A green chemistry-based method for removing sodium citrate combustibles

Abstract

The application belongs to the technical field of sodium citrate production, and particularly relates to a method for removing easy carbonization substances of sodium citrate based on green chemistry, which comprises the following steps: adding an alkaline solution to a sodium citrate mother liquor, adjusting the pH value to 7-8, microwave heating, cooling, coarse filtering, fine filtering, adding tetrasodium glutamate diacetate, stirring for 20-30 min, standing for 3-5 h, filtering, adding a magnetic porous adsorbent to the filtrate, stirring for 20-30 min, standing for 5-10 h, magnetic separation, filtering, adding a sodium-containing alkaline solution, uniformly stirring, adjusting the pH value to 7.5-8.5, then heating, keeping warm for 20-30 min, cooling, filtering, adding a decolorizing agent, filtering, concentrating and crystallizing the filtrate, centrifuging, drying, and obtaining sodium citrate. The application combines microwave, filtering, magnetic field separation, chelation, molecular reconfiguration and functional adsorbent, and the steps are logically rigorous and echo each other, so that the complex easy carbonization substances in the sodium citrate mother liquor are deeply, greenly and efficiently removed.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium citrate production, and specifically relates to a method for removing easy carbon compounds of sodium citrate based on green chemistry. BACKGROUND

[0002] Sodium citrate is an important additive and is widely used in the food, beverage, medicine and other industries. The core process of its production includes microbial fermentation to produce a fermentation liquor containing citric acid, reaction of the fermentation liquor with an alkaline solution, extraction and purification, neutralization and conversion, and crystallization and drying to obtain sodium citrate.

[0003] The easy carbon compounds present in sodium citrate are prone to Maillard reaction and other degradation behaviors under storage or processing conditions, which can cause coloring and irritating volatile substances in food and beverages, thereby affecting the taste, etc. Therefore, for food-grade sodium citrate, the easy carbon value needs to be strictly controlled. There are easy carbon compounds such as polysaccharides and proteins in the fermentation liquor, and the purification of the fermentation liquor will produce a citric acid mother liquor containing more polysaccharides, proteins, alkaline solution and uncrystallized citric acid.

[0004] After searching, in order to remove the easy carbon compounds in the citric acid fermentation liquor or citric acid mother liquor and reduce the easy carbon value, a purification treatment method for citric acid mother liquor is disclosed in Chinese patent No. CN202111287031.6, which dilutes the citric acid mother liquor, denatures and precipitates the proteins through organic solvents and first heating, then chelates through disodium ethylenediaminetetraacetate, completely agglomerates the chelate through second heating, removes the chelate through first precision filtration, adjusts the pH through an alkaline solution containing sodium, and then through third heating, evaporation and concentration, centrifugation, decolorization and cation exchange resin, to obtain a pure sodium citrate solution. This scheme utilizes the different solubilities of different impurities at different temperatures and the chelation of ethylenediaminetetraacetic acid disodium, which can effectively remove the easy carbon compounds in the citric acid mother liquor. However, the introduction of ethylenediaminetetraacetic acid disodium can easily cause residues, resulting in sodium citrate products that do not meet the standards of the food industry, and multiple heating and holding are required, which consumes a lot of energy in actual production and is not conducive to industrial production.

[0005] A Chinese patent with the patent number CN201410009974.6 discloses a method for removing sodium citrate charring substance, which adds concentrated sulfuric acid and calcium source into a citric acid mother liquor, and removes the charring substance in the citric acid mother liquor by adopting a plate and frame filtration treatment method, so that the charring value in the sodium citrate product is significantly reduced, and the prepared sodium citrate crystal has stable quality and high quality. However, the method uses concentrated sulfuric acid for charring, and the charring reaction end point depends on pH control (1-3), and the charring substance (especially complex colloidal protein) may not be completely charring, or may be over-charring to generate furfural colorant or Maillard reaction product, thereby increasing new colored impurities.

[0006] At present, the methods for removing the charring substance all have defects such as incomplete removal of residual sugar, low removal rate of protein, and large amount of waste water and waste residue. SUMMARY

[0007] The present application aims to provide a method for removing sodium citrate charring substance based on green chemistry, which combines microwave, filtration, magnetic field separation, chelation, molecular reconstruction and functional adsorbent, and realizes deep, green and efficient removal of complex charring substance in the sodium citrate mother liquor.

[0008] The present application solves the technical problem by adopting the following technical scheme.

