CN110152733B

CN110152733B - Catalyst, preparation method thereof and application of catalyst in catalyzing reaction of glycerol and urea

Info

Publication number: CN110152733B
Application number: CN201910345085.XA
Authority: CN
Inventors: 王华军; 龚建; 徐杏
Original assignee: Huazhong University of Science and Technology
Current assignee: Huazhong University of Science and Technology
Priority date: 2019-04-26
Filing date: 2019-04-26
Publication date: 2020-06-09
Anticipated expiration: 2039-04-26
Also published as: CN110152733A

Abstract

The invention discloses a catalyst, a preparation method thereof and application of the catalyst in catalyzing reaction of glycerol and urea, and belongs to the field of novel catalysts. The preparation method comprises the following steps: reacting heteropoly acid with potassium salt to obtain potassium heteropoly acid; the supported catalyst is obtained by immersing potassium heteropolyacid powder in a zinc-based solution and then drying the solution to remove the solvent. Furthermore, roasting for 3-5 hours at 300-700 ℃ to decompose zinc in the supported catalyst to obtain zinc oxide, thus obtaining the composite catalyst. The prepared supported catalyst is used for synthesizing glycerol carbonate by the reaction of glycerol and urea, the glycerol conversion rate can reach 94.8%, and the yield of the glycerol carbonate can reach 85.8%. The zinc-based composite heteropolyacid salt catalyst disclosed by the invention has the advantages of high catalytic activity, easiness in recovery, environmental friendliness, good thermal stability, no corrosion and damage to equipment and the like.

Description

Catalyst, preparation method thereof and application of catalyst in catalyzing reaction of glycerol and urea

Technical Field

The invention belongs to the field of novel catalysts, and particularly relates to a catalyst and a preparation method thereof, and application of the catalyst in catalyzing reaction of glycerol and urea, and more particularly relates to a zinc-based composite heteropolyacid salt catalyst for synthesizing glycerol carbonate through reaction of glycerol and urea, and a preparation method and application of the zinc-based composite heteropolyacid salt catalyst.

Background

The glycerol carbonate is an important glycerol derivative with high added value, has the characteristics of no toxicity, quick biodegradation, good water solubility, high flash point (fp 165.9 ℃) and high boiling point (bp 353.9 ℃), and has wide application in the field of chemical industry. The glycerol carbonate can be used as a high-boiling point solvent, a cleaning agent, a lithium ion battery liquid component and a surfactant component, can also be used as a polymerization monomer and a reaction intermediate, can also be used for preparing a gas separation membrane and the like, and has very wide market prospect. At present, the synthesis of glycerol carbonate by using glycerol as a raw material is a research hotspot in the field of chemical industry. The glycerol used in the synthesis process is a by-product of the biodiesel production process. With the annual increase in biodiesel production worldwide, the glycerol production also increases dramatically, with a serious market excess. Therefore, the glycerol is converted into the glycerol carbonate, so that the additional value of the glycerol can be obviously improved, the economic benefit of biodiesel manufacturers can be increased, and the development of the biodiesel industry is promoted.

At present, several methods for synthesizing glycerol carbonate by using glycerol as a raw material mainly include a reaction method of glycerol and dimethyl carbonate, a reaction method of glycerol and carbon dioxide, a reaction method of glycerol and urea and the like. Although the reaction method of glycerol and dimethyl carbonate has the advantages of mild reaction conditions and high conversion rate, organic carbonates such as dimethyl carbonate have high price, and the economical efficiency of the process for producing glycerol carbonate is reduced. The reaction method of glycerol and carbon dioxide has high atom economy, can effectively utilize greenhouse gas carbon dioxide, has economic benefit and environmental benefit, and is an attractive method, but because the carbon dioxide is a highly stable molecule and is difficult to activate, the reaction condition of the synthesis method is severe, the conversion rate of reactants is low, and the industrialization process is limited. In comparison, the glycerol and urea reaction method has the following advantages: (1) the urea is actually a derivative of carbon dioxide, and the ammonia produced by the reaction can react with the carbon dioxide to regenerate the urea, so that the method can indirectly consume the carbon dioxide; (2) the physical and chemical properties of urea are more active than that of carbon dioxide, so compared with the carbon dioxide reaction method, the reaction condition of the urea reaction method is milder and is easy to carry out; (3) the urea has wide source and low price, so that the raw material cost of the product is obviously reduced, and the economic benefit is obvious. Therefore, the reaction method of the glycerol and the urea has good industrialization prospect. The reaction equation is:

