Preparation method of low-odor 1, 2-hexanediol

Abstract

The invention provides a preparation method of low-odor 1, 2-hexanediol, and belongs to the technical field of organic synthesis. According to the invention, purified o-hydroxyhexanoate is used as a raw material, and under the action of a hydrogenation catalyst, the purified o-hydroxyhexanoate and hydrogen are subjected to a continuous hydrogenation reaction to obtain the low-odor 1, 2-hexanediol. According to the method, the o-hydroxyhexanoate raw material is purified before reaction, so that impurities such as aldehyde, hydrocarbon and the like are reduced. According to the invention, the copper-based catalyst is selected to control the reaction at lower temperature and pressure. Particularly, the copper-zinc-aluminum catalyst is adopted, so that the ester group can be catalytically hydrogenated under mild reaction conditions, aldehyde impurities can be hydrogenated and converted into alcohol, and the unpleasant odor caused by aldehyde compounds can be eliminated. According to the invention, a continuous production process is adopted, and compared with an intermittent production process, higher conversion rate and yield and fewer by-products can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of organic synthesis, and in particular to a method for preparing low-odor 1,2-hexanediol. Background Art

[0002] 1,2-Hexanediol is a very popular chemical. It is a transparent, colorless to pale yellow liquid with a boiling point of 223-224°C. It is highly soluble in alcohol and water, safe and harmless to the human body, and possesses both antiseptic and moisturizing properties. 1,2-Hexanediol is widely used in toiletries, pharmaceuticals, inkjet printers, solvents, and other fields. In particular, in cosmetics, it serves as a skin moisturizer, antibacterial agent, defoamer, and solubilizer. For example, patents WO2019120572A1, US2010216892A1, and MY135988A disclose the use of 1,2-Hexanediol as a humectant and surfactant in cosmetic emulsions. Patents KR102043869B1 and WO2006045743A1 apply 1,2-Hexanediol as an antibacterial agent and a preservative in cosmeceuticals, respectively.

[0003] Based on the aforementioned application scenarios, especially in cosmetics and toiletries, the market and consumers have very strict requirements for the odor of 1,2-hexanediol, that is, it should emit as neutral an odor as possible. However, the synthesis process of 1,2-hexanediol often inevitably produces unpleasant odors, which are emitted by byproducts with structures similar to 1,2-hexanediol. To eliminate the odor, it is necessary to start with the removal of byproducts. Removal of byproducts requires complex post-treatment processes or processing techniques, but the results are often difficult to meet people's expectations. Therefore, finding a production process to produce high-purity, low-odor 1,2-hexanediol is a current research difficulty and hot topic.

[0004] Currently, 1,2-hexanediol is primarily produced from 1-hexene, which is oxidized with peroxide to form the corresponding epoxide. This is then hydrolyzed with acid and post-treated to yield 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 formation of various aldehyde byproducts during subsequent production, which are the primary source of unpleasant odors.

[0005] Patent WO2020069731A1 uses alkylene glycol and 1-olefin as raw materials with an olefin-alkenol ratio of 1:1~50. Under the action of a free radical initiator, 150~180°C and self-pressure are used to prepare 1,2-alkanediol. The product yield is only 41.3% and the purity is 98%.

[0006] Patent CN110272329A uses hexene, acetonitrile, methanol, and potassium bicarbonate as raw materials to prepare 1,2-epoxyhexane in the presence of hydrogen peroxide, and then obtains 1,2-hexanediol through hydrolysis reaction with a purity greater than 99%.

[0007] Patent EP4331684A2 reacts 1-olefins with formic acid in the presence of hydrogen peroxide to produce a formate ester, which is then decarboxylated to produce 1,2-hexanediol. The first ester-forming reaction uses an olefin:formic acid ratio of 1:1.5-2.5, and an olefin:hydrogen peroxide ratio of 1:0.5-1.5, at 50-100°C for 4-10 hours, yielding a theoretical yield exceeding 95%. The second decarboxylation step uses a supported nickel or palladium catalyst at a dosage of 0.5-20 wt%, at 180-220°C for 2-6 hours, yielding a theoretical yield of 70-97%. Distillation is then performed to obtain a clear, odorless, colorless liquid with a purity of 99.5%.

[0008] However, 1,2-hexanediol produced via the hydrogen peroxide method inevitably contains aldehydes and ketones with strong odors. Even 1,2-hexanediol with a purity of 99.5% may appear pleasant initially, but its odor changes over time, becoming increasingly stronger. This is likely due to condensation reactions with residual aldehydes in the product, forming unpleasant-smelling byproducts. Therefore, the purity of 1,2-hexanediol needs to be further improved to remove impurities (especially aldehydes) and odor. 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 yield.

