Preparation of HMF catalyzed by a mixture of salt and acid

Abstract

The present invention relates to a method for the production of 5-hydroxymethylfurfural (HMF), which converts a fructose-containing component using a catalyst system comprising a solution of a salt and acid mixture at a temperature of 90 to 200° C. and leads to obtaining an HMF-containing product mixture, wherein advantageously a high HMF selectivity with significantly lower by-product formation is achieved at the same time.

Claims

1. A method for the production of 5-hydroxymethylfurfural (HMF) comprising the following steps: a) providing a fructose-containing component and a catalyst system comprising a solution of a salt and acid mixture, b) mixing the fructose-containing component with the catalyst system to obtain a reaction solution, c) converting the fructose present in the reaction solution to HMF at a temperature of 90° C. to 200° C. to obtain a liquid HMF-containing product mixture and d) obtaining a liquid HMF-containing product mixture, wherein no organic solvent is used in steps a) to d) and the salt is an alkaline or alkaline earth metal salt.

2. The method according to claim 1, wherein the acid is a mineral acid and/or an organic acid and the salt is a salt of a mineral acid and/or an organic acid.

3. The method according to claim 1, wherein the mineral acid is selected in particular from the group consisting of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid; and the organic acid is selected in particular from the group consisting of acetic acid, citric acid, tartaric acid, oxalic acid, glycolic acid and gluconic acid.

4. The method according to claim 1, wherein the salt of a mineral acid is selected from the group consisting of alkaline halides, alkaline earth halides, alkaline nitrates, alkaline earth nitrates, alkaline sulfates, alkaline earth sulfates, alkaline phosphates, alkaline earth phosphates and mixtures thereof; and the salt of an organic acid is selected in particular from the group consisting of acetates, citrates, tartrates, oxalates, glycolates, gluconates and mixtures thereof.

5. The method according to claim 1, wherein the concentration of the salt and acid mixture is 0.01 to 2.00 wt.-% (based on the total weight of the reaction solution obtained in method step b)).

6. The method according to claim 1, wherein the pH of the reaction solution obtained in method step b) is 1.2 to 4.5.

7. They method according to claim 1, wherein in method step b) a reaction solution with a carbohydrate content of 5 to 50 wt.-% (dry matter carbohydrate in relation to the total weight of the reaction solution) is obtained and used in method step c).

8. The method according to claim 1, wherein in method step b) a reaction solution with a fructose content of 40 to 100 wt.-% (dry matter fructose in relation to dry matter carbohydrate) is obtained and used in method step c).

9. The method according to claim 1, wherein the fructose-containing component is a solid fructose-containing component, in particular fructose, or a liquid fructose-containing component, in particular a fructose syrup or a fructose solution.

10. The method according to claim 1, wherein the ratio of salt to free acid in the reaction solution obtained in method step b) is 0.8 to 10 (mol/mol).

11. The method according to claim 1, wherein the ratio of anions of the salt and acid mixture to cations of the salt of the salt and acid mixture in the reaction solution obtained in method step b) is 0.5 to 4 (mol/mol).

12. The method according to claim 1, wherein the concentration of anions of the catalyst system in the reaction solution obtained in method step b) is 1×10.sup.−5 to 0.6 mol/L.

13. The method according to claim 1, wherein the fructose-containing component provided in method step a), the catalyst system or both are set to a temperature of 90° C. to 200° C. before method step b) or wherein the reaction solution obtained in method step b) is set to a temperature of 90° C. to 200° C.

14. The method according to claim 1, wherein the process is carried out such that a fructose conversion of 1 to 50 mol-% is achieved in method step c).

15. The method according to claim 1, wherein the method is set so that in method step c) an HMF selectivity of 60 to 100 mol-% is obtained.

16. The method according to claim 1, wherein apart from the catalyst system, no further catalytically active component is used in the process.

17. The method according to claim 1, comprising the following step: e) cooling the liquid HMF product mixture to a temperature of 20° to 80° C.

18. The method according to claim 1, comprising the following step: f) filtration, decolorization and/or purification of the liquid HMF product mixture.

19. The method according to claim 1, comprising the following step: g) setting the liquid HMF product mixture to a dry matter content of 20 to 70 wt.-%.

