A method for preparing low-odor 1,2-hexanediol

Abstract

This invention provides a method for preparing low-odor 1,2-hexanediol, belonging to the field of organic synthesis technology. The invention uses purified o-hydroxyhexanoate as a raw material, and conducts a continuous hydrogenation reaction with hydrogen in the presence of a hydrogenation catalyst to obtain low-odor 1,2-hexanediol. Before the reaction, the o-hydroxyhexanoate raw material is purified to reduce impurities such as aldehydes and hydrocarbons. A copper-based catalyst is used to control the reaction at relatively low temperature and pressure. Specifically, a copper-zinc-aluminum catalyst is employed, which can catalyze the hydrogenation of the ester group under mild reaction conditions while also hydrogenating aldehyde impurities to convert them into alcohols, thereby eliminating the unpleasant odor caused by aldehyde compounds. This invention employs a continuous production process, which, compared to batch production processes, achieves higher conversion rates and yields, as well as fewer byproducts.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and specifically to a method for preparing low-odor 1,2-hexanediol. Background Technology

[0002] 1,2-Hexanediol is a very popular chemical, a transparent, colorless to pale yellow liquid with a boiling point of 223-224°C. It is highly miscible with alcohols and water, safe and harmless to the human body, and possesses preservative and moisturizing properties. 1,2-Hexanediol is widely used in personal care products, pharmaceuticals, inkjet printing, and solvents, especially in the cosmetics industry, where it is used as a skin moisturizer, antibacterial agent, defoamer, and solubilizer. For example, patents WO2019120572A1, US2010216892A1, and MY135988A disclose the application of 1,2-hexanediol as a moisturizer and surfactant in cosmetic emulsions. Patents KR102043869B1 and WO2006045743A1 respectively apply 1,2-hexanediol to antibacterial agents and cosmeceutical preservatives.

[0003] Based on the aforementioned applications, particularly in cosmetics and personal care products, the market and consumers have very strict requirements regarding the odor of 1,2-hexanediol, aiming for a neutral scent. However, unpleasant odors are often unavoidably generated during the synthesis of 1,2-hexanediol. These unpleasant odors are emitted by byproducts with structures similar to 1,2-hexanediol. Eliminating these odors requires removing these byproducts, which necessitates complex post-processing or manufacturing processes, but the results often fall short of expectations. Therefore, finding a production process for high-purity, low-odor 1,2-hexanediol is currently a research challenge and a hot topic.

[0004] Currently, 1,2-hexanediol is mainly produced from 1-hexene, which is oxidized by peroxides to form corresponding epoxides. This epoxide is then hydrolyzed with acid and further processed to obtain 1,2-hexanediol. 1-Hexene contains hydrocarbon impurities such as n-hexane, 3-hexene, 2-hexene, and 2-methyl-1-pentene. The presence of these impurities inevitably leads to the generation of various aldehyde byproducts during subsequent production, which are the main source of the unpleasant odor.

[0005] Patent WO2020069731A1 uses alkylene glycols and 1-olefins as raw materials, with an enol ratio of 1:1 to 50, to prepare 1,2-alkanediols at 150 to 180°C and under its own pressure under the action of a free radical initiator. The product yield is only 41.3% and the purity is 98%.

[0006] Patent CN110272329A describes the preparation of 1,2-epoxyhexane using hexene, acetonitrile, methanol, and potassium bicarbonate as raw materials in the presence of hydrogen peroxide, followed by hydrolysis to obtain 1,2-hexanediol with a purity greater than 99%.

[0007] Patent EP4331684A2 describes a process where 1-olefins react with formic acid in the presence of hydrogen peroxide to produce formate esters, which are then decarboxylated to yield 1,2-hexanediol. In the first ester formation reaction, the ratio of olefin to formic acid is 1:1.5–2.5, and the ratio of olefin to hydrogen peroxide is 1:0.5–1.5. The reaction is carried out at 50–100 °C for 4–10 h, with a theoretical yield greater than 95%. In the second decarboxylation reaction, nickel or palladium supported on a support is used as a catalyst at an addition amount of 0.5–20 wt%, and the reaction is carried out at 180–220 °C for 2–6 h, with a theoretical yield of 70–97%. After distillation, a tasteless, colorless, and clear liquid with a purity of 99.5% is obtained.

[0008] However, 1,2-hexanediol prepared by the hydrogen peroxide method inevitably contains aldehydes and ketones with strong odors. Even 1,2-hexanediol with a purity of up to 99.5% may seem to have a pleasant odor initially, but its odor changes and gradually intensifies over time. The root cause is likely the condensation reaction of residual aldehydes with these compounds to form unpleasant-smelling byproducts. Therefore, the purity of 1,2-hexanediol needs to be further improved to remove impurities (especially aldehydes) and odors. Summary of the Invention

[0009] In view of this, the object of the present invention is to provide a method for preparing low-odor 1,2-hexanediol. The present invention can obtain low-odor 1,2-hexanediol in high yield and high output.

