Method for continuous and efficient extraction in ultrasonic microreactor

Abstract

The application discloses a kind of based on wettability difference capillary ultrasonic microreactor and continuous efficient extraction method.The reactor includes sandwich type ultrasonic transducer and the capillary microreactor of segmented design along fluid flow direction: inner wall of front-end pipe section is coated with polytetrafluoroethylene, is hydrophobic, facilitate oil phase continuous and excite a large number of acoustic cavitation bubbles;Back-end pipe section is bare hydrophilic base material, guarantee efficient transmission of acoustic energy, enhance bubble vibration intensity.Through axial wettability gradient design, synergistic control cavitation bubble quantity and intensity, and induce liquid-liquid system to occur controllable phase state overturn in flow, significantly strengthen interface update and mass transfer.The system structure is compact, easy to operate, suitable for a variety of not mutually soluble liquid-liquid system, in 2-100 seconds can complete efficient extraction, compared with traditional microextraction method (2-60 minutes) efficiency is improved several times.

Description

Technical Field

[0001] This application relates to an ultrasonic microreactor designed based on axial wettability differences and its application in continuous high-efficiency liquid-liquid extraction, belonging to the field of microchemical engineering and ultrasonic process enhancement technology. Background Technology

[0002] Microchemical technology is a novel chemical process intensification technology that emerged in the early 1990s in response to the demands of sustainable development. Compared to traditional scale chemical equipment, microreactors typically have sub-millimeter channel characteristic dimensions, offering significant advantages such as large specific surface area, high heat and mass transfer efficiency, strong process controllability, and ease of modular scaling. This provides a new technological approach for enhancing liquid-liquid extraction processes and accelerating the transformation of laboratory research results into industrial applications, demonstrating broad application potential in fields such as fine chemicals, pharmaceutical intermediate synthesis, nuclear fuel reprocessing, functional material preparation, and high-risk reaction substitution.

[0003] However, the physical behavior at the microscale differs fundamentally from that of macroscopic systems. While miniaturization of the characteristic scale endows microreactors with numerous advantages, it also introduces a series of new technical challenges. Under microscale conditions, fluid flow is typically laminar, and interface renewal mainly relies on molecular diffusion mechanisms, making it difficult to achieve rapid and efficient mixing between immiscible phases with high viscosity or significant differences in physical properties. Furthermore, unlike conventional batch reactors where the flow field structure and mixing intensity can be flexibly controlled through mechanical stirring, the operating parameters of microreactors are relatively limited, and the degree of freedom in adjusting reaction conditions is low. These factors result in insufficient mixing and mass transfer efficiency and limited process control flexibility in liquid-liquid systems within microreactors, becoming a significant bottleneck restricting the further promotion and application of microchemical extraction technology.

[0004] To overcome the aforementioned limitations, researchers have actively explored coupling external energy into microreactor systems to achieve non-contact, highly responsive, and programmable process enhancement. Among these, ultrasound technology, due to its excellent media penetration, non-polluting nature, lack of moving parts, and wide applicability, is considered an effective means of enhancing microscale extraction processes. When ultrasound is introduced into a microreactor, the liquid medium undergoes periodic compression and expansion under alternating sound pressure, thereby activating the existing microbubble nuclei within the liquid. These bubble nuclei undergo complex nonlinear dynamic processes such as growth, oscillation, contraction, and even collapse under the influence of the acoustic field, forming acoustic cavitation. Acoustic cavitation can highly concentrate dispersed ultrasonic energy in the vicinity of the bubbles, accompanied by various mechanical effects such as shock waves, microjets, and acoustic flow, thereby promoting the stretching, folding, and renewal of the liquid-phase interface, which is beneficial for improving the mass transfer efficiency of the liquid-liquid extraction process. Existing research shows that in ultrasonic microreactors, the dispersion and extraction behavior of immiscible solution-liquid two-phase systems is closely related to acoustic cavitation characteristics. Acoustic cavitation bubbles are mainly generated in the continuous phase fluid that is in direct contact with the wall of the microchannel and oscillate near the liquid-liquid interface, causing the dispersed phase to break up and form an emulsion, thereby significantly increasing the mass transfer area between phases and improving the extraction efficiency (AIChE J., 64(4): 1412-1423; J. Flow Chem., 14: 569-584).

[0005] Further research revealed that the ultrasonic enhancement effect is mainly constrained by two key factors: First, the wetting properties of the microreactor. The distribution of the continuous phase within the microchannel is significantly affected by the hydrophilicity or oleophilicity of the reactor material, and the solubility of the gas in the continuous phase directly determines the number of acoustic cavitation bubbles generated. Second, the acoustic transmission efficiency of the microreactor. The higher the degree of matching between the acoustic impedance of the reactor material and the ultrasonic source, the greater the acoustic energy transmission efficiency. Under the same ultrasonic input conditions, the higher the sound intensity formed within the reactor, and the greater the vibration intensity of the acoustic cavitation bubbles.

