Supported catalysts, their preparation methods, and their application in the preparation of methyl glyoxylate.

Abstract

This invention relates to a supported catalyst, its preparation method, and its application in the preparation of methyl glyoxylate. The catalyst consists of a support and an active metal component supported on the surface of the support; the support is lanthanum phosphate, and the active metal component is vanadium oxide and molybdenum oxide; wherein the mass percentage of vanadium oxide and molybdenum oxide in the supported catalyst is 20-40%. This catalyst exhibits excellent performance in the oxidative dehydrogenation reaction of methyl glycolate, with high feed conversion rate and target selectivity, and has broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of catalyst materials technology, particularly supported catalysts, their preparation methods, and their application in the preparation of methyl glyoxylate. Background Technology

[0002] Due to the expansion of the ethylene glycol market and my country's energy structure characterized by abundant coal, scarce oil, and limited natural gas, the coal-based syngas-to-ethylene glycol process has developed rapidly in my country. Currently, domestic coal-based syngas-to-ethylene glycol plants are operating at approximately 80% capacity. This process generates a large amount of intermediate or byproduct methyl glycolate; therefore, utilizing methyl glycolate can improve the efficiency of the coal-based syngas-to-ethylene glycol process.

[0003] Currently, methyl glycolate is mainly used in two ways: firstly, as a solvent for cellulose, resins, and rubber; and secondly, to convert it into downstream chemicals such as glycolic acid, methyl malonate, glycine, and methyl glyoxylate. Among these, the conversion to methyl glyoxylate is particularly noteworthy.

[0004] Methyl glyoxylate is a colorless, transparent liquid chemical substance containing both aldehyde and ester functional groups on its α-carbon. It is widely used in chemical, pharmaceutical, and materials industries. Furthermore, hydrolysis of methyl glyoxylate yields glyoxylic acid, which has numerous derivatives and is an important fine chemical raw material for the synthesis of vanillin fragrance, allantoin, and acetophenone, showing great promise. Several methods for producing methyl glyoxylate have been reported, but their development is limited by harsh reaction conditions, poor product quality, and low yield. In contrast, the oxidation of methyl glycolate to prepare methyl glyoxylate has the greatest development potential due to its simple process, lower cost, higher product quality, and environmental friendliness.

[0005] The oxidative dehydrogenation of methyl glycolate is complex. Due to its numerous functional groups, it is prone to side reactions such as cracking, hydrolysis, and polymerization at high temperatures, leading to the formation of many byproducts. To steer methyl glycolate towards the target product, methyl glyoxylate, and thus improve its conversion rate, a key factor is the selection and design of the catalyst. Currently, many transition metals have been used as catalysts for the oxidation of alcohols to aldehydes. Among them, iron, copper, molybdenum, palladium, and vanadium-based catalysts exhibit the best performance. Current research on catalysts for this system mainly focuses on iron-based catalysts supported on molybdenum oxide or vanadium-based catalysts supported on titanium oxide. However, when these catalysts are used for the oxidative dehydrogenation of methyl glycolate, the reaction temperature is generally high (usually above 300°C). Furthermore, Chinese Patent 201610368002.5 discloses a method for oxidizing glycolate to glyoxylate, which involves contacting nitrogen oxides, oxygen-containing gas, and glycolate to generate glyoxylate. The method uses a mixture of nitrogen oxides and oxygen (with a molar ratio of 4-50:1) as the oxidant to selectively oxidize methyl glycolate, achieving a methyl glycolate conversion rate of 97% and a glyoxylate selectivity of 92% at 120°C. The introduction of nitrogen oxides effectively avoids excessive oxidation of the hydroxyl groups, but inevitably leads to environmental pollution.

[0006] Therefore, there is an urgent need to find a new catalyst that can achieve high conversion and selectivity at lower reaction temperatures, so as to facilitate large-scale industrial use. Summary of the Invention

[0007] The purpose of this invention is to find a new catalyst that can enable the oxidative dehydrogenation of methyl glycolate to methyl glyoxylate at a lower reaction temperature, with high conversion and selectivity, so as to facilitate large-scale industrial use.

