A process for the production of a hard water resistant detergent surfactant

Abstract

Disclosed is a method for producing a surfactant for hard water-resistant detergents, comprising the steps of: adding Ba 2+ and Ca 2+ The MOF-74 modified by ion exchange method is used as a solid acid-base dual catalyst, filled in a fixed bed reactor, and used to catalyze the ethoxylation reaction of fatty alcohol and ethylene oxide under the conditions of a reaction temperature of 150-170 DEG C and a pressure of 0.3-0.8 MPa. The space confinement effect of the one-dimensional hexagonal channel of MOF-74 blocks the six-membered ring transition state required for the generation of 1,4-dioxane from the mechanism, the residual 1,4-dioxane in the product is less than 0.1 ppm, the addition number of ethylene oxide is accurately controlled in the narrow distribution interval of 7-9, the polydispersity coefficient is not more than 1.02, the cumulative proportion of effective components is not less than 80%, the calcium soap dispersing force is significantly better than that of the existing process, the solid catalyst can be regenerated in situ, the neutralization, decolorization, filtration and vacuum stripping processes are omitted, and the production and operation cost is reduced by about 30%.

Description

Technical Field

[0001] This invention belongs to the field of surfactant preparation technology, specifically relating to a production method for preparing surfactants for hard water detergents by catalytic ethoxylation of fatty alcohols using a metal-organic framework solid catalyst in a fixed-bed reactor. Background Technology

[0002] Groundwater and tap water in most parts of the world contain high concentrations of calcium ions (Ca). 2+ ) and magnesium ions (Mg 2 + Water hardness is usually expressed as calcium carbonate equivalent. In most parts of China, the water hardness is between 150 and 450 mg / L (calculated as CaCO3). When divalent cations in hard water combine with ordinary anionic surfactants, they form insoluble calcium soap precipitates, which leads to a significant decrease in detergent power. Therefore, the industry generally uses fatty alcohol polyoxyethylene ether (AEO) and its derivative fatty alcohol polyoxyethylene ether sulfate (AES) as anti-hard water surfactants. The polyoxyethylene segments endow the molecules with hydrophilicity and produce a steric hindrance effect on divalent metal ions.

[0003] The mainstream method for industrial production of hard water-resistant surfactants is the KOH homogeneous alkaline catalytic ethoxylation process. A typical process involves mixing a fatty alcohol with a KOH catalyst, heating and dehydrating to form a homogeneous potassium alkoxide activation system. Then, gaseous ethylene oxide (EO) is continuously introduced at 150–200°C and 0.2–0.5 MPa, causing an anionic chain-growth addition reaction. After the reaction, multiple post-treatment processes, including neutralization, activated carbon decolorization and filtration, and vacuum stripping, are required to obtain a qualified product. This process has the following three fundamental defects: Defect 1: The 1,4-dioxane byproduct is unavoidable. In the high-temperature and high-pressure system catalyzed by KOH, EO molecules themselves are prone to intramolecular dehydration and cyclization side reactions. After intermolecular condensation, two EO molecules undergo intramolecular cyclization to generate a thermodynamically favorable six-membered chair conformation transition state, forming 1,4-dioxane, which has a high carcinogenic risk. This side reaction runs parallel to the main reaction and is difficult to eliminate by adjusting the operating parameters. The initial content of 1,4-dioxane in the crude product is usually as high as 100-500 ppm. Although the end-stage vacuum stripping process can reduce it to 5-50 ppm, the separation efficiency has reached its limit under the requirement of no more than 1 ppm in many countries' regulations, and the compliance cost has increased sharply.

[0004] Defect 2: The wide distribution of EO addition number leads to poor hard water resistance. Under homogeneous KOH catalysis, the addition of EO to fatty alcohols follows a statistical Poisson distribution law. The half-peak width of the EO addition number distribution in the product covers ±4 to 6 EO units, and the polydispersity index (PDI) is usually 1.05 to 1.20. Only the molecular components with EO addition number between 7 and 9 have the best calcium soap dispersing power (LSDA) and hard water detergency. However, the proportion of this effective active component in the total product is only about 30% to 40%, resulting in low raw material utilization and poor batch stability of performance.

