Bio-based flocculant and application thereof in sugarcane juice clarification

Abstract

Raw materials of the bio-based flocculant comprise sodium alginate and itaconic acid, the raw materials are synthesized through free radical polymerization reaction in a grafting mode, and an initiator K2S2O8 and a cross-linking agent MBA are further added in the preparation process. The decoloring agent is applied to a sugar refining clarification process, a very high turbidity removal effect can be achieved under the condition of low dosage, and meanwhile, a relatively good decoloring effect is also achieved. Compared with the traditional flocculant PAM, the SI has outstanding advantages in the aspects of safety compatibility, use convenience and decoloration.

Description

Technical Field

[0001] The invention belongs to the technical field of flocculants, and in particular relates to a bio-based flocculant and application thereof in sugarcane juice clarification. Background Art

[0002] Sugar products are an indispensable resource for human beings, and the safety of the sugar production process is closely related to human health. In sugar production, the use of flocculants is crucial to the quality and yield of sugar products. The traditional sugar clarification method is to use clarification aids such as phosphoric acid, sulfurous acid, lime milk and flocculants to precipitate suspended particles, pigments, colloids and other impurities in sugarcane juice, effectively reduce the turbidity and color value of sugarcane juice, and obtain clarified sugarcane juice for subsequent sugar production processes. Polyacrylamide (PAM) is a flocculant widely used in the sugar industry at home and abroad. The precursor of synthetic PAM is a petroleum processing product, which is non-renewable, and toxic monomers are easily left during use, which will bring potential risks to sugar safety. In addition, PAM is usually used in the form of a solution, which takes several hours to dissolve and is not easy to preserve. The concentration is generally controlled at about 0.1%, which will bring a lot of water and bring additional load to the subsequent process. Therefore, it is urgent to develop green, non-toxic, safe and efficient flocculants that do not need to be dissolved and can be directly added to meet the growing demand.

[0003] In recent years, biomass flocculants have gradually attracted attention in sugarcane juice clarification and flocculation due to their wide sources, adjustable charge, biodegradability and other characteristics. In the prior art: 1. In the paper "Synthesis and Characterization of Promising Economic Biopolymer Composite as a Clarifying Agent for Sugar Industry" (Sugar Tech (2023), author: M Mahgoub, AN Gad, AM El-Naggar, H Dardeer), chitosan flocculants (Chs / CMC) and dextran-based flocculants were developed for sugarcane juice clarification processes. However, both flocculants only produce significant flocculation effects at high doses (200 ppm and 118 ppm, respectively).

[0004] 2. Another existing paper: "Grafted sesbania gum: A novel derivative for sugarcane juice clarification" ( Int. J. Biol. Macromol. 114 (2018) pp. 349–356, author: P Pal, JP Pandey, G Sen) prepared sesbania gum-based flocculant (SG-gP (CA)). Although the optimal dosage of the flocculant was low, the turbidity of the sugarcane juice after flocculation was still high (about 350 NTU).

[0005] 3. There is also an existing paper: "Moringa seed extract with a potential similar flocculant activity to a synthetic polymer during sugarcane clarification" (Biomass Convers. Biorefinery 13 (2023), pages 5197–5203, author: Vitor Teixeira et al.) uses Moringa seed extract as a flocculant. Although the sedimentation rate of this flocculant after flocculation is comparable to that of PAM (3.74 cm / Min), the turbidity removal rate (79.1%) is much lower than that of PAM (87.8%).

[0006] In summary, the biomass materials reported so far for sugarcane juice flocculation still have the problem of large dosage and poor flocculation effect. Therefore, it is still urgent to develop new biomass flocculants that can achieve excellent clarification effect with small dosage. Summary of the invention

[0007] In order to solve the above problems, the present invention provides a bio-based flocculant and its application in sugarcane juice clarification. The bio-based flocculant is applied in the sugar clarification process and can achieve a high turbidity removal effect at a low dosage, while also having a good decolorization effect. Compared with the traditional flocculant PAM, SI has outstanding advantages in safety compatibility, ease of use and decolorization.

