Composite adsorbent for purifying urea in dialysate as well as preparation method and application of composite adsorbent

Abstract

The invention belongs to the technical field of materials, and relates to an adsorption material, in particular to a composite adsorbent for purifying urea in dialysate, and a preparation method and application of the composite adsorbent. The composite adsorbent for purifying urea in dialysate is composed of oxidized microcrystalline cellulose and activated carbon according to the weight ratio of (1-10): (1-2), the oxidized microcrystalline cellulose is prepared after microcrystalline cellulose is subjected to periodate oxidation modification, the surface aldehyde group content of the oxidized microcrystalline cellulose is 5-20 mmol / g, and the specific surface area of the oxidized microcrystalline cellulose is 50-500 m / g. The adsorbent has a high specific surface area and rich surface functional groups, has a remarkable synergistic promotion effect on adsorption of urea in the dialysate, the static equilibrium adsorption capacity and the dynamic clearance rate of the urea are remarkably higher than those of a single-component adsorption material, regeneration of the dialysate can be rapidly and efficiently achieved, and the service life of the adsorbent is prolonged. The device is especially suitable for an artificial kidney dialysate regeneration system. The composite adhesive is simple and convenient in preparation method and low in cost, can be stored for a long time at normal temperature, and has a wide application prospect and an important practical value.

Description

Technical Field

[0001] The invention belongs to the technical field of materials and relates to an adsorption material, in particular to a composite adsorbent for purifying urea in dialysate, and also relates to a preparation method and use thereof. Background Art

[0002] Dialysis therapy is a life-sustaining treatment method widely used in patients with renal failure, especially for patients with end-stage renal disease. The main function of dialysis is to simulate the detoxification and water regulation of the kidneys, and to maintain the electrolyte and acid-base balance in the blood by removing waste, toxins and excess water accumulated in the body. Common dialysis treatment methods include hemodialysis and peritoneal dialysis. The traditional dialysis method dialysis equipment is bulky and complicated to operate, which brings inconvenience to dialysis patients and increases the pressure on medical resources. With the continuous development of dialysis technology, portable artificial kidneys have brought convenience to dialysis patients. The key is to be able to efficiently recycle limited dialysate, continuously remove various wastes produced by human metabolism, and ensure the smooth progress of the dialysis process.

[0003] Urea is one of the main metabolic wastes in patients with renal failure. Its accumulation will have a serious impact on health. Therefore, achieving dynamic removal of urea in dialysate and improving its removal efficiency has always been the research focus of portable artificial kidneys. At present, there are three main technical solutions for removing urea from dialysate: enzyme catalysis, electrochemical method and physical adsorption method. Among them, physical adsorption method is simple to operate, relatively low in cost and not easy to produce harmful byproducts, which helps to ensure the safety of dialysate. Traditional adsorption materials such as activated carbon and silica gel can adsorb urea to a certain extent, but their adsorption capacity is only about 10-30 mg / g. The amount of urea produced by adult metabolism per day is about 300-500 mmol (18-30 g). If all of it is adsorbed, about 1-3 kg of adsorbent is required per day, which is difficult to meet the requirements of lightweight portable artificial kidneys. In order to solve the above problems, the development of efficient, low-cost and lightweight urea adsorption materials has become one of the key directions of WAK research. Summary of the invention

[0004] In view of the problems and shortcomings in the prior art, the purpose of the present invention is to provide a composite adsorbent for purifying urea in dialysate, and also to a preparation method and use thereof.

[0005] Based on the above purpose, the present invention adopts the following technical solution:

[0006] The first aspect of the present invention provides a composite adsorbent for purifying urea in a dialysate, which is composed of oxidized microcrystalline cellulose and activated carbon in a weight ratio of (1-10):(1-2).

[0007] Preferably, the oxidized microcrystalline cellulose is prepared by oxidizing microcrystalline cellulose with periodate, and the surface aldehyde content of the oxidized microcrystalline cellulose is 5 to 20 mmol / g, and the specific surface area is 50 to 500 m 2 / g.

[0008] Preferably, the particle size of the microcrystalline cellulose is 20 to 100 μm.

[0009] Preferably, the activated carbon is any one of coconut shell activated carbon, sawdust activated carbon and fruit shell activated carbon, the activated carbon has an iodine value of 500-1200 mg / g and a particle size of 200-300 mesh (50-75 μm).

[0010] More preferably, the activated carbon is fruit shell activated carbon, the iodine value of the activated carbon is 900-1200 mg / g, and the particle size is 200-250 mesh (60-75 μm).

[0011] The second aspect of the present invention provides a method for preparing the composite adsorbent described in the first aspect, comprising the following steps:

[0012] S1: dispersing microcrystalline cellulose in water and stirring to obtain a microcrystalline cellulose suspension with a mass percentage concentration of 10%, adding sodium periodate solution to carry out oxidation reaction, adding glycerol to terminate the reaction after the reaction is completed, and centrifuging, washing, drying, crushing, and sieving the product to obtain oxidized microcrystalline cellulose;

[0013] S2: The oxidized microcrystalline cellulose prepared in S1 is mixed evenly with activated carbon, and after sieving, a composite adsorbent for purifying urea in the dialysate is obtained.

