Special silica gel for pressure swing adsorption hydrogen extraction and preparation method thereof

Abstract

The invention relates to the technical field of gas adsorption materials, in particular to special silica gel for pressure swing adsorption hydrogen extraction and a preparation method thereof. The special silica gel for pressure swing adsorption hydrogen extraction comprises pretreated adsorption silica gel and advanced treatment adsorption silica gel, wherein the pretreated silica gel is specially used for capturing polar molecules; and the silica gel is deeply treated to accurately adsorb small-molecule gas. During preparation, a graded functionalization strategy is adopted, the stability of a silica gel framework is enhanced through acid activation, a multi-stage adsorption interface is constructed through amino / fluorocarbon directional grafting, and active components are fixed through chemical bonding to avoid loss. During application, a double-tower pressure swing adsorption process is adopted, the pretreatment adsorption tower preferentially removes strong adsorbate, the deep treatment adsorption tower improves hydrogen purity through hydrophobic screening, and gradient pressure reduction and pulse nitrogen desorption technologies are matched, so that efficient regeneration of the adsorbent is realized. A single material system breaks through a mass transfer barrier of a traditional multi-adsorbent combination, has the characteristics of high-selectivity adsorption and low-energy-consumption desorption, and is suitable for efficient recovery of hydrogen resources in synthesis ammonia tail gas.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas adsorption materials, in particular to a special silica gel for pressure swing adsorption hydrogen extraction and a preparation method thereof. BACKGROUND

[0002] In the field of hydrogen purification, pressure swing adsorption (PSA) technology is widely used in hydrogen extraction from tail gas of synthetic ammonia due to its high efficiency and energy saving characteristics. The existing technology generally uses a combination system of multiple types of adsorbents, among which silica gel is often used in combination with molecular sieves, activated carbon and other materials to deal with complex gas components. In the prior art, a silica gel-5A molecular sieve composite adsorption bed is used, which uses silica gel to preliminarily remove H2O and CO2, and then molecular sieve to further adsorb N2, CH4 and other components. However, the differences in physicochemical properties between different adsorbents increase the mass transfer resistance, and the mismatch of regeneration temperature causes energy loss. Moreover, the molecular sieve lattice is easily damaged by the hydroxyl groups migrated from silica gel after multiple cycles, and the adsorption capacity decreases significantly after multiple cycles. In the prior art, there is also a design of layered loading of silica gel and activated carbon, which improves the CO adsorption efficiency, but the microporous structure of activated carbon is easily blocked by NH3 molecules, which requires frequent high-temperature activation, resulting in increased energy consumption of the system. Such mixed adsorption system has inherent defects: the differences in adsorption kinetics of different materials cause the overlapping of breakthrough curves, the preferential adsorption of silica gel for polar molecules will weaken the capture efficiency of molecular sieve for small molecules in the subsequent stage, and the overlapping of multi-component desorption peaks in the desorption stage aggravates the purity fluctuation of product gas.

[0003] In recent years, functional modification of single adsorbent has become a research hotspot, but the existing technology still has significant limitations. In the prior art, amino-modified silica gel is developed to enhance NH3 adsorption, but in the CO / CH4 coexisting system, the active sites are easily occupied by CO, resulting in an increase in NH3 desorption residue. More importantly, the existing modified silica gel focuses on a single function and fails to achieve the synergistic effect of multi-component gradient adsorption, so it still needs to be combined with other adsorbents to complete deep purification, resulting in complex process flow. SUMMARY

[0004] The purpose of the present application is to solve the problems in the prior art and to provide a special silica gel for pressure swing adsorption hydrogen extraction and a preparation method thereof.