[0008] The specific scheme of the present invention is: A bio-based flocculant, whose raw materials include sodium alginate and itaconic acid, which are grafted and synthesized through free radical polymerization.

[0009] The weight ratio of the sodium alginate to itaconic acid is 1:3 to 3:1.

[0010] The raw materials also include initiator K2S2O8, and the amount of K2S2O8 used is 1-5 wt% of the total weight of the raw materials.

[0011] The raw materials also include a crosslinking agent MBA, and the amount of MBA used is 1-5 wt% of the total weight of the raw materials.

[0012] The preparation method of the flocculant comprises the following steps: (1) Weigh sodium alginate and itaconic acid separately and dissolve them in pure water, then mix the two solutions in a container; (2) Place the container in a 65-75 ℃ water bath and keep stirring continuously; (3) N2 is introduced into the container to purge and remove dissolved oxygen in the mixed solution; (4) Add 1-5% of the monomer ratio of the initiator potassium persulfate K2S2O8 to the solution; (5) After 10-15 minutes, add MBA, a crosslinking agent, at a monomer ratio of 1-5%; continue to purge with N2 at 65-75 °C for 1-5 h; (6) Cooling the mixture in the container to room temperature, and adding about 40-80 mL of ice anhydrous ethanol to the mixture to precipitate the prepared polymer; (7) Collect the precipitate by centrifugation and wash with anhydrous ethanol; finally, vacuum dry the precipitate at -60 to -80 °C for 36 h to obtain the flocculant, grind it into powder, pass it through a 40-80 mesh sieve, and then seal it for storage.

[0013] The bio-based flocculant is used in clarifying sugarcane juice in sugar production. In the process of sulfite sugar production, the flocculant is added when the sugarcane juice reaches the secondary heating temperature.

[0014] The added amount of the bio-based flocculant is 0-25 ppm.

[0015] The secondary heating temperature is 70-105°C.

[0016] Sodium alginate (SA) is a natural polysaccharide that is widely used in the food and pharmaceutical industries because of its abundant sources, environmental friendliness, biodegradability, safety and non-toxicity. SA has a large number of hydroxyl and carboxyl groups in its molecular structure, which has the ability to interact with suspended particles and can effectively neutralize suspended particles in the adsorption system through charge neutralization. In addition, SA reacts with Ca²⁺ to form a unique "egg box" structure, which helps to capture suspended particles. However, due to the relatively low molecular weight of SA and the lack of complex branching structure, when SA is used directly to treat cationic pollutants, its flocculation effect is not ideal. In order to improve the flocculation effect, SA can be grafted with other monomers to obtain products with higher molecular weight and charge density.

[0017] Itaconic acid (IA) is an organic acid extracted from starch, cellulose and other biomass, which is widely recognized for its green, non-toxic and sustainable renewable properties. Itaconic acid contains polymerizable olefin bonds, which enable it to react with various monomers by initiating polymerization to produce graft copolymers with larger molecular weight and higher charge density. Therefore. Introducing IA monomer into the SA main chain can make the grafted product have a longer polymer chain, higher charge density, and thus improve the flocculation performance.

[0018] In the process of synthesizing SI flocculants, the monomer ratio, initiator content, crosslinker content and polymerization time will affect the functional group properties, charge density, molecular weight and grafting rate of the final product, thus having a significant impact on the flocculation performance. The ratio of SA to IA determines the density of the functional groups introduced from the raw materials and the final molecular weight. If the ratio of SA to IA is too high, the concentration of the reactive monomer IA in the system will be insufficient, resulting in too low a grafting rate, too small a charge density and molecular weight of the polymer, and weakening the charge neutralization and adsorption bridging during the flocculation process. If the ratio of SA to IA is too low, there are insufficient available reaction sites for SA in the system, resulting in the inability to effectively graft IA, and aggravated side reactions during the polymerization process. Initiators can generate free radicals, promote free radical polymerization reactions and increase the grafting rate. When the initiator concentration is low, the insufficient number of free radicals will limit the initiation of the polymerization reaction, resulting in too low a molecular weight of the polymer after the reaction and a loose structure. However, excessive initiators will accelerate the termination reaction, resulting in shortened polymer chains, reduced molecular weight, and ultimately reduced flocculation performance. Adding a cross-linking agent will form enough cross-linking points to connect different polymer chains through covalent bonds, thus forming a three-dimensional network structure. This network structure not only increases the viscosity and molecular weight of the polymer, but also improves the stability and mechanical strength of the flocculant, making it more effective in aggregating and settling particles. Insufficient cross-linking agent content will result in weaker polymer network connections, affecting the integrity structure required for flocculation, while excessive cross-linking agent content will result in a too tight polymer structure, reduced network structure size, limited solubility, and affect the charge neutralization and adsorption bridging ability of the polymer. The polymerization time will affect the degree of grafting and molecular weight. If the polymerization time is too low, the degree of polymerization will be low and the molecular weight of the polymer will be too small. Prolonging the polymerization time can fully complete the reaction and form a high molecular weight polymer, but too long a reaction time will lead to aggravated side reactions and thermal degradation, destroying the structural integrity of the flocculant and reducing performance.

