CN115108912A - Strongly alkaline ionic liquid catalyzed CO 2 Method for synthesizing dimethyl carbonate catalyst - Google Patents
Strongly alkaline ionic liquid catalyzed CO 2 Method for synthesizing dimethyl carbonate catalyst Download PDFInfo
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- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
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- C07C68/06—Preparation of esters of carbonic or haloformic acids from organic carbonates
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
- B01J31/02—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides
- B01J31/0277—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides comprising ionic liquids, as components in catalyst systems or catalysts per se, the ionic liquid compounds being used in the molten state at the respective reaction temperature
- B01J31/0278—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides comprising ionic liquids, as components in catalyst systems or catalysts per se, the ionic liquid compounds being used in the molten state at the respective reaction temperature containing nitrogen as cationic centre
- B01J31/0279—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides comprising ionic liquids, as components in catalyst systems or catalysts per se, the ionic liquid compounds being used in the molten state at the respective reaction temperature containing nitrogen as cationic centre the cationic portion being acyclic or nitrogen being a substituent on a ring
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- B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
- B01J31/02—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides
- B01J31/0277—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides comprising ionic liquids, as components in catalyst systems or catalysts per se, the ionic liquid compounds being used in the molten state at the respective reaction temperature
- B01J31/0298—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides comprising ionic liquids, as components in catalyst systems or catalysts per se, the ionic liquid compounds being used in the molten state at the respective reaction temperature the ionic liquids being characterised by the counter-anions
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- C—CHEMISTRY; METALLURGY
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- C07D—HETEROCYCLIC COMPOUNDS
- C07D317/00—Heterocyclic compounds containing five-membered rings having two oxygen atoms as the only ring hetero atoms
- C07D317/08—Heterocyclic compounds containing five-membered rings having two oxygen atoms as the only ring hetero atoms having the hetero atoms in positions 1 and 3
- C07D317/10—Heterocyclic compounds containing five-membered rings having two oxygen atoms as the only ring hetero atoms having the hetero atoms in positions 1 and 3 not condensed with other rings
- C07D317/32—Heterocyclic compounds containing five-membered rings having two oxygen atoms as the only ring hetero atoms having the hetero atoms in positions 1 and 3 not condensed with other rings with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
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- C07D317/36—Alkylene carbonates; Substituted alkylene carbonates
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- B01J2231/00—Catalytic reactions performed with catalysts classified in B01J31/00
- B01J2231/40—Substitution reactions at carbon centres, e.g. C-C or C-X, i.e. carbon-hetero atom, cross-coupling, C-H activation or ring-opening reactions
- B01J2231/49—Esterification or transesterification
Abstract
Strongly alkaline ionic liquid catalyzed CO 2 A method for synthesizing dimethyl carbonate catalyst relates to a method for synthesizing dimethyl carbonate catalyst, and the method synthesizes ionic liquid based on strong basicity and new structure of a reaction raw material system with high yield to catalyze Propylene Oxide (PO) and CO 2 And methanol (MeOH) as a raw material to synthesize dimethyl carbonate (DMC) in one step; continuous catalysis of PO-CO without separation of catalyst 2 Cycloaddition and PC-MeOH ester exchange two-stage chain reaction process; first of all, PO and CO 2 The cycloaddition reaction is carried out, the PO conversion rate of 99.03 percent and the Propylene Carbonate (PC) yield rate of nearly 99.03 percent are achieved under the mild condition, and the PC conversion rate reaches 71.22% DMC selectivity was greater than 99%, the DMC overall yield was close to 71.22%, and the TON value was 57.38. The new-structure ionic liquid derived from the product system has the advantages of simple synthesis process, environmental friendliness, strong basicity and excellent catalytic activity, and has important industrial application value in the field of carbonate synthesis.
Description
Technical Field
The invention relates to a catalyst synthesis method, in particular to a method for catalyzing CO by strongly alkaline ionic liquid 2 A method for synthesizing a dimethyl carbonate catalyst.
Background
FossilExcess energy consumption causes atmospheric CO 2 、CH 4 The content of greenhouse gases is continuously increased, which causes global warming, extreme weather, continuous rise of sea level, continuous deterioration of human living environment and the like. The 'double carbon' strategy in China advocates a green, environment-friendly and low-carbon life style and accelerates the pace of reducing carbon emission. Energy end product CO 2 As a nontoxic, cheap and renewable carbon resource, the method has important research value and application prospect in converting low energy consumption into valuable chemicals, and is an optimal strategy for human sustainable development.
By using CO 2 And MeOH to synthesize DMC directly or indirectly is of great interest. DMC synthesis methods include direct synthesis, urea alcoholysis, direct/indirect oxidative carbonylation of methanol, and transesterification. Wherein CO is 2 The direct synthesis of DMC by reaction with MeOH is simple, environmentally friendly, but is limited by thermodynamics and equilibrium, CO 2 The one-step conversion rate is low, and the reaction needs to be carried out under the reaction conditions of high temperature and high pressure. Methyl carbamate, an intermediate product in the urea alcoholysis process, is easily decomposed into byproducts such as isocyanic acid and the like, and is polymerized into biuret, cyanuric acid and the like, so that a reaction pipeline is blocked, and the stability of continuous operation of the device in the demonstration process is poor. Direct oxidative carbonylation of methanol process O 2 The method has the advantages of direct participation, many byproducts and potential safety hazard. The methanol indirect oxidation carbonylation method adopts a chlorine-containing catalyst and takes NOx as an oxidant for recycling, generates a large amount of acid-containing wastewater, and is easy to corrode equipment. From PO or Ethylene Oxide (EO) feedstocks respectively with CO 2 The cycloaddition of the (C) to obtain PC or Ethylene Carbonate (EC), and then the transesterification of the (C) and MeOH to obtain DMC and the byproduct 1, 2-propylene glycol or ethylene glycol. Compared with other DMC synthesis routes, the ester exchange method is a more environment-friendly and more efficient synthesis way and is a domestic DMC main industrial production method.
