Sugarcane juice clarifying and decoloring method based on dolomite

Abstract

The method comprises the following steps: adding a dolomite digestion product into the sugarcane juice, carrying out primary heating and heat preservation decoloration, then adjusting the pH value by using a phosphoric acid solution, and carrying out secondary heating and heat preservation decoloration; adding a flocculating agent, uniformly stirring, and removing precipitate to obtain primary clear juice; adding a phosphoric acid solution into the primary clear juice, adjusting the pH value by using a dilute sulfuric acid solution, heating to boiling, preserving heat and decoloring, adding a flocculating agent, uniformly stirring, and removing precipitate to obtain clarified and decolored secondary clear juice; according to the method, the dolomite digestion product with the main components of magnesium hydroxide and calcium hydroxide is added into the sugarcane juice, the first-time decolorization operation can be carried out, only the dosage of the dolomite digestion product needs to be controlled in the process, the subsequent phosphoric acid adding and pH adjusting steps are simple regulation and control processes, the production operation difficulty is reduced, and the production cost is reduced. The method is easier to popularize and apply in actual production, and the decoloring stability of the product is ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of sugarcane juice clarification and decolorization, and particularly relates to a dolomite-based sugarcane juice clarification and decolorization method. Background Art

[0002] With rising living standards, heightened awareness of food safety, and the need for the sugar industry to develop, demand for sugarcane sugar in China will continue to grow. my country's sugar industry is enormous, with sugarcane sugar production ranking among the highest in the world. However, domestic sugar mills currently rely on traditional, outdated production processes and equipment, which are far from meeting market demand. Product quality, production efficiency, and energy efficiency lag significantly behind those of sugar mills in developed countries. The sugar production process generally includes juice extraction, purification, evaporation, sugar boiling, honey separation, and packaging. Purification is the most critical step, as its effectiveness directly determines the final quality of the sugar product. The main task of the purification process is clarification and decolorization to produce a low-color, high-purity clarified juice. Chinese sugar mills generally use the sulfite process to produce white sugar. This process requires sulfur dioxide as a decolorizing agent in the purification stage to bleach and remove pigments from the sugarcane juice. However, the sulfur fumigation intensity of this sugar-making process is typically in the range of 20-26g / L, which results in the presence of carcinogenic sulfite residues in white sugar, which has adverse health effects. Currently, domestic white sugar manufacturers mostly use sodium sulfite for detoxification. However, sodium sulfite is relatively expensive and severely corrosive to equipment. In addition, the color value, turbidity, and ash content of the clarified juice are relatively high, which makes the produced white sugar easily hygroscopic and yellowish in color. The final sugar product is of low quality and lacks competitiveness. Therefore, the search for green and efficient low-sulfur purification processes in the sugar-making field is a hot topic of research both domestically and internationally.

[0003] Patents related to sugar juice decolorization have been found, including patent application number 202010620458.2, which discloses a method for decolorizing sugar juice using phosphorus-magnesium flotation. This method involves adding phosphoric acid and a magnesium source to the juice, then adjusting the juice to alkalinity with lime milk. This allows the phosphoric acid and magnesium source to in situ generate calcium phosphate and magnesium hydroxide, which have strong adsorption properties for pigments and other impurities in the juice. Bubbles are then introduced, and a flocculant is added for flocculation. This is followed by phosphorus-magnesium flotation, which removes most non-sugar impurities such as pigments and colloids from the juice, resulting in a clear, alkaline juice with a low color value. While this method claims to achieve an 87.0% decolorization rate, the initial heating and decolorization process requires precise control of the synergistic ratio of the three ingredients during the addition process, making it difficult to implement and prone to deviations during production, affecting the stability of the decolorization effect. On the other hand, this method only focuses on decolorization and pays insufficient attention to other key indicators such as the purity of the sugar juice. If too much sucrose or other soluble solids are adsorbed during the decolorization process, although the decolorization rate may increase, the purity will decrease, which may lead to the subsequent sugar products being lacking in quality and making it difficult to meet the market demand for high-quality sugar products. Summary of the Invention

[0004] The purpose of the present invention is to solve the above technical problems and provide a dolomite-based sugarcane juice clarification and decolorization method that is easy to industrially control, can reduce decolorization costs, and has high decolorization rate and purity.

[0005] To achieve the above-mentioned purpose, the technical solution of the present invention is:

[0006] A dolomite-based method for clarifying and decolorizing sugarcane juice comprises the following steps:

[0007] (1) Adding 300-500 mg of dolomite digestion product to 1 L of sugarcane juice, heating and preserving the solution for decolorization, then adjusting the pH to 10.0-12.0 with a phosphoric acid solution, and heating and preserving the solution for decolorization again; then adding a flocculant and stirring evenly to remove the precipitate to obtain a clear juice;

[0008] (2) Add 300-500 mg of phosphoric acid per 1 L of the primary clear juice, add phosphoric acid solution to the primary clear juice, and adjust the pH to 7.0-8.0 with dilute sulfuric acid solution. Heat to boiling and then keep warm for decolorization. Then add flocculant and stir evenly to remove the precipitate to obtain a clarified and decolorized secondary clear juice.

