Preparation and application of a dual-functional ionic polymer material

Abstract

The present invention belongs to the technical field of synthesis of ionic polymer catalytic materials, and discloses the preparation and application of a bifunctional ionic polymer material. Specifically, a "bifunctional" ionic polymer catalytic material is prepared by polymerization reaction with ionic liquid monomer, 1-vinyl imidazole and divinylbenzene monomer. The material immobilizes halogen anions with CO2 activation function and tertiary nitrogen groups with catalytic effect on transesterification on a polymer skeleton, and the ionic polymer catalytic material has the advantages of uniform distribution of active sites, good stability, simple synthesis process, and green environmental protection. The present invention applies the prepared "bifunctional" ionic polymer catalytic material to catalyze the two-step reaction of synthesizing propylene carbonate from carbon dioxide and propylene oxide and synthesizing dimethyl carbonate from propylene carbonate and methanol, which not only shows excellent catalytic performance under relatively mild reaction conditions, but also realizes that a catalyst catalyzes two-step reactions simultaneously.

Description

Technical Field

[0001] The invention belongs to the technical field of synthesis of ionic polymer catalytic materials, and specifically involves the preparation of a "bifunctional" ionic polymer catalytic material through polymerization reaction and its application in catalytic conversion of carbon dioxide. Background Art

[0002] Since the Industrial Revolution, with the rapid development of economy, CO 2 The amount of carbon dioxide emissions has also accumulated, exceeding the natural absorption capacity, breaking the carbon balance in nature, leading to frequent extreme weather and a series of climate problems. At the same time, the imbalance in energy consumption structure has also led to an increase in CO 2 The concentration of CO in the atmosphere has increased dramatically. 2 The concentration (419 ppm, data from May 2021) has far exceeded the safety value (350 ppm). Therefore, reducing the excessive CO in the atmosphere 2 concentration is an environmental problem that needs to be addressed urgently. 2 The reduction and resource utilization of CO2 have become a hot topic in research. For a long time in the future, fossil energy will still dominate. 2 To solve the problem of excessive concentration, we should vigorously develop clean energy and adjust the energy structure; on the other hand, we should 2 Carry out capture, storage and utilization (CCUS) to turn waste into treasure.

[0003] CO 2 It is widely used in production and life, and has the advantages of abundant sources, low cost, non-toxicity and renewable, and is an environmentally friendly C1 resource. 2 The resource utilization of CO not only helps to reshape the carbon cycle system, but also realizes the reuse of waste resources. 2 A green chemical product with high value utilization, it is a simple organic carbonate, whose molecular structure contains -CO, -CO-OCH 3 、-OCH 3 、-CH 3 It can be used as carbonylation reagent, methylation reagent and gasoline additive. 2 There are two main routes for synthesizing DMC as raw materials: direct synthesis and two-step transesterification. The difference between the two routes lies in the presence or absence of coupling with high-energy reaction substrates.

[0004] CO 2 The main reason why resource utilization is limited: CO 2 The molecules are in a straight line in space. , which is thermodynamically stable and kinetically inert. In the ground state, the molecular energy is very low, the chemical properties are stable, and it is not easy to activate. Therefore, CO 2 The conversion usually requires high temperature and high pressure. A new type of efficient catalyst was designed and synthesized to catalyze CO under mild conditions. 2 The conversion into DMC has become a research hotspot. Most of the reported catalysts have shortcomings, for example: soluble base catalysts are corrosive and prone to alcoholysis, causing environmental problems; metal oxide catalysts are prone to hydrolysis, and the active sites are unevenly distributed; ion exchange resin catalysts have complex regeneration processes, high costs, and low economic benefits. Ionic liquids (ILs) or ionic polymers have received widespread attention and application in recent years because of their high designability and the ability to give them specific functions.

