Selective removal agents, methods of making and using the same

Abstract

The present application relates to the field of adsorption separation technology, and particularly relates to a selective removal agent, a preparation method and application thereof. The selective removal agent contains calcium-scan double-metal layered hydroxide and diatomite, and the mass ratio of diatomite to calcium-scan double-metal layered hydroxide is greater than or equal to 0.14. The chemical formula of the calcium-scan double-metal layered hydroxide is [Ca x Sc(OH) y ]OH, x is 2-3, and y is 6-8. The selective removal agent provided in the present application has good selectivity to heat-stable salts and hydrogen phosphate, the selectivity adsorption ratio of hydrogen phosphate to heat-stable salt anions is greater than 6000, efficient separation of heat-stable salts and hydrogen phosphate can be achieved, the stability is good, the working cycle can be prolonged, and the selective removal agent is suitable for industrial popularization.

Description

Technical Field

[0001] This invention relates to the field of adsorption separation technology, specifically to a selective removal agent, its preparation method, and its application. Background Technology

[0002] In recent years, my country has set increasingly lower limits on the SO2 content in exhaust gases, and conventional amine solvents are finding it increasingly difficult to meet the emission standards for H2S, SO2, and COS organic sulfur by removing them.

[0003] Formulated solvents are a series of novel desulfurization and decarbonization solvents developed based on N-methyldiethanolamine (MDEA) aqueous solutions, designed to enhance the removal depth of H2S, SO2, and COS organic sulfur. By adding ammonium hydrogen phosphate to the MDEA aqueous solution to appropriately lower the solvent pH, the competitive absorption of H2S by CO2 can be reduced, improving the H2S purification degree, thus obtaining a formulated amine solution with enhanced H2S selective absorption.

[0004] Like conventional amine solutions, H2S selectively formulated amine solutions are susceptible to contamination from upstream gas extraction residues during gas purification. Many highly corrosive inorganic heat-stabilized salts accumulate in the solution, potentially causing corrosion and perforation issues. When the content of inorganic heat-stabilized salts, especially sodium chloride and calcium chloride, reaches 2% or higher, production quality problems such as excessive H2S content in the product gas may occur. When the content of sodium chloride and calcium chloride reaches 3% or higher, blockages may appear in the unit, causing operational difficulties.

[0005] While using existing reactivation technology to remove heat-stable salts from the enhanced H2S selective amine solution, hydrogen phosphate is also removed, resulting in poorer H2S selective amine solution after reactivation and serious exceedance of H2S content in the product gas.

[0006] Therefore, currently, purification plants, refineries, and chemical plants using H2S selectively absorbent alkanolamine solvents address production problems caused by solution deterioration by replacing the solution. The deteriorated amine solution removed can only be disposed of as waste. Because the deteriorated amine solution contains 40% or more of organic matter such as alkanolamines, and also contains toxic hydrogen sulfide, it is classified as hazardous waste. Waste disposal is difficult and costly, causing significant economic losses and environmental pressure for these production units.

[0007] To address the issue of simultaneous removal of heat-stable salts and hydrogen phosphate, hydrogen phosphate can be separated from the deteriorated amine solution using a selective adsorbent for either phosphate or hydrogen phosphate. Then, the heat-stable salts in the amine solution can be removed using conventional methods. Finally, the hydrogen phosphate on the adsorbent can be eluted back into the amine solution from which the heat-stable salts have been removed, thus achieving the goal of removing heat-stable salts without losing hydrogen phosphate.

[0008] Current research and inventions on the selective adsorption of phosphate or hydrogen phosphate in solution are all focused on wastewater dephosphorization research aimed at curbing eutrophication. Unlike H2S selective adsorption formulations of amine solutions, which involve high hydrogen phosphate content and strong competitive adsorption ions, these research and inventions target water bodies with low phosphate or hydrogen phosphate content and the absence of strongly competitive adsorption ions such as oxalate and thiosulfate. Related inventions are as follows:

[0009] CN101691250A discloses a selective adsorbent and method for the coexistence of chloride, nitrate, sulfate, and hydrogen phosphate ions. The adsorbent provided by this invention essentially does not remove chloride or nitrate ions, and exhibits slight desorption of sulfate ions, but its selective adsorption capacity for oxalate and thiosulfate ions, which have strong adsorption capabilities, is poor. Since the purpose of removing hydrogen phosphate ions from a H2S-enhancing selectively formulated amine solution is to separate it from the heat-stable salt anions, after the heat-stable salt anions are removed using conventional methods, the phosphate ions adsorbed on the adsorbent need to be eluted back into the amine solution. Therefore, the adsorbent is required to adsorb only hydrogen phosphate or phosphate ions, and not other anions.

[0010] CN101691250A is used to enhance the selective adsorption of H2S in a formulation of alcohol amine solution. It has a high co-adsorption rate of oxalate and thiosulfate, and also adsorbs sulfate to a certain extent, but its selectivity does not meet the requirements.

[0011] The remover provided by CN101691250A has a low adsorption capacity of 20 mg / g, suitable for selective adsorption of low to medium concentrations of anions. However, in H2S selective adsorption formulations of amine solutions, the concentrations of hydrogen phosphate and thermally stable salt anions are high, requiring the adsorbent or remover to have an adsorption capacity >100 mg / g. Therefore, the remover provided by this invention does not meet the selectivity and capacity requirements for enhanced H2S selective adsorption of hydrogen phosphate in amine solutions.

