A complexing agent for separating and purifying a mixture of o-, m- and p-cresol isomers and a method for separating and purifying a mixture of o-, m- and p-cresol isomers

Abstract

The application relates to the separation technical field and provides a complexing agent for separating and purifying a phenyl carbinol isomer mixture and a method for separating and purifying the phenyl carbinol isomer mixture. The complexing agent for separating and purifying the phenyl carbinol isomer mixture comprises 10-15% of a nitrogen-containing heterocyclic compound, 5-8% of a transition metal salt and 77-85% of a diluent. The method for separating and purifying the phenyl carbinol isomer mixture comprises dissolving the phenyl carbinol isomer mixture in n-hexane, filtering impurities, then performing acidic extraction and / or neutral extraction in a gradient pH three-stage extraction separation and finally performing basic back extraction. The complexing agent and the method provided by the application are based on the inherent difference of the complex stability constant of o-, m- and p-cresol and Cu 2+ The inherent difference of the complex stability constant, the innovative dual-function complex system, the multiple molecular synergistic effect, the accurate identification and separation of the three isomers, the selectivity coefficient of more than 20 and the product purity of greater than or equal to 99%.

Description

Technical Field

[0001] This application belongs to the field of separation technology, and in particular relates to a ligand for separating and purifying a mixture of benzophenol isomers and a method for separating and purifying a mixture of benzophenol isomers. Background Technology

[0002] Phenolic isomers (such as cresol isomers) are key raw materials for the synthesis of vitamin E, antioxidants and pesticide intermediates, but their separation faces the following technical bottlenecks: (1) Similar physical properties: the boiling points of m-cresol (boiling point 202.8℃) and p-cresol (201.8℃) differ by only 1℃. Traditional distillation requires an ultra-high number of trays (>100 trays), resulting in high energy consumption (energy consumption per ton of separation >600kWh); (2) Insufficient extraction selectivity: traditional solvents (such as methyl isobutyl ketone MIBK) rely on polarity differences, and the selectivity coefficient (β) for ortho / m / p-cresol is <2.5, requiring multiple extractions (stages >10 stages) to meet the separation requirements; (3) Poor environmental friendliness: sulfonation and azeotropic distillation methods use large amounts of acids, alkalis or volatile organic solvents (VOCs), resulting in large wastewater / waste gas emissions, which do not meet the requirements of green chemical industry.

[0003] Coordination chemistry separation technology utilizes the differences in coordination interactions between metal ions and phenolic hydroxyl groups, providing a new approach for precise separation. The coordination stability constant (lgK) is a key thermodynamic parameter measuring the strength of the bond between a metal ion and a ligand. For cresol isomers, their interaction with metal ions (such as Cu)... 2+ The coordination ability of ) is mainly affected by the steric hindrance and electronic effects of the ortho-substituent at the hydroxyl position: p-cresol: the hydroxyl group is methyl at the para position, which has less steric hindrance and the electronic effect is favorable for coordination, but its coordination with Cu 2+ The coordination stability constant of Cu is relatively low (lgK ≈ 4.8); m-cresol: the meta-hydroxyl position is methyl, the electronic effect is more favorable for coordination, the steric hindrance is moderate, and it is compatible with Cu. 2+ The coordination stability constant of the hydroxyl group is the highest (lgK≈5.2); o-cresol: the hydroxyl group at the ortho-methyl position introduces significant steric hindrance, which severely inhibits the coordination with metal ions, and its coordination stability constant is the lowest (lgK<4.5).

[0004] The aforementioned differences in coordination stability constants (intermediate > para > ortho) provide a theoretical basis for selective coordination extraction under gradient pH control. Essentially, pH affects the dissociation state of the phenolic hydroxyl group (Ar-OH). Ar-O - + H +Coordination ability is regulated. Under acidic conditions (pH=3-4): the phenolic hydroxyl group dissociates to a low degree (mainly in the form of Ar-OH), and can only form a weak coordination complex with p-cresol with moderate lgK (m-cresol requires Ar-O with a higher electron cloud density). - Only with efficient coordination can o-cresol coordinate effectively (o-cresol cannot coordinate due to insufficient lgK); under neutral conditions (pH=7-8): the phenolic hydroxyl group partially dissociates (Ar-O). - With increased proportions, the electron cloud density increases, allowing it to form a strong coordination complex with m-cresol, which has the largest lgK (p-cresol has already separated in the acidic region, while o-cresol cannot coordinate due to steric hindrance); alkaline conditions (pH=9-10): OH - Will with Cu 2+ The combination forms Cu(OH)2 precipitate, thus disrupting [Cu(Ar-O)2]. 2- The coordination bond allows the target phenol to be Ar-O - The form enters the aqueous phase, achieving back-extraction.

