Preparation method of graphene oxide composite film

Abstract

The invention provides a preparation method of a graphene oxide composite membrane. The preparation method comprises the following steps: raw material pretreatment, rough filtration and concentration, membrane adsorption and purification, elution and regeneration, and post-treatment. According to the preparation method of the graphene oxide composite membrane, the purity is high, phlorizin and impurities can be efficiently separated through the unique performance of the graphene oxide composite membrane, the purity of the phlorizin can be remarkably improved, the purity of the phlorizin treated through the method can reach 95% or above, even can reach 98% or above under the optimized condition, and the graphene oxide composite membrane is suitable for industrial production. The strict requirements of the fields of medicine, food and the like on high-purity phlorizin are met, high efficiency and low cost are achieved, the whole extraction and purification process is easy and convenient to operate, and compared with a traditional method, the technological process is shortened.

Description

Technical Field

[0001] The present invention relates to the field of extraction and purification of natural products, and particularly to a method for preparing a graphene oxide composite membrane. Background Art

[0002] Litsea coreana Levl. is a widely distributed plant containing various bioactive components. Among them, phloridzin has attracted much attention. Phloridzin has multiple effects such as hypoglycemic, antioxidant, and anti-inflammatory. In the pharmaceutical field, it is expected to become a raw material for new drugs for the treatment of chronic diseases such as diabetes and cardiovascular diseases; in the food field, phloridzin can be used as a natural antioxidant and functional food additive to improve the quality and nutritional value of food.

[0003] However, there are many problems with the current methods for extracting and purifying phloridzin from Litsea coreana Levl. The traditional solvent extraction method usually uses a large amount of organic solvents, not only with low extraction efficiency but also incomplete removal of impurities. For example, when using organic solvents such as ethanol for extraction, many other impurities will be extracted together with phloridzin, resulting in low purity of the obtained phloridzin and affecting its subsequent application effects. Moreover, the use of organic solvents also has safety hazards such as flammability, explosiveness, and environmental pollution. Some existing purification technologies, such as column chromatography, although can improve the purity of phloridzin to a certain extent, have a cumbersome operation process, require professional technicians and complex equipment. Column chromatography needs to fill a large amount of adsorbent, and the elution process requires precise control of the flow rate and the composition of the eluent, which not only increases the production cost but also is difficult to achieve large-scale production and cannot meet the growing market demand for phloridzin.

[0004] Therefore, it is necessary to provide a method for preparing a graphene oxide composite membrane to solve the above technical problems. Summary of the Invention

[0005] The present invention provides a method for preparing a graphene oxide composite membrane, which solves the problems of low efficiency, low purity, and cumbersome operation existing in the existing extraction and purification methods.

[0006] To solve the above technical problems, a method for preparing a graphene oxide composite membrane provided by the present invention includes the following steps:

[0007] S1. Raw material pretreatment: Dry the stems of Litsea coreana Levl. and crush them to 40 - 60 mesh, degrease with n-hexane in a way of a material-liquid ratio of 1:10, and remove fat-soluble impurities through two hours. Subsequently, perform dynamic countercurrent circulation extraction with subcritical water three times to obtain a phloridzin extract, and the dissolution rate of phloridzin ≥ 85%.

[0008] S2, Coarse Filtration and Concentration: Remove macromolecular proteins and polysaccharides through a 100 kDa ultrafiltration membrane under the working conditions of an operating pressure of 0.3 MPa and a temperature of 25 °C. Then, concentrate the extract to 1 / 5 of the original volume using a spiral wound nanofiltration membrane, with the phloridzin retention rate > 95%;

[0009] S3, Membrane Adsorption Purification: Perform cross-flow filtration on the concentrated solution through a graphene composite membrane system. Meanwhile, the membrane area in the entire system is 0.5 m 2 , the feed flow rate is 10 L / h, the transmembrane pressure is 0.5 MPa, adsorb for 30 min under the conditions of pH 5.0 and a temperature of 35 °C. Real-time detect the phloridzin adsorption amount on the membrane surface through near-infrared spectroscopy, and predict the adsorption saturation degree using the PLS algorithm;

[0010] S4, Elution and Regeneration: Elute with a 50% ethanol - 0.1 M NaOH mixed solution with a volume ratio of 3:1, and the elution efficiency ≥ 93%. The membrane regeneration is carried out by reverse flushing with an operating pressure of 0.2 MPa combined with circulating the alkaline cleaning solution for 20 min, and the flux recovery rate > 90%;

[0011] S5, Post-treatment: The eluate is rotary evaporated and concentrated under the conditions of a set temperature of 40 °C and an operating pressure of -0.09 MPa, and then spray dried to obtain powdery phloridzin with a purity ≥ 98%.

[0012] Preferably, the conditions for subcritical water dynamic countercurrent extraction in S1 are: temperature 140 °C, pressure 5 MPa, and cycle extraction three times. This specific extraction condition is determined through a large number of experimental studies. At this temperature and pressure, the physicochemical properties of subcritical water can make phloridzin in Lithocarpus litseifolius more soluble, and multiple cycle extractions can further improve the extraction rate of phloridzin to ensure full extraction of phloridzin from the raw materials.

