Method for separating 5-hydroxymethylfurfural and humic substance from product solution of dehydration reaction of six-carbon (c 6) carbohydrate

Abstract

The present invention relates to an extractant and a method for separating 5-hydroxymethylfurfural and a humic substance from a product solution of a dehydration reaction of a six-carbon (C6) carbohydrate, which is suitable for treating a product solution generated by a dehydration reaction of a six-carbon (C6) carbohydrate in an aprotic polar solvent, to separate out a humic substance therefrom, so as to prevent the humic substance from hindering a subsequent HMF purification operation, so that a high-purity HMF crystal is finally separated. The present invention relates to a use of a hydrophobic solvent, such as toluene, having a positive octanol-water separation coefficient (logP) between 2.45 and 3.00 and a water solubility of less than 0.100 wt%, as an extractant to perform extraction the product solution, thereby obtaining a hydrophobic phase liquid rich in the HMF and an aqueous phase liquid rich in the humic substance. Due to the fact that the HMF and the humic substance exist in two different phases, the HMF and the humic substance can be separated by means of a simple phase separation process.

Description

A method for separating 5-hydroxymethylfurfural and humins from a product solution of a six-carbon (C6) carbohydrate dehydration reaction Technical Field

[0001] The present invention relates to a product solution generated by dehydrating a six-carbon (C6) carbohydrate, and more particularly to an extractant and method for separating 5-hydroxymethylfurfural and humins from the product solution to facilitate subsequent HMF purification operations. Background Art

[0002] 5-Hydroxymethylfurfural is a biomass-derived platform chemical, primarily prepared from six-carbon (C6) carbohydrates through hydrolysis and dehydration reactions in different systems. Its derivatives can be further developed into various resins, polymers, solvents, and fuels, and therefore have the potential to replace or substitute petrochemical materials.

[0003] The dehydration reaction of hexoses is primarily affected by the catalyst, temperature, and solvent. Acidic catalysts are typically used in various solvents, with the solvent significantly impacting HMF conversion. Dimethyl sulfoxide (DMSO) has been shown to offer high conversion rates, but subsequent separation of HMF from the product solution presents another challenge. Numerous studies have attempted to separate HMF using solvent extraction methods such as MIBK, molecular distillation, or adsorption, with adsorption considered the most cost-effective technique.

[0004] After hexose dehydration to HMF, it often undergoes a secondary hydration reaction with water to produce levulinic acid (LA) and formic acid (FA), which then copolymerize with hexose to form humins. The presence of humins often deactivates or renders adsorbents in downstream purification processes inoperable. Therefore, removing highly water-soluble humin impurities from the dehydrated product solution presents a new challenge in integrating adsorption technology into the HMF purification process. While activated carbon filtration can remove some humins, it cannot guarantee the activity and functionality of the subsequent adsorbent. Furthermore, the heating required for distillation is not suitable for temperature-sensitive HMF. Therefore, the industry urgently needs a low-temperature method for separating HMF from byproducts to ensure that HMF can be economically competitively used as a sustainable, biomass-derived platform chemical. Figure 1 illustrates the reaction flow of this conventional technology.

[0005] Summary of the Invention

[0006] Because both HMF and humins are highly hydrophilic, it is generally believed that they are difficult to separate based on their solubility differences in specific solvents. However, the inventors of the present invention unexpectedly discovered that using a hydrophobic solvent, preferably toluene, with a log P (octanol-water partition coefficient) between 2.45 and 3.00 and a solubility in water of less than 0.100 wt%, as an extractant for extracting a product solution produced by dehydration of six-carbon (C6) carbohydrates in an aprotic polar solvent (such as DMSO), results in the hydrophilic HMF being present in the hydrophobic organic phase along with the aprotic polar solvent, while the humins remain in the aqueous phase. In other words, the addition of the hydrophobic solvent promotes the separation of the product solution into two immiscible phases, with HMF and humins existing in separate phases. This allows the HMF and humins to be separated and removed via a simple phase separation process. Accordingly, the present invention solves the existing problem that the prior art cannot effectively remove humins, can prevent humins from interfering with subsequent HMF purification operations, and is conducive to the final separation of high-purity HMF crystals.

