Method for preparing citronellal

Abstract

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

Description

Technical Field

[0001] The invention relates to the field of recycling of effective chemical components, and in particular to a method for preparing citronellal and a method for recovering effective components in a post-production treatment process of citronellal. Background Art

[0002] Citronellal is one of the main components of essential oils such as eucalyptus oil and citronella oil. As an important isolated fragrance, it has a strong, fresh, green citrus-like, slightly woody aroma and is widely used in the food, fragrance and cosmetics industries. Citronellal is widely used in edible flavors, citrus and cherry flavors, and is also used to prepare low-grade soap flavors. At the same time, citronellal is also an important intermediate for the synthesis of other flavors, such as hydroxycitronellal, citronellol and menthol.

[0003] Citronellal can be obtained from two sources: natural extraction and chemical synthesis. Naturally extracted citronellal is subject to changes in natural conditions, resulting in large fluctuations in its yield and quality, which is contrary to the market's demand for stability. Synthetic citronellal can avoid the above situation. The main synthesis routes include: (1) using β-pinene as a raw material, and performing 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, the synthesis process is complex, the yield of citronellal is low, and there are many three wastes; (2) Using citral as a raw material, hydrogenation to obtain citronellal is the mainstream synthesis route, but considering the special structure of citral, high-yield hydrogenation to obtain citronellal is technically very challenging.

[0004]

[0005] According to literature reports, when using metal palladium as a catalyst, the hydrogenation reaction only occurs at carbon-carbon double bonds, and it has high selectivity for carbon-carbon double bonds and basically no selectivity for other unsaturated bonds. Based on this, using precious metal Pd as an active component for selective hydrogenation of citral to prepare citronellal has a high technical advantage.

[0006] CN1234385A discloses a method for preparing citronellal by selective liquid phase hydrogenation of citral in the presence of powdered rhodium and / or palladium catalysts and in the presence of an organic base. The maximum selectivity of citronellal in this method is 94%, and the remaining products include citronellal isomers and dihydrocitronellal, an over-hydrogenation product. However, this method cannot realize the application of the catalyst Pd / C, and the catalyst loses its activity after one use. The catalyst cannot be restored by washing with a solvent.

[0007] Marco Burgener et al. (Journal of Catalysis 228 (2004) 152-161) conducted a detailed study on the catalyst deactivation phenomenon that occurs during the hydrogenation of citral using Pd-based catalysts. The study showed that during the reaction, Pd-based catalysts will cause some citral to undergo aldehyde decomposition to produce CO, which can easily combine with metal Pd and cause it to lose its catalytic activity. In response to this phenomenon, the literature proposes to introduce oxygen into the deactivated reaction system to restore the activity of the catalyst. Although this method can restore the activity of the catalyst, there are great safety risks when it is applied to industrialization. Overall, the disclosed technology has great technical and safety risks.

[0008] Based on the above reasons, it is particularly important to study new reaction systems to replace Pd catalysts. CN108794314A provides a method for preparing citronellal by hydrogenation of citral, using citral as raw material, sequentially adding catalysts of nickel molybdenum, palladium molybdenum, ruthenium cobalt or rhodium iron, cocatalysts of sodium carbonate hydrogen, potassium tert-butoxide, sodium methoxide, sodium ethoxide, ethylamine or diethanolamine and solvent, the highest selectivity of citronellal in the disclosed embodiment reaches 96%, and is accompanied by by-products such as tetrahydrogeraniol. Although the process has a high yield of citronellal, a large amount of alkaline additives and solvents are used, which has high requirements for equipment, and there are more three wastes, and the treatment is cumbersome, which obviously does not meet the concept of green chemistry.

[0009] Therefore, the catalyst research for the hydrogenation of citral to prepare citronellal has been very sufficient. In the existing hydrogenation catalyst system, it is very important to improve the yield of citronellal. Summary of the invention

[0010] One of the purposes of the present invention is to provide a method for preparing citronellal, which can improve the yield of citronellal.

[0011] Another object of the present invention is to provide a method for recycling the mixed material in the post-processing process of the production process for preparing citronellal, so as to realize the recycling of the effective components.