[0009] The dolomite digestion product is a mixed product obtained by calcining and digesting dolomite, the main components of which are magnesium hydroxide and calcium hydroxide; the calcination is to calcine dolomite powder with a particle size of 0.5 to 5 mm at 700 to 1000° C. for 2 to 4 hours to obtain the calcined product; the digestion is to add the calcined product into water at a solid-liquid ratio of (1 to 6) g: 25 L at room temperature, and stir and digest for 20 to 30 minutes.

[0010] The reaction process of calcining dolomite is:

[0011] CaMg(CO3)2→CaO+MgO+2CO2

[0012] The reaction process of digesting the calcined product is:

[0013] CaO+H2O→Ca(OH)2

[0014] MgO+H2O→Mg(OH)2

[0015] As a further technical solution, the sugarcane juice mentioned above is a mixed juice obtained by squeezing and extracting sugarcane, with a pH value of 5.4-6.4, a color value of 2000-10000 IU, and a purity of 70-75%.

[0016] As a further technical solution, in the above-mentioned one-time heating and heat preservation decolorization, the heating temperature is 50-80° C. and the heat preservation time is 30-90 minutes.

[0017] As a further technical solution, in the above-mentioned secondary heating and heat preservation decolorization, the heating temperature is 50-80° C. and the heat preservation time is 30-90 minutes.

[0018] As a further technical solution, the mass fraction of phosphoric acid in the above phosphoric acid solution is 5-10%.

[0019] As a further technical solution, the mass fraction of sulfuric acid in the above-mentioned dilute sulfuric acid solution is 5-10%.

[0020] As a further technical solution, the flocculant in the above step (1) is a polyacrylamide solution with a mass fraction of 0.1%, and 3 mg of polyacrylamide is added to every 1 L of the mixed juice after secondary heating, insulation and decolorization.

[0021] As a further technical solution, the flocculant in the above step (2) is a polyacrylamide solution with a mass fraction of 0.1%, and 1 mg of polyacrylamide is added per 1 L of clear juice.

[0022] As a further technical solution, the decolorization rate of the above-mentioned secondary clear juice is 85-95%, and the purity is 75-85%.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention is easy to industrially control and ensures the stability of the decolorization effect.

[0025] The present invention performs a first decolorization operation by adding a dolomite digestion product whose main components are magnesium hydroxide and calcium hydroxide to sugarcane juice. During this process, it is only necessary to control the amount of the dolomite digestion product. The subsequent phosphoric acid addition and pH adjustment steps are also relatively simple control processes. This not only reduces the difficulty of production operation, but also makes it easier to promote and apply in actual production, and ensures the decolorization stability of the product.

[0026] 2. The present invention can reduce decolorization costs.

[0027] The present invention cleverly adds a dolomite digestion product whose main components are magnesium hydroxide and calcium hydroxide (lime milk) to sugarcane juice. Not only does it utilize the characteristics of magnesium hydroxide and calcium hydroxide that they can produce decolorization and coagulation with negatively charged colloids when added to sugarcane juice to produce colloidal precipitation, but the magnesium hydroxide and calcium hydroxide can also adjust the pH value of the sugarcane juice, avoiding the additional addition of lime milk and reducing the decolorization cost.

[0028] 3. The decolorization rate and purity of the present invention are high.

[0029] The present invention first directly uses dolomite digestion products for the first decolorization. The main components of dolomite digestion products, magnesium hydroxide and calcium hydroxide, have strong positive charges and can generate decolorization aggregation with negatively charged colloids in sugarcane juice. Secondly, the present invention adds phosphoric acid to the sugarcane juice. The phosphoric acid reacts with the dolomite digestion products to generate calcium phosphate with a strong positive charge. The magnesium hydroxide and calcium phosphate act synergistically to enhance the dolomite digestion products to adsorb or embed negatively charged pigments, inorganic salts and organic impurities in the sugarcane juice through electrical neutralization, thereby greatly improving the decolorization effect. Finally, the present invention adds phosphoric acid again to the primary clear juice. The phosphoric acid reacts with unreacted calcium hydroxide to generate calcium phosphate, which continues to adsorb colored substances in the sugar juice, thereby effectively removing impurities and ultimately achieving a decolorization rate of 85-95%. During the decolorization process, the present invention effectively controls the addition amount of dolomite digestion products and phosphoric acid solution, heating temperature and time, etc., which not only ensures the decolorization rate, but also avoids excessive adsorption of sucrose or other soluble solids, achieving a simple purity of 75-85% in the secondary clear juice, and ensuring the quality of the sugar product.