[0010] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions: The present invention provides a method for preparing low-odor 1,2-hexanediol, comprising the following steps: Using purified o-hydroxyhexanoic acid ester as raw material, a continuous hydrogenation reaction is carried out with hydrogen in the presence of a hydrogenation catalyst to obtain low-odor 1,2-hexanediol. The o-hydroxyhexanoate has a structure shown in Formula 1: Formula 1; In Formula 1, R represents an alkyl group having 1 to 30 carbon atoms; The hydrogenation catalyst comprises a catalyst matrix and a catalyst promoter supported on the surface and interior of the catalyst matrix, wherein the components of the catalyst matrix include copper oxide, zinc oxide and aluminum oxide, and the components of the catalyst promoter include active metals and / or active metal oxides; The temperature of the continuous hydrogenation reaction is 100-200° C., and the pressure is 16-25 MPa.

[0011] 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; In the catalyst matrix, the copper oxide accounts for 35-55 wt %, the zinc oxide accounts for 35-55 wt %, and the aluminum oxide accounts for 8-25 wt % by weight; The active metal includes one or more of Mn, Ce, Ni, Sn, Co, Ba, Ca, Se, Pt, Pd and Re.

[0012] Preferably, the preparation method of the hydrogenation catalyst comprises the following steps: Providing a water-soluble aluminum salt solution, a first water-soluble copper salt and zinc salt mixed solution, a second water-soluble copper salt and zinc salt mixed solution, and a water-soluble active metal salt solution; wherein the copper-zinc molar ratio in the second water-soluble copper salt and zinc salt mixed solution is higher than that in the first water-soluble copper salt and zinc salt mixed solution; Mixing the water-soluble aluminum salt solution with the first portion of the water-soluble copper salt and zinc salt mixed solution, adjusting the pH value to 7, to obtain a premixed solution; The premixed solution is mixed with a second portion of a water-soluble copper salt and zinc salt mixed solution, the pH value is adjusted to 7, a precipitation reaction is carried out, and the obtained precipitate is dried and first calcined to obtain a catalyst matrix; The catalyst matrix is ​​immersed in the water-soluble active metal salt solution, and after solid-liquid separation, drying, second calcination and molding are carried out in sequence to obtain a hydrogenation catalyst.

[0013] Preferably, the molar ratio of copper to zinc in the first water-soluble copper salt and zinc salt mixed solution is 0.1 to 0.2:1; The molar ratio of copper to zinc in the second water-soluble copper salt and zinc salt mixed solution is 4 to 10:1; The molar ratio of copper atoms in the first water-soluble copper salt and zinc salt mixed solution to the second water-soluble copper salt and zinc salt mixed solution is 1:2-20.

[0014] Preferably, the o-hydroxyhexanoate is reacted in a solvent-free state or dissolved in an organic solvent for reaction.

[0015] Preferably, the continuous hydrogenation reaction is carried out in a fixed bed; The molar ratio of hydrogen to o-hydroxyhexanoate in the continuous hydrogenation reaction is 1000-100:1.

[0016] Preferably, the space velocity of o-hydroxyhexanoate in the continuous hydrogenation reaction is 80 to 200 h-1 .

[0017] Preferably, the method for purifying o-hydroxyhexanoate preferably comprises the following steps: The o-hydroxyhexanoate is sequentially washed with an inorganic alkali aqueous solution, washed with water and distilled.

[0018] Preferably, before the continuous hydrogenation reaction, the hydrogenation catalyst is further reduced.

[0019] Preferably, after the continuous hydrogenation reaction, the obtained product is further subjected to distillation and / or rectification; The distillation temperature is 110-120° C., and the number of distillations is 3-5 times; The distillation temperature is 120-160° C., and the pressure is 2-20 mmHg.

[0020] The present invention provides a method for preparing low-odor 1,2-hexanediol, comprising the following steps: Using purified o-hydroxyhexanoate as raw material, a continuous hydrogenation reaction is carried out under the action of a hydrogenation catalyst to obtain low-odor 1,2-hexanediol. The reaction route is shown in Formula A: Formula A.

