Deep eutectic solvent catalyst synthesized based on agricultural straw as well as preparation method and application of deep eutectic solvent catalyst
The preparation of eutectic solvent catalysts from agricultural straw ash has solved the problems of high catalyst cost and low efficiency in PET recycling, achieving efficient and stable PET degradation, and promoting the development of green chemical processes and the resource utilization of agricultural waste.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-31
- Publication Date
- 2026-04-10
AI Technical Summary
In existing PET recycling technologies, catalysts are costly and inefficient, and traditional catalysts may cause metal residues or environmental pollution. There is insufficient systematic research on biomass catalysts, and deep eutectic solvents rely on commercial raw materials, resulting in resource waste and a heavy environmental footprint.
Potassium carbonate extracted from agricultural straw ash is synthesized with mannitol and glycerol to form a deep eutectic solvent catalyst for the degradation reaction of PET, achieving high-efficiency catalysis through a green and low-cost method.
It achieves efficient degradation of PET with high yield and significantly improved degradation efficiency. The catalyst has good stability, long service life and low catalyst consumption, promoting the sustainable development of plastic pollution control and green chemical processes.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to a deep eutectic solvent (DES) catalyst based on agricultural straw synthesis and its preparation method and application, belonging to the technical field of environmental catalysis and waste resource utilization. BACKGROUND
[0002] With the widespread use of plastic products in daily life, the recycling and disposal of plastics have become increasingly prominent. Polyethylene terephthalate (PET) is one of the most produced polyester plastics, widely used in beverage bottles, textiles, and packaging materials. However, the long-term accumulation and widespread disposal of PET has caused a persistent burden on the ecological environment, therefore, it is urgent to develop efficient and targeted PET recycling technologies to reduce its negative environmental impact and improve recycling levels.
[0003] Among current PET chemical recycling methods, glycolysis technology is considered one of the most promising recycling paths due to its mild reaction conditions and high value-added products. However, the glycolysis reaction rate without catalyst is extremely low, and the degradation efficiency is highly dependent on the performance of the catalyst. Therefore, developing green, environmentally friendly, low-cost, and efficient catalyst systems has become an important issue to be addressed.
[0004] Compared with traditional metal catalysts that may cause metal residues, low conversion rates of zeolite catalysts, high cost and toxicity of ionic liquid catalysts, biomass catalysts derived from natural resources have the advantages of low cost, environmental friendliness, and low corrosion, gradually becoming a hot topic in catalyst research. However, current research on biomass catalysts mostly focuses on the utilization of specific plant components, and the systematic study and application of agricultural waste (such as straw) are still insufficient. On the other hand, the ash generated during biomass power generation often fails to be properly disposed of, which not only wastes valuable resources but also may cause secondary pollution. Most deep eutectic solvent (DES) catalyst systems rely on commercial pure chemicals (such as choline chloride, pure organic acids, or polyols) as raw materials, and their synthesis is relatively mature, but still faces problems such as high raw material cost, high energy consumption in the preparation process, and heavy environmental footprint. Therefore, if we can extract effective substances (such as potassium carbonate) from agricultural waste and synthesize deep eutectic solvent (DES) catalysts, not only can we effectively slow down the activity decline of biomass catalysts, but also can realize the high-value utilization of waste, providing an innovative solution to plastic pollution management.
[0005] In summary, systematic study of the mechanism of agricultural straw derivatives as catalysts in the PET degradation process and optimization of their catalytic performance have important scientific significance and practical application value. This research not only helps to promote plastic pollution management and the development of green chemical processes, but also provides new ideas and technical paths for the resource utilization of agricultural waste. SUMMARY
[0006] The present application aims to overcome some technical problems existing in the prior art, and provides a deep eutectic solvent (DES) catalyst based on agricultural straw and a preparation method and application thereof, in particular, a deep eutectic solvent (DES) catalyst derived from agricultural waste (such as straw ash), aiming to provide an efficient, green and low-cost PET degradation catalyst technology.