[0030] 4. The present invention can realize the comprehensive utilization of magnesium-containing dolomite ore resources.

[0031] my country is rich in magnesium-containing dolomite resources. This method utilizes magnesium-containing dolomite ore through calcination and digestion to produce a dolomite digestate for sugarcane juice clarification and decolorization, achieving comprehensive resource utilization and aligning with the concept of sustainable development. Given the current sugar industry's pursuit of green, efficient, and low-sulfur purification processes, this method has significant practical significance and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a process flow chart of a dolomite-based sugarcane juice clarification and decolorization method of the present invention;

[0033] Figure 2 The XRD characterization analysis pattern of the dolomite used in the embodiment of the present invention;

[0034] Figure 3 This is the XRD characterization analysis pattern of the dolomite calcined product used in the examples of the present invention;

[0035] Figure 4 This is a sample diagram of a clear juice according to Example 4 of the present invention;

[0036] Figure 5 This is a sample diagram of the secondary clear juice of Example 4 of the present invention;

[0037] Figure 6 This is the XRD characterization analysis pattern of the primary precipitate of Example 4 of the present invention;

[0038] Figure 7 This is the XRD characterization analysis pattern of the secondary precipitate of Example 4 of the present invention;

[0039] Figure 8 This is a SEM image of the primary precipitate of Example 4 of the present invention;

[0040] Figure 9 This is the SEM image of the secondary precipitate of Example 4 of the present invention. DETAILED DESCRIPTION

[0041] The present invention will be further described in detail below with reference to examples, but the embodiments of the present invention are not limited to the scope of the examples.

[0042] 1. Materials:

[0043] Sugarcane juice: It is a mixed juice obtained by squeezing sugarcane juice. It comes from a Guangxi Sugar Industry Co., Ltd. Its test indicators are shown in Table 1.

[0044] Table 1

[0045] pH Color value (IU) Purity (%) sugarcane juice 5.8 8560 73.86

[0046] Dolomite: Sourced from a mining company in Guangxi.

[0047] Phosphoric acid, sulfuric acid, and polyacrylamide were purchased from a commercial chemical company.

[0048] II. Instruments and Equipment

[0049] UV-550 UV-visible spectrophotometer, WZZ-2S automatic polarimeter, WAY-2S Abbe refractometer, TGL18M desktop high-speed refrigerated centrifuge, S210 pH meter, MFLC-8-14P muffle furnace, DK-98-11 electric furnace.

[0050] 3. Preparation of dolomite digestion products

[0051] Dolomite was mechanically crushed to 0.5-5 mm, and the powder was placed in a crucible muffle furnace and calcined at 1000 ° C for 2 hours to obtain a calcined product; water was added at a solid-liquid ratio of 2g:25L at room temperature, and magnetic stirring was used for digestion for 20 minutes to obtain a dolomite digestion product. The XRD characterization results of dolomite and dolomite calcined product are shown in Figure 2. Figure 2 and Figure 3 The main chemical compositions of the dolomite calcined products are shown in Table 2:

[0052] Table 2 Chemical composition of dolomite calcined products

[0053] Element calcium oxide magnesium oxide Alumina Iron oxide Silicon dioxide content 30.30％ 22.85％ 0.06％ 0.16％ 0.51％

[0054] 4. Analysis and calculation methods

[0055] 1) Calculation method of Brix and corresponding apparent density

[0056] Take two drops of distilled water to calibrate the WAY-2S digital Abbe refractometer, wipe the mirror dry, and add 2-3 drops of the mixed juice to measure its refractive index, corrected index, and temperature. Then, use the corrected index value table to find the corresponding apparent density (20°C).

[0057] 2) Color value determination and decolorization rate calculation method

[0058] Color value determination and decolorization rate calculation refer to the "Analysis Method for Chemical Management of Sugarcane Sugar Production". After adjusting the sugar juice to an appropriate pH value, the absorbance at a wavelength of 560nm is measured using a UV-722S visible ultraviolet spectrophotometer. The color value of the sugar juice solution is then calculated using formula (1) based on the measured brix, the corresponding apparent density, and the temperature.

[0059] IU 560 =A 560 ÷(b×c)×1000 (1)

[0060] Where: A 560is the absorbance measured at a wavelength of 560 nm; b is the thickness of the cuvette, cm; c is the concentration of the solute (c = refractive index of the clear juice × corresponding apparent density (20°C) / 100), g / mL.

[0061] The decolorization rate is calculated according to formula (2).

[0062] D=(IU 前 -IU 后 ) / IU 前 ×100% (2)

[0063] Where: D is the decolorization rate, %; IU 前 is the color value of sugarcane juice before treatment; IU 后 It is the color value of the secondary clear juice after treatment.

[0064] 3) Determination of purity

[0065] The purity determination shall refer to the Chemical Management and Analysis Method of Sugarcane Sugar Refining.

