METHOD FOR CHEMICAL CONVERSION OF SUGARS OR SUGAR ALCOHOLS TO GLYCOLS

Abstract

Methods for chemically converting sugars or sugar alcohols into polyols/glycols, wherein the sugars or sugar alcohols are converted by means of hydrogenolysis in the presence of a catalyst comprising at least one metal and on a carbon support, wherein a nitrogen-doped carbon support is used as a catalyst support. The disclosure provides methods for chemically converting sugars or sugar alcohols into glycols which permits the preparation of glycols with higher selectivity and reduces the formation of lactic acid as a by-product.

Claims

1-12. (canceled)

13. A method for chemically converting sugars or sugar alcohols into polyols/glycols, comprising: converting sugars or sugar alcohols by hydrogenolysis in the presence of a catalyst comprising at least one metal and on a carbon support, and using a nitrogen-doped carbon support as a catalyst support.

14. The method of claim 13, wherein, in a two-stage process, firstly a sugar is hydrogenated to give a sugar alcohol and thereafter the sugar alcohol is converted into polyols in a second step by means of hydrogenolysis.

15. The method of claim 13, including converting, by hydrogenation/hydrogenolysis, a C6 sugar or a C6 sugar alcohol or a C5 sugar or a C5 sugar alcohol into polyols/glycols.

16. The method of claim 13, wherein a nitrogen-doped activated carbon or nitrogen-doped carbon black is used as the catalyst support.

17. The method of claim 16, wherein a carbon support is used as catalyst, the surface of which has been doped with nitrogen atoms by reductive methods.

18. The method of claim 17, wherein said reductive methods uses ammonia and/or nitrogen and/or hydrogen.

19. The method of claim 13, wherein nitrogen-doped carbon nanotubes are used as the catalyst support.

20. The method of claim 19, wherein the carbon nanotubes are cylindrical carbon hollow bodies having a diameter of 0.4 to 100 nm which were additionally doped with nitrogen during the production thereof.

21. The method of claim 13, wherein the catalyst comprises one or more metals selected from the group comprising: Ru, Pt, Ni, Os, Rh, Ir, Pd, and also Au, Ni, Cu, Fe and Co.

22. The method of claim 13, wherein a base is used as co-catalyst.

23. The method of claim 22, wherein the base is an alkali metal hydroxide or an alkaline earth metal hydroxide.

24. The method of claim 23, wherein the base is selected from the group comprising: (NaOH), KOH, LiOH, Mg(OH).sub.2, Ca(OH).sub.2, Sr(OH).sub.2 and Ba(OH).sub.2.

25. The method of claim 13, wherein the conversion is effected at a reaction temperature in the range from 20 C. to approximately 400 C.

26. The method of claim 13, wherein the conversion is effected at a reaction temperature in the range between 170 C. to approximately 200 C.

27. The method of claim 13, wherein the hydrogenolysis is effected at a hydrogen pressure in the range from approximately 1 bar to approximately 300 bar.

28. The method of claim 13, wherein the hydrogenolysis is effected at a hydrogen pressure in the range from 50 bar to approximately 80 bar.

Description

[0039] The present invention is described in more detail below on the basis of exemplary embodiments with reference to the accompanying drawings. In the figures:

[0040] FIG. 1 shows the product formation over time for N-600,5-Ru (conditions: T=200 C., p(H.sub.2)=80 bar, m(cat)=0.1563 g, m(xylitol)=1.50 g, m(Ca(OH).sub.2)=0.225 g, 15 ml H.sub.2O);

[0041] FIG. 2 shows the product formation over time for CRu;

[0042] FIG. 3 shows a comparison of the catalysts (conditions: T=200 C., p(H.sub.2)=80 bar, m(Ru)=0.01 g, m(xylitol)=1.50 g, m(Ca(OH).sub.2)=0.225 g, 15 ml H.sub.2O);

[0043] FIG. 4 shows screening of metals on nitrogen-containing carbons (conditions: T=200 C., p(H.sub.2) =80 bar, m(M)=5 mg, m(xylitol)=1.00 g, m(Ca(OH).sub.2)=0.150 g, 10 ml H.sub.2O);

[0044] FIG. 5 shows the temperature and pressure variation for Ru/N-900-C (conditions: m(Ru)=5 mg, m(xylitol)=1 g, m(Ca(OH).sub.2)=0.150 g, 10 ml H.sub.2O);

[0045] FIG. 6 shows the hydrogenolysis of sorbitol over N-900,5-Ru (conditions: T=200 C., p(H.sub.2)=80 bar, m(Ru)=5 mg, m(sorbitol)=1.20 g, m(Ca(OH).sub.2)=0.150 g, 10 ml H.sub.2O).

