Heteropolyacid catalyst as well as preparation and application thereof

Abstract

The invention relates to a heteropolyacid catalyst for preparing methyl glycolate through condensation of formaldehyde and methyl formate. A preparation method of the heteropolyacid catalyst comprises the following steps: (1) loading an active component; and (2) carrying out overflow hydrogen reduction. The catalyst is prepared by taking common silicon oxide as a carrier and loading active components by adopting a co-impregnation method, the conditions are mild, and the process is stable and controllable. By doping a proper amount of metal, overflow hydrogen is induced to be generated to reduce a distribution site atom in the middle of heteropolyacid to serve as an alkaline site, and the alkaline site and a strongly acidic site of the heteropolyacid have a synergistic effect to promote cross condensation of formaldehyde and methyl formate, so that the reaction activity and selectivity are improved. The prepared catalyst has the advantages of low reaction temperature, high activity, good selectivity and the like.

Description

Technical Field

[0001] The invention relates to a catalytic method for preparing methyl glycolate by condensing formaldehyde and methyl formate, and in particular to a catalytic condensation method of formaldehyde and methyl formate on a doped supported heteropolyacid catalyst. Background Art

[0002] Methyl glycolate is an important chemical raw material. It can be used to produce glycine, methyl glyoxylate, ethylene glycol, methyl malonate and polyglycolic acid through amination, oxidation, hydrogenation, carbonylation and polymerization. Polyglycolic acid has excellent biocompatibility and degradability, and has wide applications and industrialization prospects in the fields of medicine, oil and gas extraction and packaging. The existing production route of methyl glycolate is the chloroacetic acid hydrolysis esterification method. This route has low product yield, heavy pollution, and serious corrosion to equipment, making it difficult to form large-scale industrial production. Formaldehyde and methyl formate have large production capacity and are easy to obtain, with resource advantages. Using formaldehyde and methyl formate as raw materials, designing efficient catalysts, preparing methyl glycolate through cross-condensation, and expanding the key link of methanol downstream to biodegradable materials such as polyglycolic acid can not only meet the country's growing demand for degradable materials, but also an important means to improve the technical economy and market risk resistance of coal chemical industry.

[0003] The development of efficient catalysts is the key to the condensation of formaldehyde and methyl formate to produce methyl glycolate. The catalysts used for the condensation of formaldehyde and methyl formate mainly include liquid strong acid and solid acid catalysts. Germany's Hoechst Company (DE2652072) reported a sulfuric acid or organic sulfonic acid catalytic system. At 90°C and normal pressure, formaldehyde and methyl formate react to produce methyl glycolate, and the yield of methyl glycolate is 24%-69%. The Chengdu Institute of Organic Chemistry of the Chinese Academy of Sciences disclosed a catalytic system composed of sulfuric acid metal carbonyl compounds, aminosulfonic acid, p-toluenesulfonic acid and metal halides. The process conditions are mild and the product yield is high (ZL97107692.8, ZL2005100211146.5 and ZL200610022389.5). This catalytic system is easy to corrode equipment and the waste liquid is difficult to treat. Mitsubishi Chemical of Japan uses Diaion (cation exchange resin) as a catalyst. At 110°C and 6MPa, the yield of methyl glycolate is 56% (Japanese Patent Gazette: 57-46934). Shanxi Coal Research Institute of the Chinese Academy of Sciences has disclosed a catalytic system with alumina and silica composite solid acid as active components and VIII group non-precious metal oxides as active additives. The catalytic system has the characteristics of high raw material conversion rate, high product selectivity, and low corrosiveness (ZL201210486084.5). This method solves the problem of equipment corrosion, but requires a higher reaction pressure, and the cost and safety issues are more prominent.

[0004] The present invention develops a new method for preparing a condensation catalyst of formaldehyde and methyl formate. Active metals are introduced while loading the active components of heteropolyacids, and some ligand atoms of the heteropolyacids are reduced by overflow hydrogen to make them alkaline, and methyl formate and formaldehyde are activated in coordination with the strong acid center of the heteropolyacid, and their cross condensation is promoted to prepare methyl glycolate, thereby improving the reaction activity of the catalyst. Summary of the invention

[0005] The problem to be solved by the present invention is to provide a method for preparing a formaldehyde-methyl formate condensation catalyst with high efficiency, mild reaction conditions, controllable preparation process and simple steps. The prepared catalyst has the advantages of mild reaction conditions, high activity, good selectivity and the like, can be applied to acid-base synergistic catalytic condensation reactions and has broad application prospects.

