Compound flocculant and application thereof

Abstract

The application discloses a compound flocculating agent and application thereof, and belongs to the technical field of flocculating agents. The compound flocculating agent comprises flocculating agent A and flocculating agent B. The flocculating agent A comprises attapulgite and bamboo charcoal, and the flocculating agent B comprises chitosan quaternary ammonium salt and polyacrylamide. The compound flocculating agent is applied to the flocculation of stevia extract liquid, and has the advantages of fast flocculation settling speed, low cost, simple operation, low loss rate of steviol glycosides, high clarification rate and good flocculation and impurity removal effects.

Description

Technical Field

[0001] This invention relates to the field of plant extract separation and purification technology, specifically to a compound flocculant and its application. Background Technology

[0002] In the purification process of steviol glycosides, preliminary impurity removal and decolorization treatment of the stevia extract is required to reduce the difficulty of subsequent separation and purification and extend the service life of the resin. Existing production processes mainly use inorganic flocculants, such as iron salts and aluminum salts. Flocculation is low-cost and simple to operate, but it leads to inorganic ion pollution and significant loss of steviol glycosides. Moreover, the flocculation speed is slow and the separation of flocs is difficult.

[0003] Chinese patent publication CN114437152A discloses a method for decolorizing and removing impurities from steviol glycoside aqueous extract. The method involves adding a chitosan-aluminum hydroxide composite material to the steviol glycoside aqueous extract, stirring thoroughly, and then filtering to obtain steviol glycosides after impurity removal. However, the flocculent structure of this composite material is relatively loose, has a slow sedimentation rate, is difficult to dehydrate, has a high process cost, and is prone to aluminum ion residue. Therefore, the steviol glycosides obtained may pose certain food safety risks when used as flavorings and fragrances.

[0004] Chinese patent publication CN112645419A discloses a flocculant for stevia purification, the raw materials of which include modified porous silica microspheres, chitosan quaternary ammonium salt and polyferric sulfate; wherein the modified porous silica microspheres are obtained by mixing calcium hydroxide and ammonia solution, then adding dropwise to an ethanol solution of tetraethyl orthosilicate, and then filtering and calcining; although the loss of stevia is small when using this flocculant, the floc volume is large, the post-processing is difficult and costly, and it is not suitable for industrial production.

[0005] Chinese patent publication CN109432153A discloses a method for preparing stevia polyphenols using a composite chitosan flocculation method. This method uses a composite chitosan-acetic acid aqueous solution as a flocculant for impurity removal. However, this method requires strict control of component ratios and process conditions, resulting in high costs. Other processes use zeolite, palygorskite, palygorskite, bentonite, etc., as flocculants, but these are not suitable for large-scale production due to operability, pretreatment, and cost considerations. Summary of the Invention

[0006] The purpose of this invention is to provide a compound flocculant and its application to solve at least one aspect of the problems and defects mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A compound flocculant includes flocculant A and flocculant B, wherein flocculant A comprises attapulgite and bamboo charcoal, and flocculant B comprises chitosan quaternary ammonium salt and polyacrylamide.

[0008] As a further embodiment of the present invention, the mass ratio of attapulgite clay to bamboo charcoal in flocculant A is (3~5):1.

[0009] As a further embodiment of the present invention, the mass ratio of chitosan quaternary ammonium salt to polyacrylamide in flocculant B is 1:(2~4).

[0010] As a further embodiment of the present invention, the flocculant A is obtained by ultrasonically dispersing attapulgite clay and bamboo charcoal.

[0011] As a further aspect of the present invention, the power of the ultrasonic dispersion is 200~300W.

[0012] As a further aspect of the present invention, the ultrasonic dispersion time is 1 to 3 hours.

[0013] As a further aspect of the present invention, the preparation process of the flocculant A includes raw material acidification, wherein the acidification uses an inorganic acid.

[0014] As a further aspect of the present invention, the inorganic acid is selected from at least one of hydrochloric acid, sulfuric acid, and nitric acid.

[0015] As a further aspect of the present invention, the concentration of the inorganic acid is 0.1~2.5 mol / L.