[0009] In one aspect, the present application provides a method for removing sodium citrate charring substance based on green chemistry, comprising the following steps:

[0010] S1, adding an alkaline solution to the citric acid mother liquor, adjusting the pH value to 7-8, microwave heating, cooling, coarse filtering, fine filtering, and obtaining a first treatment liquid;

[0011] S2, adding tetrasodium glutamate diacetate to the first treatment liquid, stirring for 20-30 min, standing for 3-5 h, filtering, adding a magnetic porous adsorbent to the filtrate, stirring for 20-30 min, standing for 5-10 h, and magnetically separating to obtain a second treatment liquid;

[0012] S3, adding a sodium-containing alkaline solution to the second treatment liquid, stirring uniformly, adjusting the pH value to 7.5-8.5, then heating, keeping warm for 20-30 min, cooling, filtering, and obtaining a third treatment liquid;

[0013] S4, adding a decolorizing agent to the third treatment liquid, filtering, and then concentrating and crystallizing the filtrate, centrifuging, and drying to obtain sodium citrate.

[0014] In some embodiments of the present application, in step S1, the temperature of microwave heating is 75-85℃, the holding time is 5-10 min, and the microwave power is 500-800 W.

[0015] In some embodiments of the present application, in step S1, the alkaline solution is sodium carbonate solution or sodium bicarbonate solution.

[0016] In some embodiments of the present application, in step S2, the mass of tetrasodium glutamate diacetate is 0.05-0.15% of the mass of the first treatment solution.

[0017] In step S2, the mass of the magnetic porous adsorbent is 0.8-1.5% of the mass of the first treatment solution.

[0018] In some embodiments of the present application, the magnetic porous adsorbent is prepared by the following method:

[0019] Preparation of magnetic powder: dissolve divalent iron salt and trivalent iron salt in deionized water to obtain a mixed iron salt solution; heat to 60-70℃ under nitrogen protection and mechanical stirring; then add concentrated ammonia water dropwise until the pH of the solution is 10-11; then add sodium citrate aqueous solution and react for 30-60 min; stop heating and mature for 1-2 hours under stirring; apply an external magnetic field and discard the supernatant; wash, dry, and grind to obtain the magnetic powder;

[0020] Coating of a silica layer: disperse the magnetic powder in an ethanol-water mixed solution and perform ultrasonic treatment; add tetraethyl orthosilicate dropwise under stirring, then add ammonia water, and react at 40-50℃ for 6-12 h; filter and dry to obtain the magnetic particles;

[0021] Construction of mesoporous structure: disperse the magnetic particles in water, add cetyltrimethylammonium bromide, stir uniformly, then add tetraethyl orthosilicate and ammonia water dropwise again, and react at 70-80℃ for 24-48 h; separate by magnetic field, and calcine the obtained product at 500-550℃ for 3-4 h to obtain the magnetic mesoporous particles;

[0022] Functionalization: disperse the magnetic mesoporous particles in toluene, add aminopropyltriethoxysilane, and reflux react at 80-85℃ for 12-24 h under nitrogen atmosphere; cool to room temperature, separate by magnetic field, and dry to obtain the magnetic porous adsorbent. Refluxing at 80-85℃ for 12-24 h can ensure that the aminopropyltriethoxysilane molecules have enough kinetic energy to diffuse into the deep mesoporous channels and fully react with the internal surface silicon hydroxyl groups. Lower temperature or shorter time will result in uneven surface grafting and low internal functionalization degree.

[0023] The preparation method of the magnetic porous adsorbent provided by the application controls the particle size of the magnetic nanoparticles, prevents agglomeration, and endows the particles with good water dispersibility and initial stability by in-situ modification with sodium citrate. The coating of the dense silica layer solves the problem of chemical dissolution of the magnetic nanoparticle core in acidic aqueous solution, greatly improving the chemical stability and service life of the adsorbent. The construction of the mesoporous structure creates a large specific surface area and ordered channels, providing sufficient space for the adsorption of macromolecular pigments, and the adsorption capacity is improved by orders of magnitude. The amino group grafting makes the surface of the adsorbent positively charged (–NH3 + ) under pH conditions, which can precisely target and adsorb negatively charged pigment molecules, polysaccharides and other impurities through strong electrostatic interaction, realizing function-oriented high-efficiency adsorption.

[0024] The polysaccharides, proteins and other impurities in the citric acid mother liquor are usually negatively charged under weakly acidic to neutral conditions, and are easy to form stable colored complexes with metal ions. The amino-functionalized magnetic mesoporous silica adsorbent provided by the application has a positively charged –NH3 + under the pH environment of the mother liquor, which efficiently captures negatively charged impurity molecules and their complexes through strong electrostatic interaction, realizing function-oriented precise adsorption. The mesoporous silica shell layer has a tunable pore size of 2-50 nm, and its channel structure provides sufficient access and adsorption space for macromolecular impurities (such as polysaccharides and proteins), solving the problem of low efficiency caused by insufficient pore size of ordinary adsorbents. The magnetic core realizes rapid separation and recovery of the adsorbent; the silica shell layer ensures chemical stability; and the amino functional group provides high-density adsorption sites. The combination of the above three functions makes the magnetic porous adsorbent produce unexpected technical effects in adsorption capacity, separation efficiency and reusability.