[0005] To achieve the above purpose, the present application provides a preparation method of a special silica gel for pressure swing adsorption hydrogen extraction, which comprises pretreated adsorption silica gel and deep treated adsorption silica gel, and the preparation method comprises: The preparation process of silica gel comprises the following steps: The solid sodium silicate is crushed to a particle size of ≤5 cm, added to a deionized water in a material preparation kettle, and steam at 0.6-0.8 MPa is introduced to heat to 150-160℃ for stirring and dissolving for 4-6 h, and then cooled to 35-40℃ to obtain a water glass solution. Concentrated sulfuric acid with a concentration of 98% is diluted with water to a 30% sulfuric acid solution, and then cooled to 25-30℃. The prepared water glass solution and the 30% sulfuric acid solution are simultaneously injected into a reaction kettle in a parallel flow method at a volume ratio of 1.8-2.2:1. The mixture is stirred at 20-30℃ and pH=7-9 for 5-8 min, and then the stirring is stopped after the gel is formed. The gel is solidified at room temperature for 1-2 h, cut into 5-8 mm particles, soaked in 0.5-1.0 mol / L dilute sulfuric acid at 40-50℃ for 8-12 h, then washed with deionized water in a countercurrent flow until pH=4-5, then soaked in 0.016%-0.02% dilute sulfuric acid at 25-30℃ for 12 h, then dehydrated by centrifugation until the water content is ≤60%, and finally dried at 120-150℃ until the water content is <5%. After grinding and sieving, the silica gel with a particle size of 300-400 mesh is obtained. In the preparation process of the silica gel, the solid sodium silicate and the deionized water are in a weight ratio of 1-2.5. The preparation process of the pretreated adsorption silica gel includes the following steps: S1. The silica gel is added to a 10% hydrochloric acid solution, stirred and reacted at room temperature for 2-3 h, filtered, washed with deionized water until neutral, and dried to obtain acid-activated silica gel. S2. The acid-activated silica gel and 3-aminopropyltriethoxysilane are added to ethanol, heated to 60-80℃, stirred and reacted for 6-8 h, cooled to room temperature, filtered, washed, and dried to obtain aminated silica gel. The chemical reaction is shown in the following scheme: Formula (1); S3. The aminated silica gel and copper sodium ethylenediaminetetraacetate Na2[Cu(EDTA)] are added to deionized water, and the pH is adjusted to 3-4 with a 10% hydrochloric acid solution. The mixture is heated to 60-80℃ and reacted for 2-4 h, cooled to room temperature, filtered, washed, and dried to obtain pretreated adsorption silica gel. The chemical reaction is shown in the following equation: Formula (2); The preparation process of the deep treatment adsorption silica gel includes the following steps: Ⅰ. The silica gel is added to a 10% hydrochloric acid solution, stirred and reacted at room temperature for 2-3 h, filtered, washed with deionized water until neutral, and dried to obtain acid-activated silica gel. II. Acid-activated silica gel, heptadecafluorodecyltrimethoxysilane and 3-aminopropyltriethoxysilane are added into ethanol, heated to 60-80℃, stirred for 6-8h, cooled to room temperature, filtered, washed, dried to obtain amino-fluorinated silica gel, and the chemical reaction is shown in the following schematic diagram: Formula (3); III. Amino-fluorinated silica gel and ammonium molybdate are added into deionized water, and the pH is adjusted to 5-6 with a 10% hydrochloric acid solution, heated to 60-80℃, stirred for 4-6h, cooled to room temperature, filtered, washed, dried to obtain deep treatment adsorption silica gel, and the chemical reaction is shown in the following schematic diagram: Formula (4).

[0006] Preferably, the silica gel and the 10% hydrochloric acid solution in S1 are in a weight ratio of 1:8-12.

[0007] Preferably, the acid-activated silica gel, 3-aminopropyltriethoxysilane and ethanol in S2 are in a weight ratio of 1:0.2-0.4:8-12.

[0008] Preferably, the amino-fluorinated silica gel, sodium copper ethylenediaminetetraacetate and deionized water in S3 are in a weight ratio of 1:0.2-0.4:8-12.

[0009] Preferably, the silica gel and the 10% hydrochloric acid solution in I are in a weight ratio of 1:8-12.

[0010] Preferably, the acid-activated silica gel, heptadecafluorodecyltrimethoxysilane, 3-aminopropyltriethoxysilane and ethanol in II are in a weight ratio of 1:0.2-0.4:0.2-0.4:8-12.

[0011] Preferably, the amino-fluorinated silica gel, ammonium molybdate and deionized water in III are in a weight ratio of 1:0.5-0.8:8-12.

[0012] Further, the present application also provides a special silica gel for pressure swing adsorption hydrogen extraction, which is prepared by the above preparation method.

[0013] Preferably, the special silica gel for pressure swing adsorption hydrogen extraction is applied to purification and hydrogen extraction in synthetic ammonia tail gas, and the specific method comprises: (1) Double-tower adsorption stage: a. Pretreatment adsorption tower adsorption: the pretreatment adsorption silica gel is loaded, and the synthetic ammonia tail gas is passed into the pretreatment adsorption tower at a flow rate of 1500-1800Nm³ / h·m³, the adsorption pressure is 2-3MPa, the adsorption temperature is 25-35℃, and the adsorption period is 180-240s, to obtain pretreated synthetic ammonia tail gas. b. Deep treatment adsorption tower adsorption: the pre-processed synthetic ammonia tail gas is passed into the deep treatment adsorption tower at a flow rate of 800-1200 Nm³ / h·m³, the adsorption pressure is 2-3 MPa, the adsorption temperature is 30-40℃, and the adsorption cycle is 120-150 s, to obtain purified hydrogen; (2) Desorption stage of double towers: c. Desorption of the pretreatment adsorption tower: the pressure is reduced to 0.05-0.1 bar, the temperature is increased to 45-55℃, 80-100℃ nitrogen gas with a pressure of 1.5-2 bar is used for reverse pulse blowing, the flow rate is 500-600 Nm³ / h·m³, the pulse time is 5-10 s, the interval is 15 s, and the duration is 60-90 s; d. Desorption of the deep treatment adsorption tower: the pressure is reduced to 0.01-0.03 bar, the temperature is increased to 50-60℃, 80-100℃ nitrogen gas with a pressure of 1.5-2 bar is used for reverse pulse blowing, the flow rate is 400-600 Nm³ / h·m³, the pulse time is 3-5 s, the interval is 5 s, and the duration is 40-60 s.