[0013] Preferably, the ultrafiltration membrane in S2 is a Pall Corporation ultrafiltration membrane with a molecular weight cut-off of 100 kDa, an operating pressure of 0.3 MPa, and a temperature of 25 °C. The ultrafiltration membrane of Pall Corporation has good filtration performance and stability. The molecular weight cut-off of 100 kDa can accurately intercept macromolecular impurities. Meanwhile, at an operating pressure of 0.3 MPa and a temperature of 25 °C, the ultrafiltration membrane has the best filtration effect, good permeability to phloridzin, and will not have an adverse impact on the structure and properties of phloridzin.

[0014] Preferably, the nanofiltration membrane in S2 is an NF270 spiral wound nanofiltration membrane, and concentrate to 1 / 5 of the original volume. The NF270 spiral wound nanofiltration membrane has a high desalination rate and retention performance for small molecule organic substances. It can effectively concentrate the phloridzin extract while better retaining phloridzin, with its retention rate greater than 95%, providing a solution with a suitable concentration for subsequent purification and post-treatment.

[0015] Preferably, in S3, the graphene composite membrane system adopts a cross-flow filtration mode, and the membrane area is 0.5 m 2 , the feed flow rate is 10 L / h, and the transmembrane pressure is 0.5 MPa. The cross-flow filtration mode can make the feed liquid form a turbulent flow on the membrane surface, reduce concentration polarization and membrane fouling, improve the filtration efficiency and service life of the membrane. The membrane area of 0.5 m 2 , the feed flow rate of 10 L / h, and the transmembrane pressure of 0.5 MPa are optimized parameters, which can ensure the adsorption and filtration effect of the graphene composite membrane on phloridzin and achieve an efficient purification process.

[0016] Preferably, in S4, the eluent is a mixed solution of 50% ethanol and 0.1 M NaOH, and the elution efficiency ≥ 93%. The eluent formula is determined through experimental screening. The 50% ethanol and 0.1 M NaOH are mixed at a volume ratio of 3:1, which can interact with the phloridzin adsorbed on the graphene composite membrane and effectively elute it. The elution efficiency is not less than 93%, ensuring the recovery amount of phloridzin.

[0017] Preferably, in S4, the membrane regeneration is carried out by reverse flushing combined with circulating the alkaline cleaning solution for 20 min, and the flux recovery rate > 90%. The membrane regeneration method combining reverse flushing and circulating the alkaline cleaning solution can effectively remove impurities and pollutants on the membrane surface and inside. The reverse flushing pressure of 0.2 MPa can loosen and remove some impurities, and circulating the alkaline cleaning solution for 20 min can further dissolve and remove the remaining impurities, making the flux recovery rate of the membrane exceed 90%, extending the service life of the membrane and reducing production costs.

[0018] Preferably, in S5, the post-treatment includes rotary evaporation concentration and spray drying, and finally powdery phloridzin with a purity ≥ 98% is obtained. The rotary evaporation is carried out under the conditions of 40 °C and -0.09 MPa, which can concentrate the solution at a lower temperature and avoid the loss or deterioration of phloridzin due to high temperature. The inlet temperature of 180 °C and the outlet temperature of 80 °C for spray drying can quickly dry the concentrated solution into powder and ensure the stability of the structure and properties of phloridzin. Finally, high-quality powdery phloridzin with a purity not less than 98% is obtained.

[0019] Preferably, a mixing device is used when the powder of the stem of Lithocarpus litseifolius and the extraction liquid are mixed in S1. The mixing device includes a box body, a mixing box, two positioning components, a box cover, a stirring device, a first feeding component, and a second feeding component. The mixing box is arranged inside the box body. The two positioning components are respectively arranged between the box body and the mixing box. The box cover is arranged on the top of the box body. The stirring device is arranged between the box cover and the mixing box. The first feeding device and the second feeding component are respectively arranged on the surface of the box cover. The first feeding component includes a first feeding box, a plurality of conveying pipes, and a plurality of mounting heads. The plurality of conveying pipes are all connected to the bottom of the first feeding box. The plurality of mounting heads are respectively installed at the bottom ends of the plurality of conveying pipes. The second feeding component includes a second feeding box, a pipeline, and a connector. The pipeline is connected to the bottom of the second feeding box. The connector is connected to one end of the pipeline.

[0020] Preferably, the positioning component includes a positioning groove and a positioning block. The positioning groove is opened on the inner wall of the box body. The positioning block is arranged inside the positioning groove. The stirring device includes a motor and a stirring member. The motor is installed at the central position on the surface of the box cover. The stirring member is connected to one end of the motor. A conveying member is connected between the box body and the mixing box.

