A method for continuously producing nanoemulsions in an ultrasonic micro-packed bed reactor

Abstract

The application discloses a method for continuously preparing nanoemulsion in an ultrasonic micro-packed bed reactor. The ultrasonic micro-packed bed reactor is connected with a large-radiation-area horn-shaped sandwich transducer and a capillary microreactor, and solid fillers are arranged in the microreactor, so that effective interception of acoustic cavitation bubbles under high liquid flow conditions can be realized, and ultrasonic energy efficiency is improved. The capillary microreactors are connected through a stepped structure, so that the fillers can be freely disassembled, and the filler structure, size and material can be conveniently replaced. Through continuous conveying equipment, the continuous phase and the dispersed phase are mixed and emulsified in the reactor, so that efficient and rapid preparation (2-180s) of nanoemulsion (average size 20-500nm) can be realized. The application shortens the preparation time of nanoemulsion (5-60min in the prior art), realizes continuous production, and is simple to operate and easy to integrate and parallel scale up.

Description

Technical Field

[0001] This invention belongs to the fields of microchemical technology and ultrasonic applications. Specifically, it is a method for enhancing the emulsification process in a microreactor by using solid packing material to assist ultrasonic vibration. Background Technology

[0002] Microchemical technology is a new type of chemical process intensification technology that emerged in the early 1990s in response to the needs of sustainable development. Unlike conventional scale chemical equipment, microreactors have channel characteristic dimensions down to the sub-millimeter level, which have advantages such as fast heat and mass transfer rates, easy process control, and direct scale-up, providing a new opportunity to improve the efficiency of chemical process transfer and rapidly promote the transformation of laboratory research results into industrial applications (AIChE J, 2017, 63(3): 858-869). The miniaturization of characteristic dimensions is the source of many advantages of microreactors, but it also brings new challenges to their development. At the microscale, fluids are usually in a laminar flow state, and the mixing process is controlled by molecular diffusion, making it difficult to achieve efficient and rapid mixing between high-viscosity liquid phases. In addition, unlike conventional batch operation, where the reactor flow field structure and mixing efficiency are adjusted by mechanical forces such as stirring, the operating parameters of microreactors are often relatively simple, making it impossible to flexibly control the reaction conditions. Undoubtedly, the difficulty in mixing high-viscosity fluids and the poor operating flexibility of reactors have become important limiting factors for the promotion and application of microchemical technology. In order to improve the applicability of micro-reaction systems, it is necessary to make reasonable optimization and improvement to the existing microchemical equipment (Chem Commun., 2012, 48(89): 10935-10947).

[0003] Ultrasonic microreactors are a novel process intensification technique that couples ultrasonic fields with microreactors and applies them to chemical production processes. Introducing ultrasound into a microreactor induces periodic compression and expansion within the liquid, activating tiny bubble nuclei (cavitation nuclei). These cavitation nuclei grow with the sound waves, exhibiting a series of nonlinear dynamic behaviors, including oscillation, contraction, and even collapse, collectively known as acoustic cavitation. Acoustic cavitation concentrates dispersed ultrasonic energy near the bubbles, accompanied by mechanical effects such as shock waves, microjets, and acoustic flow, which helps promote stretching and folding between fluids, improving dispersion efficiency. In recent years, ultrasonic microreactors have been widely used in the emulsification of immiscible solutions. Studies have shown that the efficiency of ultrasonic emulsification within microreactors is severely limited by the flow rate of the reactants. The flow behavior of cavitation bubbles in microreactors is influenced by both the viscous drag of the continuous phase fluid and the secondary B-order forces of acoustic radiation. Under high liquid flow conditions, the bubbles are rapidly expelled from the channel due to the viscous drag of the fluid and cannot remain in the reactor for extended periods. Since emulsification between liquid phases is mainly initiated by acoustic cavitation bubbles, this undoubtedly leads to low ultrasonic emulsification efficiency (AIChE J, 2018, 64(4): 1412-1423). Given the stepwise transmission mechanism between acoustic cavitation and ultrasonic emulsification, the key to improving the dispersion efficiency between liquid phases in microreactors under high reactant flow rates lies in achieving efficient retention of acoustic cavitation bubbles under high liquid flow rate conditions in microchannels. This is also a prerequisite for the large-scale industrial application of ultrasonic microemulsification technology.

