Complex iron desulfurizer and preparation method thereof

Abstract

The invention relates to the technical field of environmental catalysis and pollution treatment, in particular to a complex iron desulfurizer and a preparation method thereof. According to the desulfurizing agent, double-path nano silicon dioxide is adopted to cooperate with surface modification, and through alkoxy silane grafting in an acid environment and an alkali environment, the system is endowed with high hydrophilicity and excellent dispersity, and the colloid stability and the interfacial activity are remarkably improved. Meanwhile, due to the design of a composite buffer shell of N-methyldiethanolamine and borax decahydrate, the pH and coordination stability of an active center of complex iron are effectively maintained, the carbon dioxide interference resistance is improved, and the cycle life is prolonged. The desulfurizer has excellent performance under the conditions of desulfurization efficiency, penetration time, volume sulfur capacity and multiple cycles, can still keep high efficiency in a high carbon dioxide atmosphere, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of environmental catalysis and pollution control technology, and in particular to a complexed iron desulfurizing agent and its preparation method. Background Technology

[0002] With the acceleration of industrialization, the treatment of harmful gases such as hydrogen sulfide has become an important issue in the field of environmental protection. Complexed iron desulfurization technology, as a highly efficient wet desulfurization process, is widely used in natural gas purification, coal gas desulfurization, and biomass gas purification due to its advantages such as mild reaction, good selectivity, and recyclability.

[0003] Traditional complexed iron desulfurizers mainly utilize ferric ions to form stable complexes with polycarboxylic acid chelating agents, converting hydrogen sulfide into elemental sulfur through redox reactions and restoring activity during oxidation regeneration. However, existing technologies have several shortcomings: First, complexed iron desulfurizers face serious dispersion stability problems in practical applications. Due to the insufficient surface charge density of complexed iron particles, they are prone to agglomeration and sedimentation in high ionic strength environments, leading to a sharp decrease in active surface area and a significant reduction in desulfurization efficiency. Especially in complex gas environments containing high concentrations of carbon dioxide, pH fluctuations caused by carbon dioxide absorption further exacerbate the instability of complexed iron, making the system prone to deactivation.

[0004] Secondly, low gas-liquid mass transfer efficiency is a key bottleneck restricting the improvement of desulfurization performance. Traditional desulfurizing agents have high surface tension, making it difficult to form an effective gas-liquid contact interface, which increases the resistance to hydrogen sulfide mass transfer from the gas phase to the liquid phase. At the same time, in gas-liquid contact equipment such as bubble column, the slow interface renewal rate makes it difficult to form a fresh liquid film, further reducing the mass transfer driving force and reaction rate.

[0005] Third, the regeneration performance is unstable. During multiple oxidation-regeneration cycles, the active centers of the complexed iron are easily interfered with by impurity ions, causing changes in the coordination environment and a decrease in redox reversibility. Especially in the absence of an effective buffer system, drastic fluctuations in pH can cause the complex to dissociate or form an inactive polymeric state, severely affecting long-term performance.

[0006] Fourth, existing modification strategies have limitations. Although some studies have attempted to improve the performance of desulfurizers by adding surfactants or dispersants, these additives often lead to side effects such as excessive foaming and interfacial contamination. Simple chemical modification cannot simultaneously meet the dual requirements of dispersion stability and mass transfer efficiency, often resulting in a trade-off between the two.

[0007] Fifth, the buffer system design is unreasonable. Traditional desulfurizers lack an effective pH buffering mechanism, and are prone to sudden pH drops under the impact of acidic gases such as carbon dioxide. This leads to instability of the complexed iron state, a reduction in the number of active sites, and a significant decrease in desulfurization capacity and reaction kinetics. Existing buffer systems either have insufficient buffering capacity or compete with the complexed iron system for coordination.

[0008] Based on the current state of the technology, there is an urgent need to develop a new method for preparing complexed iron desulfurizing agents. Through reasonable component ratios, surface modification, and process optimization, this method can simultaneously solve key technical problems such as poor dispersion stability, low mass transfer efficiency, and unstable cycle performance, in order to meet the stringent requirements of industrial applications. Summary of the Invention

[0009] In view of this, the purpose of this invention is to provide a complexed iron desulfurizing agent and its preparation method, so as to prepare a complexed iron desulfurizing agent with high dispersion stability and excellent gas-liquid mass transfer efficiency.