[0007] Based on the high selectivity of the hydrophobic solvent for HMF and humins, and the resulting excellent separation effect of humins, a first embodiment of the present invention provides an extractant for separating 5-hydroxymethylfurfural and humins from a product solution of a six-carbon (C6) carbohydrate dehydration reaction, wherein the product solution comprises at least one aprotic polar solvent, 5-hydroxymethylfurfural (HMF), humins, and a specific proportion of water, wherein the specific proportion of water is between 0.5% and 10% by weight based on the total weight of the product solution; the extractant comprises at least one hydrophobic solvent, and the extractant and the product solution are mixed at a volume ratio of greater than or equal to 4:1 to form a mixed solution, such that the hydrophobic solvent and the aprotic polar solvent are miscible, forcing water and humins originally dissolved in the aprotic polar solvent to precipitate. Finally, the mixed solution separates into a hydrophobic phase rich in the aprotic polar solvent and HMF, and an aqueous phase rich in humins.

[0008] The hydrophobic solvent has an n-octanol-water partition coefficient (log P) between 2.45 and 3.00, and a solubility in water of less than 0.100 wt %.

[0009] According to a second embodiment of the present invention, a method for separating 5-hydroxymethylfurfural and humins from a product solution of a six-carbon (C6) carbohydrate dehydration reaction is provided, comprising the following steps:

[0010] A) providing a product solution of a six-carbon (C6) carbohydrate dehydration reaction, the product solution comprising an aprotic polar solvent, 5-hydroxymethylfurfural (HMF), humins, and a specific proportion of water, wherein the specific proportion of water is a water content ranging from 0.5 wt % to 10 wt % based on the total weight of the product solution;

[0011] B) mixing a hydrophobic solvent and the product solution in a volume ratio of greater than or equal to 4:1 to form a mixed solution, wherein the hydrophobic solvent has an n-octanol-water partition coefficient (log P) of 2.45 to 3.00 and a solubility in water of less than 0.100 wt %, such that the hydrophobic solvent and the aprotic polar solvent are miscible, forcing water and humins originally dissolved in the aprotic polar solvent to precipitate, thereby separating the mixed solution into a hydrophobic phase rich in HMF and the aprotic polar solvent, and an aqueous phase rich in humins; and

[0012] C) separating the hydrophobic phase and the aqueous phase.

[0013] In a preferred embodiment, the aprotic polar solvent is selected from the group consisting of dimethyl sulfoxide (DMSO), dimethylacetamide (DMAC), dimethylformamide (DMF), methyl pyrrolidone (NMP), and combinations thereof. In a more preferred embodiment, the aprotic polar solvent is selected from DMSO.

[0014] In a preferred embodiment, the specific proportion of water is a water content between 0.5 wt % and 10 wt % based on the total weight of the product solution, more preferably a water content between 0.5 wt % and 5 wt %, and most preferably a water content between 1 wt % and 3 wt %.

[0015] In a preferred embodiment, the extractant and the product solution are mixed into the mixed solution in a volume ratio greater than or equal to 9:1. In a more preferred embodiment, the extractant and the product solution are mixed into the mixed solution in a volume ratio greater than or equal to 15:1.

[0016] In a preferred embodiment, the hydrophobic solvent is selected from benzene solvents, more preferably selected from toluene. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other objects, features and effects of the present invention will become apparent from the following description of preferred embodiments taken in conjunction with the accompanying drawings, in which:

[0018] FIG1 shows a conventional method for producing HMF and by-products from the dehydration reaction of six-carbon (C6) carbohydrates.

[0019] FIG2A is a schematic flow diagram of a method for separating 5-hydroxymethylfurfural and humins from a product solution of a six-carbon (C6) carbohydrate dehydration reaction according to an embodiment of the present invention.

[0020] 2B is a schematic flow diagram of a method for separating 5-hydroxymethylfurfural and humins from a product solution of a six-carbon (C6) carbohydrate dehydration reaction according to another embodiment of the present invention.

[0021] FIG2C is a schematic flow diagram of a method for separating 5-hydroxymethylfurfural and humins from a product solution of a six-carbon (C6) carbohydrate dehydration reaction according to yet another embodiment of the present invention.

[0022] FIG. 3A is a HMF calibration curve according to an embodiment of the present invention.

[0023] FIG. 3B is a DMSO calibration curve according to an embodiment of the present invention.

[0024] FIG. 3C is an LA calibration curve according to an embodiment of the present invention.

