Method for selectively removing iron ions in cobalt manganese acetate catalyst system
By controlling the pH value in steps and using hydrogen peroxide oxidation, the problem of removing iron ions in the cobalt manganese acetate catalyst was solved, and the efficient recovery and resource utilization of the cobalt manganese catalyst was achieved, reducing costs and environmental pollution.
Patent Information
- Application Number
- CN202510837688.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2025-03-14
- Filing Date
- 2025-06-23
- Publication Date
- 2025-09-23
AI Technical Summary
In the existing technology, in the PTA production process, it is difficult to selectively remove iron ions in the cobalt manganese acetate catalyst system, resulting in a high loss rate of the cobalt manganese catalyst, increased acetic acid consumption, and the risk of environmental pollution.
A step-by-step method is adopted, including mother liquor concentration, initial dissolution, redissolution, solid-liquid separation, oxidative decomplexation and selective precipitation. Sodium carbonate solution and oxalic acid are used to control the precipitation process of cobalt, manganese and iron at different pH values. Hydrogen peroxide is combined to oxidize iron ions, and iron ions are removed by selective precipitation with oxalic acid.
The efficient recovery of cobalt-manganese catalyst was achieved, the cobalt-manganese loss rate was reduced to below 1%, the acetic acid consumption was reduced, the process stability and environmental protection were improved, and the by-product iron oxalate could be recycled, reducing costs and carbon emissions.
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of catalyst recovery and utilization, in particular to a method for selectively removing iron ions in a cobalt manganese acetate catalyst system. Background Art
[0002] The circulating solvents used in the PTA production process are highly corrosive acids: hydrobromic acid and acetic acid. These acids, under high temperature and pressure, are corrosive to metal pipes and equipment, causing free iron ions to enter the system, impacting the efficiency of the cobalt-manganese catalyst system in promoting the reaction. Therefore, when the cobalt-manganese acetate catalyst is separated and recovered through carbonate precipitation, it is often accompanied by iron ion impurities. This is especially true when an iron-cobalt complex is present, as the iron ions exist in a stable complex state, making selective separation difficult using the transmission precipitation method.
[0003] Most existing separation methods use acetic acid dissolution, filtration and other measures to separate the iron-cobalt complex, and ultimately treat the insoluble iron-cobalt complex as hazardous waste. This will also lead to increased acetic acid consumption, requiring additional acetic acid supplementation, and the loss rate of cobalt and manganese is as high as over 15%.
[0004] In addition, in a high-acid environment, such as a 20% acetic acid environment, conventional sulfide precipitation and ion exchange methods fail due to the high stability of the iron complex, and the presence of sulfur in the recovered catalyst causes the palladium-containing catalyst in the process equipment to be poisoned. Therefore, in most cases, the iron-cobalt catalyst can only be treated as solid waste, resulting in some economic losses. In terms of environmental protection, it is easily treated as hazardous waste and easily causes environmental pollution.
[0005] Therefore, it is necessary to develop a process that can selectively remove iron ion impurities in a complex solution containing high concentrations of acetic acid, cobalt acetate, manganese acetate and iron-cobalt complex. Summary of the Invention
[0006] In order to solve the above technical deficiencies, the present invention provides a method for selectively removing iron ions in a cobalt manganese acetate catalyst system, which can effectively remove iron ions while reducing the loss rate of cobalt and manganese.