EXAMPLE 1: PRODUCTION OF NITROGEN-CONTAINING CARBON SUPPORTS (NC)

[0046] The example illustrates the production of nitrogen-doped carbon supports. 5 g of activated carbon are admixed with 35 ml of HNO.sub.3 (30%) and refluxed for 8 h. The carbon is subsequently washed to neutral with water and dried. 1 g of the oxidized carbon is placed into a 50 ml autoclave charged with 8 bar of NH.sub.3 and 52 bar of N.sub.2. The autoclave is heated to 200 C. while stirring. The reduction of the carbon takes place over 4 h. For the carbon support described (NHNO.sub.3), a nitrogen content of 5.54% results according to CHN analysis. If the support is subsequently reduced further with hydrogen for 7 h at 350 C. (NHNO.sub.3, H.sub.2), a nitrogen content of 4.65% results. In this way, however, the proportion of oxygen on the carbon is also reduced. The sum total of C, H and N is now 91.50%, whereas in the case of NHNO.sub.3 it is 84.62%.

[0047] A different way of doping carbon supports with nitrogen is reduction with gaseous ammonia. Temperatures of between 600 and 900 C. and times of 1 to 5 h are chosen for the reduction and various carbons are obtained. The use of commercial nitrogen-doped carbon nanotubes (N-CNT) is also possible. Prior to use, the NCNTs are heated under reflux with 10% by weight of HCl for 2 h. They are subsequently washed to neutral with water and dried. A summary of the nitrogen contents obtained for the various carbon supports is given in table 1.

EXAMPLE 2: IMPREGNATION OF THE SUPPORT

[0048] The example illustrates the loading of a nitrogen-containing carbon support with a noble metal. Ruthenium is used by way of example. 500 mg of the carbon supports produced are each added, together with 75.72 mg of dichloro(p-cymene)ruthenium(II) dimer, to 145 ml of ethanol and coordinated in an oil bath under protective gas at 60 C. The coordination is terminated after 71 hours and the catalyst is filtered off. The maximum possible loading with ruthenium by this method is 5% by weight. The uncoordinated ruthenium in the solvent is analyzed by means of ICP MS and the loading of the catalyst is determined therefrom by calculation. The loading does not correlate with the nitrogen content and can be seen in table 1.

EXAMPLE 3: HYDROGENOLYSIS OF XYLITOL

[0049] By way of example, the example illustrates the hydrogenolysis of sugars and sugar alcohols on the basis of the use of xylitol (Xyl). The hydrogenolysis is effected at 200 C. and 80 bar hydrogen pressure in a 50 ml autoclave. 1.50 g of xylitol, 0.225 g of Ca(OH).sub.2 and 15 ml of water are added to the autoclave. In addition, an amount of catalyst sufficient for there to be 7.5 mg of Ru in the reaction solution is added. For the catalyst N-800,1-Ru there is thus an amount of 0.1563 g, for Ru/C (CRu) there is 0.1500 g. The reaction was conducted over 3 to 4 h. Samples were taken at regular intervals in order to obtain kinetics. The product formation over time for N-600,5-Ru and CRu is shown in FIGS. 1 and 2. The desired products ethylene glycol (EG) and propylene glycol (PG) are formed as main products. Glycerol (Gly) and lactic acid (LA) are formed only in small amounts as by-products.

[0050] For all nitrogen-containing catalysts, EG (ethylene glycol) and PG (propylene glycol) are formed as main products under these conditions. The sum total of the two selectivities (S(Glycols)) in either case reaches above 67% for nitrogen-doped supports. However, for CRu, decomposition of the products can be observed in the case of a longer reaction time as a result of undesirable side-reactions (FIG. 2). A comparison of the catalysts is shown in FIG. 3. The maximum obtained glycol selectivity is 83% (N-600,5-Ru). Numerical values can be found in table 1.

TABLE-US-00001 TABLE 1 Prepared carbon supports, nitrogen content, metal loading and hydrogenolysis results. Carbon Nitrogen Ru loading/% Reaction S(EG)/ S(PG)/ X(Xyl)/ support content/% by weight time/h % % % N-600,1 0.49 4.43 3 38 36 70 N-600,5 0.56 4.80 3 43 40 76 N-800,1 1.64 3.36 1 37 30 52 N-800,5 1.91 3.35 2 38 36 89 N-900,1 1.41 1.36 3 41 41 94 N-900,5 1.11 5.00 N-HNO.sub.3 5.54 4.80 2 38 40 86 N-HNO.sub.3,H.sub.2 4.65 3.85 3 36 38 91 N-CNT 4.20 4.99 1 32 42 21 C 0.00 5.00 1 31 29 86

EXAMPLE 4: SCREENING OF METALS ON NITROGEN-CONTAINING CARBONS

[0051] The metals Ni, Pt and Ru are compared. They were loaded onto the support N-800,5. Impregnation was effected in a manner equivalent to example 2. After loading, N-800,5-Pt and N-800,5-Ni were reduced in a stream of hydrogen. The reduction was effected at 350 C. for 7 h. The hydrogenolysis was effected in a manner equivalent to example 3. The results are presented in FIG. 4 and table 2. It is clearly apparent that the catalytic activity for N-800,5-Pt and N-800,5-Ni decreases, yet the selectivities for glycols obtained are unchanged and high.

