Photothermal green catalytic synthesis method of 5-hydroxymethylfurfural

Abstract

The invention provides a photo-thermal green synthesis method of 5-hydroxymethylfurfural (HMF), which comprises the following steps: heating a reaction system through photo-thermal by taking carbon-based solid sulfonic acid as a catalyst under the radiation of simulated sunlight, and carrying out selective catalytic dehydration on fructosyl carbohydrate to generate the 5-hydroxymethylfurfural. According to the method, a black carbon-based solid material containing a sulfonic group (-SO3H) active center is used as a photo-thermal conversion material and a catalyst, and the fructose-based carbohydrate is subjected to photo-thermal directional catalytic dehydration in a neutral aprotic organic solvent with the boiling point greater than or equal to 100 DEG C to generate the 5-hydroxymethylfurfural. The carbon-based solid photo-thermal catalytic material and the organic solvent are matched and combined, a photo-thermal catalytic material-organic solvent photo-thermal green catalytic system is constructed, selective conversion of fructose structures in carbohydrates can be achieved, the yield of generated HMF reaches 90% or above, and the selectivity of HMF can reach 95% or above.

Description

Technical Field

[0001] The invention belongs to the technical field of green catalytic synthesis of furan-based chemicals, and specifically relates to a photothermal green catalytic synthesis method of 5-hydroxymethylfurfural. Background Art

[0002] Renewable biomass-based 5-hydroxymethylfurfural (HMF) is a very important platform chemical. Its molecule contains unique active aldehyde (—CHO), hydroxymethyl (—CH2OH) and conjugated double bond (—C=C—C=C—) functional groups. It can be derived into many high value-added chemicals through special chemical reactions (Formula 1). It has become an ideal substitute for petroleum-based chemicals and has great potential to replace traditional fossil energy.

[0003]

[0004] Fructose-based carbohydrate chemicals are important raw materials for the preparation of HMF. In the presence of an acid catalyst, the conversion reaction of the raw materials to HMF can be completed by heating the reaction system. Traditional heating methods mainly include direct heating, microwave heating, etc. The current heating method relies too much on fossil energy, so it is urgent to develop a new green heating method for the catalytic synthesis of HMF.

[0006] Solar energy is the most basic energy on earth, and most of the energy comes directly or indirectly from sunlight. At the same time, solar energy has the advantages of wide distribution, greenness and safety. It is a clean energy with broad application prospects and can replace traditional fossil energy to a certain extent.

[0007] There are two main ways to utilize solar energy: photothermal conversion and photoelectric conversion. Among them, photothermal conversion is the most traditional utilization mode, which has accompanied the progress of human social history. In recent years, with the advancement of solar energy utilization technology and the rapid development of material science and technology, the clean and efficient conversion of solar energy into thermal energy and its utilization has once again become a hot area in solar energy utilization research. In the field of photothermal conversion technology, black photothermal conversion materials have attracted widespread attention from scientific researchers because they have a wide solar spectrum absorption characteristic and can make full use of solar energy resources. Therefore, black materials (substances), as solar energy absorbers, can efficiently convert solar energy into thermal energy and become the first choice for preparing photothermal conversion materials.

[0008] Therefore, the development of a new photothermal catalytic system that is green and environmentally friendly, has low dependence on fossil energy, high conversion efficiency, and mild reaction conditions has become an inevitable choice for the green catalytic synthesis of 5-hydroxymethylfurfural. Summary of the invention

[0009] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a photothermal green catalytic synthesis method for 5-hydroxymethylfurfural. The present invention uses a black carbon-based solid material containing a sulfonic acid group (—SO3H) as a photothermal conversion material and catalyst, and combines it with a neutral aprotic organic solvent with a boiling point ≥100°C to construct a new green catalytic reaction system for the selective conversion of fructose-based carbohydrates to 5-hydroxymethylfurfural.

[0010] To achieve the above-mentioned purpose, the present invention provides the following technical scheme: a photothermal green catalytic synthesis method of 5-hydroxymethylfurfural, which uses carbon-based solid sulfonic acid as a catalyst under the radiation of simulated sunlight, heats the reaction system by photothermal means, and selectively catalyzes the dehydration of fructose-based carbohydrates to generate 5-hydroxymethylfurfural.

