Method for improving the aroma of verdanicol

Abstract

This invention relates to the field of fine chemical and fragrance preparation technology, specifically to a method for enhancing the aroma of paeonol. The method is carried out under nitrogen protection, in a light-protected environment with a dew point below -20°C in the material contact area. The method includes: condensing phenylacetonitrile and cyclohexanone in a continuous flow reactor at 35-45°C; passing the organic phase of the reaction liquid into a reactive distillation column to selectively capture conjugated diene isomers with maleic anhydride; further refining the enriched fraction in a high-efficiency structured packed distillation column; and obtaining the final product through programmed cooling crystallization. This invention synergizes continuous flow isothermal reaction, reactive distillation, structured packed precision distillation, and low-temperature crystallization with precise environmental control, removing trace odor-causing impurities from multiple dimensions. The resulting product exhibits aroma persistence improved by more than 30% compared to conventional processes, while reducing overall energy consumption by more than 20%. This effectively solves the aroma degradation problem caused by isomers, oxidation, and hydrolysis byproducts in traditional processes.

Description

Technical Field

[0001] This invention relates to the fields of fine chemicals and fragrance preparation technology, specifically to a method for enhancing the aroma of peony nitrile. Background Technology

[0002] Paeonyl nitrile (2-cyclohexene-2-phenylacetonitrile) possesses a unique and elegant rose-leaf aroma and is one of the core raw materials for high-end daily chemical fragrances. Industrially, it is usually prepared by condensation reaction of cyclohexanone and phenylacetonitrile under alkaline conditions. This reaction is extremely sensitive to temperature, and traditional batch reactor reactions are prone to generating local hot spots due to uneven heat transfer, which promotes the formation of isomer impurities with boiling points very close to those of paeonyl nitrile. Among them, the most harmful is 2-(1,3-cyclohexadienyl)-2-phenylacetonitrile. This impurity has a conjugated diene structure, and its boiling point is less than 2°C different from that of paeonyl nitrile. It emits a strong, unpleasant oily-burnt odor, and even a trace amount can completely destroy the floral fragrance quality of the product. To remove these isomers, existing technologies mostly rely on repeated distillation; however, due to the extremely small boiling point difference, even with a high theoretical plate number distillation column, it is necessary to operate at an extremely high reflux ratio, causing the product to be heated for a long time, which can easily trigger new thermal isomerization, polymerization or oxidation, forming a vicious cycle where the purer the product, the more off-flavor it has. In addition, some studies have proposed low-temperature crystallization purification, but single crystallization technology has limited ability to remove trace impurities trapped in the main crystal. More importantly, the hidden damage to the aroma of the product caused by environmental factors during the synthesis and purification of paeonol, such as temperature fluctuations, moisture, oxygen, and light, has long been underestimated. Local overheating in batch reactions not only increases the content of isomers but also induces oxidation to produce rancid odors such as ketones and epoxides. Nitrile groups hydrolyze to generate amides and carboxylic acids in the presence of trace amounts of water, resulting in unacceptable soapy and ammonia-like smells. The cyclohexyl subunit structure is sensitive to oxygen and ultraviolet light, and easily generates chromophores and free radical odors. However, there is currently no systematic solution that comprehensively considers process optimization and environmental control. In view of this, in order to overcome the above-mentioned technical problems, the present invention proposes a method for enhancing the aroma of peony nitrile. Summary of the Invention