[0005] The present invention designs a "bifunctional" ionic polymer material to obtain a higher DMC yield at a lower pressure and temperature. ILs are a homogeneous catalyst that is difficult to separate from the reaction system, while ionic polymer materials combine the characteristics of polymers and ionic liquids, providing a platform for adjusting the catalyst structure and catalytic active sites. The two-step transesterification method is based on CO 2 It reacts with epoxide to generate cyclic carbonate, which is then esterified with methanol to synthesize DMC. The advantage of this ionic polymer material as a catalyst is that it can catalyze both steps of the reaction at the same time. The reason is that the halogen anion has a good catalytic effect on the cycloaddition reaction, and the tertiary nitrogen group on the imidazole ring can be used to catalyze the second step of ester exchange reaction without promoting the formation of side reactions, thereby further improving the yield of DMC. Summary of the invention

[0006] The main purpose of the present invention is to prepare a "bifunctional" ionic polymer material through polymerization reaction and to catalyze CO 2 Two-step reaction in the synthesis of DMC by transesterification.

[0007] In order to achieve the above-mentioned purpose of the invention, the present invention adopts the following technical solutions:

[0008] A "bifunctional" ionic polymer material: 1-vinyl imidazole, ionic liquid monomer and divinyl benzene are used to undergo a polymerization reaction under the action of a chain initiator, and the ionic liquid monomer and imidazole group are bonded to the polymer skeleton through covalent bonds. Specific synthesis steps:

[0009] (1) The imidazole-containing compound and the halogenated compound are dissolved in organic solvents respectively to prepare solutions of certain concentrations, which are denoted as solution A and solution B; then solution A is added dropwise to solution B, and the mixture is stirred at a suitable temperature. After the reaction is completed, the mixture is washed and dried to obtain an ionic liquid monomer containing a halogen anion.

[0010] (2) Add the imidazole-containing compound, ionic liquid monomer and divinylbenzene (DVB) to a mixed organic solvent in sequence, add a chain initiator at the same time, stir thoroughly at a suitable temperature, and after the polymerization reaction is completed, wash and dry to obtain a "bifunctional" ionic polymer material.

[0011] The imidazole-containing compound in step (1) is 1-vinylimidazole (VIM).

[0012] In step (1), the halogenated compound is one of n-butyl bromide and 1,4-dibromobutane.

[0013] The organic solvent in step (1) is acetonitrile.

[0014] The suitable temperature in step (1) is 60 °C and the stirring time is 12 to 24 h.

[0015] In step (1), the molar ratio of 1-vinylimidazole to the halogenated compound is 1.0:1.0-1.0:2.0.

[0016] The organic solvent in step (2) is a mixture of ethanol, acetonitrile, water and ethyl acetate.

[0017] The mid-chain initiator in step (2) is azobisisobutyronitrile (AIBN).

[0018] The suitable temperature in step (2) is 80 °C and the stirring time is 12 to 24 h.

[0019] The imidazole-containing compound in step (2) is 1-vinylimidazole.

[0020] In step (2), the molar ratio of the ionic liquid monomer to the imidazole-containing compound is 1:3 to 3:1; the molar ratio of the ionic liquid monomer plus the imidazole-containing compound to divinylbenzene is 1:1.

[0021] The present invention uses the "bifunctional" ionic polymer material as a catalyst in the two-step synthesis of dimethyl carbonate from carbon dioxide and methanol. The specific operation is as follows: propylene oxide and the bifunctional ionic polymer material are added to a high-pressure reactor, and 0.5-2.5 MPa of CO is charged into the reactor. 2 , stir the reaction at a temperature of 80-160 °C for 0.5-3 h to obtain the intermediate product propylene carbonate, then add methanol to the high-pressure reactor, stir the reaction at a temperature of 80-160 °C for 1-5 h, and the alcohol-ester molar ratio is 2.5:1-20:1 to obtain the final product dimethyl carbonate.

[0022] The beneficial effects of the present invention are:

[0023] The present invention utilizes 1-vinylimidazole, [DVIM]Br / [VIM]Br and divinylbenzene, and can generate a polymerization reaction under the action of a chain initiator. The imidazole group and the ionic liquid monomer are bonded to the polymer skeleton through a covalent bond. The polymer material prepared by the method solves the problem that conventional catalytic materials such as metal oxides have few and unevenly distributed surface active sites.