[0066] The sugar content was calculated according to formula (3): a small amount of sugarcane juice solution was taken and its temperature, refractive index and corrected index were measured using a WAY-2S digital Abbe refractometer. The corresponding sugar content factor was found in the sugar content factor table. 30 mL of sugarcane juice was taken and measured three times using a WZZ-2S automatic polarimeter. The average value was taken to obtain the optical rotation reading.

[0067] Sugar content = optical rotation reading × sugar content factor (3)

[0068] The purity is calculated according to formula (4)

[0069] Simple purity (%) = Brix / Hammer × 100% (4)

[0070] 5. XRD test

[0071] The sediment sample to be verified was dried and ground into powder, and the composition of the sample was detected by X-ray diffraction analysis. The scanning angle was 5° to 80°, the scanning speed was 2° / min, the test target was a copper target, the wavelength was 0.15406nm, the voltage was 40kV, and the current was 40mA.

[0072] 6. SEM test

[0073] The precipitate samples under the optimal combination conditions were ground into powder and measured using a scanning electron microscope (SEM).

[0074] Example 1:

[0075] 100 mL of sugarcane juice was placed in a beaker, and 35 mg of dolomite digestion product was added. The mixture was heated to 50°C for 60 minutes. The pH was then adjusted to 10.8 with 8% phosphoric acid solution, and the mixture was heated to 50°C for 60 minutes. 0.3 mL of a 0.1% polyacrylamide flocculant solution (i.e., 3 mg / L to sugarcane juice) was added. The mixture was centrifuged (4000 rpm, 25°C, 20 minutes) to separate the supernatant and obtain the primary clear juice. 35 mg of a 9% phosphoric acid solution was then added, and the mixture was stirred evenly. The pH was adjusted to 7.2 with 5% sulfuric acid solution, and the mixture was heated to boiling. 0.1 mL of a 0.1% polyacrylamide flocculant solution (i.e., 1 mg / L to primary clear juice) was added. The mixture was filtered to obtain the secondary clear juice. The brix and absorbance (wavelength 560 nm) of the secondary clear juice were measured, and the calculated decolorization rate was 87.88% and the purity was 78.64%.

[0076] Example 2:

[0077] 100 mL of sugarcane juice was placed in a beaker, 40 mg of dolomite digestion product was added, and the mixture was heated to 70°C for 60 minutes. Then, 8.5% by mass phosphoric acid solution was added to adjust the pH to 10.8, and the mixture was heated to 70°C for 60 minutes. 0.3 mL of 0.1% by mass polyacrylamide flocculant solution (i.e., 3 mg / L to sugarcane juice) was added. The mixture was centrifuged (4000 r / min, 25°C, 20 minutes) to separate the supernatant and obtain the primary clear juice. Then add 40 mg of 8.5% by mass phosphoric acid solution and stir evenly. Add 5% by mass sulfuric acid solution to adjust the pH to 7.5, heat to boiling, add 0.1 mL of 0.1% by mass polyacrylamide flocculant solution (i.e., 1 mg / L to sugarcane juice ratio), filter to obtain secondary clear juice, measure the brix and absorbance (wavelength 560 nm) of the secondary clear juice, and calculate the decolorization rate to be 93.52% and the purity to be 81.38%.

[0078] Example 3:

[0079] 100 mL of sugarcane juice was placed in a beaker, 42 mg of dolomite digestion product was added, and the mixture was heated to 80°C for 60 minutes. Then, 8.5% by mass phosphoric acid solution was added to adjust the pH to 11.2. The mixture was heated to 80°C for 60 minutes. 0.3 mL of 0.1% by mass polyacrylamide flocculant solution (i.e., 3 mg / L to sugarcane juice) was added. The mixture was centrifuged (4000 r / min, 25°C, 20 minutes) to separate the supernatant and obtain the primary clear juice. Then, 42 mg of 8.5% by mass phosphoric acid solution was added and stirred evenly. After adjusting the pH value to 7.0 with 5% by mass sulfuric acid solution, the mixture was heated to boiling. 0.1 mL of 0.1% by mass polyacrylamide flocculant solution (i.e., 1 mg / L to sugarcane juice ratio) was added and filtered to obtain secondary clear juice. The brix and absorbance (wavelength 560 nm) of the secondary clear juice were measured, and the decolorization rate and the purity were calculated to be 92.73% and 79.96%.