at present, the catalysts used for the reaction of glycerol with urea are mainly homogeneous catalysts and heterogeneous catalysts. Wherein, the homogeneous catalyst mainly comprises zinc salts (such as zinc chloride, zinc bromide, zinc iodide, zinc sulfate, etc.) and zinc oxide, etc. Park et al examined the catalytic activity of zinc salts such as zinc chloride, zinc bromide, zinc iodide, and found that among these zinc salt catalysts, zinc chloride activity was the highest, and that reaction of glycerol and urea at 150 ℃ for 2 hours at 2.67kPa with zinc chloride as the catalyst gave 80.4% glycerol conversion and 80.2% glycerol carbonate yield (Park J H, Choi J S, Woo S K, ethyl.isolation and Catalysis of interfacial Catalysis in the Zn-catalyzed glycerol Catalysis of urea [ J ] Applied Catalysis A: General,2012,433-434: 35-45.). The homogeneous catalyst has high activity, but the separation and purification of the product after reaction are difficult, and the catalyst is difficult to recycle. The heterogeneous catalyst mainly comprises a metal oxide catalyst (such as magnesium oxide, calcium oxide, lanthanum oxide and the like), a supported ionic liquid catalyst, a supported metal nanoparticle catalyst (such as Au/MgO nanoparticle catalyst), a hydrotalcite catalyst and the like. Chinese patent (application publication No. CN102794189A) discloses a catalyst for synthesizing glycerol carbonate by the reaction of glycerol and urea, which is composed of magnesium oxide and other metal oxides (such as zinc oxide, calcium oxide, etc.) supported on hydroxyapatite. The catalyst is used for catalyzing the reaction of glycerol and urea, the yield of glycerol carbonate can reach 78.0 percent at most, but acetonitrile is required to be used as a solvent in the reaction process, so that the difficulty of separating and purifying products is increased. Although the heterogeneous catalyst is easy to recycle, the catalyst activity is low, the preparation process is complex, and the cost of the metal nanoparticle catalyst and the ionic liquid catalyst is high, which is not beneficial to industrial application.

Heteropolyacids (salts) as a new class of green solid acid catalysts, having defined composition and structure and being stronger than inorganic acids (sulfuric acid, hydrochloric acid)

The catalyst is acidic and can be used as a bifunctional catalyst for acid and oxidation. The heteropoly acid (salt) has the advantages of mild reaction conditions, no toxicity, no corrosion to equipment, stable structure, high thermal stability and the like in the aspect of catalytic reaction, and is receiving more and more attention.

At present, no relevant report exists on the use of zinc complex heteropolyacid salt as a catalyst for synthesizing glycerol carbonate by the reaction of glycerol and urea.

Disclosure of Invention

The invention solves the technical problems that the catalytic activity of the catalyst for catalyzing the reaction of urea and glycerol is not high and the catalyst is difficult to recycle in the prior art. The invention obtains the compound of zinc system and heteropoly acid salt by dipping the zinc system into heteropoly acid salt solution. When the compound is used for catalyzing the reaction of urea and glycerol, the catalytic activity is high, the cost is low, and the compound is easy to recycle, so that the technical problems of low activity, difficult recycling and high cost of the existing catalyst are solved.

According to a first aspect of the present invention, there is provided a process for the preparation of a catalyst comprising the steps of:

(1) dissolving heteropoly acid in water to obtain heteropoly acid solution, and dripping a potassium salt water solution into the heteropoly acid solution to react heteropoly acid with potassium salt to obtain potassium heteropoly acid;

(2) sequentially drying and grinding the potassium heteropoly acid obtained in the step (1) to obtain powdery potassium heteropoly acid;

(3) dissolving a zinc system in a solvent with the boiling point less than or equal to that of water, wherein the zinc system is zinc nitrate, zinc acetate or basic zinc carbonate to obtain a zinc system solution; adding the powdery potassium heteropoly acid in the step (2) into the zinc solution to immerse the potassium heteropoly acid in the zinc solution, and then drying to remove the solvent to obtain the zinc and potassium heteropoly acid supported catalyst.

Preferably, after the step (3), the obtained supported catalyst is calcined at 300-700 ℃ for 3-5 hours, so that zinc systems in the supported catalyst are decomposed to obtain zinc oxide, and the zinc oxide and ligand atoms in potassium heteropoly acid are re-coordinated to form inorganic salt, so as to obtain the composite catalyst.

Preferably, the heteropolyacid is phosphotungstic acid, phosphomolybdic acid or silicotungstic acid.

Preferably, the potassium salt is potassium chloride, potassium oxalate or potassium acetate.

