A method for synthesizing ultrapure 1,2-pentanediol or 1,2-hexanediol without odor

Abstract

The application discloses a synthesis method of super-pure 1,2-pentanediol or 1,2-hexanediol without odor, and relates to the technical field of organic synthesis. The method comprises three steps of raw material purification, catalytic hydrogenation and crude alcohol refining and stabilization. Ion impurities are removed to less than or equal to 0.5 ppm through rectification and ion exchange. High-selectivity hydrogenation is carried out under a Cu-Zn-Ag alloy catalyst. The crude alcohol is refined through vacuum rectification, deep desalination and directional adsorption of a composite adsorbent. The method realizes hydrogenation selectivity of more than 97%, product purity of more than or equal to 99.7%, no irritating odor, no regeneration after 12 months of storage, long catalyst service life and suitability for high-end daily chemicals and medical fields.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, specifically to a method for synthesizing ultrapure, odorless 1,2-pentanediol or 1,2-hexanediol. Background Technology

[0002] 1,2-Pentanediol and 1,2-Hexanediol are important fine chemical products with wide applications in additives, daily chemicals, pharmaceuticals, coatings, and plastics. In recent years, in particular, the quality requirements for 1,2-pentanediol and 1,2-hexanediol have become increasingly stringent, demanding not only high purity and low impurity content but also the absence of irritating odors to meet the formulation requirements of high-end skincare products.

[0003] The preparation methods of 1,2-pentanediol mainly include petrochemical processes such as the n-pentene method, the n-valeric acid method, and the n-pentanol method. However, these processes suffer from problems such as complex production processes, corrosion of reaction equipment, difficulty in product separation, and severe environmental pollution. 1,2-hexanediol is primarily produced from 1-hexene, but the presence of various hydrocarbon impurities in 1-hexene, such as n-hexane, 3-hexene, and 2-hexene, becomes the main source of unpleasant odors in subsequent production. Furthermore, the synthesis of 1,2-pentanediol or 1,2-hexanediol using catalytic hydrogenation of methyl 2-hydroxyvalerate or methyl 2-hydroxyhexanoate with metal catalysts stands out due to its high efficiency and low pollution.

[0004] However, the catalytic hydrogenation process using metal catalysts generally faces three fundamental bottlenecks: 1. Catalysts are easily poisoned and have short lifespans: Cl in the raw materials - SO4 2- Anions (5-30 ppm) are strongly adsorbed onto the active sites of Cu-based catalysts, causing irreversible sintering and loss of activity. Conventional catalysts have a lifespan of only 200-400 hours, resulting in extremely high industrial costs. Existing water / alkali washing methods can only remove some impurities and cannot remove them to a depth of less than 1 ppm.

[0005] 2. Odor cannot be completely eliminated and is prone to recurrence: Existing processes rely solely on distillation to remove odors, leaving trace amounts of aldehydes, ketones, unsaturated hydrocarbons, and acetals (ppb level). Initially, the odor is slight, but after 1-3 months of storage, a self-condensation / oxidation reaction occurs, generating strong irritating off-odor substances, which cannot meet the requirements of "fragrance-free and long-lasting stability".

[0006] 3. Low hydrogenation selectivity and many byproducts: Conventional Cu-based catalysts are prone to over-hydrogenation, dehydroxylation and cracking side reactions, resulting in low crude product purity, heavy post-processing burden and low yield, and byproducts further aggravate odor problems.

[0007] In summary, existing technologies have not yet formed an integrated process solution that can simultaneously solve the problems of deep impurity control of raw materials, long catalyst life, and odorless and stable products. The industry urgently needs a synthesis technology that allows for controllable raw material impurities, catalysts that are resistant to poisoning, high hydrogenation selectivity, and ultra-pure, odorless, and long-term stable products to meet the demands of the high-end market. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for synthesizing ultrapure and odorless 1,2-pentanediol or 1,2-hexanediol, achieving hydrogenation selectivity >97%, product purity ≥99.7%, no irritating odor, no reversion after 12 months of storage, long catalyst life, and applicable to high-end daily chemical and pharmaceutical fields.