[0012] The study found that the ratio and content of cis- and trans-isodecadienal in the citral raw material that are too high or too low will affect the yield of the preparation of citronellal, resulting in the formation of a large amount 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 invention objectives, the present invention adopts the following technical solutions:

[0014] A first aspect of the present invention provides a method for preparing citronellal.

[0015] A method for preparing citronellal, which is obtained by hydrogenating citral under the action of a precious 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%;

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

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

[0018]

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

[0020] Preferably, the carrier is calcium carbonate;

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

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

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

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

[0025] (1) The mixed material in the post-processing process of citronellal production is subjected to vacuum distillation in a light removal distillation tower to remove the light components of isopentenyl alcohol and diisoprene ether mixture.

[0026] (2) The bottom liquid of the light distillation tower enters the de-isopentank tower for vacuum distillation to remove isopentank acid.

[0027] (3) The bottom liquid of the de-isopentenylation tower is treated with an effective component recovery tower, and a mixture of cis- and trans-isodecadienal is taken out from the top of the tower and reused in the catalytic hydrogenation reaction.

[0028] In the recycling method, the mixed material in the post-processing process of citronellal production includes: 2.8-4.2wt% of isopentanol, 7.9-9wt% of diisoprene ether, 14-16wt% of isopentanic acid, 15-17.5wt% of 7-methyl-3-methylene-6-octenal, 13-14wt% of 3,7-dimethyl-3,6-octadienal, 9-11wt% of cis- and trans-isodecadienal, and 29-32wt% of 3-methyl-6-(1-methylvinyl)cyclohex-2-ene-1-ol;

[0029] The material structure is as follows:

[0030]

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

[0032] A mixture of isopentanol and diisoprene ether is obtained at the top of the tower.

[0033] In the recycling method, in step (2), the theoretical number of plates of the de-isopentenyl acid tower is 20 to 32, the reflux ratio is 1:1 to 6:1, the material is fed in the middle of the tower, and the operating pressure (absolute pressure) is 0.10 to 0.25 bar;

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

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

[0036] A mixture of cis- and trans-isodecadienal is obtained at the top of the tower.

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

[0038] In the present invention, after the reaction for preparing citronellal is completed, the reaction solution is subjected to light and heavy removal treatments to obtain citronellal 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 have an important influence on the catalyst. Excessive or low ratios and contents of cis- and trans-isodecadienal significantly reduce the selectivity of citronellal and significantly increase the content of over-hydrogenated products. According to the partial hydrogenation raw materials of alkynols, the reason is speculated to be: the coordination ability of alkynes is stronger than that of monoolefins. In the normal reaction process, alkynes preferentially coordinate with noble metal catalysts and form monoolefins through partial hydrogenation. Since the coordination ability of monoolefins is lower than that of alkynes, they fall off the noble metal catalysts and are replaced by alkynols. The presence of cis- and trans-isodecadienal in the system destroys this replacement trend, resulting in monoolefins not being easy to fall off and being further hydrogenated to form over-hydrogenated products.

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

[0041] The positive effects of the present invention are:

[0042] 1. The present invention can effectively improve the ee value of citronellal by controlling the ratio of cis-trans isodecanal in the citral raw material to 3:2-4:2 and the content to be between 0.2-0.5wt%, which is impossible in the prior art.

[0043] 2. The preparation method of the present invention is simple and easy to operate, does not require complicated equipment and strict operating conditions, reduces production costs, and is conducive to large-scale production. The preparation method can not only improve the purity of citronellal, but also improve its yield, solve the separation problem of neral and citronellal, avoid the generation of excessive hydrogenation products, and improve the quality and market competitiveness of the product.

[0044] 3. The preparation method of the present invention can not only improve the purity of citronellal, but also improve its yield, which has dual advantages. However, the existing technology can only improve one aspect and cannot meet both requirements at the same time.

[0045] 4. The preparation method of the present invention solves the problem of the ratio and content of cis- and trans-isodecadienal in the citral raw material, avoids the formation of excessive hydrogenation products, and improves the quality and market competitiveness of the product. Citronellal, as an important isolated fragrance, has a strong, fresh, green citrus-like, slightly woody aroma and is widely used in the food, fragrance and cosmetics industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The present invention is a schematic flow diagram of the recovery of effective components in the post-treatment process of citronellal.