[0025] 4A-4C are photographs taken after the product solution was extracted with toluene, showing a relatively transparent hydrophobic phase and a dark lower aqueous phase.

[0026] FIG5 shows the functional relationship between temperature (horizontal axis) and HMF recovery (vertical axis) at different toluene / product solution volume ratios.

[0027] Explanation of symbols: 1 hydrophobic phase liquid 2 aqueous phase liquid. DETAILED DESCRIPTION

[0028] As shown in Figure 1, the final product solution contains, in addition to the aprotic polar solvent and the target product HMF, byproducts such as LA, FA, water, and humins. The present invention focuses on separating the humins, allowing the partially purified product solution (comprising the aprotic polar solvent, HMF, LA, and FA) to be further purified through chemical separation steps, such as fractional distillation and / or chromatography, to ultimately isolate high-purity HMF crystals. Referring to the flow chart shown in Figure 2A, the method comprises: (A) providing a product solution of hexa-carbon (C6) carbohydrate dehydration, comprising an aprotic polar solvent, HMF, humins, and a specific ratio of water; (B) extracting the product solution with a hydrophobic solvent to separate the resulting solution into a hydrophobic phase rich in HMF and the aprotic polar solvent, and an aqueous phase rich in humins; and (C) separating the hydrophobic phase from the aqueous phase.

[0029] According to the present invention, the term "product solution of a six-carbon (C6) carbohydrate dehydration reaction," or simply "product solution," as used herein, refers to a product solution comprising an aprotic polar solvent, HMF, humins, and water in a specific ratio. "Humins" as referred to herein refer to the predominantly amorphous oligomeric or polymeric byproducts produced by the dehydration reaction of a six-carbon carbohydrate, typically exhibiting a dark color. In certain embodiments, the product solution may also contain levulinic acid (LA) and formic acid (FA). Suitable aprotic polar solvents for use in the present invention include dimethyl sulfoxide (DMSO), dimethylacetamide (DMAC), dimethylformamide (DMF), methylpyrrolidone (NMP), and combinations thereof. In preferred embodiments, the product solution is a product solution produced by a six-carbon carbohydrate dehydration reaction using an aprotic polar solvent, more preferably DMSO, as the solvent. The six-carbon carbohydrate is preferably selected from the group consisting of fructose, glucose, and combinations thereof, with fructose being particularly preferred. A solid acid is preferably used as a catalyst for the dehydration reaction. As shown in Figure 1, the six-carbon carbohydrate undergoes dehydration to produce 5-hydroxymethylfurfural and water. Water then reacts with 5-hydroxymethylfurfural to produce levulinic acid (LA) and formic acid (FA). Levulinic acid and formic acid polymerize with water and then copolymerize with 5-hydroxymethylfurfural to produce humins. Therefore, the resulting solution contains byproducts such as LA, FA, water, and humins, in addition to the aprotic polar solvent and the target product HMF.

[0030] According to the present invention, the product solution must contain a specific proportion of water. This specific proportion of water allows the product solution to separate into two immiscible phases after extraction in step (B), and assists the hydrophobic solvent in separating the humins, thereby obtaining a more optimal separation boundary between the hydrophobic and aqueous phases. The specific proportion of water can be 0.5% to 10% by weight of the total weight of the product solution, preferably 0.5% to 5% by weight, and more preferably 1% to 3% by weight, as shown in Example 1 below. If the water content of the product solution is less than 1% by weight, or even less than 0.5% by weight, the product solution will not easily separate into an aqueous phase in step (B). If the water content of the product solution is greater than 10% by weight, the volume of solution required for extraction is excessive, which is not only uneconomical but also significantly reduces the recovery rate of HMF. Therefore, in a preferred embodiment of the present invention, step (A) comprises adjusting the water content of the product solution to the specific proportion. In one embodiment, referring to Figure 2B, step (A) comprises dehydrating the product solution until the product solution retains the specific proportion of water. Dehydration treatment methods applicable to the present invention include any mild dehydration method that does not substantially destroy the HMF molecular structure or induce chemical changes. Preferably, a dehydrating agent is added at a relatively low temperature, such as room temperature. Suitable dehydrating agents include, but are not limited to, molecular sieves, anhydrous sodium sulfate, calcium hydride, activated alumina, barium oxide, and barium sulfate. To more precisely control the weight ratio of water, in another embodiment of the present invention, as shown in FIG2C , step (A) comprises dehydrating the product solution to a water content of less than 1% by weight based on the total weight of the product solution, and then replenishing the water to the aforementioned specific ratio by a method selected from the group consisting of dehydration and water addition. The water content of the product solution can be measured using a Karl Fischer moisture titrator.

