A method for producing dimethyl carbonate

Abstract

The application discloses a preparation method of dimethyl carbonate. The method comprises the following steps: adding an activated catalyst, methanol and a dehydrating agent into a closed container, filling carbon dioxide, and reacting to obtain dimethyl carbonate; the stoichiometric composition of the catalyst is Fe a Ce 1‑a O x , wherein 0.01<=a<=0.45, and the grain size of the catalyst is 5-50 nm. The nanometer powder oxide catalyst is prepared by a sol-gel self-propagating combustion method, has the characteristics of high product purity, uniform dispersion, less particle agglomeration and high activity site exposure degree, and combines the dehydration pulling effect of the original reaction system caused by the introduction of the dehydrating agent, so that the carbon dioxide and the methanol are catalyzed to react to prepare the dimethyl carbonate. On the premise of getting rid of the kinetic lag and the thermodynamic limitation of the reaction, the synthesis of the dimethyl carbonate is greatly promoted, and excellent catalytic performance is shown.

Description

TECHNICAL FIELD

[0001] The application relates to a dimethyl carbonate preparation method and belongs to the technical field of dimethyl carbonate preparation. BACKGROUND

[0002] The massive consumption of fossil resources leads to a sharp increase in the emission of greenhouse gases dominated by carbon dioxide (CO2), and the excessively high concentration of carbon dioxide in the atmosphere causes a series of severe ecological and environmental problems, such as global warming, sea level rise and ocean acidification. At the same time, as a non-toxic, abundant and inexpensive renewable carbon source, carbon dioxide can also be used as a raw material to synthesize various chemicals and fuels, achieving the purpose of emission reduction while realizing the effective circulation of global carbon resources.

[0003] Dimethyl carbonate (DMC) is an environmentally friendly green organic chemical intermediate with the characteristics of non-toxicity, non-corrosion and biodegradability. The existence of various active functional groups in the molecular structure makes it possible to be used as a methylating agent and a carbonylating agent to replace traditional corrosive and toxic phosgene and dimethyl sulfate, and it can also be used as a raw material to synthesize polycarbonate, isocyanate and other chemical products. In addition, DMC has a higher oxygen content and an ideal octane rating, and is expected to replace methyl tert-butyl ether as a new environmentally friendly fuel additive to improve combustion efficiency and reduce pollutant emissions.

[0004] Among the many synthesis processes of DMC, the direct synthesis of dimethyl carbonate from carbon dioxide and methanol through non-reduction conversion is a new green synthesis path of DMC that has attracted much attention in recent years. Considering the environmentally friendly nature of the reaction, the wide source and low cost of raw materials, the high atom utilization rate and the only by-product water, this synthesis path is attracting more and more attention.

[0005] However, due to the high thermodynamic stability of the CO2 molecule, the kinetic inertness of the substrate and the severe thermodynamic equilibrium limitation of the reaction itself The low yield of DMC limits its industrial application. The presence of by-product water in the known reaction system is the key factor that makes it difficult to improve the yield of DMC. The presence of water not only induces the reverse hydrolysis of DMC, but more seriously, the hydrogen ion and hydroxyl ion species generated by hydrolysis will be firmly combined on the active sites of the catalyst surface, shielding the catalytic effect of the active sites, resulting in a decrease in the activation rate of the substrate and a low yield of the product. The only method at present is to remove the water generated in the reaction process in time through physical or chemical methods, promote the reaction to proceed in the positive direction, and thus increase the methanol conversion rate and the DMC yield. SUMMARY

[0006] In view of the problems existing in the prior art, this application provides a method for preparing dimethyl carbonate, which uses nano-powder oxide prepared by sol-gel-self-propagating combustion as a catalyst, and combines the dehydration pull effect of the original reaction system after the introduction of a dehydrating agent. On the basis of overcoming the problems of reaction kinetic stagnation and thermodynamic limitation, the synthesis of dimethyl carbonate is greatly promoted.

