CN113563189A - One-step method for efficiently catalyzing CO2Method for converting dimethyl carbonate catalyst - Google Patents
One-step method for efficiently catalyzing CO2Method for converting dimethyl carbonate catalyst Download PDFInfo
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Abstract
One-step method for efficiently catalyzing CO2A method for converting dimethyl carbonate catalyst relates to a method for preparing catalyst, and the method synthesizes ionic liquid 1-ethyl-3-methylimidazolium imidazolium salt ([ Emim ] with high thermal stability and strong basicity and new structure]IM), base strength 18.4<H‑<22.3, corresponding to sodium tert-butoxide, 2.83 mmol/g of alkali and the decomposition temperature higher than 144 ℃. The catalyst realizes PO and CO2Dimethyl carbonate (DMC) was synthesized in one step in high yield (36.27%) with MeOH starting material and a TON of 37.04. A new process route for synthesizing DMC by a two-stage interlocking method without catalyst separation is developed: first of all, PO and CO2Performing cycloaddition reaction97.40% PO conversion and nearly 97.40% PC yield are achieved under mild conditions with a TON value of 99.49; then MeOH was introduced and the transesterification was carried out, [ Emim]The IM synthesis process is simple and environment-friendly, has strong basicity, high thermal stability and excellent catalytic activity, and has important industrial application value in the field of carbonate synthesis.
Description
Technical Field
The invention relates to a method for preparing a catalyst, in particular to a method for preparing a catalystOne-step method for efficiently catalyzing CO2A process for the conversion of a dimethyl carbonate catalyst.
Belongs to the field of chemistry and chemical engineering, and carbonate synthesis industry. In particular to catalyzing CO2A synthesis method of novel high-efficiency strong-basicity ionic liquid for efficiently converting into dimethyl carbonate by one step and a two-section fixed bed series reaction process based on the catalyst.
Background
CO in atmosphere caused by transitional consumption of fossil energy2、CH4When the content of greenhouse gases exceeds the standard, the global warming, extreme weather and sea level are continuously increased, and the living environment of human beings is continuously deteriorated. From the aspects of carbon neutralization and environmental protection, the energy end product CO is used2As a nontoxic, cheap and renewable carbon resource, the conversion of low energy consumption into valuable chemicals has important academic value and application prospect, and is the optimal strategy for human sustainable development.
By using CO2And the coal chemical industry platform compound methanol (MeOH) directly or indirectly synthesized dimethyl carbonate (DMC) is of great interest. DMC has slight fragrance, and is a non-toxic, easily biodegradable and environmentally friendly bulk chemical. The molecular oxygen atom number is more than 53%, and the molecular oxygen atom number contains abundant functional groups, and can perform various chemical reactions. The DMC has wide application, and can be used as a monomer for synthesizing five engineering plastics, namely polycarbonate, a pesticide and a medical intermediate, a green solvent, a lithium ion battery solvent and the like. The additive can also be added into gasoline, so that the octane number of the gasoline is improved, the shock resistance is enhanced, and the emission of PM2.5 and NOx is obviously reduced.
DMC synthesis methods include direct synthesis, urea alcoholysis, direct/indirect oxidative carbonylation of methanol, and transesterification. Wherein CO is2The direct synthesis of DMC with MeOH is simple, intrinsically safe, but is thermodynamically limited (. DELTA.. theta. = -27.9 kJ/mol,. DELTA.. theta. = -32.6 kJ/mol), the exothermic reaction does not proceed spontaneously, and CO does not proceed spontaneously2Chemical inertness and failure to remove the water by-product in time cause equilibrium limitation and other factors, resulting in lower DMC yield. The urea alcoholysis route has cheap and easily-obtained raw materials and benefits from the scale effect of synthetic ammoniaThe production cost is relatively low. However, the intermediate methyl carbamate is easy to decompose into byproducts such as isocyanic acid and the like, so that reaction equipment is blocked, the continuous operation stability of the device in the demonstration process is poor, and the DMC yield is low. The raw materials of the CO gas phase/liquid phase oxidation carbonylation method are cheap and easy to obtain, DMC and water are mainly generated, and the by-products are few. The indirect oxidative carbonylation process is the carbonylation of MeOH to DMC via the intermediate methyl nitrite. The raw material cost is low, the process is simple, and the DMC yield is high; but the Cl-containing catalyst and NOx are adopted as the oxidant for circulation, so that a large amount of acid-containing wastewater is generated, and byproducts of various oxygen-containing compounds such as dimethyl oxalate, methyl formate and the like exist. Direct oxidative carbonylation of methanol process O2The method has the advantages of direct participation, more byproducts and potential safety hazard. With Propylene Oxide (PO) or Ethylene Oxide (EO) as the starting material and CO2After cycloaddition, Propylene Carbonate (PC) and Ethylene Carbonate (EC) are obtained, DMC is obtained through ester exchange of MeOH, and 1, 2-propylene glycol or ethylene glycol as a byproduct is obtained. Compared with other DMC synthesis routes, the ester exchange method is a more environment-friendly and more efficient synthesis way and is a domestic main DMC industrial production method.
Wen et al first studied KHCO3High temperature (140 ℃) and high pressure (CO) as catalysts2Pressure 12 MPa) PO and CO2And MeOH as a starting material to synthesize DMC in one step. After 6 h of reaction, the PO conversion reached 96.87%, but the DMC yield was only 16.84%. Chun et al react for 6 h at 120 ℃ and 2.5 MPa with choline chloride/MgO as a catalyst, the DMC yield reaches 65.4%, and the DMC yield is reduced to 12.58% after 4 times of repeated use. Chen et al use 1-butyl-3-methylimidazolium tetrafluoroborate and sodium methoxide composite catalyst to realize PO conversion rate up to 95% and DMC yield up to 67.5% at 150 ℃. However, the ionic liquid is incompatible with sodium methoxide powder, cannot be separated from the reaction system, and is difficult to reuse. Tia, etc. adopts tetrabutyl ammonium bromide and tertiary amine composite catalyst, and at high temperature of 150 deg.C and higher CO2The initial pressure is 15 MPa, the PO conversion rate reaches 98 percent, and the DMC yield reaches 84 percent. In summary, the DMC synthesized by one-step method using PO as reaction raw material has over-high reaction temperatureHigher CO2The initial pressure is that the composite catalyst of quaternary ammonium salt or halogen and over two components of strong alkali salt is used, so that the catalyst is difficult to reuse.
Disclosure of Invention
The invention aims to provide a one-step method for efficiently catalyzing CO2The invention provides a method for one-step efficient conversion of CO2 into dimethyl carbonate by using a strong-base ionic liquid with a single component, a novel structure, high temperature resistance and high stability to catalyze, and provides a novel process for one-step synthesis of dimethyl carbonate by using a two-end fixed bed without separation of a catalyst based on a developed homogeneous ionic liquid catalyst.