[0021] Compared with the related art, a preparation method of a graphene oxide composite film provided by the present invention has the following beneficial effects:

[0022] The present invention provides a preparation method of a graphene oxide composite film. High purity: Utilizing the unique properties of the graphene composite film, phloridzin and impurities can be efficiently separated, significantly improving the purity of phloridzin. After being processed by the method of the present invention, the purity of phloridzin can reach more than 95%, and even can reach 98% and above under optimized conditions, meeting the strict requirements for high-purity phloridzin in fields such as medicine and food.

[0023] High efficiency and low cost: The entire extraction and purification process is simple to operate. Compared with the traditional method, the technological process is shortened.

[0024] Guarantee of activity: The conditions in the extraction process are mild. In the processes of subcritical water extraction, membrane filtration, etc., conditions such as temperature and pressure are carefully designed, reducing the damage to the active ingredients of phloridzin and ensuring the quality and biological activity of the product. This enables the extracted phloridzin to fully exert its efficacy in medical and food applications. Description of the Drawings

[0025] Figure 1 It is a schematic structural diagram of the first embodiment of a preparation method of a graphene oxide composite film provided by the present invention.

[0026] Figure 2 Schematic diagram of the purification principle of the graphene composite membrane;

[0027] Figure 3 Schematic diagram of the structure of the graphene composite membrane;

[0028] Figure 4 Schematic diagram of the process flow;

[0029] Figure 5 Schematic diagram of the working principle of the membrane adsorption and elution system;

[0030] Figure 6 Schematic diagram of the infrared real-time monitoring system;

[0031] Figure 7 Schematic diagram of the purity comparison of the implementation case;

[0032] Figure 8 Schematic diagram of the structure of the second embodiment of the preparation method of the graphene oxide composite membrane provided by the present invention;

[0033] Figure 9 For Figure 8 Enlarged schematic diagram of part A shown;

[0034] Figure 10 For Figure 8 Stereoscopic structure schematic diagram of the first perspective of the mixing device shown;

[0035] Figure 11 For Figure 8 Stereoscopic structure schematic diagram of the second perspective of the mixing device shown.

[0036] Reference numerals in the figure: 1, box body; 2, mixing box;

[0037] 3, positioning component; 31, positioning groove; 32, positioning block;

[0038] 4, box cover;

[0039] 5, stirring device; 51, motor; 52, stirring member;

[0040] 6, first feeding component; 61, first feeding box; 62, conveying pipe; 63, installation head;

[0041] 7, second feeding component; 71, second feeding box; 72, pipeline; 73, connecting head;

[0042] 8, conveying member. Detailed implementation manners

[0043] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0044] First embodiment

[0045] Please refer to Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 and Figure 7 , where Figure 1 is a schematic structural diagram of the first embodiment of a method for preparing a graphene oxide composite membrane provided by the present invention; Figure 2 is a schematic diagram of the purification principle of the graphene composite membrane; Figure 3 is a schematic structural diagram of the graphene composite membrane; Figure 4 is a schematic process flow diagram; Figure 5 is a schematic diagram of the working principle of the membrane adsorption and elution system; Figure 6 is a schematic diagram of the infrared real-time monitoring system; Figure 7 is a schematic diagram of the purity comparison of the implementation cases. A method for preparing a graphene oxide composite membrane includes the following steps:

[0046] S1. Raw material pretreatment: Dry the stem of Lithocarpus litseifolius and crush it to 40-60 mesh, degrease it with n-hexane in a way that the material-liquid ratio is 1:10, remove fat-soluble impurities through two hours, and then obtain phloridzin extract by subcritical water dynamic countercurrent circulation extraction three times, with the phloridzin dissolution rate ≥ 85%;

[0047] S2. Coarse filtration and concentration: Remove macromolecular proteins and polysaccharides through a 100 kDa ultrafiltration membrane under the working state with an operating pressure of 0.3 MPa and a temperature of 25°C, and then concentrate the extract to 1 / 5 of the original volume using a spiral wound nanofiltration membrane, with the phloridzin retention rate > 95%;

[0048] S3. Membrane adsorption purification: Pass the concentrated solution through the graphene composite membrane system for cross-flow filtration. At the same time, the membrane area in the whole system is 0.5 m 2 , the feed flow rate is 10 L / h, the transmembrane pressure is 0.5 MPa, adsorb for 30 min under the conditions of pH 5.0 and a temperature of 35°C, and detect the phloridzin adsorption amount on the membrane surface in real time through near-infrared spectroscopy, and predict the adsorption saturation degree by the PLS algorithm;

[0049] S4. Elution and regeneration: Elute with a 50% ethanol - 0.1 M NaOH mixed solution with a volume ratio of 3:1, with an elution efficiency ≥ 93%. The membrane regeneration is carried out by reverse flushing with an operating pressure of 0.2 MPa combined with circulating the alkaline cleaning solution for 20 min, and the flux recovery rate > 90%;

[0050] S5. Post-treatment: The eluate is concentrated by rotary evaporation and then spray-dried under the conditions of a set temperature of 40°C and an operating pressure of -0.09 MPa to obtain powdery phloridzin with a purity ≥ 98%.