[0008] The technical solution to achieve the purpose of this invention is as follows:

[0009] A supported catalyst comprises a support and an active metal component supported on the surface of the support; the support is lanthanum phosphate, and the active metal component is vanadium oxide and molybdenum oxide; wherein the mass percentage of vanadium oxide and molybdenum oxide in the supported catalyst is 20-40%.

[0010] Furthermore, the molar ratio of vanadium to molybdenum in the active metal component is 1:0.5 to 1:6.

[0011] A method for preparing a supported catalyst includes the following preparation steps:

[0012] S1. Dissolve lanthanum nitrate hexahydrate in deionized water, and then add hypophosphite solution dropwise while stirring to obtain a suspension;

[0013] S2. Ammonium metavanadate and ammonium heptamolybdate are dissolved sequentially in an ammonia solution with a concentration of 1-20%, and then added to the suspension obtained in step S1 to obtain a mixture. The mixture is heated to 95℃-100℃ and maintained until the pH of the mixture is ≤7.5. Heating is then stopped and the mixture is allowed to cool naturally. The mixture is then filtered and washed with deionized water until the conductivity is <200μs / cm. After drying and calcination, the supported catalyst is obtained.

[0014] Furthermore, in step S1, the hypophosphite solution is added dropwise over a period of 1 hour.

[0015] Furthermore, in step S2, the drying temperature is 120°C and the time is 12 hours; and / or, the calcination temperature is 450°C, the heating rate is 10°C / min, and the time is 4 hours.

[0016] Furthermore, in step S2, the mixture is heated to 95°C to 100°C within 2 hours.

[0017] A method for preparing methyl glyoxylate includes the following steps: crushing the above-mentioned supported catalyst, loading it into a fixed-bed reactor, introducing nitrogen and oxygen, heating and then isothermal treatment, then lowering the temperature to 180°C, pumping in the raw material methyl glycolate, reacting, and cooling and collecting the reaction liquid to obtain methyl glyoxylate.

[0018] The significant advantages of this invention compared to existing technologies are:

[0019] This invention utilizes hypophosphite and lanthanum nitrate hexahydrate. In solution, hypophosphite combines with lanthanum ions to form a precipitate. The precipitate surface is rich in hydroxyl and hydrogen groups, which facilitates the formation of hydrogen bonds and van der Waals forces with metavanadate and molybdate ions. This promotes the dispersion and bonding of ammonium metavanadate and ammonium heptamolybdate on the precipitate surface, resulting in better dispersion and a more balanced proportion of vanadium oxide and molybdenum oxide particles on the supported catalyst surface. Simultaneously, lanthanum acts as both a support and an active component, synergistically participating in catalysis with vanadium and molybdenum. Applied to the oxidative dehydrogenation of methyl glycolate to methyl glyoxylate, it exhibits high feed conversion and target selectivity, and the reaction temperature (only 180℃) is relatively mild, which is beneficial for large-scale industrial production. In particular, it achieves better catalytic effects compared to traditional catalysts, showing broad application prospects. Especially in the coal-based syngas to ethylene glycol process, the low-temperature utilization of the byproduct methyl glycolate reduces energy consumption and improves the economic efficiency of the coal-based syngas to ethylene glycol process. Attached Figure Description

[0020] Figure 1 This is the XRD pattern of the carrier prepared in Example 1 of the present invention.

[0021] Figure 2This is a scanning electron microscope image of the carrier prepared in Example 1 of the present invention. Detailed Implementation

[0022] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0023] Example 1

[0024] The supported catalyst is prepared by the following steps:

[0025] S1. Dissolve 107.2g of lanthanum nitrate hexahydrate in 2L of deionized water, and then slowly add 90g of 50wt% hypophosphite solution dropwise over a period of 1h under stirring to obtain a suspension.