[0010] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0011] This invention provides a method for preparing low-odor 1,2-hexanediol, comprising the following steps:

[0012] Using purified o-hydroxyhexanoate as a raw material, a continuous hydrogenation reaction was carried out with hydrogen in the presence of a hydrogenation catalyst to obtain low-odor 1,2-hexanediol.

[0013] The o-hydroxyhexanoate has the structure shown in Formula 1:

[0014] Formula 1;

[0015] In Formula 1, R represents an alkyl group having 1 to 30 carbon atoms;

[0016] The hydrogenation catalyst includes a catalyst matrix and catalyst promoters supported on the surface and interior of the catalyst matrix. The catalyst matrix comprises copper oxide, zinc oxide and aluminum oxide, and the catalyst promoters comprise active metals and / or oxides of active metals.

[0017] The continuous hydrogenation reaction is carried out at a temperature of 100-200°C and a pressure of 16-25 MPa.

[0018] Preferably, in the hydrogenation catalyst, the catalyst matrix accounts for 95-99.9 wt% of the total mass of the hydrogenation catalyst, and the catalyst promoter accounts for 0.1-5 wt% of the total mass of the hydrogenation catalyst.

[0019] In the catalyst matrix, by mass percentage, copper oxide accounts for 35-55 wt%, zinc oxide accounts for 35-55 wt%, and aluminum oxide accounts for 8-25 wt%.

[0020] The active metal includes one or more of Mn, Ce, Ni, Sn, Co, Ba, Ca, Se, Pt, Pd and Re.

[0021] Preferably, the method for preparing the hydrogenation catalyst includes the following steps:

[0022] The solution comprises a water-soluble aluminum salt solution, a first water-soluble copper-zinc salt mixed solution, a second water-soluble copper-zinc salt mixed solution, and a water-soluble active metal salt solution; the copper-zinc molar ratio in the second water-soluble copper-zinc salt mixed solution is higher than that in the first water-soluble copper-zinc salt mixed solution.

[0023] The water-soluble aluminum salt solution is mixed with the first water-soluble copper and zinc salt mixed solution, and the pH value is adjusted to 7 to obtain a premixed solution.

[0024] The premixed solution was mixed with a second water-soluble copper and zinc salt mixed solution, the pH was adjusted to 7, a precipitation reaction was carried out, the resulting precipitate was dried and subjected to a first calcination to obtain the catalyst matrix;

[0025] The catalyst matrix is ​​immersed in the water-soluble active metal salt solution, and after solid-liquid separation, it is dried, calcined a second time, and shaped to obtain the hydrogenation catalyst.

[0026] Preferably, the copper-zinc molar ratio of the first water-soluble copper-zinc salt mixed solution is 0.1~0.2:1;

[0027] The copper-zinc molar ratio of the second water-soluble copper-zinc salt mixed solution is 4~10:1;

[0028] The molar ratio of copper atoms in the first part of the water-soluble copper-zinc salt mixed solution to that in the second part of the water-soluble copper-zinc salt mixed solution is 1:2~20.

[0029] Preferably, the o-hydroxyhexanoate is reacted in a solvent-free state or dissolved in an organic solvent.

[0030] Preferably, the continuous hydrogenation reaction is carried out in a fixed bed;

[0031] In the continuous hydrogenation reaction, the molar ratio of hydrogen to o-hydroxyhexanoate is 1000~100:1.

[0032] Preferably, the space velocity of o-hydroxyhexanoate in the continuous hydrogenation reaction is 80-200 h⁻¹. -1 .

[0033] Preferably, the purification method for the o-hydroxyhexanoate includes the following steps:

[0034] o-hydroxyhexanoate was subjected to washing with an inorganic alkaline aqueous solution, water washing, and distillation in sequence.

[0035] Preferably, before the continuous hydrogenation reaction, the hydrogenation catalyst is further reduced.

[0036] Preferably, after the continuous hydrogenation reaction, the product is further subjected to distillation and / or rectification.

[0037] The distillation temperature is 110~120℃, and the distillation is performed 3~5 times;

[0038] The distillation temperature is 120~160℃ and the pressure is 2~20 mmHg.

[0039] This invention provides a method for preparing low-odor 1,2-hexanediol, comprising the following steps:

[0040] Using purified o-hydroxyhexanoate as a raw material, a continuous hydrogenation reaction is carried out in the presence of a hydrogenation catalyst to obtain low-odor 1,2-hexanediol. The reaction route is shown in Formula A:

[0041] Formula A.