[0021] Compared to existing technologies, the advantages of the present invention are: ① Addressing the troublesome odor problem in traditional production processes, the present invention purifies the o-hydroxyhexanoate raw material before the reaction to reduce impurities such as aldehydes and hydrocarbons. ② Compared to the traditional method for preparing 1,2-hexanediol from 1-hexene, the present invention uses o-hydroxyhexanoate as the raw material and reacts it in the presence of a hydrogenation catalyst, hydrogenating the ester groups to hydroxyl groups to produce 1,2-hexanediol. The copper-based catalyst prepared in the present invention controls the reaction at relatively low temperatures and pressures. The copper-zinc-aluminum catalyst, in particular, can catalyze the hydrogenation of ester groups under mild reaction conditions while also hydrogenating aldehyde impurities, converting them into alcohols, thereby eliminating the unpleasant odor caused by these aldehyde compounds. ③ The present invention limits the continuous hydrogenation reaction conditions to 100-200°C and 16-25 MPa. After hydrogenation, simple separation is performed to obtain high-purity, low-odor 1,2-hexanediol. Furthermore, the present invention utilizes a continuous production process, which, compared to batch production processes, can achieve higher conversion rates and yields, as well as fewer by-products. The preparation method provided by the invention has simple process, low investment and low energy consumption, and is conducive to industrial production.

[0022] 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-ester ratio of 600:1, the conversion rate of 1,2-hexanediol can reach 99.9%, the selectivity reaches 99.0%, the purity is as high as 99.6%, and the product has a low odor. Even if it is left for a long time, the odor remains stable and does not become heavier. DETAILED DESCRIPTION

[0023] The present invention provides a method for preparing low-odor 1,2-hexanediol, comprising the following steps: Using purified o-hydroxyhexanoic acid ester as raw material, a continuous hydrogenation reaction is carried out with hydrogen in the presence of a hydrogenation catalyst to obtain low-odor 1,2-hexanediol.

[0024] In the present invention, the o-hydroxyhexanoate has a structure shown in Formula 1: Formula 1; In Formula 1, R represents an alkyl group having 1 to 30 carbon atoms. In the present invention, R is preferably a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a 2-ethylhexyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an eicosyl group, a heneicosyl group, or a docosyl group, and more preferably a methyl group or an ethyl group.

[0025] In the present invention, the hydrogenation catalyst comprises a catalyst substrate and a catalyst promoter supported on the surface and interior of the catalyst substrate. The catalyst substrate comprises copper oxide, zinc oxide, and aluminum oxide, and the catalyst promoter comprises an active metal and / or an active metal oxide. In the present invention, the active metal preferably comprises one or more of Mn, Ce, Ni, Sn, Co, Ba, Ca, Se, Pt, Pd, and Re.

[0026] In the present invention, in the hydrogenation catalyst, the catalyst matrix preferably accounts for 95% to 99.9% by weight of the total mass of the hydrogenation catalyst, specifically 95% by weight, 96% by weight, 97% by weight, 98% by weight, 99% by weight or 99.9% by weight; the catalyst promoter preferably accounts for 0.1% to 5% by weight of the total mass of the hydrogenation catalyst, specifically 0.1% by weight, 0.5% by weight, 1% by weight, 2% by weight, 3% by weight, 4% by weight or 5% by weight.

[0027] In the present invention, in the catalyst matrix, the copper oxide preferably accounts for 35-55 wt%, specifically 35 wt%, 40 wt%, 50 wt%, or 55 wt%; the zinc oxide preferably accounts for 35-55 wt%, specifically 35 wt%, 40 wt%, 45 wt%, 50 wt%, or 55 wt%; and the aluminum oxide preferably accounts for 8-25 wt%, specifically 8 wt%, 10 wt%, 15 wt%, 20 wt%, or 25 wt%. The hydrogenation catalyst used in the present invention can simultaneously hydrogenate aldehydes while performing ester hydrogenation, converting them into alcohols. Unpleasant odors can be eliminated by simple separation and removal in the early stages of preparation, and no unpleasant odors will be generated over time.

[0028] Furthermore, the hydrogenation catalyst employed in the present invention not only effectively hydrogenates the ester groups into alcohols 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 an incomplete hydrogenation reaction, a long reaction time, and low efficiency. When the pressure is above 25 MPa, the ortho-hydroxyl groups dehydrate, producing a monoalcohol byproduct with a strong odor. When the temperature is below 100°C, the reaction rate is slow, the efficiency is low, and it is difficult to fully hydrogenate the ortho-hydroxyhexyl ester. When the temperature is above 200°C, the excessively high temperature is likely to cause the ortho-hydroxyhexyl ester to undergo over-hydrogenation, producing byproducts such as saturated alkanes. In summary, the hydrogenation catalyst employed in the present invention is suitable, having the ability to effectively catalyze the hydrogenation of ester and aldehyde groups, while also being able to catalyze the reaction under relatively stable reaction conditions without over-hydrogenation.