[0007] To achieve the above technical purpose, the present application adopts the following technical scheme: The present application first provides a method for synthesizing a deep eutectic solvent (DES) catalyst based on agricultural straw, which comprises the following steps: Mixing straw ash with pure water, stirring and heating for reaction, collecting the filtrate, washing the residue, combining the washing liquid and the filtrate, evaporating and concentrating to obtain a concentrated solution; After cooling the concentrated solution, CO2 is introduced under stirring to adjust the pH value, and then ethanol is added, and after stirring, cooling and standing, the filter cake is collected and dried and heated to obtain potassium carbonate; Mixing the obtained potassium carbonate with mannitol and glycerol, heating to form a clear, transparent and uniform liquid to obtain a deep eutectic solvent catalyst.
[0008] Further, the straw includes rice straw, corn straw or wheat straw, and the use amount ratio of the straw ash to pure water is 1g:10mL; the rotary heating reaction is stirring and heating at 70℃ for 30min, then heating at 75℃ for 1h; the residue is washed with pure water; the evaporation and concentration is carried out at 80℃, and the solution is concentrated to 60% of the original solution volume.
[0009] Further, the cooling is cooling the concentrated solution to 30℃; the CO2 is introduced to adjust the pH value to 8-9; the amount of ethanol added is 19 times the volume of the concentrated solution; the cooling and standing is cooling to 5℃ and standing for 30min; the drying and heating is drying at 60℃ and then heating for 1h until the temperature reaches 150℃.
[0010] Further, the molar ratio of potassium carbonate, mannitol and glycerol is 1:1:7, and the heating is carried out at 120℃.
[0011] The present application also provides a deep eutectic solvent (DES) catalyst synthesized by the method.
[0012] The present application also provides the application of the deep eutectic solvent (DES) catalyst in degrading PET.
[0013] The application also provides a method for degrading PET, comprising: The deep eutectic solvent (DES) catalyst is added to the PET plastic for mixing, and then ethylene glycol is added for oil bath reaction.
[0014] Preferably, the amount of the deep eutectic solvent (DES) catalyst is 20% of the amount of PET.
[0015] Preferably, the ratio of the amount of ethylene glycol to the amount of PET is 12 mL: 1 g.
[0016] Preferably, the oil bath reaction is carried out at 180℃ for 4 h.
[0017] Compared with the prior art, the application has the following beneficial effects:
[0018] (1) The preparation method is green, pollution-free and low in cost: the application provides a preparation method of a deep eutectic solvent (DES) catalyst based on agricultural straw, which uses agricultural waste (such as rice straw ash) as raw material. The preparation method of the catalyst makes full use of agricultural waste, especially the alkali metal components in straw ash, by extracting potassium carbonate and synthesizing DES with mannitol and glycerol, a green, efficient and low-cost catalytic system is successfully constructed. This method extracts potassium carbonate from straw ash and synthesizes DES catalyst with glycerol and mannitol, which avoids the use of expensive chemical catalysts or metal salts, significantly reduces the preparation cost of the catalyst, and at the same time meets the concept of green chemistry, successfully constructing a green, efficient and low-cost catalytic system. The process is simple, and can effectively realize the high-value utilization of agricultural waste, has high economic and environmental benefits, not only provides an effective solution for the resource recycling of waste PET, but also promotes the sustainable development of plastic pollution control and green chemical process, and has a wide commercial application prospect.
[0019] (2) The catalyst prepared by the method has high catalytic activity and selectivity: the DES catalyst prepared by the method utilizes the alkali metal (such as potassium) component in the rice straw ash to form a deep eutectic solvent catalyst with high selectivity in the synthesis process, which can efficiently catalyze the degradation reaction of PET. The DES catalyst has good reaction selectivity, and in the PET degradation reaction, the main product is bis-hydroxyethyl terephthalate (BHET), the yield is high and the degradation efficiency is significantly improved, which is significantly higher than the zeolite catalyst, sodium carbonate catalyst and acetylcholine catalyst commonly used in the prior art. In addition, due to the unique properties of the DES catalyst, its catalytic effect remains stable in multiple cycles, showing a long service life and low catalyst consumption. It has been verified by experiments that after five cycles of catalytic experiments, the performance of the DES catalyst prepared by the method is slightly decreased, but still has a degradation rate of 60%. BRIEF DESCRIPTION OF DRAWINGS
[0020] Figure 1 The Fourier infrared spectrum (left) and thermogravimetric analysis (right) of the deep eutectic solvent (DES) catalyst, glycerol Gly, mannitol Mtl and potassium carbonate K2CO3 described in Example 1. Figure 1 Figure 1
[0021] Figure 2 The degradation effect of the potassium carbonate synthesized DES catalyst prepared at different pH values of the reaction solution.