20. The method according to claim 1, comprising the following steps: h) purification of the liquid HMF product mixture using chromatography, ultra- and/or nanofiltration, extraction with a suitable extractant, adsorption on a suitable material and subsequent targeted desorption and/or electrodialysis to separate at least one HMF fraction, and i) obtaining at least one HMF fraction.

21. The method according to claim 20, wherein the liquid HMF product mixture is separated in step h) using chromatography into at least four fractions comprising an HMF fraction, a glucose fraction, a fructose fraction and an organic acid fraction, and in step i) at least an HMF fraction, a glucose fraction, a fructose fraction and an organic acid fraction are obtained.

22. The method according to claim 21, wherein the fructose fraction obtained in method step i) is recycled into step a).

23. The method according to claim 21, wherein the glucose fraction obtained in method step i) is used for the production of ethanol.

24. The method according to claim 21, wherein the organic acid fraction obtained in method step i) is used to isolate levulinic and formic acid.

25. The method according to claim 21, wherein the HMF fraction obtained in method step i) is oxidized directly and is oxidized in a further step to 2,5-furandicarboxylic acid (FDCA) without the need for further purification.

Description

(1) The invention is explained in more detail with reference to the following exemplary embodiments and the associated figures.

(2) The figures show:

(3) FIG. 1 is a schematic representation of the reactor system used according to the invention.

(4) FIG. 2 is a schematic representation of the method according to the invention, wherein the components provided in step a) are initially mixed in step b) and the reaction solution obtained is subsequently heated and an HMF fraction is obtained after the purification step h) (step i)).

(5) FIG. 3 is a schematic representation of the method according to the invention analogous to FIG. 2, wherein in step h) a column chromatographic separation is carried out and an HMF fraction, a glucose fraction, a fructose fraction and an organic acid fraction are obtained (step i)).

(6) FIG. 4 is a schematic representation of the method according to the invention, wherein the components provided in step a) are heated separately from one another and only subsequently mixed in step b) to obtain a reaction solution, and wherein an HMF fraction is obtained after purification step h) (step i)).

(7) FIG. 5 is a schematic representation of the method according to the invention analogous to FIG. 4, wherein a column chromatographic separation is carried out in step h) and an HMF fraction, a glucose fraction a fructose fraction and an organic acid fraction are obtained (step i)).

(8) FIG. 6 shows the results of the HMF synthesis with 20% DM KH (85% fructose purity) and 0.08 wt.-% HCl without the addition of salt at temperatures of 145-152° C. Fructose conversion, HMF, levulinic acid and formic acid selectivity and the balance are represented.

(9) FIG. 7 shows the results of the HMF synthesis with 20% DM KH (85% fructose purity) and 0.18 wt.-% HNO.sub.3 without addition of salt at temperatures of 145-152° C. Fructose conversion, HMF, levulinic acid and formic acid selectivity and the balance are represented.

(10) FIG. 8 shows the reaction temperatures which are necessary for a fructose conversion of ˜18% as a function of the sodium content with a constant chloride content as well as HMF, levulinic acid and formic acid selectivities and the balance at this point.

(11) FIG. 9 shows the reaction temperatures necessary for a fructose conversion of ˜20% as a function of the sodium content with a constant nitrate content as well as HMF, levulinic acid and formic acid selectivities and the balance at this point.

(12) FIG. 10 shows the reaction temperatures necessary for a fructose conversion of ˜20% as a function of the concentration of the salt and acid mixture with a constant chloride/sodium ratio as well as HMF, levulinic acid and formic acid selectivities and the balance at this point.

(13) FIG. 11 shows the reaction temperatures necessary for a fructose conversion of ˜27% as a function of the concentration of the salt and acid mixture with a constant nitrate/sodium ratio as well as HMF, levulinic acid and formic acid selectivities and the balance at this point.

(14) FIG. 12 shows the HMF synthesis with 20% DM KH (85% fructose purity) and 0.12 wt.-% HCl/CaCl.sub.2 at temperatures of 165-169° C. Fructose conversion, HMF, levulinic acid and formic acid selectivity and the balance are represented.

