CN111304373A - Method for decoloring sugar juice by using spherical porous magnesium silicate - Google Patents
Method for decoloring sugar juice by using spherical porous magnesium silicate Download PDFInfo
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Abstract
The invention relates to a method for decoloring sugar juice by using spherical porous magnesium silicate, which comprises the steps of firstly preparing the spherical porous magnesium silicate by using magnesium chloride and silica gel balls as precursors by combining a hydrothermal synthesis method and a template method, and then adding the spherical porous magnesium silicate into the sugar juice for adsorption decoloring. The results of sugar juice decolorization experiments show that the decolorization rate of spherical porous magnesium silicate on sugar juice is 69.8% when the dosage is 0.10g, the adsorption temperature is 30 ℃, the adsorption time is 40min, and the pH value is 6.0. The spherical porous magnesium silicate prepared by the invention has good adsorption performance on gallic acid in sugar juice, good decoloring performance on the sugar juice, good reproducibility, environmental protection and certain application prospect in the low-sulfur and sulfur-free sugar industry.
Description
Technical Field
The invention relates to a method for decoloring sugar juice, in particular to a method for decoloring sugar juice by using spherical porous magnesium silicate.
Background
The clarification of the sugar juice is a key process influencing the sugar quality, and the task is to treat the sugar juice from a pressing process, remove non-sugar components in the sugar juice, reduce the viscosity and color value of the sugar juice, improve the pH value of the sugar juice and reduce the conversion of cane sugar so as to provide high-quality raw material syrup for a sugar boiling process. At present, sugar factories in China mainly adopt a sulfurous acid method and a carbonic acid method, and develop improvement methods related to cleaning processes and equipment aiming at the defects of the sulfurous acid method, but the improvement methods solve a plurality of defects of a sulfur-containing process to a certain extent, but have low utilization rate and cause pollution to the environment, so that the long-term development of the improvement methods is limited. In order to overcome the defects of various cleaning processes, researchers are also seeking new sugar-making detergents and auxiliary agents to assist the traditional processes so as to improve the quality and the production efficiency of sugar products; the research on the detergent and the detergent additive is the most extensive, and according to the statistics of Lippmann et al, more than 700 kinds of the detergent, the decoloration and the purification additives are applied to sugar juice. The detergent is one of the essential chemical assistants in the sugar juice cleaning process, and the use of the detergent directly influences the cleaning effect. The sugar manufacturing process is continuously perfected, but the essence of the sugar manufacturing process is to achieve the purpose of clarifying the sugar juice by generating inorganic salt materials, such as calcium sulfite in a sulfurous acid method, calcium carbonate in a carbonic acid method and the like. The influence on the sugar juice cleaning process is researched by synthesizing calcium sulfites with different shapes by Fuyou and the like, and the research shows that the maximum decolorization rate of the new calcium sulfites on the sugar juice is 20.5%.
Inorganic porous materials have attracted much attention and research because of their advantages such as low relative density, large specific surface area, strong adsorptivity, large porosity, etc. Xiamebo et al use the filter residue after flocculation and clarification by a phosphoric acid-lime method as a research object, remove impurities on the surface of calcium phosphate by high-temperature calcination, use the obtained porous calcium phosphate for sugar juice decolorization research, and determine that the maximum decolorization rate of the porous calcium phosphate to sugar juice is 38.15% by a single-factor experiment and an optimal response surface analysis method. Other inorganic porous materials have also been developed for research and use in sugar juice purification, such as: activated carbon, modified bentonite, bone charcoal (the main components are 85% of calcium phosphate and 10% of carbon), zeolite, diatomite, porous magnesium oxide, porous inorganic/polymer composite materials and the like. Although the research on the inorganic porous material effectively solves the problems of environmental pollution, resource waste and the like caused by the traditional sugar juice decoloring process, the decoloring rate is too low, and the industrial production cannot be realized.
In recent years, silicate series materials have been widely researched and paid attention to due to their rich pore channel structures and large specific surface areas, and have become one of the leading fields of material science research. The porous magnesium silicate has a crystal structure which is open, has a large number of holes and pore channels, has good adsorption performance, strong chemical stability, low preparation investment cost, environmental friendliness and the like, and is widely applied. However, no report has been found on the application of porous magnesium silicate to decolouring of sugar juice.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the method for decoloring sugar juice by using spherical porous magnesium silicate is characterized by firstly preparing the spherical porous magnesium silicate and applying the spherical porous magnesium silicate to decoloring the sugar juice to obtain a good decoloring effect.