[0022] Figure 3 The HPLC chart of the PET glycolysis product in Example 2.
[0023] Figure 4 The catalytic effect of different types of catalysts (Zeolite 4A: zeolite 4A, Na2CO3: sodium carbonate, DES-1: Zn(OAC)2+ChCl (acetylcholine), DES: K2CO3+Gly+Mtl) in Example 2 at 180℃, ethylene glycol 12 mL for 4 h.
[0024] Figure 5 The catalytic effect of the DES catalyst under different catalyst dosages (100mg, 200mg, 300mg, 400mg, 500mg) in Example 2, with ethylene glycol being 10 mL, the reaction temperature being 180℃ and the reaction time being 5 h.
[0025] Figure 6 The catalytic effect of the DES catalyst under different temperatures (reaction temperature 170~ 190℃) in Example 2, with ethylene glycol being 10 mL, the DES catalyst being added in an amount of 20% of the PET dosage and the reaction time being 5 h.
[0026] Figure 7 The catalytic effect of different catalytic time (reaction time 2-6 h) in Example 2, addition of 10 mL of ethylene glycol, reaction temperature of 180°C, and 20% of the amount of DES catalyst added to the amount of PET.
[0027] Figure 8 The catalytic effect of different ethylene glycol addition amounts (8-16 mL) in Example 2, reaction time of 4 h, reaction temperature of 180°C, and 20% of the amount of DES catalyst added to the amount of PET.
[0028] Figure 9 The catalytic effect of the DES catalyst after 5 cycles of catalysis in Example 2. DETAILED DESCRIPTION
[0029] In order for those skilled in the art to better understand the technical solutions of the present application, the preferred embodiments of the present application are described in detail below, but the following embodiments do not limit the protection scope of the present application.
[0030] In the embodiments of the present application, those not described in detail are completed using conventional experimental methods, and those not described in detail in the embodiments are understood and easily realized by those skilled in the art according to product instructions or basic knowledge in the art, and therefore are not described in detail.
[0031] Example 1: Preparation method of deep eutectic solvent (DES) catalyst based on agricultural straw
[0032] S1. Mix rice straw ash and pure water at a ratio of 1 g:10 mL, place in a stirring reactor, and stir and heat at 70°C for 30 minutes, then increase the temperature to 75°C and continue to stir and heat for 1 hour to promote the dissolution of soluble potassium salts in the straw ash, to obtain a mixed solution.
[0033] S2. Filter the obtained mixed solution, collect the filtrate and wash the residue with pure water, and combine the washing liquid and the filtrate.
[0034] S3. Place the combined washing liquid and filtrate in an evaporative concentration at 80°C until the solution volume is reduced to about 6 mL (original solution volume about 10 mL), to obtain a concentrated solution.
[0035] S4. Cool the concentrated solution to 30°C, slowly pass in carbon dioxide gas (CO2) under stirring conditions, and adjust the pH value of the solution to 8 or 9 to promote the generation of potassium bicarbonate.
[0036] S5. Add 114 mL of ethanol to the solution after adjusting the pH value, stir for 5 minutes to promote the precipitation of carbonate crystals. Then cool the mixed solution to 5°C and stand for 30 minutes to enhance the precipitation of crystals.
[0037] S6. The mixture obtained after standing is filtered, the filter cake is collected and dried at 60 °C, and the dried material is heated to 150 °C for 1 hour to cause thermal decomposition of the potassium bicarbonate to potassium carbonate, to obtain the potassium carbonate product.
[0038] S7. The potassium carbonate obtained is mixed with mannitol and glycerol in a molar ratio of 1:1:7, and heated to form a clear, transparent and homogeneous liquid at 120 °C to obtain the deep eutectic solvent (DES) catalyst.