[0014] Preferably, the pretreatment adsorption silica gel forms a coordination bond with Cu 2+ in the sodium copper ethylenediaminetetraacetate through the amino group on the surface of the amino silica gel, and combines chemical adsorption and polar adsorption, and is mainly used for adsorbing NH3, CO2 and H2O in the synthetic ammonia tail gas; the deep treatment adsorption silica gel repels water molecules through the hydrophobic layer of the heptadecafluorodecyl on the surface of the silica gel, and combines ammonium molybdate to specifically adsorb small molecule gases such as CO, N2, CH4 and Ar in the synthetic ammonia tail gas by using the hydrophobic sieving effect and weak chemical adsorption. Advantages of the present application: 1. The traditional pressure swing adsorption hydrogen extraction process needs to rely on the synergistic effect of multiple adsorbents such as silica gel, molecular sieve and activated carbon, but the differences in the physicochemical properties of different materials lead to mismatched adsorption kinetics, high regeneration energy consumption and poor system stability. The present application modifies the silica gel by grading functionalization, and constructs a "pretreatment-deep treatment" two-stage adsorption mechanism in a single material system: the pretreatment silica gel surface selectively captures NH3, CO2 and other strong polar molecules through the amino-Cu 2+ coordination bond; the deep treatment silica gel precisely sieves CO, N2 and other weakly adsorbed small molecules through the synergistic effect of the fluorocarbon hydrophobic layer and the active sites of ammonium molybdate. This intrinsic synergistic mechanism avoids the mass transfer barrier at the interface of heterogeneous materials, and the desorption stage can realize efficient desorption of all components under single regeneration conditions.

[0015] 2. The present application solves the problem of competitive adsorption caused by the coexistence of polar molecules and non-polar small molecules in the synthetic ammonia tail gas by molecular-level surface engineering design: on the one hand, the protonated amino group of the aminosilica gel forms a coordination bond with Cu 2+The strong coordination bond is formed, the polar molecules are preferentially anchored and the diffusion of the polar molecules to the deep pores is blocked; on the other hand, the super-hydrophobic interface constructed by the long-chain heptadecafluorodecyl group can reduce the surface energy of the silica gel, and the weak chemical adsorption of ammonium molybdate to small molecules is strengthened through the steric hindrance effect. The "polar capture-hydrophobic screening" coupling mechanism greatly improves the purity of hydrogen, and the stable performance can be maintained under multiple adsorption and desorption cycles.

[0016] 3. The residual accumulation problem caused by incomplete desorption of the traditional adsorbent is broken through by precise matching of the desorption parameters and the material characteristics: the pretreated silica gel is subjected to medium-pressure pulse purging, the high-temperature nitrogen gas turbulent shear force is used to destroy the Cu 2+ -NH3 coordination bond; the deeply treated silica gel is subjected to ultra-low pressure environment to excite the desorption activity of ammonium molybdate, and the short-period pulse disturbance is combined to remove the residual gas at the end of the pores. The gradient desorption strategy reduces the decay rate of the adsorbent working capacity after 100 cycles, and the desorption energy consumption is also greatly reduced compared with the conventional vacuum desorption, thereby greatly prolonging the service life of the adsorbent.

[0017] 4. The acid-activated pretreatment is used to enhance the compactness of the silica gel skeleton, and the chelation loading technology of sodium copper ethylenediaminetetraacetate and ammonium molybdate is combined to firmly anchor the active components to the surface of the silica gel in the form of chemical bonds, thereby avoiding the loss of the active components caused by the traditional impregnation method, greatly improving the retention amount of the active components during the multiple adsorption and desorption cycles of the silica gel, and improving the use stability of the silica gel.

[0018] 5. The single silica gel material system used in the present application simplifies the complex tower structure required by the traditional multi-adsorbent packing, reduces the equipment investment cost, and at the same time, the staged adsorption-desorption mechanism is highly adapted to the characteristics of the synthetic ammonia tail gas components, without the need for additional gas pretreatment unit, the process flow is shortened, and it is particularly suitable for energy-saving modification of the existing synthetic ammonia device, thereby providing key technical support for large-scale application of hydrogen energy. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The process flow chart of the special silica gel for pressure swing adsorption hydrogen extraction prepared in the present application when purifying hydrogen from the synthetic ammonia tail gas. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical scheme and advantages of the present application more clear and explicit, the present application is further described in detail below in combination with specific examples.