[0011] Further, the method specifically includes the following steps:

[0012] (1) adding a certain amount of carbon-based solid sulfonic acid into an organic solvent to form a photothermal catalytic dehydration reaction system;

[0013] (2) adding a certain amount of fructose-based carbohydrates into the photothermal reaction system, stirring magnetically, and performing a photothermal catalytic dehydration reaction under the radiation of simulated sunlight;

[0014] The carbon-based solid sulfonic acid is a black carbon-based solid catalytic material containing a sulfonic acid group (—SO3H) active center;

[0015] The organic solvent is one or more neutral aprotic organic solvents.

[0016] Furthermore, the mass fraction of the carbon-based solid sulfonic acid relative to the raw material fructose-based carbohydrate is ≤15%.

[0017] Furthermore, the mass volume ratio of the raw material fructose-based carbohydrate to the organic solvent is (1-50) g:100 mL.

[0018] Furthermore, the fructosyl carbohydrate is a carbohydrate containing a fructose structural unit.

[0019] Furthermore, the carbohydrate is fructose, sucrose or inulin.

[0020] Furthermore, the boiling point of the neutral aprotic organic solvent is ≥100°C.

[0021] Furthermore, the neutral aprotic organic solvent is dimethyl sulfoxide or sulfolane.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention uses a black carbon-based solid material containing a sulfonic acid group (-SO3H) active center as a photothermal conversion material and catalyst, and dehydrates fructose-based carbohydrates to generate 5-hydroxymethylfurfural through photothermal directional catalytic dehydration in a neutral aprotic organic solvent with a boiling point ≥100°C; the carbon-based solid photothermal catalytic material is combined with an organic solvent to construct a "photothermal catalytic material-organic solvent" photothermal green catalytic system, which can achieve the selective conversion of fructose structure in carbohydrates, and the yield of HMF generated reaches more than 90%, and the selectivity of HMF can reach 95%.

[0024] 2. Compared with the existing preparation methods, the preparation method provided by the present invention has the advantages of low carbon, green, environmental protection, low dependence on fossil energy, mild reaction conditions, wide source of raw materials, easy recycling of catalysts, high product selectivity, etc., which can accelerate the green industrial production of 5-hydroxymethylfurfural.

[0025] 3. The photothermal green catalytic reaction system of the present invention mainly utilizes the black carbon-based component in the carbon-based solid sulfonic acid to have excellent photothermal conversion ability for sunlight, directly converting sunlight into heat for heating the reaction system. At the same time, the sulfonic acid group (-SO3H) in the carbon-based solid sulfonic acid has a strong catalytic dehydration ability. In the presence of sunlight, the heating and catalytic dehydration reactions of the catalytic reaction system can be carried out simultaneously, thereby accelerating the directional conversion of fructose-based raw materials to 5-hydroxymethylfurfural. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The digital camera photos of two carbon-based solid sulfonic acids (C1-SO3H and C2-SO3H);

[0027] Figure 2 The infrared spectra of two carbon-based solid sulfonic acids (C1-SO3H and C2-SO3H);

[0028] Figure 3 It is a photothermal catalytic reaction device;

[0029] Figure 4 This is the relationship between fructose concentration and chromatographic peak area obtained by liquid chromatography standard curve method;

[0030] Figure 5 It is the relationship diagram between HMF concentration and chromatographic peak area obtained by liquid chromatography standard curve method;

[0031] Figure 6 The photothermal catalytic effect comparison diagram of C1-SO3H and C2-SO3H (the result comparison diagram of Example 1 and Example 2, (a): reaction temperature; (b): raw material conversion rate; (c): HMF yield; (d): HMF selectivity);

[0032] Figure 7 The effect of the amount of carbon-based solid catalyst on the photothermal catalytic efficiency (comparison of the results of Examples 3 and 4 with those of Example 1, (a): reaction temperature; (b): feedstock conversion rate; (c): HMF yield; (d): HMF selectivity);

[0033] Figure 8 The effect of solvent type on photothermal catalytic efficiency (comparison of the results of Example 5 and Example 1 (a): reaction temperature; (b): feedstock conversion rate; (c): HMF yield; (d): HMF selectivity);

[0034] Fig. 9 The effect of raw material concentration on the photothermal catalytic efficiency (comparison of the results of Examples 6 and 7 with those of Example 1, (a): reaction temperature; (b): raw material conversion rate; (c): HMF yield; (d): HMF selectivity);

[0035] Fig.10 The results of raw material expansion (comparison of the results of Examples 8 and 9 with those of Example 1 (a): reaction temperature; (b): HMF yield) DETAILED DESCRIPTION

[0036] The method of the present invention is described in detail below in conjunction with specific embodiments. In the present invention, 5-hydroxymethylfurfural can be abbreviated as HMF.

