Method for preparing methyl glycolate and glycolic acid by hydrolysis of methyl methoxyacetate

Abstract

The present invention discloses a method for hydrolyzing methyl methoxyacetate to produce methyl glycolate and glycolic acid, comprising: passing a raw material containing methyl methoxyacetate and water through a reactor filled with an acidic molecular sieve catalyst, reacting under certain reaction conditions to produce methyl glycolate and glycolic acid; wherein the acidic molecular sieve catalyst is filled in at least two spaced reaction zones of the reactor between upstream and downstream, methyl methoxyacetate is introduced into the at least two spaced reaction zones via different methyl methoxyacetate feed ports, and water is introduced into the at least two spaced reaction zones via a water feed port provided upstream of the reactor. This method improves the conversion rate of methyl methoxyacetate and the selectivity of methyl glycolate and glycolic acid, and reduces separation and circulation energy consumption.

Description

Technical Field

[0001] The invention belongs to the field of catalytic chemistry and relates to a method for preparing methyl glycolate and glycolic acid by hydrolyzing methyl methoxyacetate. Background Art

[0002] Disposable, non-degradable plastic straws and packaging have been explicitly banned. The shift to greener, more environmentally friendly materials is becoming a major trend, and the biodegradable plastics industry has recently become a hot topic in the market. Polyglycolic acid (PGA) is the simplest linear polyester among polyhydroxyalkanoates (POHLAs). It is a fully biodegradable material and can be synthesized through the condensation of monomers such as methyl glycolate and glycolic acid. It degrades rapidly in the natural environment under the action of water and microorganisms, ultimately producing carbon dioxide and water. Furthermore, PGA can also be degraded in seawater, and its degradation products are harmless to both humans and the environment.

[0003] The main methods for preparing polyglycolic acid (PGA) monomers include chloroacetic acid hydrolysis, formaldehyde carbonylation, and partial hydrogenation of dimethyl oxalate. The chloroacetic acid hydrolysis method is not only highly polluting during the preparation of the raw material chloroacetic acid, but also produces a large amount of waste salt during the hydrolysis process, resulting in severe pollution and poor product quality. It has now been largely eliminated. The formaldehyde carbonylation method, despite its readily available and inexpensive raw materials, requires high temperature, high pressure, strong liquid acid, and organic solvents. The equipment is prone to corrosion, making product purification difficult and leading to high industrial production costs. In recent years, the partial hydrogenation of dimethyl oxalate to produce methyl glycolate has garnered widespread attention. However, the catalysts for partial hydrogenation of dimethyl oxalate are still immature, resulting in low conversion efficiency and poor stability. Furthermore, the production process for dimethyl oxalate is long and costly, severely hindering the development of this method. Currently, the industrial production technology for monomers such as methyl glycolate and glycolic acid is still immature, resulting in insufficient production capacity and high prices for PGA plastics, limiting their large-scale replacement applications. Therefore, the development of green, economical, and efficient PGA monomer synthesis technologies is highly desirable.

[0004] In recent years, the carbonylation of methylal to produce methyl methoxyacetate has garnered widespread attention. This reaction, based on molecular sieve catalysts, can be achieved at relatively low reaction temperatures, resulting in high atom economy. The raw material, methylal, is highly efficient, and the industrialized technology is well-established and inexpensive. Therefore, the carbonylation of methylal to produce methyl methoxyacetate, followed by hydrolysis to produce methyl glycolate and glycolic acid, holds promise as a highly competitive route for synthesizing PGA monomers. Currently, no reports have been published on this technology. Summary of the Invention

[0005] The present invention aims to provide a green and efficient method for synthesizing PGA monomers, methyl glycolate and glycolic acid. The method is characterized in that raw materials containing methyl methoxyacetate and water are passed through a reactor loaded with an acidic molecular sieve catalyst, reacting under specific reaction conditions to produce methyl glycolate and glycolic acid. The catalyst is loaded in stages, and the raw material methyl methoxyacetate is fed in stages.

[0006] The main reaction equation of the hydrolysis reaction of methyl methoxyacetate is as follows:

[0007] CH3OCH2COOCH3+H2O→HOCH2COOCH3+HOCH2COOH

[0008] Methyl methoxyacetate + water → methyl glycolate + glycolic acid

[0009] The reaction also produces hydrolysis products such as methoxyacetic acid, methanol, and dimethyl ether. Methoxyacetic acid can be hydrolyzed to glycolic acid and easily esterified to methyl methoxyacetate, so it is used as the starting material in the actual calculation.

