A method for effectively improving the purity of linalool product

Abstract

This invention provides a method for effectively improving the purity of linalool products. A catalyst is added to the reaction solution of dehydrolinalool selectively hydrogenated to produce linalool. This catalyst catalyzes the incomplete conversion of the dehydrolinalool feedstock to undergo an isomerization reaction, generating 3,7-dimethyl-3,6-octadien-2-one and citral, whose boiling points differ significantly from linalool. These are then separated. In the selective hydrogenation of dehydrolinalool to produce linalool, a small amount of dehydrolinalool feedstock remains in the resulting hydrogenation reaction solution. Because dehydrolinalool and linalool have very similar boiling points and are prone to self-cyclization reactions, generating cyclized impurities with similar boiling points to linalool, the distillation purification of linalool suffers from drawbacks such as high plate number, large reflux ratio, and significant product loss. This invention uses a method of adding a small amount of catalyst to the reaction solution to catalyze the isomerization of residual dehydrolinalool into high-boiling-point impurities such as citral. Compared to the traditional distillation process, this invention effectively reduces distillation energy consumption and product loss, obtaining higher purity linalool products at a lower separation cost.

Description

Technical Field

[0001] This invention belongs to the fields of fine chemicals and fragrances, specifically relating to a method for adding a small amount of catalyst to a reaction solution for the selective hydrogenation of dehydrolinalool to prepare linalool, thereby catalyzing the incompletely converted dehydrolinalool to isomerize into impurities with significantly different boiling points from linalool in the bottom of a distillation column, thus achieving efficient separation of dehydrolinalool-related impurities and improving the purity of linalool products. Background Technology

[0002] Linalool is a colorless, oily liquid at room temperature, insoluble in water, but miscible with common solvents such as ethanol, ether, ethyl acetate, and tetrahydrofuran. Linalool has a sweet, typical floral and woody aroma, and also a fresh lily scent. It can be used to formulate various floral fragrances such as lily, orange blossom, lilac, lavender, and rose. Besides floral fragrances, linalool can also be used in non-floral fragrances such as fruity, fresh, woody, aldehyde, oriental, and amber scents. It can also be used to formulate artificial essential oils such as orange leaf, bergamot, lavender, and mixed lavender oils. Furthermore, it is used in perfumes, daily chemical products, personal care products, and food products. According to relevant statistics, linalool is one of the most frequently used fragrance ingredients in perfume and daily chemical formulations.

[0003] Linalool from different sources has slightly different aromas. Natural linalool isolated from essential oils is generally more light and pronounced, but often not a single fragrance; while synthetic linalool has higher purity, a simpler composition, and its aroma is generally purer. The aromas of natural linalool from different plants also vary. Linalool isolated from rosewood oil has a light, sweet, woody aroma; linalool isolated from magnolia leaf oil has a floral note, possibly due to trace amounts of floral components; linalool isolated from camphor oil often has traces of camphor and other aromas, and its fragrance is relatively weaker. Besides being used directly as a fragrance ingredient, linalool is also an important synthetic intermediate, used to synthesize various other fragrance products, such as nerolidol, tetrahydrolinalool, and linalyl acetate. Linalool is also a key intermediate in the synthesis of tocopherol and tocopheryl acetate.

[0004]

[0005] As shown above, selective triple bond hydrogenation of dehydrolinalool can easily yield linalool. This reaction generally uses a Lindela catalyst. The main side reaction is the further hydrogenation of linalool to form dihydrolinalool. Excessive dihydrolinalool will reduce the product yield; therefore, in actual reactions, it is necessary to terminate the reaction in a timely manner. In addition to the main product linalool, the main impurity in the reaction solution is a small amount of residual dehydrolinalool. Dehydrolinalool has a boiling point of 198.0℃, while linalool has a boiling point of 196.3℃. Their boiling points are very close, making distillation separation extremely difficult. Moreover, dehydrolinalool will undergo an intramolecular cyclization reaction under heating conditions, generating a five-membered cyclic alcohol byproduct. The boiling point of this byproduct is also close to that of linalool, further increasing the difficulty of linalool purification. Therefore, current distillation purification of linalool requires a very high number of trays and a high reflux ratio, resulting in significant material loss and high energy consumption.

