Caffeic acid adsorbent based on cycleanine polymer as well as preparation method and application of caffeic acid adsorbent

Abstract

The invention discloses a caffeic acid adsorbent based on cycleanine polymer as well as a preparation method and application thereof, the adsorbent is prepared by taking cycleanine as a functional monomer through cross-linking polymerization with tri (bromomethyl) benzene, and the adsorbent has a specific porous structure and surface chemical properties. The preparation method comprises the steps of reflux reaction in an acetonitrile solvent, washing, drying and the like. During application, the adsorbent is added into a sucrose solution, and phenolic substances such as caffeic acid and the like can be efficiently removed under optimized conditions. The adsorption capacity of the adsorbent to caffeic acid is remarkably higher than that of a traditional material, the adsorbent can be regenerated and reused through alkali washing, and the technical problems that an existing clarification process is low in phenolic substance removal rate and secondary pollution is generated are solved. The technology can be embedded into an existing production line of a sugar factory, clean production is achieved while the quality of the white granulated sugar is improved, and the technology has important application value.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of clarification technology in sugar industry, and particularly relates to a caffeic acid adsorbent based on cyclanolin polymer and a preparation method and application thereof. BACKGROUND

[0002] Cane sugar produced from sugarcane accounts for more than 50% of the consumption of sugar in China. In the production process of sugarcane sugar, the color and color value of cane sugar are one of the main indicators for evaluating the quality of cane sugar, and the content of phenolic substances in cane juice is the main factor affecting the indicators. There are many phenolic substances in sugarcane, and the main water-soluble pigments with high content are chlorogenic acid, gallic acid and caffeic acid, among which the content of caffeic acid is the highest. In the processing of sugarcane sugar, phenolic substances enter the intermediate material cane juice, and form dark substances under the action of enzymes and amino acids, so that the color value of the key indicator of white granulated sugar increases, thereby affecting the quality of white granulated sugar.

[0003] Caffeic acid is a common polyphenolic compound, which exists in many foods and beverages, especially in coffee. Although caffeic acid has various biological activities, however, the excessive content of caffeic acid in cane sugar solution in the production of cane sugar can adversely affect the quality and stability of the product.

[0004] In the clarification process of cane juice, the removal rate of phenolic substances has a great influence on the quality of cane sugar products. At present, there are mainly two kinds of clarification production processes for sugarcane sugar: one is sulfite method, and the other is carbonic acid method. Although these two methods are very common in sugar factories and have been used for a long time, they still have many shortcomings. About 90% of the sugarcane sugar factories in China use the sulfite method for clarification production process, which mainly includes pre-ash addition of phosphorus, primary heating, sulfur fumigation neutralization, secondary heating, sedimentation and filtration, etc. The equipment operation is simple, and the production cost is low, but it is not sufficient in removing the turbidity and colority of the original cane juice, and only 1 / 3 of the phenolic substances can be removed. Moreover, sulfur dioxide is needed as a clarifying agent, which can easily increase the sulfur content of the finished sugar, leading to certain food safety hazards. Although the carbonic acid method produces finished sugar with better quality than the sulfite method, and mainly uses lime milk and carbon dioxide as clarifying agents, it has the problems of long production process, many equipment, high production cost, high content of filter mud calcium salt and difficult treatment of alkaline waste, which can easily cause environmental pollution.

[0005] Therefore, it is of great significance to develop an adsorbent for efficiently removing caffeic acid in cane sugar solution. SUMMARY

[0006] In view of the above, it is necessary to provide a caffeic acid adsorbent based on cyclanolin polymer and a preparation method and application thereof, to solve the technical defects of low removal rate of caffeic acid and secondary pollution in the existing clarification process.

[0007] To achieve the above object, the technical scheme adopted by the present application is:

[0008] A caffeic acid adsorbent based on cyclam polymer, which is prepared by cross-linking polymerization reaction of cyclam (1,4,7,10-tetraazacyclododecane) and tris(bromomethyl)benzene.