[0042] Compared to existing technologies, the advantages of this invention are: ① Addressing the troublesome odor problem in traditional preparation processes, this invention purifies the o-hydroxyhexanoate raw material before the reaction, reducing impurities such as aldehydes and hydrocarbons. ② Compared to the traditional method of preparing 1,2-hexanediol from 1-hexene, this invention uses o-hydroxyhexanoate as a raw material in the presence of a hydrogenation catalyst, hydrogenating the ester group to a hydroxyl group to prepare 1,2-hexanediol. The copper-based catalyst prepared in this invention controls the reaction at lower temperatures and pressures. Specifically, the use of a copper-zinc-aluminum catalyst allows for the catalytic hydrogenation of the ester group under mild reaction conditions, while also hydrogenating aldehyde impurities to convert them into alcohols, thereby eliminating the unpleasant odor caused by aldehyde compounds. ③ This invention limits the continuous hydrogenation reaction conditions to 100-200℃ and 16-25 MPa. After hydrogenation, simple separation yields high-purity, low-odor 1,2-hexanediol. Furthermore, this invention employs a continuous production process, which, compared to batch production processes, achieves higher conversion rates and yields, as well as fewer byproducts. The preparation method provided by this invention is simple, requires little investment, and consumes little energy, which is beneficial for industrial production.

[0043] The results of the examples show that, based on the preparation method of the present invention, in a fixed bed using a copper-zinc-aluminum catalyst, under the conditions of a temperature of 180°C, a pressure of 22 MPa, and a hydrogen-to-ester ratio of 600:1, the conversion rate of 1,2-hexanediol can reach 99.9%, the selectivity can reach 99.0%, the purity can reach 99.6%, the product has a low odor, and even after long-term storage, the odor remains stable and does not become stronger. Detailed Implementation

[0044] This invention provides a method for preparing low-odor 1,2-hexanediol, comprising the following steps:

[0045] Using purified o-hydroxyhexanoate as a raw material, a continuous hydrogenation reaction with hydrogen is carried out in the presence of a hydrogenation catalyst to obtain low-odor 1,2-hexanediol.

[0046] In this invention, the o-hydroxyhexanoate has the structure shown in Formula 1:

[0047] Formula 1;

[0048] In Formula 1, R represents an alkyl group having 1 to 30 carbon atoms. In this invention, R is preferably methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecanyl, octadecyl, nonadecanyl, eicosyl, dodecyl or docosyl, more preferably methyl or ethyl.

[0049] In this invention, the hydrogenation catalyst comprises a catalyst matrix and a catalyst promoter supported on the surface and interior of the catalyst matrix. The catalyst matrix comprises copper oxide, zinc oxide, and aluminum oxide, and the catalyst promoter comprises an active metal and / or an oxide of an active metal. In this invention, the active metal preferably comprises one or more of Mn, Ce, Ni, Sn, Co, Ba, Ca, Se, Pt, Pd, and Re.

[0050] In this invention, the catalyst matrix preferably accounts for 95-99.9 wt% of the total mass of the hydrogenation catalyst, specifically 95 wt%, 96 wt%, 97 wt%, 98 wt%, 99 wt%, or 99.9 wt%; the catalyst promoter preferably accounts for 0.1-5 wt% of the total mass of the hydrogenation catalyst, specifically 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%.

[0051] In this invention, the catalyst matrix preferably contains 35-55 wt% copper oxide, specifically 35 wt%, 40 wt%, 50 wt%, or 55 wt% by mass; zinc oxide preferably contains 35-55 wt%, specifically 35 wt%, 40 wt%, 45 wt%, 50 wt%, or 55 wt%; and alumina preferably contains 8-25 wt%, specifically 8 wt%, 10 wt%, 15 wt%, 20 wt%, or 25 wt%. The hydrogenation catalyst used in this invention can hydrogenate aldehydes simultaneously with ester hydrogenation, converting them into alcohols. The unpleasant odor can be eliminated through simple separation in the initial preparation stage, preventing the development of an unpleasant odor over time.

[0052] Furthermore, the hydrogenation catalyst used in this invention not only effectively converts ester groups into alcohols through hydrogenation, but also maintains the hydrogenation reaction under relatively stable conditions, namely a reaction pressure of 16-25 MPa and a temperature of 100-200°C. When the pressure is below 16 MPa, the catalyst cannot fully exert its catalytic activity, resulting in incomplete hydrogenation, a long reaction time, and low efficiency. When the pressure is above 25 MPa, the ortho-hydroxyl group undergoes dehydration, producing a strong-smelling monool byproduct. When the temperature is below 100°C, the reaction rate is slow, efficiency is low, and ortho-hydroxyhexyl esters are difficult to hydrogenate completely. When the temperature is above 200°C, excessively high temperatures may cause over-hydrogenation of ortho-hydroxyhexyl esters, generating byproducts such as saturated alkanes. In summary, the hydrogenation catalyst used in this invention is suitable, possessing the ability to effectively catalyze the hydrogenation of ester and aldehyde groups, while simultaneously catalyzing the reaction under relatively stable conditions without over-hydrogenation.

[0053] In this invention, the method for preparing the hydrogenation catalyst preferably includes the following steps:

[0054] The solution comprises a water-soluble aluminum salt solution, a first water-soluble copper-zinc salt mixed solution, a second water-soluble copper-zinc salt mixed solution, and a water-soluble active metal salt solution; the copper-zinc molar ratio in the second water-soluble copper-zinc salt mixed solution is higher than that in the first water-soluble copper-zinc salt mixed solution.

[0055] The water-soluble aluminum salt solution is mixed with the first water-soluble copper and zinc salt mixed solution, and the pH value is adjusted to 7 to obtain a premixed solution.