[0014] Preferably, in step S1, the mass ratio of sodium periodate to microcrystalline cellulose is (1-2):(1-10).

[0015] Preferably, the oxidation reaction temperature in step S1 is 20 to 35° C., and the reaction time is 12 to 48 hours.

[0016] More preferably, the oxidation reaction temperature in step S1 is 25° C. and the reaction time is 24 hours.

[0017] Preferably, the mixing device used in the mixing step in step S2 is a V-type mixer or a three-dimensional mixer, the speed of the device is 30 to 60 rpm, and the mixing time is 30 to 60 minutes.

[0018] Preferably, before the activated carbon is mixed with the oxidized microcrystalline cellulose in step S2, the activated carbon needs to be dried at a temperature of 60 to 80° C. for a drying time of 3 to 6 hours.

[0019] Preferably, the mesh size of the sieving process in step S2 is 10 to 40 meshes.

[0020] Preferably, the activated carbon requires high-temperature activation treatment, the high-temperature activation conditions are CO2 atmosphere, CO2 flow rate of 100-300 mL / min, activation temperature of 600-900°C, activation time of 1-3 hours, so that the moisture content is less than 5%, meeting the purity and safety requirements of medical adsorption materials.

[0021] The third aspect of the present invention provides the use of the composite adsorbent for purifying urea in dialysate as described in the first aspect above, wherein the adsorbent is loaded into an adsorption column, and then the adsorption column is connected to a medical dialysate circulation loop for adsorbing and purifying urea in the medical dialysate; the pH value of the medical dialysate is 6.8-7.5, and the temperature is 20-40°C. .

[0022] The present invention is based on actual clinical needs and takes easy implementation as a starting point. It screens and modifies existing medical safety materials. After multiple attempts, the combination of modified microcrystalline cellulose and activated carbon is determined. Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention achieves synergistic enhancement of urea adsorption by oxidizing the active aldehyde groups on microcrystalline cellulose and chemically adsorbing urea molecules, while combining the rich microporous structure provided by activated carbon, and significantly improves the static and dynamic urea adsorption performance of the adsorbent. Experiments show that the adsorption efficiency of the adsorbent for urea in the dialysate is significantly higher than that of a single component adsorbent material.

[0024] (2) Microcrystalline cellulose is a low-cost and commercialized cellulose material. It is considered to be an ideal cellulose matrix material due to its high specific surface area and excellent structural stability. However, since the surface of microcrystalline cellulose is mainly composed of hydroxyl groups and lacks specific adsorption sites for urea, its adsorption capacity for urea is very limited. The present invention modifies microcrystalline cellulose by oxidation, and the aldehyde content of the obtained oxidized microcrystalline cellulose is 5 to 20 mmol / g. The main purpose of oxidation is to introduce active aldehyde groups into microcrystalline cellulose, provide chemical adsorption sites through the Schiff base reaction of aldehyde groups with amino groups on urea molecules, and improve its adsorption capacity for urea.

[0025] (3) The activated carbon selected in the present invention is coconut shell activated carbon, fruit shell activated carbon or other wood activated carbon, which plays an important role in the composite adsorbent, specifically: the activated carbon provides a rich microporous structure and a high specific surface area for the adsorption system, effectively prevents the adhesion between the oxidized microcrystalline cellulose particles, ensures that the physical and chemical adsorption sites are fully exposed, and is conducive to the diffusion and capture of urea molecules. More importantly, by utilizing the synergistic effect of the physical adsorption of activated carbon and the physical and chemical adsorption of urea by the surface active groups (such as hydroxyl and aldehyde groups) of oxidized microcrystalline cellulose, it is possible to form an adsorption mode with a special interface effect at the interface of the two components, and synergistically improve the adsorption efficiency and removal performance of the adsorbent for urea in the dialysate. The preferred activated carbon particle size of the present invention is 200-250 mesh, and the iodine value is 900-1200 mg / g. The higher the iodine value, the stronger its adsorption capacity. The purpose of optimizing the activated carbon particle size is to disperse the oxidized microcrystalline cellulose particles while ensuring the specific surface area and pore structure of the adsorbent, prevent them from adhering to form a dense structure, improve the permeability of the dialysate when passing through, avoid blockage, and reduce the pressure of the adsorption column. In addition, this particle size range helps to evenly mix with oxidized microcrystalline cellulose, improve the synergistic adsorption effect of the two, and further improve the adsorption efficiency of urea in the dialysate.