[0009] In the present application, further, the infrared spectrum of the adsorbent has O—H stretching vibration peak at 3640.8 cm -1 , N—H stretching vibration peak at 1636.1 cm -1 , and rough porous structure on the surface.

[0010] In the present application, further, the specific surface area of the adsorbent is 80-150 m 2 / g, the pore volume is 0.3-0.6 cm 3 / g, and the isoelectric point pHpzc is 8.29-8.33.

[0011] The present application also proposes a preparation method of the above-mentioned cyclam-based polymer adsorbent, which comprises the following steps:

[0012] (a) dissolving cyclam, tris(bromomethyl)benzene and potassium carbonate in acetonitrile in a molar ratio of 1:1.05-1.15:3.0-3.5;

[0013] (b) then refluxing at 78-82℃ for 23.5-24.5h;

[0014] (c) after the reaction, sequentially washing the product with N,N-dimethylformamide, dimethyl sulfoxide, distilled water and ethanol;

[0015] (d) vacuum drying the washed product at 59-62℃ for 11.5-12.5h to obtain the porous polymer adsorbent PCT.

[0016] The present application also proposes a method for removing caffeic acid from a sucrose solution by using the above-mentioned adsorbent, which comprises the following steps:

[0017] (1) adjusting the pH of the sucrose solution to 5.0-7.0;

[0018] (2) adding PCT adsorbent at an addition amount of 0.9-1.1 g / L;

[0019] (3) adsorbing and treating at 23-27℃ and a shaking speed of 240-260 r / min for 570-630 min.

[0020] In the application, further, the initial concentration of caffeic acid in the sucrose solution is 200-400 mg / L; the removal rate of caffeic acid is greater than or equal to 95% at adsorption equilibrium, and the maximum adsorption capacity is 375.94 mg / g (Langmuir model fitting value).

[0021] In the application, further, the adsorption process conforms to the pseudo-second-order kinetics model (R 2 ≥0.997), and the rate constant k2 is 1.96*10 -4 -3.22*10 -4 g / (mg*min).

[0022] In the application, further, the adsorbed adsorbent PCT is regenerated by desorption with 0.1 mol / L NaOH solution, the desorption time is 7.5-8.5 h, and the adsorption rate is maintained greater than or equal to 90% after 5 cycles of use.

[0023] The application also provides a sucrose clarification process, specifically, after the sulfite method or carbonic acid method clarification process, the method according to any one of claims 5-6 is used to remove caffeic acid, so that the color value of the finished white granulated sugar is reduced by greater than or equal to 30%.

[0024] The application has the following beneficial effects:

[0025] The application provides a caffeic acid adsorbent based on lycium barbarum L. polymer, a preparation method and application thereof, solves the technical defects of low removal rate of caffeic acid and secondary pollution in the existing clarification process, and has the following breakthroughs:

[0026] (1) Pioneering material design: the medical-grade lycium barbarum L. material is first innovatively applied to the sugar industry, a three-dimensional porous polymer network is constructed through a specific crosslinking process, the unique pore size distribution and surface chemical properties thereof realize efficient recognition and capture of caffeic acid molecules, and the bottleneck of poor selectivity of traditional adsorption materials is broken through.

[0027] (2) Process compatibility innovation: the adsorption-regeneration integrated process developed in the application can be directly embedded into the existing sugar production line, and operates under mild conditions (room temperature, near-neutral pH), which not only avoids the high energy consumption problem of the carbonic acid method, but also completely solves the sulfur residue hidden danger of the sulfite method, and realizes clean production.

[0028] (3) Resource recycling breakthrough: the adsorbent of the application can be regenerated and reused by simple alkaline washing, a caffeic acid resource recycling channel is first established in the sugar industry field, the regenerated wastewater is non-toxic and can be reused, and the generation of filter mud and other solid wastes is eliminated from the source.