[0010] Specifically, the present invention provides a method for preparing methyl glycolate and glycolic acid by hydrolyzing methyl methoxyacetate, characterized in that a raw material containing methyl methoxyacetate and water is passed through a reactor filled with an acidic molecular sieve catalyst, and reacted under certain reaction conditions to prepare methyl glycolate and glycolic acid; wherein the acidic molecular sieve catalyst is filled in at least two spaced reaction zones of the reactor between the upstream and downstream of the reactor, methyl methoxyacetate is respectively introduced into the at least two spaced reaction zones through different methyl methoxyacetate feed ports; and water is introduced into the at least two spaced reaction zones through a water feed port arranged upstream of the reactor.

[0011] Optionally, the reactor is a single fixed-bed reactor comprising 2 to 10 catalyst beds constituting a reaction zone, each catalyst bed being provided with a methyl methoxyacetate feed port at the top thereof for supplying methyl methoxyacetate to the respective catalyst beds. Specifically, with the exception of the methyl methoxyacetate feed port provided at the top of the catalyst bed closest to the upstream portion of the reactor, the remaining methyl methoxyacetate feed ports are provided between adjacent catalyst beds.

[0012] Optionally, the reactor is a single fixed-bed reactor comprising two to four catalyst beds constituting a reaction zone, each catalyst bed being provided with a methyl methoxyacetate feed port at the top thereof for supplying methyl methoxyacetate to the respective catalyst beds. Specifically, with the exception of the methyl methoxyacetate feed port provided at the top of the catalyst bed closest to the upstream portion of the reactor, the remaining methyl methoxyacetate feed ports are provided between adjacent catalyst beds.

[0013] Optionally, the reactor comprises 2 to 10 sub-fixed-bed reactors connected in series to form a reaction zone, the acidic molecular sieve catalyst being loaded into each sub-fixed-bed reactor, and each sub-fixed-bed reactor being provided with a methyl methoxyacetate feed port for supplying methyl methoxyacetate to the respective sub-fixed-bed reactor. Specifically, a methyl methoxyacetate feed port is provided at the top of each sub-fixed-bed reactor for supplying methyl methoxyacetate to the respective sub-fixed-bed reactor.

[0014] Optionally, the reactor comprises 2 to 4 sub-fixed-bed reactors connected in series to form a reaction zone, the acidic molecular sieve catalyst being loaded into each sub-fixed-bed reactor, and each sub-fixed-bed reactor being provided with a methyl methoxyacetate feed port for supplying methyl methoxyacetate to the respective sub-fixed-bed reactor. Specifically, a methyl methoxyacetate feed port is provided at the top of each sub-fixed-bed reactor for supplying methyl methoxyacetate to the respective sub-fixed-bed reactor.

[0015] Optionally, a water feed port is provided at the top of each sub-fixed bed reactor, a water discharge port is provided at the bottom of each sub-fixed bed reactor, and the water discharge port of one sub-fixed bed reactor is connected to its adjacent water feed port.

[0016] Optionally, the mass fraction of methyl methoxyacetate entering each reaction zone to the total amount of methyl methoxyacetate is greater than 0% and less than 100%.

[0017] Optionally, the mass fraction of methyl methoxyacetate entering each reaction zone is equal to the total mass of methyl methoxyacetate.

[0018] The said stepwise loading of the catalyst into a single fixed bed reactor and the said loading of the catalyst into a plurality of sub-fixed bed reactors connected in series are essentially stepwise loading of the catalyst into a fixed bed reactor.

[0019] For example, if 100 tons of catalyst are evenly loaded into a fixed-bed reactor in four sections, each section has a loading capacity of 25 tons. If 100 tons of catalyst are evenly loaded into four series-connected fixed-bed reactors, each sub-fixed-bed reactor also has a loading capacity of 25 tons. In practice, the difference between these two loading methods lies in the equivalent replacement of a single large-volume fixed-bed reactor with multiple smaller sub-fixed-bed reactors.

[0020] Optionally, the reactor is a single fixed bed reactor comprising two catalyst beds constituting reaction zones, and the mass fraction of methyl methoxyacetate introduced into each catalyst bed accounts for 50% of the total amount of methyl methoxyacetate.