[0051] The drying treatment in S1 is to remove the moisture in the stems of Lithocarpus litseifolius, avoiding the interference of moisture on the subsequent extraction process. Crushing to 40 - 60 mesh can increase the contact area between the raw material and the extraction solvent, improving the extraction efficiency. Using n - hexane for defatting is because n - hexane can effectively dissolve fat - soluble impurities. By appropriate solid - liquid ratio and defatting time, these impurities can be removed to the greatest extent, reducing their impact on the extraction and purification of phloridzin. The sub - critical water dynamic counter - current extraction technology, utilizing the special properties of sub - critical water at specific temperature and pressure, can make phloridzin dissolve more fully from the raw material, and multiple - cycle extraction further improves the dissolution rate.

[0052] In S2, the ultrafiltration membrane can screen the components in the extract according to molecular size. The cut - off molecular weight of 100 kDa can effectively intercept macromolecular proteins and polysaccharides, while allowing small - molecule substances such as phloridzin to pass through. At an operating pressure of 0.3 MPa and a temperature of 25 °C, it can not only ensure the filtration efficiency but also avoid damaging the structure of phloridzin. The spiral - wound nanofiltration membrane is used to further concentrate the extract, reducing its volume to 1 / 5 of the original volume while ensuring a high retention rate of phloridzin and reducing the loss of phloridzin.

[0053] In S3, the graphene composite membrane has a unique structure and excellent adsorption performance. The cross - flow filtration mode can reduce the concentration polarization phenomenon on the membrane surface, improving the filtration effect and the service life of the membrane. Adsorbing under specific pH value, temperature and time conditions can make the adsorption of phloridzin by the graphene composite membrane reach the best effect. Near - infrared spectroscopy real - time detection and PLS algorithm prediction of adsorption saturation can accurately control the adsorption process, timely judge whether the adsorption reaches saturation, and avoid over - adsorption or insufficient adsorption.

[0054] In S4, choosing the appropriate eluent is crucial for the efficient elution of phloridzin. The 50% ethanol - 0.1 M NaOH mixture (volume ratio 3:1) can effectively elute the phloridzin adsorbed on the graphene composite membrane with a high elution efficiency. During the membrane regeneration process, back - flushing can remove some impurities on the membrane surface, and the circulation of the alkaline cleaning solution can more thoroughly remove the residual impurities and pollutants, effectively restoring the membrane flux for reuse.

[0055] In S5, rotary evaporation is carried out under low temperature and negative pressure conditions, which can avoid the decomposition or deterioration of phloridzin due to high temperature and concentrate the eluent. Spray drying then converts the concentrated solution into powdered phloridzin. By controlling the inlet and outlet temperatures, the quality and purity of phloridzin can be guaranteed, and finally a high - purity powdered product is obtained.

[0056] The conditions for subcritical water dynamic countercurrent extraction in S1 are: temperature 140°C, pressure 5 MPa, and cyclic extraction three times. This specific extraction condition is determined through a large number of experimental studies. At this temperature and pressure, the physicochemical properties of subcritical water can make phloridzin in Litsea cubeba (Lour.) Pers. more soluble. Multiple cyclic extractions can further improve the extraction rate of phloridzin and ensure sufficient acquisition of phloridzin from the raw materials.

[0057] The ultrafiltration membrane in S2 is the Pall Corporation ultrafiltration membrane with a molecular weight cut-off of 100 kDa. The operating pressure is 0.3 MPa and the temperature is 25°C. The ultrafiltration membrane of Pall Corporation has good filtration performance and stability. The molecular weight cut-off of 100 kDa can accurately intercept macromolecular impurities. At the same time, at an operating pressure of 0.3 MPa and a temperature of 25°C, the ultrafiltration membrane has the best filtration effect, good permeability to phloridzin, and will not have an adverse impact on the structure and properties of phloridzin.

[0058] The nanofiltration membrane in S2 is the NF270 spiral wound nanofiltration membrane, concentrated to 1 / 5 of the original volume. The NF270 spiral wound nanofiltration membrane has a high salt rejection rate and the ability to retain small molecular organics. It can effectively concentrate the phloridzin extract while better retaining phloridzin, with a retention rate greater than 95%, providing a solution with a suitable concentration for subsequent purification and post-treatment.

[0059] The graphene composite membrane system in S3 adopts a crossflow filtration mode, with a membrane area of 0.5 m 2 , a feed flow rate of 10 L / h, and a transmembrane pressure of 0.5 MPa. The crossflow filtration mode can make the feed liquid form a turbulent flow on the membrane surface, reduce concentration polarization and membrane fouling, and improve the filtration efficiency and service life of the membrane. The membrane area of 0.5 m 2 , a feed flow rate of 10 L / h, and a transmembrane pressure of 0.5 MPa are optimized parameters, which can ensure the adsorption and filtration effect of the graphene composite membrane on phloridzin and achieve an efficient purification process.

