METHOD FOR PREPARING GLYCOLIC ACID THROUGH HYDROLYSIS OF ALKOXYACETATE

Abstract

A method for preparing glycolic acid through hydrolysis of alkoxyacetate is provided. The method includes: subjecting raw materials including the alkoxyacetate and water to a reaction in the presence of an acidic molecular sieve catalyst to produce the glycolic acid, where the alkoxyacetate is at least one selected from the group consisting of compounds with a structural formula shown in formula I; and in formula I, R.sub.1 and R.sub.2 each are independently any one selected from the group consisting of C.sub.1-C.sub.5 alkyl groups. The glycolic acid production method in the present application can be implemented by a traditional fixed-bed reactor under an atmospheric pressure, which is very suitable for continuous production.

Claims

1. A method for preparing glycolic acid through a hydrolysis of alkoxyacetate, comprising: subjecting raw materials comprising the alkoxyacetate and water to a reaction in the presence of an acidic molecular sieve catalyst to produce the glycolic acid, wherein the alkoxyacetate is at least one selected from the group consisting of compounds with a structural formula shown in formula I: ##STR00003## wherein R.sub.1 and R.sub.2 each are independently one selected from the group consisting of C.sub.1-C.sub.5 alkyl groups.

2. The method according to claim 1, wherein R.sub.1 is one selected from the group consisting of methyl, ethyl, propyl, and butyl; and R.sub.2 is one selected from the group consisting of methyl, ethyl, propyl, and butyl.

3. The method according to claim 1, wherein the acidic molecular sieve catalyst comprises an acidic molecular sieve.

4. The method according to claim 3, wherein the acidic molecular sieve is at least one selected from the group consisting of an acidic MFI-structured molecular sieve, an acidic FAU-structured molecular sieve, an acidic FER-structured molecular sieve, an acidic BEA-structured molecular sieve, an acidic mordenite (MOR)-structured molecular sieve, and an acidic MWW-structured molecular sieve.

5. The method according to claim 4, wherein the acidic molecular sieve is at least one selected from the group consisting of an acidic ZSM-5 molecular sieve, an acidic Y molecular sieve, an acidic ZSM-35 molecular sieve, an acidic ? molecular sieve, an acidic MOR molecular sieve, and an acidic MCM-22 molecular sieve.

6. The method according to claim 5, wherein the acidic molecular sieve is at least one selected from the group consisting of a hydrogen-type ZSM-5 molecular sieve, a hydrogen-type Y molecular sieve, a hydrogen-type ZSM-35 molecular sieve, a hydrogen-type ? molecular sieve, a hydrogen-type MOR molecular sieve, and a hydrogen-type MCM-22 molecular sieve.

7. The method according to claim 3, wherein a Si/Al atom ratio of the acidic molecular sieve is 3 to 500.

8. The method according to claim 3, wherein the acidic molecular sieve catalyst further comprises a forming agent; the forming agent is an oxide; the oxide is at least one selected from the group consisting of alumina and silicon oxide; and a content of the forming agent in the acidic molecular sieve catalyst is m, and 0<m?50 wt %.

9. The method according to claim 1, wherein conditions of the reaction are as follows: a reaction temperature is 60? C. to 260? C.; a reaction pressure is 0.1 MPa to 10 MPa; a molar ratio of the alkoxyacetate to the water is 1:20 to 20:1; and a weight hourly space velocity (WHSV) of the alkoxyacetate is 0.1 h.sup.?1 to 3 h.sup.?1.

10. The method according to claim 9, wherein the conditions of the reaction are as follows: the reaction temperature is 130? C. to 260? C.; the reaction pressure is 0.1 MPa to 0.3 MPa; the molar ratio of the alkoxyacetate to the water is 1:2 to 1:8; and the WHSV of the alkoxyacetate is 0.3 h.sup.?1 to 1 h.sup.?1.

11. The method according to claim 1, wherein the reaction is conducted in one fixed-bed reactor or a plurality of fixed-bed reactors.

12. The method according to claim 11, wherein the plurality of fixed-bed reactors are connected in series and/or parallel.

13. The method according to claim 1, wherein the reaction is conducted in an inactive atmosphere; and the inactive atmosphere comprises one selected from the group consisting of nitrogen and an inert gas.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0052] The present application will be described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0053] Unless otherwise specified, the raw materials in the embodiments of the present application all are purchased from commercial sources.

[0054] Possible embodiments are described below.

[0055] Specifically, the present application provides a method for preparing glycolic acid through hydrolysis of alkoxyacetate, where raw materials of alkoxyacetate and water are allowed to pass through a reaction zone loaded with an acidic molecular sieve catalyst, such that the raw materials undergo a reaction under specified conditions to produce glycolic acid.