[0026] S2. Dissolve 13.4 g of ammonium metavanadate and 18.6 g of ammonium heptamolybdate sequentially in dilute ammonia water (concentration 1%), and add this to the suspension obtained in step S1 to obtain a mixture. Place the mixture in a double-walled glass reactor, turn on the heating system (raise the reaction temperature to 95℃~100℃ in about 2 hours and maintain it, cooling and refluxing if necessary), react for about 18 hours until the pH of the mixture is ≤7.5, then stop heating and allow it to cool naturally to room temperature. Then filter and wash with deionized water until the conductivity is <200μs / cm. After that, dry the filter cake in an oven at 120℃ for 12 hours. Pulverize the dried material and then calcine it in an inert atmosphere muffle furnace (heat to 450℃ at a heating rate of 10℃ / min) for 4 hours to obtain the supported catalyst.

[0027] The suspension from step S1 was taken, filtered, dried, and the catalyst support was analyzed by XRD and scanning electron microscopy. Figure 1 The image shown is the XRD pattern of the catalyst support; specific peak values ​​are shown in Table 1.

[0028] Table 1. List of diffraction peaks for each carrier.

[0029]

[0030]

[0031] like Figure 2 As shown, electron microscopy clearly reveals that the support is plate-like, approximately 10 μm in size, increasing the specific surface area. This facilitates the dispersion and bonding of ammonium metavanadate and ammonium heptamolybdate on its surface, resulting in better dispersion and a more balanced ratio of vanadium pentoxide and molybdenum trioxide particles on the catalyst surface. Furthermore,

[0032] The carrier surface is rough because it has a very rich number of hydroxyl and hydrogen groups, which makes it more conducive to the formation of hydrogen bonds and van der Waals forces between metavanadate and molybdate ions in dilute ammonia solutions of ammonium metavanadate and ammonium heptamolybdate.

[0033] Example 2

[0034] The same method for preparing the supported catalyst as in Example 1 was used, except that in step S2, a dilute ammonia solution containing 20.1 g of ammonium metavanadate and 9.3 g of ammonium heptamolybdate was added.

[0035] Example 3

[0036] The same method for preparing the supported catalyst as in Example 1 was used, except that in step S2, a dilute ammonia solution containing 6.7 g of ammonium metavanadate and 27.3 g of ammonium heptamolybdate was added.

[0037] Comparative Example 1

[0038] The same method for preparing the supported catalyst as in Example 1 was used, except that a dilute ammonia solution containing 26.8 g of ammonium metavanadate was added.

[0039] Comparative Example 2

[0040] The same method for preparing the supported catalyst as in Example 1 was used, except that a dilute ammonia solution containing 37.2 g of ammonium heptamolybdate was added.

[0041] Preparation of methyl glyoxylate and performance evaluation of the catalyst

[0042] The catalysts prepared in Examples 1-3 and Comparative Examples 1 and 2 were pulverized to 20 mesh and packed into a fixed-bed reactor. A mixture of nitrogen and oxygen (oxygen content 21%) was introduced, and the reactor was heated to 360°C and kept at that temperature for 4 hours to allow the active components in the catalyst to fully react with the oxygen. Then, the temperature of the fixed-bed reactor system was lowered to 180°C. After the system stabilized (system stability means that the pressure, temperature, and flow rate in the reaction system no longer changed), methyl glycolate was pumped in (methyl glycolate feed rate 0.03 mL / min, pressure maintained below 0.3 MPa) to carry out the catalytic reaction. The reaction liquid was cooled and collected to obtain methyl glyoxylate.

[0043] In the above reaction, there is no particular restriction on the ratio of nitrogen to oxygen in actual production applications. The fixed-bed reactor can be purged with nitrogen first, and then air can be introduced. The oxygen content of the air is about 21%.