[0006]

[0007] In summary, linalool is an important fragrance product that can be obtained by selective hydrogenation of dehydrolinalool. However, dehydrolinalool is generally not completely converted during the reaction, resulting in a small amount of dehydrolinalool residue in the product liquid. Because dehydrolinalool and linalool have similar boiling points, and cyclization side reactions occur during distillation, generating cyclization byproducts, the distillation separation of linalool requires a high number of plates, leading to significant product loss and high energy consumption. Therefore, there is a need to develop new distillation purification methods for linalool to improve its distillation yield and reduce energy consumption. Summary of the Invention

[0008] The purpose of this invention is to provide a method for effectively improving the purity of linalool products. By adding a small amount of catalyst to the hydrogenation reaction solution of dehydrolinalool, the residual dehydrolinalool is catalyzed into more easily separable impurities, thereby improving the purity of the linalool product. This invention is novel in its approach, converting the difficult-to-separate dehydrolinalool into easily separable citral and 3,7-dimethyl-3,6-octadien-2-one, and completing the conversion during distillation. The method has advantages such as simple operation, mild conditions, and low catalyst usage, and has good potential application value.

[0009] To achieve the above objectives and technical effects, the present invention adopts the following technical solution:

[0010] A method for effectively improving the purity of linalool products is as follows: a catalyst is added to the reaction solution for the selective hydrogenation of dehydrolinalool to prepare linalool, catalyzing the incompletely converted dehydrolinalool raw material to undergo an isomerization reaction, generating 3,7-dimethyl-3,6-octadien-2-one and citral, which have boiling points that differ significantly from linalool, thereby achieving efficient separation and effectively improving the purity of linalool products.

[0011] The reaction route is shown below:

[0012]

[0013] In this invention, the content of the raw material dehydrolinalool in the selective hydrogenation reaction solution of dehydrolinalool is 0.05-0.5 wt%.

[0014] In this invention, the catalyst is composed of a metal catalyst and an acid catalyst; the metal catalyst is obtained by in-situ complexation of a metal salt and a ligand, and the metal salt may be, but is not limited to, gold salt, copper salt, silver salt, etc. Preferably, the metal salt is gold chloride, gold bromide, chlorocarbonyl gold, tetrachloroauric acid, dimethyl (acetylacetone) gold, dimethyl (trifluoroacetylacetone) gold, triphenylphosphine chloride gold, silver tetrafluoroborate, silver trifluoromethanesulfonate, silver bis(trifluoromethanesulfonyl)imide, silver bis(trifluoromethanesulfonyl)imide, silver hexafluorophosphate, cuprous tetrafluoroborate, copper tetrafluoroborate, ketone trifluoromethanesulfonate, copper bis(trifluoromethanesulfonyl)imide, copper chloride, cuprous chloride, etc. The amount of the metal salt is 0.001-0.01 wt% of the reaction solution mass;

[0015] In this invention, the ligand can be, but is not limited to, phosphine ligands, nitrogen-phosphorus ligands, pyridine ligands, sulfur ligands, etc. Preferably, the ligand is triphenylphosphine, tris(3-methylphenyl)phosphine, tris(4-methylphenyl)phosphine, 1,2-diphenylphosphinoethane, 1,3-diphenylphosphinopropane, 1,4-diphenylphosphinobutane, 1,8-bis(diphenylphosphine)naphthalene, tributylphosphine, tricyclohexylphosphine, tricyclopentylphosphine, 2-(diadamantylphosphine)biphenyl, 1-[2-di-tert-butylphosphinophenyl]-3,5-diphenyl-1-Hpyrazole, etc., and the amount of the ligand is 0.002-0.02 wt% of the reaction solution mass.