[0005] Defect 3: Homogeneous catalysts are difficult to recover, the process is lengthy, KOH is completely dissolved in the product system, and after the reaction, multiple processes such as acid neutralization, activated carbon adsorption, and pressure filtration are required to obtain qualified products, resulting in large material losses and high salt content in wastewater.

[0006] Currently, there is no industrial production method that can simultaneously solve the above three defects from the perspective of reaction mechanism. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for producing a surfactant for hard water detergents, which blocks the formation pathway of 1,4-dioxane from the reaction mechanism, while precisely controlling the EO addition number within a narrow distribution range of 7 to 9, and realizing automatic phase separation and recyclability of the catalyst, eliminating the need for post-processing steps such as neutralization, decolorization, filtration and vacuum stripping.

[0008] To address the aforementioned technical problems, this invention provides a method for producing a surfactant for hard water detergents. The method uses a metal-organic framework material modified with two Group IIA metal ions, possessing a regular one-dimensional pore structure with an inner diameter of 9–12 Å, as a solid catalyst. Fatty alcohols and ethylene oxide are introduced into a fixed-bed reactor for a heterogeneous ethoxylation reaction. The solid catalyst, through the spatial confinement effect of its one-dimensional pores, concentrates the ethylene oxide addition number distribution within a target range of 7–9, and blocks the formation of the six-membered cyclization transition state required for the formation of 1,4-dioxane from the reaction mechanism, thus obtaining a surfactant for hard water detergents.

[0009] The metal-organic framework material is preferably MOF-74, and the two Group IIA metal ions are preferably Ba. 2+ and Ca 2+ Ba was converted to Ba by ion exchange. 2+ and Ca 2+ By introducing open metal sites into the MOF-74 framework, a Ba / Ca-MOF-74 solid catalyst was prepared, in which Ba... 2+ Provides Lewis basicity sites, Ca 2+Providing Lewis acidic sites, both synergistically catalyze the ethoxylation reaction, wherein the Ba 2+ With Ca 2+ The preferred molar ratio is 3:7.

[0010] The operating conditions for the ethoxylation reaction are: reaction temperature 150–170 °C, reaction pressure 0.3–0.8 MPa, and fatty alcohol heavy hourly space velocity (WHSV) 0.5–2.0 h⁻¹. -1 The target EO bonus range is 7 to 9.

[0011] The present invention can further employ a dynamic adjustment method for the EO feed ratio based on online feedback: by real-time detection of the EO addition number distribution spectrum of the product by online gas chromatography, the cumulative proportion of components and polydispersity coefficient of the product within the target range are calculated, and the molar feed ratio of EO to fatty alcohol and the catalyst bed temperature are dynamically adjusted according to the proportional control strategy to achieve closed-loop feedback control.

[0012] Compared with the existing KOH homogeneous catalytic ethoxylation process, the present invention has the following advantages: 1. This invention fundamentally eliminates 1,4-dioxane. The inner diameter of the MOF-74 pores is approximately 11 Å, while the minimum space required for the six-membered cyclization transition state of the 1,4-dioxane precursor is approximately 14–16 Å. The physical space of the pores mechanistically blocks the formation of this transition state, resulting in a 1,4-dioxane residue in the product that is below the instrument detection limit (below 0.1 ppm). This fundamentally meets the most stringent global regulatory requirements and eliminates the vacuum stripping process, reducing production and operating costs by approximately 30%.

[0013] 2. This invention achieves narrow-distribution precision ethoxylation. The synergistic catalysis of Ba / Ca bimetallic sites precisely locks the EO addition number within a narrow distribution range of 7 to 9. The product polydispersity index (PDI) is no greater than 1.02, the cumulative proportion of components with EO addition numbers of 7 to 9 is no less than 80% (approximately 30% to 40% in existing processes), and the calcium soap dispersing power (LSDA value) is no greater than 20% (35% to 45% in existing processes). It can maintain excellent detergency in water with a hardness of 400 mg / L without the need for additional phosphorus or nitrogen chelating agents.