[0009] The technical solution of this invention is as follows: A method for synthesizing ultrapure, odorless 1,2-pentanediol or 1,2-hexanediol, comprising the following steps: S1 Raw Material Purification: Methyl 2-hydroxyvalerate or methyl 2-hydroxyhexanoate raw materials are subjected to distillation pretreatment and ion exchange treatment in sequence to reduce the impurity ion content to ≤0.5ppm; distillation pretreatment removes high-boiling-point organic impurities and some volatile odor precursors and reduces the subsequent ion exchange load. S2 catalytic hydrogenation: The purified raw material is subjected to catalytic hydrogenation reaction under the action of Cu-Zn-Ag alloy catalyst to obtain crude 1,2-pentanediol or crude 1,2-hexanediol. S3 Crude Alcohol Purification and Stabilization: Crude 1,2-pentanediol or crude 1,2-hexanediol are subjected to vacuum distillation in sequence to remove low-boiling odor-causing impurities (aldehydes, ketones) and high-boiling byproducts in steps, deep desalination by ion exchange, and directional adsorption by composite adsorbent to obtain ultrapure odorless 1,2-pentanediol or 1,2-hexanediol. The Cu-Zn-Ag alloy catalyst carrier is activated carbon. Based on the total mass of the Cu-Zn-Ag alloy catalyst, it is loaded with CuO 55-65wt.%, ZnO 5-8wt.% and Ag 0.05-0.5wt.%. Ag is introduced as an electronic aid to regulate the electron density of Cu active sites through electron transfer, inhibiting the agglomeration and sintering of Cu nanoparticles. At the same time, it selectively activates the C=O bond of ester groups to avoid the side reaction of CO bond breaking. The composite adsorbent is composed of coconut shell activated carbon, molecular sieve X and modified diatomaceous earth in a mass ratio of (6-8):(1-3):1. The activated carbon adsorbs large molecular hydrocarbons and acetals, the molecular sieve X directionally captures small molecular aldehydes and ketones, and the modified diatomaceous earth adsorbs polar impurities, so as to achieve deep removal of all components of odor-causing impurities.

[0010] Preferably, in step S1, the distillation pretreatment uses a distillation column with 35-45 theoretical plates, controls the reflux ratio to 2-3, and the column bottom temperature to 155-165℃, preferentially removing high-boiling-point organic impurities and some volatile odor precursors, improving the purity of the raw materials and reducing the subsequent ion exchange load.

[0011] Preferably, in step S1, the ion exchange treatment uses a series column of a strongly acidic cation exchange resin, a strongly basic anion exchange resin, and a chelating resin. The strongly acidic cation exchange resin removes Na+. + K + Fe 3+ Metal ions; directional adsorption of Cl by anion exchange resin - SO4 2- PO4 3- Plasma; chelating resins deeply capture residual trace heavy metal ions (such as Cu). 2+ Pb 2+ (etc.) to eliminate catalyst poisoning causes.

[0012] Preferably, in step S1, during ion exchange treatment, 3-8 wt.% of a mixed solvent is added to the raw material. The mixed solvent consists of water and methanol in a mass ratio of 1:(4-6).

[0013] Preferably, in step S2, the conditions for the catalytic hydrogenation reaction are: pressure of 15-20 MPa, temperature of 170-200 °C, and molar ratio of hydrogen to raw material of (75-130):1.

[0014] Preferably, in step S3, the reduced pressure distillation is carried out using a distillation column with 45-60 trays, a pressure of -0.08 to -0.1 MPa, a bottom temperature of 175-185℃, and a reflux ratio of 1.5-3.5.

[0015] Preferably, in step S3, the ion exchange deep desalination is performed using a column of anion exchange resin and chelating resin in series.

[0016] Preferably, in step S3, the directional adsorption temperature is 25-35℃ and the directional adsorption time is 2-3h.