[0016] In this invention, the acid catalyst may be, but is not limited to, benzenesulfonic acid, p-methylbenzenesulfonic acid, p-chlorobenzenesulfonic acid, p-bromobenzenesulfonic acid, naphthalenesulfonic acid, methanesulfonic acid, ethanesulfonic acid, 2-butylsulfonic acid, fluorosulfonic acid, 2-iodobenzenesulfonic acid, benzylsulfonic acid, cresolsulfonic acid, methylbenzylmethanesulfonic acid, hexylsulfonic acid, and 2-(N-morpholine)ethanesulfonic acid. Preferably, the amount of the acid catalyst is 0.002-0.02 wt% of the reaction solution mass.

[0017] In this invention, the metal salt, ligand, and acid catalyst are simultaneously added to the selective hydrogenation reaction solution of dehydrolinalool.

[0018] Optionally, this invention includes a step of separating and recovering the solvent from the selective hydrogenation reaction solution of dehydrolinalool before the catalytic isomerization reaction, preferably by vacuum distillation.

[0019] In this invention, the temperature of the catalytic isomerization reaction is 90-120℃, and the reaction time is 2-6 hours.

[0020] In this invention, the impurities generated by the catalytic isomerization of dehydrolinalool and the isomerization catalyst are ultimately distributed in the heavy components in the bottom of the deheavy column and discharged from the distillation system along with the heavy components, thereby achieving separation from the product linalool.

[0021] The present invention, by adopting the above technical solution, has the following positive effects:

[0022] 1. This invention has a novel approach: adding a catalyst to the hydrogenation reaction solution converts the residual dehydrolinalool into high-boiling-point impurities, thereby reducing the number of trays and energy consumption in the distillation separation of linalool and effectively improving the purity of the linalool product.

[0023] 2. This invention employs a synergistic catalysis of metal catalyst and acid catalyst to efficiently convert residual dehydrolinalool in the reaction solution. Detailed Implementation

[0024] The present invention is described in detail below through embodiments, but the present invention is not limited to the embodiments described below.

[0025] The main raw material information is as follows:

[0026] Dehydrolinalool, 98% purity, Aladdin reagent; 5% palladium calcium carbonate, Inokai; 1% palladium calcium carbonate, Evonik catalyst; Methanol, ethanol, reagent grade, Bailingwei reagent, 99% purity; Gold chloride, silver tetrafluoroborate, silver bis(fluorosulfonyl)imide, dimethyl (acetylacetone) gold, Alfa Esa, 99% purity; Triphenylphosphine gold chloride, silver hexafluorophosphate, 99% purity, Aldrich reagent; Bis(trifluoromethanesulfonyl)copper, triphenylphosphine, tricyclohexylphosphine, 99% purity, Bailingwei reagent; 2-(bisadamantylphosphine)biphenyl, 1,4-diphenylphosphinobutane, 1-[2-bis-tert-butylphosphinophenyl]-3,5-diphenyl-1-Hpyrazole, 98% purity, Xinnoco catalyst;

[0027] p-Toluenesulfonic acid, p-chlorobenzenesulfonic acid, and cresolsulfonic acid, 99% purity, Aladdin Reagent; methanesulfonic acid, 99% purity, Sinopharm Reagent; 2-(N-morpholine)ethanesulfonic acid, 99% purity, Maclean Reagent. Linalool standard and citral standard, 99% purity, Mairui Biochemical Technology.

[0028] The gas chromatography test conditions of this invention are as follows:

[0029] Instrument model: Agilent 8890B; Column: HP-5 capillary column (30m × 0.30mm × 0.25μm); Initial temperature 60℃, increased to 110℃ at a rate of 5℃ / min; then increased to 170℃ at a rate of 10℃ / min and held for 5.0 min. Carrier gas: high-purity nitrogen, split ratio 35:1, split flow rate 42mL / min. Carrier gas saving: 19mL / min, initial waiting time 5.0 min. Injection temperature 250℃, detector: FID, detector temperature 250℃, air flow rate 350mL / min, hydrogen flow rate 30mL / min, make-up gas flow rate 60mL / min, injection volume 0.1μL.