The technical scheme for solving the technical problems is as follows: a method for decolorizing sugar juice with spherical porous magnesium silicate comprises the following steps:
(1) SiO with a mass of 4.7-4.9g is first weighed2Placing the mixture into a beaker, adding 58-62mL of deionized water into the beaker, carrying out constant temperature ultrasonic treatment to uniformly mix the mixture for later use, and weighing 12.1-12.3g of MgCI2·6H2Pouring O into a beaker, and adding 4.9-5.1g of NH460.0mL of deionized water of Cl, rapidly stirring to completely dissolve the Cl, then adding 2.9-3.1mL of ammonia water under the stirring condition, rapidly and uniformly mixing the two solutions under the stirring condition, stirring for 3-8min at normal temperature, then pouring the mixture into a digestion tank cup, assembling the digestion tank, placing the digestion tank filled with the mixed solution in a 185-plus 195 ℃ oven for hydrothermal reaction for 700-plus 750min, filtering by a Buchner funnel after the reaction is finished, washing the product with deionized water for multiple times, and checking by using silver nitrateFiltering until no white precipitate is generated, centrifuging, and oven drying the product in oven at 78-83 deg.C to obtain spherical porous magnesium silicate;
(2) heating sugar juice 100mL to 28-32 deg.C, adjusting pH to 5.9-6.1, adding spherical porous magnesium silicate 0.08-0.12g into sugar juice, adsorbing for 35-45min to obtain clarified liquid.
The sugar juice is sugarcane mixed juice, brown granulated sugar redissolving syrup or raw sugar redissolving syrup.
Further, the substance for adjusting the pH value of the sugar juice is NaOH or HCI of 0.5 mol/L.
The invention aims at the key problems of preparation and appearance of porous magnesium silicate for sugar juice purification, and controllably prepares porous magnesium silicate and applies the porous magnesium silicate to sugar juice decolorization so as to solve the problem of pollution in the sugar juice decolorization process by a sulfurous acid method and a carbonic acid method at present; provides a new method and basis for the preparation of the porous magnesium silicate and the application of the porous magnesium silicate in the decolorization of sugar juice.
Research and development of a novel sulfur-free sugar preparation process are problems to be solved urgently in the field of sugar preparation engineering at present. The adsorption and flocculation sedimentation of non-sugar components are the key and the foundation of cane sugar juice cleaning technology. Aiming at sugar manufacturing process and the current research situation of inorganic porous materials at home and abroad, the invention takes the porous magnesium silicate detergent as a research object and carries out systematic research on the controllable preparation and the sugar juice decoloring application of the porous magnesium silicate detergent. Firstly, combining a hydrothermal synthesis method and a template method, and preparing porous magnesium silicate by using magnesium chloride and silica gel balls as precursors. Various characterization means prove that the prepared porous material is micron-sized porous magnesium silicate, and the structure is produced because hydroxide ions can break silicon dioxide chains to generate silicate ion groups in high-temperature alkaline solution. In the reaction system, the free magnesium ions react with silicate ions released from the silicon dioxide silicon template to form magnesium silicate attached to the template in situ. Along with the reaction, silicon in the template is gradually released from the silica gel ball in the form of silicate ions, and generates magnesium silicate with magnesium ions to be accumulated on the template, and finally the magnesium silicate ball with a good pore structure is formed. XRD detected samples showed typical magnesium silicate diffraction peaks at 20 °, 34 °, 60 ° 2 θ. The detection results of the samples are matched, the chemical phase is magnesium silicate crystal (JCPDSno.03-0174), and the structure is consistent with that of talc. The method takes the porous magnesium silicate as an adsorbent, takes the decolorization rate as an index, and examines the influence of the dosage, adsorption temperature, adsorption time and pH value of the porous magnesium silicate on the decolorization performance of the sugarcane raw sugar solution. The results show that the decolorization rate of the porous magnesium silicate on the sugar juice is 69.8 percent when the dosage is 0.1g, the adsorption temperature is 30 ℃, the adsorption time is 40min and the pH value is 6.0. Fitting shows that the adsorption process of the porous magnesium silicate on the sugar juice pigment accords with a quasi-second-order kinetic adsorption equation and a Langmuir isothermal adsorption equation. After the spherical porous magnesium silicate is used for many times, the decolorization rate of the sugar juice can still reach 58.6 percent.