[0025] In some embodiments of the application, the molar ratio of the divalent iron salt to the trivalent iron salt is 1:1.5-1:2, and the concentration of total iron ions in the mixed iron salt solution is 0.1-0.5 mol / L.

[0026] In some embodiments of the application, the concentration of the sodium citrate aqueous solution is 0.5-1.0 M, and the molar ratio of sodium citrate to total iron ions is (0.1-0.3):1.

[0027] In some embodiments of the application, in the step of coating the silica layer, the mass ratio of tetraethyl orthosilicate to magnetic powder is (0.5-1.5):1.

[0028] In some embodiments of the application, in the step of constructing the mesoporous structure, the molar ratio of tetraethyl orthosilicate to cetyltrimethylammonium bromide is (3-6):1, and the mass ratio of cetyltrimethylammonium bromide to magnetic particles is (0.2-0.5):1.

[0029] In some embodiments of the application, in the functionalization step, the concentration of the magnetic mesoporous particles in the dispersion is 10-20 mg / mL, and the mass ratio of the aminopropyltriethoxysilane to the magnetic mesoporous particles is (0.5-1.5):1. Under this ratio, the chemical grafting coverage can be ensured, while the waste of expensive reagents and the generation of excessive by-products can be avoided.

[0030] Compared with the prior art, the application has the following beneficial effects:

[0031] S1 of the application uses microwave-assisted alkaline pretreatment. The alkaline condition (pH 7-8) can neutralize the acidity of the mother liquor, and make part of the colloids, proteins and other impurities lose stability and precipitate. Microwave heating (500-800 W) has the characteristics of instant, endogenous and uniform, and can accelerate the reaction at the molecular level, so that the precipitation is more complete and the particles are more uniform, which is convenient for subsequent filtration.

[0032] S2 uses biodegradable green chelating agent tetrasodium glutamate diacetate (GLDA), which can efficiently and selectively complex metal ions such as Fe 3+ , Cu 2+ , which catalyze the color development reaction, and destroy the existing metal-pigment complex. Then, the magnetic porous adsorbent is used to adsorb the acid pigment molecules, and the external magnetic field is used to separate instead of traditional filtration, so that the solid-liquid separation can be quickly and completely realized, the problem of filtration difficulty of nano adsorbent is solved, and the recovery efficiency of the adsorbent is improved. Moreover, the magnetic porous adsorbent can be regenerated by washing after adsorption saturation, and can be recycled, which greatly reduces the operation cost and the generation of solid waste, and forms a closed loop process.

[0033] S3 is heated (88-92℃) under weak alkaline condition (pH 8.2-8.5), which promotes the Cannizzaro reaction of residual small molecule aldehydes (such as furfural) that are difficult to be adsorbed, so that the small molecule aldehydes are disulfided and converted into harmless carboxylate and alcohol, thereby completely eliminating the color development groups; after heat preservation, the liquid can be filtered again to remove a small amount of insoluble substances or flocculation that may be generated in the process, so as to ensure the extreme clarity of the liquid.

[0034] In S4, a small amount of decolorizing agent is added for further adsorption and decolorization, and the concentration and crystallization are further removed to remove volatile substances.

[0035] The application combines microwave, filtration, magnetic field separation, chelation, molecular restructuring and functional adsorbent, and the steps are logically rigorous and echo each other, so that the complex carbonizable substances in the sodium citrate mother liquor can be deeply, greenly and efficiently removed. DETAILED DESCRIPTION

[0036] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. If the specific conditions are not indicated in the embodiments, the conventional conditions or the conditions suggested by the manufacturers are adopted. If the manufacturers of the reagents or instruments are not indicated, the conventional products that can be purchased in the market are adopted.

[0037] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to specific embodiments.