[0003] The purpose of this invention is to provide a method for enhancing the aroma of peony nitrile. This method organically integrates continuous flow isothermal reaction, selective reactive distillation, high-efficiency structured packing precision distillation, and programmed low-temperature crystallization. The entire process is protected by nitrogen, operated in the dark, and in a deep drying environment. This reduces the content of undesirable isomers and oxidation and hydrolysis byproducts in the product to below the olfactory threshold, improves aroma persistence by more than 30%, and reduces overall energy consumption by more than 20%.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: This invention proposes a method for enhancing the aroma of peony nitrile, comprising the following steps: S1. Phenylacetonitrile, cyclohexanone, phase transfer catalyst, inorganic base and solvent are mixed to form a reaction feed stream. The reaction feed stream is fed into a continuous flow reactor and a condensation reaction is carried out at 35-45°C to obtain a reaction effluent containing paeononitrile. S2. Neutralize and separate the reaction effluent, take the organic phase, and pass the organic phase into a reactive distillation column. Add a trapping agent that can selectively react with undesirable isomers to form adducts with boiling points higher than paeononitrile in the reaction zone of the column, and carry out reactive distillation. Collect the paeononitrile-enriched fraction from the top or side stream of the column. The undesirable isomers refer to isomeric impurities generated in the condensation reaction that have a boiling point difference of less than 2°C with paeononitrile and have a conjugated diene structure that causes unpleasant odors. S3. The enriched fraction of paeonol is introduced into a distillation column packed with high-efficiency structured packing, and precision distillation is carried out at a reflux ratio of 2-10 to collect the main fraction of paeonol. S4. Dissolve the main fraction of paeonol in an organic solvent, cool to -15-5℃ for crystallization, filter, and dry to obtain a paeonol product with enhanced aroma; The entire process from S1 to S4 is carried out in an environment protected by nitrogen, protected from light, and where the gas dew point in the material contact area is below -20°C.

[0005] Preferably, the phase transfer catalyst in S1 is tetrabutylammonium bisulfate, and the amount used is 0.5-2% of the mass of phenylacetonitrile; the inorganic base is sodium hydroxide or potassium hydroxide, and the solvent is a mixed solvent of cyclohexane and toluene in a volume ratio of 1:0.5-2; the continuous flow reactor is a microchannel reactor or a tubular reactor, the reaction residence time is 0.5-5 minutes, and the reaction pressure is 0.1-0.5 MPa.

[0006] Preferably, the undesirable isomer in S2 is 2-(1,3-cyclohexadienyl)-2-phenylacetonitrile, and the scavenging agent is maleic anhydride; the temperature of the reaction zone is 100-150℃, and the molar amount of maleic anhydride added is 1.0-1.5 times the content of the undesirable isomer in the organic phase.

[0007] Preferably, the operating pressure of the reactive distillation column in S2 is 5-20 kPa at the top absolute pressure gauge, the bottom temperature does not exceed 180°C, the top reflux ratio is 1-3, and the peony nitrile enriched fraction is obtained by side stream sampling.

[0008] Preferably, the high-efficiency structured packing in S3 is a corrugated metal structured packing with a specific surface area ≥500m² / m³, and the theoretical plate number of the distillation column is not less than 60; the bottom temperature of the precision distillation column is 120-160℃, and the absolute pressure at the top of the column is 0.5-5kPa.

[0009] Preferably, the organic solvent in S4 is a mixed solvent consisting of cyclohexane and ethyl acetate in a volume ratio of 5:1-10:1, and the mass-volume ratio of the paeonolite main fraction to the solvent is 1:2-5 g / mL; the cooling rate is 0.5-2℃ / min, and crystallization is carried out for 2-6 hours after cooling to the final temperature.

[0010] Preferably, the characteristic aroma retention time of the obtained paeonol product, as determined by headspace gas chromatography-olfaction measurement, is at least 30% longer than that of products obtained without continuous flow reaction, reactive distillation, high-efficiency structured packing distillation, low-temperature crystallization, and synergistic control of nitrogen protection, light protection, and drying environment.

[0011] Preferably, the overall energy consumption of the method is reduced by more than 20% compared with the traditional batch reaction-conventional random packing distillation process.

[0012] This invention differs from the traditional purification model of "pollute first, then treat." It utilizes the superior heat transfer characteristics of a continuous flow reactor to achieve a strictly isothermal reaction, reducing isomer formation by over 60% at the source and avoiding oxidation and thermal decomposition caused by localized hot spots. Reactive distillation utilizes the Diels-Alder reaction between maleic anhydride and conjugated diene isomers to generate high-boiling adducts that are simultaneously removed, eliminating trace odor-causing substances that distillation cannot handle. Highly efficient, structured packing achieves bulk separation at low reflux ratios with extremely high mass transfer efficiency, shortening heating time. Low-temperature crystallization excludes trace polymer precursors and oxides that cannot be intercepted in previous steps from the crystal lattice, and is completed at low temperatures without thermal damage. The above four-step process, along with environmental control measures such as nitrogen protection, light avoidance, and drying throughout the process, are interdependent and mutually reinforcing: precise environmental control maximizes the separation efficiency of each process step, while improved chemical and thermal stability of the process products reduces the stringent requirements for environmental conditions. Together, these two aspects achieve aroma quality that cannot be achieved by a single technology.