[0010] To achieve the above objectives, the present invention provides a complexed iron desulfurizing agent, which, by weight, contains the following components per 1600 parts of raw material: 54 parts of ferric chloride hexahydrate, 75-89 parts of ethylenediaminetetraacetic acid disodium dihydrate, 30-36 parts of citric acid monohydrate, 130-190 parts of sodium hydroxide solution, 5-9 parts of N-methyldiethanolamine, 15-23 parts of borax decahydrate, 0.8-1.2 parts of nano-silica A, 0.8-1.2 parts of nano-silica B, and the balance being deionized water.

[0011] Preferably, the concentration of the sodium hydroxide solution is 4 wt%.

[0012] Furthermore, the nano-silica A is obtained by grafting triethoxysilyl ethyl-terminated polydimethylsiloxane and methoxy polyethylene glycol triethoxysilane onto nano-silica after high-temperature dehydroxylation under an alkaline environment.

[0013] Preferably, the weight ratio of the nano-silica, triethoxysilyl ethyl-terminated polydimethylsiloxane, and methoxy polyethylene glycol triethoxysilane is 10:0.3-0.6:0.15-0.3.

[0014] Preferably, the high-temperature dehydroxylation is performed at 350-450°C for 1.5-3 hours.

[0015] Preferably, the alkaline environment is constructed from triethylamine, anhydrous ethanol, and deionized water in a weight ratio of 3-7:320-380:180-120.

[0016] Furthermore, the nano-silica B is obtained by grafting triethoxysilyl ethyl-terminated polydimethylsiloxane and methoxy polyethylene glycol triethoxysilane onto nano-silica after reflux and re-hydroxylation under acidic conditions.

[0017] Preferably, the weight ratio of the nano-silica, triethoxysilyl ethyl-terminated polydimethylsiloxane, and methoxy polyethylene glycol triethoxysilane is 10:0.3-0.6:0.15-0.3.

[0018] Preferably, the reflux hydroxylation is performed by refluxing and stirring in deionized water for 30-60 minutes.

[0019] Preferably, the acidic environment is constructed from glacial acetic acid, anhydrous ethanol, and deionized water in a weight ratio of 3-7:320-380:180-120.

[0020] Preferably, the grafting conditions are: stirring at 25°C for 30-60 minutes and then refluxing and stirring at 60°C for 3-5 hours.

[0021] Preferably, the average particle size of the nano-silica is 50 nm.

[0022] Preferably, the weight-average molecular weight of the triethoxysilyl ethyl-terminated polydimethylsiloxane is 800-900.

[0023] Preferably, the weight-average molecular weight of the methoxy polyethylene glycol triethoxysilane is 18,000-22,000.

[0024] Furthermore, the present invention also provides a method for preparing a complexed iron desulfurizing agent, comprising the following steps: (1) Add ferric chloride hexahydrate, part of ethylenediaminetetraacetic acid disodium dihydrate, citric acid monohydrate and part of sodium hydroxide solution to part of deionized water, stir at 35-45°C for 25-40 min to obtain complex intermediate solution; (2) Add N-methyldiethanolamine, borax decahydrate and some deionized water to the complex intermediate solution in step (1), and stir at 33-38°C for 20-30 min to obtain a complex dispersion with a buffer shell. (3) Add nano silica A and nano silica B to the complex dispersion encapsulated in the buffer shell of step (2), and stir at 33-38°C for 20-30 min to obtain a stable dispersion; (4) Add the remaining ethylenediaminetetraacetic acid disodium dihydrate and the remaining sodium hydroxide solution to the stable dispersion of step (3), let it stand at 25°C for 10-14 hours, and then make up the volume with the remaining deionized water to obtain the complexed iron desulfurizer.

[0025] Preferably, the weight ratio of ethylenediaminetetraacetic acid disodium dihydrate in step (1) to ethylenediaminetetraacetic acid disodium dihydrate in step (4) is 42-48:33-41.

[0026] Preferably, the weight ratio of the sodium hydroxide solution in step (1) to the sodium hydroxide solution in step (4) is 50-70:80-120.

[0027] The complexed iron desulfurizer of the present invention achieves significant improvements in dispersion stability, mass transfer efficiency and recycling performance through innovative dual-path nano-silica surface modification and stepwise complexation process.

[0028] Regarding dispersion stability, differentiated surface chemical environments were constructed by introducing dehydroxylated nano-silica A and rehydroxylated nano-silica B. Nano-silica A, after co-grafting modification under alkaline conditions, formed a high density of silanol groups and organosilicon segments on its surface, providing strong electrostatic repulsion and steric hindrance effects. Nano-silica B, after co-grafting modification under acidic conditions, retained a moderate hydroxyl density, forming a continuous hydrophilic brush layer structure. The synergistic effect of the two modified nanomaterials maintained a high negative potential value for the desulfurizer, effectively suppressing van der Waals attraction between particles, significantly reducing the tendency for aggregation and sedimentation, and ensuring long-term dispersion stability of the system.

