Liquid-core waveguide photoreactor and liquid-core waveguide photolysis method

Abstract

The application discloses a liquid-core waveguide light reactor and a liquid-core waveguide light irradiation method. The light transmission satisfies the total reflection condition by setting the included angle between the light and the channel wall, and the light is transmitted by multiple total reflections in the medium in the channel as the light guide medium, so that the light guide method similar to the optical fiber is realized. The liquid-core waveguide light irradiation method repeatedly passes the light in the longitudinal direction through the inner channel multiple times, can keep strong and uniform light irradiation in the flow light reactor with a length of several centimeters, and improves the effective light irradiation length of the photocatalytic organic reaction sample in the channel. The liquid-core waveguide light irradiation method is favorable for shortening the time consumption of the photocatalytic organic reaction, efficiently and quickly completing the reaction, reducing the loss of the light caused by refraction, scattering and absorption, significantly improving the light utilization rate, and meeting the development demand of green chemistry.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalytic organic reactions, and particularly relates to a liquid-core waveguide light reactor and a liquid-core waveguide light irradiation method. BACKGROUND

[0002] Photocatalytic organic reactions have become one of the powerful tools for researchers due to their low cost, high safety, environmental friendliness, green environmental protection, simple equipment, and fewer side reactions, which significantly expand the application range of organic synthesis. However, due to the problems of insufficient light intensity, low light utilization rate and uniformity in the commonly used light reactors, photocatalytic organic reactions often take several hours or even several days to complete, which requires researchers to invest a lot of time and effort ([1] S. Steiner et al., Science, 2019, 363, 144-144.). The ideal light irradiation method and light reactor design are expected to shorten the time consumption of photocatalytic organic reactions, improve the screening throughput, reduce sample consumption, precisely control the reaction conditions, and have high repeatability. To achieve the above goals, developing new light reactors is a key technology to realize the high-throughput screening and rapid development of the conditions of photocatalytic organic reactions, which has important significance for the in-depth research and expansion of the application field of such reactions.

[0003] At present, the commonly used light reactors mainly include traditional batch light reactors, micro-batch light reactors and flow light reactors. The traditional batch light reactor has simple structure and is widely used, but it has large sample consumption and long reaction time. The micro-batch light reactor improves the reaction throughput through parallel micro-reactors (such as 96, 384, 1536 well plates), but has problems such as difficulty in scaling up the reaction, difficulty in integrating online detection methods, and limited screening throughput due to the detection throughput. The flow light reactor is based on the channel structure constructed by pipelines or chips. Due to the fact that the channel size (micron to millimeter) is close to the effective light irradiation distance, and the surface area to volume ratio is high, the reaction time can be shortened to several hours or even several minutes ([1] L. D. Elliott et al., Chem. Eur. J., 2014, 20, 15226-15232; [2] P. Sagmeister et al., Angew. Chem., Int. Ed., 2021, 60, 8139-8148; [3] J. H. Harenberg et al., Angew. Chem., Int. Ed., 2021, 60, 731-735.). Due to these advantages, in recent years, some research groups have applied flow light reactors to photocatalytic organic synthesis. However, due to the problems of weak light intensity, low uniformity and low light utilization rate in the commonly used light irradiation method, side light irradiation method, the reaction time in the flow light reactor is still difficult to meet the requirements of high-throughput screening.

[0004] Currently, the common photoreactor (including traditional batch photoreactor, micro-batch photoreactor and flow photoreactor) usually adopts side-lighting method, i.e. simply setting a side light source at the side of the reaction flask or test tube. The side-lighting method is widely used in the design of photoreactor because of its simple device and low cost. However, the side-lighting method has great room for improvement in terms of light penetration depth, intensity, uniformity and light utilization. In fact, light will be lost when penetrating the container wall, and this side-lighting method can only utilize a small part of light energy, and the remaining majority of light energy is wasted, which does not meet the development requirements of green chemistry; in addition, according to Lambert-Beer law, light will exponentially decay with the increase of the penetration depth after entering the photoreactor, so the side-lighting method can only ensure that the very thin liquid layer on the surface of the photoreactor is effectively illuminated. Similarly, the axial-lighting method is to set the light source so that the light irradiates from the outlet of the channel inward, which also has problems of low effective depth and uniformity of light. For photocatalytic organic synthesis, non-uniform light will affect the reaction results and may lead to undesirable by-products.

[0005] The liquid-core waveguide lighting method utilizes the difference in refractive index between the channel wall and the medium outside the channel, and uses the medium in the channel as the light guide medium for multiple total reflection transmission, realizing a light guide method similar to optical fiber. In the reported work, the liquid-core waveguide lighting method has been used for online detection of micro-sample long-path absorption spectrum ([1] M. P. Duggan et al., Analyst, 2003 128, 1336-1340; [2] J.-Z. Pan et al., Anal. Chem., 2010, 82, 3394-3398.). There is no report in the prior art about applying the liquid-core waveguide lighting method to photoreactor. SUMMARY

[0006] The existing photoreactor uses side-lighting method, which has problems of insufficient light intensity, low uniformity and low light utilization, which leads to long time consumption, many by-products and poor reproducibility of photocatalytic organic synthesis reaction. The liquid-core waveguide lighting method previously used for online spectrum analysis is introduced into the design of photoreactor in the present application, which significantly improves the light intensity and uniformity, and can maintain strong light in the range of several centimeters of photoreactor. This new reactor can shorten the time consumption of photocatalytic organic synthesis reaction, reduce the occurrence of side reactions, and has high yield of target product and good reproducibility of reaction. In addition, the liquid-core waveguide lighting method significantly improves the light utilization and reduces the light loss, which meets the development requirements of green chemistry.