[0038] Embodiment one

[0039] The magnetic porous adsorbent is prepared by the following method:

[0040] The magnetic powder is prepared as follows: divalent iron salt and trivalent iron salt are dissolved in deoxygenated deionized water in a molar ratio of 1:1.5 to obtain a mixed iron salt solution, and the concentration of total iron ions is 0.5 mol / L; under nitrogen protection and mechanical stirring, heating is performed to 60°C; then concentrated ammonia water is added dropwise until the pH of the solution is 10-11; then 0.5M sodium citrate aqueous solution is added in a molar ratio of 0.3:1 of sodium citrate to total iron ions, and the reaction is performed for 60 min; heating is stopped, and aging is performed for 2 hours under stirring; an external magnetic field is applied, and the supernatant is discarded; washing, drying and grinding are performed to obtain the magnetic powder;

[0041] The silica layer is coated as follows: the magnetic powder is dispersed in an ethanol-water mixed solution (the volume ratio of ethanol to water is 3:1), and ultrasonic treatment is performed, and the concentration of the magnetic powder is 15 mg / mL; tetraethyl orthosilicate is added dropwise under stirring in a mass ratio of 1:1 of tetraethyl orthosilicate to the magnetic powder, and then ammonia water (25% by mass fraction) is added, and the reaction is performed at 50°C for 12 h, and then filtering and drying are performed to obtain the magnetic particles;

[0042] The mesoporous structure is constructed as follows: the magnetic particles are dispersed in water, and hexadecyl trimethyl ammonium bromide is added in a mass ratio of 0.5:1 of hexadecyl trimethyl ammonium bromide to the magnetic particles, and then tetraethyl orthosilicate and ammonia water are added again in a molar ratio of 3:1 of tetraethyl orthosilicate to hexadecyl trimethyl ammonium bromide after uniform stirring, and the reaction is performed at 80°C for 24 h; magnetic field separation is performed, and the obtained product is calcined at 500-550°C for 4 h to obtain the magnetic mesoporous particles;

[0043] Functionalization is performed as follows: the magnetic mesoporous particles are dispersed in toluene in a concentration of 10 mg / mL of the magnetic mesoporous particles and a mass ratio of 0.5:1 of aminopropyl triethoxysilane to the magnetic mesoporous particles, and then aminopropyl triethoxysilane is added; the reaction is performed under reflux at 80°C in a nitrogen atmosphere for 12 h; cooling is performed to room temperature, and magnetic field separation and drying are performed to obtain the magnetic porous adsorbent.

[0044] Embodiment two

[0045] A magnetic porous adsorbent was prepared by the following method:

[0046] Preparation of magnetic powder: divalent iron salt and trivalent iron salt were dissolved in deoxygenated deionized water at a molar ratio of 1:2 to obtain a mixed iron salt solution, with a total iron ion concentration of 0.5 mol / L; heated to 60°C under nitrogen protection and mechanical stirring; then add concentrated ammonia water dropwise until the solution pH = 10-11; then add 0.5M sodium citrate aqueous solution at a molar ratio of sodium citrate to total iron ions of 0.2:1, and react for 60 min; after stopping heating, stir for 2 hours; apply an external magnetic field, discard the supernatant; wash, dry, and grind to obtain magnetic powder;

[0047] Silica coating: disperse the magnetic powder in an ethanol-water mixed solution (volume ratio of ethanol to water 3:1), ultrasonic treatment, concentration of magnetic powder 15 mg / mL; add tetraethyl orthosilicate dropwise under stirring at a mass ratio of tetraethyl orthosilicate to magnetic powder of 1:1, then add ammonia water (mass fraction 25%), react at 50°C for 12h, filter, dry to obtain magnetic particles;

[0048] Construction of mesoporous structure: disperse the magnetic particles in water, add cetyltrimethylammonium bromide at a mass ratio of cetyltrimethylammonium bromide to magnetic particles of 0.2:1, then add tetraethyl orthosilicate and ammonia water again at a molar ratio of tetraethyl orthosilicate to cetyltrimethylammonium bromide of 5:1, stir uniformly, then react at 80°C for 24h; magnetic field separation, the obtained product is calcined at 500-550°C for 3-4h to obtain magnetic mesoporous particles;

[0049] Functionalization: disperse the magnetic mesoporous particles in toluene at a concentration of 15 mg / mL of magnetic mesoporous particles and a mass ratio of aminopropyltriethoxysilane to magnetic mesoporous particles of 1:1, add aminopropyltriethoxysilane; reflux at 80°C under nitrogen atmosphere for 20h; cool to room temperature, magnetic field separation, dry to obtain the magnetic porous adsorbent.

