Melamine modified resin-based activated carbon and preparation method and application thereof

Abstract

The present application relates to melamine modified resin-based activated carbon and its preparation method and application, belong to pressure swing adsorption technical field.The technical problem solved by the present application is to provide a preparation method of melamine modified resin-based activated carbon.The method reacts resorcinol and formaldehyde solution to obtain resorcinol resin solution;Melamine and formaldehyde solution are reacted to obtain melamine resin solution;Then the resorcinol resin solution and the melamine resin solution are mixed uniformly, and the hydrothermal reaction is carried out to obtain melamine modified resorcinol resin;Then the melamine modified resorcinol resin is carbonized in a protective atmosphere to obtain melamine modified resin-based activated carbon.The melamine modified resin-based activated carbon of the present application has the advantages of simple preparation method, good adsorption performance, and can be applied in adsorption separation of methane-nitrogen, excellent CH4 adsorption capacity and separation performance, and the adsorption material can be recycled, low replacement cost and low energy consumption.

Description

TECHNICAL FIELD

[0001] The present application relates to melamine modified resin-based activated carbon and its preparation method and application, and belongs to the technical field of pressure swing adsorption. BACKGROUND

[0002] Methane (CH4) is a typical nonpolar molecule, which is the cleanest energy with the highest H / C ratio and has good chemical inertness. As the main component of natural gas (more than 85 vol%), its combustion heat value is high, which can reach 9510 kcal / Nm 3 . Since the combustion products are only water (H2O), carbon dioxide (CO2) and a small amount of nitrogen oxides (NO x ), natural gas has been considered a relatively clean fossil fuel. In addition, natural gas is also the most important modern industrial raw material. In the process of global carbon-intensive fossil energy turning to cleaner energy, traditional natural gas resources will not be able to meet the demand, and the difficulty of conventional natural gas exploitation will also greatly increase with the rapid consumption of resources. Therefore, unconventional natural gas, due to its abundant resource reserves and wide distribution, is likely to become the most powerful support for the sustainable development of the natural gas industry.

[0003] CH4 is the second largest greenhouse gas after CO2, and its global warming potential is 28 times that of CO2 in 100 years. Low-concentration methane (<30% CH4) in unconventional natural gas (such as coal mine ventilation) is usually burned or discharged. Therefore, energy waste and environmental pollution problems are caused. Therefore, CH4 is not only an important low-carbon clean energy connecting fossil resources and future sustainable energy, but also a worrying climate change pollutant. Therefore, it is of great significance to find an efficient CH4 enrichment technology for the utilization of unconventional natural gas and the recovery of CH4-containing tail gas in industry, and to overcome the shortage of natural gas. More importantly, it is of great significance to find an economical and effective CH4 emission reduction method for rebalancing atmospheric CH4 circulation and slowing down the rise of global average temperature. In the above purification of CH4 resources, efficient separation of CH4-N2 is one of the key problems for realizing low-quality CH4 enrichment and CH4 recovery.

[0004] At present, the high-efficiency separation technologies of CH4-N2 mixture include cryogenic rectification, adsorption, absorption, hydrate separation and membrane separation. Among them, pressure swing adsorption (PSA) is a new type of gas adsorption separation technology, which has the advantages of high product purity, general operation at room temperature and low pressure, no heating during bed regeneration, high product purity, simple equipment, easy operation and maintenance, continuous cycle operation, complete automation and good economy. In the pressure swing adsorption process, the development of adsorbent is very important and cannot be bypassed. CH4 and N2 have similar physical and chemical properties. Except for the different critical temperatures, CH4 and N2 have similar kinetic diameters, polarizabilities and quadrupole moments, and both of them are nonpolar molecules without dipole moment. This leads to the challenge of their separation. The enhancement of the adsorbent affects their adsorption in a similar way. However, the slight difference in their kinetic diameters (0.36 and 0.38 nm for N2 and CH4, respectively) makes CH4 more polarizable. CH4 has a relatively high capacity and sufficient selectivity on common adsorbents such as activated carbon (AC). Compared with N2, CH4 shows stronger interaction with AC, so its adsorption capacity is higher than that of N2. The weak gas-solid interaction force formed by the adsorption of CH4 and N2 on AC makes the adsorbent easy to regenerate, and the excellent water vapor resistance and low price of AC greatly reduce the cost of the adsorbent. However, pure AC has low CH4 adsorption capacity and separation performance. SUMMARY

[0005] In view of the above defects, the technical problem solved by the present application is to provide an AC adsorbent with excellent CH4 adsorption capacity and separation performance, namely a melamine modified resin based activated carbon and a preparation method thereof.

