An experimental device and method for simulating the preparation of nitric acid by photochemical reaction of early atmosphere of the earth

Abstract

The application discloses an experimental device and method for preparing nitric acid by simulating early atmospheric photochemical reaction on the earth, wherein the experimental device comprises a UV photochemical reaction system, a reaction gas source feeding system, a water vapor generator and a nitric acid freezing collector; the UV photochemical reaction system comprises a UV light source and a reaction chamber, the UV light source is arranged outside an MgF2 glass window and provides the required UV light for the reaction chamber; the reaction gas source feeding system is communicated with the reaction chamber and is used for feeding the required gas for generating nitric acid by UV photochemical reaction into the reaction chamber; the water vapor generator is used for providing water vapor for the reaction chamber; the water vapor generator is provided with a water vapor outlet, and the water vapor outlet of the water vapor generator is connected with a water vapor inlet of the reaction chamber; and the nitric acid freezing collector is connected with a product outlet of the reaction chamber and is used for collecting the nitric acid generated by photochemical reaction in the reaction chamber. The application realizes the process of preparing nitric acid by simulating early atmospheric photochemical reaction on the earth.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of earth science research, and particularly relates to an experimental device and method for preparing nitric acid by simulating early atmospheric photochemical reactions on earth. BACKGROUND

[0002] It is currently believed that the oxygen concentration of the early atmosphere on earth is less than one hundred thousandth of the oxygen level of the modern atmosphere. The increase in atmospheric oxygen concentration is a prerequisite for the birth of life on earth and the formation of a habitable earth. The oxidizing components such as H2O2 and O2 generated by the photolysis of H2O, CO2 and other oxygen-containing gas components in the atmosphere may be an important source of oxygen in the pre-biological atmosphere and ocean on the early earth, but there is a lack of direct geological evidence. Atmospheric origin nitrate is the mineral with the largest oxygen isotope non-mass fractionation (Δ 17 O) on earth, and is a sensitive and effective indicator for tracing atmospheric photochemical processes. Nitrate generated by photochemical reactions in the modern oxygen-rich atmosphere is widely present, but it is unclear whether similar ultraviolet photochemical reactions exist in the early oxygen-poor atmosphere on earth and whether the generated nitrate has oxygen isotope non-mass fractionation.

[0003] However, the experimental device and method in the prior art cannot simulate the process of generating nitrate by photochemical reactions in the early oxygen-free / poor oxygen atmosphere environment on earth, and therefore there is an urgent need to provide an experimental device and method for preparing nitric acid by simulating early atmospheric photochemical reactions on earth. SUMMARY

[0004] In view of the above analysis, the embodiments of the present application aim to provide an experimental device and method for preparing nitric acid by simulating early atmospheric photochemical reactions on earth, which realizes the process of generating nitrate by photochemical reactions in the early oxygen-free / poor oxygen atmosphere environment on earth.

[0005] The purpose of the present application is achieved as follows:

[0006] On the one hand, an experimental device for preparing nitric acid by simulating early atmospheric photochemical reactions on earth is provided, comprising:

[0007] An ultraviolet photochemical reaction system, comprising an ultraviolet light source and a reaction chamber, the reaction chamber having an ultraviolet light inlet, a reaction gas inlet, a water vapor inlet and a product outlet; a MgF2 glass window that transmits ultraviolet light is sealingly installed at the ultraviolet light inlet, and the ultraviolet light source is arranged outside the MgF2 glass window to provide the required ultraviolet light for the reaction in the reaction chamber through the MgF2 glass window;

[0008] A reaction gas source supply system in communication with the reaction gas inlet for supplying the required gas for generating nitric acid by ultraviolet photochemical reactions into the reaction chamber to simulate the composition of the early atmosphere on earth;

[0009] A water vapor generator is used to provide water vapor to the reaction chamber to simulate the humidity of the early atmosphere of the earth; the water vapor generator has a water vapor outlet, and the water vapor outlet of the water vapor generator is connected with the water vapor inlet;

[0010] A nitric acid freezing collector is connected with the product outlet and used to collect the nitric acid produced by the photochemical reaction in the reaction chamber.

[0011] Further, the reaction gas supply system comprises a gas supply pipeline, the outlet end of the gas supply pipeline is connected with the reaction gas inlet, and the inlet end of the gas supply pipeline is provided with a first gas supply device, a second gas supply device and a third gas supply device; wherein the first gas supply device is used to supply a mixed gas of NO x and N2 to the reaction chamber; the second gas supply device is used to supply CO2 to the reaction chamber; and the third gas supply device is used to supply pure O2 or a mixed gas of O2 and He to the reaction chamber.

[0012] Further, the gas supply pipeline comprises a main gas pipeline, a first branch gas pipeline, a second branch gas pipeline and a third branch gas pipeline; one end of the main gas pipeline is connected with the reaction gas inlet, and the other end of the main gas pipeline is connected with the first branch gas pipeline, the second branch gas pipeline and the third branch gas pipeline through a four-way joint; the first gas supply device has an independent N2 gas cylinder and an NO x gas cylinder; the second gas supply device has a CO2 gas cylinder; the third gas supply device has an independent O2 gas cylinder and a He gas cylinder; and the main gas pipeline, the first branch gas pipeline, the second branch gas pipeline and the third branch gas pipeline are all provided with a gas flow controller.