[0004] In summary, given the limited material flow rate faced by existing ultrasonic microreactors when applied to the emulsification process of immiscible solutions, it is necessary to propose a novel ultrasonic microreactor assembly method that balances ultrasonic energy efficiency and operating flow range to optimize the existing ultrasonic microemulsification process. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a modular ultrasonic micro-filled bed reactor and applies it to the continuous preparation process of nanoemulsions. Capillary action exists between the solid filler material filling the microchannels and the acoustic cavitation bubbles, effectively counteracting the drag caused by the gas-liquid interface flow difference and achieving effective retention of acoustic cavitation bubbles under high liquid flow conditions. Furthermore, the filler material can concentrate acoustic energy, increasing the sound pressure amplitude and energy density in the microchannel reaction region. The ultrasonic micro-filled bed reactor connects a large-radiating-surface horn-shaped sandwich transducer and a capillary microreactor using epoxy resin adhesive, and fills the reaction tube with solid filler material, achieving efficient concentration and utilization of ultrasonic energy and improving ultrasonic energy efficiency. The continuous phase and dispersed phase flow into the reactor via a fluid transport device, where they are rapidly dispersed and emulsified under ultrasonic action.

[0006] The present invention adopts the following technical solution:

[0007] A microreactor system for continuous preparation of nanoemulsions includes a raw material supply end, an ultrasonic micro-filled bed reactor, and a product collection end connected in sequence. The ultrasonic micro-filled bed reactor includes an ultrasonic transducer and a micro-filled bed reaction section, wherein the ultrasonic transducer and the micro-filled bed reaction section are bonded together. The micro-filled bed reaction section includes a capillary microreactor and solid packing material. The interior of the capillary microreactor is filled with solid packing material, and both ends of the capillary microreactor are provided with constriction structures for material inflow and outflow. A screen is installed at the constriction to encapsulate and replace the solid packing material.

[0008] As a preferred technical solution, the narrowing structure is a stepped narrowing structure.

[0009] As a preferred technical solution, the solid filler is mechanically packed and embedded into the capillary microreactor, and then connected to the ultrasonic transducer via epoxy resin adhesive.

[0010] As a preferred technical solution, the capillary microreactor has a stepped constriction structure at both the inlet and outlet. The constriction structure is connected to the raw material supply end and the product collection end, and the reactants flow into / out of the microreactor through the constriction structure A.

[0011] As a preferred technical solution, the ultrasonic transducer is bonded to the micro-filled bed reaction section via the front radiating surface.

[0012] As a preferred technical solution, the shape of the constricted structure cross-section is preferably circular; the capillary microreactor is one or more; when there are multiple capillary microreactors, they are flexibly connected; preferably, multiple capillary microreactors can be connected and disassembled between different microreactors by means of elastic tubes and flexible connection through the constricted structure, and the material, structure and size of the packing can be flexibly adjusted.

[0013] As a preferred technical solution, the capillary microreactor has an inner diameter of 3.0-9.0 mm. Depending on the applicable conditions, the microreactor can be made of metal (such as stainless steel, Harbin alloy, copper, etc.) or plastic (polytetrafluoroethylene, polyetheretherketone, etc.).

[0014] As a preferred technical solution, the ultrasonic transducer is a sandwich-type ultrasonic transducer.

[0015] As a preferred technical solution, the capillary microreactor has through holes on its wall, which are connected to the raw material supply end; the reactants flow in through the constriction structure and the through holes respectively; the aperture of the stepped constriction structure is preferably 4.0-10.0 mm, and the aperture of the through holes is preferably 1.0-6.0 mm.

[0016] As a preferred technical solution, the solid filler is prepared by 3D printing. The filler contains distributed channels to trap and capture acoustic cavitation bubbles. The channels have a spherical structure with cross-sections of circles, triangles, rectangles, etc., preferably circles. The pore size is preferably 30-500 μm, more preferably 100-400 μm. Depending on the applicable conditions, the filler material can be stainless steel, titanium alloy, aluminum alloy, etc.

[0017] As a preferred technical solution, the microreactor is equipped with screens at both the inlet and outlet to achieve effective filling of solid packing materials and pre-mixing of the liquid phase. The screens have several through-holes through which materials flow in and out, achieving pre-emulsification of the materials. The screen diameter is consistent with the orifice size of the microreactor and has evenly distributed circular holes, preferably with a pore size of 20-500 μm. Depending on the applicable conditions, the screen material can be stainless steel, titanium alloy, aluminum alloy, etc.

