A method for purifying isopropyl alcohol as a reagent for spectral analysis

Abstract

This invention discloses a purification method for isopropanol, a reagent for spectroscopic analysis. The method includes: S1 mixing industrial-grade isopropanol with an alkali metal compound, adjusting the pH to 7.0–8.0, and obtaining a neutralized filtrate through solid-liquid separation; S2 continuously adsorbing and removing impurities from the neutralized filtrate by passing it sequentially through a molecular sieve adsorption unit, a modified activated carbon adsorption unit, and a γ-alumina adsorption unit; S3 subjecting the adsorbed liquid to staged total reflux distillation, controlling the reflux ratio at 5–15:1 and the total reflux time at 1–3 hours, and collecting the top product; S4 filling and sealing the top product under inert gas protection. This invention achieves closed-loop control of the entire process by setting online conductivity and moisture sensors, infrared detection devices, and online concentration sensors at key nodes. This method has the advantages of high purity, low energy consumption, high recovery rate, and process controllability, and is suitable for the industrial production of high-purity isopropanol for spectroscopic analysis.

Description

Technical Field

[0001] This invention relates to the field of chemical reagent purification technology, specifically to a method for purifying isopropanol, a reagent for spectroscopic analysis. Background Technology

[0002] Reagents used in spectroscopic analysis require extremely high purity, especially isopropanol (2-propanol), a commonly used solvent. Even trace impurities in isopropanol can significantly affect the detection sensitivity and baseline stability of UV-Vis, IR, Raman, and fluorescence spectra. The national standard GB / T9721-2006 "General Rules for Molecular Absorption Spectrophotometry of Chemical Reagents (UV and Visible Part)" and the industry standard T / CRIAC0113-2026 "Isopropanol for Spectroscopic Analysis" impose strict requirements on key indicators for isopropanol: content ≥99.7wt%, moisture ≤0.1wt% (recommended ≤0.03wt% for spectroscopic analysis), pH ≤0.0001mmol / g, UV absorbance (220nm) ≤0.4, and concentration of fluorescent precursors (aldehydes, ketones, unsaturated hydrocarbons) ≤1µg·g⁻¹. Any deviation from the above indicators will produce significant background absorption or fluorescence noise in the corresponding wavelength range, leading to baseline drift, increased detection limit and increased quantitative error of the spectrometer [Acta Physico-Chem. Sin. 2013, 29(4), 453-460; J. Mol. Liquids2022, 362, 119932].

[0003] Currently, industrially produced isopropanol is mainly obtained through petroleum cracking-alcoholization or alcohol acylation followed by single-stage atmospheric or vacuum distillation. This process can control the product content to 99.5%–99.8% (wt) and moisture content to 0.10%–0.30% (wt), accompanied by trace amounts of impurities such as acetic acid, formic acid, aldehydes, ketones, and unsaturated hydrocarbons. These residual impurities produce additional absorption peaks and fluorescence interference in the 200–400 nm region, increasing the spectrometer baseline noise by 10%–20% or even higher. In FT-IR, the OH stretching peak caused by moisture (≈3400 nm) is observed. The peaks overlap with the characteristic peaks of the sample, and in the Raman spectrum, there is a C=C stretching peak (≈1600). Even a concentration of only 10 ppm can severely interfere with analytical results [J. Anal. Chem. 2019, 74(6), 1243-1250; Sep. Purif. Technol. 2019, 210, 125-138]. Therefore, relying solely on conventional distillation is insufficient to meet all the requirements for reagents used in spectroscopic analysis.

[0004] While existing technologies include patents (such as CN105085183A) that disclose multi-stage combined processes involving pH neutralization, molecular sieve dehydration, modified activated carbon adsorption, alumina aldehyde removal, and total reflux distillation, the following shortcomings remain: First, the modified activated carbon's adsorption rate for aldehydes and ketones is only about 30%, making it difficult to reduce the concentration of fluorescent precursors to 1 µg. The following issues are addressed: Secondly, the temperature, reflux ratio, and total reflux time in the rectification section lack systematic parameter coupling, leading to significant fluctuations in moisture content during production; thirdly, the alternation of multi-stage rectification and activated carbon regeneration results in high energy consumption per unit (≥12 kWh). The problems include: low raw material recovery rate (85%–90%); lack of online monitoring and closed-loop control methods; reliance on offline testing for product quality; and difficulty in achieving real-time process optimization.