[0080] Example 4:

[0081] Take 100mL of sugarcane juice in a beaker, add 45mg of dolomite digestion product, heat to 80℃, and keep warm for 80 minutes; then add 10% mass fraction phosphoric acid solution to adjust the pH to 11.0, heat to 80℃, and keep warm for 80 minutes, add 0.3mL of 0.1% mass fraction polyacrylamide flocculant solution (i.e. 3mg / L to sugarcane juice ratio), centrifuge (4000r / min, 25℃, 20min) to separate the supernatant and obtain the primary clear juice (such as Figure 4 The precipitate was subjected to XRD and SEM tests, and the results were as follows Figure 6 and Figure 8 Then add 40 mg of 10% phosphoric acid solution, stir evenly, add 5% sulfuric acid solution to adjust the pH to 7.6, heat to boiling, add 0.1 mL of 0.1% polyacrylamide flocculant solution (i.e. 1 mg / L to sugarcane juice ratio), filter, and obtain secondary clear juice (such as Figure 5 The secondary clear juice was measured for brix and absorbance (wavelength 560nm), and the decolorization rate was calculated to be 94.58% and the purity was 84.21%. The secondary precipitate was tested by XRD and SEM. The results are shown in the figure. Figure 7 and Figure 9 As shown. Figure 6 It can be seen that the main components of the primary precipitate are magnesium hydroxide, calcium salt components, pigment substances and other impurities, and the characteristic peaks are sharp and significant. Figure 7The secondary precipitate is primarily composed of magnesium hydroxide, calcium carbonate, and other impurities, with relatively low peaks for pigments. The characteristic peaks in the material signature spectrum are numerous and complex, not sharp, and have low significance. This is because most of the pigments and other impurities are removed through adsorption and precipitation by the magnesium hydroxide and calcium salt components. This demonstrates the feasibility of using dolomite digestion products in sugarcane juice clarification and decolorization processes.

[0082] Depend on Figure 8 It can be seen from the SEM analysis of the primary precipitate that there are mainly blocky particles, spherical particles and small spherical particles, and the surface of the particles is relatively rough. This is because magnesium hydroxide and calcium phosphate adsorb and embed the pigments and impurities in the sugarcane juice, and the crystallinity is significantly reduced. Figure 9 The SEM images of the secondary heating precipitate show that it primarily consists of large and small lumps with smooth surfaces. This is because after separation of the primary heating precipitate, most of the calcium and magnesium compounds, pigments, and impurities in the juice have been removed, resulting in a higher sucrose content and significantly higher crystallinity in the secondary precipitate, resulting in a smooth, crystalline, blocky surface. This comparison demonstrates that the dolomite digestion product achieves clarification and decolorization of sugarcane juice through the adsorption and embedding effects of magnesium hydroxide and calcium phosphate.

[0083] Example 5:

[0084] 100 mL of sugarcane juice was placed in a beaker, and 50 mg of dolomite digestion product was added. The mixture was heated to 80°C for 60 minutes. A 10% phosphoric acid solution was then added to adjust the pH to 11.2. The mixture was heated to 80°C for 60 minutes. 0.3 mL of a 0.1% polyacrylamide flocculant solution (i.e., 3 mg / L to sugarcane juice) was added. The mixture was centrifuged (4000 rpm, 25°C, 20 minutes) to separate the supernatant and obtain the primary clear juice. 50 mg of a 10% phosphoric acid solution was then added, and the mixture was stirred evenly. The pH was adjusted to 7.2 with a 5% sulfuric acid solution. The mixture was heated to boiling, and 0.1 mL of a 0.1% polyacrylamide flocculant solution (i.e., 1 mg / L to sugarcane juice) was added. The mixture was filtered to obtain the secondary clear juice. The brix and absorbance (wavelength 560 nm) of the secondary clear juice were measured, resulting in a decolorization rate of 93.78% and a purity of 82.02%.

[0085] Example 6:

[0086] 100 mL of sugarcane juice was placed in a beaker, 30 mg of dolomite digestion product was added, and the mixture was heated to 50° C. and kept warm for 60 minutes. 6.5% phosphoric acid solution was then added to adjust the pH to 10.8, and the mixture was heated to 50° C. and kept warm for 60 minutes. 0.3 mL of 0.1% polyacrylamide flocculant solution (i.e., 3 mg / L to sugarcane juice) was added, and the mixture was centrifuged (4000 rpm, 25° C., 20 minutes) to separate the supernatant and obtain the primary clear juice. Then add 32 mg of 9.5% by mass phosphoric acid solution and stir evenly. Add 5% by mass sulfuric acid solution to adjust the pH to 7.5, heat to boiling, add 0.1 mL of 0.1% by mass polyacrylamide flocculant solution (i.e., 1 mg / L to sugarcane juice ratio), filter to obtain secondary clear juice, measure the brix and absorbance (wavelength 560 nm) of the secondary clear juice, and calculate the decolorization rate of 88.43% and the purity of 76.87%.

[0087] As can be seen from Examples 1 to 6, the decolorization rate and simple purity of Example 4 are the best. According to the conditions of Example 4, we conducted three parallel experiments, and the decolorization rate and simple purity of the obtained secondary clear juice are shown in Table 3.

[0088] Table 3

[0089]

[0090] As can be seen from Table 3, the method of the present invention has good reproducibility, and the decolorization rate and purity results are stable.

