Supported metal catalyst and use thereof for selective oxidation of glycerol

Abstract

A method for oxidation of glycerol into glyceric acid is described, which includes a step of treating glycerol with a supported metal catalyst in the presence of oxygen, said catalyst including platinum and a metal element selected from the group comprising tin, molybdenum, bismuth and a mixture thereof.

Claims

1. A process for oxidation of glycerol to glyceric acid, the process comprising contacting glycerol with a metal catalyst in presence of oxygen, wherein the metal catalyst is supported by alumina, said metal catalyst comprising platinum and a metal element chosen from the group consisting of tin, molybdenum, and a mixture thereof.

2. The process as claimed in claim 1, wherein the contacting is carried out in the presence of a base.

3. The process as claimed in claim 2, wherein the base comprises sodium hydroxide.

4. The process as claimed in claim 2, wherein the base consists of sodium hydroxide.

5. The process as claimed in claim 1, wherein the contacting is carried out at a temperature from 15° C. to 100° C.

6. The process as claimed in claim 5, wherein the temperature is from 20° C. to 60° C.

7. The process as claimed in claim 5, wherein the temperature is from 28° C. to 60° C.

8. The process as claimed in claim 1, wherein the metal catalyst comprises tin and platinum.

9. The process as claimed in claim 1, wherein the glycerol is unrefined glycerol.

10. The process as claimed in claim 1, wherein the contacting results in reaction products, wherein the products are predominantly glyceric acid and tartronic acid in yield percentage.

11. The process as claimed in claim 10, further comprising separating glyceric acid and tartronic acid.

12. The process as claimed in claim 1, further comprising separating reaction products resulting from the contacting.

13. The process as claimed in claim 1, further comprising regenerating said catalyst before the contacting a regenerated supported metal catalyst with glycerol.

14. The process as claimed in claim 13, wherein said regenerating comprises washing and drying the catalyst.

15. The process as claimed in claim 14 wherein the drying comprises heating at 105° C. for 24 hours.

16. A process for oxidation of glycerol to glyceric acid, the process comprising contacting glycerol with a supported metal catalyst in presence of oxygen, wherein the metal catalyst comprises molybdenum and platinum.

17. The process as claimed in claim 16, wherein the metal catalyst further comprises tin.

18. The process as claimed in claim 16, wherein the contacting is carried out in the presence of a base.

19. The process as claimed in claim 16, wherein the glycerol is unrefined glycerol.

20. The process as claimed in claim 16, further comprising regenerating said catalyst before the contacting a regenerated supported metal catalyst with glycerol.

Description

KEY TO THE FIGURES

(1) FIG. 1 represents a graph showing the percentage of products obtained over time in the context of the reaction for the oxidation of glycerol at 100° C. in the absence of base. The axis of the abscissae represents the time, expressed in minutes, and the axis of the ordinates represents the percentage of products. The key to FIG. 1 is as follows:

(2) 1: carbon balance

(3) 2: glyceraldehyde

(4) 3: degree of conversion of the glycerol [%]

(5) 4: glyceric acid

(6) 5: dihydroxyacetone (or 1,3-dihydroxy-2-propanone, or DHA)

(7) 6: glycolic acid

(8) 7: tartronic acid

(9) 8: oxalic acid

(10) FIG. 2 represents a graph showing the percentage of products obtained over time in the context of the reaction for the oxidation of glycerol at 60° C. in the presence of base. The axis of the abscissae represents the time, expressed in minutes, and the axis of the ordinates represents the percentage of products. The key to FIG. 2 is as follows:

(11) 1: carbon balance

(12) 2: degree of conversion of the glycerol [%]

(13) 3: glyceric acid

(14) 4: tartronic acid

(15) 5: glycolic acid

(16) 6: formic acid

(17) 7: oxalic acid

(18) FIG. 3 represents a graph showing the percentage of products obtained over time in the context of the reaction for the oxidation of glycerol at 40° C. in the presence of base. The axis of the abscissae represents the time, expressed in minutes, and the axis of the ordinates represents the percentage of products. The key to FIG. 3 is as follows:

