Process for the direct preparation of acrylic acid from methyl acetate and catalyst

Abstract

The application discloses a method and a catalyst for directly preparing acrylic acid from methyl acetate. The method comprises the following steps: in a fixed bed reactor, methyl acetate is reacted with oxygen or air under the action of a catalyst to obtain acrylic acid; the catalyst is a supported molybdenum phosphate salt; in the catalyst, the mass fraction of molybdenum is 1-30% in terms of metallic molybdenum, and the molar ratio of molybdenum to phosphorus is 0.05-0.4. The method provided by the application can efficiently prepare acrylic acid without adding additional methanol or formaldehyde or additional water, has high atomic economy, and is easy to separate the product; the catalyst is efficient and stable in performance; the yield of the target product is high, and the by-products are few; and the method has low requirements on equipment, small investment cost, and important application value.

Description

Technical Field

[0001] This invention relates to a method and catalyst for the direct preparation of acrylic acid from methyl acetate, belonging to the field of chemical synthesis. Background Technology

[0002] Acrylic acid is a very important bulk chemical with wide applications in printing, coatings, synthetic fibers, and adhesives. Currently, the main industrial production method for acrylic acid is the two-step oxidation process of propylene, in which propylene is first oxidized to acrolein, and then further oxidized to obtain acrylic acid. However, this process suffers from the drawbacks of over-oxidation of propylene and acrolein, as well as the reliance on fossil fuels. Therefore, developing a green route for acrylic acid production has significant scientific and economic value.

[0003] Methyl acetate is an inexpensive, non-toxic, and widely available chemical. Besides the synthetic route of esterification with acetic acid and methanol, the carbonylation of dimethyl ether has also developed into a highly promising industrial route for the production of methyl acetate. Methyl acetate is a raw material for many important chemicals; it can be used to prepare acetic anhydride via carbonylation and ethanol via hydrogenation. Furthermore, to increase the added value of downstream products of methyl acetate, the preparation of acrylic acid (methyl ester) via aldol condensation of methyl acetate and formaldehyde has attracted increasing attention.

[0004] Patent application (US 20130237724) discloses a method for preparing acrylic acid by reacting acetic acid with formaldehyde solution, using a V-Ti-P mixed oxide catalyst. Patent application (CN 201310566202) discloses a catalyst for synthesizing acrylic acid from formaldehyde aqueous solution and acetic acid, and its preparation method. The catalyst support includes activated carbon, alumina, and silicon dioxide, and the supported active component is mainly phosphorus pentoxide. Patent application (CN 201410103826) discloses a VPO catalyst and its application in the reaction of acetic acid (ester) with formaldehyde to produce acrylic acid (ester), with acetic acid or methyl acetate and formaldehyde as reactants. It is known that currently, in the process of efficiently preparing acrylic acid (methyl ester) using methyl acetate as a raw material, formaldehyde needs to be added to promote the conversion of methyl acetate. Furthermore, since methyl acetate can be hydrolyzed, the resulting products are mostly mixtures of acrylic acid and methyl acrylate, which brings considerable difficulties to the separation and purification of the products. Therefore, it is necessary to provide a method for directly synthesizing acrylic acid from methyl acetate without adding formaldehyde or methanol. Summary of the Invention

[0005] The purpose of this invention is to provide a method for the direct preparation of acrylic acid from methyl acetate. Under the action of a catalyst, acrylic acid is obtained in high yield through the self-hydrolysis, oxidation and aldol condensation of methyl acetate.

[0006] The method for directly preparing acrylic acid from methyl acetate provided by this invention includes the following steps:

[0007] In a fixed-bed reactor, methyl acetate reacts with oxygen or air in the presence of a catalyst to produce acrylic acid.

[0008] The catalyst is a supported molybdenum phosphate.