[0012] CN110575811A discloses the selective adsorption of phosphate in phosphorus-rich eutrophic water using a prepared zirconium-modified kaolin adsorbent. Results show that in a mixed solution with equal concentrations of sulfate, chloride, and phosphate, the zirconium-modified kaolin adsorbent achieved a phosphate removal rate of 63.39%, while the sulfate removal rate was 1.3% and the chloride removal rate was 1.82%. The maximum adsorption capacity of the adsorbent for phosphate was 12.43 mg / g.

[0013] CN110394150A discloses a method for selectively adsorbing phosphate ions using lanthanum-modified mesoporous silica aerogel. The provided adsorbent can selectively adsorb phosphate ions when chloride, nitrate, fluoride, sulfate, and phosphate ions coexist, with a maximum adsorption capacity of 42.08 mg / g.

[0014] In summary, existing inventions regarding the selective adsorption of phosphate or hydrogen phosphate cannot meet the selectivity and capacity requirements for enhancing the adsorption of hydrogen phosphate in H2S-selective formulations of alcoholic amine solutions. Therefore, there is an urgent need to provide a selective removal agent with good selectivity for hydrogen phosphate and thermally stable salts. Summary of the Invention

[0015] The purpose of this invention is to overcome the problem in the existing technology that the heat-stable salt and hydrogen phosphate ions are simultaneously removed during the regeneration process of the modified enhanced H2S selective amine solution, and to provide a selective removal agent, its preparation method and application.

[0016] A first aspect of the present invention provides a selective removal agent comprising a calcium scandium bimetallic layered hydroxide and diatomaceous earth; wherein the mass ratio of the diatomaceous earth to the calcium scandium bimetallic layered hydroxide is ≥0.14; and the chemical formula of the calcium scandium bimetallic layered hydroxide is [Ca...]. x Sc(OH) y ]OH, where x is 2-3 and y is 6-8.

[0017] A second aspect of the present invention provides a method for preparing a selective removal agent, the method comprising the following steps:

[0018] (1) The first alkaline solution and the active solution are mixed and reacted to obtain a precipitate; wherein the active solution contains a soluble calcium-containing compound and a soluble scandium-containing compound;

[0019] (2) The precipitate is modified by contacting it with a second alkaline solution to obtain the calcium scandium bimetallic layered hydroxide;

[0020] (3) The calcium scandium bimetallic layered hydroxide is mixed with diatomaceous earth and water and then granulated to obtain the selective removal agent.

[0021] The third aspect of the present invention provides the application of the selective dephosphorizing agent described in the first aspect of the present invention or the selective dephosphorizing agent prepared by the method described in the second aspect of the present invention in dephosphorization, preferably in the dephosphorization of deteriorated amine solution.

[0022] The beneficial technical effects that can be obtained by the present invention through the above technical solution are as follows:

[0023] 1) The selective removal agent provided in this invention has good selectivity for thermally stable salts and hydrogen phosphate ions. The selectivity ratio of hydrogen phosphate ions to thermally stable salt anions is >6000, which can achieve efficient separation of thermally stable salts and hydrogen phosphate ions.

[0024] 2) The selective removal agent provided in this invention has an adsorption capacity of up to 100 mg / g for hydrogen phosphate and a good removal effect on hydrogen phosphate.

[0025] 3) The preparation method of the selective removal agent provided in this invention has a simple process, and the product has high selectivity, adsorption capacity and stability, making it suitable for industrial promotion. Attached Figure Description

[0026] Figure 1 This is the X-ray diffraction pattern of the calcium scandium bimetallic layered hydroxide prepared in Preparation Example 1 of this invention;

[0027] Figure 2 This is the X-ray diffraction pattern of the calcium scandium bimetallic layered hydroxide prepared in Comparative Example 1 of this invention;

[0028] Figure 3 This is the infrared spectrum of the calcium scandium bimetallic layered hydroxide prepared in Preparation Example 1 of this invention.

[0029] Figure 4 A physical image of the selective adsorbent prepared in Example 1 of this invention. Detailed Implementation

[0030] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0031] A first aspect of the present invention provides a selective removal agent, wherein the selective removal agent comprises a calcium scandium bimetallic layered hydroxide and diatomaceous earth; wherein the mass ratio of the diatomaceous earth to the calcium scandium bimetallic layered hydroxide is ≥0.14; and the chemical formula of the calcium scandium bimetallic layered hydroxide is [Ca...]. x Sc(OH) y ]OH, where x is 2-3 and y is 6-8.

[0032] The heat-stable salts in deteriorated amine solutions generally include sulfates, oxalates, thiosulfates, chlorides, formates, acetates, and glycolates. The anions OH- between the layers of calcium-scandium bimetallic layered hydroxides... -It can exchange with other anions in the deteriorated amine solution. Among these, the higher the charge and the smaller the radius of the anion, the better it reacts with OH-. - The stronger the exchange capacity of hydrogen phosphate, the lower the exchange capacity of oxalate, thiosulfate, and phosphate.

[0033] However, due to the bimetallic layered hydroxide [Ca] provided in this invention (2～3) Sc(OH) (6～8) OH is strongly alkaline, and because calcium hydroxide is only slightly soluble, it forms a precipitate in [Ca...] (2～3) Sc(OH) (6～8) The interface between OH and the deteriorated amine solution can form a strongly alkaline thin layer. Therefore, under strongly alkaline conditions, hydrogen phosphate will be converted into phosphate, which is superior to oxalate and thiosulfate in the reaction with OH. - An exchange occurs. In addition, phosphate reacts with [Ca]. (2～3) Sc(OH) (6～8) The electrostatic interaction of scandium ions on the OH layer is greater than that of oxalate, thiosulfate, sulfate, chloride, formate, acetate, and glycolate.

