Method of catalytic conversion of carbohydrates to low-carbon diols by using alloy catalysts

Abstract

This invention provides a method for catalytic conversion of carbohydrates to low-carbon diols using alloy catalysts. In the process, carbohydrates as the feedstock are subjected to one-step catalytic conversion to realize the highly efficient and selective production of ethylene glycol etc. under hydrothermal conditions, with an alloy catalyst composed of tin, and a transition metal such as iron, cobalt, nickel, rhodium, ruthenium, palladium, iridium, platinum and copper, or a mixture thereof. The reaction is carried out in water at a temperature range of 120-300 C., with a hydrogen pressure range of 1-13 MPa. Compared with the present petroleum based synthesis technology of ethylene glycol, the method in this invention possesses advantages of using renewable feedstock, high atom economy and environmental friendly. Besides, compared with other technologies using biomass as feedstock to produce ethylene glycol, the alloy catalyst in this invention possesses the advantages of few leaching amount, good hydrothermal stability and easy to recycle.

Claims

1. A method for catalytic conversion of carbohydrates to low-carbon diols, comprising: subjecting a carbohydrate feedstock to catalytic hydrogenation at an elevated pressure in water in the presence of an alloy catalyst, wherein the alloy catalyst consists of tin and one or more transition metals selected from the group consisting of nickel, iron, cobalt, rhodium, ruthenium, palladium, iridium, copper, and a mixture thereof, wherein a weight ratio between tin and the one or more transition metals is in a range of 0.01-100, wherein the catalytic hydrogenation reaction is conducted in a reactor filled with hydrogen at a temperature higher than 120 C. for a reaction time no less than 5 minutes or at a liquid hourly space velocity of not more than 20 h.sup.1, wherein a weight concentration of the alloy catalyst in the reaction system is between 0.1 wt % and 50 wt %, and wherein the low-carbon diol comprises ethylene glycol and 1,2-propylene glycol, wherein a yield of ethylene glycol is higher than a yield of 1,2-propylene glycol, and wherein tin in the alloy is metallic.

2. The method of claim 1, wherein the hydrogen is filled in the reactor prior to the catalytic hydrogenation reaction, and an initial hydrogen pressure at room temperature is between 1 and 12 MPa, and the reaction temperature is lower than a thermal decomposition temperature of the low carbon diol.

3. The method of claim 1, wherein the reaction temperature is between 200 C. and 280 C. and the initial hydrogen pressure at room temperature is between 3 and 7 MPa.

4. The method of claim 1, wherein the alloy catalyst is a skeletal alloy catalyst composed of a nickel-tin alloy, the weight ratio between tin and nickel is in the range of 0.1-10, and the weight concentration of alloy catalyst in the reaction system is between 1 wt % and 30 wt %.

5. The method of claim 4, wherein the weight ratio between tin and nickel in the skeleton alloy catalyst is in the range of 0.5-2; the weight concentration of alloy catalyst in the reaction system is between 2 wt % and 20 wt %.

6. The method of claim 1, wherein the alloy catalyst is a supported catalyst, wherein metallic tin and the one or more transition metals are supported on a carrier, wherein the carrier is selected from the group consisting of activated carbon, alumina, silica, silicon carbide, zirconia, zinc oxide and titanium dioxide, and a mixture thereof, wherein a the weight concentration of alloy in the supported catalyst is between 0.01 wt % and 50 wt %, and wherein the weight ratio between tin and the one or more transition metals in the supported catalyst is in the range of 0.1-10.

7. The method of claim 6, wherein the weight concentration of alloy in the supported catalyst is between 1 wt % and 35 wt %, and wherein the weight ratio between tin and the one or more transition metals in the supported catalyst is in the range of 0.5-2.

8. The method of claim 1, wherein the carbohydrate feedstock comprises cellulose, starch, hemicellulose, glucose, mannose, xylose, arabinose, xylooligosaccharide, erythrose, chitosan, or a mixture thereof.

