Conversion and purification of biomass

Abstract

The present invention relates to a method for synthesizing an optionally substituted furoic acid by dehydrating a biomass and oxidizing the optionally substituted furan derived from the dehydration reaction. Water extraction has been incorporated as a step between the dehydration and the oxidation in order to purify the intermediate optionally substituted furan before having it oxidized. Prior to this water extraction, the organic solvent used for dehydration may be separated by evaporation. The provision of the water extraction allows impurities to be separated from the intermediate optionally substituted furan.

Claims

1. A method for synthesizing an optionally substituted furoic acid, comprising: converting a biomass to an optionally substituted furan, wherein said furan is unsubstituted or substituted by at least one C.sub.1-C.sub.10-alkyl-OH group, via a dehydration reaction in the presence of an organic solvent; purifying the optionally substituted furan by first evaporating the organic solvent from the optionally substituted furan produced from said dehydration reaction to obtain a solid residue or an aqueous slurry, followed by adding water to the residue or aqueous slurry for extraction of the optionally substituted furan with water, collecting the supernatant separately from the residue; and oxidizing the extracted optionally substituted furan to form the optionally substituted furoic acid.

2. The method according to claim 1, wherein the water extraction is repeated several times and the extracts containing the optionally substituted furan are combined.

3. The method according to claim 1, wherein said dehydration reaction is an acid catalyzed dehydration reaction.

4. The method according to claim 1, wherein said optionally substituted furan is 5-(hydroxymethyl)furfural.

5. The method according to claim 1, wherein said organic solvent is selected from the group consisting of alcohols, ketones, tetrahydrofuran, -valerolactone and mixtures thereof.

6. The method according to claim 5, wherein the organic solvent is selected from the group consisting of isopropanol, 1-butanol and methyl isobutyl ketone.

7. The method according to claim 5 which comprises an ionic liquid as the co-solvent used in the dehydration reaction.

8. The method according to claim 1, wherein the oxidization of the optionally substituted furan is carried out in the presence of oxygen, a catalytic system and optionally a base.

9. The method according to claim 8, wherein said catalytic system is a supported catalytic system comprising gold/hydrotalcite, gold-palladium/hydrotalcite or platinum/carbon.

10. The method according to claim 8, wherein said catalytic oxidation is carried out for about 1 to 3 hours at about 30 to 70 C.

11. The method according to claim 8, wherein said catalytic oxidation is further carried out for 4 to 10 hours at 80 to 110 C.

12. The method according to claim 1, wherein said biomass is Jerusalem artichoke.

13. The method according to claim 1, wherein said biomass comprises a carbohydrate.

14. The method according to claim 1, wherein said optionally substituted furoic acid is 2,5-furandicarboxylic acid.

15. The method according to claim 1, wherein said optionally substituted furoic acid is 5-hydroxymethyl-2-furancarboxylic acid.

16. The method according to claim 2, wherein the water extraction is repeated for 2 to 3 times.

17. The method according to claim 3, wherein said acid catalyzed dehydration reaction occurs in the presence of a mono-phase solvent system or a biphasic solvent system.

18. The method according to claim 5, wherein the organic solvent is isopropanol.

19. The method according to claim 7, wherein said ionic liquid is water.

20. The method according to claim 13, wherein said carbohydrate is selected from the group consisting of cellulose, fructose and glucose.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The accompanying drawings illustrate a disclosed embodiment and serve to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

(2) FIG. 1 depicts an as synthesized HMF isopropanol solution (left vial), raw HMF product after evaporation of solvent (middle vial) and HMF re-dissolved in water (right vial).

(3) FIG. 2 depicts a plot of the number of extraction against the HMF recovery rate.

(4) FIG. 3 depicts an integrated process for the conversion of fructose to FDCA.

(5) FIG. 4 shows a plot of the FDCA yield against the number times the Au.sub.8Pd.sub.2/HT catalyst is recycled.