[0039] The deep eutectic solvent catalyst obtained in step S7 is characterized using thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) characterization techniques.
[0040] The characterization results of TGA and FTIR are shown in Figure 1 , wherein the thermogravimetric analysis image Figure 1 (right) shows that the glycerol (Gly) is completely evaporated at 272 °C, while the DES catalyst still retains 45% of the weight, and the mannitol (Mtl) is completely evaporated at 405 °C, while the DES catalyst retains 25% of the mass. The mass residue of the DES catalyst prepared in this application at these two temperatures is greater than that of the simple physical mixture of the three substances (potassium carbonate, mannitol and glycerol in a molar ratio of 1:1:7) at these two temperatures, indicating that the formation of hydrogen bonds reduces the effect of temperature, proving the synthesis of the DES catalyst.
[0041] The FTIR image further reveals that glycerol has a typical -OH stretching vibration peak at 3300 cm -1 , and a C-O stretching peak near 1040 cm -1 . Mannitol has similar hydroxyl characteristic peaks, but the peak shape is more sharp near 1080 cm -1 , indicating that the intramolecular hydrogen bond is weaker. In the potassium carbonate spectrum, the main CO3 -1 symmetric stretching vibration peak appears at 1380 cm 2- . In the spectrum of the synthesized DES catalyst, the -OH stretching vibration peak obviously moves to a lower wave number (red shift from about 3300 cm -1 to about 3200 cm -1 ), and the C-O stretching peak also has a slight shift and a broadening characteristic, indicating that the hydrogen bond interaction is enhanced, indicating that the glycerol and mannitol molecules form a stable hydrogen bond network through the induction of potassium carbonate. These changes prove that new intermolecular interactions are formed inside the DES catalyst, rather than simple physical mixing.
[0042] The potassium carbonate synthetic DES catalysts prepared under pH 8 and pH 9 were used to investigate their degradation effects on PET under the same conditions, and the results are shown in Table 1. Figure 2 As can be seen from Table 1, the BHET yields of the potassium carbonate synthetic DES catalysts prepared under the two pH conditions are similar (the PET degradation rates are both above 99%). Therefore, it can be determined that the preparation pH of potassium carbonate has little effect on the catalytic performance of the final DES catalyst. Figure 2
[0043] The efficiency of glycolysis is mainly evaluated by PET conversion rate and BHET yield, and the optimization can realize high conversion rate of PET and high selectivity of BHET, thereby simultaneously improving the BHET yield. In the present application, the PET conversion rate (degradation rate) and BHET yield are calculated according to the following methods: 1.0 g of polyethylene terephthalate (PET), 12 mL of ethylene glycol (EG) and the DES catalyst obtained in Example 1 were added into a round-bottom flask equipped with a condenser, the round-bottom flask was immersed in an oil bath, and the reaction was carried out at 175℃ for 5 h. After the reaction, the unreacted PET sheet was removed by hot filtration with tweezers, washed with methanol, dried in an oven for 5 h, and weighed to calculate the PET conversion rate by formula (1):
[0044] wherein m 0，PET is the initial weight of PET plastic sheet (g), m 1，PET is the weight of unreacted PET after glycolysis reaction (g).
[0045] The main components of the filtrate are composed of glycolysis products, EG and catalyst. The purified filtrate was determined by high performance liquid chromatography, and based on the determination results, the BHET yield of glycolysis products can be calculated by formula (2):
[0046] wherein M BEHT is the molecular weight of BHET (M BEHT = 254 g / mol), M PET is the molecular weight of PET repeating unit (M PET = 192 g / mol); m BHET is the weight of BHET (g), which is calculated from the measurement results of high performance liquid chromatography (HPLC). The glycolysis product purification method is as follows: The filtrate was cooled in a refrigerator at -10 °C for 12 h and then filtered to obtain a solid containing BHET and oligomers. The solid was dissolved in 35 g of deionized water, heated at 60 °C for 30 min, and then filtered to obtain water-insoluble substances (oligomers). The aqueous solution was cooled in a refrigerator at 5 °C for 12 h and then filtered to obtain BHET solid. The BHET was determined by high performance liquid chromatography (LC-20 A, Shimadzu, Japan) with formic acid-acetonitrile-water (1:2:7 by volume) as the mobile phase, a flow rate of 1 mL / min, an injection volume of 20 μL, a column oven temperature of 30 °C, and a running time of 11 min. The results are shown in Table 1. Figure 3 As shown in Table 1, among the reaction products of PET glycolysis catalyzed by the DES catalyst, BHET occupies a significant advantage, indicating that the deep eutectic solvent DES as a catalyst has high selectivity.