[0007] The present application first provides a liquid-core waveguide photoreactor for photocatalytic organic reaction flow synthesis, comprising:

[0008] The flow light reactor of nested channel structure comprises an outer channel and an inner channel arranged in nest, the inner cavity of the inner channel is used for passing the photocatalytic organic reaction sample, and the cavity between the inner side wall of the outer channel and the outer side wall of the inner channel is used for passing the cooling fluid,

[0009] The temperature control device controls the reaction temperature of the photocatalytic organic reaction flow synthesis by controlling the cooling fluid passing into the cavity between the inner side wall of the outer channel and the outer side wall of the inner channel,

[0010] The optical fiber-based light coupling and conducting device comprises an optical fiber, the optical fiber has an incident end and an emission end, the incident end is used for coupling with a light source in use, the emission end extends into the cavity between the inner side wall of the outer channel and the outer side wall of the inner channel of the flow light reactor, and the angle of the light emitted by the emission end satisfies the total reflection of the light on the side wall of the outer channel.

[0011] The light source can be configured together with the liquid-core waveguide light reactor as a whole or can be configured separately and assembled together in use. The light source can be an LED, a laser, an incandescent lamp, a halogen lamp, a fluorescent lamp or other light source with high light intensity. Preferably, the liquid-core waveguide light reactor further comprises a light source coupled with the incident end of the optical fiber for providing the light required by the photocatalytic organic reaction flow synthesis. The laser is a preferred light source. The light source required by the present application should be able to output strong light to ensure the progress of the photocatalytic organic synthesis reaction, and the output light intensity of the light source should be greater than 100 mW, and the light intensity is flexibly adjustable. The diameter of the light spot after focusing of the light source should be as small as possible to ensure the coupling ratio of the light from the light source to the optical fiber, reduce the light loss, and the diameter of the light spot after focusing should be less than 600 μm.

[0012] The optical fiber can be a high-purity quartz optical fiber, a plastic optical fiber or a multi-component glass optical fiber with light transmission performance. Preferably, the material is glass, quartz or PEEK / PFA / PTFE.

[0013] The realization of multiple total reflection transmission of light should comprehensively consider the numerical aperture angle of the optical fiber, the included angle between the optical fiber and the outer channel and the refractive index of the side wall of the outer channel as the medium.

[0014] The interface where the total reflection occurs in the liquid-core waveguide light irradiation method is determined by the refractive index of the medium of the side wall of the outer channel and the fluid medium inside it. No matter which one, the light emitted from the optical fiber needs to meet the conditions for total reflection to occur: (A) the light is transmitted from the optically dense medium to the optically sparse medium, that is, the refractive index of the incident medium is greater than the refractive index of the emission medium; (B) the incident angle is greater than the critical angle.

[0015] In order to meet condition (A), the refractive indexes of the medium of the side wall of the outer channel and the medium inside and outside it need to be considered.

[0016] Preferably, the angle of the light emitted from the exit end satisfies the total reflection condition when the light is totally reflected at the side wall of the outer channel, which is either the inner side wall surface or the outer side wall surface.

[0017] More preferably, if the total reflection occurs at the inner side wall surface of the outer channel, the refractive index of the cooling fluid as the medium is greater than the refractive index of the outer channel side wall as the medium.

[0018] If the total reflection occurs at the outer side wall surface of the outer channel, the refractive index of the outer channel side wall as the medium needs to be greater than the refractive index of the environment outside the outer channel as the medium, or a reflective layer with a refractive index greater than that of the outer channel side wall is provided on the outer side wall surface of the outer channel, and the refractive index of the reflective layer as the medium is greater than the refractive index of the environment outside the outer channel as the medium. For example, the reflective layer can be a silver plating layer.

[0019] The refractive index of the medium on both sides of the total reflection interface also determines the critical angle of total reflection of light, according to which the placement angle of the exit end of the optical fiber in the optical reactor is designed so that the incident angle of light is greater than the critical angle, satisfying the total reflection condition (B). The incident angle of light = the included angle between the exit end of the optical fiber and the total reflection interface + the numerical aperture angle of the optical fiber.

[0020] Generally, the included angle between the exit end of the optical fiber and the channel wall where total reflection occurs should be within the range of 0-45°; after the light exits from the exit end of the optical fiber, it disperses uniformly according to its numerical aperture angle. In order to make the light satisfy the requirement that the total reflection incident angle is greater than the critical angle when it reaches the outer channel wall, the specific included angle between the exit end of the optical fiber and the channel wall should be considered in the light of the influence of the numerical aperture angle on the angle of the emitted light. In addition, the light beam emitted from the optical fiber will naturally spread according to the numerical aperture angle, and the numerical aperture angle (NA value) of a general multimode optical fiber is within the range of 0.1-0.5, corresponding to an angle of 6-30°. In the actual design of the optical reactor, the specific angle of the included angle between the exit end of the optical fiber and the outer channel should be determined by comprehensively considering the above factors, so that the light satisfies the total reflection condition (B) when it reaches the interface.

