Method for continuously preparing nano-emulsion in ultrasonic micro-packed bed reactor

Abstract

The invention discloses a method for continuously preparing nano-emulsion in an ultrasonic micro-packed bed reactor. According to the ultrasonic micro-packed bed reactor disclosed by the invention, the large-radiating-surface horn-shaped sandwich type transducer and the capillary microreactor are glued, and the solid filler is assembled in the microreactor, so that effective interception of acoustic cavitation bubbles under the condition of high liquid phase flow can be realized, and the ultrasonic energy efficiency is improved. The capillary microreactors are connected through a stepped structure, so that the filler can be freely detached, and the structure, size and material of the filler are convenient to replace. Through continuous conveying equipment, a continuous phase and a dispersed phase are mixed and emulsified in the reactor, and efficient and rapid preparation (2-180s) of the nano-emulsion (the average size is 20-500nm) can be realized. According to the method, the preparation time of the nano-emulsion is shortened (5-60 minutes in the prior art), continuous production is realized, and the method is simple and convenient to operate and easy to integrate and amplify in parallel.

Description

Technical Field

[0001] The invention belongs to the field of micro-chemical technology and ultrasonic application, and specifically is a method for strengthening the emulsification process in a micro-reactor by using solid filler to assist ultrasonic vibration. Background Art

[0002] Microchemical technology is a new chemical process intensification technology that emerged in the early 1990s in response to the needs of the era of sustainable development. Unlike conventional scale chemical equipment, the characteristic dimensions of microreactor channels are as low as sub-millimeter level. They have the advantages of fast heat and mass transfer rates, easy process control and direct amplification, which provides a new opportunity to improve the efficiency of chemical process transfer and quickly promote the transformation of laboratory research results to industrialization (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 state, and the mixing process is controlled by molecular diffusion, so it is difficult to achieve efficient and rapid mixing between high-viscosity phases. In addition, unlike conventional kettle operation, which uses mechanical forces such as stirring to adjust the reactor flow field structure and mixing efficiency, the operating parameters of microreactors are often relatively simple, and it is impossible to achieve flexible regulation of reaction conditions. There is no doubt that the difficulty of mixing between high-viscosity fluids and the poor flexibility of reactor operation 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 rationally optimize the design and improve the current micro-chemical equipment (Chem Commun., 2012, 48(89): 10935-10947).

[0003] Ultrasonic microreactor is a new process intensification method that couples ultrasonic field with microreactor and is applied to chemical production process. After ultrasound is introduced into the microreactor, periodic compression and expansion will occur inside the liquid, thereby activating the tiny bubble nuclei (cavitation nuclei) in the liquid. The cavitation nuclei grow with the sound waves and show a series of nonlinear dynamic behaviors such as oscillation, contraction and even collapse, collectively referred to as acoustic cavitation. Acoustic cavitation gathers the dispersed ultrasonic energy near the bubble, accompanied by mechanical effects such as shock waves, microjets, and acoustic streaming, which helps to promote stretching and folding between fluids and improve the dispersion efficiency between fluids. In recent years, ultrasonic microreactors have been widely used in the emulsification process between immiscible liquid phases. Studies have shown that the efficiency of ultrasonic emulsification in microreactors is severely limited by the flow rate of the reaction materials. The flow behavior of cavitation bubbles in microreactors is affected by the viscous drag of the continuous phase fluid and the secondary B-order force of acoustic radiation. Under high liquid phase flow conditions, bubbles are affected by the viscous drag of the fluid and flow out of the channel quickly, and cannot be retained in the reactor for a long time. Since the emulsification between liquid phases is mainly initiated by acoustic cavitation bubbles, this will undoubtedly lead to low efficiency of ultrasonic emulsification (AIChE J, 2018, 64(4): 1412-1423). In view of the existence of a step-by-step conduction mechanism between acoustic cavitation and ultrasonic emulsification, the key to improving the dispersion efficiency between liquid phases in microreactors under high reactant flow rates is to achieve efficient retention of acoustic cavitation bubbles under high liquid phase flow conditions in microchannels, which is also the prerequisite for the large-scale industrial application of ultrasonic microemulsification technology.