[0037] 1. A photothermal green catalytic synthesis method of 5-hydroxymethylfurfural

[0038] Example 1

[0039] A photothermal green catalytic synthesis method of 5-hydroxymethylfurfural, the steps are as follows:

[0040] 1) The carbon-based solid sulfonic acid (C1-SO3H) used in this example is prepared by reacting glucose with p-toluenesulfonic acid (TsOH).

[0041] The specific method is as follows: 4.0 g of glucose was mixed with 6.0 g of p-toluenesulfonic acid and 5.0 g of anhydrous sodium sulfate, respectively, and then transferred to a 100 mL hydrothermal reactor after grinding, and reacted and aged at 180°C for 48 h. After the reaction was completed, the black material was collected from the reactor and washed with hot water until no sulfate was detected in the filtrate (Ba 2+ Finally, dry in a vacuum oven at 100°C for 24 hours to obtain carbon-based solid sulfonic acid C1-SO3H (2.8825 g), grind to a certain mesh size and set aside (see Figure 1 Its structure was characterized by infrared spectroscopy (FT-IR) (see Figure 2), and the acid-base titration method measured the C1-SO3H acid content to be 1.5521mmol / g. The elemental analysis calculated the sulfonic acid content to be 1.2425mmol / g.

[0042] 2) 1.0 g of carbon-based solid sulfonic acid C1-SO3H with a particle size of 60-80 mesh and 9.0 g of fructose (50 mmol) were added to a 250 mL quartz reactor, followed by 100 mL of dimethyl sulfoxide (DMSO) as a solvent, covered with a quartz cover sheet, and stirred magnetically. After the raw materials were dissolved, the light source was turned on and the timing was started to examine the performance of C1-SO3H in photothermal catalysis of fructose dehydration to form HMF (photothermal reaction device see Figure 3 ). During the reaction, the temperature of the reaction system was measured once every 10 minutes using a thermometer to monitor the temperature change of the reaction system in real time; at the same time, a pipette was used to take a sample once every 10 minutes (0.1 mL), and the sample was fixed to 100 mL with deionized water; finally, high performance liquid chromatography (HPLC) was used to measure the concentration of the raw materials and products in the reaction system, and the raw material conversion rate and the yield of the target product were calculated to monitor the reaction progress.

[0043] Example 2

[0044] A photothermal green catalytic synthesis method of 5-hydroxymethylfurfural, the steps are as follows:

[0045] 1) The carbon-based solid sulfonic acid (C2-SO3H) used in this example is prepared by reacting glucose with 1,4-butane sultone. The specific method is as follows: 4.0g of glucose and 15.0g of 1,4-butane sultone are placed in a hydrothermal reactor and reacted at 180°C for 48h. After the reaction is completed, the black material is collected and washed with hot water until no sulfate is detected in the filtrate (Ba 2+ Finally, the mixture was dried in a vacuum oven at 100°C for 24 h to obtain carbon-based solid sulfonic acid C2-SO3H (2.6781 g), which was ground to a certain mesh size for later use (see Figure 1 Its structure was characterized by infrared spectroscopy (FT-IR) (see Figure 2 ), and the acid-base titration method measured the C2-SO3H acid content to be 1.1645mmol / g. The elemental analysis calculated the sulfonic acid content to be 1.0341mmol / g.

[0046] 2) 1.0 g of carbon-based solid sulfonic acid C2-SO3H with a particle size of 60-80 mesh and 9.0 g of fructose (50 mmol) were added to a 250 mL quartz reactor, followed by 100 mL of dimethyl sulfoxide (DMSO) as a solvent, covered with a quartz cover sheet, and stirred magnetically. The subsequent experimental process steps were the same as in Example 1.