[0005] Although coordination chemistry has provided a framework for the separation of phenols, existing processes still have the following problems when dealing with mixed systems of ortho / m / p-cresol: Insufficient utilization of stability constants: Most processes only target m-cresol and p-cresol (lgK difference 0.4), neglecting the separation of o-cresol (lgK difference 0.8-1.2), resulting in the inability to simultaneously purify the three isomers; Single ligand: Only metal salts (such as CuCl2) are used as ligands, lacking the synergistic effect of auxiliary ligands (such as 8-hydroxyquinoline), failing to overcome the steric hindrance of o-cresol, resulting in o-cresol recovery rate <75%; Crude pH control: Using a two-stage process of "acidic extraction-alkaline back-extraction," the separation selectivity coefficient β of m-cresol and p-cresol is <3.0, requiring multiple extractions (>8 stages), making the process complex; Low ligand recovery rate: In existing processes, Cu... 2+ Easy to react with OH - Precipitation and loss occur, the recycling rate of the coordinating agent is less than 80%, and the wastewater contains a large amount of Cu. 2+ There is significant environmental pressure.

[0006] This invention introduces 8-hydroxyquinoline as a hydrogen bonding / π-π interaction enhancer, which interacts with Cu 2+ It forms a dual coordination system and, combined with three-stage pH gradient control, significantly improves separation selectivity and operational stability. Summary of the Invention

[0007] The purpose of this application is to provide a coordinating agent for separating and purifying a mixture of phenol isomers and a method for separating and purifying a mixture of phenol isomers, so as to solve the above-mentioned problems.

[0008] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows: In a first aspect, this application provides a coordinating agent for separating and purifying a mixture of phenol isomers, comprising, by weight (100%): Nitrogen-containing heterocyclic compounds 10-15%, transition metal salts 5-8%, and diluents 77-85%.

[0009] The main ligand is a nitrogen-containing heterocyclic compound (such as 8-hydroxyquinoline), which forms a [Ar-OH•••8-hydroxyquinoline] hydrogen bond and π-π conjugation with the phenolic hydroxyl group.

[0010] The auxiliary ligand is a transition metal salt (such as copper acetate Cu(OAc)2), which forms [Cu(Ar-O)2] with the phenolic hydroxyl group. 2- Coordination bonds, with coordination stability constants differing by ≥1 order of magnitude (m-cresol > p-cresol > o-cresol).

[0011] Optionally, the amount of nitrogen-containing heterocyclic compound can be any value between 10%, 11%, 12%, 13%, 14%, 15% or 10-15%, the amount of transition metal salt can be any value between 5%, 6%, 7%, 8% or 5-8%, and the amount of diluent can be any value between 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85% or 77-85%.

[0012] Preferably, the nitrogen-containing heterocyclic compound includes 8-hydroxyquinoline, the transition metal salt includes copper acetate, and the diluent includes sulfonated kerosene.

[0013] Secondly, this application provides a method for separating and purifying a mixture of benzophenol isomers, characterized in that it includes: The mixture of benzophenol isomers was subjected to a three-stage gradient pH extraction process, including acidic extraction and / or neutral extraction, followed by alkaline back-extraction. The gradient pH three-stage extraction and separation includes: The ligand and the mixture of benzophenol isomers are mixed and subjected to acid extraction under acidic conditions to separate the first aqueous phase and the first organic phase. The first aqueous phase and the complexing agent were mixed and subjected to neutral extraction under neutral conditions to separate the second aqueous phase and the second organic phase. The second aqueous phase was extracted with n-hexane to obtain the third organic phase; The first organic phase, the second organic phase, and the third organic phase were respectively subjected to alkaline back-extraction using sodium hydroxide aqueous solution as the back-extraction agent. Then, the back-extraction solutions were subjected to vacuum distillation and molecular distillation in sequence to obtain p-benzophenol, m-benzophenol, and o-benzophenol. The ligand is the same ligand used for separating and purifying a mixture of benzophenol isomers.