(6) FIG. 5 shows the integrated process for the conversion of JAT biomass to FDCA.

(7) FIG. 6 is a TEM image showing the synthesized Au/HT catalyst.

(8) FIG. 7 shows the X-ray diffraction of the synthesized Au/HT catalyst.

(9) FIG. 8 depicts a H NMR spectrum of the isolated FDCA product.

(10) FIG. 9 depicts HMF treated with 0.1 g of active carbon (left eppendorf tube), HMF treated with 1.0 g of active carbon (middle eppendorf tube) and a purified aqueous solution of HMF in water (right eppendorf tube).

(11) FIG. 10 shows the HPLC testing results for the conversion of HMF to FDCA using Au/HT catalyst without purification for 20 h at 95 C.

(12) FIG. 11 shows the HPLC testing results for the conversion of purified HMF to FDCA using Au/HT catalyst for 7 h at 95 C.

(13) FIG. 12 shows the kinetic studies of converting commercially pure HMF (pure HMF) and purified HMF (water extracted fructose-derived HMF) to FDCA using different catalysts.

(14) FIG. 13 depicts HMF prepared in water/MIBK biphasic system without purification (left vial), and after purification and dissolved in water (right vial).

(15) FIG. 14 shows the Au/HT recyclability test with purified HMF via water extraction.

(16) FIG. 15 shows the Au/HT recyclability test with pure HMF from Aldrich.

(17) FIG. 16 depicts the integrated scheme for the conversion of fructose to FDCA.

DETAILED DESCRIPTION OF DRAWINGS

(18) FIG. 3 depicts an integrated process for the conversion of fructose to FDCA. In this process, D-fructose was first dissolved in isopropanol. Hydrochloric acid was then added as a catalyst for the dehydration reaction to form HMF. The HMF obtained after dehydration was then separated into two equivalent portions.

(19) Using the first portion, the HMF was not purified and undergoes oxidation in the presence of oxygen and Au/HT catalyst. Step 100 depicts the pathway for producing FDCA using this unpurified HMF. Consequently, a mixture of 5-hydroxymethyl-2-furancarboxylic acid (HFCA) and FDCA was obtained as the final product. The FDCA yield was less than 35%.

(20) As for the second portion, the HMF was purified via extraction with water. The purified extracts were then combined. The combined extracts are then subjected to the same oxidation step as described above. Step 102 depicts the pathway for producing FDCA using this purified HMF extracts. Consequently, only FDCA was obtained as the final product. The FDCA yield was about 98%. This means that the overall conversion yield was improved to about 83%.

(21) FIG. 16 shows the integrated scheme for the conversion of fructose to FDCA. Reactor 100 is where the dehydration reaction occurs. Fructose and the various starting reactants, particularly isopropanol and 5% mol HCl, are added into this reactor 100. The isopropanol is added from tank 106. Isopropanol from reactor 100 may be first evaporated to form an aqueous slurry after the dehydration reaction ends. This aqueous slurry containing the crude HMF may have residual traces of isopropanol. This aqueous slurry is then passed through a water extraction tank 102 where water is added from tank 108. The HMF is extracted with the water from the aqueous slurry leaving behind the impurities, namely humins which are not soluble in water. The isopropanol may be recovered from tank 102 and recycled into tank 106. The extracted purified HMF is then transferred to the catalytic oxidation tank 104 to be subjected to air bubbling in the presence of an oxidation catalyst. Optionally, a base may be added to tank 104. FDCA formed from the oxidation of HMF are isolated from the resultant mixture.

EXAMPLES

(22) Non-limiting examples of the invention and a comparative example will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Materials

(23) D-Fructose was from Alfa Aesar. 5-hydroxymethylfurfural (HMF) and 2,5-furandicarboxylic acid (FDCA) were purchased from Sigma-Aldrich. Dry isopropanol and hydrogen chloride (37%) were purchased from Merck. All the chemicals were used directly without any pre-treatment. Au/HT catalyst (hydrotalcite supported gold nanoparticles) was prepared as described below. The Pt/C catalyst (5 wt %) was from Aldrich.