[0017] This invention, through an integrated technical solution of deep impurity control of raw materials, highly selective catalytic hydrogenation, and multi-stage coupled deep refining, effectively overcomes industry pain points in existing technologies, such as easy catalyst poisoning, short lifespan, difficulty in eliminating product odors, easy regeneration during storage, low hydrogenation selectivity, numerous by-products, and low yield. It achieves the following significant technical effects: 1. Achieve deep removal of ions from raw materials, inhibit catalyst poisoning at the source, and significantly extend service life. This invention achieves deep desalination by combining distillation pretreatment with a series of strong acid cation exchange resin, strong base anion exchange resin, and chelating resin, thereby removing Cl from the raw materials.- SO4 2- PO4 3- The concentration of heavy metal ions is stably controlled at ≤0.5 ppm, eliminating the poisoning effect of anions on the active sites of Cu-based catalysts. Experimental data show that the catalyst of this invention only begins to decline in activity after more than 700 hours of continuous operation, significantly reducing industrial production costs.

[0018] 2. Highly selective catalytic hydrogenation with fewer byproducts, higher crude product purity, and significantly improved yield. This invention uses a Cu-Zn-Ag alloy catalyst. Ag acts as an electron auxiliary agent, regulating the electron density of Cu active sites through electron transfer, inhibiting the agglomeration and sintering of Cu nanoparticles. Simultaneously, it highly selectively activates the C=O bonds of ester groups, avoiding CO bond breaking side reactions. Hydrogenation selectivity is >97%, feed conversion rate is ≥99.7%, significantly reducing the subsequent purification load, and the total yield of the target product is >92%, achieving efficient and highly selective synthesis.

[0019] 3. A closed-loop deep deodorization system is constructed, resulting in ultra-pure, odorless products that remain stable during long-term storage without reversion. This invention employs a multi-stage refining process: stepwise removal of low-boiling-point odor-causing impurities and high-boiling-point byproducts via vacuum distillation, deep desalination via ion exchange, and directional adsorption using a composite adsorbent of coconut shell activated carbon / molecular sieve X / modified diatomaceous earth. This process achieves deep removal of all components of odor-causing impurities at the ppb level, such as aldehydes, ketones, unsaturated hydrocarbons, and acetals. The resulting 1,2-pentanediol or 1,2-hexanediol product has a purity ≥99.7%, ionic impurities ≤0.5ppm, and no irritating odor. After 12 months of storage at room temperature, there is no deterioration in purity or odor, solving the problem of reversion during storage in existing products and meeting the stringent quality requirements of high-end daily chemicals, pharmaceuticals, and electronic chemicals.

[0020] 4. The process route of this invention is simple, highly continuous, environmentally friendly, and has strong industrial feasibility. This invention uses methyl 2-hydroxyvalerate or methyl 2-hydroxyhexanoate as raw materials, which are widely available and cost-controllable; the process involves no highly corrosive media, produces minimal waste, and has high atom economy; the reaction conditions are mild and controllable, the equipment requirements are conventional, and continuous and stable production can be achieved. It has significant economic and social value and broad prospects for industrial application. Detailed Implementation

[0021] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention.

[0022] Example 1 The method for synthesizing ultrapure, odorless 1,2-pentanediol in this embodiment includes the following steps: S1 Raw Material Purification 50 kg of industrial-grade methyl 2-hydroxyvalerate (approximately 98.5% purity) was distilled in a high-efficiency structured packed distillation column with 40 theoretical trays, a reflux ratio of 2.5, and a reboiler temperature of 160°C. After distillation, Cl... - Content 27.5 ppm, SO4 2- The concentration was 19.3 ppm. The distilled feedstock was then passed sequentially through the strongly acidic cation exchange resin Tulsimer. ® T-42(NS)H, strongly basic anion exchange resin Tulsimer ® A-23 and chelating resin Tulsimer ® A CH-90Na tandem column was used, with a mixed solvent of water and methanol in a 1:5 mass ratio, comprising 5% of the feed mass after distillation. Analysis revealed that the Cl- after ion exchange treatment... - SO4 2- Na + K + Fe 3+ PO4 3- Cu 2+ Pb 2+ The content of all samples was less than 0.5 ppm.