[0050] Example Three

[0051] A magnetic porous adsorbent was prepared by the following method:

[0052] Preparation of magnetic powder: divalent iron salt and trivalent iron salt were dissolved in deoxygenated deionized water at a molar ratio of 1:1.5 to obtain a mixed iron salt solution, with a total iron ion concentration of 0.3 mol / L; heated to 70°C under nitrogen protection and mechanical stirring; then add concentrated ammonia water dropwise until the solution pH = 10-11; then add 0.5M sodium citrate aqueous solution at a molar ratio of sodium citrate to total iron ions of 0.2:1, and react for 60 min; after stopping heating, stir for 2 hours; apply an external magnetic field, discard the supernatant; wash, dry, and grind to obtain magnetic powder;

[0053] Coating silica layer: the magnetic powder was dispersed in an ethanol-water mixed solution (volume ratio of ethanol to water 3:1) and ultrasonically treated, the concentration of the magnetic powder being 10 mg / mL; tetraethyl orthosilicate was added dropwise under stirring at a mass ratio of tetraethyl orthosilicate to magnetic powder 1.5:1, and then ammonia water (25% by mass) was added, and the reaction was carried out at 50°C for 6 h, followed by filtration and drying to obtain the magnetic particles;

[0054] Constructing mesoporous structure: the magnetic particles were dispersed in water, and cetyltrimethylammonium bromide was added at a mass ratio of cetyltrimethylammonium bromide to magnetic particles 0.2:1, and then tetraethyl orthosilicate and ammonia water were added dropwise again at a molar ratio of tetraethyl orthosilicate to cetyltrimethylammonium bromide 6:1, and the reaction was carried out at 70°C for 48 h; the product was separated by a magnetic field and calcined at 500-550°C for 3-4 h to obtain the magnetic mesoporous particles;

[0055] Functionalization: the magnetic mesoporous particles were dispersed in toluene at a concentration of 20 mg / mL and at a mass ratio of aminopropyltriethoxysilane to magnetic mesoporous particles 1.5:1, and aminopropyltriethoxysilane was added; the reaction was carried out under reflux at 80°C for 24 h under a nitrogen atmosphere; the reaction system was cooled to room temperature, and the product was separated by a magnetic field and dried to obtain the magnetic porous adsorbent.

[0056] Example Four

[0057] The magnetic porous adsorbent was prepared as follows:

[0058] Preparation of magnetic powder: divalent iron salt and trivalent iron salt were dissolved in deoxygenated deionized water at a molar ratio of 1:1.5 to obtain a mixed iron salt solution, the concentration of total iron ions being 0.1 mol / L; the solution was heated to 60°C under nitrogen protection and mechanical stirring; concentrated ammonia water was then added dropwise until the pH of the solution was 10-11; 0.1 M sodium citrate aqueous solution was added at a molar ratio of sodium citrate to total iron ions 0.1:1, and the reaction was carried out for 60 min; after the heating was stopped, the solution was aged for 2 hours under stirring; an external magnetic field was applied, and the supernatant was discarded; the product was washed, dried, and ground to obtain the magnetic powder;

[0059] Coating silica layer: the magnetic powder was dispersed in an ethanol-water mixed solution (volume ratio of ethanol to water 4:1) and ultrasonically treated, the concentration of the magnetic powder being 15 mg / mL; tetraethyl orthosilicate was added dropwise under stirring at a mass ratio of tetraethyl orthosilicate to magnetic powder 0.5:1, and then ammonia water (25% by mass) was added, and the reaction was carried out at 40°C for 12 h, followed by filtration and drying to obtain the magnetic particles;

[0060] Constructing mesoporous structure: disperse the magnetic particles in water, add cetyltrimethylammonium bromide at a mass ratio of cetyltrimethylammonium bromide to magnetic particles of 0.2:1, stir uniformly, then add tetraethyl orthosilicate and ammonia water at a molar ratio of tetraethyl orthosilicate to cetyltrimethylammonium bromide of 5:1, react at 70°C for 24h; separate by magnetic field, calcine the obtained product at 500-550°C for 3-4h to obtain magnetic mesoporous particles;

[0061] Functionalization: disperse the magnetic mesoporous particles in toluene at a concentration of 20mg / mL, add aminopropyltriethoxysilane at a mass ratio of aminopropyltriethoxysilane to magnetic mesoporous particles of 1:1, reflux at 80°C under nitrogen atmosphere for 24h; cool to room temperature, separate by magnetic field, and dry to obtain the magnetic porous adsorbent.