(15) FIG. 13 shows the HMF synthesis with 20% DM KH (85% fructose purity) and 0.12 wt.-% HCl/MgCl.sub.2 at temperatures of 162-169° C. Fructose conversion, HMF, levulinic acid and formic acid selectivity and the balance are represented.

EXAMPLES

(16) In the method according to the invention, a fructose-containing component which has a variable ratio of fructose to glucose and an aqueous solution of a salt and acid mixture are used as starting materials. The fructose-containing component is mixed with the aqueous solution of a salt and acid mixture so that a reaction solution with a dry matter content of ≥20% DM is obtained. The reaction solution obtained in this way was pumped into the heated tubular reactor (outer diameter 8 mm, inner diameter 6 mm, length 630 mm) with the aid of an HPLC pump. The tubular reactor is designed as a double tube heat exchanger in counterflow, the temperature is controlled by means of a thermal oil in the outer jacket of the heat exchanger, the temperature of the thermal oil is controlled by a thermostat. After this so-called heating zone of the tubular reactor, the transition to the cooling zone occurs directly. This is also designed as a double-tube heat exchanger in counterflow (dimensions of the product-carrying inner tube: outer diameter 8 mm, inner diameter 6 mm, length 125 mm). The reaction solution is cooled to room temperature within the cooling zone and the conversion is stopped. The product mixture is then filtered through a metal sinter filter (pore size 7 μm) and any insoluble humic substances that may have formed are removed. The pressure in the reactor system is set with the aid of a pressure holding valve so that boiling of the reaction solution and thus the occurrence of vapor bubbles is avoided (approx. 1 MPa at 180° C.).

(17) The following examples show the implementation of the method according to the invention with different salts and acids, different acid or salt concentrations, and at different temperatures. Furthermore, comparative experiments were carried out without the addition of salt.

(18) In all experiments, samples were taken during the test and analyzed by means of HPLC (BIORAD Aminex 87-H, 5 mmol/L sulfuric acid, 50° C.). Fructose conversion, HMF selectivity and the balance (balance=(total of unconverted sugar, HMF and formic acid (in mol)*100/sugar used (in mol)) were subsequently calculated from the analytical results. Levulinic acid is not taken into account in the balance, since one molecule of formic acid and one molecule of levulinic acid are produced from one molecule of HMF.

Example 1: HMF Synthesis with 0.08 wt.-% Hydrochloric Acid (Comparative Experiment Without Added Salt)

(19) A fructose syrup with 85% fructose purity and a DM content of 75% was used as starting material. The fructose syrup was diluted with deionized water and mixed with hydrochloric acid so that the resulting solution had a dry matter content of 20% DM and a hydrochloric acid content of 0.08 wt.-% based on the total solution (corresponding to 0.025 mol/L). The pH of the reaction solution was 1.52. This reaction solution was then reacted with a residence time of 5.6 min. in the heating zone at a temperature of 145° C.-152° C. (temperature of the thermal oil). After each temperature increase, the system was given 2 hours to reach steady state. The results on fructose conversion, HMF, levulinic acid and formic acid selectivity and balance are shown in FIG. 6 and Table 1.

(20) TABLE-US-00001 TABLE 1 Fructose conversion, HMF, levulinic acid and formic acid selectivity and balance as a function of the reaction temperature when using 0.08 wt-% of HCl. Temperature Fructose HMF Levulinic acid Formic acid Balance [° C.] conversion [%] selectivity [%] selectivity [%] selectivity [%] [%] 145 13.7 83.0 2.7 5.0 99.6 148 16.9 84.1 3.2 6.8 99.7 150 19.6 85.2 4.6 8.2 98.5 152 23.8 83.3 5.3 8.2 97.8

Example 2: HMF Synthesis with 0.18 wt.-% Nitric Acid (Comparative Experiment Without Added Salt)

(21) A fructose syrup with 85% fructose purity and a DM content of 75% was used as starting material. The fructose syrup was diluted with deionized water and mixed with nitric acid so that the resulting solution had a dry matter content of 20% DM and a nitric acid content of 0.18 wt.-% based on the total solution (corresponding to 0.03 mol/L). The pH of the reaction solution was 1.44. This reaction solution was then converted with a residence time of 5.6 min in the heating zone at a temperature of 145° C.-150° C. (temperature of the thermal oil). After each temperature increase, the system was given 2 hours to reach steady state. The results on fructose conversion, HMF, levulinic acid and formic acid selectivity and balance are shown in FIG. 7 and Table 2.