[0026] (4) The adsorbent of the present invention has good biocompatibility, is safe and non-toxic, and uses oxidized microcrystalline cellulose and medical-grade activated carbon as raw materials. Both materials have excellent biocompatibility and safety, and will not cause secondary pollution to the dialysate. They are very suitable for use as adsorption consumables for biomedical equipment such as artificial kidneys, meeting their strict requirements for efficient and safe adsorption materials. The adsorbent of the present invention has good permeability during the adsorption process, and the particle size of the activated carbon is optimized, which effectively guarantees the flow rate and permeability of the dialysate during the use of the adsorbent, avoids the adhesion and clogging of the oxidized microcrystalline cellulose particles affecting the adsorption effect, and ensures stable adsorption performance.

[0027] (5) The preparation method of the oxidized microcrystalline cellulose / activated carbon composite adsorbent of the present invention is simple and the process flow is short. The preparation process does not require complex equipment or high-energy consumption processes, has good operability, and is suitable for mass production of artificial kidney adsorption column consumables. At the same time, the preparation cost is low and the source of raw materials is wide. The main raw materials of the present invention are commercial microcrystalline cellulose and medical activated carbon, which are derived from natural renewable resources, are inexpensive, easy to obtain, and the amount of chemical reagents used in the preparation process is small, which has high economy. In addition, the adsorbent has excellent regeneration performance. The modified cellulose-based composite adsorbent of the present invention has stable chemical properties and can be regenerated by simple elution and drying treatment. The adsorption capacity remains stable after multiple cycles of use, which effectively reduces the cost of use and meets the requirements of sustainable development.

[0028] (6) The adsorbent of the present invention has a wide range of applications. It is not only suitable for the removal of urea in dialysate, but can also be expanded to the removal of urea in industrial wastewater and biological samples, achieving efficient purification and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the structure of a composite adsorbent dynamic adsorption device;

[0030] Figure 2 The static adsorption curves of composite adsorbent A and comparative adsorbents (activated carbon, microcrystalline cellulose, oxidized microcrystalline cellulose and mesoporous silica molecular sieve);

[0031] Figure 3 is the static adsorption curve of composite adsorbent B;

[0032] Figure 4 is the static adsorption curve of composite adsorbent C;

[0033] Figure 5 is the static adsorption curve of composite adsorbent D;

[0034] Figure 6 is the static adsorption curve of composite adsorbent E;

[0035] Figure 7 is the difference between the theoretical urea equilibrium adsorption capacity of composite adsorbent A and the experimental value (ΔQ) and the difference between the theoretical urea dynamic removal rate and the experimental value (ΔC);

[0036] Figure 8 is the difference between the theoretical urea equilibrium adsorption capacity of composite adsorbent B and the experimental value (ΔQ) and the difference between the theoretical urea dynamic removal rate and the experimental value (ΔC);

[0037] Fig. 9 is the difference between the theoretical urea equilibrium adsorption capacity of composite adsorbent C and the experimental value (ΔQ) and the difference between the theoretical urea dynamic removal rate and the experimental value (ΔC);

[0038] Fig.10 is the difference between the theoretical urea equilibrium adsorption capacity of composite adsorbent D and the experimental value (ΔQ) and the difference between the theoretical urea dynamic removal rate and the experimental value (ΔC);

[0039] Fig.11 is the difference between the theoretical urea equilibrium adsorption capacity of composite adsorbent E and the experimental value (ΔQ) and the difference between the theoretical urea dynamic removal rate and the experimental value (ΔC). DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below through embodiments in combination with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0041] (I) Sample preparation of composite adsorbent for purifying urea in dialysate

[0042] Example 1

[0043] A composite adsorbent A for purifying urea in dialysate is composed of oxidized microcrystalline cellulose and coconut shell activated carbon in a weight ratio of 1:2.

[0044] The preparation method of the composite adsorbent A for purifying urea in dialysate comprises the following steps:

[0045] S1: Disperse microcrystalline cellulose powder (particle size range: 50-100 μm) in deionized water and stir evenly to obtain a microcrystalline cellulose suspension with a mass percentage concentration of 10%. Subsequently, slowly add sodium periodate solution to the suspension, control the mass ratio of sodium periodate to microcrystalline cellulose to be 1:10, and react at 30°C and slowly stir for 48 hours. After the reaction is completed, add glycerol of 2% of the reaction solution volume to terminate the reaction to obtain an oxidized microcrystalline cellulose suspension, centrifuge the oxidized microcrystalline cellulose suspension, repeatedly wash the precipitate with deionized water, remove excess sodium periodate and reaction by-products, until the pH value of the washing solution is close to neutral, and then freeze-dry the precipitate (-50°C, 10Pa, 12 hours) to constant weight, crush it in a mortar, and pass it through a 40-mesh sieve to remove large particles to obtain oxidized microcrystalline cellulose.