[0018] As a preferred technical solution, the sandwich-type ultrasonic transducer preferably includes a front cover plate, a piezoelectric ceramic stack, and a rear cover plate arranged sequentially. The front cover plate is typically made of a lightweight metal, such as aluminum, titanium, magnesium, or alloys. The rear cover plate is typically made of a heavyweight metal, such as stainless steel, copper, or copper-steel alloys. The front cover plate, piezoelectric ceramic stack, and rear cover plate are connected by bolts, preferably with the front cover plate, piezoelectric ceramic stack, and rear cover plate connected at the center by high-strength metal bolts. In this invention, the adhesive bonding area between the micro-filled bed reactor and the ultrasonic transducer is located on the surface of the front cover plate away from the piezoelectric ceramic stack.

[0019] As a preferred technical solution, the operating frequency of the sandwich transducer is preferably 10-1000 kHz, and more preferably 18-600 kHz.

[0020] When the ultrasonic micro-filled bed reactor of this invention is excited, the piezoelectric ceramic crystal stack converts the electrical signal into mechanical vibration, which is then transmitted to the microreactor through the transducer front cover. The solid packing further concentrates the acoustic energy, increasing the acoustic power density inside the microreactor, which can significantly enhance the mixing and mass transfer between reactants within the microreactor.

[0021] The operating frequency of the ultrasonic micro-filled bed reactor of the present invention is determined by the sandwich ultrasonic transducer, the material and size of the solid packing, and the material and size of the microreactor.

[0022] A method for rapid and continuous preparation of nanoemulsions employs the aforementioned microreactor system. Through a continuous conveying device, a continuous phase (such as water or octane) flows in through a constricted structure A, while a dispersed phase (such as vitamin E or carotene) flows in through a through-hole B. Under ambient temperature conditions, the continuous and dispersed phases are dispersed and emulsified within the reactor, enabling the efficient and rapid preparation of nanoemulsions.

[0023] As a preferred technical solution, the input power of the ultrasonic micro-filled bed reactor is 5-150W, preferably 20-120W, and the residence time of the material in the reactor is 2-180s, preferably 2-120s.

[0024] The average size of the nanoemulsion described in this invention is 20-500 nm, preferably 20-300 nm.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] (1) The capillary microreactors of the present invention are flexibly connected by stepped slots, which makes the operation highly flexible and allows the inlet and outlet of the microreactor to be freely disassembled and the packing shape, size and material to be replaced.

[0027] (2) The ultrasonic micro-filled bed reactor of the present invention has high energy efficiency. By comparing the temperature distribution inside the microreactor with and without filler under ultrasonic power of 40W and radiation time of 120s, the temperature inside the unfilled microreactor rose by 7.7℃, while the temperature inside the filled microreactor rose by 17.1℃. This shows that solid filler can effectively concentrate acoustic energy and solve the problem of uneven acoustic energy distribution in common ultrasonic microreactors.

[0028] (3) The ultrasonic micro-packed bed reactor of the present invention has high operational flexibility. The solid packing material can efficiently capture acoustic cavitation bubbles, solving the problem of acoustic cavitation difficulties under high liquid flow conditions. Taking water as an example, to ensure the cavitation effect, the upper limit of liquid flow velocity is 2.36 cm / s without packing, while the upper limit of liquid flow velocity is increased to 9.44 cm / s with packing. Therefore, the ultrasonic micro-packed bed reactor can solve the problem of low efficiency of ultrasonic microreactors and improve the liquid phase operation range within the ultrasonic microreactor.

[0029] (4) The ultrasonic micro-filled bed microreactor of the present invention has high dispersion efficiency. After the reactants flow in, they undergo pre-emulsification by a screen, shearing of the packing material, and mechanical mixing by acoustic cavitation bubbles, which effectively improves the emulsification efficiency.

[0030] In summary, the method for continuous preparation of nanoemulsions based on an ultrasonic micro-filled bed reactor proposed in this invention is highly flexible, easy to operate, and can achieve efficient and rapid production of fine nanoemulsions. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of an ultrasonic micro-filled bed reactor, where 1.1 is a sandwich-type ultrasonic transducer, 1.2 is a capillary microreactor, 1.3 is a micro-filled bed reactor, and 1.4 is an elastic tube.

[0032] Figure 2The diagram shows the structure of a sandwich-type ultrasonic transducer. 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.

[0033] Figure 3 The diagram shows the structure of a capillary microreactor. 3.1 is a stepped constriction structure, 3.2 is a sieve, and 3.3 is a through hole. Detailed Implementation

[0034] The present invention will be further illustrated by the following examples.