[0030] Example 1:

[0031] Selective hydrogenation of dehydrolinalool to prepare linalool

[0032] At room temperature, methanol (441g), dehydrolinalool (883g, 5.8mol), and 5.0% Lindela catalyst (4.4g, 0.5wt% of substrate mass) were sequentially added to a 2L autoclave. The autoclave was sealed and pressure-tested for leaks for 30 minutes. After confirming no issues, the air inside the autoclave was purged three times with nitrogen, followed by three purgings with hydrogen. Finally, 5 barG of hydrogen was introduced. The autoclave was then stirred and kept at a constant temperature. The internal cooling coils and stirring shaft were also activated to maintain the temperature at 30°C. The reaction was carried out for 3 hours, with periodic sampling and analysis, and GC monitoring of the reaction progress. When the conversion rate of dehydrolinalool reached or exceeded 99.5%, the stirring and hydrogen feed were promptly shut off, and the hydrogen was slowly vented using the venting method. The hydrogen gas was replaced with nitrogen three times, and then the reaction solution was forced out of the reaction vessel through a filter using nitrogen. The reaction solution was then analyzed by GC again. The main components of the reaction solution were as follows (solvent peaks removed, area normalized): methyl heptenone 0.27%, dehydrolinalool 0.32%, linalool 95.54%, dihydrolinalool 1.46%, and heavy components 2.41%.

[0033] Example 2:

[0034] Selective hydrogenation of dehydrolinalool to prepare linalool

[0035] At room temperature, ethanol (1157 g), dehydrolinalool (1157 g, 7.6 mol), and 1.0% Lindela catalyst (9.3 g, 0.8 wt% of substrate) were sequentially added to a 5 L autoclave. The autoclave was sealed, and after a 30-minute pressure test to ensure no leaks, the air inside the autoclave was purged three times with nitrogen, followed by three purgings with hydrogen. Finally, 10 barG of hydrogen was introduced. The autoclave was then stirred and kept at a constant temperature. The internal cooling coils and stirring shaft were also activated to maintain the temperature at 50°C. The reaction was carried out for 4 hours, with periodic sampling and analysis, and GC monitoring of the reaction progress. When the conversion rate of dehydrolinalool reached or exceeded 99.5%, the stirring and hydrogen feed were promptly shut off, and the hydrogen was slowly vented using the venting method. The hydrogen gas was replaced with nitrogen three times, and then the reaction solution was forced out of the reaction vessel through a filter using nitrogen. The reaction solution was then analyzed by GC again. The main components of the reaction solution were as follows (solvent peaks removed, area normalized): methyl heptenone 0.26%, dehydrolinalool 0.43%, linalool 95.63%, dihydrolinalool 1.36%, and heavy components 2.32%.

[0036] Example 3:

[0037] The selective hydrogenation reaction solution of dehydrolinalool was purified from the reaction solution obtained in Example 1.

[0038] First, the solvent was separated and recovered by vacuum distillation at a temperature of 71-73℃ and a pressure of 60 kPa. After 1 hour of distillation, no product was collected from the condenser at the flask neck, and the methanol content in the reaction solution after vacuum distillation was less than 0.1%. At room temperature, the solvent-removed dehydrolinalool selective hydrogenation reaction solution (206.0 g), gold chloride (2.1 mg), silver tetrafluoroborate (2.1 mg), and triphenylphosphine (4.1 mg) were added sequentially to a 2L three-necked flask equipped with a magnetic stirrer, and finally p-toluenesulfonic acid (4.1 mg). After all materials were added, a 1-m long distillation column and a reflux ratio controller were connected above the 2L three-necked flask. The column was filled with 3*3 three-legged spiral packing, and the total number of trays was ~30. The three-necked flask was placed in an oil bath, and the oil bath stirring and heating were turned on. The stirring was controlled at 600 rpm, and the oil bath temperature was controlled at 120℃, so that the temperature inside the three-necked flask was maintained at 100℃. Turn on the overhead condensate and vacuum systems, controlling the condensation temperature at 5°C and the overhead pressure at 1 kPa. Once the temperature and pressure at the top and bottom of the column stabilize, and stable reflux begins at the top, turn on the reflux ratio controller. The reflux ratio at the top should be 5–7:1. The light components and product are collected after being liquefied by cooling in the overhead condenser. The initial condensation temperature of the light components at the top is approximately 90°C, and the residence time of the material in the bottom of the column is 3 hours. Samples of the overhead product are taken periodically for GC analysis of the sample composition. The results are shown below. Under the above conditions, the composition of linalool obtained by top distillation is as follows: methyl heptenone (0.290%), dehydrolinalool + 3,7-dimethyl 3,6-octadien-2-one (0.007%), linalool (98.324%), dihydrolinalool (1.327%), and heavy components (0.053%). Among them, the sum of linalool and dihydrolinalool is 99.651%, reaching the level of superior grade, with a distillation yield of 91.3%. The composition of the bottom distillation is as follows: methyl heptenone (0.062%), citral and 3,7-dimethyl 3,6-octadien-2-one (3.621%), linalool (66.183%), dihydrolinalool (2.866%), and heavy components (27.268%).