[0021] Preparation example: the preparation process of the silica gel includes the following steps: 1 kg of solid sodium silicate is broken into particles with a particle size of ≤5 cm, added to a dissolving kettle with 2.5 kg of deionized water, and water vapor with a pressure of 0.6-0.8 MPa is introduced to heat the mixture to 150-160 °C and stir for 4-6 h to dissolve the sodium silicate. The mixture is then cooled to 35-40 °C to obtain a water glass solution. Concentrated sulfuric acid with a concentration of 98% is diluted with water to obtain a 30% sulfuric acid solution, and the solution is cooled to 25-30 °C. The prepared water glass solution and the 30% sulfuric acid solution are simultaneously injected into a reaction kettle in a parallel flow manner at a volume ratio of 1.8-2.2:1. The mixture is stirred for 5-8 min at 20-30 °C and pH=7-9, and the stirring is stopped after the gel is formed. The gel is solidified at room temperature for 1-2 h, cut into particles with a size of 5-8 mm, soaked in 0.5-1.0 mol / L dilute sulfuric acid at 40-50 °C for 8-12 h, washed with deionized water in a countercurrent manner until the pH value is 4-5, then soaked in 0.016%-0.02% dilute sulfuric acid at 25-30 °C for 12 h, and finally dehydrated by centrifugation until the water content is ≤60%, dried at 120-150 °C until the water content is <5%, ground and sieved to obtain silica gel with a particle size of 300-400 mesh.

[0022] Example 1: A specific preparation method of a special silica gel for pressure swing adsorption hydrogen extraction, comprising the following steps: The special silica gel for pressure swing adsorption hydrogen extraction includes pretreated adsorption silica gel and deeply treated adsorption silica gel. The preparation method of the pretreated adsorption silica gel comprises the following steps: S1. 10 kg of silica gel prepared according to the preparation example is added to 80 kg of a 10% hydrochloric acid solution, stirred at room temperature for 2 h, filtered, washed with deionized water until neutral, and dried to obtain acid-activated silica gel; S2. 10 kg of the acid-activated silica gel and 2 kg of 3-aminopropyltriethoxysilane are added to 80 kg of ethanol, heated to 60 °C, stirred for 6 h, cooled to room temperature, filtered, washed, and dried to obtain aminated silica gel; S3. 10 kg of the aminated silica gel and 2 kg of copper sodium ethylenediaminetetraacetate are added to deionized water, the pH value is adjusted to 3 with a 10% hydrochloric acid solution, heated to 60 °C, reacted for 2 h, cooled to room temperature, filtered, washed, and dried to obtain pretreated adsorption silica gel; The deeply treated adsorption silica gel comprises the following steps: Ⅰ. 10 kg of silica gel prepared according to the preparation example is added to 80 kg of a 10% hydrochloric acid solution, stirred at room temperature for 2 h, filtered, washed with deionized water until neutral, and dried to obtain acid-activated silica gel; II. 10 kg of acid-activated silica gel, 2 kg of heptadecafluorodecyltrimethoxysilane and 2 kg of 3-aminopropyltriethoxysilane were added to 80 kg of ethanol, heated to 60°C, stirred for 6 h, cooled to room temperature, filtered, washed, and dried to obtain aminofluorinated silica gel; III. 10 kg of aminofluorinated silica gel and 5 kg of ammonium molybdate were added to deionized water, the pH was adjusted to 5 with a 10% hydrochloric acid solution, heated to 60°C, stirred for 4 h, cooled to room temperature, filtered, washed, and dried to obtain deeply treated adsorption silica gel.

[0023] Example 2: A specific preparation method of a special silica gel for pressure swing adsorption hydrogen extraction, comprising the following steps: The special silica gel for pressure swing adsorption hydrogen extraction includes pretreated adsorption silica gel and deeply treated adsorption silica gel; the preparation method of the pretreated adsorption silica gel comprises the following steps: S1. 10 kg of silica gel prepared according to the preparation example was added to 100 kg of a 10% hydrochloric acid solution, stirred at room temperature for 2.5 h, filtered, washed with deionized water until neutral, and dried to obtain acid-activated silica gel; S2. 10 kg of acid-activated silica gel and 3 kg of 3-aminopropyltriethoxysilane were added to 100 kg of ethanol, heated to 70°C, stirred for 7 h, cooled to room temperature, filtered, washed, and dried to obtain aminated silica gel; S3. 10 kg of aminated silica gel and 3 kg of copper sodium ethylenediaminetetraacetate were added to 100 kg of deionized water, the pH was adjusted to 3.5 with a 10% hydrochloric acid solution, heated to 70°C, reacted for 3 h, cooled to room temperature, filtered, washed, and dried to obtain pretreated adsorption silica gel; The deeply treated adsorption silica gel comprises the following steps: I. 10 kg of silica gel prepared according to the preparation example was added to 100 kg of a 10% hydrochloric acid solution, stirred at room temperature for 2.5 h, filtered, washed with deionized water until neutral, and dried to obtain acid-activated silica gel; II. 10 kg of acid-activated silica gel, 3 kg of heptadecafluorodecyltrimethoxysilane and 3 kg of 3-aminopropyltriethoxysilane were added to 100 kg of ethanol, heated to 70°C, stirred for 7 h, cooled to room temperature, filtered, washed, and dried to obtain aminofluorinated silica gel; III. 10 kg of aminofluorinated silica gel and 6.5 kg of ammonium molybdate were added to 100 kg of deionized water, the pH was adjusted to 5.5 with a 10% hydrochloric acid solution, heated to 70°C, stirred for 5 h, cooled to room temperature, filtered, washed, and dried to obtain deeply treated adsorption silica gel.