[0005] To address the aforementioned technical problems, this invention provides a closed-loop controlled purification method for isopropanol used in spectroscopic analysis. By optimizing the process sequence and parameters of each adsorption unit, and combining online sensing and closed-loop adjustment, continuous production with high purity, low energy consumption, and high recovery rate is achieved, meeting the stringent requirements for reagents used in spectroscopic analysis. Summary of the Invention

[0006] The purpose of this invention is to provide a purification method for isopropanol, a reagent for spectral analysis, to solve the technical problems of incomplete removal of fluorescent precursors, high energy consumption, low recovery rate, and lack of online closed-loop control in the prior art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for purifying isopropanol, a reagent used in spectroscopic analysis, includes the following steps: S1: Mix industrial-grade isopropanol with an alkali metal compound, adjust the pH of the system to 7.0-8.0, so that acidic impurities form salt precipitates, and obtain the neutralized filtrate through solid-liquid separation; S2: The neutralized filtrate is sequentially passed through a molecular sieve adsorption unit, a modified activated carbon adsorption unit, and a γ-alumina adsorption unit for continuous adsorption and impurity removal; S3: Perform staged heating and total reflux distillation on the liquid after S2 treatment, controlling the reflux ratio at 5 to 15:1 and the total reflux time at 1 to 3 hours, and collect the top product; S4: Fill and seal the top section of the product under inert gas protection.

[0009] Furthermore, the molecular sieve adsorption unit described in S2 employs... Molecular sieves, particle size 20–100 mesh, adsorption flow rate 0.5–30 BV. The effluent moisture content is ≤0.03wt%; the modified activated carbon adsorption unit uses activated carbon that has been impregnated with hypochlorous acid, nitric acid, sulfuric acid or perchloric acid at a volume concentration of 5% to 60% and then dried, with a particle size of 20 to 100 mesh; the γ-alumina adsorption unit has a particle size of 20 to 200 mesh.

[0010] Furthermore, the flow rate of each adsorption unit in S2 is independently 0.5–30 BV. Furthermore, each adsorption unit operates in series.

[0011] Furthermore, the segmented heating total reflux distillation described in S3 adopts a dual-tower distillation device, with the main tower heating temperature at 83-95°C, the bottom liquid temperature at 83-86°C, and the outlet liquid temperature at 81-82°C.

[0012] Furthermore, in S3, the product content is monitored in real time by an online concentration sensor. When the content is lower than 99.997wt%, the total reflux time is automatically extended or the reflux ratio is increased to ensure that the final product content is ≥99.998wt%.

[0013] Furthermore, in S2, an online conductivity or moisture sensor is installed at the outlet of the molecular sieve adsorption unit for real-time monitoring of moisture content; and an infrared or near-infrared online detection device is installed at the outlet of the γ-alumina adsorption unit for monitoring the intensity of characteristic absorption peaks of aldehydes and ketones.

[0014] Furthermore, the inert gas mentioned in S4 is nitrogen, the filling pressure is 0.2 MPa, the filling container is a glass bottle, and it is sealed with nitrogen.

[0015] Furthermore, the molecular sieve adsorption unit in S2 is replaced with a membrane permeation dehydration device with an operating pressure of 0.6 MPa, a selectivity of ≥30, and an effluent moisture content of ≤0.01 wt%.

[0016] Furthermore, the modified activated carbon adsorption unit in S2 is replaced with an ionic liquid extraction device, using 1-butyl-3-methylimidazolium tetrafluoroborate as the extraction phase. After extraction, the ionic liquid is recovered and recycled.

[0017] Furthermore, the final product contains ≥99.997 wt% of the active ingredient, ≤0.018 wt% of moisture, and ≤0.9 µg of fluorescent precursor. Recovery rate ≥ 95%, unit energy consumption ≤ 9 .