[0056] The premixed solution was mixed with a second water-soluble copper and zinc salt mixed solution, the pH was adjusted to 7, a precipitation reaction was carried out, the resulting precipitate was dried and subjected to a first calcination to obtain the catalyst matrix;

[0057] The catalyst matrix is ​​immersed in the water-soluble active metal salt solution, and after solid-liquid separation, it is dried, calcined a second time, and shaped to obtain the hydrogenation catalyst.

[0058] This invention provides a water-soluble aluminum salt solution, a first water-soluble copper-zinc salt mixed solution, a second water-soluble copper-zinc salt mixed solution, and a water-soluble active metal salt solution; the copper-zinc molar ratio in the second water-soluble copper-zinc salt mixed solution is higher than that in the first water-soluble copper-zinc salt mixed solution. The water-soluble aluminum salt, water-soluble copper salt, water-soluble zinc salt, and water-soluble active metal salt described in this invention are preferably halides, sulfates, or nitrates of the corresponding metals, and the solvent used is deionized water.

[0059] In this invention, the mass concentration of the water-soluble aluminum salt solution is preferably 20-30 wt%.

[0060] In this invention, the copper-zinc molar ratio of the first water-soluble copper-zinc salt mixed solution is preferably 0.1 to 0.2:1, specifically 0.1:1, 0.15:1, or 0.2:1. In this invention, the copper-zinc molar ratio of the second water-soluble copper-zinc salt mixed solution is preferably 4 to 10:1, more preferably 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1.

[0061] In this invention, the preferred molar ratio of copper atoms between the first part of the water-soluble copper-zinc salt mixed solution and the second part of the water-soluble copper-zinc salt mixed solution is 1:2 to 20, specifically 1:2, 1:5, 1:8, 1:10, 1:15 or 1:20.

[0062] In this invention, the mass concentration of the water-soluble active metal salt solution is preferably 5-10 wt%.

[0063] The water-soluble aluminum salt solution is mixed with a first water-soluble copper-zinc salt mixed solution, and the pH value is adjusted to 7 to obtain a premixed solution. This invention does not have special requirements for the mixing method; any mixing method well-known in the art can be used, such as stirring. Preferably, this invention uses a first alkaline reagent to adjust the pH value, which is preferably one or more of sodium hydroxide, sodium carbonate, and ammonia water. In this invention, the pH adjustment is preferably carried out under stirring conditions. The purpose of this invention, by premixing the water-soluble aluminum salt solution with the first water-soluble copper-zinc salt mixed solution, is to gradient-load copper and zinc, increase the copper and zinc loading, and simultaneously stabilize the catalyst structure.

[0064] After obtaining the premixed solution, the present invention mixes the premixed solution with a second water-soluble copper-zinc salt mixed solution, adjusts the pH value to 7, performs a precipitation reaction, and dries and first calcines the resulting precipitate to obtain the catalyst matrix. The present invention preferably uses a second alkaline reagent to adjust the pH value, which is preferably one or more of sodium hydroxide, sodium carbonate, and ammonia water. In the present invention, the pH adjustment is preferably carried out under stirring conditions. The present invention aims to achieve a gradient distribution of copper and zinc in the composite oxide (catalyst matrix) by controlling the copper / zinc molar ratio in the second water-soluble copper-zinc salt mixed solution to be higher than that in the first water-soluble copper-zinc salt mixed solution. The higher copper / zinc molar ratio in the second water-soluble copper-zinc salt mixed solution can form a copper-rich region on the outer layer of the composite oxide; this gradient structure can enhance the mechanical strength and thermal stability of the hydrogenation catalyst.

[0065] In this invention, the temperature of the precipitation reaction is preferably 25~50℃, more preferably 30~40℃, and the time is preferably 5~12 h, more preferably 8~10 h.

[0066] Following the precipitation reaction, the resulting precipitate is preferably filtered and washed. In this invention, the drying temperature is preferably 100-150°C, more preferably 100-120°C; the drying time is preferably 5-24 h, more preferably 5-12 h. In this invention, the first calcination temperature is preferably 500-1000°C, more preferably 600-800°C; the first calcination time is preferably 4-12 h, more preferably 4-6 h. In this invention, the atmosphere for the first calcination is preferably air.

[0067] After obtaining the catalyst matrix, the present invention impregnates the catalyst matrix in the water-soluble active metal salt solution, and after solid-liquid separation, it is successively dried, calcined a second time, and shaped to obtain a hydrogenation catalyst. In the present invention, the impregnation temperature is preferably 25~50℃, more preferably 30~40℃, and the time is preferably 5~12 h, more preferably 8~10 h.

[0068] In this invention, the solid-liquid separation method is preferably filtration, and after solid-liquid separation, the resulting solid is preferably washed. In this invention, the drying temperature is preferably 100-150°C, more preferably 100-120°C; the drying time is preferably 5-24 h, more preferably 5-12 h. In this invention, the second calcination temperature is preferably 500-1000°C, more preferably 600-800°C; the second calcination time is preferably 4-12 h, more preferably 4-6 h. In this invention, the atmosphere for the second calcination is preferably air.