[0031] The term "hydrophobic solvent" as used herein refers to a poorly water-soluble solvent having an octanol-water partition coefficient (log P) between 2.45 and 3.00. The "octanol-water partition coefficient" herein refers to the value described in Sangster, J., Octanol-water partition coefficients of simple organic compounds, J. Phys. Chem. Ref. Data, 18(3): 1111-1229 (1989), which represents the ratio of the solubility of a given hydrophobic solvent in octanol (a non-polar solvent) to that in water (a polar solvent); the higher the value, the less water-soluble the solvent. Preferably, the solubility of the hydrophobic solvent in water is less than 0.100% by weight. Examples of suitable hydrophobic solvents include, but are not limited to, toluene, 1-hexyne, 1,5-hexadiene, cyclopentane, 1,3-cyclohexadiene, cyclohexene, 1,3,5-cycloheptatriene, styrene, 1-octanol, 2-octanol, 4-octanol, 2,3,6-trimethylphenol, 2,4,6-trimethylphenol, benzhydrol, 4-phenylcyclohexanone, diphenylacetic acid, ethyl benzoate, carbon tetrachloride, 1-chlorobutane, 1-fluorobutane, bromobenzene, chlorobenzene, benzyl bromide, 1-methylindole, 2-methylindole, 3-methylindole, 5-methylindole, 2-phenylpyrrole, 2-phenylpyridine, 4-phenylpyridine, N-phenylpyridine, octanonitrile, 3-nitrotoluene, and combinations thereof. In the present invention, a preferred embodiment is a benzene-based solvent, particularly toluene. According to experiments described below, toluene has excellent Humins separation performance. The use and method of this material are not disclosed in the prior art or literature and are key to the present invention. In a preferred embodiment, the specific gravity of the hydrophobic solvent is substantially less than that of water, so that the hydrophobic phase obtained after extraction and demixing is located in the upper layer. The log P values ​​and solubility in water of these hydrophobic solvents are listed in Table 1 below.

[0032] Table 1. Octanol-water partition coefficients (log P) and solubility in water of hydrophobic solvents

[0033] Step (B) involves mixing at least one hydrophobic solvent as defined above with the product solution as an extractant to perform extraction. "Extraction" herein refers to the process of separating HMF and humins in the product solution by exploiting their differing solubility in the hydrophobic solvent, and "extractant" refers to the solvent system comprising at least one hydrophobic solvent as defined above, used to perform the extraction. While the hydrophobic solvent used in the present invention exhibits high selectivity for HMF, "extraction" should not be construed as achieving 100% separation of HMF and humins. According to the present invention, after extraction, the mixture separates into two immiscible layers: a hydrophobic phase and an aqueous phase. The inventors discovered that the hydrophobic phase contains, in addition to the hydrophobic solvent and HMF, an aprotic polar solvent, LA, and FA, while the aqueous phase is primarily composed of humins, resulting in the aqueous phase appearing dark in color while the hydrophobic phase is relatively transparent, as shown in Example 2 and Figures 4A-4C below. The distribution of HMF in the two phases can be quantitatively analyzed by HPLC, while the distribution of humins in the two phases can be qualitatively determined by observing the color depth of the liquid.

[0034] The inventors discovered that hydrophobic solvents such as toluene act as antisolvents in the extraction process of the present invention. They are miscible with aprotic polar solvents such as DMSO, allowing the hydrophobic solvent and the aprotic polar solvent to coexist in the same phase, forcing the water and humins originally dissolved in the aprotic polar solvent to precipitate. Because the hydrophobic solvents used in this case have an n-octanol-water partition coefficient (log P) between 2.45 and 3.00, they effectively form two immiscible phases in the product solution. Furthermore, the hydrophobic solvents have a very low solubility in water, for example, less than 0.100% by weight, ensuring that they effectively dissolve within the molecular structure of the aprotic polar solvent, thereby disrupting the bond between the aprotic polar solvent and the humins and facilitating the precipitation of the humins from the aprotic polar solvent. Accordingly, the present invention further proposes a novel use of the hydrophobic solvent (particularly toluene), which is used as an extractant for separating humins from the product solution of the aforementioned six-carbon (C6) carbohydrate dehydration reaction.