[0060] The eluent in S4 is a mixture of 50% ethanol and 0.1 M NaOH, and the elution efficiency ≥ 93%. This eluent formula is determined through experimental screening. 50% ethanol and 0.1 M NaOH are mixed in a volume ratio of 3:1, which can interact with phloridzin adsorbed on the graphene composite membrane and effectively elute it. The elution efficiency is not less than 93%, ensuring the recovery amount of phloridzin.

[0061] In S4, the membrane regeneration is achieved by reverse flushing combined with circulating an alkaline cleaning solution for 20 min, and the flux recovery rate is >90%. The membrane regeneration method combining reverse flushing and circulating an alkaline cleaning solution can effectively remove impurities and contaminants on the surface and inside of the membrane. The reverse flushing pressure of 0.2 MPa can loosen and remove some impurities, and circulating the alkaline cleaning solution for 20 min can further dissolve and remove the remaining impurities, making the flux recovery rate of the membrane exceed 90%, prolonging the service life of the membrane, and reducing production costs.

[0062] The post-treatment in S5 includes rotary evaporation concentration and spray drying, and finally powdery phloridzin with a purity ≥98% is obtained. The rotary evaporation is carried out under the conditions of 40°C and -0.09 MPa, which can achieve the concentration of the solution at a relatively low temperature, avoiding the loss or deterioration of phloridzin due to high temperature. The inlet temperature of 180°C and the outlet temperature of 80°C for spray drying can quickly dry the concentrated solution into powder form and ensure the stability of the structure and properties of phloridzin, finally obtaining high-quality powdery phloridzin with a purity not lower than 98%.

[0063] An application of a graphene composite membrane in the extraction and purification of phloridzin. The graphene composite membrane is used for adsorbing and separating phloridzin from the extraction solution of Lithocarpus litseifolius. The adsorption conditions are pH 5.0 and temperature 35°C, and the elution conditions are a 50% ethanol - 0.1 M NaOH mixed solution (volume ratio 3:1). The unique structure and surface properties of the graphene composite membrane enable it to selectively adsorb phloridzin in the extraction solution of Lithocarpus litseifolius under specific adsorption conditions, realizing the separation from other impurities, while the specific elution conditions can efficiently elute the adsorbed phloridzin, providing key technical support for the extraction and purification of phloridzin.

[0064] A device for extracting and purifying phloridzin from Lithocarpus litseifolius includes the following units:

[0065] The pretreatment unit: used for washing, drying, and pulverizing the Lithocarpus litseifolius raw material. This unit is the starting link of the entire extraction and purification process. Washing can remove dust, impurities, microorganisms, etc. on the surface of the raw material, drying can reduce the moisture content of the raw material, facilitating subsequent pulverization and storage, and the pulverization treatment is to increase the contact area between the raw material and the extraction solvent, improving the extraction efficiency;

[0066] The extraction unit: includes a reaction vessel, a heating device, and a stirring device, and is used for mixing the Lithocarpus litseifolius powder with the extraction solvent and carrying out an extraction reaction. The reaction vessel provides a space for the extraction reaction, the heating device can control the reaction temperature, enabling the extraction process to proceed at an appropriate temperature, and the stirring device can fully mix the Lithocarpus litseifolius powder with the extraction solvent, accelerating the dissolution and diffusion of phloridzin, and improving the extraction effect;

[0067] Filtering unit: Set after the extraction unit, used for preliminary filtration of the extract. Preliminary filtration can remove large particle impurities in the extract, such as incompletely crushed raw material particles, insoluble residues, etc., protecting the subsequent purification unit and equipment from clogging and damage, and at the same time providing a purer feed liquid for the subsequent purification process;

[0068] Purification unit: Connected to the filtering unit, containing a graphene composite membrane module, used for purifying the preliminary filtrate. The graphene composite membrane module is the core of the purification unit. Its unique structure and adsorption properties can effectively separate phloridzin from impurities and improve the purity of phloridzin. By selecting a suitable graphene composite membrane and operating conditions, an efficient purification process can be achieved;

[0069] Concentration and drying unit: Connected to the purification unit, used for concentrating and drying the purified liquid to obtain phloridzin finished products. This unit can remove the solvent in the purified liquid, concentrate and dry phloridzin, and finally form phloridzin finished products that are convenient for storage and use. Different concentration and drying methods can be selected according to actual needs to ensure the quality and purity of the product.

[0070] The graphene composite membrane module includes a membrane shell, a graphene composite membrane, and inlet and outlet pipelines. The graphene composite membrane is fixed inside the membrane shell, and the inlet and outlet pipelines are respectively connected to the membrane shell, used for introducing the preliminary filtrate and discharging the purified liquid. The membrane shell plays a role in protecting and supporting the graphene composite membrane to ensure its stability during use. The graphene composite membrane is the key component for realizing the purification of phloridzin, and the inlet and outlet pipelines are responsible for transporting the preliminary filtrate into the membrane module and discharging the purified liquid to achieve a continuous purification process.