(22) TABLE-US-00002 TABLE 2 Fructose conversion, HMF, levulinic acid and formic acid selectivity and balance depending on the reaction temperature when using 0.18 wt.-% of HNO.sub.3. Temperature Fructose HMF Levulinic acid Formic acid Balance [° C.] conversion [%] selectivity [%] selectivity [ %] selectivity [%] [%] 145 15.0 85.4 3.6 6.1 98.7 148 19.7 86.3 4.2 7.0 98.0 150 21.1 88.4 5.2 9.8 97.8

(23) Example 3: HMF Synthesis with Sodium Chloride/Hydrochloric Acid Mixtures—Influence of the Sodium Chloride/Hydrochloric Acid Ratio

(24) A fructose syrup with 85% fructose purity and a DM content of 75% was used as starting material. The fructose syrup was diluted with deionized water and mixed with hydrochloric acid and sodium chloride in the desired ratio so that the resulting solution had a dry matter content of 20% DM and a chloride content of 0.09 wt.-% based on the total solution (corresponding to 0.03 mol/L). The chloride/sodium ratios, the salt/acid ratio and the resulting pH values are indicated in Table 3.

(25) TABLE-US-00003 TABLE 3 Chloride contents, chloride/sodium ratio, salt/acid ratio and pH values and reaction temperatures used in the reaction solutions used in Example 3. Ratio Chloride Sodium chloride/ Ratio Reaction content content sodium salt/acid pH temperatures Test [mg/L] [mg/L] [mol/mol] [mol/mol] [—] [° C.] 1 890 0 / / 1.52 145-152 2 890 330 1.75 1.34 1.95 160-168 3 890 400 1.44 2.26 2.24 165-172 4 890 490 1.15 6.48 2.52 169-176

(26) These reaction solutions were then converted with a residence time of 5.6 min. in the heating zone at the reaction temperatures indicated in Table 3 (temperature of the thermal oil). After each temperature increase, the system was given 2 hours to reach steady state.

(27) In FIG. 8 and Table 4, the necessary reaction temperatures and the resulting HMF, levulinic acid and formic acid selectivities and balances are shown in each case at a fructose conversion of ˜18%.

(28) TABLE-US-00004 TABLE 4 HMF, levulinic acid and formic acid selectivity and balance at the reaction temperature necessary for 18% fructose conversion depending on the sodium content (with constant chloride concentration). Sodium Temperature Fructose HMF Levulinic acid Formic acid Balance content [mg/L] [° C.] conversion [%] selectivity [%] selectivity [%] selectivity [%] [%] 0 145 13.7 83.0 2.7 5.0 99.6 (pH 1.52) 148 16.9 84.1 3.2 6.8 99.7 150 19.6 85.2 4.6 8.2 98.5 152 23.8 83.3 5.3 8.2 97.8 330 160 17.6 89.9 2.6 5.2 98.6 (pH 1.95) 162 20.7 90.3 2.7 5.6 98.5 165 25.0 92.3 3.3 5.8 98.3 168 32.5 90.1 4.0 6.4 97.9 400 165 15.1 88.3 1.2 1.5 98.9 (pH 2.24) 167 17.5 89.3 1.6 2.6 98.7 169 19.9 91.7 1.8 3.5 98.5 172 24.8 91.1 2.6 3.7 98.0 500 169 11.52 89.5 0.8 2.0 99.1 (pH 2.52) 172 15.98 90.3 1.0 2.4 98.9 174 18.91 94.1 1.1 2.9 98.7 176 22.63 92.5 1.2 4.1 98.5

(29) It is found that with increasing sodium content and thus increasing pH, a higher temperature is necessary to achieve the same conversion (see FIG. 6), but at the same time the selectivity achieved for HMF increases from 85% without sodium up to 94% at 500 mg/L sodium.