[0069] In this invention, prior to the continuous hydrogenation reaction, the hydrogenation catalyst is further reduced. In this invention, the reducing agent used for the reduction is preferably one or more of hydrogen, carbon monoxide, hydrogen sulfide, sodium borohydride, lithium aluminum hydride, and phosphoric acid, more preferably hydrogen. This invention activates the hydrogenation catalyst through this reduction.

[0070] In this invention, when the reducing agent is hydrogen, the hydrogen is preferably injected under normal or low pressure conditions, and the pressure under the low pressure conditions is preferably 0.5~10 bar, more preferably 1~2 bar. In this invention, the hydrogen is preferably added under diluted or undiluted conditions, and the gas used to dilute the hydrogen is preferably nitrogen or helium. In this invention, the reduction temperature is preferably 400~600℃, specifically 400℃, 500℃, or 600℃; the time is preferably 1~24 hours.

[0071] In this invention, the o-hydroxyhexanoate ester is reacted in a solvent-free state or dissolved in an organic solvent. Preferably, the organic solvent is cyclohexane or an alcohol solvent, and the alcohol solvent is preferably one or more of methanol, ethanol, propanol, and isopropanol. The concentration of the o-hydroxyhexanoate ester ester in the organic solvent is preferably 10-70 wt%, specifically 10 wt%, 30 wt%, 50 wt%, or 70 wt%.

[0072] In this invention, the o-hydroxyhexanoate ester needs to be purified before use. The purification method for the o-hydroxyhexanoate ester preferably includes the following steps:

[0073] o-hydroxyhexanoate was subjected to washing with an inorganic alkaline aqueous solution, water washing, and distillation in sequence.

[0074] In this invention, the inorganic base is preferably one or more of sodium hydroxide, sodium carbonate, and sodium bicarbonate, more preferably sodium carbonate. In this invention, the concentration of the inorganic base aqueous solution is preferably 5-30 wt%, more preferably 10-20 wt%, and specifically preferably a saturated sodium carbonate solution. In this invention, the inorganic base aqueous solution is preferably washed at least once. Since o-hydroxyhexanoate may contain some acidic impurities, especially aldehyde impurities, washing with the inorganic base aqueous solution can remove these impurities as much as possible.

[0075] In this invention, the water washing is preferably done with deionized water; the number of water washings is preferably three. In this invention, the distillation temperature is preferably 100-120°C, more preferably 110°C, and the pressure is preferably 20-100 mmHg, more preferably 50 mmHg. This invention, by fractionating and refining the raw materials through distillation, combined with subsequent continuous hydrogenation reactions and post-treatment steps, can maximally suppress the odor emitted by aldehydes.

[0076] In this invention, the continuous hydrogenation reaction is preferably carried out in a fixed bed. This invention employs a continuous production method, conducted in a fixed bed, where o-hydroxyhexanoate or o-hydroxyhexanoate and a solvent of choice are continuously supplied to the reactor at a specified temperature and pressure in the presence of a catalyst, while maintaining a continuous supply of hydrogen. The product is collected from the outlet of the fixed bed while the material supply reaction proceeds.

[0077] In this invention, the continuous hydrogenation reaction is carried out at a temperature of 100–200°C, preferably 180–190°C, and at a pressure of 16–25 MPa, preferably 20–23 MPa. This invention can hydrogenate esters to the corresponding alcohols using temperatures of 100–200°C and hydrogen pressures in the range of 16–25 MPa. However, since the hydrogenation rate typically increases with increasing temperature, it is generally necessary to operate within a range of approximately 180–190°C to maximize the conversion and utilization of commercial hydrogenation facilities. A highly attractive feature of this invention is the use of hydrogen pressures below 25 MPa, particularly in the range of 20–23 MPa, where the hydrogenation reaction exhibits good conversion rates, especially when combined with hydrogenation temperatures in the range of 180–190°C, resulting in even higher conversion rates. Conducting the hydrogenation reaction at lower hydrogen pressures helps reduce energy and equipment costs.

[0078] In this invention, the molar ratio of hydrogen to o-hydroxyhexanoate (hydrogen-to-ester ratio) in the continuous hydrogenation reaction is preferably 1000-100:1, specifically 1000:1, 800:1, 600:1, 300:1, or 100:1. A higher hydrogen-to-ester ratio in this invention provides more hydrogen, promoting complete reaction and also helping to reduce the formation of byproducts.

[0079] In this invention, the space velocity of o-hydroxyhexanoate in the continuous hydrogenation reaction is preferably 80-200 h⁻¹. -1 More preferably 80 h -1 100 h -1 120 h -1 150 h -1 180 h -1 or 200 h -1 .

