METHOD FOR PREPARING GLYCOLIC ACID

Abstract

Provided is a method for preparing glycolic acid which comprises oxidizing glycolaldehyde with molecular oxygen in the presence of a solvent and a supported catalyst. Said supported catalyst comprises (i) a noble metal selected from the group consisting of Pt, Pd, Ru and Rh, (ii) Bi and (iii) a support. Advantageously, the supported metallic catalyst is more active than the catalysts used in prior art. Furthermore, the catalyst is more stable at oxygen rich conditions.

Claims

1. A method for preparing glycolic acid comprising oxidizing glycolaldehyde with molecular oxygen in the presence of a solvent and a supported catalyst comprising (i) a noble metal selected from the group consisting of Pt, Pd, Ru and Rh, (ii) Bi and (iii) a support.

2. The method according to claim 1, wherein the weight ratio of Bi to the noble metal in the supported catalyst ranges from 0.03 to 1.

3. The method according to claim 2, wherein the weight ratio of Bi to the noble metal in the supported catalyst ranges from 0.2 to 0.3.

4. The method according to claim 1, wherein the loading of the noble metal ranges from 1 to 10 wt. % based on total weight of catalyst.

5. The method according to claim 4, wherein the loading of the noble metal ranges from 3 to 5 wt. % based on total weight of catalyst.

6. The method according to claim 1, wherein the weight ratio of the supported catalyst to glycolaldehyde is from 5 to 50%.

7. The method according to claim 6, wherein the weight ratio of the supported catalyst to glycolaldehyde is from 5 to 10%.

8. The method according to claim 1, wherein the noble metal is Pt.

9. The method according to claim 1, wherein the support is carbon or aluminum oxide.

10. The method according to claim 1, wherein molecular oxygen is supplied in the form of oxygen gas or air.

11. The method according to claim 10, wherein molecular oxygen is supplied in the form of oxygen gas having a purity of at least 99%.

12. A mixture comprising glycolaldehyde, molecular oxygen, a solvent and a supported catalyst comprising (i) a noble metal selected from the group consisting of Pt, Pd, Ru and Rh, (ii) Bi and (iii) a support.

13. The mixture according to claim 12, wherein molecular oxygen is in the form of oxygen gas having a purity of at least 99%.

14. The mixture according to claim 12, wherein the solvent is water.

15. The mixture according to claim 12, wherein the noble metal is Pt.

16. The mixture according to claim 12, wherein the support is carbon.

Description

DETAILS OF THE INVENTION

[0021] Glycolaldehyde subject to molecular oxygen oxidation can be a bio-based raw material. Bio-based raw material refers to a product consisting of a substance, or substances, originally derived from living organisms. These substances may be natural or synthesized organic compounds that exist in nature. For example, it is known that glycolaldehyde can be produced by high-temperature fragmentation of carbohydrates to produce a mixture of Ci-C3 oxygenates such as described in U.S. Pat. Nos. 7,094,932, 5,397,582 and WO 2017/216311.

[0022] The carbohydrate used for thermal fragmentation to provide a Ci-C3 oxygenate mixture may be mono- and/or disaccharide. In an embodiment, the mono- and/or di-saccharide is selected from the group consisting of sucrose, lactose, xylose, arabinose, ribose, mannose, tagatose, galactose, glucose and fructose; or mixtures thereof. In a further embodiment, the monosaccharide is selected from the group consisting of glucose, galactose, tagatose, mannose, fructose, xylose, arabinose, ribose; or mixtures thereof.

[0023] As used herein, molecular oxygen is a diatomic molecule that is composed of two oxygen atoms held together by a covalent bond.

[0024] In one embodiment, molecular oxygen is supplied in the form of oxygen gas. Preferably, the purity of oxygen gas is of at least 99%. The oxidation reaction is performed at an O.sub.2 partial pressure which is advantageously in the range of 1 to 10 bar in this embodiment.

[0025] In another embodiment, molecular oxygen is supplied in the form of air. The oxidation reaction is performed at an air partial pressure which is advantageously in the range of 0.15 to 1 bar in this embodiment.

[0026] The reaction may be carried out in a batch type reactor or in a continuous type reactor. In batch type reactor, the molar ratio of molecular oxygen to glycolaldehyde preferably ranges from 1 to 10 mol/mol. In continuous type reactor, the molecular oxygen flow rate preferably ranges from 0.1 to 0.5 L/min.

[0027] The noble metal in the supported catalyst is selected from the group consisting of Pt, Pd, Ru and Rh. Preferably, the noble metal is Pt.

[0028] The support to the metal catalyst is not particularly limited. It can notably be a metal oxide chosen in the group consisting of aluminum oxide (Al.sub.2O.sub.3), silicon dioxide (SiO.sub.2), titanium oxide (TiO.sub.2), zirconium dioxide (ZrO.sub.2), calcium oxide (CaO), magnesium oxide (MgO), lanthanum oxide (La.sub.2O.sub.3), niobium dioxide (NbO.sub.2), cerium oxide (CeO.sub.2) and mixtures thereof.