[0018] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention employs a specific sequence of "neutralization → dehydration → modified activated carbon → γ-alumina → distillation". Neutralization is performed beforehand to prevent acidic impurities from catalyzing side reactions to generate aldehydes and ketones during subsequent adsorption. Dehydration is performed beforehand to avoid water competing for adsorption sites, ensuring that each adsorption unit fully performs its function. The final product content is ≥99.997wt%, moisture ≤0.018wt%, and fluorescent precursor ≤0.9µg· It is significantly superior to existing technologies; (2) By optimizing parameters such as adsorption flow rate, reflux ratio, and total reflux time, the unit energy consumption is ≤9kWh· The raw material recovery rate is ≥95%, and the energy consumption is reduced by more than 25% compared with the existing technology, while the recovery rate is increased by 5 to 10 percentage points; (3) Online pH electrodes, conductivity sensors, infrared detection devices and concentration sensors are set at key nodes and linked with PLC to realize closed-loop regulation of the whole process, which improves the product qualification rate; (4) Membrane permeation dehydration can be used to replace molecular sieve columns, or ionic liquid extraction can be used to replace modified activated carbon columns to meet the needs of different scenarios. Attached Figure Description

[0019] Figure 1 This is a flowchart of a method for purifying isopropanol, a reagent for spectroscopic analysis, according to the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Please see Figure 1 This invention provides a method for purifying isopropanol, a reagent for spectroscopic analysis, comprising the following core steps:

[0022] S1: Acid-base neutralization and solid-liquid separation. Industrial-grade isopropanol is mixed with an alkali metal compound, and the pH is adjusted to 7.0–8.0 to cause acidic impurities (mainly acetic acid and formic acid) to form salt precipitates. The neutralized filtrate is obtained through solid-liquid separation.

[0023] S2: Continuous adsorption for impurity removal. The neutralized filtrate is passed sequentially through a molecular sieve adsorption unit, a modified activated carbon adsorption unit, and a γ-alumina adsorption unit to remove water, unsaturated hydrocarbons and fluorescent impurities, as well as polar impurities such as aldehydes, ketones, and peroxides.

[0024] S3: Segmented heating total reflux distillation. The adsorbed liquid is distilled, with the reflux ratio controlled at 5 to 15:1 and the total reflux time at 1 to 3 hours. The top product is collected.

[0025] S4: Inert gas protected filling. The top section of the product is filled and sealed under the protection of inert gases such as nitrogen to prevent secondary contamination.

[0026] The order of the above process steps plays a crucial role: first, neutralization can prevent acidic impurities from catalyzing side reactions to generate new aldehydes and ketones during subsequent adsorption; then, dehydration can avoid water competing for adsorption sites, ensuring the adsorption efficiency of activated carbon and γ-alumina for the target impurities; finally, distillation further removes residual trace impurities, ensuring that the product meets the stringent requirements for reagents used in spectroscopic analysis.

[0027] The industrial-grade isopropanol used is a commercially available product with a content of 99.5% to 99.8 wt%, a moisture content of 0.10% to 0.30 wt%, and contains trace amounts of impurities such as acetic acid, formic acid, aldehydes, ketones, and unsaturated hydrocarbons.

[0028] The preferred alkali metal compound is sodium carbonate or sodium bicarbonate, with a mass fraction of 1% to 10%, more preferably 5%. Sodium carbonate can react with acetic acid and formic acid to produce sodium acetate and sodium formate precipitates.

[0029] Molecular screening Molecular sieves, with a particle size of 20–100 mesh, are preferred. Composite filling is used to balance water absorption efficiency and selectivity.

[0030] The modified activated carbon is prepared by immersing activated carbon (particle size 20-100 mesh) in a solution of hypochlorous acid, nitric acid, sulfuric acid or perchloric acid with a volume concentration of 5%-60% for 6-24 hours (preferably 12 hours), and then drying it at 100-150℃ (preferably 120℃) for 1-4 hours (preferably 2 hours) to obtain modified activated carbon with a surface rich in polar groups such as carboxyl and hydroxyl groups, which enhances the adsorption capacity for unsaturated hydrocarbons and fluorescent precursors.

[0031] The γ-alumina selected has a particle size of 20-200 mesh, a specific surface area ≥200m² / g, and a pore volume ≥0.4mL / g, and exhibits good adsorption selectivity for aldehydes, ketones, peroxides, and metal ions.

[0032] The process parameters are required as follows:

[0033] The flow rate of each adsorption unit is independently 0.5–30 BV. (Bed volume / hour), preferably 0.5~5 BV. This ensures sufficient adsorption contact time.

[0034] An online conductivity sensor or moisture sensor is installed at the outlet of the molecular sieve adsorption unit. When the conductivity is ≤0.5µS· If the moisture content is ≤0.03wt%, the effluent can proceed to the next unit; if the threshold is exceeded, the system will automatically alarm or switch to the standby column.