[0047] Example 3

[0048] 1) The carbon-based solid sulfonic acid used in this example is C1-SO3H, with an amount of 0.50 g. Its preparation method is shown in Example 1.

[0049] 2) 0.50 g of carbon-based solid sulfonic acid C1-SO3H with a particle size of 60-80 mesh and 9.0 g of fructose (50 mmol) were added to a 250 mL quartz reactor, followed by 100 mL of dimethyl sulfoxide (DMSO) as a solvent, covered with a quartz cover sheet, and stirred magnetically. The subsequent experimental process steps were the same as in Example 1.

[0050] Example 4

[0051] 1) The carbon-based solid sulfonic acid used in this example is C1-SO3H, with an amount of 1.25 g. Its preparation method is shown in Example 1.

[0052] 2) 1.25 g of carbon-based solid sulfonic acid C1-SO3H with a particle size of 60-80 mesh and 9.0 g of fructose (50 mmol) were added to a 250 mL quartz reactor, followed by 100 mL of dimethyl sulfoxide (DMSO) as a solvent, covered with a quartz cover sheet, and magnetically stirred. The subsequent experimental process steps were the same as in Example 1.

[0053] Example 5

[0054] 1) The carbon-based solid sulfonic acid used in this example is 1.0 g C1-SO3H, and the solvent is sulfolane.

[0055] 2) 1.0 g of carbon-based solid sulfonic acid C1-SO3H with a particle size of 60-80 mesh and 9.0 g of fructose (50 mmol) were added to a 250 mL quartz reactor, followed by 100 mL of sulfolane as a solvent, covered with a quartz cover sheet, and stirred magnetically. The subsequent experimental process steps were the same as in Example 1.

[0056] Example 6

[0057] 1) The carbon-based solid sulfonic acid used in this example is 1.0 g C1-SO3H, and the amount of fructose is 4.5 g (25 mmol).

[0058] 2) 1.0 g of carbon-based solid sulfonic acid C1-SO3H with a particle size of 60-80 mesh and 4.5 g of fructose (25 mmol) were added to a 250 mL quartz reactor, followed by 100 mL of dimethyl sulfoxide (DMSO) as a solvent, covered with a quartz cover sheet, and stirred magnetically. The subsequent experimental process steps were the same as in Example 1.

[0059] Example 7

[0060] 1) The carbon-based solid sulfonic acid used in this example is 1.0 g C1-SO3H, and the amount of fructose used is 13.5 g (75 mmol).

[0061] 2) 1.0 g of carbon-based solid sulfonic acid C1-SO3H with a particle size of 60-80 mesh and 13.5 g of fructose (75 mmol) were added to a 250 mL quartz reactor, followed by 100 mL of dimethyl sulfoxide (DMSO) as a solvent, covered with a quartz cover sheet, and stirred magnetically. The subsequent experimental process steps were the same as in Example 1.

[0062] Example 8

[0063] 1) The carbon-based solid sulfonic acid used in this example is 1.0 g C1-SO3H, and the raw material is 17.1 g (50 mmol) of sucrose.

[0064] 2) 1.0 g of carbon-based solid sulfonic acid C1-SO3H with a particle size of 60-80 mesh and 17.1 g of sucrose (50 mmol) were added to a 250 mL quartz reactor, followed by 100 mL of dimethyl sulfoxide (DMSO) as a solvent, covered with a quartz cover sheet, and stirred magnetically. The subsequent experimental process steps were the same as in Example 1.

[0065] Example 9

[0066] 1) The carbon-based solid sulfonic acid used in this example is 1.0 g C1-SO3H, and the raw material is 8.1 g inulin (50 mmol fructose structural unit).

[0067] 2) 1.0 g of carbon-based solid sulfonic acid C1-SO3H with a particle size of 60-80 mesh and 8.1 g (50 mmol fructose structural unit) were added to a 250 mL quartz reactor, followed by 100 mL of dimethyl sulfoxide (DMSO) as a solvent, covered with a quartz cover sheet, and stirred magnetically. The subsequent experimental process steps were the same as in Example 1.