[0029] In the present invention, the preparation method of the hydrogenation catalyst preferably comprises the following steps: Providing a water-soluble aluminum salt solution, a first water-soluble copper salt and zinc salt mixed solution, a second water-soluble copper salt and zinc salt mixed solution, and a water-soluble active metal salt solution; wherein the copper-zinc molar ratio in the second water-soluble copper salt and zinc salt mixed solution is higher than that in the first water-soluble copper salt and zinc salt mixed solution; Mixing the water-soluble aluminum salt solution with the first portion of the water-soluble copper salt and zinc salt mixed solution, adjusting the pH value to 7, to obtain a premixed solution; The premixed solution is mixed with a second portion of a water-soluble copper salt and zinc salt mixed solution, the pH value is adjusted to 7, a precipitation reaction is carried out, and the obtained precipitate is dried and first calcined to obtain a catalyst matrix; The catalyst matrix is ​​immersed in the water-soluble active metal salt solution, and after solid-liquid separation, drying, second calcination and molding are carried out in sequence to obtain a hydrogenation catalyst.

[0030] The present invention provides a water-soluble aluminum salt solution, a first water-soluble copper salt and zinc salt mixed solution, a second water-soluble copper salt and zinc salt mixed solution, and a water-soluble active metal salt solution; the copper-to-zinc molar ratio in the second water-soluble copper salt and zinc salt mixed solution is higher than that in the first water-soluble copper salt and 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 the present invention are preferably halides, sulfates, or nitrates of the corresponding metals, and the solvent used is deionized water.

[0031] In the present invention, the mass concentration of the water-soluble aluminum salt solution is preferably 20-30 wt%.

[0032] In the present invention, the copper-zinc molar ratio of the first water-soluble copper salt-zinc salt mixed solution is preferably 0.1 to 0.2: 1, specifically 0.1: 1, 0.15: 1 or 0.2: 1. In the present invention, the copper-zinc molar ratio of the second water-soluble copper salt-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.

[0033] In the present invention, the molar ratio of copper atoms in the first water-soluble copper salt and zinc salt mixed solution to the second water-soluble copper salt and zinc salt mixed solution is preferably 1:2-20, specifically 1:2, 1:5, 1:8, 1:10, 1:15 or 1:20.

[0034] In the present invention, the mass concentration of the water-soluble active metal salt solution is preferably 5-10 wt%.

[0035] The water-soluble aluminum salt solution is mixed with the first water-soluble copper salt and zinc salt mixed solution, and the pH value is adjusted to 7 to obtain a premixed solution. The present invention has no special requirements for the mixing method, and the mixing method well known in the art can be applied, such as stirring and mixing. The present invention preferably uses a first alkaline reagent to adjust the pH value, and the first alkaline reagent is preferably one or more of sodium hydroxide, sodium carbonate and ammonia. In the present invention, the pH value is preferably adjusted under stirring. The present invention premixes the water-soluble aluminum salt solution with the first water-soluble copper salt and zinc salt mixed solution, with the aim of loading copper and zinc in a gradient, increasing the loading amount of copper and zinc, and stabilizing the catalyst structure.

[0036] After obtaining the premixed liquid, the present invention mixes the premixed liquid with a second water-soluble copper salt and zinc salt mixed solution, adjusts the pH value to 7, performs a precipitation reaction, and dries and performs a first calcination on the obtained precipitate to obtain a catalyst matrix. The present invention preferably uses a second alkaline agent to adjust the pH value, and the second alkaline agent is preferably one or more of sodium hydroxide, sodium carbonate and ammonia water. In the present invention, the pH value adjustment is preferably carried out under stirring. The present invention controls the copper-zinc molar ratio in the second water-soluble copper salt and zinc salt mixed solution to be higher than that in the first water-soluble copper salt and zinc salt mixed solution, in order to achieve a gradient distribution of copper and zinc in the composite oxide (catalyst matrix). The higher copper / zinc molar ratio of the second water-soluble copper salt and zinc salt mixed solution can form a copper-rich region in the outer layer of the composite oxide. This gradient structure can enhance the mechanical strength and thermal stability of the hydrogenation catalyst.

[0037] In the present invention, the precipitation reaction temperature is preferably 25-50° C., more preferably 30-40° C., and the precipitation reaction time is preferably 5-12 h, more preferably 8-10 h.

[0038] After the precipitation reaction, the present invention preferably filters and washes the resulting precipitation reaction product. In the present invention, the drying temperature is preferably 100-150°C, more preferably 100-120°C; the drying time is preferably 5-24 hours, more preferably 5-12 hours. In the present invention, the first calcination temperature is preferably 500-1000°C, more preferably 600-800°C; the first calcination time is preferably 4-12 hours, more preferably 4-6 hours. In the present invention, the first calcination atmosphere is preferably air.