[0009] The reaction equation involved in the method of this invention is as follows:

[0010] CH3COOCH3+0.5O2=CH2CHCOOH+H2O

[0011] Specifically, in the method of the present invention, the microscopic process of converting methyl acetate into acrylic acid is as follows: methyl acetate first reacts with hydroxyl groups on the surface of the catalyst under the action of the catalyst, dissociating into acetic acid and methanol; the generated methanol reacts with oxygen to produce water and formaldehyde, wherein the water further promotes the hydrolysis of methyl acetate, while formaldehyde and acetic acid undergo aldol condensation reaction to produce water and acrylic acid; the water generated during the reaction can continuously maintain the hydrolysis of methyl acetate.

[0012] In the above preparation method, the reaction temperature can be 325-400℃, such as 350-375℃, preferably 375℃.

[0013] In the above preparation method, the mass hourly space velocity (WHSV) of the methyl acetate can be 1.0–10 L·g. -1 ·h -1 For example, 3.0~6 L·g -1 ·h -1 .

[0014] In the above preparation method, the reaction is carried out under normal pressure.

[0015] The partial pressure of the methyl acetate can be 0.1 to 10 kPa, such as 3 to 6 kPa, preferably 3 kPa, and the partial pressure of the oxygen or the air can be 0.1 to 10 kPa, such as 1.2 to 1.5 kPa, preferably 1.2 kPa.

[0016] In the above preparation method, the molar ratio of oxygen or oxygen in the air to methyl acetate can be 0.5 to 1, and the molar amount of air is measured by the amount of oxygen therein.

[0017] In the above preparation method, the mass fraction of molybdenum in the catalyst can be 1-30%, such as 5-15%, 5-10% or 10%, and the molar ratio of molybdenum to phosphorus can be 0.05-0.4, such as 0.2-0.5, 0.2-0.25, 0.2, 0.25 or 0.5.

[0018] The catalyst can be prepared by a method including the following steps:

[0019] A mixed aqueous solution of molybdenum precursor and phosphoric acid is added to a carrier, stirred, and the water is removed to obtain a solid; the solid is then dried and calcined to obtain the final product.

[0020] Specifically, the molybdenum precursor may be at least one of ammonium metamolybdate, molybdic acid, and ammonium molybdate;

[0021] The carrier may be at least one of titanium oxide, zirconium oxide, magnesium oxide, hydrotalcite, molecular sieve, silicon oxide and cerium oxide, wherein the titanium oxide is preferably titanium oxide P25 or anatase titanium oxide;

[0022] The drying temperature can be 80–140°C, and the time can be 3–12 hours;

[0023] The roasting temperature can be 350–550°C, and the time can be 1–6 hours;

[0024] The roasting is carried out in an air atmosphere or an oxygen atmosphere.

[0025] Preferably, the method further includes the step of adding an auxiliary agent to the carrier;

[0026] The auxiliary agent may be an oxide of at least one of V, Mn, W and Pb;

[0027] In the catalyst, the mass content of the auxiliary agent is 0-5%.

[0028] This invention provides a method for the direct conversion of methyl acetate to acrylic acid using a multifunctional supported molybdenum phosphate catalyst. This method can efficiently produce acrylic acid without the need for the addition of methanol or formaldehyde, or water. It has high atom economy, easy product separation, efficient and stable catalyst, high yield of target product, and few by-products. Furthermore, this method has low equipment requirements and low investment cost, and has significant application value. Detailed Implementation

[0029] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0030] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0031] The main body described in the following examples is prepared from methyl acetate to produce acrylic acid.

[0032] In the following examples, the catalytic reaction of methyl acetate was carried out in a fixed-bed microreactor at atmospheric pressure.

[0033] In the following examples, the catalysts were diluted with quartz sand to eliminate local overheating caused by localized exothermic reactions.

[0034] In the following examples, methyl acetate, the raw material, is introduced into the reaction system in a bubbling manner, with high-purity nitrogen gas used as the bubbling and equilibrium gas. To prevent the raw materials and products from condensing and clogging the pipelines, all gas pipelines are insulated with heating belts at a temperature above 120°C.