[0007] According to one aspect of this application, a method for preparing dimethyl carbonate is provided, wherein an activated catalyst, methanol, and a dehydrating agent are added to a sealed container, carbon dioxide is introduced, and the reaction is carried out to obtain dimethyl carbonate.

[0008] The stoichiometric composition of the catalyst is Fe a Ce 1-a O x Where 0.01≤a≤0.45, and the crystal size of the catalyst is 5~50nm.

[0009] The dehydrating agent is selected from at least one of nitrile compounds, ketal compounds, orthoester compounds, and trimethyl phosphate and dicyclohexylcarbodiimide. Optionally, the nitrile compound is selected from at least one of acetonitrile, benzonitrile, 2-cyanopyrimidine, 2-cyanopyrazine, and 2-cyanopiperazine.

[0010] Optionally, the ketal compound is selected from at least one of dimethoxymethane, 2,2-dimethoxypropane, and 2,2-diethoxypropane.

[0011] Optionally, the orthoester compound is selected from at least one of trimethyl orthoformate and triethyl orthoformate.

[0012] Optionally, the mass ratio of the catalyst to methanol and the dehydrating agent is 1:20-30:16-82.

[0013] Optionally, the mass ratio of the catalyst to methanol and the dehydrating agent is any ratio within the corresponding threshold range.

[0014] Optionally, the pressure of the sealed container after being filled with carbon dioxide is 1 to 5 MPa.

[0015] Optionally, the pressure of the sealed container after being filled with carbon dioxide is any value among 1MPa, 2MPa, 3MPa, 4MPa, and 5MPa, or a range between two values.

[0016] Optionally, the activation conditions for the catalyst are: under an inactive atmosphere, the activation temperature is 300–600°C, and the activation time is 1–5 h.

[0017] Optionally, the inactive atmosphere is selected from at least one of nitrogen, argon, and helium.

[0018] Optionally, the activation temperature is selected from any value of 300℃, 400℃, 500℃, 600℃ or a range between two values.

[0019] Optionally, the activation time is selected from any value of 1h, 3h, 5h or a range between two values.

[0020] Optionally, the reaction temperature is 80–160°C, the reaction pressure is 2–10 MPa, and the reaction time is 0.5–24 h.

[0021] Optionally, the temperature of the reaction is any value among 80°C, 120°C, and 160°C, or a range between two values.

[0022] Optionally, the reaction time is any value among 0.5h, 8h, 16h, and 24h, or a range between two values.

[0023] Optionally, the method for preparing the catalyst includes the following steps:

[0024] A) A soluble salt solution containing iron and cerium is mixed with an organic complexing agent, the pH is adjusted, reaction I is carried out, water is removed and the solution is concentrated and dried to obtain a honeycomb-like dry gel solid.

[0025] B) Grind the honeycomb-shaped dry gel solid, heat it, and initiate self-propagating combustion to obtain a powder oxide precursor;

[0026] C) The powder oxide precursor is heat-treated to obtain a nano-powder oxide catalyst.

[0027] Optionally, the soluble salt solution containing iron and cerium contains at least one of iron and cerium nitrates, sulfates, acetates, and chlorides.

[0028] Optionally, the molar ratio of iron ions to cerium ions in the soluble salt solution containing iron and cerium is a:1-a, where 0.01≤a≤0.45.

[0029] Optionally, the concentration of the iron and cerium-containing soluble salt solution is 0.2–1.0 mol / L, calculated as the molar concentrations of iron and cerium ions.

[0030] Optionally, the organic complexing agent is selected from at least one of urea, glucose, glycine, and citric acid.

[0031] Optionally, the concentration of the organic complexing agent is 0.1–2.0 mol / L.

[0032] Optionally, the molar ratio of the iron and cerium-containing soluble salt solution to the organic complexing agent is 0.5 to 2:1, and the iron and cerium-containing soluble salt solution is expressed in terms of the molar amounts of iron ions and cerium ions.