[0046] S2: Place the coconut shell activated carbon powder with a mesh size of 200, an iodine value of 500 mg / g, and high temperature activation (CO2 flow rate of 100 mL / min, 600°C, 2 hours) in a 60°C oven and dry for 6 hours to ensure its dry state. Then add the oxidized microcrystalline cellulose prepared in S1 and the dried coconut shell activated carbon into a V-type mixer at a speed of 60 rpm, mix at room temperature for 30 minutes, and after mixing evenly, pass through a 10-mesh sieve to remove large particles or unmixed lumps, and obtain the composite adsorbent A for purifying urea in the dialysate. Finally, seal the adsorbent and store it in a dry, inert atmosphere.

[0047] Example 2

[0048] A composite adsorbent B for purifying urea in dialysate is composed of oxidized microcrystalline cellulose and sawdust activated carbon in a weight ratio of 2:1.

[0049] The preparation method of the composite adsorbent B for purifying urea in dialysate comprises the following steps:

[0050] S1: Disperse microcrystalline cellulose powder (particle size range: 50-100 μm) in deionized water and stir evenly to obtain a microcrystalline cellulose suspension with a mass percentage concentration of 10%. Subsequently, slowly add sodium periodate solution to the suspension, control the mass ratio of sodium periodate to microcrystalline cellulose to be 1:5, and react at 30°C and slowly stir for 48 hours. After the reaction is completed, add glycerol at 2% of the volume of the reaction solution to terminate the reaction to obtain an oxidized microcrystalline cellulose suspension, centrifuge the oxidized microcrystalline cellulose suspension, repeatedly wash the precipitate with deionized water, remove excess sodium periodate and reaction by-products, until the pH value of the washing solution is close to neutral, and then freeze-dry the precipitate (-50°C, 10Pa, 12 hours) to constant weight, crush it in a mortar, and pass it through a 40-mesh sieve to remove large particles to obtain oxidized microcrystalline cellulose.

[0051] S2: Place the wood chip activated carbon powder with a mesh size of 300, an iodine value of 800 mg / g, and high temperature activation (CO2 flow rate 100 mL / min, 600°C, 3 hours) in a 60°C oven and dry for 6 hours to ensure its dry state. Then add the oxidized microcrystalline cellulose prepared in S1 and the dried wood activated carbon into a V-type mixer at a speed of 60 rpm, mix at room temperature for 30 minutes, and after mixing evenly, pass through a 40-mesh sieve to remove large particles or unmixed lumps, and obtain the composite adsorbent B for purifying urea in the dialysate. Finally, seal the adsorbent and store it in a dry, inert atmosphere.

[0052] Example 3

[0053] A composite adsorbent C for purifying urea in dialysate is composed of oxidized microcrystalline cellulose and fruit shell activated carbon in a weight ratio of 4:1.

[0054] The preparation method of the composite adsorbent C for purifying urea in dialysate comprises the following steps:

[0055] S1: Disperse microcrystalline cellulose powder (particle size range: 50-100 μm) in deionized water and stir evenly to obtain a microcrystalline cellulose suspension with a mass percentage concentration of 10%. Subsequently, slowly add sodium periodate solution to the suspension, control the mass ratio of sodium periodate to microcrystalline cellulose to be 1:2, and react for 35 hours at 25°C and slow stirring. After the reaction is completed, add glycerol with a volume of 2% of the reaction solution to terminate the reaction to obtain an oxidized microcrystalline cellulose suspension, centrifuge the oxidized microcrystalline cellulose suspension, repeatedly wash the precipitate with deionized water, remove excess sodium periodate and reaction by-products, until the pH value of the washing solution is close to neutral, and then vacuum dry the precipitate to constant weight, crush it in a mortar, and pass it through a 40-mesh sieve to remove large particles to obtain oxidized microcrystalline cellulose. .

[0056] S2: Place the fruit shell activated carbon powder with a mesh size of 200, an iodine value of 1000 mg / g and high temperature activation (CO2 flow rate 200 mL / min, 800°C, 2 hours) in a 60°C oven and dry for 6 hours to ensure its dry state. Then add the oxidized microcrystalline cellulose prepared in S1 and the dried fruit shell activated carbon into a three-dimensional mixer at a speed of 50 rpm, mix at room temperature for 45 minutes, and after mixing evenly, pass through a 40-mesh sieve to remove large particles or unmixed lumps, and obtain the composite adsorbent C for purifying urea in the dialysate. Finally, seal the adsorbent and store it in a dry, inert atmosphere.

[0057] Example 4

[0058] A composite adsorbent D for purifying urea in dialysate is composed of oxidized microcrystalline cellulose and coconut shell activated carbon in a weight ratio of 6:1.

