Photocatalytic oxidation air purification device and method

Abstract

The invention discloses a photocatalytic oxidation air purification device and method. The device comprises at least one surface coated with anatase type titanium dioxide, at least one ultraviolet radiation source, an air circulation loop and an air circulation driving module, the air circulation driving module and the air circulation loop are matched to form an air circulation system, and the surface coated with the anatase type titanium dioxide is arranged in the air circulation system; in the working process, the ultraviolet radiation source irradiates the surface coated with anatase type titanium dioxide, air to be purified is formed in the air circulation system to form airflow, and photocatalytic degradation reaction is conducted to achieve purification. The device forms a complete air circulation system, air to be purified forms airflow in the air circulation system for photocatalytic degradation, the air purification effect is improved, and meanwhile the device has the advantages of being simple and compact in structural design, flexible in size, wide in application scene and low in cost.

Description

Technical Field

[0001] The present invention relates to the technical field of air purification, and in particular to a photocatalytic oxidation air purification device and method. Background Art

[0002] The quality of air directly affects people's health and life safety. People spend most of their time indoors during work and life, so the improvement of indoor air will directly benefit most people. In the existing technology, traditional air purification methods such as activated carbon, air fresheners, ozone, formaldehyde removers and other measures do not have sustainable air purification effects, and some methods may even have harmful effects. The photocatalytic oxidation of TiO2 can not only effectively degrade harmful volatiles (formaldehyde, benzene, ammonia, TVCO, etc.) in the air, eliminate the odor of smoke, alcohol, food, etc., and kill suspended bacteria and viruses. It can also be used to remove ethylene produced by fruits and vegetables in the transportation and storage of fruits and vegetables, which is very important for keeping food fresh. However, the air purification devices designed by photocatalysis are currently expensive in actual use and have poor environmental adaptability, which limits their application scenarios. Summary of the invention

[0003] In order to solve the technical problems of complex structure and limited application scenarios of the photocatalytic oxidation air purification device described in the above-mentioned prior art, the present invention provides a photocatalytic oxidation air catalytic device and method, which purifies the air through ultraviolet light photolysis. At the same time, the device constitutes a complete air circulation system, which has the advantages of simple and compact structural design, flexible size, wide application scenarios and low cost, and can also achieve rapid and sufficient purification of pollutants in the air.

[0004] The technical solution of the present invention is specifically described as follows.

[0005] The present invention provides a photocatalytic oxidation air purification device, which comprises at least one surface coated with anatase titanium dioxide, at least one ultraviolet radiation source, an air circulation loop and an air circulation drive module, wherein the air circulation drive module and the air circulation loop cooperate to form an air circulation system, and the surface coated with anatase titanium dioxide is placed in the air circulation system; when working, the ultraviolet radiation source irradiates the surface coated with anatase titanium dioxide, and the air to be purified forms an airflow in the air circulation system to carry out a photocatalytic degradation reaction to achieve purification.

[0006] In the present invention, the air circulation drive module uses a diaphragm pump or a fan to achieve air flow and circulation.

[0007] In the present invention, the air circulation driving module adopts a refrigeration / heating device to realize air flow and circulation.

[0008] The present invention further comprises an evaporator, which is located upstream or downstream of the surface coated with anatase titanium dioxide.

[0009] In the present invention, at least one surface coated with anatase type titanium dioxide is the inner cylindrical surface of the cylindrical tube.

[0010] The present invention further comprises a purification subsystem connected in series or in parallel to the air circulation loop, wherein at least one surface coated with anatase titanium dioxide is arranged in the purification subsystem.

[0011] The present invention also provides a photocatalytic oxidation air purification method for eliminating volatile organic compounds and other oxidizable substances in the air. The method is carried out using the above-mentioned device and specifically comprises: irradiating at least one surface coated with anatase titanium dioxide with at least one ultraviolet radiation source; The air to be purified passes through an air circulation loop to form an air flow, which is cyclically contacted with at least one surface coated with anatase-type titanium dioxide to undergo photocatalytic degradation, thereby achieving purification.