[0016] As a further embodiment of the present invention, the acidification temperature is 50~90℃.

[0017] As a further aspect of the present invention, the acidification time is 3-6 hours.

[0018] As a further aspect of the present invention, the acidification of the attapulgite soil uses hydrochloric acid with a concentration of 0.1~0.5 mol / L, an acidification temperature of 50~70℃, and an acidification time of 3~5 h.

[0019] As a further aspect of the present invention, the attapulgite clay is acidified, dried, and pulverized to a particle size of <0.5μm, preferably 0.1~0.5μm.

[0020] As a further aspect of the present invention, the bamboo charcoal is acidified using nitric acid at a concentration of 1.0~2.5 mol / L, at an acidification temperature of 70~90℃, and for an acidification time of 3~6 h.

[0021] As a further embodiment of the present invention, the flocculant A is prepared by the following method: soaking bamboo charcoal powder in water for about 10 minutes, then adding attapulgite clay, stirring thoroughly, with the mass ratio of attapulgite clay to bamboo charcoal being (3~5):1 and the material-to-liquid ratio being 1:(5~8) g / mL, dispersing under ultrasonic power of 200~300W for 1~3 hours, filtering after the reaction is completed, collecting the solid and vacuum drying to obtain flocculant A.

[0022] As a further aspect of the present invention, the particle size of the flocculant A is 0.1~0.5μm, preferably 0.2~0.4μm.

[0023] As a further embodiment of the present invention, the flocculant B is obtained by adding a polyacrylamide solution with a concentration of 20-50 mg / mL to a chitosan quaternary ammonium salt solution with a concentration of 50-80 mg / mL and stirring.

[0024] As a further embodiment of the present invention, the stirring temperature is 35~45℃.

[0025] As a further embodiment of the present invention, the stirring time is 1 to 3 hours.

[0026] As a further embodiment of the present invention, the stirring speed is 100~200 rpm.

[0027] As a further embodiment of the present invention, the flocculant B is prepared by the following method: A 20-50 mg / mL aqueous solution of polyacrylamide is added to a 50-80 mg / mL aqueous solution of chitosan quaternary ammonium salt at a mass ratio of chitosan quaternary ammonium salt to polyacrylamide of 1:(2-4). The mixture is stirred at 35-45°C for 1-3 hours at a stirring speed of 100-200 rpm. After the reaction is complete, the mixture is cooled, and calcium hydroxide is added to adjust the pH to 6.5-8.0. Unreacted substances are removed by filtration to obtain flocculant B.

[0028] As a further aspect of the present invention, the polyacrylamide aqueous solution and the chitosan quaternary ammonium salt aqueous solution can be heated at a temperature not exceeding 50°C to accelerate dissolution.

[0029] Application of compound flocculants as described above in stevia extraction.

[0030] As a further aspect of the present invention, the application includes adding the compound flocculant to stevia extract for flocculation, with an addition amount of 0.5~5g / L, preferably 2~3g / L.

[0031] As a further aspect of the present invention, the pH of the stevia extract is adjusted using a calcium salt, preferably calcium hydroxide.

[0032] As a further embodiment of the present invention, the stevia extract is prepared by the following method: stevia leaves are crushed, water is added for extraction, the material-to-liquid ratio is 1g:(5~10)mL, the extraction temperature is 70~90℃, reflux extraction or continuous countercurrent extraction is used, the number of extractions is 1~3 times, and the extraction time is 1~3h to obtain stevia extract.

[0033] As a further aspect of the present invention, the solid content of the stevia extract is 5-6%.

[0034] As a further aspect of the present invention, the pH of the stevia extract is 4.0 to 5.0.

[0035] As a further aspect of the present invention, the concentration of steviol glycoside (stv) in the stevia extract is 0.4~0.6 mg / mL.

[0036] As a further aspect of the present invention, the concentration of riboflavin A (RA) in the stevia extract is 2.5~3.0 mg / mL.