The purpose of the invention is realized by the following technical scheme:
one-step method for efficiently catalyzing CO2A process for converting a dimethyl carbonate catalyst, the process comprising the steps of:
propylene oxide, CO2And the dimethyl carbonate is obtained with high yield by taking methanol as a raw material to react with a homogeneous phase ionic liquid catalyst.
The catalyst needs no separation and has two-stage chain reaction process, the first stage is fixed bed reactor, the catalyst first catalyzes propylene oxide and CO2Synthesizing propylene carbonate; then, the catalyst is mixed with methanol without separation and enters a second-stage reaction-rectification tower after being cooled, dimethyl carbonate-methanol azeotrope is extracted from the tower top, and 1, 2-propylene glycol is extracted from the tower bottom to realize CO2And propylene oxide to synthesize dimethyl carbonate in one step with high yield;
the catalyst is ionic liquid;
the ionic liquid comprises a cation and an anion;
the anion and the cation both contain a nitrogen-containing heterocycle.
The one-step method is used for efficiently catalyzing CO2The method for converting the dimethyl carbonate catalyst comprises the steps of reacting at 100-130 ℃ for 2-9 h at CO2The initial pressure is 1.8-3.8 MPa, and the amount of the catalyst is 0.5-10% of the PO mass; the reaction temperature in the ester exchange process is 68 ℃;
preferably, the reaction temperature is 120 ℃;
preferably, the reaction time is 9 h;
preferably, the CO is2The initial pressure is 2.6 MPa;
preferably, the amount of the catalyst is 3% of the PO mass;
preferably, the transesterification reaction temperature is 68 ℃;
preferably, the cation has the formula
Or formula
The structure shown;
the anion has the formula
A and B type
Or formula
The structure shown;
wherein R is1Independently selected from one of C1-C6 alkane group, C2-C6 alkene group and C3-C6 aromatic hydrocarbon group;
preferably, the raw material containing the propylene oxide, the carbon dioxide and the methanol has a molar ratio of the propylene oxide to the carbon dioxide to the methanol of 1:1: 10-1: 2.8: 15;
preferably, the molar ratio of the propylene oxide to the carbon dioxide in the raw material containing the propylene oxide and the carbon dioxide is 1: 1-1: 2.8;
preferably, the molar ratio of the propylene carbonate to the methanol in the raw material containing the propylene carbonate and the methanol is 1: 10;
preferably, the reaction time is 2-9 hours;
preferably, the chemical equilibrium is reached within 9h of reaction at 120 ℃;
preferably, the reaction is carried out for 30 min at 68 ℃ to reach chemical equilibrium;
preferably, R1、R2Is independently selected from-CH3、-CH2CH3、-(CH2)2CH3、-(CH2)3CH3One kind of (1).
The one-step method is used for efficiently catalyzing CO2A process for the conversion of a dimethyl carbonate catalyst, said catalyst being an ionic liquid.
The one-step method is used for efficiently catalyzing CO2A process for the conversion of a dimethyl carbonate catalyst, the preparation of said ionic liquid comprising the steps of:
a1) adding alkali into the solution I containing the ionic liquid anion source, and reacting to obtain ionic liquid anion metal salt;
a2) and dissolving the ionic liquid anion metal salt in a solvent, adding an ionic liquid cation salt, and reacting to obtain the ionic liquid.
The one-step method is used for efficiently catalyzing CO2A method for converting a dimethyl carbonate catalyst, wherein in the step a 1), the solvent in the solution I is at least one selected from ethanol, benzene, toluene and xylene;
the alkali is organic alkali or inorganic alkali;
the organic base comprises sodium methoxide, sodium ethoxide, sodium tert-butoxide, potassium methoxide, potassium ethoxide or potassium tert-butoxide;
the inorganic base includes lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide;
the ionic liquid anionic metal salt is selected from at least one of ionic liquid anionic Li salt, anionic Na salt, anionic K salt and ionic liquid anionic Cs salt;
preferably, in the step a 1), the concentration of the ionic liquid anion source in the solution I is 0.05-0.8 g/mL;
the molar ratio of the ionic liquid anion source to the base is 0.9-1.1;
preferably, in step a 1), the ionic liquid anion source comprises imidazole, pyrrole or morpholine;
preferably, in step a 1), the reaction conditions are: reacting for 24 hours in ice bath;
preferably, step a 1) further comprises: after the reaction is finished, removing the solvent to obtain imidazole anion salt, pyrrole anion salt or morpholine anion salt;
preferably, in step a 2), the solvent comprises a water-carrying agent;
the water-carrying agent is selected from at least one of methanol, ethanol, benzene, toluene and xylene;
the ionic liquid cation salt is selected from 1-R1-3-methyl-imidazolium bromide, 1-R1-3-methyl-imidazolium iodide, N-methyl-N-R2Morpholine bromide, N-methyl-N-
R2-at least one morpholine iodonium salt;
preferably, in the step a 2), the ratio of the ionic liquid anionic metal salt to the solvent is 0.1-0.9: 0.05-1.2 g/mL;
preferably, in step a 2), the reaction conditions are: reacting for 24 hours at room temperature;
preferably, step a 2) further comprises: and after the reaction is finished, removing the solvent to obtain the high-purity ionic liquid.
The one-step method is used for efficiently catalyzing CO2A method for converting a dimethyl carbonate catalyst, wherein the method comprises a two-stage chain reaction process without separating the catalyst; in the first stage of fixed bed reactor, the catalyst firstly catalyzes propylene oxide and CO2Synthesizing propylene carbonate; then, the catalyst is mixed with methanol without separation and directly enters a second-stage reaction-rectification tower after being cooled, dimethyl carbonate-methanol azeotrope is extracted from the tower top, and 1, 2-propylene glycol is extracted from the tower bottom to realize CO2And propylene oxide to synthesize the dimethyl carbonate in one step with high yield.
The invention has the advantages and positive effects that:
1. the invention provides a high-efficiency one-step catalytic CO2The catalyst and the process method for converting the ionic liquid into the dimethyl carbonate have the characteristics of high temperature resistance, high stability and strong basicity, and can efficiently catalyze the cycloaddition and the ester exchange reaction.
2. The two-stage chain reaction process without separating the catalyst provided by the invention can obviously shorten the reaction flow and reduce the production energy consumption.
