Composite solvent for improving naphtha aromatic hydrocarbon recovery rate in liquid-liquid extraction process and extraction method thereof

Abstract

The invention discloses a composite solvent for improving the recovery rate of naphtha aromatic hydrocarbon for a liquid-liquid extraction process and an extraction method of the composite solvent, and belongs to the technical field of liquid-liquid extraction processes, and the composite solvent for improving the recovery rate of naphtha aromatic hydrocarbon for the liquid-liquid extraction process is composed of a hydrophilic eutectic solvent and a hydrophobic eutectic solvent. The composite solvent for improving the naphtha aromatic hydrocarbon recovery rate for the liquid-liquid extraction process can be suitable for extraction of low-boiling-point naphtha, has relatively good dissolving capacity on polar and non-polar aromatic hydrocarbons, improves the naphtha aromatic hydrocarbon recovery rate, and avoids possible acid-base reactivity of a hydrophilic eutectic solvent.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid-liquid extraction processes, and particularly to a composite solvent for improving the recovery rate of aromatics in a liquid-liquid extraction process and an extraction method thereof. Background Art

[0002] Aromatics and non-aromatics form azeotropes, making it difficult to obtain pure aromatics by simple distillation. Aromatics must be separated by extraction. Although there are various process routes for aromatics extraction, they can be classified into two categories according to the process principle: liquid-liquid extraction and extractive distillation. Liquid-liquid extraction is a process that utilizes the different solubilities of a solvent in various hydrocarbon components in the aromatics extraction raw material and can form two liquid phases with different densities by layering to achieve the separation of aromatics and non-aromatics. Extractive distillation is a process that adds a polar solvent to the raw material and utilizes the different effects of the solvent on the relative volatilities of various hydrocarbon components to increase the relative volatility between the target aromatics and other components to achieve the separation of aromatics and non-aromatics.

[0003] The aromatics extraction raw material includes naphtha that can boil in the range of 36°C to 180°C, gas oil that can boil in the range of 180°C to 370°C, and vacuum gas oil that can boil in the range of 370°C to 650°C. Due to the volatility of naphtha, the extraction solvent needs to be used at normal temperature or a lower temperature to reduce volatility and safety problems, which limits the range of solvent selection because high-boiling-point, low-volatility solvents may have insufficient solubility at low temperatures and cannot effectively extract aromatics.

[0004] Changes in the pH value or chemical properties of hydrophilic deep eutectic solvents may affect their solubility in aromatics, resulting in a decrease in the recovery rate of aromatics. For example, when the pH value of a hydrophilic deep eutectic solvent increases, its selectivity for aromatics may decrease, causing some aromatics to not be effectively extracted. Changes in the recovery rate of aromatics: After the hydrophilic deep eutectic solvent reacts with acidic and basic substances in naphtha, its solubility in aromatics may also change, thereby affecting the recovery rate of aromatics and leading to a deterioration in the overall extraction effect. Decrease in the stability of hydrophilic deep eutectic solvents: Frequent acid-base reactions may lead to a decrease in the chemical stability of hydrophilic deep eutectic solvents, making them more likely to decompose or polymerize. This will not only reduce the service life of hydrophilic deep eutectic solvents but also increase the loss and regeneration cost of hydrophilic deep eutectic solvents.

[0005] The Udex process is a traditional liquid-liquid extraction technology with the following technical problems: The Udex process uses diethylene glycol (DEG) and diethylene glycol amine (DGA) as solvents. These solvents have limited selectivity for aromatics, which may result in insufficient recovery rate and purity of aromatics. In addition, DEG and DGA are prone to volatilization during operation, leading to an increase in solvent loss. The Tetra process uses tetraethylene glycol as a solvent, with the following technical problems: Tetraethylene glycol is prone to volatilization during operation, resulting in an increase in solvent loss. The Tetra process has certain requirements for the aromatic content of the raw material and has poor adaptability to raw materials with a low aromatic content. Summary of the Invention

[0006] As described in the above prior art, one of the objectives of the present invention is to provide a composite solvent for improving the recovery rate of naphtha aromatics in the liquid-liquid extraction process. This composite solvent for improving the recovery rate of naphtha aromatics in the liquid-liquid extraction process can be suitable for the extraction of low-boiling naphtha, has good solubility for polar and non-polar aromatics, improves the recovery rate of naphtha aromatics, and avoids possible acid-base reactivity of hydrophilic deep eutectic solvents.