[0012] In the present invention, irradiating a surface coated with anatase titanium dioxide with a wavelength equal to or greater than its band gap (ultraviolet light) triggers a photocatalytic reaction. Absorbed photons cause electrons (e-) to be excited from the valence band to the conduction band. During the photoexcitation process, holes (h+) are generated in the valence band. These holes oxidize water molecules and produce *OH radicals, while superoxide anions (*O2-) are formed by the reaction between oxygen and electrons. The highly active free radicals generated on the surface of the photocatalyst can decompose pollutants into harmless compounds. Compared with the prior art, the beneficial effects of the present invention are: 1) In the present invention, an ultraviolet radiation source is used to irradiate the surface coated with anatase titanium dioxide, which can achieve full and accelerated decomposition of oxidizable pollutants in the air flowing through the surface under photocatalytic action. Anatase titanium dioxide has high stability, its crystal surface can provide more reactive active sites, and has a strong absorption capacity for ultraviolet light, thereby improving the photocatalytic efficiency; 2) In the present invention, the air to be purified is subjected to photocatalytic degradation by forming an airflow in an air circulation system, and the photocatalytic degradation efficiency is high; 3) The present invention further adopts a cooling / heating device to force air flow and integrates an evaporator to adjust the temperature and control the humidity. In an environment with appropriate humidity, the surface of titanium dioxide will absorb more water, which helps to produce active hydroxyl radicals (OH.) and superoxide anion radicals (O2-). These two free radicals are active substances with strong oxidizing ability, which can effectively mineralize and degrade environmental pollutants and inhibit bacteria and kill bacteria; 4) The entire device of the present invention constitutes a complete air circulation system, which has the advantages of simple and compact structural design, flexible size, wide application scenarios and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0014] Figure 1 The reactor designed and used in the experiments conducted contains a photocatalytic material consisting of electrolytic titanium oxide plates.

[0015] Figure 2 . Transmission spectra obtained for ethylene, spectroscopy grade quartz windows, and quartz body in the range 2000 cm⁻¹ to 4000 cm⁻¹.

[0016] Figure 3 . Time evolution of the relative concentration of the ethylene / nitrogen mixture in the reactor when no electrolytic titanium oxide plate is inserted.

[0017] Figure 4 . Absorption spectrum of ethylene / nitrogen mixture in air (40 cm) in a reactor without air circulation after inserting the electrolytic titanium oxide plate 3 ) changes over time.

[0018] Figure 5 . Relative concentration of ethylene / nitrogen mixture in air in the reactor (40 cm 3 ) changes over time, without air circulation.

[0019] Figure 6 . The photocatalytic reactor contains a surface coated with titanium dioxide inside (left) and an analytical reactor (right).

[0020] Figure 7 . Absorption spectrum of ethylene / nitrogen mixture in air (40 cm) in a reactor with air circulation after inserting the titanium dioxide-coated surface. 3 ) changes over time.

[0021] Figure 8 . Evolution of the concentration of ethylene oxide (in kg / m²) per unit area of ​​the titanium dioxide-coated surface in a reactor with air circulation during the photocatalytic process, by feeding 40 cm³ of an ethylene / nitrogen mixture into the reactor.

[0022] Fig. 9 . Schematic diagram of a configuration of a purification device, in which a surface coated with anatase titanium dioxide is located in a purification subsystem, connected in series in a circulation loop of an air flow to be purified.

[0023] Fig.10 . Schematic diagram of another possible configuration of a purification device, in which a surface covered with anatase titanium dioxide is located in a purification subsystem connected in parallel in a circulation loop including the air flow to be purified.

[0024] Fig.11 . Illustration of a cylindrical tube having an inner surface coated with anatase titanium dioxide and a source of ultraviolet radiation irradiating the anatase titanium dioxide coated surface. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0026] The embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0027] The photocatalytic oxidation air purification device 1 of the present invention comprises at least one surface 3 coated with anatase titanium dioxide. Anatase titanium dioxide can be formed by, for example, electrochemical, electrolytic or deposition followed by appropriate temperature treatment.