[0068] 2. Sample Analysis

[0069] 0.1 mL of the reaction solution was added to a 100 mL volumetric flask and fixed to volume with deionized water. The fixed volume solution was filtered through a 0.22 μm microporous filter membrane and analyzed by high performance liquid chromatography (HPLC, Agilent 1200), and quantified by external standard method. When analyzing the fructose conversion rate, an HPX-87H column (300×7.8 mm, 5 μm) was used, H2SO4 solution (5 mM) was used as the mobile phase, the flow rate was set to 0.6 mL / min, the column temperature was maintained at 65 °C, and the differential detector (RID) was used; when analyzing the yield of HMF, a C18 reverse phase column (250×4.6 mm, 5 μm) was used, CH3OH / H2O with a volume ratio of 1:4 was used as the mobile phase, the flow rate was set to 0.6 mL / min, the column temperature was maintained at 30 °C, and the ultraviolet detector (UV) was used, and the detection wavelength was 284 nm.

[0070] When using the external standard method to quantify fructose and products, it is necessary to first establish a corresponding standard curve, which is established by using the peak areas of different concentrations of fructose, HMF and other standards during HPLC analysis (e.g. Figure 4 and Figure 5 ).

[0071] During the sample analysis process, the raw material conversion rate (Conv., mol%) and HMF yield (Y HMF , mol%) and the corresponding selectivity (S HMF , mol%). The calculation formula is as shown in 1-3.

[0072]

[0073] Where M RF M F are the moles of fructose remaining in the reaction system and the fructose added at the beginning of the reaction, respectively; M HMF is the number of moles of HMF produced during the reaction.

[0074] Table 1 shows the reaction time when the HMF selectivity reaches the maximum value, the conversion rate of the raw material and the HMF yield of Examples 1 to 9

[0075]

[0076] Wherein: the raw material used in Example 8 is sucrose, which contains 1 molecule of fructose and 1 molecule of glucose structural unit in its molecule. During the photothermal catalytic conversion process, the fructose structural unit can be catalytically dehydrated to form HMF. Therefore, the yield and selectivity of HMF are calculated based on the fructose structural unit in the sucrose molecule; the raw material used in Example 9 is inulin (a fructan), and the fructose structural unit of inulin is catalytically depolymerized to form fructose during the photothermal reaction, and then further catalytically dehydrated to form HMF. The conversion of inulin is a step-by-step depolymerization process, so the conversion rate and HMF selectivity of inulin cannot be calculated in this embodiment, and the HMF yield can only be calculated by the amount of HMF generated and the number of fructose structural units in inulin.

[0077] from Figure 1 It can be seen that the two carbon-based solid sulfonic acids (C1-SO3H and C2-SO3H) prepared by carbonization of glucose and sulfonation reagent are black and have typical photothermal conversion function. The molecular structure of the prepared carbon-based solid sulfonic acid was characterized by infrared spectroscopy ( Figure 2 ), the results confirmed that both C1-SO3H and C2-SO3H contain sulfonic acid groups (—SO3H). -1 The characteristic peaks of 2800-2900 cm -1 The characteristic peaks of 1167cm are respectively attributed to the stretching vibration of C=C and CH in solid sulfonic acid, confirming the carbon-based properties of C1-SO3H and C2-SO3H. -1 and 1039cm -1 The characteristic peaks belong to the symmetric stretching vibration of O=S=O in the sulfonic acid group (—SO3H) and the sulfonic acid radical (—SO3 － ) stretching vibration. In addition, Figure 2 Medium 1700cm -1 and 3400cm -1 The characteristic peaks of are derived from the vibration absorption of C=O and OH, and are between 2300 and 2700 cm -1 The presence of obvious absorption bands indicates the presence of carboxyl (—COOH) structures in carbon-based solid sulfonic acids, a result that is consistent with the evolution of groups in the preparation of carbon-based materials using glucose as a raw material. Infrared spectroscopy results confirm the carbon-based solid sulfonic acid properties of C1-SO3H and C2-SO3H, which can be used as solid acid catalysts.