[0059] The preparation method of the composite adsorbent D for purifying urea in dialysate comprises the following steps:

[0060] S1: Disperse microcrystalline cellulose powder (particle size range: 20-60 μm) in deionized water and stir evenly to obtain a microcrystalline cellulose suspension with a mass percentage concentration of 10%. Subsequently, slowly add sodium periodate solution to the suspension, control the mass ratio of sodium periodate to microcrystalline cellulose to be 1:1, and react for 35 hours at 25°C and slow stirring. After the reaction is completed, add 2% glycerol by volume of the reaction solution to terminate the reaction to obtain an oxidized microcrystalline cellulose suspension, centrifuge the oxidized microcrystalline cellulose suspension, repeatedly wash the precipitate with deionized water to remove excess sodium periodate and reaction by-products until the pH value of the washing solution is close to neutral, and then vacuum dry the precipitate to constant weight, crush it in a mortar, and pass it through a 40-mesh sieve to remove large particles to obtain oxidized microcrystalline cellulose.

[0061] S2: Place the coconut shell activated carbon powder with a mesh size of 200, an iodine value of 800 mg / g and high temperature activation (CO2 flow rate 200 mL / min, 800°C, 2 hours) in a 60°C oven and dry for 6 hours to ensure that it is fully dehumidified. Then add the oxidized microcrystalline cellulose prepared in S1 and the dried coconut shell activated carbon into a three-dimensional mixer at a speed of 50 rpm and mix at room temperature for 45 minutes. After mixing evenly, pass through a 10-mesh sieve to remove large particles or incompletely mixed lumps, and obtain the composite adsorbent D for purifying urea in the dialysate. Finally, seal the adsorbent and store it in a dry, inert atmosphere.

[0062] Example 5

[0063] A composite adsorbent E for purifying urea in dialysate, which is composed of oxidized microcrystalline cellulose and coconut shell activated carbon in a weight ratio of 6:1.

[0064] The preparation method of the composite adsorbent E for purifying urea in dialysate comprises the following steps:

[0065] S1: Disperse microcrystalline cellulose powder (particle size range: 20-60 μm) in deionized water and stir evenly to obtain a microcrystalline cellulose suspension with a mass percentage concentration of 10%. Subsequently, slowly add sodium periodate solution to the suspension, control the mass ratio of sodium periodate to microcrystalline cellulose to be 2:1, and react for 24 hours at 25°C and slow stirring. After the reaction is completed, add glycerol at a volume of 5% of the reaction solution to terminate the reaction to obtain an oxidized microcrystalline cellulose suspension, centrifuge the oxidized microcrystalline cellulose suspension, repeatedly wash the precipitate with deionized water, remove excess sodium periodate and reaction by-products, until the pH value of the washing solution is close to neutral, and then freeze-dry the precipitate (-50°C, 10Pa, 12 hours) to constant weight, crush it in a mortar, and pass it through a 40-mesh sieve to remove large particles to obtain oxidized microcrystalline cellulose.

[0066] S2: Place the coconut shell activated carbon powder with a mesh size of 300, an iodine value of 800 mg / g and high temperature activation (CO2 flow rate 300 mL / min, 900°C, 1 hour) in a 60°C oven and dry for 4 hours to ensure that it is fully dehumidified. Then add the oxidized microcrystalline cellulose prepared in S1 and the dried coconut shell activated carbon into a V-type mixer at a speed of 50 rpm and mix at room temperature for 45 minutes. After mixing evenly, pass through a 40-mesh sieve to remove large particles or incompletely mixed lumps, and obtain the composite adsorbent E for purifying urea in the dialysate. Finally, seal the adsorbent and store it in a dry, inert atmosphere.

[0067] Comparative Example 1

[0068] A composite adsorbent F for purifying urea in dialysate consists of a molecular sieve and oxidized microcrystalline cellulose in a weight ratio of 6:1.

[0069] The preparation method of the composite adsorbent F for purifying urea in dialysate comprises the following steps:

[0070] S1: The preparation method of oxidized microcrystalline cellulose is the same as the preparation method of oxidized microcrystalline cellulose in step S1 of Example 5.

[0071] S2: molecular sieve SBA-15 mesoporous silica (pore size 6-11 nm, specific surface area 600-800 m 2 / g) powder was placed in an oven at 60°C and dried for 4 hours, and passed through a 40-mesh sieve to remove possible agglomerated particles. Subsequently, the oxidized microcrystalline cellulose prepared by S1 and SBA-15 were added to a V-type mixer at a mass ratio of 6:1, and the equipment speed was 50 rpm, and mixed at room temperature for 45 minutes to ensure that the two were evenly compounded. After mixing, large particles or incompletely mixed lumps were removed by sieving to obtain a composite adsorbent F for purifying urea in dialysate.

[0072] Comparative Example 2

[0073] A coconut shell activated carbon adsorbent is selected from coconut shell activated carbon with a mesh size of 40 and an iodine value of 8000 mg / g and activated at high temperature. Before the adsorption experiment, it is placed in an oven at 60°C for 4 hours and passed through a 40-mesh sieve to remove possible agglomerated particles.

[0074] Comparative Example 3

[0075] A microcrystalline cellulose adsorbent is selected from pharmaceutical grade microcrystalline cellulose in powder form with a polymerization degree of 3000 to 10000. Before the adsorption experiment, the microcrystalline cellulose is sieved with a 40-mesh sieve to remove possible agglomerated particles.