[0006] The preparation method of the melamine modified resin based activated carbon of the present application comprises the following steps:

[0007] a. Preparation of resorcinol resin: mixing and reacting an ammonium ion containing basic compound, resorcinol, formaldehyde solution and solvent to obtain a resorcinol resin solution;

[0008] b. Preparation of melamine resin: mixing and reacting an ammonium ion containing basic compound, melamine, formaldehyde solution and solvent to obtain a melamine resin solution;

[0009] c. Hydrothermal reaction: uniformly mixing the resorcinol resin solution obtained in step a and the melamine resin solution obtained in step b, and reacting at a constant temperature of 100-140℃ for 20-30h, and then taking the solid after cooling to obtain a melamine modified resorcinol resin;

[0010] d. Carbonization: under a protective atmosphere, the melamine modified resorcinol resin obtained in step c is heated to 180-220℃ and kept for 1-3h, then heated to 700-900℃ and kept for 3-5h, and cooled to obtain the melamine modified resin based activated carbon.

[0011] In some embodiments of the present application, the ratio of resorcinol to formaldehyde solution in step a is 4-6g:8mL, and the ratio of melamine to formaldehyde solution in step b is 0.5-2g:4mL. Preferably, the ratio of resorcinol to formaldehyde solution in step a is 5g:8mL, and the ratio of melamine to formaldehyde solution in step b is 1g:4mL.

[0012] In one specific embodiment, the basic compound containing ammonium ion in the present application is ammonia, ammonium carbonate or ammonium phosphate. In one specific example, the basic compound containing ammonium ion is ammonia.

[0013] In some embodiments of the present application, the solvent in steps a and b is an aqueous solution of ethanol, wherein the volume ratio of ethanol to water is 2-3:4-5.

[0014] In some embodiments of the present application, the volume ratio of ammonia, solvent and formaldehyde solution in step a is 0.3-0.5:70-90:8, and the volume ratio of ammonia, solvent and formaldehyde solution in step b is 0.05-0.2:30-40:4. Preferably, the volume ratio of ammonia, solvent and formaldehyde solution in step a is 0.4:80:8, and the volume ratio of ammonia, solvent and formaldehyde solution in step b is 0.2:32:4.

[0015] In one embodiment of the present application, the mass ratio of melamine in step b to resorcinol in step a is 0.1-0.4 when mixed in step c. In one specific example, the mass ratio of melamine in step b to resorcinol in step a is 0.2 when mixed in step c.

[0016] In one specific example of the present application, the reaction is carried out at a constant temperature of 120℃ for 24h in step c, and the temperature is raised to 200℃ for 2h and then to 800℃ for 4h in step d.

[0017] In one embodiment of the present application, the heating rate is 0.5-2℃ / min and the cooling rate is 3-10℃ / min in step d. Preferably, the heating rate is 1℃ / min and the cooling rate is 5℃ / min.

[0018] The present application also provides a melamine modified resin based activated carbon prepared by the method for preparing the melamine modified resin based activated carbon according to the present application.

[0019] The melamine modified resin-based activated carbon has good pore structure and pore size distribution, so that the adsorption and separation performance of methane and nitrogen is changed.

[0020] The application also provides application of the melamine modified resin-based activated carbon in adsorption and separation of methane-nitrogen.

[0021] The melamine modified resin-based activated carbon can be applied in adsorption and separation of methane-nitrogen, and has excellent CH4 adsorption capacity and separation performance.

[0022] Compared with the prior art, the melamine modified resin-based activated carbon has the following beneficial effects:

[0023] The melamine modified resin-based activated carbon has the advantages of simple preparation method, good adsorption performance, excellent CH4 adsorption capacity and separation performance, recyclable adsorption material, low replacement cost and low energy consumption. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The figure is a schematic diagram of an adsorption performance evaluation test device of the application. In the figure, 1 is a He gas inlet end, 2 is a CH4 gas inlet end, 3 is an N2 gas inlet end, 4 is a pressure transmitter, 5 is a reference tank, 6 is an adsorption tank, 7 is a constant-temperature water bath tank, 8 is a vacuum control end, 9 is a needle-type regulating valve, and 10 is an electromagnetic valve.

[0025] Figure 2 The figure is N2 adsorption / desorption isotherms and pore size distribution curves of products of examples and comparative examples. In the figure, (a) is an N2 adsorption / desorption isotherm, and (b) is a pore size distribution curve.

[0026] Figure 3 The figure is methane adsorption isotherms and nitrogen adsorption isotherms of products of examples and comparative examples. In the figure, (a) is a methane adsorption isotherm, and (b) is a nitrogen adsorption isotherm.

[0027] Figure 4 The figure is methane / nitrogen adsorption and separation ratios of products of examples and comparative examples.

[0028] Figure 5 The figure is adsorption kinetics curves of methane and nitrogen on products of examples and comparative examples. In the figure, the initial pressure is 0.85 MPa, and the temperature is 303 K. (a) is an adsorption kinetics curve of methane, and (b) is an adsorption kinetics curve of nitrogen. DETAILED DESCRIPTION

[0029] The preparation method of the melamine modified resin-based activated carbon comprises the following steps:

[0030] a. Preparation of resorcinol resin: A basic compound containing ammonium ions, resorcinol, formaldehyde solution and solvent are mixed and reacted to obtain a resorcinol resin solution;

[0031] b. Preparation of melamine resin: A basic compound containing ammonium ions, melamine, formaldehyde solution and solvent are mixed and reacted to obtain a melamine resin solution;

[0032] c. Hydrothermal reaction: The resorcinol resin solution obtained in step a and the melamine resin solution obtained in step b are mixed evenly and reacted at a constant temperature of 100-140℃ for 20-30 hours. After cooling, the solid is taken to obtain melamine-modified resorcinol resin.