Drawings
FIG. 1(A) is a photograph of potassium imidazolium synthesized in example 1 of the present invention;
FIG. 1(B) is a photograph of [ Emim ] Im ionic liquid synthesized in example 1 of the present invention;
FIG. 2 is nuclear magnetic H spectrum of [ Emim ] Im ionic liquid synthesized in example 1 of the present invention;
FIG. 3 is nuclear magnetic C spectrum of [ Emim ] Im ionic liquid synthesized in example 1 of the present invention;
FIG. 4 is an infrared image of [ Emim ] Im ionic liquid synthesized in example 3 of the present invention;
FIG. 5 is a thermogravimetric-differential thermal map of [ Emim ] Im ionic liquid synthesized in example 4 of the present invention;
FIG. 6 is a schematic diagram of example 5 of the present invention in which CO is catalyzed by a single-component liquid2Synthesizing DMC reaction effect in one step;
FIG. 7 shows the effect of KI, TBAB and [ Emim ] IM on the PO cycloaddition in example 6 of the present invention;
FIG. 8 shows the effect of KI, TBAB and [ Emim ] IM on the carbonate transesterification reaction in example 6 of the present invention;
FIG. 9 is a graph showing the effect of reaction temperature on the cycloaddition reaction of example 7 in accordance with the present invention;
FIG. 10 is a graph showing the effect of reaction time on the cycloaddition reaction of example 8 in accordance with the present invention;
FIG. 11 shows example 9 CO of the present invention2The effect of the initial pressure on the cycloaddition reaction;
FIG. 12 is a graph showing the effect of catalyst content on cycloaddition reaction in example 10 of the present invention;
FIG. 13 is a graph showing the effect of reaction time on DMC yield at different temperatures in example 11 according to the present invention;
FIG. 14 shows the recycling effect of the catalyst of example 12 of the present invention;
FIG. 15 shows the mechanism of the cycloaddition and transesterification reactions presumed in example 13 of the present invention.
Detailed Description
The present invention will be described in detail below with reference to embodiments shown in the drawings, but the present invention is not limited to these embodiments.
Emim synthesized by first stage fixed bed reactor]IM ionic liquid first catalyzes PO and CO2And (3) synthesizing the PC. Then, the catalyst is not separated, mixed with MeOH and cooled, and then enters a second-stage reaction-rectification tower, DMC-MeOH azeotrope is extracted from the tower top, 1, 2-propylene glycol is extracted from the tower bottom, and CO is realized2And PO are not separated to synthesize DMC and coproduce the product 1, 2-propylene glycol in high yield.
Screening out the best reaction conditions of cycloaddition in the first-stage fixed bed reactor: the mass of the catalyst is 3 percent of PO, the reaction temperature is 120 ℃, and CO is2The initial pressure is 2.6 MPa, the reaction is carried out for 9h, the PO conversion rate is up to 97.40%, and the PC selectivity is more than 99%. Then, the reaction product enters a second-stage reaction-rectifying tower for reaction, MeOH with the molar weight 10 times that of theoretically generated PC is added for ester exchange, the DMC yield reaches 83.63% and the selectivity reaches 99% under the condition of the reaction temperature of 68 ℃, and the catalyst achieves the fact of synthesizing DMC under ultrahigh catalysis. The catalyst is repeatedly used for seven times without obvious inactivation. The prepared novel strong alkaline ionic liquid is directly used for replacing potassium iodide, tetrabutylammonium bromide, potassium methoxide, sodium methoxide and conventional imidazole ionic liquid. [ Emim]The IM synthesis process is simple and environment-friendly, has strong basicity, high thermal stability and excellent catalytic activity, and has important industrial application prospect in the field of carbonate synthesis.
The preparation method of the dimethyl carbonate is characterized by comprising the following steps:
propylene oxide, CO2And the dimethyl carbonate is obtained with high yield by taking methanol as a raw material to react with a homogeneous phase ionic liquid catalyst.
The catalyst needs no separation and has two-stage chain reaction process, the first stage is fixed bed reactor, the catalyst first catalyzes propylene oxide and CO2Synthesizing propylene carbonate. Then, hastenThe catalyst is mixed with methanol without separation and cooled, and then enters a second-stage reaction-rectification tower, dimethyl carbonate-methanol azeotrope is extracted from the tower top, and 1, 2-propylene glycol is used in the tower kettle to realize CO2And propylene oxide to synthesize the dimethyl carbonate in one step with high yield.
The catalyst is ionic liquid;
the ionic liquid comprises a cation and an anion;
the anion and the cation both contain a nitrogen-containing heterocycle.
The reaction temperature is 100-130 ℃, the reaction time is 2-9 h, and CO is2The initial pressure is 1.8-3.8 MPa, and the amount of the catalyst is 0.5-10% of the PO mass; the reaction temperature in the ester exchange process is 68 ℃;
preferably, the reaction temperature is 120 ℃;
preferably, the reaction time is 9 h;
preferably, the CO is2The initial pressure is 2.6 MPa;
preferably, the amount of the catalyst is 3% of the PO mass;
preferably, the transesterification reaction temperature is 68 DEG C
Preferably, the cation has the formula
Or formula
The structure shown;
the anion has the formula
A and B type
Or formula
The structure shown;
wherein R is1Independently selected from one of C1-C6 alkane group, C2-C6 alkene group and C3-C6 aromatic hydrocarbon group;
preferably, the raw material containing the propylene oxide, the carbon dioxide and the methanol has a molar ratio of the propylene oxide to the carbon dioxide to the methanol of 1:1: 10-1: 2.8: 15;
preferably, the molar ratio of the propylene oxide to the carbon dioxide in the raw material containing the propylene oxide and the carbon dioxide is 1: 1-1: 2.8;
preferably, the molar ratio of the propylene carbonate to the methanol in the raw material containing the propylene carbonate and the methanol is 1: 10;
preferably, the reaction time is 2-9 hours;
preferably, the chemical equilibrium is reached within 9h of reaction at 120 ℃;
preferably, the reaction is carried out for 30 min at 68 ℃ to reach chemical equilibrium;
preferably, R1、R2Is independently selected from-CH3、-CH2CH3、-(CH2)2CH3、-(CH2)3CH3One kind of (1).
The catalyst is ionic liquid; the preparation method of the ionic liquid comprises the following steps:
a1) adding alkali into the solution I containing the ionic liquid anion source, and reacting to obtain ionic liquid anion metal salt;
a2) and dissolving the ionic liquid anion metal salt in a solvent, adding an ionic liquid cation salt, and reacting to obtain the ionic liquid.
The solvent in the solution I is at least one selected from ethanol, benzene, toluene and xylene;
the alkali is organic alkali or inorganic alkali;
the organic base comprises sodium methoxide, sodium ethoxide, sodium tert-butoxide, potassium methoxide, potassium ethoxide or potassium tert-butoxide;
the inorganic base includes lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide;
the ionic liquid anionic metal salt is selected from at least one of ionic liquid anionic Li salt, anionic Na salt, anionic K salt and ionic liquid anionic Cs salt;
preferably, in the step a 1), the concentration of the ionic liquid anion source in the solution I is 0.05-0.8 g/mL;
the molar ratio of the ionic liquid anion source to the base is 0.9-1.1;
preferably, in step a 1), the ionic liquid anion source comprises imidazole, pyrrole or morpholine;
preferably, in step a 1), the reaction conditions are: reacting for 24 hours in ice bath;
preferably, step a 1) further comprises: after the reaction is finished, removing the solvent to obtain imidazole anion salt, pyrrole anion salt or morpholine anion salt;
preferably, in step a 2), the solvent comprises a water-carrying agent;
the water-carrying agent is selected from at least one of methanol, ethanol, benzene, toluene and xylene;
the ionic liquid cation salt is selected from 1-R1-3-methyl-imidazolium bromide, 1-R1-3-methyl-imidazolium iodide, N-methyl-N-R2Morpholine bromide, N-methyl-N-
R2-at least one morpholine iodonium salt;
preferably, in the step a 2), the ratio of the ionic liquid anionic metal salt to the solvent is 0.1-0.9: 0.05-1.2 g/mL;
preferably, in step a 2), the reaction conditions are: reacting for 24 hours at room temperature;
preferably, step a 2) further comprises: and after the reaction is finished, removing the solvent to obtain the high-purity ionic liquid.