[0091] Experimental study on parameter influence

[0092] 1. Experiment on the effect of dolomite digestion product dosage on decolorization rate and purity

[0093] Experimental method: Prepare multiple beakers, take 100mL of sugarcane juice into each beaker, add 30, 35, 40, 45, and 50mg of dolomite digestion product, heat to 80°C, and keep warm for 80 minutes; then add 10% phosphoric acid solution to adjust the pH to 11.0, heat to 80°C, keep warm for 80 minutes, add 0.3mL of 0.1% polyacrylamide flocculant solution (i.e., 3mg / L to sugarcane juice), centrifuge (4000r / min, 25°C, 20min), separate the supernatant, and obtain the primary clear juice. Then, 40 mL of a 10% by mass phosphoric acid solution was added and stirred evenly. After adjusting the pH to 7.6 with a 5% by mass sulfuric acid solution, the mixture was heated to boiling. 0.1 mL of a 0.1% by mass polyacrylamide flocculant solution (i.e., 1 mg / L to sugarcane juice ratio) was added and filtered to obtain a secondary clear juice. The brix and absorbance (wavelength 560 nm) of the secondary clear juice were measured, and the decolorization rate and purity were calculated. The results are shown in Table 4.

[0094] Table 4

[0095] Experimental samples 1 2 3 4 5 Dolomite digestion product addition amount / mg 30 35 40 45 50 Decolorization rate / % 90.76 92.59 93.78 94.43 94.76 Simple purity / % 81.44 82.53 83.74 84.83 84.88

[0096] As can be seen from Table 4, with the increase in the amount of dolomite digestion product, the decolorization rate first increased and then decreased. The purity first increased and then tended to be flat, reaching the highest point when the amount of dolomite digestion product added was 450 mg / L, after which the decolorization rate dropped significantly. The increase in purity tended to be flat after the amount of dolomite digestion product added reached 450 mg / L. This may be because excessive magnesium ions react with phosphoric acid to form magnesium hydrogen phosphate, which has a weak ability to adsorb pigments. This process consumes some phosphoric acid, resulting in a decrease in the amount of calcium phosphate generated and the content of magnesium hydroxide. In addition, increasing the amount of dolomite digestion product will make the magnesium hydroxide product looser, which may make the residue more difficult to separate, and thus adversely affect the decolorization rate and subsequent filtration operations. Therefore, the optimal amount of dolomite digestion product was determined to be 450 mg / L.

[0097] 2. Experiment on the influence of primary decolorization temperature on decolorization rate and purity

[0098] Experimental method: Prepare multiple beakers, take 100mL of sugarcane juice into each beaker, add 450mg of dolomite digestion product, and heat to 50, 60, 70, 80, and 90℃ respectively, and keep warm for 80 minutes; then add 10% by mass phosphoric acid solution to adjust the pH to 11.0, heat to 80℃, keep warm for 80 minutes, add 0.3mL of 0.1% by mass polyacrylamide flocculant solution (i.e., 3mg / L to sugarcane juice), centrifuge (4000r / min, 25℃, 20min), separate the supernatant and obtain the primary clear juice. Then, 40 mL of a 10% by mass phosphoric acid solution was added and stirred evenly. After adjusting the pH to 7.6 with a 5% by mass sulfuric acid solution, the mixture was heated to boiling. 0.1 mL of a 0.1% by mass polyacrylamide flocculant solution (i.e., 1 mg / L to sugarcane juice ratio) was added and filtered to obtain a secondary clear juice. The brix and absorbance (wavelength 560 nm) of the secondary clear juice were measured, and the decolorization rate and purity were calculated. The results are shown in Table 5.

[0099] Table 5

[0100] Experimental samples 1 2 3 4 5 Primary decolorization heating temperature / ℃ 50 60 70 80 90 Decolorization rate / % 89.23 91.36 93.45 94.52 93.15 Simple purity / % 80.80 81.92 83.85 84.53 83.47

[0101] Table 5 shows that as the primary decolorization temperature increases, the decolorization rate and pure purity first increase and then decrease. The decolorization rate reaches its highest point, 85.12%, at 80°C. This is because increasing temperature promotes flocculation and precipitation, which accelerates the decolorization of sugarcane juice. Above 80°C, both the decolorization rate and pure purity decrease. This is likely due to the high temperature under strong alkaline conditions, which increases the destruction of reducing sugars and leads to an increase in solution color. Therefore, the optimal decolorization temperature is determined to be 80°C.