[0033] d. Carbonization: Under a protective atmosphere, the melamine-modified resorcinol resin obtained in step c is heated to 180-220℃ and held for 1-3 hours, then heated to 700-900℃ and held for 3-5 hours, and then cooled to obtain melamine-modified resin-based activated carbon.

[0034] The formaldehyde content of the formaldehyde solution described in this invention is 35% to 40%.

[0035] Step a involves preparing resorcinol resin by reacting formaldehyde with resorcinol to obtain resorcinol resin RF. This reaction can be carried out at room temperature.

[0036] The ratio of resorcinol to formaldehyde is a common ratio for phenolic resins. In some embodiments of the present invention, in step a, the ratio of resorcinol to formaldehyde solution is 4-6 g: 8 mL. In a specific embodiment, the ratio of resorcinol to formaldehyde solution is 5.00 g: 8 mL.

[0037] In one specific embodiment, ammonia and solvent are first mixed, then resorcinol is added and stirred at 20–40°C for 1–3 hours, followed by the addition of formaldehyde and stirring for another 5–7 hours to obtain RF. In another specific embodiment, ammonia and solvent are first mixed, then resorcinol is added and stirred at 30°C for 2 hours, followed by the addition of formaldehyde and stirring for another 6 hours to obtain RF.

[0038] In step a, the alkaline compound containing ammonium ions is a conventional alkaline catalyst in the art. In one specific embodiment, the alkaline compound containing ammonium ions described in this invention is ammonia, ammonium carbonate, or ammonium phosphate. In one specific embodiment, the alkaline compound containing ammonium ions is ammonia. Its dosage can be the conventional dosage in the art.

[0039] In some embodiments of the present invention, in step a, the solvent used is an aqueous solution of ethanol, wherein the volume ratio of ethanol to water is 2-3:4-5.

[0040] In some embodiments of the present application, the volume ratio of the ammonia, the solvent and the formaldehyde solution in step a is 0.3-0.5:70-90:8. Preferably, the volume ratio of the ammonia, the solvent and the formaldehyde solution is 0.4:80:8.

[0041] Step b is to prepare the melamine resin. The melamine reacts with the formaldehyde under the action of the catalyst to obtain the melamine resin MF.

[0042] In some embodiments of the present application, the ratio of the melamine and the formaldehyde solution in step b is 0.5-2 g:4 mL. In a specific embodiment, the ratio of the melamine and the formaldehyde solution in step b is 1 g:4 mL.

[0043] In a specific embodiment, the ammonia, the solvent are mixed first, then the melamine and the formaldehyde are added, and the solution is continuously stirred at 50-70℃ until the solution is clear, and then cooled to obtain the MF. In a specific embodiment, the solution is continuously stirred at 60℃ until the solution is clear.

[0044] In step b, the basic catalyst is still the basic compound containing the ammonium ion, and the amount thereof can be the conventional amount in the art.

[0045] In some embodiments of the present application, the solvent in step b is the aqueous solution of ethanol, wherein the volume ratio of the ethanol and the water is 2-3:4-5.

[0046] In some embodiments of the present application, the volume ratio of the ammonia, the solvent and the formaldehyde solution in step b is 0.05-0.2:30-40:4. In a specific embodiment, the volume ratio of the ammonia, the solvent and the formaldehyde solution in step b is 0.2:32:4.

[0047] The steps a and b of the present application have no time sequence. Step a can be performed first, then step b, or step b can be performed first, then step a, or steps a and b can be performed simultaneously.

[0048] Step c is to mix the MF and the RF, and to perform the hydrothermal reaction to obtain the melamine modified resorcinol resin (MRF).

[0049] In an embodiment of the present application, the melamine in step b and the resorcinol in step a are mixed according to the mass ratio of 0.1-0.4. That is, the mixing ratio of the melamine resin and the resorcinol resin is calculated according to the raw materials thereof, so as to ensure that the mass ratio of the melamine in the raw materials of the melamine resin to the resorcinol in the raw materials of the resorcinol resin is 0.1-0.4. In a specific embodiment, the melamine in step b and the resorcinol in step a are mixed according to the mass ratio of 0.2.

[0050] In some embodiments of the present application, the mixing is preferably accompanied by stirring, and the stirring time is 1 h.

[0051] In one specific embodiment of the present application, the hydrothermal reaction is carried out at a constant temperature of 120℃ for 24 h.

[0052] The d step is carbonization. The melamine-modified resorcinol resin obtained in the c step is heated to 180-220℃ under a protective atmosphere, and then heated to 700-900℃ for 3-5 h, and then cooled to obtain the product.

[0053] The protective atmosphere described in the present application is an atmosphere that does not participate in the reaction, and includes but is not limited to a nitrogen atmosphere or an inert atmosphere.

[0054] In one specific embodiment, in the d step, the temperature is raised to 200℃ for 2 h, and then raised to 800℃ for 4 h.