[0039] Example 4:

[0040] The selective hydrogenation reaction solution of dehydrolinalool was purified from the reaction solution obtained in Example 1.

[0041] First, the solvent was separated and recovered by vacuum distillation at 71-73℃ and 60kPa. After 1 hour of distillation, no product was collected from the condenser at the flask neck, and the methanol content in the reaction solution after vacuum distillation was less than 0.05%. At room temperature, the solvent-removed dehydrolinalool selective hydrogenation reaction solution (238.0g), dimethyl (acetylacetone) gold (23.8mg), and 2-(diadamantylphosphine) biphenyl (47.6mg) were added sequentially to a 2L three-necked flask equipped with a magnetic stirrer, followed by p-chlorobenzenesulfonic acid (47.6mg). After all materials were added, a 1m long distillation column and reflux ratio controller were connected above the 2L three-necked flask. The column was filled with 3*3 triangular spiral packing, with a total number of trays of approximately 30. The three-necked flask was placed in an oil bath, and the oil bath stirring and heating were turned on. The stirring was controlled at 600rpm, and the oil bath temperature was controlled at approximately 103℃, maintaining the temperature inside the three-necked flask at 95℃. Turn on the overhead condensate and vacuum systems, controlling the condensation temperature at 5°C and the overhead pressure at 0.7 kPa. Once the temperature and pressure at the top and bottom of the column have stabilized, and stable reflux has begun, turn on the reflux ratio controller. The reflux ratio at the top of the column should be 5–7:1. The light components and product are collected after being liquefied by cooling in the overhead condenser. The initial condensation temperature of the light components at the top of the column is approximately 83°C, and the residence time of the material in the bottom of the column is 1 hour. Samples of the overhead product are taken periodically for GC analysis of the sample composition. The results are shown below. Under the above conditions, the composition of linalool obtained by top distillation is as follows: methyl heptenone (0.281%), dehydrolinalool + 3,7-dimethyl 3,6-octadien-2-one (0.003%), linalool (98.436%), dihydrolinalool (1.254%), and heavy components (0.026%). Among them, the sum of linalool and dihydrolinalool is 99.690%, reaching the level of superior grade, with a distillation yield of 93.2%. The composition of the bottom distillation is as follows: methyl heptenone (0.119%), citral and 3,7-dimethyl 3,6-octadien-2-one (4.642%), linalool (56.000%), dihydrolinalool (4.279%), and heavy components (34.960%).

[0042] Example 5:

[0043] The selective hydrogenation reaction solution of dehydrolinalool was purified from the reaction solution obtained in Example 1.