[0029] In summary, through the whole-chain innovation of "molecular design-process optimization-recycling", the quality of sucrose products (color value, purity, etc. core indicators) is significantly improved, and the sugar industry is promoted to green and low-carbon transformation, which has important industrial popularization value. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 SEM microstructure diagram of the product of Example 1;

[0031] Figure 2 SEM microstructure diagram of the product of Example 1;

[0032] Figure 3 Effect of pH on adsorption;

[0033] Figure 4 Fitting curve of intraparticle diffusion model;

[0034] Figure 5 Effect of temperature on adsorption;

[0035] Figure 6 Effect of concentration on adsorption;

[0036] Figure 7 Effect of adsorbent addition amount on adsorption;

[0037] Figure 8 Regeneration performance results;

[0038] Figure 9 Adsorption material comparison experiment results.

DETAILED DESCRIPTION

[0039] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. In the following description, a large number of specific details are set forth in order to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the spirit of the present application, therefore the present application is not limited to the specific implementation disclosed below.

[0040] Example 1: Preparation and characterization of PCT adsorbent

[0041] This embodiment provides a preparation method of PCT adsorbent, and the synthesis process includes the following steps:

[0042] (1) Under the protection of nitrogen, 1.0 g of cyclotriveratrylene (4.6 mmol), 2.76 g of tris(bromomethyl)benzene (5.1 mmol) and 2.5 g of potassium carbonate were added to 150 mL of anhydrous acetonitrile;

[0043] (2) The reaction was refluxed in an oil bath at 80°C for 24 hours, and the reaction progress was monitored by TLC (developing solvent: methanol / chloroform = 1:9, Rf = 0.3);

[0044] (3) After filtration, wash three times each with N,N-dimethylformamide DMF, dimethyl sulfoxide DMSO, deionized water (conductivity <5μS / cm), and ethanol.

[0045] (4) The washed product was vacuum dried at 60°C for 12 h to obtain white porous polymer PCT (2.41 g, yield 86.2%).

[0046] Structural characterization:

[0047] Please refer to the infrared spectrum of the product. Figure 1 3640.8cm -1 A broad peak indicates the stretching vibration of free OH groups (due to residual solvent ethanol).

[0048] 1636.1cm -1 Strong peak: secondary amine NH bending vibration (ring ring Tennin unit); 1480-1520 cm⁻¹ -1 Bimodal: Benzene ring skeleton vibration (tribromomethylbenzene crosslinking agent).

[0049] Please refer to the SEM microstructure image. Figure 2 , Figure 2 A(PCB): Smooth and dense surface, average pore size <5nm; Figure 2 B(PCT): The surface forms a honeycomb porous structure with a pore size distribution of 20-50nm (the pores indicated by the arrows are caffeic acid adsorption channels).

[0050] Example 2: Adsorption process parameter optimization experiment

[0051] 1. pH effect:

[0052] step:

[0053] Prepare a 400 mg / L caffeic acid sucrose solution (sucrose concentration 12%, simulating actual sugar juice);

[0054] Adjust the pH to 5.0, 6.0, 7.0, 8.0, and 9.0 using 0.1 mol / L HCl / NaOH.

[0055] Take 30 mL of each solution, add 0.03 g of PCT adsorbent, and shake at 25 °C for 10 h.

[0056] The results are as follows Figure 3As shown, within the pH range of 5–9, the adsorption rate curve of PCT for caffeic acid varies significantly with increasing pH. At pH 6, the adsorption rate is 90.13%, while the adsorption rates at other pH values ​​are all below 90%. Therefore, this experiment indicates that pH 6 is the optimal pH for the experiment.

[0057] 2. Adsorption kinetics:

[0058] step:

[0059] Take 30 mL of 200 mg / L caffeic acid solution (pH = 6) and add 0.03 g of PCT adsorbent;

[0060] Oscillate at 250 rpm at 25℃, and take samples for testing at 10, 30, 60...600 min.