[0023] S2 catalytic hydrogenation The purified methyl 2-hydroxyvalerate was introduced into a fixed-bed hydrogenation reactor, which was packed with a Cu-Zn-Ag alloy catalyst at a depth of 420 cm³. 3 The reaction mixture, using activated carbon as a carrier, contained 65% copper (calculated as CuO), 8% zinc (calculated as ZnO), and 0.5% silver (calculated as Ag). Reaction conditions: hydrogenation pressure 17 MPa, reaction temperature 180℃, hydrogen flow rate 1 L / min (residual hydrogen was recovered using a circulating pump), and feed flow rate 10 mL / min. The reaction product, after condensation and separation, yielded crude 1,2-pentanediol. Gas chromatography analysis showed a 1,2-pentanediol selectivity of 98.1% and a feed conversion rate of 99.9%.

[0024] S3 crude alcohol purification and stabilization Crude 1,2-pentanediol was introduced into a 50-plate distillation column for vacuum distillation at a reboiler temperature of 180℃, a pressure of -0.09 MPa, and a reflux ratio of 2 to remove low-boiling and high-boiling components. The distillate was then passed through a series column of anion exchange resin and chelating resin to remove residual ionic impurities. Subsequently, it was subjected to directional adsorption treatment at 30℃ for 2 hours using a composite adsorbent consisting of activated carbon (coconut shell-based, pore size 1-3 nm), molecular sieve X, and modified diatomaceous earth (mass ratio 7:2:1), with a solid-liquid ratio of 1:20. Filtration yielded the final 1,2-pentanediol product.

[0025] The final 1,2-pentanediol product is a colorless and transparent liquid. Gas chromatography analysis showed a purity ≥99.8%, a total yield of 93.3%, and all impurity ion concentrations ≤0.5 ppm. The odor was assessed as non-irritating. After 12 months of storage at room temperature, the product purity and odor showed no deterioration. The product fully meets cosmetic-grade requirements. In this embodiment, the activity of the Cu-Zn-Ag alloy catalyst began to decrease after 744 hours of continuous operation, with the 1,2-pentanediol selectivity decreasing to 95.7% and the feed conversion rate decreasing to 98.3%.

[0026] Example 2 The method for synthesizing ultrapure, odorless 1,2-pentanediol in this embodiment includes the following steps: S1 Raw Material Purification 50 kg of industrial-grade methyl 2-hydroxyvalerate (approximately 98.5% purity) was distilled in a high-efficiency structured packed distillation column with 35 theoretical trays, a reflux ratio of 2, and a reboiler temperature of 155°C. After distillation, Cl... - Content 26.2 ppm, SO4 2- The concentration was 18.1 ppm. The distilled feed was then passed sequentially through the strongly acidic cation exchange resin Tulsimer. ® T-42(NS)H, strongly basic anion exchange resin Tulsimer ® A-23 and chelating resin Tulsimer ® A CH-90Na tandem column was used, with a mixed solvent of water and methanol in a 1:4 mass ratio, comprising 3% of the feed mass after distillation. Analysis revealed that the Cl- after ion exchange treatment... - SO4 2- Na + K + Fe 3+ PO4 3- Cu 2+ Pb 2+ The content of all samples was less than 0.5 ppm.

[0027] S2 catalytic hydrogenation The purified methyl 2-hydroxyvalerate was introduced into a fixed-bed hydrogenation reactor, which was packed with a Cu-Zn-Ag alloy catalyst at a depth of 420 cm³. 3 The reaction mixture, using activated carbon as a carrier, contained 55% copper (calculated as CuO), 5% zinc (calculated as ZnO), and 0.05% silver (calculated as Ag). Reaction conditions were: hydrogenation pressure 15 MPa, reaction temperature 170 °C, hydrogen flow rate 1 L / min (residual hydrogen was recovered using a circulating pump), and feed flow rate 5.4 mL / min. The reaction product was condensed and separated to obtain crude 1,2-pentanediol. Gas chromatography analysis showed a 1,2-pentanediol selectivity of 97.6% and a feed conversion rate of 99.7%.