[0080] In this invention, after the continuous hydrogenation reaction, the resulting product is preferably subjected to distillation and / or rectification. In this invention, the distillation is preferably steam distillation, the distillation temperature is preferably 110-120°C, more preferably 115°C, and the number of distillations is preferably 3-5 times. This invention, through 3-5 distillation purification operations, can significantly improve the purity of 1,2-hexanediol and reduce odor. If the number of distillations is less than 3 times, it is difficult to obtain a high-purity target product; while if the number of distillations is more than 5 times, the purity improvement is limited, and the economic benefits are low.

[0081] In this invention, the distillation temperature is preferably 120~160℃, more preferably 130~155℃, and the pressure is preferably 2~20 mmHg, more preferably 10~15 mmHg.

[0082] Following the continuous hydrogenation reaction, the present invention preferably includes the recovery and reuse of unreacted starting materials, hydrogenation catalysts, and organic solvents.

[0083] The preparation method of low-odor 1,2-hexanediol provided by the present invention will be described in detail below with reference to the embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0084] Example 1

[0085] Preparation of hydrogenation catalysts:

[0086] 190 g of aluminum nitrate nonahydrate was dissolved in 500 mL of deionized water to obtain a water-soluble aluminum salt solution. 420 g of zinc nitrate hexahydrate and 376 g of copper sulfate pentahydrate were dissolved separately in 300 mL of deionized water. 55.0 g and 550.0 g of the solutions from the copper sulfate pentahydrate and zinc nitrate hexahydrate solutions, respectively, were mixed to obtain the first water-soluble copper-zinc salt mixed solution (copper-zinc molar ratio of 0.11:1). The remaining solutions were mixed to obtain the second water-soluble copper-zinc salt mixed solution (copper-zinc molar ratio of 4.18:1, and the copper atom molar ratio of the first to the second water-soluble copper-zinc salt mixed solution was 1:11.5). The water-soluble aluminum salt solution was mixed with the first water-soluble copper-zinc salt mixed solution, and sodium hydroxide solution was added under stirring to adjust the pH to 7, resulting in a premixed solution. Subsequently, a second water-soluble copper-zinc salt mixed solution was added to the premixed solution. Sodium hydroxide solution was added under stirring to adjust the pH to 7. The solution was filtered, washed, dried at 120°C, and calcined at 500°C for 4 h in air to obtain the catalyst matrix. 8 g of manganese nitrate tetrahydrate was dissolved in 100 mL of deionized water to obtain a water-soluble active metal salt solution. The catalyst matrix prepared above was then added to the water-soluble active metal salt solution under vigorous stirring and impregnated for 24 h. The solution was filtered, washed, dried at 120°C, and calcined at 500°C for 4 h in air to obtain the hydrogenation catalyst.

[0087] Preparation of low-odor 1,2-hexanediol:

[0088] First, methyl o-hydroxyhexanoate was washed with a saturated sodium carbonate solution, allowed to stand and separate into layers, and the organic phase was washed three times with water to maintain the pH at 7. The organic phase was then distilled at 50 mmHg and 110 °C. 100 g of the hydrogenation catalyst prepared by the above method was packed into a fixed bed, and 5% H₂ / Ar gas was introduced. The temperature was increased to 500 °C at a rate of 10 °C / min, and activated at this temperature for 3 h. The treated methyl o-hydroxyhexanoate was then continuously introduced into the fixed bed at a rate of 0.3 mL / min, and the reaction temperature was controlled at 160 °C, the hydrogen pressure at 22 MPa, and the hydrogen / catalyst volume hourly space velocity at 114 h⁻¹. -1 The hydrogen-to-ester ratio was 483.3:1, and the reaction proceeded continuously. The collected product was steam distilled in an atmospheric distillation column at a steam temperature of 115℃; then purified by adsorption using activated carbon, followed by rectification at 10 mmHg and 130℃. The collected fractions were repeated for three distillations. Gas chromatography (GC) analysis was performed throughout the process, and the reaction test data are listed in Table 1.

[0089] Examples 2-10

[0090] The hydrogenation catalyst was prepared according to the method in Example 1. The preparation method of 1,2-hexanediol in Examples 2-10 was the same as in Example 1. The specific reaction conditions are shown in Table 1, and the reaction results are shown in Table 1.

[0091] Table 1. Reaction conditions and results of Examples 1-10

[0092]

[0093] Example 11

[0094] Preparation of hydrogenation catalysts:

[0095] 190 g of aluminum nitrate nonahydrate was dissolved in 500 mL of deionized water to obtain a water-soluble aluminum salt solution. 400 g of zinc nitrate hexahydrate and 420 g of copper sulfate pentahydrate were dissolved separately in 300 mL of deionized water. 55.0 g and 550.0 g of the solutions from the copper sulfate pentahydrate and zinc nitrate hexahydrate solutions, respectively, were mixed to obtain the first water-soluble copper-zinc salt mixed solution (copper-zinc molar ratio of 0.12:1). The remaining solutions were mixed to obtain the second water-soluble copper-zinc salt mixed solution (copper-zinc molar ratio of 5.34:1, and the copper atomic molar ratio of the first and second water-soluble copper-zinc salt mixed solutions was 1:11.92). The water-soluble aluminum salt solution was mixed with the first water-soluble copper-zinc salt mixed solution, and sodium hydroxide solution was added under stirring to adjust the pH to 7, resulting in a premixed solution. Subsequently, a second water-soluble copper-zinc salt mixed solution was added to the premixed solution. Sodium hydroxide solution was added under stirring to adjust the pH to 7. The solution was filtered, washed, dried at 120°C, and calcined at 500°C for 4 h in air to obtain the catalyst matrix. 5 g of palladium nitrate was dissolved in 100 mL of deionized water to obtain a water-soluble active metal salt solution. The catalyst matrix prepared above was then added to the water-soluble active metal salt solution under vigorous stirring and impregnated for 24 h. The solution was filtered, washed, dried at 120°C, and calcined at 500°C for 4 h in air to form the hydrogenation catalyst.

