A stepwise separation method for tobacco extracts based on a cascade nanofiltration membrane combination process and its application

Abstract

The invention discloses a tobacco extract stepwise separation method and application based on a cascade nanofiltration membrane combination process, belonging to the field of membrane separation technology, comprising: combining multiple nanofiltration membranes to filter tobacco extract to achieve stepwise separation of tobacco extract; during the filtration process, the permeate separated by the previous nanofiltration membrane is used as the feed liquid for the next nanofiltration membrane; the nanofiltration membrane is a polyamide nanofiltration membrane, and the tobacco extract includes at least two of acidic substances, alkaline substances or neutral substances; before each stage of filtration, the charge state of the nanofiltration membrane surface and the protonation and deprotonation behavior of the tobacco extract molecules are regulated by adjusting the pH value of the solution to be filtered, so that at the corresponding pH value, the tobacco extract with the same charge as the nanofiltration membrane surface is retained, and the remaining tobacco extract permeates through the nanofiltration membrane, and the pH value of the permeate obtained by filtration is re-adjusted and the next nanofiltration membrane filtration step is performed until the target separation degree is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane separation, and in particular to a tobacco extract stepwise separation method based on a cascade nanofiltration membrane combination process and its application. Background Art

[0002] Tobacco extract is a key product of the tobacco industry, containing a rich array of bioactive components such as alkaloids, organic acids, and polyphenols. Tobacco extract not only imparts a unique flavor and taste to tobacco, but also demonstrates broad and profound potential for application in a wide range of fields, including fine chemicals, biopharmaceuticals, and agricultural environmental protection.

[0003] At present, the preparation method of tobacco extract includes extracting active ingredients from tobacco leaves with an extracting solution, and further separating and purifying these extracts by extraction, distillation, chromatography, adsorption and other methods. The Chinese patent document with publication number CN101570717A discloses a preparation method of tobacco extract and its application. The method uses enzymatic hydrolysis technology, ultrasonic extraction and combined with chromatographic separation to obtain a tobacco extract whose main components are damascone, dihydrodamascone, solanone, geranylacetone, farnesylacetone, megastigmatrienone, neophytadiene, etc. The Chinese patent document with publication number CN113508919A discloses a tobacco extract and its preparation method and application. The method uses extraction, reaction of tobacco extract with alcohol solvent, organic solvent extraction, distillation and purification to extract nicotine and flavor substances. However, due to the complex composition of tobacco extract and the wide distribution of molecular weight (mostly between 100 and 500 Da), these traditional methods show problems of high energy consumption and low separation efficiency, making it difficult to achieve high-value utilization of tobacco crops.

[0004] Compared to separation technologies like extraction and distillation, nanofiltration offers advantages such as low process energy consumption, high separation precision, and the absence of solvent addition. Most nanofiltration membranes are thin composite membranes prepared by interfacial polymerization of aqueous and oily phase monomers on a porous support layer. The separation layer formed by interfacial polymerization has nanoscale pores and charge characteristics, which facilitate the selective separation of molecules. Furthermore, the nanofiltration process does not undergo the phase transitions seen in traditional separation methods, resulting in no physical changes leading to mass loss or purity reduction, thus ensuring the integrity and stability of the bioactive components in tobacco extracts.

[0005] However, the similar properties of many components in tobacco extracts, such as the similar molecular weights of acidic, neutral, and alkaline active ingredients, have limited the application of nanofiltration technology in tobacco extract separations. This is due to the rapid reaction rate of the interfacial polymerization process and the uneven distribution of aqueous monomers at the interface, resulting in a wide pore size distribution in the formed polyamide nanofiltration membrane. Therefore, existing nanofiltration membranes have difficulty directly and accurately screening molecules of similar sizes, especially when the compound size is smaller than the pore size, making separation difficult.