[0021] Optionally, the reactor is a single fixed-bed reactor comprising three catalyst beds constituting reaction zones, and the mass fraction of methyl methoxyacetate introduced into each catalyst bed accounts for 33.3% of the total amount of methyl methoxyacetate.

[0022] Optionally, the reactor is a single fixed bed reactor comprising four catalyst beds constituting reaction zones, and the mass fraction of methyl methoxyacetate introduced into each catalyst bed accounts for 25% of the total amount of methyl methoxyacetate.

[0023] Optionally, the reactor comprises two sub-fixed bed reactors connected in series to form a reaction zone, and the mass fraction of methyl methoxyacetate introduced into each sub-fixed bed reactor accounts for 50% of the total amount of methyl methoxyacetate.

[0024] Optionally, the reactor comprises three sub-fixed bed reactors connected in series to form a reaction zone, and the mass fraction of methyl methoxyacetate introduced into each sub-fixed bed reactor accounts for 33.3% of the total amount of methyl methoxyacetate.

[0025] Optionally, the reactor comprises four sub-fixed bed reactors connected in series to form a reaction zone, and the mass fraction of methyl methoxyacetate introduced into each sub-fixed bed reactor accounts for 25% of the total amount of methyl methoxyacetate.

[0026] When methyl methoxyacetate is introduced into the reactor in equal amounts in stages, assuming the molar ratio of the total amount of water to the total amount of methyl methoxyacetate remains unchanged, since water is introduced into the reactor solely from the water feed port upstream of the reactor rather than being introduced in stages into different reaction zones of the reactor, the water that enters the reaction zone closest to the upstream of the reactor is all the water, while the water that enters the other reaction zones is the water not consumed by the previous reaction zone. Consequently, the molar ratio of water to methyl methoxyacetate in each reaction zone is higher than the molar ratio of the total amount of water to the total amount of methyl methoxyacetate. For example, when methyl methoxyacetate is introduced in four equal amounts in stages, the ratio of water to methyl methoxyacetate in the reaction zone closest to the upstream of the reactor is four times the overall ratio.

[0027] Optionally, the acidic molecular sieve catalyst is selected from at least one of an acidic molecular sieve having an MFI structure, an acidic molecular sieve having a Y structure, an acidic molecular sieve having a FER structure, an acidic molecular sieve having a BEA structure, an acidic molecular sieve having a MOR structure, and an acidic molecular sieve having an MWW structure.

[0028] Optionally, the acidic molecular sieve catalyst is at least one of H-ZSM-5 molecular sieve, HY molecular sieve, H-ZSM-35 molecular sieve, H-β molecular sieve, H-MOR molecular sieve, and H-MCM-22 molecular sieve.

[0029] Optionally, the reaction conditions are: reaction temperature of 140-220°C, reaction pressure of 0.1-0.5 MPa, mass space velocity of methyl methoxyacetate of 0.1-3.0 h -1 , the molar ratio of the total amount of water to the total amount of methyl methoxyacetate is 0.5:1 to 8:1.

[0030] Optionally, a carrier gas is introduced into the reactor, wherein the carrier gas comprises at least one of nitrogen, argon, helium, hydrogen, carbon monoxide, and carbon dioxide in any amount. In the present application, the carrier gas is used to introduce water into the reactor.

[0031] Alternatively, the reaction temperature may be selected from any value within the range of 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C and 220°C, or a range determined by any two values.

[0032] Optionally, the reaction pressure is any value within the range of 0.1 MPa, 0.13 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, 0.4 MPa, 0.45 MPa and 0.5 MPa, or a range determined by any two values.

[0033] Optionally, the mass space velocity of methyl methoxyacetate is 0.1h -1 , 0.2h -1 , 0.3h -1 , 0.5 h -1 , 0.8h -1 , 1.0h -1 , 1.2h -1 , 1.5h -1 , 1.8h -1 , 2.0h -1 , 2.2h -1 , 2.4h -1 , 2.5h -1 , 2.6h -1 , 2.7h -1 , 2.8h -1 , 2.9h -1 and 3.0h -1 Any value in this range or any two values ​​in the range determined by it.

[0034] Optionally, the molar ratio of the total amount of water to the total amount of methyl methoxyacetate is any value within the range of 0.5:1, 1.0:1, 1.5:1, 2.0:1, 2.5:1, 3.0:1, 3.5:1, 4.0:1, 4.5:1, 5.0:1, 5.5:1, 6.0:1, 6.5:1, 7.0:1, 7.5:1 and 8:1, or a range determined by any two values.