[0102] 3. Experiment on the influence of secondary decolorization pH value on decolorization rate and purity

[0103] Experimental method: Prepare multiple beakers, take 100mL of sugarcane juice into each beaker, add 450mg of dolomite digestion product, heat to 80℃, and keep warm for 80 minutes; then add 10% mass fraction phosphoric acid solution to adjust the pH to 10, 10.8, 11, 11.2, and 12 respectively, heat to 75℃, keep warm for 80 minutes, add 0.3mL of 0.1% mass fraction polyacrylamide flocculant solution (i.e., 3mg / L to sugarcane juice ratio), centrifuge (4000r / min, 25℃, 20min), separate the supernatant and obtain the primary clear juice. Then, 40 mg of 10% by mass phosphoric acid solution was added and stirred evenly. After adjusting the pH to 7.6 with 5% by mass sulfuric acid solution, the mixture was heated to boiling. 0.1 mL of 0.1% by mass polyacrylamide flocculant solution (i.e., 1 mg / L to sugarcane juice ratio) was added and filtered to obtain secondary clear juice. The brix and absorbance (wavelength 560 nm) of the secondary clear juice were measured, and the decolorization rate and purity were calculated. The results are shown in Table 6.

[0104] Table 6

[0105] Experimental samples 1 2 3 4 5 pH 10 10.8 11 11.2 12 Decolorization rate / % 92.05 93.61 94.45 93.27 92.41 Simple purity / % 82.48 83.28 84.79 84.09 83.30

[0106] Table 6 shows that as the pH value of the secondary decolorization process increases, the purity and decolorization rate initially increase and then decrease, reaching a maximum at pH 11.0. This is likely because pH 11.0 is the isoelectric point of sugarcane juice. At this point, non-sugar impurities, particularly colloids, in the juice aggregate, creating a positive synergistic effect with the charge adsorption of magnesium hydroxide colloids, aiding in the removal of impurities and pigments. As the amount of calcium hydroxide added increases, the amount of calcium phosphate formed by the reaction of calcium ions with phosphoric acid in the mixed juice increases. When the pH exceeds 11.0, this is likely due to over-alkalinity, which causes the juice to turn red and increases the content of soluble calcium salts, leading to a significant decrease in decolorization rate and purity. Therefore, the optimal pH value for secondary decolorization is determined to be 11.0.

[0107] 4. Experiment on the influence of secondary decolorization temperature on decolorization rate and purity

[0108] Experimental method: Prepare multiple beakers, take 100mL of sugarcane juice into each beaker, add 450mg of dolomite digestion product, heat to 80℃, and keep warm for 80 minutes; then add 10% by mass phosphoric acid solution to adjust the pH to 11.0, heat to 50, 60, 70, 75, 80, and 90℃ respectively, and keep warm for 80 minutes, add 0.3mL of 0.1% by mass polyacrylamide flocculant solution (i.e., 3mg / L to sugarcane juice), centrifuge (4000r / min, 25℃, 20min), separate the supernatant and obtain the primary clear juice. Then, 40 mg of 10% by mass phosphoric acid solution was added and stirred evenly. After adjusting the pH to 7.6 with 5% by mass sulfuric acid solution, the mixture was heated to boiling. 0.1 mL of 0.1% by mass polyacrylamide flocculant solution (i.e., 1 mg / L to sugarcane juice ratio) was added and filtered to obtain secondary clear juice. The brix and absorbance (wavelength 560 nm) of the secondary clear juice were measured, and the decolorization rate and purity were calculated. The results are shown in Table 7.

[0109] Table 7

[0110] Experimental samples 1 2 3 5 6 Secondary decolorization heating temperature / ℃ 50 60 70 80 90 Decolorization rate / % 91.78 92.19 93.21 94.76 92.78 Simple purity / % 79.30 80.41 82.31 84.69 83.26

[0111] Table 7 shows that as the secondary decolorization temperature increases, the decolorization rate and pure purity first increase and then decrease. The decolorization rate reaches its highest point, 93.76%, at 80°C. This is because increasing temperature promotes flocculation and precipitation, which promotes decolorization of the sugarcane juice. Above 80°C, both the decolorization rate and pure purity decrease. This is likely due to the high temperature under strong alkaline conditions, which increases the destruction of reducing sugars and leads to an increase in solution color. Therefore, the optimal decolorization temperature is determined to be 80°C.

[0112] 5. Experiment on the influence of the amount of phosphoric acid used in the second time on the decolorization rate and purity

[0113] Experimental method: Prepare multiple beakers, take 100mL of sugarcane juice into each beaker, add 450mg of dolomite digestion product, heat to 80℃, and keep warm for 80 minutes; then add 10% by mass phosphoric acid solution to adjust the pH to 11.0, heat to 80℃, keep warm for 80 minutes, add 0.3mL of 0.1% by mass polyacrylamide flocculant solution (i.e., 3mg / L to sugarcane juice), centrifuge (4000r / min, 25℃, 20min), separate the supernatant and obtain the primary clear juice. Then, 30, 35, 40, 45, and 50 mg of 10% phosphoric acid solution were added, respectively, and stirred evenly. After adding 5% sulfuric acid solution to adjust the pH to 7.6, the mixture was heated to boiling. 0.1 mL of 0.1% polyacrylamide flocculant solution (i.e., 1 mg / L to sugarcane juice ratio) was added, and the mixture was filtered to obtain secondary clear juice. The brix and absorbance (wavelength 560 nm) of the secondary clear juice were measured, and the decolorization rate and purity were calculated. The results are shown in Table 8.