[0021] The liquid-core waveguide illumination method makes the light undergo total reflection along the longitudinal direction of the optical reactor multiple times, repeatedly passing through the inner channel, and providing uniform high light intensity in a range of several centimeters. In order to ensure the transmission of light, the material of the channel wall of the inner channel should be able to withstand common organic reaction samples and not absorb light of the target wavelength; the inner and outer surfaces of the two channels should be smooth and flat, without structures that change the symmetry of the surface, to avoid the total reflection condition of light being destroyed or being lost due to scattering or refraction.

[0022] In addition, the design of the photoreactor also needs to consider the temperature control of the photocatalytic organic synthesis reaction. The liquid-core waveguide illumination method confines the strong light in the photoreactor, which can cause temperature rise that is not conducive to the photocatalytic organic reaction. The temperature control device timely removes the unwanted heat through the cooling fluid flowing through the outer channel to control the temperature of the photocatalytic organic synthesis reaction.

[0023] Preferably, one end of the flow photoreactor with the nested channel structure is provided with the optical fiber, or both ends of the flow photoreactor with the nested channel structure are provided with the optical fiber. When both ends of the flow photoreactor with the nested channel structure are provided with the optical fiber, the optical fibers at both ends are preferably arranged in a symmetrical distribution. The number of optical fibers at each end is one, or a plurality of optical fibers are arranged around the end face.

[0024] The number of optical fibers and the position of the optical fiber exit end in the photoreactor can be set according to the requirements of the specific reaction. Preferably, the number of optical fibers can be greater than 1 to improve the illumination intensity in the photoreactor. Preferably, when the number of optical fiber exit ends arranged on the left and right sides of the photoreactor is equal (the number of optical fibers on each side can be greater than 1), that is, when the distribution is symmetrical, the light uniformity of the liquid-core waveguide illumination method can be further improved. If the number of optical fibers fixed on the photoreactor is greater than 1, the number of light sources also increases accordingly, and the light source corresponds to one optical fiber.

[0025] The diameters of the inner and outer channels of the nested channel structure and the thickness of the channel wall will affect the effect of the liquid-core waveguide illumination method. Preferably, the outer diameter of the inner channel is less than 2 mm, and the outer diameter of the outer channel is not more than 10 times the outer diameter of the inner channel. The thickness of the side wall of the inner and outer channels is as thin as possible. The thickness of the side wall of the inner channel is as thin as possible to ensure that the organic reaction sample in the inner channel can be effectively illuminated. The thickness of the side wall of the outer channel is as thin as possible to ensure the uniformity and utilization rate of light under the liquid-core waveguide illumination method. Preferably, the thickness of the side wall of the inner channel is less than 1 mm, and the thickness of the side wall of the outer channel is less than 2 mm.

[0026] The length of the photoreactor should not be too long or too short. Considering the uniformity of light, the length of the photoreactor should not be too long. When the length of the photoreactor exceeds a certain limit, as the length of the photoreactor increases, the illumination uniformity and temperature uniformity of the cross section of the inner channel decrease, which can cause unwanted side reactions. At the same time, the length of the photoreactor should not be too short to ensure the effective residence time of the organic reaction sample under illumination. Preferably, the length of the flow photoreactor is 1-20 cm.

[0027] The fiber core diameter needs to be considered comprehensively in view of the light utilization in the optical reactor, and the fiber diameter should not be too large so that the proportion of the inner channel to the outer channel cross-sectional area is as large as possible to ensure high light utilization; meanwhile, in order to ensure that the light at the light source can be coupled into the optical fiber at a high proportion and reduce light loss, the fiber diameter should not be too small. Preferably, the fiber core diameter is 50-1500 μm. More preferably, the fiber core diameter is 100-600 μm.

[0028] The length of the optical fiber should be selected in consideration of the connection of the optical fiber with the light source and the optical reactor and to ensure effective transmission of light in the optical fiber. Preferably, the length of the optical fiber is 1-5 m. The optical fiber is a single-mode optical fiber or a multi-mode optical fiber, and preferably the type of the optical fiber is a multi-mode optical fiber. Such a fiber has a thicker core, a suitable length, less loss in short-distance light transmission, and more uniform light at the fiber exit end. When the optical fiber is a multi-mode optical fiber, the NA value of the multi-mode optical fiber is 0.1-0.5. More preferably, the NA value of the multi-mode optical fiber should be in the range of 0.18-0.37.

[0029] Preferably, the exit end of the optical fiber is a plane or an inclined plane. If it is an inclined plane, the inclined plane can be directly opposite to the side wall facing the outer channel or directly opposite to the side wall facing the inner channel, or it can be inclined. Preferably, it is directly opposite to the side wall facing the outer channel, which is advantageous for improving light utilization. More preferably, when the exit end of the optical fiber is an inclined plane, the included angle between the inclined plane and the side wall of the outer channel is not less than 60°. For example, the included angle can be 75°. When the exit end of the optical fiber is an inclined plane, the light utilization in the reactor can be further improved.

