Method for continuously producing citronellal from citral and process system thereof
By using an activating gas (NO or NO2) to activate the catalyst in the process of preparing citronellol from citral hydrogenation, the problem of catalyst susceptibility to CO poisoning was solved, and the long-term stable operation of the catalyst and the improvement of product purity were achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- WANHUA CHEM GRP CO LTD
- Filing Date
- 2023-11-17
- Publication Date
- 2026-05-19
AI Technical Summary
In the existing process for preparing citronellol by hydrogenation of citral, the catalyst is easily poisoned by CO produced by the decomposition of aldehydes, leading to catalyst deactivation, which increases the cost of catalyst input and the difficulty of subsequent product purification.
Hydrogen gas containing 100–600 ppm of activation gas (NO or NO2) is used for hydrogenation reaction. The activation gas reacts with CO under the action of a noble metal catalyst to generate CO2 and N2, thereby achieving continuous activation of the catalyst and avoiding CO poisoning.
This achieved long-term stable operation of the catalyst, improved product purity and conversion rate, reduced separation difficulty and energy consumption, and extended the operating cycle of the unit.
Smart Images
Figure CN120020109B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the technical field of citronellol preparation, specifically to a method for selectively hydrogenating citral to prepare citronellol. Background Technology
[0002] Citral (3,7-dimethyl-2,6-octadienyl) is an important acyclic monoterpene aldehyde, and also a crucial pharmaceutical intermediate and raw material for fragrances. Citronellol (3,7-dimethyl-6-octenal), similar to citral, possesses lemon, lemongrass, and rose aromas, and is primarily used in food flavorings, as well as in the formulation of low-grade soap fragrances. Citronellol is a downstream product of citral, an important precursor to citronellol and citronellol nitrile, and can also be used in the synthesis of vitamin E. It is also a key intermediate in the synthesis of menthol.
[0003] Citronellol can be extracted from citronella oil and lemon eucalyptus oil, but the quality of naturally prepared citronellol varies greatly due to factors such as the climate of the producing region and the extraction process. Currently, it is mainly synthesized industrially through chemical synthesis. In existing technologies, most methods obtain citronellol through a batch reaction with a catalyst. After each batch reaction, the catalyst needs to be treated and reused, resulting in numerous auxiliary operations. Furthermore, the hydrogen absorption and heat release in the batch process are unstable, increasing the difficulty of controlling stable operation.
[0004] CN101185904A discloses a catalyst suitable for the selective liquid-phase catalytic hydrogenation of unsaturated carbonyl groups to produce corresponding saturated carbonyl compounds or unsaturated alcohols. The catalyst is a metal component supported on structured composite carbon nanofibers and can be installed in a reactor, making it easier to separate from the material compared to homogeneous catalysts. However, the catalyst preparation process is relatively complex, requiring numerous accessories within the reactor for catalyst fixation. CN108794314A discloses a method for the hydrogenation of citral to citronellol, using citral as a raw material and nickel-molybdenum and palladium-molybdenum as catalysts, successively adding an alkaline co-catalyst and a solvent to prepare citronellol. CN102935384 discloses a novel catalyst, a chiral diphosphorus ligand noble metal complex catalyst, which involves reacting a noble metal compound with perchlorate in an organic polar solvent, followed by the addition of diphosphorus ligands to obtain the catalyst. This catalyst has a long preparation time, and the catalyst and solvent form a homogeneous phase, making catalyst recovery and recycling impossible. Furthermore, the reaction liquid requires washing with water before entering the distillation system for separation, increasing the complexity of the separation process.
[0005] CN110961154A discloses a method for preparing citronellol by hydrogenation of citral, using rare earth catalysts, metal oxides, and Pd as hydrogenation catalysts, and adding N-heterocyclic compounds as promoters to reduce the possibility of aldehyde decomposition to produce CO and suppress catalyst poisoning. However, N-heterocyclic compounds usually have a pungent odor and a low threshold value. To ensure the aroma of citronellol, N-heterocyclic compounds need to be removed, increasing the complexity of post-processing.
[0006] Marco Burgener et al. conducted a detailed study on the catalyst deactivation phenomenon of noble metal catalysts in aldehyde and hydrogen systems. The results showed that the aldehyde group is easy to decompose and produce trace amounts of CO during the reaction, which has a poisoning effect on Pd catalysts, leading to the loss of catalyst activity.