[0028] S3 crude alcohol purification and stabilization Crude 1,2-pentanediol was introduced into a 45-plate distillation column for vacuum distillation at a reboiler temperature of 175°C, a pressure of -0.08 MPa, and a reflux ratio of 1.5 to remove low-boiling and high-boiling components. The distillate was then passed through a series column of anion exchange resin and chelating resin to remove residual ionic impurities. Subsequently, it was subjected to directional adsorption treatment at 25°C for 3 hours using a composite adsorbent consisting of activated carbon (coconut shell-based, pore size 1-3 nm), molecular sieve X, and modified diatomaceous earth (mass ratio 6:1:1), with a solid-liquid ratio of 1:20. Filtration yielded the final 1,2-pentanediol product.

[0029] The final 1,2-pentanediol product is a colorless and transparent liquid. Gas chromatography analysis showed a purity ≥99.8%, a total yield of 92.8%, and all impurity ion contents ≤0.5 ppm. The odor was assessed as non-irritating. After 12 months of storage at room temperature, the product purity and odor showed no deterioration. The product fully meets cosmetic-grade requirements. In this embodiment, the activity of the Cu-Zn-Ag alloy catalyst began to decrease after 768 hours of continuous operation, with the 1,2-pentanediol selectivity decreasing to 96.1% and the feed conversion rate decreasing to 98%.

[0030] Example 3 The method for synthesizing ultrapure, odorless 1,2-hexanediol in this embodiment includes the following steps: S1 Raw Material Purification 50 kg of industrial-grade methyl 2-hydroxyhexanoate (purity approximately 98.8%) was distilled in a high-efficiency structured packed distillation column with 45 theoretical trays, a reflux ratio of 3, and a reboiler temperature of 165°C. After distillation, Cl... - Content 22.3 ppm, SO4 2- The concentration was 15.5 ppm. The distilled feedstock was then passed sequentially through the strongly acidic cation exchange resin Tulsimer. ® T-42(NS)H, strongly basic anion exchange resin Tulsimer ® A-23 and chelating resin Tulsimer ® A CH-90Na tandem column was used, with a mixed solvent of water and methanol in a 1:6 mass ratio, comprising 8% of the feed mass after distillation. Analysis revealed that the Cl- after ion exchange treatment... - SO4 2- Na + K + Fe 3+ PO4 3- Cu 2+ Pb 2+ The content of all samples was less than 0.5 ppm.

[0031] S2 catalytic hydrogenation The purified methyl 2-hydroxyhexanoate was introduced into a fixed-bed hydrogenation reactor, which was packed with a Cu-Zn-Ag alloy catalyst at a depth of 420 cm³. 3 The reaction mixture, using activated carbon as a carrier, contained 60% copper (calculated as CuO), 6% zinc (calculated as ZnO), and 0.2% silver (calculated as Ag). Reaction conditions: hydrogenation pressure 20 MPa, reaction temperature 200℃, hydrogen flow rate 1 L / min (residual hydrogen was recovered using a circulating pump), and feed flow rate 10 mL / min. The reaction product, after condensation and separation, yielded crude 1,2-hexanediol. Gas chromatography analysis showed a 1,2-hexanediol selectivity of 97.8% and a feed conversion rate of 99.9%.