[0014] 3. This invention simplifies the production process. The solid catalyst enables automatic phase separation between the catalyst and the product, eliminating the need for three post-processing steps: neutralization, decolorization, and filtration. It supports continuous fixed-bed production, allows for in-situ catalyst regeneration, and is designed to operate continuously for no less than 500 hours (between two regenerations) with a cumulative regeneration count of no less than 10 times. Attached Figure Description

[0015] Figure 1 This is a flow chart of the preparation process of the Ba / Ca-MOF-74 solid catalyst of the present invention; Figure 2 This is a flowchart of the fixed-bed continuous ethoxylation reaction and the dynamic adjustment and control process of EO feed ratio based on online feedback according to the present invention. Figure 3 This is a flow chart of the in-situ catalyst regeneration process of the present invention. Detailed Implementation

[0016] The following is in conjunction with the appendix Figure 1-3 The specific embodiments of the present invention will be further described below. It should be noted that the description of these embodiments is for the purpose of helping to understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0017] Example 1: Preparation of Ba / Ca-MOF-74 solid catalyst According to Mg 2+ Magnesium nitrate hexahydrate and DHTA ligand were weighed in a molar ratio of 2:1 with 2,5-dihydroxyterephthalic acid (DHTA), dissolved in a mixed solvent with a volume ratio of V(DMF):V(ethanol):V(H2O) = 15:1:1, and magnetically stirred until clear to prepare Mg 2+ A precursor solution with a concentration of 0.1 mol / L was transferred to a polytetrafluoroethylene-lined stainless steel hydrothermal reactor, sealed, and heated to 125°C at a rate of 2°C / min. The reactor was then kept at this temperature for 72 hours and allowed to cool naturally to room temperature. The crystallized product was filtered and washed three times each with DMF and anhydrous methanol (each time soaking for 12 hours to fully replace any residual organic template agent in the pores). The product was then dried at 80°C for 24 hours to obtain Mg-MOF-74 matrix powder.

[0018] The obtained Mg-MOF-74 matrix powder was subjected to a 1×10⁻⁶ pyrolysis. -3 Under vacuum of Pa and at 250℃, the temperature was increased at 1℃ / min and kept constant for 12 hours to completely remove the residual solvent and coordinated water molecules in the pores, fully exposing the open metal sites on the inner wall of the pores, thus obtaining activated Mg-MOF-74 powder.

[0019] Press Ba 2+ With Ca 2+ Barium nitrate and calcium nitrate tetrahydrate were weighed out in a molar ratio of 3:7 and dissolved in deionized water to prepare a mixed modified solution with a total metal ion concentration of 0.05 mol / L. The activated Mg-MOF-74 powder was then immersed in this mixed modified solution at a liquid-to-solid ratio of 20:1 (mL:g). The solution was then placed in a sealed container at room temperature and shaken at 100 rpm for 72 hours to allow the Ba... 2+ and Ca 2 +It fully enters the open metal sites of the MOF-74 framework, partially replacing Mg in the original framework. 2+ The ion exchange product was filtered and washed five times with deionized water until no nitrate ions were found in the filtrate (tested with silver nitrate solution). The filtrate was then dried at 120°C for 24 hours to obtain Ba / Ca-MOF-74 catalyst powder.

[0020] The obtained powder was mixed with 5% by mass of pseudoboehmite, and an appropriate amount of deionized water was added to knead the mixture. It was then extruded into cylindrical strips with a diameter of 2–3 mm, dried at 120°C, and then... -3 Activation at 300℃ for 12 hours under vacuum (Pa) yielded a shaped Ba / Ca-MOF-74 solid catalyst with good mechanical strength and fully exposed active sites.

[0021] The obtained catalyst was characterized and confirmed by the following indicators: the XRD pattern retained the characteristic diffraction peaks of MOF-74, the crystal form was intact without obvious collapse, and the BET specific surface area was not less than 800 m². 2 / g, pore volume not less than 0.5 cm³ 3 / g, NH3-TPD (acidity) and CO2-TPD (baseity) characterization confirmed the existence of acid-base bifunctional sites, and ICP-OES analysis was used to analyze the actual loading of Ba and Ca and verify the molar ratio.