The catalyst does not need a new two-stage chain reaction process for separation, the catalyst firstly catalyzes propylene oxide and CO in a first fixed bed reactor2Synthesizing propylene carbonate. Then, the catalyst is mixed with methanol without separation and directly enters a second-stage reaction-rectification tower after being cooled, dimethyl carbonate-methanol azeotrope is extracted from the tower top, and 1, 2-propylene glycol is extracted from the tower bottom to realize CO2And propylene oxide to synthesize the dimethyl carbonate in one step with high yield.
As an embodiment, the catalyst is a homogeneous strong base ionic liquid.
The preparation method of the homogeneous phase strong alkaline ionic liquid catalyst comprises the following steps:
(1) synthesizing imidazole potassium salt: dissolving 34 g (0.5 mol) of imidazole in 500 mL of absolute ethyl alcohol at room temperature, slowly adding 28 g (0.5 mol) of KOH powder under the ice bath condition, continuously stirring for 24 h until the KOH powder is completely dissolved, filtering the mixed product, carrying out reduced pressure rotary distillation on the filtrate at 80 ℃ for 1h, separating generated water and ethanol solvent, cooling to room temperature to obtain brown solid imidazole potassium salt, and calculating the yield of the imidazole potassium to reach 96.62%.
(2) 1-ethyl-3-methyl-imidazolium salt [ Emim ] IM synthesis: 57.3 g (0.23 mol) of a methanol solution containing 75% by mass of 1-ethyl-3-methylimidazolium bromide is added with 200 mL of absolute ethanol and stirred at room temperature for 20 min. 23.85 g (0.23 mol) of potassium imidazolium were slowly added and the temperature was controlled around 25 ℃ to generate a large amount of white KBr precipitate, which was filtered after stirring for 24 h. The rotary distillation was carried out at 65 ℃ under-0.1 MPa for 2h to give 38.92 g of a viscous yellow liquid, giving 1-ethyl-3-methyl-imidazolium [ Emim ] IM in a calculated yield of 95.07%.
The imidazole ionic liquid has the following reaction formula
The homogeneous catalyst is high-purity active ionic liquid, and the purity is more than 99%.
In the present invention, "[ Emim ] Im" means 1-ethyl-3-methylimidazolium salt.
In the present invention, "PO" means propylene oxide.
In the present invention, "MeOH" refers to methanol.
In the present invention, "PC" means propylene carbonate.
In the present invention, "DMC" means dimethyl carbonate.
In the present invention, "PG" is 1, 2-propanediol.
In the present invention, "PM 1" is 1-methoxy-2-propanol.
In the present invention, "PM 2" is 2-methoxy-1-propanol.
In the present invention, "HPMC" is 1-hydroxy-2-propyl methyl carbonate.
In the present invention, "HMC" is 2-hydroxypropyl methyl carbonate.
In the present invention, C1-C6 represent the number of carbon atoms contained. For example, the term "C1-C6 alkyl group" refers to an alkyl group containing 1-6 carbon atoms.
In the present invention, the "alkyl group" is a group formed by losing any one hydrogen atom on the molecule of the alkane compound. The alkane compound comprises straight-chain alkane, branched-chain alkane, cycloalkane and cycloalkane with branched chain.
In the present invention, the "alkenyl group" is a group formed by losing any one hydrogen atom in the molecule of an olefin compound.
In the present invention, the "aromatic hydrocarbon group" is a group formed by losing one hydrogen atom on the aromatic ring on the aromatic compound molecule; such as p-tolyl, formed by toluene losing the hydrogen atom para to the methyl group on the phenyl ring.
The specific embodiment of the invention is as follows:
unless otherwise specified, the raw materials and catalysts in the examples of the present invention were all purchased from commercial sources.
In the embodiment of the invention, density analysis, viscosity analysis, alkali strength analysis, alkali quantity analysis, nuclear magnetic H spectrum analysis, nuclear magnetic C spectrum analysis, infrared spectrum analysis and thermogravimetry-differential thermal (TG-DTA) characterization analysis are all conventional operations, and a person skilled in the art can operate the method according to the instruction of an instrument.
The conversion and selectivity in the examples of the invention were calculated as follows:
in the examples of the invention, the conversion, selectivity and yield were calculated as:
XPO/%=(nPC+nDMC+nPM1+nPM2)×100/(nPC+nDMC+nPM1+nPM2+nunreacted PO)
SPC/%= nPC×100/(nPC+nDMC+nPM1+nPM2)
SDMC/%=nDMC×100/(nDMC+nPC+nPM1+nPM2)
SPM1/%=nPM1×100/(nPC+nDMC+nPM2)
SPM2/%=nPM2×100/(nPC+nDMC+nPM1)
YDMC/% =XPO×SDMC
YPM1/% =XPO×SPM1
YPM2/% =XPO×SPM2
TON=nTarget/nCat=(nPO×XPO×STarget)/ (nCat)
In the formula: PM1 is 1-methoxy-2-propanol, PM2 is 2-methoxy-1-propanol; XPO is the percent conversion of propylene oxide; SPC is the selectivity of propylene carbonate,%; SDMC is the selectivity to dimethyl carbonate,%; SPM1 is selectivity to 1-methoxy-2-propanol,%; SPM2 is the selectivity of 2-methoxy-1-propanol,%; yield of dimethyl carbonate,%, YDMC; YPM1 was used in% yield of 1-methoxy-2-propanol; YPM2 was obtained in% yield from 2-methoxy-1-propanol; n is the molar mass, mol, of the target product; nPO is the molar weight, mol, of propylene oxide; nPC is the molar weight of propylene carbonate,%; nPM1 is the molar amount of 1-methoxy-2-propanol,%; nPM2 is the molar mass, mol, of 2-methoxy-1-propanol; nDMC is the molar weight, mol of dimethyl carbonate; nCat is the molar weight of the active site of the catalyst, mol; s target is the selectivity,%, of the target product.