[0037] As a further aspect of the present invention, the flocculation of the stevia extract includes the following steps: First, adjust the pH of the stevia extract to 5.5-6.5 using calcium hydroxide; Add 0.5-1.0 g of flocculant B to each liter of stevia extract, place at 50-60℃ and shake / stir, with a stirring / vibration frequency of 60-80 times / min, and a reaction time of 5-8 min; Add 1.0~2.0 g of flocculant A to each liter of stevia extract and continue the reaction for 30~40 min. After the reaction is complete, cool and filter to remove the flocculent matter to obtain the stevia extract after flocculation and impurity removal.

[0038] As a further aspect of the present invention, the flocculent material can be used to prepare organic acids such as chlorogenic acid.

[0039] As a further aspect of the present invention, the flocculant A and flocculant B can be used directly as solid powders or prepared into a 3-5 wt% solution.

[0040] The present invention has at least the following technical effects: A compound flocculant was prepared by combining attapulgite clay, bamboo charcoal, chitosan quaternary ammonium salt, and polyacrylamide. This flocculant was applied to the flocculation of stevia extract, and the pH of the system was adjusted using calcium salts during application. The porosity and large specific surface area of ​​attapulgite clay can capture impurities through physical adsorption, while the interlayer cations Ca... 2+It can act as a bridge to connect colloidal particles and promote floc formation; bamboo charcoal can perform physical adsorption, and the three-dimensional network formed by its interwoven fibers can mechanically trap colloidal particles. The combination of the two can accelerate the sedimentation of flocs and promote the separation of flocs from liquid. Quaternary ammonium salt groups can neutralize negatively charged components in stevia extract, such as polysaccharides and phenolic substances; the long-chain structure of chitosan can form a network of flocs through entanglement or cross-linking, which enhances mechanical strength and prevents the flocs from breaking; polyacrylamide can electrostatically adsorb impurities in stevia extract, and when used in combination with chitosan quaternary ammonium salt, it can have a synergistic effect, and can also reduce the amount of chitosan quaternary ammonium salt used, thus reducing the cost of use; The raw materials for the flocculation scheme of this invention are readily available, low in cost, simple to operate, and the flocs settle quickly. Compared with the use of chitosan for flocculation, the speed is increased by more than 75%, the loss rate of steviol glycosides is reduced to less than 3%, the clarification rate is >85%, and the solution color changes from dark brown to bright yellow, demonstrating good flocculation and impurity removal effects. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, and not all embodiments.

[0042] Therefore, the following detailed description of embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0043] In the following embodiments: Chitosan quaternary ammonium salt was provided by Nantong Lvshen Bioengineering Co., Ltd., with a substitution degree ≥90% and a 60-mesh sieve pass rate ≥95%. The polyacrylamide is cationic, with an ionicity of 30-70%, and is supplied by Zhengzhou Daqian Environmental Protection Technology Co., Ltd. It has a molecular weight of 10 million and a solid content of 90%. Chitosan was provided by Nantong Lvshen Bioengineering Co., Ltd., with a degree of deacetylation ≥90% and a fineness of 60~100 mesh; The content of steviol glycosides and rebaudioside A in stevia used in the experiment was determined by high performance liquid chromatography, and the detection method was in accordance with GB 1886.355-2022 National Food Safety Standard for Food Additives Steviosides. The method for detecting the clarity rate of the solution refers to the "Ultraviolet-Visible Spectrophotometry" in the "General Rules of the 2020 Edition of the Chinese Pharmacopoeia". The detection wavelength is 670 nm. The determination of the clarity rate of the extract is corrected with pure water. The absorbance of the extract A0 and the absorbance of the flocculated solution at the above wavelength A1 are calculated. The clarity rate B (%) is calculated by the following formula: B / % = (A0-A1) / A0 × 100%; The method for determining the solid content is in accordance with NY / T 2637-2014 Determination of soluble solids content in fruits and vegetables by refractometer method.

[0044] Unless otherwise specified, the particle size described in this invention is D50.

[0045] Example 1: Preparation of flocculant A compound flocculant is composed of flocculant A and flocculant B. Flocculant A is composed of attapulgite clay and bamboo charcoal, and flocculant B is composed of chitosan quaternary ammonium salt and polyacrylamide.