[0022] Example 2: Fixed-bed continuous ethoxylation reaction The shaped Ba / Ca-MOF-74 solid catalyst particles prepared in Example 1 were packed into a 316L stainless steel tubular fixed-bed reactor with a rated pressure of not less than 5 MPa. The height-to-diameter ratio (L / D) of the catalyst bed was controlled between 10:1 and 20:1 to ensure the ideal plug flow state of the reactants in the bed and reduce axial backmixing. Inert α-Al2O3 ceramic balls with a diameter of 3-5 mm were filled at the top and bottom of the catalyst bed as a support and distribution layer. The reactor was equipped with a precision temperature-controlled heating jacket with no less than 3 temperature measuring points (top, middle and bottom of the bed) to ensure that the bed temperature uniformity was within ±2℃.

[0023] After the catalyst was loaded, an airtightness test was performed using nitrogen at 1.0 MPa. After maintaining the pressure for 30 minutes without leakage, the system was replaced three times with high-purity nitrogen (purity not less than 99.999%) at a flow rate of 200 mL / min to ensure that the residual oxygen content in the system was less than 10 ppm. Subsequently, the fixed-bed reactor was heated to 200℃ under nitrogen protection and activated by constant temperature purging for 4 hours to further remove trace amounts of moisture and air that may have been adsorbed by the catalyst during loading and restore the catalyst's activity.

[0024] Refined lauryl alcohol (C 12(The purity is not less than 99.5%, and the moisture content is not higher than 50 ppm) is placed in a raw material storage tank and kept at 80-90°C by electric heating. It is then pumped into the top of the fixed-bed reactor by a high-precision metering pump, and the bed temperature is slowly increased to the operating temperature of 160°C at a rate of 1°C / min, while maintaining lauryl alcohol at a constant temperature for approximately 0.5 hours. -1 The heavy space velocity passes through the bed for initial wetting.

[0025] In this invention, the weight time airspeed (WHSV) is defined as: ; in, The value represents the mass of fatty alcohol feed entering the reactor per unit time, expressed in g / h. The total mass of the catalyst bed is expressed in grams. The unit is h -1 The operating range of this invention is 0.5 to 2.0 hours. -1 .

[0026] Once the fixed bed temperature stabilizes at 160℃ and the fatty alcohol feed is stable, start the EO high-pressure feed system and introduce EO gas into the reactor through a mass flow controller (MFC). The molar ratio of EO to fatty alcohol is... Set as follows: ; in, The target EO addition number is set to 8 in this embodiment. The single-pass conversion rate of EO is determined by real-time monitoring of the EO concentration downstream of the back pressure valve using an online exhaust gas analyzer, with a value ranging from 0.90 to 0.98. The pressure of the reaction system is controlled at 0.5 MPa by the back pressure valve.

[0027] Triple synergistic catalytic mechanism of Ba / Ca-MOF-74 catalyst Within the fixed-bed reactor, the Ba / Ca-MOF-74 catalyst exerts a triple synergistic effect to achieve precise control over the ethoxylation reaction: Firstly, the Ca on the inner wall of the channel 2+ Lewis acid sites coordinate and activate the aliphatic alcohol -OH groups entering the pores, enhancing OH bond polarization and increasing nucleophilic activity at the O end, forming an activated alcohol-oxygen anion equivalent active species, ready to launch a nucleophilic attack on the EO monomer.

[0028] Secondly, the EO monomer entering the pores, the oxygen atom of its epoxy group reacts with the Ba atom on the inner wall of the pores. 2+ The Lewis basic site undergoes end-group coordination, causing the EO molecule to be adsorbed and fixed in an oriented posture with the carbon end facing the activated alcohol oxy ion. This forces the EO monomer to be nucleophilically attacked by the activated alcohol oxy ion in a linear ring-opening manner, completing a single-step addition.

[0029] Third, the inner diameter of the MOF-74 pores is about 11 Å, while the minimum space requirement for the six-membered cyclization transition state of the 1,4-dioxane precursor (which requires two EO molecules to approach each other in a specific curved configuration) is about 14 to 16 Å, far exceeding the capacity of the pore diameter. Therefore, this six-membered cyclization transition state cannot be physically formed in the pores, thus completely blocking the formation pathway of 1,4-dioxane from the perspective of the reaction mechanism.

[0030] Example 3: Dynamic Adjustment and Control of EO Feed Ratio Based on Online Feedback To achieve precise control of the EO add-in number within a narrow distribution range of 7 to 9, this invention employs a dynamic adjustment method for the EO feed ratio based on online feedback. The initial parameters are set as follows: target EO add-in number range. Target cumulative percentage threshold , PDI upper limit Initial molar feed ratio Initial reaction temperature Online detection sampling cycle min.