[0032] S3 crude alcohol purification and stabilization Crude 1,2-hexanediol was introduced into a 60-plate distillation column for vacuum distillation at a reboiler temperature of 185℃, a pressure of -0.1 MPa, and a reflux ratio of 3.5 to remove low-boiling and high-boiling components. The distillate was then passed through a series column of anion exchange resin and chelating resin to remove residual ionic impurities. Subsequently, it was subjected to directional adsorption treatment at 35℃ for 2 hours using a composite adsorbent consisting of activated carbon (coconut shell-based, pore size 1-3 nm), molecular sieve X, and modified diatomaceous earth (mass ratio 8:3:1), with a solid-liquid ratio of 1:20. Filtration yielded the final 1,2-hexanediol product.

[0033] The final 1,2-hexanediol product is a colorless and transparent liquid. Gas chromatography analysis showed a purity ≥99.7%, a total yield of 93%, and all impurity ion contents ≤0.5 ppm. The odor was assessed as non-irritating. After 12 months of storage at room temperature, the product purity and odor showed no deterioration. The product fully meets cosmetic-grade requirements. In this embodiment, the activity of the Cu-Zn-Ag alloy catalyst began to decrease after 720 hours of continuous operation, with the 1,2-hexanediol selectivity decreasing to 96.5% and the feed conversion rate decreasing to 98.4%.

[0034] Comparative Example 1 The difference from Example 1 is that step S1 is not performed.

[0035] After 336 hours of operation, the selectivity for 1,2-pentanediol in the methyl 2-hydroxyvalerate hydrogenation catalyst decreased to 95.8%, and the feed conversion rate decreased to 98.2%, indicating a significant decline in catalyst activity. After 384 hours of operation, the selectivity for 1,2-pentanediol further decreased to 94.1%, and the feed conversion rate decreased to 97.5%, also showing a significant decline in catalyst activity. Analysis revealed Cl- on the catalyst surface. - With SO4 2- The significantly increased content indicates that the anionic impurities in the raw materials have caused irreversible poisoning to the active sites of the catalyst.

[0036] In Comparative Example 1, the lack of raw material purification in step S1 resulted in a significant reduction in the catalyst life of the Cu-Zn-Ag alloy. The raw material did not undergo distillation and ion exchange, leading to a decrease in Cl... - SO4 2- The high content of heavy metal ions directly and strongly adsorbs onto the active sites of the Cu-Zn-Ag alloy catalyst, causing irreversible sintering, covering of active centers, and agglomeration and growth of Cu particles, leading to rapid catalyst poisoning and a lifespan shortened by more than half. Furthermore, the hydrogenation selectivity of the Cu-Zn-Ag alloy catalyst decreases significantly because anionic impurities alter the electronic environment of the Cu active centers, weakening the electronic regulation effect of the Ag promoter, resulting in poor catalyst selectivity, increased excessive hydrogenation / dehydroxylation / cracking side reactions, and higher impurity content in the crude product. Simultaneously, the reduced feed conversion rate and increased byproducts are due to the decreased ester group activation ability after catalyst poisoning, leading to incomplete reactions and increased unconverted feedstock; at the same time, side reactions are exacerbated, with a significant increase in aldehydes, ketones, and hydrocarbon impurities in the crude alcohol, greatly increasing the burden on subsequent refining. Finally, the crude product contains many impurities, and trace amounts of odor-causing precursors remain after refining, making it prone to reversion and the development of an irritating odor after 1-3 months of storage.

[0037] Comparative Example 2 The difference from Example 3 is that in step S3, only vacuum distillation is performed, without ion exchange deep desalination and directional adsorption of composite adsorbent.

[0038] The 1,2-hexanediol product achieved a purity of 99.5% as determined by gas chromatography, which meets the basic purity requirements. However, it exhibits a slightly irritating odor in the odor evaluation, failing to meet the stringent requirements for high-end cosmetic formulations.