[0114] Table 8

[0115] Experimental samples 1 2 3 4 5 Second phosphoric acid dosage / mg 30 35 40 45 50 Decolorization rate / % 93.21 93.67 94.76 94.38 94.02 Simple purity / % 83.68 83.99 84.96 84.47 84.07

[0116] As shown in Table 8, as the secondary phosphoric acid dosage increases, the decolorization rate and purity initially rise and then level off. This is because as the secondary phosphoric acid dosage gradually increases, the amount of calcium phosphate generated in the primary clear juice also increases, more effectively removing impurities and pigments from the primary clear juice, thereby improving the decolorization rate and purity of the sugarcane juice. However, when the secondary phosphoric acid dosage reaches 400 mg / L, the increase in the dosage level off. Excessive addition of phosphoric acid not only increases production costs but also forms loose flocculent material, making subsequent filtration operations difficult. It is necessary to add an appropriate amount of phosphoric acid according to actual production requirements. Therefore, the optimal secondary phosphoric acid dosage is determined to be 400 mg / L.

[0117] Through single-factor experiments, it can be seen that the present invention comprehensively considers the two indicators of decolorization rate and simple purity, and then limits the amount of dolomite digestion product, the first decolorization temperature, the second decolorization pH value, the second decolorization temperature and the second phosphoric acid amount, and finally achieves an excellent effect of a decolorization rate of 85-95% and a simple purity of 75-85%.

[0118] The above embodiments are only specific examples to further illustrate the purpose, technical solutions and beneficial effects of the present invention, and the present invention is not limited thereto. Any modifications, equivalent replacements, improvements, etc. made within the scope of the present invention are included in the scope of protection of the present invention.

Claims

1. A dolomite-based sugarcane juice clarification and decolorization method, characterized in that: The following steps are involved: (1) Add 300-500 mg of dolomite digestion product to the sugarcane juice, heat and keep it warm for decolorization, then adjust the pH to 10.0-12.0 with phosphoric acid solution, heat and keep it warm for decolorization again; then add flocculant and stir evenly to remove the precipitate to obtain a clear juice; (2) Add 300-500 mg of phosphoric acid per 1 L of primary clear juice, add phosphoric acid solution to the primary clear juice, and adjust the pH to 7.0-8.0 with dilute sulfuric acid solution. Heat to boiling and then keep warm for decolorization. Then add flocculant and stir evenly to remove the precipitate to obtain a clarified and decolorized secondary clear juice. The dolomite digestion product is a mixed product obtained by calcining and digesting dolomite, the main components of which are magnesium hydroxide and calcium hydroxide; the calcination is to calcine dolomite powder with a particle size of 0.5 to 5 mm at 700 to 1000° C. for 2 to 4 hours to obtain a calcined product; the digestion is to add the calcined product into water at a solid-liquid ratio of (1 to 6) g: 25L at room temperature, and stir and digest for 20 to 30 minutes.

2. The dolomite-based sugarcane juice clarification and decolorization method according to claim 1, characterized in that: The sugarcane juice is a mixed juice obtained by squeezing and extracting sugarcane, with a pH value of 5.4-6.4, a color value of 2000-10000 IU, and a purity of 70-75%.

3. The dolomite-based sugarcane juice clarification and decolorization method according to claim 1, characterized in that: In the one-time heating and heat preservation decolorization, the heating temperature is 50-80° C. and the heat preservation time is 30-90 minutes.

4. The dolomite-based sugarcane juice clarification and decolorization method according to claim 1, characterized in that: In the secondary heating and heat preservation decolorization, the heating temperature is 50-80° C. and the heat preservation time is 30-90 minutes.

5. The dolomite-based sugarcane juice clarification and decolorization method according to claim 1, characterized in that: The mass fraction of phosphoric acid in the phosphoric acid solution is 5-10%.

6. The dolomite-based sugarcane juice clarification and decolorization method according to claim 1, characterized in that: The mass fraction of sulfuric acid in the dilute sulfuric acid solution is 5-10%.

7. The dolomite-based sugarcane juice clarification and decolorization method according to claim 1, characterized in that: The flocculant in step (1) is a polyacrylamide solution with a mass fraction of 0.1%, and 3 mg of polyacrylamide is added to every 1 L of the mixed juice after secondary heating, insulation and decolorization.

8. The dolomite-based sugarcane juice clarification and decolorization method according to claim 1, characterized in that: The flocculant in step (2) is a polyacrylamide solution with a mass fraction of 0.1%, and 3 mg of polyacrylamide is added per 1 L of clear juice.

9. The dolomite-based sugarcane juice clarification and decolorization method according to claim 1, characterized in that: The decolorization rate of the obtained secondary clear juice is 85-95%, and the purity is 75-85%.

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