[0006] However, existing ultrasonic microreactors are mostly constructed using a single homogeneous material (such as monolithic glass, quartz, or polymers), leading to a fundamental contradiction between wettability and acoustic performance. This makes it difficult to simultaneously achieve the dual goals of "high bubble quantity" and "high bubble strength." For example, microreactors made of polymers such as polycarbonate (PC) typically exhibit strong oleophilic properties, making it easier for the oil phase within the channel to form a continuous phase with high gas solubility, thus enabling the generation of a large number of acoustic cavitation bubbles. However, the acoustic transmission efficiency of such materials is relatively low, making it difficult to ensure sufficient vibration intensity for the bubbles. Conversely, glass (GLS) microreactors have high acoustic transmission efficiency, creating a strong sound field within the reactor, resulting in intense vibration of the acoustic cavitation bubbles. However, due to its hydrophilicity, the continuous phase within the channel is mostly aqueous, with low gas solubility, limiting the number of acoustic cavitation bubbles.

[0007] More notably, most current ultrasonic microreactor designs neglect the functional zoning and dynamic control requirements along the flow direction. Traditional structures maintain consistent wettability and geometry throughout the channel length, failing to adapt to the phased evolution of extraction—"initial dispersion—thorough mixing—phase separation"—making it difficult to achieve phased optimized control of "efficient fragmentation first, then deep mass transfer, and finally ordered separation." Although some studies have attempted to construct wettability gradient surfaces using methods such as photolithography, plasma treatment, or micro-contact printing, these technologies generally suffer from complex processes, poor durability, difficulty in integration into closed multilayer microchannels, and susceptibility to fluid erosion. Furthermore, they do not consider the spatial synergy with the acoustic field, limiting their practicality and scalability.

[0008] Furthermore, existing systems mostly employ externally attached ultrasonic transducers, requiring acoustic energy to pass sequentially through the encapsulation layer, adhesive layer, and reactor wall before acting on the working fluid. In this path, issues such as uneven adhesive layer thickness, interface debonding, air gaps, or acoustic impedance mismatch significantly weaken acoustic coupling efficiency, leading to energy loss, localized heating, and even equipment failure. Especially under high-frequency or high-power operating conditions, this can easily cause adhesive layer aging, channel deformation, or cracking, severely impacting the system's long-term stability and industrial application prospects. Therefore, achieving a harmonious balance between efficient sound field introduction, adjustable wall wettability, and controllable two-phase flow has become a core scientific and engineering challenge that urgently needs to be addressed in the development of high-performance ultrasonic microextraction technology.

[0009] To address these challenges, an innovative microreactor structural design is urgently needed, breaking away from the traditional paradigm of homogeneous materials and uniform wettability. This design involves constructing functional zones with axial wettability gradients along the fluid flow direction, combined with an acoustically optimized composite structural design, to achieve synergistic control of continuous phase distribution and acoustic energy transmission. The ideal design should promote oil phase continuity and cavitation initiation at the front end, ensure efficient acoustic energy injection and cavitation enhancement at the back end, and reduce acoustic energy loss through structural matching. This allows for the simultaneous increase in the number and intensity of cavitation bubbles without sacrificing system stability, achieving efficient, stable, and adjustable full-cycle enhancement of complex liquid-liquid extraction processes.

[0010] Therefore, developing a novel ultrasonic microreactor system and method that integrates wettability gradient control, efficient acoustic coupling, and continuous flow characteristics is not only a technological upgrade to existing microchemical equipment, but also an important practice to deepen the application of ultrasonic cavitation theory at the microscale. This is of great significance for improving my country's high-end specialty chemical manufacturing capabilities and achieving a green and low-carbon chemical industry transformation. The development of this technology also aligns with the current global strategic focus on cutting-edge directions such as "smart chemistry," "digital twin reactors," and "intelligent process intensification," and is expected to become one of the key enabling technologies for next-generation microchemical platforms. Summary of the Invention

[0011] To address the aforementioned problems, this invention provides an ultrasonic microextraction reactor with capillary coupling based on wettability differences, and applies it to a continuous extraction process. The capillary microreactor is made of a hydrophilic material with high acoustic transmission efficiency and is connected to a large-radiating-surface horn-shaped sandwich transducer via epoxy resin. The front channel of the capillary microreactor is coated with polytetrafluoroethylene (PTFE) to form an oleophilic end, while the rear channel is uncoated. The oil phase in the front channel is continuous, generating a sufficient number of acoustic cavitation bubbles (cavitation excitation zone); the rear channel has high acoustic transmission efficiency, resulting in sufficient bubble cavitation intensity (cavitation vibration zone). Based on this structure, the number of acoustic cavitation bubbles and vibration intensity are simultaneously optimized. The extractant and feed liquid flow into the reactor via a fluid transport device, where they are rapidly dispersed and mass transferred under ultrasonic action, reaching extraction equilibrium. This invention adopts the following technical solution: A microreactor system for continuous and efficient extraction is characterized by comprising a raw material supply end, an ultrasonic microextraction reactor, and a product collection end connected in sequence. The ultrasonic microextraction reactor includes an ultrasonic transducer and a capillary microreactor. The capillary microreactor is provided with constriction structures A at both ends to connect the raw material inlet and outlet pipes; The capillary microreactor is divided into a front channel and a rear channel along the fluid flow direction. The inner wall of the front channel is covered with polytetrafluoroethylene, exhibiting hydrophobic properties, while the rear channel is an uncovered bare substrate, exhibiting hydrophilic properties, resulting in a significant difference in axial wettability. The ultrasonic transducer is bonded to the capillary microreactor via an acoustic adhesive through its front radiating surface, and the front radiating surface is an arc-shaped concave surface that matches the capillary.

