Preparation method of high-purity iron-based complex

Abstract

The invention discloses a preparation method of a high-purity iron-based complex, and belongs to the technical field of wet catalytic oxidation desulfurization. Converting soluble ferric iron salt into ferric hydroxide precipitate, and filtering and washing to remove inorganic salt impurities; then, reacting the obtained ferric hydroxide with a soluble organic acid complexing agent to generate an iron-based complex; after the reaction, filtering the solution to remove insoluble impurities, and removing moisture under low-temperature and vacuum conditions to obtain high-purity iron-based complex powder; the iron-based complex powder can be used in the fields of industrial cleaning, desulfurizers, rust removers, dye production, medicines, food additives and the like; as a desulfurizing agent, the catalyst is applied to removal of high-concentration H2S in a CO2 atmosphere, and the desulfurization rate is 99.95% or above.

Description

Technical Field

[0001] The present invention belongs to the technical field of wet catalytic oxidation desulfurization, and particularly relates to a preparation method of a high-purity iron-based complex. Background Art

[0002] In industrial production, especially in the fields of coal chemical industry, petrochemical industry and natural gas treatment, the wet catalytic oxidation desulfurization process is widely used to treat high-acid gases containing hydrogen sulfide (H2S). The presence of hydrogen sulfide not only causes environmental pollution, but also causes serious corrosion to equipment and threatens the health of operators. Therefore, how to effectively remove hydrogen sulfide has become an urgent issue to be solved.

[0003] Iron-based complexes, due to their high catalytic performance, excellent regeneration ability and relatively high sulfur capacity, are particularly suitable for treating high-concentration hydrogen sulfide gas and thus become important catalysts in wet catalytic oxidation desulfurization. During the wet catalytic oxidation desulfurization process, the main role of iron-based complexes is to convert hydrogen sulfide into elemental sulfur through redox reactions, thereby achieving the desulfurization effect. This process generally consists of the following two steps: Redox reaction: The trivalent iron (Fe 3+ ) complex in the iron-based complex reacts with hydrogen sulfide to form elemental sulfur and is reduced to divalent iron (Fe 2+ ).

[0004] 2Fe 3+ +H2S→2Fe 2+ +S+2H + Regeneration reaction: The divalent iron (Fe 2+ ) is oxidized by oxygen under aerobic conditions and re-converted into trivalent iron (Fe 3+ ), thereby restoring the catalytic activity and being recycled.

[0005] 4Fe 2+ +O2+4H + →4Fe 3+ +2H2O The performance of the catalyst depends to a large extent on its purity, and the impurities in the iron-based complex will directly affect its catalytic performance and regeneration efficiency. The traditional preparation method of iron-based complexes usually involves reacting iron salts (such as ferrous sulfate, ferric nitrate or ferric chloride) with complexing agents (such as EDTA, citric acid, etc.) to form iron complexes. However, these iron salt solutions often contain impurities such as sulfate, nitrate or chloride ions that cannot be ignored. These impurities are very difficult to completely remove during the preparation process, which not only affects the catalytic effect of the iron-based complex, but also easily leads to the following problems: (1)Equipment corrosion: Impurities such as sulfate, nitrate, and chloride ions have strong corrosiveness. Especially under acidic conditions, they will accelerate the corrosion of steel equipment, shorten the service life of the equipment, and increase maintenance costs. Chloride ions are particularly likely to cause pitting corrosion of stainless steel, seriously affecting the safety of the equipment.

[0006] (2)Decline in catalytic performance: The presence of impurities will affect the binding ability of iron ions with complexing agents, reduce the stability of the complex, and thus affect the progress of the desulfurization reaction. Iron-based complexes containing impurities show low activity and poor regeneration ability during the catalytic desulfurization process, resulting in a decrease in the removal efficiency of hydrogen sulfide.

[0007] (3)By-product formation: Sulfate and nitrate may react with iron-based complexes or other solution components during the desulfurization process to form insoluble precipitates or by-products, which not only affect the effective use of the catalyst but also may clog the equipment and increase the maintenance difficulty.