[0029] In terms of mass transfer enhancement, the introduction of triethoxysilyl ethyl-terminated polydimethylsiloxane reduces the surface tension of the liquid film, promotes bubble rupture and interface renewal, and increases the gas-liquid contact area. Simultaneously, the hydrophilic segments formed by methoxy polyethylene glycol triethoxysilane enhance interfacial wettability and fluidity, reducing mass transfer resistance. The synergistic modification of the two-component silane achieves a balance between "low surface energy drainage" and "high wetting mass transfer," significantly improving the efficiency of hydrogen sulfide transfer from the gas phase to the liquid phase.

[0030] In terms of buffer stability, the buffer shell composed of N-methyldiethanolamine and borax decahydrate effectively resists pH shocks caused by carbon dioxide absorption. When carbon dioxide dissolution leads to a decrease in the system's pH, the buffer system rapidly releases hydroxide ions, maintaining the pH stability of the microenvironment around the complexed iron and preventing the complex from dissociating and precipitating. This localized pH buffering mechanism ensures the stability of the coordination structure of the active center of the complexed iron, maintaining high catalytic activity.

[0031] In terms of reaction kinetics, the stepwise complexation process avoids the problem of competing coordination and non-target ligands occupying internal coordination sites by rhythmically controlling the process through partial complexation, buffering, and then full complexation. The intermediate formed by the initial complexation provides an ordered binding pathway for subsequent ligands, ultimately forming an active complex with an optimized coordination environment. This control strategy not only improves the complexation efficiency but also enhances the redox reversibility of the complex.

[0032] In terms of regeneration performance, surface-modified nano-silica serves as a support framework, providing a stable loading environment for the complexed iron and preventing the loss and aggregation of active components during regeneration. Simultaneously, the buffer shell maintains local pH stability during oxidative regeneration, ensuring the stability of Fe... 3+ / Fe 2+ The reversibility of redox reactions significantly improves cycle life.

[0033] In terms of anti-interference capability, the multi-layer protective structure constructed by dual-path surface modification can effectively isolate the interference of impurity ions and reduce poisoning. Especially under high carbon dioxide concentration conditions, the presence of the buffer system enables the desulfurizer to maintain high activity, exhibiting excellent anti-interference performance.

[0034] In summary, this invention, through systematic material design and process innovation, achieves comprehensive performance improvement in stability, efficiency, and durability of complexed iron desulfurizer, providing reliable technical support for industrial applications. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0036] Figure 1 Viscosity-shear rate curves of the complexed iron desulfurizing agents prepared in Examples 1-3 and Comparative Examples 1-7 of this invention; Figure 2 The infrared spectra of nano-silica, nano-silica A, and nano-silica B in Example 2 of this invention are shown. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0038] Example 1: (1) 10g of nano silica (average particle size 50nm) was heated in a muffle furnace at 350°C for 1.5h, cooled and collected, and then dispersed in 320g of anhydrous ethanol and 180g of deionized water. The mixture was ultrasonically treated for 20min, and then 3g of triethylamine, 0.3g of triethoxysilyl ethyl-terminated polydimethylsiloxane (weight average molecular weight 840, Gelest, DMS-XT11) and 0.15g of methoxy polyethylene glycol triethoxysilane (weight average molecular weight 20000, Creative PEG Works, mPEG-Silane) were added. The mixture was stirred at 25°C for 30min and then refluxed at 60°C for 3h. After centrifugation, the mixture was washed three times with anhydrous ethanol and vacuum dried at 40°C for 6h to obtain nano silica A. (2) Add 10g of nano silica (average particle size 50nm) to 100g of deionized water, reflux and stir for 30min, cool and centrifuge to collect wet gel, then add 320g of anhydrous ethanol and 180g of deionized water, sonicate for 20min, add 3g of glacial acetic acid, 0.3g of triethoxysilyl ethyl-terminated polydimethylsiloxane (weight average molecular weight 840, Gelest, DMS-XT11) and 0.15g of methoxy polyethylene glycol triethoxysilane (weight average molecular weight 20000, Creative PEG Works, mPEG-Silane), stir at 25°C for 30min and then reflux at 60°C for 3h, centrifuge, wash 3 times with anhydrous ethanol, and vacuum dry at 40°C for 6h to obtain nano silica B; (3) Add 54g of ferric chloride hexahydrate, 42g of ethylenediaminetetraacetic acid disodium dihydrate, 30g of citric acid monohydrate and 50g of sodium hydroxide solution with a concentration of 4wt% to 850g of deionized water and stir at 35°C for 25min to obtain the complex intermediate liquid. (4) Add 5g N-methyldiethanolamine, 15g borax decahydrate and 120g deionized water to the complex intermediate solution in step (3), stir at 33°C for 20min to obtain a complex dispersion with a buffer shell. (5) Add 0.8g of nano silica A and 0.8g of nano silica B to the complex dispersion encapsulated in the buffer shell of step (4), and stir at 33°C for 20 min to obtain a stable dispersion. (6) Add 33g of disodium ethylenediaminetetraacetate dihydrate and 80g of sodium hydroxide solution with a concentration of 4wt% to the stable dispersion in step (5), let it stand at 25°C for 10h to mature, and then make up to 1600g with deionized water to obtain complexed iron desulfurizer.