Preferably, the step (2) further comprises a process of roasting the powdery potassium heteropoly acid to remove crystal water; the solvent in the step (3) is ethanol, methanol or distilled water; the time for the impregnation in the step (3) is 5 to 12 hours.

According to another aspect of the present invention there is provided a catalyst prepared by any of the methods described herein.

According to another aspect of the invention, there is provided the use of said catalyst for catalysing the reaction of glycerol with urea to produce glycerol carbonate.

Preferably, after the catalytic reaction, the catalyst is recovered by filtration, and the reaction of the glycerol and the urea is catalyzed again; preferably, the number of times of re-catalysis is less than or equal to 5 times;

preferably, the mass ratio of catalyst to glycerol is (0.01-0.1): 1.

preferably, the reaction temperature of the glycerol and the urea is 120-160 ℃, the reaction time is 1-5 hours, the mass ratio of the glycerol and the urea is 2 (1-4), and the reaction pressure is 2-3 kPa.

In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:

(1) in the preparation method, double decomposition reaction of heteropoly acid and potassium salt is adopted to generate potassium heteropoly acid, because the heteropoly acid salt of potassium exchange has good thermal stability; meanwhile, potassium heteropoly acid is a heterogeneous catalyst for the reaction of glycerol and urea, and is easy to recover after the reaction; meanwhile, the potassium salt required for preparing the potassium heteropoly acid is low in price and wide in source. In the invention, the prepared supported catalyst is roasted, zinc system in the supported catalyst is decomposed to obtain zinc oxide, and in the high-temperature calcination process, the zinc oxide (surface hydroxyl) generated by calcination and a heteropoly acid structure generate strong interaction, so that the heteropoly acid structure is cracked into different unit bodies, wherein a large amount of coordination unit bodies and Zn-O form a new phase, and the new inorganic zinc salt is compounded to stably exist.

(2) The catalyst prepared by the invention has high catalytic activity and can be repeatedly used. The catalyst prepared by the invention is used for synthesizing glycerol carbonate by the reaction of glycerol and urea, has higher catalytic activity, can achieve 85.8 percent of glycerol carbonate yield by catalyzing the reaction of the glycerol and the urea by the uncalcined supported catalyst, and has higher activity compared with single zinc nitrate and potassium heteropoly acid; the calcined composite catalyst can also reach 73.5 percent of glycerol carbonate yield, and the catalytic activity of the catalyst is higher than that of zinc sulfate which is a homogeneous catalyst. Meanwhile, after the uncalcined supported catalyst is recycled for 5 times, 96.5% of glycerol conversion rate and 69.5% of glycerol carbonate yield can still be obtained. The excellent catalytic performance of the calcined composite catalyst is attributed to the co-assistance of Lewis acid sites and Lewis basic sites. The active component of the calcined composite catalyst is mainly ZnWO₄Or ZnMoO₄In which Zn ion can act as Lewis acid site to activate carbonyl group of urea, and WO₄ ^2-And MoO₄ ^2-Can be used as Lewis basic site to activate the hydroxyl of glycerol, thereby activating two raw materialsAnd (4) carrying out a reaction.

(3) The catalyst prepared by the method is easy to recycle. The catalyst prepared by the invention is a heterogeneous catalyst, the dissolution amount of active components is small, the catalyst exists in a solid form in the reaction process, and the catalyst can be recycled by simple methods such as filtration and the like.

(4) The catalyst prepared by the method is environment-friendly and has no corrosion and damage to equipment. The catalyst prepared by the invention is an environment-friendly catalyst, and cannot corrode or damage a reactor in the reaction process.

(5) The preparation method has the advantages of cheap raw materials, wide sources, simple preparation process of the catalyst and low cost. The precursor of the active species of the catalyst is common zinc salt and heteropoly acid salt, the raw materials are cheap and have wide sources, the preparation method is an impregnation method, and the process is simple and easy to implement.

Drawings

FIG. 1 is an XRD spectrum of a zinc-based complex potassium phosphotungstate catalyst prepared in example 1.

FIG. 2 shows FT-IR spectra of zinc-based composite potassium phosphotungstate catalysts prepared in examples 1 and 2.

FIG. 3 shows FT-IR spectra of zinc-based complex potassium phosphotungstate catalysts obtained in examples 1, 3 and 4.

FIG. 4 shows FT-IR spectra of zinc-based composite potassium heteropolyacid catalysts obtained in example 1 and example 8.

FIG. 5 is a schematic diagram showing the reaction mechanism of the zinc-based complex potassium phosphotungstate catalyst prepared in example 1.

