Method for simultaneously removing formaldehyde and synthesizing metal complex and application thereof
Technical Field
The invention belongs to the field of environmental protection, and particularly relates to a method for simultaneously removing formaldehyde and synthesizing a metal complex and application of the method in CO2Application in cycloaddition reactions.
Background
The formaldehyde treatment method mainly comprises an oxidation method, a biological treatment method, a blow-off method, a condensation method, a lime method and the like. Among them, a technique of capturing formaldehyde and then converting it into a resin [ CN201710494960.1], a methylal [ CN200910032554.9], or a urea-formaldehyde resin adhesive [ CN201210037079.6] by condensation has been receiving attention. However, no data report is available at present for the resource utilization of formaldehyde as a catalyst for catalyzing organic reactions.
In 5 months 2020, scientists monitored atmospheric CO2The concentration exceeds 417ppm, and the innovation of the product is high. By CO in industrial waste gas2The cyclic carbonate synthesized by cycloaddition reaction with epoxide has high added value, changes waste into valuable, and has important significance for relieving greenhouse effect from the aspect of replacing the original carbonate synthesis process. In addition, the process has the advantages of high atom utilization rate, few byproducts and the like, and conforms to the principle of green chemistry. At present, quaternary ammonium salt, metal salt and the like are mainly used for preparing cyclic carbonate in industry, the reaction conditions are harsh (high temperature and high pressure are needed), and the energy consumption is increased to cause indirect emission of more CO2。
After the metal salt reacts with the organic ligand to form the metal complex, the activity is improved, but the application of the catalyst in the cyclic carbonate process is limited by the complicated preparation process, high price, unsatisfactory stability and the like of the metal complex or the organic ligand.
Disclosure of Invention
In order to solve the problems in the prior art, the invention aims to provide a method for simultaneously removing formaldehyde and synthesizing a metal complex and application thereof2And (3) performing cycloaddition reaction.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for removing formaldehyde and synthesizing metal complex at the same time, add ammonium salt and soluble metal salt into 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.
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 nitrate, chloride, bromide, iodide, fluoride, phosphate, hydrogen phosphate and dihydrogen phosphate of Zn, Fe, Ca or Mg.
Preferably, the molar ratio of the ammonium salt to the soluble metal salt is 4-20: 1.
preferably, 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.
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 stirring reaction time is 10 min-6 h.
The invention also provides the application of the metal complex, which is used for catalyzing epoxide and CO2Cycloaddition reaction 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.
with zinc bromide hexamethylenetetramine metal complex (ZnBr)22Hatm), formula (1) is the reaction process of formaldehyde removal and metal complex synthesis of the present invention:
ZnBr2+8NH4Br+12HCHO=ZnBr2·2Hatm+8HBr+12H2O (1)
as is clear from the formula (1), the metal salt (ZnBr)2) Introduction of formaldehyde with ammonium salt (NH)4Br) is converted into more stable metal complex (ZnBr) in time2And 2Hatm), not only can improve the removal rate of formaldehyde, but also can avoid secondary pollution caused by the decomposition of hexamethylenetetramine into formaldehyde.
Compared with the prior art, the invention has the technical effects that:
(1) the method is suitable for treating the formaldehyde wastewater and the formaldehyde waste gas, and has the advantages of simple method for removing the formaldehyde, mild conditions, low cost, high efficiency and high speed.
(2) The invention adopts a coupling strategy to remove formaldehyde and simultaneously recycle to obtain high-efficiency CO2The cycloaddition catalyst saves resources and avoids secondary pollution of formaldehyde.
(3) The hexamethylene tetramine metal complex prepared by the invention is rich in basic sites (4 mol of tertiary amine is contained in 1mol of molecule), has a cage-shaped structure, is stable to water, and can catalyze CO with high selectivity and high yield under mild conditions2And epoxide cycloaddition reaction to synthesize the cyclic carbonate.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to specific embodiments below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
323g (3.3mol) of ammonium bromide and 1.12g (0.825mol) of zinc bromide are respectively added into 10L of water with 10g/L of formaldehyde concentration (3.3mmol), the mixture is stirred for 6 hours, the formaldehyde concentration is reduced to 1.4mg/L, then evaporation crystallization is carried out, crude products are obtained by suction filtration, and after washing by ethanol, 95 wt.% of ethanol is added for recrystallization, thus obtaining zinc bromide hexamethylenetetramine metal complex-1.
Example 2
177g (3.3mol) of ammonium chloride and 61g (0.55mol) of calcium chloride are respectively added into 100L of water with 0.5g/L of formaldehyde (1.65mol), the mixture is stirred for 10min, the concentration of the formaldehyde is reduced to 0.8mg/L, then evaporation crystallization is carried out, suction filtration is carried out to obtain a crude product, the crude product is washed by ethanol, and 95 wt.% of ethanol is added for recrystallization to obtain the calcium chloride hexamethylenetetramine metal complex.
Example 3
Respectively adding 32.3g (0.33mol) of ammonium bromide and 2.72g (20mmol) of zinc bromide into 1L of water for dissolving, introducing 30L (the gas flow rate is 100mL/min) of 100mg/L formaldehyde gas under stirring, reducing the formaldehyde concentration in the gas to 0.8mg/L, stirring for 6 hours, then obtaining the solution with the formaldehyde concentration of 0.6mg/L, evaporating for crystallization, carrying out suction filtration to obtain a crude product, washing with ethanol, adding 95 wt.% ethanol for recrystallization to obtain the zinc bromide hexamethylenetetramine metal complex-2.
