A method for the enriched extraction of citral

Abstract

This invention relates to a method for enriching and extracting citral, comprising: adding crude natural essential oil containing citral to an acetone aqueous solution, then adding an ionic liquid, stirring and mixing at room temperature, allowing the mixture to stand and separate into layers, and then distilling the ionic liquid layer under reduced pressure to obtain an essential oil product enriched with citral. The essential oil product enriched and extracted by this method has a citral content of over 92%, and this essential oil product can be further purified to obtain a high-content pure citral product through distillation. This invention enriches and extracts citral from crude natural oil containing citral, with a simple process, easy operation, high selectivity and extraction rate of citral, and the ionic liquid can be recycled and reused, making it environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of citral extraction technology, and more particularly to a method for enriching and extracting citral. Background Technology

[0002] Citral, also known as 3,7-dimethyl-2,6-octadien-1-aldehyde, has the common English name Citral, CAS number 5392-40-5, and chemical formula C64-12-Octadien-1-aldehyde. 10 H 16 Citral, with a boiling point of 228–229°C, is a colorless or slightly yellow liquid with a strong lemon aroma. It is a permitted food flavoring in my country, with a wide range of applications, particularly essential in citrus flavor formulations. Citral is commonly used in blending flavors of oranges, lemons, sour lemons, apples, cherries, grapefruits, and grapes. Besides its use as a flavoring agent, citral is also an important intermediate in the synthesis of ionones, methyl ionones, and vitamin A. Therefore, the market demand for citral is increasing, and it has broad application prospects.

[0003] Citral is naturally found in the essential oils of some plants, such as lemongrass oil, lemon oil, white lemon oil, citrus oil, clove basil oil, lemon leaf oil, litsea cubeba oil, and verbena oil. Currently, the production of natural citral mainly involves collecting the branches and leaves of plants such as lemongrass and the fruits of litsea cubeba, obtaining crude essential oils through steam distillation, and then extracting citral from these crude oils. Typically, a high-efficiency vacuum fractionation method is used first to obtain a high content of citral. To obtain high-purity citral, it is necessary to treat it with sodium sulfite to generate an adduct, hydrolyze the sulfonate adduct with alkali, and then fractionate the resulting citral under vacuum to obtain a pure product with an aldehyde content of over 98%. However, because citral is a mixture of cis and trans isomers (the trans isomer is called geranialdehyde, and the cis isomer is called neraldehyde), and the trans isomer has high solubility in sodium sulfite while the cis isomer has low solubility, significant losses of the cis isomer are easily caused during the extraction process. Furthermore, the chemical method of treating citral with sodium sulfite requires a large amount of alkali, and subsequent wastewater treatment also requires a large amount of acid. Therefore, this method not only has a relatively low extraction rate but also requires the treatment of a large amount of wastewater, thus having certain limitations. In addition, there is a traditional method for citral extraction that utilizes the difference in boiling points between citral and other components in the essential oil, achieving separation directly under high vacuum conditions through reduced pressure distillation. This avoids the use of sodium sulfite, but the process requires more stringent conditions and the equipment is expensive. Summary of the Invention

[0004] The purpose of this invention is to provide a method for enriching and extracting citral, which can conveniently enrich and extract citral from lemongrass crude oil with different citral contents, with a high extraction rate, and the process is simple, easy to operate, and environmentally friendly.

[0005] To achieve the above objectives, this invention discloses a method for enriching and extracting citral, comprising the following steps:

[0006] Crude natural essential oil containing citral was added to an aqueous acetone solution, followed by the addition of an ionic liquid. The mixture was stirred and mixed at room temperature, and after standing and separating into layers, the ionic liquid layer was distilled under reduced pressure to obtain an essential oil product enriched with citral.

[0007] Preferably, the mass ratio of the ionic liquid to the acetone aqueous solution is 0.8 to 1:1.

[0008] Preferably, the mass concentration of the acetone aqueous solution is 30-40%.

[0009] Preferably, the mass ratio of the crude natural essential oil to the ionic liquid is 0.5 to 1:1.

[0010] Preferably, the ionic liquid is N-phenyl-3-methylpyridine bis(trifluoromethanesulfonyl)imide salt.