[0007] Another objective of the present invention is to provide a manufacturing method for the composite solvent for improving the recovery rate of naphtha aromatics in the liquid-liquid extraction process. This method has simple steps and can be industrialized.

[0008] One of the objectives of the present invention is achieved by adopting the following technical solutions:

[0009] The composite solvent for improving the recovery rate of naphtha aromatics in the liquid-liquid extraction process is composed of a hydrophilic deep eutectic solvent and a hydrophobic deep eutectic solvent.

[0010] Further, the volume ratio of the hydrophilic deep eutectic solvent to the hydrophobic deep eutectic solvent is 1:2 to 2:1.

[0011] Further, the hydrogen bond donor of the hydrophilic deep eutectic solvent is a sugar-derived polyol. For the DES composed of betaine and glucose, when the sugar-derived polyol is used as the hydrogen bond donor, the DESs usually show neutrality

[0012] Further, the sugar-derived polyol is one of sorbitol, xylitol, maltitol, erythritol, and isomaltulose.

[0013] Further, the hydrophilic deep eutectic solvent and polyvinyl alcohol form a hydrophilic deep eutectic solvent-polyvinyl alcohol copolymer deep eutectic gel.

[0014] Further, the preparation method of the hydrophilic deep eutectic solvent-polyvinyl alcohol copolymer deep eutectic gel includes the following steps:

[0015] S1. Dissolve polyvinyl alcohol powder in deionized water, stir at 95 °C for 3 h to obtain a polyvinyl alcohol aqueous solution, and then perform ultrasonic treatment on this solution for 1 h to remove any air bubbles;

[0016] S2. After defoaming, pour the polyvinyl alcohol solution into a 1-mm-thick glass mold and soak it in the hydrophilic deep eutectic solvent for 24 h to form a hydrophilic deep eutectic solvent-polyvinyl alcohol copolymer deep eutectic gel;

[0017] S3. During the soaking process, replace the hydrophilic deep eutectic solvent every 6 h to ensure that the water in the polyvinyl alcohol solution is completely replaced, and obtain the hydrophilic deep eutectic solvent-polyvinyl alcohol copolymer deep eutectic gel.

[0018] Furthermore, it also includes a porous material modified with a cationic surfactant.

[0019] Furthermore, the porous material is one of activated carbon and zeolite; the cationic surfactant is cetyltrimethylammonium bromide.

[0020] Furthermore, the method steps for the uniformly distributed porous material modified with a cationic surfactant in the composite solvent for enhancing the aromatics recovery rate of naphtha in the liquid-liquid extraction process are as follows:

[0021] S1. Add the porous material modified with a cationic surfactant to a container, slowly add the composite solvent for enhancing the aromatics recovery rate of naphtha in the liquid-liquid extraction process and mix to ensure that the porous material is completely immersed;

[0022] S2. Let it stand for 24 h to allow the porous material modified with a cationic surfactant to fully contact and adsorb with the composite solvent for enhancing the aromatics recovery rate of naphtha in the liquid-liquid extraction process;

[0023] S3. Separate the porous material modified with a cationic surfactant by centrifugation or filtration, and leave the composite solvent for enhancing the aromatics recovery rate of naphtha that has adsorbed the porous material modified with a cationic surfactant.

[0024] The second object of the present invention is achieved by adopting the following technical solution:

[0025] An extraction method for a composite solvent for enhancing the aromatics recovery rate of naphtha in the liquid-liquid extraction process, comprising the following steps:

[0026] S1. Mix the composite solvent for enhancing the aromatics recovery rate of naphtha in the liquid-liquid extraction process with naphtha, heat it to between 40 °C and 60 °C, and extract for 3 h, with stirring during the extraction process;

[0027] S2. After extraction is completed, the two phases are separated by standing or centrifugation. The aromatics in the naphtha are transferred to the composite solvent phase for the liquid-liquid extraction process to improve the aromatics recovery rate of naphtha, obtaining a composite solvent phase rich in aromatics for the liquid-liquid extraction process to improve the aromatics recovery rate of naphtha and a naphtha phase after de-aromatization.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] (1) The composite solvent for the liquid-liquid extraction process to improve the aromatics recovery rate of naphtha provided by the present invention is composed of a hydrophilic deep eutectic solvent and a hydrophobic deep eutectic solvent. The hydrophilic deep eutectic solvent has a stronger dissolution ability for polar aromatics, and the hydrophobic deep eutectic solvent has a better dissolution ability for non-polar aromatics. Mixing the two can cover the extraction requirements of polar and non-polar aromatics at the same time and improve the extraction efficiency of aromatics in naphtha.