[0008] Therefore, in order to improve the efficiency of wet catalytic oxidation desulfurization, reduce equipment corrosion, and ensure the long-term stable operation of the system, the preparation of impurity-free and high-purity iron-based complexes has become a key technical requirement. Summary of the Invention

[0009] The present invention overcomes the deficiencies of the prior art and provides a method for preparing a high-purity iron-based complex; it is applied to the removal of H2S; the main technical concept of the present invention is to first prepare iron hydroxide from a soluble iron salt, then react with an organic acid complexing agent to form a pure iron-based complex, and finally apply it to the removal of high-concentration H2S under a CO2 atmosphere. This method has a simple process, is easy to industrialize, and the obtained product has high purity and stable performance.

[0010] The present invention is realized through the following technical solutions: A method for preparing a high-purity iron-based complex, comprising the following steps: S1. Dissolve a soluble ferric salt in deionized water, add an alkali solution, and after the reaction is complete, filter and wash the generated Fe(OH)3 precipitate; Dissolve the soluble ferric salt in water to obtain Fe 3+ ions, gradually add an alkali solution to form a ferric hydroxide (Fe(OH)3) precipitate, and filter the precipitate; wash it with deionized water in small amounts multiple times to remove excess impurities such as Na + , SO4 2- , Cl⁻ and NH4 + ions, and then detect Na + , SO4 2- , Cl⁻ and NH4 +After the concentration is lower than 0.1 mg / L, the washing end point is determined; finally, the Fe(OH)3 precipitate is dried to obtain high-purity Fe(OH)3. The reaction equation is as follows: Fe 3+ + 3NaOH = Fe(OH)3↓ + 3Na + S2. Disperse the prepared Fe(OH)3 precipitate in deionized water, and gradually add an organic acid complexing agent under stirring conditions for reaction. After the reaction is completed, filter to remove insoluble substances to obtain a complex solution; the reaction temperature is 55 - 65 °C, and the reaction time is 0.5 - 1 h; Disperse the prepared Fe(OH)3 in deionized water, and gradually add an organic acid complexing agent under stirring conditions. Control the reaction temperature at 55 - 65 °C and continue the reaction for 1 - 2 hours to ensure complete reaction of iron hydroxide with the complexing agent. During the reaction, Fe(OH)3 gradually dissolves to form a complex solution. The reaction equation is as follows: Fe(OH)3 + xHA = [Fe(A) x + 3H2O In the formula, HA: organic acid, where "A" represents an anion (such as citrate, aminotrimethylenephosphonate, etc.); [Fe(A) x represents an iron-based complex formed by iron ions and an organic acid; x: the coordination number in the organic acid, with a value range of 1 - 3 (depending on the structure and chelating ability of the acid).

[0011] S3. Dry the complex solution to obtain an iron-based complex [Fe(A) x ; the coordination number x = 1 - 3.

[0012] Preferably, wash the Fe(OH)3 precipitate with deionized water to make the impurity ion concentration lower than 0.1 mg / L.

[0013] Preferably, the alkali solution is a NaOH solution or a KOH solution.

[0014] Preferably, the soluble ferric salt is one or any combination of ferric sulfate, ferric chloride, ferric nitrate, and ammonium ferric sulfate.

[0015] Preferably, the solubility of the iron-based complex [Fe(A) x is greater than 50 g / L.

[0016] More preferably, the ligand A is any one of citrate, gluconate, hydroxyethylidene diphosphonate, and aminotrimethyl phosphonate.

[0017] Preferably, in step S3, the drying is carried out under vacuum conditions, and the complex solution is freeze-dried by the freeze-drying method.

[0018] Preferably, the lyophilization method is vacuum drying at a temperature below -40°C.

[0019] Preferably, before the complex solution is treated by the lyophilization method, it further includes the step of concentrating the complex solution by vacuum distillation.

[0020] After drying, the iron-based complex forms large lumps, which are crushed into fine powder using a grinding device, and then the powder is sieved using a sieve with an appropriate mesh number to ensure uniform particle size of the powder. When storing the prepared iron-based complex, it should be noted to avoid high temperature, light, and humid environment. It is recommended to use a light-proof and sealed container for storage to maintain dry and low-temperature conditions.