[0024] Example 3: A specific preparation method of a special silica gel for pressure swing adsorption hydrogen extraction, comprising the following steps: The special silica gel for pressure swing adsorption hydrogen extraction comprises pretreated adsorption silica gel and deeply treated adsorption silica gel; the preparation method of the pretreated adsorption silica gel comprises the following steps: S1. 10 kg of silica gel prepared according to the preparation example is added into 120 kg of hydrochloric acid solution with a concentration of 10%, stirred at room temperature for 3 h, filtered, washed with deionized water until neutral, and dried to obtain acid-activated silica gel; S2. 10 kg of the acid-activated silica gel and 4 kg of 3-aminopropyl triethoxysilane are added into 120 kg of ethanol, heated to 80 ℃, stirred for 8 h, cooled to room temperature, filtered, washed, and dried to obtain aminosilica gel; S3. 10 kg of the aminosilica gel and 4 kg of copper sodium ethylenediaminetetraacetate are added into 120 kg of deionized water, the pH is adjusted to 4 with a 10% hydrochloric acid solution, heated to 80 ℃, reacted for 4 h, cooled to room temperature, filtered, washed, and dried to obtain pretreated adsorption silica gel; The deeply treated adsorption silica gel comprises the following steps: I. 10 kg of silica gel prepared according to the preparation example is added into 120 kg of hydrochloric acid solution with a concentration of 10%, stirred at room temperature for 3 h, filtered, washed with deionized water until neutral, and dried to obtain acid-activated silica gel; II. 10 kg of the acid-activated silica gel, 4 kg of heptadecafluorodecyl trimethoxysilane, and 4 kg of 3-aminopropyl triethoxysilane are added into ethanol, heated to 80 ℃, stirred for 8 h, cooled to room temperature, filtered, washed, and dried to obtain aminofluorosilica gel; III. 10 kg of the aminofluorosilica gel and 8 kg of ammonium molybdate are added into 120 kg of deionized water, the pH is adjusted to 6 with a 10% hydrochloric acid solution, heated to 80 ℃, stirred for 6 h, cooled to room temperature, filtered, washed, and dried to obtain deeply treated adsorption silica gel.

[0025] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that the special silica gel for pressure swing adsorption hydrogen extraction only comprises pretreated adsorption silica gel.

[0026] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that the special silica gel for pressure swing adsorption hydrogen extraction only comprises deeply treated adsorption silica gel.

[0027] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that the preparation methods of the pretreated adsorption silica gel and the deeply treated adsorption silica gel are interchanged.

[0028] Comparative Example 4: Comparative Example 4 differs from Example 2 in that the operation of the pretreated adsorption silica gel preparation step S3 is changed to "adding 10 kg of aminated silica gel and 3 kg of copper sodium ethylenediaminetetraacetate into 100 kg of deionized water, stirring at room temperature for 3 h, and then filtering, washing, and drying to obtain pretreated adsorption silica gel".

[0029] Comparative Example 5: Comparative Example 5 differs from Example 2 in that no heptadecafluorodecyltrimethoxysilane is added in the deep treatment adsorption silica gel preparation step II.

[0030] Comparative Example 6: Comparative Example 6 differs from Example 2 in that no 3-aminopropyltriethoxysilane is added in the deep treatment adsorption silica gel preparation step II.

[0031] Performance test: The pressure swing adsorption hydrogen extraction special silica gel prepared in Examples 1-3 and Comparative Examples 1-6 is applied to the adsorption purification and hydrogen extraction in the synthesis ammonia tail gas, which specifically includes the following process: A simulated synthesis ammonia tail gas is used, in which the gas components are 64% H2, 21% N2, 7% CH4, 3% NH3, 3% Ar, 1% CO2, 0.5% CO, and 0.5% H2O in volume percentage.

[0032] (1) Double-tower adsorption stage: a. Pretreated adsorption tower adsorption: the pretreated adsorption silica gel is loaded, and the synthesis ammonia tail gas is passed into the pretreated adsorption tower at a flow rate of 1500-1800 Nm³ / h·m³, the adsorption pressure is 2-3 MPa, the adsorption temperature is 25-35℃, and the adsorption cycle is 180-240 s, to obtain the pretreated synthesis ammonia tail gas; b. Deep treatment adsorption tower adsorption: the deep treatment adsorption silica gel is loaded, and the pretreated synthesis ammonia tail gas is passed into the deep treatment adsorption tower at a flow rate of 800-1200 Nm³ / h·m³, the adsorption pressure is 2-3 MPa, the adsorption temperature is 30-40℃, and the adsorption cycle is 120-150 s, to obtain the purified hydrogen; (2) Double-tower desorption stage: c. Pretreated adsorption tower desorption: the pressure is reduced to 0.05-0.1 bar, the temperature is increased to 45-55℃, and 80-100℃ nitrogen gas is used for reverse pulse blowing at a pressure of 1.5-2 bar, a flow rate of 500-600 Nm³ / h·m³, a pulse time of 5-10 s, an interval of 15 s, and a continuous time of 60-90 s. d. Deeply treated adsorption tower desorption: reduce the pressure to 0.01-0.03 bar, increase the temperature to 50-60℃, use 80-100℃ nitrogen with a pressure of 1.5-2 bar to reverse pulse blowing, the flow rate is 400-600Nm³ / h·m³, the pulse time is 3-5s, the interval is 5s, and the duration is 40-60s.