[0078] As shown in Table 1, the constructed carbon-based solid sulfonic acid has good photothermal catalytic activity. Under the irradiation of simulated sunlight, C1-SO3H and C2-SO3H both show good catalytic activity in DMSO. With fructose as the raw material, the selectivity of generating HMF reaches more than 95%. It can be considered that the fructose raw material can be directed converted under the photothermal catalytic reaction conditions ( Figure 6 ).from Figure 6 As can be seen from a, the temperature of the reaction system shows a rapid upward trend with the extension of the illumination time. When the illumination time reaches 1.0h, the temperature of the reaction system reaches above 110℃, indicating that the added C1-SO3H and C2-SO3H have good photothermal conversion performance; if the illumination time is further extended, the temperature of the reaction system remains unchanged at 114℃. Figure 6 It can be seen from bd that when the reaction system reaches a certain temperature, the dehydration reaction of fructose can be started and quickly converted to form HMF. With the continuous increase of reaction temperature (or the extension of illumination time), the conversion rate of fructose and the yield and selectivity of HMF all show an upward trend. The highest conversion rate of fructose reaches more than 98%, and the maximum yield and selectivity of HMF are both above 95%, indicating that C1-SO3H and C2-SO3H also have good catalytic activity in fructose dehydration. Overall, C1-SO3H and C2-SO3H have good photothermal conversion ability and acid catalytic activity, and can be used as catalytic materials for the preparation of HMF by green and efficient photothermal catalytic dehydration of fructose-based carbohydrates.

[0079] The amount of catalyst used has a great influence on the photothermal catalytic efficiency of the reaction system ( Figure 7 ). Figure 7 a It can be seen that with the increase in the amount of catalyst, the photothermal efficiency of the reaction system also shows an upward trend; when 0.50g C1-SO3H is used as the catalyst (Example 3), the photothermal conversion efficiency of the reaction system is significantly lower than 1.0g C1-SO3H (Example 1) and 1.25g C1-SO3H (Example 4), and the final photothermal temperature (102°C) is also much lower than Example 1 (114°C) and Example 4 (115°C). In addition, the amount of catalyst also has a great influence on the photothermal catalytic dehydration conversion efficiency of fructose ( Figure 7 bd). The reaction system with high catalyst dosage has high photothermal conversion efficiency. Meanwhile, the number of catalytic active centers in the catalyst is large (Example 4), which can realize the rapid photothermal catalytic dehydration reaction of fructose ( Figure 7 b); however, in the reaction system with high catalyst dosage, the probability of side reactions is higher and the yield of HMF is ( Figure 7 c) and selectivity ( Figure 7 d) is too low. For example, when 0.50g C1-SO3H is used as a catalyst (Example 3), the photothermal catalytic conversion efficiency of fructose is lower than that of 1.0g C1-SO3H (Example 1), the maximum yield of HMF is 85.1%, the selectivity is 90.4%, and the fructose conversion rate is only 94.2%. The time to achieve the best HMF yield is 120min (Example 3) ( Figure 7However, when the catalyst dosage was 1.25 g (Example 4), the conversion rate of fructose increased, but the yield (85.9%) and selectivity (86.5%) of HMF were much lower than those in Example 1 ( Figure 7 c,d).

[0080] The effect of solvent on the photothermal catalytic dehydration efficiency of fructose is also obvious ( Figure 8 ), DMSO is a common universal solvent, which has good solubility for carbohydrates such as fructose, and can also stabilize the HMF generated in the reaction system. Therefore, when DMSO is used as the solvent (Example 1), the yield of HMF is much higher than that of the photothermal catalytic system using sulfolane as the solvent (Example 5). Figure 8 As can be seen in a, in the presence of the photothermal catalytic material C1-SO3H, the reaction system can be quickly heated by light, and the maximum temperature of the reaction system can reach 114°C. However, through the analysis of the photothermal catalytic dehydration conversion efficiency of fructose in different solvent systems, it was found that when cyclopentane was used as the solvent, the dehydration conversion efficiency of fructose was low ( Figure 8 bd), the possible reason is that the solubility of fructose in sulfolane solvent is much lower than that in DMSO solvent system, which leads to the contact efficiency between fructose and catalyst being much lower than that in DMSO system, resulting in low fructose conversion efficiency.

