A method for efficiently preparing r-citronellal
By pretreating citral feedstock to reduce formaldehyde content and using a porous support and a catalyst loaded with active components, the problem of low catalyst activity in the asymmetric hydrogenation of citral to R-citronellol was solved, achieving efficient R-citronellol production, reducing production costs and improving economic benefits.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- WANHUA CHEM GRP CO LTD
- Filing Date
- 2020-02-24
- Publication Date
- 2026-05-19
AI Technical Summary
In the existing technology, the method of preparing R-citronellol by asymmetric hydrogenation of citral has low catalyst activity under high S/C conditions, resulting in high production costs and complicated recycling process, which makes it difficult to meet actual production needs.
The formaldehyde content was reduced by pretreating citral raw material, and polyoxymethylene was adsorbed and depolymerized using a porous support. Combined with a catalyst supported on active components, the activity and stability of the catalyst under high S/C conditions were improved. A catalyst generated by complexing Rh-based metal compounds with bisphosphine ligands was used to reduce the formaldehyde content to less than 100 ppm.
High conversion rate and selectivity of R-citronellol were achieved under high S/C conditions, reducing recycling and improving production efficiency and economic benefits.
Abstract
Description
Technical Field
[0001] This invention belongs to the field of fine chemical synthesis, specifically relating to an efficient method for preparing R-citronellol. Background of the Invention
[0002] Citronellol, also known as 3,7-dimethyl-6-octenal, contains a single chiral carbon atom in its molecule, thus exhibiting both R and S configurations. Citronellol possesses a strong, fresh, citrus-like aroma with a slight woody note, and it has wide applications in food, fragrances, and cosmetics. R-citronellol is an important fragrance component and a key precursor in the synthesis of the important fragrance L-menthol.
[0003] Currently, there are two main methods for industrially synthesizing R-citronellol: one is the asymmetric catalytic synthesis of R-citronellol from geraniol by Takasago Ltd. of Japan, and the other is the selective hydrogenation synthesis of R-citronellol from citral by BASF Ltd. The latter has a wider range of applications.
[0004] There are several synthetic routes for citral (neraldehyde and / or geranialdehyde), one of which uses formaldehyde and isobutylene as starting materials and involves multiple steps of oxidation, transposition, condensation, and rearrangement to synthesize citral, offering significant technological advantages. However, this synthetic route results in the final product, citral, containing a certain amount of formaldehyde monomers and polymers. Because the polymerization of formaldehyde monomers and the depolymerization of formaldehyde polymers are constantly in progress, simple distillation cannot remove the formaldehyde from the product, leading to the presence of formaldehyde monomers and polymers in the final citral product.
[0005] CN101932543A and CN101039894B both disclose methods for preparing R-citronellol from citral by asymmetric hydrogenation. These methods specifically specify that the catalyst used must have at least one carbon monoxide ligand, and that the substrate must be pre-treated with a gas containing a certain amount of CO before the reaction. While the reported methods have the advantages of high chemoselectivity and high stereoselectivity, the homogeneous transition metal catalysts described in these methods suffer from low hydrogenation efficiency, especially at high S / C ratios (substrate / catalyst greater than 5000:1), where the reaction conversion rate significantly decreases, failing to meet the needs of practical production. Therefore, this catalytic system can only be repeatedly recycled at low S / C ratios (substrate / catalyst less than 5000:1) to improve catalyst utilization. However, this leads to increased complexity in the recycling process, increased equipment investment, and losses during recycling, resulting in persistently high production costs.
[0006] Therefore, it is necessary to find a reasonable solution to enable the asymmetric hydrogenation of citral to prepare R-citronellol under high S / C conditions, thereby reducing production costs and improving economic efficiency. Summary of the Invention
[0007] The purpose of this invention is to provide an efficient method for preparing R-citronellol, which allows the reaction to prepare R-citronellol to be carried out under high S / C (substrate / catalyst) conditions, reducing recycling and thus significantly improving production efficiency.
[0008] The applicant has surprisingly discovered that by reducing the formaldehyde content in the substrate (nerol and / or geraniol), the catalytic activity of the catalyst under high S / C conditions can be significantly improved, thus solving the problem of low catalytic hydrogenation efficiency of homogeneous transition metal catalysts in the prior art.
[0009] To achieve the above-mentioned objectives, the technical solution adopted by the present invention is as follows:
[0010] A method for efficiently preparing R-citronellol from citral, the method comprising the following steps:
[0011] S1: Pre-treat citral raw materials to reduce the formaldehyde content in citral;
[0012] S2: R-citronellol is prepared by asymmetric hydrogenation of catalytically treated citral.