[0071] In the concentration and drying unit, a vacuum distillation device is sequentially connected to a freeze-drying device or a spray-drying device. The vacuum distillation device can remove most of the solvent in the purified liquid at a lower temperature to achieve preliminary concentration, and the freeze-drying device or the spray-drying device further dries the concentrated liquid according to the requirements and characteristics of the product to obtain phloridzin finished products in different forms. This combination method can meet different production needs and improve the quality and production efficiency of the product.

[0072] Example 1: Raw material pretreatment: Take 100 g of fresh leaves of Lithocarpus litseifolius, wash them, dry them to constant weight in an oven at 60 °C, and then crush them with a pulverizer and pass through an 80-mesh sieve to obtain Lithocarpus litseifolius powder;

[0073] Extraction: Add the Lithocarpus litseifolius powder to 500 mL of an ethanol-water mixed solution with a volume fraction of 50%, and extract in a reaction vessel at 50 °C and a stirring speed of 200 r / min for 4 h;

[0074] Filtration: The extract was preliminarily filtered through a 0.45 μm filter membrane to remove large particle impurities, and the preliminary filtrate was obtained.

[0075] Purification with graphene composite membrane: The preliminary filtrate was purified through a graphene composite membrane with a molecular weight cut-off of 1000 Da and carboxyl groups on the surface. Filtration was carried out under the condition of a pressure of 0.2 MPa to obtain the purified solution.

[0076] Concentration and drying: The purified solution was concentrated by vacuum distillation with the temperature controlled at 50 °C and the vacuum degree at 0.06 MPa. After being concentrated to 1 / 10 of the original volume, it was freeze-dried to obtain the phloridzin finished product. After detection, the purity of phloridzin reached 96%, and the extraction rate was 85%.

[0077] Example 2: Raw material pretreatment: Take 150 g of Lithocarpus litseifolius fruits, wash, dry, crush them and then pass through a 60-mesh sieve.

[0078] Extraction: Using water as the extraction solvent, with a material-liquid ratio of 1:10, extract at 60 °C and a stirring speed of 250 r / min for 3 h.

[0079] Filtration: Conduct preliminary filtration with filter paper.

[0080] Purification with graphene composite membrane: Use a graphene composite membrane with a molecular weight cut-off of 1500 Da and amino groups on the surface for purification under a pressure of 0.3 MPa.

[0081] Concentration and drying: The vacuum distillation temperature is 45 °C and the vacuum degree is 0.07 MPa. After concentration, it is spray-dried. After detection, the purity of phloridzin is 94%, and the extraction rate is 82%.

[0082] Compared with the related technology, a preparation method of a graphene oxide composite membrane provided by the present invention has the following beneficial effects:

[0083] The present invention provides a preparation method of a graphene oxide composite membrane. High purity: Utilizing the unique properties of the graphene composite membrane, it can efficiently separate phloridzin from impurities, significantly improving the purity of phloridzin. After being treated by the method of the present invention, the purity of phloridzin can reach more than 95%, and even can reach 98% and above under optimized conditions, meeting the strict requirements for high-purity phloridzin in fields such as medicine and food.

[0084] High efficiency and low cost: The whole extraction and purification process is simple to operate. Compared with the traditional method, the technological process is shortened.

[0085] Guarantee of activity: The conditions in the extraction process are mild. In the processes of subcritical water extraction and membrane filtration, conditions such as temperature and pressure are carefully designed, reducing the damage to the active ingredients of phloridzin and ensuring the quality and biological activity of the product. This enables the extracted phloridzin to fully exert its efficacy in medical and food applications.

[0086] Second Embodiment

[0087] Please refer to Figure 8 、 Figure 9 、 Figure 10 and Figure 11 Based on a method for preparing a graphene oxide composite membrane provided in the first embodiment of the present application, the second embodiment of the present application proposes another method for preparing a graphene oxide composite membrane. The second embodiment is merely a preferred manner of the first embodiment, and the implementation of the second embodiment will not affect the independent implementation of the first embodiment.

[0088] Specifically, the difference in a method for preparing a graphene oxide composite membrane provided in the second embodiment of the present application is that in a method for preparing a graphene oxide composite membrane, when the powder of Lithocarpus litseifolius stems is mixed with the extract, a mixing device will be used. The mixing device includes a box body 1, a mixing box 2, two positioning components 3, a box cover 4, a stirring device 5, a first feeding component 6 and a second feeding component 7. The mixing box 2 is arranged inside the box body 1. The two positioning components 3 are respectively arranged between the box body 1 and the mixing box 2. The box cover 4 is arranged on the top of the box body 1. The stirring device 5 is arranged between the box cover 4 and the mixing box 2. The first feeding device 6 and the second feeding component 7 are respectively arranged on the surface of the box cover 4. The first feeding component 6 includes a first feeding box 61, a plurality of conveying pipes 62 and a plurality of mounting heads 63. The plurality of conveying pipes 62 are all connected to the bottom of the first feeding box 61. The plurality of mounting heads 63 are respectively installed at the bottom ends of the plurality of conveying pipes 62. The second feeding component 7 includes a second feeding box 71, a pipe 72 and a connector 73. The pipe 72 is connected to the bottom of the second feeding box 71. The connector 73 is connected to one end of the pipe 72.

