Phenolic resin modified carbon molecular sieve as well as preparation method and application thereof

Abstract

The invention relates to a phenolic resin modified carbon molecular sieve and a preparation method and application thereof, and belongs to the technical field of adsorbents. The technical problem to be solved by the invention is to provide the phenolic resin modified carbon molecular sieve, and the adsorption selectivity is improved. The method comprises the following steps: a, in-situ polymerization: mixing phenolic resin polymerization mother liquor with a carbon molecular sieve, standing for adsorption, and heating the adsorbed carbon molecular sieve for polymerization reaction to obtain a polymerization product; the phenolic resin polymerization mother liquor comprises a phenolic substance, an aldehyde substance and a solvent; and b, carbonization modification: roasting the polymerization product in a protective atmosphere to obtain the phenolic resin modified carbon molecular sieve. The carbon molecular sieve is modified through phenolic resin in-situ polymerization, and the method is simple, low in cost, high in reaction controllability and suitable for industrial production. The phenolic resin modified carbon molecular sieve has selective adsorbability, can be applied to an N2 / CH4 system, selectively adsorbs N2, and is high in separation ratio and good in stability.

Description

Technical Field

[0001] The present invention relates to a phenolic resin modified carbon molecular sieve, its preparation method and application, belonging to the technical field of adsorbents. Background Art

[0002] As a relatively clean fossil fuel, natural gas is bound to play an important role in achieving the carbon emission target. With the rapid consumption of resources, the difficulty of conventional natural gas extraction will increase significantly. Unconventional natural gas resources are rich in reserves and widely distributed, and may become the most powerful support for the sustainable development of the natural gas industry. However, the separation of a large number of impurities in unconventional natural gas has become a key technical obstacle to large-scale utilization, especially the efficient separation of nitrogen-containing natural gas.

[0003] At present, the main processes for natural gas denitrification include cryogenic distillation, membrane separation, molecular sieve adsorption, and pressure swing adsorption. Among them, the cryogenic distillation process is suitable for large-scale gas separation, but requires more energy consumption and high capital costs. Although membrane gas separation is more cost-effective than traditional cryogenic distillation, it is difficult to achieve high selectivity for methane. In contrast, pressure swing adsorption has attracted much attention in natural gas denitrification due to its high selectivity.

[0004] The pressure swing adsorption (PSA) process is a process that separates gases from a gas mixture based on the different abilities of gases to adsorb onto solid materials at different pressures. By contacting the gas mixture with a solid adsorbent in an adsorption column, a specific gas component in the gas mixture is selectively adsorbed onto the adsorbent at a specific pressure, thereby enriching the gas stream of the component with weaker adsorption in the feed. The components adsorbed in the adsorbent can be desorbed by reducing the bed pressure, thereby regenerating the adsorbent. Undoubtedly, the development of high-performance adsorbents is a key link in continuously improving the efficiency of natural gas denitrification by adsorption separation. Currently, commonly used porous adsorbents include: carbon molecular sieve (CMS), zeolite, ETS-4, MOFs, etc. Different adsorbents have different selectivities for different components, which usually depends on the pore size and surface properties of the adsorbent itself and the molecular diameter properties of the components to be adsorbed.

[0005] Among them, carbon molecular sieve has shown its advantages in the adsorption separation of CH4 / N2 mixtures. Its effectively controllable pore structure, optimized surface properties and mass transfer resistance control provide new ideas for customizing the performance of CH4 / N2 separation adsorbents. However, there is still great potential for further optimization and improvement of the adsorption selectivity and capacity of carbon molecular sieve in the future industrialization process. The stability and cost control of composite modified adsorbents based on carbon molecular sieve also require more in-depth research. Summary of the Invention

[0006] In view of the above defects, the technical problem to be solved by the present invention is to provide a phenolic resin modified carbon molecular sieve to improve its adsorption selectivity.

[0007] The preparation method of the phenolic resin modified carbon molecular sieve of the present invention comprises the following steps:

[0008] a. In-situ polymerization: Mix the phenolic resin polymerization mother liquor and the carbon molecular sieve, and after static adsorption, heat up the adsorbed carbon molecular sieve for polymerization reaction to obtain a polymerization product; the phenolic resin polymerization mother liquor comprises phenolic substances, aldehyde substances and a solvent;

[0009] b. Carbonization modification: Bake the polymerization product under a protective atmosphere to obtain a phenolic resin modified carbon molecular sieve.