[0007] As can be seen from the above, the process of hydrogenating citral to citronellol focuses on catalyst research. Furthermore, the citral hydrogenation system is prone to producing trace amounts of CO due to the decomposition of aldehydes, which can lead to catalyst deactivation and reduced catalyst utilization. To address the catalyst deactivation problem in the reaction of citral to citronellol, complex catalyst treatment or the use of multiple auxiliaries is required, increasing the catalyst input cost in the process and also making subsequent product purification more difficult. Summary of the Invention
[0008] To overcome the shortcomings of the prior art, this invention provides a method and apparatus for the continuous preparation of citronellol from citral. The catalyst can be recycled inside the reactor and is equipped with online catalyst activation measures, which overcomes the disadvantage that precious metal catalysts in aldehyde systems are easily poisoned by CO generated from aldehyde decomposition.
[0009] To achieve the above objectives, the present invention adopts the following technical solution:
[0010] The present invention provides a method for the continuous production of citronellol from citral in the first aspect, wherein citronellol is produced by hydrogenation reaction of citral under the catalysis of a catalyst; wherein the hydrogen introduced in the hydrogenation reaction contains 100 to 600 ppm of an activation gas; the activation gas is selected from NO or NO2.
[0011] The preparation method of the present invention continuously introduces H2 containing trace amounts of NO or NO2 into the reaction vessel. NO or NO2 reacts with CO under the action of a noble metal catalyst to generate CO2 and N2, thereby achieving continuous activation of the catalyst and overcoming the disadvantage that noble metal catalysts in aldehyde systems are easily poisoned by CO generated from aldehyde decomposition.
[0012] In some specific embodiments, the hydrogen gas introduced during the hydrogenation reaction contains 200 to 500 ppm of NO.
[0013] In some specific embodiments, the hydrogenation reaction is carried out in the presence of diethyl ether or a mixture of water and diethyl ether as solvent; the amount of solvent added is 10% to 80% of the mass of citral, preferably 40% to 60%.
[0014] In some specific embodiments, the amount of catalyst added is 0.5 to 5% of the mass of citral, preferably 1.5 to 3%.
[0015] In some specific embodiments, the catalyst is selected from palladium catalysts supported on activated carbon, ruthenium catalysts supported on activated carbon, or palladium catalysts supported on molecular sieves.
[0016] In some specific embodiments, the temperature of the hydrogenation reaction is 35–150°C, preferably 50–90°C; the operating pressure is 0–1.0 MPaG, preferably 0.2–0.5 MPaG.
[0017] In a second aspect, the present invention provides a process system for the continuous production of citronellol using the above-described method, comprising:
[0018] Hydrogen feed line: used to supply hydrogen into the reactor;
[0019] Raw material feed line: used to transport citral and solvent into the reactor;
[0020] Catalyst feed line: Used to deliver catalyst into the reactor;
[0021] Activation gas delivery pipeline: Connected to the activation gas inlet at the bottom of the reactor, used to deliver activation gas into the reactor;
[0022] Reactor: used to provide a reaction site for the hydrogenation reaction of citral and hydrogen; the top of the reactor is provided with a gas phase outlet, which is connected to distillation column I; the bottom of the reactor is provided with a discharge port and an activation gas inlet, which is connected to distillation column II.
[0023] Distillation column I is used to separate the gas phase in the reactor; the liquid phase condensed at the top of the column is recycled back to the reactor as a solvent; the gas phase at the top of the column is compressed and connected to the activation gas delivery pipeline and then returned to the reactor; the separated product liquid containing light components is transported to distillation column II for purification.
[0024] Distillation column II is used to refine the product from the outlet of the reactor and the product liquid containing light components collected from the side stream of distillation column I to obtain light components, heavy components and citronellal products.