[0062] Example Five

[0063] Prepare the magnetic porous adsorbent as follows:

[0064] Prepare the magnetic powder: dissolve divalent iron salt and trivalent iron salt in deoxygenated deionized water at a molar ratio of 1:1.5 to obtain a mixed iron salt solution, the concentration of total iron ions is 0.5mol / L; heat to 60°C under nitrogen protection and mechanical stirring; then add concentrated ammonia water to the solution until the pH is 10-11; then add 0.5M sodium citrate aqueous solution at a molar ratio of sodium citrate to total iron ions of 0.5:1, react for 60min; stop heating, mature for 2 hours under stirring; apply an external magnetic field, discard the supernatant; wash, dry, and grind to obtain the magnetic powder;

[0065] Coat a silica layer: disperse the magnetic powder in an ethanol-water mixed solution (volume ratio of ethanol to water is 3:1) at a concentration of 10mg / mL, ultrasonic treatment; add tetraethyl orthosilicate under stirring at a mass ratio of tetraethyl orthosilicate to magnetic powder of 1:1, then add ammonia water (mass fraction 25%), react at 50°C for 12h, filter, and dry to obtain the magnetic particles;

[0066] Constructing mesoporous structure: disperse the magnetic particles in water, add cetyltrimethylammonium bromide at a mass ratio of cetyltrimethylammonium bromide to magnetic particles of 0.2:1, stir uniformly, then add tetraethyl orthosilicate and ammonia water at a molar ratio of tetraethyl orthosilicate to cetyltrimethylammonium bromide of 5:1, react at 70°C for 24h; separate by magnetic field, calcine the obtained product at 500-550°C for 3-4h to obtain magnetic mesoporous particles;

[0067] Functionalization: dispersing the magnetic mesoporous particles in toluene at a concentration of 20 mg / mL, adding a mass ratio of 1.5:1 of aminopropyltriethoxysilane to the magnetic mesoporous particles, and refluxing at 80°C under a nitrogen atmosphere for 12 hours; cooling to room temperature, separating under a magnetic field, and drying to obtain the magnetic porous adsorbent.

[0068] Example Six

[0069] A sodium citrate mother liquor prepared by a corn fermentation method in a certain factory was taken as a treatment object and treated according to the following method:

[0070] S1, adding a sodium carbonate solution to the sodium citrate mother liquor (diluted 10 times) to adjust the pH value to 7.5, heating to 85°C under microwave (800W), maintaining for 10 minutes, cooling to room temperature, coarse filtering, and fine filtering to obtain a first treatment liquid;

[0071] S2, adding tetrasodium glutamate diacetate (0.15%) to the first treatment liquid, stirring for 30 minutes, standing for 5 hours, filtering, adding the magnetic porous adsorbent prepared in Example One (1.5%) to the filtrate, stirring for 30 minutes, standing for 10 hours, and performing magnetic separation under an external magnetic field to obtain a second treatment liquid;

[0072] S3, adding a sodium carbonate solution to the second treatment liquid, stirring to uniform, adjusting the pH value to 8.5, then heating and maintaining for 30 minutes, cooling, filtering, and obtaining a third treatment liquid;

[0073] S4, adding activated carbon to the third treatment liquid, filtering, and then performing concentration crystallization, centrifugation, and drying on the filtrate to obtain sodium citrate.

[0074] Before the treatment, it was measured that the sodium citrate in the sodium citrate mother liquor was 20-25%, polysaccharides and oligosaccharides were 2-3%, proteins, polypeptides, and amino acids were 1-1.5%, and metal ions (Fe 3+ , Cu 2+ , Mn 2+ , Ca 2+ , Mg 2+ ) were 100-200 ppm.

[0075] Example Seven

[0076] Based on the sodium citrate mother liquor in Example Six, the following method was used for treatment:

[0077] S1, adding a sodium carbonate solution to the sodium citrate mother liquor (diluted 10 times) to adjust the pH value to 7.5, heating to 85°C under microwave (800W), maintaining for 10 minutes, cooling to room temperature, coarse filtering, and fine filtering to obtain a first treatment liquid;

[0078] S2, to the first treatment liquid, add tetrasodium glutamate diacetate (0.1%), stir for 30 min, stand for 5 h, filter, to the filtrate, add the magnetic porous adsorbent prepared in Example 2 (1%), stir for 30 min, stand for 10 h; magnetic separation under an external magnetic field, filter, to obtain a second treatment liquid;

[0079] S3, to the second treatment liquid, add sodium carbonate solution, stir uniformly, adjust the pH value to 8.5, then warm, and keep warm for 30 min, then cool, filter, to obtain a third treatment liquid;

[0080] S4, to the third treatment liquid, add activated carbon, filter, then concentrate and crystallize the filtrate, centrifuge, and dry, to obtain sodium citrate.