[0034] Based on the two factors mentioned above, the hydrogen phosphate ions in the deteriorated amine solution can first cross [Ca]... (2～3) Sc(OH) (6～8) The interface between OH and the deteriorated amine solution is converted into phosphate ions at the interface and then enters the bimetallic layered hydroxide [Ca]. (2～3) Sc(OH) (6～8) The interlayer space of OH groups occupies adsorption sites. At these sites, phosphate ions react with calcium ions to form calcium phosphate deposits on the inner surface, promoting faster entry of phosphate ions into the interlayer space and increasing the adsorption capacity. Therefore, the bimetallic layered hydroxide [Ca] provided in this invention... (2～3) Sc(OH) (6～8) ]OH has good selectivity for heat-stable salts and hydrogen phosphate, which can achieve efficient separation of heat-stable salts and hydrogen phosphate.

[0035] Because calcium hydroxide is slightly soluble, calcium ions from the calcium-scandium bimetallic layered hydroxide will be lost upon contact with deteriorated amine solution, leading to crystal destruction. Mixing the calcium-scandium bimetallic layered hydroxide with diatomaceous earth for granulation increases the electronegativity of the selective remover particle surface, locking calcium ions onto the surface of the selective remover. This solves the problems of calcium ion loss and crystal destruction while maintaining the strongly alkaline thin layer.

[0036] In a preferred embodiment, the mass ratio of the diatomaceous earth to the calcium-scandium bimetallic layered hydroxide is 0.14-1, preferably 0.14-0.5.

[0037] In this invention, when the mass ratio of diatomaceous earth to calcium scandium bimetallic layered hydroxide is ≥0.14, the selective removal agent exhibits high adsorption selectivity and capacity, good stability, and significant industrial application value. As the diatomaceous earth content increases, the adsorption selectivity, capacity, and stability of the selective removal agent gradually increase. When the mass ratio of diatomaceous earth to calcium scandium bimetallic layered hydroxide is ≥1, the adsorption selectivity, capacity, and stability of the selective removal agent decrease somewhat, but still meet the requirements for industrial applications. The selective removal agent exhibits optimal overall performance when the mass ratio of diatomaceous earth to calcium scandium bimetallic layered hydroxide is between 0.14 and 0.5.

[0038] In a preferred embodiment, the chemical formula of the calcium scandium bimetallic layered hydroxide is [Ca2Sc(OH)6]OH or [Ca3Sc(OH)8]OH.

[0039] In a preferred embodiment, the selective adsorbent has an adsorption capacity for hydrogen phosphate ≥100 mg / g, preferably 120-150 mg / g.

[0040] In a preferred embodiment, the selective adsorbent has a selectivity ratio for hydrogen phosphate and thermally stable salt anions >6000, preferably 8000-20000, and more preferably 10000-17000.

[0041] In a preferred embodiment, the selective adsorbent maintains essentially unchanged adsorption performance after 10-50 days of operation.

[0042] A second aspect of the present invention provides a method for preparing a selective removal agent, the method comprising the following steps:

[0043] (1) The first alkaline solution and the active solution are mixed and reacted to obtain a precipitate; wherein the active solution contains a soluble calcium-containing compound and a soluble scandium-containing compound;

[0044] (2) The precipitate is modified by contacting it with a second alkaline solution to obtain the calcium scandium bimetallic layered hydroxide;

[0045] (3) The calcium scandium bimetallic layered hydroxide is mixed with diatomaceous earth and water and then granulated to obtain the selective removal agent.

[0046] In step (1),

[0047] In a preferred embodiment, the alkali in the first alkaline solution is selected from one or more of potassium hydroxide, sodium hydroxide, and lithium hydroxide.

[0048] In a preferred embodiment, the concentration of alkali in the first alkaline solution is 2-7 mol / L, preferably 3-5 mol / L.

[0049] In a preferred embodiment, the soluble calcium-containing compound is selected from one or more of calcium nitrate, calcium chloride, and calcium bromide, preferably calcium nitrate.

[0050] In a preferred embodiment, the soluble calcium-containing compound is selected from scandium nitrate and / or scandium chloride, preferably scandium nitrate.

[0051] In a preferred embodiment, the concentration of the soluble calcium-containing compound in the active liquid is 0.5-2.5 mol / L, preferably 1-2 mol / L.

[0052] In a preferred embodiment, the molar ratio of the soluble calcium-containing compound to the soluble scandium-containing compound is 3-1:1, preferably 2-3:1.

[0053] In this invention, the molar ratio of the soluble calcium-containing compound to the soluble scandium-containing compound can be approximately equal to the heating molar ratio of calcium and scandium in the prepared calcium-scandium bimetallic layered hydroxide.

[0054] In a preferred embodiment, the ratio of the first alkaline solution to the active solution is 100-300 mL: 100 g, preferably 125-185 mL: 100 g.

[0055] In a preferred embodiment, the reaction process includes: stirring the mixture obtained by mixing at 70-95°C for 4-12 hours, then heating to 80-95°C and letting it stand for 5-30 hours; more preferably, stirring the mixture obtained by mixing at 80-90°C for 6-8 hours, then heating to 85-95°C and letting it stand for 8-24 hours.

[0056] In this invention, a higher reaction temperature is beneficial for obtaining layered hydroxides with high crystallinity and good crystal structure. Standing at a higher temperature accelerates crystal growth, and a longer standing time allows for a more complete crystal structure.

[0057] In a preferred embodiment, after the reaction is completed, the resulting product is sequentially filtered, washed, and dried to obtain the precipitate. The washing is performed using water, preferably distilled water, until the pH of the effluent after washing is 7-8; the drying is carried out under vacuum at a temperature of 50-90°C.