Example 4
Respectively taking 17.7g (0.33mol) of ammonium chloride and 1.36g (10mmol) of zinc chloride, adding the ammonium chloride and the zinc chloride into 100mL of water for dissolving, introducing 50L (gas flow rate is 100mL/min) of 5mg/L of formaldehyde gas under stirring, reducing the formaldehyde concentration in the gas to 0.4mg/L, stirring for 2 hours, then, obtaining a crude product by evaporation crystallization and suction filtration, washing by using ethanol, and adding 95 wt.% of ethanol for recrystallization to obtain the zinc chloride hexamethylenetetramine metal complex.
Comparative example 1
177g (3.3mol) of ammonium chloride was added to 100L of water having a formaldehyde (1.65mol) concentration of 0.5g/L, and the mixture was stirred for 10 minutes to reduce the formaldehyde concentration to 0.1 g/L.
Comparative example 2
17.7g (0.33mol) of ammonium chloride was dissolved in 100mL of water, and 50L of 5mg/L formaldehyde gas was introduced with stirring (gas flow rate: 100mL/min), whereby the formaldehyde concentration in the gas was reduced to 3.2 mg/L.
Application example 1
At room temperature, sequentially adding 10.6 mmol of zinc bromide hexamethylenetetramine metal complex prepared in example 1, 0.15g of internal standard substance biphenyl and 30mmol of epoxy chloropropane into a 30mL high-pressure reaction kettle, and introducing 2MPa CO under stirring at room temperature2Then putting the reaction kettle into an oil bath reactor with magnetic stirring to react for 5 hours at the temperature of 80 ℃, and after the reaction is finished, putting the reaction kettle into a cold stateCooling in water and subsequent release of CO2Taking out the reactant, centrifuging, taking the supernatant for GC analysis: the yield of cyclic carbonate was 92.8% with a selectivity of 99.8%.
Application example 2
At room temperature, 0.3mmol of calcium chloride hexamethylenetetramine metal complex prepared in example 2, 0.15g of internal standard substance biphenyl and 30mmol of propylene oxide are sequentially added into a 30mL high-pressure reaction kettle, and 1.5MPa of CO is introduced into the kettle under the condition of room temperature stirring2Then putting the reaction kettle into an oil bath reactor with magnetic stirring to react for 10 hours at 80 ℃, putting the reaction kettle into cold water to cool after the reaction is finished, and then releasing CO2Taking out the reactant, centrifuging, taking the supernatant for GC analysis: the yield of propylene carbonate was 96.3% with a selectivity of 99.7%.
Application example 3
At room temperature, the zinc bromide hexamethylenetetramine metal complex-21.5 mmol prepared in the example 3, 0.15g of internal standard substance biphenyl and 30mmol of propylene oxide are added in turn into a 10mL reaction tube, and the reaction tube and 1L of CO are added2Connecting the air bags, placing the reaction tube into an oil bath reactor with magnetic stirring to react for 24h at 30 ℃, and releasing CO after the reaction is finished2Taking out the reactant, centrifuging, taking the supernatant for GC analysis: the yield of propylene carbonate was 82.5% with a selectivity of 99.8%.
Application example 4
0.3mmol of zinc chloride hexamethylenetetramine metal complex prepared in example 4, 0.15g of internal standard substance biphenyl and 30mmol of propylene oxide are sequentially added into a 30mL high-pressure reaction kettle at room temperature, and 2MPa CO is introduced into the kettle under the condition of room temperature stirring2Then putting the reaction kettle into an oil bath reactor with magnetic stirring to react for 12 hours at the temperature of 80 ℃, putting the reaction kettle into cold water to cool after the reaction is finished, and then releasing CO2Taking out the reactant, centrifuging, taking the supernatant for GC analysis: the yield of propylene carbonate was 78.4% with a selectivity of 99.8%.
Application comparative example 1
At room temperature, 0.3mmol of zinc chloride, 0.15g of internal standard substance biphenyl and 30mmol of propylene oxide are sequentially added into a 30mL high-pressure reaction kettle,introducing 2MPa CO under stirring at room temperature2Then putting the reaction kettle into an oil bath reactor with magnetic stirring to react for 12 hours at the temperature of 80 ℃, putting the reaction kettle into cold water to cool after the reaction is finished, and then releasing CO2Taking out the reactant, centrifuging, taking the supernatant for GC analysis: the yield of propylene carbonate was 32.1% with a selectivity of 99.8%.
Comparative application example 2
At room temperature, sequentially adding 0.3mmol of hexamethylenetetramine, 0.15g of internal standard substance biphenyl and 30mmol of propylene oxide into a 30mL high-pressure reaction kettle, and introducing 2MPa CO under the stirring at room temperature2Then putting the reaction kettle into an oil bath reactor with magnetic stirring to react for 12 hours at the temperature of 80 ℃, putting the reaction kettle into cold water to cool after the reaction is finished, and then releasing CO2Taking out the reactant, centrifuging, taking the supernatant for GC analysis: the yield of propylene carbonate was 1.2% with a selectivity of 92.8%.