[0014] Preferably, the pH of the acidic extraction system is 3-4, and is adjusted using hydrochloric acid; The volume ratio of the ligand to the mixture of benzophenol isomers is (0.2-1:2), the extraction temperature is 20-40℃, and the stirring time is 30-120 min.

[0015] Optionally, the volume ratio of the ligand and the mixture of phenol isomers can be any value between 0.2:2, 0.5:2, 1:2, or (0.2-1:2), the extraction temperature can be any value between 20℃, 30℃, 40℃, or 20-40℃, and the stirring time can be any value between 30min, 60min, 90min, 120min, or 30-120min.

[0016] Preferably, the pH of the neutral extraction system is 7-8 (it can be any value between 7, 7.5, 8 or 7-8), and is adjusted using a mixed solution of sodium carbonate and sodium bicarbonate; The volume ratio of the ligand to the first aqueous phase is (0.5-1:1), the extraction temperature is 30-50℃, and the stirring time is 30-90 min.

[0017] Optionally, the volume ratio of the ligand to the first aqueous phase can be any value between 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, or (0.5-1:1), the extraction temperature can be any value between 30℃, 40℃, 50℃, or 30-50℃, and the stirring time can be any value between 30min, 60min, 90min, or 30-90min.

[0018] Preferably, the volume ratio of the second aqueous phase to n-hexane is 1.1-1.5:1, the extraction temperature is 30-35℃, the stirring time is 30-120 min, and the pH of the system is 6-8.

[0019] Optionally, the volume ratio of the second aqueous phase to n-hexane can be any value between 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, or 1.1-1.5:1; the extraction temperature can be any value between 30℃, 31℃, 32℃, 33℃, 34℃, 35℃, or 30-35℃; the stirring time can be any value between 30min, 50min, 60min, 80min, 100min, 120min, or 30-120min; and the system pH can be any value between 6, 7, 8, or 6-8.

[0020] Preferably, the pH of the alkaline back-extraction system is 9-10 (it can be any value between 9, 9.5, 10 or 9-10), and is adjusted using an aqueous sodium hydroxide solution; The volume ratio of the first organic phase, the second organic phase, and the third organic phase to the back-extraction agent is (1-2:1), the back-extraction temperature is 40-60℃, and the stirring time is 10-60min.

[0021] Optionally, the volume ratio of the first organic phase, the second organic phase, and the third organic phase to the back-extraction agent can be any value between 1:1, 1.5:1, 2:1, or (1-2:1), the back-extraction temperature can be any value between 40℃, 50℃, 60℃, or 40-60℃, and the stirring time can be any value between 10min, 20min, 30min, 40min, 50min, 60min, or 10-60min.

[0022] In the gradient pH three-stage extraction and separation process described above, under acidic conditions (pH=3-4), the ligand preferentially forms a weak coordination complex with p-cresol, which enters the organic phase; under neutral conditions (pH=7-8), m-cresol forms a strong coordination complex with the ligand, which is selectively extracted; under alkaline conditions (pH=9-10), the coordination bond is broken, and the target phenol is back-extracted, achieving segmented collection.

[0023] Preferably, the amount of diluent used is adjusted to adjust the viscosity of the complexing agent to no more than 15 mPa·s.

[0024] Preferably, the alkaline back-extraction is followed by: The respective back-extraction solutions were subjected to vacuum distillation and molecular distillation in sequence. The pressure of the vacuum distillation shall not exceed 5 kPa and the temperature shall not exceed 100℃. The molecular distillation temperature is 150-180℃ (it can be any value between 150℃, 160℃, 170℃, 180℃, or 150-180℃), and the vacuum degree is not higher than 10. -3 kPa.

[0025] Preferably, the process further includes, after the molecular distillation: The distillation residue was mixed with acetic acid solution, and the pH of the system was adjusted to 3-4 to obtain the regenerated complexing agent.

[0026] Compared with the prior art, this application has the following beneficial effects: The ligand and method for separating and purifying a mixture of phenol isomers provided in this application have the following significant advantages: (1) Ultra-high selectivity separation: based on ortho, meta, and p-cresols and Cu 2+ Due to the inherent differences in coordination stability constants (lgK-inter>lgK-pair>lgK-ortho), an innovative 8-hydroxyquinoline / copper acetate bifunctional coordination system was adopted. Through multiple molecular synergistic effects, the precise identification and separation of the three isomers were achieved, with a selectivity coefficient (β) exceeding 20, product purity ≥99%, and yield ≥92%.