[0039] Example 2: (1) 10g of nano silica (average particle size 50nm) was heated in a muffle furnace at 400°C for 2h, cooled and collected, and then dispersed in 350g of anhydrous ethanol and 150g of deionized water. The mixture was ultrasonically treated for 30min, and then 5g of triethylamine, 0.4g of triethoxysilyl ethyl-terminated polydimethylsiloxane (weight average molecular weight 840, Gelest, DMS-XT11) and 0.2g of methoxy polyethylene glycol triethoxysilane (weight average molecular weight 20000, Creative PEG Works, mPEG-Silane) were added. The mixture was stirred at 25°C for 45min and then refluxed at 60°C for 4h. After centrifugation, the mixture was washed 3 times with anhydrous ethanol and dried under vacuum at 40°C for 8h to obtain nano silica A. (2) Add 10g of nano silica (average particle size 50nm) to 100g of deionized water, reflux and stir for 45min, cool and centrifuge to collect wet gel, then add 350g of anhydrous ethanol and 150g of deionized water, sonicate for 30min, add 5g of glacial acetic acid, 0.4g of triethoxysilyl ethyl-terminated polydimethylsiloxane (weight average molecular weight 840, Gelest, DMS-XT11) and 0.2g of methoxy polyethylene glycol triethoxysilane (weight average molecular weight 20000, Creative PEG Works, mPEG-Silane), stir at 25°C for 45min and then reflux at 60°C for 4h, centrifuge, wash 3 times with anhydrous ethanol, and vacuum dry at 40°C for 8h to obtain nano silica B; (3) Add 54g of ferric chloride hexahydrate, 45g of ethylenediaminetetraacetic acid disodium dihydrate, 32g of citric acid monohydrate and 60g of sodium hydroxide solution with a concentration of 4wt% to 800g of deionized water and stir at 40°C for 30min to obtain the complex intermediate liquid. (4) Add 7g N-methyldiethanolamine, 19g borax decahydrate and 100g deionized water to the complex intermediate solution in step (3), stir at 35°C for 20min to obtain a complex dispersion with a buffer shell. (5) Add 1g of nano silica A and 1g of nano silica B to the complex dispersion encapsulated in the buffer shell of step (4), and stir at 35°C for 20 min to obtain a stable dispersion. (6) Add 37g of disodium ethylenediaminetetraacetate dihydrate and 100g of sodium hydroxide solution with a concentration of 4wt% to the stable dispersion in step (5), let it stand at 25°C for 12h to mature, and then make up to 1600g with deionized water to obtain complexed iron desulfurizer.