[0089] The positioning component 3 includes a positioning groove 31 and a positioning block 32. The positioning groove 31 is opened on the inner wall of the box body 1. The positioning block 32 is arranged inside the positioning groove 31. The stirring device 5 includes a motor 51 and a stirring member 52. The motor 51 is installed at the central position on the surface of the box cover 4. The stirring member 52 is connected to one end of the motor 51. A conveying member 8 is connected between the box body 1 and the mixing box 2.

[0090] The use of the mixing box 2 facilitates its removal from the interior of the box body 1 for cleaning. The use of the positioning block 32 and the positioning groove 31 facilitates the installation, positioning, and limiting of the mixing box 2 inside the box body 1 to prevent the rotation of the mixing box 2 during operation. The stirring member 52 is composed of a rotating rod and multiple stirring blades. Installation through holes adapted to the mounting head 63 and the connecting head 73 are provided on the surface of the box cover 4. The conveying member 8 is composed of a connecting pipe and a valve, which facilitates the discharge after the powder of Lithocarpus litseifolius stems and the extract are fully mixed.

[0091] The working principle of a method for preparing a graphene oxide composite film provided by the present invention is as follows:

[0092] During use, when the powder of Lithocarpus litseifolius stems is mixed with the extract, first add the powder of Lithocarpus litseifolius stems to the interior of the first blanking box 61, and then evenly convey it to each position inside the mixing box 2 through multiple conveying pipes 62 with mounting heads 63. At the same time, add the extract to the interior of the second blanking box 71 and convey it to the interior of the mixing box 2 through the pipe 72 with the connecting head 73, and then start the motor 51 to drive the stirring member 52 to mix the powder of Lithocarpus litseifolius stems and the extract inside the mixing box 2.

[0093] Compared with the related art, a method for preparing a graphene oxide composite film provided by the present invention has the following beneficial effects:

[0094] The present invention provides a method for preparing a graphene oxide composite film. Through the cooperative operation among the stirring device 5, the first blanking component 6, and the second blanking component 7 provided on the box body 1 with the mixing box 2 and two positioning components 3 and the box cover 4, when the powder of Lithocarpus litseifolius stems is mixed with the extract, the powder of Lithocarpus litseifolius stems can be evenly blanked at each position inside the mixing box 2, thereby increasing the uniformity of the mixing between the powder of Lithocarpus litseifolius stems and the extract.

[0095] The above are only the embodiments of the present invention, and thus do not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the specification and drawings of the present invention, or directly or indirectly applied to other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A method for preparing a graphene oxide composite film, characterized in that: The following steps are involved: S1. Raw material pretreatment: the stem of Ligusticum chuanxiong was dried and crushed into 40-60 mesh, and the fat-soluble impurities were removed by using n-hexane for two hours in a ratio of 1:10, and then the phlorizin extract was obtained by using subcritical water dynamic countercurrent circulation extraction three times, and the phlorizin dissolution rate was ≥85%; S2, coarse filtration and concentration: remove macromolecular proteins and polysaccharides by using a 100 kDa ultrafiltration membrane with an operating pressure of 0.3 MPa and a temperature of 25°C, and then use a spiral nanofiltration membrane to concentrate the extract to 1 / 5 of the original volume, with a phlorizin retention rate of >95%; S3, membrane adsorption purification: The concentrated liquid is filtered through the graphene composite membrane system for cross-flow filtration. At the same time, the membrane area of ​​the whole system is 0.5m 2 , feed flow rate 10L / h, transmembrane pressure 0.5MPa, adsorption for 30min under pH 5.0 and temperature 35℃, near infrared spectroscopy was used to detect the amount of phlorizin adsorbed on the membrane surface in real time, and the PLS algorithm was used to predict the adsorption saturation; S4, elution and regeneration: elution was carried out using a mixed solution of 50% ethanol and 0.1M NaOH in a volume ratio of 3:1, with an elution efficiency of ≥93%. The membrane was regenerated by reverse flushing at an operating pressure of 0.2MPa combined with alkaline cleaning solution circulation for 20min, and the flux recovery rate was >90%; S5. Post-treatment: The eluate is concentrated by rotary evaporation at a temperature of 40° C. and an operating pressure of -0.09 MPa, and then spray-dried to obtain powdered phlorizin with a purity of ≥98%.

2. The method for preparing a graphene oxide composite film according to claim 1, wherein The conditions of the subcritical water dynamic countercurrent extraction in S1 are: temperature 140°C, pressure 5MPa, and three cycles of extraction. This specific extraction condition is determined after a large number of experimental studies. At this temperature and pressure, the physicochemical properties of subcritical water can make the phlorizin in the Ligusticum chuanxiong easier to dissolve, and multiple cycles of extraction can further improve the extraction rate of phlorizin, ensuring that phlorizin is fully obtained from the raw material.