[0061] After shaking, remove the conical flask, filter it with filter paper, transfer 1 mL of the filtrate, and measure the absorbance according to procedure 2.3.1. The recorded data can be calculated using the following equation:

[0062] Quasi-first-order dynamic model: ln(q) e -q t )=lnq e -k1t;

[0063] Quasi-second-order dynamic model:

[0064] Intraparticle diffusion model: q t =k d t 1 / 2 +c;

[0065] In the formula: q t q represents the adsorption amount at time t, in mg / g; e K1 is the equilibrium adsorption capacity, mg / g; K1 is the pseudo-first-order kinetic constant, min. -1 K2 is the pseudo-second-order kinetic constant, g / (mg·min); K d It is the constant of the intraparticle diffusion equation, mg / (g·min) 1 / 2 ).

[0066] As shown in Table 1:

[0067] Table 1 Adsorption kinetic fitting parameters

[0068]

[0069] It can be seen that the quasi-second-order model fits: R 2 =0.99796, k2 = 3.22 × 10 -4g / (mg·min); theoretical equilibrium adsorption capacity qe = 197.62 mg / g (measured 198.68 mg / g). During the adsorption of caffeic acid and sucrose solutions at 200 mg / L and 400 mg / L, the correction parameters R² for the pseudo-second-order adsorption kinetics fitting (0.99769 and 0.99738) were higher than those for the pseudo-first-order adsorption kinetics fitting (0.90736 and 0.86769) and the intraparticle diffusion model fitting (0.91550 and 0.96268). Furthermore, since the calculated pseudo-second-order kinetic parameter qe values ​​(197.62 mg / g and 361.01 mg / g) more closely approximate the values ​​of qe exp (198.68 mg / g and 361.78 mg / g), the pseudo-second-order kinetic model, which primarily involves chemisorption, is more suitable for the PCT adsorption of caffeic acid.

[0070] Intraparticle diffusion model, such as Figure 4 The fitting curves of the intraparticle diffusion model show that the adsorption curves of 200 mg / L and 400 mg / L caffeic acid sucrose solutions did not pass through the origin. This indicates that intraparticle diffusion is not the only limiting factor affecting the PCT adsorption process. Boundary effects, surface adsorption, and the synergistic effect of intraparticle diffusion must also be considered.

[0071] 3. Temperature effect experiment:

[0072] step:

[0073] Prepare a 500 mg / L caffeic acid solution (pH = 6.0) and dispense it into 5 portions of 30 mL each;

[0074] The temperatures were controlled at 25, 30, 40, 50, and 60℃ respectively (water bath accuracy ±0.5℃);

[0075] Add 0.03g PCT, shake at 250rpm for 12 hours, and then test.

[0076] Result: As Figure 5 As shown, within the temperature range of 25–60℃, the adsorption capacity of PCT for caffeic acid increases with increasing temperature. This increase in adsorption capacity may be due to the increased surface porosity and active sites of PCT for caffeic acid as the temperature gradually rises, leading to a faster adsorption rate. However, higher temperatures also increase economic costs. Therefore, considering energy consumption during the experiment, the optimal temperature is 25–40℃.

[0077] 4. Effect of initial concentration:

[0078] step:

[0079] Prepare caffeic acid solutions of 100, 200, 250, 300, and 400 mg / L (pH = 6.0);

[0080] Take 30 mL of each sample, add 0.03 g of PCT, and shake at 25°C and 250 rpm for 12 h.

[0081] As a result, Figure 6 As shown, when the concentration is between 0 and 400 mg / L, the adsorption capacity of PCT for caffeic acid increases continuously with increasing concentration. This is because there are more adsorption sites on its surface, resulting in a faster adsorption rate; however, the adsorption rate decreases continuously. When the concentration is less than 300 mg / L, the adsorption rate is close to 100%, indicating oversaturation; at a concentration of 400 mg / L, the adsorption rate is less than 90%; and at a concentration of 300 mg / L, the adsorption rate is 95.96%. In conclusion, the optimal concentration should be 300 mg / L.

[0082] 5. Optimization of adsorbent dosage:

[0083] step:

[0084] Take 30 mL of 300 mg / L caffeic acid solution (pH = 6.0) and divide it into 5 portions;

[0085] Add 0.01, 0.02, 0.03, 0.04, and 0.05 g of PCT (0.33-1.67 g / L) respectively;

[0086] Shake at 25℃ and 250rpm for 10 hours.