[0019] The advantages of the present invention are: 1. The bioflocculant of the present invention shows excellent effects in multiple evaluation indicators such as color value, turbidity removal rate, and floc sedimentation rate. The bioflocculant of the present invention performs well in color removal, and the color removal rate is slightly higher than that of traditional PAM, indicating that it has a stronger ability to remove pigment molecules in sugar solution. Although SI is slightly lower than PAM in sedimentation rate and filtration rate, it is still within the acceptable range of sugar factory technology and will not affect actual production needs.

[0020] 2. The optimal dosage of the bioflocculant of the present invention in the sugar clarification process is lower than that of most existing flocculants.

[0021] 3. The bioflocculant of the present invention is green and safe to use in the sugar production process, and its safety is more prominent than that of PAM. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the preparation mechanism of SI: The graft copolymer SI flocculant was prepared by free radical polymerization. The initiator potassium persulfate decomposed under heating conditions to produce sulfate radicals (SO4• - ), sulfate radical attacks the hydroxyl group on the SA molecule, causing the hydrogen atom in SA to leave and generate SA alkoxy radical (RO•), which undergoes addition polymerization with the double bond (C=C) of IA, and the IA molecules continue to polymerize to form long chains. The self-crosslinking of the graft copolymer and the crosslinking of the vinyl groups at the end of MBA occur as the graft chain grows, thus forming a network structure and eventually forming an SI copolymer with a long molecular chain and a crosslinked network.

[0023] Figure 2 This is a microscopic morphology photograph of SI, which has a network structure with more pores; it proves that SA and IA reacted successfully to form a cross-linked structure that can provide more adsorption sites for flocculants.

[0024] Figure 3 The FTIR spectra of SA, IA, and SI of the present invention are as follows: the spectrum shows a broad and weak absorption peak at 3450 cm-¹, which is attributed to the OH stretching vibration. This absorption peak is not shown in the IA spectrum, but exists in the SA spectrum, indicating that the OH peak in SI comes from SA. In addition, the SI spectrum shows absorption peaks generated by COC stretching vibration at 1100 cm-¹ and 1030 cm-¹, which are characteristic absorption peaks introduced by the grafted monomer SA. The absorption peak of polymer SI at 1705 cm-¹ is introduced by the grafted monomer IA, corresponding to the C=O stretching vibration. These findings show that the characteristic peaks of SA and IA exist simultaneously in the SI spectrum, indicating that SA and IA are successfully grafted to synthesize SI polymer.

[0025] Figure 4 The XRD patterns of SA, IA and SI of the present invention are as follows: SA has a broad peak at 13.50°, indicating that it is a non-crystalline structure, and IA has a sharp peak at 19.15°, indicating that it has a high degree of crystallinity. When SA and IA are grafted to form SI, the XRD pattern of SI shows broad peaks and sharp peaks at 13.50° and 19.15°, respectively, and a new sharp peak appears at 20.40°. This is because the interchain hydrogen bonding between the carboxylic acid groups in the SI polymer enhances the molecular orientation order, thereby improving the degree of crystallinity. These results further confirm the successful grafting of IA and SA.