[0039] After obtaining the catalyst substrate, the present invention immerses the catalyst substrate in the water-soluble active metal salt solution. After solid-liquid separation, drying, secondary calcination, and molding are sequentially performed to obtain a hydrogenation catalyst. In the present invention, the immersion temperature is preferably 25-50°C, more preferably 30-40°C, and the immersion time is preferably 5-12 hours, more preferably 8-10 hours.

[0040] In the present invention, the solid-liquid separation method is preferably filtration. After the solid-liquid separation, the present invention preferably washes the obtained solid. In the present invention, the drying temperature is preferably 100-150°C, more preferably 100-120°C; the drying time is preferably 5-24 hours, more preferably 5-12 hours. In the present invention, the temperature of the second calcination is preferably 500-1000°C, more preferably 600-800°C; the time of the second calcination is preferably 4-12 hours, more preferably 4-6 hours. In the present invention, the atmosphere of the second calcination is preferably air.

[0041] In the present invention, prior to the continuous hydrogenation reaction, the hydrogenation catalyst is further reduced. In the present invention, the reducing agent used in the reduction is preferably one or more of hydrogen, carbon monoxide, hydrogen sulfide, sodium borohydride, lithium aluminum hydride, and phosphoric acid, more preferably hydrogen. The present invention activates the hydrogenation catalyst through the reduction.

[0042] In the present invention, when the reducing agent is hydrogen, the hydrogen is preferably injected under normal pressure or micro-pressure, with the micro-pressure preferably being 0.5 to 10 bar, more preferably 1 to 2 bar. In the present invention, the hydrogen is preferably added with or without dilution, with the gas used to dilute the hydrogen being preferably nitrogen or helium. In the present invention, the reduction temperature is preferably 400 to 600°C, specifically 400°C, 500°C, or 600°C, and the reduction time is preferably 1 to 24 hours.

[0043] In the present invention, the o-hydroxyhexanoic acid ester is reacted in the absence of a solvent or dissolved in an organic solvent. In the present invention, the organic solvent is preferably cyclohexane or an alcoholic solvent, and the alcoholic solvent is preferably one or more of methanol, ethanol, propanol, and isopropanol. In the present invention, the concentration of the o-hydroxyhexanoic acid ester in the organic solvent is preferably 10 to 70 wt%, specifically 10 wt%, 30 wt%, 50 wt%, or 70 wt%.

[0044] In the present invention, the o-hydroxyhexanoic acid ester needs to be purified before use. In the present invention, the purification method of the o-hydroxyhexanoic acid ester preferably comprises the following steps: The o-hydroxyhexanoate is sequentially washed with an inorganic alkali aqueous solution, washed with water and distilled.

[0045] In the present invention, the inorganic base is preferably one or more of sodium hydroxide, sodium carbonate, and sodium bicarbonate, more preferably sodium carbonate. In the present invention, the concentration of the inorganic base aqueous solution is preferably 5 to 30 wt%, more preferably 10 to 20 wt%, and more preferably a saturated sodium carbonate solution. In the present invention, the number of washings with the inorganic base aqueous solution is preferably ≥ 1. Since o-hydroxyhexanoic acid ester may contain some acidic impurities, particularly aldehyde impurities, washing with the inorganic base aqueous solution can remove these impurities as much as possible.

[0046] In the present invention, the water wash is preferably performed with deionized water; the water wash is preferably performed three times. In the present 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. The present invention fractionates and refines the raw materials through distillation, and in combination with subsequent continuous hydrogenation and post-treatment steps, can minimize the odor emitted by aldehydes.

[0047] In the present invention, the continuous hydrogenation reaction is preferably carried out in a fixed bed. The present invention adopts a continuous production process and is carried out in a fixed bed. That is, at a specified temperature and pressure, in the presence of a catalyst, o-hydroxyhexanoic acid ester or o-hydroxyhexanoic acid ester and a solvent as required are continuously supplied to a reactor while maintaining a continuous supply of hydrogen. While the material supply reaction is carried out, the product is collected from the discharge port of the fixed bed.

[0048] In the present invention, the temperature of the continuous hydrogenation reaction is 100-200°C, preferably 180-190°C, and the pressure is 16-25 MPa, preferably 20-23 MPa. The present 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 generally increases with increasing temperature, operation within a range of approximately 180-190°C is generally necessary to maximize conversion and utilization of commercial hydrogenation facilities. A particularly attractive feature of the present invention is that the hydrogenation reaction achieves good conversion using hydrogen pressures below 25 MPa, particularly within the range of 20-23 MPa, particularly when combined with a hydrogenation temperature in the range of 180-190°C. Performing the hydrogenation reaction at lower hydrogen pressures can help reduce energy and equipment costs.