[0044] First, the solvent was recovered by vacuum distillation at 71-73℃ and 60kPa. After 1 hour of distillation, no product was collected from the condenser at the flask neck, and the methanol content in the reaction solution after vacuum distillation was less than 0.05%. At room temperature, the solvent-removed dehydrolinalool selective hydrogenation reaction solution (387.0g), silver bis(fluorosulfonyl)imide (19.4mg), and 1,4-diphenylphosphine butane (38.7mg) were added sequentially to a 2L three-necked flask equipped with a magnetic stirrer, followed by p-methanesulfonic acid (77.4mg). After all materials were added, a 1m long distillation column and reflux ratio controller were connected above the 2L three-necked flask. The column was filled with 3*3 triangular spiral packing, with a total number of trays of approximately 30. The three-necked flask was placed in an oil bath, and the oil bath was stirred and heated. The stirring speed was controlled at 600rpm, and the oil bath temperature was controlled at approximately 125℃, maintaining the temperature inside the three-necked flask at 110℃. Turn on the overhead condensate and vacuum systems, controlling the condensation temperature at 5°C and the overhead pressure at 1 kPa. Once the temperature and pressure at the top and bottom of the column have stabilized, and stable reflux has begun, turn on the reflux ratio controller. The reflux ratio at the top should be 5–7:1. The light components and product are collected after being liquefied by cooling in the overhead condenser. The initial condensation temperature of the light components at the top is approximately 90°C, and the residence time of the material in the bottom of the column is 6 hours. Samples of the overhead product are taken periodically for GC analysis of the sample composition. The results are shown below. Under the above conditions, the composition of linalool obtained by top distillation is as follows: methyl heptenone (0.286%), dehydrolinalool + 3,7-dimethyl 3,6-octadien-2-one (0.017%), linalool (98.238%), dihydrolinalool (1.407%), and heavy components (0.052%). Among them, the sum of linalool and dihydrolinalool is 99.645%, reaching the level of superior grade, with a distillation yield of 93.4%. The composition of the bottom distillation is as follows: methyl heptenone (0.041%), citral and 3,7-dimethyl 3,6-octadien-2-one (4.581%), linalool (57.588%), dihydrolinalool (2.200%), and heavy components (35.590%).

[0045] Example 6:

[0046] The selective hydrogenation reaction solution of dehydrolinalool was purified from the reaction solution obtained in Example 2.

[0047] First, the solvent was separated and recovered by vacuum distillation at 71-73℃ and 60kPa. After 1 hour of distillation, no product was collected from the condenser at the flask neck, and the ethanol content in the reaction solution after vacuum distillation was less than 0.05%. At room temperature, the solvent-removed dehydrolinalool selective hydrogenation reaction solution (483.0g), bis(trifluoromethanesulfonylimide) copper (48.3mg), and tricyclohexylphosphine (58.0mg) were added sequentially to a 2L three-necked flask equipped with a magnetic stirrer. Finally, 2-(N-morpholine)ethanesulfonic acid (72.5mg) was added. After all materials were added, a 1m long distillation column and a reflux ratio controller were connected above the 2L three-necked flask. The column was filled with 3*3 three-legged spiral packing, with a total number of trays of approximately 30. The three-necked flask was placed in an oil bath, and the oil bath stirring and heating were turned on. The stirring was controlled at 600rpm, and the oil bath temperature was controlled at 120℃, maintaining the temperature inside the three-necked flask at 100℃. Turn on the overhead condensate and vacuum system, controlling the condensation temperature at 5℃ and the overhead pressure at 1 kPa. Once the temperature and pressure at the top and bottom of the column stabilize, and stable reflux begins at the top, turn on the reflux ratio controller. The overhead reflux ratio is 2–5:1. The light components and product are collected after liquefaction through the overhead condenser. The initial condensation temperature of the light components at the top is approximately 90℃, and the residence time of the material in the bottom is 3 hours. Samples of the overhead product are taken periodically for GC analysis. The results are shown below. Under the above conditions, the linalool obtained from the overhead distillation has the following composition: methyl heptenone (0.278%), dehydrolinalool (0.009%), linalool (98.509%), dihydrolinalool (1.170%), and heavy components (0.044%). The sum of linalool and dihydrolinalool is 99.679%, reaching the superior grade level, with a distillation yield of 94.2%. The composition of the column bottom is as follows: methyl heptenone (0.134%), dehydrolinalool + citral and 3,7-dimethyl 3,6-octadien-2-one (7.222%), linalool (49.169%), dihydrolinalool (4.429%), and heavy components (39.046%).

[0048] Example 7:

[0049] The selective hydrogenation reaction solution of dehydrolinalool was purified from the reaction solution obtained in Example 2.

