A process for the preparation of citronellal

Abstract

The present application provides a method for preparing citronellal. By controlling the ratio of cis, trans isodecadienal in citral raw material to be 3:2-4:2, and the content to be 0.2-0.5wt%, the ee value of citronellal can be effectively improved, the generation of excessive hydrogenation products can be reduced, and the yield of citronellal can be improved.

Description

Technical Field

[0001] This invention relates to the field of chemical active component recycling, specifically to a method for preparing citronellol and a method for recovering active components in the post-production processing of citronellol. Background Technology

[0002] Citronellol is a major component of plant essential oils such as eucalyptus oil and citronella oil. As an important isolated fragrance, it possesses a strong, fresh, green citrus-like aroma with a slight woody note, and has wide applications in the food, fragrance, and cosmetic industries. Citronellol is widely used in food flavorings, for formulating citrus and cherry flavorings, and also as a base for low-end soap fragrances. Furthermore, citronellol is an important intermediate in the synthesis of other fragrances, such as hydroxycitronellol, citronellol, and menthol.

[0003] Citronellol can be obtained through natural extraction or chemical synthesis. Naturally extracted citronellol is subject to changes in natural conditions, resulting in significant fluctuations in its yield and quality, which contradicts the market's demand for stability. Synthetic citronellol avoids these issues. The main synthetic routes include: (1) using β-pinene as a raw material, through pyrolysis, chlorination, hydrolysis, catalytic hydrogenation, and air oxidation. The β-pinene used in this route also comes from natural extracts, and its supply is subject to natural conditions. In addition, this synthetic process is complex, resulting in low citronellol yield and a large amount of waste. (2) Using citral as a raw material, hydrogenation to obtain citronellol is the mainstream synthetic route. However, considering the special structure of citral, achieving a high yield of citronellol through hydrogenation presents a significant technical challenge.

[0004]

[0005] According to literature reports, when using palladium as a catalyst, the hydrogenation reaction occurs only at the carbon-carbon double bond, exhibiting high selectivity for carbon-carbon double bonds, while showing virtually no selectivity for other unsaturated bonds. Based on this, using the noble metal Pd as the active component for the selective hydrogenation of citral to prepare citronellol has significant technical advantages.

[0006] CN1234385A discloses a method for the selective liquid-phase hydrogenation of citral to citronellol in the presence of powdered rhodium and / or palladium catalysts and an organic base. This method achieves a maximum selectivity of 94% for citronellol, with remaining products including citronellol isomers and the over-hydrogenation product dihydrocitronellol. However, this method cannot reuse the Pd / C catalyst, and the catalyst loses its activity after a single use. Solvent washing of the catalyst fails to restore its activity.

[0007] Marco Burgener et al. (Journal of Catalysis 228(2004)152-161) conducted a detailed study on the catalyst deactivation phenomenon in the hydrogenation of citral using Pd-based catalysts. Their research showed that during the reaction, Pd-based catalysts cause some citral to undergo aldehyde decomposition to produce CO. CO readily combines with metallic Pd, leading to the loss of catalytic activity. To address this phenomenon, the literature proposes introducing oxygen into the deactivated reaction system to restore catalyst activity. Although this method can restore catalyst activity, it poses significant safety risks when applied industrially. In summary, the disclosed technologies present substantial technical and safety risks.

[0008] For the above reasons, researching new reaction systems to replace Pd-based catalysts is particularly important. CN108794314A provides a method for preparing citronellal by hydrogenation of citral, using citral as a raw material, and sequentially adding catalysts such as nickel-molybdenum, palladium-molybdenum, ruthenium-cobalt or rhodium-iron, co-catalysts such as sodium hydrogen carbonate, potassium tert-butoxide, sodium methoxide, sodium ethoxide, ethylamine or diethanolamine, and solvent. In the disclosed examples, the highest selectivity for citronellal reaches 96%, accompanied by byproducts such as tetrahydrogeraniol. Although this process has a high yield of citronellal, it uses a large amount of alkaline additives and solvents, places high demands on equipment, and generates a lot of waste, which is cumbersome to treat and clearly does not conform to the concept of green chemistry.