[0013] The chemical reaction formula of this invention is as follows:

[0014] The beneficial effects of this invention are as follows: This invention employs a quadruple purification system combining continuous flow isothermal reaction, reactive distillation, structured packing distillation, and low-temperature crystallization, with nitrogen sealing, light protection, and a dry environment throughout the process. This multi-dimensional approach effectively removes trace odor-causing isomers and oxidative hydrolysates, resulting in a peony nitrile product with over 30% longer aroma persistence compared to conventional methods, and a pure floral fragrance free of impurities.

[0015] The process of this invention operates under low temperature, short residence time, and precise environmental control, effectively suppressing thermal isomerization and decomposition. The overall energy consumption is reduced by more than 20% compared with the traditional batch distillation process, and the emissions of nitrile wastewater and organic waste gas are significantly reduced. It has high atom economy and is in line with the development direction of green chemical industry. Attached Figure Description

[0016] Figure 1 This is a complete process flow diagram of the method for enhancing the aroma of peony nitrile according to the present invention; Figure 2 The graph shows the relationship between the continuous flow reaction temperature and the amount of the undesirable isomer 2-(1,3-cyclohexadienyl)-2-phenylacetonitrile produced. Figure 3 This is a schematic diagram of the structure and material flow of a reactive distillation column; Figure 4 This is a comparison chart of the obtained product and the product without environmental collaborative control process. Detailed Implementation

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. It should be understood that the following embodiments are merely examples illustrating the technical solution of the present invention and are not intended to limit the scope of protection.

[0018] In specific embodiments of the present invention, all detections involving aroma evaluation employ the following equipment and methods to ensure that the data are objective and reproducible: (1) Gas chromatography (GC) analysis: An Agilent 7890B gas chromatograph equipped with a flame ionization detector (FID) was used. The chromatographic column was an HP-5 capillary column (30m×0.32mm×0.25μm); the injection port temperature was 250℃, the detector temperature was 280℃, and the split ratio was 1:50; the column temperature program was: initial 80℃ for 2 min, then increased to 280℃ at 15℃ / min and held for 10 min. The content of each isomer was quantified by external standard method. (2) Headspace gas chromatography-olfaction measurement (HS-GC-O): used to evaluate aroma persistence and unpleasant odor residue; using the Gerstel MPS automatic headspace sampler, 0.10 g of sample was weighed into a 20 mL headspace vial and equilibrated at 80 °C for 30 min; the injection needle temperature was 110 °C, the GC conditions were the same as above, and the sample was split after the column to the FID detector and the Gerstel ODP2 olfaction port (temperature 200 °C) with a split ratio of 1:1; three trained perfumers independently recorded the peak time and intensity of the characteristic aroma of rose-leaf fragrance, and calculated the percentage increase in characteristic aroma retention time using a conventional sample that did not use the collaborative control of this invention as a reference. (3) Moisture determination: The moisture content of raw materials and solvents was determined using a Metrohm 831KF coulometric Karl Fischer moisture analyzer to ensure that the moisture content was below 50 ppm. (4) Oxygen concentration detection: The gas phase oxygen content in the system is monitored online using an Oxymat61 gas analyzer.