[0006] Electrostatic interactions between molecules and membrane surface charges provide another selectivity mechanism. The charge of a compound typically originates from dissociable or protonable groups, such as carboxyl groups, amine groups, and pyridyl groups. The charge on the membrane surface, on the other hand, originates from unreacted residual amine groups or acyl chloride groups. When a charged molecule approaches a membrane surface with the same charge, the transmembrane energy barrier for the molecule increases significantly, resulting in its rejection by the membrane. By manipulating this interaction, the membrane's selectivity for charged molecules can be significantly improved, and it is even possible to achieve selective separation of mixture molecules when the molecular size is smaller than the membrane pore size. Based on this, the present invention provides a stepwise separation method for tobacco extracts based on a cascade nanofiltration membrane combination process. Summary of the Invention

[0007] In order to address the shortcomings of the existing technology, the present invention provides a tobacco extract step-by-step separation method based on a cascade nanofiltration membrane combination process. This method can achieve the step-by-step separation of all charged molecules in the tobacco extract by regulating the charge state of the nanofiltration membrane surface and the protonation and deprotonation behavior of the tobacco extract molecules, which helps to promote the application of nanofiltration technology in the separation of tobacco extracts.

[0008] The specific technical solutions adopted are as follows:

[0009] A method for the stepwise separation of tobacco extracts based on a cascade nanofiltration membrane combination process comprises: filtering tobacco extracts using multiple nanofiltration membranes to achieve stepwise separation of tobacco extracts; during the filtration process, the permeate separated by the nanofiltration membrane of the previous stage is used as the feed liquid for the nanofiltration membrane of the next stage;

[0010] The nanofiltration membrane is a polyamide nanofiltration membrane, and the tobacco extract includes at least two of acidic substances, alkaline substances or neutral substances;

[0011] Before each stage of filtration, the charge state of the nanofiltration membrane surface and the protonation and deprotonation behavior of the tobacco extract molecules are regulated by adjusting the pH value of the solution to be filtered. At the corresponding pH value, the tobacco extract with the same charge as the nanofiltration membrane surface is retained, and the remaining tobacco extract permeates through the nanofiltration membrane. The pH value of the filtered permeate is re-adjusted and the next nanofiltration membrane filtration step is performed until the target separation degree is achieved.

[0012] The present invention is based on the relationship between the pH value of the solution to be filtered and the ionization state of the surface groups of the nanofiltration membrane: when the pH value of the solution to be filtered is higher than the isoelectric point of the nanofiltration membrane, the surface of the nanofiltration membrane is negatively charged, and when the pH value of the solution to be filtered is lower than the isoelectric point of the nanofiltration membrane, the surface of the nanofiltration membrane is positively charged; and based on the relationship between the pH value of the solution to be filtered and the dissociation constant pKa of the tobacco extract molecules: for acidic tobacco extract molecules, when the pH value of the solution to be filtered is higher than its molecular dissociation constant pKa, the molecules will be deprotonated and negatively charged, and for alkaline tobacco extract molecules, when the pH value of the solution to be filtered is lower than its molecular dissociation constant pKa, the molecules will be protonated and positively charged; by changing the pH value of the solution to be filtered, the charge properties of the nanofiltration membrane surface and the tobacco extract molecules are regulated at the same time. Under electrostatic interaction, the tobacco extract is retained when it has the same charge as the nanofiltration membrane surface, and the rest of the tobacco extract is permeated. The desired separation effect is achieved by combining multiple nanofiltration membranes.

[0013] Preferably, the nanofiltration membrane is a polyamide nanofiltration membrane prepared by interfacial polymerization, has an average effective pore size of 0.2-1.0 nm, and contains unreacted amino groups or acyl chloride groups on the surface.

[0014] Preferably, the molecular weight of the tobacco extract is 100-500 Da.

[0015] Specifically, the acidic substance includes phthalic acid, benzoic acid, malic acid, proline or ethyl vanillin, the alkaline substance includes nicotine, and the neutral substance includes megastigmatrienone, 2-phenylethanol or neophytadiene.

[0016] Specifically, when the tobacco extract in the tobacco extract includes acidic substances, alkaline substances and neutral substances, two-stage nanofiltration membranes are used in combination to achieve the separation of acidic substances, alkaline substances and neutral substances in the tobacco extract.

[0017] Specifically, when the tobacco extract in the tobacco extract liquid includes x acidic substances, y alkaline substances and z neutral substances, x+y level nanofiltration membranes are used in combination to achieve the separate separation and extraction of each acidic substance and each alkaline substance.