[0030] (2) For the composite solvent for the liquid-liquid extraction process to improve the aromatics recovery rate of naphtha provided by the present invention, the hydrophilic deep eutectic solvent and polyvinyl alcohol form a hydrophilic deep eutectic solvent-polyvinyl alcohol copolymer deep eutectic gel. This gel exhibits good stability in an aqueous environment, reducing the possibility of the composite solvent for the liquid-liquid extraction process to improve the aromatics recovery rate of naphtha reacting with organic acids and basic nitrogen compounds in naphtha and avoiding affecting the effect of naphtha aromatics extraction.

[0031] (3) For the composite solvent for the liquid-liquid extraction process to improve the aromatics recovery rate of naphtha provided by the present invention, the porous material can be modified by surfactants to enhance the adsorption ability for aromatics. For example, after modifying the porous material with hexadecyltrimethylammonium bromide (HDTMA), its adsorption ability for aromatics is significantly enhanced, while its adsorption ability for non-aromatics is relatively low; and it can improve the dispersibility of the porous material in the composite solvent for the liquid-liquid extraction process to improve the aromatics recovery rate of naphtha, thereby achieving suspension. Detailed implementation manners

[0032] Next, in combination with specific embodiments, the present invention will be further described. It should be noted that on the premise of no conflict, the following-described embodiments or technical features can be arbitrarily combined to form new embodiments.

[0033] The information of the hydrogen bond donor of the hydrophilic deep eutectic solvent is generally as follows:

[0034] Sulfolane, boiling point: 285.6 °C. Volatility: It has low volatility at normal temperature, but its volatility is significantly enhanced under high temperature conditions. Applicability: Due to its high boiling point and low volatility, sulfolane is suitable for use at relatively high temperatures, but not suitable for the extraction of low-boiling naphtha.

[0035] Ethylene glycol (EG), boiling point: 197.6 °C. Volatility: It has low volatility at room temperature, but its volatility increases significantly under high-temperature conditions. Applicability: Due to its high boiling point and low volatility, ethylene glycol is suitable for use at relatively high temperatures, but not suitable for the extraction of naphtha with low boiling points.

[0036] Diethylene glycol (DEG): Boiling point: 245 °C; Volatility: It has low volatility at room temperature, but its volatility increases under high-temperature conditions; Applicability: Diethylene glycol has a relatively high boiling point and is suitable for use at relatively high temperatures, but not suitable for the extraction of naphtha with low boiling points.

[0037] Triethylene glycol (TEG): Boiling point: 289.4 °C; Volatility: It has low volatility at room temperature, but its volatility increases under high-temperature conditions. Applicability: Triethylene glycol has a relatively high boiling point and is suitable for use at relatively high temperatures, but not suitable for the extraction of naphtha with low boiling points.

[0038] N-Methylpyrrolidone (NMP): Boiling point: 202 °C; Volatility: It has low volatility at room temperature, but its volatility increases under high-temperature conditions. Applicability: NMP has a relatively high boiling point and is suitable for use at relatively high temperatures, but not suitable for the extraction of naphtha with low boiling points.

[0039] Dimethyl sulfoxide (DMSO): Boiling point: 189 °C; Volatility: It has low volatility at room temperature, but its volatility increases under high-temperature conditions. Applicability: DMSO has a relatively high boiling point and is suitable for use at relatively high temperatures, but not suitable for the extraction of naphtha with low boiling points.

[0040] Example 1

[0041] This example provides a composite solvent for improving the aromatic hydrocarbon recovery rate of naphtha in the liquid-liquid extraction process, which is composed of a hydrophilic deep eutectic solvent and a hydrophobic deep eutectic solvent, and the volume ratio of the hydrophilic deep eutectic solvent to the hydrophobic deep eutectic solvent is 1:2.

[0042] The hydrogen bond donors of the hydrophilic deep eutectic solvent and the hydrophobic deep eutectic solvent are sugar-derived polyols. When sugar-derived polyols are used as hydrogen bond donors, DESs usually exhibit neutrality. In this example, the sugar-derived polyol is sorbitol. Selection of hydrogen bond donors: In the hydrophilic deep eutectic solvent and the hydrophobic deep eutectic solvent, different hydrogen bond donors will affect the acidity and basicity of the deep eutectic solvent. When sugar-derived polyols are used as hydrogen bond donors, the deep eutectic solvent usually exhibits neutrality, avoiding the reaction between the hydrophilic deep eutectic solvent and organic acids and basic nitrogen compounds in naphtha, which may affect the performance of the solvent.