[0024] Ionic liquids carry halogen anions, which have excellent ring-opening properties. Halogen anions attack the CO bond on PO, causing PO to be activated and open. After the ring opening, hydrogen bonds still exist between the oxygen anion on the intermediate and [DVIM]Br / [VIM]Br, which enhances the nucleophilic ability of the oxygen anion. 2 It is a typical thermodynamically stable acidic molecule that can react with CO 2 The change of the molecule from linear to geometric bending is a way to activate it. The electrons near the tertiary nitrogen have the weakest binding force and are prone to nucleophilic reactions. In addition, VIM can provide a Lewis base environment to attract Lewis acidic molecules to the P-BVD-2 / 3 / 5 skeleton, so CO 2 Under the activation of the tertiary nitrogen of VIM, the C=O double bond becomes a single bond and is inserted into the intermediate after ring opening. Due to the electrostatic effect of VIM, the C-Br bond provided by the donor is easily broken to form a CO bond, which promotes the formation of propylene carbonate PC. The methanol molecule can form a hydrogen bond with the tertiary nitrogen group on VIM, and after being polarized, the OH bond is extended, releasing a methoxy group (CH 3 O - As the hydrogen atom leaves CH 3 OH, the tertiary nitrogen on VIM is nucleophilic. At the same time, the hydrogen bond formed between the oxygen atom on C=O on propylene carbonate PC and [DVIM]Br / [VIM]Br makes PO polarized. The dissociated CH 3 O - Immediately attacks the CO bond on PC, causing it to open the ring. Another molecule CH 3 OH forms a hydrogen bond with the oxygen anion on the intermediate after ring opening, and then releases a molecule of CH 3 O - The CO bond at the other end of the ring-opened PC is attacked to generate DMC. The other part of the intermediate after ring-opening dissociates to form a hydrogen bond with VIM with a hydrogen atom, and after polarization, a hydroxyl group is formed, and finally 1,2-propylene glycol (PG) is generated as a byproduct.

[0025] In addition, this method has a certain universality, and a variety of ionic liquid monomers and a variety of compounds can be used to synthesize corresponding functionalized ionic polymer materials.

[0026] When the halogenated compound is bromobutane, the prepared ionic polymer catalyst is named "P-BVD-n / m / (m+n)", and when the halogenated compound is 1,4-dibromobutane, the prepared ionic polymer catalyst is named "P-2BVD-n / m / (m+n)", wherein "n / m / (m+n)" represents the initial molar ratio of "ionic liquid / VIM / DVB". BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Synthetic diagram for the preparation of P-2BVD-2 / 3 / 5;

[0028] Figure 2 XRD spectra of P-2BVD-2 / 3 / 5, P-2BVD-3 / 0 / 3 and P-2BVD-0 / 3 / 3;

[0029] Figure 3 The infrared spectra of P-2BVD-2 / 3 / 5, P-2BVD-3 / 0 / 3 and P-2BVD-0 / 3 / 3;

[0030] Figure 4 The scanning electron microscope images are P-2BVD-2 / 3 / 5 (b), P-2BVD-3 / 0 / 3 (a), and P-2BVD-0 / 3 / 3 (c);

[0031] Figure 5 The catalytic activity is P-2BVD-3 / 0 / 3, P-2BVD-3 / 1 / 4, P-2BVD-3 / 2 / 5, P-2BVD-1 / 1 / 2, P-2BVD-2 / 3 / 5, P-2BVD-1 / 3 / 4 and P-2BVD-0 / 3 / 3. Specific implementation methods

[0032] The present invention is further described by the following specific examples, but the protection scope of the present invention is not limited to the following examples.