[0013] The principle of the pretreatment step of the citral feedstock in this invention is as follows: The catalyst used in the asymmetric hydrogenation of citral to R-citronellol in S2 is a complex catalyst, such as the complexation of Rh-based metal compounds with bisphosphine ligands, i.e., Rh(CO)2acac and (R,R)-chiraphos. The catalyst contains a carbonyl group and has poor stability, which may lead to the removal of the carbonyl group (C=O) from Rh(CO)2acac, resulting in the loss of catalyst activity. Therefore, CO gas is added for pretreatment before the reaction. The purpose of pretreatment is to allow the decarbonylated catalyst to regain the carbonyl group, thereby regaining catalytic activity. The formaldehyde brought by citral also contains a carbonyl group, which will compete with the added CO gas to enter the decarbonylated Rh(CO)2acac. Once formaldehyde enters the decarbonylated Rh(CO)2acac, it will lead to a decrease in catalyst stability, which in turn leads to a decrease in catalyst activity. This decrease in activity becomes more pronounced with the increase of S / C. To address the aforementioned issues, the catalyst prepared in this invention reduces formaldehyde content through the adsorption of formaldehyde monomers on a porous support. Simultaneously, it depolymerizes paraformaldehyde by loading active centers, and the resulting formaldehyde monomers are also adsorbed by the porous support. Through the combined effect of these two pathways, the formaldehyde content in the substrate is reduced, thereby increasing the reaction rate under high S / C conditions.
[0014] In this invention, the method for reducing the formaldehyde content in citral as described in S1 is to catalytically decompose polyoxymethylene and / or adsorb formaldehyde; the adsorbed formaldehyde includes the original formaldehyde in citral and the formaldehyde formed by the catalytic decomposition of polyoxymethylene.
[0015] In this invention, the process for reducing the formaldehyde content in citral involves packing catalyst A into a pretreatment tower, where citral undergoes catalytic decomposition of the contained polyoxymethylene and / or adsorption of formaldehyde through the catalyst bed, and the pretreated citral enters reactor S2.
[0016] Preferably, the catalyst bed packing height in the pretreatment tower is 0.3–0.5 m, and citral is added at a concentration of 400–800 h⁻¹. -1 The air velocity passes through the catalyst bed and then enters the reactor of S2.
[0017] In some embodiments, the formaldehyde content in citral after S1 treatment is less than 100 ppm, preferably less than 50 ppm, more preferably less than 20 ppm, while the formaldehyde content in untreated citral is generally 100-200 ppm.
[0018] In this invention, the S2 reaction process involves adding catalyst B into a reaction vessel, replacing the air in the vessel with nitrogen, adding the substrate citral, replacing the nitrogen in the vessel with H2, continuing to purge with H2, purging with CO gas, and then heating up to carry out the reaction.
[0019] In some embodiments, the molar ratio (S / C) of citral to catalyst B in S2 is greater than 5000:1, preferably (10,000-100,000):1. It is known in the art that in the prior art, S / C is generally less than 5000:1; therefore, the above-mentioned S / C greater than 5000:1 represents a high substrate / catalyst ratio. Of course, it is understood that the method of the present invention is also applicable to cases where S / C is less than 5000:1.
[0020] Another object of the present invention is to provide a catalyst for controlling the formaldehyde content in citral.
[0021] A catalyst A for controlling the formaldehyde content in citral in the citronellol preparation method.
[0022] In this invention, catalyst A comprises a support and an active component;
[0023] Preferably, the carrier is a porous carrier, preferably selected from one or more of Al2O3, activated carbon, all-silica molecular sieve, kaolin and attapulgite, and more preferably Al2O3;
[0024] Preferably, the active component is a group VIII element, preferably one or more of Pt, Ru, and Co, more preferably Pt; the Pt may be derived from one or more of platinum dichloride, sodium chloroplatinate, platinum nitrate, chloroplatinic acid, platinum acetylacetonate, and potassium chloroplatinate.
[0025] In this invention, in order to eliminate the influence of internal diffusion, improve the catalyst processing capacity, and reduce the amount of active component, it is preferable to load the active component of catalyst A onto the outer surface of the support.
[0026] To load the active component onto the outer surface of the support, the preferred catalyst raw material combination of the present invention is Al2O3 and chloroplatinic acid, because Al2O3 and chloroplatinic acid have a strong adsorption effect, and the active component Pt can be highly concentrated on the outer surface of Al2O3.
[0027] In this invention, the loading amount of the active component is 1 wt% to 10 wt% of the carrier mass, preferably 3 wt% to 8 wt%. The loading method is impregnation.