[0027] (2) High efficiency and energy saving: Three-stage gradient pH extraction replaces traditional high-energy-consuming distillation or multi-stage extraction. The process is short and efficient, reducing energy consumption per ton of product by about 50% (only 280kWh) and reducing equipment investment costs by more than 30%.

[0028] (3) Green, economical and sustainable: The recycling rate of the complexing agent is >95%, and it can be stably recycled more than 50 times, which greatly reduces material consumption. The discharge of waste gas, wastewater and solid waste is significantly reduced (COD of wastewater <500mg / L, VOCs are close to zero discharge), avoiding the use of strong acids and alkalis, and meeting the requirements of green chemical industry.

[0029] (4) Easy to promote industrialization: The process parameters are easy to control and it is easy to realize automated continuous production, providing an efficient and reliable solution for the large-scale preparation of high-purity phenols in the fields of medicine and pesticides. Detailed Implementation

[0030] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0031] The following description is based on specific embodiments.

[0032] Example 1 This embodiment provides a ligand, with the following raw materials: 12 kg (12%) of 8-hydroxyquinoline, 6 kg (6%) of copper acetate (Cu(OAc)2), and 82 kg (82%) of sulfonated kerosene.

[0033] The preparation method of the ligand is as follows: 8-Hydroxyquinoline and Cu(OAc)₂ were added to a reaction vessel, sulfonated kerosene was injected, and the mixture was stirred at 60°C for 60 minutes to form a homogeneous and transparent liquid. The Cu content in the complexing agent was measured. 2+ The concentration was 0.15 mol / L, and the concentration of 8-hydroxyquinoline was 0.4 mol / L.

[0034] This embodiment also provides a method for separating and purifying a mixture of phenol isomers, the specific steps of which are as follows: (1) Raw material pretreatment: Take 50L of a phenol mixture (49.8% m-cresol, 50.2% p-cresol, total concentration 25wt%), dissolve it in 50L of n-hexane, and filter it through a 5μm filter cartridge to obtain a pretreated solution (viscosity 4.8mPa•s, moisture content <0.1%).

[0035] (2) Acidic extraction section (separation of p-cresol): Add 25 L of complexing agent and 50 L of pretreatment solution to the extraction vessel, stir at 300 rpm, add 1 mol / L HCl dropwise to adjust the pH of the aqueous phase to 3.0, and react at 30℃ for 30 min. After standing for 15 minutes to separate the layers, the upper organic phase (containing p-cresol) was collected. The concentration of p-cresol in the organic phase was 18.2 wt%, the residue of m-cresol was 1.5 wt%, the partition coefficient D(p-cresol) = 12.3, D(m-cresol) = 0.8, and the selectivity coefficient β(p / m) = 15.4.

[0036] (3) Neutral extraction stage (separation of m-cresol): Take the aqueous phase after acid extraction (containing 23.5 wt% m-cresol), add 25 L of fresh complexing agent, adjust the pH to 7.2 with NaHCO3 / Na2CO3 buffer, and stir at 40℃ and 350 rpm for 45 min. After standing for 20 minutes to separate the layers, the upper organic phase (containing m-cresol) was collected. The concentration of m-cresol in the organic phase was 22.8 wt%, and the residual p-cresol was 0.9 wt%. The partition coefficients D(m-cresol) = 25.1, D(p-cresol) = 1.2, and the selectivity coefficient β(m- / p-cresol) = 20.9.

[0037] (4) Alkaline back-extraction section: p-Cresol organic phase: mixed with 15 L 5% NaOH solution, stirred at 50℃ and 400 rpm for 20 min. The aqueous phase was tested and found to have a p-cresol concentration of 16.5 wt% and a back-extraction rate of 98.3%. m-Cresol organic phase: Mixed with 15L of 5% NaOH solution, stirred at 50℃ and 400rpm for 20min. The concentration of m-cresol in the aqueous phase was measured to be 20.3wt%, and the back-extraction rate was 98.6%.

[0038] (5) Product Refining: The back-extraction solution was subjected to vacuum distillation (4 kPa, 90 °C) to remove water, and then subjected to molecular distillation (150 °C, 5 × 10⁻⁶ m³ / h). - 4 (kPa) yielded p-cresol (purity 99.1%, yield 91.5%) and m-cresol (purity 99.3%, yield 92.2%).

[0039] Detection method: Concentration determination: Gas chromatography (GC-FID), HP-5 column (30m×0.32mm×0.25μm), temperature program: 80℃ (5min) → 250℃ (10℃ / min), injection port 280℃, detector 300℃, internal standard method to calculate content.