[0010] In an embodiment of the present invention, in step a, the phenolic substances are phenol, catechol, resorcinol or hydroquinone, and the aldehyde substance is formaldehyde.

[0011] In an embodiment of the present invention, the molar ratio of the phenolic substance to the aldehyde substance is 0.3 - 0.4:1. In a specific embodiment, the molar ratio of the phenolic substance to the aldehyde substance is 0.36:1.

[0012] In an embodiment of the present invention, in the phenolic resin polymerization mother liquor, the concentration of the phenolic substance is 0.1 - 0.5 g / mL.

[0013] In an embodiment of the present invention, in step a, the static adsorption time is 0.5 - 12 h; preferably, the static adsorption time is 1 h.

[0014] In an embodiment of the present invention, in step a, the polymerization reaction temperature is 80 - 120 °C, and the reaction time is 20 - 40 h; preferably, the polymerization reaction temperature is 100 °C, and the reaction time is 24 h.

[0015] In an embodiment of the present invention, in step b, the baking temperature is 600 - 800 °C, and the baking time is 1 - 5 h; preferably, the baking temperature is 700 °C, and the baking time is 2 h.

[0016] The present invention also provides a phenolic resin modified carbon molecular sieve prepared by the preparation method of the phenolic resin modified carbon molecular sieve of the present invention.

[0017] For the phenolic resin modified carbon molecular sieve of the present invention, in-situ polymerization modification with phenolic resin reduces the surface fragmentation degree of the carbon molecular sieve, increases the pore mouth resistance, and also reduces its specific surface area, average micropore diameter and micropore volume. This modified molecular sieve has better adsorption performance, can increase the nitrogen adsorption amount, and is beneficial to the selective separation of nitrogen in the N2 / CH4 system.

[0018] The present invention also provides the use of the phenolic resin-modified carbon molecular sieve of the present invention for adsorbing N2 in the N2 / CH4 system.

[0019] The phenolic resin-modified carbon molecular sieve of the present invention can be applied in the N2 / CH4 system to selectively adsorb N2, with a high separation ratio and strong stability.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention uses in-situ polymerization of phenolic resin to modify carbon molecular sieve. The method is simple, with low cost and high reaction controllability, and is suitable for industrial production.

[0022] The phenolic resin-modified carbon molecular sieve of the present invention has selective adsorption properties and can be applied in the N2 / CH4 system to selectively adsorb N2, with a high separation ratio and good stability. Brief Description of the Drawings

[0023] Figure 1 It is a device diagram used to evaluate the adsorption performance in Example 4 of the present invention. In the figure, 1 is the He inlet end, 2 is the CH4 inlet end, 3 is the N2 inlet end, 4 is the reference tank, and 5 is the adsorption tank.

[0024] Figure 2 It is the adsorption isotherm of nitrogen and methane adsorbed by the examples, comparative examples and raw material CMS of the present invention. Among them, a is for nitrogen adsorption and b is for methane adsorption.

[0025] Figure 3 It is the adsorption separation ratio diagram of nitrogen and methane adsorbed by the examples, comparative examples and raw material CMS of the present invention.

[0026] Figure 4 It is the adsorption amount cycle stability diagram of the examples, comparative examples and raw material CMS of the present invention. Detailed Embodiments

[0027] The preparation method of the phenolic resin-modified carbon molecular sieve of the present invention includes the following steps:

[0028] a. In-situ polymerization: Mix the phenolic resin polymerization mother liquor and the carbon molecular sieve, and after static adsorption, heat up the adsorbed carbon molecular sieve for polymerization reaction to obtain a polymerization product; the phenolic resin polymerization mother liquor includes phenolic substances, aldehyde substances and solvents;

[0029] b. Carbonization modification: Bake the polymerization product in a protective atmosphere to obtain the phenolic resin-modified carbon molecular sieve.

[0030] In an embodiment of the present invention, in step a, the phenolic substance is phenol, catechol, resorcinol or hydroquinone, and the aldehyde substance is formaldehyde.