[0035] Example 1

[0036] like Figure 1-3 As shown, this embodiment provides a microreactor system for the continuous preparation of nanoemulsions, including a raw material supply end, an ultrasonic micro-filled bed reactor, and a product collection end connected in sequence. The ultrasonic micro-filled bed reactor is a modular ultrasonic micro-filled bed reactor with a resonant frequency of 20 kHz. The ultrasonic micro-filled bed reactor includes an ultrasonic transducer and a micro-filled bed reaction section. The ultrasonic transducer and the micro-filled bed reaction section are bonded together. The micro-filled bed reaction section includes solid packing and a capillary microreactor 1.2. The interior of the capillary microreactor is filled with solid packing, which is a spring-structured packing. The capillary microreactor 3.2 has stepped constriction structures 3.1 at both ends, and a screen 3.2 is installed at the constriction. The wall surface of the capillary microreactor 3.2 has through holes 3.3.

[0037] The capillary microreactor 1.2 in this embodiment is a single capillary microreactor 1.2. The capillary body is made of glass, with an outer diameter of 5.0 mm, an inner diameter of 3.0 mm, and a length of 65 mm. The stepped constriction structure 3.1 has an inner diameter of 4 mm and a length of 10 mm. The through hole 3.3 has a diameter of 1.0 mm and is located 15 mm from the capillary inlet. The solid packing is made of Hastelloy alloy, with a spring configuration, a spring length of 2 mm, and a cross-sectional diameter of 1 mm. After the spring packing is pressed into the capillary microreactor 1.2 through the constriction structure, it is sealed with a sieve 3.2. The sieve 3.2 is a circular sheet made of stainless steel, with a diameter of 4 mm and a sieve aperture diameter of 200 μm. The sandwich-type ultrasonic transducer 2 operates at a frequency of 20 kHz and has a maximum input power of 150 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 stainless steel 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 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 1.1 to the capillary microreactor 1.2 and encapsulating it with solid packing material, the ultrasonic micro-filled bed reactor has a resonant frequency of 20.8 kHz and a maximum input power of 150 W.

[0038] Under ultrasonic power of 40W, deionized water was encapsulated in the capillary microreactor of this embodiment, and the water temperature was monitored using an infrared thermal imager. During an irradiation time of 120s, the water temperature increased from 20.2℃ to 37.3℃, a rise of 17.1℃.

[0039] Example 2

[0040] like Figure 1-3 As shown, this embodiment provides a microreactor system for the continuous preparation of nanoemulsions, including a raw material supply end, an ultrasonic micro-filled bed reactor, and a product collection end connected in sequence. The ultrasonic micro-filled bed reactor is a modular ultrasonic micro-filled bed reactor with a resonant frequency of 40 kHz. The ultrasonic micro-filled bed reactor includes an ultrasonic transducer and a micro-filled bed reaction section. The ultrasonic transducer and the micro-filled bed reaction section are bonded together. The micro-filled bed reaction section includes solid packing and a capillary microreactor 3.2. The interior of the capillary microreactor is filled with solid packing, which is a triangular spiral structure packing. The capillary microreactor 3.2 has stepped constriction structures 3.1 at both ends, and a screen 3.2 is installed at the constriction. The wall surface of the capillary microreactor 3.2 has through holes 3.3.

[0041] The capillary microreactor 1.2 in this embodiment is a single capillary microreactor 1.2. The capillary body is made of FEP (perfluoroethylene propylene) material, with an outer diameter of 8.0 mm, an inner diameter of 4.0 mm, and a length of 55 mm. The stepped constriction structure 3.1 has an inner diameter of 6 mm and a length of 10 mm. The through hole 3.3 has a diameter of 2.0 mm and is located 15 mm from the capillary inlet. The solid packing is made of stainless steel and has a triangular helix configuration with a triangular helix size of 3 mm. After the triangular helix packing is pressed into the capillary microreactor 1.2 through the constriction structure, it is sealed with a sieve 3.2. The sieve is a circular sheet made of stainless steel with a diameter of 6 mm and a sieve aperture diameter of 300 μm. The sandwich-type ultrasonic transducer 2 operates at a frequency of 40 kHz and has a maximum input power of 80 W. It is composed of a front cover plate 2.1, a piezoelectric ceramic crystal stack 2.2, and a rear cover plate 2.3 connected at the center by high-strength stainless steel 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 1.1 to the capillary microreactor 1.2 and encapsulating it with solid packing material, the ultrasonic micro-filled bed reactor has a resonant frequency of 39.7 kHz and a maximum input power of 80 W.

[0042] Under an ultrasonic power of 30W, deionized water at different flow rates was continuously introduced into the capillary microreactor of this embodiment, and the number of cavitation bubbles in the reactor was recorded using a high-speed photomicrography device. When the deionized water flow rate was 0.1-20 mL / min, a large number of acoustic cavitation bubbles were observed in the reactor. When the deionized water flow rate was increased to 40 mL / min (liquid phase velocity 9.44 cm / s), almost no acoustic cavitation bubbles were observed.