FIG. 6 is an XRD spectrum of the zinc-based composite potassium phosphomolybdate catalyst prepared in example 7.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

The invention provides a catalyst for synthesizing glycerol carbonate by the reaction of glycerol and urea. The catalyst is formed by loading a zinc system on heteropoly acid salt, wherein the zinc system precursor is zinc nitrate, zinc acetate or basic zinc carbonate, and the heteropoly acid salt is potassium phosphotungstate, potassium phosphomolybdate or potassium silicotungstate. Wherein the mass of the zinc system is 20-70% of that of the heteropolyacid salt (calculated by the mass of zinc oxide completely generated by roasting the zinc system relative to the mass of potassium heteropolyacid).

The invention provides a preparation method of a catalyst for synthesizing glycerol carbonate by the reaction of glycerol and urea, which comprises the following steps:

(1) crystallizing phosphotungstic acid hydrate (H)₃PW₁₂O₄₀·_XH₂O) was calcined at 110 ℃ for 2 hours to remove most of the crystal water and ground to obtain a solid powder.

(2) Dissolving the phosphotungstic acid solid powder obtained in the step (1) in a small amount of distilled water, stirring to dissolve the phosphotungstic acid solid powder to obtain a clear transparent phosphotungstic acid solution, dissolving potassium chloride in a stoichiometric ratio in the distilled water to prepare a solution, slowly dropwise adding the potassium chloride solution into the phosphotungstic acid solution, stirring vigorously, gradually generating white precipitates in the reaction process, and after the dropwise adding of the potassium chloride solution is finished, continuously stirring for a period of time and standing for 12 hours.

(3) Centrifuging the mixture obtained in the step (2), and washing the obtained solid with distilled water for several times until the solution is free of Cl^-Dried, ground and calcined at 300 ℃ for 2 hours to give a white powder sample of potassium phosphotungstate, noted as K3 PW.

(4) Dissolving a certain amount of zinc-based precursor in a proper amount of solvent, adding the K3PW obtained in the step (3) under stirring, stirring and soaking at room temperature for 12 hours, drying the obtained mixture for 12 hours, and grinding to obtain the supported catalyst precursor. The zinc precursor is zinc nitrate, zinc acetate or basic zinc carbonate, preferably zinc nitrate; the solvent is distilled water or absolute ethyl alcohol, and preferably distilled water.

(5) And (3) roasting the dried catalyst precursor in a muffle furnace at 100-700 ℃ for 3-5 hours, and taking out the obtained white solid matter and marking as ZnO/K3PW, namely the catalyst for synthesizing glycerol carbonate by the reaction of glycerol and urea.

The catalyst for synthesizing the glycerol carbonate by the reaction of the glycerol and the urea has the catalytic reaction temperature of 120-160 ℃, the reaction time of 1-5 hours, the molar ratio of the glycerol to the urea of 2: 1-1: 2, the reaction pressure of 2-3 kPa and the mass ratio of the catalyst to the glycerol of 1-10%.

The reaction mechanism of the calcined composite catalyst is shown in fig. 5. The excellent catalytic performance of the composite catalyst is attributed to the co-assistance of Lewis acid sites and Lewis basic sites. The active component of the calcined composite catalyst is mainly ZnWO₄Or ZnMoO₄In which Zn ion can act as Lewis acid site to activate carbonyl group of urea, and WO₄ ^2-Can be used as Lewis basic site to activate the hydroxyl of glycerin, so as to activate two raw materials and catalyze the reaction.

Example 1

The catalyst for synthesizing glycerol carbonate by the reaction of glycerol and urea comprises zinc series supported on heteropoly acid salt, wherein zinc series precursor is zinc nitrate, and the heteropoly acid salt is potassium phosphotungstate. Wherein the zinc nitrate is 50% of the weight of the potassium phosphotungstate (calculated by the weight of zinc oxide generated by roasting the zinc system completely relative to the weight of the potassium phosphotungstate), and the roasting temperature of the catalyst is 500 ℃.

The preparation method of the zinc-based composite heteropolyacid salt catalyst comprises the following steps:

(4) Dissolving a certain amount of zinc nitrate in a proper amount of distilled water, adding the K3PW obtained in the step (3) under stirring, stirring and soaking at room temperature for 12 hours, drying the obtained mixture for 12 hours, and grinding to obtain the supported catalyst precursor.

(5) And (3) putting the dried catalyst precursor into a muffle furnace, and burning for 4 hours at 500 ℃, and taking out the obtained white solid matter to be recorded as ZnO/K3PW, namely the catalyst for synthesizing the glycerol carbonate by the reaction of the glycerol and the urea.