[0056] The alkoxyacetate has a structural formula as follows:

##STR00002##

[0057] where R.sub.1 is any one selected from the group consisting of methyl (CH.sub.3), ethyl (C.sub.2H.sub.5), propyl (C.sub.3H.sub.7), and butyl (C.sub.4H.sub.9); R.sub.2 is any one selected from the group consisting of methyl (CH.sub.3), ethyl (C.sub.2H.sub.5), propyl (C.sub.3H.sub.7), and butyl (C.sub.4H.sub.9); and R.sub.1 and R.sub.2 can be the same or different.

[0058] The acidic molecular sieve is a molecular sieve with acidity.

[0059] The reaction zone includes a single fixed-bed reactor, or a plurality of fixed-bed reactors connected in series and/or parallel.

[0060] Conditions of the reaction are as follows: a reaction temperature is 60? C. to 260? C., a molar ratio of the alkoxyacetate to the water is 1:20 to 20:1, a reaction pressure is 0.1 MPa to 10 MPa, and a WHSV of the alkoxyacetate is 0.1 h.sup.?1 to 3 h.sup.?1.

[0061] A reaction equation for hydrolysis of the alkoxyacetate is as follows:

R.sub.1OCH.sub.2COOR.sub.2+2 H.sub.2O=R.sub.1OH+R.sub.2OH+HOCH.sub.2COOH(1).

[0062] There are also two partial hydrolysis reactions for the alkoxyacetate as follows:

R.sub.1OCH.sub.2COOR.sub.2+H.sub.2O=R.sub.2OH+R.sub.1OCH.sub.2COOH(2) and

R.sub.1OCH.sub.2COOR.sub.2+H.sub.2O=R.sub.1OH+HOCH.sub.2COOR.sub.2(3).

[0063] Products of the two partial hydrolysis reactions can be further hydrolyzed under the same catalyst and reaction conditions to produce glycolic acid:

R.sub.1OCH.sub.2COOH+H.sub.2O=R.sub.1OH+HOCH.sub.2COOH(4) and

HOCH.sub.2COOR.sub.2+H.sub.2O=R.sub.2OH+HOCH.sub.2COOH(5).

[0064] In addition, alcohols R.sub.1OH and R.sub.2OH resulting from hydrolysis can also be partially dehydrated to produce corresponding ethers.

[0065] The acidic molecular sieve is one or a mixture of two or more selected from the group consisting of an acidic MFI-structured molecular sieve, an acidic FAU-structured molecular sieve, an acidic FER-structured molecular sieve, an acidic BEA-structured molecular sieve, an acidic MOR-structured molecular sieve, and an acidic MWW-structured molecular sieve.

[0066] The acidic molecular sieve is one or a mixture of two or more selected from the group consisting of an acidic ZSM-5 molecular sieve, an acidic Y molecular sieve, an acidic ZSM-35 molecular sieve, an acidic ? molecular sieve, an acidic MOR molecular sieve, and an acidic MCM-22 molecular sieve.

[0067] The acidic molecular sieve is one or a mixture of two or more selected from the group consisting of a hydrogen-type ZSM-5 molecular sieve, a hydrogen-type Y molecular sieve, a hydrogen-type ZSM-35 molecular sieve, a hydrogen-type ? molecular sieve, a hydrogen-type MOR molecular sieve, and a hydrogen-type MCM-22 molecular sieve.

[0068] A Si/Al atom ratio of the acidic molecular sieve is 3 to 500.

[0069] In addition to an acidic molecular sieve, the acidic molecular sieve catalyst further includes a catalyst forming agent; and the catalyst forming agent is one selected from the group consisting of alumina and silicon oxide, and has a weight percentage content of 0% to 50%.

[0070] The acidic molecular sieve catalyst is prepared by mixing the catalyst forming agent and the acidic molecular sieve and molding a resulting mixture into a strip.

[0071] In the alkoxyacetate, R.sub.1 and R.sub.2 both are methyl, that is, the alkoxyacetate is methyl methoxyacetate (CH.sub.3OCH.sub.2COOCH.sub.3).

[0072] The methyl methoxyacetate is prepared by a DMM carbonylation method.

[0073] When the alkoxyacetate is methyl methoxyacetate, according to principles of reactions (1) to (5), hydrolysis products include glycolic acid, methoxyacetic acid (CH.sub.3OCH.sub.2COOH), methyl glycolate (HOCH.sub.2COOCH.sub.3), methanol, and dimethyl ether (DME). The methoxyacetic acid and methyl glycolate can be further hydrolyzed into glycolic acid, and methanol and DME can be returned to a DMM synthesis reactor to synthesize DMM.

[0074] When the alkoxyacetate is methyl methoxyacetate, according to the principles of reactions (1) to (5), the selectivity of the hydrolysis product glycolic acid can be as high as 50% based on a carbon number calculation theory.