[0047] Example 2: Analysis of influencing factors of PET glycolysis S1. Comparison of degradation effects of different catalysts
[0048] To determine the degradation effect of the deep eutectic solvent DES catalyst prepared by the method described in Example 1, this example compares the catalyst Zeolite 4A (5% of the PET dosage, purchased from Shanghai Macklin Biochemical Company), sodium carbonate Na2CO3 (5% of the PET dosage, purchased from National Pharmaceutical Chemical Reagent Co., Ltd.), acetylcholine DES-1: Zn(OAC)2+ChCl (5% of the PET dosage, from Shanghai Macklin Biochemical Company) with the DES catalyst (K2CO3+Gly+Mtl) synthesized in this application (5% of the PET dosage).
[0049] 1 g of PET plastic was added with 5% of the PET dosage of catalyst Zeolite 4A, sodium carbonate Na2CO3, acetylcholine DES-1, and the DES catalyst synthesized in this application, respectively, and then 12 mL of ethylene glycol was added. The degradation reaction was carried out at 180 °C for 4 h in an oil bath to verify the catalytic effect of each catalyst.
[0050] As shown in Table 2, PET was degraded to different degrees within 4 h, and the yield of BHET was the highest (88.4%) when the deep eutectic solvent DES was used as the catalyst, and the PET degradation rate was 99.1%. Figure 4
[0051] S2. Catalyst dosage exploration experiment
[0052] The PET degradation experiment was carried out with the deep eutectic solvent DES as a catalyst to verify the optimal catalyst dosage; the PET addition amount was 1 g, the catalyst dosage was set to be 10, 20, 30, 40 and 50% (mass percentage) of the PET amount, the reaction temperature was 175 DEG C, 10 mL of ethylene glycol was added, and the reaction time was 5 h.
[0053] As shown in the results Figure 5 , too low catalyst dosage is difficult to promote the reaction, resulting in too low monomer yield. In contrast, when the catalyst addition amount is 20% (200 mg) of the PET amount, the monomer yield is the highest, and the reaction reaches equilibrium; further addition of catalyst will promote the formation of by-products, thereby reducing the yield, so the optimal catalyst dosage is 20%.
[0054] S3. Reaction temperature exploration experiment
[0055] The PET degradation experiment was carried out with the prepared deep eutectic solvent DES as a catalyst to verify the optimal reaction temperature; the PET addition amount was 1 g, the reaction time was set to be 170, 175, 180, 185 and 190 DEG C, 20% of the PET amount of catalyst was added, and 10 mL of ethylene glycol was added, and the reaction time was 5 h.
[0056] As shown in the results Figure 6 , with the increase of temperature, the BHET yield gradually increases, and the PET conversion rate also increases, and the monomer yield is the highest at 180 DEG C; based on cost-effectiveness, the optimal oil bath reaction temperature is 180 DEG C.
[0057] S4. Reaction time exploration experiment
[0058] The PET degradation experiment was carried out with DES as a catalyst to verify the optimal reaction time; the PET addition amount was 1 g, the reaction time was set to be 2, 3, 4, 5 and 6 h, the reaction temperature was 180 DEG C, 10 mL of ethylene glycol was added, and the catalyst dosage was 20% of the PET amount.
[0059] As shown in the results Figure 7 , the monomer yield reaches the highest after 4 h of degradation experiment, and too long reaction time will cause the re-polymerization of monomers.
[0060] S5. Ethylene glycol dosage exploration experiment
[0061] The PET degradation experiment was carried out with DES as a catalyst to verify the optimal ethylene glycol dosage; the PET addition amount was 1 g, the ethylene glycol dosage was set to be 8, 10, 12, 14 and 16 mL, the reaction temperature was 180 DEG C, the reaction time was 4 h, and the catalyst dosage was 20%.