[0035] According to the present invention, the volume ratio of the hydrophobic solvent to the product solution is greater than or equal to 4 / 1, preferably greater than or equal to 9 / 1, and more preferably greater than or equal to 15 / 1, in order to achieve a satisfactory HMF recovery rate in the hydrophobic phase, as shown in Example 2 and Figure 5 below. The separation of the hydrophobic and aqueous phases can be further stabilized by allowing the mixed solution to stand in a temperature-controlled environment. According to one embodiment of the present invention, the controlled temperature can be in the range of -40°C to 60°C, preferably -20°C to 60°C, and more preferably -10°C to 40°C, as shown in Example 2 and Figure 5 below. This temperature-controlled standing process not only facilitates separation and achieves a satisfactory HMF recovery rate in the hydrophobic phase, but also ensures that the humin content in the hydrophobic phase is sufficiently low so as not to substantially hinder subsequent HMF purification operations. If the standing temperature exceeds 80°C, HMF is more likely to polymerize and form humins.

[0036] Step (C), performed subsequent to step (B), involves separating the hydrophobic phase from the aqueous phase. Applicable separation procedures include all conventional liquid-liquid separation procedures. Because the hydrophobic and aqueous phases are substantially immiscible, they can be separated by simple separation methods. The resulting aqueous phase is enriched in humins, an undesirable byproduct, and also contains some residual HMF. This aqueous phase can be discarded directly, or steps (B) and (C) can be repeated to perform a secondary extraction on the aqueous phase, as described in Example 3 below. Specifically, the aqueous phase is extracted with the hydrophobic solvent, and the layers are separated to yield a secondary hydrophobic phase enriched in HMF and a secondary aqueous phase enriched in humins. The extraction and separation steps of step (B) and the separation steps of step (C) can be repeated multiple times, and the hydrophobic phases obtained from multiple extractions can be combined to increase the overall recovery of HMF.

[0037] The following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0038] Preparation of 5-hydroxymethylfurfural solution.

[0039] The exemplary product solution containing 5-hydroxymethylfurfural (HMF) used in each example is produced by dehydrating a hexose in dimethyl sulfoxide (DMSO). The dehydration reaction is catalyzed by a solid acid. In addition to HMF and DMSO, the product solution also contains levulinic acid, formic acid, water, and humins.

[0040] The product solution is subjected to a dehydration step to remove most of the water in the product solution, as described in Example 1.

[0041] Example 1: Dehydration of product solution.

[0042] 1.1 First, filter the product solution through a filter membrane with a pore size of 0.22 μm;

[0043] 1.2 Then The product solution and the molecular sieve can be dehydrated at a ratio of, for example, 10 mL: 3 g. The mixture is allowed to stand at room temperature for 2 hours to obtain a dehydrated product solution.

[0044] The dehydrated product solution has a dark color, and its color mainly comes from the dark humins.

[0045] Analytical method.

[0046] In this example, an analytical method for HMF, DMSO, and LA was established using HPLC / UV equipment. This method was used to quantitatively analyze HMF, DMSO, and LA in samples containing HMF, DMSO, and LA, including the first supernatant, first lower layer, and extract. The equipment and operating conditions are exemplified below.

[0047] HPLC column: Phenomenex 5μm C18 4.6×250mm

[0048] Wash mode and flow rate: isocratic elution, 1 mL / min.

[0049] UV wavelength: 280nm for detecting HMF, 220nm for detecting DMSO, and 266nm for detecting LA.

[0050] Injection volume: 5 μl

[0051] In this example, a series of standard solutions of varying concentrations were prepared for HMF, DMSO, and LA to generate calibration curves. The HMF concentrations were 0.126, 0.314, 0.628, 0.942, and 1.26 mg / mL; the DMSO concentrations were 2.646, 6.614, 9.912, 13.23, and 19.84 mg / mL; and the LA concentrations were 1.0653, 2.6634, 5.3268, and 7.9902 g / L. As shown in Figures 3A-3C , the horizontal axis represents the injected concentration (x) and the vertical axis represents the peak area (y) of the HPLC chromatogram. A standard curve was generated, and the regression equations were: y = 28712x(HMF), y = -7.2851x 2 +335.59x (DMSO), and y=35.43x (LA).

