , then put the reaction kettle into an oil bath reactor with magnetic stirring and react at 80°C for 12 hours. After the reaction, the reaction kettle was cooled in cold water, and then CO ₂ was released. The supernatant was subjected to GC analysis: the yield of propylene carbonate was 78.4% and the selectivity was 99.8%.

Application Example 1

At room temperature, 0.3 mmol of zinc chloride, 0.15 g of internal standard biphenyl, and 30 mmol of propylene oxide were successively added to a 30 mL autoclave, and 2 MPa CO ₂ was fed under stirring at room temperature, and then the reactor was placed in an oil with magnetic stirring. The reaction was carried out in a bath reactor at 80 °C for 12 hours. After the reaction was completed, the reactor was cooled in cold water, and then CO ₂ was released. The reactants were taken out. After centrifugation, the supernatant was taken for GC analysis: the yield of propylene carbonate was 32.1 %, the selectivity is 99.8%.

Application Comparative Example 2

At room temperature, 0.3 mmol of hexamethylenetetramine, 0.15 g of internal standard biphenyl, 30 mmol of propylene oxide were successively added to a 30 mL autoclave, and 2 MPa CO ₂ was fed under stirring at room temperature, and then the In a stirred oil bath reactor, the reaction was carried out at 80 °C for 12 h. After the reaction was completed, the reaction kettle was cooled in cold water, and then CO ₂ was released. The reactants were taken out. After centrifugation, the supernatant was taken for GC analysis: the production of propylene carbonate. The rate was 1.2% and the selectivity was 92.8%.

Claims (6)

1. The application of a metal complex is characterized in that: it is used to catalyze epoxides and CO₂Synthesizing cyclic carbonate through cycloaddition reaction;

the synthesis method of the metal complex specifically comprises the following steps: adding an ammonium salt and a soluble metal salt to a formaldehyde-containing solution; or introducing formaldehyde-containing gas into a mixed solution of ammonium salt and soluble metal salt; stirring for reaction, crystallizing and purifying to obtain a metal complex;

the ammonium salt is selected from one or more of ammonium nitrate, ammonium chloride, ammonium bromide, ammonium iodide, ammonium fluoride, ammonium phosphate, ammonium hydrogen phosphate, ammonium dihydrogen phosphate and ammonium acetate;

the soluble metal salt is one of zinc bromide, calcium chloride and zinc chloride;

the molar ratio of the ammonium salt to the soluble metal salt is 4-20: 1;

the metal complex is one of zinc bromide hexamethylenetetramine metal complex, calcium chloride hexamethylenetetramine metal complex and zinc chloride hexamethylenetetramine metal complex.

2. Use of a metal complex according to claim 1, characterized in that: in the formaldehyde-containing solution, the concentration of formaldehyde is 0.1-10 g/L, and the molar ratio of ammonium salt to formaldehyde is 1-10: 1.

3. use of a metal complex according to claim 1, characterized in that: in the formaldehyde-containing gas, the concentration of formaldehyde is 5-100 mg/L, and the molar ratio of ammonium salt to formaldehyde is 1-10: 1.

4. use of a metal complex according to claim 1, characterized in that: the stirring reaction time is 10 min-6 h.

5. Use of a metal complex according to claim 1, characterized in that: the epoxide is one or more of ethylene oxide, epichlorohydrin, propylene oxide, butylene oxide, cyclohexene oxide, cyclopentene oxide and styrene oxide.

6. Use of a metal complex according to claim 5, wherein: the molar ratio of the metal complex to the epoxide is 0.005-0.05: 1.