[0055] In some embodiments, in the d step, the heating rate is 0.5-2℃ / min, and the cooling rate is 3-10℃ / min; preferably, the heating rate is 1℃ / min, and the cooling rate is 5℃ / min.

[0056] The melamine-modified resin-based activated carbon of the present application is prepared by the above method, and has a good pore structure and pore size distribution, thereby changing its adsorption and separation performance for methane and nitrogen.

[0057] The melamine-modified resin-based activated carbon of the present application can be used in the adsorption and separation of methane-nitrogen, and has excellent CH4 adsorption capacity and separation performance.

[0058] The specific embodiments of the present application are further described below in conjunction with examples, and the present application is not limited in the scope of the described examples. The chemical reagents used in the examples are: formaldehyde (AR, 37wt%, Chengdu Kolon Chemical Co., Ltd.), resorcinol (AR, ≥99.5wt%, Chengdu Kolon Chemical Co., Ltd.), melamine (AR, 99wt%, Shanghai Titan Science and Technology Co., Ltd.), ammonia water (AR, 25wt%, Chengdu Kolon Chemical Co., Ltd.), ethanol (AR, Chengdu Jinshan Chemical Reagent Co., Ltd.), deionized water. The protective gas used for carbonization is nitrogen gas (99.99%) provided by Southwest Chemical Engineering Design Institute. The methane (99.99%), nitrogen (99.99%) and helium (99.999%) used for adsorption performance testing are all provided by Southwest Chemical Engineering Design Institute.

[0059] Example 1

[0060] The melamine-modified resin-based activated carbon is prepared by the following method:

[0061] a. Preparation of Resorcinol Resin (RF): 0.4 mL of ammonia, 30 mL of absolute ethanol, 50 mL of deionized water were mixed uniformly, then 5.00 g of resorcinol was added and stirred at 30 °C for 2 h, then 8 mL of formaldehyde solution was added and stirred for 6 h to obtain RF.

[0062] b. Preparation of Melamine Resin (MF): 0.2 mL of ammonia, 12 mL of ethanol, 20 mL of deionized water were added with 0.5 g of melamine and 4 mL of formaldehyde solution, continuously stirred at 60 °C until the solution was clear, cooled to 30 °C to obtain MF.

[0063] c. Hydrothermal reaction: The obtained MF was mixed with RF and stirred for 1 h, then moved into a hydrothermal kettle and reacted at a constant temperature of 120 °C for 24 h, cooled to room temperature, and the product was centrifuged to obtain a solid product, melamine modified resorcinol resin (MRF n ).

[0064] d. Carbonization: MRF n was heated to 200 °C at a heating rate of 1 ° / min under N2 atmosphere, kept for 2 h, then heated to 800 °C at the same heating rate, kept for 4 h, then decreased to room temperature at a heating rate of -5 ° / min to obtain carbonized melamine resorcinol resin, denoted as MRF-AC1, and dried in a 120 °C oven for 12 h.

[0065] Example 2

[0066] The melamine modified resin-based activated carbon was prepared according to the following method:

[0067] a. Preparation of Resorcinol Resin (RF): 0.4 mL of ammonia, 30 mL of absolute ethanol, 50 mL of deionized water were mixed uniformly, then 5.00 g of resorcinol was added and stirred at 30 °C for 2 h, then 8 mL of formaldehyde solution was added and stirred for 6 h to obtain RF.

[0068] b. Preparation of Melamine Resin (MF): 0.2 mL of ammonia, 12 mL of ethanol, 20 mL of deionized water were added with 1 g of melamine and 4 mL of formaldehyde solution, continuously stirred at 60 °C until the solution was clear, cooled to 30 °C to obtain MF.

[0069] c. Hydrothermal reaction: The obtained MF was mixed with RF and stirred for 1 h, then moved into a hydrothermal kettle and reacted at a constant temperature of 120 °C for 24 h, cooled to room temperature, and the product was centrifuged to obtain a solid product, melamine modified resorcinol resin (MRF n ).

[0070] d. Carbonization: MRF nThe temperature was raised to 200 °C at a rate of 1 ° / min under N2atmosphere, and held for 2 h, then raised to 800 °C at the same rate, and held for 4 h, and then decreased to room temperature at a rate of -5 ° / min, to obtain carbonized melamine resorcinol resin, noted MRF-AC2, which was dried in an oven at 120 °C for 12 h.

[0071] Example 3

[0072] A melamine modified resin based activated carbon was prepared according to the following method:

[0073] a. Preparation of resorcinol resin (RF): 0.4 mL of ammonia, 30 mL of absolute ethanol, 50 mL of deionized water were mixed homogeneously, then 5.00 g of resorcinol was added and stirred at 30 °C for 2 h, then 8 mL of formaldehyde solution was added and stirred for 6 h to obtain RF.

[0074] b. Preparation of melamine resin (MF): 0.2 mL of ammonia, 12 mL of ethanol, 20 mL of deionized water were mixed, then 1.5 g of melamine and 4 mL of formaldehyde solution were added, and the solution was continuously stirred at 60 °C until it was clear, then cooled to 30 °C to obtain MF.