[0007] The present invention discloses a method for selectively removing iron ions in a cobalt manganese acetate catalyst system, comprising the following steps:
[0008] Step 1, mother liquor concentration: concentrating the mother liquor containing the cobalt-manganese catalyst, evaporating it to dryness and grinding it into powder to form catalyst impurity powder;
[0009] Step 2, initial dissolution: add 32% sodium carbonate solution to the catalyst impurity powder to dissolve it, and control the pH value between 6.2-6.3 and the temperature of the mixture between 85-87°C. The residence time of this step is 2-2.5 hours;
[0010] Step 3, re-dissolving: continue to add 32% sodium carbonate solution to the solution in step 2, control the pH value between 8.1-8.2, control the temperature between 86-88°C, and the residence time of this step is 3-4 hours;
[0011] Step 4, separation of the organic liquid from the cobalt-manganese carbonate: solid-liquid separation is performed through a metal powder sintered filter, 85% acetic acid is added to dissolve the cobalt-manganese carbonate, and the dissolved solution is discharged into a catalyst receiving tank. Water is further added to wash the metal powder sintered filter, and the washing liquid is discharged into the catalyst receiving tank;
[0012] Step 5, separation of the iron-cobalt complex: the solid residue in the metal powder sintering filter is washed with deionized water until the pH value of the drainage water is 6-7, and then the iron-cobalt complex is discharged into the decomplexation tank by nitrogen backflushing;
[0013] Step 6, oxidative decomplexation: add excess oxidant to the decomplexation tank, control the temperature between 40-60°C and stir for 1-2 hours;
[0014] Step 7, selective precipitation: control the system pH to 1.8-2.5, add oxalic acid in an amount of 1.05-1.1 times the molar amount of iron, and react for 0.5-1 hour to form iron oxalate precipitate;
[0015] Step 8, solid-liquid separation and acidity recovery: Separate the precipitate using a filter press and wash it with deionized water. Add the initial acetic acid concentration to the filtrate. The solid enters the collection tank through backflushing to remove iron ions. The filtrate enters the catalyst collection tank and is sent to the process unit for recycling.
[0016] The acetic acid content in the mother liquor of the cobalt-manganese catalyst is between 15% and 25%.
[0017] In step 2, sodium carbonate solution is added to dissolve the organic matter in the powder, wherein the organic matter mainly includes: benzoic acid, terephthalic acid, phthalic acid, isophthalic acid, and trimellitic acid.
[0018] In step 2, the powder is initially dissolved and the pH value is controlled between 6.2-6.3. In a weakly acidic environment, sodium carbonate preferentially neutralizes the free H + , causing the iron ions to precipitate as Fe(OH)3, while cobalt and manganese remain dissolved due to their high complex stability. At the same time, organic acids (such as benzoic acid) have high solubility at this pH value and can be effectively removed.
[0019] In step 3, the solution is dissolved again and the pH value is controlled between 8.1 and 8.2. The pH value is increased to allow cobalt and manganese to form carbonate precipitates CoCO3 and MnCO3. Iron has already precipitated or formed a complex in the early stage, avoiding competition with cobalt and manganese for precipitation, thereby achieving efficient recovery of cobalt and manganese.
[0020] The temperature of step 2 and step 3 is controlled between 85-88℃. The high temperature accelerates the precipitation of carbonate, shortens the reaction time, and inhibits the formation of impurity ions such as Ca 2+ Mg 2+ interference and improve precipitation selectivity.
[0021] The solution entering the catalyst receiving tank in step 4 is heated to 92-95°C, solid-liquid separation is performed using a metal powder sintered filter, and the solution is sent to the catalyst storage tank for recycling in the process unit; the solid is washed with deionized water to a discharge pH of 6-7, and then the iron-cobalt complex is discharged into the decomplexation tank by nitrogen backflushing.
[0022] The metal powder sintered filter has a pore size of 0.4 μm.
[0023] In step 1, the mother liquor containing the cobalt-manganese catalyst is first evaporated and concentrated to 16-18%, then evaporated to dryness in a crucible and ground into powder.
[0024] The oxidant in step 6 is 30% hydrogen peroxide. Hydrogen peroxide is selected as the oxidant because it is a green oxidant, the reaction product is water, and there is no secondary pollution. Its oxidizing ability is enhanced under acidic conditions, and Fe 2+ Rapidly oxidized to Fe 3+ , while destroying the coordination bonds in the iron-cobalt complex and releasing free Fe 3+ The dosage of hydrogen peroxide is excessive, and the optimized dosage is 1.2-1.5 times the molar amount of iron. Excessive hydrogen peroxide ensures complete dissociation of the complex, but attention should be paid to the online spectrometer in the process flow, using the UV-visible method, using Co 2+ (λ_max=510nm) and Co 3+ (λ_max=620nm), Mn 2+ (λ_max=405nm) and Mn 3+ The characteristic absorption peak of (λ_max=480nm) is used to track the valence state changes in real time to avoid the valence state changes of cobalt / manganese caused by excessive oxidation, which will affect the selectivity of subsequent precipitation.