The prepared catalyst is used for synthesizing glycerol carbonate by the reaction of glycerol and urea, and the reaction conditions are as follows: the reaction temperature is 140 ℃, the reaction time is 4 hours, the molar ratio of the glycerol to the urea is 1:1, the reaction pressure is 3kPa, and the mass ratio of the catalyst to the glycerol is 5%. After the reaction is finished, the reaction product is taken out, and the composition of the product is analyzed by gas chromatography, so that the conversion rate of the obtained glycerol is 86.4 percent, and the yield of the glycerol carbonate can reach 73.5 percent.

The catalyst is characterized, as shown in figure 1, XRD analysis shows that the main component of the catalyst is zinc tungstate, a small amount of zinc oxide exists, and no obvious characteristic peak of potassium phosphotungstate species is found in an XRD spectrogram. The zinc tungstate species in the XRD spectrum is formed from zinc nitrate and potassium phosphotungstate during calcination.

Example 2

The catalyst for synthesizing glycerol carbonate by the reaction of glycerol and urea comprises zinc system loaded on heteropoly acid salt, wherein the zinc system is zinc nitrate, and the heteropoly acid salt is potassium phosphotungstate. Wherein the zinc nitrate accounts for 50 percent of the mass of the potassium phosphotungstate (based on the mass of zinc oxide generated by completely roasting a zinc system relative to the potassium phosphotungstate)).

The preparation method of the zinc-based supported heteropolyacid salt catalyst is the same as that in example 1, and the drying temperature used in the step (4) is 100 ℃, and the step (5) is not included. The prepared catalyst is used for synthesizing glycerol carbonate by the reaction of glycerol and urea, the reaction conditions are the same as those in the embodiment 1, after the reaction is finished, reaction products are taken out, the composition of the products is analyzed by gas chromatography, the conversion rate of the obtained glycerol is 94.8%, and the yield of the glycerol carbonate can reach 85.8%. The catalyst was recovered, washed 3 times with methanol and used directly in the next reaction, and according to the above conditions, the catalyst was recycled 5 times, and the product composition was analyzed by gas chromatography, and after the fifth reaction, the glycerol conversion was 96.5% and the yield of glycerol carbonate was 69.5%.

In this embodiment, the drying temperature in step (4) is 100 ℃, the influence of the amount of the supported catalyst prepared in step (4) on the reaction activity of urea and glycerol is shown in table 1, the influence of the reaction time of the supported catalyst prepared in step (4) for catalyzing the reaction of urea and glycerol on the reaction activity is shown in table 2, the influence of the reaction temperature of the supported catalyst prepared in step (4) for catalyzing the reaction of urea and glycerol on the reaction activity is shown in table 3, and the influence of the ratio of the amount of glycerol and urea substance in the reaction of urea and glycerol by the supported catalyst prepared in step (4) is shown in table 4.

TABLE 1 Effect of catalyst dosage on Urea-Glycerol reactivity

TABLE 2 Effect of reaction time on reactivity

TABLE 3 influence of reaction temperature on the reactivity

TABLE 4 influence of the ratio of the amounts of glycerol and urea species on the reactivity

Example 3

A catalyst for synthesizing glycerol carbonate through the reaction of glycerol and urea is composed of zinc system supported on heteropoly acid salt, zinc acetate as zinc system precursor, and potassium phosphotungstate as heteropoly acid salt. Wherein the zinc acetate is 50% of the weight of the potassium phosphotungstate (calculated by the weight of zinc oxide generated by roasting the zinc system completely relative to the weight of the potassium phosphotungstate), and the roasting temperature of the catalyst is 500 ℃.

The preparation method of the zinc-based composite heteropolyacid salt catalyst is the same as that of the zinc-based composite heteropolyacid salt catalyst in the embodiment 1, but the zinc-based precursor is changed into zinc acetate. The prepared catalyst is used for synthesizing glycerol carbonate by the reaction of glycerol and urea, the reaction conditions are the same as those in the example 1, after the reaction is finished, reaction products are taken out, the composition of the products is analyzed by gas chromatography, the conversion rate of the glycerol is 85.6 percent, and the yield of the glycerol carbonate is 67.3 percent.

Example 4

A catalyst for synthesizing glycerol carbonate by the reaction of glycerol and urea is composed of zinc system supported on heteropoly acid salt, basic zinc carbonate as zinc precursor, and potassium phosphotungstate as heteropoly acid salt. Wherein the basic zinc carbonate is 50 percent of the mass of the potassium phosphotungstate (calculated by the mass of zinc oxide generated by roasting the zinc system completely relative to the mass of the potassium phosphotungstate), and the roasting temperature of the catalyst is 500 ℃.