[0031] In one embodiment of the present invention, the molar ratio of the phenolic substance to the aldehyde substance is 0.3 to 0.4:1. In a specific embodiment, the molar ratio of the phenolic substance to the aldehyde substance is 0.36:1.

[0032] In one embodiment of the present invention, in the phenolic resin polymerization mother liquor, the concentration of the phenolic substance is 0.1 to 0.5 g / mL.

[0033] The static adsorption described in the present invention is to put the carbon molecular sieve into the phenolic resin polymerization mother liquor so that the liquid submerges the carbon molecular sieve, and wait for a period of time. In one embodiment of the present invention, in step a, the static adsorption time is 0.5 to 12 h; preferably, the static adsorption time is 1 h.

[0034] In one embodiment of the present invention, in step a, the temperature of the polymerization reaction is 80 to 120 °C, and the reaction time is 20 to 40 h; preferably, the temperature of the polymerization reaction is 100 °C, and the reaction time is 24 h.

[0035] In one embodiment of the present invention, in step b, the calcination temperature is 600 to 800 °C, and the calcination time is 1 to 5 h; preferably, the calcination temperature is 700 °C, and the calcination time is 2 h.

[0036] The present invention also provides a phenolic resin-modified carbon molecular sieve prepared by the preparation method of the phenolic resin-modified carbon molecular sieve described in the present invention.

[0037] For the phenolic resin-modified carbon molecular sieve of the present invention, in-situ polymerization modification with phenolic resin reduces the surface fragmentation degree of the carbon molecular sieve, increases the pore mouth resistance, and also reduces its specific surface area, average micropore diameter, and micropore volume. This modified molecular sieve has excellent adsorption performance, can increase the nitrogen adsorption amount, and is beneficial to the selective separation of nitrogen in the N2 / CH4 system.

[0038] The present invention also provides the use of the phenolic resin-modified carbon molecular sieve of the present invention for adsorbing N2 in the N2 / CH4 system.

[0039] The phenolic resin-modified carbon molecular sieve of the present invention can be applied in the N2 / CH4 system to selectively adsorb N2, with a high separation ratio and strong stability.

[0040] The following further describes the specific embodiments of the present invention in conjunction with the examples, and the present invention is not limited to the scope of the described examples.

[0041] Examples 1-3

[0042] 1. Adsorbent pretreatment: Put the carbon molecular sieve substrate into an oven at 130 °C and dry it overnight to remove the gas residue of the carbon molecular sieve.

[0043] 2. Preparation of phenolic resin mother liquor: Weigh a certain amount of phenol, sodium hydroxide, and 38% formaldehyde solution into a 100 mL beaker respectively, then dilute it to 90 mL with deionized water. Next, use a magnetic stirrer to stir for 2 h at room temperature to obtain a uniformly mixed phenolic resin polymerization mother liquor. The dosages of phenol, sodium hydroxide, and 38% formaldehyde solution in each example and comparative example are shown in Table 1.

[0044] 3. In-situ polymerization of phenolic resin: Take multiple clean beakers, weigh 10.00 g of adsorbent into each beaker respectively, and use a pipette to slowly add 9 mL of the mixed solution dropwise into the beaker containing the adsorbent. After the addition is completed, let it stand at room temperature for 1 h to ensure complete adsorption. After standing, place it in an oven at 100 °C and react for 24 h.

[0045] 4. Carbonization modification of phenolic resin: Transfer the completely dried adsorbent after reaction to a tube furnace and calcine it at 700 °C under the protection of He for 2 h. After completion, transfer it to a glass desiccator for storage to obtain phenolic resin modified carbon molecular sieves with different phenolic ratios, denoted as CMS-PF-X respectively, where X is the phenolic ratio of the phenolic resin mother liquor.

[0046] Table 1

[0047] Example Number Sample Number CMS / g Phenol / g NaOH / g 38% Formaldehyde / g Example 1 CMS-PF-1 10 15 0.8 35 Example 2 CMS-PF-2 10 20 1.1 47 Example 3 CMS-PF-3 10 25 1.3 59 Comparative Example 1 CMS-PF-0 10 0 0 0

[0048] Example 4

[0049] The adsorption performance of Examples 1-3, Comparative Example 1, and the raw material CMS was evaluated. The specific method is as follows:

[0050] 1. Measuring device and process

[0051] Use the Figure 1 gas adsorption measuring instrument MGSORP LP shown in the figure to measure the adsorption isotherm and kinetic curve. This device can obtain the adsorption isotherm through the gas adsorption manometry method and consists of an inlet end, a measuring end, a vacuum end, and a control end.