[0025] The reactor used in the process system of this invention is a commonly used high-pressure resistant reactor, for example, with a height-to-diameter ratio of 1.2:1 to 1 and an elliptical head. In some specific embodiments, a filter is installed above the outlet of the reactor, and multiple activation gas inlets are arranged around the outlet. After the activation gas enters the bottom of the reactor through the inlets, it blows the catalyst attached to the filter screen away from the filter screen and intercepts it inside the reactor, ensuring the catalyst concentration in the bulk of the reaction liquid. This system also functions as both catalyst filtration and gas dispersion. At the same time, it enhances the mass transfer within the reactor, reduces the power of the agitator inside the reactor, and thus ensures continuous recycling of the catalyst and long-term operation of the device.
[0026] In some specific implementations, citral and solvent are continuously introduced into the reactor together, and hydrogen is fed through a conventional inlet pipe. The hydrogen is dispersed in the reactor by stirring.
[0027] In some specific embodiments, the reactor in this invention transfers heat through solvent vaporization within the reactor, and maintains the temperature inside the reactor by adjusting the liquid temperature at the bottom of the condenser at the top of distillation column I. Compared to the traditional reactor with internal coils, this heat transfer method greatly simplifies the complexity of in-reactor processing, while simultaneously achieving coarse separation of solvent and light components, reducing energy consumption in the separation process.
[0028] In the specific process system of this invention, the top gas phase obtained by separation in distillation column I is condensed in the exhaust condenser, then compressed by the compressor and returned to the reactor along with the activated gas in the activated gas delivery pipeline. The process system of this invention achieves online activity of the hydrogenation reaction catalyst by controlling the content of activated gas in the activated gas delivery pipeline, improves the problem of precious metal catalysts in the aldehyde system being easily poisoned by CO generated by aldehyde decomposition, and improves the stable operating time of the hydrogenation reaction catalyst.
[0029] In some specific implementations, the compressor outlet also has an exhaust line for discharging non-condensable gases from the system. An exhaust valve is installed on the line, and the pressure inside the reactor can be indirectly adjusted by regulating the opening of the exhaust valve.
[0030] In some specific process systems, the gas phase pipeline at the top of the reactor is drawn out to distillation column I to separate the product from the solvent, while also removing heat from the reactor.
[0031] In some specific embodiments, a nitrogen outlet can be provided in the catalyst feed line to blow the catalyst into the reactor; in some more specific embodiments, the catalyst can be fed by blowing the solid catalyst into the reactor with hot nitrogen carrying water vapor. Specifically, a nitrogen preheater and a water tank can be provided in the catalyst feed line to achieve the feeding of the catalyst with hot nitrogen carrying water vapor, thereby reducing the dust problem of the solid catalyst.
[0032] The above technical solution achieves the following technical effects:
[0033] This invention utilizes hydrogen gas containing NO to achieve online activation of the catalyst, effectively maintaining the long-term operational stability of the catalyst, with a stable operating time of up to 3600 hours. Simultaneously, NO, as an oxidizing gas, can react with CO generated from aldehydes under the influence of precious metals to produce CO2 and N2, resulting in environmentally friendly products without generating excess substances.
[0034] The substances generated by the online activation of the catalyst form a minimum azeotrope with the light components of the reaction, reducing the difficulty of separation, improving product purity, and reducing the content of light components in the product.
[0035] The process system of this invention uses solvent evaporation to remove heat, which maximizes the utilization of the latent heat of the solvent and improves the heat removal efficiency; it also uses distillation to achieve solvent recycling and reduce the energy consumption of solvent separation. Attached Figure Description
[0036] Figure 1 This is a specific embodiment of the process system for preparing citronellal from citral provided by the present invention;
[0037] Among them, 1. Nitrogen preheater, 2. Water tank, 3. Reactor, 4. Distillation column I, 5. Distillation column II, 6. Exhaust condenser, and 7. Compressor. Detailed Implementation
[0038] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.
[0039] The following analytical instruments and methods were used for the products in the following examples: Agilent 7890 gas chromatograph with a capillary column (DB-5, 30m × 0.25mm × 0.25μm), injection port temperature of 300℃, and a split ratio of 50:1. Carrier gas flow rate was 50ml / min. The temperature program was: 120℃ for 15min, then increased to 250℃ at a rate of 10℃ / min and held for 10min. The detector temperature was 280℃. This instrument was used to characterize the conversion rate of citral and the selectivity of citronellol.