[0012] Optionally, the ultrasonic transducer is a sandwich-type ultrasonic transducer; Preferably, the ultrasonic transducer consists of a piezoelectric ceramic plate, front and rear metal cover plates, and a pre-tightening screw; Preferably, the front radiating surface is made of titanium alloy or aluminum alloy, and the surface is polished to reduce sound energy loss.

[0013] Optionally, the constriction structure A is prepared by laser micromachining or mechanical tapering, with a constriction diameter of 1.0-12.0 mm, to reduce inlet fluid impact and induce flow pattern change; Preferably, the capillary microreactor is made of glass or metal capillary.

[0014] Optionally, the length of the front-end channel accounts for 0.05-0.90% of the total length of the capillary. Preferably, the thickness of the polytetrafluoroethylene coating is 10μm-100μm, and the contact angle of the coating surface is greater than 90°, which is conducive to the spread of the oil phase to form a continuous phase.

[0015] Optionally, the contact angle of the exposed substrate surface of the rear channel is less than 30°; Preferably, the length of the rear channel is 0.10-0.95 of the total length of the capillary, in order to ensure that the ultrasonic waves are efficiently introduced into the liquid from the transducer.

[0016] Optionally, the capillary microreactor has a through-hole structure B on its sidewall; Preferably, the through-hole structure B is prepared by laser drilling or side windowing process, and is used to connect the sample inlet pipeline or detection sensor.

[0017] A continuous and efficient extraction method for a microreactor system includes the following steps: S1. The raw material liquid and extractant are injected into the capillary microreactor through the constriction structure A at the raw material supply end. S2. When the mixture flows through the front channel, under the synergistic effect of the hydrophobic surface and ultrasonic cavitation, the oil phase forms a continuous phase and generates a large number of cavitation bubbles. S3. When the mixture flows through the rear channel, the sound energy is efficiently transmitted and the vibration intensity of the cavitation bubbles is enhanced under the action of the hydrophilic surface, which induces the fluid to undergo phase reversal, thereby achieving intense mass transfer and micro-mixing. S4. The reaction products flow out through the product collection end.

[0018] Optionally, the ultrasonic microextraction reactor has an input power of 5-150 W, an operating frequency of 10-1000 KHz, a material residence time in the reactor of 2-100 s, and a volume flow ratio of the raw material liquid to the extractant of 1:1 to 1:10. Preferably, the ultrasonic microextraction reactor operates at a frequency of 20-100 kHz.

[0019] Optionally, in step S2, the fluid in the front-end channel is in the oil phase as the continuous phase, and the hydrophobic surface is used to reduce the cavitation threshold and excite micro-jets to impact the fluid interface.

[0020] Optionally, in step S3, the fluid in the rear channel undergoes phase reversal under the action of a high-intensity acoustic field, transforming into a continuous phase with water as the phase. By utilizing the low acoustic impedance characteristics of the hydrophilic surface, high micro-jet velocity is ensured when cavitation bubbles collapse, thereby enhancing micro-mixing.

[0021] The beneficial effects that this application can produce include: (1) The ultrasonic microextraction reactor of the present invention has a wettability difference between the front and back ends. By utilizing the abrupt change in wettability between the front and back ends, the liquid-liquid system is driven to undergo dynamic phase reversal of "oil-in-water → water-in-oil" during the flow process under the action of ultrasound. This greatly enhances the interface disturbance, stretching and renewal rate, breaks through the mass transfer limitation dominated by molecular diffusion at the microscale, and realizes the active control of micro-mixing.

[0022] (2) The front channel of the ultrasonic microextraction reactor of the present invention is coated with polytetrafluoroethylene to form a cavitation excitation zone; the rear channel is uncoated to form a cavitation vibration zone; thus, the number of acoustic cavitation bubbles and the vibration intensity can be optimized simultaneously.

[0023] (3) The ultrasonic microextraction reactor of the present invention has flexible parameter control. The lengths of the front polytetrafluoroethylene coating area (cavitation excitation area) and the rear end (cavitation vibration area) can be flexibly adjusted, which solves the problem of the single wettability of conventional ultrasonic microreactors. It can be precisely optimized for different physical property systems (viscosity, interfacial tension, density difference) and has good modular and continuous production potential.