[0075] The conditions of the reaction are preferably as follows: a reaction temperature is 130? C. to 200? C., a molar ratio of the alkoxyacetate to the water is 1:8 to 1:2, a reaction pressure is 0.1 MPa to 0.3 MPa, and a WHSV of the alkoxyacetate is 0.3 h.sup.?1 to 1 h.sup.?1.

[0076] When the raw materials are allowed to pass through a reaction zone loaded with an acidic molecular sieve catalyst, an inert carrier gas selected from the group consisting of nitrogen and argon is introduced.

[0077] Analysis methods and conversion rate and selectivity calculation in the embodiments are as follows:

[0078] An Agilent7890B gas chromatograph is used to analyze products other than glycolic acid and unreacted raw materials, where an FID detector is connected to a DB-FFAP capillary column and a TCD detector is connected to a Porapak Q packed column. A liquid chromatograph is used to analyze glycolic acid, where a separation column is a Cis column and a detector is an ultraviolet (UV) detector.

[0079] In an embodiment of the present application, both a conversion rate and selectivity are calculated based on a mole number of carbon:

alkoxyacetate conversion rate=[(mole number of carbon in fed alkoxyacetate)?(mole number of carbon in discharged alkoxyacetate)]?(mole number of carbon in fed alkoxyacetate)?100% and

selectivity for a product=(mole number of carbon in a discharged product)?(total mole number of carbon in all discharged carbon-containing products)?100%.

[0080] The present application will be described in detail below with reference to examples, but the present application is not limited to these examples.

Catalyst Performance Test

Example 1

[0081] An acidic H-ZSM-5 molecular sieve with a Si/Al ratio of 20 produced by Zhongke Catalysis New Technology (Dalian) Co., Ltd. was selected, crushed, and sieved to obtain 0.4 mm to 0.8 mm particles; 2 g of the particles was taken and filled into a stainless steel reaction tube with an inner diameter of 8 mm and activated with 50 mL/min nitrogen at 500? C. for 4 h; a reaction was conducted for 24 h under the following conditions: a reaction temperature (T) was 150? C., and a reaction pressure (P) was 0.1 MPa; a molar ratio of methyl methoxyacetate to water was 1:4; and a WHSV of methyl methoxyacetate was 1.0 h.sup.?1; and after the reaction was completed, products were analyzed by gas chromatography and liquid chromatography. Reaction results based on a mole number of carbon were shown in Table 1.

Examples 2 to 9

[0082] The catalyst, reaction conditions, and reaction results were shown in Table 1. Other operations were the same as in Example 1.

TABLE-US-00001 TABLE 1 Catalytic reaction results in Examples 1 to 9 Methyl Methanol Acidic methoxy Glycolic Methyl Methoxyacetic and molecular acetate acid glycolate acid DME sieve Si/Al Reaction conversion selectivity selectivity selectivity selectivity Example catalyst Manufacturer ratio conditions rate (%) (%) (%) (%) (%) 1 H-ZSM-5 Zhongke 20 T = 150? C., P = 81.2 36.4 7.3 8.1 48.2 Catalysis 0.1 MPa, WHSV = New 1.0 h.sup.?1, and Technology methyl (Dalian) Co., methoxyacetate:water = Ltd. 1:4 2 H-Y Zhongke 3 T = 150? C., P = 60.3 30.4 14.4 10.0 45.2 Catalysis 0.1 MPa, WHSV = New 1.0 h.sup.?1, and Technology methyl (Dalian) Co., methoxyacetate:water = Ltd. 1:4 3 H-ZSM-35 Catalyst 50 T = 150? C., P = 78.9 37.0 7.5 7.0 48.5 Plant of 0.1 MPa, WHSV = Nankai 1.0 h.sup.?1, and University methyl methoxyacetate:water = 1:4 4 H-? Zhongke 500 T = 150? C., P = 40.3 26.2 10.7 20.0 43.1 Catalysis 0.1 MPa, WHSV = New 1.0 h.sup.?1, and Technology methyl (Dalian) Co., methoxyacetate:water = Ltd. 1:4 5 H- Yanchang 10 T = 150? C., P = 50.7 29.0 14.0 12.5 44.5 Mordenite Zhongke 0.1 MPa, WHSV = (Dalian) 1.0 h.sup.?1, and Energy methyl Technology methoxyacetate:water = Co., Ltd. 1:4 6 H-MCM- Yanchang 100 T = 150? C., P = 37.9 34.2 7.7 11.0 47.1 22 Zhongke 0.1 MPa, WHSV = (Dalian) 1.0 h.sup.?1, and Energy methyl Technology methoxyacetate:water = Co., Ltd. 1:4 7 H-ZSM-5 Zhongke 20 T = 260? C., P = 10 88.6 32.4 14.3 7.1 46.2 Catalysis MPa, WHSV = New 3.0 h.sup.?1, and Technology methyl (Dalian) Co., methoxyacetate:water = Ltd. 1:20 8 H-ZSM-5 Zhongke 20 T = 60? C., 2.0 11.0 28.5 30.0 30.5 Catalysis P = 0.3 MPa, New WHSV = 0.1 h.sup.?1, Technology and methyl (Dalian) Co., methoxyacetate:water = Ltd. 20:1 9 H-ZSM-5 Zhongke 20 T = 150? C., P = 77.6 36.0 8.9 7.1 48.0 Catalysis 0.1 MPa, WHSV = New 1.0 h.sup.?1, Technology methyl (Dalian) Co., methoxyacetate:water = Ltd. 1:4, and nitrogen = 50 mL/min