[0018] Specifically, the pH value of the solution to be filtered is adjusted in the range of 3-12.

[0019] Preferably, before each filtration, the adjustment range of the pH value of the solution to be filtered is jointly determined by the isoelectric point of the nanofiltration membrane and the pKa of the target retained tobacco extract in the solution to be filtered; when the target retained tobacco extract is an acidic substance, the pH value of the solution to be filtered is adjusted to be greater than the isoelectric point of the nanofiltration membrane and the pH value of the solution to be filtered is greater than the pKa of the target retained tobacco extract, and the target acidic substance is retained; when the target retained tobacco extract is an alkaline substance, the pH value of the solution to be filtered is adjusted to be less than the isoelectric point of the nanofiltration membrane and the pH value of the solution to be filtered is less than the pKa of the target retained tobacco extract, and the target alkaline substance is retained.

[0020] When the tobacco extract contains phthalic acid, benzoic acid, ethyl vanillin, nicotine, and 2-phenylethanol, the method comprises the following steps: firstly adjusting the pH value of the solution to be filtered to 3.0-4.0, performing a first-stage nanofiltration membrane filtration separation to obtain nicotine and a permeate solution 1, then adjusting the pH value of the permeate solution 1 to 5.0-6.0, performing a second-stage nanofiltration membrane filtration separation to obtain phthalic acid and a permeate solution 2, then adjusting the pH value of the permeate solution 2 to 7.0-9.0, performing a third-stage nanofiltration membrane filtration separation to obtain benzoic acid and a permeate solution 3, then adjusting the pH value of the permeate solution 3 to 10.0-12.0, and performing a fourth-stage nanofiltration membrane filtration separation to obtain ethyl vanillin and 2-phenylethanol.

[0021] In the cascade nanofiltration membrane combination process of the present invention, each level of nanofiltration membrane undertakes a specific separation task. By finely controlling the pH value of the solution to be filtered at each level, the separation of specific tobacco extracts under specific pH conditions is achieved in sequence. Through the step-by-step nanofiltration steps, the method of the present invention can achieve effective step-by-step separation of all acidic tobacco extracts or alkaline tobacco extracts. This separation method not only improves the separation efficiency, but also improves the accuracy and purity of the separation.

[0022] The present invention also provides the application of the tobacco extract stepwise separation method based on the cascade nanofiltration membrane combination process in the fields of electronic cigarettes, high-value utilization of waste tobacco, etc.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The process of the present invention is simple and highly controllable. By adjusting the pH value of the solution to be filtered, the charge properties of the nanofiltration membrane and the tobacco extract molecules can be flexibly changed to achieve step-by-step separation of tobacco extracts. It is easy to implement, has low equipment requirements, is highly universal, and has many advantages such as energy saving, environmental protection, and cost-effectiveness.

[0025] (2) The present invention utilizes the relationship between the pH value of the solution to be filtered and the isoelectric point of the nanofiltration membrane, and the pH value of the solution to be filtered and the pKa of the tobacco extract molecules to regulate the surface charge of the nanofiltration membrane and the protonation and deprotonation behavior of the tobacco extract molecules under different pH conditions, and realizes the step-by-step separation of molecules with different charges through electrostatic interaction, making the separation more effective and the purity of the separated tobacco extract higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the separation principle of the tobacco extract stepwise separation method based on the cascade nanofiltration membrane combination process of the present invention;

[0027] Figure 2 This is a process flow chart for the stepwise separation of tobacco extract using the cascade nanofiltration membrane combination process used in Example 1 of the present invention. DETAILED DESCRIPTION

[0028] In order to make the objects, features and advantages of the present invention more clearly understood, a detailed description is given below using specific embodiments. In the following description, many specific details are set forth to fully understand the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. The technical features in the various embodiments of the present invention can be combined accordingly without conflicting with each other.

[0029] The procedures for the following examples, in which specific conditions are not specified, generally follow conventional conditions or those recommended by the manufacturer. Any material not described in detail in this specification belongs to the prior art known to those skilled in the art. The experimental materials used in the following examples, unless otherwise specified, can be purchased from conventional biochemical reagent companies.