[0087] As a result, Figure 7 As shown, when the PCT addition amount is between 0.01 and 0.05 g, the adsorption capacity curve shows a decreasing trend, decreasing from 649.04% to 181.73% with increasing addition amount; the adsorption rate curve, however, shows an increasing trend. When the addition amount is greater than 0.03 g, the adsorption rate gradually stabilizes. This is because the surface active sites of PCT gradually increase with increasing addition amount, leading to an increase in adsorption rate. However, when adsorption tends to stabilize, the surface active sites of PCT adsorbing caffeic acid decrease, thus slowing down the adsorption rate, resulting in a smaller change in adsorption rate. Therefore, the optimal addition amount of PCT is 0.03 g (i.e., a concentration of 1.0 g / L).

[0088] Example 3: Industrial-grade regeneration and stability testing

[0089] 1. Regeneration operation procedure:

[0090] The PCT saturated by adsorption was separated by filter paper and dried at 60°C for 2 hours.

[0091] Immerse in 100 mL of 0.1 mol / L NaOH solution and shake at 25 °C for 8 h (to dissolve the caffeic acid-amino complex);

[0092] Wash with water until neutral (pH = 7.0 ± 0.2), then vacuum dry at 60°C for later use.

[0093] 2. Cyclic performance test results are as follows: Figure 8 As shown, after 5 cycles, the adsorption rate of PCT can still be maintained at about 90%. This shows that PCT not only has good regeneration performance, but also can effectively adsorb caffeic acid in sucrose solution, and can be used as a clarifier for sucrose.

[0094] Example 4: Integrated Scheme for Pilot-Scale Processes in Sugar Factories

[0095] 1. Process conditions:

[0096] Target material: Sugarcane juice pre-clarified by the sulfite process; Processing capacity: 2 tons / hour; Initial caffeic acid concentration: 350±20 mg / L; PCT loading: 15 kg (fixed bed adsorption tower).

[0097] Adsorption tower parameters (material: 316L stainless steel, filled with PCT adsorbent): Tower height: 1.2m; Diameter: 0.8m; Bed height: 1.0m;

[0098] Operating conditions: Flow rate: 3 BV / h; Contact time: 40 min (to ensure adsorption equilibrium); Temperature: 25-30℃; pH: 6.0±0.2

[0099] 2. Recycling process:

[0100] Regeneration solution: 0.1 mol / L NaOH solution, liquid-to-solid ratio 10:1 (L / kg); regeneration method: countercurrent regeneration; regeneration time: 8 h; regeneration temperature: 25 ℃; regeneration cycle: once every 8 hours.

[0101] After regeneration, PCT is returned to the adsorption tower for reuse, with a loss rate of <3% / cycle.

[0102] 3. Key equipment configuration is shown in Table 2:

[0103] Table 2 Key Equipment Configuration

[0104]

[0105] 4. The running results are shown in Table 3:

[0106] Table 3. Operational Results (30 consecutive days)

[0107]

[0108] The results show that the PCT integrated process achieves significant improvements compared to the traditional sulfite process: the white sugar color value is reduced by 45.1%, caffeic acid residue is reduced by 91.4%, and filter mud generation is completely eliminated while steam consumption is reduced by 10.7%. This process not only significantly improves product quality but also achieves cleaner production, demonstrating significant economic and environmental benefits.

[0109] Example 5: Key Comparative Experiment

[0110] 1. Effects of different crosslinking agents:

[0111] Please see Figure 9 When the concentration ranges from 0 to 600 mg / L, the adsorption capacity of both PCB and PCT for caffeic acid in sucrose solution increases with increasing concentration. However, the adsorption capacity of PCT is significantly higher than that of PCB. Therefore, PCT has a more significant effect on the adsorption of caffeic acid in sucrose solution than PCB, and its adsorption effect is better. Figure 2 PCB has a layered structure with low porosity, while PCT has three-dimensional interconnected channels. Therefore, PCT was chosen as the adsorption material for subsequent experiments.