[0058] In step (2),

[0059] In this invention, the interlayer anion in the precipitate obtained in step (1) is NO3.- and Cl - To modify the precipitate, the OH- in the second alkaline solution can be used. - Replace NO3 - and Cl - Thus, the interlayer anion is OH. - Layered hydroxides [Ca x Sc(OH) y ]OH.

[0060] In a preferred embodiment, the alkali in the second alkaline solution is selected from one or more of potassium hydroxide, sodium hydroxide, and lithium hydroxide.

[0061] In a preferred embodiment, the concentration of alkali in the second alkaline solution is >1 mol / L, preferably 2-3 mol / L.

[0062] In a preferred embodiment, the volume ratio of the second alkaline solution to the precipitate is ≥1, preferably 2-8.

[0063] In a preferred embodiment, the modification process includes: soaking the precipitate in the second alkaline solution at room temperature for 10-40 hours, preferably 20-30 hours.

[0064] In this invention, by controlling the alkaline solution and soaking time, NO3 in the precipitate can be removed. - All replaced with OH - To obtain [Ca] of a certain purity x Sc(OH) y ]OH. Room temperature has a commonly known meaning in the art, and the present invention does not specifically limit room temperature, which can be 10-35°C.

[0065] In a preferred embodiment, after the modification is completed, the modified product is first washed with a washing solution and then dried to obtain the calcium scandium bimetallic layered hydroxide.

[0066] In a preferred embodiment, the washing solution is selected from alcohol and / or water, preferably an aqueous solution of alcohol. The alcohol is selected from methanol and / or ethanol, and the concentration of the alcohol in the aqueous solution is 45-75 wt%, preferably 50-60 wt%.

[0067] In this invention, the use of an aqueous alcohol solution for cleaning results in a more uniform particle size of the prepared calcium-scandium bimetallic layered hydroxide powder.

[0068] In step (3),

[0069] In a preferred embodiment, the mass ratio of the diatomaceous earth to the calcium-scandium bimetallic layered hydroxide is ≥0.14 (i.e. ≥1 / 7), preferably 0.14-1, and more preferably 0.14-0.5 (i.e. 1 / 7-1 / 2).

[0070] In this invention, the calcium-scandium bimetallic layered hydroxide is mixed with diatomaceous earth and water and then granulated. This process increases the surface electronegativity of the selective remover, locks the calcium ions in the calcium-scandium bimetallic layered hydroxide onto the surface of the spheres, and forms a non-leaking, strongly alkaline thin layer on the surface of the selective remover. This enhances the selective adsorption and stability of the selective remover for hydrogen phosphate.

[0071] In a preferred embodiment, the mass ratio of the sum of the calcium scandium bimetallic layered hydroxide and diatomaceous earth to water is 5-8:1, preferably 6-7.5:1.

[0072] In a preferred embodiment, the granulation is performed in a pelletizing machine. The pelletizing machine rotates at a speed of 40-80 r / min, preferably 60-70 r / min; the rotation time is 5-20 min, preferably 8-10 min.

[0073] In this invention, excessively long rotation times result in large-diameter microspheres, leading to insufficient removal agent in a column of the same volume and thus low column capacity. Conversely, excessively short rotation times result in small-diameter microspheres with insufficient crushing resistance, making them prone to breakage in industrial applications and limiting their industrial value. Higher rotation speeds are beneficial for obtaining microspheres with high crushing resistance, but excessive crushing resistance can lead to overly dense microspheres, hindering anion diffusion and exchange. The inventors discovered that rotating at 60-70 r / min for 8-10 minutes produces microspheres with a diameter of 2-5 mm and a crushing resistance of 120-160 N / sphere, which is most suitable for industrial applications and provides the best adsorption effect.

[0074] The third aspect of the present invention provides the application of the selective dephosphorizing agent described in the first aspect of the present invention or the selective dephosphorizing agent prepared by the method described in the second aspect of the present invention in dephosphorization, preferably in the dephosphorization of deteriorated amine solution.

[0075] The selective removal agent provided in this invention can be used for the treatment of phosphorus-containing wastewater, especially for the treatment of deteriorated amine solutions. When used to treat deteriorated amine solutions, compared with existing phosphorus adsorbents, the selective removal agent provided in this invention has better selectivity for thermally stable salts and hydrogen phosphate ions. The selectivity ratio of hydrogen phosphate ions to thermally stable salt anions is >6000, which can achieve efficient separation of thermally stable salts and hydrogen phosphate ions.

[0076] The present invention will be described in detail below through embodiments.

[0077] Example 1: Preparation of calcium scandium bimetallic layered hydroxides

[0078] (1) Calcium nitrate and scandium nitrate were added to distilled water to obtain 217.9 g of active solution; wherein the molar concentration of calcium nitrate was 1.234 mol / L and the molar concentration of scandium nitrate was 0.617 mol / L; the above active solution was transferred to a stainless steel kettle with a polytetrafluoroethylene liner, and 283 mL of 4 mol / L sodium hydroxide aqueous solution was added. The stirrer was turned on and the temperature was raised to 80 °C. The reaction was carried out for 8 h, and then the temperature was raised to 85 °C. The mixture was allowed to stand at 85 °C for 24 h, and then cooled to room temperature for filtration. The mixture was washed with distilled water until the pH of the effluent was 7-8. The filtrate was placed in a vacuum drying oven and dried at 70 °C to obtain the precipitate.