[0025] In step 7, oxalic acid is added in multiple intervals, and the reaction temperature in step 7 is controlled at 45-50°C.
[0026] Under the conditions of step 7, the solubility of cobalt oxalate and manganese oxalate is much higher than that of ferric oxalate, so selective separation can be achieved. Adding oxalic acid twice can avoid the instantaneous supersaturation of cobalt / manganese oxalate caused by excessive local concentration, reducing the risk of its entrainment into the precipitate. In addition, the pH value of step 7 is 1.8-2.5, which is under the condition of a lower pH value. Its advantages are: inhibiting the formation of cobalt oxalate / manganese oxalate precipitates, and its solubility increases with decreasing pH value. At the same time, ferric oxalate still maintains extremely low solubility under strong acidity, and its Ksp≈10 -30 , achieving efficient separation.
[0027] In step 8, the acidity is restored to the initial concentration, which is substantially 20%, and the retention rate of cobalt and manganese is ≥99.5%.
[0028] The method for selectively removing iron ions from a cobalt manganese acetate catalyst system obtained by the present invention has the following technical effects:
[0029] 1. Synergistic optimization mechanism of iron removal rate and low cobalt / manganese loss rate
[0030] Synergistic effect of selective oxidation and precipitation: Fe 2+ Oxidized to Fe 3+ , which not only destroys the stability of the iron-cobalt complex, but also makes Fe 3+ It preferentially forms insoluble ferric oxalate (Fe2(C2O4)3·5H2O) with oxalate. The solubility of the complex formed by cobalt / manganese with oxalic acid is significantly higher than that of iron (2-3 orders of magnitude higher) at the same pH value (1.8-2.5), thus achieving selective separation.
[0031] Step-by-step precipitation control: iron ions are preferentially precipitated in the initial dissolution stage (pH 6.2-6.3), while cobalt / manganese carbonates are precipitated in the re-dissolution stage (pH 8.1-8.2). By adjusting the pH in steps, co-precipitation of metal ions is avoided and cobalt / manganese entrainment losses are reduced.
[0032] 2. The underlying mechanism behind the reduction in acetic acid consumption
[0033] Dynamic acidity balance design: In step 8, the initial concentration of the system (20%) is restored by adding acetic acid, without the need to introduce additional strong acid or adjust the overall acidity, thus avoiding the waste of acetic acid caused by repeated acid adjustments in traditional processes.
[0034] Direct decomplexation of the complex: The iron-cobalt complex structure is destroyed through an oxidative decomplexation step, avoiding the need for large amounts of acetic acid to dissolve the complex in traditional processes and saving acid consumption.
[0035] 3. High purity and resource value of by-product ferric oxalate
[0036] Dual purification mechanism: Fe after oxidation and decomplexation 3+The release of ensures the singleness of oxalic acid precipitation. At the same time, oxalic acid is added in batches (with intervals of 10-15 minutes) to avoid local oversaturation and impurity co-precipitation. The purity of the final product is >99.5%.
[0037] Double benefits of economy and environment: Ferric oxalate can be directly used in magnetic materials, lithium battery cathode precursors or pigment industry, replacing traditional hazardous waste treatment and realizing resource recycling.
[0038] 4. Significant improvement in process stability
[0039] Through step-by-step pH gradient control (6.2-6.3 for initial dissolution, 8.1-8.2 for re-dissolution) and precise temperature control (±2°C), the impurity ions (such as Ca 2+ Mg 2+ ) interference, reduce the co-precipitation phenomenon, make the fluctuation range of cobalt / manganese recovery rate less than 0.5%, and the process repeatability reaches industrial grade standards.