Preparation of Au/HT and Au8Pd2/HT Catalyst

(24) Au/HT catalyst was prepared by known deposition-precipitation method using NH.sub.3 aqueous solution followed by calcination at 473 K (about 199.9 C.).

(25) Au.sub.8Pd.sub.2/HT catalyst was also prepared using the above method. 0.1 mmol of HAuCl.sub.4 and 0.025 mmol of NaPdCl.sub.4 were dissolved in 40 ml water. To this solution, hydrotalcite (1 g) was added, followed by addition of NH.sub.3 aqueous solution (29.5%, 0.425 mL) until pH 10 was reached. The solution was vigorously stirred for 6 h and refluxed for 30 min at 373 K (about 99.9 C.). The resulting solid was filtered, washed thoroughly with water, and heated at 473 K (199.9 C.) overnight.

Reaction Procedure for Producing HMF from Fructose

(26) In a 8 ml thick wall sealed glass tube, 2.5 mmol fructose (0.45 g), 4.85 ml water-free isopropanol, 0.15 ml water (3 vol %), and 10 ul 37% HCl (5 mol %) were added. This solution was purged thoroughly with argon gas for 3 times to remove all possible presence of air. Under magnetic stirring at 700 rpm, the reaction was heated to 120 C. in oil bath for 3 hours. After the reaction, the solution was cooled down using an ice bath. The solution was then diluted in water for HPLC testing. For 1 mmol and 5 mmol of fructose as starting materials, the experiment was conducted in 4 ml and 15 ml sealed glass tube, respectively. The addition of 0.15 ml water is not for dissolving the HCl. This small amount of water serves to increase HMF yield. Notably, water is miscible with isopropanol and forms a single phase solvent system.

Reaction Procedure to Produce HMF from JAT

(27) In a 8 ml thick wall sealed glass tube, 0.3 g dried JAT powder (equivalent to 1.25 mmol fructose), 1.2 ml 0.25 M HCl saturated with NaCl, 4 ml MIBK were added. The solution was purged thoroughly with argon gas 3 times until all the air was removed. Under magnetic stirring at 700 rpm, the reaction was heated to 180 C. in a heating block for 30 minutes. After the reaction, the solution was cooled down with ice and centrifuged. The MIBK layer was taken out for further usage.

Procedure to Purify HMF Via Water Extraction

(28) 1 mmol of HMF original solution in isopropanol was evaporated (90 mbar, 40 C.). The evaporation was completed before adding water for extraction. A dark brown thick liquid of raw HMF product was obtained. 5 ml of water was then added and centrifuged until the dark impurities detached from the water solution and collect as a residue at the bottom and along the bottle's wall. The solution bottle from each of these steps is shown in FIG. 1. The transparent yellowish supernatant was extracted and the black impurities remained on the surface of bottle wall. Another 5 ml of water was put in and rotated for another 15 min and the supernatant was collected. The collected solution was mixed and centrifuged to remove residue, if any, and a transparent yellowish solution was obtained. This water extraction process is very efficient and 99% of HMF was recovered within two rounds of extraction (see FIG. 2). This solution was used for further reaction.

Catalytic Reaction of HMF to FDCA

(29) For this reaction, Na.sub.2CO.sub.3 was used as the base. 1 g of extracted HMF was first dissolved in 5 g of water. The Na.sub.2CO.sub.3 was separately prepared by dissolving Na.sub.2CO.sub.3 in water. The oxidation catalyst was then added follow by the HMF solution at ambient room temperature. With oxygen gas bubbling, the solution was first heated to 50 C. for 2 hours, and HMF was fully converted to HFCA. After that, the reaction was heat to 95 C. and kept for 7 hour. The pH of the aqueous solution was then adjusted to 1 and FDCA was precipitated from the solution. The precipitate was filtered and washed with ethanol.