[0030] In the following embodiments, the separation principle diagram of the tobacco extract step separation method based on the cascade nanofiltration membrane combination process is as follows: Figure 1 As shown; the tobacco extract is provided by Yunnan Tobacco Research Institute, and contains acidic substances (phthalic acid, benzoic acid and ethyl vanillin), alkaline substances (nicotine) and neutral substances (2-phenylethanol); the nanofiltration membrane can be prepared by conventional interfacial polymerization method, and the preparation method can be selected:

[0031] (1) Pour the prepared piperazine aqueous solution (piperazine mass concentration of 0.05-0.5 wt%, additive Na3PO4 mass concentration of 0.2-0.8 wt%) onto the surface of the fixed polysulfone porous support membrane, soak for 1-10 min, then pour out the aqueous solution and remove the residual solution on the surface of the porous support membrane;

[0032] (2) pouring the prepared trimesoyl chloride oil phase solution (the mass concentration of trimesoyl chloride is 0.05-0.5wt%) onto the surface of the porous support membrane obtained in step (1) to carry out interfacial polymerization reaction for 1-10 minutes, then pouring out the oil phase solution and immediately placing it in an oven for heat treatment at a temperature of 50-100°C and a holding time of 1-15 minutes to obtain a polyamide nanofiltration membrane; the corresponding nanofiltration membrane has an average effective pore size of 0.2-1.0 nm, and the surface contains unreacted amino groups or acyl chloride groups.

[0033] Example 1

[0034] The tobacco extract contains acidic substances (phthalic acid, benzoic acid and ethyl vanillin), alkaline substances (nicotine) and neutral substances (2-phenylethanol). The process flow chart of the cascade nanofiltration membrane combination process for the stepwise separation of tobacco extracts used in this embodiment is as follows: Figure 2 shown.

[0035] The pH value of the tobacco extract is adjusted to 3.2, so that the corresponding pH value is less than the isoelectric point of the nanofiltration membrane and the corresponding pH value is less than the pKa value of nicotine. After separation through the first-stage nanofiltration membrane, a retentate (nicotine) and a permeate (phthalic acid, benzoic acid, ethyl vanillin, and 2-phenylethanol) are obtained. The purity of nicotine in the retentate is 80%.

[0036] The pH of the permeate 1 was adjusted to 5.6, such that the corresponding pH value was greater than the isoelectric point of the nanofiltration membrane and the corresponding pH value was greater than the pKa of phthalic acid. After separation through a second-stage nanofiltration membrane, a retentate 2 (phthalic acid) and a permeate 2 (benzoic acid, ethyl vanillin, and 2-phenylethanol) were obtained. The purity of the phthalic acid in the retentate 2 was 78%.

[0037] The pH of the permeate II was adjusted to 8.3, such that the corresponding pH value was greater than the isoelectric point of the nanofiltration membrane and the corresponding pH value was greater than the pKa of benzoic acid. After separation through a third-stage nanofiltration membrane, the retentate III (benzoic acid) and the permeate III (ethyl vanillin and 2-phenylethanol) were obtained. The purity of the benzoic acid in the retentate III was 72%.

[0038] The pH value of the permeate three was adjusted to 11.5, so that the corresponding pH value was greater than the isoelectric point of the nanofiltration membrane and the corresponding pH value was greater than the pKa of ethyl vanillin. After filtration and separation through a fourth-stage nanofiltration membrane, a retentate four (ethyl vanillin) and a permeate four (2-phenylethanol) were obtained. The purity of the ethyl vanillin in the retentate four was 75%, and the purity of the 2-phenylethanol in the permeate four was 90%.

[0039] Example 2

[0040] Tobacco extract contains acidic substances (phthalic acid, benzoic acid and ethyl vanillin), alkaline substances (nicotine) and neutral substances (2-phenylethanol);

[0041] The pH of the tobacco extract was adjusted to 11.5, such that the corresponding pH value was greater than the isoelectric point of the nanofiltration membrane and greater than the pKa value of the acidic substance. After separation through a first-stage nanofiltration membrane, a retentate (phthalic acid, benzoic acid, ethyl vanillin) and a permeate (nicotine, 2-phenylethanol) were obtained. The purity of the phthalic acid in the retentate was 35%, the purity of the benzoic acid was 32%, and the purity of the ethyl vanillin was 33%.