In addition, the invention also inspects the adsorption performance of the porous magnesium silicate on the gallic acid, and discovers that the initial concentration of the gallic acid is 25 mg.L through the research of adsorption kinetics-1、50mg·L-1、75mg·L-1Correlation coefficient R of time, quasi-second order dynamics20.9965, 0.9941 and 0.9941 respectively, and the dynamic adsorption process conforms to a quasi-second-order dynamic model. Fitting the adsorption process of the porous magnesium silicate to the gallic acid through isothermal adsorption fitting research, wherein the adsorption process of the porous magnesium silicate to the gallic acid conforms to Freundlich isothermal adsorption equation, and obtaining a correlation coefficient R through linear fitting of an adsorption model2Is 0.9926.
The results show that the spherical porous magnesium silicate has good adsorption performance on gallic acid in sugar juice, good decoloring performance on the sugar juice, good reproducibility, environmental protection and certain application prospect in the low-sulfur and sulfur-free sugar industry.
The method uses green and easily-obtained silicate as a decoloring agent, belongs to a sulfur-free sugar preparation process, can realize high-efficiency clarification and decoloring of sugar juice without using toxic sulfur dioxide gas, and has no problems of environmental pollution, sulfite residue and the like.
Drawings
FIG. 1 is an SEM image of spherical porous magnesium silicate.
FIG. 2 is an X-ray diffraction pattern of the porous magnesium silicate.
FIG. 3 is an infrared spectrum of spherical porous magnesium silicate.
FIG. 4 is a nitrogen adsorption desorption isotherm diagram of a spherical porous magnesium silicate sample.
FIG. 5 is a graph showing a pore size distribution of a sample of spherical porous magnesium silicate.
FIG. 6 is a SEM comparison of spherical porous magnesium silicate before and after adsorption on sugar juice, wherein a is before adsorption; b is after adsorption.
FIG. 7 is an XRD pattern of spherical porous magnesium silicate before and after adsorption of sugar juice, wherein a is after adsorption and b is before adsorption.
FIG. 8 is a graph showing the effect of the amount of spherical porous magnesium silicate on the decolorization of sugar juice.
FIG. 9 is a graph showing the effect of adsorption temperature of spherical porous magnesium silicate on the decolorization of sugar juice.
FIG. 10 is a graph showing the effect of adsorption time of spherical porous magnesium silicate on sugar juice decolorization.
FIG. 11 is a graph of the effect of pH of sugar juice on the decolorization of sugar juice by spherical porous magnesium silicate.
FIG. 12 is a graph of the results of the spherical porous magnesium silicate fitting an in-particle diffusion model and a quasi-second order kinetic adsorption equation for the sugar juice decolorization process, wherein: a, an intra-granular diffusion model; b, a quasi-first-order kinetic adsorption equation; and c, a quasi-second-order kinetic adsorption equation.
FIG. 13 is a graph of the results of an isothermal line fit of spherical porous magnesium silicate to sugar juice decolorization process, wherein, a, Langmuir's isothermal adsorption equation; b, Freundlich isothermal adsorption equation.
FIG. 14 is a graph showing the results of the decolorization rate of sugar juice when the adsorbent spherical porous magnesium silicate is reused 3 times.
FIG. 15 is a graph showing the effect of spherical porous magnesium silicate on the first decolorization of sugar juice, wherein the original sugar solution is shown on the left and the decolorized sugar solution is shown on the right.