[0024] (4) The ultrasonic microextraction reactor of the present invention has high extraction efficiency, fast processing speed and wide applicability. Under normal temperature and pressure, the present invention can complete efficient extraction within 2-100 seconds, with an extraction efficiency of 88%-99%, and is applicable to a variety of immiscible solution-liquid systems (such as water / toluene, water / n-octanol, ionic liquid / organic phase, etc.), with strong process adaptability.

[0025] (5) The ultrasonic microextraction reactor of the present invention has a simple structure, is easy to manufacture, and has good stability. Functional zones can be constructed simply by segmenting and coating PTFE with the bare substrate, without the need for complex micro-machining or surface patterning processes; the arc-shaped front radiation surface is matched with the capillary and bonded with acoustic adhesive to ensure tight acoustic coupling and low energy loss; the system operates stably for a long time in a wide frequency range of 5-150 W power and 10-1000 kHz without debonding, clogging or performance degradation. Attached Figure Description

[0026] Figure 1 The diagram shows an ultrasonic microextraction reactor, where 1.1 is a sandwich-type ultrasonic transducer and 1.2 is a capillary microreactor.

[0027] Figures 2-5 This is a wireframe view of the ultrasonic microextraction reactor (view 6).

[0028] Figure 6 The diagram shows the structure of a sandwich-type ultrasonic transducer, where 2.1 is the front cover plate of the transducer, 2.2 is the piezoelectric ceramic crystal stack, and 2.3 is the rear cover plate of the transducer.

[0029] Figure 7The diagram shows the structure of a capillary microreactor with different wettability. In the diagram, 3.1 is a stepped constriction structure, 3.2 is a through hole, 3.3 is a polytetrafluoroethylene (PTFE) coated end (cavitation excitation zone), and 3.4 is an uncoated PTFE end (cavitation vibration zone).

[0030] Figures 8-9 Six wireframe views of a capillary microreactor with wettability difference. Detailed Implementation

[0031] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0032] Example 1 This embodiment uses an ultrasonic microextraction reactor with a resonant frequency of 20 kHz as an example. Figure 1 As can be seen, the ultrasonic microextraction reactor in this embodiment is composed of a sandwich ultrasonic transducer and a wettability differential capillary microreactor connected together.

[0033] The ultrasonic microextraction reactor includes a sandwich ultrasonic transducer and a capillary microreactor.

[0034] The capillary microreactor 3 in this embodiment is made of glass, with an outer diameter of 6.0 mm, an inner diameter of 3.0 mm, and a length of 60 mm. It has stepped constriction structures A (3.1) at both ends, prepared by mechanical tapering, with an inner diameter of 4.0 mm and a length of 5.0 mm, used to connect the inlet / outlet pipes and reduce inlet fluid impact and induce flow pattern changes. A through-hole structure B (3.3) with a 1.0 mm diameter is provided on the capillary sidewall 20 mm from the inlet, prepared by laser drilling, used to connect auxiliary sampling or online detection devices. The front channel of the capillary microreactor is soaked and dried in a 30% solids content polytetrafluoroethylene emulsion, with a coating length of 30.0 mm and a coating layer thickness of approximately 50 μm. The surface water contact angle, measured by a contact angle meter, is 98°, exhibiting significant hydrophobicity. The rear channel is uncoated, 30.0 mm in length, with a surface water contact angle of 25°, exhibiting hydrophilicity, creating a significant difference in axial wettability. The sandwich-type ultrasonic transducer 2 operates at a frequency of 20 kHz and has a maximum input power of 100 W. It consists of a front cover plate 2.1, a piezoelectric ceramic stack 2.2, and a rear cover plate 2.3, all connected at the center by high-strength metal bolts. The piezoelectric ceramic stack 2.2 is a cylinder with a thickness of 10 mm, formed by two coaxially stacked piezoelectric ceramic sheets. Each piezoelectric ceramic sheet is 5 mm thick and 45 mm in diameter. The piezoelectric ceramic sheets are bonded together with strong adhesive. The rear cover plate 2.3 is made of steel and has a cylindrical shape with a diameter of 45 mm and a thickness of 35 mm. The front cover plate 2.1 is made of aluminum alloy and has a conical shape, with a front radiating surface diameter of 66 mm, a rear radiating surface diameter of 45 mm, and a thickness of 47 mm. After bonding the ultrasonic transducer to the capillary microreactor with acoustic adhesive and encapsulating it with solid filler, the ultrasonic filler microreactor has a resonant frequency of 20.8 kHz and a maximum input power of 100 W.

[0035] Example 2 This embodiment uses an ultrasonic microextraction reactor with a resonant frequency of 20 kHz as an example. Figure 1 As can be seen, the ultrasonic microextraction reactor in this embodiment is composed of a sandwich ultrasonic transducer and a wettability differential capillary microreactor connected together.

[0036] The ultrasonic microextraction reactor includes a sandwich ultrasonic transducer and a capillary microreactor.