[0026] Figure 5 1H NMR spectra of SA, IA and SI of the present invention: The peaks at 3.77-4.01 ppm in the SA spectrum are attributed to the C1~C5 protons in the SA pyranose ring, and these peaks also appear in the SI spectrum, indicating that SA is successfully introduced into SI. In addition, in the SI spectrum, the signal peaks at 3.41, 5.86 and 6.28 ppm correspond to the proton signals on the saturated carbon C3 and double bond carbon in IA, respectively, which also confirms that IA is successfully introduced into the SI polymer. In the nuclear magnetic hydrogen spectrum of the SI sample, the two characteristic peaks of 1.96 ppm and 1.15 ppm can be attributed to the introduction of the crosslinker MBA. Among them, 1.96 ppm corresponds to the methylene bridge (-CH2-) of MBA, and 1.15 ppm comes from the saturated C–H bond generated after MBA participates in the crosslinking reaction. The presence of these two peaks proves that the active groups of MBA successfully participate in the crosslinking reaction to form a network structure. The above results confirm the successful preparation of SI.

[0027] Figure 6 The molecular weight of SA, IA, and SI of the present invention is 214817 g / mol, which is significantly higher than the molecular weight of SA (822.4 g / mol) and IA (130.1 g / mol). Flocculants with high molecular weight will enhance the adsorption bridging effect and have better flocculation performance. In addition, the charge carried by the flocculation also plays an important role in the flocculation performance. The absolute value of the Zeta potential can characterize the amount of charge carried by the substance. The higher the Zeta potential of the flocculant, the easier it is to play a role in charge neutralization and the better the flocculation performance.

[0028] Figure 7Thermogravimetric analysis curves of SA, IA, and SI of the present invention: Thermogravimetric analysis (TGA) was used to analyze the thermal stability of the bio-based flocculant SI of the invention. The degradation of SI is divided into three stages: the first stage is between 35-138°C, with a weight loss of about 10.95%, mainly due to the evaporation of water in the SI polymer. The second stage occurs between 138 and 299°C, and the third stage occurs between 299 and 600°C, with a total weight loss of 73.82% and a residual mass of 26.18%. In contrast, the total weight loss of the raw materials SA and IA is 63.07% and 95.66%, respectively, and the residual mass is 36.93% and 4.34%, respectively. Compared with SA, SI has a higher total weight loss rate, which may be due to the lower thermal stability of IA. After IA is successfully grafted onto the SA polysaccharide backbone, a large number of carboxyl groups are introduced, making SI more susceptible to decarboxylation at high temperatures, leading to degradation. In the process of clarifying sugarcane juice in sugar factories, the use temperature of flocculants is usually around 100°C. From the thermogravimetric analysis, it can be seen that the prepared SI flocculant has remarkable thermal stability at the specified temperature and shows no signs of degradation at about 100 °C. Therefore, it is suitable for use in the actual sugarcane juice clarification process.

[0029] Figure 8 Zeta potential of SA, IA, SI and PAM solutions of the present invention: Compared with the Zeta potential of SA, IA monomer and PAM (-41.52, -2.71 and -30.26 mv, respectively), the absolute value of Zeta potential of graft copolymer SI is higher, which is -48.53 mv. This indicates that SI itself carries a higher negative charge and is easier to neutralize the charge, thereby improving the flocculation efficiency.

[0030] Fig. 9 The influence of different samples on the color value of sugarcane juice; Fig.10 The effect of different samples on the transmittance of sugarcane juice; Fig.11 The effect of different samples on the turbidity of sugarcane juice; Fig.12 The effect of different samples on the floc settling rate and filtration rate of sugarcane juice; Fig.13 The effect of flocculant dosage on the potential and particle size of the supernatant after flocculation of sugarcane juice; Fig.14 The effects of secondary heating temperature and flocculant dosage on the chromaticity removal rate of sugarcane juice; Fig.15 The effects of secondary heating temperature and flocculant dosage on sugarcane juice turbidity; Fig.16 The effect of secondary heating temperature and flocculant dosage on floc settling velocity; Fig.17 The effects of secondary heating temperature and flocculant dosage on the filtration rate of clear juice; Fig.18 Comparison of SI, PAM and SI (DL) in terms of color removal rate and light transmittance; Fig.19 Comparison of SI, PAM and SI (DL) in turbidity; Fig. 20 Comparison of floc settling velocity and clear juice filtration velocity among SI, PAM and SI (DL); Fig.21 The physical comparison of SI, PAM and SI (DL) after flocculation of sugarcane juice; Fig. 22 Cell viability after co-culture (72 h) of GES-1 cells with SI and PAM flocculated sugarcane juice at different dilution concentrations. DETAILED DESCRIPTION Example