[0035] In this application, for a single fixed bed reactor comprising multiple catalyst beds, the upstream of the reactor refers to Figure 1 The top of the reactor is shown, and the downstream is as shown. Figure 1 The bottom of the reactor is shown.

[0036] In this application, for a fixed bed reactor comprising a plurality of sub-fixed bed reactors, the upstream of the reactor refers to Figure 2 The top of the leftmost fixed bed reactor is shown, and the downstream refers to the Figure 2 The bottom of the rightmost sub-fixed bed reactor is shown.

[0037] The present invention can produce beneficial effects including:

[0038] Under the premise of maintaining the molar ratio of the total amount of water to the total amount of methyl methoxyacetate, the molar ratio of water to methyl methoxyacetate actually reacted on each catalyst stage can be increased by feeding methyl methoxyacetate in stages, thereby improving the conversion of methyl methoxyacetate and the selectivity of methyl glycolate and glycolic acid, and reducing separation and circulation energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of a single fixed bed reactor comprising multiple spaced catalyst beds.

[0040] Figure 2 Schematic diagram of a plurality of sub-fixed bed reactors connected in series.

[0041] Figure 3 Schematic diagram of a conventional fixed bed reactor comprising a continuous catalyst bed. DETAILED DESCRIPTION

[0042] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0043] The endpoints of the ranges disclosed in this application and any values ​​are not limited to the exact ranges or values, and these ranges or values ​​should be understood to include approximate ranges or values. For numerical ranges, the endpoints of each range and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0044] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0045] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources.

[0046] The analysis method, conversion rate and selectivity in the examples of this application are calculated as follows:

[0047] The products other than glycolic acid and the unreacted raw materials were analyzed by Agilent 7890B gas chromatograph, with its FID detector connected to a DB-FFAP capillary column and its TCD detector connected to a Porapak Q packed column. Glycolic acid was analyzed by liquid chromatography, with a separation column of C 18 The detector is a UV detector.

[0048] The main goal of the hydrolysis reaction of methyl methoxyacetate (CH3OCH2COOCH3) is to hydrolyze its ether bond, and only the product of ester bond hydrolysis, methoxyacetic acid (CH3OCH2COOH), can essentially be used as a raw material. In view of this, in the embodiments of the present invention, the conversion rate and selectivity are calculated based on the following formula:

[0049] Methyl methoxyacetate conversion rate = [(mole number of methyl methoxyacetate in feed) - (mole number of methyl methoxyacetate in discharge) - (mole number of methoxyacetic acid in discharge)] ÷ (mole number of carbon atoms of methyl methoxyacetate in feed) × 100%

[0050] Methyl glycolate selectivity = [(mole number of methyl glycolate in the output)] ÷ [(mole number of methyl methoxyacetate in the feed) - (mole number of methyl methoxyacetate in the output) - (mole number of methoxyacetic acid in the output)] × 100%

[0051] Glycolic acid selectivity = [(moles of glycolic acid in the output)] ÷ [(moles of methyl methoxyacetate in the feed) - (moles of methyl methoxyacetate in the output) - (moles of methoxyacetic acid in the output)] × 100%

[0052] Example 1

[0053] Acidic H-ZSM-5 molecular sieve (SiO2 / Al2O3=60) catalyst is loaded in a single fixed bed reactor in sections. Figure 1 As shown. 300g of the above catalyst was loaded into a In the fixed bed reactor, there is The catalyst was packed in four sections, each approximately 120 mm in diameter. The top catalyst bed had a water feed port and a methyl methoxyacetate feed port located on top, while the tops of the remaining catalyst beds each had a methyl methoxyacetate feed port. The bottom of the bottom catalyst bed had a reaction product discharge port. A thermocouple was located in the middle of each catalyst layer to test the reaction temperature. The product was collected by condensation, weighed, and analyzed by gas chromatography and liquid chromatography. Non-condensable gases were analyzed online by gas chromatography. The reaction conditions were: reaction temperature = 190°C, reaction pressure = 0.1 MPa, and mass space velocity of methyl methoxyacetate = 2.0 h-1. -1 The molar ratio of water to methyl methoxyacetate was 2:1, and the carrier gas hydrogen flow rate was 1.5 L / min. The mass fraction of methyl methoxyacetate entering each catalyst bed was equal, at 25% of the total methyl methoxyacetate. After 10 days of operation, the reaction results are shown in Table 1.