[0096] The preparation of low-odor 1,2-hexanediol was carried out according to Example 1. The specific reaction conditions are shown in Table 2, and the reaction results are shown in Table 2.

[0097] Examples 12-15

[0098] The hydrogenation catalyst was prepared according to the method of Example 11. The preparation method of 1,2-hexanediol in Examples 12-15 is the same as that in Example 11. The specific reaction conditions are shown in Table 2, and the reaction results are shown in Table 2.

[0099] Table 2 Reaction conditions and results of Examples 11-15

[0100]

[0101] Example 16

[0102] Preparation of hydrogenation catalysts:

[0103] 190 g of aluminum nitrate nonahydrate was dissolved in 500 mL of deionized water to obtain a water-soluble aluminum salt solution. 410 g of zinc nitrate hexahydrate and 460 g of copper sulfate pentahydrate were dissolved in 300 mL of deionized water respectively. 55.0 g and 550.0 g of the solutions from the copper sulfate pentahydrate and zinc nitrate hexahydrate solutions were mixed to obtain the first water-soluble copper-zinc salt mixed solution (copper-zinc molar ratio of 0.12:1). The remaining solutions were mixed to obtain the second water-soluble copper-zinc salt mixed solution (copper-zinc molar ratio of 5.51:1, and the copper atomic molar ratio of the first and second water-soluble copper-zinc salt mixed solutions was 1:13.15). The water-soluble aluminum salt solution was mixed with the first water-soluble copper-zinc salt mixed solution, and sodium hydroxide solution was added under stirring to adjust the pH to 7, resulting in a premixed solution. Subsequently, a second water-soluble copper-zinc salt mixed solution was added to the premixed solution. Sodium hydroxide solution was added under stirring to adjust the pH to 7. The solution was filtered, washed, dried at 120°C, and calcined at 500°C for 4 h in air to obtain the catalyst matrix. 3 g of nickel chloride and 3 g of selenium sulfate were dissolved in 100 mL of deionized water to obtain a water-soluble active metal salt solution. The catalyst matrix prepared above was then added to the water-soluble active metal salt solution under vigorous stirring and impregnated for 24 h. The solution was filtered, washed, dried at 120°C, and calcined at 500°C for 4 h in air to obtain the hydrogenation catalyst.

[0104] The preparation of low-odor 1,2-hexanediol was carried out in accordance with Example 1. The specific reaction conditions are shown in Table 3, and the reaction results are shown in Table 3.

[0105] Examples 17-20

[0106] The hydrogenation catalyst was prepared according to the method of Example 16. The preparation method of 1,2-hexanediol in Examples 17-20 was the same as that in Example 16. The specific reaction conditions are shown in Table 3, and the reaction results are shown in Table 3.

[0107] Table 3 Reaction conditions and results of Examples 16-20

[0108]

[0109] Comparative Example 1

[0110] 100 g of commercially available ordinary Cu-Zn / Al catalyst (copper-zinc-aluminum molar ratio of 2.36:1:1.25) was packed into a fixed bed, and 5% H2 / Ar gas was introduced. The temperature was increased to 500 °C at a rate of 10 °C / min, and activated at this temperature for 3 h. Methyl o-hydroxyhexanoate was then continuously introduced into the fixed bed at a rate of 0.3 mL / min. The reaction temperature was controlled at 160 °C, the hydrogen pressure at 22 MPa, and the hydrogen / catalyst volume hourly space velocity at 114 h⁻¹. -1 The reaction continued. The collected product was steam distilled in an atmospheric distillation column at a temperature of 115°C; then purified by adsorption using activated carbon, followed by rectification at 10 mmHg and 130°C. The distillate was collected and repeated three times. Gas chromatography (GC) analysis was performed throughout the process, and the reaction test data are listed in Table 4.

[0111] Comparative Example 2

[0112] 100 g of the catalyst prepared in Example 1 was packed into a fixed bed, and 5% H2 / Ar gas was introduced. The temperature was increased to 500°C at a rate of 10°C / min, and activated at this temperature for 3 h. Methyl o-hydroxyhexanoate was then continuously introduced into the fixed bed at a rate of 0.3 mL / min. The reaction temperature was controlled at 220°C, the hydrogen pressure at 22 MPa, and the hydrogen / catalyst volume hourly space velocity at 114 h⁻¹. -1 The reaction continued. The collected product was steam distilled in an atmospheric distillation column at a temperature of 115°C; then purified by adsorption using activated carbon, followed by rectification at 10 mmHg and 130°C. The distillate was collected and repeated three times. Gas chromatography (GC) analysis was performed throughout the process, and the reaction test data are listed in Table 4.