[0043] Example 3

[0044] The ultrasonic micro-filled bed reactor had the same structure as in Example 1, using water as the continuous phase (Tween 80, 10 wt.%) and a mixture of vitamin E (60 wt.%) and medium-chain triglycerides (40 wt.%) as the dispersed phase. Two streams of materials were delivered to the ultrasonic micro-filled bed reactor using a horizontal flow pump. The continuous phase flow rate was 2.7 mL / min, and the dispersed phase flow rate was 0.3 mL / min. Under ambient temperature conditions, the ultrasonic power was 50 W, and the residence time was 9.18 s. The emulsion was collected at the outlet into a sample collection tank, diluted 20-fold with the continuous phase, and analyzed using a Malvern particle size analyzer, which showed an average emulsion size of 105 nm.

[0045] Example 4

[0046] The process was the same as in Example 3, except that the reactant flow rates were changed: the continuous phase flow rate was 10.8 mL / min, the dispersed phase flow rate was 1.2 mL / min, the residence time was 2.30 s, and the average emulsion size was 145 nm.

[0047] Comparative Example 1

[0048] The ultrasonic micro-filled bed reactor was the same as in Example 1, except that the solid packing material was removed. Deionized water was encapsulated inside the capillary microreactor, and the water temperature was monitored using an infrared thermal imager. During a 120-second irradiation period, the water temperature increased from 20.2°C to 27.9°C, a rise of 7.7°C.

[0049] Comparative Example 2

[0050] The ultrasonic micro-packed bed reactor was the same as in Example 2, except that the solid packing material was removed. Different flow rates of deionized water were continuously introduced into the capillary microreactor, and the number of cavitation bubbles inside the reactor was recorded using a high-speed photomicrograph. When the deionized water flow rate was increased to 10 mL / min (liquid phase velocity 2.36 cm / s), almost no acoustic cavitation bubbles were observed.

[0051] Comparative Example 3

[0052] The process is the same as in Example 4, except that the solid filler is removed from the ultrasonic microreactor. Without the assistance of filler, the average size of the emulsion is 518 nm.

Claims

1. A microreactor system for continuous preparation of nanoemulsions, characterized in that: The device includes a raw material supply end, an ultrasonic micro-packed bed reactor, and a product collection end connected in sequence. The ultrasonic micro-packed bed reactor includes an ultrasonic transducer and a micro-packed bed reaction section, with the ultrasonic transducer bonded to the micro-packed bed reaction section. The micro-packed bed reaction section includes solid packing material and a capillary microreactor. The capillary microreactor is filled with solid packing material and has constricted ends with screens installed at the constricted ends. The capillary microreactor has through holes on its wall surface.

2. The microreactor system for continuous preparation of nanoemulsions according to claim 1, characterized in that: The ultrasonic transducer is a sandwich-type ultrasonic transducer; the constriction structure is a stepped constriction structure.

3. The microreactor system for continuous preparation of nanoemulsions according to claim 1, characterized in that: The capillary microreactor may be one or more, and when there are multiple capillary microreactors, they are flexibly connected to each other.

4. The microreactor system for continuous preparation of nanoemulsions according to claim 3, characterized in that: Multiple capillary microreactors are connected by elastic tubes.

5. The microreactor system for continuous preparation of nanoemulsions according to claim 1, characterized in that: The constricted structure has a circular cross-section; the capillary microreactor has an inner diameter of 3.0-9.0 mm; the constricted structure has a pore size of 4.0-10.0 mm, and the through-hole has a pore size of 1.0-6.0 mm.

6. The microreactor system for continuous preparation of nanoemulsions according to claim 1, characterized in that: The solid filler has a spherical pore structure with a pore size of 30-500 μm.

7. The microreactor system for continuous preparation of nanoemulsions according to claim 1, characterized in that: The screen has several through holes with a diameter of 20-500 μm.

8. A method for rapid and continuous preparation of nanoemulsions, characterized in that: Using the microreactor system described in any one of claims 1-7, the continuous phase flows in through the constricted structure and the dispersed phase flows in through the through-hole, and the mixture and emulsify are carried out in the reactor under ambient temperature conditions.

9. The method according to claim 8, characterized in that: The ultrasonic micro-filled bed reactor has an input power of 5-150 W, a frequency of 10-1000 kHz, and a material residence time of 2-180 s.

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