[0040] Example 3: (1) 10g of nano silica (average particle size 50nm) was heated in a muffle furnace at 450°C for 3h, cooled and collected, and then dispersed in 380g of anhydrous ethanol and 120g of deionized water. The mixture was ultrasonically treated for 40min, and then 7g of triethylamine, 0.6g of triethoxysilyl ethyl-terminated polydimethylsiloxane (weight average molecular weight 840, Gelest, DMS-XT11) and 0.3g of methoxy polyethylene glycol triethoxysilane (weight average molecular weight 20000, Creative PEG Works, mPEG-Silane) were added. The mixture was stirred at 25°C for 60min and then refluxed at 60°C for 5h. After centrifugation, the mixture was washed 3 times with anhydrous ethanol and vacuum dried at 40°C for 10h to obtain nano silica A. (2) Add 10g of nano silica (average particle size 50nm) to 100g of deionized water, reflux and stir for 60min, cool and centrifuge to collect wet gel, then add 380g of anhydrous ethanol and 120g of deionized water, sonicate for 40min, add 7g of glacial acetic acid, 0.6g of triethoxysilyl ethyl-terminated polydimethylsiloxane (weight average molecular weight 840, Gelest, DMS-XT11) and 0.3g of methoxy polyethylene glycol triethoxysilane (weight average molecular weight 20000, Creative PEG Works, mPEG-Silane), stir at 25°C for 60min and then reflux at 60°C for 5h, centrifuge, wash 3 times with anhydrous ethanol, and vacuum dry at 40°C for 10h to obtain nano silica B; (3) Add 54g of ferric chloride hexahydrate, 48g of ethylenediaminetetraacetic acid disodium dihydrate, 36g of citric acid monohydrate and 70g of sodium hydroxide solution with a concentration of 4wt% to 750g of deionized water and stir at 45°C for 40min to obtain the complex intermediate liquid; (4) Add 9g N-methyldiethanolamine, 23g borax decahydrate and 80g deionized water to the complex intermediate solution in step (3), stir at 38°C for 30min to obtain a complex dispersion with a buffer shell. (5) Add 1.2g of nano silica A and 1.2g of nano silica B to the complex dispersion encapsulated in the buffer shell of step (4), and stir at 38°C for 30 min to obtain a stable dispersion. (6) Add 41g of disodium ethylenediaminetetraacetate dihydrate and 120g of sodium hydroxide solution with a concentration of 4wt% to the stable dispersion in step (5), let it stand at 25°C for 14h to mature, and then make up to 1600g with deionized water to obtain complexed iron desulfurizer.

[0041] Comparative Example 1 The difference between Comparative Example 1 and Example 2 is that: the surface organosilane co-grafting modification of nano silica is not carried out, and the addition of triethoxysilyl ethyl-terminated polydimethylsiloxane and methoxy polyethylene glycol triethoxysilane in steps (1) and (2) of Example 2 is omitted. Nano silica without organic modification is directly used in the subsequent dispersion process (5).

[0042] Comparative Example 2 The difference between Comparative Example 2 and Example 2 is that only polydimethylsiloxane single-agent grafting is performed, and the addition of methoxy polyethylene glycol triethoxysilane is omitted. That is, in steps (1) and (2), only triethoxysilyl ethyl-terminated polydimethylsiloxane is added, and methoxy polyethylene glycol triethoxysilane is not added.

[0043] Comparative Example 3 The difference between Comparative Example 3 and Example 2 is that only methoxy polyethylene glycol triethoxysilane single-agent grafting is performed, and the addition of triethoxysilyl ethyl-terminated polydimethylsiloxane is omitted. That is, only methoxy polyethylene glycol triethoxysilane is added in steps (1) and (2), and triethoxysilyl ethyl-terminated polydimethylsiloxane is not added.

[0044] Comparative Example 4 The difference between Comparative Example 4 and Example 2 is that: the buffer shell design is not adopted, and the addition of N-methyldiethanolamine and borax decahydrate in step (4) is omitted. That is, a weak base buffer shell is not formed on the outer layer of the complexing intermediate liquid, and nano-silica is directly added to the complexing intermediate liquid without a buffer shell to carry out step (5).

[0045] Comparative Example 5 The difference between Comparative Example 5 and Example 2 is that the order of complexation and pH plateau are changed, and the sequential control of first half complexation, then buffering and then complexation in steps (3) and (4) is omitted. Instead, ferric chloride hexahydrate, ethylenediaminetetraacetic acid disodium dihydrate, N-methyldiethanolamine and borax decahydrate are added to deionized water and stirred for 50 min at room temperature.

[0046] Comparative Example 6 The difference between Comparative Example 6 and Example 2 is that the density regulation of silanol on the surface of silica is changed, the 400°C dehydroxylation and reflux rehydroxylation operation is not performed, and the original nano silica powder is directly used for the corresponding treatments in steps (1) and (2), while other conditions remain unchanged.

[0047] Comparative Example 7 The difference between Comparative Example 7 and Example 2 is that the catalytic conditions for the hydrolysis-condensation of alkoxysilanes are changed, and the base catalysis / acid catalysis conditions in step (1) and step (2) are interchanged. Specifically, glacial acetic acid is used for acid catalysis in step (1) and triethylamine is used for base catalysis in step (2), while other conditions remain unchanged.

[0048] Performance testing: Dispersion stability: The sample was diluted with deionized water to a solid content of 0.1 wt%, and the Zeta potential was determined by electrophoretic light scattering. The test temperature was 25°C, the equilibration time was 120 s, and the test was repeated 3 times and the average value was taken. The Zeta potential after standing for 0 h and 168 h was recorded. The results are shown in Table 1.