[0049] In the present 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. In the present invention, a higher hydrogen-to-ester ratio can provide more hydrogen, promote the complete reaction, and also help reduce the formation of byproducts.

[0050] In the present invention, the space velocity of o-hydroxyhexanoate in the continuous hydrogenation reaction is preferably 80 to 200 h -1 , more preferably 80 h -1 , 100 h -1 , 120 h -1 , 150 h -1 , 180 h -1 or 200 hours -1 .

[0051] In the present invention, after the continuous hydrogenation reaction, the resulting product is preferably subjected to distillation and / or rectification. In the present 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. The present invention significantly improves the purity of 1,2-hexanediol and reduces odor through 3-5 distillation purification operations. If the distillation is performed less than 3 times, it is difficult to obtain a high-purity target product; if the distillation is performed more than 5 times, the purity improvement is limited, and the economic benefits are low.

[0052] In the present invention, the distillation temperature is preferably 120-160° C., more preferably 130-155° C., and the pressure is preferably 2-20 mmHg, more preferably 10-15 mmHg.

[0053] After the continuous hydrogenation reaction, the present invention preferably further comprises recovering and reusing unreacted starting materials, hydrogenation catalyst and organic solvent.

[0054] The preparation method of the low-odor 1,2-hexanediol provided by the present invention is described in detail below with reference to the examples, but they should not be construed as limiting the scope of protection of the present invention.

[0055] Example 1 Preparation of hydrogenation catalyst: Dissolve 190 g of aluminum nitrate nonahydrate in 500 mL of deionized water to obtain a water-soluble aluminum salt solution. Dissolve 420 g of zinc nitrate hexahydrate and 376 g of copper sulfate pentahydrate in 300 mL of deionized water, respectively. Take 55.0 g of the copper sulfate pentahydrate solution and 550.0 g of the zinc nitrate hexahydrate solution, respectively, and mix them to obtain a first water-soluble copper salt zinc salt mixed solution (copper:zinc molar ratio of 0.11:1). The remaining solutions are mixed to obtain a second water-soluble copper salt zinc salt mixed solution (copper:zinc molar ratio of 4.18:1, and the copper atomic molar ratio between the first water-soluble copper salt zinc salt mixed solution and the second water-soluble copper salt zinc salt mixed solution is 1:11.5). The water-soluble aluminum salt solution and the first water-soluble copper salt zinc salt mixed solution are mixed, and sodium hydroxide solution is added under stirring to adjust the pH to 7 to obtain a premixed solution. A second portion of the water-soluble copper and zinc salt mixture was then 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 an air atmosphere 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 immersed for 24 h. The solution was filtered, washed, dried at 120°C, and calcined at 500°C for 4 h in an air atmosphere to obtain the hydrogenation catalyst.

[0056] Preparation of low-odor 1,2-hexanediol: First, methyl o-hydroxyhexanoate was washed with a saturated sodium carbonate solution, allowed to stand and separate, and the organic phase was washed three times with water to maintain a pH of 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 filled into a fixed bed, 5% H2 / Ar gas was introduced, and the temperature was raised to 500°C at a rate of 10°C / min. Activation was carried out at this temperature for 3 h. The treated methyl o-hydroxyhexanoate was 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 was 22 MPa, and the hydrogen / catalyst volume space velocity was 114 h / min. -1 The reaction continued with a hydrogen-to-ester ratio of 483.3:1. The collected product was subjected to steam distillation in an atmospheric distillation tower at 115°C. It was then purified by adsorption using activated carbon and then subjected to rectification at 10 mmHg and 130°C. The collected fractions were then distilled three times. Sampling was performed throughout the process using gas chromatography (GC). The reaction test data are listed in Table 1.

[0057] Examples 2 to 10 The hydrogenation catalyst was prepared according to the method of Example 1. The preparation methods of 1,2-hexanediol in Examples 2 to 10 refer to Example 1. The specific reaction conditions and reaction results are shown in Table 1.