[0042] The pH value of the tobacco extract was adjusted to 3.3, so that the corresponding pH value was less than the isoelectric point of the nanofiltration membrane and the corresponding pH value was less than the pKa value of nicotine. After filtration and separation through a second-stage nanofiltration membrane, a second retentate (nicotine) and a second permeate (2-phenylethanol) were obtained. The purity of nicotine in the second retentate was 79%, and the purity of 2-phenylethanol in the second permeate was 88%.

[0043] Example 3

[0044] Tobacco extract contains acidic substances (phthalic acid, benzoic acid and ethyl vanillin), alkaline substances (nicotine) and neutral substances (2-phenylethanol);

[0045] The pH value of the tobacco extract is adjusted to 4.0, so that the corresponding pH value is less than the isoelectric point of the nanofiltration membrane and the corresponding pH value is less than the pKa value of nicotine. After separation through the first-stage nanofiltration membrane, a retentate (nicotine) and a permeate (phthalic acid, benzoic acid, ethyl vanillin, and 2-phenylethanol) are obtained. The purity of nicotine in the retentate is 70%.

[0046] The pH of the permeate 1 was adjusted to 6.0, such that the corresponding pH value was greater than the isoelectric point of the nanofiltration membrane and the corresponding pH value was greater than the pKa of phthalic acid. After separation through a second-stage nanofiltration membrane, a retentate 2 (phthalic acid) and a permeate 2 (benzoic acid, ethyl vanillin, and 2-phenylethanol) were obtained. The purity of the phthalic acid in the retentate 2 was 72%.

[0047] The pH of the permeate II was adjusted to 8.5, such that the corresponding pH value was greater than the isoelectric point of the nanofiltration membrane and the corresponding pH value was greater than the pKa of benzoic acid. After separation through a third-stage nanofiltration membrane, retentate III (benzoic acid) and permeate III (ethyl vanillin and 2-phenylethanol) were obtained. The purity of benzoic acid in retentate III was 68%.

[0048] The pH value of the permeate three was adjusted to 10.5, so that the corresponding pH value was greater than the isoelectric point of the nanofiltration membrane and the corresponding pH value was greater than the pKa of ethyl vanillin. After filtration and separation through a fourth-stage nanofiltration membrane, a retentate four (ethyl vanillin) and a permeate four (2-phenylethanol) were obtained. The purity of the ethyl vanillin in the retentate four was 73%, and the purity of the 2-phenylethanol in the permeate four was 85%.

[0049] Example 4

[0050] Tobacco extract contains acidic substances (phthalic acid, benzoic acid and ethyl vanillin), alkaline substances (nicotine) and neutral substances (2-phenylethanol);

[0051] The pH value of the tobacco extract was adjusted to 3.0, such that the corresponding pH value was less than the isoelectric point of the nanofiltration membrane and the corresponding pH value was less than the pKa value of nicotine. After separation through a first-stage nanofiltration membrane, a retentate (nicotine) and a permeate (phthalic acid, benzoic acid, ethyl vanillin, and 2-phenylethanol) were obtained. The purity of nicotine in the retentate (1) was 86%.

[0052] The pH value of the permeate 1 was adjusted to 11.6, so that the corresponding pH value was greater than the isoelectric point of the nanofiltration membrane and the corresponding pH value was greater than the pKa of the acidic substance. After filtration and separation through a second-stage nanofiltration membrane, a retentate 2 (phthalic acid, benzoic acid, ethyl vanillin) and a permeate 2 (2-phenylethanol) were obtained. In the retentate 2, the purity of phthalic acid was 36%, the purity of benzoic acid was 30%, and the purity of ethyl vanillin was 35%. In the permeate 2, the purity of 2-phenylethanol was 88%.

[0053] Example 5

[0054] Tobacco extract contains acidic substances (phthalic acid, benzoic acid and ethyl vanillin), alkaline substances (nicotine) and neutral substances (2-phenylethanol);

[0055] The pH value of the tobacco extract was adjusted to 3.3, such that the corresponding pH value was less than the isoelectric point of the nanofiltration membrane and the corresponding pH value was less than the pKa value of nicotine. After separation through a first-stage nanofiltration membrane, a retentate (nicotine) and a permeate (phthalic acid, benzoic acid, ethyl vanillin, and 2-phenylethanol) were obtained. The purity of nicotine in the retentate (1) was 78%.