[0035] An infrared or near-infrared online detection device is installed at the outlet of the γ-alumina adsorption unit to monitor 1720. The intensity of the characteristic absorption peak of the carbonyl group nearby. When the peak intensity is ≤10% (equivalent to an aldehyde or ketone concentration ≤0.8µg), the concentration is considered low. When the adsorption time exceeds the threshold, the liquid enters the distillation unit; if the adsorption time exceeds the threshold, the adsorption time is extended or the temperature of the adsorption column is increased (25-40℃) to enhance the adsorption efficiency.

[0036] The distillation unit employs a dual-tower total reflux distillation apparatus. The main tower is 3m high and 200mm in diameter, filled with high-efficiency glass corrugated packing; the secondary tower is 1.5m high and 120mm in diameter, used for secondary refining. The main tower heating temperature is 83–95℃, the bottom liquid temperature is 83–86℃, and the outlet liquid temperature is 81–82℃. The reflux ratio is automatically adjusted by a PLC based on feedback from online concentration and conductivity sensors to ensure a product content ≥99.997wt%.

[0037] The following comparative experiments will be conducted using three sets of example cases and two sets of comparative cases to verify the results.

[0038] Example 1.

[0039] S1: Acid-base neutralization and solid-liquid separation

[0040] 100 kg (approximately 131 L) of industrial-grade isopropanol was added to a 250 L stainless steel stirred tank at 25 °C and a stirring speed of 300 rpm. 5 kg of sodium carbonate (5% by mass) was added in a single batch, and the mixture was stirred for 30 min. The pH was monitored and automatically adjusted using an online pH electrode to stabilize the system pH at 7.25 ± 0.05. Stirring was stopped, and the mixture was allowed to stand for 1 h to allow complete sedimentation of sodium acetate and sodium formate. The upper organic phase was filtered through a 0.45 µm PTFE membrane to obtain approximately 125 L of neutralized filtrate.

[0041] S2: Continuous adsorption for impurity removal

[0042] Neutralize the filtrate at 0.5 BV. The flow rate passes sequentially through three fixed-bed adsorption columns:

[0043] (1) Molecular sieve column: packed with Molecular sieve 300mL, particle size 20-100 mesh, column temperature 25℃, effluent conductivity ≤0.5µS· (Corresponding moisture content ≤ 0.018wt%)

[0044] (2) Modified activated carbon column: Activated carbon was impregnated with 10% hypochlorous acid for 12h and dried at 120℃ for 2h and then packed into 300mL. The column temperature was 25℃ and the absorbance at 254nm was monitored by online UV-Vis with a value of ≤0.001AU.

[0045] (3) γ-alumina column: 300 mL γ-alumina, particle size 20-200 mesh, column temperature 25℃, infrared monitoring 1720 Peak intensity ≤10% (corresponding to aldehydes and ketones ≤0.8µg·) ).

[0046] S3: Segmented heating total reflux distillation

[0047] After adsorption, the liquid enters a dual-tower distillation unit. The main column bottom temperature is 93℃, the bottom liquid temperature is 84℃, and the top temperature is 80℃. The reflux ratio is 12:1, and the total reflux time is 1.8 hours. The PLC adjusts the reflux valve based on feedback from online concentration and conductivity sensors to ensure that the product content is ≥99.997wt% and the moisture content is ≤0.018wt%.

[0048] S4: Nitrogen-filled packaging

[0049] The top distillation product is conveyed to a nitrogen glove box, purged with 0.2MPa pure nitrogen, automatically filled into 4L glass bottles, and sealed.

[0050] Quality testing: Tested according to GB / T9721-2006, GB / T9736-2008, and GB / T605-2000, the results are as follows: content 99.998wt%, pH 7.33, moisture 0.014wt%, fluorescent precursor 0.68µg. Energy consumption per unit: 8.6 kWh The recovery rate was 96%.

[0051] Example 2.

[0052] The difference between this embodiment and embodiment 1 is that the molecular sieve adsorption unit in S2 is replaced by a membrane permeation dehydration device.

[0053] S1 is the same as in Example 1.