[0006] The technical solution is:

[0007] The method for preparing a heteropolyacid catalyst for preparing methyl glycolate by condensing formaldehyde and methyl formate comprises the following steps:

[0008] (1) Loading metal additives and active components: The raw salts are prepared into a solution, and the solution is co-impregnated onto a silica carrier, and the catalyst precursor is obtained after aging, drying and calcination;

[0009] (2) Overflow hydrogen reduction: The catalyst precursor obtained in step 1 is placed in a reducing atmosphere and treated at a certain temperature to obtain a catalyst for the condensation of formaldehyde and methyl formate. This step is a key step of the present invention, and its function is to obtain a suitable content of metal by loading, generate overflow hydrogen in a reducing atmosphere to reduce some of the coordinated atoms in the heteropoly acid as a base center, and synergistically activate methyl formate and formaldehyde with the acid center of the heteropoly acid, promote their cross condensation to prepare methyl glycolate, thereby improving the activity and selectivity of the catalyst.

[0010] Preferably, in step (1), the carrier is silicon oxide, and the properties are: specific surface area 350±100m 2 / g, pore volume 0.8±0.4mL / g, average pore diameter 12±6nm.

[0011] Preferably, the active component in step (1) is one or more of phosphomolybdic acid, phosphotungstic acid and silicotungstic acid, and the content of the active component is 10-40wt%.

[0012] Preferably, in step (1), the auxiliary agent is metal Cu, and the molar ratio of Cu to the coordinating atoms in the heteropolyacid is 1:12.

[0013] Preferably, in step (1), the Cu source in the raw salt is Cu(NO3)2·3H2O, and the Cu salt and the heteropolyacid solution are impregnated onto the carrier by a co-impregnation method, aged for 12 hours, dried at 120°C for 12 hours, and calcined at 300°C for 4 hours to obtain a catalyst precursor loaded with an auxiliary agent and an active component.

[0014] Preferably, the reducing atmosphere in step (2) is a mixture of hydrogen and nitrogen with a hydrogen content of 10 vol%. After treating at 250° C. for 4 h, the temperature is cooled to room temperature in a nitrogen atmosphere to obtain a catalyst.

[0015] The invention discloses an application of a heteropolyacid catalyst in the condensation of formaldehyde and methyl formate to prepare methyl glycolate.

[0016] Preferably, a fixed bed reactor is used, the raw materials are trioxymethylene and methyl formate, the molar ratio of formaldehyde is 1:1.5, the reaction temperature is 140-160°C; the reaction pressure is 0.5-1.5MPa; the mass space velocity is 1-5h -1 .

[0017] The present invention uses common silicon oxide as a carrier and adopts a co-impregnation method to load active components to prepare a catalyst, with mild conditions and a stable and controllable process. By doping a suitable amount of metal, overflow hydrogen is induced to reduce part of the coordinated atoms in the heteropoly acid as alkaline sites, which synergize with the strong acid sites of the heteropoly acid to promote the cross condensation of formaldehyde and methyl formate, thereby improving the reaction activity and selectivity. The prepared catalyst has the advantages of low reaction temperature, high activity, good selectivity, etc.

[0018] Beneficial technical effects

[0019] 1. The present invention prepares a formaldehyde-methyl formate condensation catalyst with simple steps, mild conditions, and a controllable process. The prepared catalyst has an acid-base dual function, can synergistically activate formaldehyde and methyl formate, promote their efficient cross-condensation to prepare methyl glycolate, and improve reaction activity and selectivity;

[0020] 2. The catalyst has the advantages of low reaction temperature and good stability. The reaction process is simple, controllable and easy to operate, and has broad application prospects. DETAILED DESCRIPTION

[0021] In order to further explain the present invention in detail, several specific implementation cases are given below, but the present invention is not limited to these embodiments.

[0022] The properties of the silicon oxide carrier used in the following examples are: specific surface area 285m 2 / g, pore volume 0.79mL / g, pore diameter 5.2-13.8nm, average pore diameter 12.6nm.

[0023] Example 1

[0024] (1) Loading additives and active components: Weigh 5.0 g of silica carrier and add it to 10 mL of 1.67 g H3PMo 12 O 40 ·xH2O and 0.22gCu(NO3)2·3H2O aqueous solution, mature at room temperature for 12h, dry at 120℃ for 12h, and calcine at 300℃ for 4h to obtain a catalyst precursor loaded with auxiliary agents and active components.

[0025] (2) Overflow hydrogen reduction: The catalyst precursor prepared in step (1) was placed in a mixture of hydrogen and nitrogen (wherein the hydrogen content was 10 vol%), treated at 250°C for 4 h, and then cooled to room temperature in a nitrogen atmosphere to obtain a catalyst, which was designated as catalyst 1. XRD results showed that the crystalline phase was H3PMo 12 O 40 , XRF results show that the content of Mo in the catalyst is 15.8wt%, and the content of Cu is 0.9wt%.