[0056] The pH value of the permeate 1 was adjusted to 4.0, and after the second-stage nanofiltration membrane filtration separation, the tobacco extract in the permeate 1 could not be retained, thereby obtaining the permeate 2 (phthalic acid, benzoic acid, ethyl vanillin, 2-phenylethanol);

[0057] The pH of the permeate II was adjusted to 7.5, such that the corresponding pH value was greater than the isoelectric point of the nanofiltration membrane and the corresponding pH value was greater than the pKa values ​​of phthalic acid and benzoic acid. After separation through a third-stage nanofiltration membrane, a retentate III (phthalic acid and benzoic acid) and a permeate III (ethyl vanillin and 2-phenylethanol) were obtained. The purity of the phthalic acid in the retentate III was 58%, and the purity of the benzoic acid was 42%.

[0058] The pH value of the permeate three was adjusted to 10.0, so that the corresponding pH value was greater than the isoelectric point of the nanofiltration membrane and the corresponding pH value was greater than the pKa of ethyl vanillin. After filtration and separation through a fourth-stage nanofiltration membrane, a retentate four (ethyl vanillin) and a permeate four (2-phenylethanol) were obtained. The purity of the ethyl vanillin in the retentate four was 70%, and the purity of the 2-phenylethanol in the permeate four was 84%.

[0059] Example 6

[0060] Tobacco extract contains acidic substances (phthalic acid, benzoic acid and ethyl vanillin), alkaline substances (nicotine) and neutral substances (2-phenylethanol);

[0061] The pH value of the tobacco extract is adjusted to 3.5, so that the corresponding pH value is less than the isoelectric point of the nanofiltration membrane and the corresponding pH value is less than the pKa value of nicotine. After separation through the first-stage nanofiltration membrane, a retentate (nicotine) and a permeate (phthalic acid, benzoic acid, ethyl vanillin, and 2-phenylethanol) are obtained. The purity of nicotine in the retentate (1) is 75%.

[0062] The pH of the permeate 1 was adjusted to 8.0, such that the corresponding pH value was greater than the isoelectric point of the nanofiltration membrane and the corresponding pH value was greater than the pKa values ​​of phthalic acid and benzoic acid. After separation through a second-stage nanofiltration membrane, a retentate 2 (phthalic acid and benzoic acid) and a permeate 2 (ethyl vanillin and 2-phenylethanol) were obtained. The purity of the phthalic acid in the retentate 2 was 57%, and the purity of the benzoic acid was 43%.

[0063] The pH value of the permeate II was adjusted to 10.0, so that the corresponding pH value was greater than the isoelectric point of the nanofiltration membrane and the corresponding pH value was greater than the pKa of ethyl vanillin. After filtration and separation through the third-stage nanofiltration membrane, the retentate III (ethyl vanillin) and the permeate III (2-phenylethanol) were obtained. The purity of ethyl vanillin in the retentate III was 70%, and the purity of 2-phenylethanol in the permeate III was 78%.

[0064] Example 7

[0065] Tobacco extract contains acidic substances (phthalic acid, benzoic acid and ethyl vanillin), alkaline substances (nicotine) and neutral substances (2-phenylethanol);

[0066] The pH value of the tobacco extract was adjusted to 3.5, such that the corresponding pH value was less than the isoelectric point of the nanofiltration membrane and the corresponding pH value was less than the pKa value of nicotine. After separation through the first-stage nanofiltration membrane, a retentate (nicotine) and a permeate (phthalic acid, benzoic acid, ethyl vanillin, and 2-phenylethanol) were obtained. The purity of nicotine in the retentate (1) was 78%.

[0067] The pH of the permeate 1 was adjusted to 5.5, such that the corresponding pH value was greater than the isoelectric point of the nanofiltration membrane and the corresponding pH value was greater than the pKa of phthalic acid. After separation through a second-stage nanofiltration membrane, a retentate 2 (phthalic acid) and a permeate 2 (benzoic acid, ethyl vanillin, and 2-phenylethanol) were obtained. The purity of the phthalic acid in the retentate 2 was 80%.