[0079] (2) The dried precipitate was placed in a 3.0 mol / L sodium hydroxide aqueous solution with a volume of 5 times that of the precipitate and soaked for 20 h. Then, the alkali solution was washed off with a 50% ethanol aqueous solution and dried at 70 °C to obtain calcium scandium bimetallic layered hydroxide sample 1.

[0080] Example 2 of the preparation of calcium scandium bimetallic layered hydroxide

[0081] (1) Calcium nitrate and scandium nitrate were added to distilled water to obtain 218.6 g of active solution, wherein the molar concentration of calcium nitrate was 1.665 mol / L and the molar concentration of scandium nitrate was 0.555 mol / L; the above active solution was transferred to a stainless steel kettle with a polytetrafluoroethylene liner; 393 mL of 4 mol / L sodium hydroxide aqueous solution was added, the stirrer was turned on, the temperature was raised to 90 °C, and the reaction was carried out for 6 h. Then the temperature was raised to 95 °C and allowed to stand at 95 °C for 8 h. Then the solution was cooled to room temperature and filtered. The solution was washed with distilled water until the pH of the effluent was 7-8. The filtrate was placed in a vacuum drying oven and dried at 80 °C to obtain the precipitate.

[0082] (2) The dried precipitate was placed in a 2.5 mol / L sodium hydroxide aqueous solution with a volume of 6 times that of the precipitate and soaked for 24 h. Then, the alkali solution was washed off with a 60% ethanol aqueous solution and dried at 80 °C to obtain calcium scandium bimetallic layered hydroxide sample 2.

[0083] Preparation of Comparative Example 1

[0084] (1) Calcium nitrate and scandium nitrate were added to distilled water to obtain 190.2 g of active solution, wherein the molar concentration of calcium nitrate was 0.278 mol / L and the molar concentration of scandium nitrate was 0.555 mol / L; the above active solution was transferred to a stainless steel kettle lined with polytetrafluoroethylene; 393 mL of 4 mol / L sodium hydroxide aqueous solution was added, the stirrer was turned on, the temperature was raised to 90 °C, and the reaction was carried out for 6 h. Then the temperature was raised to 95 °C and allowed to stand at 95 °C for 8 h. Then the solution was cooled to room temperature and filtered. The solution was washed with distilled water until the pH of the effluent was 7-8. The filtrate was placed in a vacuum drying oven and dried at 80 °C to obtain the precipitate.

[0085] (2) The dried precipitate was placed in a 2.5 mol / L sodium hydroxide aqueous solution with a volume of 6 times that of the precipitate and soaked for 24 h. Then, the alkali solution was washed off with a 60% ethanol aqueous solution and dried at 80 °C to obtain calcium scandium bimetallic compound comparative sample 1.

[0086] Preparation of Comparative Example 2

[0087] (1) Calcium nitrate and scandium nitrate were added to distilled water to obtain 218.6 g of active solution, wherein the molar concentration of calcium nitrate was 2.220 mol / L and the molar concentration of scandium nitrate was 0.555 mol / L; the above active solution was transferred to a stainless steel kettle lined with polytetrafluoroethylene; 393 mL of 4 mol / L sodium hydroxide aqueous solution was added, the stirrer was turned on, the temperature was raised to 90 °C, and the reaction was carried out for 6 h. Then the temperature was raised to 95 °C and allowed to stand at 95 °C for 8 h. Then the solution was cooled to room temperature and filtered. The solution was washed with distilled water until the pH of the effluent was 7-8. The filtrate was placed in a vacuum drying oven and dried at 80 °C to obtain the precipitate.

[0088] (2) The dried precipitate was placed in a 2.5 mol / L sodium hydroxide aqueous solution with a volume of 6 times that of the precipitate and soaked for 24 h. Then, the alkali solution was washed off with a 60% ethanol aqueous solution and dried at 80 °C to obtain calcium scandium bimetallic compound comparative sample 2.

[0089] Test Example 1

[0090] The calcium-scandium bimetallic layered hydroxide sample 1 prepared in Example 1 was characterized by XRD, and the results are as follows: Figure 1 As shown.

[0091] Depend on Figure 1 It can be seen that the calcium scandium bimetallic layered hydroxide prepared in Example 1 exhibits diffraction peaks near 11°, 22°, and 34°, and a double diffraction peak at 60°, possessing the characteristic X-ray diffraction peaks of bimetallic layered hydroxides. This indicates that the material prepared in step (2) of Example 1 is a bimetallic layered hydroxide with the molecular formula [M 2+x N 3+ y (OH) z [A] n- ] m Where M and N represent metallic elements, and A represents metallic elements. n- This represents exchangeable anions.

[0092] X-ray diffraction analysis was performed on the calcium-scandium bimetallic compound prepared in Comparative Example 1, as shown in the results below. Figure 2 As shown. Obviously, Figure 2 No diffraction peaks were detected, indicating that the calcium-scandium bimetallic layered hydroxide could not be obtained when the molar ratio of the soluble calcium-containing compound to the soluble scandium-containing compound was 0.5:1.

[0093] X-ray diffraction analysis was performed on the calcium-scandium bimetallic compound prepared in Comparative Example 2, and the results were consistent with those of Comparative Sample 2. Figure 2 The results were essentially the same, and no diffraction peaks were detected, indicating that the calcium-scandium bimetallic layered hydroxide could not be obtained when the molar ratio of the soluble calcium-containing compound to the soluble scandium-containing compound was 4:1.

[0094] Test Example 2

[0095] The calcium-scandium bimetallic layered hydroxide sample 1 prepared in Example 1 was characterized by infrared spectroscopy. The characterization results are as follows: Figure 3 As shown.

