Porous adsorbent for extracting xanthophyll through supercritical fluid as well as preparation method and application of porous adsorbent

Abstract

The invention relates to a porous adsorbent for supercritical fluid extraction of xanthophyll as well as a preparation method and application of the porous adsorbent. The porous adsorbent takes surface-alkylated mesoporous silica as a carrier, loads natural vegetable oil or active ingredients of the natural vegetable oil in modified mesoporous channels to serve as a cosolvent and a stabilizer, and is used for a supercritical carbon dioxide extraction process of xanthophyll in marigold. The adsorbent has triple functions of selective adsorption, in-situ protection and extraction process optimization: 1) the alkylated surface and confinement pore channels have high affinity and selectivity to xanthophyll molecules; 2) lutein molecules are confined in a pore microenvironment containing vegetable oil, light oxygen is isolated, the lutein molecules are effectively prevented from being degraded, and the product stability is improved; and 3) the loaded vegetable oil is locally released in the pore channels, and the loaded vegetable oil and the supercritical carbon dioxide have a synergistic effect on dissolution and mass transfer of the xanthophyll, so that the addition amount of a cosolvent is reduced, and the separation and recovery steps of a target product are simplified.

Description

Technical Field

[0001] This invention belongs to the field of natural product extraction technology, specifically relating to a porous adsorbent for supercritical fluid extraction of lutein, its preparation method and application, and is particularly suitable for supercritical carbon dioxide extraction and separation of lutein from marigolds. Background Technology

[0002] Lutein is an important natural carotenoid pigment widely used in food additives, health products, pharmaceuticals, and animal feed, possessing strong antioxidant activity and visual protection functions. Marigold is currently the main raw material for industrial lutein extraction. Traditional lutein extraction methods (such as organic solvent extraction) have drawbacks such as solvent residue, high-temperature degradation of lutein, high energy consumption, and significant environmental pollution. Supercritical carbon dioxide extraction technology, with its advantages of being non-toxic, operating at low temperatures, and allowing for easy solvent removal, is considered a green and efficient alternative extraction method for lutein.

[0003] However, lutein molecules have low polarity and large molecular weight, resulting in limited solubility in carbon dioxide fluid and low extraction efficiency. To improve solubility, existing technologies typically add liquid co-solvents such as ethanol, acetone, or natural plant oils to the carbon dioxide. Among these, natural plant oils have attracted increasing attention due to their good lipid solubility and safety. However, existing co-solvent systems still have two significant drawbacks. First, liquid plant oils are miscible with the extract, making separation and recovery difficult. This usually requires additional distillation, molecular distillation, or column chromatography steps, leading to high energy consumption, high costs, and unsatisfactory recovery rates, limiting the economic viability of large-scale applications. Second, in subsequent processing, thermosensitive lutein faces risks such as oxidative degradation. There is an urgent need to develop a technology that can effectively improve the efficiency of supercritical carbon dioxide extraction of lutein, prevent lutein degradation, and significantly reduce and simplify the use of liquid co-solvents.

[0004] Therefore, this invention attempts to introduce a special multifunctional adsorbent that can synergistically enhance the supercritical carbon dioxide / vegetable oil system, selectively adsorb, provide in-situ protection, and replace / reduce the liquid co-solvent, in order to solve this problem. Summary of the Invention

[0005] This invention aims to address the problems of low efficiency, difficult co-solvent separation and recovery, and easy degradation of products in existing supercritical carbon dioxide extraction of lutein. It provides a porous adsorbent for supercritical fluid extraction of lutein, its preparation method, and its application. The porous adsorbent uses surface-alkylated mesoporous silica as a carrier, loading natural plant oil or its active ingredients into the modified mesoporous channels as a co-solvent and stabilizer, for use in the supercritical carbon dioxide extraction process of lutein from marigolds. This adsorbent possesses three functions: selective adsorption, in-situ protection, and extraction process optimization: 1) The alkylated surface and confined channels exhibit high affinity and selectivity for lutein molecules; 2) Lutein molecules are confined within the plant oil-containing microenvironment of the channels, isolating them from light and oxygen, effectively preventing degradation and improving product stability; 3) The local release of the loaded plant oil within the channels synergistically with the dissolution and mass transfer of lutein by supercritical carbon dioxide, reducing the amount of co-solvent required and simplifying the separation and recovery steps of the target product.