Wen et al first studied KHCO 3 High temperature (140 ℃) and high pressure (CO) as catalysts 2 Pressure 12 MPa) PO and CO 2 And one-step synthesis of D from MeOH by epoxidation and transesterificationAnd (C) MC. After 6 h of reaction, the PO conversion reached 96.87%, but the DMC yield was only 16.84%. Chun et al used choline chloride/MgO as catalyst, reacted for 6 h at 120 deg.C and 2.5 MPa, and DMC yield reached 65.40%, but DMC yield dropped to 12.58% after 4 times of repeated use. Chen et al, using a 1-butyl-3-methylimidazolium tetrafluoroborate and sodium methoxide composite catalyst, achieved 95.00% PO conversion and 67.50% DMC yield at 150 ℃, but ionic liquids were not soluble in sodium methoxide powder and could not be separated from the reaction system, and were difficult to reuse. Tia, etc. adopts tetrabutyl ammonium bromide and tertiary amine composite catalyst, and at high temperature of 150 deg.C and higher CO 2 The initial pressure is 15 MPa, the PO conversion rate reaches 98.00 percent, and the DMC yield reaches 84.00 percent. Liu et al as alkali metal halide (K) 2 CO 3 Adding zinc powder NaBr-ZnO) as composite catalyst, high-temp. (160 deg.C) and CO 2 PO and CO under the pressure of 2 MPa 2 And MeOH as raw materials, and the DMC is synthesized by a one-step method for 5 hours, and the DMC yield reaches 40.2 percent. Valerie et al with Mg (OCH) 3 ) 2 As catalyst, high temperature (150 ℃) and high pressure (CO) 2 Pressure 12 MPa) PO and CO 2 And MeOH as a raw material to synthesize DMC in one step, the reaction lasts for 8 h, the PO conversion rate is 99.60 percent, and the DMC yield is 34.40 percent.
In summary, the existing one-step method for synthesizing DMC by taking PO as reaction raw material has the disadvantages of over high reaction temperature and CO 2 The initial pressure is high, and the catalyst is difficult to separate and cannot be reused by adopting the composite catalyst with more than two components of quaternary ammonium salt or halogen and strong alkali salt.
Disclosure of Invention
The invention aims to provide a strong-alkaline ionic liquid for catalyzing CO 2 The invention discloses a method for synthesizing a dimethyl carbonate catalyst, and particularly relates to a method for synthesizing single-component 1, 2-propylene glycol-tetraethylammonium (PG-TEA), 1, 2-propylene glycol-tetrabutylammonium (PG-TBA) and 1, 2-propylene glycol-choline (PG-CH) strongly-alkaline ionic liquids which are derived from a product 1, 2-propylene glycol system and based on 1, 2-propylene glycol negative ions, wherein the ionic liquids have the function of efficiently catalyzing CO 2 The reaction generates cyclic carbonate and catalyzes the transesterification of propylene carbonate and methanol.
The purpose of the invention is realized by the following technical scheme:
strongly alkaline ionic liquid catalyzed CO 2 A method of synthesizing a dimethyl carbonate catalyst, the method comprising the process of:
epoxy compound, CO 2 The catalyst reacts with methanol as a raw material, and the homogeneous phase ionic liquid can realize one-step synthesis of dimethyl carbonate or firstly catalyze epoxy compounds and CO 2 Synthesizing cyclic carbonate, then, the catalyst is mixed with MeOH without separation and cooled, and then enters a second-stage reaction-rectification tower, a dimethyl carbonate-methanol azeotrope is extracted from the tower top, and the tower bottom is a corresponding dihydric alcohol product, so that CO is realized 2 And synthesizing dimethyl carbonate in one step with high yield;
the epoxy compound comprises epoxy butane, or epoxy chloropropane, epoxy styrene, allyl glycidyl ether, glycidol and phenyl glycidyl ether;
the temperature of the cycloaddition reaction is 100-140 ℃, the reaction time is 1-10 h, and CO 2 The initial pressure is 1.0-4.0 MPa; the reaction temperature during the transesterification of PC and MeOH is 60-80 ℃.
The strongly basic ionic liquid catalyzes CO 2 A method for synthesizing a dimethyl carbonate catalyst, wherein the catalyst is an ionic liquid, and the ionic liquid comprises cations and anions; the anion contains oxyanions of alcohols of different chain lengths; amines with different side chain lengths of the cation containing a nitrogen atom.
The strongly basic ionic liquid catalyzes CO 2 The method for synthesizing the dimethyl carbonate catalyst comprises the following steps of: adding strong base into dihydric alcohol, heating for reaction, and separating product water to obtain metal salt containing oxygen anion; dissolving metal salt containing oxygen anion in a solvent, adding ionic liquid cation salt, filtering the precipitate after reaction, and separating the solvent to obtain the ionic liquid.