[0054] S2: The neutralized filtrate is passed through a silica / polyether composite permeation membrane (effective area 2.5 m², selectivity ≥30) at an operating pressure of 0.6 MPa and a temperature of 30°C. Water (≤0.01 wt%) is collected on the permeate side for system cooling, while the concentrate (approximately 98 wt%) directly enters the modified activated carbon column and the γ-alumina column, with the flow rate increased to 0.6 BV. .

[0055] S3: Distillation vessel temperature 83-88℃, reflux ratio 10:1, total reflux time 1.4h.

[0056] S4 is the same as in Example 1.

[0057] Test results: Content 99.997 wt%, Moisture 0.012 wt%, Fluorescent precursor 0.58 µg. Energy consumption per unit: 6.9 kWh The recovery rate was 97%.

[0058] Example 3.

[0059] The difference between this embodiment and Embodiment 1 is that the modified activated carbon adsorption unit in S2 is replaced by an ionic liquid extraction device.

[0060] S1 is the same as in Example 1, with a neutralized pH of 7.3 ± 0.05, and 1% v / v of 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid is added.

[0061] S2: The mixture is passed through an extraction column (2m high, 150mm diameter, packed with ceramic rings) at 50℃ and 1BV. Contact at a flow rate of 10 min. The lower aqueous phase is then introduced into a modified activated carbon column (impregnated with 15% hypochlorous acid) and a γ-alumina column (350 mL) for adsorption. The upper organic phase is distilled to recover the ionic liquid and then recycled.

[0062] S3: Distillation vessel temperature 85-92℃, reflux ratio 12:1, total reflux time 2h.

[0063] S4 is the same as in Example 1.

[0064] Test results: Content 99.998 wt%, Moisture 0.015 wt%, Fluorescent precursor 0.42 µg. Energy consumption per unit: 9.2 kWh The recovery rate was 95.5%.

[0065] Comparative Example 1.

[0066] Compared to Example 1, the molecular sieve dehydration unit was placed after the modified activated carbon and γ-alumina adsorption. Other parameters remained unchanged.

[0067] Because the raw material moisture (approximately 0.15 wt%) was not pre-removed, the moisture competed for adsorption sites, leading to a decrease in the adsorption efficiency of activated carbon and γ-alumina for unsaturated hydrocarbons and aldehydes and ketones. The high moisture content at the inlet of the molecular sieve dehydration section necessitates extending the treatment time to 3 hours to reach the conductivity threshold.

[0068] Test results: Content 99.992 wt%, Moisture 0.045 wt%, Fluorescent precursor 4.2 µg. Energy consumption per unit: 10.5 kWh The recovery rate was 91%.

[0069] Comparative Example 2.

[0070] Compared to Example 1, activated carbon and γ-alumina adsorption were performed first, followed by neutralization.

[0071] Unneutralized organic acids in the raw materials undergo catalytic oxidation within the micropores of activated carbon and γ-alumina, generating new aldehydes and ketones, which leads to increased UV-Vis absorbance. Although some impurities are precipitated and removed after neutralization, the already formed aldehydes and ketones are difficult to completely remove.

[0072] Test results: Content 99.985 wt%, Moisture 0.028 wt%, Fluorescent precursor 8.5 µg. Energy consumption per unit: 11.2 kWh The recovery rate was 88%.

[0073] The overall experimental results are compared in the following table:

[0074] Results analysis:

[0075] Comparative Example 1: When industrial-grade raw materials with high moisture content are directly introduced into the adsorption column, water molecules, being highly polar molecules, preferentially occupy the active adsorption sites of modified activated carbon and alumina (competitive adsorption), leading to a significant decrease in the removal efficiency of unsaturated hydrocarbons and aldehydes / ketones. Simultaneously, a large amount of moisture enters subsequent processing stages with the material, causing the molecular sieve to be overloaded.

[0076] Comparative Example 2: Without acid-base neutralization, the raw materials containing trace amounts of acetic acid and formic acid were directly adsorbed. The organic acids in the industrial raw materials were not neutralized, and the oxidation or condensation side reactions of alcohols were easily induced in the micropores of activated carbon and alumina, producing new aldehyde and ketone impurities, which led to an increase in absorbance instead of a decrease.

[0077] Through comparative experiments, the decisive influence of the order of each step in the preparation of isopropanol for spectral analysis on the quality of the final product was systematically verified.