Detailed Description
Example 1: a method for decolorizing sugar juice with spherical porous magnesium silicate comprises the following steps:
(1) SiO was first weighed to a mass of 4.80g2Placing the mixture into a 100mL beaker, adding 60.0mL deionized water into the beaker, and carrying out constant temperature ultrasonic treatmentIt is mixed well for subsequent use, 12.20g of MgCI are weighed2·6H2O is poured into a 200mL beaker and 5.00g NH dissolved therein is added460.0mL of deionized water of Cl, rapidly stirring to completely dissolve the Cl, then adding 3.0mL of ammonia water under the stirring condition, rapidly and uniformly mixing the two solutions in the two beakers under the stirring condition, stirring for 5min at normal temperature, then pouring the mixture into a digestion tank cup, assembling the digestion tank, placing the digestion tank filled with the mixed solution in a 190 ℃ oven to perform hydrothermal reaction for 720min, filtering the reaction product by a Buchner funnel after the reaction is finished, washing the product with deionized water for multiple times, checking the filtrate with silver nitrate until no white precipitate is generated, performing centrifugal separation, putting the product in the oven, and drying at 80 ℃ to obtain spherical porous magnesium silicate;
(2) heating sugar juice 100mL to 30 deg.C, adjusting pH to 6.0 with 0.5mol/L NaOH or HCI, adding spherical porous magnesium silicate 0.10g into sugar juice, adsorbing for 40min to obtain clarified liquid with sugar juice decolorization rate of 69.8%.
The preparation method of the invention comprises the following optimization experiments:
1. preparation of spherical porous magnesium silicate.
Spherical porous magnesium silicate prepared by the step (1) described in example 1 was used.
2. Characterization of spherical porous magnesium silicate.
(1) The morphology of magnesium silicate was analyzed by scanning electron microscope (Nano405, hitachi co., ltd., japan) (SEM): spreading the prepared magnesium silicate sample on double-sided adhesive on a sample table, and blowing by an ear washing ball to make the magnesium silicate uniformly adhere to the double-sided adhesive, wherein the test voltage is 5 kV.
(2) The crystal structure was analyzed by X-ray diffractometry (XRD, Bruker AXS, Inc., Germany): taking a proper amount of ground magnesium silicate powder, tabletting, and placing on a sample tray for detection; the range is 10-70 degrees, the speed is 0.1 degrees/s, the tube voltage is 40kV, and the current is 40 mA.
(3) The molecular composition of magnesium silicate was analyzed using a fourier transform infrared spectrometer (PerkinEler model, soviet mass inc): the test range is 450--1Resolution of 4cm-1The sample was mixed with the characterizing potassium bromide 1:100 and tableted.
(4) The specific surface area and pore structure of magnesium silicate were determined using a pore size and specific surface area analyzer (model ASAP2020, Micromeritics, Germany): with N2For adsorption media, at a temperature of 77K and a relative pressure (P/P0) of 10-6Range of-1 for N2And (4) adsorption measurement. Before the measurement, the sample was degassed at 90 ℃ for 6 hours. Specific surface area by B.E.T method based on N2And (4) calculating an adsorption isotherm, and calculating the pore size distribution according to BJH and HK methods.
3. And measuring color value and adsorption quantity.
Color value measurement was performed according to the regulations of the international committee for the unified methods of sugar analysis. After adjusting the pH of the sugar solution to 7.00, the solution was filtered, and the filtrate was collected and its absorbance at 560nm was measured using an ultraviolet spectrophotometer (UV-2000 model, Shanghai precision instruments, Ltd.), and the refractive index of the sugar juice and the solution temperature were measured using an Abbe refractometer (WAJ-2S model, Shanghai Pinxuan scientific instruments, Ltd.). And calculating the color value and the decolorization ratio of the sugar juice.
Calculating the formula:
decolorization ratio calculation formula:
wherein: IU (International Union of China)560A color value measured at a wavelength of 560 nm; a. the560Is the absorbance at a wavelength of 560nm as measured using an ultraviolet spectrophotometer; b represents the thickness (cm) of the cuvette; c represents the concentration of the solute in the sample solution (g/mL), and c is the refractive weight of the juice × the apparent density (20 ℃ C.)/100. D represents the percentage of decolorization (%); before IU and after IU represent the color values of the sugar solution before and after treatment.
The adsorption capacity is expressed by the following formula:
in the formula:q represents the adsorption quantity of the spherical porous magnesium silicate per unit mass to the pigment when the color value of the sugar juice is reduced from the original color value to the final color value; c is residual concentration of pigment in sugar juice, and S is used1/S0Denotes S0The color value, S, of the sugar juice before decolouration is shown1Representing the colour value of the decolourised sugar juice; m is the mass of the spherical porous magnesium silicate added during decolorization, g.