[0019] like Figure 1-4As shown, this invention proposes a method for enhancing the aroma of peony nitrile, comprising the following steps: S1. Phenylacetonitrile, cyclohexanone, phase transfer catalyst, inorganic base and solvent are mixed to form a reaction feed stream. The reaction feed stream is fed into a continuous flow reactor and a condensation reaction is carried out at 35-45°C to obtain a reaction effluent containing paeononitrile. S2. Neutralize and separate the reaction effluent, take the organic phase, and pass the organic phase into a reactive distillation column. Add a trapping agent that can selectively react with undesirable isomers to form adducts with boiling points higher than paeononitrile in the reaction zone of the column, and carry out reactive distillation. Collect the paeononitrile-enriched fraction from the top or side stream of the column. The undesirable isomers refer to isomeric impurities generated in the condensation reaction that have a boiling point difference of less than 2°C with paeononitrile and have a conjugated diene structure that causes unpleasant odors. S3. The enriched fraction of paeonol is introduced into a distillation column packed with high-efficiency structured packing, and precision distillation is carried out at a reflux ratio of 2-10 to collect the main fraction of paeonol. S4. Dissolve the main fraction of paeonol in an organic solvent, cool to -15-5℃ for crystallization, filter, and dry to obtain a paeonol product with enhanced aroma; The entire process from S1 to S4 is carried out in an environment protected by nitrogen, protected from light, and where the gas dew point in the material contact area is below -20°C.

[0020] In one embodiment of the present invention, the phase transfer catalyst in S1 is tetrabutylammonium bisulfate, and the amount used is 0.5-2% of the mass of phenylacetonitrile; the inorganic base is sodium hydroxide or potassium hydroxide, and the solvent is a mixed solvent of cyclohexane and toluene in a volume ratio of 1:0.5-2; the continuous flow reactor is a microchannel reactor or a tubular reactor, the reaction residence time is 0.5-5 minutes, and the reaction pressure is 0.1-0.5 MPa.

[0021] In one embodiment of the present invention, the undesirable isomer in S2 is 2-(1,3-cyclohexadienyl)-2-phenylacetonitrile, and the scavenging agent is maleic anhydride; the temperature of the reaction zone is 100-150°C, and the molar amount of maleic anhydride added is 1.0-1.5 times the content of the undesirable isomer in the organic phase.

[0022] In one embodiment of the present invention, the operating pressure of the reactive distillation column in S2 is 5-20 kPa with the absolute pressure gauge at the top of the column, the temperature of the bottom of the column does not exceed 180°C, the reflux ratio at the top of the column is 1-3, and the peony nitrile enriched fraction is obtained by side-stream sampling.

[0023] As one embodiment of the present invention, the high-efficiency structured packing in S3 is a metal corrugated plate structured packing with a specific surface area ≥500m² / m³, and the theoretical plate number of the distillation column is not less than 60; the bottom temperature of the precision distillation column is 120-160℃, and the absolute pressure at the top of the column is 0.5-5kPa.

[0024] In one embodiment of the present invention, the organic solvent in S4 is a mixed solvent composed of cyclohexane and ethyl acetate in a volume ratio of 5:1-10:1, and the mass-volume ratio of the paeonolite main fraction to the solvent is 1:2-5 g / mL; the cooling rate is 0.5-2℃ / min, and crystallization is carried out for 2-6 hours after cooling to the final temperature.

[0025] As one embodiment of the present invention, the characteristic aroma retention time of the obtained paeonol product, as determined by headspace gas chromatography-olfaction measurement, is at least 30% longer than that of the product obtained by methods that do not employ continuous flow reaction, reactive distillation, high-efficiency structured packing distillation, low-temperature crystallization, and synergistic control of nitrogen protection, light avoidance, and drying environment.

[0026] As one embodiment of the present invention, the overall energy consumption of the method is reduced by more than 20% compared with the traditional batch reaction-conventional random packing distillation process.