[0031] A bio-based flocculant, whose raw materials include sodium alginate and itaconic acid, which are grafted and synthesized through free radical polymerization.

[0032] The weight ratio of the sodium alginate to itaconic acid is 1:2.

[0033] The raw materials also include initiator K2S2O8, and the amount of K2S2O8 used is wt% 1 of the total weight of the raw materials.

[0034] The raw materials also include a crosslinking agent MBA, and the amount of MBA used is wt% 1 of the total weight of the raw materials.

[0035] The preparation method of the flocculant comprises the following steps: (1) Weigh 1.0 g SA and 2.0 g IA and dissolve them in 50 mL and 20 mL pure water respectively. Mix the two solutions in a three-necked flask. (2) Place the container in a 65-75 °C water bath and stir continuously at 500 rpm. (3) Purge the container with N2 for 20 min to remove dissolved oxygen in the mixed solution; (4) Add 0.03 g of initiator potassium persulfate K2S2O8 at a monomer ratio of 1% to the solution; (5) After 10 minutes, add 0.03 g of cross-linking agent MBA with a monomer ratio of 1%; continue to purge with N2 at 70 °C for 3 hours; (6) Cool the mixture in the container to room temperature, and when the mixture reaches room temperature, add about 50 mL of ice-cold anhydrous ethanol to precipitate the prepared polymer; (7) Collect the precipitate by centrifugation and wash with anhydrous ethanol. Finally, vacuum dry the precipitate at -80 °C for 36 h to obtain the flocculant, grind it into powder, pass it through a 40-mesh sieve, and seal it for storage.

[0036] The bio-based flocculant is used in clarifying sugarcane juice in sugar production. In the sulfite sugar production method, the flocculant is added when the sugarcane juice reaches the secondary heating temperature.

[0037] The added amount of the bio-based flocculant is 10 ppm.

[0038] The secondary heating temperature is 90°C.

[0039] Application examples: Sodium alginate (C6H9NaO6) was purchased from Chengdu Kelong Chemical Co., Ltd.

[0040] Potassium persulfate (K2S2O8), itaconic acid (C5H6O4, molecular weight 130.1 g / mol) and N,N'-methylenebisacrylamide (C7H 10 N2O2, MBA, 99% electrophoresis grade) was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.

[0041] Calcium oxide (CaO) was purchased from Tianjin Aopusheng Chemical Co., Ltd.

[0042] Phosphoric acid (H3PO4), sulfurous acid (H2SO3, SO2 ≥ 6%) and anionic polyacrylamide (PAM) were from Tianjin Damao Chemical Reagent Factory.

[0043] The mixed sugarcane juice came from Mingyang Sugar Factory in Nanning, Guangxi.