[0075] c. Hydrothermal reaction: the obtained MF and RF were mixed and stirred for 1 h, then transferred into a hydrothermal kettle and reacted at a constant temperature of 120 °C for 24 h, then cooled to room temperature, and the product was centrifuged to obtain a solid product, melamine modified resorcinol resin (MRF n ).

[0076] d. Carbonization: the MRF n The temperature was raised to 200 °C at a rate of 1 ° / min under N2atmosphere, and held for 2 h, then raised to 800 °C at the same rate, and held for 4 h, and then decreased to room temperature at a rate of -5 ° / min, to obtain carbonized melamine resorcinol resin, noted MRF-AC2, which was dried in an oven at 120 °C for 12 h.

[0077] Example 4

[0078] A melamine modified resin based activated carbon was prepared according to the following method:

[0079] a. Preparation of resorcinol resin (RF): 0.4 mL of ammonia, 30 mL of absolute ethanol, 50 mL of deionized water were mixed homogeneously, then 5.00 g of resorcinol was added and stirred at 30 °C for 2 h, then 8 mL of formaldehyde solution was added and stirred for 6 h to obtain RF.

[0080] b. Preparation of melamine resin (MF): To 0.2 mL of ammonia water, 12 mL of ethanol, 20 mL of deionized water, 2 g of melamine and 4 mL of formaldehyde solution were added, continuously stirred at 60 °C until the solution was clear, cooled to 30 °C, to obtain MF.

[0081] c. Hydrothermal reaction: The obtained MF was mixed with RF and stirred for 1 h, then moved into a hydrothermal kettle to react at a constant temperature of 120 °C for 24 h, cooled to room temperature, and the product was centrifuged to obtain the solid product melamine modified resorcinol resin (MRF n ).

[0082] d. Carbonization: The MRF n was heated to 200 °C at a heating rate of 1 ° / min under N2atmosphere, kept for 2 h, then heated to 800 °C at the same heating rate, kept for 4 h, and then decreased to room temperature at a heating rate of -5 ° / min, to obtain carbonized melamine resorcinol resin, denoted as MRF-AC4, which was dried in a 120 °C oven for 12 h.

[0083] Comparative Example 1

[0084] The modified resin-based activated carbon was prepared according to the following method:

[0085] a. Preparation of resorcinol resin (RF): 0.4 mL of ammonia water, 30 mL of anhydrous ethanol, 50 mL of deionized water were uniformly mixed, then 5.00 g of resorcinol was added and stirred at 30 °C for 2 h, then 8 mL of formaldehyde solution was added and stirred for 6 h to obtain RF.

[0086] b. Preparation of melamine resin (MF): To 0.2 mL of ammonia water, 12 mL of ethanol, 20 mL of deionized water, 0 g of melamine and 4 mL of formaldehyde solution were added, continuously stirred at 60 °C until the solution was clear, cooled to 30 °C, to obtain MF.

[0087] c. Hydrothermal reaction: The obtained MF was mixed with RF and stirred for 1 h, then moved into a hydrothermal kettle to react at a constant temperature of 120 °C for 24 h, cooled to room temperature, and the product was centrifuged to obtain the solid product melamine modified resorcinol resin (MRF n ).

[0088] d. Carbonization: The MRF n was heated to 200 °C at a heating rate of 1 ° / min under N2atmosphere, kept for 2 h, then heated to 800 °C at the same heating rate, kept for 4 h, and then decreased to room temperature at a heating rate of -5 ° / min, to obtain carbonized melamine resorcinol resin, denoted as MRF-AC0, which was dried in a 120 °C oven for 12 h.

[0089] Test Example

[0090] The adsorbent performance of the products of Examples 1-4 and Comparative Example 1 (collectively referred to as MRF-ACn) was evaluated.

[0091] 1. Test device:

[0092] The test used a self-made gas adsorption measuring device, and the amount of gas adsorbed by the adsorbent was measured by the volumetric method, which is one of the most widely used techniques worldwide, simple and efficient. The device is based on the volumetric method and studies the adsorption behavior of a given pressure gas under constant temperature conditions.

[0093] As shown in the schematic Figure 1 , the device mainly consists of four parts: the gas inlet end, the measurement end, the vacuum end, and the control end.

[0094] The raw gas flow is controlled by the needle-type regulating valve 9 and the solenoid valve 10, so that the pressure in the system can be slowly adjusted as needed and will not cause a huge impact on the system when the required pressure of the system is reached. The measurement end is in a constant temperature control area, mainly composed of a reference tank 5, an adsorption tank 6, a pressure transmitter 4, and a constant temperature water bath 7. The pressure values before and after the adsorbent is adsorbed are read by the pressure transmitter 4, and the P-V-T balance relationship is established by the gas state equation, so that the gas adsorption amount n of the adsorbent with a mass of m under a fixed temperature (T) and different adsorption pressures (P) is obtained. The balance relationship is represented by equation (1):

[0095] n / m = f(p) T (1)

[0096] 2. Adsorption parameter calculation method

[0097] (1) Adsorption isotherm

[0098] The adsorption isotherm is the relationship curve between the adsorbate capacity in the adsorbent and the corresponding equilibrium pressure when the gas-phase adsorbate diffuses into the solid-phase adsorbent to reach adsorption equilibrium state at a specific temperature under different pressures. Its relationship can be represented by equation (2). It describes the adsorption capacity and selectivity of the adsorbent to the target gas component under different pressures.