[0040] Purity determination: High performance liquid chromatography (HPLC-UV), C18 column (250mm×4.6mm), mobile phase methanol / water = 70 / 30, flow rate 1.0mL / min, detection wavelength 275nm.

[0041] Recycling process: Steps: Add 10% acetic acid solution to the back-extraction residue (containing complexing agent, a small amount of phenols and NaOH) to adjust the pH to 4.0, let it stand for 30 min to separate the organic phase; Distillation: The organic phase is distilled under reduced pressure (10 kPa, 120 °C) to recover sulfonated kerosene. The residual solids are supplemented with 5% 8-hydroxyquinoline and 3% Cu(OAc)2, stirred evenly, and then recycled.

[0042] The loop results are shown in Table 1 below: Table 1. Loop Results Conclusion: After 50 cycles, the performance retention rate of the ligand is >93%, and the copper ion loss rate is <5%, which meets the requirements for long-term industrial operation.

[0043] Example 2 The ligand used in this embodiment is the same as that in Embodiment 1.

[0044] This embodiment also provides a method for separating and purifying a mixture of phenol isomers, the specific steps of which are as follows: (1) Acidic extraction stage (separation of p-cresol) Procedure: 25L complexing agent + 50L pretreatment solution (dissolved in n-hexane), adjust pH to 3.5 with HCl, stir at 35℃ for 40 min; Results: The organic phase contained 19.8 wt% p-cresol (yield 95%), and o- / m-cresol residues were <2%.

[0045] (2) Neutral extraction stage (separation of m-cresol) Procedure: Take the acidic aqueous phase (containing o- / m-cresol), add 25 L of fresh complexing agent, adjust the pH to 7.5 with NaHCO3 buffer, and stir at 45℃ for 50 min; Results: The organic phase contained 21.5 wt% m-cresol (yield 93%), and o-cresol residue was <1.5%.

[0046] (3) o-Cresol enrichment segment Procedure: The neutral aqueous phase (containing o-cresol) was extracted with 10 L of n-hexane at pH 7.0 and stirred at 30 °C for 30 min. Results: The organic phase contained 16.2 wt% o-cresol (yield 90%).

[0047] (4) Alkaline back-extraction and purification p- / m-cresol organic phases: back-extracted with 5% NaOH (same as in Example 1); o-Cresol organic phase: back-extracted with 5% NaOH (50℃, 20 min); Refining: The three-component back-extraction solution was subjected to vacuum distillation and molecular distillation respectively to obtain: p-Cresol had a purity of 99.2% and a yield of 91%; m-Cresol had a purity of 99.4% and a yield of 92%; o-Cresol had a purity of 99.2% and a yield of 90.5%.

[0048] Example 3 The ligand used in this embodiment is the same as that in Embodiment 1.

[0049] This embodiment also provides a method for separating and purifying a mixture of phenol isomers, the specific steps of which are as follows: Raw material pretreatment: Take 30L of a phenol mixture (33.3% o-cresol, 33.3% m-cresol, 33.4% p-cresol, total concentration 25wt%), dissolve it in 30L of n-hexane, and filter it through a 5μm filter cartridge to obtain a pretreated solution.

[0050] Gradient pH three-stage extraction and separation: Acidic extraction stage (pH=3.5, adjusted with HCl): Add 15 L of complexing agent and 30 L of pretreatment solution, stir at 30℃ and 300 rpm for 40 min; allow to stand and separate into layers, collect the organic phase (mainly containing p-cresol); the remaining components in the aqueous phase are: o-cresol 32.1%, m-cresol 32.8%, and p-cresol 0.5%. Neutral extraction stage (pH=7.5, adjusted with NaHCO3 / Na2CO3 buffer): Add 15 L of fresh complexing agent to the above aqueous phase, stir at 40℃ and 350 rpm for 50 min; allow to stand and separate into layers, collect the organic phase (mainly containing m-cresol); the remaining components in the aqueous phase are: o-cresol 31.8%, m-cresol 0.9%, and p-cresol 0.2%.

[0051] Alkaline back-extraction section (pH=9.5, 5% NaOH solution): Back-extract the two organic phases separately, add 10L of 5% NaOH to each, stir at 50℃ and 400rpm for 20min; collect the aqueous phase to obtain p-cresol and m-cresol back-extraction solutions respectively.