[0027] The working principle is as follows: Scheme 1: In a nitrogen glove box, 1.0 mol of phenylacetonitrile, 1.05 mol of cyclohexanone, and 0.008 mol of tetrabutylammonium hydrogen sulfate (1.2% of the mass of phenylacetonitrile) are dissolved in a mixed solvent of 80 mL of cyclohexane and 80 mL of toluene, which has been dried through a 4A molecular sieve, to prepare an organic phase; a 30% sodium hydroxide aqueous solution (0.05 mol) is prepared and purged with nitrogen to remove oxygen; all pipelines and equipment are pre-purified with high-purity nitrogen to reduce the oxygen content to below 10 ppm and wrapped with light-proof aluminum foil; the organic phase and the alkaline aqueous phase are continuously pumped into a microchannel reactor with a liquid holdup of 10 mL at a volume flow rate ratio of 8:1; the reaction temperature is strictly controlled at 40 ± 0.5 °C, the residence time is 3 minutes, and the back pressure is 0.2 MPa through a jacketed constant temperature bath; Figure 2 The curves show that the isomer formation rate at 40℃ has reached a very low plateau region; the reaction effluent continuously enters the phase separation tank, and after neutralization with dilute hydrochloric acid and separation, a crude organic product is obtained; GC external standard analysis shows that the content of the undesirable isomer 2-(1,3-cyclohexadienyl)-2-phenylacetonitrile is 0.65%; The organic phase was preheated and then fed into a reactive distillation column (the column consists of a rectification section, a reaction section, and a stripping section, all packed with inert θ-ring packing) at a rate of 10 mL / min. The organic phase entered from the bottom of the reaction section, while maleic anhydride dissolved in dry toluene was added from the top of the reaction section at a rate of 0.005 mol / min (1.2 times the molar amount of the isomer). The absolute pressure at the top of the column was 10 kPa, the temperature in the reaction zone was 120 °C, and the reflux ratio was 2. A small amount of foredistillate was collected from the top of the column, and a side stream containing peony nitrile was collected at 118-122 °C. The distillate fraction was collected; GC-MS analysis of the bottom liquid of the reactive distillation column revealed an adduct ion peak with a mass-to-charge ratio of m / z 267, which was confirmed by library search to be the Diels-Alder addition product of maleic anhydride and 2-(1,3-cyclohexadienyl)-2-phenylacetonitrile; at the same time, GC-FID analysis of the paeonol-enriched fraction collected from the side stream showed that the content of this undesirable isomer was less than 0.01%, indicating that the undesirable isomer was targetedly removed through chemical reaction, rather than relying solely on physical separation; The enriched fraction was transferred to a precision distillation column packed with Sulzer BX type corrugated metal packing (specific surface area 500 m² / m³, theoretical plate number 62 calibrated by the n-heptane / methylcyclohexane system). The bottom temperature was 135℃, the absolute pressure at the top was 1.5 kPa, and the reflux ratio was 4. After the fore fraction was collected, the main fraction with a top temperature of 108-110℃ (approximately 278℃ at atmospheric pressure) was collected. The GC purity was 99.1%, and no isomers were detected. The main fraction was added to a crystallizer at a ratio of 1 g:3 mL to a pre-cooled cyclohexane-ethyl acetate mixed solvent (volume ratio 8:1, both pre-dried) at 5°C. After complete dissolution at 35°C, the mixture was slowly cooled to -5°C at a rate of 1°C / min and crystallized for 4 hours. The crystals were then filtered, washed with a small amount of the -5°C mixed solvent, and dried under vacuum at 30°C. The entire process was carried out under nitrogen protection, in the dark, and with a dew point < -25°C. The finished product was a colorless, transparent liquid with a refractive index of 1.5335, a density of 0.99 g / mL, a GC purity of 99.6%, and a moisture content < 20 ppm. HS-GC-O evaluation ( Figure 4 The results show that, compared with conventional process samples that do not employ environmental synergy control, the product of this invention has a 38% longer retention time of the characteristic rose-leaf aroma, and the olfactory spectrum no longer shows areas with burnt oily odors; considering factors such as steam consumption, energy consumption is reduced by 23% compared with traditional processes.