The preparation method of the zinc compound type heteropolyacid salt catalyst is the same as that of the zinc compound type heteropolyacid salt catalyst in the embodiment 1, but the zinc precursor is changed into basic zinc carbonate. The prepared catalyst is used for synthesizing glycerol carbonate by the reaction of glycerol and urea, the reaction conditions are the same as those in example 1, after the reaction is finished, reaction products are taken out, and the product composition is analyzed by gas chromatography, so that the glycerol conversion rate is 84.6%, and the yield of the glycerol carbonate is 60.6%.

FIG. 2 shows FT-IR spectra of zinc-based composite potassium phosphotungstate catalysts prepared in examples 1 and 2. In FIG. 2, the curve (a) is FT-IR spectrum of the zinc-based composite potassium phosphotungstate catalyst prepared in example 1, and it can be seen that the absorption peak of zinc tungstate is clearly 877cm^-1And 834cm^-1The peak belongs to the vibration absorption peak of Zn-O-W, 705cm^-1And 633cm^-1The peak belongs to the vibration absorption peak of W-O, 538cm^-1And 472cm^-1The peak belongs to the vibration absorption peak of Zn-O. In FIG. 2, the curve (b) is FT-IR spectrum of zinc-based supported potassium phosphotungstate catalyst obtained in example 2, and it is evident that it belongs to the absorption peak of potassium phosphotungstate and has a wavelength of 1081cm in fingerprint region^-1、986cm^-1、890cm^-1And 803cm^-1The peak belongs to the characteristic peak of potassium phosphotungstate and is positioned at 1387cm^-1The absorption peak at (A) indicates NO₃ ^-Is present.

FIG. 3 shows FT-IR spectra of zinc-based composite potassium phosphotungstate catalysts obtained in examples 1, 3 and 4. In FIG. 3, curve (a) shows the FT-IR spectrum of the zinc-based composite potassium phosphotungstate catalyst obtained in example 1. In FIG. 3, the curve (b) is FT-IR spectrum of the zinc-based composite potassium phosphotungstate catalyst obtained in example 3, which shows that the zinc phosphotungstate catalyst apparently belongs to the absorption peak of zinc tungstate, 877cm^-1And 834cm^-1The peak belongs to the vibration absorption peak of Zn-O-W, 705cm^-1And 633cm^-1The peak belongs to the vibration absorption peak of W-O, 538cm^-1And 472cm^-1The peak belongs to the vibration absorption peak of Zn-O. These characteristic peaks are substantially identical to those of the sample of example 1. In FIG. 3, the curve (c) is FT-IR spectrum of the zinc-based composite potassium phosphotungstate catalyst obtained in example 4, which shows that the zinc phosphotungstate catalyst apparently belongs to the absorption peak of zinc tungstate, 877cm^-1And 834cm^-1The peak belongs to the vibration absorption peak of Zn-O-W, 705cm^-1And 633cm^-1The peaks belong to the vibration absorption peaks of W-O, 538 and 472cm^-1The peak belongs to the vibration absorption peak of Zn-O. These characteristic peaks are substantially identical to the characteristic peaks of the sample of example 1 and the characteristic peaks of the sample of example 3.

Example 5

The catalyst for synthesizing glycerol carbonate by the reaction of glycerol and urea comprises zinc series supported on heteropoly acid salt, wherein zinc series precursor is zinc nitrate, and the heteropoly acid salt is potassium phosphotungstate. Wherein the zinc nitrate accounts for 50 percent of the mass of the potassium phosphotungstate (based on the mass of zinc oxide generated by completely roasting a zinc system relative to the potassium phosphotungstate).

The preparation method of the zinc-series compound heteropolyacid salt catalyst is the same as that of the zinc-series compound heteropolyacid salt catalyst in the embodiment 1, but the roasting temperature is changed to be 300-700 ℃. The prepared catalyst is used for synthesizing glycerol carbonate by the reaction of glycerol and urea, the reaction conditions are the same as those in example 1, after the reaction is finished, reaction products are taken out, the composition of the products is analyzed by gas chromatography, and the catalytic performance is shown in table 5.

TABLE 5 Effect of calcination temperature on catalyst catalytic Activity

Example 6

The catalyst for synthesizing glycerol carbonate by the reaction of glycerol and urea comprises zinc series supported on heteropoly acid salt, wherein zinc series precursor is zinc nitrate, and the heteropoly acid salt is potassium phosphotungstate.