[0037] In this embodiment, a glass capillary tube (outer diameter 15 mm, inner diameter 14 mm, total length 100 mm) is used. The front end is covered with polytetrafluoroethylene for 70 mm (0.70%), and the rear end is exposed for 30 mm (0.30%). The contact angles are 96° and 26° respectively.

[0038] The constricted structure A was fabricated using laser micromachining, with an inner diameter of 1.0 mm, and connected to a Φ1.0 mm polytetrafluoroethylene feed tube. Experiments showed that the pressure drop inside the capillary microreactor was large, and the droplets were evenly dispersed.

[0039] Example 3 This embodiment uses an ultrasonic microextraction reactor with a resonant frequency of 20 kHz as an example. Figure 1 As can be seen, the ultrasonic microextraction reactor in this embodiment is composed of a sandwich ultrasonic transducer and a wettability differential capillary microreactor connected together.

[0040] The ultrasonic microextraction reactor includes a sandwich ultrasonic transducer and a capillary microreactor.

[0041] In this embodiment, a glass capillary tube (outer diameter 15 mm, inner diameter 14 mm, total length 100 mm) is used. The front end is covered with polytetrafluoroethylene for 70 mm (0.70%), and the rear end is exposed for 30 mm (0.30%). The contact angles are 96° and 26° respectively.

[0042] The constricted inner diameter is 12.0 mm, which is close to the inner diameter of a capillary tube, and it is mainly used in high-throughput scenarios (>20 mL / min).

[0043] Example 4 This embodiment uses an ultrasonic microextraction reactor with a resonant frequency of 40 kHz as an example. Figure 1 As can be seen, the ultrasonic microextraction reactor in this embodiment is composed of a sandwich ultrasonic transducer and a wettability differential capillary microreactor connected together.

[0044] The capillary microreactor 3 in this embodiment is made of stainless steel, with an outer diameter of 6.0 mm, an inner diameter of 4.0 mm, and a length of 40 mm. The stepped constriction structure A (3.1) has an inner diameter of 5.0 mm and a length of 5.0 mm. The through-hole structure B (3.3) has a pore diameter of 2.0 mm and is located 10 mm from the capillary inlet. The front channel of the capillary microreactor is soaked in and dried with a 50% solids content polytetrafluoroethylene emulsion, with a coating length of 15.0 mm, a coating thickness of approximately 80 μm, and a contact angle of 95°. The rear channel is uncoated, with a length of 25.0 mm and a contact angle of 28°. The sandwich-type ultrasonic transducer 2 operates at a frequency of 40 kHz and has a maximum input power of 60 W. It is composed of a front cover plate 2.1, a piezoelectric ceramic stack 2.2, and a rear cover plate 2.3 connected at the center by high-strength metal bolts. The piezoelectric ceramic stack 2.2 consists of two piezoelectric ceramic sheets coaxially stacked to form a cylinder with a thickness of 10 mm. Each piezoelectric ceramic sheet is 5 mm thick and 38 mm in diameter. The piezoelectric ceramic sheets are bonded together with strong adhesive. The rear cover plate 2.3 is made of steel and has a cylindrical shape with a diameter of 38 mm and a thickness of 18 mm. The front cover plate 2.1 is made of titanium alloy and has a conical shape with a front radiating surface diameter of 58 mm, a rear radiating surface diameter of 38 mm, and a thickness of 40 mm. After bonding the ultrasonic transducer to the capillary microreactor with acoustic adhesive and encapsulating it with solid filler, the ultrasonic filler microreactor has a resonant frequency of 39.7 kHz and a maximum input power of 60 W.

[0045] Example 5 This embodiment uses an ultrasonic microextraction reactor with a resonant frequency of 40 kHz as an example. Figure 1 As can be seen, the ultrasonic microextraction reactor in this embodiment is composed of a sandwich ultrasonic transducer and a wettability differential capillary microreactor connected together.

[0046] The ultrasonic microextraction reactor includes a sandwich ultrasonic transducer and a capillary microreactor.

[0047] The fixed capillary has a total length of 100 mm (glass material, inner diameter 4 mm), a contact angle of 28° at the hydrophilic section at the rear end, and an ultrasonic power of 50 W.

[0048] The front end is coated with PTFE for 5 mm and has a contact angle of 92°. Although it can form a continuous oil phase, the cavitation region is too short, the total number of bubbles is low, and the extraction efficiency is 82.3%.

[0049] Example 6 This embodiment uses an ultrasonic microextraction reactor with a resonant frequency of 40 kHz as an example. Figure 1 As can be seen, the ultrasonic microextraction reactor in this embodiment is composed of a sandwich ultrasonic transducer and a wettability differential capillary microreactor connected together.

[0050] The ultrasonic microextraction reactor includes a sandwich ultrasonic transducer and a capillary microreactor.

[0051] The fixed capillary has a total length of 100 mm (glass material, inner diameter 4 mm), a contact angle of 28° at the hydrophilic section at the rear end, and an ultrasonic power of 50 W.