[0050] First, the solvent was separated and recovered by vacuum distillation at 71-73℃ and 60kPa. After 1 hour of distillation, no product was collected from the condenser at the flask neck, and the ethanol content in the reaction solution after vacuum distillation was less than 0.05%. At room temperature, the solvent-removed dehydrolinalool selective hydrogenation reaction solution (519.0g), triphenylphosphine chloride (5.2mg), silver hexafluorophosphate (7.8mg), and 1-[2-di-tert-butylphosphinophenyl]-3,5-diphenyl-1-H-pyrazole (15.6mg) were added sequentially to a 2L three-necked flask equipped with a magnetic stirrer. Finally, cresolsulfonic acid (51.9mg) was added. After all materials were added, a 1m long distillation column and a reflux ratio controller were connected above the 2L three-necked flask. The column was filled with 3*3 tri-legged spiral packing, and the total number of trays was ~30. Place the three-necked flask in an oil bath, turn on the oil bath stirring and heating, controlling the stirring at 600 rpm and the oil bath temperature at approximately 120℃, so that the temperature inside the three-necked flask is maintained at 100℃. Turn on the overhead condensate and vacuum system, controlling the condensation temperature at 5℃ and the overhead pressure at 1 kPa. After the temperature and pressure at the top and bottom of the column stabilize, and after the reflux at the top of the column begins to stabilize, turn on the reflux ratio controller, with a reflux ratio of 1 to 5:1. The light components and products are collected after being cooled and liquefied by the overhead condenser. The initial temperature of the light components at the top of the column is approximately 90℃, and the residence time of the material in the bottom of the column is 2 hours. Sample the liquid collected from the top of the column at regular intervals, and perform GC analysis on the sample composition. The results are shown below. Under the above conditions, the composition of linalool obtained by top distillation is as follows: methyl heptenone (0.274%), dehydrolinalool + 3,7-dimethyl 3,6-octadien-2-one (0.008%), linalool (98.522%), dihydrolinalool (1.145%), and heavy components (0.049%). Among them, the sum of linalool and dihydrolinalool is 99.667%, reaching the level of superior grade, with a distillation yield of 93.9%. The composition of the bottom distillation is as follows: methyl heptenone (0.042%), citral and 3,7-dimethyl 3,6-octadien-2-one (6.864%), linalool (51.406%), dihydrolinalool (4.652%), and heavy components (37.035%).

[0051] Comparative Example

[0052] The selective hydrogenation reaction solution of dehydrolinalool was purified without the addition of an isomerizing catalyst. The reaction solution was derived from Example 2.

[0053] First, the solvent was recovered by vacuum distillation at 71-73℃ and 60kPa. After 1 hour of distillation, no product was collected from the condenser at the flask neck, and the ethanol content in the reaction solution after vacuum distillation was less than 0.05%. At room temperature, 519.0g of the desolventized dehydrolinalool selective hydrogenation reaction solution was added sequentially to a 2L three-necked flask equipped with a magnetic stirrer. After the addition was complete, a 1m long rectification column and a reflux ratio controller were connected above the 2L three-necked flask. The column was filled with 3*3 triangular spiral packing, with a total number of trays of approximately 30. The three-necked flask was placed in an oil bath, and the oil bath stirring and heating were turned on. The stirring was controlled at 600rpm, and the oil bath temperature was controlled at approximately 120℃, maintaining the temperature inside the three-necked flask at 100℃. The top condensate and vacuum systems were turned on, controlling the condensation temperature at 5℃ and the top pressure at 1kPa. After the temperature and pressure at the top and bottom of the column stabilized, and reflux at the top began to stabilize, the reflux ratio controller was turned on. The reflux ratio at the top was 1–5:1. The light components and products were collected after being cooled and liquefied by the top condenser. The temperature of the light components before condensation at the top was approximately 90°C, and the residence time of the material in the bottom was 2 hours. Samples of the top product were taken periodically, and the composition of the samples was analyzed by GC. The results are shown below. Under the above conditions, the composition of linalool obtained by distillation at the top of the column is as follows: methyl heptenone (0.293%), dehydrolinalool (0.455%), linalool (97.976%), dihydrolinalool (1.223%), and heavy components (0.053%). Among them, the sum of linalool and dihydrolinalool was 99.199%, and the distillation yield was 87.8%. Compared with the addition of an isomer catalyst, both data were reduced to some extent. The composition of the column bottom is as follows: methyl heptenone (0.021%), dehydrolinalool (0.248%), linalool (78.676%), dihydrolinalool (2.350%), and heavy components (18.705%). Since dehydrolinalool, linalool, and dihydrolinalool have similar boiling points, a relatively large amount of linalool remains in the column bottom.