[0043] The volatility of the mixed DES system is low, reducing the volatilization loss of the solvent during operation and environmental pollution.

[0044] Hydrophilic deep eutectic solvents: Usually composed of hydrophilic hydrogen bond acceptors (such as choline chloride) and hydrogen bond donors (such as sugar-derived polyols like glycerol and ethylene glycol). The DESs formed by these combinations have good hydrophilicity and can form hydrogen bonds with water, thus showing high solubility and stability in aqueous environments.

[0045] Hydrophobic deep eutectic solvents: The preparation of hydrophobic DESs usually requires the selection of hydrophobic hydrogen bond acceptors (such as certain quaternary ammonium salts) and hydrogen bond donors (such as menthol, long-chain fatty acids, etc.).

[0046] Sorbitol, chemical formula: C6H 14 O6; Structure: Sorbitol is a six-carbon polyol with six hydroxyl groups. Characteristics: Sorbitol has good moisture retention and sweetness and is commonly used as an ingredient in food additives and oral care products.

[0047] This embodiment also provides an extraction method of a composite solvent for improving the aromatic hydrocarbon recovery rate of naphtha in the liquid-liquid extraction process, including the following steps:

[0048] S1. Mix the composite solvent for improving the aromatic hydrocarbon recovery rate of naphtha in the liquid-liquid extraction process with naphtha, heat to 50 °C, extract for 3 h, and stir during the extraction process;

[0049] S2. After the extraction is completed, separate the two phases by standing or centrifugation. The aromatic hydrocarbons in the naphtha are transferred to the composite solvent phase for improving the aromatic hydrocarbon recovery rate of naphtha in the liquid-liquid extraction process, obtaining a composite solvent phase rich in aromatic hydrocarbons for improving the aromatic hydrocarbon recovery rate of naphtha in the liquid-liquid extraction process and a naphtha phase after de-aromatization.

[0050] If the density difference between the two phases is small, the two phases are more likely to mix during the flow process, forming an emulsion. The formation of the emulsion will increase the complexity of mass transfer, reduce the mass transfer efficiency, and also increase the difficulty of subsequent separation. Therefore, two phases with a large density difference are more likely to achieve good hydrodynamic flow characteristics in the extraction column.

[0051] Example 2

[0052] This embodiment provides a composite solvent for improving the aromatic hydrocarbon recovery rate of naphtha in the liquid-liquid extraction process, which is composed of a hydrophilic deep eutectic solvent and a hydrophobic deep eutectic solvent, and the volume ratio of the hydrophilic deep eutectic solvent to the hydrophobic deep eutectic solvent is 1:1.

[0053] The hydrogen bond donors of the hydrophilic deep eutectic solvent and the hydrophobic deep eutectic solvent are sugar-derived polyols. When sugar-derived polyols are used as hydrogen bond donors, the DESs usually show neutrality. In this embodiment, the sugar-derived polyol is xylitol.

[0054] Xylitol, chemical formula: C5H12 O5; Structure: Xylitol is a pentavalent polyol with five hydroxyl groups. Characteristics: Xylitol has low calories and a sweet taste and is commonly used in food and oral care products.

[0055] This embodiment also provides an extraction method of a composite solvent for improving the aromatics recovery rate of naphtha in a liquid-liquid extraction process, including the following steps:

[0056] S1. Mix the composite solvent for improving the aromatics recovery rate of naphtha in a liquid-liquid extraction process with naphtha, heat to 40°C, extract for 3 hours, and stir during the extraction process;

[0057] S2. After the extraction is completed, separate the two phases by standing or centrifugation. The aromatics in the naphtha are transferred to the composite solvent phase for improving the aromatics recovery rate of naphtha in a liquid-liquid extraction process, obtaining a composite solvent phase rich in aromatics for improving the aromatics recovery rate of naphtha in a liquid-liquid extraction process and a naphtha phase after de-aromatization.

[0058] Example 3

[0059] This embodiment provides a composite solvent for improving the aromatics recovery rate of naphtha in a liquid-liquid extraction process, which is composed of a hydrophilic deep eutectic solvent and a hydrophobic deep eutectic solvent, and the volume ratio of the hydrophilic deep eutectic solvent to the hydrophobic deep eutectic solvent is 2:1.