9. The method of claim 1, wherein the reaction time is between 0.5 h and 5 h in a sealed high pressure reactor.

10. The method of claim 1, wherein the reactor has a liquid hourly space velocity between 0.1 and 20 h.sup.1 in a semi continuous high pressure reactor or a continuous high pressure reactor, wherein the liquid hourly space velocity is a ratio of a total dry mass of the carbohydrate feedstock into the reactor per hour to a total mass of catalyst in the reactor.

11. The method of claim 1, wherein the alloy catalyst is converted from the precursor of the alloy catalyst in situ in the reactor, wherein the precursor of the alloy catalyst comprises a precursor of tin and a precursor of the one or more transition metals, wherein the precursor of tin is metallic tin, one or more tin compounds, or a mixture thereof, and the precursor of the one or more transition metals are selected from the group consisting of metallic and chemical compounds of nickel, iron, cobalt, rhodium, ruthenium, palladium, iridium, copper, and a mixture thereof.

12. The method of claim 11, wherein the precursor of the one or more transition metals is supported on a carrier, and the carrier is the precursor of tin, and wherein a weight concentration of transition metals in the catalyst is between 0.01 wt % and 50 wt %.

13. The method of claim 11, wherein the precursor of tin is supported on a carrier and the carrier is the precursor of the one or more transition metals, and the weight concentration of tin in the catalyst is between 0.01 wt % and 50 wt %.

14. The method of claim 11, wherein the precursor of tin is metallic tin, stannous fluoride, stannous fluoride, stannous bromide, stannous iodide, stannic fluoride, stannic chloride, stannic bromide, stannic iodide, stannic hydroxide, stannous hydroxide, stannous oxide, stannic oxide, stannous mono-sulphate, stannic acetate, stannous oxalate, sodium stannate, potassium stannate, calcium stannate, tin phosphide, stannous pyrophosphate, or a mixture thereof.

15. The method of claim 11, wherein the precursor of the one or more transition metals is metallic iron, metallic cobalt, metallic rhodium, metallic ruthenium, metallic palladium, metallic iridium, metallic copper, skeletal iron (Raney iron), skeletal cobalt (Raney cobalt), skeletal copper (Raney copper), ferric nitrate, cobalt nitrate, ruthenium nitrosyl nitrate, rhodium nitrate, palladium nitrate, iridium nitrate, copper nitrate, ferric chloride, cobalt chloride, ruthenium chloride, rhodium chloride, palladium chloride, iridium chloride, copper chloride, ferric oxide, ferroferric oxide, ferrous oxide, iron sulfate, cobalt(II) oxide, cobalt sesquioxide, cobaltosic oxide, cobaltous sulfate, nickel sulfate, copper oxide and copper sulfate, or a mixture thereof.

16. The method of claim 1, wherein the carbohydrate feedstock is cellulose, starch, hemicellulose, xylose, and/or glucose and a yield of ethylene glycol is higher than a yield of propylene glycol.

17. A method for catalytic conversion of carbohydrates to low-carbon diols, comprising: subjecting a carbohydrate feedstock to catalytic hydrogenation at an elevated pressure in water in the presence of an alloy catalyst, wherein the alloy catalyst is a skeletal nickel-tin catalyst, a skeletal copper-tin catalyst, or a skeletal cobalt-tin catalyst, wherein a weight ratio between tin and the one or more transition metals is in a range of 0.01-100. wherein the catalytic hydrogenation reaction is conducted in a reactor filled with hydrogen at a temperature higher than 120 C. for a reaction time no less than 5 minutes or at a liquid hourly space velocity of not more than 20 h.sup.1, wherein a weight concentration of the alloy catalyst in the reaction system is between 0.1 wt % and 50 wt %, and wherein the low-carbon diol comprises ethylene glycol and 1,2-propylene glycol, wherein a yield of ethylene glycol is higher than a yield of 1,2-propylene glycol, and wherein tin in the alloy is metallic.