[0058] Table 1 Reaction conditions and reaction results of Examples 1 to 10

[0059] Example 11 Preparation of hydrogenation catalyst: Dissolve 190 g of aluminum nitrate nonahydrate in 500 mL of deionized water to obtain a water-soluble aluminum salt solution. Dissolve 400 g of zinc nitrate hexahydrate and 420 g of copper sulfate pentahydrate in 300 mL of deionized water, respectively. 55.0 g and 550.0 g of the copper sulfate pentahydrate and zinc nitrate hexahydrate solutions, respectively, are mixed to obtain a first water-soluble copper salt zinc salt mixed solution (copper:zinc molar ratio of 0.12:1). The remaining solutions are mixed to obtain a second water-soluble copper salt zinc salt mixed solution (copper:zinc molar ratio of 5.34:1, and the copper atomic molar ratio of the first water-soluble copper salt zinc salt mixed solution to the second water-soluble copper salt zinc salt mixed solution is 1:11.92). The water-soluble aluminum salt solution and the first water-soluble copper salt zinc salt mixed solution are mixed, and sodium hydroxide solution is added under stirring to adjust the pH to 7 to obtain a premixed solution. A second portion of the water-soluble copper and zinc salt mixture was then 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 an air atmosphere 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 immersed for 24 h. The solution was filtered, washed, dried at 120°C, and calcined at 500°C for 4 h in an air atmosphere to obtain the hydrogenation catalyst.

[0060] The preparation of low-odor 1,2-hexanediol was carried out as described in Example 1. The specific reaction conditions and reaction results are shown in Table 2.

[0061] Examples 12 to 15 The hydrogenation catalyst was prepared according to the method of Example 11. The preparation method of 1,2-hexanediol in Examples 12 to 15 refers to Example 11. The specific reaction conditions are shown in Table 2, and the reaction results are shown in Table 2.

[0062] Table 2 Reaction conditions and reaction results of Examples 11 to 15

[0063] Example 16 Preparation of hydrogenation catalyst: Dissolve 190 g of aluminum nitrate nonahydrate in 500 mL of deionized water to obtain a water-soluble aluminum salt solution. Dissolve 410 g of zinc nitrate hexahydrate and 460 g of copper sulfate pentahydrate in 300 mL of deionized water, respectively. 55.0 g and 550.0 g of the copper sulfate pentahydrate and zinc nitrate hexahydrate solutions, respectively, are mixed to obtain a first water-soluble copper salt zinc salt mixed solution (copper:zinc molar ratio of 0.12:1). The remaining solutions are mixed to obtain a second water-soluble copper salt zinc salt mixed solution (copper:zinc molar ratio of 5.51:1, and the copper atomic molar ratio between the first water-soluble copper salt zinc salt mixed solution and the second water-soluble copper salt zinc salt mixed solution is 1:13.15). The water-soluble aluminum salt solution and the first water-soluble copper salt zinc salt mixed solution are mixed, and sodium hydroxide solution is added under stirring to adjust the pH to 7 to obtain a premixed solution. A second portion of the water-soluble copper and zinc salt mixture was then 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 an air atmosphere 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 immersed for 24 h. The solution was filtered, washed, dried at 120°C, and calcined at 500°C for 4 h in an air atmosphere to obtain the hydrogenation catalyst.

[0064] The preparation of low-odor 1,2-hexanediol was carried out as described in Example 1. The specific reaction conditions and reaction results are shown in Table 3.

[0065] Examples 17-20 The hydrogenation catalyst was prepared according to the method of Example 16. The preparation method of 1,2-hexanediol in Examples 17 to 20 refers to Example 16. The specific reaction conditions and reaction results are shown in Table 3.

[0066] Table 3 Reaction conditions and reaction results of Examples 16 to 20

[0067] Comparative Example 1 100 g of commercially available ordinary Cu-Zn / Al catalyst (copper, zinc, and aluminum molar ratio of 2.36:1:1.25) was filled into a fixed bed, and 5% H2 / Ar gas was introduced. The temperature was raised to 500°C at a rate of 10°C / min and activated at this temperature for 3 h. Methyl o-hydroxyhexanoate was directly introduced into the fixed bed at a rate of 0.3 mL / min. The reaction temperature was controlled at 160°C, the hydrogen pressure was 22 MPa, and the hydrogen / catalyst volume space velocity was 114 h / min. -1The reaction continued. The collected product was subjected to steam distillation in an atmospheric distillation tower at 115°C. It was then purified by adsorption using activated carbon and then subjected to rectification at 10 mmHg and 130°C. The collected fractions were then distilled three times. Sampling and testing were performed throughout the process using gas chromatography (GC). The reaction test data are listed in Table 4.

[0068] Comparative Example 2 100 g of the catalyst prepared in Example 1 was filled into a fixed bed, and 5% H2 / Ar gas was introduced. The temperature was raised to 500°C at a rate of 10°C / min and activated at this temperature for 3 h. Methyl o-hydroxyhexanoate was directly introduced into the fixed bed at a rate of 0.3 mL / min. The reaction temperature was controlled at 220°C, the hydrogen pressure was 22 MPa, and the hydrogen / catalyst volume space velocity was 114 h / min. -1 The reaction continued. The collected product was subjected to steam distillation in an atmospheric distillation tower at 115°C. It was then purified by adsorption using activated carbon and then subjected to rectification at 10 mmHg and 130°C. The collected fractions were then distilled three times. Sampling and testing were performed throughout the process using gas chromatography (GC). The reaction test data are listed in Table 4.