Example 4: HMI Synthesis with Sodium Nitrate/Nitric Add Mixtures—Influence of the Sodium Nitrate/Nitric Acid Ratio

(30) A fructose syrup with 85% fructose purity and a DM content of 75% was used as starting material. The fructose syrup was diluted with deionized water and mixed with nitric acid and sodium nitrate in the desired ratio so that the resulting solution had a dry matter content of 20% DM and a nitrate content of 0.19 wt.-% based on the total solution (corresponding to (0.03 mol/L). The nitrate/sodium ratios, the salt/acid ratio and the resulting pH values are indicated in Table 5.

(31) TABLE-US-00005 TABLE 5 Nitrate contents, nitrate/sodium ratio, salt/acid ratio and pH values and reaction temperatures used for the reaction solutions used in Example 4. Nitrate/ Nitrate Sodium- sodium Salt/ Reaction content content ratio acid ratio temperatures Test [mg/L] [mg/L] [mol/mol] [mol/mol] pH [° C.] 1 1900 0 / / 1.44 145-155 2 1900 320 2.23 0.83 1.71 155-160 3 1900 450 1.57 1.77 1.86 155-165 4 1900 510 1.38 2.62 2.05 162-172 5 1900 600 1.17 5.74 2.50 160-178

(32) These reaction solutions were then converted with a residence time of 5.6 min. in the head zone at the reaction temperatures indicated in Table 5 (temperature of the thermal oil). After each temperature increase, the system was given 2 hours to reach steady state.

(33) In FIG. 9 and Table 6, the necessary reaction temperatures and the resulting HMF, levulinic acid and formic acid selectivities and the balances are shown in each case with a fructose conversion of ˜20%.

(34) Here, too, it can be seen that with increasing sodium content and thus increasing pH, a higher temperature is necessary in order to achieve the same conversion, but at the same time the selectivity to HMF increases significantly from 86.3% (at 19.7% conversion) without sodium to 93.1% (at 17.6% conversion) at 600 mg/L sodium. The selectivities for the byproducts levulinic and formic acid are also lower in the presence of sodium, if the same conversions are compared.

(35) TABLE-US-00006 TABLE 6 HMF, levulinic acid and formic acid selectivity and carbon balance at the reaction temperature required for 18% fructose conversion, depending on the sodium content (with constant nitrate concentration). Sodium Temperature Fructose HMF Levulinic acid Formic acid Balance content [mg/L] [° C.] conversion [%] selectivity [%] selectivity [%] selectivity [%] [%] 0 145 15.0 85.4 3.6 6.1 98.7 (pH 1.4) 148 19.7 86.3 4.2 7.0 98.0 150 21.1 88.4 5.2 9.8 97.8 320 155 19.1 88.3 2.9 4.9 98.6 (pH 1.7) 157 21.8 88.9 3.4 5.3 98.7 160 26.8 90.0 4.5 7.8 98.8 450 155 14.3 86.9 1.9 3.2 98.5 (pH 1.9) 157 16.1 90.7 2.8 4.3 98.7 160 19.7 92.9 3.2 6.7 98.9 162 22.0 94.7 3.7 7.3 98.8 165 30.5 89.1 4.5 6.8 98.4 510 162 15.4 89.7 1.7 2.9 98.7 (pH 2.1) 165 19.9 92.5 2.3 4.5 98.8 169 25.7 92.8 3.1 5.3 98.8 172 33.7 89.4 3.5 6.0 97.9 600 160 4.4 87.6 0.00 0.00 99.3 (pH 2.50) 165 8.0 88.0 1.2 2.9 99.6 169 10.8 93.0 1.5 2.2 99.4 174 17.6 93.1 1.9 4.0 99.4 178 24.0 93.0 2.1 5.9 99.1

Example 5: HMF Synthesis with Hydrochloric Acid/Sodium Chloride Mixtures—Influence of the Concentration of the Acid/Salt Mixture

(36) A fructose syrup with 85% fructose purity and a DM content of 75% was used as starting material. The fructose syrup was diluted with deionized water and mixed with a mixture of hydrochloric acid and sodium chloride, which had a chloride/sodium ratio of 1.3. Various reaction solutions were prepared, all of which had a dry matter content of 20% DM and a variable acid/salt mixture concentration between 0.01 and 0.75 wt.-% based on the total solution.