Claims

1. A method for improving the purity of linalool products, specifically comprising: adding a catalyst to the reaction solution for the selective hydrogenation of dehydrolinalool to prepare linalool, catalyzing the incompletely converted dehydrolinalool raw material to undergo an isomerization reaction to generate 3,7-dimethyl-3,6-octadien-2-one and citral, which have boiling points significantly different from linalool, and separating them; wherein the catalyst is composed of a metal catalyst and an acid catalyst; the metal catalyst is obtained by in-situ complexation of a metal salt and a ligand, wherein the metal salt is selected from one or more of gold salts, copper salts, and silver salts.

2. The method as described in claim 1, characterized in that, In the selective hydrogenation reaction solution of dehydrolinalool, the content of the raw material dehydrolinalool is 0.05-0.5 wt%.

3. The method as described in claim 1, characterized in that, The metal salt is gold chloride, gold bromide, gold chlorocarbonyl chloride, tetrachloroauric acid, dimethyl (acetylacetone) gold, dimethyl (trifluoroacetylacetone) gold, triphenylphosphine gold chloride, silver tetrafluoroborate, silver trifluoromethanesulfonate, silver bis(trifluoromethanesulfonyl)imide, silver bis(trifluoromethanesulfonyl)imide, silver hexafluorophosphate, cuprous tetrafluoroborate, copper tetrafluoroborate, ketone trifluoromethanesulfonate, copper bis(trifluoromethanesulfonyl)imide, copper chloride, or cuprous chloride. The amount of the metal salt used is 0.001-0.01 wt% of the reaction solution mass.

4. The method according to any one of claims 1-3, characterized in that, The ligand is selected from phosphine ligands, nitrogen-phosphorus ligands, pyridine ligands, and sulfur ligands, and the amount of the ligand is 0.002-0.02 wt% of the mass of the reaction solution.

5. The method according to any one of claims 1-3, characterized in that, The ligands are triphenylphosphine, tris(3-methylphenyl)phosphine, tris(4-methylphenyl)phosphine, 1,2-diphenylphosphine ethane, 1,3-diphenylphosphine propane, 1,4-diphenylphosphine butane, 1,8-bis(diphenylphosphine)naphthalene, tributylphosphine, tricyclohexylphosphine, tricyclopentylphosphine, 2-(diadamantylphosphine)biphenyl, and 1-[2-bis-tert-butylphosphine]-3,5-diphenyl-1-Hpyrazole.

6. The method according to any one of claims 1-3, characterized in that, The acid catalyst is selected from one or more of benzenesulfonic acid, p-methylbenzenesulfonic acid, p-chlorobenzenesulfonic acid, p-bromobenzenesulfonic acid, naphthalenesulfonic acid, methanesulfonic acid, ethanesulfonic acid, 2-butylsulfonic acid, fluorosulfonic acid, 2-iodobenzenesulfonic acid, benzylsulfonic acid, cresolsulfonic acid, methylbenzylmethanesulfonic acid, hexylsulfonic acid, and 2-(N-morpholine)ethanesulfonic acid, and the amount of the acid catalyst is 0.002-0.02 wt% of the reaction solution mass.

7. The method according to any one of claims 1-3, characterized in that, Optionally, the reaction may include a step of separating and recovering the solvent from the selective hydrogenation reaction solution of dehydrolinalool before the catalytic isomerization reaction, using vacuum distillation.

8. The method according to any one of claims 1-3, characterized in that, The catalytic isomerization reaction is carried out at a temperature of 90-120℃ for 2-6 hours.

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