[0033] Hydrogen purity test: the purity of hydrogen in the treated synthetic ammonia tail gas was measured using a gas chromatograph (GC), and the experimental results are shown in Table 1.

[0034] Hydrogen recovery rate test: the recovery rate , and the experimental results are shown in Table 1.

[0035] Cyclic stability test: the silica gel samples prepared in Examples 1-3 and Comparative Examples 1-6 were subjected to 100 adsorption-desorption cycles in the adsorption tower, with steps a-d as one cycle, and the hydrogen purity and hydrogen recovery rate were tested every 20 times, and the experimental results are shown in Table 1.

[0036] Table 1 Performance test results

[0037] Performance analysis: As can be seen from the experimental data in Table 1, the special silica gel for pressure swing adsorption hydrogen extraction prepared by the application in the examples can effectively separate and purify hydrogen in synthetic ammonia tail gas using only silica gel as the adsorbent, with high purification and recovery efficiency, and can maintain good performance during multiple adsorption and desorption cycles, among which the comprehensive performance of Example 2 is the best.

[0038] As can be seen from the experimental data of Comparative Example 1 and Example 2, the pretreated silica gel in Comparative Example 1 adsorbs NH3, CO2 and H2O through coordination between the amino group and Cu 2+ , but lacks the synergistic effect of the hydrophobic layer (heptadecafluorodecyl) and ammonium molybdate of the deeply treated silica gel, resulting in the inability to effectively remove small molecules such as CO, N2 and CH4, and the accumulation of small molecule impurities that have not been removed in the adsorption tower, which are discharged together with hydrogen, reducing the purity of hydrogen; at the same time, the residual H2O can form a weak alkaline environment with NH3 in the subsequent gas, causing the destruction of the Cu 2+ coordination structure, further weakening the adsorption capacity, and during multiple adsorption and desorption cycles, the structure of the silica gel itself is destroyed, resulting in a decrease in the purification and hydrogen extraction performance of the silica gel.

[0039] From the experimental data of Comparative Example 2 and Example 2, it can be seen that in Comparative Example 2, the deep-processed silica gel relies on the hydrophobic layer to repel H2O and remove small molecules by weak chemical adsorption. However, when not pretreated, NH3, CO2 and H2O in the synthetic ammonia tail gas directly enter the adsorption tower, and the polar molecules destroy the structure of the hydrophobic layer, occupy the adsorption sites of ammonium molybdate, and cause the target impurities such as CH4, CO and N2 to be unable to be effectively adsorbed. At the same time, NH3 reacts with ammonium molybdate to generate NH3·MoO4 2- , consumes active components, weakens specific adsorption capacity, and causes the adsorbent to be quickly saturated due to impurity overload. Higher energy is required for desorption, but the actual desorption conditions are not adjusted, resulting in incomplete desorption, extremely low recovery rate, further accumulation of impurities in the cycle, and accelerated performance degradation.

[0040] From the experimental data of Comparative Example 3 and Example 2, it can be seen that in Example 2, the pretreated silica gel needs to preferentially remove polar molecules such as NH3 and H2O to provide a "clean" environment for the hydrophobic screening of the deep-processed silica gel. In Comparative Example 3, the processing order is reversed, and the deep-processed silica gel directly contacts polar gases such as NH3 and H2O, causing the low-surface-energy advantage of the deep-processed silica gel to be unable to be exerted, the hydrophobic surface of the deep-processed silica gel being unable to adsorb H2O, a large amount of polar gas occupying the space around the silica gel, and the silica gel losing its adsorption capacity for CO, N2, CH4 and Ar. At the same time, when the pretreated silica gel is placed last, its amino-Cu 2+ sites may also be occupied by small molecule gases, causing the removal efficiency of NH3 and CO2 to decrease, the synergistic effect of the two types of silica gel being broken, the overall capacity and selectivity of the adsorption tower decreasing, the hydrogen purity and recovery rate being affected, and the problem of incomplete desorption in the cycle being superimposed, with the performance continuously deteriorating.