[0099] Q = f(p) T (2)

[0100] Mozaffari Majd et al. described various models of adsorption isotherms in detail. The model used in this study is the LF model, which is a relatively simple adsorption model with fewer parameters. Since the LF model is a hybrid model of the Langmuir model and the Freundlich model, it has certain applicability under different conditions.

[0101]

[0102] The LF equation for fitting the adsorption isotherm is shown in equation (3):

[0103] where Q i is the adsorption amount of component i, Q m，i is the saturated adsorption amount of component i, B is the Langmuir equilibrium constant, p represents the adsorption equilibrium pressure, and n i is the heterogeneity constant of component i, and when n = 1, the adsorption type becomes Langmuir monolayer adsorption.

[0104] (2) Adsorption kinetics

[0105] Adsorption kinetics studies the mass transfer process between the adsorbate and the adsorption sites on the surface of the adsorbent during the adsorption process. It reflects the adsorption rate of the adsorbate on the surface of the adsorbent. Understanding the mass transfer process and kinetic characteristics between the adsorbate and the adsorbent helps to improve the efficiency of the adsorption process and optimize the design of the adsorbent.

[0106] The pseudo-second-order kinetics model (PSO) model is widely used to describe the adsorption kinetics under non-equilibrium conditions. This model assumes that the adsorption process follows second-order reaction kinetics, i.e., the adsorption rate is proportional to the square of the fraction of occupied adsorption sites. The PSO model was first used to simulate the adsorption of lead on peat. Subsequently, the PSO model was widely used to describe the adsorption process of adsorbates from the gas or liquid phase onto the surface of solid adsorbents. A large number of published papers used the PSO model to fit the adsorption kinetic data and calculate the adsorption rate constant. In this study, the PSO model was used to fit the CH4-N2 kinetic data, and the PSO equation is as follows:

[0107]

[0108] The boundary conditions are:

[0109] t = 0, Q t = 0 (5)

[0110] t = t, Q t = Q e (6)

[0111] where Q t is the gas adsorption capacity at time t (mL.g -1 ), k l is the adsorption rate constant (g.mL -1 .s -1 ), and Q e is the equilibrium gas adsorption amount.

[0112] The integral simplification gives the change equation:

[0113]

[0114] The experimental data of the test were used to calculate x = Q t / Q e The data were fitted by changing formula (7) to obtain the commonly used kinetic parameters k l and Q e .

[0115] (3) Adsorption separation ratio

[0116] The adsorption separation ratio is an important parameter that describes the relative adsorption capacity or adsorption performance of two or more components on the adsorbent in the adsorption process. It is widely used in adsorption separation technology to evaluate and compare the adsorption behavior between different components, thereby guiding the design and optimization of the separation process.

[0117] The adsorption separation ratio reflects the selectivity of the adsorbent to the adsorbed substance, and is usually represented by α i，j = (x i / y j ) / (x j / y i ). In this experiment, pure components were used to study the performance of the adsorbent, so y i = y j = 1, and the separation ratio expression becomes:

[0118]

[0119] where x and y represent the molar fraction of the adsorption phase and the feed gas components, respectively, and Q represents the gas adsorption capacity at a certain temperature and pressure.

[0120] 3. Adsorption performance analysis

[0121] (1) Pore structure analysis

[0122] The specific surface area, pore volume, and average pore size parameters of the products MRF-ACn of Examples 1-4 and Comparative Example 1 were determined, and the results are shown in Table 1.

[0123] Table 1

[0124] Sample Specific surface area / (m 2 ·g -1 )]]> cm 3 ·g -1 )]]> Average pore size / (nm) MRF-AC0 522.6137 0.2198 1.68 MRF-AC1 545.8848 0.2344 1.72 MRF-AC2 597.9754 0.2570 1.72 MRF-AC3 567.1694 0.2105 1.78 MRF-AC4 531.9157 0.2148 1.74

[0125] It can be seen that compared with the adsorbent material without adding melamine, the specific surface area and average pore size of the adsorbent material after adding melamine have increased to different degrees, and the specific surface area increases first and then decreases with the increase of the proportion of melamine. When the ratio of melamine to resorcinol is 0.2, the specific surface area reaches a maximum of 597.9 m 2 ·g -1The pore volume of the adsorbent material also reached the maximum at this time, which was 0.257 cm 3 ·g -1 This shows that the introduction of different concentrations of melamine adjusts the pore structure of the adsorbent material to different degrees.

[0126] The N2adsorption-desorption isotherms of the products MRF-ACn of Examples 1-4 and Comparative Example 1 were determined, and the results are shown in Figure Figure 2 (a), the pore size distribution curves thereof were determined, and the results are shown in Figure Figure 2 (b).