[0004] In summary, the existing ultrasonic microreactor faces the problem of limited material flow when used in the emulsification process between immiscible liquid phases. It is necessary to propose a new ultrasonic microreactor assembly method that takes into account both ultrasonic energy efficiency and operating flow range to optimize the existing ultrasonic microemulsification process. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a modular ultrasonic micro-packed bed reactor, and applies it to the continuous preparation process of nanoemulsion. There is a capillary effect between the solid filler filled in the microchannel and the acoustic cavitation bubbles, which can effectively counteract the drag caused by the flow difference at the gas-liquid interface and achieve effective retention of acoustic cavitation bubbles under high liquid phase flow conditions. In addition, the filler can gather acoustic energy and increase the sound pressure amplitude and energy density in the microchannel reaction area. The ultrasonic micro-packed bed reactor connects the large radiation surface horn-shaped sandwich transducer and the capillary microreactor through epoxy resin glue, and fills the solid filler in the reaction tube to achieve efficient aggregation and utilization of ultrasonic energy and improve ultrasonic energy efficiency. The continuous phase and the dispersed phase flow into the reactor via a fluid conveying device and are quickly dispersed and emulsified under the action of ultrasound.

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

[0007] A microreactor system for continuously preparing nanoemulsion comprises a raw material supply end, an ultrasonic micro-filled bed reactor and a product collection end which are connected in sequence; the ultrasonic micro-filled bed reactor comprises an ultrasonic transducer and a micro-filled bed reaction part, the ultrasonic transducer is glued to the micro-filled bed reaction part; the micro-filled bed reaction part comprises a capillary microreactor and a solid filler; the capillary microreactor is filled with the solid filler, and both ends of the capillary microreactor are provided with a constriction structure for material inflow and outflow; a screen is installed at the constriction to encapsulate and replace the solid filler.

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

[0009] As a preferred technical solution, the solid filler is embedded in the capillary microreactor via mechanical filling and connected to the ultrasonic transducer via epoxy resin glue.

[0010] As a preferred technical solution, the inlet and outlet of the capillary microreactor are both provided with a stepped necking structure, the necking structure is connected to the raw material supply end and the product collection end, and the reaction material flows into / out of the microreactor via the necking structure A.

[0011] As a preferred technical solution, the ultrasonic transducer is glued to the micro-packed bed reaction part via the front radiation surface.

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

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

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

[0015] As a preferred technical solution, the wall of the capillary microreactor is provided with a through hole, which is connected to the raw material supply end; the reaction materials flow in through the necking structure and the through hole respectively; the aperture of the step-type necking structure is preferably 4.0-10.0 mm, and the aperture of the through hole is preferably 1.0-6.0 mm.

[0016] As a preferred technical solution, the solid filler is prepared by 3D printing. There are channels distributed in the filler to achieve the interception and capture of acoustic cavitation bubbles. The channel is a spherical channel structure, and the channel cross-section is circular, triangular, rectangular, etc., preferably circular. The pore diameter is preferably 30-500μm, more preferably 100-400μm. Depending on the applicable conditions, the filler material is stainless steel, titanium alloy, aluminum alloy, etc.

[0017] As a preferred technical solution, the inlet and outlet of the microreactor are provided with a screen to achieve effective filling of solid fillers and premixing between liquid phases. The screen is provided with a plurality of through holes, and the material flows in and out through the through holes to achieve pre-emulsification of the material. The diameter of the screen is consistent with the size of the microreactor shrinkage hole, and circular holes are evenly distributed, and the pore size is preferably 20-500μm. Depending on the applicable conditions, the screen material is stainless steel, titanium alloy, aluminum alloy, etc.