[0044] 1. Synthesis optimization of flocculants and evaluation of clarification effects The flocculation test was conducted by simulating the sulfite clarification process commonly used in sugarcane sugar factories. The specific process is as follows: 500 ml of mixed sugarcane juice was placed in a beaker, and 10% by weight of phosphoric acid was added to make the P2O5 concentration in the sugarcane reach 300 ppm. The mixed sugarcane juice was stirred at 300 rpm and heated to 65 °C. Subsequently, 20 mL of sulfurous acid was added to the mixed sugarcane juice for sulfur fumigation neutralization, and then the pH value was adjusted to 7.2 with lime milk. After the sulfur-fumigated neutralized juice of sugarcane was heated to 90 °C for the second time, a flocculant was quickly added to it, and after stirring it evenly, the sugarcane juice in the beaker was transferred to a 500 mL measuring cylinder for observation. The timing started after the sugarcane juice was transferred to the measuring cylinder, and the height of the flocculent body settled after 3 minutes was used as the standard to calculate the sedimentation rate of the flocculated impurities (Formula 2). After the flocculation and sedimentation for 15 min, a small amount of supernatant juice was taken to measure the turbidity with a portable turbidity meter (HACH 2100Q, USA). The remaining sugarcane juice was then filtered with slow qualitative filter paper, and the time taken to collect 100 mL of filtered clear juice and the clear juice filtration rate were recorded (Formula 3). The absorbance and transmittance of the clear juice at a wavelength of 560 nm were detected using an ultraviolet spectrophotometer (UV752, Shanghai). The color value (Formula 4) and color removal rate (Formula 5) of the sugarcane juice were measured and calculated according to the ICUMSA color value method. The flocculent sedimentation rate, supernatant turbidity, supernatant filtration rate, sugarcane juice transmittance and color removal rate were used as indicators to comprehensively evaluate the flocculation and clarification effect of SI on sugarcane juice.

[0045] Grafting rate of SI: Formula 1:

[0046] Where W g is the mass of SI after polymerization, W o It is the original quality of SA.

[0047] Formula 2:

[0048] Where: v1 is the floc sedimentation velocity (mL / min), h is the sedimentation height of the floc in the measuring cylinder (mL), and t is the floc sedimentation time (min).

[0049] Formula 3:

[0050] Where: v2 is the filtration rate of the supernatant juice (mL / min), T is the time taken to collect 100 mL of filtered clear juice (min) Formula 4:

[0051] Formula 5:

[0052] Where: R is the color removal rate (%), Q0 is the color value of the mixed juice (IU560), Q1 is the color value of the clear juice after flocculation (IU560), A is the absorbance of the filtered sample measured at a wavelength of 560nm, b is the thickness of the cuvette (cm), E is the relative apparent density of the filtered sample (g / cm³), and F is the refractive hammer of the filtered sample (°Bx).

[0053] Table 1:

[0054] According to the SI grafting rate and dynamic viscosity shown in Table 1, and Figure 9-12 The flocculation effect of sugarcane juice was used as the synthesis optimization index. The selected SI2 had the highest grafting rate (15.6%) and viscosity (28 cP), and the flocculation performance of sugarcane juice was also optimal. The color removal rate and light transmittance reached 66.9% and 71.8%, the residual turbidity of sugarcane juice was 12.4 NTU, and the flocculent sedimentation rate and clear juice filtration rate were 76.11 and 66.09 mL / min, respectively. The optimal synthesis conditions were determined as follows: SA:IA ratio of 1:2, initiator content of 1 wt%, crosslinker content of 1 wt%, and polymerization time of 3 hours. Therefore, the raw material component ratio of SI2 was selected for implementation.

[0055] 2. Flocculant dosage experiment like Fig.13 As shown in Figure 2, in the sugar production process, the amount of flocculant is a key factor affecting flocculation performance and industrial cost management. In order to determine the optimal amount of SI flocculant, we studied the effect of different SI flocculant amounts on the flocculation effect of sugarcane juice. Fig.15As shown in Figure 2, when the dosage of SI flocculant increased from 0 ppm to 10 ppm, the color removal rate, floc settling rate and clear juice filtration rate of sugarcane juice increased from 21.60%, 31.78 mL / min and 40.41 mL / min to 66.90%, 76.11 mL / min and 66.09 mL / min, respectively. In addition, the turbidity of the clear juice also decreased from 91.0 to 12.4 NTU. However, when the dosage was further increased from 10 ppm to 25 ppm, all performance indicators showed a downward trend. These research results show that the flocculation effect of SI on sugarcane juice will first increase with the increase in dosage, but will weaken after exceeding 10 ppm. This is because, at a lower flocculant dosage, the amount of SI is not enough to neutralize the charge on all suspended particles, resulting in insufficient colloid binding force and poor aggregation effect. As the dosage increases, more colloidal particles will be neutralized and aggregated into larger flocs, which effectively removes colored impurities and suspended particles, thereby improving the removal of color and turbidity. However, once the optimal dosage is exceeded, all positively charged colloidal particles will be neutralized and the system will reach saturation. Excessive flocculants will cause charge reversal, causing the colloidal particles to stabilize again, thereby inhibiting flocculation and reducing clarification efficiency. Therefore, 10ppm is the optimal SI flocculant dosage.