Product Analysis

(30) HMF and FDCA were analyzed by HPLC (Agilent Technologies, 1200 series) and its isolation yield further ascertained the presence. The isolation yield was obtained by weighing the FDCA product after it was separated from the HMF. The HPLC working conditions are: column (Agilent Hi-Plex H, 7.7300 mm, 8 m), solvent 10 mM H.sub.2SO.sub.4, flow rate 0.7 ml/min, 25 C., UV detector at 280 nm for HMF and 254 nm for FDCA. The retention times for detected compounds were 20.7 min, 24.4 min, 29.4 min and 36.5 min for FDCA, HFCA, FFCA and HMF, respectively. Fructose was measured using a Sugar Analyzer (DKK-TOA Corporation, Japan. Model: SU-300).

Characterization

(31) The FDCA product was characterized by .sup.1H and .sup.13C NMR (Brucker AV-400). The synthesized Au/HT catalyst was characterized by TEM (FEI Tecnai F20) and XRD (PANalytical x-ray diffractometer, X'pert PRO, with Cu K radiation at 1.5406 ). These TEM, XRD and NMR spectra are depicted in FIGS. 6 to 8.

Comparative Example 1

(32) Complete removal of the organic solvent from the HMF solution serves as a key to achieving high quality HMF. This was done by first evaporating isopropanol from the original HMF solution at 90 mbar and 40 C., followed by evaporation at lower vacuum conditions (using a continuous evaporation mode of a rotary evaporator) to completely remove the organic solvent.

(33) Without the latter step, the trace amount of isopropanol that remains in the crude HMF will introduce noticeable impurities to the subsequent water extraction solution, thereby producing a darker coloured aqueous solution and a slower catalytic reaction of HMF to FDCA occurs.

(34) Complete evaporation of the organic solvent may also be achieved by first evaporating isopropanol from the original solution of HMF at 90 mbar and 40 C., and subsequently leaving the crude HMF to dry in air overnight.

(35) An alternative experiment was also performed by first mixing an equal volume of water with the HMF isopropanol solution. The isopropanol is then evaporated from the solution. After removing the impurities from the aqueous solution by either filtration or centrifuge, more than 99% of the HMF remained in the water solution. However, more dark impurities also appeared in the aqueous solution. This may be due to the presence of a small amount of isopropanol which remained in the solution and therefore more impurities are dissolved in the liquid phase. Hence, it would advantageous to completely evaporate the organic solvent used for the dehydration reaction before adding water for extraction. Otherwise, the remaining solution would contain a higher amount of impurities.

Comparative Example 2

(36) The use of active carbon absorbents have been carried out so as to understand the purification yield through this method.

(37) Table 1 below shows the various HMF recovery percentages using different amount of active carbon. A pure HMF solution has a characteristic clear pale yellow colour (as denoted by the lighter shade of the solution in the right eppendorf tube of FIG. 9). Although using 0.1 g of active carbon provides a higher HMF recovery of 88% as compared to 1 g of active carbon which has only a 49% recovery yield, the solution colour obtained for the latter was a yellowish clear solution (see center eppendorf tube of FIG. 9, as denoted by a darker shade relative to the solution contained in the right most eppendorf tube of FIG. 9) compared to the earlier which had a dark brown appearance containing traces of impurities (see left eppendorf tube of FIG. 9, as denoted by the darker shade relative to the other two eppendorf tubes).

(38) TABLE-US-00001 TABLE 1 HMF recovery using different amount of active carbon Type of HMF Solution HMF recovery 1 mmol HMF treated with 0.1 g active carbon 88% 1 mmol HMF treated with 1 g active carbon 49% Pure HMF solution Not applicable

(39) From this study, active carbons are not as effective as water extraction which allows up to more than 98% recovery yield as illustrated in comparative example 3.