[0047] Among them, C001 is a light fractionation tower, C002 is a de-isoprene acid tower, and C003 is an effective component recovery tower. DETAILED DESCRIPTION

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

[0049] Ruthenium catalyst: the loaded precious metal is ruthenium, the loaded ruthenium metal mass content ranges from 2 to 15wt%, and the carrier 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] Mixed materials in the post-processing process of citronellal production: including: 2.8-4.2wt% of isopentanol, 7.9-9wt% of diisoprene ether, 14-16wt% of isopentanic acid, 15-17.5wt% of 7-methyl-3-methylene-6-octenal, 13-14wt% of 3,7-dimethyl-3,6-octadienal, 9-11wt% of cis- and trans-isodecadienal, and 29-32wt% of 3-methyl-6-(1-methylvinyl)cyclohex-2-ene-1-ol; Wanhua Chemical Group Co., Ltd.

[0052] Analytical methods:

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

[0054] Example 1

[0055] The number of theoretical plates of the light-removal distillation tower is 30, the reflux ratio is 1.2:1, and the vacuum pump is used to reduce the pressure (absolute pressure) to 0.01 bar for vacuum distillation. A mixture of isopentanol and diisopentyl ether is taken from the top of the tower. The composition of the bottom liquid is analyzed by gas chromatography (GC). The content of the mixture of isopentanol and diisopentyl ether is 0.04wt%. The number of theoretical plates of the deisopentyl acid tower is 30, the reflux ratio is 2:1, and the vacuum pump is used to reduce the pressure (absolute pressure) to 0.2 bar for vacuum distillation to remove isopentanic acid. The bottom liquid of the deisopentyl acid tower enters the effective component recycling tower, 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-isodecadienal is taken from the top of the tower. The composition of the bottom liquid is analyzed by gas chromatography (GC). The ratio of cis- and trans-isodecadienal is 1.6:1, and the total content of the mixture is 99wt%.

[0056] The mixture of cis- and trans-isodecadienal is added to fresh citral raw material, and the content of the mixture of cis- and trans-isodecadienal in the raw material is 0.3 wt%.

[0057] First, add 1050g of citral mixture containing 0.3wt% of cis-trans isoisodecadienal and 2g of noble metal ruthenium catalyst to the autoclave, wherein the noble metal catalyst has a ruthenium content of 5% and the carrier is aluminum oxide. The autoclave is sealed, nitrogen is replaced 3 times, and nitrogen is pressed to 9.0MPa to confirm that the autoclave is well sealed. Then, the nitrogen is vented, hydrogen is replaced 6 times, the stirring paddle is turned on, the hydrogen pressure is maintained at 8.0MPa, and the temperature in the reactor is maintained at 50°C for 6h. After stopping stirring and venting the hydrogen in the reactor, GC analysis of the reaction solution shows that the conversion rate of citral is 93.5wt%, the selectivity of citronellal is 98.3wt%, and the over-hydrogenation product is 0.2wt%.

[0058] The reaction liquid was treated with light and heavy removal, the number of theoretical plates of the distillation tower was 25, the reflux ratio was 1.5:1, the vacuum pump was used to reduce the pressure (absolute pressure) to 0.2 KPa for vacuum distillation. Citronellal was extracted at the 10th theoretical plate, and the purity of citronellal was 99.8 wt%.

[0059] Example 2

[0060] The number of theoretical plates of the light removal distillation tower is 26, the reflux ratio is 3:1, the vacuum pump is used to reduce the pressure (absolute pressure) to 0.02 bar for vacuum distillation to remove isopentenol and diisoprene ether, and the isopentenol and diisoprene ether mixture is taken out from the top of the tower. The composition of the bottom liquid is analyzed by gas chromatography (GC). The content of the isopentenol and diisoprene ether mixture is 0.035wt%. The number of theoretical plates of the deisoprene acid tower is 26, the reflux ratio is 1.8:1, and the vacuum pump is used to reduce the pressure (absolute pressure) to 0.25 bar for vacuum distillation to remove isopentenic acid. The bottom liquid of the de-isopentenic acid tower enters an effective component recovery 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-isodecadienal is taken out from the top of the tower. The composition of the bottom liquid is analyzed by gas chromatography (GC). The ratio of cis- and trans-isodecadienal is 2:1, and the total content of the mixture is 98.6wt%.