[0041] From the experimental data of Comparative Example 4 and Example 2, it can be seen that in Example 2, by adjusting the pH to be acidic and heating, the —NH2 on the surface of the aminated silica gel is protonated to —NH3 + , forms a stable coordination bond with Cu 2+ in sodium copper ethylenediaminetetraacetate, this chemical bonding causes Cu 2+ to be firmly anchored on the surface of the silica gel, forming a high-density active site, while in Comparative Example 4, Cu 2+ is loaded by physical impregnation, sodium copper ethylenediaminetetraacetate is dispersed in the pores of the silica gel in a physically adsorbed form, does not form a chemical bond with the amino group, and Cu 2+ has weak binding force with the silica gel, is easily eluted during the desorption stage, causes the active site to be quickly lost, and significantly reduces the cycle stability. When physical impregnation occurs in Comparative Example 4, sodium copper ethylenediaminetetraacetate may accumulate in the pores of the silica gel in an agglomerated state, causing part of Cu 2+ to be wrapped and unable to contact NH3 and CO2 in the gas, the underutilized Cu 2+ reducing the impurity adsorption efficiency, causing the hydrogen purity to decrease, and finally the unbound Cu 2+Adsorption tower may be free and react with NH3, H2O, etc., such as generating copper ammonia complex, occupying pores and releasing H + , destroying the surface structure of silica gel, these by-products further block the pore, reduce the mass transfer efficiency, lead to the deterioration of adsorption kinetics, and the hydrogen purity and recovery rate decrease synchronously.

[0042] As can be seen from the experimental data of Comparative Example 5 and Example 2, the hydrophobic layer of heptadecafluorodecyl in Example 2 is the core design of the deep-processed silica gel, and the long-chain fluorocarbon structure can effectively repel H2O, avoid the occupation of the active site of ammonium molybdate, and when the component is lacking, H2O molecules directly contact ammonium molybdate, forming MoO4 2- ·nH2O complex, hindering its weak chemical adsorption of CH4 and other gases, resulting in the decrease of hydrogen purity and recovery efficiency; at the same time, when the hydrophobic layer is not introduced, the surface polarity of the silica gel is high, which may cause non-specific physical adsorption of various gases, for example, CH4 and Ar need to be adsorbed, but the physical adsorption strength is low, and they are easy to desorb in the desorption stage; and trace amounts of polar molecules (such as CO) may compete with ammonium molybdate due to the enhanced surface polarity, reducing its specific adsorption efficiency, resulting in incomplete adsorption and poor adsorption in the adsorption and desorption cycle, leading to the decrease of hydrogen purity, finally, the repeatedly desorption-readsorption of the physically adsorbed gas in the desorption stage aggravates the fatigue of the adsorbent structure, and the cycle stability deteriorates.

[0043] As can be seen from the experimental data of Comparative Example 6 and Example 2, in Example 2, 3-aminopropyltriethoxysilane provides amino groups for anchoring ammonium molybdate, and in Comparative Example 6, when the amino group is lacking, ammonium molybdate is only loaded on the surface of silica gel by physical adsorption, the binding force is weak, and it is easy to fall off in the desorption or cycle, resulting in the decrease of active sites, although the residual amount of ammonium molybdate is high in the initial stage, but its purification and hydrogen extraction performance in the adsorption and desorption cycle process rapidly decays with the cycle number.

[0044] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can make equivalent replacement or change according to the technical scheme and inventive concept of the present application within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for preparing silica gel for pressure swing adsorption hydrogen extraction, characterized in that, The special silica gel for pressure swing adsorption hydrogen extraction comprises pretreated adsorption silica gel and deeply treated adsorption silica gel, and the preparation method comprises the following steps: The preparation process of the silica gel comprises the following steps: The solid sodium carbonate is crushed to a particle size of ≤5 cm, added into a material dissolving kettle with deionized water, and then 0.6-0.8 MPa water vapor is introduced to heat to 150-160 ℃ for stirring and dissolving for 4-6 h, and then cooled to 35-40 ℃ to obtain a water glass solution; concentrated sulfuric acid with a concentration of 98% is diluted with water to a 30% sulfuric acid solution, and then cooled to 25-30 ℃; the prepared water glass solution and the 30% sulfuric acid solution are simultaneously injected into a reaction kettle by a parallel flow method at a volume ratio of 1.8-2.2:1 under the conditions of 20-30 ℃ and pH=7-9, and then stirred for 5-8 min; after the gel is formed, the stirring is stopped, and the gel is solidified at room temperature for 1-2 h; the gel is cut into particles with a size of 5-8 mm, and then soaked in 0.5-1.0 mol / L dilute sulfuric acid at 40-50 ℃ for 8-12 h; then the particles are washed with deionized water in a countercurrent manner until the pH value is 4-5; then the particles are soaked in 0.016%-0.02% dilute sulfuric acid at 25-30 ℃ for 12 h; then the particles are centrifuged and dehydrated until the water content is ≤60%; finally, the particles are dried at 120-150 ℃ until the water content is <5%, and then ground and sieved to obtain silica gel with a particle size of 300-400 mesh. In the preparation process of the silica gel, the solid sodium carbonate and the deionized water are in a weight ratio of 1-2.