Comparative Example 3

(40) HMF before and after purification have been tested in the oxidation reaction with Au/HT or Pt/C catalyst. As shown in trial 1 and 2 of table 2 below, reactions with un-purified HMF all encountered catalyst deactivation problem as observed from its lower FDCA yield. Consequently, a mixture product comprising HFCA and FDCA was obtained as final product (see FIG. 3 step 100). Even with an extended reaction time of 20 hours, no improvement was observed.

(41) However, for the water extracted HMF, the reaction was completed in 7 hours for Au/HT catalyst and 4.25 hours for Pt/C catalyst, and more importantly, only FDCA having a yield of more than 98% was detected as the final product (see FIG. 3 step 102).

(42) As Na.sub.2CO.sub.3 was used as the base for this catalytic oxidation, no obvious leaching of Mg.sup.2+ from the hydrotalcite (HT) support in the Au/HT catalytic system was observed. Leaching is also avoided when NaOH is used. If no base is used, FDCA as an acid, will react with HT to form FDCA Magnesium salt.

(43) TABLE-US-00002 TABLE 2 Oxidation of HMF to FDCA Time FDCA Trial HMF Catalyst (hours) Yield 1 No Water Au/HT 20 39% + HFCA Extraction 2 No Water Pt/C 20 51% + HFCA Extraction 3 Water Extracted Au/HT 7 99% 4 Water Extracted Pt/C 4.25 98%

(44) For trials 1 and 3, an aqueous solution containing 1 mmol of HMF in 10 ml H.sub.2O was used. Amount of Au/HT catalyst used was 0.25 g. The ratio of HMF to Au is 40 mol/mol. Oxidation was carried out under 1 mmol Na.sub.2CO.sub.3 with O.sub.2 bubbling at a temperature of 50 C. for the first 2 hr followed by 95 C. for the remaining 18 hours.

(45) The conditions of trials 2 and 4 are 10 ml H.sub.2O, 0.4 g Pt/C Catalyst, HMF/Pt of 10 mol/mol, 0.5 g NaOH. For these trials, 1 mmol of HMF in 5 ml H.sub.2O was added dropwise under O.sub.2 bubbling at 25 C.

(46) The HPLC product analysis for trials 1 and 3 are shown in FIGS. 10 and 11. When catalyst deactivation occurs due to impurities such as humins, dual FDCA and HFCA peaks are observed in FIG. 10. Only a single FDCA product peak was observed in FIG. 11 for the water extracted HMF.

Comparative Example 4

(47) Kinetic Studies were conducted for oxidation of both commercial HMF and water extracted purified HMF using Au/HT catalyst under the same reaction conditions (1 mmol HMF in water together with catalyst and Na.sub.2CO.sub.3, aliquot of solution was taken out every hour for HPLC measurements) (see FIG. 12).

(48) The conversion of purified HMF to FDCA obtained from natural fructose was completed within 7 hours. This was slightly slower than the conversion using commercial HMF which finished in 4 hours (see FIG. 12). After further investigation, the optimum reaction conditions for the purified HMF were determined as follow.

(49) The reaction mixture was first kept under oxygen gas at 50 C. for 2 hours, in which most of the HMF was converted to HFCA. The reaction temperature was then raised to 95 C. for another 7 hours in which all the HFCA was fully converted to FDCA with a yield up to 99%.

(50) Alternatively, kinetic study for a palladium-modified gold catalyst (Au.sub.8Pd.sub.2/HT) using water extracted HMF is also demonstrated (see FIG. 12). This AU.sub.8Pd.sub.2/HT catalyst was capable of converting purified HMF to FDCA in 7 h with 95% to 99% yield at 95 C. without the need for pre-treatment at a lower temperature of 50 C. for 2 h (see FIG. 12).