[0039] In Comparative Example 2, step S3 only involves vacuum distillation without ion exchange deep desalination and directional adsorption with the composite adsorbent. This results in the inability to effectively remove ppb-level odor-causing impurities, leading to a pungent odor. This is because vacuum distillation can only remove high-content, high / low-boiling-point impurities, and cannot remove ppb-level aldehydes, ketones, unsaturated hydrocarbons, acetals, and other strongly odor-causing trace impurities. Only the composite adsorbent of this invention can achieve deep removal of odor-causing substances from all components, which vacuum distillation alone cannot do. Furthermore, residual ions can catalyze the self-condensation and oxidation of trace aldehydes and ketones, generating strongly pungent off-odor substances after long-term storage, leading to a reversion phenomenon. Ion exchange deep desalination is a crucial step in ensuring the long-term odor stability of the product. In addition, trace organic and ionic impurities cannot be removed by vacuum distillation, lowering the upper limit of product purity and failing to meet high-end standards.

Claims

1. A method for synthesizing ultrapure, odorless 1,2-pentanediol or 1,2-hexanediol, characterized in that, Includes the following steps: S1 raw material purification: Methyl 2-hydroxyvalerate or methyl 2-hydroxyhexanoate raw materials are subjected to distillation pretreatment and ion exchange treatment in sequence to reduce the impurity ion content to ≤0.5ppm; S2 catalytic hydrogenation: The purified raw material is subjected to catalytic hydrogenation reaction under the action of Cu-Zn-Ag alloy catalyst to obtain crude 1,2-pentanediol or crude 1,2-hexanediol. S3 Crude Alcohol Purification and Stabilization: Crude 1,2-pentanediol or crude 1,2-hexanediol is subjected to vacuum distillation, deep desalination by ion exchange, and directional adsorption by composite adsorbent in sequence to obtain ultrapure and odorless 1,2-pentanediol or 1,2-hexanediol. The Cu-Zn-Ag alloy catalyst support is activated carbon, and based on the total mass of the Cu-Zn-Ag alloy catalyst, it is loaded with CuO 55-65wt.%, ZnO 5-8wt.% and Ag 0.05-0.5wt.%; the composite adsorbent is composed of coconut shell activated carbon, molecular sieve X and modified diatomaceous earth in a mass ratio of (6-8):(1-3):

1.

2. The method for synthesizing ultrapure, odorless 1,2-pentanediol or 1,2-hexanediol as described in claim 1, characterized in that, In step S1, the distillation pretreatment uses a distillation column with 35-45 theoretical plates, controls the reflux ratio to 2-3, and the reboiler temperature to 155-165℃.

3. The method for synthesizing ultrapure, odorless 1,2-pentanediol or 1,2-hexanediol as described in claim 1, characterized in that, In step S1, the ion exchange treatment uses a series column of strongly acidic cation exchange resin, strongly basic anion exchange resin, and chelating resin.

4. The method for synthesizing ultrapure, odorless 1,2-pentanediol or 1,2-hexanediol as described in claim 1, characterized in that, In step S1, during ion exchange treatment, 3-8 wt.% of a mixed solvent is added to the raw material. The mixed solvent consists of water and methanol in a mass ratio of 1:(4-6).

5. The method for synthesizing ultrapure, odorless 1,2-pentanediol or 1,2-hexanediol as described in claim 1, characterized in that, In step S2, the conditions for the catalytic hydrogenation reaction are: pressure of 15-20 MPa, temperature of 170-200℃, and the molar ratio of hydrogen to feedstock of (75-130):

1.

6. The method for synthesizing ultrapure, odorless 1,2-pentanediol or 1,2-hexanediol as described in claim 1, characterized in that, In step S3, the reduced pressure distillation is carried out using a distillation column with 45-60 trays, a pressure of -0.08 to -0.1 MPa, a bottom temperature of 175-185℃, and a reflux ratio of 1.5-3.

5.

7. The method for synthesizing ultrapure, odorless 1,2-pentanediol or 1,2-hexanediol as described in claim 1, characterized in that, In step S3, the ion exchange deep desalination is performed using a tandem column of anion exchange resin and chelating resin.

8. The method for synthesizing ultrapure, odorless 1,2-pentanediol or 1,2-hexanediol as described in claim 1, characterized in that, In step S3, the directional adsorption temperature is 25-35℃ and the directional adsorption time is 2-3h.