4. Preparing sugar juice and detecting the adsorbability of spherical porous magnesium silicate.
Weighing 75.00g of raw sugar in a beaker, adding a proper amount of ultrapure water, stirring until the raw sugar is completely dissolved, transferring the sugar solution into a volumetric flask with the specification of 500mL for constant volume, and obtaining the raw sugar solution with the concentration of 0.15 g/mL.
0.10g of the prepared spherical porous magnesium silicate was added to a 100mL beaker, 50.0mL of a 0.15g/mL raw sugar solution was added to the beaker, the mixture was mixed uniformly, the pH of the solution was adjusted to 5.20, and the mixture was magnetically stirred at room temperature for 1 hour. And (5) calculating the color value after decolorization. And collecting filter residues, and characterizing by XRD and SEM.
5. Static adsorption experiments.
Accurately transferring 50.0mL of the raw sugar solution with the concentration of 0.15g/mL into a beaker, accurately weighing 0.10g of spherical porous magnesium silicate in the beaker, magnetically stirring, adjusting the pH value of the solution to 5.00, and magnetically stirring at constant temperature. After the reaction, the reaction mixture was filtered, and the filtrate was collected and the color value of the sugar solution was measured by the 1.2.3 color value measuring method.
(1) Influence of dosage the influence of different dosages (0.05, 0.10, 0.20, 0.30, 0.40g) of the adsorbent on the decolorization rate of the sugar juice was examined at a pH of 5.00 and a temperature of 20 ℃ for a reaction time of 60 min.
(2) Temperature influence, namely the use amount of the spherical porous magnesium silicate is 0.10g, the pH value is 5.00, the reaction time is 60min, and the influence of different adsorption temperatures (20, 30, 40, 50 and 60 ℃) on the decolorization rate of the sugar juice is examined.
(3) Influence of time the influence of different reaction times (15, 30, 45, 60, 80, 100min) on the decolourisation rate of the sugar juice was examined, with a spherical porous magnesium silicate dosage of 0.10g, a pH of 5.00 and a temperature of 30 ℃.
(4) Influence of pH the influence of different pH values (5.00, 6.00, 6.50, 7.00, 8.00) on the decolorization rate of the sugar juice was examined, with a spherical porous magnesium silicate dosage of 0.10g, a temperature of 30 ℃ and a reaction time of 60 min.
6. Study of adsorption kinetics.
0.10g of spherical porous magnesium silicate was placed in a beaker containing 50.0mL of raw sugar solution and stirred magnetically until mixed well. Setting the water bath temperature at 30 deg.C, adjusting pH to 6.00, measuring the adsorption amount of spherical porous magnesium silicate to sugar juice under different adsorption time (5, 10, 15, 20, 30, 40, 60, 80min), and calculating formula (3).
And fitting the intra-particle diffusion model (formula 4) with the quasi-first-stage and quasi-second-stage dynamic adsorption model (formula 5).
qt＝kpt0.5(4)
In the formula (4), kpRepresents the intra-particle diffusion rate constant (mg/(g.min)0.5))，qtThe adsorption amount (g) of the spherical porous magnesium silicate at t-1) With qtFor t0.5Plotting the slope of the linear portion as the diffusion rate constant k in the particlep。
ln(qe-qt)＝lnqe-k1t (5)
In the formulae (5) and (6), qtThe adsorption amount (g) of the spherical porous magnesium silicate at t-1)；qeIs the equilibrium adsorption capacity (g) of spherical porous magnesium silicate-1)；k1Is the rate constant, k, of the quasi-first order kinetic model2Rate constants for the quasi-secondary kinetic model.
7. Study of adsorption isotherms.
Various amounts (0.05, 0.10, 0.20, 0.30, 0.40g) of spherical porous magnesium silicate were placed in a beaker containing 50.0mL of raw sugar solution and stirred magnetically until well mixed. Setting the water bath temperature at 30 ℃, adjusting the pH value of the reaction system to 6.00, reacting for 60min, and adopting a formula (3) as a calculation formula for measuring the adsorption quantity of the spherical porous magnesium silicate on the sugar juice.