[0033] Optionally, the molar ratio of the iron and cerium-containing soluble salt solution to the organic complexing agent is any value among 0.5:1, 1:1, 1.5:1, 2:1, or a range between two values.

[0034] Optionally, the pH range is 1 to 8.

[0035] Optionally, the temperature of reaction I is 30–60°C, and the reaction time is 0.5–2 h.

[0036] Optionally, the temperature for water removal and concentration is 80–100°C, and the time for water removal and concentration is 4–8 hours.

[0037] Optionally, the drying temperature is 100–150°C, and the drying time is 12–24 hours.

[0038] Optionally, the heating temperature is 250–350°C, and the heating time is 10–30 minutes.

[0039] Optionally, the heat treatment temperature is 400–800°C, and the heat treatment time is 3–6 hours.

[0040] As one specific embodiment of this application, the specific method for preparing the catalyst is as follows:

[0041] (1) Dissolve soluble salts containing metal elements Fe and Ce in deionized water according to stoichiometric ratio to obtain solution A. Dissolve organic complexing agent in deionized water to obtain ligand solution B. Add ligand solution B dropwise to mixed metal salt solution A under stirring at room temperature. Adjust the pH value with ammonia water to obtain mixed solution C. Place mixed solution C in a constant temperature water bath for heating and heat preservation to form a uniform sol. Further stir, evaporate, remove water and concentrate the obtained sol to obtain a transparent viscous gel. Place the obtained gel in a drying oven for complete drying to obtain a honeycomb-shaped dry gel solid.

[0042] (2) The honeycomb-shaped dry gel solid is crushed and ground, heated and ignited to initiate self-propagating combustion, and a fluffy and porous powder oxide precursor is obtained.

[0043] (3) The powder oxide precursor is further heat-treated in a tube furnace to obtain a nano powder oxide catalyst.

[0044] The beneficial effects that this application can produce include:

[0045] 1) The method for preparing dimethyl carbonate provided in this application uses a fine-particle nano-polymetallic oxide catalyst, which exhibits excellent catalytic performance during the catalytic process. Under the pull of the dehydration coupling effect of the dehydrating agent, the influence of water on the yield of dimethyl carbonate is reduced, and the methanol conversion rate and the yield of dimethyl carbonate are significantly improved, which has potential practical application value and prospects.

[0046] 2) The catalyst preparation method provided in this application uses a sol-gel-self-propagating combustion method to prepare nano-multimetallic powder oxides, which has the characteristics of high product purity, uniform dispersion, low particle agglomeration and high degree of active site exposure. It exhibits excellent catalytic performance when applied to the direct synthesis of dimethyl carbonate from carbon dioxide and methanol.

[0047] 3) The catalyst preparation method provided in this application is simple and efficient, the raw materials are cheap and readily available, the synthesis cycle is short and the energy consumption is low, and the synthesis of different batches of catalysts has good repeatability. Attached Figure Description

[0048] Figure 1 Transmission electron microscope images of the nanopowder oxide catalysts prepared in Examples 1-5 under a 50 nm scale.

[0049] Figure 2 High-resolution transmission electron microscope images of the nanopowder oxide catalysts prepared in Examples 1-5 under a 10 nm scale. Detailed Implementation

[0050] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0051] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0052] The analysis methods and calculations of conversion rate and selectivity in the examples are as follows:

[0053] Qualitative and quantitative analysis of the products was performed offline using an Agilent 7890A gas chromatograph, with separation using Agilent HP-PLOT Q and CP-WAX capillary columns, and detection and analysis using a flame ionization detector (FID).

[0054] Methanol conversion rate = (Total methanol mass - Remaining methanol mass) / Total methanol mass * 100%

[0055] DMC selectivity = (number of moles of DMC * 2) / number of moles of methanol converted * 100%.