The strongly basic ionic liquid catalyzes CO 2 A process for synthesizing dimethyl carbonate catalyst features that the diol is at least one of ethanediol, 1, 3-propanediol, 1, 2-propanediol, 1, 4-butanediol, etc.
The strong alkaline ionCO catalysis by sub-liquid 2 A method for synthesizing a dimethyl carbonate catalyst, wherein the strong base is organic strong base or inorganic strong base; the organic strong base comprises sodium methoxide, sodium ethoxide, sodium tert-butoxide, potassium methoxide, potassium ethoxide or potassium tert-butoxide; inorganic strong bases include lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide.
The strongly basic ionic liquid catalyzes CO 2 The method for synthesizing the dimethyl carbonate catalyst comprises the step of selecting at least one of ionic liquid anionic Li salt, anionic Na salt, anionic K salt and ionic liquid anionic Cs salt from the ionic liquid anionic metal salt.
The strongly basic ionic liquid catalyzes CO 2 A method for synthesizing a dimethyl carbonate catalyst, the solvent being selected from at least one of ethanol, acetonitrile, acetone, benzene, toluene and xylene.
The strongly basic ionic liquid catalyzes CO 2 A method for synthesizing a dimethyl carbonate catalyst, the ionic liquid cation salt being selected from at least one of tetraethylammonium bromide salt, tetrabutylammonium bromide salt, 2-hydroxyethyltrimethylammonium chloride salt and 2-hydroxyethyltrimethylammonium bromide salt.
The invention has the advantages and effects that:
1) the strongly basic ionic liquid derived from the system has the capability of catalyzing cycloaddition reaction and ester exchange reaction, has high thermal stability, strong basicity and circulation stability, and simultaneously has the capability of catalyzing CO 2 Have general applicability to the production of cyclic carbonates with a variety of epoxides.
2) The anion of the strongly alkaline ionic liquid derived from the system provided by the invention is derived from reaction raw materials, and no additional impurity is introduced. The catalyst does not need to separate the chain catalytic cycloaddition reaction and the ester exchange reaction, and can obviously shorten the reaction flow and reduce the production energy consumption.
Drawings
FIG. 1 is a synthesis process of ionic liquids PGK, PG-TEA, PG-TBA and PG-CH;
FIG. 2 (a) is a photograph of potassium 1, 2-Propanediol (PGK) synthesized in example 1;
FIG. 2 (b) is a photograph of ionic liquids PG-TEA, PG-TBA and PG-CH synthesized in example 1;
FIG. 3 is nuclear magnetic H spectrum of ionic liquid PG-TEA synthesized in example 1;
FIG. 4 is the nuclear magnetic C spectrum of ionic liquid PG-TEA synthesized in example 1;
FIG. 5 shows the nuclear magnetic H spectrum of the PG-TBA ionic liquid synthesized in example 1;
FIG. 6 shows the nuclear magnetic C spectrum of the PG-TBA ionic liquid synthesized in example 1;
FIG. 7 shows the nuclear magnetic H spectrum of the PG-CH ionic liquid synthesized in example 1;
FIG. 8 is the nuclear magnetic C spectrum of PG-CH ionic liquid synthesized in example 1;
FIG. 9 is an infrared image of 3 ionic liquids synthesized in example 3;
FIG. 10 is a schematic representation of liquid catalyzed CO of example 4 with a single component separator 2 Synthesizing DMC reaction effect in one step;
FIG. 11 shows the catalysis of CO by PG-TEA, PG-TBA, and PG-CH of example 5 2 A cycloaddition effect;
FIG. 12 is a comparison of the performance of the catalysts of the transesterification reaction of example 5;
FIG. 13 is a graph showing the effect of reaction time on PC yield at different temperatures in example 6;
FIG. 14 is a graph of the effect of reaction time on DMC yield at different temperatures for example 7.
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.
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, the alkali intensity analysis, the alkali amount calculation, the nuclear magnetic H spectrum analysis, the nuclear magnetic C spectrum analysis and the infrared spectrum analysis characterization analysis are all conventional operations, and the operation can be performed by a person skilled in the art according to the instruction of an instrument.
The conversion, selectivity and yield in the examples of the invention were calculated as follows:
X PO /%=(n PC +n DMC +n PM1 +n PM2 )×100/(n PC +n DMC +n PM1 +n PM2 +n unreacted PO )
S PC /%= n PC ×100/(n PC +n DMC +n PM1 +n PM2 )
S DMC /%=n DMC ×100/(n DMC +n PC +n PM1 +n PM2 )
S PM1 /%=n PM1 ×100/(n PC +n DMC +n PM2 )
S PM2 /%=n PM2 ×100/(n PC +n DMC +n PM1 )
Y DMC /% =X PO ×S DMC
Y PM1 /% =X PO ×S PM1
Y PM2 /% =X PO ×S PM2
TON=n Target /n Cat =(n PO ×X PO ×S Target )/ (n Cat )
In the formula: PM1 is 1-methoxy-2-propanol, PM2 is 2-methoxy-1-propanol; x PO Is the conversion of propylene oxide,%; s PC Selectivity for propylene carbonate,%; s DMC Selectivity for dimethyl carbonate,%; SPM1 is selectivity to 1-methoxy-2-propanol,%; SPM2 is the selectivity of 2-methoxy-1-propanol,%; y is DMC Yield as dimethyl carbonate,%; y is PM1 Yield of 1-methoxy-2-propanol,%; y is PM2 Yield for 2-methoxy-1-propanol,%; n is the molar mass, mol, of the target product; n is PO Is the molar weight of propylene oxide, mol; n is PC Is the mol weight of propylene carbonate,%; n is PM1 Is the molar amount of 1-methoxy-2-propanol,%; n is PM2 Is the molar weight, mol, of 2-methoxy-1-propanol; n is DMC Is the molar weight, mol, of dimethyl carbonate; n is Cat Is the molar weight of the active site of the catalyst, mol; s target is the selectivity,%, of the target product.