[0026] (3) Catalyst evaluation: The catalyst was evaluated in a fixed bed tubular reactor. The raw materials were trioxymethylene and methyl formate (the molar ratio of formaldehyde to methyl formate was 1:1.5). The reaction temperature was 160°C, the reaction pressure was 1.0 MPa, and the mass space velocity was 1.0 h -1 After the product was separated into gas and liquid, the product composition was measured by gas chromatography and liquid chromatography, and the conversion rate of formaldehyde and the selectivity of methyl glycolate were calculated.

[0027] Comparative Example 1

[0028] The difference between Comparative Example 1 and Example 1 is that in step (1), no metal additive is added to the 10 mL impregnation solution, and the remaining processes and conditions are exactly the same as those of Example 1; the prepared catalyst is recorded as Catalyst 2.

[0029] Comparative Example 2

[0030] Compared with Example 1, Comparative Example 2 differs in that step (2) is omitted, and the solid catalyst obtained in step (1) is directly applied to the catalytic reaction evaluation, and the remaining processes and conditions are exactly the same as those in Example 1; the obtained catalyst is recorded as Catalyst 3.

[0031] Example 2: Different Cu content

[0032] Compared with Example 1, Example 2 differs in that in step (1), 10 mL of the impregnation solution contains 0.11 g of Cu(NO3)2·3H2O, and the rest of the process and conditions are exactly the same as those of Example 1; the prepared catalyst is recorded as Catalyst 4.

[0033] Example 3: Different Cu content

[0034] Compared with Example 1, Example 3 differs in that in step (1), 10 mL of the impregnation solution contains 0.44 g of Cu(NO3)2·3H2O, and the rest of the process and conditions are exactly the same as those of Example 1; the prepared catalyst is recorded as Catalyst 5.

[0035] Example 4: Different contents of phosphomolybdic acid

[0036] Example 4 is different from Example 1 in that in step (1), 10 mL of the impregnation solution contains 0.56 g H3PMo 12 O 40 ·xH2O and 0.07gCu(NO3)2·3H2O, and the rest of the process and conditions are exactly the same as in Example 1; the prepared catalyst is recorded as Catalyst 6.

[0037] Example 5: Different contents of phosphomolybdic acid

[0038] Example 5 is different from Example 1 in that in step (1), 10 mL of the impregnation solution contains 3.33 g H3PMo 12 O 40 ·xH2O and 0.44gCu(NO3)2·3H2O, and the rest of the process and conditions are exactly the same as in Example 1; the prepared catalyst is recorded as Catalyst 7.

[0039] Example 6: Different H2 content, reduction temperature and reduction time

[0040] Compared with Example 1, Example 6 differs in that in step (2), the hydrogen content in the reducing atmosphere is 1 vol%, the reduction time is 10 h, and the remaining processes and conditions are exactly the same as those in Example 1; the prepared catalyst is recorded as Catalyst 8.

[0041] Example 7: Different H2 content, reduction temperature and reduction time

[0042] Compared with Example 1, Example 7 differs in that in step (2), the hydrogen content in the reducing atmosphere is 1 vol%, the reduction temperature is 350°C, and the remaining processes and conditions are exactly the same as those in Example 1; the prepared catalyst is recorded as Catalyst 9.

[0043] Example 8: Different H2 content, reduction temperature and reduction time

[0044] Compared with Example 1, Example 8 differs in that in step (2), the hydrogen content in the reducing atmosphere is 50 vol%, the reduction time is 1 h, and the remaining processes and conditions are exactly the same as those in Example 1; the prepared catalyst is recorded as Catalyst 10.

[0045] Example 9: Different H2 content, reduction temperature and reduction time

[0046] Compared with Example 1, Example 9 differs in that in step (2), the hydrogen content in the reducing atmosphere is 50 vol%, the reduction temperature is 150°C, and the remaining processes and conditions are exactly the same as those in Example 1; the prepared catalyst is recorded as Catalyst 11.

[0047] Example 10: Different types of metals

[0048] Compared with Example 1, Example 10 differs in that in step (1), 10 mL of the impregnation solution contains 0.27 g of Ni(NO3)2·6H2O, and the rest of the process and conditions are exactly the same as those of Example 1; the prepared catalyst is recorded as Catalyst 12.

[0049] Example 11: Different types of metals

[0050] Compared with Example 1, Example 11 differs in that in step (1), 10 mL of the impregnation solution contains 0.24 g of Pd(NO3)2·2H2O, and the rest of the process and conditions are exactly the same as those of Example 1; the prepared catalyst is recorded as Catalyst 13.

[0051] Example 12: Different types of metals

[0052] Compared with Example 1, Example 12 differs in that in step (1), 10 mL of the impregnation solution contains 0.29 g of Pt(NO3)4, and the rest of the process and conditions are exactly the same as those of Example 1; the prepared catalyst is recorded as Catalyst 14.