[0030] The application further provides a liquid-core waveguide light irradiation method for photocatalytic organic reaction flow synthesis, which uses the liquid-core waveguide light reactor and comprises the following steps:

[0031] (1) introducing a photocatalytic organic reaction sample into the cavity of the inner channel and introducing a cooling fluid into the cavity between the inner side wall of the outer channel and the outer side wall of the inner channel;

[0032] (2) introducing light into the entrance end of the optical fiber from the light source, and the light emitted from the exit end of the optical fiber undergoes continuous total reflection on the side wall of the outer channel so that the light acts on the photocatalytic organic reaction sample to realize photocatalytic organic reaction flow synthesis, and during the reaction, the temperature control device controls the reaction temperature of the photocatalytic organic reaction flow synthesis by controlling the cooling fluid introduced into the cavity between the inner side wall of the outer channel and the outer side wall of the inner channel.

[0033] When multiple total reflection transmission of light occurs, the cooling fluid in the outer channel acts as a heat dissipation medium, a light guide medium and a light uniformization medium; the nested channel structure and the temperature control device can provide strong light while achieving temperature control of the photocatalytic organic reaction sample.

[0034] The cooling fluid should have a high specific heat capacity, which can timely take away the unwanted heat caused by strong light in the photo reactor; the cooling fluid needs to be light-transmitting, and does not affect the multiple total reflection transmission of light when flowing through the photo reactor. Preferably, the cooling fluid is a homogeneous, light-transmitting liquid or gas. When the cooling fluid is a liquid, it is specifically water, ethanol or fluorine oil.

[0035] Compared with the prior art, the present application has the beneficial effects that:

[0036] Unlike the side light method adopted by traditional batch reactors, micro-batch reactors and flow reactors, the flow photo reactor of the present application adopts a liquid core waveguide light method. The liquid core waveguide light method utilizes the difference in refractive index between the channel wall and the medium outside the channel wall, sets the angle between the light and the channel wall to make the transmission of light meet the total reflection condition, and performs multiple total reflection transmission with the medium in the channel as the light guide medium, to realize a light guide method similar to optical fiber. The liquid core waveguide light method makes the light repeatedly pass through the inner channel in the longitudinal direction, can maintain strong and uniform light in a flow photo reactor as long as several centimeters, and can increase the effective light length of the photocatalytic organic reaction sample in the inner channel from 2mm of the side light method to several centimeters. The liquid core waveguide light method is beneficial to shorten the time consumption of photocatalytic organic reaction, efficiently and quickly complete the reaction, and also reduces the loss of light due to refraction, scattering and absorption, significantly improves the light utilization rate, and meets the development needs of green chemistry. In addition, the nested channel structure and temperature control device of the photo reactor of the present application can timely take away the unwanted heat caused by strong light, realize effective and accurate temperature control of photocatalytic organic reaction, and avoid the increase of side reactions caused by the deviation of actual temperature from the optimal reaction temperature. The liquid core waveguide photo reactor for photocatalytic organic reaction flow synthesis of the present application has the advantages of simple structure, easy operation, integration, automation, micro system, green environmental protection, repeatability, high universality, short time consumption and high efficiency of photocatalytic organic reaction, and is suitable for mechanism exploration and high-throughput screening of reaction conditions in the research and development stage of photocatalytic organic reaction. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 is a schematic diagram of light transmission of the liquid core waveguide light method, wherein A: the schematic diagram of the liquid core waveguide light method in which total reflection occurs on the outer side wall surface of the outer channel; B: the schematic diagram of the liquid core waveguide light method in which total reflection occurs on the inner side wall surface of the outer channel.

[0038] Figure 2 is a schematic diagram of the device structure of the liquid core waveguide photo reactor with optical fiber on one side.

[0039] Figure 3 is a schematic diagram of the device structure of the liquid core waveguide photo reactor with optical fiber on both sides and in symmetrical distribution.

[0040] Figure 4 Figure 1 is a schematic diagram of the device structure of a liquid-core waveguide photoreactor with microstructured fiber exit end.

[0041] Reference signs:

[0042] Outer channel 1, including outer channel inlet 11, outer channel outlet 12;

[0043] Inner channel 2, including inner channel inlet 21, inner channel outlet 22;

[0044] Three-way structure 3, including three-way connection inner channel end 31, three-way connection outer channel end 32, three-way connection temperature control device end 33;

[0045] Optical coupling and conduction device 4, including fiber entrance end 41, fiber exit end 42, light source 43;

[0046] Temperature control device 5. Specific implementation method

[0047] A liquid-core waveguide photoreactor for photocatalytic organic reaction flow synthesis, comprising:

[0048] A nested channel structure flow photoreactor, comprising a nested outer channel and inner channel, the inner cavity of the inner channel is used to pass through a photocatalytic organic reaction sample, and the cavity between the inner side wall of the outer channel and the outer side wall of the inner channel is used to pass through a cooling fluid,

[0049] A temperature control device for controlling the reaction temperature of photocatalytic organic reaction flow synthesis by controlling the cooling fluid passing through the cavity between the inner side wall of the outer channel and the outer side wall of the inner channel,

[0050] An optical coupling and conduction device based on an optical fiber, comprising an optical fiber, the optical fiber has an entrance end and an exit end, the entrance end is used to be coupled with a light source in use, the exit end extends into the cavity between the inner side wall of the outer channel and the outer side wall of the inner channel of the flow photoreactor, and the angle of the light emitted by the exit end satisfies the total reflection of the light on the side wall of the outer channel.