[0028] The surfaces 3 coated with anatase titanium dioxide are configured to be exposed to ultraviolet radiation generated by at least one ultraviolet radiation source 4, wherein the ultraviolet radiation source 4 is preferably of low energy consumption type, such as LED lamps or suitable fluorescent lamps. All surfaces 3 coated with anatase titanium dioxide are configured to be in contact with an air flow 5 to be purified.

[0029] The surface 3 coated with anatase titanium dioxide is designed according to the volume of air to be purified. The larger the volume of air to be purified, the larger the area of ​​the surface 3 coated with anatase titanium dioxide used, and the greater the air flow rate.

[0030] At least one surface 3 coated with anatase titanium dioxide is inserted into an air flow 5 to be purified and irradiated by at least one ultraviolet radiation source 4, resulting in the elimination of odor-causing volatile organic components by photocatalytic oxidation.

[0031] In one embodiment, the photocatalytic oxidation air purification device 1 includes an air circulation loop 6 and an air drive module. The air circulation drive module 6 and the air circulation loop cooperate to form an air circulation system. The surface 3 coated with anatase titanium dioxide is placed in the air circulation system, and the air to be purified that forms an airflow is purified in the air circulation system. The air circulation system can be a building and a vehicle air conditioning system. The air flow 5 to be purified passes through the air circulation loop and is purified in the photocatalytic indoor / outdoor circulation where the surface coated with anatase titanium dioxide is located.

[0032] In another embodiment, the photocatalytic oxidation air purification device 1 includes an air circulation loop 6 and an air drive module. The air drive module may include a fan, a diaphragm pump, etc.

[0033] In another embodiment, the photocatalytic oxidation air purification device 1 includes an air circulation loop 6 and an air drive module. The refrigeration / heating device 60 can force air to flow to form an airflow, and can act as an air circulation drive module. The surface 3 coated with anatase titanium dioxide of the photocatalytic oxidation air purification device 1 is inserted into the refrigeration / heating device 60. The refrigeration / heating device 60 can generate a temperature difference with other areas in the air circulation loop 6. When there is a temperature difference between the areas, the gas in the hotter area will become thinner due to thermal expansion and the density will decrease; while the gas in the colder area will be relatively dense and have a higher density. According to the principles of fluid mechanics, gas always flows from a high-pressure area to a low-pressure area. Therefore, under the action of the temperature difference, the gas will flow from the colder area to the hotter area to form an airflow.

[0034] In another embodiment, the refrigeration / heating device 60 includes an evaporator 40, and the surface 3 coated with anatase titanium dioxide is inserted upstream or downstream of the evaporator 40. The evaporator 40 can be used to further control the temperature and humidity so that the titanium dioxide surface absorbs more moisture, which helps to produce active hydroxyl radicals (OH.) and superoxide anion radicals (O2-) to effectively mineralize and degrade environmental pollutants and inhibit bacteria and sterilize. Preferably, the surface 3 coated with anatase titanium dioxide is inserted after the refrigeration stage because the air flow 5 to be purified will be more saturated and humid.

[0035] In another embodiment, the surface 3 of the photocatalytic oxidation air purification device 1 coated with anatase titanium dioxide is a part of the cooling / heating device 60 , such as the fins of the evaporator 40 .

[0036] In another embodiment, the surface 3 coated with anatase titanium dioxide of the photocatalytic oxidation air purification device 1 is placed in the air circulation loop 6 and exposed to the air flow 5 to be purified. The surface 3 coated with anatase titanium dioxide can be any surface newly added to the air circulation loop 6, and the surface is exposed to the ultraviolet radiation source 4.