[0013] Further, the reaction chamber adopts a stainless steel barrel with one end open and the other end closed, the open end of the stainless steel barrel is used as the ultraviolet light inlet, the axial length of the stainless steel barrel is 20 cm, and the inner diameter of the stainless steel barrel is 2.5 cm;

[0014] Preferably, the axis of the stainless steel barrel is arranged horizontally, the ultraviolet light inlet and the product outlet are arranged at the two axial ends of the stainless steel barrel, and the reaction gas inlet and the water vapor inlet are arranged on the side wall of the stainless steel barrel.

[0015] Further, the water vapor generator comprises a water tank and a helium source, the water tank contains ultrapure water, the water vapor outlet is arranged at the top of the water tank, the bottom of the water tank is provided with a helium inlet, the helium inlet is connected with the helium source through a helium path, and the water vapor outlet is connected with the water vapor inlet through a water vapor path;

[0016] Preferably, the water vapor path and the helium path both adopt quartz capillary tubes, the water vapor path has a first diameter, the helium path has a second diameter, and the first diameter is 3-5 times of the second diameter.

[0017] Preferably, the first diameter is 1 / 8 mm and the second diameter is 1 / 32 mm.

[0018] Further, the reaction chamber is provided with a first heating device configured to control the temperature in the reaction chamber at 65±0.5℃; and the water tank is externally provided with a second heating device configured to maintain the ultrapure water in the water tank at 25-65℃.

[0019] Further, the nitric acid freezing collector comprises a cold source container and a collecting tube, the top of the cold source container is open, the cold source container is filled with a freezing liquid at -50±5℃, the top of the collecting tube is provided with a product feeding tube extending to the bottom of the collecting tube, and the upper sidewall of the collecting tube is provided with a product outlet tube; the product outlet is connected with the product feeding tube through a stainless steel tube.

[0020] Preferably, the top of the product feeding tube extends upwardly to form a reduced diameter section, and the inner diameter of the reduced diameter section is smaller than that of the product feeding tube.

[0021] Preferably, the distance between the bottom of the collecting tube and the bottom of the cold source container is 2-4 cm, and the bottom opening of the product feeding tube is located 4 cm above the liquid level of the freezing liquid.

[0022] Preferably, the collecting tube and the cold source container are both quartz glass tubes; the inner diameter of the cold source container is 3 cm; the outer diameter of the collecting tube is 18 mm and the inner diameter is 15 mm; the outer diameter of the product feeding tube is 12 mm and the inner diameter is 9 mm; the outer diameter of the reduced diameter section is 6.4 mm; and the outer diameter of the product outlet tube is 6.4 mm.

[0023] In another aspect, a method for preparing nitric acid by simulating the photochemical reaction of the early atmosphere of the earth is also provided, which uses the experimental device for preparing nitric acid by simulating the photochemical reaction of the early atmosphere of the earth described above; and the method comprises the following steps:

[0024] According to the data of the components of the early atmosphere of the earth, the reaction gas source feeding system is used to feed the gas components required for the reaction into the reaction chamber, and the water vapor generator is used to feed water vapor into the reaction chamber; after the flow rates of the various gases are stabilized, the ultraviolet light source is turned on, and the collecting tube of the nitric acid freezing collector is placed in the freezing liquid in the cold source container to freeze the HNO3 generated in the reaction.

[0025] Further, when the reaction gas source feeding system is used to feed the gas components required for the reaction into the reaction chamber, the first gas feeding device feeds NO xThe first gas supply device supplies N2 and H2O to the reaction chamber at a flow rate of 100 mL / min; the second gas supply device supplies CO2 to the reaction chamber at a predetermined concentration and flow rate, and the flow rate is 0.5 mL / min; the third gas supply device supplies pure O2 or a mixture of O2 and He to the reaction chamber at a predetermined concentration and flow rate; wherein the flow rate of pure O2 or the mixture of O2 and He is set according to the concentration of oxygen in the reaction chamber.

[0026] When the water vapor generator is used to supply water vapor into the reaction chamber, the flow rate of helium is 2.2 mL / min.

[0027] Further, the method further comprises a system impurity removal pretreatment step:

[0028] Before formally starting the reaction, the reaction chamber is continuously purged with high-purity N2, and high-purity He is supplied into the ultrapure water in the water tank to remove impurities and dissolved trace O2 in the ultrapure water.

[0029] Compared with the prior art, the present application can at least achieve one of the following beneficial effects:

[0030] A) The experimental device for preparing nitric acid by simulating the photochemical reaction of the early atmosphere of the earth provided by the present application has a simple structure and is easy to operate, and the experimental process does not require complex manual operation, thereby improving the experimental efficiency; and the nitric acid generated in the experiment can be efficiently recovered through the nitric acid freezing collector, and the experiment does not generate toxic gas and does not pollute the environment, thereby being green and environmentally friendly.