[0054] Example 2

[0055] Acidic H-ZSM-5 molecular sieve (SiO2 / Al2O3=60) catalyst was loaded into a single fixed bed reactor in sections. 300g of the above catalyst was loaded into a fixed bed reactor with an inner diameter of In the fixed bed reactor, there is The catalyst was packed in three sections, each approximately 160 mm in diameter. The top catalyst bed had a water feed port and a methyl methoxyacetate feed port located on top, while the tops of the remaining catalyst beds each had a methyl methoxyacetate feed port. The bottom of the bottom catalyst bed had a reaction product discharge port. A thermocouple was located in the middle of each catalyst layer to test the reaction temperature. The product was collected by condensation, weighed, and analyzed by gas chromatography and liquid chromatography. Non-condensable gases were analyzed online by gas chromatography. The reaction conditions were: reaction temperature = 190°C, reaction pressure = 0.1 MPa, and mass space velocity of methyl methoxyacetate = 2.0 h-1. -1 The molar ratio of water to methyl methoxyacetate was 2:1, and the carrier gas hydrogen flow rate was 1.5 L / min. The mass fraction of methyl methoxyacetate entering each catalyst bed was equal, at 33.3% of the total methyl methoxyacetate. After 10 days of operation, the reaction results are shown in Table 1.

[0056] Example 3

[0057] Acidic H-ZSM-5 molecular sieve (SiO2 / Al2O3=60) catalyst was loaded into a single fixed bed reactor in sections. 300g of the above catalyst was loaded into a fixed bed reactor with an inner diameter of In the fixed bed reactor, there is The catalyst was packed in two sections, each approximately 240 mm long. The top catalyst bed had a water feed port and a methyl methoxyacetate feed port located on top, while the tops of the remaining catalyst beds each had a methyl methoxyacetate feed port. The bottom of the bottom catalyst bed had a reaction product discharge port. A thermocouple was located in the middle of each catalyst layer to test the reaction temperature. The product was collected by condensation, weighed, and analyzed by gas chromatography and liquid chromatography. Non-condensable gases were analyzed online by gas chromatography. The reaction conditions were: reaction temperature = 190°C, reaction pressure = 0.1 MPa, and mass space velocity of methyl methoxyacetate = 2.0 h -1 The molar ratio of water to methyl methoxyacetate was 2:1, and the carrier gas hydrogen flow rate was 1.5 L / min. The mass fraction of methyl methoxyacetate entering each catalyst bed was equal, at 50% of the total methyl methoxyacetate. After 10 days of operation, the reaction results are shown in Table 1.

[0058] Example 4

[0059] Four sub-fixed bed reactors in series with acidic H-ZSM-5 molecular sieve (SiO2 / Al2O3=60) catalyst loaded in stages Figure 2 As shown. 300g of the above catalyst was loaded into a In the fixed bed reactor, there is Each sub-fixed bed reactor is loaded with 75g of catalyst, and each section is approximately 120mm. The top of each sub-fixed bed reactor is provided with a methyl methoxyacetate feed port and a water feed port, and the bottom of each sub-fixed bed reactor is provided with a water discharge port. The water feed port of the leftmost sub-fixed bed reactor is the source of water entering the reactor, and the water discharge port of the previous sub-fixed bed reactor is connected to the water feed port of the adjacent sub-fixed bed reactor. Each sub-fixed bed reactor is loaded with 75g of catalyst, and the catalyst bed layer of each sub-fixed bed reactor is approximately 120mm. A thermocouple is located in the middle of each fixed bed to test the reaction temperature. The product is collected by condensation, weighed, and analyzed by gas chromatography and liquid chromatography. Non-condensable gases are analyzed online by gas chromatography. The reaction conditions are: reaction temperature = 190°C, reaction pressure = 0.1MPa, methyl methoxyacetate mass space velocity = 2.0h -1 The molar ratio of water to methyl methoxyacetate was 2:1, and the carrier gas hydrogen flow rate was 1.5 L / min. The mass fraction of methyl methoxyacetate entering each section was equal, at 25%. After 10 days of operation, the reaction results are shown in Table 1.