[0076] Comparative Example 4

[0077] The invention discloses an oxidized microcrystalline cellulose adsorbent, which is prepared by oxidizing and modifying microcrystalline cellulose with periodate.

[0078] The method for preparing the above oxidized microcrystalline cellulose adsorbent is the same as step S1 of Example 5, which is the preparation of oxidized microcrystalline cellulose.

[0079] Comparative Example 5

[0080] A molecular sieve adsorbent, using SBA-15 mesoporous silica, pore size 6 to 11 nm, specific surface area 600 to 800 m 2 Before the adsorption experiment, the precipitate was dried in an oven at 60°C for 4 hours and passed through a 40-mesh sieve to remove possible agglomerated particles.

[0081] (II) Evaluation method of urea adsorption effect in dialysate

[0082] Static and dynamic adsorption experiments were used to evaluate the adsorption and removal effects of different composite adsorbents on urea in dialysate, providing indirect and direct references for their application in artificial kidney devices. The specific methods for testing the equilibrium adsorption capacity and dynamic clearance rate of urea are as follows:

[0083] Static method: 1) Use medical dialysate as solvent to prepare simulated dialysate containing urea, with an initial urea concentration (c0) of 38 mM (2.28 mg / mL) to simulate the average urea concentration in the dialysate of uremia patients. 2) Weigh 1.0 g of adsorbent. 3) Add the weighed adsorbent to 100 mL of simulated dialysate, place in a constant temperature oscillator, control the temperature to 37°C, and the oscillation speed to 150 rpm. 4) Take 2 mL of dialysate after a certain time interval t, centrifuge and use ultraviolet spectrophotometry to determine the concentration of residual urea in the supernatant c t . 5) The calculation formula of adsorption amount (Q) is as follows: Q = (c0-c t )×V / m, where V is the volume of the solution (mL) and m is the mass of the adsorbent (g). The equilibrium adsorption capacity (mg / g) of the adsorbent is the amount of urea adsorbed when the adsorption equilibrium is reached.

[0084] Dynamic method: 1) Build a simulated dialysate circulation system, including a peristaltic pump, adsorption column and reagent bottle ( Figure 1 ) to ensure that the dialysate continues to circulate in the system. 2) Weigh 10g of adsorbent and load it into the adsorption column. The filling method is gravity sedimentation filling without applying pressure. 3) Measure 100mL of simulated dialysate with a urea concentration of 38mM, and control the flow rate of the dialysate to 20mL / min to simulate the actual operating conditions in the artificial kidney device. 4) After the dialysate circulates and adsorbs for 3 hours, use ultraviolet spectrophotometry to determine the residual urea concentration in the simulated dialysate, calculate the urea clearance rate, and evaluate the dynamic adsorption effect. Calculate the urea dynamic clearance rate (C e ), the calculation formula is as follows: C e (%) = (c0-c e )×100 / c0. Where c e is the urea concentration in the dialysate after the adsorption cycle.

[0085] The adsorbents prepared in Examples 1 to 5 and Comparative Examples 1 to 5 were evaluated for their urea removal effects in the dialysate using the above-mentioned static and dynamic methods. The equilibrium adsorption amount and urea dynamic removal rate data are shown in Table 1.

[0086] Table 1 Equilibrium adsorption capacity and dynamic removal rate of urea of ​​adsorbents in Examples 1 to 5 and Comparative Examples 1 to 5

[0087]

[0088]

[0089] As shown in Table 1, the urea equilibrium adsorption capacity of coconut shell activated carbon and microcrystalline cellulose is only 32.1 mg / g and 18.0 mg / g, respectively, and the urea equilibrium adsorption capacity of oxidized microcrystalline cellulose is higher than that of unmodified microcrystalline cellulose, which is 65.4 mg / g. The urea dynamic removal rates of coconut shell activated carbon, microcrystalline cellulose and oxidized microcrystalline cellulose are only 18.4%, 8.6% and 28.6%, respectively.

[0090] Static adsorption experiments showed that Figures 2 to 6 From the static adsorption curves of adsorbents A to E, it can be seen that compared with the single-component materials of Comparative Examples 2 to 5, the equilibrium adsorption amount of urea of ​​adsorbents A to E in the dialysate is much higher than that of the single-component materials of Comparative Examples 2 to 5, and the adsorption equilibrium can be reached quickly within 30 minutes. According to Table 1, the static equilibrium adsorption amount of composite adsorbents A to E gradually increases. This is because the increase in the amount of sodium periodate increases the aldehyde content of oxidized microcrystalline cellulose, loosens the cellulose structure, and enhances the static adsorption capacity of the composite system for urea; while composite adsorbent C shows the highest dynamic clearance rate, which may be attributed to the fact that its component ratio optimizes the synergistic effect of oxidized microcrystalline cellulose and fruit shell activated carbon. In addition, the structural density of the adsorbent is moderate, which not only ensures good dialysate permeability, but also enables urea molecules to diffuse quickly and be efficiently adsorbed, thereby showing excellent urea removal performance under dynamic conditions.