[0062] Results are shown in Figure 8 Table 2. The degradation experiment has the highest yield of BHET (about 88%) when the amount of EG is 12 mL. Too low amount of EG will reduce the contact of catalyst with PET, and too high amount of EG will reduce the concentration of catalyst, so the optimal amount of EG is 12 mL.
[0063] Catalyst recycling experiment:
[0064] PET plastic bottle fragments (1 g), DES catalyst (200 mg, 20% of the amount of PET) and EG (12 mL) were heated at 180°C for 4 h. After the reaction was completed, the solid was separated by filtration, and the unreacted PET plastic fragments were separated with tweezers and rinsed with methanol. The residual plastic was weighed, and the monomer yield was determined by HPLC.
[0065] Results are shown in Figure 9 After five cycles of catalytic experiments, the performance of the catalyst decreased slightly, but the degradation rate was still 60%, indicating that the catalyst had good recycling properties.
[0066] The above description is only a preferred embodiment of the present application, and does not limit the present application in any form. Any person skilled in the art can make many possible changes and modifications to the technical solutions of the present application, or modify equivalent embodiments, without departing from the spirit and technical solutions of the present application, by using the disclosed methods and technical contents. Therefore, any simple modification, equivalent replacement, equivalent change and modification of the above embodiments by any person skilled in the art within the technical range disclosed by the present application, according to the technical essence of the present application, should be covered within the protection scope of the present application.
Claims
1. A method for synthesizing a deep eutectic solvent catalyst based on agricultural straw, characterized in that, The method includes: Straw ash is mixed with pure water, stirred and heated to react, the filtrate is collected, the residue is washed, the washing liquid and filtrate are combined, and the mixture is evaporated and concentrated to obtain a concentrated liquid. After cooling the obtained concentrate, CO2 was introduced under stirring to adjust the pH value, then ethanol was added, stirred, cooled and allowed to stand, filtered to collect the filter cake, dried and heated to obtain potassium carbonate. The obtained potassium carbonate was mixed with mannitol and glycerol and heated until a clear, transparent and homogeneous liquid was formed, thus obtaining a deep eutectic solvent catalyst.
2. The method according to claim 1, characterized in that, The straw includes rice straw, corn straw, or wheat straw, and the ratio of straw ash to purified water is 1g:10mL; the stirring and heating reaction is carried out by rotating and heating at 70℃ for 30 min, then raising the temperature to 75℃ and continuing to heat for 1 h; the washing residue is washed with purified water; the evaporation and concentration are carried out at 80℃ until the solution volume is 60% of the original solution volume.
3. The method according to claim 1, characterized in that, The cooling process involves cooling the concentrate to 30°C; the pH value is adjusted to 8-9; the amount of ethanol added is 19 times the volume of the concentrate; the cooling and settling process involves cooling to 5°C and settling for 30 minutes; the drying and heating process involves drying at 60°C and then heating for 1 hour until the temperature reaches 150°C.
4. The method according to claim 1, characterized in that, The molar ratio of potassium carbonate, mannitol and glycerol is 1:1:7, and the heating is carried out at 120°C.
5. The eutectic solvent catalyst synthesized by the method according to any one of claims 1-4.
6. The application of the eutectic solvent catalyst synthesized by the method of any one of claims 1-4 or the eutectic solvent catalyst of claim 5 in the degradation of PET.
7. A method for degrading PET, characterized in that, The method includes: The eutectic solvent catalyst synthesized by any one of claims 1-4 or the eutectic solvent catalyst of claim 5 is added to PET plastic and mixed, and then ethylene glycol is added to carry out an oil bath reaction.
8. The method according to claim 7, characterized in that, The amount of the deep eutectic solvent catalyst is 10-50% of the amount of PET, the amount of ethylene glycol to PET is 8-16 mL: 1 g, and the oil bath reaction is carried out at 170-190℃ for 2-6 hours.
9. The method according to claim 8, characterized in that, The amount of deep eutectic solvent (DES) catalyst is 20% of the amount of PET, the amount of ethylene glycol to PET is 12 mL: 1 g, and the oil bath reaction is carried out at 180°C for 4 hours.