[0081] Substrate concentration is also a key consideration in this photothermal catalytic system ( Fig. 9 ).from Fig. 9 As can be seen from a, the fructose concentration has little effect on the photothermal conversion efficiency of the reaction system. As the illumination time increases, the temperature change pattern of the reaction system is close, and the final reaction temperature is maintained at 114°C. However, the fructose concentration has a great influence on the conversion efficiency of its photothermal catalytic dehydration to prepare HMF. Fructose can undergo rapid dehydration reaction at low concentrations (Example 6) and high concentrations (Example 7) ( Fig. 9 b), but the efficiency of generating HMF varies greatly ( Fig. 9 c, d). When the amount of fructose added is small, the efficiency of photothermal catalytic conversion to form HMF is significantly higher than that of the reaction system with high fructose concentration. With the increase of fructose concentration, the yield and selectivity of HMF both show a downward trend, indicating that the reaction system with high fructose concentration has more by-products, which is not conducive to the directional conversion of fructose to HMF; however, low fructose concentration will also affect the production capacity of HMF. Overall, the fructose concentration in Example 1 is relatively appropriate, and the HMF yield and selectivity are both higher than 95%, which can be considered as the directional conversion of fructose to HMF.

[0082] In addition, the photothermal catalytic system also has a certain substrate applicability. The fructose structural unit contained in the raw material can be efficiently converted into HMF ( Fig.10 ).from Fig.10 As can be seen in a, the type of raw material does not affect the photothermal conversion efficiency of the reaction system. However, the efficiency of dehydration conversion to HMF of raw materials with different structures is obviously different ( Fig.10 b). For example, when sucrose (containing 1 molecule of fructose and 1 molecule of glucose structural unit) is used as raw material, the yield of HMF can reach 73.7% (Example 8); when fructan (inulin) is used as raw material, the yield of HMF can still reach 40.9% (Example 9), but both are lower than the reaction system directly using fructose as raw material (95.2%, Example 1). This shows that the photothermal catalytic system can also catalyze sucrose, fructan, etc. to form HMF through processes such as hydrolysis and dehydration. However, due to the limited contact between the carbon-based solid sulfonic acid catalyst and the fructan substrate, the yield of HMF is low. Overall, the constructed green photothermal catalytic reaction system has certain raw material applicability.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A photothermal green catalytic synthesis method of 5-hydroxymethylfurfural, characterized in that: Under the radiation of simulated sunlight, carbon-based solid sulfonic acid is used as a catalyst to heat the reaction system through photothermal heating, and fructose-based carbohydrates are selectively catalytically dehydrated to produce 5-hydroxymethylfurfural.

2. The 5-hydroxymethylfurfural photothermal green catalytic synthesis method according to claim 1, characterized in that: The specific steps include: (1) adding a certain amount of carbon-based solid sulfonic acid into an organic solvent to form a photothermal catalytic dehydration reaction system; (2) adding a certain amount of fructose-based carbohydrates into the photothermal reaction system, stirring magnetically, and performing a photothermal catalytic dehydration reaction under the radiation of simulated sunlight; The carbon-based solid sulfonic acid is a black carbon-based solid catalytic material containing a sulfonic acid active center; The organic solvent is one or more neutral aprotic organic solvents.

3. The photothermal green catalytic synthesis method of 5-hydroxymethylfurfural according to claim 2, characterized in that: The mass fraction of the carbon-based solid sulfonic acid relative to the raw material fructose-based carbohydrate is ≤15%.

4. The photothermal green catalytic synthesis method of 5-hydroxymethylfurfural according to claim 1, characterized in that: The mass volume ratio of the raw material fructose-based carbohydrate to the organic solvent is (1-50) g:100 mL.

5. The photothermal green catalytic synthesis method of 5-hydroxymethylfurfural according to claim 1, characterized in that: The fructosyl carbohydrates are carbohydrates containing fructose structural units.

6. The photothermal green catalytic synthesis method of 5-hydroxymethylfurfural according to claim 5, characterized in that: The carbohydrate is fructose, sucrose or inulin.

7. The photothermal green catalytic synthesis method of 5-hydroxymethylfurfural according to claim 1, characterized in that: The boiling point of the neutral aprotic organic solvent is ≥100°C.

8. The photothermal green catalytic synthesis method of 5-hydroxymethylfurfural according to claim 7, characterized in that: The neutral aprotic organic solvent is dimethyl sulfoxide or sulfolane.

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