[0051] The light source can be configured as a whole with the liquid-core waveguide photoreactor, or can be configured separately and assembled together when in use. The light source can be a LED, a laser, an incandescent lamp, a halogen lamp, a fluorescent lamp or other light source with high light intensity. Preferably, the liquid-core waveguide photoreactor further comprises a light source coupled with the incident end of the optical fiber for providing light required for photocatalytic organic reaction flow synthesis. The laser is a preferred light source. The light source required by the present application should be able to output strong light to ensure the progress of photocatalytic organic synthesis reaction, and the output light intensity of the light source should be greater than 100 mW, and the light intensity is flexibly adjustable. The diameter of the focused light spot should be as small as possible to ensure the coupling ratio of light from the light source to the optical fiber and reduce light loss. Preferably, the diameter of the focused light spot should be less than 600 μm.

[0052] The optical fiber can be a high-purity quartz optical fiber, a plastic optical fiber or a multi-component glass optical fiber with light transmission performance. Preferably, the material is glass, quartz or PEEK / PFA / PTFE.

[0053] The angle of the light emitted from the exit end of the optical fiber satisfies the total reflection of the light on the side wall of the outer channel, and the total reflection occurs on the inner side wall surface or the outer side wall surface of the outer channel.

[0054] The light emitted from the optical fiber needs to satisfy the condition of total reflection: (A) the light is transmitted from a light-dense medium to a light-sparse medium, that is, the refractive index of the incident medium is greater than the refractive index of the exit medium; (B) the incident angle is greater than the critical angle.

[0055] In order to satisfy condition (A), if the total reflection occurs on the inner side wall surface of the outer channel, the refractive index of the cooling fluid as the medium is greater than the refractive index of the side wall of the outer channel as the medium; if the total reflection occurs on the outer side wall surface of the outer channel, it is required that the refractive index of the side wall of the outer channel as the medium is greater than the refractive index of the environment outside the outer channel as the medium, or a reflective layer with a refractive index greater than the side wall of the outer channel is provided on the outer side wall surface of the outer channel, and the refractive index of the reflective layer as the medium is greater than the refractive index of the environment outside the outer channel as the medium. For example, the reflective layer can be a silver plating layer.

[0056] The refractive index of the medium on both sides of the total reflection interface also determines the critical angle of the total reflection of light, and accordingly the placement angle of the exit end of the optical fiber in the photoreactor is designed to make the incident angle of light greater than the critical angle, satisfying the total reflection condition (B). The incident angle of light = the included angle between the exit end of the optical fiber and the total reflection interface + the numerical aperture angle of the optical fiber.

[0057] Generally, the angle between the fiber exit end and the channel wall where total reflection occurs should be in the range of 0-45°; the light from the fiber exit end is uniformly dispersed according to its numerical aperture angle, in order to make the light meet the requirement that the total reflection incident angle is greater than the critical angle when reaching the outer channel wall, the specific angle between the fiber exit end and the channel wall should be set considering the influence of the numerical aperture angle on the angle of the exiting light. In addition, the light beam from the fiber will naturally spread according to the numerical aperture angle, and the numerical aperture angle (NA value) of a general multimode fiber is in the range of 0.1-0.5, corresponding to an angle of 6-30°. In the actual design of the photoreactor, the specific angle between the fiber exit end and the outer channel should be set considering the above factors, so that the light meets the total reflection condition (B) when reaching the interface.

[0058] The liquid-core waveguide illumination method makes the light repeatedly undergo total reflection along the longitudinal direction of the photoreactor, repeatedly pass through the inner channel, and provide uniform high light intensity in a range of several centimeters. In order to ensure the transmission of light, the material of the channel wall of the inner channel should be able to withstand common organic reaction samples and not absorb light of the target wavelength; the inner and outer surfaces of the two channels should be smooth and flat, without structures that change the symmetry of the surface, to avoid the total reflection condition of the light being destroyed or being lost due to scattering or refraction.

[0059] One end of the nested channel structure flow photoreactor is provided with the optical fiber, or both ends of the nested channel structure flow photoreactor are provided with the optical fiber. The number of optical fibers provided at each end is one, or multiple optical fibers are arranged around the end face. The number of optical fibers and the position of the fiber exit end in the photoreactor can be set according to the requirements of the specific reaction. Preferably, the number of optical fibers can be greater than 1, so as to improve the light intensity in the photoreactor. Preferably, when the number of fiber exit ends arranged on the left and right sides of the photoreactor is equal (the number of optical fibers on each side can be greater than 1), that is, when the distribution is symmetrical, the light uniformity of the liquid-core waveguide illumination method can be further improved. If the number of optical fibers fixed on the photoreactor is greater than 1, the number of light sources also increases accordingly, and the light source corresponds to one optical fiber.