[0035] In the following examples, the reactants and products were analyzed online using a Shimadzu GC-2010 gas chromatograph. The gas chromatograph was configured with dual gas paths and dual detectors. One path was a TCD detector, mainly used to detect inert gases such as nitrogen, and the chromatographic column was a Porapak Q and 13X molecular sieve packed column. The other path was an FID detector, and the chromatographic column was an LZP35, used for the quantitative analysis of methyl acetate, methanol, and acrylic acid, etc.

[0036] The formulas for calculating conversion rate and selectivity are as follows:

[0037]

[0038]

[0039] Example 1: Preparation of supported phosphomolybdate catalyst

[0040] A certain amount of a mixed solution of ammonium metamolybdate and phosphoric acid was added to the support and stirred at room temperature for 6 hours. Then, the water was removed by vacuum distillation. The resulting solid was dried in an oven at 120°C for 6 hours and then calcined in air at 450°C for 3 hours to obtain the catalyst, denoted as m-MoPO-n / MO. x Where m represents the loading mass fraction of Mo, n represents the molar ratio of P to Mo, and MO x This represents the catalyst support.

[0041] Following the steps described above, the following supported phosphomolybdate catalyst was obtained:

[0042] 10-MoPO-4 / SiO2, 10-MoPO-4 / ZrO2, 10-MoPO-4 / TiO2 (P25), 10-MoPO-4 / TiO2 (anatase), 5-Mo PO-4 / TiO2(P25), 15-MoPO-4 / TiO2(P25), 10-MoPO-5 / TiO2(P25), 10-MoPO-2 / TiO2(P25).

[0043] Example 2: Preparation of acrylic acid from methyl acetate catalyzed by 10-MoPO-4 / SiO2 catalyst.

[0044] The catalyst used is 10-MoPO-4 / SiO2.

[0045] In a micro-scale atmospheric pressure fixed-bed reactor, methyl acetate and oxygen are the reactants, and nitrogen is the equilibrium gas, with a gas hourly space velocity (GHSV) of 3.0 L·h⁻¹. -1 ·g -1 The methyl acetate content was 2 kPa, and the oxygen content was 1.2 kPa. Using 0.6 g of catalyst, the reaction was carried out at 375 °C, achieving a 100% conversion of methyl acetate and a 44.3% yield of acrylic acid.

[0046] Example 3: Preparation of acrylic acid from methyl acetate catalyzed by 10-MoPO-4 / ZrO2 catalyst.

[0047] The catalyst used is 10-MoPO-4 / ZrO2.

[0048] In a micro-scale atmospheric pressure fixed-bed reactor, methyl acetate and oxygen are the reactants, and nitrogen is the equilibrium gas, with a gas hourly space velocity (GHSV) of 3.0 L·h⁻¹. -1 ·g -1 The methyl acetate content was 2 kPa, and the oxygen content was 1.2 kPa. Using 0.6 g of catalyst, the reaction was carried out at 375 °C, achieving a 100% conversion of methyl acetate and a 53.6% yield of acrylic acid.

[0049] Example 4: Preparation of acrylic acid from methyl acetate using 10-MoPO-4 / TiO2 (P25) catalyst.

[0050] The catalyst used is 10-MoPO-4 / TiO2 (P25).

[0051] In a micro-scale atmospheric pressure fixed-bed reactor, methyl acetate and oxygen are the reactants, and nitrogen is the equilibrium gas, with a gas hourly space velocity (GHSV) of 3.0 L·h⁻¹. -1 ·g -1 The methyl acetate content was 2 kPa, and the oxygen content was 1.2 kPa. Using 0.6 g of catalyst, the reaction was carried out at 375 °C, achieving a 100% conversion of methyl acetate and a 70.8% yield of acrylic acid.

[0052] Example 5: Preparation of acrylic acid from methyl acetate using 10-MoPO-4 / TiO2 (anatase) catalyst.

[0053] The catalyst used is 10-MoPO-4 / TiO2 (anatase).