[0018] As a preferred technical solution, the sandwich ultrasonic transducer preferably includes a front cover plate, a piezoelectric ceramic stack and a rear cover plate which are arranged in sequence. The front cover plate is usually made of light metals, such as aluminum, titanium, magnesium and other metals and alloys. The rear cover plate is usually made of heavy metals, such as stainless steel, copper, copper-steel alloy, etc. The front cover plate, the piezoelectric ceramic stack and the rear cover plate are connected by bolts, and preferably the front cover plate, the piezoelectric ceramic stack and the rear cover plate are connected by high-strength metal bolts at the center. In the present invention, the bonding area between the micro-packed bed reactor and the ultrasonic transducer is located on the side 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, more preferably 18-600 kHz.

[0020] When the ultrasonic micro-packed bed reactor of the present invention is excited, the piezoelectric ceramic crystal stack converts the electrical signal into mechanical vibration and transmits it to the micro-reactor through the front cover of the transducer. The solid filler further gathers the acoustic energy, increases the acoustic power density inside the micro-reactor, and can significantly enhance the mixing and mass transfer between the reaction materials in the micro-reactor.

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

[0022] A method for rapidly and continuously preparing a nanoemulsion adopts the microreactor system, through a continuous conveying device, a continuous phase (such as water, octane) flows in from a constriction structure A, and a dispersed phase (such as vitamin E, carotene) flows in from a through hole B, and the continuous phase and the dispersed phase are dispersed and emulsified in the reactor under normal temperature conditions, so that the nanoemulsion can be prepared efficiently and rapidly.

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

[0024] The average size of the nanoemulsion of the present 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 have high operational flexibility and can realize free disassembly of the inlet and outlet of the microreactor and replacement of the shape, size and material of the filler.

[0027] (2) The ultrasonic micro-packed bed reactor of the present invention has high energy efficiency. By comparing the temperature distribution in the micro-reactor with and without filler filling under the condition of ultrasonic power of 40W, the temperature in the micro-reactor without filler rose by 7.7°C and the temperature in the micro-reactor with filler rose by 17.1°C. This shows that solid fillers can effectively gather sound energy and solve the problem of non-concentrated sound energy distribution in common ultrasonic micro-reactors.

[0028] (3) The ultrasonic micro-packed bed reactor of the present invention has high operational flexibility. Solid fillers can efficiently capture acoustic cavitation bubbles and solve the difficulty of acoustic cavitation under high liquid phase flow conditions. Taking water as an example, in order to ensure the cavitation effect, the upper limit of the liquid phase flow rate is 2.36 cm / s when there is no filler filling, and the upper limit of the liquid phase flow rate is increased to 9.44 cm / s when there is filler filling. Therefore, the ultrasonic micro-packed bed reactor can solve the problem of low efficiency of ultrasonic microreactors and improve the liquid phase operation range in ultrasonic microreactors.

[0029] (4) The ultrasonic micro-packed bed microreactor of the present invention has high dispersion efficiency. After the reaction materials flow in, they undergo the processes of screen pre-emulsification, filler shearing, and acoustic cavitation bubble mechanical mixing, and the emulsification efficiency is effectively improved.

[0030] In summary, the method for continuously preparing nanoemulsion based on an ultrasonic micro-packed bed reactor proposed in the present invention has high flexibility, simple operation, and can achieve efficient and rapid production of fine nanoemulsion. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of an ultrasonic micro-packed bed reactor, wherein 1.1 is a sandwich ultrasonic transducer, 1.2 is a capillary microreactor, 1.3 is a micro-packed bed reactor, and 1.4 is an elastic tube.

[0032] Figure 2It is a structural diagram of a sandwich ultrasonic transducer, 2.1 is the front cover of the transducer, 2.2 is the piezoelectric ceramic crystal stack, and 2.3 is the rear cover of the transducer.

[0033] Figure 3 It is a structural diagram of a capillary microreactor, 3.1 is a stepped necking structure, 3.2 is a screen, and 3.3 is a through hole. DETAILED DESCRIPTION

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

[0035] Example 1

[0036] like Figure 1-3 As shown, this embodiment provides a microreactor system for continuously preparing 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 resonance frequency of 20 kHz, the ultrasonic micro-filled bed reactor includes an ultrasonic transducer and a micro-filled bed reaction part, the ultrasonic transducer is glued to the micro-filled bed reaction part, the micro-filled bed reaction part includes a solid filler and a capillary microreactor 1.2; the capillary microreactor is filled with a solid filler, and the solid filler is a spring structure filler; both ends of the capillary microreactor 3.2 are provided with a stepped necking structure 3.1, and a screen 3.2 is installed at the necking; the wall of the capillary microreactor 3.2 is provided with a through hole 3.3.