[0056] Example 1

[0057] Preparation of nanopowder oxide catalysts

[0058] (1) Weigh 0.29 g of ferric nitrate nonahydrate and 10.11 g of cerium nitrate hexahydrate in a molar ratio of n(Fe):n(Ce) = 0.03:0.97 and dissolve them completely in 50.0 mL of deionized water to obtain a mixed metal salt solution A with a total metal ion concentration of 0.48 mol / L. Weigh 2.52 g of citric acid in a molar ratio of organic complexing agent to metal ions of n(organic complexing agent):n(Fe+Ce) = 0.5:1 and dissolve it completely in 50.0 mL of deionized water to obtain... A ligand solution B with a concentration of 0.24 mol / L was prepared. The ligand solution B was added dropwise to the mixed metal salt solution A under stirring at room temperature. The pH of the solution was adjusted to 6 using ammonia water (25 wt%) to obtain a mixed solution C. Solution C was heated in a constant temperature water bath at 50℃ for 2 hours to form a homogeneous sol. The obtained sol was further stirred and evaporated at 80℃, and the water was removed and concentrated to obtain a transparent viscous gel. The obtained gel was placed in a drying oven at 120℃ for 12 hours to obtain a honeycomb-shaped dry gel solid.

[0059] (2) After crushing and grinding the obtained dry gel solid, it was heated and ignited at 280°C, and the loose and porous powder oxide precursor was collected.

[0060] (3) The obtained powdered oxide precursor was placed in a tube furnace and further heat-treated at 550°C for 6 hours. The resulting catalyst was denoted as Fe. 0.03 Ce 0.97 O x -CA.

[0061] Examples 2-20

[0062] Preparation of nanopowder oxide catalysts

[0063] Following the synthesis conditions and operating steps of Example 1, a series of nanoparticle oxide catalysts were prepared by varying the amount of metal salt precursor, the type and amount of organic complexing agent, the pH value of the mixed solution system, and the heat treatment conditions. The catalyst preparation conditions are shown in Table 1.

[0064] Table 1 Catalyst Preparation Conditions

[0065]

[0066]

[0067] Examples 21-57

[0068] Synthesis of dimethyl carbonate

[0069] Dimethyl carbonate was synthesized using a 100 mL high-pressure reactor: 1.0 g each of the catalysts prepared in Examples 1 and 2-20 were activated at 400 °C for 4 h in a helium atmosphere. This activated catalyst was then mixed with 25 g of methanol and 400 mmol of dehydrating agent and added to the high-pressure reactor, which was then sealed. The reactor was purged with nitrogen three times. After the air was completely removed, high-pressure CO2 gas was introduced to the set pressure, and the heating and stirring switches were turned on. The reaction time was recorded when the reactor reached the reaction temperature. After a certain reaction time, the reaction was stopped, the reactor was removed, and rapidly cooled in an ice-water bath. After cooling, the pressure was slowly released and the reactor was opened. The liquid phase product was quantitatively analyzed using the internal standard method on an Agilent 7890A gas chromatograph equipped with a flame ionization detector (FID) and a CP-WAX capillary column. The catalyst performance evaluation results are shown in Table 2.

[0070] Example 58

[0071] Synthesis of dimethyl carbonate

[0072] The catalyst obtained from the reaction evaluation and separation recovery in Example 49 is denoted as Fe. 0.15 Ce 0.85 O x -CA-R1, Fe is prepared in the same manner as in Example 49. 0.15 Ce 0.85 O x -CA-R1 was used in the synthesis of dimethyl carbonate, and the results are shown in Table 2.

[0073] Example 59

[0074] Synthesis of dimethyl carbonate

[0075] The catalyst obtained from the reaction evaluation and separation recovery in Example 58 is denoted as Fe. 0.15 Ce 0.85 O x -CA-R2, Fe is prepared in the same manner as in Example 58. 0.15 Ce 0.85 O x -CA-R2 was used in the synthesis of dimethyl carbonate, and the results are shown in Table 2.

[0076] Comparative Example 1

[0077] Synthesis of dimethyl carbonate

[0078] The synthesis process of dimethyl carbonate was the same as in Example 23, except that the activated catalyst was only mixed with methanol and added to the autoclave and sealed, without the addition of a dehydrating agent. The results are shown in Table 2.