[0040] 5. Optimizing energy efficiency and reducing carbon emissions
[0041] The low-temperature oxidation decomplexation at 40-60°C and the short-time reaction design of 1-2 hours reduce energy consumption by about 25% compared with the traditional high-temperature and high-pressure process. At the same time, the closed-loop circulation design allows the acetic acid, cobalt / manganese catalyst and by-products to be fully reused, reducing carbon emissions from raw material mining and waste treatment.
[0042] 6. Double improvement of operational safety and environmental protection
[0043] Hydrogen peroxide is used to replace traditional highly toxic reagents such as hydrogen sulfide and cyanide, eliminating the risk of highly toxic gas leakage; no harmful by-products are generated in the oxalic acid precipitation step, and the process wastewater can meet discharge standards (pH 6-7) after simple neutralization, reducing environmental treatment costs by more than 30%, in line with the principles of green chemistry.
[0044] The method for selectively removing iron ions from a cobalt-manganese acetate catalyst system achieved by this invention achieves a cobalt / manganese loss rate of ≤1%. Based on an annual processing capacity of 100,000 tons of mother liquor in the PTA industry, this method can reduce catalyst replenishment costs by over 10 million yuan, increase acetic acid recycling by 30%, and reduce raw material procurement and waste acid disposal costs. Hazardous waste (iron-cobalt complex) is converted into high-value-added iron oxalate, reducing landfill volume by over 90%. The pH of the process wastewater is adjusted to 6-7 through washing, meeting emission standards, and reducing neutralization treatment costs.
[0045] The method for selectively removing iron ions in a cobalt manganese acetate catalyst system obtained by the present invention can recycle the recovered cobalt acetate and manganese acetate for use in an oxidation reaction process, and the byproduct iron oxalate can be used for preparing magnetic materials or pigments. DETAILED DESCRIPTION
[0046] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the following preferred embodiments will describe in detail the specific implementation methods, structures, features and effects of the present invention.
[0047] Example 1:
[0048] The present invention discloses a method for selectively removing iron ions in a cobalt manganese acetate catalyst system, comprising the following steps:
[0049] Step 1, mother liquor concentration:
[0050] The mother liquor containing cobalt-manganese catalyst (acetic acid concentration of 20%) was extracted from the PTA production device and evaporated and concentrated to an acetic acid concentration of 17% using a falling film evaporator at a vacuum of 0.08 MPa and a temperature of 85°C. The mother liquor was then transferred to a crucible for drying and ground into a powder with a particle size of ≤100 μm for later use.
[0051] Step 2, initial dissolution:
[0052] The evaporated powder was mixed with 32% sodium carbonate solution in a mass ratio of 1:3, the pH was controlled to 6.2, and the mixture was stirred at 85°C for 2 hours to dissolve organic matter (benzoic acid, terephthalic acid, etc.) and form a precipitation of iron ions.
[0053] Step 3, re-dissolve:
[0054] 32% sodium carbonate solution was further added to the above solution, the pH was adjusted to 8.1, the temperature was raised to 87° C. and stirred for 3.5 hours to completely convert the cobalt and manganese ions into carbonate precipitates.
[0055] Step 4, separation of organic liquid and cobalt manganese carbonate:
[0056] Intermittent separation was performed using a 0.4 μm metal powder sintered filter, and the solid was dissolved with 85% acetic acid and then recovered to a catalyst receiving tank; the filtrate (containing the iron-cobalt complex) was transferred to the next step.
[0057] Step 5, separation of the iron-cobalt complex:
[0058] The filtrate was heated to 94°C and separated by a 0.4 μm metal powder sintered filter. The retained solid was washed with deionized water until the drainage pH was 6.5, and then transferred to a decomplexation tank after nitrogen backflushing.
[0059] Step 6, oxidative decomplexation:
[0060] Add 30% hydrogen peroxide (1.3 times the molar amount of iron) to the decomplexing tank and stir at 50°C for 1.5 hours to make Fe 2+ Oxidized to Fe 3+ , the complex structure is destroyed.