[0009] Therefore, the research on catalysts for the hydrogenation of citral to citronellol is already quite extensive. Within the existing hydrogenation catalyst system, improving the yield of citronellol is of paramount importance. Summary of the Invention

[0010] One of the objectives of this invention is to provide a method for preparing citronellol, which can improve the yield of citronellol.

[0011] Another objective of this invention is to provide a method for recycling the mixture in the post-processing flow of the production process for preparing citronellol, thereby achieving the recycling of effective components.

[0012] The study found that the ratio and content of cis- and trans-isodecadienal in the citral raw material being too high or too low can affect the yield of citronellol preparation, leading to the generation of a large number of by-products, such as nerol, which affects the purity and yield of the product.

[0013] Based on the above research, in order to achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0014] In a first aspect, the present invention provides a method for preparing citronellol.

[0015] A method for preparing citronellol involves hydrogenating citral in the presence of a noble metal hydrogenation catalyst, wherein the ratio of cis to trans isodecadienal in the citral raw material is 3:2 to 4:2, and the total content is between 0.2 and 0.5 wt%.

[0016] Preferably, the purity of the citral raw material is above 98 wt%;

[0017] The structure of the isodecadienal is shown below:

[0018]

[0019] In the preparation method, the partial hydrogenation catalyst is a supported noble metal catalyst, preferably with ruthenium as the supported noble metal and aluminum oxide and / or calcium carbonate as the support;

[0020] Preferably, the carrier is calcium carbonate;

[0021] Preferably, the ruthenium metal content is in the range of 2–15 wt%, more preferably 5–10 wt%.

[0022] Preferably, the amount of catalyst used accounts for 0.1 to 1 wt% of the raw material mass.

[0023] In the preparation method, the hydrogen pressure is 1.0–10.0 MPa (absolute pressure), preferably 5–9 MPa (absolute pressure), the reaction temperature is 0–100℃, preferably 40–90℃, and the reaction time is 0.1–24 h.

[0024] A second aspect of the present invention provides a method for recycling mixed materials in the post-production processing of citronellol, comprising the following steps:

[0025] (1) The mixture in the post-processing of citronellol production is subjected to vacuum distillation in a light component removal distillation tower to remove the light component mixture of isopentenol and diisoprene ether.

[0026] (2) The bottom liquid of the light distillation column enters the isoprene distillation column for vacuum distillation to remove isoprene acid.

[0027] (3) The bottom liquid of the deisoprene acid tower is treated by the effective component recovery tower, and the mixture of cis and trans isopredependialdehyde is collected from the top of the tower and reused in the catalytic hydrogenation reaction.

[0028] In the recycling method, the mixed materials in the post-processing flow of citronellol production include: isopentenol 2.8-4.2 wt%, diisoprene ether 7.9-9 wt%, isopentenic acid 14-16 wt%, 7-methyl-3-methylene-6-octenal 15-17.5 wt%, 3,7-dimethyl-3,6-octadienal 13-14 wt%, cis, trans isoisodecadienal 9-11 wt%, and 3-methyl-6-(1-methylvinyl)cyclohex-2-en-1-ol 29-32 wt%.

[0029] The material structure is shown below:

[0030]

[0031] In the recycling method, in step (1), the theoretical number of plates in the light distillation column is 20 to 35, the reflux ratio is 1:1 to 4.5:1, the material is fed into the lower part of the column, and the operating pressure (absolute pressure) is 0.01 to 0.1 bar.

[0032] A mixture of isopentenol and diisoprene ether was obtained at the top of the column.

[0033] In the aforementioned recycling method, in step (2), the theoretical number of trays in the deisoprene acid removal tower is 20 to 32, the reflux ratio is 1:1 to 6:1, the material is fed into the middle of the tower, and the operating pressure (absolute pressure) is 0.10 to 0.25 bar.

[0034] A mixture containing isopentenic acid was obtained at the top of the column.

[0035] In the recycling method, in step (3), the theoretical number of trays in the effective component recovery tower is 19 to 30, the reflux ratio is 1:1 to 3:1, the material is fed from the bottom of the tower, and the operating pressure (absolute pressure) is 0.05 to 0.20 bar.