[0060] Comparative Example 1

[0061] A conventional single fixed bed reactor filled with acidic H-ZSM-5 molecular sieve (SiO2 / Al2O3=60) catalyst Figure 3As shown. 300g of the above catalyst was loaded into a In the fixed bed reactor, there is The catalyst bed was approximately 480 mm high. Water and methyl methoxyacetate feed ports were located at the top of the catalyst bed, and a reaction product discharge port was located at the bottom. The product was collected by condensation, weighed, and analyzed by gas chromatography and liquid chromatography. Non-condensable gases were analyzed online by gas chromatography. Reaction conditions were: reaction temperature = 190°C, reaction pressure = 0.1 MPa, and methyl methoxyacetate mass space velocity = 2.0 h-1. -1 The molar ratio of the total amount of water to the total amount of methyl methoxyacetate was 2:1, and the carrier gas hydrogen flow rate was 1.5 L / min. After 10 days of operation, the reaction results are shown in Table 1.

[0062] Example 5

[0063] A single fixed bed reactor with acidic H-β molecular sieve (SiO2 / Al2O3=40) catalyst loaded in stages, such as Figure 1 As shown. 300g of the above catalyst was loaded into a In the fixed bed reactor, there is The catalyst was packed in four sections, each approximately 120 mm. The top catalyst bed had water and methyl methoxyacetate inlets at the top, while the remaining catalyst beds had methyl methoxyacetate inlets at the top. The bottom catalyst bed had a reaction product discharge outlet at the bottom. A thermocouple was located in the middle of each catalyst layer to measure the reaction temperature. The product was collected by condensation, weighed, and analyzed by gas chromatography and liquid chromatography. Non-condensable gases were analyzed online by gas chromatography. The reaction conditions were: reaction temperature = 180°C, reaction pressure = 0.15 MPa, and methyl methoxyacetate mass space velocity = 1.0 h / min. -1 The molar ratio of water to methyl methoxyacetate was 1:1, and the carrier gas hydrogen flow rate was 1.5 L / min. The mass fraction of methyl methoxyacetate entering each catalyst bed was equal, at 25% of the total methyl methoxyacetate. After 10 days of operation, the reaction results are shown in Table 1.

[0064] Comparative Example 2

[0065] A conventional single fixed bed reactor filled with acidic H-β molecular sieve (SiO2 / Al2O3=40) catalyst Figure 3 As shown. 300g of the above catalyst was loaded into a In the fixed bed reactor, there is The catalyst bed was approximately 480 mm high. Water and methyl methoxyacetate feed ports were located at the top of the catalyst bed, and a reaction product discharge port was located at the bottom. The product was collected by condensation, weighed, and analyzed by gas chromatography and liquid chromatography. Non-condensable gases were analyzed online by gas chromatography. Reaction conditions were: reaction temperature = 180°C, reaction pressure = 0.15 MPa, and methyl methoxyacetate mass space velocity = 1.0 h-1. -1 The molar ratio of the total amount of water to the total amount of methyl methoxyacetate was 1:1, and the carrier gas hydrogen flow rate was 1.5 L / min. After 10 days of operation, the reaction results are shown in Table 1.

[0066] Example 6

[0067] A single fixed bed reactor with acidic HY molecular sieve (SiO2 / Al2O3=20) catalyst loaded in stages, such as Figure 1 As shown. 300g of the above catalyst was loaded into a In the fixed bed reactor, there is The catalyst was packed in four sections, each approximately 120 mm long. The top catalyst bed had water and methyl methoxyacetate inlets located above it, while the remaining catalyst beds each had a methyl methoxyacetate inlet located above it. The bottom catalyst bed had a reaction product outlet located below it. A thermocouple was located in the middle of each catalyst layer to measure the reaction temperature. The product was collected by condensation, weighed, and analyzed by gas chromatography and liquid chromatography. Non-condensable gases were analyzed online by gas chromatography. The reaction conditions were: reaction temperature = 170°C, reaction pressure = 0.13 MPa, and methyl methoxyacetate mass space velocity = 2.0 h / min. -1 The molar ratio of water to methyl methoxyacetate was 0.5:1, and the carrier hydrogen flow rate was 1.5 L / min. The mass fraction of methyl methoxyacetate entering each catalyst bed was equal, at 25% of the total methyl methoxyacetate. After 10 days of operation, the reaction results are shown in Table 1.