[0046] It is prepared by the following method: S1. Preparation of flocculant A S1-1. Pretreatment of attapulgite: The attapulgite was crushed to a particle size of 0.5 μm, acidified by heating in a 0.1 mol / L dilute hydrochloric acid solution at 50°C for 3 hours, washed with deionized water until the pH of the effluent was 6.5~7.0, and the insoluble matter was vacuum dried (80°C, vacuum degree of -0.085MPa to -0.095MPa) and then crushed to a particle size of 0.3 μm. S1-2. Bamboo charcoal pretreatment: Powdered bamboo charcoal (particle size 0.5μm) is added to a 1mol / L HNO3 solution and heated at 80℃ for 3h to acidify. It is then washed with deionized water until the effluent is neutral (pH=6.5~7.0). The insoluble matter is then vacuum dried (80℃, vacuum degree -0.085MPa to -0.095MPa). S1-3, Compounding: First, soak the bamboo charcoal powder obtained in step S1-2 in deionized water for 10 minutes, then add the attapulgite clay obtained in step S1-1 into it and stir thoroughly. The mass ratio of attapulgite clay to bamboo charcoal is 3:1, and the total mass of attapulgite clay and bamboo charcoal to the volume ratio of deionized water is 1g:5mL. Then, it is ultrasonically assisted dispersed (power 200W, ultrasonic time 1h), filtered and collected, and vacuum dried (70℃, vacuum degree -0.085MPa to -0.095MPa). Finally, it is pulverized to a particle size of 0.4μm to prepare solid flocculant A. S2, Preparation of flocculant B Chitosan quaternary ammonium salt was prepared into an aqueous solution with a concentration of 50 mg / mL, and polyacrylamide was prepared into an aqueous solution with a concentration of 20 mg / mL (heating at 40℃ accelerates dissolution). The polyacrylamide solution was slowly added to the chitosan quaternary ammonium salt solution at a mass ratio of 1:2. The mixture was stirred at 45℃ for 1 hour at a stirring speed of 100 rpm. After the reaction was completed, the mixture was cooled to room temperature (25℃), and the pH was adjusted to 6.5~8 with calcium hydroxide suspension. Unreacted substances were removed by filtration, and the filtrate was liquid flocculant B.

[0047] Example 2: Preparation of flocculant A compound flocculant is composed of flocculant A and flocculant B. Flocculant A is composed of attapulgite clay and bamboo charcoal, and flocculant B is composed of chitosan quaternary ammonium salt and polyacrylamide.

[0048] It is prepared by the following method: S1. Preparation of flocculant A S1-1. Pretreatment of attapulgite: The attapulgite was crushed to a particle size of 0.1 μm, acidified by heating in a 0.5 mol / L dilute hydrochloric acid solution at 70°C for 3 hours, washed with deionized water until the pH of the effluent was 6.5~7, and the insoluble matter was vacuum dried (70°C, vacuum degree -0.085MPa to -0.095MPa) and then crushed to a particle size of 0.1 μm. S1-2. Bamboo charcoal pretreatment: Powdered bamboo charcoal (particle size 0.1μm) is added to a 2.5mol / L HNO3 solution and heated at 90℃ for 6 hours for acidification. Then, it is washed with deionized water until the effluent is neutral (pH=6.5~7). The insoluble matter is vacuum dried (70℃, vacuum degree -0.085MPa to -0.095MPa). S1-3, Compounding: First, soak the bamboo charcoal powder obtained in step S1-2 in deionized water for 10 minutes, then add the attapulgite clay obtained in step S1-1 and stir thoroughly. The mass ratio of attapulgite clay to bamboo charcoal is 5:1, and the total mass of attapulgite clay and bamboo charcoal to the volume ratio of deionized water is 1g:8mL. Dispersion is assisted by ultrasound (power 300W, ultrasound time 1h). After the reaction is completed, filter, collect the solid and vacuum dry (70℃, vacuum degree -0.085MPa to -0.095MPa), then pulverize to a particle size of 0.2μm to prepare solid flocculant A. S2, Preparation of flocculant B Chitosan quaternary ammonium salt was prepared into an aqueous solution with a concentration of 80 mg / mL, and polyacrylamide was prepared into an aqueous solution with a concentration of 50 mg / mL (dissolution was accelerated by heating at 40℃). The polyacrylamide solution was slowly added to the chitosan quaternary ammonium salt solution at a mass ratio of 1:4. The mixture was stirred at 35℃ for 1 hour at a stirring speed of 200 rpm. After the reaction was completed, the mixture was cooled to room temperature (25℃), and the pH was adjusted to 6.5~8 by adding calcium hydroxide suspension. Unreacted substances were removed by filtration. The filtrate was concentrated to a solid content of 20%, and then spray-dried (inlet air temperature 150℃, outlet air temperature 80℃) to produce powdered flocculant B.