(19) 1: carbon balance

(20) 2: degree of conversion of the glycerol [%]

(21) 3: glyceric acid

(22) 4: tartronic acid

(23) 5: formic acid

(24) 6: glycolic acid

(25) 7: oxalic acid

(26) FIG. 4 represents a graph showing the percentage of products obtained over time in the context of the reaction for the oxidation of glycerol at 28° C. in the presence of base. The axis of the abscissae represents the time, expressed in minutes, and the axis of the ordinates represents the percentage of products. The key to FIG. 4 is as follows:

(27) 1: carbon balance

(28) 2: degree of conversion of the glycerol [%]

(29) 3: glyceric acid

(30) 4: tartronic acid

(31) 5: formic acid

(32) 6: glycolic acid

(33) 7: oxalic acid

EXAMPLES

Example 1

Synthesis of a Support Pt/Sn Bimetal Catalyst

(34) The supported catalyst is prepared by incipient wetness impregnation of an alumina (15.7271 g) (Merck) with a solution of SnCl.sub.2.2H.sub.2O (5.3232 g) (Aldrich), followed by drying at 110° C. for 24 h and by calcination under air at 550° C. for 3 h, in order to obtain a support comprising 1.5 mmol of Sn per gram of alumina.

(35) The support (Sn/alumina) (4.487 g) is immersed in water and brought to reflux for 30 min. 20.809 ml of an aqueous solution of K.sub.2PtCl.sub.6 salt (0.0164 mol.l.sup.−1) are then added dropwise with strong stirring and reduced with NaBH.sub.4 (2 mol.l.sup.−1). After one hour of stirring and reflux, the solution is cooled to ambient temperature and filtered, and the filter residue is washed with water. Finally, the powder, comprising 1.4 wt % of Pt and 14.9 wt % of tin, is dried at 100° C. for 24 h before being used in the reaction for the oxidation of glycerol.

Example 2

Experimental Conditions

(36) The same conditions were applied for all the catalytic tests presented in examples 3 to 6, namely: an oxygen pressure of 5 bar, a rotational speed of stirring of 1500 rpm, an initial glycerol concentration of 0.3M, an NaOH/glycerol ratio=4 or 0 and, finally, a glycerol/catalyst ratio=11 (g/g). The range of temperatures studied is between 28 and 100° C.

(37) The experiments for the oxidation of pure glycerol in the liquid phase were carried out in a 300 ml stainless steel reactor equipped with a gas entrainment impeller, with four baffles, with a thermocouple and with a system for feeding with thermally regulated oxygen. In each experiment, 200 ml of an aqueous glycerol solution ([glycerol]=0.3M) are heated to the desired temperature and the reaction begins when the sodium hydroxide solution and/or the catalyst are introduced into the reactor (t0) and when the system is placed under oxygen pressure (5 bar) with continuous stirring (1500 rpm). The amount of base is adjusted in order to obtain an NaOH/glycerol molar ratio of between 0 and 4. The glycerol/catalyst weight ratio is 11. The temperature and the O.sub.2 partial pressure are continuously monitored while the sampling is carried out periodically. The products are analyzed with an HPLC Agilent 1200 device equipped with a Rezex ROA-Organic Acid H+ column (300×7.8 mm) and a refractive index detector (RID). A solution of H.sub.2SO.sub.4 (0.0025M) in demineralized water (0.5 ml.min.sup.−1) was used as eluent. The identification and the quantification of the products obtained are carried out by comparison with the corresponding calibration curves.

Example 3

Oxidation of Glycerol in the Presence of a Supported Pt/Sn Bimetal Catalyst at 100° C. in the Absence of Base

(38) The reaction is carried out under the conditions described in example 2 at a temperature of 100° C. and in the absence of base.

(39) The results are represented in FIG. 1.

(40) The conversion of glycerol reaches a maximum of 43.1% after 2.5 h of reaction. The predominant products are glyceraldehyde and glyceric acid, with respective yields of 16.8 and 15.6%.