[0068] The pH value of the permeate II was adjusted to 10.0, so that the corresponding pH value was greater than the isoelectric point of the nanofiltration membrane and the corresponding pH value was greater than the pKa values ​​of benzoic acid and ethyl vanillin. After filtration and separation through a third-stage nanofiltration membrane, a retentate III (benzoic acid, ethyl vanillin) and a permeate III (2-phenylethanol) were obtained. The purity of the benzoic acid in the retentate III was 52%, the purity of the ethyl vanillin was 48%, and the purity of the 2-phenylethanol in the permeate III was 84%.

[0069] Comparative Example 1

[0070] Without adjusting the pH of the solution, the tobacco extract is filtered and separated through a first-stage nanofiltration membrane to obtain a permeate 1 (phthalic acid, benzoic acid, ethyl vanillin, nicotine, and 2-phenylethanol); the permeate 1 is filtered and separated through a second-stage nanofiltration membrane to obtain a permeate 2 (phthalic acid, benzoic acid, ethyl vanillin, nicotine, and 2-phenylethanol); and the permeate 2 is filtered and separated through a third-stage nanofiltration membrane to obtain a permeate 3 (phthalic acid, benzoic acid, ethyl vanillin, nicotine, and 2-phenylethanol);

[0071] The test showed that the method in this comparative example could not achieve the separation of tobacco extract. Comparative Example 1 Compared with Example 1, the method in Comparative Example 1 did not control the pH value of the solution and separated the tobacco extract based on the pore size screening mechanism. However, due to the small molecular weight of the tobacco extract, the pore size of the nanofiltration membrane could not meet the separation requirements.

[0072] The embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A stepwise separation method for tobacco extracts based on a cascade nanofiltration membrane combination process, characterized in that: include: The tobacco extract is filtered by combining multiple nanofiltration membranes to achieve step-by-step separation of the tobacco extract. During the filtration process, the permeate separated by the previous nanofiltration membrane is used as the feed liquid for the next nanofiltration membrane; The nanofiltration membrane is polyamide nanofiltration membrane; Before each stage of filtration, the charge state of the nanofiltration membrane surface and the protonation and deprotonation behavior of the tobacco extract molecules are regulated by adjusting the pH value of the solution to be filtered. At the corresponding pH value, the tobacco extract with the same charge as the nanofiltration membrane surface is retained, and the remaining tobacco extract permeates through the nanofiltration membrane. The permeate obtained by filtration is re-adjusted for pH and filtered through the next nanofiltration membrane step until the target separation degree is achieved; The tobacco extract contains phthalic acid, benzoic acid, ethyl vanillin, nicotine and 2-phenylethanol. The pH value of the solution to be filtered is first adjusted to 3.0-4.0, and a first-stage nanofiltration membrane filtration separation is performed to obtain nicotine and a permeate I. The pH value of the permeate I is then adjusted to 5.0-6.0, and a second-stage nanofiltration membrane filtration separation is performed to obtain phthalic acid and a permeate II. The pH value of the permeate II is then adjusted to 7.0-9.0, and a third-stage nanofiltration membrane filtration separation is performed to obtain benzoic acid and a permeate III. The pH value of the permeate III is then adjusted to 10.0-12.0, and a fourth-stage nanofiltration membrane filtration separation is performed to obtain ethyl vanillin and 2-phenylethanol.

2. The tobacco extract stepwise separation method based on the cascade nanofiltration membrane combination process according to claim 1, characterized in that: The nanofiltration membrane is a polyamide nanofiltration membrane prepared by interfacial polymerization, has an average effective pore size of 0.2-1.0 nm, and contains unreacted amino groups or acyl chloride groups on the surface.

3. The tobacco extract stepwise separation method based on a cascade nanofiltration membrane combination process according to claim 1, characterized in that: The molecular weight of the tobacco extract is 100-500 Da.

4. Application of the tobacco extract stepwise separation method based on the cascade nanofiltration membrane combination process according to any one of claims 1 to 3 in the fields of electronic cigarettes and high-value utilization of waste tobacco.

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