18. The method of claim 17, wherein a total yield of ethylene glycol and 1,-propylene glycol is higher than 20%.

19. The method of claim 17, wherein the skeletal tin-nickel catalyst is prepared by hydrothermal reaction between metallic tin and skeletal nickel.

Description

DESCRIPTION OF THE DRAWING

(1) FIG. 1 XRD pattern of the skeletal NiSn alloy catalyst prepared by hydrothermal treatment

DETAILED DESCRIPTION OF THE EMBODIMENTS

(2) For further illustrating the invention, detailing experiments are described below. It should be noted that the following examples are intended to describe but not to limit the invention.

Example 1

(3) The preparation of supported alloy catalysts: the metal salts of tin and iron, cobalt, nickel, rhodium, ruthenium, palladium, iridium and platinum were supported on a carrier by an incipient impregnation method. Water is used as the solvent to dissolve metal salts and the carrier is selected from activated carbon, alumina, silica, silicon carbide, zirconia, zinc oxide and titanium dioxide, or a mixture thereof. The catalyst was dried overnight at 120 C., and then reduced at 300 C. for 2 h. Finally, the catalyst should be passivated under 1% O.sub.2/N.sub.2 (V/V) for 4 h before use.

Example 2

(4) The preparation of nickel supported on stannic oxide catalyst: 1.8 g Ni(NO.sub.3).sub.2.6H.sub.2O were dissolved in 20 ml water, then 1.5 g SnO.sub.2 was added to the prepared solution followed by stirring at 25 C. for 12 h until the complete evaporation of water. The catalyst was dried at 120 C. for 8 h, and then calcined at 300 C. for 2 h under N.sub.2, and finally reduced at 300 C. for 2 h under H.sub.2.

Example 3

(5) The preparation of nickel supported on ferric oxide catalyst: 0.9 g SnCl.sub.4.5H.sub.2O was dissolved in 20 ml water, then 1.5 g Fe.sub.2O.sub.3 was added to the prepared solution followed by stirring at 25 C. for 12 h until the complete evaporation of water. The catalyst was dried at 120 C. for 8 h, and then calcined at 300 C. for 2 h under N.sub.2, and finally reduced at 300 C. for 2 h under H.sub.2.

Example 4

(6) The preparation of hydrogenation catalyst: platinum chloride, palladium chloride, ruthenium chloride, rhodium chloride, iridium chloride, nickel nitrate, ferric nitrate, cobalt nitrate and copper nitrate were dissolved in water, respectively. The prepared different metal salts solutions were impregnated on a carrier by an incipient impregnation method, respectively. The catalyst was dried at 120 C. overnight.

(7) For the supported precious catalysts of platinum, palladium, ruthenium, rhodium, iridium, etc., the catalyst were reduced at 250 C. for 2 h, followed by passivated under 1% O.sub.2/N.sub.2 (V/V) for 4 h before use. For the supported non-precious catalysts of nickel, iron, cobalt, copper, etc., the catalyst were reduced at 450 C. for 2 h, followed by passivated under 1% O.sub.2/N.sub.2 (V/V) for 4 h before use.

Example 5

(8) The in situ preparation of the alloy catalyst: The combination of metallic tin or tin compounds, or a mixture thereof and metallic hydrogenation catalyst or skeletal catalyst was put into the reactor. The reaction conditions are the same as Example 7, and the alloy catalyst is in situ formed.

Example 6

(9) The preparation of skeletal alloy catalyst (hydrothermal treatment): 0.6 g metallic tin, 1.0 g skeletal nickel catalyst (Raney Ni) and 10-100 mL water were put into the kettle. The hydrothermal treatment was carried out under 7 MPa H.sub.2 at 250 C. for 3 h. After the treatment, the obtained catalyst was dried overnight at 120 C. before use. FIG. 1 was the XRD spectra of the obtained NiSn alloy catalyst prepared by hydrothermal treatment. The XRD results showed that the formation of NiSn alloy after hydrothermal treatment.