(37) These reaction solutions were then reacted with a residence time of 5.6 min. in the heating zone at the reaction temperatures indicated in Table 7 (temperature of the thermal oil). After each temperature increase, the system was given 2 hours to reach steady state.

(38) TABLE-US-00007 TABLE 7 Concentration of the hydrochloric acid/sodium chloride mixture, pH values and reaction temperatures of the reaction solutions used in Example 5. Concentration of the acid/sait mixture pH Test (HCl/NaCl) [wt.-%] [—] Reaction-temperatures [° C.] 1 0.01 3.34 169-180 2 0.12 2.29 165-172 3 0.45 1.72 153-159 4 0.75 1.51 150-152

(39) In FIG. 10 and Table 8, the necessary reaction temperatures and the resulting HMF, levulinic acid and formic acid selectivities and the balances are shown for a fructose conversion of ˜20%.

(40) TABLE-US-00008 TABLE 8 HMF, levulinic acid and formic acid selectivity as well as balance at different reaction temperatures depending on the concentration of the acid/salt mixture with a constant chloride/sodium ratio. Concentration of HCl/NaCl Temperature Fructose HMF Levulinic acid Formic acid Balance mixture [wt.-%] [° C.] conversion [%] selectivity [%] selectivity [%] selectivity [%] [%] 0.01 169 4.6 91.4 0.0 0.0 99.5 (pH 3.34) 172 4.9 91.5 0.0 0.0 99.4 176 7.8 92.5 0.0 3.0 99.4 180 12.7 92.3 0.0 1.8 99.3 0.12 165 13.7 89.2 1.3 1.7 98.8 (pH 2.29) 169 19.3 90.4 1.4 3.6 98.4 172 24.9 90.1 1.8 3.7 98.3 0.45 153 18.3 91.9 3.0 5.1 98.6 (pH 1.72) 155 21.4 91.9 3.4 5.4 98.7 157 25.2 91.3 3.7 5.5 98.4 159 29.6 90.3 4.3 6.3 98.0 0.75 150 23.6 91.7 4.3 6.8 98.3 (pH 1.51) 152 31.3 89.7 5.2 8.1 97.9

(41) With increasing salt concentration, significantly lower temperatures are necessary to achieve the same conversion. It can also be seen that the high HMF selectivities of ˜90% are still achieved even with high fructose conversions of >30%.

Example 6: HMF Synthesis with Nitric Acid/Sodium Nitrate Mixtures—Influence of the Concentration of the Acid/Salt Mixture

(42) A fructose syrup with 85% fructose purity and a DM content of 75% was used as starting material. The fructose syrup was diluted with deionized water and mixed with a mixture of nitric acid and sodium nitrate, which had a nitrate/sodium ratio of 1.2. Various reaction solutions were prepared, all of which had a dry matter content of 20% DM and a variable acid/salt mixture concentration between 0.01 and 1.5 wt.-% based on the total solution. These reaction solutions were then reacted with a residence time of 5.6 min. in the heating zone at the reaction temperatures indicated in Table 9 (temperature of the thermal oil). After each temperature increase, the system was given 2 hours to reach steady state.

(43) TABLE-US-00009 TABLE 9 Concentration of the nitric acid/sodium nitrate mixture, pH values and reaction temperatures of the reaction solutions used in Example 5. Concentration of the acid/salt mixture pH Test (HNO.sub.3/NaNO.sub.3) [wt.-%] [—] Reaction-temperatures [° C.] 1 0.01 3.34 169-180 2 0.22 2.29 165-172 3 0.75 1.93 150-152 4 1.5 1.62 155-165

(44) In FIG. 11 and Table 10, the necessary reaction temperatures and the resulting HMF, levulinic acid and formic acid selectivities and the balances are shown for a fructose conversion of ˜27%.