[0036] A mixture of cis and trans isodecadienal was obtained at the top of the column.

[0037] In the recycling method, the isodecadienal mixture recovered in step (3) is mixed with fresh raw material citral to make the cis:trans ratio 3:2 to 4:2, and the total content of cis and trans isodecadienal is between 0.2 and 0.5 wt%, so that citronellal can be prepared according to the aforementioned method.

[0038] In this invention, after the reaction to prepare citronellol is completed, the reaction solution is subjected to light and heavy weight removal treatment to obtain citronellol with a purity of ≥99.5%.

[0039] During the implementation of this scheme, it was found that the ratio and content of cis- and trans-isodecadienal significantly affected the catalyst. Excessively high or low ratios and contents of cis- and trans-isodecadienal significantly reduced the selectivity of citronellol and led to a significant increase in the content of over-hydrogenation products. Based on the partial hydrogenation feedstock of alkynols, the reason is speculated to be that alkynes have a stronger coordination ability than mono-olefins. In the normal reaction process, alkynes preferentially coordinate with the noble metal catalyst, undergoing partial hydrogenation to form mono-olefins. Since the mono-olefins have a lower coordination ability than alkynes, they are removed from the noble metal catalyst and replaced by alkynols. The presence of cis- and trans-isodecadienal disrupts this substitution trend, making it difficult for mono-olefins to be removed and leading to further hydrogenation and the formation of over-hydrogenation products.

[0040] Furthermore, the reaction solution is subjected to light and heavy weight removal treatments to obtain citronellal with a purity ≥99.5wt% and a yield ≥89.5wt%. This method can achieve efficient separation and purification of citronellal by selecting appropriate separation equipment and operating conditions, such as distillation, extraction, and crystallization.

[0041] The positive effects of this invention are as follows:

[0042] 1. This invention can effectively increase the ee value of citronellol by controlling the ratio of cis to trans isodecadienal in the citral raw material to 3:2 to 4:2 and the content to be between 0.2 and 0.5 wt%, which is something that existing technologies cannot achieve.

[0043] 2. The preparation method of this invention is simple and easy to implement, requiring no complex equipment or strict operating conditions, thus reducing production costs and facilitating large-scale production. This method not only improves the purity of citronellol but also increases its yield, solves the separation problem between nerol and citronellol, avoids the formation of excessive hydrogenation products, and improves product quality and market competitiveness.

[0044] 3. The preparation method of this invention can not only improve the purity of citronellol, but also increase its yield, which has a dual advantage. Existing technologies often can only improve one aspect and cannot meet both requirements at the same time.

[0045] 4. The preparation method of this invention solves the problem of the ratio and content of cis and trans isodecadienal in citral raw materials, avoids the formation of excessive hydrogenation products, and improves product quality and market competitiveness. Citronellol, as an important single-fragrance compound, has a strong, fresh, green citrus-like aroma with a slight woody note, and has wide applications in the food, fragrance, and cosmetic industries. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of a process for recovering effective components during the post-treatment of citronellol in this invention.

[0047] Among them, C001 is a light component removal distillation column, C002 is an isopentenyl acid removal column, and C003 is an effective component recovery column. Detailed Implementation

[0048] The following embodiments will further illustrate the process provided by the present invention, but the present invention is not limited to the listed embodiments, and should also include any other known modifications within the scope of the claims of the present invention.

[0049] Ruthenium catalyst: The supported precious metal is ruthenium, with a ruthenium metal mass content ranging from 2 to 15 wt%, and the support is aluminum oxide and / or calcium carbonate;

[0050] Fresh citral raw material: The purity of citral raw material is above 98wt%, Wanhua Chemical Group Co., Ltd.

[0051] The mixed materials in the post-processing of citronellol production include: isopentenol 2.8–4.2 wt%, diisoprene ether 7.9–9 wt%, isopentenic acid 14–16 wt%, 7-methyl-3-methylene-6-octenal 15–17.5 wt%, 3,7-dimethyl-3,6-octadienal 13–14 wt%, cis- and trans-isodecadienal 9–11 wt%, and 3-methyl-6-(1-methylvinyl)cyclohex-2-en-1-ol 29–32 wt%; Wanhua Chemical Group Co., Ltd.