[0052] Inlet end: It contains the pure gas N2, CH4 to be measured, and the calibration gas He. The gas volume input of these three gases is controlled by a regulating valve and a solenoid valve.

[0053] Measuring end: It consists of a reference cell, an adsorption cell, and a pressure transmitter. The gas pipeline part is completely immersed in a constant temperature water bath to achieve constant temperature measurement of the adsorption behavior. All the information required for the adsorption isotherm is obtained from the pressure sensor. Generally speaking, it includes the pressure of the gas in the reference cell V ref and the pressure of the gas expanding into the adsorption cell V ads containing the adsorbent at each time period. Once the equilibrium is established, the adsorption amount is calculated using the change in pressure. They measure the gas adsorption amount (n a) is related to the solid mass (m s ) and the equilibrium pressure (p) at a constant temperature (T), and is expressed by the following formula:

[0054] n a / m s =f(p) T

[0055] Control end: S7-200 CN produced by SIEMENS is used as the control center of the device to realize the automatic operation and data recording of the whole adsorption device.

[0056] Vacuum end: A vacuum pump is used as the vacuum source of the device, and vacuum desorption is carried out to achieve the purpose of adsorbent purification.

[0057] 2. Determination of adsorption isotherm

[0058] The adsorbents studied in this embodiment are all based on commercial adsorbents. The test conditions are kept somewhat relevant to the actual PSA process, and the equilibrium points on its adsorption isotherm are not thermodynamic equilibrium points.

[0059] 1) Operating procedure

[0060] Adsorbent pretreatment: The adsorbent to be tested is placed in an oven at 100 °C and dried overnight to remove the gas residue on the adsorbent;

[0061] Adsorbent loading: Weigh about 2 g of the adsorbent and place it in the adsorption tank. The upper part is sealed with absorbent cotton to prevent the adsorbent powder from entering the pipeline and affecting the operation of the solenoid valve and the measurement accuracy. Connect the adsorption tank to the adsorption device and wait for measurement;

[0062] Leak detection of the adsorption device: The adsorption device is placed in a constant temperature water bath at the temperature to be measured, and 0.6 MPa of He is filled into the adsorption device for leak detection to ensure the airtightness of the gas path;

[0063] Determination of adsorption isotherm: Start the automatic operation of the measuring device. During the automatic process, first fill helium to measure the dead volume of the device, and then perform the isotherm determination of the adsorbent. During the measurement, the gas to be measured is filled to the specified pressure. Then measure the corresponding pressures before and after adsorption respectively. Since the adsorption of N2 and CH4 on the adsorbent is reversible, it can be desorbed and regenerated under vacuum. Therefore, after the adsorption isotherm of N2 is measured, it is necessary to desorb under vacuum for 20 min and then perform the CH4 isotherm determination.

[0064] Adsorbent recovery: After the measurement process is completed, take out the adsorbent and put it in an oven at 100 °C for drying and regeneration, and wait for subsequent treatment;

[0065] 2) Experimental data processing

[0066] The objects studied in this embodiment are N2 and CH4 at 0 to 1.0 MPa and room temperature. The ideal gas state equation that ignores the intermolecular interaction cannot meet the needs of actual calculations. According to the Redlich-Kwong (RK) equation, calculating the P-V-T relationship of the gas can meet the actual accuracy requirements.

[0067] The R-K equation can usually be described as:

[0068]

[0069] To find the molar volume V, the above equation can be written in the following form:

[0070]

[0071] Substitute the initial value V0:

[0072]

[0073] Among them, a and b are related to the physical property parameters of the gas and can be obtained by fitting the P-V-T data of the experiment.

[0074]

[0075]

[0076] Among them, the relevant parameters of the gas involved are shown in Table 2.