TABLE-US-00002 TABLE 2 Screening of metals on nitrogen-containing carbons metal loading, hydrogenolysis results. Metal Reaction loading/ time/ S(EG)/ S(PG)/ X(Xyl)/ Catalyst % h % % % N-800, 5-Ru 3.35 0.5 37 31 39 N-800, 5-Pt 4.99 2 40 41 14 N-800, 5-Ni 2.41 3 34 42 4

EXAMPLE 5: COMPARISON WITH THE LITERATURE

[0052] The results of the hydrogenolysis of sugars and sugar alcohols from the present invention are compared hereafter with other catalysts and processes from the relevant prior art in respect of product selectivity and catalyst activity. The comparison is made under similar conditions and using similar substrates (see table 3).

TABLE-US-00003 TABLE 3 Comparison of the present invention with the prior art. Cat.: T/ p(H.sub.2)/bar, S(Glycols)/ Ref. Substrate Catalyst Base Sub C. RT t/h X/% % [1] sorbitol Ni-Re/C KOH 1:10 220 83 4 56 46 [2] xylitol Ru/C KOH 1:0.8 230 12 45 73 [3] xylitol Ni-Re/C KOH 1:10 200 83 50 65 * xylitol Ru/N-C Ca(OH).sub.2 1:10 200 80 3 76 83 *present invention

[0053] [1] T. Werpy, J. Frye, A. Zacher, D. Miller, US20030119952 A1, 2003. [2] S. P. Chopade, D. J. Miller, J. E. Jackson, T. A. Werpy, J. G. Frye, Jr., A. H. Zacher, WO2001066499, 2001. [3] J. G. Frye, D. J. Miller, T. A. Werpy, A. H. Zacher, WO2003035593 B1, 2003.

EXAMPLE 6: TEMPERATURE AND PRESSURE VARIATION FOR Ru/NC

[0054] A variation of the temperature and pressure was conducted for the catalyst N-900-Ru. In addition to 200 C., 170 C. was also used, and in addition to 80 bar H.sub.2, 50 bar H.sub.2 was also used. The hydrogenolysis was conducted in a manner equivalent to example 3 and the results are presented in a comparative manner in FIG. 5 and table 4. The reaction proceeds more slowly for lower temperatures. It is difficult to compare the selectivities, since comparison at an identical conversion is not possible. Nevertheless, glycols remain the main products of the reaction.

TABLE-US-00004 TABLE 4 Prepared carbon supports, nitrogen content, metal loading and hydrogenolysis results. Catalyst Reaction time/h p/h T/ C. S(EG)/% S(PG)/% X(Xyl)/% N-900,1-Ru 0.5 80 200 31 28 51 N-900,5-Ru 1 80 170 23 17 17 N-900,5-Ru 1 50 200 17 23 20

EXAMPLE 7: HYDROGENOLYSIS OF SORBITOL

[0055] The example illustrates the hydrogenolysis of sugars and sugar alcohols on the basis of the use of sorbitol (Sor). The hydrogenolysis is effected at 200 C. and 80 bar hydrogen pressure in a 50 ml autoclave. 1.197 g of sorbitol, 0.150 g of Ca(OH).sub.2 and 10 ml of water are added to the autoclave. In addition, an amount of catalyst sufficient for there to be 5 mg of Ru in the reaction solution is added. For the catalyst N-900,5-Ru there is thus an amount of 0.100 g. The reaction was conducted over 3 h. Samples were taken at regular intervals in order to obtain kinetics. The product formation over time for N-900,5-Ru is shown in FIG. 6. The selectivity for EG after 2 h of reaction is 18%, the selectivity for PG is 30%.

[0056] Comparative experiments were conducted within the context of the present invention in which carbon nanotubes that were not doped with nitrogen were used as catalyst supports. Here, conditions comparable to those in the aforementioned examples according to the invention were used. It was determined that the catalyst supports according to the invention are superior here, since they have an influence on the selectivities for the target products.

[0057] Comparative experiments were conducted within the context of the present invention in which activated carbon that was not doped with nitrogen was used as catalyst support. Here, conditions comparable to those in the aforementioned examples according to the invention were used. It was determined that the catalyst supports according to the invention are superior here, since the nitrogen doping has a dramatic, positive influence on the selectivities for the target products. In addition, decomposition of the products (e.g. in the case of Ru/C vs Ru/NC) is significantly slowed/reduced by means of the nitrogen doping of the carbon support.