[0033] Example 1

[0034] (1) Synthesis of [VIM]Br ionic liquid monomer

[0035] Weigh 20 mmol of n-butane bromide and dissolve it in 10 mL of acetonitrile to prepare solution A. Weigh 20 mmol of 1-vinylimidazole and dissolve it in 10 mL of acetonitrile to prepare solution B. Add solution A into solution B, and stir magnetically at 60 °C for 24 h under nitrogen protection. Collect the light yellow oily liquid, wash with ethyl acetate and dry it to obtain the monoimidazole ionic liquid monomer [VIM]Br.

[0036] (2) Synthesis of [DVIM]Br ionic liquid monomer

[0037] Weigh 20 mmol of 1,4-dibromobutane and dissolve it in 10 mL of acetonitrile to prepare solution A. Weigh 40 mmol of 1-vinylimidazole and dissolve it in 10 mL of acetonitrile to prepare solution B. Add solution A into solution B, and stir magnetically at 60 °C for 24 h under nitrogen protection. Collect the light yellow oily liquid, wash with ethyl acetate and dry it to obtain the diimidazole ionic liquid monomer [DVIM]Br.

[0038] (3) Synthesis of P-BVD-2 / 3 / 5

[0039] 4 mmol [VIM] Br, 6 mmol 1-vinylimidazole and 10 mmol divinylbenzene were weighed respectively and dissolved in a mixed solvent of 6 ml ethanol, 10 ml ethyl acetate, 6 ml acetonitrile and 6 ml water, and then transferred to a three-necked flask, and 0.87 mmol AIBN was added. The mixture was stirred at room temperature for 30 min. After the added substances were fully dissolved, they were magnetically stirred at 80 °C for 24 h under a nitrogen atmosphere. The white precipitate was collected, washed with ethanol and dried to obtain the monoimidazole "bifunctional" ionic polymer material P-BVD-2 / 3 / 5.

[0040] (4) Synthesis of P-2BVD-2 / 3 / 5

[0041] 4 mmol [DVIM] Br, 6 mmol 1-vinylimidazole and 10 mmol divinylbenzene were weighed separately and dissolved in a mixed solvent of 6 ml ethanol, 6 ml ethyl acetate, 6 ml acetonitrile and 10 ml water, and then transferred to a three-necked flask, and 0.87 mmol AIBN was added. The mixture was stirred at room temperature for 30 min. After the added substances were fully dissolved, they were magnetically stirred at 80 °C for 24 h under a nitrogen atmosphere. The white precipitate was collected, washed with ethanol and dried to obtain the bi-imidazole "bifunctional" ionic polymer material P-BVD-2 / 3 / 5.

[0042] Figure 1 It is the synthesis diagram of P-2BVD-2 / 3 / 5 prepared in this example.

[0043] Figure 2It is the XRD spectra of ionic polymer materials P-2BVD-3 / 0 / 3, P-2BVD-2 / 3 / 5 and P-2BVD-0 / 3 / 3 prepared by the present embodiment. From the XRD spectra, it can be observed that a series of ionic polymer materials after polymerization only have dispersion peaks near 20 ° of angles, indicating that P-2BVD-3 / 0 / 3, P-2BVD-2 / 3 / 5 and three kinds of polymers of P-2BVD-0 / 3 / 3 are amorphous, and there is no crystalline form, which is caused by disordered polymer stacking mode. Meanwhile, the position and peak shape of the dispersion peak of P-2BVD-2 / 3 / 5 containing different content anions are slightly different when subjected to the interaction between different anions and cations.

[0044] Figure 3 The infrared spectra of the ionic polymer materials P-2BVD-3 / 0 / 3, P-2BVD-2 / 3 / 5 and P-2BVD-0 / 3 / 3 prepared in this example are shown in FIG. -1 The characteristic peak centered at is attributed to the stretching vibration of CN in the aminoalkyl chain of the [DVIM]Br monomer. Comparison of P-2BVD-3 / 0 / 3, P-2BVD-2 / 3 / 5 and P-2BVD-0 / 3 / 3 shows that this characteristic peak exists in P-2BVD-3 / 0 / 3 and P-2BVD-2 / 3 / 5, but not in P-2BVD-0 / 3 / 3, indicating that [DVIM]Br is successfully aggregated into the polymer backbone of P-2BVD-3 / 0 / 3 and P-2BVD-2 / 3 / 5, but not into the polymer backbone of P-2BVD-0 / 3 / 3. At 1450 cm -1 and 862 cm -1 The two characteristic peaks are attributed to the folding vibration of the imidazole ring. Without the addition of VIM, 862 cm-1 was not observed in P-2BVD-3 / 0 / 3. -1 The peaks at , and the characteristic peaks of imidazole rings at two locations can be observed in P-2BVD-2 / 3 / 5 and P-2BVD-0 / 3 / 3 with added VIM, which confirms that the monomer VIM has been successfully introduced into the polymer backbone.