[0077] Table 2

[0078]

[0079] 3. Separation ratio of adsorbent

[0080] In the PSA process, the change of the adsorption amounts of the two components in the mixed gas with the pressure cycle process is a relatively key factor in the separation process. Usually, the difference in the adsorption amounts of the main adsorption component at high pressure and low pressure is used to measure the adsorption capacity of the adsorbent. That is, the adsorption capacity of the adsorbent depends on the adsorption amounts of each component under the mixing conditions. However, in the actual calculation process, the adsorption isotherm of the pure component can meet the requirements.

[0081] The adsorption separation ratio is defined as W:

[0082]

[0083] Among them, V i is the volume adsorption amount of component i on the adsorbent. For the adsorbent studied in this research for the VPSA process, it can be completely desorbed after vacuum desorption. At this time, V i,0 = 0, and the above equation can be simplified to:

[0084]

[0085] 4. Stability of the adsorbent

[0086] In the actual PSA process, the cyclic stability of the adsorption capacity of the adsorbent is an important performance index of the adsorbent. The adsorbent developed in this example is regenerated by vacuum desorption purification. During the first 9 tests of cyclic stability, after each adsorption isotherm test, vacuum desorption is carried out for 20 minutes, and the last time is treated by drying at 120 °C for 12 hours.

[0087] 5. Measurement results and analysis

[0088] (1) Adsorption isotherm

[0089] At 303 K, the adsorption isotherms of nitrogen and methane adsorbed by the examples, comparative examples and raw material CMS are measured, and the results are shown in Figure 2 , where a is the adsorption isotherm of nitrogen adsorption, and b is the adsorption isotherm of methane adsorption. It can be seen that the adsorption capacity of the molecular sieve has changed to a certain extent after in-situ polymerization carbonization modification with phenolic resin. The PF-0 sample is obtained by calcining CMS at 700 °C under N2 protection. It can be seen that the methane adsorption capacity has been greatly improved. Its adsorption capacity at 0.7 MPa has increased from 35.4 mL / g to 43.2 mL / g, and at the same time, the specific surface area and pore diameter have also increased to a certain extent. This is because during the calcination process, the residual hydrocarbons in the molecular sieve further escape, expand the pores on the original voids, increase the pore volume and pore diameter, and make the molecular sieve gradually change from kinetic adsorption to equilibrium adsorption control.

[0090] The parameters are obtained by fitting with the Sips model, and the results are shown in Table 3. By comparing with the experimental data, it can be seen that methane is far from reaching adsorption saturation on the adsorbent at 0.7 MPa. With the increase of the phenolic resin polymerization ratio, the adsorption capacity of nitrogen does not change significantly, but the adsorption capacity of methane decreases significantly. Combining Table 3, it can be seen that after carbonization modification with phenolic resin, the pore channels of the carbon molecular sieve have been greatly improved, and the pore size distribution is more concentrated. However, due to the pore expansion of the carbon molecular sieve itself after calcination at 700 °C, the adsorption capacity does not decrease significantly compared with the uncalcined and unmodified CMS. After phenolic resin polymerizes in the larger pores, many large pores that are not suitable for adsorption form more sites suitable for the adsorption process; another part attaches to the pore mouth and near the pore channels to polymerize, increasing the diffusion resistance of methane with a larger kinetic diameter during the diffusion process and reducing the adsorption capacity at the same pressure, while nitrogen with a smaller kinetic diameter is less affected by the increase in diffusion resistance, and the adsorption capacity remains almost unchanged, which can be obtained from the fitting of the kinetic curve.

[0091] ​Table 3 Variation of Adsorption Capacity of Different Samples with Pressure

[0092]

[0093] (2) Adsorption Separation Ratio

[0094] Based on the adsorption isotherm of phenolic resin modified carbon molecular sieve, the corresponding adsorption parameters are obtained, and further the adsorption separation ratios of carbon molecular sieve before and after being modified by phenolic resin are obtained, as Figure 3 shown in Table 4. It can be seen that the adsorption separation ratio of the CMS-PF-0 sample obtained after calcination at 700 °C has a significant decrease compared with the unmodified sample. This is because after calcination at 700 °C, the pores of the carbon molecular sieve expand, and the separation ability for nitrogen and methane decreases. After further modification by in-situ polymerization and carbonization of phenolic resin, its separation ratio gradually increases. This is because after modification, the micropores change, the average pore diameter becomes smaller, and for methane with a larger kinetic diameter compared to nitrogen with a smaller one, the diffusion resistance is greater, and it is more difficult to diffuse to the adsorption sites. At the same time, the tetrahedral spatial structure of methane further increases the diffusion resistance compared to the linear nitrogen molecule. As a result, the adsorption amount of methane decreases rapidly, and the adsorption separation ratio rises rapidly.