[0049] Viscosity-shear properties: Performed according to GB / T 2794-2022; samples were allowed to stand for 30 min to remove bubbles, then loaded onto a rotational rheometer and kept at a constant temperature of 25.0±0.2℃; pre-shearing was performed for 100 s. -1 After 60 seconds of continuous operation, allow the sample to stand for 300 seconds to reach equilibrium; then perform an upward scan of the shear rate from 0.1 to 100. -1Record the viscosity-shear rate curve, and the results are as follows: Figure 1 As shown.

[0050] Desulfurization removal rate, breakthrough time, and sulfur capacity: An acrylic bubbling absorption column (30 mm inner diameter, 300 mm height) was used, with a working liquid volume of 500 mL; the inlet gas was a pre-mixed standard gas: hydrogen sulfide volume fraction 3000 ppm, carbon dioxide volume fraction 5%, with the balance being nitrogen, and a total flow rate of 1.0 L·min. -1 The temperature was 30±1°C, and the system operated continuously at atmospheric pressure. Sampling ports were set at both the inlet and outlet. The hydrogen sulfide concentrations at the inlet and outlet were in accordance with HJ 1388-2024. Sampling, color development, measurement procedures, and quality control were carried out according to the standard. The breakthrough criterion was that the outlet hydrogen sulfide concentration / inlet hydrogen sulfide concentration ≥ 5%. Regeneration was performed by air bubbling after breakthrough (0.5 vvm, 30 min). After standing for 5 min, the system entered the next cycle. A total of 5 cycles were performed, and the desulfurization removal rate was recorded after 5 cycles. The results are shown in Table 1.

[0051] Anti-carbon dioxide interference: Increase the volume fraction of inlet carbon dioxide from 5% to 15%, keep the rest unchanged, run continuously, maintain each platform for 60 min, and record the pH (online electrode, calibrated at 25°C, NIST buffer) and desulfurization removal rate after 60 min.

[0052] Fourier transform infrared spectroscopy: The results were obtained using a Fourier transform infrared spectrometer. Figure 2 As shown.

[0053] Table 1 Performance Test Results ; Data Analysis: As can be seen from the data in Examples 1-3 of Table 1, the complexed iron desulfurizer prepared in this invention exhibits stable and balanced excellent performance in terms of dispersion stability, single-cycle desulfurization efficiency, breakthrough time, volumetric sulfur capacity, cycle retention rate, and carbon dioxide interference tolerance. This is mainly due to the pretreatment of the silanol density on the surface of nano-silica and the co-grafting of alkoxysilanes via both acid and alkali routes. On the one hand, a uniform hydrophilic brush layer is constructed to reduce intercolloidal adhesion and maintain a high Zeta potential; on the other hand, low surface energy fragments promote bubble film drainage and interface renewal, thus balancing dispersion stability and gas-liquid mass transfer. The complexation stage adopts a rhythm of first semi-complexation, then buffering, and then re-complexation, which avoids the sudden pH drop caused by carbon dioxide absorption and reduces the occupation of internal coordination sites by non-target ligands, thereby maintaining activity and kinetic advantages in continuous bubbling and cyclic regeneration. Therefore, the desulfurizer prepared in this invention can maintain a high level of desulfurization and a long breakthrough time even under complex gas compositions and multiple regeneration scenarios.

[0054] As can be seen from the data in Table 1 for Example 2 and Comparative Example 1, the absolute value of the Zeta potential in Comparative Example 1 is significantly lower and decays more significantly over time; the desulfurization removal rate, breakthrough time, and volumetric sulfur capacity are all significantly lower, and the retention rate under circulation and carbon dioxide interference is also worse. This may be due to the lack of synergy between triethoxysilyl ethyl-terminated polydimethylsiloxane and methoxy polyethylene glycol triethoxysilane, resulting in insufficient surface hydration layer and low surface energy drainage effect, making the colloid more prone to coalescence and sedimentation, inhibiting interface renewal, and amplifying local pH and ionic strength fluctuations, thus comprehensively weakening the mass transfer-reaction-regeneration chain.

[0055] As can be seen from the data in Table 1 for Example 2 and Comparative Example 2, the negative amplitude of the Zeta potential in Comparative Example 2 is lower and the long-term decay is greater; the overall performance indicators are lower than those in Example 2, and the decline is more obvious under carbon dioxide conditions. This may be because there are only low surface energy segments and the lack of a hydrophilic brush layer of methoxy polyethylene glycol triethoxysilane, resulting in insufficient hydration layer and electrostatic repulsion, leading to a decrease in dispersion stability and specific interface area; although there is some bubble film drainage, the mass transfer benefit is offset by agglomeration and sedimentation, which is manifested as a simultaneous decrease in breakthrough and sulfur capacity.