[0091] The dynamic adsorption experiment shows that after 3 hours of dynamic cyclic adsorption, the dynamic removal rate of urea of ​​the composite adsorbent composed of oxidized microcrystalline cellulose and activated carbon is also much higher than that of the single-component adsorption material (Comparative Examples 2 to 5). This is because the components in the composite adsorbent material interact with each other and exert a synergistic effect. Specifically, oxidized microcrystalline cellulose can form a strong chemical adsorption with urea molecules, while the pore structure of activated carbon provides more physical adsorption sites, which promotes the diffusion and capture of urea molecules. In addition, the composite material enhances the specific surface area of ​​the adsorbent and avoids the adhesion phenomenon between oxidized cellulose particles, thereby providing more effective adsorption space, making the adsorption process of urea more efficient and rapid. Therefore, adsorbents A to E exhibit higher adsorption capacity and stronger dynamic removal ability, which has a significant performance improvement compared to single-component materials.

[0092] Further, based on Example 5, we changed the activated carbon in the adsorbent to molecular sieve (SBA-15 mesoporous silica) to prepare the composite adsorbent F of Comparative Example 1. After evaluating its urea removal effect in the dialysate by static and dynamic methods, we found that its equilibrium adsorption capacity and urea dynamic removal rate were 63.2 mg / g and 27.2%, respectively. Compared with the equilibrium adsorption capacity of 65.4 mg / g and the urea dynamic removal rate of 28.6% of oxidized microcrystalline cellulose, the composite of the two did not show obvious synergistic adsorption effect. This is because although the SBA-15 molecular sieve has a large specific surface area and a regular pore structure, it lacks effective interfacial interaction with the oxidized microcrystalline cellulose, resulting in the failure to produce obvious synergistic effect.

[0093] SBA-15 molecular sieve mainly relies on physical adsorption mechanism to adsorb urea molecules. The regularity and uniformity of its pore structure make the molecular sieve adsorb urea relatively simple, and most of the adsorption sites can only provide physical adsorption. The surface of oxidized microcrystalline cellulose contains abundant hydroxyl and aldehyde groups. These functional groups can form strong bonds with urea molecules through hydrogen bonds, electrostatic effects or other chemical interactions, but these strong interactions are limited to the oxidized microcrystalline cellulose itself, and the interface between it and SBA-15 lacks similar interactions.

[0094] In the composite system provided by the present invention, rich interfacial interactions can be formed between oxidized microcrystalline cellulose and activated carbon, which enhances the synergistic effect between the two. Activated carbon not only provides more physical adsorption sites through its microporous structure, but also can further improve the adsorption capacity of urea by interacting with the groups on the surface of oxidized microcrystalline cellulose. However, the interaction between SBA-15 and oxidized microcrystalline cellulose is weak, lacking effective interfacial coupling, resulting in the composite material being unable to give full play to the advantages of the two when adsorbing urea, and the adsorption effect is relatively limited. Therefore, composite adsorbent F failed to show obvious synergistic effect, and the urea removal ability was not significantly improved.

[0095] (III) Discussion on the synergistic effect of adsorbents

[0096] Assuming that there is no synergistic or inhibitory effect between activated carbon and oxidized microcrystalline cellulose, the theoretical urea equilibrium adsorption capacity (Q t ) and theoretical urea dynamic clearance rate (C t ):

[0097] Q t =x1×Q1+x2×Q2

[0098] C t =x1×C1+x2×C2

[0099] Where x1 and x2 are the mass percentages of activated carbon and oxidized microcrystalline cellulose, respectively, Q1 and Q2 are the experimental values ​​of the equilibrium adsorption of urea by activated carbon and oxidized microcrystalline cellulose, respectively, and C1 and C2 are the experimental values ​​of the dynamic removal rate of urea by activated carbon and oxidized microcrystalline cellulose, respectively. In Example 1, x1≈33.3%, x2≈66.6%, and the Q of composite adsorbent A can be calculated from the above formula: t =42.8mg / g, C t =21.5%.

[0100] In order to analyze the synergistic adsorption effect of activated carbon and oxidized cellulose components on urea in composite adsorbent A, the difference between the theoretical equilibrium adsorption capacity and the experimental value (ΔQ) and the difference between the theoretical dynamic removal rate and the experimental value (ΔC) of the composite adsorbent were calculated by the following formulas:

[0101] ΔQ=Q e -Q t

[0102] ΔC=C e -C t

[0103] Where Q e and C e are the experimental values ​​of equilibrium adsorption capacity and dynamic removal rate of composite adsorbent A. If ΔQ and ΔC are positive values, it indicates that the composite of activated carbon and oxidized cellulose has a synergistic effect on urea adsorption; if ΔQ and ΔC are negative values, it indicates that the composite of the two has an inhibitory effect on the adsorption of urea. The results are shown in Figure 7 As shown, it can be seen that ΔQ and ΔC are both positive values, indicating that the mixture of oxidized microcrystalline cellulose and coconut shell activated carbon in Example 1 has a significant synergistic promoting effect on urea adsorption.