5. The preparation process of the pretreated adsorption silica gel comprises the following steps: S1. The silica gel is added into a 10% hydrochloric acid solution, and then stirred and reacted at room temperature for 2-3 h; then the silica gel is filtered, washed with deionized water until neutral, and dried to obtain acid-activated silica gel; S2. The acid-activated silica gel and 3-aminopropyltriethoxysilane are added into ethanol, and then heated to 60-80 ℃ for stirring and reaction for 6-8 h; then the silica gel is cooled to room temperature, filtered, washed, and dried to obtain aminated silica gel; S3. The aminated silica gel and copper sodium ethylenediaminetetraacetate are added into deionized water, and then a 10% hydrochloric acid solution is used to adjust the pH value to 3-4; then the mixture is heated to 60-80 ℃ for reaction for 2-4 h; then the mixture is cooled to room temperature, filtered, washed, and dried to obtain pretreated adsorption silica gel. The preparation process of the deeply treated adsorption silica gel comprises the following steps: Ⅰ. The silica gel is added into a 10% hydrochloric acid solution, and then stirred and reacted at room temperature for 2-3 h; then the silica gel is filtered, washed with deionized water until neutral, and dried to obtain acid-activated silica gel; Ⅱ. The acid-activated silica gel, heptadecafluorodecyltrimethoxysilane, and 3-aminopropyltriethoxysilane are added into ethanol, and then heated to 60-80 ℃ for stirring and reaction for 6-8 h; then the silica gel is cooled to room temperature, filtered, washed, and dried to obtain aminated fluorinated silica gel; Ⅲ. The aminated fluorinated silica gel and ammonium molybdate are added into deionized water, and then a 10% hydrochloric acid solution is used to adjust the pH value to 5-6; then the mixture is heated to 60-80 ℃ for stirring and reaction for 4-6 h; then the mixture is cooled to room temperature, filtered, washed, and dried to obtain deeply treated adsorption silica gel.

2. The method of claim 1, wherein the method is characterized by: In S1, the silica gel and the 10% hydrochloric acid solution are in a weight ratio of 1:8-12.

3. The method for preparing silica gel for pressure swing adsorption hydrogen extraction according to claim 1, characterized in that, The acid-activated silica gel, 3-aminopropyl triethoxysilane and ethanol in S2 are in a weight ratio of 1:0.2-0.4:8-12.

4. The method of claim 1, wherein the method is characterized by: The aminated silica gel, sodium copper ethylenediaminetetraacetate and deionized water in S3 are in a weight ratio of 1:0.2-0.4:8-12.

5. The method for preparing silica gel for pressure swing adsorption hydrogen extraction according to claim 1, characterized in that, The silica gel and hydrochloric acid solution with a concentration of 10% in I are in a weight ratio of 1:8-12.

6. The method of claim 1, wherein the method is characterized by: The acid-activated silica gel, heptadecafluorodecyl trimethoxysilane, 3-aminopropyl triethoxysilane and ethanol in II are in a weight ratio of 1:0.2-0.4:0.2-0.4:8-12.

7. The method of claim 1, wherein the method is characterized by: The aminated fluorinated silica gel, ammonium molybdate and deionized water in III are in a weight ratio of 1:0.5-0.8:8-12.

8. A silica gel for pressure swing adsorption hydrogen extraction, characterized by comprising: The preparation method of the special silica gel for pressure swing adsorption hydrogen extraction according to any one of claims 1-7 is adopted.

9. The silica gel for pressure swing adsorption hydrogen extraction according to claim 8, wherein The special silica gel for pressure swing adsorption hydrogen extraction is applied to purify and extract hydrogen from synthetic ammonia tail gas, and the specific method comprises the following steps: (1) double-tower adsorption stage: a. pretreatment adsorption tower adsorption: the pretreatment adsorption silica gel is filled, the synthetic ammonia tail gas is introduced into the pretreatment adsorption tower at a flow rate of 1500-1800 Nm³ / h·m³, the adsorption pressure is 2-3 MPa, the adsorption temperature is 25-35 ℃, the adsorption cycle is 180-240 s, and the pretreated synthetic ammonia tail gas is obtained; b. deep treatment adsorption tower adsorption: the deep treatment adsorption silica gel is filled, the pretreated synthetic ammonia tail gas is introduced into the deep treatment adsorption tower at a flow rate of 800-1200 Nm³ / h·m³, the adsorption pressure is 2-3 MPa, the adsorption temperature is 30-40 ℃, the adsorption cycle is 120-150 s, and the purified hydrogen is obtained; (2) double-tower desorption stage: c. pretreatment adsorption tower desorption: the pressure is reduced to 0.05-0.1 bar, the temperature is increased to 45-55 ℃, the 80-100 ℃ nitrogen gas with a pressure of 1.5-2 bar is used for reverse pulse blowing at a flow rate of 500-600 Nm³ / h·m³, the pulse time is 5-10 s, the interval is 15 s, and the duration is 60-90 s; d. deep treatment adsorption tower desorption: the pressure is reduced to 0.01-0.03 bar, the temperature is increased to 50-60 ℃, the 80-100 ℃ nitrogen gas with a pressure of 1.5-2 bar is used for reverse pulse blowing at a flow rate of 400-600 Nm³ / h·m³, the pulse time is 3-5 s, the interval is 5 s, and the duration is 40-60 s.

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