[0021] The iron-based complex prepared by the method of the present invention can be used as a desulfurizer in the wet catalytic oxidation desulfurization process for catalytic removal of H2S. A specific schematic process is described as follows: Weigh an appropriate amount of the iron-based complex and dissolve it in deionized water. After stirring until completely dissolved, adjust the pH value to 8-9 using one or more of Na2CO3, K2CO3, NaOH, KOH, or ammonia water, and place it in an absorption-regeneration device for wet catalytic oxidation to remove H2S for H2S removal. The main reactions are as follows, and the reaction equations are as follows: H2S + OH - → HS - + H2O 2Fe 3+ + HS - → 2Fe 2+ + S Fe 3+ : represents a trivalent iron complex; H2S: hydrogen sulfide; S: elemental sulfur; Fe 2+ : the generated divalent iron complex.

[0022] Regeneration reaction of complex iron - During the regeneration process, the divalent iron (Fe 2+ ) complex is oxidized back to trivalent iron (Fe 3+ ) under the action of oxygen and can continue to be used for the catalytic removal reaction of hydrogen sulfide. This process usually occurs in an aerobic environment.

[0023] 4Fe 2+ + O2 + 4H + → 4Fe 3+ + 2H2O Fe 2+ : divalent iron complex; O2: oxygen, used to oxidize iron ions; Fe 3+ : The regenerated ferric complex; H2O: The generated water.

[0024] The beneficial effects of the present invention compared with the prior art are as follows: The present invention provides a method for preparing a high-purity iron-based complex. The iron-based complex is synthesized through the acid-base neutralization reaction and complexation reaction of synthesized iron hydroxide and an organic acid complexing agent. Due to the high solubility and high purity of the organic acid complexing agent, in the acid-base neutralization reaction, the molar ratio of iron hydroxide to the organic acid complexing agent is precisely controlled to avoid the residue of excessive iron hydroxide or organic acid. At the same time, the reaction conditions (pH value control, reaction time control, etc.) are strictly controlled. The synthesized complex has strong coordination stability, can effectively prevent the oxidation or reduction of iron ions, and maintain stability for a long time. Corresponding hydroxides can be synthesized by selecting iron salts with different valence states according to the requirements of the final product, and the properties of the product can be flexibly adjusted; it is applicable to a variety of industrial fields, especially applications that require high-purity iron-based complexes, such as catalytic oxidation for H2S removal, food, medicine, and water treatment. Description of the Drawings

[0025] Figure 1 It is a schematic process flow diagram of high-concentration H2S desulfurization under a CO2 atmosphere in Example 8 of the present invention. Detailed Embodiments

[0026] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention will be further described in detail below in conjunction with the embodiments and the drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. The technical solutions of the present invention will be described in detail below in conjunction with the embodiments and the drawings, but the protection scope is not limited by this.

[0027] Example 1 This example proposes a method for preparing a high-purity iron-based complex, which specifically includes the following steps: S1. Preparation of iron hydroxide: Dissolve 56.20 g of Fe2(SO4)3·9H2O in 300 mL of deionized water to obtain a solution of Fe 3+ ions and SO4 2- ions. Gradually add 200 mL of a NaOH solution with a concentration of 3 mol / L under stirring to form a Fe(OH)3 precipitate, and filter the precipitate; wash the precipitate with deionized water in small amounts several times to remove excess impurities and Na⁺ and SO4 2- ions, and then detect Na⁺ and SO4 2-After the ion concentration is lower than 0.1 mg / L, the washing end point is determined. Finally, the Fe(OH)3 precipitate is dried to obtain high-purity Fe(OH)3. The reaction equation is as follows: Fe 3+ +3NaOH = Fe(OH)3↓+3Na + Preparation of S2 and iron-based complex: Weigh 10.69 g of the prepared Fe(OH)3 powder and 21.13 g of citric acid and disperse them in 200 mL of deionized water. Control the reaction temperature at 60°C ± 2°C and continuously stir and react for 0.5 hours to ensure the complete complexation reaction between iron hydroxide and citric acid. During the reaction process, the red-brown Fe(OH)3 particles gradually dissolve to form a light-brown iron citrate complex [Fe(C6H5O7)] solution. The reaction equation is as follows: Fe(OH)3+xHA = [Fe(A) x +3H2O In the formula, HA: citric acid, where "A" represents the citrate ion; [Fe(A) x represents the iron-based complex formed by iron ions and citric acid; x: the coordination number in the organic acid, with a value range of 1 to 3 (depending on the structure and chelating ability of the acid).