[0037] In another embodiment, the photocatalytic oxidation air purification device 1 comprises a purification subsystem 7 connected in series with an air circulation loop 6, for an air flow 5 to be purified, at least one surface 3 coated with anatase titanium dioxide is arranged in the purification subsystem 7 (see Fig. 9 ).

[0038] In another embodiment, the photocatalytic oxidation air purification device 1 comprises a purification subsystem 7 connected in parallel with the air circulation loop 6, for the air flow 5 to be purified, and the surface 3 coated with anatase titanium dioxide is arranged in the purification subsystem 7 (see Fig.10 ).

[0039] In another embodiment, the photocatalytic oxidation air purification device 1 includes a cylindrical tube 8 or a tube of other shapes. In particular, in this implementation, the surface 3 coated with anatase titanium dioxide is the inner surface 81 of the cylindrical tube 8. The cylindrical tube 8 forms anatase titanium dioxide inside thereof by electrolysis or deposition, and the inside thereof is irradiated by at least one ultraviolet radiation source 4, which can be at least one lamp or at least one group of LEDs configured to emit ultraviolet rays, and the ultraviolet radiation source 4 is used to irradiate the surface 3 ( Fig.11 ). The cylindrical tubes 8 should be arranged in a staggered, inserted or integrated manner in the air flow 5 to be purified or in an existing air flow, for example in a ventilation or cooling / heating system of a car, truck or house, or in an air flow 5 to be purified created specifically for this purpose. In an environment with low humidity, it is preferably arranged after the refrigeration stage because the air flow will have a higher humidity. When the photocatalytic oxidation air purification device 1 is arranged in a staggered, inserted or integrated manner in the air flow 5 to be purified, anatase titanium dioxide is an active photocatalyst that, with the help of the moisture present in the air, can oxidize organic compounds present in the air, thereby eliminating them.

[0040] In one example, the material of the cylindrical tube 8 can be titanium metal, which is converted into an active form of TiO2, anatase, by electrochemical oxidation and treatment at an appropriate temperature, and TiO2 nanotubes with appropriate arrangement (larger active surface area) can be formed. The cylindrical tube 8 can also be a plastic material and coated with a photocatalytic coating available on the market.

[0041] Example 1

[0042] See also Figure 1 , an implementation example of the present invention. This embodiment is used to demonstrate two different configurations, and is intended to demonstrate by comparison the photocatalytic reaction generated by ultraviolet light irradiating the titanium dioxide surface and the influence of the air circulation system on the efficiency of the air purification device. The ultraviolet light source uses an ultraviolet lamp with a wavelength of 254nm. The first configuration provides the air to be purified to enter a photocatalytic chamber 12 without air circulation. The second configuration provides the air to be purified to enter a photocatalytic chamber 12 and an analysis chamber 17, and the air is circulated between the photocatalytic chamber 12 and the analysis chamber 17.

[0043] The photocatalytic chamber 12 includes a quartz body 16 having a first longitudinal end 18 and a second longitudinal end 19, a first window 20 made of quartz connected to the first longitudinal end 18, and a second window 21 made of quartz connected to the second longitudinal end 19, thereby forming a photocatalytic cavity 13 of the photocatalytic chamber 12. In addition, the photocatalytic chamber 12 includes a first conduit 28 communicating with the photocatalytic cavity 13 and a second conduit 29 communicating with the photocatalytic cavity 13.

[0044] See also Figure 6 The analysis chamber 17 comprises a glass body 22 having a first transverse end 23 and a second transverse end 24. A fluorite window 25 is connected to the first transverse end 23, and another fluorite window 26 is connected to the second transverse end 24, thereby forming the chamber 14 of the analysis chamber 17. In addition, the analysis chamber 17 comprises a third conduit 30 connected to the chamber 14 of the analysis chamber 17 and a fourth conduit 31 connected to the chamber 14 of the analysis chamber 17, which facilitates the entry and exit of the gas mixture for analysis, the mixture coming from the photocatalytic chamber 12.