[0006] This invention provides a porous adsorbent for supercritical fluid extraction of lutein, comprising: a) a mesoporous silica support; b) an alkylated surface formed by alkylating the mesoporous silica support; and c) a natural plant oil or its active ingredient loaded inside the mesoporous channels of the alkylated surface.

[0007] Preferably, the mesoporous silica support is selected from at least one of MCM-41, SBA-15, KIT-6, and mesoporous silica nanospheres, and its pore size is 2-30 nm.

[0008] Preferably, the surface alkylation modification is performed using an alkylsilane alkylating agent, wherein the alkylsilane alkylating agent is an alkyltrialkoxysilane with a carbon chain length of C8-C18; more preferably, it is octadecyltrimethoxysilane or hexadecyltrimethoxysilane.

[0009] Preferably, the natural plant oil is coconut oil, palm oil, soybean oil, corn oil, or olive oil; the active ingredient of the plant oil is medium-chain triglycerides (MCT); and the loading of the natural plant oil or its active ingredient accounts for 10-50 wt% of the total weight of the porous adsorbent.

[0010] The present invention also provides a method for preparing the aforementioned porous adsorbent, comprising the following steps: S1 Alkylation modification: dispersing a mesoporous silica support in an organic solvent, adding an alkylsilane reagent, and reacting at 50-80°C for 6-48 hours under nitrogen protection and drying conditions. After the reaction, the alkylated mesoporous silica support is separated; S2 Plant oil loading: mixing the alkylated mesoporous silica support obtained in step S1 with natural plant oil or its active ingredient, and soaking it under vacuum conditions and / or at 40-80°C for 2-24 hours to allow it to be fully absorbed into the pores; S3 Filtering to remove excess unloaded natural plant oil or its active ingredient to obtain the porous adsorbent.

[0011] Preferably, in step S1, before the alkylation modification reaction, the mesoporous silica support is calcined under vacuum at 100-300°C for 2-12 hours; the organic solvent is isopropanol or ethanol; the amount of alkylsilane oxidizing agent is 5-30 wt% of the weight of the mesoporous silica support; in step S2, the amount of natural plant oil or its active ingredient is 1-3 times the estimated pore volume of the alkylated mesoporous silica support.

[0012] This invention also provides a method for extracting lutein using the aforementioned porous adsorbent, applied to the supercritical carbon dioxide extraction process of lutein from marigolds. The method includes: loading the porous adsorbent as a stationary phase into an extraction device; allowing a carbon dioxide fluid or a carbon dioxide / natural plant oil mixture containing marigold raw materials and / or marigold extracts to flow through the porous adsorbent; enriching lutein through the selective adsorption of the porous adsorbent and confining it within a pore microenvironment containing plant oil or its active ingredients for protection; and after the adsorption step is completed, desorption is performed by adjusting the pressure and temperature of the extraction device or introducing an eluent to obtain an extract rich in lutein.

[0013] Furthermore, the porous adsorbent can be applied in the following ways: a column filled with the porous adsorbent can be connected in series after the marigold raw material extraction vessel, so that the fluid carrying the preliminarily extracted lutein flows through the adsorption column; or it can be used as part of an integrated extraction / adsorption bed assembly; or the crude extract after extraction can be separated, enriched and protected in the adsorption column.

[0014] Preferably, the amount of free liquid vegetable oil added in the fluid flowing through the porous adsorbent is reduced by 30%-100% compared to supercritical carbon dioxide extraction of the same scale without the porous adsorbent; the eluent is supercritical carbon dioxide or a supercritical fluid containing a small amount of polar solvent.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] The adsorbent of this invention has three functions: selective adsorption, in-situ protection, and extraction process optimization: 1) The alkylated surface and confined pores have high affinity and selectivity for lutein molecules; 2) Lutein molecules are confined in the microenvironment of the pores containing plant oil, which isolates them from light and oxygen, effectively preventing their degradation and improving product stability; 3) The local release of the loaded plant oil in the pores and the synergistic effect of supercritical carbon dioxide on the dissolution and mass transfer of lutein reduce the amount of co-solvent added and simplify the separation and recovery steps of the target product. Detailed Implementation

[0017] In the following examples, when preparing the adsorbent, ensure that the reaction system (solvent, reagent, container) is in an anhydrous state.