[0031] Every The system automatically samples from the product collection tank's sampling port over time, and performs rapid online gas chromatography analysis to obtain the EO addition number distribution spectrum of the current product. ,in For the first One EO addition number, For the corresponding normalized area response value, satisfying , This represents the highest EO addition number detected in the spectrum.

[0032] Based on the distribution spectrum data, the following key quality indicators are calculated in real time: Cumulative percentage of components within the current target range : ; Current product number average addition With weight average addition number : ; ; Current product polydispersity index: ; in, , These are the lower and upper limits of the target EO bonus range, respectively. This represents the cumulative mass fraction of molecules in the product with EO addition numbers falling within the target range during the current detection period (approximately represented by gas chromatographic area). The EO addition is the average of the numbers. The weight-average EO addition factor. This represents the polydispersity coefficient of the current product.

[0033] Based on the above calculation results, the control action is determined according to the following logic: like and If the product quality meets the standards, the current level will be maintained. and reaction temperature If unchanged, proceed to the next sampling period.

[0034] If the sum of numbers is equal (If the overall distribution is low and the EO feed rate is relatively insufficient), then adjust the forward feed ratio: ; If the sum of numbers is equal (If the overall distribution is too high and the EO feed rate is relatively excessive), then execute a negative feed ratio adjustment: ; like Within the target range but (If the distribution is too wide, it indicates that the catalyst's spatial confinement effect is weakened), then cooling adjustment will be implemented: ; This also triggers a catalyst regeneration early warning signal.

[0035] In the above formulas, , The first Second and third The adjusted EO / alcohol molar feed ratio This is the proportional control coefficient, with a value ranging from 0.05 to 0.15. The midpoint value of the target bonus range. For the first The number-average EO addition calculated for each sampling period, , These are the current and adjusted target temperatures of the catalyst bed, respectively. The temperature adjustment step size is set to 2–5℃.

[0036] The new calculation The value is transmitted to the EO feed mass flow controller via a distributed control system (DCS) command, adjusting the EO feed flow rate to bring the new... The value is transmitted to the bed heating jacket temperature controller, waiting for 1... After the system stabilizes within a 30-minute cycle, it returns to online sampling to begin a new round of feedback adjustment.

[0037] In-situ regeneration of catalyst When a cooling warning is triggered for three consecutive sampling cycles, or When the concentration exceeds 1.05, stop feeding EO and fatty alcohol, switch to a high-purity nitrogen atmosphere, and purge at a constant temperature of 300℃ for 4 hours at a rate of 5℃ / min to remove high molecular weight byproducts accumulated in the pores. Then, purge at a 1×10⁻⁵ atmosphere. -3 After evacuating the catalyst under vacuum of 300°C for 2 hours to complete in-situ regeneration, normal feeding operations are resumed. The catalyst is designed to run continuously for no less than 500 hours (between two regenerations) and the cumulative number of regenerations is no less than 10.

[0038] Product quality testing and performance comparison The product liquid flowing from the bottom of the fixed-bed reactor is depressurized by a back pressure valve and enters the product collection tank. Samples are taken periodically for the following tests: EO addition number distribution is determined by matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF-MS); 1,4-dioxane residue is detected by headspace gas chromatography-mass spectrometry (HS-GC-MS); and LSDA is determined according to the ASTM D4251 standard method (hard water hardness 400 mg / LasCaCO3).

[0039] The key performance indicators of the product obtained by this invention are compared with those of products obtained by existing KOH homogeneous catalytic processes, as shown in the table below:

[0040] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, any modifications, equivalent changes and alterations 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 shall fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for producing a surfactant for hard water resistant detergents, characterized in that, Using a metal-organic framework material modified with two Group IIA metal ions, having a regular one-dimensional pore structure and an inner diameter of 9–12 Å as a solid catalyst, fatty alcohols and ethylene oxide were introduced into a fixed-bed reactor to carry out a heterogeneous ethoxylation reaction. The solid catalyst, through the spatial confinement effect of its one-dimensional channels, concentrates the ethylene oxide addition number distribution within the target range of 7 to 9, and blocks the formation of the six-membered cyclization transition state required for the formation of 1,4-dioxane from the reaction mechanism, thus producing a surfactant for hard water detergents.