[0061] The mixture of cis- and trans-isodecadienal is added to fresh citral raw material, and the content of the mixture of cis- and trans-isodecadienal in the raw material is 0.2 wt%.

[0062] First, add 890g of citral mixed material containing 0.2wt% of cis-trans isoisodecadienal and 5g of noble metal ruthenium catalyst to the autoclave, the noble metal catalyst ruthenium content is 8%, and the carrier is aluminum oxide. The autoclave is sealed, nitrogen is replaced 3 times, and nitrogen is pressed to 9MPa to confirm that the autoclave is well sealed. Then, the nitrogen is vented, hydrogen is replaced 6 times, the stirring paddle is turned on, the hydrogen pressure is maintained at 8.5MPa, and the temperature in the reactor is maintained at 48°C for 7.25h. After stopping stirring and venting the hydrogen in the reactor, GC analysis of the reaction solution shows that the citral conversion rate is 91.45wt%, the citronellal selectivity is 98.23wt%, and the over-hydrogenation product is 0.36wt%.

[0063] The reaction liquid was treated with light and heavy removal, the number of theoretical plates of the distillation tower was 30, the reflux ratio was 2:1, the vacuum pump was used to reduce the pressure (absolute pressure) to 0.3 KPa for vacuum distillation. Citronellal was extracted at the 15th theoretical plate, and the purity of citronellal was 99.5 wt%.

[0064] Example 3

[0065] The number of theoretical plates of the light-removal distillation tower is 32, the reflux ratio is 1:1, and the vacuum pump is used to reduce the pressure (absolute pressure) to 0.018 bar for vacuum distillation. A mixture of isopentanol and diisopentyl ether is taken from the top of the tower, and the composition of the tower bottom liquid is analyzed by gas chromatography (GC). The content of the mixture of isopentanol and diisopentyl ether is 0.02wt%. The number of theoretical plates of the deisopentyl acid tower is 32, the reflux ratio is 1:1, and the vacuum pump is used to reduce the pressure (absolute pressure) to 0.15 bar for vacuum distillation to remove isopentanic acid. The bottom liquid of the deisopentyl acid tower enters the effective component recycling tower, with 30 theoretical plates, reflux ratio of 2.5:1, and operating pressure (absolute pressure) of 0.18 bar. A mixture of cis- and trans-isodecadienal is taken from the top of the tower, and the composition of the tower bottom is analyzed by gas chromatography (GC). The ratio of cis- and trans-isodecadienal is 1.5:1, and the total content of the mixture is 95.1wt%.

[0066] A mixture of cis- and trans-isodecadienal is added to the citral raw material, wherein the content of the mixture of cis- and trans-isodecadienal in the raw material is 0.5 wt %.

[0067] First, add 750g of citral mixture containing 0.5wt% of cis-trans isoisodecadienal and 3.4g of noble metal ruthenium catalyst to the autoclave, the noble metal catalyst ruthenium content is 10%, and the carrier is aluminum oxide. The autoclave is sealed, nitrogen is replaced 3 times, and nitrogen is pressed to 9MPa to confirm that the autoclave is well sealed. Then, the nitrogen is vented, hydrogen is replaced 6 times, the stirring paddle is turned on, the hydrogen pressure is maintained at 7.6MPa, and the temperature in the reactor is maintained at 57°C for 8h. After stopping stirring and venting the hydrogen in the reactor, GC analysis of the reaction solution shows that the citral conversion rate is 92.14wt%, the citronellal selectivity is 97.98wt%, and the over-hydrogenation product is 0.28wt%.

[0068] The reaction liquid was treated with light and heavy removal. The number of theoretical plates of the distillation tower was 28, the reflux ratio was 1.2:1, and the vacuum pump was used to reduce the pressure (absolute pressure) to 0.15 KPa for vacuum distillation. Citronellal was extracted at the 16th theoretical plate, and the purity of citronellal was 99.65 wt%.