Example 1
The preparation method of the homogeneous strong-base ionic liquid catalyst comprises the following steps:
(1) 1, 2-propylene glycol potassium salt (PGK) synthesis: 1 mol of 1, 2-Propanediol (PG) solution was added to a 500 mL beaker, 0.5 mol of potassium hydroxide (KOH) was added to the 1, 2-propanediol solution, and dissolved completely using an ultrasonic instrument, and then rotary evaporated at 135 ℃ for 3 hours using a rotary evaporator, respectively. The process is to separate the byproduct water generated by the reaction of KOH and 1, 2-propanediol out of the reaction system to obtain 1, 2-propanediol and 1, 2-propanediol potassium salt (PGK) catalyst with approximate molar ratio of 1:1, and after the completion, 100 g of MeOH solution is additionally added to be uniformly mixed, and then the mixture is stored at room temperature, as shown in FIG. 1 (a).
(2) The base amount of PGK was 4.88 mmol/g as calculated from base titration, a fixed mass of PGK (0.091 mol) was ion-exchanged with equimolar amounts of tetraethylammonium bromide (19.12 g), tetrabutylammonium bromide (29.46 g) and choline chloride (12.71 g), stirred at room temperature for 24 hours, then KBr (KCl) precipitate was filtered off, and it was rotary evaporated using a rotary evaporator at 60 ℃ for 3 hours to give homogeneous ionic liquids of 1, 2-propyleneglycoltetraethylammonium (PG-TEA), 1, 2-propyleneglycoltetrabutylammonium (PG-TBA) and 1, 2-propyleneglycolated-choline (PG-CH), as shown in FIG. 1 (b), whose yields were 96.57%, 97.02% and 96.68%, respectively.
The quaternary ammonium salt ionic liquid comprises the following reaction steps:
see FIG. 1 for the synthesis of PGK (a) and PG-TEA, PG-TBA and PG-CH ionic liquids (b).
The homogeneous catalyst is high-purity active ionic liquid, and the yield is 96.57%, 97.02% and 96.68% respectively.
1, 2-propylene glycol potassium salt (PGK) synthesis: 1 mol of 1, 2-Propanediol (PG) solution was added to a 500 mL beaker, 0.5 mol of potassium hydroxide (KOH) was added to the 1, 2-propanediol solution, and dissolved completely using an ultrasonic instrument, and then rotary evaporated at 135 ℃ for 3 hours using a rotary evaporator, respectively. The process is to separate the byproduct water generated by the reaction of KOH and 1, 2-propanediol out of the reaction system to obtain 1, 2-propanediol and 1, 2-propanediol potassium salt (PGK) catalyst with approximate molar ratio of 1:1, and after the completion, 100 g of MeOH solution is additionally added to be uniformly mixed, and then the mixture is stored at room temperature, as shown in FIG. 2 (a).
The base amount of PGK was 4.88 mmol/g as calculated from base titration, a fixed mass of PGK (0.091 mol) was ion-exchanged with equimolar amounts of tetraethylammonium bromide (19.12 g), tetrabutylammonium bromide (29.46 g) and choline chloride (12.71 g), stirred at room temperature for 24 hours, then KBr (KCl) precipitate was filtered off, and it was rotary evaporated using a rotary evaporator at 60 ℃ for 3 hours to give homogeneous ionic liquids 1, 2-propanediol-tetraethylammonium (PG-TEA), 1, 2-propanediol-tetrabutylammonium (PG-TBA) and 1, 2-propanediol-choline (PG-CH), respectively, whose yields were 96.57%, 97.02% and 96.68% as shown in FIG. 2 (b).
See fig. 2 pgk (a) and PG-TEA (b. (1)), PG-TBA (b. (2)), and PG-CH (b. (3)) ionic liquids.
Prepared ionic liquid 1 H NMR and 13 the C NMR characterization results are as follows: nuclear magnetic field results for 1, 2-propanediol-tetraethylammonium (PG-TEA): 1 H NMR (500 MHz, DMSO-d6) δ 3.56–3.46 (m, 1H), 3.18 (s, 3H), 1.13 (d, J = 3.2 Hz, 2H), 0.90 (s, 3H). 13 C NMR (126 MHz, DMSO) δ 68.81, 68.10, 51.88, 20.51, 7.55.
nuclear magnetic results of 1, 2-propanediol-tetrabutylammonium (PG-TBA): 1 H NMR (500 MHz, DMSO-d6) δ 3.77 (q, J = 6.0 Hz, 1H), 3.42 (d, J = 2.0 Hz, 2H), 3.41 (s, 3H), 1.81 (m, 2H), 1.54 (m, 2H), 1.18 (s, 3H). 13 C NMR (126 MHz, DMSO-d6) δ 68.56, 68.01, 57.98, 23.54, 20.47, 19.69, 13.98.