[0049] Example 3: Preparation of Stevia extract (small-scale test) 50g of dried stevia leaves were crushed and passed through a 24-mesh sieve as the first raw material. Pure water was added to the first raw material for extraction at a material-to-liquid ratio of 1g:10mL and an extraction temperature of 70℃. The first raw material was extracted with pure water three times, with each extraction lasting 1 hour. The third extract was used as the second extraction solvent. Next, 50g of dried stevia leaves were crushed and passed through a 24-mesh sieve as the second raw material. The second extraction solvent was added to the second raw material for the first extraction, with a material-to-liquid ratio of 1g:10mL, an extraction temperature of 70℃, and an extraction time of 1h. Then, the second extraction solvent was replaced with pure water, and the second and third extractions were carried out according to the material-to-liquid ratio, temperature, and time of the first extraction. The extracts from the three extractions were collected and combined to obtain the stevia extract.

[0050] The stevia extract was tested and found to have a solid content of 5%, a pH of 4.5, a steviol glycoside (stv) concentration of 0.45 mg / mL, a rebaudioside A (RA) concentration of 2.62 mg / mL, and an absorbance value A0 = 0.6288.

[0051] Example 4: Flocculation of Stevia extract The flocculation treatment of the stevia extract prepared in Example 3 was carried out using a suspension of flocculant A and flocculant B prepared in Example 1 and calcium hydroxide as a coagulant aid, including the following steps: Take 20 mL of stevia extract, adjust the pH to 5.5 using calcium hydroxide suspension, add 0.4 mL of flocculant B, and shake at 50 °C for 60 times / min for 5 min. Then add 25 mg of flocculant A and dilute to 25 mL with pure water. Continue the reaction for 30 min, observing and recording the floc settling speed during the reaction. After the reaction is complete, cool and filter to remove the flocs. Collect the supernatant and determine the content of steviol glycosides, rebaudioside, and solids.

[0052] Flocculation results: After adding flocculant B to stevia extract, flocs were formed, but the sedimentation was slow. After adding flocculant A, the flocs settled within 5 minutes, and the supernatant changed from brownish-yellow to bright yellow. The solid content in the supernatant was 3.3%, the clarification rate was 86.77%, the stevioside recovery rate was 97.80%, and the riboflavin A recovery rate was 97.97%.

[0053] Example 5: Flocculation of Stevia extract The flocculation treatment of the stevia extract prepared in Example 3 was carried out using a suspension of flocculant A and flocculant B prepared in Example 2 and a coagulant aid calcium hydroxide, including the following steps: Take 20 mL of stevia extract, adjust the pH of the extract to 6.5 using calcium hydroxide suspension, then add 25 mg of flocculant B, and shake at 50 °C with a shaking frequency of 80 times / min. After reacting for 8 min, add 50 mg of flocculant A, and then bring the volume to 25 mL. Continue the reaction for 40 min, observing and recording the sedimentation rate of the flocs during the reaction. After the reaction is completed, cool and filter to remove the flocs; collect the supernatant and detect the content of steviol glycosides, rebaudioside, and solids.