[0127] According to the IUPAC classification, all the isotherms are type I isotherms. This type of isotherm indicates that the adsorption sites on the surface of the adsorbent material are rapidly occupied at low concentrations or low pressures, but as the adsorption sites are saturated, the adsorption rate gradually decreases, and finally reaches adsorption equilibrium. The sharp increase in N2adsorption at very low relative pressures indicates that there are abundant micropores in several adsorbent materials. Since MRF-AC2 has a higher specific surface area, pore volume, and especially a developed micropore, the N2adsorption-desorption isotherm of MRF-AC2 is obviously higher than that of the other several materials. From Figure Figure 2 (b), it can be seen that compared with other adsorbent materials, sample MRF-AC2 has more micropores, with seven peaks at 0.5, 0.6, 0.7, 0.85, 1.2, 1.4, and 1.6 nm, combined with Figure Figure 2 (a), it indicates that the pore size distribution at these positions is conducive to the physical adsorption of N2by MRF-AC2.

[0128] (2) Static adsorption performance

[0129] The adsorbent material needs to be dried in a constant temperature drying box at 120°C for 6h before each time the adsorption amount of CH4and N2is tested by pressure swing adsorption experiment, so as to reduce the interference of residual gas in the adsorbent material on the experimental results. When testing the static adsorption performance of MRF-AC n with different concentrations of melamine, 1.00g of adsorbent material was weighed each time for testing in the adsorption tank. The capacity method was used to determine the adsorption performance of CH4and N2of the five adsorbent materials at 303K, 0-0.70MPa.

[0130] Figure 3 MRF-AC nThe adsorption isotherm data were fitted with the LF model, and the related parameters are listed in Table 2. It can be seen that the LF model can be well applied to the adsorption equilibrium data of CH4 and N2 on the several adsorbents. The isotherms all show the same trend, i.e., the adsorption capacity of CH4 and N2 on the adsorbents increases with the increase of pressure. With the increase of the ratio of melamine to resorcinol (M / R), the adsorption capacity of CH4 and N2 shows a trend of first increasing and then decreasing, and the increasing rate of CH4 is obviously higher than that of N2, which indicates that, compared with CH4, N2 is closer to Langmuir monolayer adsorption on MRF-AC n The maximum adsorption capacity of CH4 and N2 is reached at M / R = 0.2, i.e., MRF-AC2 sample, and is 45.20 and 22.23 mL.g -1 -1, respectively, which is increased by 32.8% and 7.5% compared with MRF-AC0 without melamine. The difference in the adsorption capacity of CH4 and N2 among the different samples is mainly due to the difference in the specific surface area and pore volume, and especially the micropore volume is the main factor controlling the physical adsorption of CH4 and N2 on the porous carbon materials. This is consistent with the fact that the specific surface area and pore volume of MRF-AC2 are the largest in the pore structure parameters in Table 1.

[0131] Figure 4 The adsorption separation ratio of CH4 and N2 on MRF-AC n at 303 K. It can be seen that the separation ratio of MRF-AC2 is obviously better than that of the other samples at 0-0.8 MPa, and the highest adsorption separation ratio of CH4 and N2 reaches 5.46 at the micro-positive pressure (0.1-0.2 MPa), which indicates that Figure 2 The seven peaks of MRF-AC2 distributed at 0.5, 0.6, 0.7, 0.85, 1.2, 1.4 and 1.6 nm are not only beneficial to the adsorption of CH4 and N2, but also beneficial to the adsorption separation of CH4 and N2.

[0132] Table 2

[0133]

[0134] Table 2 is the related parameters of the adsorption equilibrium data of CH4 and N2 on MRF-AC n at 303 K fitted with the LF model. It can be seen that R 2 is greater than 0.99, which indicates that the LF model can be well fitted with the adsorption equilibrium data of CH4 and N2 on MRF-AC n . The maximum adsorption capacity of CH4 and N2 on MRF-AC2 is obviously higher than that on the other samples, and the heterogeneity constant n of N2 is closer to 1, so it is closer to Langmuir monolayer adsorption, which is consistent with the above results.

[0135] (3) Adsorption kinetics

[0136] The PSO model was used to fit the adsorption kinetic data of several different adsorbents, and the fitting results are shown in Table 3. Figure 5 It can be seen that at 303 K, N2 reached 90% of the saturated adsorption capacity on several adsorbents in 20 s, while CH4 needed 50 s. The initial apparent adsorption rate of N2 on several adsorbents was higher than that of CH4, which was due to the kinetic diameters of CH4 and N2 being and The kinetic diameter of CH4 was larger than that of N2, so N2 showed a faster adsorption rate at the beginning. In addition, CH4 reached adsorption equilibrium at 350 s, and the adsorption equilibrium time of N2 was about 700 s, CH4 reached adsorption equilibrium faster than N2, which indicated that the diffused CH4 was more easily combined with the adsorbent than N2, because CH4 had a larger molecular polarizability than N2, so it was more easily adsorbed by MRF-AC n materials. It can also be seen that the kinetic curves of CH4 and N2 of MRF-AC2 had faster adsorption rates and equilibrium times than the other several adsorbents, which indicated that the larger specific surface area and hierarchical pore structure of MRF-AC2 were more conducive to the adsorption of CH4 and N2.