[0060] The diameters of the inner and outer channels and the thickness of the channel wall of the nested channel structure will affect the effect of the liquid-core waveguide illumination method. Preferably, the outer diameter of the inner channel is less than 2 mm, and the outer diameter of the outer channel is not more than 10 times the outer diameter of the inner channel. Moreover, the thickness of the side wall of the inner and outer channels is as thin as possible. The thickness of the side wall of the inner channel is as thin as possible, so as to ensure that the organic reaction sample in the inner channel can be effectively illuminated. The thickness of the side wall of the outer channel is as thin as possible, so as to ensure the uniformity and utilization rate of light under the liquid-core waveguide illumination method. Preferably, the thickness of the side wall of the inner channel is less than 1 mm, and the thickness of the side wall of the outer channel is less than 2 mm.

[0061] The length of the photoreactor should not be too long or too short. Preferably, the length of the flowing photoreactor is 1–20 cm. The core diameter of the optical fiber needs to take into account the light utilization in the photoreactor; preferably, the core diameter is 50–1500 μm. More preferably, the core diameter is 100–600 μm. The length of the optical fiber should be selected considering the connection between the optical fiber and the light source and the photoreactor, and to ensure effective light transmission in the optical fiber; preferably, the length of the optical fiber is 1–5 m. The optical fiber can be single-mode or multimode, preferably multimode, as it has a thicker core, a suitable length, less loss in short-distance light transmission, and more uniform light at the output end. When the optical fiber is multimode, the NA value is 0.1–0.5. More preferably, the NA value should be in the range of 0.18–0.37.

[0062] The cooling fluid should have a high specific heat capacity to effectively remove unwanted heat caused by strong light from the photoreactor. The cooling fluid also needs to be light-transmitting, ensuring that it does not interfere with multiple total internal reflections of light as it flows through the photoreactor. Preferably, the cooling fluid is a homogeneous, light-transmitting liquid or gas. When the cooling fluid is a liquid, it is specifically water, ethanol, or fluorinated oil.

[0063] Example 1

[0064] Figure 1 This is a schematic diagram of light transmission using the liquid-core waveguide illumination method. Based on the principle of total internal reflection, light undergoes multiple total internal reflections within the photoreactor channel, propagating and ultimately achieving a uniform light distribution. For light to reach the outer channel sidewall, two conditions must be met simultaneously: light must travel from an optically denser medium to an optically less dense medium, and the angle of incidence must be greater than the critical angle. Whether total internal reflection occurs on the outer or inner surface of the outer channel sidewall depends on the refractive index difference between the fluid in the outer channel cavity and the outer channel sidewall. If the refractive index of the outer channel sidewall is greater than that of the fluid in the outer channel cavity, and also greater than that of the medium outside the outer channel, then total internal reflection occurs on the outer surface of the outer channel sidewall; conversely, if the refractive index of the outer channel sidewall is less than that of the fluid in the outer channel cavity, then total internal reflection occurs on the inner surface of the outer channel sidewall.

[0065] Figure 1 A is a schematic diagram of the liquid core waveguide illumination method in a photoreactor with a nested channel structure, where multiple total internal reflections occur on the outer surface of the outer channel sidewall.

[0066] Figure 1 B is a schematic diagram of the liquid core waveguide illumination method in a photoreactor with a nested channel structure, where multiple total internal reflections occur on the inner surface of the outer channel sidewall.

[0067] Example 2

[0068] Figure 2Figure 1 is a schematic diagram of the device structure of the liquid-core waveguide photoreactor with optical fiber on one side. The photoreactor consists of a flow photoreactor with nested channel structure, light coupling and conducting device, and temperature control device.

[0069] The flow photoreactor with nested channel structure is used to provide strong and uniform light irradiation and control the reaction temperature by flowing organic reaction sample. The nested channel structure consists of outer channel 1, inner channel 2, and three-way structure 3. The outer channel 1 and inner channel 2 are nested. The outer channel 1 flows through cooling fluid, and the inner channel 2 flows through photocatalytic organic reaction sample. Between the outer channel 1 and inner channel 2, the three-way connection inner channel end 31 and three-way connection outer channel end 32 of the two three-way structures 3 are respectively sealed and connected with the inner channel side wall and outer channel side wall by stopcock or other methods, allowing the inner channel to pass through the outer channel to form a nested structure, ensuring that the fluids between the two channels do not contact each other. In addition, the three-way structure 3 allows the optical fiber exit end 42 to be placed between the inner and outer channels. The three-way connection temperature control device end 33 is connected to the temperature control device through the cooling fluid.

[0070] The light coupling and conducting device 4 includes the optical fiber incident end 41, optical fiber exit end 42, and light source 43. The optical fiber incident end 41 couples strong light at the light source 43, which is then transmitted through the optical fiber to the optical fiber exit end 42 placed between the outer channel 1 and inner channel 2 in the photoreactor. Light is introduced into the photoreactor and realizes the liquid-core waveguide light irradiation method.