[0011] Preferably, the ionic liquid is prepared by: adding bromobenzene and N-3-methylpyridine into a reaction vessel at a molar ratio of 1:1, then adding toluene as a solvent, the amount of toluene being 4 to 5 times the molar amount of N-3-methylpyridine; stirring the reaction at 70 to 90°C under an inert gas atmosphere to obtain a lower layer product; mixing the obtained lower layer product with lithium bis(trifluoromethanesulfonate)imide at a molar ratio of 1:1, and stirring the mixture in ethyl acetate at room temperature, the amount of ethyl acetate being 4 to 6 times the molar amount of lithium bis(trifluoromethanesulfonate)imide; removing the ethyl acetate after the reaction to obtain N-phenyl-3-methylpyridine bis(trifluoromethanesulfonate)imide.

[0012] Preferably, the crude natural essential oil is added to an acetone aqueous solution, and after adding the ionic liquid, the mixture is stirred and mixed at room temperature for 2-3 hours.

[0013] Preferably, the chromatographic content of citral in the crude natural essential oil is 46.3-65.4%.

[0014] Preferably, the crude natural essential oil is lemongrass crude oil.

[0015] The present invention has the following beneficial effects:

[0016] The essential oil product obtained by the enrichment and extraction method of this invention contains a citral content of over 92%. This essential oil product can be further purified to obtain a high-content pure citral by distillation. This invention enriches and extracts citral from natural crude oil containing citral in a simple and convenient process with high selectivity and extraction rate. Furthermore, the essential oil product enriched with citral is obtained by vacuum distillation using an ionic liquid layer. Since the ionic liquid has a high boiling point and low volatility, it can be recycled and reused, making it environmentally friendly. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments.

[0018] This invention discloses a method for enriching and extracting citral, comprising: adding crude natural essential oil containing citral to an acetone aqueous solution with a mass concentration of 30-40%; then adding an ionic liquid, specifically N-phenyl-3-methylpyridine bis(trifluoromethanesulfonyl)imide salt, to the acetone aqueous solution; stirring and mixing at room temperature for 2-3 hours; allowing the mixture to stand and separate into layers; and then distilling the ionic liquid layer under reduced pressure to obtain an essential oil product enriched with citral. In the above process, the mass ratio of the ionic liquid to the acetone aqueous solution is 0.8-1:1; and the mass ratio of the crude natural essential oil to the ionic liquid is 0.5-1:1. Furthermore, to improve the enrichment efficiency of citral, the chromatographic content of citral in the crude natural essential oil is preferably 46.3-65.4%.

[0019] The preparation method of the ionic liquid is as follows: bromobenzene and N-3-methylpyridine are added to a reaction vessel in a molar ratio of 1:1, and then toluene is added as a solvent. The amount of toluene is 4 to 5 times the molar amount of N-3-methylpyridine. The reaction is carried out under an inert gas atmosphere at 70 to 90 °C with stirring to obtain the lower layer product. The obtained lower layer product is mixed with lithium bis(trifluoromethanesulfonate)imide in a molar ratio of 1:1 and placed in ethyl acetate and stirred at room temperature. The amount of ethyl acetate is 4 to 6 times the molar amount of lithium bis(trifluoromethanesulfonate)imide. After the reaction is completed, the ethyl acetate is removed to obtain N-phenyl-3-methylpyridine bis(trifluoromethanesulfonate)imide.

[0020] The following is an explanation through specific examples.

[0021] Example 1

[0022] 100g of crude lemongrass oil (the chromatographic content of its main components is: citral 54.8%, geraniol 10.3%, geraniol acetate 4.3%, caryophyllene 3.7%, pinene 6.5%, eucalyptol 1.2%, p-lethalol 2.2%, linalool 1.6%, verbenol 3.1%, citronellol 0.8%, nerol 1.2%, juniperene 1.9%, and geraniol 1.1%) was added to a reactor containing 250g of a 30% acetone aqueous solution. Then, 200g of the ionic liquid N-phenyl-3-methylpyridine bis(trifluoromethanesulfonyl)imide salt was added. The mixture was stirred at room temperature for 2.5 hours, allowed to stand and separate into layers. The ionic liquid layer was then distilled under reduced pressure to obtain 58.2g of citral essential oil, in which the chromatographic content of citral was 93.2%. The ionic liquid obtained after reduced pressure distillation can be directly recycled.

[0023] Example 2

[0024] 140g of crude lemongrass oil (the chromatographic content of its main components is: citral 65.4%, geraniol 9.1%, geraniol acetate 3.5%, caryophyllene 2.4%, pinene 6.7%, eucalyptol 0.5%, p-lethalol 1.4%, linalool 1.1%, verbenol 3.4%, citronellol 0.6%, nerol 1.0%, juniperene 1.9%, and geraniol 0.3%) was added to a reactor containing 200g of a 35% acetone aqueous solution. Then, 200g of the ionic liquid N-phenyl-3-methylpyridine bis(trifluoromethanesulfonyl)imide salt was added to the reactor. The mixture was stirred at room temperature for 3 hours, allowed to stand and separate into layers. The ionic liquid layer was then distilled under reduced pressure to obtain 98.5g of citral essential oil, in which the chromatographic content of citral was 92.2%. The ionic liquid obtained after reduced pressure distillation can be directly recycled.