1, 2-propyleneglycolated-choline (PG-CH) nuclear magnetic results: 1 H NMR (500 MHz, DMSO-d6) δ 4.16 (t, J = 5.2 Hz, 2H), 3.82–3.75 (m, 1H), 3.34 (s, 9H), 1.18 (s, 3H). 13 C NMR (126 MHz, DMSO) δ 69.79, 68.55, 68.05, 58.44, 53.55, 20.36.
based on the developed homogeneous ionic liquid catalyst, the catalyst can be directly synthesized into dimethyl carbonate through two continuous steps without separation. The ionic liquid synthesized in the first stage firstly catalyzes PO and CO 2 And (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 realized 2 And PO are not separated to synthesize DMC and coproduce the product 1, 2-propylene glycol in high yield.
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. The ionic liquid with the new structure has simple synthesis process, is environment-friendly, has strong basicity and excellent catalytic activity, and has important industrial application prospect in the field of carbonate synthesis.
The strongly alkaline ionic liquid derived from the system catalyzes CO 2 Catalyst for synthesizing dimethyl carbonate, its epoxy compound and CO 2 Reacting with methanol as raw material, and catalyzing epoxypropane and CO by homogeneous phase ionic liquid 2 Synthesizing propylene carbonate. Then, the catalyst is mixed with MeOH without separation and enters a second-stage reaction-rectification tower after being cooled, dimethyl carbonate-methanol azeotrope is extracted from the tower top, 1, 2-propylene glycol is extracted from the tower bottom, and CO is realized 2 And synthesizing the dimethyl carbonate in one step with high yield.
The temperature of the cycloaddition reaction is 100-140 ℃, the reaction time is 1-10 h, and CO is added 2 The initial pressure is 1.0-4.0 MPa; the reaction temperature is 60-80 ℃ in the ester exchange process of PC and MeOH;
the epoxy compound includes: epoxy compounds such as butylene oxide, epichlorohydrin, epoxystyrene, allyl glycidyl ether, glycidol, and phenyl glycidyl ether.
The ionic liquid catalyst comprises a cation and an anion;
the anions comprise oxyanions of diols of different chain lengths;
the cations contain amines of different side chain lengths of the nitrogen atom.
Preferably, the cation has the formula
Or formula
The structure shown;
the anion has the formula
Or formula
The structure shown;
wherein R is 1 Independently selected from one of C1-C6 alkane group, C2-C6 alkene group and C3-C6 aromatic hydrocarbon group;
R 2 independently selected from one of C1-C6 alkane group, C2-C6 alkene group and C3-C6 aromatic hydrocarbon group;
R 3 independently selected from one of C2-C6 alkane group, C2-C6 alkene group and C3-C6 aromatic hydrocarbon group;
R 4 independently selected from one of C1-C6 alkane group, C1-C6 alkene group and C1-C6 aromatic hydrocarbon group.
Preferably, R 1 、R 2 Is independently selected from-CH 3 、-CH 2 CH 3 、-(CH 2 ) 2 CH 3 、-(CH 2 ) 3 CH 3 One kind of (1).
Preferably, R 3 、R 4 Is independently selected from-CH 3 、-CH 2 CH 3 、-(CH 2 ) 2 CH 3 、-(CH 2 ) 3 CH 3 One kind of (1).
The catalyst is ionic liquid; the preparation method of the ionic liquid comprises the following steps:
a1) adding strong base into dihydric alcohol, heating for reaction, and separating product water to obtain metal salt containing oxygen anion;
a2) and dissolving the metal salt containing the oxygen anions in a solvent, adding an ionic liquid cation salt, filtering the precipitate after reaction, and separating the solvent to obtain the ionic liquid.
The solvent is at least one selected from ethanol, acetonitrile, acetone, benzene, toluene and xylene;
the strong base is organic strong base or inorganic strong base;
the organic strong base comprises sodium methoxide, sodium ethoxide, sodium tert-butoxide, potassium methoxide, potassium ethoxide or potassium tert-butoxide;
the inorganic strong base comprises 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;
the molar ratio of the ionic liquid anion source to the base is 0.9-1.1;
preferably, in step a 1), the source of ionic liquid anions comprises ethylene glycol, 1, 2-propanediol or 1, 2-butanediol;
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, cyclohexane, benzene, toluene and xylene;
the ionic liquid cation salt is selected from at least one of tetraethylammonium bromide salt, tetrabutylammonium bromide salt, 2-hydroxyethyl trimethylammonium chloride salt and 2-hydroxyethyl trimethylammonium bromide salt;
preferably, step a 2) further comprises: and after the reaction is finished, removing the solvent to obtain the high-purity ionic liquid.
In the present invention, "PGK" means potassium 1, 2-propanediol.
In the present invention, "PG-TEA" means 1, 2-propanediol-tetraethylammonium.
In the present invention, "PG-TBA" means 1, 2-propanediol-tetrabutylammonium.
In the present invention, "PG-CH" refers to 1, 2-propyleneglycolated-choline.
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 on 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 the p-tolyl radical formed by toluene losing the hydrogen atom para to the methyl group on the phenyl ring.
See FIG. 3 for the synthesized PG-TEA ionic liquid nuclear magnetic H spectrum; FIG. 4 NMR spectrum of synthesized PG-TEA ionic liquid; FIG. 5 shows the nuclear magnetic H spectrum of synthesized PG-TBA ionic liquid; FIG. 6 shows nuclear magnetic C spectrum of synthesized PG-TBA ionic liquid; FIG. 7 shows the NMR spectrum of synthesized PG-CH ionic liquid; FIG. 8 shows the nuclear magnetic C spectrum of synthesized PG-CH ionic liquid.