[0052] Analysis method:

[0053] Gas chromatograph: Agilent 7890B, column DB-17 (30m × 0.25mm × 0.25μm), injection port temperature: 250℃; split ratio 50:1; carrier gas flow rate: 1ml / min; temperature program: 50℃ for 2 min, increase to 80℃ at 5℃ / min, hold for 0 min, then increase to 260℃ at 15℃ / min, hold for 10 min. Detector temperature: 270℃.

[0054] Example 1

[0055] The light-light distillation column has 30 theoretical plates and a reflux ratio of 1.2:1. Vacuum distillation is performed at 0.01 bar under reduced pressure (absolute pressure). A mixture of isopentenol and diisoprene ether is collected from the top of the column. Gas chromatography (GC) analysis of the bottom liquid shows a content of 0.04 wt% for the isopentenol and diisoprene ether mixture. The isopentenol removal column has 30 theoretical plates and a reflux ratio of 2:1. Vacuum distillation is performed at 0.2 bar under reduced pressure (absolute pressure) to remove isopentenol. The bottom liquid from the isopentenol removal column enters the effective component recycling column, which has 25 theoretical plates, a reflux ratio of 1.5:1, and an operating pressure (absolute pressure) of 0.15 bar. A mixture of cis and trans isopredecanal is collected from the top of this column. Gas chromatography (GC) analysis of the bottom liquid shows a ratio of cis and trans isopredecanal of 1.6:1, and a total content of 99 wt% for the mixture.

[0056] A mixture of cis and trans isodecadienal was added to fresh citral feedstock, with the mixture comprising 0.3 wt%.

[0057] First, 1050 g of a citral mixture containing 0.3 wt% of cis- and trans-isodecadienal and 2 g of ruthenium catalyst (5% ruthenium content) were added to the autoclave. The autoclave was sealed and purged with nitrogen three times. After confirming good sealing by pressurizing the autoclave to 9.0 MPa, the nitrogen was purged and the autoclave was purged with hydrogen six times. The stirrer was turned on, and the hydrogen pressure was maintained at 8.0 MPa. The reaction temperature was maintained at 50°C for 6 hours. After stopping the stirring and venting the hydrogen from the autoclave, the reaction solution was analyzed by GC. The citral conversion rate was 93.5 wt%, the citronellol selectivity was 98.3 wt%, and the over-hydrogenation product was 0.2 wt%.

[0058] The reaction solution underwent light and heavy component removal treatment. The distillation column had 25 theoretical plates and a reflux ratio of 1.5:1. A vacuum pump was used to create a vacuum, and the pressure (absolute pressure) was reduced to 0.2 kPa for vacuum distillation. Citronellol was collected at the 10th theoretical plate, with a purity of 99.8 wt%.

[0059] Example 2

[0060] The light-light distillation column has a theoretical plate count of 26, a reflux ratio of 3:1, and is subjected to vacuum distillation to remove isopentenol and diisoprene ethers. A mixture of isopentenol and diisoprene ethers is collected from the top of the column. Gas chromatography (GC) analysis of the bottom liquid composition reveals a mixture of isopentenol and diisoprene ethers of 0.035 wt%. The isopentenyl acid removal column also has a theoretical plate count of 26, a reflux ratio of 1.8:1, and is subjected to vacuum distillation to remove isopentenyl acid to remove isopentenyl acid. The bottom liquid of the deisoprene acid removal tower enters the effective component recycling tower, which has 28 theoretical plates, a reflux ratio of 3:1, and an operating pressure (absolute pressure) of 0.20 bar. A mixture of cis and trans isopredecanal is collected from the top of the tower. Gas chromatography (GC) analysis of the bottom liquid composition shows that the ratio of cis to trans isopredecanal is 2:1, and the total content of the mixture is 98.6 wt%.