[0104] The same method was used to calculate the difference between the theoretical equilibrium adsorption capacity and the experimental value (ΔQ) and the difference between the theoretical dynamic removal rate and the experimental value (ΔC) of adsorbents B to E. The results are as follows: Figures 8 to 11 As shown, it can be seen that both ΔQ and ΔC are positive values, which also shows that the mixture of oxidized microcrystalline cellulose and activated carbon in Examples 2 to 5 has a significant synergistic promoting effect on urea adsorption.

[0105] The synergistic effect of the composite of oxidized microcrystalline cellulose and activated carbon on the adsorption of urea in dialysate may be based on the following mechanism: the hydroxyl and aldehyde groups on the surface of oxidized cellulose form strong interactions with urea molecules through hydrogen bonds and chemical bonds, thereby improving the adsorption capacity; activated carbon, with its rich pore structure, provides a high specific surface area and a variety of physical adsorption sites, promoting the rapid diffusion and capture of urea molecules in the adsorption system. At the same time, the composite of activated carbon and oxidized microcrystalline cellulose significantly increases the overall specific surface area, and effectively reduces the adhesion between oxidized microcrystalline cellulose particles through the loosening effect of activated carbon on the overall structure, forming more channels that are conducive to the diffusion of urea molecules. The two materials may have a synergistic effect at the interface, which makes chemical adsorption and physical adsorption enhance each other, thereby significantly improving the comprehensive adsorption performance of the adsorbent for urea.

[0106] The above embodiments are only used to illustrate the technical solution of the present invention, rather than to limit the protection scope of the present invention. Those skilled in the art can modify or replace the technical solution of the present invention according to the idea of ​​the present invention without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A composite adsorbent for purifying urea in dialysate, characterized in that: The invention is composed of oxidized microcrystalline cellulose and activated carbon in a weight ratio of (1-10):(1-2).

2. The composite adsorbent for purifying urea in dialysate according to claim 1, characterized in that: The oxidized microcrystalline cellulose is prepared by oxidizing and modifying microcrystalline cellulose with periodate. The surface aldehyde content of the oxidized microcrystalline cellulose is 5 to 20 mmol / g, and the specific surface area is 50 to 500 m2 / g.

3. The composite adsorbent for purifying urea in dialysate according to claim 1, characterized in that: The activated carbon is any one of coconut shell activated carbon, sawdust activated carbon and fruit shell activated carbon; the iodine value of the activated carbon is 500-1200 mg / g, and the particle size is 200-300 meshes.

4. The method for preparing the composite adsorbent according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1: dispersing microcrystalline cellulose in water and stirring evenly to obtain a microcrystalline cellulose suspension with a mass percentage concentration of 10%, adding sodium periodate solution to carry out oxidation reaction, and after the reaction is completed, adding glycerol to terminate the reaction, and centrifuging, washing, drying, crushing, and sieving the product to obtain oxidized microcrystalline cellulose; S2: The oxidized microcrystalline cellulose prepared in S1 is mixed evenly with activated carbon, and after sieving, a composite adsorbent for purifying urea in the dialysate is obtained.

5. The method for preparing the composite adsorbent according to claim 4, characterized in that: In step S1, the mass ratio of sodium periodate to microcrystalline cellulose is (1-2): (1-10).

6. The method for preparing the composite adsorbent according to claim 4, characterized in that: The oxidation reaction temperature in step S1 is 20 to 35° C., and the reaction time is 12 to 48 hours.

7. The method for preparing the composite adsorbent according to claim 4, characterized in that: The mixing device used in the mixing step in step S2 is a V-shaped mixer or a three-dimensional mixer, the speed of the device is 30 to 60 rpm, and the mixing time is 30 to 60 minutes.

8. The method for preparing the composite adsorbent according to claim 4, characterized in that: Before the activated carbon is mixed with the oxidized microcrystalline cellulose in step S2, the activated carbon needs to be dried at a temperature of 60 to 80° C. for 3 to 6 hours.

9. The method for preparing the composite adsorbent according to claim 4, characterized in that: The mesh size of the sieving process in step S2 is 10 to 40 meshes.

10. Use of the composite adsorbent for purifying urea in dialysate according to any one of claims 1 to 3, characterized in that: The adsorbent is loaded into an adsorption column, which is then connected to a medical dialysate circulation loop for adsorbing and purifying urea in the medical dialysate; the pH value of the medical dialysate is 6.8-7.5, and the temperature is 20-40°C.

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