[0029] The support can also be a zeolite. Zeolites are substances having a crystalline structure and a unique ability to change ions. People skilled in the art can easily understand how to obtain those zeolites by preparation method reported, such as zeolite L is described in U.S. Pat. No. 4,503,023 or commercial purchase, such as ZSM available from ZEOLYST.

[0030] The support of catalyst can even be Kieselguhr, clay or carbon.

[0031] Preferably, the support is carbon or aluminum oxide (Al.sub.2O.sub.3). More preferably, the support is carbon.

[0032] The loading of the noble metal ranges from 1 to 10 wt. % based on total weight of catalyst and preferably from 3 to 5 wt. %.

[0033] The weight ratio of Bi to the noble metal in the supported catalyst preferably ranges from 0.03 to 1 and more preferably from 0.2 to 0.3.

[0034] It was surprisingly found that the supported catalyst comprising (i) a noble metal selected from the group consisting of Pt, Pd, Ru and Rh, (ii) Bi and (iii) a support has better catalytic activity. Thus, the loading of catalyst to substrate can be lower than prior art to achieve the same performance. Preferable weight ratio of the supported catalyst to glycolaldehyde is from 5 to 50% and more preferably from 5 to 10%.

[0035] The supported catalysts used in the method according to the present invention include those commercially available, such as Pt-Bi/C from Johnson Matthey.

[0036] The solvent used in the method according to the present invention can be water, ether, methanol or ethanol. Preferable solvent is water.

[0037] The method according to the present invention comprises the following steps:

[0038] (i) Mixing glycolaldehyde, molecular oxygen, a solvent and a supported catalyst comprising (i) a noble metal selected from the group consisting of Pt, Pd, Ru and Rh, (ii) Bi and (iii) a support;

[0039] (ii) Heating the mixture obtained at step (i) at proper temperature for proper time to prepare glycolic acid.

[0040] The proper temperature can be preferably from 20 to 120° C.

[0041] The proper time can be preferably from 0.25 h to 25 h.

[0042] The invention also concerns a mixture comprising glycolaldehyde, molecular oxygen, a solvent and a supported catalyst comprising (i) a noble metal selected from the group consisting of Pt, Pd, Ru and Rh, (ii) Bi and (iii) a support.

[0043] The following examples are included to illustrate embodiments of the invention. Needless to say, the invention is not limited to described examples.

EXPERIMENTAL PART

[0044] Materials [0045] Glycolaldehyde Dimer, CAS No. 23147-58-2, purity >95% from Adamas-beta [0046] 5% Pt-1.5% Bi/C, Type 160, CAS No. 7440-06-4, Johnson Matthey [0047] 5% Pt/C, CAS No. 7440-06-4, Johnson Matthey

Example 1

[0048] 240 mg of glycolaldehyde, 2.0 mL of water and 25 mg of 5 wt. % Pt-1.5 wt. % Bi/C catalyst were added to a stainless-steel autoclave with a Teflon insert. The autoclave was closed and charged with 10 bar of oxygen. The autoclave was heated to 80° C., stirred using a magnetic stir bar and held for 6 hours. After reaction, the products were analyzed by HPLC. The conversion of glycolaldehyde was 97% and the yield to glycolic acid was 78%.

Example 2

[0049] 240 mg of glycolaldehyde, 1.5 mL of water and 50 mg of 5 wt. % Pt-1.5 wt. % Bi/C catalyst were added to a stainless-steel autoclave with a Teflon insert. The autoclave was closed and charged with 10 bar of oxygen. The autoclave was heated to 30° C., stirred using a magnetic stir bar and held for 24 hours. After reaction, the products were analyzed by HPLC. The conversion of glycolaldehyde was 83% and the yield to glycolic acid was 74%.

Example 3

[0050] 240 mg of glycolaldehyde, 1.5 mL of water and 50 mg of 5 wt. % Pt/C catalyst were added to a stainless-steel autoclave with a Teflon insert. The autoclave was closed and charged with 10 bar of oxygen. The autoclave was heated to 30° C., stirred using a magnetic stir bar and held for 24 hours. After reaction, the products were analyzed by HPLC. The conversion of glycolaldehyde was 72% and the yield to glycolic acid was 56%.

Example 4

[0051] 480 mg of glycolaldehyde, 4.0 mL of water and 50 mg of 5 wt. % Pt-1.5 wt. % Bi/C catalyst were added to a glass flask with a condenser. Air was bubbled through the liquid mixture at 0.1 L/min. The glass flask was heated to 60° C. and held for 7 hours. After reaction, the products were analyzed by HPLC. The conversion of glycolaldehyde was 82% and the yield to glycolic acid was 71%.

Example 5

[0052] 480 mg of glycolaldehyde, 4.0 mL of water and 150 mg of 5 wt. % Pt/C catalyst were added to a glass flask with a condenser. Air was bubbled through the liquid mixture at 0.1 L/min. The glass flask was heated to 60° C. and held for 7 hours. After reaction, the products were analyzed by HPLC. The conversion of glycolaldehyde was 18% and the yield to glycolic acid was 16%.