[0081] Example Eight

[0082] Based on the citric acid mother liquor of Example Six, the following method is used for treatment:

[0083] S1, to the citric acid mother liquor (diluted 10 times), add sodium carbonate solution, adjust the pH value to 7.5, microwave (800 W) heating to 85℃, keep warm for 10 min, then cool to room temperature, coarse filter, fine filter, to obtain a first treatment liquid;

[0084] S2, to the first treatment liquid, add tetrasodium glutamate diacetate (0.05%), stir for 30 min, stand for 5 h, filter, to the filtrate, add the magnetic porous adsorbent prepared in Example 1 (0.8%), stir for 30 min, stand for 10 h; magnetic separation under an external magnetic field, filter, to obtain a second treatment liquid;

[0085] S3, to the second treatment liquid, add sodium carbonate solution, stir uniformly, adjust the pH value to 8.5, then warm, and keep warm for 30 min, then cool, filter, to obtain a third treatment liquid;

[0086] S4, to the third treatment liquid, add activated carbon, filter, then concentrate and crystallize the filtrate, centrifuge, and dry, to obtain sodium citrate.

[0087] Example Nine

[0088] Based on the citric acid mother liquor of Example Six, the following method is used for treatment:

[0089] S1, to the citric acid mother liquor (diluted 10 times), add sodium carbonate solution, adjust the pH value to 7.5, microwave (800 W) heating to 85℃, keep warm for 10 min, then cool to room temperature, coarse filter, fine filter, to obtain a first treatment liquid;

[0090] S2, to the first treatment liquid, add tetrasodium glutamate diacetate (0.15%), stir for 30 min, stand for 5 h, filter, to the filtrate, add the magnetic porous adsorbent prepared in Example 1 (0.8%), stir for 30 min, stand for 10 h; magnetic separation under an external magnetic field, filter, to obtain a second treatment liquid;

[0091] S3, to the second treatment liquid, add sodium carbonate solution, stir until uniform, adjust the pH value to 8.5, then heat, and keep warm for 30 min, then cool, filter, to obtain a third treatment liquid;

[0092] S4, to the third treatment liquid, add activated carbon, filter, then concentrate and crystallize the filtrate, centrifuge, dry, to obtain sodium citrate.

[0093] Example Ten

[0094] Based on the citric acid mother liquor of Example Six, the following method is used for treatment:

[0095] S1, to the citric acid mother liquor (diluted 10 times), add sodium carbonate solution, adjust the pH value to 7.5, heat to 85℃ under microwave (800 W), keep warm for 10 min, then cool to room temperature, coarse filter, fine filter, to obtain a first treatment liquid;

[0096] S2, to the first treatment liquid, add tetrasodium glutamate diacetate (0.05%), stir for 30 min, stand for 5 h, filter, to the filtrate, add the magnetic porous adsorbent prepared in Example 1 (1.5%), stir for 30 min, stand for 10 h; magnetic separation under an external magnetic field, filter, to obtain a second treatment liquid;

[0097] S3, to the second treatment liquid, add sodium carbonate solution, stir until uniform, adjust the pH value to 8.5, then heat, and keep warm for 30 min, then cool, filter, to obtain a third treatment liquid;

[0098] S4, to the third treatment liquid, add activated carbon, filter, then concentrate and crystallize the filtrate, centrifuge, dry, to obtain sodium citrate.

[0099] Comparative Example One

[0100] The difference from Example Six is that, in step S2, mesoporous silica is used instead of the magnetic porous adsorbent in Example Six, and the remaining steps and reagents are the same as in Example Six.

[0101] Comparative Example Two

[0102] The difference from Example Six is that, in step S2, functionalized mesoporous silica is used instead of the magnetic porous adsorbent in Example Six; wherein the functionalization step is the same as in Example Six, and the remaining steps and reagents are also the same as in Example Six.

[0103] Based on the sodium citrate obtained from examples six to ten and comparative examples one to two, the crystallinity of the sodium citrate was determined according to the standard of GB 1886.25-2016; the metal ion content in the sodium citrate was determined according to the standard of GB 1886.25-2016; the content of the carbonizable substance in the sodium citrate was determined according to the standard of GB 1886.25-2016, and the results are shown in Table 1.

[0104] The solid separated by magnetic separation in step S2 was subjected to desorption treatment and drying to obtain a magnetic porous adsorbent. The recovery rate of the magnetic porous adsorbent was calculated according to [(mass before adsorption-mass after desorption) / mass before adsorption]*100%, and the results are shown in Table 1.

[0105] Table 1

[0106]

[0107] As can be seen from the data in Table 1, the crystallinity of the sodium citrate after the treatment of the citric acid mother liquor according to the processing methods of examples six to nine is high, indicating that the purity of the sodium citrate is high, and the content of metal ions and carbonizable compounds is low, and is significantly lower than the content in the original mother liquor, indicating that the removal effect is good. The porous adsorbent in comparative example one is not functionalized and modified, and the surface does not contain amino groups, resulting in a decrease in adsorption effect.

[0108] As can be seen from the data in Table 1, the recovery efficiency of the magnetic porous adsorbent in examples six to nine is more than 90%, which can effectively recover the adsorbent.