The adsorption process was fitted using the Langmuir isothermal adsorption equation and the Freundlich isothermal adsorption equation.
The Langmuir isothermal adsorption equation is:
the Freundlich isothermal adsorption equation is: lnqe ═ lnk + nlnCe (8)
In the formulae (7) and (8), CeThe concentration of the pigment in the solution is the concentration of the pigment in the solution when the adsorption is balanced; q. q.seAll are equilibrium adsorption amounts (g) of the adsorbents-1) (ii) a b is the saturated adsorption capacity (g)-1) In (7), k is a constant; (8) where k and n are adsorption characteristic constants.
8. And (4) performing a regeneration experiment.
Accurately transferring 50mL of the raw sugar solution with the concentration of 0.15g/mL into a beaker, accurately weighing 0.10g of spherical porous magnesium silicate in the beaker, magnetically stirring, adjusting the pH value of the solution to 6.00, adjusting the water bath temperature to 30 ℃, and magnetically stirring at constant temperature for 60 min. After the reaction is finished, filtering, collecting filtrate, and detecting a color value; and collecting filter residues, washing the filter residues for multiple times by using ultrapure water, drying the filter residues at a low temperature, and calcining the filter residues in a muffle furnace for 300min at 500 ℃. The above steps are repeated, and the experimental values are recorded in sequence.
9. And (5) result and analysis.
9.1 sample characterization.
9.1.1 Scanning Electron Microscopy (SEM) analysis of spherical porous magnesium silicate.
FIG. 1 is a scanning electron micrograph of spherical porous magnesium silicate. As can be seen from the figure 1, the surface of the spherical porous magnesium silicate has rich pore channel structures, is formed by stacking irregular sheets and has irregular shapes, which shows that the spherical porous magnesium silicate is gradually corroded, and finally forms the magnesium silicate ball with good pore channel structures.
9.1.2X-ray diffraction analysis (XRD) of spherical porous magnesium silicate.
FIG. 2 is an XRD diffraction pattern of spherical porous magnesium silicate. As can be seen from fig. 2, the sample shows typical magnesium silicate diffraction peaks at 20 °, 34 °, and 60 ° 2 θ. The detection results of the samples are matched, the chemical phase is magnesium silicate crystal (JCPDS No.03-0174), the structure is consistent with that of talc, and no diffraction peak of impurities is detected. According to a scanning electron microscope image, the spherical porous magnesium silicate is prepared.
9.1.3 spherical porous magnesium silicate Infrared Spectroscopy (FTIR).
As can be seen from the infrared spectrum of the spherical porous magnesium silicate in FIG. 3, the spherical porous magnesium silicate sample is 3435cm-1、1635cm-1、1027cm-1、795cm-1、665cm-1、475cm-1Diffraction peaks were shown in the vicinity. At 3435cm-1A wider absorption peak appears, which corresponds to the vibration of hydroxyl groups of the water adsorbed on the surface of the magnesium silicate sample; 1635cm-1Corresponding to the water molecule stretching vibration bound by hydrogen bonds; 1100cm-1c corresponds to the stretching vibration of Si-O-Si; at 1027cm-1The peaks appearing nearby correspond to new bonds generated outside of Si-O-Si: Si-O-Mg bonds, indicating the formation of silicates; 795cm-1The weak absorption peak of (A) is the bending vibration of Si-O-Si; 665cm-1The weak absorption peak corresponds to the stretching vibration of Si-O-Mg at 475cm-1The strong absorption peak appears in the Mg-O, Si-O bending vibration key bending vibration. The appearance of these peaks further confirms that the sample is hydrous porous magnesium silicate.
9.1.5 adsorption and desorption isotherms and pore size distribution analysis.
As can be seen from the nitrogen adsorption and desorption isotherm diagram of the spherical porous magnesium silicate sample in FIG. 4, neither the adsorption curve nor the desorption curve of the sample are overlapped, and the hysteresis loop is obvious. According to the classification of isothermal lines by the international union of theory and applied chemistry (IUPAC), the adsorption and desorption isothermal lines of the sample are type IV, which shows that the spherical porous magnesium silicate has a mesoporous structure. As can be seen from the aperture distribution diagram of fig. 5, the apertures are mainly concentrated around 5nm and 22nm, and are more concentrated.