[0028] S3. Filtration and drying treatment: Filter the light-brown iron citrate complex solution after the reaction to remove insoluble impurities. Then freeze the filtered iron citrate complex solution to below -40°C to form a solid state. Place the frozen sample in a freeze dryer, and under vacuum conditions, the water directly sublimes into a gaseous state to form a dry iron citrate complex powder. Its advantage is that the freeze-drying method can complete the drying process at a low temperature, avoiding the influence of high temperature on the complex, and obtaining a purer iron-based complex powder; If the solution volume is large during filtration, the solution can be concentrated by vacuum evaporation to reduce the water content and increase the solid content.

[0029] S4. Powder treatment and storage: The dried iron citrate complex forms relatively large lumps. Use a grinding device to crush it into fine powder, and use a sieve with an appropriate mesh number to screen the powder to ensure uniform powder particle size; finally, store the iron citrate complex in a light-proof and sealed container under dry and low-temperature conditions.

[0030] Example 2 This example presents a method for preparing a high-purity iron-based complex, which specifically includes the following steps: S1. Preparation of iron hydroxide: Dissolve 54.06 g of FeCl3·6H2O in 300 mL of deionized water to obtain a solution of Fe³⁺ ions and Cl⁻ ions. Gradually add 200 mL of a 3 mol / L NaOH solution under stirring to form a Fe(OH)3 precipitate, and filter the precipitate; wash it with deionized water in small amounts multiple times to remove excess impurities and Na⁺ and Cl⁻ ions. Then, after detecting that the concentrations of Na⁺ and Cl⁻ ions are lower than 0.1 mg / L by ion chromatography, determine the washing end point. Finally, dry the Fe(OH)3 precipitate to obtain high-purity Fe(OH)3.

[0031] Preparation of S2 and iron-based complex: Weigh 10.69 g of the prepared Fe(OH)3 powder and 21.58 g of dextran acid and disperse them in 200 mL of deionized water. Control the reaction temperature at 60°C ± 2°C and continuously stir and react for 1 hour to ensure complete complexation reaction of iron hydroxide with malic acid. During the reaction process, the red-brown Fe(OH)3 particles gradually dissolve to form a yellowish-brown iron dextran complex [[Fe(OH)3] x ·[C6H 10 O5] n solution.

[0032] S3, Filtration and drying treatment: Filter the yellowish-brown complex solution after the reaction to remove insoluble impurities. Then freeze the filtered iron dextran complex solution to below -40°C to form a solid state. Place the frozen sample in a freeze dryer, and under vacuum conditions, the water directly sublimes into a gaseous state to form a dry iron dextran complex powder.

[0033] S4, Powder treatment and storage: The dried iron dextran complex forms relatively large lumps. Use grinding equipment to crush it into fine powder, and use a sieve with an appropriate mesh number to screen the powder to ensure uniform powder particle size; finally, store the iron dextran complex in a light-proof and sealed container under dry and low-temperature conditions.

[0034] Example 3 This example presents a preparation method of a high-purity iron-based complex, which specifically includes the following steps: Preparation of S1 and iron hydroxide: Dissolve 96.44 g of FeNH4(SO4)2·12H2O in 500 mL of deionized water to obtain Fe³⁺ ions, NH4⁻, and SO4 2-Ionic solution, 200 mL of 3 mol / L NaOH solution was gradually added under stirring to form Fe(OH)₃ precipitate, and the precipitate was filtered; the precipitate was washed with deionized water in small amounts multiple times to remove excess impurities and Na⁺ and Cl⁻ ions, and then after detecting that the concentrations of Na⁺ and Cl⁻ ions were lower than 0.1 mg / L by ion chromatography, the washing end point was determined. Finally, the Fe(OH)₃ precipitate was dried to obtain high-purity Fe(OH)₃.