[0109] The above-described embodiments are part of the embodiments of the present application, but not all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the claimed application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

Claims

1. A green chemistry-based method for removing sodium citrate charformers, characterized by, The method comprises the following steps: S1, adding a basic solution to the citric acid mother liquor, adjusting the pH value to 7-8, microwave heating, cooling, coarse filtering, fine filtering, and obtaining a first treatment liquid; S2, adding tetrasodium glutamate diacetate to the first treatment liquid, stirring for 20-30 min, standing for 3-5 h, filtering, adding a magnetic porous adsorbent to the filtrate, stirring for 20-30 min, standing for 5-10 h, magnetic separation, filtering, and obtaining a second treatment liquid; S3, adding a sodium-containing basic solution to the second treatment liquid, stirring uniformly, adjusting the pH value to 7.5-8.5, then heating, keeping warm for 20-30 min, cooling, filtering, and obtaining a third treatment liquid; S4, adding a decolorizing agent to the third treatment liquid, filtering, concentrating and crystallizing the filtrate, centrifuging, drying, and obtaining sodium citrate; The magnetic porous adsorbent is prepared by the following method: Preparation of magnetic powder: dissolving divalent iron salt and trivalent iron salt in deionized water to obtain a mixed iron salt solution; heating to 60-70 DEG C under nitrogen protection and mechanical stirring; then adding concentrated ammonia water dropwise until the solution pH = 10-11; then adding sodium citrate aqueous solution and reacting for 30-60 min; after stopping heating, stirring for 1-2 hours; applying an external magnetic field, and discarding the supernatant; washing, drying, and grinding to obtain magnetic powder; Coating a silica layer: dispersing the magnetic powder in an ethanol-water mixed solution and performing ultrasonic treatment; Under stirring, dropwise adding tetraethyl orthosilicate, then adding ammonia water, reacting at 40-50 DEG C for 6-12 h, filtering, and drying to obtain magnetic particles; Constructing a mesoporous structure: dispersing the magnetic particles in water, adding cetyltrimethylammonium bromide, stirring uniformly, then dropwise adding tetraethyl orthosilicate and ammonia water, reacting at 70-80 DEG C for 24-48 h; magnetic field separation, calcining the obtained product at 500-550 DEG C for 3-4 h to obtain magnetic mesoporous particles; Functionalization: dispersing the magnetic mesoporous particles in toluene, adding aminopropyltriethoxysilane, refluxing at 80-85 DEG C under a nitrogen atmosphere for 12-24 h; cooling to room temperature, magnetic field separation, and drying to obtain the magnetic porous adsorbent.

2. The green chemistry based sodium citrate easy char removal process according to claim 1, characterized in that, In step S1, the temperature of microwave heating is 75-85 DEG C, the holding time is 5-10 min, and the microwave power is 500-800 W.

3. The green chemistry based sodium citrate easy char removal process according to claim 1, wherein, In step S1, the basic solution is a sodium carbonate solution or a sodium bicarbonate solution.

4. The green chemistry based sodium citrate easy char removal process according to claim 1, wherein, In step S2, the mass of tetrasodium glutamate diacetate is 0.05-0.15% of the mass of the first treatment liquid. In step S2, the mass of the magnetic porous adsorbent is 0.8-1.5% of the mass of the first treatment liquid.

5. The green chemistry based sodium citrate easy char removal process according to claim 1, wherein, The molar ratio of the divalent iron salt to the trivalent iron salt is 1:1.5-1:2, and the concentration of total iron ions in the mixed iron salt solution is 0.1-0.5 mol / L.

6. The green chemistry based sodium citrate easy char removal process according to claim 1, wherein, The concentration of the sodium citrate aqueous solution is 0.5-1.0 M, and the molar ratio of sodium citrate to total iron ions is (0.1-0.3):

1.

7. The green chemistry based sodium citrate easy char removal process according to claim 1, wherein, In the step of coating a silica layer, the mass ratio of tetraethyl orthosilicate to magnetic powder is (0.5-1.5):

1.

8. The green chemistry based sodium citrate easy char removal process according to claim 1, wherein, In the step of building mesoporous structure, the molar ratio of tetraethyl orthosilicate to cetyltrimethylammonium bromide is (3-6):1, and the mass ratio of cetyltrimethylammonium bromide to magnetic particles is (0.2-0.5):

1.

9. The green chemistry based sodium citrate easy char removal process according to claim 1, wherein, In the step of functionalization, the concentration of the magnetic mesoporous particles in the dispersion is 10-20 mg / mL, and the mass ratio of the aminopropyltriethoxysilane to the magnetic mesoporous particles is (0.5-1.5):1.

Images