[0078] (1) Neutralization first can convert trace amounts of organic acids in the raw materials into inert salts, preventing them from reacting with activated carbon in subsequent processes. The adsorption stage produces acid-catalyzed aldehyde and ketone side reactions; (2) The molecular sieve dehydrates and removes most of the water following the neutralization, so that the polar sites of the adsorbent can be fully used to capture unsaturated hydrocarbons and aldehydes and ketones without being "occupied" by water and becoming ineffective. (3) Modified activated carbon then removes C=C unsaturated hydrocarbons and suppresses fluorescent precursors in the 254 nm band; (4) It is then used to capture aldehydes and ketones, forming a two-level polar / nonpolar gradient impurity remover; (5) Finally, the total reflux distillation is carried out, and under the real-time adjustment of closed-loop UV-Vis and conductivity, the remaining extremely low moisture and residual trace impurities are completely removed.

[0079] Therefore, "neutralization-dehydration-activated carbon-" The fixed sequence of "distillation" not only meets all the technical specifications of isopropanol for spectral analysis, but also demonstrates the best comprehensive performance in terms of energy consumption, recovery rate, and process safety, showing significant innovation and industrial feasibility.

[0080] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for purifying a reagent for spectroscopic analysis, isopropyl alcohol, characterized by, Includes the following steps: S1: Mix industrial-grade isopropanol with an alkali metal compound, adjust the pH of the system to 7.0-8.0, so that acidic impurities form salt precipitates, and obtain the neutralized filtrate through solid-liquid separation; S2: The neutralized filtrate is sequentially passed through a molecular sieve adsorption unit, a modified activated carbon adsorption unit, and a γ-alumina adsorption unit for continuous adsorption and impurity removal; S3: Perform staged heating and total reflux distillation on the liquid after S2 treatment, controlling the reflux ratio at 5 to 15:1 and the total reflux time at 1 to 3 hours, and collect the top product; S4: Fill and seal the top section of the product under inert gas protection.

2. The method according to claim 1, characterized in that, The molecular sieve adsorption unit in S2 uses molecular sieve, particle size 20-100 mesh, adsorption flow rate 0.5-30 BV· , the liquid effluent water content is ≤0.03wt%; the modified activated carbon adsorption unit uses activated carbon impregnated with 5%-60% by volume of hypochlorous acid, nitric acid, sulfuric acid or perchloric acid and then dried, particle size 20-100 mesh; the particle size of the γ-alumina adsorption unit is 20-200 mesh.

3. The method according to claim 1, characterized in that, The flow rate of each adsorption unit in S2 is independently 0.5-30 BV. , and each adsorption unit is operated in series.

4. The method of claim 1, wherein, The segmented heating total reflux distillation described in S3 uses a two-tower distillation apparatus, with the main tower heating temperature at 83–95°C, the bottom liquid temperature at 83–86°C, and the outlet liquid temperature at 81–82°C.

5. The method according to claim 1, characterized in that, In S3, the product content is monitored in real time by an online concentration sensor. When the content is lower than 99.997wt%, the total reflux time is automatically extended or the reflux ratio is increased to ensure that the final product content is ≥99.998wt%.

6. The method according to claim 1, characterized in that, In S2, an online conductivity or moisture sensor is installed at the outlet of the molecular sieve adsorption unit to monitor the moisture content in real time; an infrared or near-infrared online detection device is installed at the outlet of the γ-alumina adsorption unit to monitor the intensity of the characteristic absorption peaks of aldehydes and ketones.

7. The method according to claim 1, characterized in that, The inert gas mentioned in S4 is nitrogen, the filling pressure is 0.2 MPa, the filling container is a glass bottle, and it is sealed with nitrogen.

8. The method according to claim 1, characterized in that, The molecular sieve adsorption unit in S2 is replaced by a membrane permeation dehydration device with an operating pressure of 0.6 MPa, a selectivity of ≥30, and an effluent moisture content of ≤0.01 wt%.

9. The method according to claim 1, characterized in that, The modified activated carbon adsorption unit in S2 is replaced by an ionic liquid extraction device, which uses 1-butyl-3-methylimidazolium tetrafluoroborate as the extraction phase. The ionic liquid is recovered and recycled after extraction.

10. The method according to claim 1, characterized in that, The final product has a content ≥99.997wt%, moisture ≤0.018wt%, and fluorescent precursor concentration ≤0.9µg. Recovery rate ≥ 95%, unit energy consumption ≤ 9 .

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