[0040] The following examples use a stirred tank reactor, wherein the total volume of the stirred tank reactor is 0.7 m³. 3 It has a diameter of 800mm, a height of 1000mm, a diameter of 6mm for the activation gas inlet at the bottom of the vessel, and a wall thickness of 1.8mm. Figure 1 As shown, the process system of the present invention specifically includes: a reactor 3, a hydrogen feed line, a raw material feed line, a catalyst feed line, an activation gas delivery pipeline, a distillation column I 4, and a distillation column II 5; a gas phase outlet is provided at the top of the reactor 3, which is connected to the distillation column I 4; a discharge port and an activation gas inlet are provided at the bottom of the reactor 3, with the discharge port connected to the distillation column II 5. A hydrogen feed line for conveying hydrogen, a raw material feed line for conveying citral and solvent, a catalyst feed line for conveying catalyst, and an activation gas delivery pipeline for conveying activation gas into the reactor are also connected to the side wall of the reactor 3.
[0041] Distillation column I4 is used to separate the gas phase in reactor 3. The liquid phase condensed at the top of the column is recycled back to reactor 3 as a solvent. The gas phase at the top of the column is condensed in exhaust condenser 6, then compressed by compressor 7 and connected to the activation gas pipeline before being recycled back to reactor 3. The product liquid containing light components obtained from distillation column I4 is sent to distillation column II5 for purification. Distillation column II5 is used to purify the product from the outlet of reactor 3 and the product liquid containing light components collected from the side stream of distillation column I4, finally obtaining light components, heavy components, and citronellal products.
[0042] A nitrogen outlet is also provided on the catalyst feed line to purge the catalyst from the feed line into the reactor. A filter is installed above the outlet of reactor 3 to intercept the catalyst in the product within the reactor through the filter screen.
[0043] Example 1
[0044] Adopting such Figure 1 In the process system shown, nitrogen gas is preheated to 60°C by nitrogen preheater 1 and then enters water tank 2 from the bottom. The nitrogen feed rate is 20 Nm³. 3 / hr, the outlet of water tank 2 is hot nitrogen gas entrained with water, and the water content in the nitrogen gas is 1.5%.
[0045] Diethyl ether and citral are continuously fed into reactor 3 from the feed line at a ratio of 2:3, with a total feed rate of 50 kg / hr. The reaction pressure inside reactor 3 is controlled at 0.4 MPaG by the feed regulating valve on the hydrogen feed line and the exhaust regulating valve on the gas phase pipeline of distillation column 4Ⅰ. Simultaneously, the reaction temperature inside reactor 3 is 80℃. Activated carbon-supported palladium catalyst is added to reactor 3 through the catalyst feed line at a rate of 1% of the mass of citral.
[0046] During the reaction, hydrogen gas containing the activating gas NO is continuously returned to reactor 3 from the activating gas delivery pipeline, with the injection rate controlled at 10 Nm. 3 / hr, of which the NO content is 200ppm, the bottom of reactor 3 continuously discharges material, and the continuous discharge rate is 50kg / hr.
[0047] The reaction was carried out for 720 hours. Samples were taken every 6 hours from the liquid line of reactor 3 and the product outlet of distillation column II 5 to analyze the content of citronellal and citral. No decrease in citral conversion rate or selectivity was observed during the 720 hours of reaction.
[0048] Tests showed that the conversion rate of citral was 99%, the selectivity of citronellol was 95%, and the product purity was 99%.
[0049] The operating conditions were maintained for 3600 hours. Samples were taken every 24 hours from the reactor's lower liquid line and the product outlet of distillation column II to analyze the content of citronellal and citral. The conversion rate and selectivity of citral were calculated, and no significant decrease was observed. The conversion rate of citral was ≥98%, the selectivity of citronellal was ≥93%, and the purity was ≥99%. The results indicate that this method can achieve long-term operation of the catalyst.
[0050] Example 2
[0051] Example 2 used the same equipment, reaction pressure, reaction temperature, and catalyst concentration as Example 1. During the reaction, hydrogen gas containing the activating gas NO was continuously introduced into the reactor through the activating gas delivery pipeline, with the introduction rate controlled at 10 Nm. 3 / hr, NO content is 400ppm, continuous discharge from the bottom of the reactor, continuous discharge rate is 50kg / hr.