Example 7

(10) Catalytic conversion experiment: 0.25 g carbohydrate, a designed amount of composite catalyst and 25 ml water were put into the 75 ml autoclave. After flushing with hydrogen for three times, the reactor was pressurized with 5 MPa H.sub.2, and then the temperature was increased to a designed temperature and kept for 30-240 min. After the reaction, the autoclave was cooled to room temperature. The liquid products were separated from catalysts by centrifugation. The liquid products were analyzed by high performance liquid chromatography, and only the yields of ethylene glycol, hexitol (sorbitol and mannitol) and 1,2-propylene glycol were calculated.

Example 8

(11) Results of cellulose conversion to polyols over supported alloy catalysts. The alloy catalyst was composed of two components, in which one component was metallic tin and the other was transition metals. The loadings of metallic tin and transition metals were 3% and 5%, respectively. The reaction conditions are the same as Example 7.

(12) TABLE-US-00001 TABLE 1 Results of cellulose conversion to polyols over supported alloy catalysts (supported alloy catalyst 0.1 g, reaction temperature 245 C., reaction time 95 min) Conversion Yield of Yield of of ethylene 1,2-propylene Yield of Catalyst cellulose/% glycol/% glycol/%) hexitol/% Ni/AC 100 7.3 6.6 29.4 Ru/AC 100 8.1 5.7 19.2 Pt/AC 98 5.6 5.3 22.9 Ir/AC 90 7.8 11.2 20.3 NiSn/AC 100 38.7 9.5 6.1 RuSn/AC 100 39.8 9.7 5.4 PtSn/AC 100 43.6 7.5 1.5 IrSn/AC 100 54.4 13.2 4.6. Ni/SnO.sub.2 100 45.6 10.1 5.2 Sn/Fe.sub.2O.sub.3 100 26.8 11.9 6.1

(13) As shown in Table 1, supported alloy catalysts promoted the production of ethylene glycol. Comparing the yields of ethylene glycol and hexitol over alloy catalysts and transition metals hydrogenation catalyst, the formation of alloy improved the yield of ethylene glycol, but the yield of hexitol decreased.

Example 9

(14) Results of cellulose conversion to polyols over non-supported alloy catalyst. The alloy catalyst was composed of two components, in which one component was metallic tin and the other was transition metals. The reaction conditions are the same as Example 7.

(15) TABLE-US-00002 TABLE 2 Results of cellulose conversion to polyols over non-supported alloy catalysts (non-supported alloy catalyst 0.05 g, the mass ratio of tin to nickel, copper and cobalt was 1:3, 1:5 and 1:2.5 respectively, reaction temperature 245 C., reaction time 95 min) Conversion Yield of Yield of of ethylene 1,2-propylene Yield of Catalyst cellulose/% glycol/% glycol/% hexitol/% Raney Ni 82 6.4 11.5 20.1 Raney Cu 85 4.3 9.6 27.9 Raney Co 76 5.8 4.5 18.9 Raney NiSn 100 54.5 13.3 4.6 Raney CuSn 100 56.9 10.3 5.9 Raney CoSn 100 50.2 11.3 6.1

(16) As shown in Table 2, non-supported alloy catalysts promoted the production of ethylene glycol. Comparing the yields of ethylene glycol and hexitol over alloy catalysts and skeletal metals hydrogenation catalyst, the formation of alloy improved the yield of ethylene glycol, but the yield of hexitol decreased.

Example 10

(17) Catalytic conversion results of different carbohydrates to polyols. RuSn/AC was used as supported alloy catalyst for the conversion of different carbohydrates. The mass ratio of tin to ruthenium was 1:3.5, and the loading of ruthenium was 5%. The reaction conditions are the same as Example 7.