[0044] The reaction products were analyzed by liquid chromatography (Shimadzu LC-20A) to calculate the conversion and selectivity, as detailed in Table 2. An Agilent C18 column was used, with an oven temperature of 35℃, a detection wavelength of 212nm, an injection volume of 2μL, and a mobile phase of 10% acetonitrile and 0.06% phosphoric acid aqueous solution at a flow rate of 0.6mL / min. -1 .

[0045] The conversion rate mentioned in this invention refers to the ratio of the number of moles of methyl glyoxylate in the reaction solution to the number of moles of methyl glycolate in the raw material, i.e.

[0046] The selectivity described in this invention refers to the ratio of the molar number of methyl glyoxylate in the reaction solution to the total molar number of all products derived from methyl glycolate, i.e.

[0047] Table 2 Catalyst performance test results

[0048] Methyl glycolate conversion rate (%) Selectivity of the target product (%) Example 1 93.6 97.5 Example 2 97.5 98.2 Example 3 92.3 94.1 Comparative Example 1 88.5 96.3 Comparative Example 2 67.9 87.6

[0049] As shown in Table 2, the two-component active components, vanadium oxide and molybdenum oxide, supported on the surface of lanthanum phosphate to form a supported catalyst, exhibit higher conversion rates of methyl glycolate and higher selectivity for the target product (methyl glyoxylate) compared to Comparative Examples 1 and 2 due to the synergistic effect of the three components. This demonstrates that the supported catalyst provided by this invention has superior catalytic performance. Furthermore, the reaction temperature is lower, requiring only 180°C, to convert methyl glycolate to methyl glyoxylate, resulting in a milder reaction that is more conducive to industrial production.

Claims

1. A method for preparing a supported catalyst for the oxidative dehydrogenation reaction of methyl glycolate to methyl glyoxylate, characterized in that: The supported catalyst comprises a support and an active metal component supported on the surface of the support; the support is lanthanum phosphate, and the active metal component is vanadium oxide and molybdenum oxide; wherein the mass percentage of vanadium oxide and molybdenum oxide in the supported catalyst is 20-40%; the method includes the following preparation steps: S1. Dissolve lanthanum nitrate hexahydrate in deionized water, and then add hypophosphite solution dropwise while stirring to obtain a suspension; S2. Dissolve ammonium metavanadate and ammonium heptamolybdate sequentially in an ammonia solution with a concentration of 1-20%, and add it to the suspension obtained in step S1 to obtain a mixture. Heat the mixture to 95℃-100℃ and maintain it until the pH of the mixture is ≤7.5, then stop heating and allow it to cool naturally. Then filter it and wash it with deionized water until the conductivity is <200µs / cm. After drying and calcining, the supported catalyst is obtained.

2. The preparation method according to claim 1, characterized in that: The molar ratio of vanadium to molybdenum in the active metal component is 1:0.5 to 1:

6.

3. The preparation method according to claim 1, characterized in that: In step S1, the hypophosphite solution is added dropwise over a period of 1 hour.

4. The preparation method according to claim 1, characterized in that: In step S2, the drying temperature is 120°C and the time is 12 hours; and / or, the calcination temperature is 450°C, the heating rate is 10°C / min, and the time is 4 hours.

5. The preparation method according to claim 1, characterized in that: In step S2, the mixture is heated to 95°C~100°C within 2 hours.

6. A method for preparing methyl glyoxylate, characterized in that: Includes the following steps: The supported catalyst prepared according to the method described in claim 1 is pulverized, packed into a fixed-bed reactor, and nitrogen and oxygen are introduced. After heating, the reactor is kept at a constant temperature, and then the temperature is lowered to 180°C. Methyl glycolate is pumped in to carry out the reaction. The reaction liquid is collected after cooling, which is methyl glyoxylate.

7. The method for preparing methyl glyoxylate according to claim 6, characterized in that: The heating and holding temperature treatment involves heating to 360°C and then holding the temperature for 4 hours.

Images