[0069] Comparative Examples 3-4 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 refers to Comparative Example 2. The specific reaction conditions and reaction results are shown in Table 4.

[0070] Table 4 Reaction conditions and reaction results of Comparative Examples 1 to 4

[0071] The 1,2-hexanediol prepared in Examples 3 and 14 and Comparative Examples 1 and 2 was subjected to an odor test by 20 participants. The odor test results are shown in Table 5.

[0072] Table 5 Odor test results

[0073] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing low-odor 1,2-hexanediol, characterized in that: The following steps are involved: Using purified o-hydroxyhexanoic acid ester as raw material, a continuous hydrogenation reaction is carried out with hydrogen in the presence of a hydrogenation catalyst to obtain low-odor 1,2-hexanediol. The o-hydroxyhexanoate has a structure shown in Formula 1: Formula 1; In Formula 1, R represents an alkyl group having 1 to 30 carbon atoms; The hydrogenation catalyst comprises a catalyst substrate and a catalyst promoter supported on the surface and interior of the catalyst substrate, wherein the components of the catalyst substrate include copper oxide, zinc oxide and aluminum oxide, and the components of the catalyst promoter include active metals and / or active metal oxides; The temperature of the continuous hydrogenation reaction is 100-200° C., and the pressure is 16-25 MPa.

2. The preparation method according to claim 1, characterized in that 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, the copper oxide accounts for 35-55 wt %, the zinc oxide accounts for 35-55 wt %, and the aluminum oxide accounts for 8-25 wt % by weight; The active metal includes one or more of Mn, Ce, Ni, Sn, Co, Ba, Ca, Se, Pt, Pd and Re.

3. The preparation method according to claim 1 or 2, characterized in that The preparation method of the hydrogenation catalyst comprises the following steps: Providing a water-soluble aluminum salt solution, a first water-soluble copper salt and zinc salt mixed solution, a second water-soluble copper salt and zinc salt mixed solution, and a water-soluble active metal salt solution; wherein the copper-zinc molar ratio in the second water-soluble copper salt and zinc salt mixed solution is higher than that in the first water-soluble copper salt and zinc salt mixed solution; Mixing the water-soluble aluminum salt solution with the first portion of the water-soluble copper salt and zinc salt mixed solution, and then adjusting the pH value to 7 to obtain a premixed solution; The premixed solution is mixed with a second portion of a water-soluble copper salt and zinc salt mixed solution, and then the pH value is adjusted to 7 to perform a precipitation reaction, and the obtained precipitate is dried and first calcined to obtain a catalyst matrix; The catalyst matrix is ​​immersed in the water-soluble active metal salt solution, and after solid-liquid separation, drying, second calcination and molding are carried out in sequence to obtain a hydrogenation catalyst.

4. The preparation method according to claim 3, characterized in that The molar ratio of copper to zinc in the first water-soluble copper salt and zinc salt mixed solution is 0.1 to 0.2:1; The molar ratio of copper to zinc in the second water-soluble copper salt and zinc salt mixed solution is 4 to 10:1; The molar ratio of copper atoms in the first water-soluble copper salt and zinc salt mixed solution to the second water-soluble copper salt and zinc salt mixed solution is 1:2-20.

5. The preparation method according to claim 1, characterized in that The o-hydroxyhexanoic acid ester is reacted in a solvent-free state or dissolved in an organic solvent for reaction.

6. The preparation method according to claim 1, characterized in that The continuous hydrogenation reaction is carried out in a fixed bed; The molar ratio of hydrogen to o-hydroxyhexanoate in the continuous hydrogenation reaction is 1000-100:

1.

7. The preparation method according to claim 1 or 6, characterized in that The space velocity of o-hydroxyhexanoate in the continuous hydrogenation reaction is 80-200 h -1 .

8. The preparation method according to claim 1, characterized in that The purification method of o-hydroxyhexanoate comprises the following steps: The o-hydroxyhexanoate is sequentially washed with an inorganic alkali aqueous solution, washed with water and distilled.

9. The preparation method according to claim 1, characterized in that Before the continuous hydrogenation reaction, the method further comprises: reducing the hydrogenation catalyst.

10. The preparation method according to claim 1, characterized in that After the continuous hydrogenation reaction, the obtained product is distilled and / or rectified; The distillation temperature is 110-120° C., and the number of distillations is 3-5 times; The distillation temperature is 120-160° C., and the pressure is 2-20 mmHg.

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