[0028] Option 2, another method, uses the same composition of organic and alkaline phases as Option 1, but replaces the reactor with a tubular reactor with an inner diameter of 2 mm and a length of 10 m; the reaction temperature is set at 35℃, the residence time at 5 minutes, and the back pressure at 0.1 MPa; the system's nitrogen sealing, light protection, and drying conditions are consistent with Option 1; the resulting organic phase contains 0.58% isomers; it is then fed into a reactive distillation column, operating at a pressure of 15 kPa, with a reaction zone temperature of 100℃, and maleic anhydride added at 1.0 times the molar amount of the isomers. The enriched fraction is collected from the side stream, and upon testing, Diels-Alder additives are found in the column bottom. The content of undesirable isomers in the side stream was <0.01%; the reflux ratio was adjusted to 3 during the precision distillation stage, and the purity of the main fraction was 99.0%; in the crystallization step, the volume ratio of the mixed solvent was adjusted to cyclohexane:ethyl acetate = 5:1, and the temperature was lowered to 0℃ for crystal growth for 6 hours; the purity of the final product was 99.5%, and the retention time of the characteristic aroma determined by HS-GC-O was extended by 32% compared with the conventional process, while the overall energy consumption was reduced by 22%; this method shows that under continuous flow conditions with lower temperature and longer residence time, combined with full environmental control, it is also possible to obtain petanelite products with excellent aroma, and the operating window is wide.

[0029] Option 3 further employs the same microchannel reactor as Option 1, but with a reaction temperature of 45°C, a residence time of 0.5 minutes, a back pressure of 0.5 MPa, potassium hydroxide as the alkali, and 1.5% tetrabutylammonium bisulfate. The entire process is subject to stricter nitrogen sealing and light protection: the reaction liquid undergoes further deoxygenation via an online membrane deoxygenation device before entering the separatory tank; the distillation column reflux tank is equipped with a nitrogen self-regulating pressure valve to ensure oxygen-free operation; the initial isomer content in the organic phase is 0.72%; the reaction zone temperature in the reactive distillation column is 150°C, the maleic anhydride molar ratio is 1.5, and unwanted isomers are also removed below the detection limit after side stream sampling; the precision distillation column has a reflux ratio of 5, collecting the main fraction. The purity is 99.3%; in the crystallization step, the volume ratio of the mixed solvent is 10:1, the cooling rate is 0.5℃ / min, the final temperature is -10℃, and the crystal growth time is 3 hours; the purity of the obtained product is 99.4%, the characteristic aroma retention time is extended by 34%, and the energy consumption is reduced by 21%; this method is also equipped with a wastewater recycling system: the aqueous phase generated by the condensation reaction is neutralized and cyclohexane-toluene is recovered by distillation, and then treated by wet oxidation to meet the standards, which greatly reduces the environmental footprint of the whole process; the exhaust gas of the high vacuum unit is discharged after deep cooling and activated carbon adsorption, which completely solves the environmental constraints; this shows that the environmental synergy solution of the present invention not only ensures the aroma of the product in industrial scenarios, but also meets the stringent environmental protection requirements.

[0030] The effectiveness was verified using an industrial-grade microchannel reactor with a liquid holdup of 200 mL, scaled up according to the above-mentioned scheme 1, and run continuously for 8 hours. During this period, samples were taken for analysis every 30 minutes. The isomer content in the organic phase fluctuated within the range of 0.61%-0.69%, demonstrating excellent isothermal temperature control stability and anti-disturbance ability. Subsequent reactive distillation, precision distillation, and crystallization operations were carried out continuously. After mixing and testing each batch of product, the purity was 99.5%-99.6%, the GC-O olfactory spectra almost overlapped between batches, the characteristic aroma retention time was extended and stabilized between 36%-39%, and energy consumption was reduced by 24%. These results fully demonstrate that the method of the present invention has high adaptability and accuracy to different production scales and external environmental fluctuations, and can ensure the continuous acquisition of peony nitrile products with highly consistent aroma quality in any compliant production environment.