[0060] The hydrogen bond donors of the hydrophilic deep eutectic solvent and the hydrophobic deep eutectic solvent are sugar-derived polyols. When sugar-derived polyols are used as hydrogen bond donors, DESs usually exhibit neutrality. In this embodiment, the sugar-derived polyol is maltitol.

[0061] Maltitol, Chemical formula: C 14 H 24 O 10 ; Structure: Maltitol is a diol composed of two glucose units. Characteristics: Maltitol has relatively low calories and a sweet taste and is commonly used in the food industry.

[0062] This embodiment also provides an extraction method of a composite solvent for improving the aromatics recovery rate of naphtha in a liquid-liquid extraction process, including the following steps:

[0063] S1. Mix the composite solvent for improving the aromatics recovery rate of naphtha in a liquid-liquid extraction process with naphtha, heat to 60°C, extract for 3 hours, and stir during the extraction process;

[0064] S2. After the extraction is completed, the two phases are separated by standing or centrifugation. The aromatics in the naphtha are transferred to the composite solvent phase for the liquid-liquid extraction process to improve the aromatics recovery rate of naphtha, obtaining a composite solvent phase rich in aromatics for the liquid-liquid extraction process to improve the aromatics recovery rate of naphtha and a naphtha phase after de-aromatization.

[0065] Example 4

[0066] This example provides a composite solvent for the liquid-liquid extraction process to improve the aromatics recovery rate of naphtha, which is composed of a hydrophilic deep eutectic solvent and a hydrophobic deep eutectic solvent, and the volume ratio of the hydrophilic deep eutectic solvent to the hydrophobic deep eutectic solvent is 1:2.

[0067] The hydrogen bond donors of the hydrophilic deep eutectic solvent and the hydrophobic deep eutectic solvent are sugar-derived polyols. When sugar-derived polyols are used as hydrogen bond donors, DESs usually show neutrality. In this example, the sugar-derived polyol is erythritol.

[0068] Erythritol, chemical formula: C4H 10 O4; Structure: Erythritol is a four-carbon polyol with four hydroxyl groups. Characteristics: Erythritol has low calories and a sweet taste and is commonly used in the food industry.

[0069] In this example, the hydrophilic deep eutectic solvent and polyvinyl alcohol form a hydrophilic deep eutectic solvent-polyvinyl alcohol copolymer deep eutectic gel. The preparation method of the hydrophilic deep eutectic solvent-polyvinyl alcohol copolymer deep eutectic gel includes the following steps:

[0070] S1. Dissolve polyvinyl alcohol powder in deionized water and stir at 95°C for 3 h to obtain an aqueous polyvinyl alcohol solution, and then perform ultrasonic treatment on this solution for 1 h to remove any bubbles;

[0071] S2. After defoaming, pour the polyvinyl alcohol solution into a 1-mm-thick glass mold and soak it in the hydrophilic deep eutectic solvent for 24 h to form a hydrophilic deep eutectic solvent-polyvinyl alcohol copolymer deep eutectic gel;

[0072] S3. During the soaking process, replace the hydrophilic deep eutectic solvent every 6 h to ensure that the water in the polyvinyl alcohol solution is completely replaced, obtaining a hydrophilic deep eutectic solvent-polyvinyl alcohol copolymer deep eutectic gel.

[0073] In this embodiment, first, polyvinyl alcohol (PVA) is dissolved in water to form a uniformly dispersed PVA aqueous solution. Subsequently, the PVA aqueous solution is immersed in a deep eutectic solvent. Driven by the concentration gradient, water molecules diffuse out from the PVA polymer network, while deep eutectic solvent molecules diffuse in. During this process, the strong interaction between the hydrogen bond donors and acceptors in the deep eutectic solvent limits the affinity of the deep eutectic solvent molecules for external hydrogen bonds. At the same time, as water molecules are expelled, the hydrogen bond functional groups on the PVA polymer chains promote the formation of hydrogen bonds between and within the PVA chains, leading to chain aggregation and forming a high-strength and tough deep eutectic gel, which exhibits good stability in an aqueous environment.

[0074] Effect of water content: Hydrophilic deep eutectic solvents usually contain a certain amount of water, and the presence of water may enhance their acid-base reactivity. For example, water can promote the formation or breakage of hydrogen bonds, thereby affecting the chemical stability of hydrophilic deep eutectic solvents.