Example 1
Synthesizing imidazole potassium salt: 34 g (0.5 mol) of imidazole is dissolved in 500 mL of absolute ethyl alcohol at room temperature, 28 g (0.5 mol) of KOH powder is slowly added under the ice bath condition and is continuously stirred for 24 h until the KOH powder is completely dissolved, the mixed product is filtered, the filtrate is subjected to reduced pressure rotary distillation for 1h at 80 ℃, generated water and ethanol solvent are separated, and brown solid is obtained after the temperature is reduced to room temperature (as shown in figure 1 (A)), and the yield of potassium imidazole is calculated to reach 96.62%.
1-Ethyl-3-methyl-imidazolium salt [ Emim]IM synthesis: 57.3 g (0.23 mol) of a methanol solution containing 75% by mass of 1-ethyl-3-methylimidazolium bromide is added with 200 mL of absolute ethanol and stirred at room temperature for 20 min. 23.85 g (0.23 mol) of potassium imidazolium were slowly added and the temperature was controlled around 25 ℃ to generate a large amount of white KBr precipitate, which was filtered after stirring for 24 h. The rotary distillation was carried out at 65 ℃ under a pressure of-0.1 MPa for 2 hours to give 38.92 g of a viscous yellow liquid as shown in FIG. 1(B), with a calculated yield of 95.07%. The nuclear magnetic spectrum is shown in figure 2 and figure 3. FIG. 2 Synthesis of [ Emim]Im ionic liquid nuclear magnetic H spectrum:1h NMR (500 MHz, DMSO-d6) δ 7.75 (s, 1H), 7.66 (s, 1H), 7.21 (s, 1H), 6.73 (s, 3H), 4.14 (q, J = 7.3 Hz, 2H), 3.80 (s, 3H), 1.37 (t, J = 7.3 Hz, 3H); FIG. 3 Synthesis of [ Emim]Im ionic liquid nuclear magnetic C spectrum:13C NMR (126 MHz, DMSO) δ 136.99, 136.18, 123.97, 122.31, 44.51, 36.06, 15。
example 2
The physical parameters of 1-ethyl-3-methyl-imidazole ionic liquid ([ Emim ] IM) are measured, the density is about 1.1 g/mL, the viscosity is 45.6 Mpa.s, the alkali strength of the ionic liquid [ Emim ] IM is measured by a Hammett indicator method, 18.4 < H- < 22.3, and the Hammett indicator used in the process comprises the following components: phenolphthalein (9.8), 2, 4-dinitroaniline (15.0), p-nitroaniline (18.4), diphenylamine (22.3) and aniline (27.0), the alkali intensity interval being determined by the indicator colour change. The result shows that the alkali strength is equivalent to that of industrial sodium tert-butoxide, and the alkali strength is higher than that of sodium methoxide. The amount of base of the ionic liquid was calculated to be 2.83 mmol/g based on the amount of benzoic acid added, 0.1 mol/L.
Example 3
Synthesis of Ionic liquid 1-ethyl-3-methylimidazolium [ Emim]IM functional group characterization results are shown in FIG. 4, 3142, 3074 and 2976 cm-1The absorption peak is miamiAnd C-H stretching vibration peaks of substituted alkyl on the azole ring. 1668 and 1570 cm-1The absorption peak is attributed to the C = N stretching vibration peak in imidazole ring, 1448 cm-1Is the stretching vibration peak of C = C double bond in imidazole ring, 1172 cm-1Is the bending vibration peak in the C-N bond surface in the imidazole ring, 829 and 763 cm-1The absorption peaks are respectively attributed to the in-plane and out-of-plane bending vibration of the C-H bond on the imidazole ring.
Example 4
The thermal stability analysis of the synthesized ionic liquid 1-ethyl-3-methylimidazolium [ Emim ] IM under nitrogen atmosphere is shown in fig. 5, a three-stage weight loss process is provided, and 2% weight loss is provided from room temperature to 144 ℃ as a residual methanol solvent in the ionic liquid preparation process; obvious weight loss occurs at 144-262 ℃, the weight loss is 68.02%, and the decomposition of most of imidazole rings is carried out along with strong heat absorption; the imidazole ring is completely decomposed at the temperature of 262-356 ℃, the weight loss rate is 26.69 percent and the endothermic phenomenon is accompanied; the temperature is continuously increased to 500 ℃, and the rest 2 percent of the weight is kept unchanged and becomes carbon deposit after the decomposition of Emim IM. The physical properties, functional group characteristics, nuclear magnetic characterization and other results of the ionic liquids prepared in examples 1-4 can conclude that the prepared catalyst is 1-ethyl-3 methylimidazolium imidazolium salt, and Hammett titration, alkali amount determination and thermogravimetric analysis prove that the catalyst has high alkali strength (18.4 < H- < 22.3), alkali amount of 2.83 mmol/g and high thermal stability.
Example 5
Respectively using KI, tetrabutylammonium bromide (TBAB) and 1-ethyl-3-methylimidazol ([ Emim [ ])]IM) was carried out for the synthesis reaction using the catalyst, and the reaction conditions were as shown in the above catalyst evaluation method, and the reaction results are shown in fig. 6. KI and TBAB have catalytic CO only2Cycloaddition reaction capacity is generated, the PO conversion rate is 43.88 percent and 31.53 percent respectively when the reaction is carried out for 2 hours, and the PO conversion rate is 98.79 percent and 98.35 percent respectively when the reaction is carried out for 9 hours; there was essentially no catalytic PC and MeOH transesterification and no PO and MeOH alcoholysis, so both catalysts corresponded to a PC selectivity of greater than 99%, a DMC selectivity and yield of less than 1%, and a TON value of approximately zero.
Using [ Emim]IM catalyst, 2 and 9h, PO conversion of 86.90% and 98.57%, PC selectivity of 55.35% and 43.66%, DMC selectivity of 23.63%And 36.79% with DMC yields of 20.34% and 36.27%, corresponding to TON values of 20.77 and 37.04. [ Emim ] compared with KI and TBAB]IM exhibited good DMC yields, but still did not meet expectations. The reason is that: [ Emim]IM has strong basicity and not only catalyzes CO2Cycloaddition reaction occurs, and PO and MeOH are catalyzed to generate alcoholysis reaction. GC-MS analysis of the products showed that the alcoholysis products 1-methoxy-2-propanol (PM 1) and 2-methoxy-1-propanol (PM 2) were present in the system, and that the selectivity to PM1 was 12.63% and 15.59% and the selectivity to PM2 was 8.39% and 3.96% at 2 and 9h of reaction, respectively.
Example 6
The addition cyclization of PO in the absence of MeOH followed by transesterification of PC with MeOH should improve DMC selectivity and yield. Therefore, a new process for synthesizing DMC in one step by two-stage chain reaction of catalytic cycloaddition and ester exchange is designed. The specific process for one-step synthesis of DMC by two-stage chain reaction method includes the following steps, firstly, in the first stage of fixed bed reactor, under the condition of no MeOH addition [ Emim]IM catalysis of PO and CO2Synthesizing PC; then, adding necessary amount of MeOH into the system, mixing, cooling and allowing the MeOH to enter a reaction-rectification tower at the second section for further reaction and separation, wherein DMC-MeOH azeotrope overflows from the top of the tower, and 1, 2-propylene glycol is filled in the bottom of the tower, thereby realizing CO2And DMC, with PO not isolated, is synthesized in high yield.