[0053] Example 13: Different types of heteropolyacids

[0054] Example 13 is different from Example 1 in that in step (1), 10 mL of the impregnation solution contains 1.67 g H3PW 12 O 40 ·xH2O and 0.14gCu(NO3)2·3H2O, and the rest of the process and conditions are exactly the same as in Example 1; the prepared catalyst is recorded as Catalyst 15.

[0055] Example 14: Different types of heteropolyacids

[0056] Example 14 is different from Example 1 in that in step (1), 10 mL of the impregnation solution contains 1.67 g H4SiW 12 O 40 ·xH2O and 0.14gCu(NO3)2·3H2O, and the rest of the process and conditions are exactly the same as in Example 1; the prepared catalyst is recorded as Catalyst 16.

[0057] The following table lists the reaction evaluation results of the catalyst prepared by the method of the present invention:

[0058]

[0059] From Example 1 and Comparative Examples 1 and 2, it can be seen that loaded metal additives and overflow hydrogen reduction are beneficial to improving reaction activity and selectivity; from Examples 1-9, it can be seen that the conditions of Example 1 are optimal; from Examples 1, 10-12, it can be seen that the promoting effects of additives Cu, Pd and Pt are better than those of Ni, but considering the cost, the additive Cu has the best effect; from Examples 1, 13 and 14, it can be seen that the activity and selectivity of phosphomolybdic acid are higher than those of phosphotungstic acid and silicotungstic acid.

Claims

1. A method for preparing a heteropolyacid catalyst, comprising a metal promoter, a heteropolyacid and a carrier. The preparation of the catalyst comprises two parts: loading the metal promoter and the active component and overflow hydrogen reduction: (1) Loading metal additives and active components: preparing a solution of metal salt and heteropoly acid, impregnating the solution onto a silica carrier, and then aging, drying, and calcining to obtain a catalyst precursor; (2) Overflow hydrogen reduction: The catalyst precursor obtained in step (1) is placed in a reducing atmosphere to obtain a highly efficient condensation catalyst for formaldehyde and methyl formate.

2. The method according to claim 1, characterized in that: In step (1), the carrier is common silicon oxide, and its properties are: specific surface area 350±100m 2 / g, pore volume 0.8±0.4mL / g, average pore diameter 12±6nm.

3. The method according to claim 1, characterized in that: In step (1), the active component is one or more of phosphomolybdic acid, phosphotungstic acid and silicotungstic acid, and the content in the aqueous solution is 5-50wt%, preferably 10-40wt%.

4. The method according to claim 1 or 3, characterized in that: In step (1), the auxiliary agent is one or more of the metals Cu, Ni, Pd and Pt, and the molar ratio of the metal to the molybdenum and / or tungsten in the heteropolyacid is 1:(6-24), preferably 1:

12.

5. The method according to claim 4, characterized in that: In step (1), the Cu salt is Cu(NO3)2·3H2O, the Ni salt is Ni(NO3)2·6H2O, the Pd salt is Pd(NO3)2·2H2O, and the Pt salt is Pt(NO3)4.

6. The method according to claim 1, characterized in that: In step (1), the nickel salt and the heteropolyacid solution are co-impregnated onto the carrier by an impregnation method, left to mature for 4-24 hours (preferably 8-16 hours, more preferably 12 hours), dried at 80-160°C (preferably 100-140°C, more preferably 120°C) for 4-24 hours (preferably 8-16 hours, more preferably 12 hours), and calcined at 200-500°C (preferably 250-400°C, more preferably 300°C) for 1-12 hours (preferably 2-8 hours, more preferably 4 hours) to obtain a catalyst precursor loaded with a supporting agent and an active component.

7. The method according to claim 1, characterized in that: In step (2), the catalyst precursor is placed in a reducing atmosphere for treatment, the reducing gas is a mixture of hydrogen and nitrogen, the hydrogen content is 1-50vol%, preferably 10-20vol%; the treatment temperature is 150-350°C, preferably 250-300°C; the treatment time is 1-10h, preferably 4-6h; after the treatment is completed, the temperature is cooled to room temperature in a nitrogen atmosphere to obtain a catalyst.

8. A heteropolyacid catalyst for the condensation of formaldehyde and methyl formate to produce methyl glycolate, characterized in that: The catalyst used is prepared by the preparation method described in any one of claims 1 to 7.

9. Use of the heteropolyacid catalyst according to claim 8 in catalyzing the condensation of formaldehyde and methyl formate to produce methyl glycolate.

10. The use according to claim 9, characterized in that: A fixed bed reactor is used, the raw materials are trioxymethylene or formaldehyde and methyl formate, the molar ratio of formaldehyde to methyl formate is 1:0.5-5, preferably 1:1.5; the reaction temperature is 100-200°C, preferably Select 140-160℃; reaction pressure 0.1-2MPa, preferably 0.5-1.5MPa; mass space velocity 0.5-10h -1 , Preferably 1-5 hours -1 .

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