[0028] In this invention, the catalyst is prepared by mixing the active component and the support evenly, adding water, and then allowing it to stand, drying and calcining to obtain the finished catalyst.
[0029] Preferably, the settling temperature is 10-20℃ and the settling time is 10-20h;
[0030] Preferably, the drying temperature is 80-150℃ and the drying time is 3-5 hours;
[0031] Preferably, the roasting temperature is 200-300℃ and the roasting time is 3-5h.
[0032] Another object of the present invention is to provide an R-citronellol.
[0033] R-citronellol prepared by the citronellol preparation method described above or by pretreatment of citral with the catalyst described above to control formaldehyde content.
[0034] The citral described in this invention can be neraldehyde and / or geranialdehyde. As is well known in the art, neraldehyde can be obtained from citral through a common distillation process.
[0035] The present invention has the following beneficial effects:
[0036] (1) The method of the present invention can be used in high S / C (substrate / catalyst) reaction conditions, and even under high S / C conditions, a higher conversion rate (conversion rate > 90% within 8h) can be obtained. At the same time, the selectivity of R-citronellol is also slightly higher than that of the existing method, which can reduce the recycling and greatly improve production efficiency and economic benefits.
[0037] (2) The added citral pretreatment process is simple, and the catalyst preparation method is simple and easy to implement, which is suitable for practical industrial applications. Detailed Implementation
[0038] The method of the present invention will be further illustrated below through specific embodiments, 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.
[0039] Analytical instruments:
[0040] Gas chromatograph: Agilent 7890, column DB-5, injection port temperature 300℃; split ratio 50:1; carrier gas flow rate 50 ml / min; temperature program: 120℃ for 15 min, ramped to 250℃ at a rate of 10℃ / min, held for 10 min, detector temperature 280℃. This instrument was used to characterize citral conversion, R-citronellol selectivity, and formaldehyde content.
[0041] Raw materials and reagents:
[0042] Citral: Purity > 99%, Hubei Julongtang Pharmaceutical Chemical Co., Ltd.;
[0043] Neraldehyde: Purity > 99%, obtained by distillation of citral as described above, the distillation method is well known;
[0044] Chloroplatinic acid hexahydrate: Pt content 37.5%, Aladdin Reagent Co., Ltd.;
[0045] Neutral alumina: 60-100 mesh, Aladdin Reagent Co., Ltd.;
[0046] Ammonium hexachlororuthenate: Ru content 28.4%, Aladdin Reagent Co., Ltd.;
[0047] Activated carbon: 60-100 mesh, Aladdin Reagent Co., Ltd.
[0048] Catalyst B was prepared by complexing Rh-based metal compounds with bisphosphine ligands, namely Rh(CO)2acac and (R,R)-chiraphos.
[0049] S1 pretreatment tower: The inner diameter of the tower is 0.3m, and the height to which the catalyst can be filled is 0.2-1.0m;
[0050] The S2 reactor is a 2.5L batch reactor with a built-in self-priming agitator.
[0051] Example 1
[0052] Weigh 10g of Al2O3 and 0.27g of chloroplatinic acid hexahydrate into a beaker, mix them evenly, add deionized water dropwise into the beaker until the liquid level just covers the surface of the mixture, let the beaker stand at 10℃ for 10h, then dry it at 80℃ for 3h, and calcine it at 200℃ for 3h to obtain catalyst A#1.
[0053] Catalyst A (No. 1) was loaded into the pretreatment tower to a height of 0.3m, allowing nerol to react at a concentration of 400 h⁻¹. -1 The air velocity was passed through the catalyst bed to obtain 1500g of pretreated neraldehyde. Testing revealed that the formaldehyde content in the raw neraldehyde was 102ppm, and the formaldehyde content in the pretreated product was 12ppm.
[0054] (170.28 mg, 0.66 mmol) Rh(CO)₂acac and (283.8 mg, 0.66 mmol) (R,R)-chiraphos were added to a reactor (1 mol Rh(CO)₂acac and 1 mol (R,R)-chiraphos coordinate to generate 1 mol of catalyst, the same in subsequent examples). The air in the reactor was purged with nitrogen for 5 min. Then, 1000 g, 6.60 mol) neraldehyde pretreated was added to the reactor to make the S / C ratio 10,000:1. The nitrogen in the reactor was purged with H₂ for 5 min. Hydrogen was then introduced to 6 MPa (G), and CO gas was introduced to make the CO content in the reactor 5000 ppm. The temperature was started and the reactor temperature reached 60 °C, which was recorded as 0 h. After 8 h, the conversion rate was 92.1% and the selectivity of R-citronellol was 86.4%.