Example 4

Oxidation of Glycerol in the Presence of a Supported Pt/Sn Bimetal Catalyst at 60° C. and in the Presence of Base

(41) The reaction is carried out under the conditions described in example 2 at a temperature of 60° C., in the presence of base.

(42) The results are represented in FIG. 2.

(43) The conversion of glycerol reaches 95% after 1.5 h of reaction. The predominant products are glyceric acid and tartronic acid, with respective yields of 50.9% and 20.0%.

Example 5

Oxidation of Glycerol in the Presence of a Supported Pt/Sn Bimetal Catalyst at 40° C. and in the Presence of Base

(44) The reaction is carried out under the conditions described in example 2 at a temperature of 40° C., in the presence of base.

(45) The results are represented in FIG. 3.

(46) The conversion of glycerol reaches 86.3% after 1.5 h of reaction. The predominant products are glyceric acid and tartronic acid with respective yields of 56% and 13.7%.

Example 6

Oxidation of Glycerol in the Presence of a Supported of a Pt/Sn Bimetal Catalyst at 28° C. and in the Presence of Base

(47) The reaction is carried out under the conditions described in example 2 at a temperature of 28° C., in the presence of base.

(48) The results are represented in FIG. 4.

(49) The conversion of glycerol reaches 78.3% after 2.5 h of reaction. The predominant products are glyceric acid and tartronic acid with respective yields of 54.2% and 13.1%.

Example 7

Separation of the Reaction Products

(50) In order to separate the reaction products (if the selectivity for glyceric acid does not reach 100%), it is sufficient to carry out a derivation by reaction with an alcohol (e.g. methanol or ethanol) in order to obtain the corresponding esters. These esters have a broad range of boiling points, thus making possible separation by fractional distillation. Reacidification of the different fractions subsequently makes it possible to obtain the different carboxylic acids.

(51) The boiling points of the different esters obtained from the reaction of the acids with methanol are provided below. As may be seen, they are sufficiently separated to envisage different distillation stages. methyl glycerate=241.5° C. methyl glycolate=149-151° C. methyl oxalate=204° C. and 163-164° C. for the dimethyl ester methyl tartronate=316° C. methyl formate=32° C.

(52) Other methods, such as membranes selective for C.sub.2 compounds or adsorbents, can also be envisaged.

Example 8

Synthesis of the Supported Bimetal Catalyst PtBi/Al2O3

(53) The supported catalyst is prepared by incipient wetness impregnation of an alumina (15.6664 g) (Merck) with a solution of Bi(NO.sub.3).sub.3.5H.sub.2O (11.3989 g) (Avantor Performance Materials Poland S.A.), followed by drying at 110° C. for 24 h and by calcination under air at 550° C. for 3 h, in order to obtain a support comprising 1.5 mmol of Bi per gram of alumina.

(54) The support (Bi/alumina) (4.428 g) is immersed in water and brought to reflux for 30 min. 20.53 ml of an aqueous solution of K.sub.2PtCl.sub.6 salt (0.016 mol.l.sup.−1) are then added dropwise with strong stirring and reduced with NaBH.sub.4 (2 mol.l.sup.−1). After one hour of stirring and of reflux, the solution is cooled to ambient temperature and filtered, and the filter residue is washed with water. Finally, the powder, comprising 1.46 wt % of Pt and 30.84 wt % of Bi, is dried at 100° C. for 24 h before being used in the reaction for the oxidation of glycerol.

Example 9

Synthesis of the Supported Bimetal Catalyst PtMo/Al2O3

(55) The supported catalyst is prepared by impregnation of an alumina (14.9976 g) (Merck) with a solution of MoO.sub.3 (3.2381 g) (Avantor Performance Materials Poland S.A.): the solution of MoO.sub.3 is prepared beforehand by solubilization of MoO.sub.3 in a solution of water at boiling point and at reflux, in the presence of a few drops of nitric acid (the water is used in excess until complete solubilization of MoO.sub.3); then the alumina is added to this solution, under hot conditions, with stirring; after homogenization, the water is evaporated. The solid obtained is subsequently dried at 110° C. for 24 h and then calcined under air at 550° C. for 3 h, in order to obtain a support comprising 1.5 mmol of Mo per gram of alumina.