[0037] The capillary microreactor 1.2 of the present embodiment is a capillary microreactor 1.2, the capillary body is made of glass, with an outer diameter of 5.0mm, an inner diameter of 3.0mm and a length of 65mm. The stepped necking structure 3.1 has an inner diameter of 4mm and a length of 10mm. The through hole 3.3 has an aperture of 1.0mm and is 15mm away from the capillary entrance. The solid filler is made of Hastelloy, a spring configuration, a spring length of 2mm and a cross-sectional diameter of 1mm. After the spring filler is pressed into the capillary microreactor 1.2 through the necking structure, it is packaged using a screen 3.2. The screen 3.2 is disc-shaped, made of stainless steel, with a diameter of 4mm and a mesh diameter of 200μm. The sandwich ultrasonic transducer 2 has an operating frequency of 20 kHz and a maximum input power of 150W. 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 crystal stack 2.2 is composed of two piezoelectric ceramic sheets coaxially stacked into 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 fixed by strong glue. The rear cover plate 2.3 is made of steel material, and its geometric shape is a cylinder with a diameter of 45 mm and a thickness of 35 mm. The front cover plate 2.1 is made of aluminum alloy material, and its geometric shape is a cone, with a front radiation surface diameter of 66 mm, a rear radiation surface diameter of 45 mm, and a thickness of 47 mm. After gluing the ultrasonic transducer 1.1 to the capillary microreactor 1.2 and encapsulating the solid filler, the ultrasonic micro-packed bed reactor has a resonance frequency of 20.8 kHz and a maximum input power of 150 W.

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

[0039] Example 2

[0040] like Figure 1-3 As shown, this embodiment provides a microreactor system for continuously preparing 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 resonance frequency of 40 kHz, the ultrasonic micro-filled bed reactor includes an ultrasonic transducer and a micro-filled bed reaction part, the ultrasonic transducer is glued to the micro-filled bed reaction part, the micro-filled bed reaction part includes a solid filler and a capillary microreactor 1.2; the capillary microreactor is filled with a solid filler, and the solid filler is a triangular screw structure filler; both ends of the capillary microreactor 3.2 are provided with a stepped necking structure 3.1, and a screen 3.2 is installed at the necking; the wall of the capillary microreactor 3.2 is provided with a through hole 3.3.

[0041] The capillary microreactor 1.2 of the present embodiment is a capillary microreactor 1.2, and the capillary body is made of FEP (fluoroethylene propylene) material, with an outer diameter of 8.0mm, an inner diameter of 4.0mm, and a length of 55mm. The stepped necking structure 3.1 has an inner diameter of 6mm and a length of 10mm. The through hole 3.3 has an aperture of 2.0mm and is 15mm away from the capillary entrance. The solid filler is made of stainless steel, with a triangular screw configuration and a triangular screw size of 3mm. After the triangular screw filler is pressed into the capillary microreactor 1.2 through the necking structure, it is packaged using a screen 3.2. The screen is disc-shaped, made of stainless steel, with a diameter of 6mm and a mesh diameter of 300μm. The sandwich ultrasonic transducer 2 has an operating frequency of 40 kHz and a maximum input power of 80W. It is composed of a front cover plate 2.1, a piezoelectric ceramic crystal pile 2.2, and a rear cover plate 2.3 connected at the center by high-strength stainless steel bolts. The piezoelectric ceramic crystal stack 2.2 is composed of two piezoelectric ceramic sheets coaxially stacked into 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 fixed by strong glue. The rear cover plate 2.3 is made of steel material, and its geometric shape is a cylinder with a diameter of 38 mm and a thickness of 18 mm. The front cover plate 2.1 is made of titanium alloy material, and its geometric shape is a cone, with a front radiation surface diameter of 58 mm, a rear radiation surface diameter of 38 mm, and a thickness of 40 mm. After gluing the ultrasonic transducer 1.1 to the capillary microreactor 1.2 and encapsulating the solid filler, the resonant frequency of the ultrasonic micro-packed bed reactor is 39.7 kHz and the maximum input power is 80 W.