The preparation method of the zinc-based composite heteropolyacid salt catalyst is the same as that of the zinc-based composite heteropolyacid salt catalyst in example 1, but the mass percentage of zinc nitrate to potassium phosphotungstate (calculated by the mass of zinc oxide completely generated by roasting the zinc system to potassium phosphotungstate) is changed. The prepared catalyst is used for synthesizing glycerol carbonate by the reaction of glycerol and urea, the reaction conditions are the same as those in example 1, after the reaction is finished, reaction products are taken out, the composition of the products is analyzed by gas chromatography, and the catalytic performance of the product is shown in Table 6.

TABLE 6 Effect of different ZnO/K3PW on the catalytic Activity of the catalyst

Example 7

The catalyst for synthesizing glycerol carbonate by the reaction of glycerol and urea comprises zinc series supported on heteropoly acid salt, wherein the zinc series precursor is zinc nitrate, and the heteropoly acid salt is potassium phosphomolybdate. Wherein the zinc nitrate is 50% of the mass of the potassium phosphomolybdate (calculated by the mass of zinc oxide generated by completely roasting a zinc system relative to the mass of the potassium phosphomolybdate), and the roasting temperature of the catalyst is 500 ℃.

The preparation method of the zinc-based compound heteropolyacid salt catalyst comprises the following steps:

(1) crystalline hydrate of phosphomolybdic acid (H)₃PMo₁₂O₄₀·_XH₂O) was calcined at 110 ℃ for 2 hours to remove most of the crystal water and ground to obtain a solid powder.

(2) Dissolving the phosphomolybdic acid solid powder obtained in the step (1) in a small amount of distilled water, stirring to dissolve the phosphomolybdic acid solid powder to obtain a transparent phosphomolybdic acid solution, dissolving potassium chloride in a stoichiometric ratio in the distilled water to prepare a solution, slowly dropwise adding the potassium chloride solution into the phosphomolybdic acid solution, stirring vigorously, gradually generating precipitates in the reaction process, and standing for 12 hours after continuously stirring for a period of time after the potassium chloride solution is dropwise added.

(3) Centrifuging the mixture obtained in the step (2), and washing the obtained solid with distilled water for several times until the solution is free of Cl^-When present, dried, ground and calcined at 300 ℃ for 2 hours to give a yellow powder sample of potassium phosphomolybdate, noted K3 PMo.

(4) Dissolving a certain amount of zinc nitrate in a proper amount of distilled water, adding the K3PMo obtained in the step (3) under stirring, stirring and soaking at room temperature for 12 hours, drying the obtained mixture for 12 hours, and grinding to obtain the supported catalyst precursor.

(5) And (3) roasting the dried catalyst precursor in a muffle furnace at 500 ℃ for 4 hours, and taking out the obtained light yellow substance and marking as ZnO/K3PMo, namely the catalyst for synthesizing glycerol carbonate by the reaction of glycerol and urea.

The prepared catalyst is used for synthesizing glycerol carbonate by the reaction of glycerol and urea, and the reaction conditions are as follows: the reaction temperature is 140 ℃, the reaction time is 4 hours, the molar ratio of the glycerol to the urea is 1:1, the reaction pressure is 3kPa, and the mass ratio of the catalyst to the glycerol is 5%. After the reaction is finished, the reaction product is taken out, and the composition of the product is analyzed by gas chromatography, so that the conversion rate of the obtained glycerol is 91.1 percent, and the yield of the glycerol carbonate can reach 74.6 percent.

FIG. 6 is an XRD spectrum of the zinc-based composite potassium phosphomolybdate catalyst prepared in example 7. The lowest spectrum in FIG. 6 is of zinc molybdate (ZnMoO)₄) The spectrum belongs to the spectrum of the zinc-based composite potassium phosphomolybdate catalyst, and the comparison of characteristic peaks can confirm that the composite catalyst prepared in the example 7 definitely contains active ZnMoO₄。

Example 8

The catalyst for synthesizing glycerol carbonate by the reaction of glycerol and urea comprises zinc series supported on heteropoly acid salt, wherein zinc series precursor is zinc nitrate, and the heteropoly acid salt is potassium silicotungstate. Wherein the zinc nitrate is 50% of the mass of the potassium silicotungstate (calculated by the mass of zinc oxide generated by roasting a zinc system completely relative to the mass of the potassium silicotungstate), and the roasting temperature of the catalyst is 500 ℃.

(1) crystallizing silicotungstic acid hydrate (H)₄SiW₁₂O₄₀·_XH₂O) was calcined at 110 ℃ for 2 hours to remove most of the crystal water and ground to obtain a solid powder.