[0045] The dimensions of the photocatalytic chamber 12 are 4 cm in inner diameter and 10 cm in length, and the photocatalytic cavity 13 of this photocatalytic chamber 12 is used as a reactor to study the photocatalytic ability of titanium dioxide anatase-type surfaces covered, which are applied to different supports and different oxidizable compounds, such as volatile organic nitrogen oxides (e.g. ethylene), demonstrating that they can be eliminated or converted into ionic nitrates, and in the case of organic matter into carbon dioxide and water.

[0046] The total volume of the photocatalytic cavity 13 of the photocatalytic chamber 12 is approximately 132 cubic centimeters. Figure 1 The designed photocatalytic chamber 12 is shown, which contains a titanium dioxide sheet 15 as the photocatalytic material.

[0047] In order to determine the measurement area of ​​possible pollutant concentration, it is necessary to perform and obtain an infrared spectrum (IR) of the photocatalytic chamber 12 and the pollutant to be investigated. For example, the transmission spectrum of the photocatalytic chamber 12 cavity and ethylene is shown below, see Figure 2 In order to conduct dynamic experiments, the infrared spectrum (IR) of the analysis chamber 17 was obtained in the same way as the photocatalytic chamber 12, as shown in Figure 2 For this purpose, an infrared radiation source 50 is used which illuminates the analysis chamber 17.

[0048] Analysis of the graph shows that the quartz photocatalytic chamber 12 is transparent in the region of 3300 cm⁻¹ to 2700 cm⁻¹, which is the region where ethylene exhibits absorption bands and can therefore be visualized. Since quartz is transparent to UV radiation, the photocatalytic chamber 12 itself can be used to perform exposure experiments on photocatalytic materials. The gas used in the experiment was a mixture of ethylene and nitrogen with a volume fraction of 5%.

[0049] To measure the concentration of ethylene, the Lambert-Beer law will be used, A = ε·b·c. Where A is the absorbance, ε is the molar absorptivity of the compound, b is the length of the photocatalytic chamber, and c is the concentration. For the same compound and photocatalytic chamber, the absorbance is proportional to the concentration: A = constant·c.

[0050] If we measure the change in absorbance A over time during the catalytic oxidation process and divide it by the absorbance A0 at the beginning of the analysis, we can obtain a measurement of the relative concentration c / c0 and determine the reaction rate from this. A / A0 = c / c0. Next, a series of experiments were conducted to determine the optimal conditions and time of use. In order to verify the sealing of the photocatalytic chamber 12, it was completely filled with an ethylene / nitrogen mixture and then the change in absorbance of ethylene over time was measured to obtain its time change, see Figure 3 It can be observed that the relative concentration c / c0 does not change, since the time evolution is almost unchanged. Next, the analysis is performed in static mode (without air circulation) and in dynamic mode (with air circulation).

[0051] To verify that the process is running in a static manner, a titanium dioxide sheet 15 is placed in the photocatalytic chamber 12. Then 40 cm³ of a 5% ethylene / nitrogen mixture is injected into the photocatalytic chamber 12 via a syringe, and then the photocatalytic chamber 12 is irradiated with ultraviolet light using a continuous radiation ultraviolet light source 4 during the analysis. The absorbance spectrum corresponding to ethylene in the range of 3300 to 2700 cm⁻¹ mentioned above is then measured, and the change over time is shown in Figure 4 and its time variations, see Figure 5 It can be seen that the relative absorbance changes, but the decrease is small.

[0052] In order to improve the efficiency of photo-oxidation, in the second configuration, a dual-chamber system is used, namely, a photocatalytic chamber 12 as a photocatalytic reactor and another analytical chamber 17, and the gas is pushed from one chamber to the other chamber by a diaphragm pump 27 at a flow rate of 10 L / min.

[0053] The second conduit 29 of the photocatalytic chamber 12 is connected to the fourth conduit 31 of the analysis chamber 17 via a first conduit 34 including a valve 33. The third conduit 30 of the analysis chamber 17 is connected to the diaphragm pump 27 via a second conduit 35 including a valve 33. The diaphragm pump 27 is connected to the first conduit 28 of the photocatalytic chamber 12 via a third conduit 36, thereby closing the air circuit.