[0061] Step 7, selective precipitation:
[0062] The pH value of the solution was adjusted to 2.0, and oxalic acid (the total amount was 1.1 times the molar amount of iron) was added twice with an interval of 15 minutes. The mixture was reacted at 50°C for 40 minutes to form iron oxalate precipitate.
[0063] Step 8, solid-liquid separation and acidity recovery:
[0064] A plate and frame filter press is used to separate the precipitate, and the filtrate is supplemented with acetic acid to a concentration of 20% and then returned to the catalyst collection tank; the ferric oxalate is dried and used as a by-product.
[0065] Results: The iron removal rate was 99.3%, and the cobalt and manganese loss rates were 0.8% and 0.7% respectively.
[0066] Example 2:
[0067] The invention discloses a method for selectively removing iron ions in a cobalt manganese acetate catalyst system. The method is characterized in that, in step 7, oxalic acid is added three times with an interval of 10 minutes between each additions, the reaction temperature is raised to 55° C., the reaction time is 40 minutes, and the final iron removal rate is as high as 99.5%, and the cobalt and manganese loss rates are reduced to 0.5%.
[0068] Example 3:
[0069] A method for selectively removing iron ions in a cobalt manganese acetate catalyst system:
[0070] Steps 1 to 4 are the same as in Example 1;
[0071] Step 5, separation of the iron-cobalt complex:
[0072] The filtrate was heated to 93°C and separated by a 0.4 μm metal powder sintered filter. The retained solid was washed with deionized water to a drainage pH of 6.8, and then transferred to a decomplexation tank after nitrogen backflushing.
[0073] Step 6, oxidative decomplexation:
[0074] Add 30% hydrogen peroxide (1.2 times the molar amount of iron) to the decomplexing tank and stir at 52°C for 1.8 hours to make Fe 2+ Oxidized to Fe 3+ , and destroy the iron-cobalt complex structure.
[0075] Step 7, selective precipitation:
[0076] The pH value of the solution was adjusted to 2.3, and oxalic acid (the total amount was 1.08 times the molar amount of iron) was added, and the reaction was continued for 50 minutes at 48°C after every 12 minutes. This step further optimized the formation conditions of iron oxalate and improved the precipitation efficiency.
[0077] Step 8, solid-liquid separation and acidity recovery:
[0078] Same as Example 1
[0079] Results: The iron removal rate was 99.2%, and the cobalt and manganese loss rates were 0.75% and 0.65% respectively.
[0080] Example 4:
[0081] A method for selectively removing iron ions in a cobalt manganese acetate catalyst system
[0082] Step 1 to Step 5: Same as Example 3, except that the acetic acid concentration is adjusted to 21%.
[0083] Step 6, oxidative decomplexation:
[0084] Add 30% hydrogen peroxide (1.25 times the molar amount of iron) to the decomplexing tank and stir at 48°C for 2 hours while introducing nitrogen to prevent the hydrogen peroxide from decomposing too quickly at high temperature to ensure the Fe 2+ Completely oxidized to Fe 3+ .
[0085] Step 7, selective precipitation:
[0086] The pH value of the solution was adjusted to 2.1, and oxalic acid (the total amount was 1.06 times the molar amount of iron) was added twice with an interval of 18 minutes between each addition. The reaction was controlled at 52° C. for 35 minutes.
[0087] Step 8, solid-liquid separation and acidity recovery:
[0088] Same as Example 1, but acetic acid was added to the filtrate to a concentration of 21%.
[0089] Results: The iron removal rate was 99.1%, and the cobalt and manganese loss rates were 0.85% and 0.7% respectively.
[0090] Example 5:
[0091] A method for selectively removing iron ions in a cobalt manganese acetate catalyst system:
[0092] Step 1 to step 4: the same as in Example 1.
[0093] Step 5, separation of the iron-cobalt complex:
[0094] The filtrate was heated to 95°C and separated by a 0.4 μm metal powder sintered filter. The retained solid was washed with deionized water until the drainage pH was 7, and then transferred to a decomplexation tank after nitrogen backflushing.