[0052] Recovery: The remaining aqueous phase is subjected to vacuum distillation (5 kPa, 85℃) to remove water, followed by molecular distillation (160℃, 5 × 10⁻⁶ m³ / h).- 4 High-purity o-cresol was obtained by (kPa).

[0053] Product test results: p-cresol: purity 99.0%, yield 90.5%; m-cresol: purity 99.2%, yield 91.8%; o-cresol: purity 98.9%, yield 89.6%.

[0054] Coordinating agent regeneration performance: After 50 cycles, the partition coefficient of the coordinating agent to the three cresols was retained at >92%, Cu 2+ The loss rate is less than 4%, which meets the requirements for industrialization.

[0055] Comparative Example 1 The traditional MIBK extraction method was used as a control.

[0056] Take 50 L of the pretreated mixture of phenol isomers from Example 1, mix it with 50 L of methyl isobutyl ketone (MIBK), and stir for 60 min at 40 °C and pH=7 (unadjusted natural pH). After standing and phase separation, collect the organic phase and back-extract with 10% sodium hydroxide solution. After vacuum distillation and molecular distillation under the same conditions, a mixture of p-cresol and m-cresol was obtained, with purities of 94.8% and 95.2% respectively according to GC analysis, which could not be effectively separated.

[0057] Comparative Example 2 Azeotropic distillation was used as a control.

[0058] A mixture of 50 L of phenol isomers was directly added to a distillation column, with cyclohexane added as an azeotropic agent. Azeotropic distillation was carried out under the conditions of a top temperature of 80-85 °C, a bottom temperature of 190-200 °C, and a reflux ratio of 10:1. The operation was energy-intensive, and the purity of the separated product was approximately 96.5%, with residual azeotropic agent.

[0059] The results of comparing the method provided in this application with the methods of Comparative Examples 1 and 2 are shown in Table 2 below: Table 2 Comparison Results Comparative Example 3: Single ligand (using only 8-hydroxyquinoline) Objective: To verify that separation relying solely on hydrogen bonding / π-π interactions of nitrogen-containing heterocyclic compounds without metal ion coordination is ineffective.

[0060] Preparation of ligands: 12 kg (12%) of 8-hydroxyquinoline was directly dissolved in 88 kg of sulfonated kerosene to form a homogeneous solution (without transition metal salts). The concentration of 8-hydroxyquinoline in the ligand was approximately 0.4 mol / L.

[0061] Separation method: The operating steps are the same as those of the gradient pH three-stage extraction and separation in Example 3.

[0062] Acidic extraction section (pH=3.5): 15L of complexing agent is mixed with 30L of pretreatment solution and stirred at 30℃ for 40min.

[0063] Neutral extraction phase (pH=7.5): Take the aqueous phase from the acidic phase, add 15L of fresh complexing agent, and stir at 40℃ for 50min.

[0064] Alkaline back-extraction section (pH=9.5): Back-extraction is performed on each organic phase.

[0065] Results and Analysis: Acidic extraction section: The concentration of p-cresol in the organic phase was only 8.5 wt%, with partition coefficients D(p-cresol) = 3.2, D(m-cresol) = 2.8, and selectivity coefficient β(p / m) = 1.1. This indicates a deficiency of Cu²⁺. + Due to the coordination effect, the separation selectivity of p-cresol and m-cresol is extremely poor.

[0066] Neutral extraction section: The concentration of m-cresol in the organic phase is only 9.1 wt%, with a partition coefficient D(m-cresol) = 4.0 and β(m / p) = 1.3. The extraction efficiency of m-cresol is low.

[0067] Final products: After distillation, the back-extraction solution yielded p-cresol with a purity of 89.5% and a yield of 75.2%; m-cresol with a purity of 90.1% and a yield of 76.8%; and o-cresol with a purity of 88.3% and a yield of 74.5%. The purity of the products is much lower than that of this invention (≥99%), and the yield is significantly reduced.

[0068] Conclusion: Single 8-hydroxyquinoline lacks metal coordination synergy and cannot achieve accurate isomer recognition. The selectivity coefficient β<2, proving the necessity of bifunctional coordination systems.

[0069] Comparative Example 4: Single complexing agent (copper acetate only) Objective: To verify the limitations of relying solely on metal ion coordination without the synergistic effect of auxiliary ligands, particularly the stability of the ligand.