Specific validation experiments used KI, TBAB and [ Emim]IM catalyst is used for catalyzing CO firstly under the condition of not adding any solvent and auxiliary agent2And PO cycloaddition transesterification of in situ generated PC with MeOH catalyzed at low temperature. Epoxidation reaction conditions: the mass of the catalyst is 3 percent of PO, the reaction temperature is 120 ℃, and CO is2The initial pressure was 2.6 MPa. The results of gas chromatography analysis of the product after 2h and 9h of reaction are shown in FIG. 5. The PO conversion of the three catalysts at 2h was 37.49%, 46.37% and 64.90%, respectively, indicating [ Emim%]IM catalysis of CO2The epoxidation capability of PO and the catalyst is obviously better than that of KI and TBAB. The PC selectivity of the 3 catalysts reaches 99 percent, which indicates that no other side reaction occurs under the reaction condition. The PO conversion rates of the three catalysts at 9h of reaction are respectively 98.28%, 97.95% and 97.40%, and the corresponding PC selectivity is still maintainedAbove 99%, indicating that a reaction time of 9h was sufficient to evaluate the maximum catalytic performance of the 3 catalysts used in this study.
Then, MeOH, which is 10 times the molar amount of the theoretically produced PC, was directly added, the reaction temperature was 68 ℃ and the reaction product was collected at regular sampling intervals in the time range of 1-120 min and analyzed, and the results are shown in FIG. 7. Obviously, the difference of the PC ester exchange capacities catalyzed by the three catalysts is obvious, the TBAB activity is the worst, and the PC conversion rate, DMC selectivity and yield are only 33.67%, 34.67% and 11.68% when the reaction time is 120 min; KI has higher DMC selectivity, DMC yield is gradually increased along with the prolonging of reaction time, and PC conversion rate, DMC selectivity and yield at the time of 120 min reaction are only 26.63%, 67.41% and 17.96%; [ Emim]IM has excellent PC ester exchange catalytic capability, the PC conversion rate and DMC selectivity and yield are as high as 72.87%, 97.36% and 70.94% only after 5 min of reaction, and the reaction equilibrium is reached within 30 min, at which the DMC yield is 83.63%. Increasing the MeOH content to 20 times the molar PC content gave DMC selectivity and yield at 120 min of reaction of 99.84% and 87.81%, respectively. The DMC yield in this process is limited primarily by the equilibrium of the reaction (feedstock composition), and if a coupled reaction-rectification process is used, the DMC yield (as CO)2Calculated) can reach more than 98 percent.
Example 7
Reaction temperature vs. PO and CO2The effect of the cycloaddition reaction is shown in FIG. 9. Catalyst [ Emim]IM mass is 3% of PO mass and initial CO2Pressure of 2.6 MPa in CO2The molar ratio of PO to the polymer was 1.6:1, and the reaction time was 9 h. Under all reaction temperature conditions, the selectivity of the target product PC is more than 99 percent, which indicates that the synthesized Emim]IM has excellent ability to direct catalytic PO cycloaddition. At 100 ℃, the yield of PC reaches 80.69 percent, and the TON value reaches 82.42; the PC yield further increased to 89.36% and 97.40% and the TON increased to 91.28 and 99.49 when the reaction temperature was continuously increased to 110 and 120 ℃; the temperature was further raised to 130 ℃, the yield of PC was 97.75%, the TON was 99.85, and there was no significant change. Considering PO and CO2The cycloaddition reaction is a strongly exothermic reaction with reduced volume, and the reduction of the reaction temperature is beneficial to promoting the reaction to proceed towards the positive direction and improving the equilibrium conversion rate of PO. Therefore, the subsequent experiment prefers 120 ℃ reaction conditions.
Example 8
FIG. 10 shows reaction time vs. PO and CO2The effect of the cycloaddition reaction. Catalyst [ Emim]The mass of IM is 3 percent of the mass of PO, the reaction temperature is 120 ℃, and CO is2The initial pressure was 2.6 MPa. The selectivity of the target product PC is more than 99 percent in all reaction times. When the reaction time is 2 hours, the yield of PC is 64.90 percent; increasing the reaction time to 4 and 6 h, the yield of PC increased to 88.77% and 96.20%; the time is increased to 9h, and the yield of PC reaches 97.40%. Since the PC selectivity was above 99% in all sampling time intervals, TON showed a similar increasing trend with reaction as the yield increased from 63.23 at 2h to 99.49 at 9 h.
Example 9
CO2The effect of initial pressure on the cycloaddition reaction is shown in FIG. 11. Catalyst [ Emim]The IM content is 3 percent of the PO mass, the reaction temperature is 120 ℃, and the reaction time is 9 h. CO22The PC selectivity was greater than 99% at various initial pressures. When CO is present2Initial pressure 1.8 MPa, i.e. CO2When the mol ratio of the PC to the PO raw material is 1:1, the yield of the PC is 87.61 percent, and the TON is 89.49; CO22At an initial pressure of 2.0 MPa (CO 2/PO mole ratio =1.2: 1), the yield of PC was 90.94%, TON was 92.89; when CO is present2At an initial pressure of 2.4 MPa (CO 2/PO mole ratio =1.4: 1), the yield of PC was 97.03% and TON was 99.11; continuous CO increase2Initial pressure to 2.6 MPa (CO)2PO mole ratio =1.6: 1), PC yield increased significantly to 97.40%, TON increased to 99.49; continuing to promote CO2Pressure to 3.2 (CO)2mol/PO =2.2: 1) and 3.8 MPa (CO)2mol/PO =2.8: 1), the PC yield decreased to 93.96% and 93.25% instead, and the TON decreased to 95.98 and 95.25. This is consistent with the results reported in many documents, with PC yield being a function of CO in low pressure processes2Increased by increased pressure, CO2When the partial pressure exceeds a certain pressure, the yield of PC is dependent on CO2The pressure rises and slowly decreases. An excessively high initial pressure may lead to CO2Liquefying and dissolving in PO as reaction raw material, diluting catalyst concentration, weakening action between PO and catalyst active site, reducing catalytic efficiency of catalyst, and not beneficial to reaction proceeding in forward direction. Thus, subsequent experimental workPreferably CO2The initial pressure was 2.6 MPa.
Example 10
FIG. 12 shows the amount of catalyst used versus PO and CO2The effect of the cycloaddition reaction. CO22The initial pressure is 2.6 MPa, the reaction temperature is 120 ℃, and the reaction time is 9 h. The selectivity of PC is more than 99% in different catalyst dosages. When catalyst [ Emim]When the mass of IM is 0.5% of the mass of PO, the yield of PC is 66.34%, and the TON value is as high as 406.59; when the catalyst dosage is continuously increased to 1% and 3% of PO mass, the PC yield is obviously increased to 73.49% and 97.40%, and the TON value is reduced to 225.21 and 99.49; the catalyst dosage is continuously increased to 5 percent and 10 percent of the PO mass, the PC yield reaches 98.58 percent and 98.95 percent, and the promotion is not obvious. The TON value can reach 30.32 even at 10% catalyst content. For economic reasons, the catalyst was used in an amount of 3% by mass of PO.