[0055] Example 2
[0056] Weigh 10g of Al2O3 and 1g of chloroplatinic acid hexahydrate into a beaker, mix them evenly, add deionized water dropwise into the beaker until the liquid level just covers the surface of the mixture, let the beaker stand at 20℃ for 20h, then dry it at 150℃ for 5h, and calcine it at 300℃ for 5h to obtain catalyst A, No. 2.
[0057] Catalyst A (No. 2) was loaded into the pretreatment tower to a height of 0.4 m, allowing nerol to react at a concentration of 600 h⁻¹. -1 The air velocity was passed through the catalyst bed to obtain 1500g of pretreated neraldehyde. Testing revealed that the formaldehyde content in the raw neraldehyde was 110ppm, while the formaldehyde content in the pretreated product was 8ppm.
[0058] (170.28 mg, 0.66 mmol) Rh(CO)2acac and (283.8 mg, 0.66 mmol) (R,R)-chiraphos were added to a reactor. The air in the reactor was purged with nitrogen for 5 min. Then, (1000 g, 6.60 mol) neraldehyde pretreated was added to the reactor to make the S / C ratio 10,000:1. The nitrogen in the reactor was purged with H2 for 5 min. Hydrogen was then introduced to 6 MPa (G), and CO gas was introduced to make the CO content 5000 ppm. The temperature was started and the reactor temperature reached 60 °C, which was recorded as 0 h. After 8 h, the conversion rate was 98.6% and the selectivity of R-citronellol was 85.9%.
[0059] Example 3
[0060] Weigh 10g of Al2O3 and 2.66g of chloroplatinic acid hexahydrate into a beaker, mix them evenly, add deionized water dropwise into the beaker until the liquid level just covers the surface of the mixture, let the beaker stand at 15℃ for 15h, then dry it at 80℃ for 4h, and calcine it at 250℃ for 4h to obtain catalyst A#3.
[0061] Catalyst A (No. 3) was loaded into the pretreatment tower to a height of 0.5m, allowing nerol to react at a concentration of 800 h⁻¹. -1 The air velocity was passed through the catalyst bed to obtain 1500g of pretreated neraldehyde. Testing revealed that the formaldehyde content in the raw neraldehyde was 107ppm, and the formaldehyde content in the pretreated product was 16ppm.
[0062] (21.29 mg, 0.083 mmol) Rh(CO)2acac and (35.48 mg, 0.083 mmol) (R,R)-chiraphos were added to a reactor. The air in the reactor was purged with nitrogen for 5 min. Then, (1000 g, 6.60 mol) neraldehyde pretreated was added to the reactor to make the S / C ratio 80,000:1. The nitrogen in the reactor was purged with H2 for 5 min. Hydrogen was then introduced to 6 MPa (G), and CO gas was introduced to make the CO content in the reactor 5000 ppm. The temperature was started and the reactor temperature was recorded as 0 h when it reached 60 °C. After 8 h, the conversion rate was 90.9% and the selectivity of R-citronellol was 86.1%.
[0063] Example 4
[0064] Weigh 10g of activated carbon and 1.8g of ammonium hexachlororuthenate into a beaker, mix them evenly, add deionized water dropwise into the beaker until the liquid level just covers the surface of the mixture, let the beaker stand at 15℃ for 10h, then dry it at 100℃ for 4h, and calcine it at 250℃ for 4h to obtain catalyst A#4.
[0065] Catalyst A (No. 4) was loaded into the pretreatment tower to a height of 0.5m, allowing nerol to react at a concentration of 800 h⁻¹. -1 The air velocity was passed through the catalyst bed to obtain 1500g of pretreated neraldehyde. Testing revealed that the formaldehyde content in the raw neraldehyde was 118ppm, and the formaldehyde content in the pretreated product was 21ppm.
[0066] (170.28 mg, 0.66 mmol) Rh(CO)2acac and (283.8 mg, 0.66 mmol) (R,R)-chiraphos were added to a reactor. The air in the reactor was purged with nitrogen for 5 min. Then, (1000 g, 6.60 mol) neraldehyde pretreated was added to the reactor to make the S / C ratio 10,000:1. The nitrogen in the reactor was purged with H2 for 5 min. Hydrogen was then introduced to 6 MPa (G), and CO gas was introduced to make the CO content in the reactor 5000 ppm. The temperature was started and the reactor temperature reached 60 °C, which was recorded as 0 h. After 8 h, the conversion rate was 91.1% and the selectivity of R-citronellol was 85.9%.