(45) TABLE-US-00010 TABLE 10 HMF, levulinic acid and formic acid selectivity as well as balance at different reaction temperatures depending on the concentration of the acid/salt mixture with a constant nitrate/sodium ratio. Concentration of HNO.sub.3/NaNO.sub.3 Temperature Fructose HMF Levulinic acid Formic acid Balance mixture [wt.-%] [° C.] conversion [%] selectivity [%] selectivity [%] selectivity [%] [%] 0.01 165 2.2 86.1 0.0 0.0 99.7 (pH 3.34) 172 4.9 87.6 0.0 0.0 99.8 176 7.5 91.6 0.0 1.5 99.5 180 12.2 91.0 0.0 1.9 99.6 0.22 169 14.2 91.1 1.7 3.6 99.4 (pH 2.29) 172 18.3 91.6 1.3 2.4 99.5 174 21.8 92.6 1.0 2.5 99.3 174 24.1 94.8 1.4 3.2 98.4 178 27.6 93.2 1.7 3.2 97.9 0.75 165 27.5 93.8 3.2 5.5 98.3 (pH 1.93) 169 37.9 90.1 4.1 7.3 97.4 1.5 155 24.6 93.2 4.1 6.6 98.0 (pH 1.62) 157 28.4 93.2 4.7 7.7 97.9 165 46.7 88.9 6.3 9.8 97.1

(46) With increasing salt concentration, significantly lower temperatures are necessary to achieve the same conversion. It can also be seen that the high HMF selectivity of ˜90% can still be achieved even with high fructose conversions of >37%. Even with a fructose conversion of ˜47%, an HMF selectivity of ˜89% is still achieved.

Example 7: HMF Synthesis with 0.11 wt.-% Hydrochloric Acid/Calcium Chloride Mixture

(47) A fructose syrup with 85% fructose purity and a DM content of 75% was used as starting material. The fructose syrup was diluted with deionized water and mixed with a mixture of hydrochloric acid and calcium chloride, which resulted in the same amount of free acid as in Example 5 with 0.12 wt.-% HCl/NaCl, Table 7, Test 2. The pH of the reaction solution was 2.08. This reaction solution was then reacted with a residence time of 5.6 min. in the heating zone at a temperature of 165° C.-169° C. (temperature of the thermal oil). After each temperature increase, the system was given 2 hours to reach steady state. The results on fructose conversion, HMF, levulinic acid and formic acid selectivity and balance are shown in FIG. 12 and Table 11.

(48) TABLE-US-00011 TABLE 11 Fructose conversion, HMF, levulinic acid and formic acid selectivity and carbon balance as a function of the reaction temperature when using 0.12 wt.-% HCl/CaCl.sub.2. Temperature Fructose HMF Levulinic acid Formic acid Balance [° C.] conversion [%] selectivity [%] selectivity [%] selectivity [%] [%] 165 21.2 92.5 1.7 3.3 98.5 167 23.8 93.4 2.3 3.9 98.2 169 27.2 93.5 2.7 5.1 98.2

Example 8: HMF Synthesis with 0.12 wt.-% Hydrochloric Acid/Magnesium Chloride Mixture

(49) A fructose syrup with 85% fructose purity and a DM content of 75% was used as starting material. The fructose syrup was diluted with deionized water and mixed with a mixture of hydrochloric acid and magnesium chloride, which resulted in the same amount of free acid as in Example 5 with 0.12 wt.-% HCl/NaCl, Table 7, Test 2. The pH of the reaction solution was 2.09. This reaction solution was then converted with a residence time of 5.6 min. in the heating zone at a temperature of 162° C.-169° C. (temperature of the thermal oil). After each temperature increase, the system was given 2 hours to reach steady state. The results on fructose conversion, HMF, levulinic acid and formic acid selectivity and balance are shown in FIG. 13 and Table 12.

(50) TABLE-US-00012 TABLE 12 Fructose conversion, HMF, levulinic acid and formic acid selectivity as well as the balance depending on the reaction temperature when using 0.12 wt.-% HCl/MgCl.sub.2. Temperature Fructose HMF Levulinic acid Formic acid Balance [° C.] conversion [%] selectivity [%] selectivity [%] selectivity [%] [%] 162 15.7 91.3 1.7 2.9 98.6 164 18.6 91.4 2.0 3.7 98.5 167 23.1 91.8 2.4 5.0 98.4 169 27.8 90.5 3.0 5.0 97.9

(51) Examples 7 and 8 show that the positive effects with regard to the high HMF selectivities are also achieved when using other cations (here calcium and magnesium).