[0071] The temperature control device 5 includes cooling fluid and driving device for the fluid. The temperature control device 5 controls the reaction temperature of the photocatalytic organic reaction flow synthesis by controlling the cooling fluid entering the cavity between the inner side wall of the outer channel 1 and the outer side wall of the inner channel 2.

[0072] The specific use steps of the photoreactor of the present application are as follows:

[0073] Step 1: According to the requirements of the specific organic synthesis reaction, select the appropriate light source 43 with the appropriate light wavelength, determine the required light intensity, and then determine the number of optical fibers that need to be set. The number of optical fibers can be greater than 1. According to the requirements of the specific organic synthesis reaction, set the temperature range of the cooling fluid.

[0074] Step 2, coupling light from light source to photoreactor by optical fiber. First, couple the focused light at light source 43 to the entrance end of optical fiber 41, try to make most of the light into the optical fiber, and use a light-adjusting optical fiber with the same specification as the actual light coupling device and a laser power meter to detect the coupling ratio. Detect the light intensity at the light spot at the light source and at the exit end of the optical fiber 42, respectively. During the process, the relative position between the light source and the entrance end of the optical fiber 41 can be adjusted to ensure that the proportion of light coupled into the optical fiber is greater than 70% of the total light intensity of the light source. If there is more than one group of light source and optical fiber in the light coupling part, each group needs to be adjusted one by one to ensure that the coupling ratio is greater than 70%. Finally, after obtaining the ideal coupling ratio, replace the light-adjusting optical fiber with the optical fiber connected to the photoreactor.

[0075] Step 3, determine the total reflection position of the liquid-core waveguide light irradiation method according to the refractive index of the sample solvent and the cooling fluid of the photocatalytic organic reaction that needs to be carried out. Adjust and determine the placement angle of the exit end of the optical fiber 42 to ensure that there is no obvious light beam shooting out of the side wall of the outer channel of the photoreactor, and the light distribution in the photoreactor is observed to be uniform.

[0076] Step 4, according to the specific needs of the photocatalytic organic reaction, determine the number of light sources needed and the total light intensity needed, set the output power of the light source accordingly, and then turn on the power of the light source.

[0077] Step 5, introduce the photocatalytic organic reaction sample into the photoreactor through the sample introduction device from the inner channel inlet 21, and carry out the reaction under the set light wavelength, light intensity, flow rate and suitable temperature. After the reaction, the sample flows out from the inner channel outlet 22, and the sample is collected for subsequent detection.

[0078] Step 6, until the reaction is completed, disconnect all power sources and end the use.

[0079] Example 3

[0080] Figure 3 is the device structure schematic diagram of the liquid-core waveguide photoreactor with optical fibers placed on both sides and symmetrically distributed. Unlike Example 2, in Example 3, the optical fibers are placed on both sides of the photoreactor and symmetrically distributed. This symmetric structure not only significantly improves the light intensity in the photoreactor, but also significantly improves the uniformity of the light distribution in the photoreactor, shortens the time consumption of the rate of organic synthesis reaction, and reduces the unwanted side reactions. The rest of the structure and the use method are the same as Example 2.

[0081] Setup of side-lighting method in lab. Photocatalytic organic reactions require uniform light irradiation, so the commonly used light source is a coiled LED light strip. The transparent reaction vessel such as test tube or flask is placed in the middle of the coiled LED light strip, and the light irradiates the inside of the reaction vessel uniformly from the side. Considering that most photocatalytic organic reactions require temperature control, the light source should be set up to avoid excessive heat from the light irradiation causing the reaction temperature to be too high, ensuring that the photocatalytic reaction is carried out at the required room temperature or low temperature environment. Therefore, the coiled LED light strip should not be too close to the reaction vessel, and the diameter of the light strip cylinder after coiling is generally 10-20 cm.

[0082] Experimental data: In this case, the light intensity, effective light depth, and light utilization rate of the liquid-core waveguide light irradiation method and the side-lighting method are compared, and the liquid-core waveguide light irradiation method has a significant advantage. In terms of light intensity, the light intensity of the side-lighting method on the surface of the reactor is 3.4 mW / cm 2 , while the light intensity of the liquid-core waveguide light irradiation method can reach 3.5 x 10 4 mW / cm 2 , which is about 10,000 times higher. In terms of effective light depth, since the light undergoes exponential decay when penetrating the reactor, the side-lighting method can only provide effective light to samples with a depth of about 2 mm on the surface of the reactor, while the liquid-core waveguide light irradiation method can provide effective light to samples up to 5 cm through repeated multiple reflections. In comparison, the effective light depth is about 25 times higher. In addition, the light utilization rate of the liquid-core waveguide light irradiation method is about 10 times higher than that of the side-lighting method, significantly reducing the waste of light energy and more in line with the concept of green chemistry.