[0052] Extraction of 5-hydroxymethylfurfural solution.

[0053] As previously mentioned, toluene is used as the hydrophobic solvent in the preferred embodiment of the present invention. Because toluene has a lower specific gravity than water, the upper layer after extraction and stratification is a relatively transparent hydrophobic phase, primarily containing toluene and dissolved DMSO and HMF, and may also contain LA and FA. The lower layer is an aqueous phase, darker in color, primarily containing FA, water, and humins. In this example, stratification was performed using toluene / dehydrated product solution volume ratios (v / v) of 15 / 1, 9 / 1, 4 / 1, and 1 / 1. An exemplary extraction procedure is shown in Example 2.

[0054] Example 2.

[0055] 2.1 Toluene / dehydrated product solution were mixed at volume ratios (v / v) of 15 / 1, 9 / 1, 4 / 1, and 1 / 1, respectively, and five groups were performed for each ratio.

[0056] 2.2 After mixing, place the five groups in a constant temperature water bath at 60℃, 40℃, and 20℃, an ice bath at 0℃, a -20℃ refrigerator with an actual temperature of -22.5℃, and a -40℃ refrigerator with an actual temperature of -36.7℃ for 10 minutes respectively.

[0057] 2.3 After standing, the mixture was centrifuged at 13,000 rpm for 1 minute to separate the layers, yielding a first upper hydrophobic phase and a first lower aqueous phase. Figure 4A is a photograph taken after extraction and separation, showing the upper, relatively clear hydrophobic phase 1 and the lower, darker aqueous phase 2.

[0058] 2.4 Separate the first upper and first lower liquid layers and record their volumes and weights. Figures 4B and 4C show photographs of the immiscible upper and lower liquid layers after separation and their respective contents in microcentrifuge tubes. Figure 4B shows the relatively transparent first upper hydrophobic phase 1, while Figure 4C shows the dark first lower aqueous phase 2.

[0059] 2.5 The first upper layer was diluted 10-fold with acetone and analyzed by HPLC. The HMF recovery rate was calculated using the following formula:

[0060] HMF recovery rate = HMF content in the first upper hydrophobic phase (mg) / total HMF in the dehydration product solution (mg)

[0061] The results are shown in Figure 5 below, where the horizontal axis represents temperature (°C) and the vertical axis represents HMF recovery (%). This experimental chart shows that for HMF recovery to be greater than 50% at different operating temperatures, the toluene / dehydration product solution volume ratio must be greater than or equal to 4 / 1. For HMF recovery to reach 70%, the volume ratio must be greater than or equal to 7 / 1. For HMF recovery to reach 90%, the volume ratio must be greater than or equal to 15 / 1. Furthermore, Figure 5 shows that, at different toluene / dehydration product solution volume ratios, temperature and recovery rate exhibit a similar linear relationship. The lower the toluene / dehydration product solution volume ratio, the greater the slope (e.g., 0.2729 at 4 / 1). Conversely, the lower the slope (e.g., 0.1386 at 15 / 1), indicating that higher toluene / dehydration product solution volume ratios result in more stable HMF recovery at different operating temperatures, ensuring resistance to ambient temperature variations during production.

[0062] In addition, although the data in the figure show that the HMF recovery rate increases with increasing temperature, it has been observed that the color of the first upper layer liquid also increases with increasing temperature. This means that the content of humins in the first upper layer liquid also increases with increasing temperature. Therefore, temperature is also a controlling factor.

[0063] In some embodiments of the present invention, a second extraction may be performed on the first lower aqueous phase obtained in Example 2. The operation is shown in Example 3.

[0064] Example 3.

[0065] 3.1 According to Example 2.1, toluene and the dehydrated product solution were mixed in a volume ratio of 9 / 1. After mixing, the mixture was allowed to stand at room temperature and separated into layers to obtain a first upper layer and a first lower layer. The first upper layer and the first lower layer were separated and analyzed for HMF content.

[0066] 3.2 Take five 46 μl portions of the first lower layer liquid, add 100, 300, 500, 700, and 900 μl of toluene respectively, mix, let stand and separate the layers to obtain the second upper layer liquid and the second lower layer liquid.

[0067] 3.3 Separate the second upper liquid layer and the second lower liquid layer, and analyze the HMF content therein.