(56) The support (Mo/alumina) (4.430 g) is immersed in water and brought to reflux for 30 min. 20.55 ml of an aqueous solution of K.sub.2PtCl.sub.6 salt (0.016 mol.l.sup.−1) are then added dropwise with strong stirring and reduced with NaBH.sub.4 (2 mol.l.sup.−1). After one hour of stirring and of reflux, the solution is cooled to ambient temperature and filtered, and the filter residue is washed with water. Finally, the powder, comprising 1.46 wt % of Pt and 14.2 wt % of Mo, is dried at 100° C. for 24 h before being used in the reaction for the oxidation of glycerol.

Example 10

Study of Recyclability Carried Out on the Catalysts

(57) Tests:

(58) A preliminary study on recycling the catalysts is carried out by following the procedure described in example 2, with the following conditions: an oxygen pressure of 3 bar, a stirrer rotational speed of 1500 rpm, an initial glycerol concentration of 0.3M, a temperature of 60° C., an NaOH/glycerol ratio=4 and a glycerol/catalyst ratio=11 (g/g), The commercial catalyst Pt/Al.sub.2O.sub.3 is used for comparison.

(59) Recycling Procedure:

(60) After a first reaction carried out essentially under the conditions described in example 2, the catalyst is separated from the reaction medium by filtration, then washed with 200 ml of distilled water and dried at 105° C. for 24 hours. The catalyst is subsequently reused directly for a second reaction carried out under the same conditions as the first, without addition of fresh catalyst. The recycling procedure is repeated between each following reaction.

(61) TABLE-US-00001 1.sup.st test 2.sup.nd test 3.sup.rd test Pt/Al.sub.2O.sub.3 (Aldrich) 82.1% conv. 86 4% conv. 85.3% conv. 30 min 30 min 30 min Pt—Sn/Al.sub.2O.sub.3 95.4% conv. 92.4% conv. 81.9% conv. 30 min 30 min 30 min Pt—Bi/Al.sub.2O.sub.3 95.9% conv. 97.3% conv. 97.9% conv. 30 min 30 min 30 min Pt—Mo/Al.sub.2O.sub.3 99.9% conv. 98.2% conv. 99.0% conv. 30 min 30 min 30 min conv. = “degree of conversion at”

(62) The level of conversion remains constant for the bimetal catalysts Pt—Bi/Al.sub.2O.sub.3 and Pt—Mo/Al.sub.2O.sub.3. There is no loss of selectivity for glyceric acid, which remains constant (approximately 60% for the commercial catalyst, 65-75% for the bimetal catalysts).

Example 11

Oxidation of Unpurified Glycerol in the Presence of a Supported Pt/Sn Bimetal Catalyst at 60° C. and in the Presence of a Base

(63) The reaction is carried out at 60° C. under the conditions described in example 2 using crude glycerol (purity of approximately 50%). The commercial catalyst Pt/Al.sub.2O.sub.3 is used for comparison.

(64) TABLE-US-00002 Conversion (1 h) Pt/Al.sub.2O.sub.3 (Aldrich) 9.0% Pt—Sn/Al.sub.2O.sub.3 32.3%

(65) The conversion of the glycerol reaches 9.0% with the commercial catalyst Pt/Al.sub.2O.sub.3, after 1 h of reaction, and 32.3% with the catalyst Pt—Sn/Al.sub.2O.sub.3. Compared with the reactions starting from pure glycerol, the activity of the commercial catalyst Pt/Al.sub.2O.sub.3 decreases by a factor of 5 with the unpurified glycerol. This loss is by a factor of 3 with the Pt—Sn/Al.sub.2O.sub.3 bimetal catalyst. The predominant products are glyceric acid and tartronic acid, with similar yields to those obtained from the crude glycerol.

(66) The invention is not limited to the embodiments presented and other embodiments will be clearly apparent to a person skilled in the art.