According to the BET and BJH formulas, the BET specific surface area, the average pore diameter and the total pore volume of the spherical porous magnesium silicate are shown in Table 1, and the spherical porous magnesium silicate is known to belong to mesoporous materials.
TABLE 1 analysis table of specific surface area and pore structure of spherical porous magnesium silicate sample
9.2 comparison before and after pigment adsorption by spherical porous magnesium silicate.
From SEM images of the spherical porous magnesium silicate of FIG. 6 before and after decoloring the sugar juice, it is seen that the adsorbate is adsorbed on the surface of the magnesium silicate to block the pores. As can be seen from the XRD pattern of FIG. 7, the XRD pattern of the spherical porous magnesium silicate after adsorption shows diffraction peaks of sucrose at 18 degrees, 19 degrees and 24 degrees and diffraction peaks of other non-magnesium silicate, which shows that the spherical porous magnesium silicate adsorbs a little sucrose at the same time of adsorbing colored substances.
The decoloring capacity of the spherical porous magnesium silicate on sugar juice is partially derived from functional groups on the surface of the magnesium silicate, and pigments are adsorbed, condensed and settled through chemical bonds; the other part of the decolorization relies on the rich pore channel structure of the spherical porous magnesium silicate to absorb the colored substances. The good adsorption capacity of the spherical porous magnesium silicate is proved.
9.3 Single factor test results.
By adopting a single-factor method, the influence of the dosage, the adsorption temperature, the adsorption time and the pH value of the spherical porous magnesium silicate on the decolorization of the sugar juice is systematically examined, and the experimental results are shown in fig. 8-11.
As can be seen from FIG. 8, the decolorization rate of the sugar juice is gradually increased with the increase of the amount of the spherical porous magnesium silicate adsorbent. The possible reasons are: with the increase of the usage amount of the spherical porous magnesium silicate, the specific surface area for pigment substances to be adsorbed and available adsorption sites in a reaction system are increased, so that the decolorization rate of the spherical porous magnesium silicate on sugar juice is improved along with the increase of the usage amount of the spherical porous magnesium silicate. When the dosage of the spherical porous magnesium silicate is 0.10g, the decolorization rate of the spherical porous magnesium silicate on sugar juice is 40.5 percent, and the main reasons are as follows: spherical porous magnesium silicate has a high specific surface area and a large pore volume. In view of cost, the amount of spherical porous magnesium silicate to be used was finally determined to be 0.10 g.
As can be seen from FIG. 9, the spherical porous magnesium silicate has the best decolorization effect on sugar juice at 30 ℃, and the decolorization rate can reach 64.6%. And the temperature is continuously raised, and the decoloring effect of the spherical porous magnesium silicate on the sugar juice is gradually reduced. The possible reasons are that some pigment substances in the sugar juice are deepened along with the increase of the temperature, and substances which do not develop color at low temperature develop color along with the increase of the temperature, so that the difficulty of decoloring the sugar juice by the spherical porous magnesium silicate is increased; the spherical porous magnesium silicate is slightly decomposed under the high-temperature acidic condition, so that the adsorption sites are reduced; when the reaction temperature is too high, a dynamic process of adsorption and desorption of the spherical porous magnesium silicate is caused, and adsorbed substances are dissociated, so that the decolorization rate is reduced. For the above reasons, the optimum adsorption temperature of the spherical porous magnesium silicate to the sugar juice is 30 ℃.
As can be seen from fig. 10, the decoloring effect of the spherical porous magnesium silicate on the sugar juice is improved as the reaction time is prolonged, and when the reaction time is 40min, the decoloring effect of the spherical porous magnesium silicate on the sugar juice is the best; after the reaction is carried out for 40min, the time is continuously prolonged, and the decoloring effect is basically not changed, which shows that the adsorption of the spherical porous magnesium silicate on the non-sugar components reaches the maximum when the reaction is carried out for 40 min. Comprehensively considering, selecting 40min as the optimal reaction time.