[0054] In a micro-scale atmospheric pressure fixed-bed reactor, methyl acetate and oxygen are the reactants, and nitrogen is the equilibrium gas, with a gas hourly space velocity (GHSV) of 3.0 L·h⁻¹. -1 ·g -1The methyl acetate content was 2 kPa, and the oxygen content was 1.2 kPa. Using 0.6 g of catalyst, the reaction was carried out at 375 °C, achieving a 100% conversion of methyl acetate and a 66.6% yield of acrylic acid.

[0055] Comparing the reaction effects of Examples 2-5, it can be seen that the catalyst support affects the catalytic effect of the catalyst. When titanium dioxide (P25, anatase) and zirconium oxide are used as supports, they can both achieve good acrylic acid recovery rates, with titanium dioxide (P25) showing the best catalytic effect when used as a support.

[0056] Example 6: Preparation of acrylic acid from methyl acetate using 5-MoPO-4 / TiO2 (P25) catalyst.

[0057] The catalyst used is 5-MoPO-4 / TiO2(P25).

[0058] In a micro-scale atmospheric pressure fixed-bed reactor, methyl acetate and oxygen are the reactants, and nitrogen is the equilibrium gas, with a gas hourly space velocity (GHSV) of 3.0 L·h⁻¹. -1 ·g -1 The methyl acetate content was 2 kPa, and the oxygen content was 1.2 kPa. Using 0.6 g of catalyst, the reaction was carried out at 375 °C, achieving a 100% conversion of methyl acetate and a 63.5% yield of acrylic acid.

[0059] Example 7: Preparation of acrylic acid from methyl acetate using 15-MoPO-4 / TiO2 (P25) catalyst.

[0060] The catalyst used was 15-MoPO-4 / TiO2 (P25).

[0061] In a micro-scale atmospheric pressure fixed-bed reactor, methyl acetate and oxygen are the reactants, and nitrogen is the equilibrium gas, with a gas hourly space velocity (GHSV) of 3.0 L·h⁻¹. -1 ·g -1 The methyl acetate content was 2 kPa, and the oxygen content was 1.2 kPa. Using 0.6 g of 15-MoPO-4 / TiO2 (P25) catalyst, the reaction was carried out at 375 °C, achieving a 100% conversion of methyl acetate and a 54.2% yield of acrylic acid.

[0062] Comparing the reaction effects of Examples 4, 6 and 7, it can be seen that the molybdenum loading affects the catalytic effect of the catalyst. A molybdenum loading of 5% to 15% can achieve a good acrylic acid recovery rate, and a molybdenum loading of 10% has the best catalytic effect.

[0063] Example 8: Preparation of acrylic acid from methyl acetate using 10-MoPO-4 / TiO2 (P25) catalyst.

[0064] The catalyst used is 10-MoPO-4 / TiO2 (P25).

[0065] In a micro-scale atmospheric pressure fixed-bed reactor, methyl acetate and oxygen are the reactants, and nitrogen is the equilibrium gas, with a gas hourly space velocity (GHSV) of 3.0 L·h⁻¹. -1 ·g -1 The methyl acetate content was 2 kPa, and the oxygen content was 1.5 kPa. Using 0.6 g of catalyst, the reaction was carried out at 375 °C, achieving a 100% conversion of methyl acetate and a 75.1% yield of acrylic acid.

[0066] Example 9: Preparation of acrylic acid from methyl acetate using 10-MoPO-4 / TiO2 (P25) catalyst.

[0067] The catalyst used is 10-MoPO-4 / TiO2 (P25).

[0068] In a micro-scale atmospheric pressure fixed-bed reactor, methyl acetate and oxygen are the reactants, and nitrogen is the equilibrium gas, with a gas hourly space velocity (GHSV) of 6.0 L·h⁻¹. -1 ·g -1 The methyl acetate content was 2 kPa, and the oxygen content was 1.2 kPa. Using 0.6 g of catalyst, the reaction was carried out at 375 °C, achieving a methyl acetate conversion of 98.0% and an acrylic acid yield of 50.3%.

[0069] Example 10: Preparation of acrylic acid from methyl acetate using 10-MoPO-4 / TiO2 (P25) catalyst.