[0070] Preparation of ligands: Take 6 kg (6%) of copper acetate and dissolve it in 94 kg of sulfonated kerosene to form Cu²⁺. + A solution with a concentration of 0.15 mol / L (without 8-hydroxyquinoline).

[0071] Separation method: The gradient pH three-stage extraction and separation method is the same as in Example 3.

[0072] Results and Analysis: Acidic extraction section: The concentration of p-cresol in the organic phase is 15.2 wt%, the partition coefficient D(p-cresol) = 10.5, and β(p / m) = 8.2. The separation effect is acceptable, but lower than that of this invention (β = 15.4).

[0073] Neutral extraction section: The concentration of m-cresol in the organic phase is 18.3 wt%, D (m-cresol) = 15.6, and β (m- / p-cresol) = 12.1. The extraction efficiency of m-cresol is significantly lower than that of this invention (D = 25.1).

[0074] Complexing agent stability: In the alkaline back-extraction section (pH=9.5), Cu² + Easy to react with OH - The formation of Cu(OH)2 precipitate resulted in a complexing agent recovery rate of only 78.5% (which dropped to 70.2% after 50 cycles), and a copper ion loss rate as high as 12.3%.

[0075] Final products: p-cresol purity 95.8%, yield 85.1%; m-cresol purity 96.2%, yield 86.0%; o-cresol purity 94.5%, yield 82.3%. Both purity and yield are lower than those of this invention, and the coordinating agent cannot be recycled.

[0076] Conclusion: Although copper acetate alone has a certain separation effect, it lacks the stabilizing and synergistic effect of 8-hydroxyquinoline, resulting in low recovery rate and significant environmental pollution, demonstrating the environmental and economic advantages of the bifunctional system.

[0077] Comparative Example 5: Acidic extraction only (neutral and alkaline extraction stages omitted). Objective: To verify the integrity of the three-stage gradient pH extraction method, as complete separation cannot be achieved by omitting subsequent steps.

[0078] method: The acidic extraction stage of Example 3 (pH=3.5, 15 L of complexing agent mixed with 30 L of pretreatment solution) was performed only, followed by direct alkaline back-extraction of the organic phase (pH=9.5) and distillation to obtain the product. The aqueous phase was not further treated.

[0079] Results and Analysis: Results of acid extraction: The organic phase mainly contained p-cresol at a concentration of 18.5 wt%, but the p-cresol yield was only 55.3% (due to some residue in the aqueous phase), and the m-cresol residue reached 10.2%.

[0080] Final product: Only p-cresol was obtained with a purity of 98.5% (high, but due to incomplete separation), but the yield was as low as 55.3%. The aqueous intermediate cresol (approximately 32% concentration) and o-cresol (approximately 33% concentration) were not separated and were discarded as a mixture, resulting in low overall resource utilization.

[0081] Conclusion: Single-stage extraction cannot process three-component mixtures, resulting in low product yield and resource waste, demonstrating the crucial role of the three-stage process in improving yield and purity.

[0082] Comparative Example 6: Neutral extraction only (acidic and basic extraction stages omitted). Objective: To verify the limitations of using the neutral extraction segment alone, which cannot preferentially separate p-cresol.

[0083] method: The pretreatment solution was directly subjected to a neutral extraction stage (pH=7.5, 15L of complexing agent mixed with 30L of pretreatment solution), followed by alkaline back-extraction. The acidic extraction stage was omitted.

[0084] Results and Analysis: Results of the neutral extraction stage: The concentration of intermediate cresol in the organic phase was high (20.1 wt%), but p-cresol was also co-extracted in large quantities (15.8 wt%), with partition coefficients D(m-cresol) = 18.5, D(p-cresol) = 14.2, and β(m- / p-cresol) = 1.3. The selectivity was poor, and effective separation was not possible.

[0085] Final product: Back-extraction yielded a mixture of m-cresol and p-cresol with a purity of approximately 92.3%, making it impossible to obtain a single high-purity component. o-cresol remained in the aqueous phase.

[0086] Conclusion: Without the pretreatment of the acidic phase, m-cresol and p-cresol could not be separated, demonstrating the indispensability of the sequential control of gradient pH for selective extraction.

[0087] Comparative Example 7: Alkaline back-extraction only (all extraction stages omitted) Objective: To verify that direct back-extraction without coordination extraction cannot achieve any separation.

[0088] method: The pretreatment solution (n-hexane solution) was directly mixed with 5% NaOH aqueous solution (volume ratio 1:1), and back-extracted by stirring at 50℃ for 20 min, followed by distillation.