(18) TABLE-US-00003 TABLE 3 Results of catalytic conversion of different carbohydrates to polyols (RuSn/AC 0.1 g, reaction temperature 245 C., reaction time 95 min) Yield of Yield of ethylene 1,2-propylene Yield of Yield of Carbohydrate glycol/% glycol/% glycerol/%) sorbitol/% cellulose 58.7 9.5 1.8 6.1 jerusalem 11.3 24.0 3.5 4.8 artichoke soluble 27.0 19.7 6.4 16.8 starch fructose 17.3 24.2 25 0.8 xylose 49.4 20.9 12 1.5 sucrose 21.8 23.8 22 2.4 glucose 27.3 21.2 20 3.7 sorbitol 2.2 2.9 1.2 87.2 xylitol 2.5 2.4 1.0 92.5 (xylitol) glycerol 3.1 5.0 93

(19) As shown in Table 3, RuSn/AC showed higher selectivity to ethylene glycol and 1,2-propylene glycol than sorbitol, which indicated that RuSn/AC was active for the CC bond cleavage of carbohydrates bearing unsaturated bonds. The yield of ethylene glycol obtained from cellulose was higher than that form other carbohydrates. The selectivity of ethylene glycol and 1,2-propylene glycol depended on the carbohydrates. The yield of 1,2-propylene glycol would be improved, when the carbohydrates contained fructose or could be isomerized to fructose. However, RuSn/AC showed low activity towards the conversion of sorbitol, and CC bonds of sorbitol could not be selectively cracked to produce ethylene glycol and 1,2-propylene glycol. Similarity, RuSn/AC showed low activity towards the conversion of xylitol and glycerol.

Example 11

(20) Effect of reaction time. PtSn/AC (0.5% Sn, 5% Pt) was selected as supported alloy catalyst for the investigation of reaction time effect (Table 4). The reaction conditions are the same as Example 7 except for the reaction time.

(21) TABLE-US-00004 TABLE 4 Results of catalytic conversion of cellulose to polyols at different time over PtSn/AC. (PtSn/AC 0.1 g, reaction temperature 245 C.) Conversion Yield of Yield of of ethylene 1,2-propylene Yield of Time/min cellulose/% glycol/% glycol/%) hexitol/% 10 69 29.9 4.5 7.4 20 86 40.6 8.1 7.4 45 94 46.4 8.5 6.7 70 98 50.4 9.0 5.2 95 100 52.3 9.5 6.5 120 100 52.6 8.4 6.4 150 100 50.2 7.3 5.8

(22) As shown in Table 4, PtSn/AC showed good activity towards the production of ethylene glycol in a certain period. The optimum reaction time was 1 h-2.5 h.

Example 12

(23) Effect of reaction temperature. IrSn/AC (3.5% Sn, 5% Ir) was selected as supported alloy catalyst for the investigation of reaction temperature effect (Table 5). The reaction conditions are the same as Example 7 except for the reaction temperature.

(24) TABLE-US-00005 TABLE 5 Results of catalytic conversion of cellulose to polyols at different temperature over IrSn/AC (IrSn/AC 0.2 g, reaction time 95 min) Conversion Yield of Yield of of ethylene 1,2-propylene Yield of Temperature/ C. cellulose/% glycol/% glycol/% hexitol/% 215 48 18.7 2.3 11.7 225 67 34.1 2.8 7.2 235 90 52.3 9.5 5.7 245 100 64.7 9.5 6.1 255 100 50.5 9.3 3.8 265 100 46.8 6.8 1.6

(25) As shown in Table 5, IrSn/AC showed good activity towards the production of ethylene glycol in a certain temperature range. The optimum reaction temperature was 230-260 C.

Example 13

(26) The effect of mass ratio of Sn to Ir. IrSn/AC was selected as supported alloy catalyst for the investigation of mass ratio of Sn to Ir. The reaction conditions are the same as Example 7.