[0035] S2. Preparation of iron-based complex: Weigh 10.69 g of the prepared Fe(OH)₃ powder and 33.00 g of aminotrimethylenephosphonic acid and disperse them in 200 mL of deionized water. The reaction temperature was controlled at 60°C ± 2°C, and the reaction was continuously stirred for 3 hours to ensure the complete complexation reaction of iron hydroxide and aminotrimethylenephosphonic acid. During the reaction, the red-brown Fe(OH)₃ particles gradually dissolved to form a light-yellow iron aminotrimethylenephosphonate complex [Fe(C₃H 12 NO₉P₃)₃] solution.

[0036] S3. Filtration and drying treatment: The light-yellow complex solution after the reaction was filtered to remove insoluble impurities, and then the filtered iron aminotrimethylenephosphonate complex solution was frozen to below -40°C to form a solid state. The frozen sample was placed in a freeze dryer, and under vacuum conditions, the water directly sublimated into a gaseous state to form a dry iron aminotrimethylenephosphonate complex powder.

[0037] S4. Powder treatment and storage: The dried iron aminotrimethylenephosphonate complex formed relatively large lumps, which were crushed into fine powder using grinding equipment, and the powder was sieved using a sieve with an appropriate mesh number to ensure uniform powder particle size; finally, the iron aminotrimethylenephosphonate complex was stored in a light-proof and sealed container under dry and low-temperature conditions.

[0038] Example 4 This example presents a method for preparing a high-purity iron-based complex, which specifically includes the following steps: S1. Preparation of iron hydroxide: Dissolve 96.44 g of FeNH₄(SO₄)₂·12H₂O in 500 mL of deionized water to obtain Fe³⁺ ions, NH₄⁻ and SO₄ 2-Ionic solution, 200 mL of 3 mol / L NaOH solution was gradually added under stirring to form Fe(OH)₃ precipitate, and the precipitate was filtered; the precipitate was washed with deionized water in small amounts multiple times to remove excess impurities and Na⁺ and Cl⁻ ions. Then, after detecting that the concentrations of Na⁺ and Cl⁻ ions were lower than 0.1 mg / L by ion chromatography, the washing end point was determined. Finally, the Fe(OH)₃ precipitate was dried to obtain high-purity Fe(OH)₃.

[0039] S2. Preparation of iron-based complex: Weigh 10.69 g of the prepared Fe(OH)₃ powder and 22.00 g of hydroxyethane diphosphonic acid and disperse them in 200 mL of deionized water. The reaction temperature was controlled at 60°C ± 2°C, and the reaction was continuously stirred for 1 hour to ensure complete complexation reaction between iron hydroxide and hydroxyethane diphosphonic acid. During the reaction, the red-brown Fe(OH)₃ particles gradually dissolved to form a yellowish-brown iron hydroxyethane diphosphonate complex [Fe(C₂H₇O₇P₂)₃] solution.

[0040] S3. Filtration and drying treatment: Filter the yellowish-brown complex solution after the reaction to remove insoluble impurities. Then, freeze the filtered iron hydroxyethane diphosphonate complex solution to below -40°C to form a solid state. Place the frozen sample in a freeze dryer, and under vacuum conditions, the water directly sublimes into a gaseous state to form dry iron hydroxyethane diphosphonate complex powder.

[0041] S4. Powder treatment and storage: The dried iron hydroxyethane diphosphonate complex forms relatively large lumps. Use grinding equipment to crush it into fine powder, and use a sieve with an appropriate mesh number to screen the powder to ensure uniform powder particle size; finally, store the iron hydroxyethane diphosphonate complex in a light-proof and sealed container under dry and low-temperature conditions.

[0042] Example 5 Taking Examples 1, 2, 3, and 4 as examples, it is applied to the process of wet catalytic oxidation for H₂S removal. The absorption-regeneration device for wet catalytic oxidation of H₂S removal is as Figure 1 shown. Both the absorption device and the regeneration device use a jacketed reactor with an inner height of 175 mm, an inner diameter of 70 mm, a height-to-diameter ratio of 2.5:1, and a volume of 500 mL. The absorption and regeneration temperatures can be controlled separately by a constant temperature water bath. The H₂S raw gas used in the experiment was prepared in the laboratory, with high-purity CO₂ as the dilution gas. The concentration of hydrogen sulfide in the prepared mixed gas was 50000 mg / Nm 3Under atmospheric pressure conditions, the flow rates of the hydrogen sulfide mixed gas and air are regulated by a mass flow meter. The H2S feed gas and air reach the gas distributor through the mass flow meter to make full contact with the desulfurization liquid. The lean liquid and rich liquid are recycled by a peristaltic pump.