[0079] Table 2 Comparison of Catalytic Performance of Catalysts

[0080]

[0081]

[0082] The catalyst particles prepared in the embodiments of the present invention are small and uniformly distributed, with an average particle size between 13-18 nm, which is a nanocatalyst material with good dispersibility.

[0083] Furthermore, the high-performance nanopowder oxide catalyst prepared in the embodiments of the present invention, under the action of a suitable dehydrating agent, achieves rapid removal of by-product water in the original system through a coupled reaction, solving the problems of kinetic lag and thermodynamic limitation in the direct synthesis of dimethyl carbonate from methanol and carbon dioxide, and significantly improving catalyst activity and DMC yield.

[0084] Comparing the results of Examples 49 with those of 58 and 59, the catalyst prepared by this invention exhibits excellent stability. Even after multiple cycles of use, the catalyst activity and DMC yield do not show a significant decrease, demonstrating broad application prospects in practical industrial production.

[0085] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for producing dimethyl carbonate, characterized by, The activated catalyst, methanol and a dehydrating agent are put into a closed container, carbon dioxide is filled in, and reaction is carried out to obtain dimethyl carbonate; The stoichiometric composition of the catalyst is Fe a Ce 1-a O x wherein 0.01≤a≤0.45, and the grain size of the catalyst is 5-50 nm; The dehydrating agent is at least one selected from 2-cyanopyrimidine and 2-cyanopyrazine; The preparation method of the catalyst comprises the following steps: A) mixing a soluble salt solution containing iron and cerium with an organic complexing agent, adjusting pH, carrying out reaction I, concentrating by water removal, drying to obtain a honeycomb-shaped xerogel solid; the molar ratio of iron ions to cerium ions in the soluble salt solution containing iron and cerium is a:1-a, wherein 0.01≤a≤0.45; the molar ratio of the soluble salt solution containing iron and cerium to the organic complexing agent is 0.5-2:1, and the soluble salt solution containing iron and cerium is in terms of iron ions and cerium ions in moles; B) grinding the honeycomb-shaped xerogel solid, heating, and initiating self-sustaining combustion to obtain a powder oxide precursor; C) heat treating the powder oxide precursor to obtain a nanopowder oxide catalyst; The organic complexing agent is at least one selected from urea, glucose, glycine and citric acid; The pH ranges from 1 to 8.

2. The preparation method according to claim 1, wherein, The mass ratio of the catalyst to methanol and the dehydrating agent is 1:20-30:16-82; The pressure of the closed container after the carbon dioxide is filled in is 1-5 MPa.

3. The preparation method according to claim 1, characterized in that, The activation conditions of the catalyst are that the activation temperature is 300-600°C under a non-active atmosphere, and the activation time is 1-5 h; The non-active atmosphere is at least one selected from nitrogen, argon and helium.

4. The preparation method according to claim 1, characterized in that, The reaction temperature is 80-160°C, the reaction pressure is 2-10 MPa, and the reaction time is 0.5-24 h.

5. The preparation method according to claim 1, characterized in that, The soluble salt solution containing iron and cerium contains at least one of nitrate, sulfate, acetate and chloride of iron and cerium.

6. The preparation method according to claim 1, characterized in that, The concentration of the soluble salt solution containing iron and cerium is 0.2-1.0 mol / L in terms of iron ions and cerium ions in moles.

7. The preparation method according to claim 1, characterized in that, The reaction I temperature is 30-60°C, and the reaction I time is 0.5-2 h.

8. The method of claim 1, wherein, The water removal and concentration temperature is 80-100°C, and the water removal and concentration time is 4-8 h.

9. The method of claim 1, wherein, The drying temperature is 100-150°C, and the drying time is 12-24 h.

10. The method of claim 1, wherein, The heating temperature is 250-350°C, and the heating time is 10-30 min.

11. The method of claim 1, wherein, The heat treatment temperature is 400-800°C, and the heat treatment time is 3-6 h.

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