2. The production method according to claim 1, characterized in that, The metal-organic framework material is MOF-74, and the two Group IIA metal ions are Ba. 2+ and Ca 2+ Ba was converted to Ba by ion exchange. 2+ and Ca 2+ By introducing open metal sites into the MOF-74 framework, a Ba / Ca-MOF-74 solid catalyst was prepared. Where Ba 2+ Provides Lewis basic sites, Ca 2+ It provides Lewis acidic sites, and the two work together to catalyze the ethoxylation reaction.

3. The production method according to claim 2, characterized in that, The Ba 2+ With Ca 2+ The molar ratio is 3:

7.

4. The production method according to claim 2, characterized in that, The Ba / Ca-MOF-74 solid catalyst was prepared as follows: According to Mg 2+ A precursor solution was prepared with 2,5-dihydroxyterephthalic acid at a molar ratio of 2:1, and hydrothermally crystallized at 125°C for 72 hours. After washing and drying, the crystals were then subjected to a 1×10⁻⁶ crystallization process. -3 Activated Mg-MOF-74 powder was obtained by activating it under vacuum and 250℃ for 12 hours. The activated powder was immersed in Ba at a liquid-to-solid ratio of 20:1 (mL:g). 2+ With Ca 2+ In a nitrate mixture with a molar ratio of 3:7, the mixture was shaken at 100 rpm for 72 hours at room temperature. After filtration, washing, and drying, it is mixed with 5% by mass of pseudoboehmite, extruded and granulated into cylindrical particles with a diameter of 2–3 mm, and then processed at 1×10⁻⁶ mm. -3 The Ba / Ca-MOF-74 solid catalyst was obtained by activation under vacuum and 300℃ for 12 hours.

5. The production method according to claim 1, characterized in that, The operating conditions for the ethoxylation reaction are: reaction temperature 150–170 °C, reaction pressure 0.3–0.8 MPa, and fatty alcohol weight hourly space velocity 0.5–2.0 h⁻¹. -1 .

6. The production method according to claim 1, characterized in that, The target range is ethylene oxide addition number 7 to 9, the cumulative mass percentage of the component with ethylene oxide addition number 7 to 9 in the product is not less than 80%, the polydispersity index of the product is not greater than 1.02, and the residual amount of 1,4-dioxane in the product is less than 0.1 ppm.

7. The production method according to claim 1, characterized in that, The ethylene oxide addition number distribution spectrum of the product is detected in real time by online gas chromatography. The cumulative proportion of the components and the polydispersity index of the product within the target range are calculated at a sampling period of 30 minutes. When the cumulative proportion is not lower than the target threshold and the polydispersity index is not greater than the control upper limit, the current operating parameters are kept unchanged. When the number average additive number is lower than the lower limit of the target range, the molar feed ratio of ethylene oxide and fatty alcohol is positively increased; When the sum of the numbers exceeds the upper limit of the target range, the molar feed ratio is negatively reduced. When the number-average additive number is within the target range but the polydispersity coefficient exceeds the control upper limit, the catalyst bed temperature is reduced and a catalyst regeneration warning is triggered to achieve closed-loop feedback control.

8. The production method according to claim 1, characterized in that, When the polydispersity index of the product exceeds 1.05, stop feeding, switch to a high-purity nitrogen atmosphere, and purge the catalyst bed at a constant temperature of 300℃ for 4 hours while raising the temperature to 5℃ / min. Then, purge with 1×10⁻⁶ nitrogen. -3 After evacuating under vacuum of 300°C for 2 hours to complete the in-situ regeneration of the catalyst, normal feeding operations were resumed.

9. A solid catalyst for the ethoxylation of fatty alcohols, characterized in that, Using MOF-74 as a framework, Ba was converted to metallurgical substrates via ion exchange. 2+ and Ca 2+ Introducing open metal sites into the MOF-74 framework, Ba 2+ With Ca 2+ The molar ratio is 3:7, and the BET specific surface area of ​​the solid catalyst is not less than 800 m². 2 / g, pore volume not less than 0.5 cm³ 3 / g.

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