[0043] Experimental conditions: c0(H2S)=50000 mg / Nm 3 , H2S flow rate: 800 mL / min, regeneration air flow rate: 300 mL / min, absorbent liquid flow rate: 100 mL / min, regeneration liquid flow rate: 100 mL / min, reaction temperature 25 °C, height-diameter ratio 2.5:1, reaction time 8 h. The volume of the desulfurization liquid for each experiment is 1000 mL, and the concentration of Fe 3+ is 2000 mg / L. The pH value of the desulfurization liquid is adjusted to 8-9 by one or more of Na2CO3, K2CO3, NaOH, KOH or ammonia water. The H2S gas purified by the desulfurization liquid is sampled every 30 min for qualitative and quantitative analysis using gas chromatography. After the experiment, the desulfurization liquid is quantitatively analyzed for by-products and iron content. The experimental results are shown in Table 1. The desulfurization efficiency η refers to the ratio of the difference between the H2S concentration (c0) at the inlet of the absorption device and the H2S concentration (c) at the outlet to the inlet H2S concentration within a certain period of time. The formula is: In the above formula: c0 is the initial hydrogen sulfide concentration, unit mg / Nm 3 ; c is the hydrogen sulfide concentration after desulfurization, unit mg / Nm 3 .

[0044] In summary, the method for preparing the iron-based complex provided by the present invention has a simple process, high production efficiency, a high iron ion content and low impurity content in the prepared iron-based complex, can effectively improve the desulfurization effect, and has a stable complex structure, can be reused multiple times, effectively reduces the desulfurization cost, and has high practical value.

[0045] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific embodiments of the present invention are limited to this. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the premise of the present invention, several simple deductions or substitutions can still be made, which should all be regarded as belonging to the patent protection scope determined by the claims submitted by the present invention.

Claims

1. A method for preparing a high-purity iron-based complex, characterized in that, It includes the following steps: S1. Dissolve soluble ferric salt in deionized water. After adding an alkali solution and reacting completely, filter and wash the generated Fe(OH)3 precipitate. S2. Disperse the prepared Fe(OH)3 precipitate in ionized water. Gradually add an organic acid complexing agent under stirring conditions for reaction. After the reaction ends, filter to remove insoluble substances to obtain a complex solution. The reaction temperature is 55-65 °C, and the reaction time is 0.5-1 h. S3. Dry the complex solution to obtain an iron-based complex [Fe(A) x ; The coordination number x = 1 to 3.

2. The preparation method of a high-purity iron-based complex according to claim 1, characterized in that, In step S1, the Fe(OH)3 precipitate is washed with deionized water to make the impurity ion concentration lower than 0.1 mg / L.

3. The preparation method of a high-purity iron-based complex according to claim 1, characterized in that, The alkali solution is NaOH solution or KOH solution.

4. The preparation method of a high-purity iron-based complex according to claim 1, wherein, The soluble ferric salt is one or any combination of ferric sulfate, ferric chloride, ferric nitrate, ammonium ferric sulfate.

5. The preparation method of a high-purity iron-based complex according to claim 1, characterized in that, The solubility of the iron-based complex [Fe(A) x is greater than 50 g / L.

6. The preparation method of a high-purity iron-based complex according to claim 5, characterized in that, Ligand A is any one of citrate, gluconate, hydroxyethylidene diphosphonate, aminotrimethylene phosphonate.

7. The preparation method of a high-purity iron-based complex according to claim 1, characterized in that, In step S3, the drying is carried out under vacuum conditions by freeze-drying the complex solution using the freeze-drying method.

8. The preparation method of a high-purity iron-based complex according to claim 7, characterized in that, The freeze-drying method is carried out under vacuum drying at a temperature below -40 °C.

9. The preparation method of a high-purity iron-based complex according to claim 7, characterized in that, Before the complex solution is treated by the freeze-drying method, it also includes the step of concentrating the complex solution by vacuum distillation.

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