[0052] The reaction was carried out for 720 hours. Samples were taken every 6 hours from the reactor's liquid outlet and the product outlet of distillation column II to analyze the content of citronellal and citral. No decrease in citral conversion rate or selectivity was observed during the 720 hours of reaction.
[0053] The test results showed that the conversion rate of citral was 99%, the selectivity of citronellol was 95%, and the purity was 99.4%.
[0054] The operating conditions were maintained for 3600 hours. Samples were taken every 24 hours from the reactor's lower liquid line and the product outlet of distillation column II to analyze the content of citronellal and citral. The conversion rate and selectivity of citral were calculated, and no significant decrease was observed. The conversion rate of citral was ≥98%, the selectivity of citronellal was ≥93%, and the purity was ≥99%. The results indicate that this method can achieve long-term operation of the catalyst.
[0055] Example 3
[0056] Example 3 used the same equipment, reaction pressure, reaction temperature, and catalyst concentration as Example 1. During the reaction, hydrogen gas containing NO2, the activating gas, was continuously introduced into the reactor through the activating gas delivery pipeline at a controlled flow rate of 10 Nm. 3 The NO2 content is 400ppm, and the material is continuously discharged from the bottom of the reactor. The continuous output rate is 50kg / hr.
[0057] The reaction was carried out for 720 hours. Samples were taken every 6 hours from the reactor's liquid outlet and the product outlet of distillation column II to analyze the content of citronellal and citral. No decrease in citral conversion rate or selectivity was observed during the 720 hours of reaction.
[0058] Tests showed that the conversion rate of citral was 99%, the selectivity of citronellol was 95%, and the purity was 99.3%.
[0059] The operating conditions were maintained for 3600 hours. Samples were taken every 24 hours from the reactor's lower liquid line and the product outlet of distillation column II to analyze the content of citronellal and citral. The conversion rate and selectivity of citral were calculated, and no significant decrease was observed. The conversion rate of citral was ≥98%, the selectivity of citronellal was ≥93%, and the purity was ≥99%. The results indicate that this method can achieve long-term operation of the catalyst.
[0060] Comparative Example 1
[0061] This comparative example uses the same equipment, reaction pressure, reaction temperature, and catalyst concentration as Example 1. The difference is that NO or NO2 is no longer introduced into the activation gas delivery line; the hydrogen is introduced into the reactor at a rate of 10 Nm. 3 / hr, continuous discharge from the bottom of the reactor, with a continuous discharge rate of 50kg / hr.
[0062] The reaction was carried out for 720 hours. Samples were taken every 6 hours from the reactor's liquid outlet and the product outlet of distillation column II to analyze the content of citronellal and citral. It was found that the conversion rate began to decrease after 60 hours and continued until the 720-hour mark, with a citral conversion rate of 40%, a selectivity of 90%, and a product purity of 85%.
[0063] Comparative Example 2
[0064] Comparative Example 2 used the same equipment, reaction pressure, reaction temperature, and catalyst concentration as Example 1. The difference was that the activation gas NO was introduced into the reactor through the hydrogen feed line, instead of through the activation gas delivery line at the bottom of the reactor.
[0065] The reaction was carried out for 720 hours. Samples were taken every 6 hours from the reactor's liquid outlet and the product outlet of distillation column II to analyze the content of citronellal and citral. It was found that the conversion rate began to decrease from 30 hours until the 720-hour mark, with a citral conversion rate of 50%, a selectivity of 85%, and a product purity of 88%.
[0066] Comparative Example 3
[0067] This comparative example used the same equipment, reaction pressure, reaction temperature, and catalyst concentration as Example 1. During the reaction, hydrogen gas containing the activating gas NO was continuously introduced into the reactor through the activating gas delivery pipeline, with the introduction rate controlled at 10 Nm. 3 / hr, NO content is 1000ppm, continuous discharge from the bottom of the reactor, continuous discharge rate is 50kg / hr.
[0068] The reaction was carried out for 720 hours. Every 6 hours, samples were taken from the liquid outlet of the reactor and the product outlet of distillation column II to analyze the content of citronellal and citral.
[0069] Starting from 240 hours, the conversion rate of citral begins to decrease, and by 720 hours of reaction, the conversion rate of citral has decreased to 85%, the selectivity of citronellol is 90%, and the product purity is 99%.