Example 2
The physical parameters of the synthesized PG-TEA, PG-TBA and PG-CH ionic liquids were measured, and the densities thereof were about 0.87, 0.90 and 0.89 g/m, respectively. The ionic liquid PG-TEA alkali strength range is 15.0< H- <18.4, PG-TBA and PG-CH alkali strength range is 18.4 < H- < 22.3 measured by a Hammett indicator method, and the Hammett indicators used in the process comprise phenolphthalein, 2, 4-dinitroaniline, p-nitroaniline, diphenylamine and aniline. Compared with common strong bases such as sodium hydroxide, sodium methoxide and sodium tert-butoxide, the alkali strength of the ionic liquid PG-TEA is equivalent to that of potassium hydroxide, and the alkali strength of PG-TBA and PG-CH is equivalent to that of sodium tert-butoxide and higher than that of sodium methoxide. The measured alkali amounts of PG-TEA, PG-TBA and PG-CH ionic liquid by adopting a benzoic acid titration method are 1.81, 2.45 and 2.98 mmol/g respectively
Example 3
The PG-TBA, PG-TEA and PG-CH functional groups of the ionic liquid are characterized as shown in figure 9, and 3400 cm -1 The absorption peak is the stretching vibration of-OH group, 2968 cm -1 Stretching vibration of-CH 3 base, 2866 cm -1 is-CH 2 1648 cm of telescopic vibration -1 Is C-N telescopic vibration, 1384 cm -1 Is C-H symmetric bending vibration, 1289 cm -1 C-O stretching vibration, 1139 cm -1 Is the stretching vibration peak of the C-C single bond. The synthesized ionic liquid is shown to have typical cation and 1, 2-propylene glycol anion functional groups.
See FIG. 9 FTIR spectra for PG-TBA, PG-TEA, and PG-CH.
Example 4
Catalysis of CO with PG-TEA, PG-TBA and PG-CH, respectively 2 The DMC reaction was synthesized in one step, the reaction conditions were as described in the catalyst evaluation methods, and the reaction results are shown in fig. 10. PO conversion was 96.48%, 93.16, and 96.11%, PC selectivity was 12.95%, 33.74%, and 32.89%, DMC selectivity was 8.67%, 2.81%, and 3.41%, DMC yield was 8.36%, 2.62%, and 3.28%, corresponding to TON values of 10.19, 3.19, and 3.99, respectively. The reason why the three ionic liquid catalysts did not exhibit good DMC yields may be: the catalyst has strong basicity and not only catalyzes CO 2 Cycloaddition occurs and PO and MeOH are catalyzed to generate alcoholysis reaction, so that part of the intermediate product is converted into other by-products, and the expected high yield of DMC cannot be achieved. GC-MS qualitative analysis of the whole product shows that the alcoholysis product 1-methoxy-2-propanol (P) is ensured in the systemM1) and 2-methoxy-1-propanol (PM 2), and the PM1 yields at 6 h of reaction had reached 54.26%, 44.51% and 46.35%, respectively, the PM2 yields reached 21.36%, 12.46% and 14.87%, and the PC yields were 12.49%, 31.43% and 31.61%, indicating that PO is more susceptible to alcoholysis and epoxidation reactions and that the transesterification process is inhibited. We designed to successively complete PO-CO without separating the catalyst 2 A new process of two-stage reaction of cycloaddition and transesterification of PC-MeOH. PO and CO completion in the absence of MeOH 2 The selectivity and yield of DMC can be improved by cycloaddition followed by transesterification with PC and MeOH.
FIG. 10 shows that the single-component ionic liquid catalyzes PO and CO 2 One-step synthesis of DMC with methanol
Example 5
The DMC synthesis in a two-stage continuous reaction process is carried out in a specific manner by first carrying out the PO and CO in a first stage without MeOH addition 2 Performing cycloaddition reaction to synthesize PC; then, MeOH is added into the system to perform ester exchange with the PC synthesized in the previous section, thereby realizing DMC high-yield synthesis. PG-TEA, PG-TBA and PG-CH ionic liquid catalysts are respectively used, and no solvent or cocatalyst is added in the whole reaction process. Epoxidation reaction conditions: 8.00 g (0.14 mol) PO, CO 2 The initial pressure was 2.6 MPa and the catalyst amounts were all equimolar (1.13X 10) -3 mol), reaction temperature 130 ℃ and results of gas chromatography analysis of the product after 6 h of reaction are shown in FIG. 11. After the 3 ionic liquid catalysts catalyze the cycloaddition reaction, the calculated PO conversion rates are respectively 98.48%, 99.03% and 79.85%, and the TON rates are respectively 118.84, 119.51 and 96.36. Demonstration of PG-TBA catalyzed CO 2 The capability of catalyzing cycloaddition reaction with PO is better than that of PG-TEA and PG-CH. The selectivity of the product PC is over 99 percent, which indicates that no other side reaction occurs. The cycloaddition reaction process is a cationic electrophilic and anionic nucleophilic reaction, and the ring of the propylene oxide is opened under the synergistic action of anions and cations. The reason why the quaternary ammonium salt of the 1, 2-propylene glycol oxygen negative anion has higher catalytic activity is probably that the anion has stronger nucleophilicity and leaving ability due to the larger radius of the ionic group of the 1, 2-propylene glycol oxygen negative anion, larger steric hindrance, larger deformability, stronger polarization ability and stronger alkalinity. It is not only oneA strong nucleophilic group and at the same time a good leaving group. Because the ionic bond of the 1, 2-propylene glycol oxygen anion and the tetrabutylammonium cation is weaker, free anions and cations are more easily formed in the solution, so that the catalytic activity of the catalyst is enhanced, and the optimal reaction effect is achieved.