As can be seen from fig. 11, the decolorization effect of the spherical porous magnesium silicate on sugar juice increases and then decreases with the increase of the pH of the reaction system, and the optimum effect is achieved at a pH of 6.00. The pH value is increased, the decomposition amount of the spherical porous magnesium silicate is reduced, the adsorption point is increased when the pH value is relatively low, and the decoloring effect is improved; the pH value is continuously increased, the decoloring rate is relatively low, and because some non-sugar components in the sugar juice are converted into dark substances under the alkaline condition, the decoloring difficulty of the spherical porous magnesium silicate on the sugar juice is greatly increased. The pH of the reaction system was selected to be 6.00.
9.4 kinetic model fitting results.
The results of the spherical porous magnesium silicate decolorization process on sugar juice are shown in the figure 12 and the table 2 by adopting an intra-granular diffusion model and a quasi-second-order kinetic adsorption equation fitting result.
TABLE 2 kinetic model fitting parameter Table
As can be seen from the data in Table 2, the fitting correlation coefficient of the quasi-second order kinetic equation is closer to 1, so that the decolorization process of the spherical porous magnesium silicate on the sugar juice is more accurately represented by a quasi-second order kinetic model.
9.5 isothermal adsorption model fitting results.
The results of the isotherm adsorption fit are shown in figure 13 and table 3.
TABLE 3 summary of isothermal adsorption fitting parameters
As can be seen from the fitting coefficients of the two equations in Table 3, the fitting coefficient of the Langmuir isothermal adsorption equation is closer to 1, so that the decoloring process of the spherical porous magnesium silicate on the sugar juice can be better expressed by adopting the Langmuir isothermal adsorption equation.
9.6 results of regeneration experiments.
The results of the experiment are shown in FIGS. 14-15.
From fig. 14, it can be seen that the decolorization rate of the adsorbent spherical porous magnesium silicate can still reach 58.6% when the adsorbent spherical porous magnesium silicate is reused for 3 times, which indicates that the spherical porous magnesium silicate has good regeneration property, can be used for multiple times, and saves resources. FIG. 15 is a graph showing the effect of the first decoloring with spherical porous magnesium silicate, the original sugar solution on the left and the sugar solution after decoloring with spherical porous magnesium silicate on the right. The reduction in the decolorization rate may be due to some of the channels being plugged or collapsed during regeneration resulting in a slight reduction in the adsorption capacity of the spherical porous magnesium silicate.
Claims (3)
1. A method for decoloring sugar juice by using spherical porous magnesium silicate is characterized by comprising the following steps: the method comprises the following steps:
(1) SiO with a mass of 4.7-4.9g is first weighed2Placing the mixture into a beaker, adding 58-62mL of deionized water into the beaker, carrying out constant temperature ultrasonic treatment to uniformly mix the mixture for later use, and weighing 12.1-12.3g of MgCI2·6H2Pouring O into a beaker, and adding 4.9-5.1g of NH460.0mL of deionized water containing Cl, rapidly stirring to completely dissolve, adding 2.9-3.1mL of ammonia water under stirring, rapidly mixing the above two solutions under stirring, and standingStirring at the temperature for 3-8min, pouring into a digestion tank cup, assembling the digestion tank, placing the digestion tank filled with the mixed solution in a 185-plus-one 195 ℃ oven for hydrothermal reaction for 700-plus-one 750min, filtering through a Buchner funnel after the reaction is finished, washing the product with deionized water for multiple times, checking the filtrate with silver nitrate until no white precipitate is generated, performing centrifugal separation, placing the product in the oven, and drying at the temperature of 78-83 ℃ to obtain spherical porous magnesium silicate;
(2) heating sugar juice 100mL to 28-32 deg.C, adjusting pH to 5.9-6.1, adding spherical porous magnesium silicate 0.08-0.12g into sugar juice, adsorbing for 35-45min to obtain clarified liquid.
2. The method of claim 1, wherein the sugar juice is decolorized using spherical porous magnesium silicate: the sugar juice is sugarcane mixed juice, brown granulated sugar redissolving syrup or raw sugar redissolving syrup.
3. A process for the decolourisation of sugar juices using spherical porous magnesium silicate according to claim 1 or 2, characterised in that: the substance for adjusting the pH value of the sugar juice is 0.5mol/L NaOH or HCI.
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