[0052] The front end is 90 mm long and has a contact angle of 97°. There are sufficient bubbles, but the rear acoustic transmission section is too short (only 10 mm), resulting in insufficient vibration intensity and an efficiency drop to 89.6%.

[0053] Example 7 This embodiment uses an ultrasonic microextraction reactor with a resonant frequency of 20 kHz as an example. Figure 1 As can be seen, the ultrasonic microextraction reactor in this embodiment is composed of a sandwich ultrasonic transducer and a wettability differential capillary microreactor connected together.

[0054] The ultrasonic microextraction reactor includes a sandwich ultrasonic transducer and a capillary microreactor.

[0055] The capillary microreactor 3 in this embodiment is made of glass, with an outer diameter of 6.0 mm, an inner diameter of 3.0 mm, and a length of 60 mm. The front end accounts for 0.5 of the total area, and the rear end has a contact angle of 25°.

[0056] The polytetrafluoroethylene emulsion has a solid content of 10%, a thickness of approximately 10 μm after drying, and a contact angle of 91°. After 50 hours of continuous operation, it experienced localized peeling and a decrease in hydrophobicity.

[0057] Example 8 This embodiment uses an ultrasonic microextraction reactor with a resonant frequency of 20 kHz as an example. Figure 1 As can be seen, the ultrasonic microextraction reactor in this embodiment is composed of a sandwich ultrasonic transducer and a wettability differential capillary microreactor connected together.

[0058] The ultrasonic microextraction reactor includes a sandwich ultrasonic transducer and a capillary microreactor.

[0059] The capillary microreactor 3 in this embodiment is made of glass, with an outer diameter of 6.0 mm, an inner diameter of 3.0 mm, and a length of 60 mm. The front end accounts for 0.5 of the total area, and the rear end has a contact angle of 25°.

[0060] The polytetrafluoroethylene emulsion has a solid content of 60%, a thickness of approximately 100 μm, and a contact angle of 98°. The coating layer is slightly rough, but this does not affect wettability and maintains efficient extraction.

[0061] Example 9 Vanillin extraction experiments were conducted using the system described in Example 1. Toluene was used as the extractant, vanillin as the extract, and an aqueous vanillin solution as the feed solution. The initial mass concentration of vanillin in water was 100 mg / L. Two streams of materials were delivered to the ultrasonic microextraction reactor using a horizontal flow pump. The flow rate of the extractant was 3.0 mL / min, and the flow rate of the feed solution was 3.0 mL / min. Under ambient temperature conditions, the ultrasonic power was 30 W, and the residence time was 2.826 s. The extractant / feed solution was collected at the outlet into a separatory funnel, and the lower layer of the feed solution was extracted, diluted, and analyzed using a UV-Vis spectrophotometer. The extraction efficiency was found to be 98.2%.

[0062] Example 10 Vanillin extraction experiments were conducted using the system described in Example 1. Toluene was used as the extractant, vanillin as the extract, and an aqueous vanillin solution as the feed solution. The initial mass concentration of vanillin in water was 100 mg / L. Two streams of materials were delivered to the ultrasonic microextraction reactor using a horizontal flow pump. The flow rate of the extractant was 3.0 mL / min, and the flow rate of the feed solution was 3.0 mL / min. Under ambient temperature conditions, the ultrasonic power was 5 W, and the residence time was 2.826 s. The extractant / feed solution was collected at the outlet into a separatory funnel, and the lower layer of the feed solution was extracted, diluted, and analyzed using a UV-Vis spectrophotometer. The extraction efficiency was found to be 86.4%.

[0063] Example 11 Vanillin extraction experiments were conducted using the system described in Example 1. Toluene was used as the extractant, vanillin as the extract, and an aqueous vanillin solution as the feed solution. The initial mass concentration of vanillin in water was 100 mg / L. Two streams of materials were delivered to the ultrasonic microextraction reactor using a horizontal flow pump. The flow rate of the extractant was 3.0 mL / min, and the flow rate of the feed solution was 3.0 mL / min. Under ambient temperature conditions, the ultrasonic power was 150 W, and the residence time was 2.826 s. The extractant / feed solution was collected at the outlet into a separatory funnel, and the lower layer of the feed solution was extracted. After dilution, the extract was analyzed using a UV-Vis spectrophotometer. The extraction efficiency was found to be 99.1%, with no emulsification or clogging, indicating system stability.

[0064] Example 12 The same microreactor system structure as in Example 1 is adopted: the capillary microreactor (3) is made of glass with an outer diameter of 6.0 mm, an inner diameter of 3.0 mm, and a total length of 60 mm; the front channel (21) is 30.0 mm long, with the inner wall covered with a polytetrafluoroethylene layer with a thickness of about 60 μm and a water contact angle of 96°; the rear channel is 30.0 mm long, with the glass surface exposed and a water contact angle of 25°; the ultrasonic transducer is a frequency-adjustable sandwich piezoelectric transducer with a polished aluminum alloy arc concave surface on the front radiating surface, which is tightly bonded to the capillary through acoustic coupling adhesive; the system is equipped with a wideband ultrasonic signal generator (frequency range 5-1200 kHz, power 0-200 W continuously adjustable) and an impedance matching network to ensure high-efficiency energy output at different frequencies.