[0075] This embodiment also provides an extraction method of a composite solvent for improving the aromatics recovery rate of naphtha in a liquid-liquid extraction process, including the following steps:

[0076] S1. Mix the composite solvent for improving the aromatics recovery rate of naphtha in a liquid-liquid extraction process with naphtha, heat to 50 °C, and extract for 3 h, with stirring during the extraction process;

[0077] S2. After the extraction is completed, separate the two phases by standing or centrifugation. The aromatics in the naphtha are transferred to the composite solvent phase for improving the aromatics recovery rate of naphtha in a liquid-liquid extraction process, obtaining a composite solvent phase rich in aromatics for improving the aromatics recovery rate of naphtha in a liquid-liquid extraction process and a naphtha phase after aromatics removal.

[0078] Example 5

[0079] This embodiment provides a composite solvent for improving the aromatics recovery rate of naphtha in a liquid-liquid extraction process, which is composed of a hydrophilic deep eutectic solvent, a hydrophobic deep eutectic solvent, and activated carbon modified with cetyltrimethylammonium bromide. The volume ratio of the hydrophilic deep eutectic solvent to the hydrophobic deep eutectic solvent is 1:2.

[0080] The hydrogen bond donors of the hydrophilic deep eutectic solvent and the hydrophobic deep eutectic solvent are sugar-derived polyols. When sugar-derived polyols are used as hydrogen bond donors, DESs usually exhibit neutrality. In this embodiment, the sugar-derived polyol is isomaltulose.

[0081] In this embodiment, a hydrophilic deep eutectic solvent-PVA copolymer deep eutectic gel is formed between the hydrophilic deep eutectic solvent and PVA. The preparation method of the hydrophilic deep eutectic solvent-PVA copolymer deep eutectic gel includes the following steps:

[0082] S1. Dissolve polyvinyl alcohol powder in deionized water, stir at 95 °C for 3 h to obtain an aqueous polyvinyl alcohol solution, and then subject this solution to ultrasonic treatment for 1 h to remove any air bubbles;

[0083] S2. After defoaming, pour the polyvinyl alcohol solution into a 1-mm-thick glass mold and soak it in a hydrophilic deep eutectic solvent for 24 h to form a hydrophilic deep eutectic solvent-polyvinyl alcohol copolymer deep eutectic gel;

[0084] S3. During the soaking process, replace the hydrophilic deep eutectic solvent every 6 h to ensure that the water in the polyvinyl alcohol solution is completely replaced, obtaining a hydrophilic deep eutectic solvent-polyvinyl alcohol copolymer deep eutectic gel.

[0085] In this example, the method steps for the uniform distribution of cetyltrimethylammonium bromide-modified activated carbon in the composite solvent for improving the aromatic hydrocarbon recovery rate of naphtha in the liquid-liquid extraction process are as follows:

[0086] S1. Add cetyltrimethylammonium bromide-modified activated carbon to a container, slowly add the composite solvent for improving the aromatic hydrocarbon recovery rate of naphtha in the liquid-liquid extraction process and mix to ensure that the porous material is completely submerged;

[0087] S2. Let it stand for 24 h to allow the cetyltrimethylammonium bromide-modified activated carbon to fully contact and adsorb with the composite solvent for improving the aromatic hydrocarbon recovery rate of naphtha in the liquid-liquid extraction process;

[0088] S3. Separate the cetyltrimethylammonium bromide-modified activated carbon by centrifugation or filtration, leaving the composite solvent for improving the aromatic hydrocarbon recovery rate of naphtha that has adsorbed the cetyltrimethylammonium bromide-modified activated carbon.

[0089] The porous material can enhance its adsorption capacity for aromatic hydrocarbons through surfactant modification. For example, after modifying the porous material with cetyltrimethylammonium bromide (HDTMA), its adsorption capacity for aromatic hydrocarbons is significantly enhanced, while its adsorption capacity for non-aromatic hydrocarbons is relatively low; and it can improve the dispersibility of the porous material in the composite solvent for improving the aromatic hydrocarbon recovery rate of naphtha in the liquid-liquid extraction process, thus achieving suspension. The selective adsorption of aromatic hydrocarbons by the modified porous material is mainly attributed to the relatively high π electron cloud density of aromatic hydrocarbon molecules, which can form strong interactions with the functional groups on the surface of the activated carbon. For non-aromatic hydrocarbons (such as alkanes), due to their relatively simple molecular structure and lack of the π electron cloud of the aromatic ring, the interaction with the surface of the activated carbon is weak, so the adsorption capacity is low.