[0096] Among them, at 3400cm -1 The broad absorption peak appearing nearby is the absorption peak of the hydroxyl group, at 3650 cm⁻¹. -1 The sharp absorption peaks that appear nearby are from free OH groups. - The absorption peak of is observed, but no other anion absorption peaks are seen. Therefore, [the following is a possible interpretation based on the given information:] ... Figure 3 It can be seen that the molecular formula of calcium scandium bimetallic layered hydroxide sample 1 prepared in Example 1 is [M 2+ x N 3+ y (OH) z [OH] m .

[0097] The exchangeable anions OH- in the deionizing agent are removed by replacing the hydrogen phosphate ions in a sodium hydrogen phosphate aqueous solution. 1- By measuring the change in hydrogen phosphate content and the removal dosage before and after aqueous solution exchange, it can be determined that m=1, that is, the molecular formula of calcium scandium bimetallic layered hydroxide sample 1 prepared in Example 1 is [M 2+ x N 3+ y (OH) z]OH.

[0098] Test Example 3

[0099] The calcium-scandium bimetallic layered hydroxide sample 1 prepared in Example 1 was characterized by electron microscopy and energy dispersive spectroscopy. The test results show that the calcium-scandium bimetallic layered hydroxide sample 1 prepared in Example 1 contains Ca, Sc and O, but no other elements (hydrogen cannot be detected by electron microscopy and energy dispersive spectroscopy), and the content ratio of Ca, Sc and O is Ca:Sc:O = 2:1:7.

[0100] Combining XRD patterns with infrared characterization and electron microscopy energy dispersive spectroscopy results, it can be determined that the molecular formula of the calcium scandium bimetallic layered hydroxide prepared in Example 1 is [Ca2Sc(OH)6]OH.

[0101] Referring to Test Examples 1-3, the calcium scandium bimetallic layered hydroxide sample 2 prepared in Example 2 was characterized in the same way. The characterization results show that the sample prepared in Example 2 is also a bimetallic layered hydroxide with the molecular formula [Ca3Sc(OH)8]OH.

[0102] Example 1

[0103] Following the preparation example 1 of calcium-scandium bimetallic layered hydroxide, calcium-scandium bimetallic layered hydroxide sample 1 was prepared. 60g of calcium-scandium bimetallic compound (comparative sample 1) was mixed with 8.6g of diatomaceous earth and 10g of water. The mixture was then rotated on a pelletizing machine at 65r / min for 9min to form small pellets, yielding selective removal agent S1. A photograph of the actual product is shown below. Figure 4 As shown.

[0104] Example 2

[0105] Calcium scandium bimetallic layered hydroxide sample 2 was prepared according to Example 2 of calcium scandium bimetallic layered hydroxide preparation. 60g of calcium scandium bimetallic compound comparative sample 2 was mixed with 8.6g of diatomaceous earth and 10g of water, and the mixture was rotated on a pelletizing machine at a speed of 65r / min for 9min to form small pellets, thus obtaining selective removal agent S2.

[0106] Comparative Example 1

[0107] Calcium-scandium bimetallic compound sample 1 was prepared according to Comparative Example 1. 60g of calcium-scandium bimetallic compound sample 1 was mixed with 8.6g of diatomaceous earth and 10g of water, and the mixture was rotated on a pelletizing machine at a speed of 65r / min for 9min to form small pellets, thus obtaining selective removal agent DS1.

[0108] Comparative Example 2

[0109] Calcium-scandium bimetallic compound sample 2 was prepared according to Comparative Example 2. 60g of calcium-scandium bimetallic compound sample 2 was mixed with 8.6g of diatomaceous earth and 10g of water, and the mixture was rotated on a pelletizing machine at a speed of 65r / min for 9min to form small pellets, thus obtaining the selective removal agent DS2.

[0110] Test Example 4

[0111] Simulated deteriorated amine solution: A heat-stabilizing salt (sodium sulfate, oxalic acid, sodium thiosulfate, sodium chloride, sodium formate, sodium acetate, and glycolic acid) and phosphoric acid are added to a 45% aqueous solution of methyl diethanolamine to prepare a simulated deteriorated amine solution; wherein, in the simulated deteriorated amine solution, the mass fraction of the heat-stabilizing salt is 6%, the mass fraction of hydrogen phosphate is 3%, and the molar ratio of sulfate ion: oxalate ion: thiosulfate ion: chloride ion: formate ion: acetate ion: glycolate ion is 1:1:1:1:1:1:1:1.

[0112] Take 10g of strong base anion exchange resin (purchased from Jiangsu Suqing Water Treatment Engineering Group Co., Ltd., product model 201×7) and ZnAl layered bimetallic hydroxide (prepared according to Experiment 1 of CN101691250A: mix AlCl3·6H2O, urea and ZnCl2 with water to prepare a mixed solution containing 10mM Zn). 2+ 5mM Al 3+ 35 mM urea was used to heat the mixture to 100°C and reflux it for 24 hours. Then the precipitate was filtered, washed with deionized water and anhydrous ethanol, dried under vacuum at 40°C, and then calcined at 600°C in air for 4 hours. Selective desorbent S1 prepared in Example 1, selective desorbent S2 prepared in Example 2, selective desorbent DS1 prepared in Comparative Example 1 and selective desorbent DS2 prepared in Comparative Example 2 were each placed in 100 g of the above simulated deteriorated amine solution. After shaking for 5 h, the solution was separated, and the content of various anions in the solution was measured. The adsorption capacity qe of the desorbent for each anion was calculated according to formula (1). The test results are shown in Table 1.