[0095] Table 4 Adsorption Separation Ratios after Modification with Different Concentrations

[0096] Pressure MPa CMS CMS-PF-0 CMS-PF-1 CMS-PF-2 CMS-PF-3 0.8 0.49862 0.50864 0.49547 0.58687 0.92622

[0097] (3) Stability Evaluation

[0098] The adsorption capacity cycle stability of the carbon molecular sieve CMS-PF-3 modified by phenolic resin is as Figure 4 shown in Table 5. As the number of cycles increases, the adsorption capacities of the modified carbon molecular sieve at 0.5 MPa, 0.6 MPa, and 0.7 MPa generally show a downward trend. However, the decline is relatively small, because after in-situ polymerization and carbonization of phenolic resin to form a film, the pore radius is larger, which is more conducive to desorption and regeneration. At 0.7 MPa, the adsorption amount of nitrogen decreases from 25.33 mL / g in the first cycle to 23.26 mL / g in the ninth cycle, only decreasing by 2.07 mL / g, while for methane, it decreases from 27.68 mL / g to 26.15 mL / g, a decrease of 1.53 mL / g. It can be seen that the adsorbent modified by phenolic resin has good adsorption capacity stability.

[0099] Table 5 Adsorption Capacity Cycle Stability of CMS-PF-3

[0100]

[0101] It can be seen that on the phenolic resin-modified carbon molecular sieve of the present invention, the in-situ polymerization modification of phenolic resin can adjust the pore structure and pore size distribution, thereby enhancing the selective adsorption of nitrogen and strengthening its separation performance.

Claims

1. Preparation method of phenolic resin modified carbon molecular sieve, characterized in that, It includes the following steps: a. In-situ polymerization: Mix the phenolic resin polymerization mother liquor and carbon molecular sieve, and after static adsorption, heat up the adsorbed carbon molecular sieve for polymerization reaction to obtain a polymerization product; The phenolic resin polymerization mother liquor includes phenolic substances, aldehyde substances and solvents; b. Carbonization modification: Roast the polymerization product in a protective atmosphere to obtain a phenolic resin modified carbon molecular sieve.

2. The preparation method of the phenolic resin modified carbon molecular sieve according to claim 1, characterized in that: In step a, the phenolic substance is phenol, catechol, resorcinol or hydroquinone, and the aldehyde substance is formaldehyde.

3. The preparation method of the phenolic resin modified carbon molecular sieve according to claim 1, characterized in that: The molar ratio of the phenolic substance to the aldehyde substance is 0.3 - 0.4:1; preferably, the molar ratio of the phenolic substance to the aldehyde substance is 0.36:

1.

4. The preparation method of the phenolic resin modified carbon molecular sieve according to claim 1, characterized in that: In the phenolic resin polymerization mother liquor, the concentration of the phenolic substance is 0.1 - 0.5 g / mL.

5. The preparation method of the phenolic resin modified carbon molecular sieve according to claim 1, characterized in that: In step a, the time for static adsorption is 0.5 - 12 h; preferably, the time for static adsorption is 1 h.

6. The preparation method of the phenolic resin modified carbon molecular sieve according to claim 1, wherein: In step a, the temperature of the polymerization reaction is 80 - 120 °C, and the reaction time is 20 - 40 h; preferably, the temperature of the polymerization reaction is 100 °C, and the reaction time is 24 h.

7. The preparation method of the phenolic resin modified carbon molecular sieve according to claim 1, wherein: In step b, the roasting temperature is 600 - 800 °C, and the roasting time is 1 - 5 h; preferably, the roasting temperature is 700 °C, and the roasting time is 2 h.

9. The phenolic resin modified carbon molecular sieve prepared by the preparation method of the phenolic resin modified carbon molecular sieve according to any one of claims 1 - 7.

10. Use of the phenolic resin modified carbon molecular sieve according to claim 9 for adsorbing N2 in the N2 / CH4 system.

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