Example 11
FIG. 13 examines the effect of [ Emim ] IM catalyst on the efficiency of the transesterification of PC with MeOH at different reaction temperatures and times. The amount of catalyst used was 0.4 wt% based on the total mass of the reaction feed, and the PC/MeOH molar ratio was 1/10. Because [ Emim ] IM catalyzes the ester exchange reaction with extremely high efficiency, DMC selectivity reaches more than 99% under all temperature conditions, basically there is no intermediate product produced, so DMC yield is similar to PC selectivity. The reaction is carried out for 10 min at the reaction temperatures of 0, 25, 50 and 68 ℃, and the DMC yields are 7.95%, 10.21%, 21.33% and 38.01% respectively; when the reaction time is 60 min, the DMC yield is respectively improved to 18.57 percent, 27.27 percent, 58.74 percent and 71.99 percent. At 25 ℃, the reaction is balanced in 200 min; at 50 ℃, reaction equilibrium is reached in 120 min; the reaction is carried out at 68 ℃ and the equilibrium is reached within 60 min. When the reaction temperature was increased from 0 to 68 ℃ for 30 min, the TON value and DMC yield increased significantly, from 12.96 to 70.15 and from 12.81 to 68.98%, respectively. The experimental results fully show that the transesterification reaction rate of PC and MeOH has obvious dependence on the reaction temperature, and even under the extremely low temperature condition, [ Emim ] IM shows extremely high catalytic activity, can complete the transesterification reaction within extremely short time after the ring opening of PC, and has extremely strong transesterification catalytic capability.
Example 12
Study [ Emim]IM ionLiquid catalyst high-temperature catalysis CO for 7 times continuously2And PO epoxidation reaction and transesterification reaction effect of low-temperature catalysis in-situ generation of PC and MeOH. Epoxidation reaction conditions: [ Emim]IM content of 3% by mass of PO, epoxidation reaction temperature of 120 ℃, CO2Initial pressure 2.6 MPa (CO)2mol/PO =1.6: 1), reaction time 9h, sample analysis time point 9 h. Thereafter, MeOH, which had 10 times the molar amount of the theoretically produced PC, was added to the system, and after 30 min of reaction at 68 ℃ a sample was taken for analysis. No solvent or auxiliary agent is added in the whole reaction process, and only the ionic liquid [ Emim ] with the same mass added at the beginning of the reaction is used]IM continuously catalyzes the epoxidation and the ester exchange two-step reaction. After the single two-step reaction, raw materials and products such as MeOH, PC, DMC and 1, 2-propylene glycol are separated under reduced pressure at the temperature of 140 ℃ and 145 ℃, and the residual ionic liquid is recovered and directly used for the next two-step reaction cycle until the 6 th cycle is finished.
The relationship between the PO and PC conversion and DMC yield versus the number of ionic liquid [ Emim ] IM reuses is shown in FIG. 14 below. [ Emim ] when IM was used for the first time, the PO conversion was 97.40%, the PC conversion was 85.07%, and the DMC yield was 83.63%. When the catalyst is repeatedly used once, the PO conversion rate is not reduced and is increased to 98.05 percent, and the reason is that the product 1, 2-propylene glycol is remained in the ionic liquid in a small amount and promotes the opening of PO rings through hydrogen bonds. At this time, the PC conversion and the DMC yield were 84.25% and almost similar to the DMC yield in the first use, and there was no tendency to decrease. Increasing the number of reuses to the fourth time, the PO conversion dropped to 97.34% and the DMC yield dropped to 83.82%, but the decline was not significant. When the catalyst is repeatedly used for 5 times, the PO conversion rate is reduced to 96.68 percent, the DMC yield is 80.96 percent, and compared with the first time, the PO conversion rate is reduced by 0.72 percent, and the DMC yield is reduced by about 4 percent. It is emphasized here that the two product streams taken at each cycle for chromatographic analysis resulted in a loss of about 1% of the mass of ionic liquid, calculated in turn, and the actual mass of ionic liquid in the system was about 96% of the first at the 5 th reuse. Therefore, after 6 times of recycling, 0.024 g of new ionic liquid is additionally supplemented. Thus, the PO conversion, PC conversion and DMC yield of the 7 th reaction were all increased back to 97.48%, 84.58% and 83.74%, respectively, with comparable catalytic effect to the first fresh catalyst. The results prove that the [ Emim ] IM new-structure ionic liquid synthesized by the research has good thermal stability and catalytic stability, can always maintain higher cycloaddition and ester exchange reaction efficiency in the repeated use process, and has no obvious reduction of activity.
Example 13
The reaction mechanism is presumed to be shown in FIG. 15, and [ Emim ] was observed in the reaction system]IM exists in an anionic state and a cationic state, and imidazole cation electrophilically attacks an oxygen atom of the propylene oxide to elongate and deform a C-O bond; the imidazole anion attacks the C atom with lower steric resistance in the propylene oxide through nucleophilic attack, so that the C-O bond is broken to form an intermediate a. The anion and cation act together to activate the propylene oxide to open the ring, forming an intermediate species b containing oxygen anions. Subsequent nucleophilic attack of oxygen anions on CO in intermediate species b2The C atom with positive charge in the molecule generates a carbonate intermediate C; and then, the carbonate intermediate C is subjected to intramolecular substitution under the action of imidazole anions to generate a new C-O bond, so that propylene carbonate d is obtained, and 1-ethyl-3-methylimidazole cations and imidazole anions are released.
Ionic liquids [ Emim ] in transesterification]The imidazole anion in IM captures hydrogen on the hydroxyl group of methanol through hydrogen bond action, and further activates methanol to form CH3An O-group; CH (CH)3O-nucleophilic attack on the carbonyl group in pc (d) to cleave the C = O bond to form intermediate e; because of the instability of intermediate e, the four C-O bonds to C are cleaved by at least one, which is a typical nucleophilic addition-elimination reaction. The 1-position C-O bond cannot be broken under the base catalysis system because of C+And O−Can not exist stably in the form of free radical; cleavage of the 2-position C-O bond results in PC and CH3O−The C-O bonds at the 3 and 4 positions of the group are cleaved to yield intermediates f and g. The electronegativity of f and g is weaker than that of CH due to the electron withdrawing effect of O connected with C = O in the structures of f and g3O−Electronegativity and easier generation; f and g are abstracted or combined with H + in the system to generate H intermediate product 1-hydroxy-2-propyl methyl carbonate (HPMC) and i intermediate product 2-Hydroxypropyl Methyl Carbonate (HMC); CH 3O-nucleophilic attacks the carbonyl groups in the intermediate HPMC and HMC to form intermediates j and k; the 4-position C-O bond is broken due to instability of j and kForming target product DMC and intermediate product PG anions l and m; l and m are abstracted or combined with H + in the system to generate a final product PG; PG anions l and m may also attack carbonyl groups in the intermediate HPMC and HMC, breaking the C = O bond to form intermediates n and O; the C-O bond at the 3-position of the intermediate is broken to generate intermediate products p and q.