[0137] Table 3

[0138]

[0139] Table 3 shows the PSO model fitting parameters of the adsorption kinetic curves of CH4 and N2 on several adsorbents. It can be seen that R 2 is greater than 0.97, indicating that the PSO model can be well applied to the CH4 and N2 kinetic data of several adsorbents. In general, N2 has a larger adsorption rate constant k l , and among several different adsorbents, MRF-AC2 has larger CH4 and N2 adsorption rate constants, indicating that the adsorption rate of N2 is greater than that of CH4 and MRF-AC2 has a faster adsorption rate than the other adsorbents.

[0140] It can be seen that the melamine modified resin based activated carbon of the present application has good adsorption performance and can be applied in the separation of nitrogen and methane, especially MRF-AC2, i.e. when M / R = 0.2, the adsorption capacity of CH4 and N2 reaches the maximum, which is 45.20 and 22.23 mL.g -1 , respectively. Under micro-positive pressure (0.1-0.2 MPa), the adsorption separation ratio of CH4 and N2 is as high as 5.46.

Claims

1. A method for producing a melamine-modified resin-based activated carbon, characterized by, The steps are: a. Preparation of resorcinol resin: mixing and reacting an ammonium-containing basic compound, resorcinol, formaldehyde solution and solvent to obtain a resorcinol resin solution; b. Preparation of melamine resin: mixing and reacting an ammonium-containing basic compound, melamine, formaldehyde solution and solvent to obtain a melamine resin solution; c. Hydrothermal reaction: mixing and uniformly mixing the resorcinol resin solution obtained in step a and the melamine resin solution obtained in step b, and reacting at a constant temperature of 100-140 ℃ for 20-30 h, and then taking the solid after cooling to obtain a melamine-modified resorcinol resin; in step c, the mass ratio of melamine in step b to resorcinol in step a is 0.1-0.4; d. Carbonization: under a protective atmosphere, heating the melamine-modified resorcinol resin obtained in step c to 180-220 ℃, maintaining the temperature for 1-3 h, then heating to 700-900 ℃, maintaining the temperature for 3-5 h, and cooling to obtain a melamine-modified resin-based activated carbon.

2. The method for preparing a melamine-modified resin-based activated carbon according to claim 1, characterized by: In step a, the ratio of resorcinol to formaldehyde solution is 4-6 g: 8 mL, and in step b, the ratio of melamine to formaldehyde solution is 0.5-2 g: 4 mL.

3. The method for preparing a melamine-modified resin-based activated carbon according to claim 2, characterized by: In step a, the ratio of resorcinol to formaldehyde solution is 5 g: 8 mL, and in step b, the ratio of melamine to formaldehyde solution is 1 g: 4 mL.

4. The method for preparing melamine-modified resin-based activated carbon according to claim 1, characterized in that: The ammonium-containing basic compound is ammonia, ammonium carbonate or ammonium phosphate.

5. The method for preparing melamine-modified resin-based activated carbon according to claim 4, characterized in that: The ammonium-containing basic compound is ammonia.

6. The method for preparing melamine-modified resin-based activated carbon according to claim 4, characterized in that: The solvent in steps a and b is an aqueous ethanol solution, wherein the volume ratio of ethanol to water is 2-3: 4-5.

7. The method for preparing melamine-modified resin-based activated carbon according to claim 1, characterized in that: In step a, the volume ratio of ammonia, solvent to formaldehyde solution is 0.3-0.5: 70-90: 8, and in step b, the volume ratio of ammonia, solvent to formaldehyde solution is 0.05-0.2: 30-40:

4.

8. The method for preparing melamine-modified resin-based activated carbon according to claim 7, characterized in that: In step a, the volume ratio of ammonia, solvent to formaldehyde solution is 0.4: 80: 8, and in step b, the volume ratio of ammonia, solvent to formaldehyde solution is 0.2: 32:

4.

9. The method for preparing melamine-modified resin-based activated carbon according to claim 1, characterized in that: The mass ratio of melamine in step b to resorcinol in step a is 0.

2.

10. The method for preparing melamine-modified resin-based activated carbon according to claim 1, characterized in that: In step c, the reaction is carried out at a constant temperature of 120 ℃ for 24 h, and in step d, the temperature is raised to 200 ℃ for 2 h, and then raised to 800 ℃ for 4 h.

11. The method for preparing melamine-modified resin-based activated carbon according to claim 1, characterized in that: In step d, the heating rate is 0.5-2 ℃ / min, and the cooling rate is 3-10 ℃ / min.

12. The method for preparing melamine-modified resin-based activated carbon according to claim 11, characterized in that: The heating rate is 1 ℃ / min, and the cooling rate is 5 ℃ / min.

13. The melamine-modified resin-based activated carbon prepared by the method of any one of claims 1-12.

14. The use of the melamine-modified resin-based activated carbon of claim 13 in the adsorption separation of methane-nitrogen.

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