[0018] Lutein extraction rate = mass of extracted lutein / total mass of lutein in raw material × 100%;

[0019] Degradation rate = mass of lutein degradation products / (mass of lutein degradation products + mass of extracted lutein) × 100%.

[0020] Lutein degradation products refer to the total mass of hydrocarbons such as toluene, p-xylene, 1,2-dihydro-1,1,6-trimethylnaphthalene, and 2,7-dimethylnaphthalene, as well as ketones such as isophorone oxide and megastigtrienone.

[0021] Example 1: Preparation of MCM-41 based porous adsorbent and its application in lutein extraction

[0022] 1. Adsorbent preparation:

[0023] Carrier pretreatment: MCM-41 mesoporous silica (pore size 3nm) was calcined in vacuum at 200℃ for 4h to remove surface impurities.

[0024] Alkylation modification: 5g of calcined MCM-41 was dispersed in 50mL of isopropanol, and 0.5g of octadecyltrimethoxysilane (C18) was added. The mixture was reacted at 70℃ for 24h under nitrogen protection. After filtration, washing with ethanol, and drying, alkylated MCM-41 was obtained.

[0025] Vegetable oil loading: Alkylated MCM-41 was mixed with coconut oil at twice the pore volume (the amount of coconut oil was twice the pore volume of the carrier), and impregnated at 60°C under vacuum for 12 hours. Excess oil was removed by filtration to obtain the adsorbent (coconut oil loading 30wt%).

[0026] 2. Lutein Extraction Application: 5g of adsorbent was packed into an adsorption column connected in series after the extraction vessel. Carbon dioxide fluid (35MPa, 50℃) containing the initial marigold extract was flowed through the adsorption column at a flow rate of 2mL / min. After adsorption, the extract was eluted with supercritical CO2 (40MPa, 60℃) and collected.

[0027] Results: The lutein extraction rate was 85±4.2%, the degradation rate was only 4.6±0.5%, and the purity of the crude extract after separation and enrichment was 91±1.5%.

[0028] Example 2: Optimized preparation of SBA-15 based porous adsorbent

[0029] 1. Adsorbent preparation:

[0030] Carrier pretreatment: SBA-15 (pore size 8nm) was calcined in vacuum at 250℃ for 6h.

[0031] Alkylation modification: Hexadecyltrimethoxysilane (C16) was used in an amount of 10 wt% of the support, ethanol was used as the solvent, and the reaction was carried out at 60 °C for 18 h under nitrogen protection. After filtration, washing with ethanol and drying, alkylated MCM-41 was obtained.

[0032] SBA-15 loading: Medium chain triglycerides (MCT) are loaded at a rate of 1.5 times the pore volume, and the mixture is vacuum-impregnated at 40°C for 8 hours with a loading of 25 wt%.

[0033] 2. Lutein Extraction Application: The adsorbent serves as an integrated extraction / adsorption bed component, allowing a mixed fluid (30 MPa, 45°C) containing marigold raw material, consisting of carbon dioxide and natural plant oil, to flow through the integrated extraction / adsorption bed. The eluent is supercritical CO2 containing 5% ethanol. The natural plant oil in the mixed fluid is coconut oil, and its mass is 3% of the marigold powder.

[0034] Results: The lutein extraction rate was 90±3.4%, the degradation rate was only 3.3±0.5%, and the purity of the crude extract after separation and enrichment was 95±0.9%.

[0035] Comparative Example 1: Adsorbent without alkylation modification

[0036] Preparation: The alkylation step was omitted, and MCM-41 was directly loaded with coconut oil (30 wt%).

[0037] Application: Same as in Example 1.

[0038] Results: The lutein extraction rate was only 70±4.6%, the degradation rate was 18±0.5% (the protective effect was significantly reduced), and the purity of the crude extract after separation and enrichment was 86±1.3%.

[0039] Comparative Example 2: Alkylation Adsorbents Without Vegetable Oil Loading

[0040] Preparation: Alkylation modification only (C18), without coconut oil loading.

[0041] Application: Same as in Example 1.

[0042] Results: The lutein extraction rate was 75±4.4%, but the degradation rate was 15±0.6% (no in-situ protection). The purity of the crude extract after separation and enrichment was 87±0.8%.

[0043] Comparative Example 3: Traditional supercritical carbon dioxide extraction method for lutein (without using porous adsorbents)

[0044] Raw material processing: Marigold powder and coconut oil are mixed at a mass ratio of 1:2, with coconut oil serving as a co-solvent.