See FIG. 11 PG-TEA, PG-TBA, and PG-CH for CO catalysis 2 Cycloaddition effect
Then, MeOH was added directly in an amount of 10 times the molar amount of PC produced at a reaction temperature of 68 ℃ and the reaction product was collected at regular sampling intervals over a period of 1-120 min and analyzed, and the results are shown in FIG. 12. Obviously, the difference of the PC ester exchange capacities catalyzed by the three catalysts is obvious, the DMC selectivity of the 3 catalysts is over 99 percent, the PG-CH activity is the worst, and the conversion balance is achieved after 360 min of reaction; the catalytic activity of PG-TEA is improved, and the conversion balance is achieved when the reaction time is 180 min; PG-TBA has excellent ester exchange catalytic capability of PC and MeOH, the reaction equilibrium is reached only after 120 min of reaction, and the DMC yield reaches up to 71.22%. The ionic liquid shows excellent catalytic activity and is attributed to strong nucleophilicity of anions, 1, 2-propylene glycol oxygen anion and hydrogen proton in MeOH can be subjected to reversible exchange to activate MeOH to generate methoxy anion, and then the methoxy anion attacks carbon atoms on carbonyl groups to complete nucleophilic reaction, PG-TBA shows better catalytic efficiency than PG-TEA and PG-CH, and the fact that in quaternary ammonium salts with the same anion substituent, ionic bonds of 1, 2-propylene glycol anion and tetrabutylammonium cation are weaker, and free anions and cations are more easily formed in solution, so that the catalytic activity of the ionic liquid is enhanced. Therefore, the ionic liquid PG-TBA is used as a catalyst in subsequent cycloaddition and ester exchange researches.
See figure 12 for a comparison of the transesterification catalyst performance.
Example 6
FIG. 13 examines the PG-TBA catalyst for PO and CO at different reaction temperatures and times 2 Effect of cycloaddition reaction efficiency. 8.00 g (0.14 mol) PO, CO 2 Initial pressure of 2.6 MPa and catalyst amount of 1.13X 10 -3 And (mol). The experimental result shows that the PG-TBA catalytic cycloaddition reaction has extremely high efficiency, the PC selectivity reaches more than 99 percent under different temperature conditions, and basically no intermediate product is generatedSo the PO conversion rate is similar to the PC yield. The reaction is carried out for 1 h at the reaction temperatures of 115, 120, 125 and 130 ℃, and the PC yield is 47.94%, 66.78%, 83.90% and 92.49% respectively; when the reaction time is 2 hours, the yield of PC is respectively increased to 59.03%, 77.57%, 88.73% and 95.70%; when the reaction time is 4 h, the yield of PC is respectively improved to 73.01%, 86.61%, 93.79% and 97.58%; when the reaction time is 6 hours, the PC yield is respectively improved to 82.69%, 91.01%, 96.56% and 99.03%. When the reaction temperature was increased from 115 ℃ to 130 ℃ for 6 h, the TON value increased from 99.79 to 119.51. The above experimental results fully illustrate that PO and CO 2 The cycloaddition reaction rate has obvious dependence on the reaction temperature; as the cycloaddition reaction is an exothermic reaction, even under the condition of lower temperature, PG-TBA also shows extremely high catalytic activity, can promote PO ring opening in a shorter time and then complete the cycloaddition reaction, and has stronger cycloaddition catalytic capability.
See FIG. 13 effect of reaction time on PC yield at different temperatures.
Example 7
FIG. 14 examines the effect of PG-TBA catalyst on the efficiency of the transesterification of PC with MeOH at different reaction temperatures and times. The catalyst dosage is 1.13X 10 -3 mol, PC/MeOH molar ratio 1/10. Because the PG-TBA catalyzed transesterification reaction has extremely high efficiency, the DMC selectivity reaches more than 99 percent under different temperature conditions, and no intermediate product is generated basically, the DMC yield is similar to the PC conversion rate. The reaction is carried out for 30 min at the reaction temperatures of 0, 25, 50 and 68 ℃, and the DMC yields are respectively 9.92%, 13.07%, 25.52% and 37.73%; when the reaction time is 120 min, the DMC yield is respectively improved to 17.91%, 47.28%, 52.09% and 68.04%. At 25 ℃, reaction equilibrium is reached in 360 min; at 50 ℃, reaction equilibrium is reached in 300 min; the reaction was carried out at 68 ℃ and equilibrium was reached within 120 min. When the reaction temperature was increased from 0 ℃ to 68 ℃ and the reaction time was 60 min, the TON value and the DMC yield were significantly increased, increasing from 14.69 to 57.38 and from 12.03 to 47.08%, respectively. The experimental results fully show that the transesterification reaction rate of PC and MeOH has obvious dependence on the reaction temperature, and PG-TBA also shows extremely high catalytic activity even under the extremely low temperature condition, and can complete the reaction within extremely short time after the PC ring openingThe ester exchange reaction has super strong ester exchange catalytic ability.
FIG. 14 effect of reaction time on DMC yield at different temperatures.