[0068] In certain embodiments of the present invention, the dehydration product solution contains, for example, 66.89 g / L of HMF. In this case, the HMF contents obtained in the first upper layer and the first lower layer in step 3.1 may be, for example, 5.2 mg and 1.5 mg, respectively. The HMF content obtained in step 3.3 may be, for example, 0.4-0.9 mg, depending on the amount of toluene. This indicates that re-extraction can increase the amount of HMF recovered from the dehydration product solution.

[0069] In this embodiment, the formula for calculating the HMF recovery rate is as follows:

[0070] HMF recovery rate = total amount of HMF in the first upper layer liquid and the second upper layer liquid (mg) / total amount of HMF in the dehydration product solution (mg)

[0071] By re-extracting, the total recovery rate of the product solution can be further increased. For example, the recovery rate of 70% to 80% in Figure 5 can be increased to 90%.

Claims

1. A method for separating 5-hydroxymethylfurfural and humins from a six-carbon (C6) carbohydrate hydrolysis and dehydration reaction solution, characterized in that: It includes the following steps: A) providing a six-carbon (C6) carbohydrate hydrolysis and dehydration reaction solution, which comprises an aprotic polar solvent, 5-hydroxymethylfurfural (HMF), humins and a specific proportion of water, wherein the specific proportion of water is a water content between 0.5 wt % and 10 wt % based on the total weight of the product solution; B) mixing a hydrophobic solvent and the reaction solution in a volume ratio of greater than or equal to 4:1 to form a mixed solution, wherein the hydrophobic solvent has an n-octanol-water partition coefficient (log P) between 2.45 and 3.00, and a solubility in water of less than 0.100 wt %, so that the hydrophobic solvent and the aprotic polar solvent are mutually soluble, forcing water and humins originally dissolved in the aprotic polar solvent to precipitate, thereby separating the mixed solution into a hydrophobic phase liquid rich in HMF and the aprotic polar solvent, and an aqueous phase liquid rich in humins; and C) separating the hydrophobic phase and the aqueous phase.

2. The method according to claim 1, characterized in that The aprotic polar solvent is selected from the group consisting of dimethyl sulfoxide (DMSO), dimethylacetamide (DMAC), dimethylformamide (DMF), methylpyrrolidone (NMP), and combinations thereof.

3. The method according to claim 2, characterized in that The aprotic polar solvent is selected from dimethyl sulfoxide (DMSO).

4. The method according to claim 1, characterized in that The reaction solution further comprises levulinic acid (LA) and formic acid (FA).

5. The method according to claim 1, characterized in that The step (A) comprises adjusting the water content of the product solution to the specific ratio.

6. The method according to claim 5, characterized in that The step (A) comprises dehydrating the product solution until the product solution retains the specific proportion of water.

7. The method according to claim 5, characterized in that The step (A) comprises dehydrating the reaction solution to have a water content of less than 1.0 wt % based on the total weight of the reaction solution, and then adding water to achieve the water content of the specific ratio.

8. The method according to claim 1, 5 or 6, characterized in that: The specific proportion of water is a water content between 0.5 wt % and 5 wt % based on the total weight of the product solution.

9. The method according to claim 1, 5 or 6, characterized in that: The specific proportion of water is a water content between 1 wt % and 3 wt % based on the total weight of the product solution.

10. The method according to claim 1, characterized in that The step (B) comprises mixing the hydrophobic solvent and the reaction solution in a volume ratio greater than or equal to 9:1 to form the mixed solution.

11. The method according to claim 9, characterized in that The step (B) comprises mixing the hydrophobic solvent and the reaction solution in a volume ratio greater than or equal to 15:1 to form the mixed solution.

12. The method according to claim 1, characterized in that The hydrophobic solvent is selected from benzene solvents.

13. The method according to claim 11, characterized in that The hydrophobic solvent is selected from toluene.

14. The method according to claim 1, wherein: The step (B) further comprises placing the mixed solution at a temperature between -40°C and 60°C to promote the separation of the hydrophobic phase and the aqueous phase.

15. The method according to claim 14, characterized in that The step (B) comprises allowing the mixed solution to stand at a temperature between -20°C and 60°C.

16. The method according to claim 15, characterized in that The step (B) comprises allowing the mixed solution to stand at a temperature between -10°C and 40°C.

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