[0065] Toluene was used as the extractant, vanillin as the extractant, and an aqueous vanillin solution as the feedstock. The initial mass concentration of vanillin in water was 100 mg / L. Two streams of materials were delivered to the ultrasonic microextraction reactor using a horizontal flow pump. The flow rate of the extractant was 3.0 mL / min, and the flow rate of the feedstock was 3.0 mL / min. Under ambient temperature conditions, the ultrasonic power was 50 W, and the residence time was 10 s.

[0066] S1: Connect the two ends of the capillary microreactor to the feed lines for the raw material and extractant respectively via the constriction structure A, and connect the outlet to the product collection end. Turn on the ultrasonic signal generator and perform a frequency sweep test on the transducer (10-1000 kHz), record the position of the system resonance peak, and calibrate the actual output power at each target frequency to 50 W.

[0067] S2: Low-frequency band test Set the operating frequency to 10 kHz, start fluid delivery and ultrasound, and collect the outlet product for 10 minutes after the operation is stable. Repeat the above process, testing at 20 kHz and 100 kHz in sequence; After all samples were allowed to separate into layers by standing in a separatory funnel, the aqueous phase was diluted, and the residual concentration of vanillin was determined using a UV-Vis spectrophotometer to calculate the extraction efficiency.

[0068] S3: Mid-to-high frequency band test Under the same conditions, frequencies of 300 kHz, 600 kHz and 1000 kHz were set respectively. At ≥300 kHz, the size of cavitation bubbles decreased and the collapse intensity decreased, but the acoustic flow effect was enhanced, which could still promote interface renewal. Simultaneous acquisition of sound field distribution images (through high-speed camera + cavitation luminescence imaging) confirmed the existence of cavitation phenomenon.

[0069] S4: Data recording and comparison records the extraction efficiency, system temperature rise, pressure fluctuations, and whether abnormal phenomena such as blockage or over-emulsification occur at each frequency.

[0070] The experimental results are shown in Table 1.

[0071] Table 1

[0072] Comparative Example 1 The same microreactor system structure as in Example 1 was adopted: the capillary microreactor used a glass tube (outer diameter 6.0 mm, inner diameter 3.0 mm, total length 60 mm). The entire inner wall (60 mm in total length) was soaked in and dried with a polytetrafluoroethylene emulsion with a solid content of 30% to form a uniform coating layer. The coating layer thickness was about 60 μm. The water contact angle of the entire tube was measured to be 97° by a contact angle tester, which showed strong hydrophobicity.

[0073] Toluene was used as the extractant, vanillin as the extractant, and an aqueous vanillin solution as the feed solution. The initial mass concentration of vanillin in water was 100 mg / L. Two streams of materials were delivered to the ultrasonic microextraction reactor using a horizontal flow pump. The flow rate of the extractant was 3.0 mL / min, and the flow rate of the feed solution was 3.0 mL / min. Under ambient temperature conditions, the ultrasonic power was 50 W, and the residence time was 10 s. The extractant / feed solution was collected at the outlet into a separatory funnel, and the lower layer of the feed solution was extracted. After dilution, the extract was analyzed using a UV-Vis spectrophotometer, and the extraction efficiency was found to be 76.3%.

[0074] Comparative Example 2 The same microreactor system structure as in Example 1 was adopted: the capillary microreactor was an exposed glass tube without any surface treatment (outer diameter 6.0 mm, inner diameter 3.0 mm, total length 60 mm). The water contact angle of the entire tube was measured to be 25° by a contact angle tester, which showed typical hydrophilicity.

[0075] Toluene was used as the extractant, vanillin as the extractant, and an aqueous vanillin solution as the feed solution. The initial mass concentration of vanillin in water was 100 mg / L. Two streams of materials were delivered to the ultrasonic microextraction reactor using a horizontal flow pump. The flow rate of the extractant was 3.0 mL / min, and the flow rate of the feed solution was 3.0 mL / min. Under ambient temperature conditions, the ultrasonic power was 50 W, and the residence time was 10 s. The extractant / feed solution was collected at the outlet into a separatory funnel, and the lower layer of the feed solution was extracted. After dilution, the extract was analyzed using a UV-Vis spectrophotometer, and the extraction efficiency was found to be 68.9%.

[0076] Comparative Example 3 The same microreactor system structure as in Example 1 was adopted: the capillary microreactor used a glass tube (outer diameter 6.0 mm, inner diameter 3.0 mm, total length 60 mm). The entire inner wall (60 mm in total length) was soaked in and dried with a polytetrafluoroethylene emulsion with a solid content of 30% to form a uniform coating layer. The coating layer thickness was about 60 μm. The water contact angle of the entire tube was measured to be 97° by a contact angle tester, which showed strong hydrophobicity.

[0077] Without installing an ultrasonic transducer, it relies solely on passive flow mixing.