[0083] It can be seen from Table 1 that the hydrogen-type molecular sieve catalyst leads to a high methyl methoxyacetate conversion rate and high glycolic acid selectivity during the hydrolysis of methyl methoxyacetate to produce glycolic acid, indicating excellent catalytic performance.

Examples 10 to 13

[0084] Another alkoxyacetate was used instead of the methyl methoxyacetate in Example 1, and other conditions and operations remained unchanged. Reaction results were shown in Table 2.

TABLE-US-00002 TABLE 2 Catalytic reaction results in Examples 1 and 10 to 13 Glycolic Alkoxyacetate acid conversion selectivity Example Alkoxyacetate rate (%) (%) 1 Methyl methoxyacetate 81.2 36.4 CH.sub.3OCH.sub.2COOCH.sub.3 10 Ethyl methoxyacetate 80.5 28.1 CH.sub.3OCH.sub.2COOC.sub.2H.sub.5 11 n-Propyl methoxyacetate 83.9 25.1 CH.sub.3OCH.sub.2COOC.sub.3H.sub.7 12 n-Butyl methoxyacetate 78.8 25.3 CH.sub.3OCH.sub.2COOC.sub.4H.sub.9 13 Ethyl ethoxyacetate 79.1 31.1 C.sub.2H.sub.5OCH.sub.2COOC.sub.2H.sub.5

[0085] It can be seen from Table 2 that the hydrogen-type molecular sieve catalyst can hydrolyze various types of Malkoxyacetate into glycolic acid.

Examples 14 to 15

[0086] The acidic H-ZSM-5 molecular sieve with a Si/Al ratio of 20 in Example 1 was molded with alumina or silicon oxide into a strip, and after the molding, a content of the alumina or silicon oxide in the molded catalyst was 20 wt %. Other conditions and operations remained unchanged. Reaction results were shown in Table 3.

TABLE-US-00003 TABLE 3 Catalytic reaction results in Examples 1, 14, and 15 Methyl Glycolic methoxyacetate acid conversion selectivity Example Forming agent rate (%) (%) 1 None 81.2 36.4 14 Alumina 77.5 35.3 15 Silicon oxide 76.8 35.0

[0087] It can be seen from Table 3 that the catalytic activity of the acidic molecular sieve catalyst remains basically unchanged after the molding with alumina or silicon oxide.

Example 16

[0088] An acidic H-ZSM-5 molecular sieve with a Si/Al ratio of 20 produced by Zhongke Catalysis New Technology (Dalian) Co., Ltd. was selected, crushed, and sieved to obtain 0.4 mm to 0.8 mm particles; 2 g of the particles was taken and filled into a stainless steel reaction tube with an inner diameter of 8 mm and activated with 50 mL/min nitrogen at 500? C. for 4 h; a reaction was conducted under the following conditions: a reaction temperature (T) was 150? C., and a reaction pressure (P) was 0.1 MPa; a molar ratio of methyl methoxyacetate to water was 1:4; and a WHSV of methyl methoxyacetate was 1.0 h.sup.?1; and products at different time points were analyzed by gas chromatography and liquid chromatography. Reaction results based on a mole number of carbon were shown in Table 4.

TABLE-US-00004 TABLE 4 Catalytic reaction results in Example 16 Reaction Methyl methoxyacetate Glycolic acid time (h) conversion rate (%) selectivity (%) 24 81.2 36.4 100 81.1 36.3 500 81.0 36.5 1000 80.6 36.1 2000 79.9 35.7 4000 76.6 35.2 8000 73.2 34.8

[0089] It can be seen from Table 4 that the acidic molecular sieve catalyst exhibits excellent stability in the hydrolysis of methyl methoxyacetate to produce glycolic acid, and can meet the requirements of industrial use.

[0090] The above examples are merely few examples of the present application, and do not limit the present application in any form. Although the present application is disclosed as above with preferred examples, the present application is not limited thereto. Some changes or modifications made by any technical personnel familiar with the profession using the technical content disclosed above without departing from the scope of the technical solutions of the present application are equivalent to equivalent implementation cases and fall within the scope of the technical solutions.