[0070] Comparative Example 4
[0071] This comparative example used the same equipment, reaction pressure, reaction temperature, and catalyst concentration as Example 1. During the reaction, hydrogen gas containing the activating gas NO was continuously introduced into the reactor through the activating gas delivery pipeline, with the introduction rate controlled at 10 Nm. 3 The NO content is 50ppm, and the material is continuously discharged from the bottom of the reactor at a rate of 50kg / hr.
[0072] The reaction was carried out for 720 hours. Every 6 hours, samples were taken from the liquid outlet of the reactor and the product outlet of distillation column II to analyze the content of citronellal and citral.
[0073] Starting from 200 hours, the conversion rate of citral showed a decreasing trend. After testing, the conversion rate of citral decreased to 85% at 720 hours, the selectivity of citronellol was 93%, and the product purity was 98.5%.
Claims
1. A method for the continuous production of citronellol from citral, characterized in that, Citronellol is prepared by hydrogenation reaction of citral under the catalysis of a catalyst. The hydrogen gas introduced in the hydrogenation reaction contains 100-600 ppm of activation gas; the activation gas is selected from NO or NO2. The catalyst is selected from palladium catalyst supported on activated carbon, ruthenium catalyst supported on activated carbon, or palladium catalyst supported on molecular sieves. The hydrogenation reaction is carried out inside the reactor, and the activation gas is introduced through the activation gas delivery pipeline at the bottom of the reactor.
2. The method according to claim 1, characterized in that, The hydrogen gas introduced in the hydrogenation reaction contains 200-500 ppm of NO or NO2.
3. The method according to claim 1 or 2, characterized in that, The hydrogenation reaction is carried out in the presence of diethyl ether or a mixture of water and diethyl ether as solvent; The amount of solvent added is 10% to 80% of the mass of citral.
4. The method according to claim 3, characterized in that, The amount of solvent added is 40% to 60% of the mass of citral.
5. The method according to claim 1, characterized in that, The amount of catalyst added is 0.5 to 5% of the mass of citral.
6. The method according to claim 5, characterized in that, The amount of catalyst added is 1.5 to 3% of the mass of citral.
7. The method according to any one of claims 1-2 and 4-6, characterized in that, The hydrogenation reaction is carried out at a temperature of 35~150℃; The operating pressure is 0~1.0 MPaG.
8. The method according to claim 7, characterized in that, The hydrogenation reaction is carried out at a temperature of 50~90℃.
9. The method according to claim 7, characterized in that, The operating pressure is 0.2~0.5 MPaG.
10. A process system for the continuous production of citronellol using any one of claims 1 to 9, characterized in that, include: Hydrogen feed line: used to supply hydrogen into the reactor; Raw material feed line: used to transport citral and solvent into the reactor; Catalyst feed line: Used to deliver catalyst into the reactor; Activation gas delivery pipeline: Connected to the activation gas inlet at the bottom of the reactor, used to deliver activation gas into the reactor; Reactor: used to provide a reaction site for the hydrogenation reaction of citral and hydrogen; the top of the reactor is provided with a gas phase outlet, which is connected to distillation column I; the bottom of the reactor is provided with a discharge port and an activation gas inlet, which is connected to distillation column II. Distillation column I is used to separate the gas phase in the reactor; the liquid phase condensed at the top of the column is recycled back to the reactor as a solvent; the gas phase at the top of the column is compressed and connected to the activation gas delivery pipeline and then returned to the reactor; the separated product liquid containing light components is transported to distillation column II for purification. Distillation column II is used to refine the product from the outlet of the reactor and the product liquid containing light components collected from the side stream of distillation column I to obtain light components, heavy components and citronellal products.
11. The process system according to claim 10, characterized in that, The gas phase at the top of the distillation column I is compressed by the compressor and then returned to the reactor via the activation gas delivery pipeline.
12. The process system according to claim 11, characterized in that, The catalyst feed line is also equipped with a nitrogen outlet, which is used to blow the catalyst from the catalyst feed line into the reactor.
13. The process system according to claim 12, characterized in that, A filter is installed above the outlet of the reactor to intercept the catalyst in the product within the reactor through the filter screen.