[0113]

[0114] q e --------Adsorption capacity, mg / g;

[0115] C0 --------- Initial concentration of anion, mass fraction 10 -6 ;

[0116] C e ---------Anion equilibrium concentration, mass fraction 10 -6 ;

[0117] w1 --------- Solution mass, g;

[0118] w2----------Removing agent mass, g.

[0119] Table 1

[0120]

[0121]

[0122] As shown in Table 1, the samples prepared by mixing the non-bimetallic layered hydroxide calcium scandium compound prepared in Comparative Examples 1-2 with diatomaceous earth do not have the ability to remove thermally stable salt anions and hydrogen phosphate ions. The samples prepared by mixing the calcium scandium bimetallic layered hydroxide prepared in Examples 1-2 with diatomaceous earth exhibit extremely high selectivity for hydrogen phosphate ions, with a selectivity ratio of hydrogen phosphate ions to thermally stable salt anions exceeding 6000 and an adsorption capacity for hydrogen phosphate ions >100 mg / g. Both the selectivity and adsorption capacity for hydrogen phosphate ions are significantly superior to existing technologies, enabling efficient separation of thermally stable salts and hydrogen phosphate ions.

[0123] Test Example 5

[0124] Calcium scandium bimetallic layered hydroxide sample 1 was prepared in accordance with Example 1 of the preparation of calcium scandium bimetallic layered hydroxide, and selective removal agent S1 was prepared in accordance with Example 1.

[0125] Sample 1 of calcium scandium bimetallic layered hydroxide and selective removal agent S1 were respectively packed into two adsorption columns. Then, the simulated deteriorated amine solution in Test Example 4 was continuously injected into each of the two adsorption columns from top to bottom at a flow rate of 4 mL / min. 5 g of sample was taken out at intervals, and the selectivity and adsorption capacity of the sample for hydrogen phosphate were tested according to the method described in Test Example 4. The test results are shown in Table 2.

[0126] Table 2

[0127]

[0128]

[0129] Table 2 shows that the initial adsorption capacity of calcium-scandium bimetallic layered hydroxide sample 1 was 172.036 mg / g. After rinsing with simulated deteriorated amine solution for 2 days, the adsorption capacity decreased to <0.001, because the crystals of calcium-scandium bimetallic layered hydroxide sample 1 were destroyed. The initial adsorption capacity of selective remover S1 was 146.018 mg / g. After rinsing with simulated deteriorated amine solution for 50 days, the adsorption capacity and selectivity for hydrogen phosphate remained basically unchanged.

[0130] Comparison of test results between calcium-scandium bimetallic layered hydroxide sample 1 and selective remover S1 shows that while using calcium-scandium bimetallic layered hydroxide alone to reactivate deteriorated amine solution yields good initial adsorption, its stability is poor, and it completely fails after two days, resulting in very poor industrial application value. However, when calcium-scandium bimetallic layered hydroxide is mixed with diatomaceous earth to form spherical selective adsorbent particles, these particles maintain long-term performance stability, demonstrating high industrial application value.

[0131] Example 3

[0132] In accordance with Example 2 of the preparation of calcium scandium bimetallic layered hydroxide, calcium scandium bimetallic layered hydroxide sample 2 was prepared. 60g of calcium scandium bimetallic compound comparative sample 2 was mixed with 60g of diatomaceous earth and 10g of water, and the mixture was rotated on a pelletizing machine at a speed of 65r / min for 9min to form small pellets, thus obtaining selective removal agent S3.

[0133] Comparative Example 4

[0134] Calcium scandium bimetallic layered hydroxide sample 2 was prepared according to Example 2 of calcium scandium bimetallic layered hydroxide preparation. 60g of calcium scandium bimetallic compound comparative sample 2 was mixed with 7.5g of diatomaceous earth and 10g of water, and the mixture was rotated on a pelletizing machine at a speed of 65r / min for 9min to form small pellets, thus obtaining selective removal agent DS3.

[0135] Test Example 6

[0136] Referring to Test Example 5, the stability of selective removal agents S3 and DS3 was tested, and the test results are shown in Table 3:

[0137] Table 3

[0138]

[0139] As shown in Table 3, after prolonged rinsing with simulated deteriorated amine solution, the adsorption capacity and selectivity of the selective remover S3 remain essentially unchanged for a long time. However, the adsorption capacity and selectivity are slightly low. Therefore, in this invention, the mass ratio of diatomaceous earth to calcium scandium bimetallic layered hydroxide should not exceed 1.

[0140] The initial adsorption capacity of the selective remover DS3 was 140.511 mg / g. After rinsing with simulated deteriorated amine solution for 5 days, the adsorption capacity dropped to <0.001, indicating that when the mass ratio of diatomaceous earth to calcium scandium bimetallic layered hydroxide is <0.14, the prepared sample cannot maintain stable performance for a long time and has no industrial application value.

[0141] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A selective removal agent, characterized in that, The selective removal agent contains calcium scandium bimetallic layered hydroxide and diatomaceous earth; wherein the mass ratio of diatomaceous earth to calcium scandium bimetallic layered hydroxide is ≥0.14; and the chemical formula of the calcium scandium bimetallic layered hydroxide is [Ca...]. x Sc(OH) y ]OH, where x is 2-3 and y is 6-8.

2. The selective removal agent according to claim 1, wherein, The mass ratio of the diatomaceous earth to the calcium-scandium bimetallic layered hydroxide is 0.14-1; And / or, the chemical formula of the calcium scandium bimetallic layered hydroxide is [Ca2Sc(OH)6]OH or [Ca3Sc(OH)8]OH.

3. The selective removal agent according to claim 2, wherein, The mass ratio of the diatomaceous earth to the calcium-scandium bimetallic layered hydroxide is 0.14-0.