[0054] The chemical equation for the oxidation reaction is:

[0055] In order for the reaction to proceed completely, the amount of oxygen in the photocatalytic chamber 12 should be at least three times the amount of ethylene, both in terms of moles and volume. Considering that the gases are considered ideal gases under the environmental conditions used (ambient pressure and temperature). In order to verify whether there is enough oxygen to oxidize the injected ethylene under the conditions used, a preliminary calculation was performed, using standard conditions (25°C and 1 atm), which proved that these conditions are applicable. Oxygen content = (photocatalytic chamber volume - injected ethylene volume) × oxygen concentration = (132 - 40) × 21% = 19.3 cm³, ethylene content = injected ethylene volume × ethylene concentration = 40 × 5% = 2 cm³.

[0056] To verify whether the process runs better in dynamic mode, a titanium dioxide sheet 15 is placed in the photocatalytic chamber 12, and then 40 cm³ of ethylene / nitrogen mixture is injected into the photocatalytic chamber 12 through a syringe, and the photocatalytic chamber 12 is irradiated with ultraviolet light during the analysis. The mixed gas is circulated at a flow rate of 10 L / min using a diaphragm pump 27 to transport the mixture to the analysis chamber 17 (i.e., the analysis chamber 17 for measuring infrared spectra), see Figure 6 , and measure the absorbance spectrum of the ethylene / nitrogen mixture over time, see Figure 7 , measure the change of ethylene concentration over time, see Figure 8 .

[0057] from Figure 7-Figure 8 As can be seen in the figure, the concentration of ethylene gradually decreases over time, which indicates that under the action of the photocatalyst, the ethylene molecules are degraded by oxidation. This degradation is initially fast, but gradually slows down over time. Figure 8 The data adjustment can be approximated by the following equation: , the regression coefficient is very close to 1 (R² =0.9985), indicating a good fit.

[0058] It should be noted that, in this application, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0059] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A photocatalytic oxidation air purification device, characterized in that: It includes at least one surface coated with anatase titanium dioxide, at least one ultraviolet radiation source, an air circulation loop and an air circulation drive module. The air circulation drive module and the air circulation loop cooperate to form an air circulation system. The surface coated with anatase titanium dioxide is placed in the air circulation system. When working, the ultraviolet radiation source irradiates the surface coated with anatase titanium dioxide, and the air to be purified forms an airflow in the air circulation system to carry out photocatalytic degradation reaction to achieve purification.

2. The photocatalytic oxidation air purification device according to claim 1, characterized in that: The air circulation driving module adopts a diaphragm pump or a fan.

3. The photocatalytic oxidation air purification device according to claim 1, characterized in that: The air circulation drive module adopts a cooling / heating device.

4. The photocatalytic oxidation air purification device according to claim 3, characterized in that: Also included is an evaporator, which is located upstream or downstream of the surface coated with anatase titanium dioxide.

5. The photocatalytic oxidation air purification device according to claim 1, characterized in that: The at least one surface coated with anatase titanium dioxide is the inner cylindrical surface of the cylindrical tube.

6. The photocatalytic oxidation air purification device according to claim 1, characterized in that: Also included is a purification subsystem connected in series or in parallel to the air circulation loop, wherein at least one surface coated with anatase titanium dioxide is disposed within the purification subsystem.

7. A photocatalytic oxidation air purification method, characterized in that: For eliminating volatile organic compounds and other oxidizable substances in the air, the method is carried out using a device as described in any one of claims 1 to 6, specifically comprising: irradiating at least one surface coated with anatase titanium dioxide with at least one ultraviolet radiation source; The air to be purified passes through an air circulation loop to form an air flow, which is cyclically contacted with at least one surface coated with anatase-type titanium dioxide to undergo photocatalytic degradation, thereby achieving purification.

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