[0113] Comparative Examples 3-4

[0114] The hydrogenation catalyst was prepared according to the method of Example 1. The preparation method of 1,2-hexanediol in Comparative Examples 3 and 4 was the same as that in Comparative Example 2. The specific reaction conditions are shown in Table 4, and the reaction results are shown in Table 4.

[0115] Table 4. Reaction conditions and results of Comparative Examples 1-4

[0116]

[0117] Odor tests were conducted on the 1,2-hexanediol prepared in Examples 3 and 14, as well as Comparative Examples 1 and 2. A total of 20 people participated in the tests. The odor test results are shown in Table 5.

[0118] Table 5 Odor Test Results

[0119]

[0120] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing low-odor 1,2-hexanediol, characterized in that, Includes the following steps: Using purified o-hydroxyhexanoate as a raw material, a continuous hydrogenation reaction was carried out with hydrogen in the presence of a hydrogenation catalyst to obtain low-odor 1,2-hexanediol. The o-hydroxyhexanoate has the structure shown in Formula 1: Formula 1; In Formula 1, R represents an alkyl group having 1 to 30 carbon atoms; The hydrogenation catalyst includes a catalyst matrix and catalyst promoters supported on the surface and interior of the catalyst matrix. The catalyst matrix is ​​composed of copper oxide, zinc oxide and aluminum oxide, and the catalyst promoters are composed of active metals and / or oxides of active metals. In the hydrogenation catalyst, the catalyst matrix accounts for 95-99.9 wt% of the total mass of the hydrogenation catalyst, and the catalyst promoter accounts for 0.1-5 wt% of the total mass of the hydrogenation catalyst. In the catalyst matrix, by mass percentage, copper oxide accounts for 35-55 wt%, zinc oxide accounts for 35-55 wt%, and aluminum oxide accounts for 8-25 wt%. The catalyst promoter includes one or more of Mn, Ce, Ni, Sn, Co, Ba, Ca, Se, Pt, Pd and Re; The continuous hydrogenation reaction is carried out at a temperature of 100~190℃ and a pressure of 16~25 MPa. In the continuous hydrogenation reaction, the molar ratio of hydrogen to o-hydroxyhexanoate is 1000~100:1; The space velocity of o-hydroxyhexanoate in the continuous hydrogenation reaction is 80-200 h⁻¹. -1 ; The preparation method of the hydrogenation catalyst includes the following steps: The solution comprises a water-soluble aluminum salt solution, a first water-soluble copper-zinc salt mixed solution, a second water-soluble copper-zinc salt mixed solution, and a water-soluble active metal salt solution; the copper-zinc molar ratio in the second water-soluble copper-zinc salt mixed solution is higher than that in the first water-soluble copper-zinc salt mixed solution. The water-soluble aluminum salt solution is mixed with the first water-soluble copper and zinc salt mixed solution, and then the pH value is adjusted to 7 to obtain a premixed solution; The premixed solution was mixed with a second water-soluble copper and zinc salt mixed solution, and then the pH was adjusted to 7 to carry out a precipitation reaction. The resulting precipitate was dried and subjected to a first calcination to obtain the catalyst matrix. The catalyst matrix is ​​immersed in the water-soluble active metal salt solution, and after solid-liquid separation, it is dried, calcined a second time, and shaped to obtain the hydrogenation catalyst.

2. The preparation method according to claim 1, characterized in that, The first water-soluble copper-zinc salt mixed solution has a copper-zinc molar ratio of 0.1~0.2:1; The copper-zinc molar ratio of the second water-soluble copper-zinc salt mixed solution is 4~10:1; The molar ratio of copper atoms in the first part of the water-soluble copper-zinc salt mixed solution to that in the second part of the water-soluble copper-zinc salt mixed solution is 1:2~20.

3. The preparation method according to claim 1, characterized in that, The o-hydroxyhexanoate reacts in a solvent-free state or reacts in an organic solvent.

4. The preparation method according to claim 1, characterized in that, The continuous hydrogenation reaction is carried out in a fixed bed.

5. The preparation method according to claim 1, characterized in that, The purification method for the o-hydroxyhexanoate includes the following steps: o-hydroxyhexanoate was subjected to washing with an inorganic alkaline aqueous solution, water washing, and distillation in sequence.

6. The preparation method according to claim 1, characterized in that, Before the continuous hydrogenation reaction, the process also includes reducing the hydrogenation catalyst.

7. The preparation method according to claim 1, characterized in that, The continuous hydrogenation reaction further includes distillation and / or rectification of the resulting product; The distillation temperature is 110~120℃, and the distillation is performed 3~5 times; The distillation temperature is 120~160℃ and the pressure is 2~20 mmHg.

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