Example 14
According to the cycloaddition and ester exchange reaction mechanism presumed in the example 13, the synthesized ionic liquid active center with new structure is imidazole negative ion with strong affinity, and the anions such as imidazole, pyrrole and thiophene with various branched structures are in the protection scope of the patent.
The above description is only for the purpose of illustrating the present invention and is not intended to limit the present invention in any way, and the present invention is not limited to the above description, but rather should be construed as being limited to the scope of the present invention.
Claims (6)
1. One-step method for efficiently catalyzing CO2A process for the conversion of a dimethyl carbonate catalyst, characterized in that said process comprises the steps of:
propylene oxide, CO2Reacting with methanol as a raw material, and obtaining the dimethyl carbonate with high yield by using a homogeneous ionic liquid catalyst; the catalyst needs no separation and has two-stage chain reaction process, the first stage is fixed bed reactor, the catalyst first catalyzes propylene oxide and CO2Synthesizing propylene carbonate; then, the catalyst is mixed with methanol without separation and enters a second-stage reaction-rectification tower after being cooled, dimethyl carbonate-methanol azeotrope is extracted from the tower top, and 1, 2-propylene glycol is extracted from the tower bottom to realize CO2And propylene oxide to synthesize dimethyl carbonate in one step with high yield;
the catalyst is ionic liquid;
the ionic liquid comprises a cation and an anion;
the anion and the cation both contain a nitrogen-containing heterocycle.
2. The one-step method for efficiently catalyzing CO according to claim 12The method for converting the dimethyl carbonate catalyst is characterized in that the reaction temperature is 100-130 ℃, the reaction time is 2-9 h, and CO is2The initial pressure is 1.8-3.8 MPa, and the amount of the catalyst is 0.5-10% of the PO mass; the reaction temperature in the ester exchange process is 68 ℃;
preferably, the reaction temperature is 120 ℃;
preferably, the reaction time is 9 h;
preferably, the CO is2The initial pressure is 2.6 MPa;
preferably, the amount of the catalyst is 3% of the PO mass;
preferably, the transesterification reaction temperature is 68 ℃;
preferably, the cation has the formula
Or formula
The structure shown;
the anion has the formula
A and B type
Or formula
The structure shown;
wherein R is1Independently selected from one of C1-C6 alkane group, C2-C6 alkene group and C3-C6 aromatic hydrocarbon group;
preferably, the raw material containing the propylene oxide, the carbon dioxide and the methanol has a molar ratio of the propylene oxide to the carbon dioxide to the methanol of 1:1: 10-1: 2.8: 15;
preferably, the molar ratio of the propylene oxide to the carbon dioxide in the raw material containing the propylene oxide and the carbon dioxide is 1: 1-1: 2.8;
preferably, the molar ratio of the propylene carbonate to the methanol in the raw material containing the propylene carbonate and the methanol is 1: 10;
preferably, the reaction time is 2-9 hours;
preferably, the chemical equilibrium is reached within 9h of reaction at 120 ℃;
preferably, the reaction is carried out for 30 min at 68 ℃ to reach chemical equilibrium;
preferably, R1、R2Is independently selected from-CH3、-CH2CH3、-(CH2)2CH3、-(CH2)3CH3One kind of (1).
3. The one-step method for efficiently catalyzing CO according to claim 12A process for the conversion of a dimethyl carbonate catalyst, characterised in that the catalyst is an ionic liquid.
4. The one-step method for efficiently catalyzing CO according to claim 12A process for the conversion of dimethyl carbonate catalyst, characterized in that the preparation of the ionic liquid comprises the steps of:
a1) adding alkali into the solution I containing the ionic liquid anion source, and reacting to obtain ionic liquid anion metal salt;
a2) and dissolving the ionic liquid anion metal salt in a solvent, adding an ionic liquid cation salt, and reacting to obtain the ionic liquid.
5. The one-step method for efficiently catalyzing CO according to claim 42The method for converting the dimethyl carbonate catalyst is characterized in that in the step a 1), the solvent in the solution I is at least one selected from ethanol, benzene, toluene and xylene;
the alkali is organic alkali or inorganic alkali;
the organic base comprises sodium methoxide, sodium ethoxide, sodium tert-butoxide, potassium methoxide, potassium ethoxide or potassium tert-butoxide;
the inorganic base includes lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide;
the ionic liquid anionic metal salt is selected from at least one of ionic liquid anionic Li salt, anionic Na salt, anionic K salt and ionic liquid anionic Cs salt;
preferably, in the step a 1), the concentration of the ionic liquid anion source in the solution I is 0.05-0.8 g/mL;
the molar ratio of the ionic liquid anion source to the base is 0.9-1.1;
preferably, in step a 1), the ionic liquid anion source comprises imidazole, pyrrole or morpholine;
preferably, in step a 1), the reaction conditions are: reacting for 24 hours in ice bath;
preferably, step a 1) further comprises: after the reaction is finished, removing the solvent to obtain imidazole anion salt, pyrrole anion salt or morpholine anion salt;
preferably, in step a 2), the solvent comprises a water-carrying agent;
the water-carrying agent is selected from at least one of methanol, ethanol, benzene, toluene and xylene;
the ionic liquid cation salt is selected from 1-R1-3-methyl-imidazolium bromide, 1-R1-3-methyl-imidazolium iodide, N-methyl-N-R2Morpholine bromide, N-methyl-N-
R2-at least one morpholine iodonium salt;
preferably, in the step a 2), the ratio of the ionic liquid anionic metal salt to the solvent is 0.1-0.9: 0.05-1.2 g/mL;
preferably, in step a 2), the reaction conditions are: reacting for 24 hours at room temperature;
preferably, step a 2) further comprises: and after the reaction is finished, removing the solvent to obtain the high-purity ionic liquid.
6. The one-step method for efficiently catalyzing CO according to claim 12The method for converting the dimethyl carbonate catalyst is characterized in that the method comprises a two-stage chain reaction process without separating the catalyst; in the first stage of fixed bed reactor, the catalyst firstly catalyzes propylene oxide and CO2Synthesizing propylene carbonate; then, the catalyst is mixed with methanol without separation and directly enters a second-stage reaction-rectification tower after being cooled, dimethyl carbonate-methanol azeotrope is extracted from the tower top, and 1, 2-propylene glycol is extracted from the tower bottom to realize CO2And propylene oxide to synthesize the dimethyl carbonate in one step with high yield.
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