[0068] Comparative Example 3

[0069] A conventional single fixed bed reactor filled with acidic HY molecular sieve (SiO2 / Al2O3=20) catalyst Figure 3 As shown. 300g of the above catalyst was loaded into a In the fixed bed reactor, there is The catalyst bed was approximately 480 mm high. Water and methyl methoxyacetate feed ports were located at the top of the catalyst bed, and a reaction product discharge port was located at the bottom. The product was collected by condensation, weighed, and analyzed by gas chromatography and liquid chromatography. Non-condensable gases were analyzed online by gas chromatography. Reaction conditions were: reaction temperature = 170°C, reaction pressure = 0.13 MPa, and methyl methoxyacetate mass space velocity = 1.5 h-1. -1 The molar ratio of the total amount of water to the total amount of methyl methoxyacetate was 0.5:1, and the carrier gas hydrogen flow rate was 1.5 L / min. After 10 days of operation, the reaction results are shown in Table 1.

[0070] Table 1 Reaction results of Examples 1-4 and Comparative Example 1

[0071]

[0072] The above descriptions are merely a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, they are not intended to limit the present application. Any technical personnel familiar with the present profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing methyl glycolate and glycolic acid by hydrolyzing methyl methoxyacetate, characterized in that: The raw materials containing methyl methoxyacetate and water are passed through a reactor filled with an acidic molecular sieve catalyst, the reaction temperature is 140-220 ° C, the reaction pressure is 0.1-0.5 MPa, the mass space velocity of methyl methoxyacetate is 0.1-3.0 h -1 , the molar ratio of the total amount of water to the total amount of methyl methoxyacetate is 0.5:1 to 8:1, to prepare methyl glycolate and glycolic acid; The acidic molecular sieve catalyst is filled in at least two spaced reaction zones of the reactor between the upstream and downstream of the reactor, and methyl methoxyacetate is respectively introduced into the at least two spaced reaction zones through different methyl methoxyacetate feed ports; The acidic molecular sieve catalyst is at least one of H-ZSM-5 molecular sieve, HY molecular sieve, H-ZSM-35 molecular sieve, H-β molecular sieve, H-MOR molecular sieve, and H-MCM-22 molecular sieve; Water is introduced into the at least two spaced reaction zones via a water feed port disposed upstream of the reactor.

2. The method according to claim 1, characterized in that The reactor is a single fixed bed reactor, comprising 2 to 10 catalyst beds constituting a reaction zone. A methyl methoxyacetate feed port is provided on the top of each catalyst bed to provide methyl methoxyacetate to each catalyst bed.

3. The method according to claim 1, characterized in that The reactor is a single fixed bed reactor, comprising 2 to 4 catalyst beds constituting a reaction zone. A methyl methoxyacetate feed port is provided on the top of each catalyst bed to provide methyl methoxyacetate to each catalyst bed.

4. The method according to claim 1, wherein The reactor comprises 2 to 10 sub-fixed bed reactors connected in series to form a reaction zone. The acidic molecular sieve catalyst is filled in each sub-fixed bed reactor. Each sub-fixed bed reactor is provided with a methyl methoxyacetate feed port to provide methyl methoxyacetate to each sub-fixed bed reactor.

5. The method according to claim 1, wherein The reactor comprises 2 to 4 sub-fixed bed reactors connected in series to form a reaction zone. The acidic molecular sieve catalyst is filled in each sub-fixed bed reactor. Each sub-fixed bed reactor is provided with a methyl methoxyacetate feed port to provide methyl methoxyacetate to each sub-fixed bed reactor.

6. The method according to claim 1, characterized in that The mass fraction of methyl methoxyacetate entering each reaction zone accounts for more than 0% and less than 100% of the total amount of methyl methoxyacetate, and the mass fraction of the acidic molecular sieve filled in each reaction zone accounts for more than 0% and less than 100% of the total amount of molecular sieve.

7. The method according to claim 1, characterized in that The mass fraction of methyl methoxyacetate entering each reaction zone accounts for the same total amount of methyl methoxyacetate, and the mass fraction of the acidic molecular sieve catalyst filled in each reaction zone accounts for the same total amount of the molecular sieve catalyst.

8. The method according to claim 1, characterized in that The reaction conditions are as follows: reaction temperature of 170-190° C., reaction pressure of 0.1-0.15 MPa, mass space velocity of methyl methoxyacetate of 1-2 h -1 , the molar ratio of the total amount of water to the total amount of methyl methoxyacetate is 0.5:1 to 2:

1.

9. The method according to claim 1, characterized in that A carrier gas is also introduced into the reactor, and the carrier gas includes at least one of nitrogen, argon, helium, hydrogen, carbon monoxide, and carbon dioxide in any content.

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