[0045] Figure 4It is the scanning electron microscope image of the ionic polymer material P-2BVD-3 / 0 / 3, P-2BVD-2 / 3 / 5 and P-2BVD-0 / 3 / 3 prepared in the present embodiment. It can be seen from the figure that the microscopic morphology of P-2BVD-3 / 0 / 3, P-2BVD-2 / 3 / 5 and P-2BVD-0 / 3 / 3 evolves into spherical particles stacked from the irregular structure of mutual crosslinking. In P-2BVD-3 / 0 / 3, [DVIM] Br monomers are irregularly crosslinked with each other, and in P-2BVD-2 / 3 / 5, the prototype of spherical particles begins to appear, and in P-2BVD-0 / 3 / 3, uniform spherical particles are stacked with each other to form a clustered morphology. This change is attributed to the reduction of [DVIM] Br content with crosslinking characteristics in the polymer skeleton, resulting in the continuous weakening of intermolecular forces in the microstructure.

[0046] Figure 5 The ionic polymer materials P-2BVD-3 / 0 / 3, P-2BVD-3 / 1 / 4, P-2BVD-3 / 2 / 5, P-2BVD-1 / 1 / 2, P-2BVD-2 / 3 / 5, P-2BVD-1 / 3 / 4 and P-2BVD-0 / 3 / 3 prepared in this embodiment were subjected to cycloaddition reaction at a temperature of 140°C and 1.5 MPa CO 2 The performance comparison of PC and DMC yields was carried out under the conditions of 140 °C, 15:1 alcohol-ester molar ratio, 1.5 h reaction time, 3 h reaction time, and 140 °C transesterification reaction temperature. In order to further determine the optimal molar ratio of [DVIM]Br ionic liquid monomer to VIM monomer, when the molar amount of [DVIM]Br is fixed and the amount of VIM added is increased, the yields of PC and DMC increase accordingly. In P-BVD-3 / 3 / 6, the PC yield reaches 98.2% and the DMC yield reaches 60.3%. This is because the addition of excess CO during the reaction 2 Increasing the amount of VIM not only increases the activation of CO 2 The active sites of the ester exchange reaction were increased, thereby increasing the yields of PC and DMC. When the amount of VIM added was fixed and the addition of [DVIM]Br monomer was reduced, the yields of PC and DMC reached the maximum value (99.4%, 74.6%) when the molar ratio of [DVIM]Br to VIM was adjusted to 2 / 3 (P-2BVD-2 / 3 / 5). However, by further reducing the molar ratio of [DVIM]Br to VIM (P-BVD-1 / 3 / 4), the yield of PC was reduced to 92.6%. This is because when the content of [DVIM]Br can provide excess halogen anions to attack the PO ring opening, reducing its molar amount instead makes the activation rate of PO and CO 2Matching is beneficial to the formation of PC; while excessively reducing the content of [DVIM]Br will greatly reduce the polarization and ring opening of PO, thereby reducing the formation of PC. However, due to the continuity of the two-step reaction, the PC yield is reduced while the DMC yield is also reduced.