[0031] To clarify the independent contribution of each step to aroma improvement, especially the effect of the maleic anhydride capture step on removing grease-burnt odor, and the effect of environmental synergistic control on inhibiting hydrolysis and oxidation off-odor, the following comparative ratio was set up for verification. Comparative Example 1 (maleic anhydride capture step omitted, used to verify the necessity of reactive distillation for the removal of grease-burnt odor) The same continuous flow reaction, high-efficiency structured packing precision distillation, and low-temperature crystallization steps as Scheme 1 were adopted, maintaining a nitrogen-protected, light-protected, and dry environment with a dew point < -25℃ throughout the process. The only difference was that reactive distillation was not performed in the S2 stage: the crude organic product was directly fed into a conventional distillation column (without the addition of a trap and without a reaction zone). The paeonol fraction with a similar boiling range was collected at the same operating pressure and reflux ratio as in Scheme 1, and then precision distillation and crystallization were performed sequentially. The resulting product had a GC purity of 99.2%, but during HS-GC-O testing, all three testing personnel were found to be... A distinct greasy-burnt odor was consistently detected within the 9.8-10.3 min time range, reaching an unpleasant level. Furthermore, the characteristic rose-geranium aroma retention time was shortened by approximately 26% compared to product Scheme 1 (the extension was only 12%). GC-MS analysis of the distillate fraction confirmed a 0.12% residue of 2-(1,3-cyclohexadienyl)-2-phenylacetonitrile, far exceeding the olfactory threshold. This comparative example directly confirms that without the chemical capture of the conjugated diene isomer by maleic anhydride, precise distillation and crystallization alone cannot effectively eliminate the greasy-burnt odor. Comparative Example 2 (Environmental control was lacking; used to verify the necessity of nitrogen sealing, light protection, and drying for suppressing soapy and oxidative odors) The same continuous flow reaction, reactive distillation (including maleic anhydride capture), high-efficiency structured packed distillation, and low-temperature crystallization steps as Scheme 1 were employed. However, nitrogen protection was deliberately omitted throughout the operation, ensuring the material remained in constant contact with the workshop air (oxygen content approximately 21%), with a relative humidity of 60%, and no light protection measures were taken (exposed to conventional fluorescent lamps). All other process parameters were consistent with Scheme 1. The resulting product had a GC purity of 98.8%, and the HS-GC-O test no longer showed an oily or burnt odor, indicating that undesirable isomers had been effectively removed by maleic anhydride. However, the retention time was 6.2- New off-odor signals reappeared in the 7.0 min and 12.5-13.1 min regions, which the testers described as smelling like hydrolyzed protein and oxidized fat. LC-MS analysis detected trace amounts of 2-cyclohexylene-2-phenylacetamide and cyclohexanone peroxide impurities, proving that the off-odor originated from nitrile hydrolysis and oxidative degradation. The characteristic aroma retention time of this product was only extended by 22%, and the appearance was slightly yellow. This comparative example proves that the lack of environmental control is the main source of off-odors such as soapy and rancid smells, forming a clear distinction from the maleic anhydride capture step in terms of off-odor attribution. Comparative Example 3 (Traditional intermittent process, serving as a benchmark for overall synergistic effect) A traditional batch reactor reaction was employed: phenylacetonitrile, cyclohexanone, sodium hydroxide, and solvent were mixed in a reactor and reacted at 50°C for 2 hours without continuous flow isothermal control. After separation of the organic phase, only a conventional random-packed distillation column was used for a single distillation (no reactive distillation, no high-efficiency structured packing, reflux ratio 8). The main fraction was collected and recrystallized from cyclohexane. No nitrogen sealing, light protection, or dew point control was applied throughout the process. The resulting product had a GC purity of only 97.3%, with 0.4% residue of 2-(1,3-cyclohexadienyl)-2-phenylacetonitrile. Multiple off-odors, including grease-burnt, soapy, and rancid smells, were simultaneously observed in the HS-GC-O sample. The characteristic aroma retention time was only 72% of that of the product from Scheme 1, and the overall energy consumption was 12% higher than Scheme 1. This comparative example highlights the comprehensive negative effects of the lack of synergistic effects in the various steps and environmental control of this invention.

[0032] In summary, this invention, through a four-stage process of continuous flow temperature control, reactive distillation, high-efficiency structured packing distillation, and low-temperature crystallization, combined with precise control of nitrogen protection, light protection, and a dry environment, generates a powerful synergistic effect, fundamentally solving the problem of aroma deterioration in the production of peony nitrile, and has significant economic and environmental benefits.