5.

4. A method for preparing a selective removal agent, characterized in that, The method includes the following steps: (1) The first alkaline solution and the active solution are mixed and reacted to obtain a precipitate; wherein the active solution contains a soluble calcium-containing compound and a soluble scandium-containing compound; (2) The precipitate is modified by contacting it with a second alkaline solution to obtain the calcium scandium bimetallic layered hydroxide; (3) The calcium scandium bimetallic layered hydroxide is mixed with diatomaceous earth and water and then granulated to obtain the selective removal agent.

5. The preparation method according to claim 4, wherein, The alkali in the first alkaline solution is selected from one or more of potassium hydroxide, sodium hydroxide, and lithium hydroxide; And / or, the concentration of alkali in the first alkaline solution is 2-7 mol / L.

6. The preparation method according to claim 5, wherein, The concentration of alkali in the first alkaline solution is 3-5 mol / L.

7. The preparation method according to claim 4, wherein, The soluble calcium-containing compound is selected from one or more of calcium nitrate, calcium chloride, and calcium bromide; And / or, the soluble scandium-containing compound is selected from scandium nitrate and / or scandium chloride; And / or, the concentration of soluble calcium-containing compounds in the active solution is 0.5-2.5 mol / L; And / or, the molar ratio of the soluble calcium-containing compound to the soluble scandium-containing compound is 3-1:

1.

8. The preparation method according to claim 7, wherein, The soluble calcium-containing compound is calcium nitrate; And / or, the soluble scandium-containing compound is scandium nitrate; And / or, the concentration of soluble calcium-containing compounds in the active solution is 1-2 mol / L; And / or, the molar ratio of the soluble calcium-containing compound to the soluble scandium-containing compound is 2-3:

1.

9. The preparation method according to claim 4, wherein, The ratio of the first alkaline solution to the active solution is 100-300 mL: 100 g.

10. The preparation method according to claim 9, wherein, The ratio of the first alkaline solution to the active solution is 125-185 mL: 100 g.

11. The preparation method according to claim 4, wherein, The reaction process includes: stirring the mixture obtained by mixing at 70-95℃ for 4-12 hours, then heating to 80-95℃ and letting it stand for 5-30 hours.

12. The preparation method according to claim 11, wherein, The reaction process includes: stirring the mixture obtained by mixing at 80-90℃ for 6-8 hours, then heating to 85-95℃ and letting it stand for 8-24 hours.

13. The preparation method according to claim 4, wherein, After the reaction is completed, the resulting product is filtered, washed and dried in sequence.

14. The preparation method according to claim 4, wherein, The alkali in the second alkaline solution is selected from one or more of potassium hydroxide, sodium hydroxide, and lithium hydroxide; And / or, the concentration of alkali in the second alkaline solution is ≥1 mol / L.

15. The preparation method according to claim 14, wherein, The concentration of alkali in the second alkaline solution is 2-3 mol / L.

16. The preparation method according to claim 4, wherein, The volume ratio of the second alkaline solution to the precipitate is ≥1.

17. The preparation method according to claim 16, wherein, The volume ratio of the second alkaline solution to the precipitate is 2-8.

18. The preparation method according to claim 4, wherein, The modification process includes: soaking the precipitate in the second alkaline solution for 10-40 hours at room temperature.

19. The preparation method according to claim 18, wherein, The modification process includes: soaking the precipitate in the second alkaline solution for 20-30 hours at room temperature.

20. The preparation method according to claim 4, wherein, After the modification is completed, the modified product is first washed with a washing solution and then dried to obtain the calcium scandium bimetallic layered hydroxide.

21. The preparation method according to claim 20, wherein, The washing solution is selected from alcohol and / or water.

22. The preparation method according to claim 21, wherein, The washing solution is an aqueous solution of alcohol.

23. The preparation method according to claim 21, wherein, The alcohol is methanol and / or ethanol.

24. The preparation method according to claim 22, wherein, The concentration of alcohol in the aqueous solution of the alcohol is 45-75 wt%.

25. The preparation method according to claim 24, wherein, The concentration of alcohol in the aqueous solution is 50-60 wt%.

26. The preparation method according to claim 4, wherein, The mass ratio of the diatomaceous earth to the calcium-scandium bimetallic layered hydroxide is ≥0.

14.

27. The preparation method according to claim 26, wherein, The mass ratio of the diatomite to the calcium-scandium bimetallic layered hydroxide is 0.14-1.

28. The preparation method according to claim 27, wherein, The mass ratio of the diatomaceous earth to the calcium-scandium bimetallic layered hydroxide is 0.14-0.

5.

29. The preparation method according to claim 4, wherein, The mass ratio of the sum of the calcium scandium bimetallic layered hydroxide and diatomaceous earth to the mass of water is 5-8:

1.

30. The preparation method according to claim 29, wherein, The mass ratio of the sum of the calcium scandium bimetallic layered hydroxide and diatomaceous earth to water is 6-7.5:

1.

31. The preparation method according to claim 4, wherein, The granulation process is carried out in a pelletizing machine.

32. The preparation method according to claim 31, wherein, The rotation speed of the pelletizing machine is 40-80 r / min; the rotation time is 5-20 min.

33. The preparation method according to claim 32, wherein, The rotation speed of the pelletizing machine is 60-70 r / min; the rotation time is 8-10 min.

34. The application of a selective dephosphorizing agent according to any one of claims 1-3 or a selective dephosphorizing agent prepared by any one of claims 4-33 in dephosphorization.

35. The application according to claim 34, wherein, The application is in the dephosphorization of degraded amine solution.

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