[0078] Toluene was used as the extractant, vanillin as the extractant, and an aqueous vanillin solution as the feed solution. The initial mass concentration of vanillin in water was 100 mg / L. Two streams of materials were delivered to the ultrasonic microextraction reactor using a horizontal flow pump. The flow rate of the extractant was 3.0 mL / min, and the flow rate of the feed solution was 3.0 mL / min. Under ambient temperature conditions, the ultrasonic power was 0 W, and the residence time was 10 s. The extractant / feed solution was collected at the outlet into a separatory funnel, and the lower layer of the feed solution was extracted. After dilution, the extract was analyzed using a UV-Vis spectrophotometer, and the extraction efficiency was found to be 42.1%.

[0079] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A microreactor system for continuous and efficient extraction, characterized in that, It includes a raw material supply end, an ultrasonic microextraction reactor, and a product collection end connected in sequence; The ultrasonic microextraction reactor includes an ultrasonic transducer and a capillary microreactor. The capillary microreactor is provided with constriction structures A at both ends to connect the raw material inlet and outlet pipes; The capillary microreactor is divided into a front channel and a rear channel along the fluid flow direction. The inner wall of the front channel is covered with polytetrafluoroethylene, exhibiting hydrophobic properties, while the rear channel is an uncovered bare substrate, exhibiting hydrophilic properties, resulting in a significant difference in axial wettability. The ultrasonic transducer is bonded to the capillary microreactor via an acoustic adhesive through its front radiating surface, and the front radiating surface is an arc-shaped concave surface that matches the capillary.

2. The microreactor system for continuous and efficient extraction according to claim 1, characterized in that, The ultrasonic transducer is a sandwich ultrasonic transducer. Preferably, the ultrasonic transducer consists of a piezoelectric ceramic plate, front and rear metal cover plates, and a pre-tightening screw; Preferably, the front radiating surface is made of titanium alloy or aluminum alloy, and the surface is polished to reduce sound energy loss.

3. The microreactor system for continuous and efficient extraction according to claim 1, characterized in that, The constriction structure A is prepared by laser micromachining or mechanical tapering, with a constriction diameter of 1.0-12.0 mm, to reduce inlet fluid impact and induce flow pattern change; Preferably, the capillary microreactor is made of glass or metal capillary.

4. The microreactor system for continuous and efficient extraction according to claim 1, characterized in that, The length of the front-end channel accounts for 0.05-0.90% of the total length of the capillary. Preferably, the thickness of the polytetrafluoroethylene coating layer is 10μm-100μm, and the contact angle of the oil phase on the surface of the coating layer is greater than 90°, which is conducive to spreading and forming a continuous phase.

5. The microreactor system for continuous and efficient extraction according to claim 1, characterized in that, The contact angle of the exposed substrate surface of the rear channel is less than 60°; Preferably, the length of the rear channel is 0.10-0.95 of the total length of the capillary, in order to ensure that the ultrasonic waves are efficiently introduced into the liquid from the transducer.

6. The microreactor system for continuous and efficient extraction according to claim 1, characterized in that, The capillary microreactor has a through-hole structure B on its sidewall; Preferably, the through-hole structure B is prepared by laser drilling or side windowing process, and is used to connect the sample inlet pipeline or detection sensor.

7. A continuous and efficient extraction method based on the system described in any one of claims 1-6, characterized in that, Includes the following steps: S1. The raw material liquid and extractant are injected into the capillary microreactor through the constriction structure A at the raw material supply end. S2. When the mixture flows through the front channel, under the synergistic effect of the hydrophobic surface and ultrasonic cavitation, the oil phase forms a continuous phase and generates a large number of cavitation bubbles. S3. When the mixture flows through the rear channel, the sound energy is efficiently transmitted and the vibration intensity of the cavitation bubbles is enhanced under the action of the hydrophilic surface, which induces the fluid to undergo phase reversal, thereby achieving intense mass transfer and micro-mixing. S4. The reaction products flow out through the product collection end.

8. The continuous and efficient extraction method according to claim 7, characterized in that, The ultrasonic microextraction reactor has an input power of 5-150 W, an operating frequency of 10-1000 KHz, a material residence time of 2-100 s, and a volume flow ratio of 1:1 to 1:10 between the raw material liquid and the extractant. Preferably, the ultrasonic microextraction reactor operates at a frequency of 20-100 kHz.

9. The continuous and efficient extraction method according to claim 7, characterized in that, In step S2, the fluid in the front-end channel is in the oil phase as the continuous phase. The hydrophobic surface is used to reduce the cavitation threshold and excite micro-jets to impact the fluid interface.

10. The continuous and efficient extraction method according to claim 7, characterized in that, In step S3, the fluid in the rear channel undergoes phase reversal under the action of a high-intensity acoustic field, transforming into a continuous phase with water as the phase. By utilizing the low acoustic impedance characteristics of the hydrophilic surface, a high micro-jet velocity is generated when the cavitation bubbles collapse, thereby enhancing micro-mixing.

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