[0056] As can be seen from the data in Table 1 for Example 2 and Comparative Example 3, Comparative Example 3 performed relatively better in terms of dispersion stability and long-term Zeta potential, but its desulfurization removal rate, breakthrough, and sulfur capacity were still lower than those of Example 2, and there were also differences under circulation and carbon dioxide interference. This may be because the hydrophilic brush layer ensures dispersion, but lacks the dewetting and bubble film drainage effect of triethoxysilyl ethyl-terminated polydimethylsiloxane, resulting in insufficient interface renewal and gas-liquid mass transfer; the activity is not fully utilized, limiting the breakthrough time and effective sulfur capacity.

[0057] As can be seen from the data in Table 1 for Example 2 and Comparative Example 4, the Zeta potential of Comparative Example 4 decays more significantly over time, and desulfurization, breakthrough, and sulfur capacity all decrease significantly, with the decline in carbon dioxide interference being particularly pronounced. This may be because the absence of an N-methyldiethanolamine / borax decahydrate buffer shell means that the pH decline caused by carbon dioxide absorption cannot be suppressed, the iron complex state of ethylenediaminetetraacetic acid is unstable, the internal coordination sites are disturbed, and the oxidation kinetics and regeneration closed loop are disrupted, leading to a full-chain performance degradation.

[0058] As can be seen from the data in Table 1 for Example 2 and Comparative Example 5, Comparative Example 5 performed worse than Example 2 in all indicators, and its long-term stability and cycle retention were also weaker. This may be due to the loss of stepwise pH control and stepwise coordination process control, which easily leads to unfavorable coordination configurations and competition with free anions, making it difficult for the buffer shell to completely encapsulate the system. As a result, the density and accessibility of effective active sites decreased, and the system became more sensitive to fluctuations in carbon dioxide and ionic strength.

[0059] As can be seen from the data in Table 1 for Example 2 and Comparative Example 6, the Zeta potential and long-term stability of Comparative Example 6 are inferior to those of Example 2. Desulfurization, breakthrough, and sulfur capacity all decline, and cycling performance is moderately impaired. This may be due to the lack of a pre-set density for high-temperature dehydroxylation / rehydroxylation of silanols, resulting in uneven density and cross-linking of subsequent alkoxysilane grafts, producing a "patchy / bare" surface and discontinuous brushed layers; colloidal repulsion and interfacial effects weaken, and mass transfer and stability are simultaneously limited.

[0060] As can be seen from the data in Table 1 for Example 2 and Comparative Example 7, the overall indicators of Comparative Example 7 are lower than those of Example 2, showing a synergistic decrease in dispersion stability, penetration, and sulfur capacity, and the retention rate under carbon dioxide conditions is also affected. This may be because the acid / base catalytic exchange breaks the complementary pairing of "crosslinked patches / islands" and "uniform brush layer," causing a mismatch in morphology and grafting state between the two types of nano-silica, making it difficult to simultaneously achieve strong hydration stability and bubble film drainage, thus weakening the synergy of mass transfer and stabilization.

[0061] from Figure 1 It can be seen that Examples 1-3 and Comparative Examples 1-7 all exhibit significant shear thinning with increasing shear rate: among them, Example 2 shows significant shear thinning from 0.1 to 100 s. -1 The viscosity was lowest within the range and decreased monotonically; Examples 1 and 3 were slightly higher but also showed no significant upward inflection. In contrast, Comparative Example 2 had the highest overall viscosity, which peaked at approximately 65-75 seconds. -1 The most significant weak thickening was observed, with comparative examples 1 and 4 showing a small upward inflection, comparative examples 5 and 7 showing a moderate upward inflection, while comparative examples 3 and 6 remained basically monotonously thinned. This indicates that the dual silane co-grafting and buffer shell-stepwise complexation strategy not only improves dispersion stability but also suppresses high shear anomalies, thus being more conducive to gas-liquid mass transfer and circulation stability.

[0062] from Figure 1 It can be seen that, compared with the original nano-silica, both nano-silica A and B have dimensions of 2962 / 2925 / 2854 cm⁻¹. -1 A distinct CH stretching vibration peak was observed, and it was observed at 1260 cm⁻¹. -1 The presence of a strong Si-CH3 deformation vibration peak indicates successful grafting of organosilicon segments; sample A exhibits a higher peak intensity, with its 3745 / 3400 cm⁻¹ peak value being particularly high. -1 The (Si-OH / adsorbed water) ratio was significantly reduced, indicating that grafting was more thorough under alkaline catalysis; sample B, however, still retained a certain OH band width, and at 1110 cm⁻¹... -1 A weak shoulder peak (characteristic of COC in PEG) was observed, and a peak length of ~1716 cm⁻¹ was detected. -1 The weak carbonyl shoulder peak is a heterogeneous peak signal from residual acetate / acetate in the acid-catalyzed system. All three peaks maintain a common 1080 / 800 / 460 cm⁻¹. -1The Si-O-Si framework characteristics are present, but the addition of CH / Si-CH3 bands and OH attenuation in A / B compared to the original sample are direct evidence of successful modification.