[0083]

[0084] Reaction type and results: To verify the actual effect of the liquid-core waveguide light irradiation method applied to photocatalytic organic reactions, we take a typical and widely used organic photocatalytic synthesis, visible light catalyzed [2+2] cycloaddition reaction, as an example (reaction formula as formula I). This type of reaction is of great significance in organic synthesis because the cyclobutane obtained through this type of reaction is widely present in various biologically active natural products. Under the same conditions of compound composition, compound ratio, concentration, and temperature, the [2+2] cycloaddition reaction requires 4 h to complete in the side-lighting method and batch reactor, but only 3.3 s of residence time in the liquid-core waveguide light irradiation method and the corresponding photoreactor, significantly improving the reaction efficiency and reducing the time by about 4,300 times. In terms of reaction results, the yield obtained through the liquid-core waveguide light irradiation method is 91%, which is comparable to the yield obtained through the side-lighting method, which is 89%.

[0085] Therefore, the liquid-core waveguide light irradiation method can significantly improve the light irradiation intensity and effective light irradiation depth, thereby improving the light utilization rate and greatly shortening the time consumption of the [2+2] cycloaddition and other photocatalytic organic reactions.

[0086] Example 4

[0087] Figure 4 Figure 1 is a schematic diagram of the device structure of the liquid-core waveguide photoreactor with a microstructure at the fiber exit end. Unlike Example 3, in Example 4, the microstructure at the fiber exit end is processed to better control the exit angle of the light from the fiber exit end, reduce the excessive dispersion of the light after exiting the fiber due to the numerical aperture angle, avoid the refraction or scattering of part of the light when reaching the channel wall due to the failure to meet the total reflection condition, and further improve the light utilization rate. The remaining structure and use method are the same as those of Example 3.

[0088] Microstructure description: The main purpose of the microstructure at the fiber exit end is to change the shape of the fiber exit end surface, increase the proportion of the total reflection of the exiting light, and reduce the light loss. For example, a bevel is processed at the fiber exit end by sanding or other methods. The specific angle between the bevel and the outer channel side wall should be comprehensively considered in combination with the diameter of the fiber, the numerical aperture angle, and the placement situation, but should be within the range of 60° to 90°. After the fiber core end surface is sanded to form a bevel, the bevel should be polished with sandpaper or sanding paste with a mesh number higher than 5000 until the bevel is smooth and flat. When the processed fiber with the microstructure is placed in the liquid-core waveguide photoreactor, the sanded bevel should face the outer channel wall, because the light will exit from the processed microstructure bevel, first reach the outer channel side wall, and be uniformly distributed in the channel through total reflection. In addition, the bevel can also face the inner channel wall. Compared with the photoreactor without the microstructure at the fiber exit end, the light utilization rate is also slightly improved. However, the light exits from the processed microstructure bevel, first passes through the inner channel, and then reaches the outer channel side wall and realizes total reflection, which may cause the uniformity of the light distribution in the inner channel to decrease.

[0089] Experimental results: Four fibers with a core diameter of 400 μm and a microstructure bevel were placed in the photoreactor, the fiber was parallel to the channel, and the fiber NA was 0.37. The results show that when the angle between the microstructure bevel and the outer channel side wall is 75°, the light utilization rate in the reactor is further improved by about 1.5 times compared with the liquid-core waveguide light irradiation method without the microstructure at the fiber exit end in Example 3, i.e., about 15 times compared with the side light irradiation method, and the light is uniformly distributed in the inner channel (5 cm long).

[0090] When the angle between the microstructure facet and the inner channel sidewall is 75°, the light utilization in the reactor is further improved by about 1.2 times compared with the liquid core waveguide light illumination method without microstructure of the optical fiber in Example 3, i.e. about 12 times compared with the side light illumination method, but the light distribution in the inner channel (5 cm long) is reduced, and the light distribution is weak light area (0-1.5 cm)-strong light area (1.5-3.5 cm)-weak light area (3.5-5.0 cm).

Claims

1. A liquid-core waveguide photoreactor for photocatalytic flow synthesis of organic reactions, characterized in that, The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source.

2. The liquid-core waveguide photoreactor of claim 1, wherein, The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source.

3. The liquid-core waveguide photoreactor of claim 1, wherein, The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source.

4. The liquid-core waveguide photoreactor of claim 1, wherein, The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source.

5. The liquid-core waveguide photoreactor of claim 1, wherein, The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source.

6. The liquid-core waveguide photoreactor of claim 1, wherein, The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source.

7. A liquid-core waveguide illumination method for photocatalytic organic reaction flow synthesis, characterized in that, The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. 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The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, a temperature control device, a fiber-based light coupling and conducting device, and a light source. The application relates to a liquid-core waveguide photoreactor, which comprises a nested channel structure, (2) light is emitted from the incident end of the optical fiber by a light source, and the light emitted from the emitting end of the optical fiber is continuously totally reflected on the side wall of the outer channel, so that the light acts on the photocatalytic organic reaction sample to realize photocatalytic organic reaction flow synthesis, and in the reaction process, the temperature control device controls the reaction temperature of the photocatalytic organic reaction flow synthesis by controlling the cooling fluid in the cavity between the inner side wall of the outer channel and the outer side wall of the inner channel.

8. The liquid-core waveguide illumination method of claim 7, wherein, When the cooling fluid is a liquid, it is water, ethanol or fluorine oil.

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