(51) The tolerance of Au/HT catalyst for this biomass-based HMF was also studied. The Au/HT catalyst showed high activity for the first 2 runs with an FDCA yield of 98-99% (see FIG. 14). However from the 3rd run, a significant slowdown of reaction speed was observed (about 56%). In a parallel experiment with pure HMF (from Aldrich) as the starting material, a lower reaction speed of 78% was also observed for the 3rd run (see FIG. 15). To increase the durability of the catalyst, we have prepared palladium-modified Au/HT (Au.sub.8Pd.sub.2/HT) as a new catalyst, which showed excellent recyclability. The catalyst was kept at high activity for at least 5 runs with FDCA yield of 98% to 99% (see FIG. 4), using the purified HMF from fructose. The same conditions for each run are used. This conditions are 1 mmol of HMF, 1 mmol Na.sub.2CO.sub.3, 10 ml H.sub.2O, 0.25 g Au/HT, O.sub.2 bubbling, and 50 C. for the first 2 h followed by 95 C. for the next 7 h.

Integration of Dehydration and Oxidation

(52) Since we have successfully demonstrated the conversion from fructose to HMF in isopropanol and the purification of HMF by water extraction, followed by oxidation of HMF to FDCA, we have also experimented with the integration of these two processes that was previously considered to be incompatible.

(53) The two step reactions were integrated together for the direct conversion of fructose to FDCA. In this process, fructose was converted to HMF in isopropanol with 5 mol % of HCl as catalyst. After the reaction, the isopropanol was separated by evaporation and collected for the next run reaction. Then, HMF was extracted with water and this aqueous solution was directly used for the oxidization reaction. As shown in table 3 below, an overall 83% FDCA yield was achieved. During this integrated process, both solvent (isopropanol) and catalyst (Au/HT) can be recycled. The whole process did not produce any additional waste and only water was consumed during HMF purification process. Hence, it goes to show that water extraction of HMF allows FDCA from fructose to be produced in an environmentally benign manner via an integrated process that is very efficient and cost effective.

(54) TABLE-US-00003 TABLE 3 Integrated process from Fructose to FDCA Fructose HMF HPLC HMF Isolated FDCA Trial (mmol) Yield Yield Yield 1 1 85.3% .sup.84% 83% 2 5 80.2% 79.4% 78%

(55) The reaction conditions for trial 1 are 19.4 ml of iso-propanol, 0.06 ml of H.sub.2O, 0.05 mmol of HCl, 120 C. for 3 hours. Trial 2 is a scaled up of the experiment by 5 times.

(56) The reaction conditions for trial two are based on having the HMF in trial 1 extracted using 10 ml of H.sub.2O. Subsequently, oxidation to FDCA was carried out using 0.25 g of Au/HT, 1 mmol of Na.sub.2CO.sub.3, O.sub.2 bubble, 50 C. for 2 hours followed by 95 C. for 7 hours.

(57) It should be noted that the FDCA yield is the isolated overall yield based on fructose. An isolated yield refers to one where the product has been separated or isolated, and then weighed. Although this involves more effort, such an isolated yield is considered as the absolute yield. On the other hand, a HPLC yield (not the HPLC isolated yield) is a relative yield and not an absolute yield as the product is not isolated before it is being weighed to determine the yield.

Water Extraction of HMF Derived from Biphasic Systems

(58) As disclosed above, the crucial step for converting HMF to FDCA completely relies on the use of water to extract and purify HMF. This method not only removes impurities in a cost-effective manner but also generates HMF aqueous solution that can be directly used for the next step catalytic oxidation step. This purification method can be easily incorporated into any mass production processes for FDCA or other processes as demonstrated above. Relying on this, we have also experimented using HMF derived from biphasic systems. Biphasic dehydration solvent systems are widely utilized for HMF production from fructose, glucose or cellulose.

(59) To test the integrated process for the conversion of fructose to FDCA using biphasic fructose dehydration method, a MIBK/water biphasic system was used. The water used for this dehydration system is not the extracting solvent.