3. The method for preparing a graphene oxide composite film according to claim 1, wherein: The ultrafiltration membrane in S2 is a Pall Corporation ultrafiltration membrane with a molecular weight cutoff of 100 kDa, an operating pressure of 0.3 MPa, and a temperature of 25°C. The ultrafiltration membrane of Pall Corporation has good filtration performance and stability. The molecular weight cutoff of 100 kDa can accurately intercept large molecular impurities. At the same time, at an operating pressure of 0.3 MPa and a temperature of 25°C, the ultrafiltration membrane has the best filtration effect, has good permeability to phlorizin, and will not adversely affect the structure and properties of phlorizin.

4. The method for preparing a graphene oxide composite film according to claim 1, wherein The nanofiltration membrane in S2 is a NF270 rolled nanofiltration membrane, which is concentrated to 1 / 5 of the original volume. The NF270 rolled nanofiltration membrane has a high desalination rate and retention performance for small molecular organic matter. It can effectively concentrate the phlorizin extract while better retaining phlorizin, so that its retention rate is greater than 95%, providing a solution of suitable concentration for subsequent purification and post-processing.

5. The method for preparing a graphene oxide composite film according to claim 1, wherein: The graphene composite membrane system in S3 adopts cross-flow filtration mode, and the membrane area is 0.5m 2 , the feed flow rate is 10L / h, the transmembrane pressure is 0.5MPa, and the cross-flow filtration mode can make the feed liquid form turbulence on the membrane surface, reduce concentration polarization and membrane pollution, and improve the filtration efficiency and service life of the membrane. 2 The membrane area, feed flow rate of 10 L / h and transmembrane pressure of 0.5 MPa are optimized parameters, which can ensure the adsorption and filtration effect of graphene composite membrane on phlorizin and realize an efficient purification process.

6. The method for preparing a graphene oxide composite film according to claim 1, characterized in that: The eluent in S4 is a mixture of 50% ethanol and 0.1MNaOH, and the elution efficiency is ≥93%. The eluent formula is determined through experimental screening. 50% ethanol and 0.1MNaOH are mixed in a volume ratio of 3:1, which can interact with the phlorizin adsorbed on the graphene composite membrane and effectively elute it. The elution efficiency is not less than 93%, ensuring the recovery of phlorizin.

7. The method for preparing a graphene oxide composite film according to claim 1, characterized in that: The membrane regeneration in S4 is achieved by backwashing combined with circulation of alkaline cleaning solution for 20 minutes, and the flux recovery rate is >90%. The membrane regeneration method combining backwashing and circulation of alkaline cleaning solution can effectively remove impurities and pollutants on the surface and inside of the membrane. The backwashing pressure of 0.2MPa can loosen and remove some impurities, and the circulation of alkaline cleaning solution for 20 minutes can further dissolve and remove residual impurities, so that the flux recovery rate of the membrane exceeds 90%, thereby extending the service life of the membrane and reducing production costs.

8. The method for preparing a graphene oxide composite film according to claim 1, wherein: The post-treatment in S5 includes rotary evaporation concentration and spray drying, and finally a powdered phlorizin with a purity of ≥98% is obtained. The rotary evaporation is carried out under the conditions of 40°C and -0.09MPa, which can achieve concentration of the solution at a lower temperature and avoid loss or deterioration of the phlorizin due to high temperature. The inlet temperature of 180°C and the outlet temperature of 80°C for spray drying can quickly dry the concentrated solution into a powder, and ensure the stability of the structure and properties of the phlorizin, and finally obtain high-quality powdered phlorizin with a purity of not less than 98%.

9. The method for preparing a graphene oxide composite film according to claim 1, characterized in that: A mixing device is used when mixing the powder of the stem of Ligusticum chuanxiong and the extract in S1. The mixing device includes a box body, a mixing box, two positioning components, a box cover, a stirring device, a first feeding component and a second feeding component. The mixing box is arranged inside the box body, and the two positioning components are respectively arranged between the box body and the mixing box. The box cover is arranged on the top of the box body, and the stirring device is arranged between the box cover and the mixing box. The first feeding device and the second feeding component are respectively arranged on the surface of the box cover. The first feeding component includes a first feeding box, multiple conveying pipes and multiple installation heads. The multiple conveying pipes are all connected to the bottom of the first feeding box, and the multiple installation heads are respectively installed at the bottom ends of the multiple conveying pipes. The second feeding component includes a second feeding box, a pipe and a connecting head. The pipe is connected to the bottom of the second feeding box, and the connecting head is connected to one end of the pipe.

10. The method for preparing a graphene oxide composite film according to claim 9, characterized in that: The positioning assembly includes a positioning groove and a positioning block, the positioning groove is opened on the inner wall of the box body, the positioning block is arranged inside the positioning groove, the stirring device includes a motor and a stirring piece, the motor is installed at the center position of the box cover surface, the stirring piece is connected to one end of the motor, and a conveying piece is connected between the box body and the mixing box.

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