[0063] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A complexed iron desulfurizing agent, characterized in that, By weight, each 1600 parts of raw material contains the following components: 54 parts of ferric chloride hexahydrate, 75-89 parts of disodium ethylenediaminetetraacetate dihydrate, 30-36 parts of citric acid monohydrate, 130-190 parts of sodium hydroxide solution, 5-9 parts of N-methyldiethanolamine, 15-23 parts of borax decahydrate, 0.8-1.2 parts of nano silica A, 0.8-1.2 parts of nano silica B, and the balance of deionized water; The nano-silica A is obtained by grafting triethoxysilyl ethyl-terminated polydimethylsiloxane and methoxy polyethylene glycol triethoxysilane onto nano-silica under alkaline conditions after high-temperature dehydroxylation. The weight ratio of the nano-silica, triethoxysilyl ethyl-terminated polydimethylsiloxane, and methoxy polyethylene glycol triethoxysilane is 10:0.3-0.6:0.15-0.

3. The nano-silica B is obtained by grafting triethoxysilyl ethyl-terminated polydimethylsiloxane and methoxy polyethylene glycol triethoxysilane onto nano-silica after reflux and re-hydroxylation under acidic conditions. The weight ratio of the nano-silica, triethoxysilyl ethyl-terminated polydimethylsiloxane, and methoxy polyethylene glycol triethoxysilane is 10:0.3-0.6:0.15-0.

3.

2. The complexed iron desulfurizer according to claim 1, characterized in that, The concentration of the sodium hydroxide solution is 4 wt%.

3. The complexed iron desulfurizer according to claim 1, characterized in that, The high-temperature dehydroxylation process involves treatment at 350-450°C for 1.5-3 hours.

4. The complexed iron desulfurizer according to claim 1, characterized in that, The alkaline environment is constructed from triethylamine, anhydrous ethanol, and deionized water in a weight ratio of 3-7:320-380:180-120.

5. The complexed iron desulfurizer according to claim 1, characterized in that, The reflux rehydroxylation is performed by refluxing and stirring in deionized water for 30-60 minutes.

6. The complexed iron desulfurizer according to claim 1, characterized in that, The acidic environment is constructed from glacial acetic acid, anhydrous ethanol, and deionized water in a weight ratio of 3-7:320-380:180-120.

7. The complexed iron desulfurizer according to claim 1, characterized in that, The weight-average molecular weight of the triethoxysilyl ethyl-terminated polydimethylsiloxane is 800-900.

8. The complexed iron desulfurizer according to claim 1, characterized in that, The weight-average molecular weight of the methoxy polyethylene glycol triethoxysilane is 18,000-22,000.

9. A method for preparing a complexed iron desulfurizing agent according to any one of claims 1-8, characterized in that, Includes the following steps: (1) Add ferric chloride hexahydrate, part of ethylenediaminetetraacetic acid disodium dihydrate, citric acid monohydrate and part of sodium hydroxide solution to part of deionized water, stir at 35-45°C for 25-40 min to obtain complex intermediate solution; (2) Add N-methyldiethanolamine, borax decahydrate and some deionized water to the complex intermediate solution in step (1), and stir at 33-38°C for 20-30 min to obtain a complex dispersion with a buffer shell. (3) Add nano silica A and nano silica B to the complex dispersion encapsulated in the buffer shell of step (2), and stir at 33-38°C for 20-30 min to obtain a stable dispersion; (4) Add the remaining ethylenediaminetetraacetic acid disodium dihydrate and the remaining sodium hydroxide solution to the stable dispersion of step (3), let it stand at 25°C for 10-14 hours, and then make up the volume with the remaining deionized water to obtain the complexed iron desulfurizer.

10. The method for preparing the complexed iron desulfurizing agent according to claim 9, characterized in that, The weight ratio of disodium ethylenediaminetetraacetate dihydrate in step (1) to disodium ethylenediaminetetraacetate dihydrate in step (4) is 42-48:33-41; the weight ratio of sodium hydroxide solution in step (1) to sodium hydroxide solution in step (4) is 50-70:80-120.

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