[0069] Comparative Example 1

[0070] The preparation steps of citronellal are the same as those in Example 1, except that the ratio of cis-trans isodecanal to trans isodecanal is 3:1, and the content of the mixture of cis-trans isodecanal in the fresh citral raw material is 0.1wt%. The citral conversion rate is 89.34wt%, the citronellal selectivity is 92.45wt%, and the over-hydrogenation product is 1.48wt%. The reaction solution is subjected to vacuum distillation, and the purity of the extracted citronellal is 97.5wt%.

[0071] Comparative Example 2

[0072] The preparation steps of citronellal are the same as those in Example 1, except that the ratio of cis- and trans-isodecadienal is 1:1, and the content of the mixture of cis- and trans-isodecadienal in the raw material is 0.6wt%. The conversion rate of citral is 88.15wt%, the selectivity of citronellal is 90.04wt%, and the over-hydrogenation product is 2.72wt%. The reaction solution is subjected to vacuum distillation, and the purity of the extracted citronellal is 96.85wt%.

[0073] It is easy to understand that the above embodiments are only examples for clear explanation and do not mean that the present invention is limited thereto. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the present invention.

Claims

1. A method for preparing citronellal, which is obtained by catalytic hydrogenation of citral under the action of a precious 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%; preferably, the purity of the citral raw material is above 98 wt%.

2. The method according to claim 1, wherein: The catalyst is a supported noble metal catalyst, preferably the supported noble metal is ruthenium, and the carrier is aluminum oxide and / or calcium carbonate.

3. The method according to claim 2, wherein: The mass content of ruthenium in the noble metal catalyst is in the range of 2 to 15 wt%, preferably 5 to 10 wt%.

4. The method according to any one of claims 1 to 3, wherein: The amount of the catalyst used accounts for 0.1 to 1 wt% of the raw material mass.

5. The method according to any one of claims 1 to 4, wherein: The reaction hydrogen pressure is 1.0 to 10.0 MPa (absolute pressure), preferably 5 to 9 MPa (absolute pressure), the reaction temperature is 0 to 100° C., preferably 40 to 90° C., and the reaction time is 0.1 to 24 h.

6. A method for recycling mixed materials in a post-processing process of citronellal production, comprising the following steps: (1) passing the mixed material in the post-processing process of citronellal production through a light removal distillation tower for vacuum distillation to remove the light components of isopentenyl alcohol and diisoprene ether mixture; (2) The bottom liquid of the light distillation tower enters the de-isopentenic acid tower for vacuum distillation to remove isopentenic acid; (3) treating the bottom liquid of the de-isopentenylation tower with an effective component recovery tower, and extracting a mixture containing cis- and trans-isodecadienal from the top of the tower; Preferably, the mixed material in the post-processing process of citronellal production includes: 2.8-4.2wt% of isopentenol, 7.9-9wt% of diisoprene ether, 14-16wt% of isopentenic acid, 15-17.5wt% of 7-methyl-3-methylene-6-octenal, 13-14wt% of 3,7-dimethyl-3,6-octadienal, 9-11wt% of cis- and trans-isodecadienal, and 29-32wt% of 3-methyl-6-(1-methylvinyl)cyclohex-2-ene-1-ol.

7. The method according to claim 6, wherein: In step (1), the light removal distillation tower has a theoretical plate number of 20 to 35, a reflux ratio of 1:1 to 4.5:1, and an operating pressure (absolute pressure) of 0.01 to 0.1 bar.

8. The method according to claim 6, wherein: In step (2), the theoretical number of plates of the de-isopentenyl acid tower is 20 to 32, the reflux ratio is 1:1 to 6:1, and the operating pressure (absolute pressure) is 0.10 to 0.25 bar.

9. The method according to claim 6, wherein: In step (3), the effective component recovery tower has 19 to 30 theoretical plates, a reflux ratio of 1:1 to 3:1, and an operating pressure (absolute pressure) of 0.05 to 0.20 bar.

10. The method according to any one of claims 6 to 9, wherein: The cis- and trans-isodecadienal recovered in step (3) are mixed with fresh raw material 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 of any one of claims 1 to 5.

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