[0025] Example 3

[0026] 180g of crude lemongrass oil (the chromatographic content of its main components is: citral 54.8%, geraniol 10.3%, geraniol acetate 4.3%, caryophyllene 3.7%, pinene 6.5%, eucalyptol 1.2%, p-lethalol 2.2%, linalool 1.6%, verbenol 3.1%, citronellol 0.8%, nerol 1.2%, juniperene 1.9%, and geraniol 1.1%) was added to a reactor containing 200g of a 40% acetone aqueous solution. Then, 180g of the ionic liquid N-phenyl-3-methylpyridine bis(trifluoromethanesulfonyl)imide salt was added to the reactor. The mixture was stirred at room temperature for 2 hours, allowed to stand and separate into layers. The ionic liquid layer was then distilled under reduced pressure to obtain 105.4g of citral essential oil, in which the chromatographic content of citral was 92.6%. The ionic liquid obtained after reduced pressure distillation can be directly recycled.

[0027] Example 4

[0028] 160g of crude lemongrass oil (the chromatographic content of its main components is: citral 46.3%, geraniol 11.8%, geraniol acetate 5.2%, caryophyllene 4.9%, pinene 7.6%, eucalyptol 1.8%, p-lethalol 2.9%, linalool 2.2%, verbenol 3.9%, citronellol 1.1%, nerol 1.3%, juniperene 2.4%, and geraniol 1.2%) was added to a reactor containing 250g of a 35% acetone aqueous solution. Then, 200g of the ionic liquid N-phenyl-3-methylpyridine bis(trifluoromethanesulfonyl)imide salt was added. The mixture was stirred at room temperature for 2.5 hours, allowed to stand and separate into layers. The ionic liquid layer was then distilled under reduced pressure to obtain 79.6g of citral essential oil, in which the chromatographic content of citral was 92.3%. The ionic liquid obtained after reduced pressure distillation can be directly recycled.

[0029] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for the enriched extraction of citral, characterized in that, Includes the following steps: Crude natural essential oil containing citral was added to an aqueous acetone solution, followed by the addition of an ionic liquid. The mixture was stirred and mixed at room temperature, allowed to stand and separate into layers, and then the ionic liquid layer was distilled under reduced pressure to obtain an essential oil product enriched with citral. The ionic liquid is N-phenyl-3-methylpyridine bis(trifluoromethanesulfonyl)imide salt.

2. The method of claim 1, wherein the method is characterized by: The mass ratio of the ionic liquid to the acetone aqueous solution is 0.8 to 1:

1.

3. The method of claim 1, wherein the method is characterized by: The mass concentration of the acetone aqueous solution is 30-40%.

4. The method of claim 1, wherein the method is characterized by: The mass ratio of the crude natural essential oil to the ionic liquid is 0.5 to 1:

1.

5. The method of claim 1, wherein the method is characterized by: The ionic liquid is prepared as follows: bromobenzene and N-3-methylpyridine are added to a reaction vessel in a 1:1 molar ratio, and then toluene is added as a solvent. The amount of toluene is 4 to 5 times the molar amount of N-3-methylpyridine. The reaction is carried out under an inert gas atmosphere at 70 to 90°C with stirring to obtain a lower layer product. The lower layer product is mixed with lithium bis(trifluoromethanesulfonate)imide in a 1:1 molar ratio and placed in ethyl acetate for stirring at room temperature. The amount of ethyl acetate is 4 to 6 times the molar amount of lithium bis(trifluoromethanesulfonate)imide. After the reaction is completed, the ethyl acetate is removed to obtain N-phenyl-3-methylpyridine bis(trifluoromethanesulfonate)imide.

6. The method for enriching and extracting citral according to claim 1, characterized in that: Crude natural essential oils are added to an aqueous acetone solution, and after adding an ionic liquid, the mixture is stirred and mixed at room temperature for 2–3 hours.

7. The method for enriching and extracting citral according to claim 1, characterized in that: The chromatographic content of citral in the crude natural essential oil is 46.3-65.4%.

8. The method for enriching and extracting citral according to claim 1, characterized in that: The crude natural essential oil is lemongrass crude oil.