Example 8
Table 1 investigation of PG-TBA Ionic liquids catalyzing CO 2 The universality of cycloaddition reaction with various epoxy compounds. Reaction conditions are as follows: epoxide (0.14 mol), CO 2 Initial pressure 2.6 MPa, catalyst consumption 1.13X 10 -3 mol, reaction temperature of 130 ℃ and reaction time of 6 h. Epoxides with different substituents all show higher conversion rate and cyclic carbonate product selectivity of more than 99 percent. Under the same reaction conditions, the conversion rate of butylene oxide is 93.75%, which is slightly lower than that of propylene oxide 99.03%, and the alkyl substitution of the epoxide is accompanied by the growth of side chain, so that the alkyl substitution is more steric hindrance and more difficult to activate and open. The highest conversion rate of the epichlorohydrin reaches 99.29 percent because the substituent chlorine atom belongs to an electron-withdrawing group, has small steric hindrance, is easy to combine with quaternary ammonium salt cations and 1, 2-propylene glycol anions and is most easily activated to open a ring. Due to the large molecular size of epoxystyrene, allyl glycidyl ether, glycidol and phenyl glycidyl ether, the larger steric hindrance hindered nucleophilic attack of the anion, resulting in conversions of 91.15%, 89.38%, 92.56% and 90.13%, respectively, but still substantially reaching yields of cyclic carbonate higher than 90%. The above experimental results fully illustrate the universality of the quaternary ammonium salt ionic liquid based on 1, 2-propylene glycol anions, which is derived from the product 1, 2-propylene glycol system, for catalyzing cycloaddition reactions of various epoxy compounds.
TABLE 1 PG-TBA catalyzed CO 2 Cycloaddition reaction results with various epoxides
Example 9
The active center of the synthesized ionic liquid with the new structure is 1, 2-propylene glycol oxygen negative ions with strong affinity and has oxygen negative ions of alcohols with different chain lengths; amines with different side chain lengths in which the cation contains a nitrogen atom are within the scope of this 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 (8)
1. Strongly alkaline ionic liquid catalyzed CO 2 The method for synthesizing the dimethyl carbonate catalyst is characterized by comprising the following steps of:
epoxy compound, CO 2 The catalyst reacts with methanol as raw material, and the homogeneous phase ionic liquid can realize one-step synthesis of dimethyl carbonate or firstly catalyze epoxy compound and CO 2 Synthesizing cyclic carbonate, then, the catalyst is mixed with MeOH without separation and cooled, and then enters a second-stage reaction-rectification tower, a dimethyl carbonate-methanol azeotrope is extracted from the tower top, and the tower bottom is a corresponding dihydric alcohol product, so that CO is realized 2 And synthesizing dimethyl carbonate in one step with high yield;
the epoxy compound comprises epoxy butane, or epoxy chloropropane, epoxy styrene, allyl glycidyl ether, glycidol and phenyl glycidyl ether;
the temperature of the cycloaddition reaction is 100-140 ℃, the reaction time is 1-10 h, and CO is added 2 The initial pressure is 1.0-4.0 MPa; the reaction temperature during the transesterification of PC and MeOH is 60-80 ℃.
2. The strongly basic ionic liquid catalyzed CO of claim 1 2 The method for synthesizing the dimethyl carbonate catalyst is characterized in that the catalyst is ionic liquid, and the ionic liquid comprises cations and anions; the anions having different chain lengthsOxyanions of alcohol; amines with different side chain lengths of the cation containing a nitrogen atom.
3. The strongly basic ionic liquid catalyzed CO of claim 1 2 The method for synthesizing the dimethyl carbonate catalyst is characterized in that the preparation steps of the ionic liquid comprise: adding strong base into dihydric alcohol, heating for reaction, and separating product water to obtain metal salt containing oxygen anion; dissolving metal salt containing oxygen anion in a solvent, adding ionic liquid cation salt, filtering the precipitate after reaction, and separating the solvent to obtain the ionic liquid.
4. The strongly basic ionic liquid catalyzed CO of claim 3 2 The method for synthesizing the dimethyl carbonate catalyst is characterized in that the dihydric alcohol comprises at least one of ethylene glycol, 1, 3-propylene glycol, 1, 2-propylene glycol, 1, 4-butanediol and the like.
5. The strongly basic ionic liquid catalyzed CO of claim 3 2 The method for synthesizing the dimethyl carbonate catalyst is characterized in that the strong base is organic strong base or inorganic strong base; the organic strong base comprises sodium methoxide, sodium ethoxide, sodium tert-butoxide, potassium methoxide, potassium ethoxide or potassium tert-butoxide; inorganic strong bases include lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide.
6. The strongly basic ionic liquid catalyzed CO of claim 3 2 The method for synthesizing the dimethyl carbonate catalyst is characterized in that the ionic liquid anionic metal salt is at least one selected from ionic liquid anionic Li salt, anionic Na salt, anionic K salt and ionic liquid anionic Cs salt.
7. The strongly basic ionic liquid catalyzed CO of claim 3 2 A method for synthesizing a dimethyl carbonate catalyst, characterized in that the solvent is at least one selected from the group consisting of ethanol, acetonitrile, acetone, benzene, toluene and xylene。
8. The strongly basic ionic liquid catalyzed CO of claim 3 2 A method for synthesizing a dimethyl carbonate catalyst, characterized in that the ionic liquid cation salt is selected from at least one of tetraethylammonium bromide salt, tetrabutylammonium bromide salt, 2-hydroxyethyltrimethylammonium chloride salt and 2-hydroxyethyltrimethylammonium bromide salt.
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