[0042] Under the condition of ultrasonic power of 30W, deionized water of 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 microphotographic device. When the deionized water flow rate was 0.1-20mL / min, a large number of acoustic cavitation bubbles were observed in the reactor. When the deionized water flow rate was increased to 40mL / min (liquid phase flow rate 9.44cm / s), almost no acoustic cavitation bubbles were observed.

[0043] Example 3

[0044] The structure of the ultrasonic micro-packed bed reactor is the same as that of Example 1, with water as the continuous phase (Tween 80, 10wt.%), a mixture of vitamin E (60wt.%) and medium-chain triglycerides (40wt.%) as the dispersed phase, and a horizontal flow pump is used to transport two streams of materials to the ultrasonic micro-packed bed reactor. The continuous phase flow rate is 2.7 ml / min, and the dispersed phase flow rate is 0.3 ml / min. Under normal temperature conditions, the ultrasonic power is 50W and the residence time is 9.18s. The emulsion is collected at the outlet into a sample collection tank, diluted 20 times with the continuous phase, and analyzed using a Malvern particle size analyzer, and the average size of the emulsion can be tested to be 105nm.

[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-packed bed reactor was the same as in Example 1, except that only the solid filler was removed. Deionized water was encapsulated in the capillary micro-reactor, and the water temperature was monitored using an infrared thermal imager. The irradiation time was 120 s, and the water temperature increased from 20.2°C to 27.9°C, a temperature increase of 7.7°C.

[0049] Comparative Example 2

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

[0051] Comparative Example 3

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

Claims

1. A microreactor system for continuously preparing nanoemulsions, characterized in that: The invention comprises a raw material supply end, an ultrasonic micro-packed bed reactor and a product collection end which are connected in sequence; the ultrasonic micro-packed bed reactor comprises an ultrasonic transducer and a micro-packed bed reaction part, and the ultrasonic transducer is glued to the micro-packed bed reaction part; the micro-packed bed reaction part comprises a solid filler and a capillary micro-reactor; the capillary micro-reactor is filled with a solid filler, and both ends of the capillary micro-reactor are provided with a constriction structure, and a screen is installed at the constriction; the wall surface of the capillary micro-reactor is provided with a through hole.

2. The ultrasonic micro-packed bed reactor according to claim 1, characterized in that: The ultrasonic transducer is a sandwich-type ultrasonic transducer; and the necking structure is a stepped necking structure.

3. The ultrasonic micro-packed bed reactor according to claim 1, characterized in that: There are one or more capillary microreactors. When there are multiple capillary microreactors, the multiple capillary microreactors are flexibly connected.

4. The ultrasonic micro-packed bed reactor according to claim 3, characterized in that: Multiple capillary microreactors are connected by elastic tubes.

5. The ultrasonic micro-packed bed reactor according to claim 1, characterized in that: The cross-section of the necking structure is circular; the inner diameter of the capillary microreactor is 3.0-9.0 mm; the aperture of the necking structure is 4.0-10.0 mm, and the aperture of the through hole is 1.0-6.0 mm.

6. The ultrasonic micro-packed bed reactor according to claim 1, characterized in that: The solid filler is provided with a spherical channel structure with a pore diameter of 30-500 μm.

7. The ultrasonic micro-packed bed reactor according to claim 1, characterized in that: The sieve is provided with a plurality of through holes, and the hole diameter is 20-500 μm.

8. A method for rapidly and continuously preparing a nanoemulsion, characterized in that: The microreactor system according to claims 1 to 7 is adopted, the continuous phase flows in from the constriction structure, the dispersed phase flows in from the through hole, and the phases are mixed and emulsified in the reactor under normal temperature conditions.

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

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