[0056] Effect of temperature on impurity removal rate and clarification effect like Figure 14-17 As shown in Figure 1, in the sulfite sugar process, the flocculant is added when the sugarcane juice reaches the secondary heating temperature. Higher heating temperatures have a significant impact on the impurity removal efficiency and overall clarification effect. As the secondary heating temperature increases from 70°C to 90°C, the color value and turbidity removal rate of the clear juice, as well as the flocculent settling rate and filtration rate, are significantly improved. This improvement is attributed to the enhanced molecular motion and increased collision frequency between the SI flocculant and the colloid at higher temperatures, which strengthens the adsorption effect and improves the flocculation efficiency.

[0057] Changes of physical and chemical properties of sugarcane juice before and after flocculation The main physical and chemical indicators of sugarcane mixed juice, clear juice after adding SI flocculant and clear juice of control group without flocculant are shown in Table 2. Sucrose content and reducing sugar content are the most concerned indicators in the sugar production process, but due to high temperature and microbial decomposition in the sugar production process, they will inevitably lose and decompose, but the use of SI did not cause additional loss of sucrose content and reducing sugar content in sugarcane juice. The color value of sugarcane juice treated with SI flocculant was 994 IU, which was significantly lower than the color value of sugarcane juice in the control group (2312 IU), indicating that the use of SI flocculant effectively removed colored impurities in sugarcane juice and improved the purity of sugarcane juice. Conductivity ash mainly refers to the total amount of conductive ions in sugarcane juice. These ions are mainly composed of inorganic salts and metal ions (such as calcium, magnesium, potassium, sodium, etc.). The conductivity ash of sugarcane juice after SI flocculation is lower than that of the control group, indicating that SI flocculant removes these metal ions through chemical adsorption and other effects. In summary, SI can effectively remove non-sugar impurities from sugarcane juice without causing the loss of sucrose and reducing sugars.

[0058] Table 2:

[0059] 5. Comprehensive comparison with PAM like Figure 18-Figure 22 As shown in , in order to evaluate the practical application effect of SI in the flocculation treatment of sugarcane juice, this study systematically compared SI and PAM from the following three aspects: flocculation performance, ease of use, and biocompatibility.

[0060] The figure compares the flocculation effect, ease of use and biocompatibility of SI and PAM. SI in the figure represents direct addition, and SI(DL) represents pre-dissolution in SI pure water. Figure 18-Figure 21It can be seen that the color removal rate (66.3%) and light transmittance (71.8%) of sugarcane juice treated with SI flocculant are slightly higher than those of PAM (65.2% and 70.1%, respectively). However, the sedimentation rate (76.11 mL / min) and filtration rate (66.09 mL / min) of flocculants in sugarcane juice treated with SI flocculants are slightly lower than those of PAM (82.67 mL / Min and 67.80 mL / min, respectively). In summary, in multiple flocculation and clarification evaluation indicators, the turbidity removal effects of the two flocculants are basically the same, but SI is better in terms of color removal and light transmittance. This may be because SI is a natural anionic polymer with more functional groups (such as carboxyl groups), which can produce strong electrostatic interactions or hydrogen bonds with pigments and other color-causing impurities, making it more interactive and adsorbable with color-causing compounds in sugarcane juice. In terms of floc sedimentation rate and clear juice filtration rate, PAM has a better effect. This is because PAM is an organic polymer with a larger molecular weight than natural biomass flocculants, which is more conducive to bridging with flocculation adsorption, so that flocs aggregate into large flocs and promote precipitation. In sulfite sugar factories, color removal has an important impact on the quality and market competitiveness of sugar, especially in the international market, where sugar products with high transparency and low color value have more competitive advantages. SI flocculant performs well in color removal, and the color removal rate is slightly higher than that of traditional PAM, indicating that it has a stronger ability to remove pigment molecules in sugar solution. Although SI is slightly lower than PAM in terms of sedimentation velocity and filtration rate, it is still within the acceptable range of sugar factory process and will not affect actual production needs.