[0095] Step 6, oxidative decomplexation:
[0096] Add 30% hydrogen peroxide (1.4 times the molar amount of iron) to the decomplexing tank and add a small amount of copper sulfate as a catalyst to accelerate the Fe 2+ The oxidation process was stirred at 55 °C for 1.5 hours.
[0097] Step 7, selective precipitation:
[0098] The pH value of the solution was adjusted to 2.2, and oxalic acid (the total amount was 1.08 times the molar amount of iron) was added twice with an interval of 15 minutes. The reaction temperature was controlled at 50°C and the reaction time was 0.75 hours to generate iron oxalate precipitate.
[0099] Step 8, solid-liquid separation and acidity recovery:
[0100] Same as Example 4.
[0101] Results: The iron removal rate was 99.2%, and the cobalt and manganese loss rates were 0.7% and 0.6% respectively.
[0102] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any simplified modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.
Claims
1. A method for selectively removing iron ions in a cobalt manganese acetate catalyst system, characterized in that: The steps include: Step 1, mother liquor concentration: concentrating the mother liquor containing the cobalt-manganese catalyst, evaporating it to dryness and grinding it into powder to form catalyst impurity powder; Step 2, initial dissolution: add 32% sodium carbonate solution to the catalyst impurity powder to dissolve it, and control the pH value between 6.2-6.3 and the temperature of the mixture between 85-87°C. The residence time of this step is 2-2.5 hours; Step 3, redissolution: continue to add 32% sodium carbonate solution to the solution in step 2, control the pH value between 8.1-8.2, control the temperature between 86-88°C, and the residence time of this step is 3-4 hours; Step 4, separation of the organic liquid from the cobalt-manganese carbonate: solid-liquid separation is performed through a metal powder sintered filter, 85% acetic acid is added to dissolve the cobalt-manganese carbonate, and the dissolved solution is discharged into a catalyst receiving tank. Water is further added to wash the metal powder sintered filter, and the washing liquid is discharged into the catalyst receiving tank; Step 5, separation of the iron-cobalt complex: the solid residue in the metal powder sintering filter is washed with deionized water until the pH value of the drainage water is 6-7, and then the iron-cobalt complex is discharged into the decomplexation tank by nitrogen backflushing; Step 6, oxidative decomplexation: add excess oxidant to the decomplexation tank, control the temperature between 40-60°C and stir for 1-2 hours; Step 7, selective precipitation: control the system pH to 1.8-2.5, add oxalic acid in an amount of 1.05-1.1 times the molar amount of iron, and react for 0.5-1 hour to form iron oxalate precipitate; Step 8, solid-liquid separation and acidity recovery: Separate the precipitate using a filter press and wash it with deionized water. Add the initial acetic acid concentration to the filtrate. The solid enters the collection tank through backflushing to remove iron ions. The filtrate enters the catalyst collection tank and is sent to the process unit for recycling.
2. The method for selectively removing iron ions in a cobalt manganese acetate catalyst system according to claim 1, wherein: The solution entering the catalyst receiving tank in step 4 is heated to 92-95°C, solid-liquid separation is performed using a metal powder sintered filter, and the solution is sent to the catalyst storage tank for recycling in the process unit; the solid is washed with deionized water to a discharge pH of 6-7, and then the iron-cobalt complex is discharged into the decomplexation tank by nitrogen backflushing.
3. The method for selectively removing iron ions in a cobalt manganese acetate catalyst system according to claim 1 or 2, characterized in that: The metal powder sintered filter has a pore size of 0.4 μm.
4. The method for selectively removing iron ions in a cobalt manganese acetate catalyst system according to claim 1, wherein: In step 1, the mother liquor containing the cobalt-manganese catalyst is first evaporated and concentrated to 16-18%, then evaporated to dryness in a crucible and ground into powder.
5. The method for selectively removing iron ions in a cobalt manganese acetate catalyst system according to claim 1, wherein: The oxidant in step 6 is 30% hydrogen peroxide.
6. The method for selectively removing iron ions in a cobalt manganese acetate catalyst system according to claim 1, wherein: In step 7, oxalic acid is added in multiple intervals, and the reaction temperature in step 7 is controlled at 45-50°C.