[0045] Supercritical extraction: Under conditions of 40 MPa and 60 °C, a carbon dioxide fluid carrying a marigold-coconut oil mixture was passed through the extraction vessel at a flow rate of 3 mL / min.

[0046] Separation and purification: After extraction, excess coconut oil was removed by two-stage vacuum evaporation, and then lutein was purified by silica gel column chromatography.

[0047] Results: The lutein extraction rate was 65±4.5% (significantly lower than that in Example 1). The degradation rate was 27±0.6% (significantly higher than that in Example 1). The purity of the crude extract after separation and enrichment was 90±0.8%.

Claims

1. A porous adsorbent for supercritical fluid extraction of lutein, characterized in that, include: a) a mesoporous silica carrier; b) an alkylated surface formed by alkylating the mesoporous silica carrier; c) a natural plant oil or its active ingredient loaded inside the mesoporous channels of the alkylated surface.

2. The porous adsorbent according to claim 1, characterized in that, The mesoporous silica support is selected from at least one of MCM-41, SBA-15, KIT-6, and mesoporous silica nanospheres, and its pore size is 2-30 nm.

3. The porous adsorbent according to claim 1, characterized in that, The surface alkylation modification is performed using an alkylsilane alkylating agent, which is an alkyltrialkoxysilane with a carbon chain length of C8-C18; preferably octadecyltrimethoxysilane or hexadecyltrimethoxysilane.

4. The porous adsorbent according to claim 1, characterized in that, The natural plant oil is coconut oil, palm oil, soybean oil, corn oil, or olive oil; the active ingredient of the plant oil is medium-chain triglycerides (MCT); the loading of the natural plant oil or its active ingredient accounts for 10-50 wt% of the total weight of the porous adsorbent.

5. The method for preparing the porous adsorbent according to any one of claims 1-4, characterized in that, The process includes the following steps: S1 Alkylation modification: The mesoporous silica support is dispersed in an organic solvent, an alkylsilane reagent is added, and the mixture is reacted at 50-80°C for 6-48 hours under nitrogen protection and drying conditions. After the reaction, the alkylated mesoporous silica support is separated; S2 Vegetable oil loading: The alkylated mesoporous silica support obtained in step S1 is mixed with natural vegetable oil or its active ingredients, and the mixture is soaked under vacuum conditions and / or at 40-80°C for 2-24 hours to ensure that it is fully absorbed into the pores; S3 Filtering to remove excess unloaded natural vegetable oil or its active ingredients to obtain the porous adsorbent.

6. The preparation method according to claim 5, characterized in that, In step S1, before the alkylation modification reaction, the mesoporous silica support is calcined in vacuum at 100-300°C for 2-12 hours; the organic solvent is isopropanol or ethanol; the amount of alkylsilane oxidizing agent is 5-30 wt% of the weight of the mesoporous silica support; in step S2, the amount of natural plant oil or its active ingredient is 1-3 times the estimated pore volume of the alkylated mesoporous silica support.

7. A method for extracting lutein using the porous adsorbent according to any one of claims 1-4, applied to the supercritical carbon dioxide extraction process for lutein in marigolds, characterized in that, The method includes: loading the porous adsorbent as a stationary phase into an extraction device; allowing a carbon dioxide fluid or a carbon dioxide / natural plant oil mixture containing marigold raw material and / or marigold extract to flow through the porous adsorbent; and after the adsorption step is completed, desorption is performed by adjusting the pressure and temperature of the extraction device or introducing an eluent to obtain an extract rich in lutein.

8. The method according to claim 7, characterized in that, The porous adsorbent can be used in the following ways: a column filled with the porous adsorbent is connected in series after the marigold raw material extraction vessel, so that the fluid carrying the preliminarily extracted lutein flows through the adsorption column; or it can be used as part of an integrated extraction / adsorption bed assembly; or the crude extract after extraction can be separated, enriched and protected in the adsorption column.

9. The method according to claim 7 or 8, characterized in that, In the fluid flowing through the porous adsorbent, the amount of free liquid vegetable oil added is reduced by 30%-100% compared to supercritical carbon dioxide extraction of the same scale without the porous adsorbent; the eluent is supercritical carbon dioxide or a supercritical fluid containing a small amount of polar solvent.