[0061] In order for PAM to achieve its best flocculation performance, it needs to be dissolved for a long time, which is a cumbersome process. The convenient use of flocculants can improve the production efficiency of sugar factories and reduce production costs. Figure 18-Figure 21 It shows that the flocculation effect of directly adding SI is slightly better than that of dissolved SI (DL) in all aspects, indicating that SI does not need additional dissolution and is easy to use. This may be because when added directly, the flocculant molecules contact the suspended particles in the water more quickly and directly. It ensures that the flocculant quickly reaches the surface of the suspended particles in a more complete and effective molecular form, thereby accelerating the starting rate of the flocculation reaction. In addition, the molecular structure of SI is an incompletely dissolved network. Pre-dissolution may destroy the cross-linking structure therein and reduce the flocculation effect. Direct addition may make the "cross-linking network" formed between the particles stronger, forming larger flocs when dissolved in sugarcane juice, which is conducive to capturing suspended particles in sugarcane juice, and thus showing a better flocculation effect.

[0062] The green safety of SI in the sugar clarification process was evaluated by comparing the cell survival rates of SI, PAM and Control groups. Fig. 22The cell viability of three groups of sugarcane juice at different dilution concentrations (1%, 5%, and 10%) was shown. At a concentration of 10%, the cell viability of the SI group, PAM group, and Control group was 84.75%, 81.98%, and 84.45%, respectively. Substances with a cell viability of more than 70% in in vitro co-culture are generally classified as non-toxic substances. The above results indicate that the use of SI in the sugar production process is green and safe, and its safety is more prominent than that of PAM.

[0063] In summary, SI showed flocculation performance that was not inferior to that of PAM in sugarcane juice clarification, and SI showed great advantages in terms of ease of use and safety.

Claims

1. A bio-based flocculant, characterized in that: The raw materials include sodium alginate and itaconic acid which are grafted and synthesized through free radical polymerization reaction.

2. The bio-based flocculant according to claim 1, characterized in that: The weight ratio of the sodium alginate to itaconic acid is 1:3 to 3:

1.

3. The bio-based flocculant according to claim 2, characterized in that: The raw materials also include an initiator K2S2O8, and the amount of K2S2O8 used is 1-5wt% of the total weight of the raw materials.

4. The bio-based flocculant according to claim 2, characterized in that: The raw materials also include a crosslinking agent MBA, and the amount of MBA is 1-5wt% of the total weight of the raw materials.

5. The bio-based flocculant according to claim 1, characterized in that: The preparation method of the flocculant comprises the following steps: (1) Weigh sodium alginate and itaconic acid separately and dissolve them in pure water, then mix the two solutions in a container; (2) Place the container in a 65-75 ℃ water bath and keep stirring continuously; (3) N2 is introduced into the container to purge and remove dissolved oxygen in the mixed solution; (4) Add 1-5% of the monomer ratio of the initiator potassium persulfate K2S2O8 to the solution; (5) After 10-15 minutes, add MBA, a crosslinking agent, at a monomer ratio of 1-5%; continue to purge with N2 at 65-75 °C for 1-5 h; (6) Cool the mixture in the container to room temperature, and when the mixture cools to room temperature, add about 40-80 mL of ice-cold anhydrous ethanol to precipitate the prepared polymer; (7) Collect the precipitate by centrifugation and wash with anhydrous ethanol; finally, vacuum dry the precipitate at -60 to -80 °C for 36 h to obtain the flocculant, grind it into powder, pass it through a 40-80 mesh sieve, and then seal it for storage.

6. The bio-based flocculant according to claim 1, characterized in that: The bio-based flocculant is used in clarifying sugarcane juice in sugar production. In the process of sulfite sugar production, the flocculant is added when the sugarcane juice reaches the secondary heating temperature.

7. The method for preparing a bio-based flocculant according to claim 6, characterized in that: The added amount of the bio-based flocculant is 0-25 ppm.

8. The use of the bio-based flocculant in the clarification of sugarcane juice according to claim 6, characterized in that: The secondary heating temperature is 70-105°C.

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