[0054] Flocculation results: After adding flocculant B to the extract, flocculents were generated and settled slowly; after adding flocculant A, the flocs settled completely within 5 minutes, and the supernatant changed from brown to bright yellow; the solid content in the supernatant was 3.2%, the clarification rate was 87.04%, the stevioside recovery rate was 99.5%, and the rebaudioside A recovery rate was 98.64%.

[0055] Example 6: Preparation and flocculation of stevia extract (pilot-scale) 10 kg of dried stevia leaves were crushed and passed through a 10-mesh sieve as the first raw material. Pure water was added to the first raw material for extraction at a material-to-liquid ratio of 1 g: 8 mL and an extraction temperature of 80 °C. The first raw material was extracted with pure water three times, with each extraction lasting 2 hours. The third extract was used as the second extraction solvent. Next, 10 kg of dried stevia leaves were crushed and passed through a 10-mesh sieve as the second raw material. The second extraction solvent was added to the second raw material for the first extraction, with a material-to-liquid ratio of 1 g: 8 mL, an extraction temperature of 80 °C, and an extraction time of 2 h. Then, the second extraction solvent was replaced with pure water, and the second and third extractions were carried out according to the material-to-liquid ratio, temperature, and time of the first extraction. The extracts from the three extractions were collected and combined to obtain the stevia extract.

[0056] The stevia extract had a solids content of 5.8%, a pH of 5, a steviol glycoside (stv) concentration of 0.55 mg / mL, a rebaudioside A (RA) concentration of 2.95 mg / mL, and an absorbance value A0 = 0.6615.

[0057] Flocculation was performed using the compound flocculant obtained in Example 2: Calcium hydroxide suspension was added to the stevia extract to adjust the pH to 6, and 1g of flocculant B was added to each liter of extract. The mixture was heated to 50°C and stirred at a stirring rate of 80 rpm for 8 minutes. Then, 2g of flocculant A was added to each liter of extract, and the reaction was continued for 40 minutes. The settling velocity of the flocs was observed and recorded during the reaction. After the reaction was completed, the mixture was cooled and filtered to remove the flocs. The supernatant was collected, and the contents of steviol glycosides, rebaudioside, and solids were measured.

[0058] Results: After adding flocculant B, flocs were formed and settled slowly. After adding flocculant A, the flocs settled completely within 8 minutes, and the supernatant changed from brown to bright yellow. The solid content in the supernatant was 3.0%, the clarification rate was 87.23%, the stevioside recovery rate was 98.18%, and the rebaudioside A recovery rate was 98.31%.

[0059] Example 7: Preparation and flocculation (production) of stevia extract 500 kg of dried stevia leaves were pulverized and passed through a 10-mesh sieve. Pure water was added for extraction at a material-to-liquid ratio of 1 g:5 mL. Continuous countercurrent extraction was performed at 80℃ for 3 hours, and 2445 L of extract was collected to obtain the stevia extract. The stevia extract had a solids content of 6%, a pH of 4.5, a steviol glycoside (stv) concentration of 0.48 mg / mL, a rebaudioside A (RA) concentration of 2.84 mg / mL, and an absorbance value A0 = 0.6782.

[0060] Flocculation was performed using the compound flocculant obtained in Example 2: Calcium hydroxide suspension was added to the stevia extract to adjust the pH to 6, with continuous stirring during the addition process; then 1g of flocculant B was added to each liter of extract, and the mixture was stirred at 50°C at a stirring rate of 60 rpm for 8 minutes. After stirring, 2g of flocculant A was added to each liter of extract, and the reaction was continued for 40 minutes. The settling velocity of the flocs was observed and recorded during the reaction. After the reaction was completed, the mixture was cooled and filtered to remove the flocs; the supernatant was collected, and the contents of steviol glycosides, rebaudioside, and solids were detected.

[0061] Results: After adding flocculant B, flocculents were formed and settled slowly. After adding flocculant A, the flocculents settled completely within 10 minutes, and the supernatant changed from brown to bright yellow. The solid content in the supernatant was 3.2%, the clarification rate was 88.43%, the stevioside recovery rate was 97.92%, and the riboflavin A recovery rate was 98.59%.