[0089] Results and Analysis: Back-extraction results: all phenols were transferred to the aqueous phase, but without selectivity. The back-extraction solution was a homogeneous mixture of ortho-, meta-, and p-cresols, with the proportions of each component being basically the same as those of the raw material (approximately 33%).

[0090] Final product: After distillation, a mixture of cresols was obtained with the same purity as the raw materials (approximately 25 wt% total concentration), and no separation effect was observed.

[0091] Conclusion: Alkaline back-extraction can only recover phenols, but cannot separate isomers, proving that the coordination extraction stage is the core step for achieving separation.

[0092] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A ligand for separating and purifying a mixture of phenol isomers, characterized in that, Based on a total mass of 100%, including: Nitrogen-containing heterocyclic compounds 10-15%, transition metal salts 5-8%, and diluents 77-85%.

2. The ligand for separating and purifying a mixture of phenol isomers as described in claim 1, characterized in that, The nitrogen-containing heterocyclic compound includes 8-hydroxyquinoline, the transition metal salt includes copper acetate, and the diluent includes sulfonated kerosene.

3. A method for separating and purifying a mixture of phenol isomers, characterized in that, include: The mixture of benzophenol isomers was subjected to a three-stage gradient pH extraction process, including acidic extraction and / or neutral extraction, followed by alkaline back-extraction. The gradient pH three-stage extraction and separation includes: The ligand and the mixture of benzophenol isomers are mixed and subjected to acid extraction under acidic conditions to separate the first aqueous phase and the first organic phase. The first aqueous phase and the complexing agent were mixed and subjected to neutral extraction under neutral conditions to separate the second aqueous phase and the second organic phase. The second aqueous phase was extracted with n-hexane to obtain the third organic phase; The first organic phase, the second organic phase, and the third organic phase were subjected to alkaline back-extraction using an aqueous sodium hydroxide solution as the back-extraction agent to obtain p-benzophenol, m-benzophenol, and o-benzophenol. The ligand is the ligand for separating and purifying a mixture of benzophenol isomers as described in claim 1 or 2.

4. The method for separating and purifying a mixture of phenol isomers as described in claim 3, characterized in that, The pH of the acidic extraction system is 3-4, and it is adjusted using hydrochloric acid. The volume ratio of the ligand to the mixture of phenol isomers is (0.2-1:2), the extraction temperature is 20-40℃, and the stirring time is 30-120 min.

5. The method for separating and purifying a mixture of phenol isomers as described in claim 3, characterized in that, The pH of the neutral extraction system is 7-8, which is adjusted using a mixed solution of sodium carbonate and sodium bicarbonate. The volume ratio of the ligand to the first aqueous phase is (0.5-1:1), the extraction temperature is 30-50℃, and the stirring time is 30-90 min.

6. The method for separating and purifying a mixture of phenol isomers as described in claim 3, characterized in that, The volume ratio of the second aqueous phase to n-hexane is 1:1 to 1.5:1, preferably 1:1; the extraction temperature is 30-50℃; the stirring time is 30-120 min; and the pH of the system is 6-8.

7. The method for separating and purifying a mixture of phenol isomers as described in claim 3, characterized in that, The pH of the alkaline back-extraction system is 9-10, which is adjusted using an aqueous sodium hydroxide solution. The volume ratio of the first organic phase, the second organic phase, and the third organic phase to the back-extraction agent is (1-2:1), the back-extraction temperature is 40-60℃, and the stirring time is 10-60min.

8. The method for separating and purifying a mixture of phenol isomers as described in claim 3, characterized in that, The amount of diluent used is based on adjusting the viscosity of the complexing agent to no more than 15 mPa·s.

9. The method for separating and purifying a mixture of phenol isomers as described in any one of claims 3-8, characterized in that, The alkaline back-extraction process also includes: The respective back-extraction solutions were subjected to vacuum distillation and molecular distillation in sequence. The pressure of the vacuum distillation shall not exceed 5 kPa and the temperature shall not exceed 100℃. The molecular distillation is performed at a temperature of 150-180℃, with a vacuum level not exceeding 10. -3 kPa.

10. The method for separating and purifying a mixture of phenol isomers as described in claim 9, characterized in that, The molecular distillation process also includes: The distillation residue was mixed with acetic acid solution, and the pH of the system was adjusted to 3-4 to obtain the regenerated complexing agent.

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