[0112] 2. Compared with traditional adsorbents:

[0113] Take a 300 mg / L caffeic acid solution (pH = 6), and add the following adsorbent at a concentration of 1 g / L. The adsorbents and comparison results are shown in Table 4:

[0114] Table 4 Comparison results with traditional adsorbents

[0115] Adsorbent Equilibrium time (h) Adsorption capacity (mg / g) Adsorption decay rate after regeneration Activated carbon 8 210.5 > 40% (5 cycles) Cationic resin 10 185.7 Not regenerable PCT 10 375.9 <6% (5 cycles)

[0116] Table 4 shows that PCT adsorbent significantly outperforms traditional adsorbents in adsorption performance: its caffeic acid adsorption capacity reaches 375.9 mg / g, which is 1.8 times and 2 times that of activated carbon and cation exchange resin, respectively. It also exhibits excellent regenerability, with an adsorption decay rate of less than 6% after 5 cycles. This result confirms that PCT possesses both high adsorption capacity and good cycling stability, giving it significant advantages in industrial applications.

[0117] In summary, this invention provides a novel adsorbent (PCT) based on cyclohexane-based polymers, its preparation method, and its application in sucrose clarification. Through a specific cross-linking process, the adsorbent achieves an adsorption capacity of 375.9 mg / g for caffeic acid, which is more than 45% higher than that of traditional methods. Furthermore, it can be recycled more than 5 times (adsorption decay rate <6%), solving the technical problems of low removal rate of phenolic substances and generation of sulfur / calcium-containing waste in existing sugar factory clarification processes, and achieving a significant effect of reducing the color value of white sugar.

[0118] The above embodiments are merely examples of several implementations of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention.

Claims

1. A caffeic acid adsorbent based on cyclohexane polymer, characterized in that, The adsorbent was prepared by cross-linking polymerization of cyclohexane (1,4,7,10-tetraazacyclododecane) and tri(bromomethyl)benzene.

2. The adsorbent according to claim 1, characterized in that, The infrared spectrum of the adsorbent is at 3640.8 cm⁻¹. -1 An O-H stretching vibration peak exists at 1636.1 cm⁻¹. -1 There is an N-H stretching vibration peak at the point, and the surface has a rough and porous structure.

3. The adsorbent according to claim 1, characterized in that, The specific surface area of ​​the adsorbent is 80-150 m². 2 / g, pore volume 0.3-0.6cm 3 / g, isoelectric point pHpzc = 8.29-8.

33.

4. The method for preparing the ring-shaped terpinenyl polymer adsorbent according to any one of claims 1-3, characterized in that, Includes the following steps: (a) Dissolve cyclohexane, tri(bromomethyl)benzene and potassium carbonate in acetonitrile at a molar ratio of 1:1.05-1.15:3.0-3.5; (b) Then reflux at 78-82°C for 23.5-24.5 h; (c) After the reaction was completed, the product was washed sequentially with N,N-dimethylformamide, dimethyl sulfoxide, distilled water and ethanol; (d) The washed product was vacuum dried at 59-62℃ for 11.5-12.5h to obtain the porous polymer adsorbent PCT.

5. A method for removing caffeic acid from a sucrose solution using the adsorbent according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Adjust the pH of the sucrose solution to 5.0-7.0; (2) Add PCT adsorbent at a dosage of 0.9-1.1 g / L; (3) Adsorption treatment at 23-27℃ and oscillation speed of 240-260r / min for 570-630min.

6. The method according to claim 5, characterized in that, The adsorbent PCT after adsorption is regenerated by desorption with 0.1 mol / L NaOH solution for 7.5-8.5 h. After being recycled 5 times, the adsorption rate remains ≥90%.

7. A sucrose clarification process, characterized in that, Specifically, after the clarification process using the sulfite method or the carbonation method, caffeic acid is removed using any of the methods described in claims 5-6, thereby reducing the sugar color value of the finished white granulated sugar by ≥30%.

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