[0070] The catalyst used is 10-MoPO-4 / TiO2 (P25).

[0071] In a micro-scale atmospheric pressure fixed-bed reactor, methyl acetate and oxygen are the reactants, and nitrogen is the equilibrium gas, with a gas hourly space velocity (GHSV) of 3.0 L·h⁻¹. -1 ·g -1 The methyl acetate content was 2 kPa, and the oxygen content was 1.2 kPa. Using 0.6 g of catalyst, the reaction was carried out at 350 °C, achieving a 100% conversion of methyl acetate and a 65.3% yield of acrylic acid.

[0072] Example 11: Preparation of acrylic acid from methyl acetate using 10-MoPO-5 / TiO2 (P25) catalyst.

[0073] The catalyst used is 10-MoPO-5 / TiO2 (P25).

[0074] In a micro-scale atmospheric pressure fixed-bed reactor, methyl acetate and oxygen are the reactants, and nitrogen is the equilibrium gas, with a gas hourly space velocity (GHSV) of 3.0 L·h⁻¹. -1 ·g-1 The methyl acetate content was 2 kPa, and the oxygen content was 1.2 kPa. Using 0.6 g of catalyst, the reaction was carried out at 375 °C, achieving a 100% conversion of methyl acetate and a 61.5% yield of acrylic acid.

[0075] Example 12: Preparation of acrylic acid from methyl acetate using 10-MoPO-2 / TiO2 (P25) catalyst.

[0076] The catalyst used was 10-MoPO-2 / TiO2 (P25).

[0077] In a micro-scale atmospheric pressure fixed-bed reactor, methyl acetate and oxygen are the reactants, and nitrogen is the equilibrium gas, with a gas hourly space velocity (GHSV) of 3.0 L·h⁻¹. -1 ·g -1 The methyl acetate content was 2 kPa, and the oxygen content was 1.2 kPa. Using 0.6 g of catalyst, the reaction was carried out at 375 °C, achieving a 100% conversion of methyl acetate and a 53.0% yield of acrylic acid.

Claims

1. A method for directly preparing acrylic acid from methyl acetate, comprising the following steps: In a fixed-bed reactor, methyl acetate reacts with oxygen or air in the presence of a catalyst to produce acrylic acid. The catalyst is a supported molybdenum phosphate; The catalyst is prepared by a method comprising the following steps: A mixed aqueous solution of molybdenum precursor and phosphoric acid is added to a carrier, stirred, and the water is removed to obtain a solid; the solid is then dried and calcined to obtain the final product. The precursor of molybdenum is at least one of ammonium metamolybdate, molybdic acid and ammonium molybdate; The carrier is titanium dioxide P25; In the catalyst, the mass fraction of molybdenum is 10%, and the molar ratio of molybdenum to phosphorus is 0.25; The reaction temperature is 375°C. o C; The mass hourly space velocity (MSV) of the methyl acetate was 3.0 L·g. -1 ·h -1 ; The reaction was carried out under normal pressure. The partial pressure of the methyl acetate is 2 kPa, and the partial pressure of the oxygen or oxygen in the air is 1.2~1.5 kPa.

2. The method for directly preparing acrylic acid from methyl acetate according to claim 1, characterized in that: The molar ratio of oxygen or air to methyl acetate is 0.5 to 1, and the molar amount of air is measured by the amount of oxygen therein.

3. The method for directly preparing acrylic acid from methyl acetate according to claim 1, characterized in that: The drying temperature is 80~140℃. o C, the time is 3~12 hours; The calcination temperature is 350~550℃. o C, the time is 1~6 hours; The roasting is carried out in an air atmosphere or an oxygen atmosphere.

4. The method for directly preparing acrylic acid from methyl acetate according to claim 1, characterized in that: It also includes the step of adding an adjuvant to the carrier; The auxiliary agent is an oxide of at least one of V, Mn, W and Pb; In the catalyst, the mass content of the auxiliary agent is 0~5%.

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