[0047] Application Example 1

[0048] Weigh 50 mmol propylene oxide and 0.1 g P-2BVD-2 / 3 / 5 into the autoclave, and fill it with 1.5 MPaCO 2 , stirred at 140 ℃ for 1.5 h, the supernatant was analyzed by gas chromatography, and then 0.75 mol of methanol was added to the autoclave, stirred at 140 ℃ for 3 h, and the supernatant was analyzed by gas chromatography. Through single factor experimental determination, the yields of PC and DMC gradually increased with the increase of catalyst dosage until the catalyst dosage reached its equilibrium point of 0.4 g; as the reaction temperature first increased and then decreased, at 140 ℃, the yields of PC and DMC reached a peak value. The reason is that these two steps of reaction are exothermic reactions, and the temperature is too high, which is not conducive to the forward reaction; as CO 2 With the increase of pressure, the PC yield gradually increased. 2 When the pressure reached 1.5 MPa, the PC yield did not change significantly with further increase of pressure, so the optimal reaction pressure of cycloaddition was selected as 1.5 MPa; the PC yield gradually increased with the extension of reaction time, and reached equilibrium after 1.5 h of reaction. In the transesterification reaction, as the alcohol-ester ratio increased, the reaction was promoted to proceed in the forward direction; the DMC yield gradually increased until the alcohol-ester ratio was 15:1 and reached equilibrium; the DMC yield gradually increased with the extension of reaction time and reached equilibrium after 3 h of reaction. Therefore, under the optimal reaction conditions (cycloaddition: 140 ℃, 1.5 MPa, 1.5 h; transesterification: 140 ℃, alcohol-ester ratio 15:1, 3 h), the PC yield was 99.4% and the DMC yield was 74.6%.

[0049] Table 1 is a comparison of the catalytic performance of P-2BVD-2 / 3 / 5 prepared in Example 1 and other catalysts. As shown in Table 1, compared with the metal oxide ZrO 2 and Au / CeO 2 The catalyst, P-2BVD-2 / 3 / 5, not only has a faster reaction rate, but also can obtain a higher DMC yield; and for the alkaline homogeneous catalyst TBAB, the P-2BVD-2 / 3 / 5 after the reaction can be recovered by simple centrifugation, which has a strong industrial prospect.

[0050] Table 1 Comparison of catalytic performance of P-2BVD-2 / 3 / 5 and other types of catalysts

[0051]

[0052] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. An application of a bifunctional ionic polymer material, characterized in that: The bifunctional ionic polymer material is used as a catalyst in the two-step synthesis of dimethyl carbonate from carbon dioxide and methanol. The specific operation is as follows: propylene oxide and the bifunctional ionic polymer material are added to a high-pressure reactor, charged with 0.5-2.5 MPa of CO2, the reaction temperature is set to 80-160 °C, and the reaction is stirred for 0.5-3 h to obtain the intermediate product propylene carbonate, and then methanol is added to the high-pressure reactor, the reaction temperature is set to 80-160 °C, and the reaction is stirred for 1-5 h, the alcohol-ester molar ratio is 2.5:1-20:1, and the final product dimethyl carbonate is obtained; The preparation method of the bifunctional ionic polymer material comprises the following steps: (1) Weigh 20 mmol of 1,4-dibromobutane and dissolve it in 10 mL of acetonitrile to prepare solution A, weigh 40 mmol of 1-vinylimidazole and dissolve it in 10 mL of acetonitrile to prepare solution B, add solution A to solution B, and stir magnetically at 60 °C for 24 h under nitrogen protection. Collect the light yellow oily liquid, wash with ethyl acetate and dry it to obtain the diimidazole ionic liquid monomer [DVIM]Br; (2) Weigh 4 mmol [DVIM]Br, 6 mmol 1-vinylimidazole and 10 mmol divinylbenzene respectively and dissolve them in a mixed solvent of 6 ml ethanol, 6 ml ethyl acetate, 6 ml acetonitrile and 10 ml water. Then transfer them to a three-necked flask and add 0.87 mmol AIBN. Stir at room temperature for 30 min. After the added substances are fully dissolved, stir them magnetically at 80 °C for 24 h under nitrogen atmosphere. Collect the white precipitate, wash with ethanol and dry it to obtain the bi-imidazole "bifunctional" ionic polymer material P-BVD-2 / 3 / 5.

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