[0061] A mixture of cis and trans isodecadienal was added to fresh citral feedstock, with the mixture comprising 0.2 wt%.

[0062] First, 890 g of a citral mixture containing 0.2 wt% of cis- and trans-isodecadienal and 5 g of ruthenium catalyst (8% ruthenium content) were added to the autoclave. The support was alumina. The autoclave was sealed and purged with nitrogen three times. After confirming good sealing by pressing nitrogen to 9 MPa, the nitrogen was purged and the autoclave was purged with hydrogen six times. The stirrer was turned on, and the hydrogen pressure was maintained at 8.5 MPa. The reaction was carried out at 48°C for 7.25 h. After stopping the stirring and venting the hydrogen from the autoclave, the reaction solution was analyzed by GC. The citral conversion rate was 91.45 wt%, the citronellol selectivity was 98.23 wt%, and the over-hydrogenation product was 0.36 wt%.

[0063] The reaction solution underwent light and heavy component removal treatment. The distillation column had 30 theoretical plates, a reflux ratio of 2:1, and a vacuum pump was used to reduce the pressure (absolute pressure) to 0.3 kPa for vacuum distillation. Citronellol was collected at the 15th theoretical plate, with a purity of 99.5 wt%.

[0064] Example 3

[0065] The light-light distillation column has 32 theoretical plates and a reflux ratio of 1:1. Vacuum pumps are used to reduce the pressure (absolute pressure) to 0.018 bar for vacuum distillation. A mixture of isopentenol and diisoprene ether is collected from the top of the column. Gas chromatography (GC) analysis of the bottom liquid composition shows that the isopentenol and diisoprene ether mixture contains 0.02 wt%. The isoprene acid removal column also has 32 theoretical plates and a reflux ratio of 1:1. Vacuum pumps are used to reduce the pressure (absolute pressure) to 0.15 bar for vacuum distillation to remove isoprene acid. The bottom liquid from the isoprene acid removal column enters the effective component recycling column, which has 30 theoretical plates, a reflux ratio of 2.5:1, and an operating pressure (absolute pressure) of 0.18 bar. A mixture of cis and trans isoisoprenedialdehyde is collected from the top of this column. Gas chromatography (GC) analysis of the bottom liquid shows that the ratio of cis to trans isoisoprenedialdehyde is 1.5:1, and the total content of the mixture is 95.1 wt%.

[0066] A mixture of cis and trans isodecadienal was added to the citral feedstock, with the mixture comprising 0.5 wt%.

[0067] First, 750g of a citral mixture containing 0.5wt% of cis- and trans-isodecadienal and 3.4g of a ruthenium catalyst (10% ruthenium content) were added to the autoclave. The autoclave was sealed, purged with nitrogen three times, and then pressurized to 9MPa to confirm good sealing. The nitrogen was then purged, and the autoclave was purged with hydrogen six times. The stirrer was turned on, and the hydrogen pressure was maintained at 7.6MPa. The reaction temperature was kept at 57℃ for 8 hours. After stopping stirring and venting the hydrogen from the autoclave, GC analysis of the reaction solution showed a citral conversion of 92.14wt%, a citronellol selectivity of 97.98wt%, and 0.28wt% of over-hydrogenation products.

[0068] The reaction solution underwent light and heavy component removal treatment. The distillation column had 28 theoretical plates and a reflux ratio of 1.2:1. A vacuum pump was used to create a vacuum, and the pressure (absolute pressure) was reduced to 0.15 kPa for vacuum distillation. Citronellol was collected at the 16th theoretical plate, with a purity of 99.65 wt%.

[0069] Comparative Example 1

[0070] The preparation procedure for citronellal was the same as in Example 1, but the ratio of cis to trans isoisodecadienal was 3:1, and the content of the cis to trans isoisodecadienal mixture in the fresh citral feedstock was 0.1 wt%. The citral conversion rate was 89.34 wt%, the citronellal selectivity was 92.45 wt%, and the over-hydrogenation product was 1.48 wt%. The reaction solution was subjected to vacuum distillation, and the purity of the citronellal collected was 97.5 wt%.