[0067] Comparative Example 1
[0068] (170.28 mg, 0.66 mmol) Rh(CO)₂acac and (283.8 mg, 0.66 mmol) (R,R)-chiraphos were added to a reactor. The air in the reactor was purged with nitrogen for 5 min. Then, (1000 g, 6.60 mol) of untreated neraldehyde was added to the reactor, making the S / C ratio 10,000:1. The nitrogen in the reactor was purged with H₂ for 5 min, and hydrogen was introduced to 6 MPa (G). CO gas was then introduced to make the CO content in the reactor 5000 ppm. The temperature was started and increased. The time when the temperature inside the reactor reached 60 °C was recorded as 0 h. After 8 h, the conversion rate was 31.0%, and the selectivity of R-citronellol was 85.8%. The formaldehyde content in the raw material neraldehyde was 102 ppm, and the formaldehyde content in the product was 101 ppm.
[0069] By comparing the examples and comparative examples, it can be found that the method of the present invention can be used under high S / C (substrate / catalyst) reaction conditions, and even under high S / C conditions, higher conversion rates can be obtained, while the selectivity of R-citronellol is also slightly higher than that of existing methods.
[0070] Those skilled in the art will understand that modifications or adjustments can be made to the present invention based on the teachings of this specification. These modifications or adjustments should also be within the scope defined by the claims of the present invention.
Claims
1. A method for efficiently preparing R-citronellol from citral, characterized in that, The method includes the following steps: S1: Pre-treat citral raw materials to reduce the formaldehyde content in citral; S2: R-citronellol is obtained by asymmetric hydrogenation of catalytically treated citral; The method described in S1 for reducing the formaldehyde content in citral is to catalytically decompose polyoxymethylene and / or adsorb formaldehyde; the formaldehyde content in the treated citral is less than 50 ppm. Among them, the formaldehyde content of citral raw material in S1 is 100-200 ppm; S1 uses a catalyst, which includes a support and an active component. The support is a porous support, and the active component is a group VIII element. Wherein, the molar ratio of citral to catalyst in S2 is greater than 5000:1; The catalyst in S2 is formed by the complexation of an Rh-based metal compound with a bisphosphine ligand.
2. The method for preparing citronellol according to claim 1, characterized in that, The process of reducing the formaldehyde content in citral in S1 involves filling a pretreatment tower with a catalyst, where citral is catalytically decomposed by the catalyst bed and / or adsorbed as formaldehyde, and the pretreated citral enters the reactor in S2.
3. The method for preparing citronellol according to claim 2, characterized in that, The catalyst bed packing height in the pretreatment tower of S1 is 0.3~0.5m, and citral is added at a concentration of 400-800 h⁻¹. -1 The space velocity passes through the catalyst bed.
4. The method for preparing citronellol according to claim 1, characterized in that, The formaldehyde content in the citral after treatment in S1 is less than or equal to 21 ppm.
5. The method for preparing citronellol according to claim 1 or 2, characterized in that, The S2 reaction process involves adding the catalyst into the reactor, replacing the air in the reactor with nitrogen, adding the substrate citral, replacing the nitrogen in the reactor with H2, continuing to purge with H2, then purging with CO gas, and then heating up to carry out the reaction.
6. The method for preparing citronellol according to claim 1 or 2, characterized in that, The molar ratio of citral to catalyst in S2 is (10,000-100,000):
1.
7. The method for preparing citronellol according to claim 1, characterized in that, The support in S1 is selected from one or more of Al2O3, activated carbon, all-silica molecular sieve, kaolin and attapulgite; The active component in S1 is one or more of Pt, Ru, and Co.
8. The method for preparing citronellol according to claim 7, characterized in that, The carrier is Al2O3; The active component is Pt.
9. The method for preparing citronellol according to claim 1, characterized in that, The active component of the catalyst in S1 is loaded on the outer surface of the support; And / or, the loading of the active component is 1 wt% to 10 wt% of the carrier mass.
10. The method for preparing citronellol according to claim 9, characterized in that, The loading of the active component is 3wt% to 8wt% of the carrier mass.
11. The method for preparing citronellol according to claim 1, characterized in that, The catalyst in S1 is prepared by mixing the active component and the support evenly, adding water, and then allowing it to stand, dry, and calcining to obtain the finished catalyst.
12. The method for preparing citronellol according to claim 11, characterized in that, Set at 10-20℃ for 10-20 hours. Drying temperature 80-150℃, drying time 3-5 hours; The roasting temperature is 200-300℃ and the roasting time is 3-5 hours.