(60) After dehydration, HMF product (about 55% yield) present in the organic MIBK layer was dried and extracted with water. This was directly used for oxidization reaction to FDCA. The difference between HMF extracted with water and one that was not extracted with water is shown in FIG. 13. The left vial shows a dark colour solution having HMF not extracted with water (it should be noted that this solution is brown in colour which is characteristic of crude HMF co-existing with impurities). The right vial shows water extracted HMF.

(61) Under standard oxidation conditions (oxygen bubbling, Na.sub.2CO.sub.3 as base, solution first heated to 50 C. for 2 h to fully convert HMF to HFCA, followed by further reaction to FDCA at 95 C. 7 h), an FDCA yield of more than 97% with 100% HMF conversion was achieved.

(62) HMF prepared from glucose in a biphasic system of water/THF using HCl/AlCl.sub.3 as catalyst produced a HMF yield of 52%. For this as-prepared HMF in THF solution, with water extraction, more than 99% of HMF was recovered after purification and the final overall FDCA yield was 50%.

(63) The above demonstrated that a water extraction HMF purification method can be applied in different processes for the conversion of biomass to FDCA, even with different feed materials.

(64) For further illustration, the conversion of Jerusalem Artichoke (JAT) biomass to FDCA was tested using the MIBK/water biphasic system for dehydration and the Au/HT catalyzed oxidization reaction (see FIG. 5). JAT is an abundant, easy and fast growing biomass with very high inulin/fructose component (about 68 to 83% fructans). Compared to the monophasic system, the biphasic system works better for the conversion of JAT to HMF/FDCA as impurities in JAT, such as biomolecules (proteins, DNA, RNA, vitamins), ions (Na+, K+, Mg2+, Ca2+, Fe3+), fibers and gels, tend to remain in the water layer. The HMF is extracted to MIBK, making the HMF purer. After the reaction, the crude HMF in MIBK was evaporated to remove MIBK for reuse, and the raw HMF was purified with the currently disclosed water extraction method to obtain a light colored aqueous solution (this is yellow in colour due to the HMF). The HMF aqueous solution was then used as feedstock for the Au/HT-catalyzed oxidization reaction.

(65) In this process, HMF was produced with 57% yield in the first step (not optimized) and the overall yield for FDCA was 55% (based on the fructose component in JAT).

Applications

(66) The disclosed method provides an efficient and cost-effective water extraction method for purifying an optionally substituted furan which may be obtained after dehydrating a biomass.

(67) Advantageously, water is an environmentally benign solvent as compared to other organic solvents used in conventional mono-phase or biphasic dehydration reactions.

(68) Advantageously, by evaporating the organic solvents used in the dehydration reaction and adding water subsequently to extract the intermediate optionally substituted furan, deactivation of downstream catalyst used for oxidation is avoided.

(69) Accordingly, up to 99% of the HMF could be recovered and the HMF aqueous solution could be directly used for further catalytic oxidization reaction to convert to FDCA as the sole product.

(70) The disclosed method also overcomes the limitations of multiple extraction processes which consume more solvent, column chromatography or HPLC processes which are unsuitable for mass production and active carbon absorbents which do not produce a sufficiently high purification yield.

(71) The disclosed method also allows the direct conversion of a biomass to an optionally substituted furoic acid since the dehydration step and oxidation step may be integrated through the incorporation of a water extraction process. An integrated process from fructose to FDCA attained an overall FDCA yield of 83%.

(72) Holistically, the method disclosed enhances the purification yield of the intermediate optionally substituted furan and the conversion yield of the resultant optionally substituted furoic acid.

(73) By using the disclosed method, a purified aqueous solution of the optionally substituted furan, particularly HMF may be obtained. This purified aqueous solution can be subjected to downstream processing for producing other polymers without the need for further complex purification processes. Due to the advantageous features, the methods as disclosed above may be scaled up to industrial processes.

(74) It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.