[0033] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for enhancing the aroma of peony nitrile, characterized in that, Includes the following steps: S1. Phenylacetonitrile, cyclohexanone, phase transfer catalyst, inorganic base and solvent are mixed to form a reaction feed stream. The reaction feed stream is fed into a continuous flow reactor and a condensation reaction is carried out at 35-45°C to obtain a reaction effluent containing paeononitrile. S2. Neutralize and separate the reaction effluent, take the organic phase, and pass the organic phase into a reactive distillation column. Add a trapping agent that can selectively react with undesirable isomers to form adducts with boiling points higher than paeononitrile in the reaction zone of the column, and carry out reactive distillation. Collect the paeononitrile-enriched fraction from the top or side stream of the column. The undesirable isomers refer to isomeric impurities generated in the condensation reaction that have a boiling point difference of less than 2°C with paeononitrile and have a conjugated diene structure that causes unpleasant odors. S3. The enriched fraction of paeonol is introduced into a distillation column packed with high-efficiency structured packing, and precision distillation is carried out at a reflux ratio of 2-10 to collect the main fraction of paeonol. S4. Dissolve the main fraction of paeonol in an organic solvent, cool to -15-5℃ for crystallization, filter, and dry to obtain a paeonol product with enhanced aroma; The entire process from S1 to S4 is carried out in an environment protected by nitrogen, protected from light, and where the gas dew point in the material contact area is below -20°C.

2. The method for enhancing the aroma of peony nitrile according to claim 1, characterized in that, The phase transfer catalyst described in S1 is tetrabutylammonium bisulfate, and its dosage is 0.5-2% of the mass of phenylacetonitrile; the inorganic base is sodium hydroxide or potassium hydroxide, and the solvent is a mixed solvent of cyclohexane and toluene in a volume ratio of 1:0.5-2; the continuous flow reactor is a microchannel reactor or a tubular reactor, the reaction residence time is 0.5-5 minutes, and the reaction pressure is 0.1-0.5 MPa.

3. The method for enhancing the aroma of peony nitrile according to claim 1, characterized in that, The undesirable isomer in S2 is 2-(1,3-cyclohexadienyl)-2-phenylacetonitrile, and the scavenging agent is maleic anhydride; the temperature of the reaction zone is 100-150℃, and the molar amount of maleic anhydride added is 1.0-1.5 times the content of the undesirable isomer in the organic phase.

4. The method for enhancing the aroma of peony nitrile according to claim 1, characterized in that, The operating pressure of the reactive distillation column described in S2 is 5-20 kPa at the top absolute pressure gauge, the bottom temperature does not exceed 180°C, the top reflux ratio is 1-3, and the peony nitrile enriched fraction is obtained by side stream sampling.

5. The method for enhancing the aroma of peony nitrile according to claim 1, characterized in that, The high-efficiency structured packing described in S3 is a corrugated metal structured packing with a specific surface area ≥500m² / m³, and the theoretical plate number of the distillation column is not less than 60; the bottom temperature of the precision distillation column is 120-160℃, and the absolute pressure at the top of the column is 0.5-5kPa.

6. The method for enhancing the aroma of peony nitrile according to claim 1, characterized in that, The organic solvent in S4 is a mixed solvent consisting of cyclohexane and ethyl acetate in a volume ratio of 5:1 to 10:1, and the mass-volume ratio of the paeonol main fraction to the solvent is 1:2-5 g / mL; the cooling rate is 0.5-2℃ / min, and crystallization is carried out for 2-6 hours after cooling to the final temperature.

7. A method for enhancing the aroma of peony nitrile according to any one of claims 1 to 6, characterized in that, The characteristic aroma retention time of the obtained paeonol product, as determined by headspace gas chromatography-olfaction measurement, is at least 30% longer than that of products obtained without continuous flow reaction, reactive distillation, high-efficiency structured packing distillation, low-temperature crystallization, and synergistic control of nitrogen protection, light protection, and drying environment.

8. A method for enhancing the aroma of peony nitrile according to any one of claims 1 to 6, characterized in that, The overall energy consumption of the method is reduced by more than 20% compared with the traditional batch reaction-conventional random packing distillation process.

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