[0090] This example also provides an extraction method for the composite solvent for improving the aromatic hydrocarbon recovery rate of naphtha in the liquid-liquid extraction process, including the following steps:

[0091] S1. Mix the composite solvent for enhancing the aromatics recovery rate of naphtha in the liquid-liquid extraction process with naphtha, heat it to 50 °C, extract for 3 h, and stir during the extraction process;

[0092] S2. After the extraction is completed, separate the two phases by standing or centrifugation. The aromatics in the naphtha are transferred to the composite solvent phase for enhancing the aromatics recovery rate of naphtha in the liquid-liquid extraction process, obtaining a composite solvent phase rich in aromatics for enhancing the aromatics recovery rate of naphtha in the liquid-liquid extraction process and a naphtha phase after de-aromatization.

[0093] Example 6

[0094] This example provides a composite solvent for enhancing the aromatics recovery rate of naphtha in the liquid-liquid extraction process, which is composed of a hydrophilic deep eutectic solvent, a hydrophobic deep eutectic solvent, and zeolite modified by cetyltrimethylammonium bromide. The volume ratio of the hydrophilic deep eutectic solvent to the hydrophobic deep eutectic solvent is 1:2.

[0095] The hydrogen bond donors of the hydrophilic deep eutectic solvent and the hydrophobic deep eutectic solvent are sugar-derived polyols. When sugar-derived polyols are used as hydrogen bond donors, DESs usually exhibit neutrality. In this example, the sugar-derived polyol is isomaltulose.

[0096] Chemical structure: Isomaltulose is a reducing disaccharide formed by connecting 1 molecule of glucose and 1 molecule of fructose with an α-1,6 glycosidic bond.

[0097] In this example, the hydrophilic deep eutectic solvent and polyvinyl alcohol form a hydrophilic deep eutectic solvent-polyvinyl alcohol copolymer deep eutectic gel. The preparation method of the hydrophilic deep eutectic solvent-polyvinyl alcohol copolymer deep eutectic gel includes the following steps:

[0098] S1. Dissolve polyvinyl alcohol powder in deionized water, stir at 95 °C for 3 h to obtain an aqueous polyvinyl alcohol solution, and then perform ultrasonic treatment on this solution for 1 h to remove any bubbles;

[0099] S2. After defoaming, pour the polyvinyl alcohol solution into a 1-mm-thick glass mold and soak it in the hydrophilic deep eutectic solvent for 24 h to form a hydrophilic deep eutectic solvent-polyvinyl alcohol copolymer deep eutectic gel;

[0100] S3. During the soaking process, replace the hydrophilic deep eutectic solvent every 6 h to ensure that the water in the polyvinyl alcohol solution is completely replaced, obtaining a hydrophilic deep eutectic solvent-polyvinyl alcohol copolymer deep eutectic gel.

[0101] In this example, the method steps for the uniform distribution of zeolite modified by cetyltrimethylammonium bromide in the composite solvent for enhancing the aromatics recovery rate of naphtha in the liquid-liquid extraction process are as follows:

[0102] S1. Add the hexadecyltrimethylammonium bromide-modified zeolite into a container, and slowly add the composite solvent for enhancing the aromatics recovery rate of naphtha in the liquid-liquid extraction process to mix, ensuring that the porous material is completely immersed.

[0103] S2. Let it stand for 24 h to allow the hexadecyltrimethylammonium bromide-modified zeolite to fully contact and adsorb with the composite solvent for enhancing the aromatics recovery rate of naphtha in the liquid-liquid extraction process.

[0104] S3. Separate the hexadecyltrimethylammonium bromide-modified zeolite by centrifugation or filtration, leaving the composite solvent for enhancing the aromatics recovery rate of naphtha in the liquid-liquid extraction process that has adsorbed the hexadecyltrimethylammonium bromide-modified zeolite.

[0105] This embodiment also provides an extraction method for the composite solvent for enhancing the aromatics recovery rate of naphtha in the liquid-liquid extraction process, including the following steps:

[0106] S1. Mix the composite solvent for enhancing the aromatics recovery rate of naphtha in the liquid-liquid extraction process with naphtha, heat to 50 °C, and extract for 3 h, with stirring during the extraction process.

[0107] S2. After the extraction is completed, separate the two phases by standing or centrifugation. The aromatics in the naphtha are transferred to the composite solvent phase for enhancing the aromatics recovery rate of naphtha in the liquid-liquid extraction process, obtaining a composite solvent phase rich in aromatics for enhancing the aromatics recovery rate of naphtha in the liquid-liquid extraction process and a naphtha phase after de-aromatization.