[0071] Comparative Example 2

[0072] The preparation procedure for citronellal was the same as in Example 1, but the ratio of cis to trans isoisodecadienal was 1:1, and the content of the mixture of cis and trans isoisodecadienal in the raw material was 0.6 wt%. The conversion rate of citral was 88.15 wt%, the selectivity of citronellal was 90.04 wt%, and the over-hydrogenation product was 2.72 wt%. The reaction solution was subjected to vacuum distillation, and the purity of the citronellal obtained was 96.85 wt%.

[0073] It is readily understood that the above embodiments are merely illustrative examples for clear explanation and do not imply that the invention is limited thereto. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing citronellol, wherein citric acid is obtained by catalytic hydrogenation of citral under the action of a noble metal partial hydrogenation catalyst, wherein the ratio of cis to trans isodecadienal in the citral raw material is 3:2 to 4:2, and the total content is between 0.2 and 0.5 wt%.

2. The method according to claim 1, wherein, The purity of the citral raw material is above 98wt%.

3. The method according to claim 1, wherein, The catalyst is a supported noble metal catalyst, and the catalyst support is aluminum oxide and / or calcium carbonate.

4. The method according to claim 3, wherein, The noble metal in the supported noble metal catalyst is ruthenium.

5. The method according to claim 4, wherein, The ruthenium content in the precious metal catalyst ranges from 2 to 15 wt%.

6. The method according to claim 5, wherein, The mass content of ruthenium in the precious metal catalyst ranges from 5 to 10 wt%.

7. The method according to any one of claims 1 to 6, wherein, The amount of catalyst used is 0.1 to 1 wt% of the raw material.

8. The method according to any one of claims 1 to 4, wherein, The reaction hydrogen pressure is 1.0–10.0 MPa absolute, the reaction temperature is 0–100 °C, and the reaction time is 0.1–24 h.

9. The method according to claim 8, wherein, The reaction hydrogen pressure is 5–9 MPa absolute, and the reaction temperature is 40–90 °C.

10. A method for reusing mixed materials in the post-production processing of citronellol, comprising the following steps: (1) The mixture in the post-processing of citronellal production is subjected to vacuum distillation in a light component removal distillation tower to remove the light component mixture of isopentenyl alcohol and diisoprene ether. (2) The bottom liquid of the light distillation column is fed into the isopentened acid removal column for vacuum distillation to remove isopentened acid; (3) The bottom liquid of the deisoprene acid tower is treated by the effective component recycling tower, and a mixture containing cis and trans isopredependialdehyde is collected from the top of the tower.

11. The method according to claim 10, wherein, The mixture in the post-processing of citronellol production includes: 2.8–4.2 wt% isopentenol, 7.9–9 wt% diisoprene ether, 14–16 wt% isopentenic acid, 15–17.5 wt% 7-methyl-3-methylene-6-octenal, 13–14 wt% 3,7-dimethyl-3,6-octadienal, 9–11 wt% cis- and trans-isodecadienal, and 29–32 wt% 3-methyl-6-(1-methylvinyl)cyclohex-2-en-1-ol.

12. The method according to claim 10, wherein, In step (1), the theoretical number of plates in the light distillation column is 20 to 35, the reflux ratio is 1:1 to 4.5:1, and the operating pressure is absolute pressure of 0.01 to 0.1 bar.

13. The method according to claim 10, wherein, In step (2), the theoretical number of trays in the deisoprene acid tower is 20 to 32, the reflux ratio is 1:1 to 6:1, and the operating pressure is absolute pressure of 0.10 to 0.25 bar.

14. The method of claim 10, wherein, In step (3), the effective component recycling tower has 19 to 30 theoretical plates, a reflux ratio of 1:1 to 3:1, and an operating pressure of 0.05 to 0.20 bar absolute.

15. The method according to any one of claims 10 to 14, wherein, The cis- and trans-isodecadienal recovered in step (3) are mixed with fresh citral to make the ratio of cis- and trans-isodecadienal 3:2 to 4:2 and the total content between 0.2 and 0.5 wt%, and citronellal is prepared according to the method described in any one of claims 1 to 9.

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