(27) TABLE-US-00006 TABLE 6 The effect of mass ratio of Sn to Ir on the catalytic conversion of cellulose to polyols (IrSn/AC 0.1 g, reaction temperature 245 C., reaction time 95 min) Conversion Yield of Yield of of ethylene 1,2-propylene Yield of Sn/Ir cellulose/%) glycol/% glycol/%) hexitol/% 3.2 100 46.4 10.2 5.1 1.8 100 53.6 9.2 4.9 1.2 100 58.6 9.5 6.5 0.6 100 51.6 6.3 8.9 0.3 100 40.3 7.8 11.2

(28) As shown in Table 6, IrSn/AC showed good activity towards the production of ethylene glycol in a certain range of mass ratio of Sn to Ir. The optimum mass ratio was 0.6-1.8.

Example 14

(29) The effect of LHSV. 5% Ir4% Sn/AC was selected as supported alloy catalyst for the investigation of the effect of LHSV. The reaction conditions are the same as Example 7.

(30) TABLE-US-00007 TABLE 7 The effect of LHSV on the catalytic conversion of xylose to polyols (IrSn/AC 5 g, concentration of xylose aqueous solution 20 wt %, reaction temperature 245 C.) Yield of Yield of Conversion ethylene 1,2-propylene Yield of LHSV/h.sup.1 of xylose/% glycol/% glycol/%) hexitol/% 0.2 100 36.4 11.2 6.1 0.5 100 41.6 14.5 4.9 0.8 100 45.7 18.2 3.2 1.1 100 39.2 13.4 7.9 1.7 100 31.3 7.8 11.2

(31) As shown in Table 7, IrSn/AC showed good activity towards the production of ethylene glycol and 1,2-propylene glycol in a certain LHSV range. The optimum LHSV was 0.8 h.sup.1.

Example 15

(32) The investigation and comparison of the stability of different alloy catalysts. Raney NiSn, 5% Ni3% Sn/AC and 5% Ir3% Sn/AC were selected as alloy catalysts for the investigation of catalysts stability. The reaction conditions are the same as Example 7.

(33) TABLE-US-00008 TABLE 8 The investigation and comparison of the stability of alloy catalysts. (Raney Ni 0.08 g, NiSn/AC 0.1 g, reaction temperature 245 C., reaction time 95 min) Yield of Yield of Number of ethylene 1,2-propylene Yield of Catalyst usage glycol/% glycol/% hexitol/% Raney NiSn 1 60.4 13.2 4.6. Raney NiSn 2 59.8 10.9 4.2 Raney NiSn 3 54.9 11.1 5.8 Raney NiSn 4 53.7 13.6 2.9 NiSn/AC 1 38.7 9.5 6.1 NiSn/AC 2 28.5 8.2 5.4 NiSn/AC 3 20.3 6.5 4.5 NiSn/AC 4 14.4 4.2 3.1 IrSn/AC 1 54.4 13.2 4.6 IrSn/AC 2 52.3 13.0 4.0 IrSn/AC 4 50.1 12.0 4.7

(34) As shown in Table 8, Raney NiSn showed good activity towards the production of ethylene glycol in the first four cycles. ICP analysis results of the aqueous solution after every recycle showed that the concentration of nickel and tin was lower than 1 ppm, which indicated that the leaching amount of active ingredient of Raney NiSn was few. IrSn/AC also showed good activity and stability in the conversion of cellulose to ethylene glycol. However, the catalytic activity and stability of NiSn/AC were worse than that of Raney NiSn. Skeletal NiSn alloy catalyst (Raney NiSn) showed superior catalytic activity.

(35) The alloy catalyst in this invention could catalyze the highly efficient conversion of carbohydrates to ethylene glycol and 1,2-propylene glycol. The method in this invention possesses advantages of easy operation and low cost. Besides, the alloy catalysts provided by this method possess advantages of few leaching amount, good hydrothermal stability and easy to recycle.