(2) Dissolving the silicotungstic acid solid powder obtained in the step (1) in a small amount of distilled water, stirring to dissolve the silicotungstic acid solid powder to obtain a clear and transparent silicotungstic acid solution, dissolving potassium chloride in a stoichiometric ratio in the distilled water to prepare a solution, slowly dripping the potassium chloride solution into the silicotungstic acid solution, stirring vigorously, continuing to react and stir for a period of time after the potassium chloride solution is dripped, and standing for 12 hours.

(3) And (3) placing the clear solution obtained in the step (2) in an oven to dry water, grinding the white solid obtained after removing the water, and roasting at 300 ℃ for 2 hours to obtain a white powdery sample of potassium silicotungstate, which is marked as K4 SiW.

(4) Dissolving a certain amount of zinc nitrate in a proper amount of distilled water, adding the K4SiW obtained in the step (3) under stirring, stirring and soaking at room temperature for 12 hours, drying the obtained mixture for 12 hours, and grinding to obtain the supported catalyst precursor.

(5) And (3) roasting the dried catalyst precursor in a muffle furnace at 500 ℃ for 4 hours, and taking out the obtained white substance to be marked as ZnO/K4SiW, namely the catalyst for synthesizing the glycerol carbonate through the reaction of the glycerol and the urea.

The prepared catalyst is used for synthesizing glycerol carbonate by the reaction of glycerol and urea, and the reaction conditions are as follows: the reaction temperature is 140 ℃, the reaction time is 4 hours, the molar ratio of the glycerol to the urea is 1:1, the reaction pressure is 3kPa, and the mass ratio of the catalyst to the glycerol is 5%. After the reaction is finished, the reaction product is taken out, and the composition of the product is analyzed by gas chromatography, so that the conversion rate of the obtained glycerol is 75.7 percent, and the yield of the glycerol carbonate can reach 60.3 percent.

FIG. 4 is a FT-IR spectrum of the zinc-based composite potassium heteropolyacid catalyst obtained in example 1 and example 8. In FIG. 4, curve (a) shows the FT-IR spectrum of the zinc-based composite potassium phosphotungstate catalyst obtained in example 1. In FIG. 4, the curve (b) is FT-IR spectrum of the zinc-based composite potassium silicotungstate catalyst obtained in example 8, which shows that the catalyst is apparently an absorption peak of zinc tungstate, and is 885cm^-1And 818cm^-1The peak belongs to the vibration absorption peak of Zn-O-W, 720cm^-1And 610cm^-1The peak belongs to the vibration absorption peak of W-O, 472cm^-1The peak belongs to the vibration absorption peak of Zn-O. These characteristic peaks are substantially identical to those of the sample of example 1.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing a heterogeneous catalyst for catalyzing the reaction of glycerol and urea to synthesize glycerol carbonate is characterized by comprising the following steps:

2. The method for preparing the catalyst according to claim 1, wherein after the step (3), the obtained supported catalyst is calcined at 300 ℃ to 700 ℃ for 3 hours to 5 hours, so that zinc systems in the supported catalyst are decomposed to obtain zinc oxide, and the zinc oxide is re-coordinated with ligand atoms in potassium heteropoly acid to form inorganic salt, so that the composite catalyst is obtained.

3. The method for preparing a catalyst according to claim 1 or 2, wherein the heteropoly acid is phosphotungstic acid, phosphomolybdic acid or silicotungstic acid.

4. The method for preparing a catalyst according to claim 1 or 2, wherein the potassium salt is potassium chloride, potassium oxalate or potassium acetate.

5. The method for preparing the catalyst according to claim 1 or 2, wherein the step (2) further comprises a process of calcining the powdery potassium heteropolyacid to remove crystal water; the solvent in the step (3) is ethanol, methanol or distilled water; the time for the impregnation in the step (3) is 5 to 12 hours.

6. A catalyst prepared by the process as claimed in any one of claims 1 to 5.

7. Use of a catalyst according to claim 6 for the catalytic synthesis of glycerol carbonate by the reaction of glycerol with urea.

8. The use according to claim 7, wherein after the catalytic reaction, the catalyst is recovered by filtration, again catalysing the reaction between glycerol and urea.

9. Use according to claim 8, wherein the number of re-catalysations is 5 or less.

10. The use according to claim 7, wherein the mass ratio of catalyst to glycerol is (0.01-0.1): 1.

11. The use according to claim 7, wherein the reaction temperature of glycerol with urea is 120 ℃ to 160 ℃, the reaction time is 1 hour to 5 hours, the ratio of the amounts of glycerol and urea is 2 (1 to 4), and the reaction pressure is 2kPa to 3 kPa.