[0108] The above embodiments are only the preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention fall within the scope of protection required by the present invention.

Claims

1. A composite solvent for improving the recovery rate of naphtha aromatics in a liquid-liquid extraction process, characterized in that: It is composed of a hydrophilic deep eutectic solvent and a hydrophobic deep eutectic solvent.

2. The composite solvent for improving the recovery rate of naphtha aromatics in a liquid-liquid extraction process according to claim 1, characterized in that: The volume ratio of the hydrophilic deep eutectic solvent to the hydrophobic deep eutectic solvent is 1:2 to 2:

1.

3. The composite solvent for improving the recovery rate of naphtha aromatics in a liquid-liquid extraction process according to claim 1, characterized in that: The hydrogen bond donor of the hydrophilic deep eutectic solvent is a sugar-derived polyol.

4. The composite solvent for improving the recovery rate of naphtha aromatics in a liquid-liquid extraction process according to claim 3, characterized in that: The sugar-derived polyol is one of sorbitol, xylitol, maltitol, erythritol and isomaltulose.

5. The composite solvent for improving the recovery rate of naphtha aromatics in a liquid-liquid extraction process according to claim 1, characterized in that: The hydrophilic deep eutectic solvent and polyvinyl alcohol form a hydrophilic deep eutectic solvent-polyvinyl alcohol copolymer deep eutectic gel.

6. The composite solvent for improving the recovery rate of naphtha aromatics in a liquid-liquid extraction process according to claim 5, characterized in that: The method for preparing the hydrophilic low eutectic solvent-polyvinyl alcohol copolymer deep eutectic gel comprises the following steps: S1, dissolving polyvinyl alcohol powder in deionized water, stirring at 95°C for 3 h to obtain a polyvinyl alcohol aqueous solution, and then subjecting the solution to ultrasonic treatment for 1 h to remove any bubbles; S2. After defoaming, pour the polyvinyl alcohol solution into a 1 mm thick glass mold and soak it in the hydrophilic low eutectic solvent for 24 hours to form a hydrophilic low eutectic solvent-polyvinyl alcohol copolymer deep eutectic gel; S3. During the immersion process, the hydrophilic low eutectic solvent is replaced every 6 hours to ensure that the water in the polyvinyl alcohol solution is completely replaced to obtain the hydrophilic low eutectic solvent-polyvinyl alcohol copolymer deep eutectic gel.

7. The composite solvent for improving the recovery rate of naphtha aromatics in a liquid-liquid extraction process according to claim 1, characterized in that: Also included are porous materials modified with cationic surfactants.

8. The composite solvent for improving the recovery rate of naphtha aromatics in a liquid-liquid extraction process according to claim 7, characterized in that: The porous material is one of activated carbon and zeolite; the cationic surfactant is hexadecyltrimethylammonium bromide.

9. The composite solvent for improving the recovery rate of naphtha aromatics in a liquid-liquid extraction process according to claim 8, characterized in that: The method steps for uniformly distributing the porous material modified by the cationic surfactant in the composite solvent for improving the recovery rate of naphtha aromatics in the liquid-liquid extraction process are as follows: S1, adding the porous material modified by the cationic surfactant into a container, slowly adding the composite solvent for improving the recovery rate of naphtha aromatics in the liquid-liquid extraction process to mix, and ensuring that the porous material is completely immersed; S2, standing for 24 hours to allow the porous material modified by the cationic surfactant to fully contact and adsorb the composite solvent for improving the recovery rate of naphtha aromatics in the liquid-liquid extraction process; S3. Separating the porous material modified by the cationic surfactant by centrifugation or filtration, leaving the composite solvent for improving the recovery rate of naphtha aromatics adsorbed by the porous material modified by the cationic surfactant.

10. The composite solvent extraction method for improving the recovery rate of naphtha aromatics in a liquid-liquid extraction process according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1, mixing the composite solvent for improving the recovery rate of naphtha aromatics in the liquid-liquid extraction process with naphtha, heating to between 40° C. and 60° C., extracting for 3 hours, and stirring during the extraction process; S2. After the extraction is completed, the two phases are separated by standing or centrifuging, and the aromatics in the naphtha are transferred to the composite solvent phase for improving the recovery rate of naphtha aromatics in the liquid-liquid extraction process, thereby obtaining an aromatic-rich composite solvent phase for improving the recovery rate of naphtha aromatics in the liquid-liquid extraction process and a dearomatized naphtha phase.