[0062] Comparative Example 1 The stevia extract prepared in Example 3 was subjected to flocculation treatment, including the following steps: First, the pH of the stevia extract was adjusted to 5.5 using calcium hydroxide suspension. Then, 3 g / L of chitosan was added, and the mixture was shaken at 50°C at a frequency of 60 times / min. The reaction endpoint was determined when the flocs settled completely. The settling rate of the flocs was observed and recorded during the reaction. After the flocs settled completely, the mixture was cooled and filtered to remove the flocs. The supernatant was collected for the detection and calculation of the recovery rates of steviol glycoside (STV), ribobadiol A (RA), and clarification rate.

[0063] Comparative Example 2 The difference from Comparative Example 1 is that chitosan was replaced with a mixture of chitosan and chitosan quaternary ammonium salt in a mass ratio of 1:1.

[0064] Comparative Example 3 The difference from Comparative Example 1 is that chitosan was replaced with polyacrylamide.

[0065] Comparative Example 4 The difference from Comparative Example 1 is that chitosan was replaced with a mixture of calcium hydroxide and ferrous sulfate in a mass ratio of 1:2.

[0066] Comparative Example 5 The difference from Comparative Example 1 is that chitosan was replaced with flocculant B prepared in Example 2.

[0067] Comparative Example 6 The difference from Comparative Example 1 is that chitosan was replaced with flocculant A prepared in Example 2.

[0068] The flocculation results of Comparative Examples 1 to 6 are shown in Table 1.

[0069] Table 1

[0070] The results showed that, compared with Example 4, the use of chitosan, chitosan-chitosan quaternary ammonium salt, polyacrylamide, calcium hydroxide-ferrous sulfate, or flocculant A or flocculant B alone significantly reduced the settling velocity of the flocs, prolonged the settling time, and decreased the clarification rate and the recovery rate of steviol glycoside (STV) and riboboroside A (RA). This indicates that the compound flocculant of the present invention has a better flocculation and impurity removal effect on stevia extract.

[0071] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A compound flocculant, characterized in that, It includes flocculant A and flocculant B, wherein flocculant A comprises attapulgite and bamboo charcoal, and flocculant B comprises chitosan quaternary ammonium salt and polyacrylamide.

2. The compound flocculant according to claim 1, characterized in that, The mass ratio of attapulgite clay to bamboo charcoal in flocculant A is (3~5):1; And / or, the mass ratio of chitosan quaternary ammonium salt to polyacrylamide in flocculant B is 1:(2~4).

3. The compound flocculant according to claim 1, characterized in that, The flocculant A is obtained by ultrasonically dispersing attapulgite clay and bamboo charcoal.

4. The compound flocculant according to claim 3, characterized in that, It also includes a raw material acidification step, wherein the acidification uses an inorganic acid; And / or, the inorganic acid is selected from at least one of hydrochloric acid, sulfuric acid, and nitric acid; And / or, the concentration of the inorganic acid is 0.1~2.5 mol / L; And / or, the acidification temperature is 50~90℃; And / or, the acidification time is 3~6h.

5. The compound flocculant according to claim 3, characterized in that, The power of the ultrasonic dispersion is 200~300W; And / or, the ultrasonic dispersion time is 1~3h.

6. The compound flocculant according to claim 1, characterized in that, The flocculant B is obtained by adding a polyacrylamide solution with a concentration of 20-50 mg / mL to a chitosan quaternary ammonium salt solution with a concentration of 50-80 mg / mL and stirring.

7. The compound flocculant according to claim 6, characterized in that, During the stirring process: The temperature is 35~45℃; And / or, the stirring time is 1~3 hours; And / or, the stirring speed is 100~200 rpm.

8. The application of the compound flocculant as described in any one of claims 1 to 7 in the extraction of stevia.

9. The application according to claim 8, characterized in that, This includes adding the compound flocculant to stevia extract for flocculation, with an addition amount of 0.5~5g / L.

10. The application according to claim 9, characterized in that, The pH of the stevia extract was adjusted using calcium salts.

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