[0031] B) The method for preparing nitric acid by simulating the photochemical reaction of the early atmosphere of the earth provided by the present application uses ultraviolet light to irradiate the early atmosphere containing N2, H2O, CO2, trace O2, NO x , thereby realizing the process of simulating the photochemical reaction of the early atmosphere of the earth, generating nitric acid HNO3 with a significant oxygen isotope non-mass fractionation effect, and proving that the photochemical reaction in the early anoxic atmosphere of the earth can generate nitric acid, and the oxygen isotope non-mass fractionation of the generated nitric acid is closely related to the oxygen concentration, thereby using the nitrate tri-oxygen isotope non-mass fractionation effect in the early sedimentary formation (such as Proterozoic tillite and other sediments) to trace the oxygen source in the early atmosphere of the earth, providing important experimental basis for the oxygen concentration increasing event in the early Proterozoic atmosphere of the earth, and having important significance for the related research on the climate change in the early earth.

[0032] In the present application, the above technical solutions can be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present application will be described in the subsequent specification, and some advantages will become apparent from the specification or be understood by implementing the present application. The purposes and other advantages of the present application can be achieved and obtained from the specific indications in the specification and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the embodiments of this specification. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0034] Figure 1 A schematic diagram of the structure of an experimental device for producing nitric acid by simulating photochemical reactions in the early Earth atmosphere provided by the present invention;

[0035] Figure 2 A schematic structural diagram of the ultraviolet light photochemical reaction system provided by the present invention;

[0036] Figure 3 A schematic diagram of the cross-sectional structure of the ultraviolet photochemical reaction system provided by the present invention;

[0037] Figure 4 A schematic structural diagram of the reaction gas source supply system provided by the present invention;

[0038] Figure 5 A schematic structural diagram of the water vapor generator provided by the present invention;

[0039] Figure 6 A schematic structural diagram of a nitric acid freezing collector provided by the present invention;

[0040] Figure 7 This is a spectrum diagram of the L11798 ultraviolet light source provided by the present invention.

[0041] Reference numerals:

[0042] 1. UV photochemical reaction system; 11. UV light source; 12. Reaction chamber; 121. Reaction gas inlet; 122. Water vapor inlet; 123. Product outlet; 124. MgF2 glass window; 13. Sealing flange;

[0043] 2. Reaction gas supply system; 21. First gas supply device; 22. Second gas supply device; 23. Third gas supply device; 24. Main gas pipe; 25. First branch gas pipe; 251. First gas flow controller; 26. Second branch gas pipe; 261. Second gas flow controller; 27. Third branch gas pipe; 271. Third gas flow controller; 28. Cross-connection;

[0044] 3. Water vapor generator; 31. Water tank; 32. Helium source; 33. Helium gas line; 331. Fourth gas flow controller; 34. Water vapor line;

[0045] 4, Nitric acid refrigeration collector; 41, Cold source container; 42, Collection tube; 421, Product supply tube; 422, Product discharge tube; 423, Reduced diameter section. DETAILED DESCRIPTION

[0046] To make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort are within the protection scope of the present application.

[0047] To make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort are within the protection scope of the present application.

[0048] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to be limiting. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Further, to the extent that the terms "including," "includes," "having," "has," "with," or variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term "comprising." Also, it is to be noted that the term "about" and / or "substantially" as used herein are used as approximating language and not as an exact term, and as such, they are used to explain that a value, calculation, and / or provided value is not exact, but is close to an exact value, as would be recognized by a person of ordinary skill in the art.

[0049] Example 1

[0050] One specific embodiment of the present application, as shown in FIG. 1, discloses an experimental device for simulating the photochemical reaction of early atmosphere of the earth to prepare nitric acid, comprising: Figures 1 to 6

[0051] ​The ultraviolet photochemical reaction system 1 comprises an ultraviolet light source 11 and a reaction chamber 12, the reaction chamber 12 is a place for generating nitric acid by ultraviolet photochemical reaction, the reaction chamber 12 has an ultraviolet light inlet, a reaction gas inlet 121, a water vapor inlet 122 and a product outlet 123; a MgF2 glass window 124 which is transparent to ultraviolet light is sealingly installed at the ultraviolet light inlet, the ultraviolet light source 11 is arranged outside the MgF2 glass window 124, and the ultraviolet light source 11 provides the ultraviolet light required by the reaction into the reaction chamber 12 through the MgF2 glass window 124;

[0052] The reaction gas source supply system 2 is used for supplying the gas required by the ultraviolet photochemical reaction for generating nitric acid into the reaction chamber 12 to simulate the composition of the early atmosphere of the earth; the reaction gas source supply system 2 comprises a gas supply pipeline, the outlet end of the gas supply pipeline is connected to the reaction gas inlet 121 of the reaction chamber 12, and the inlet end of the gas supply pipeline is provided with a first gas supply device 21, a second gas supply device 22 and a third gas supply device 23; the first gas supply device 21 is used for supplying the mixed gas of NO x and N2 into the reaction chamber 12, wherein the mixed gas of NO x is a mixed gas of NO+NO2; the second gas supply device 22 is used for supplying CO2 into the reaction chamber 12; and the third gas supply device 23 is used for supplying pure O2 or the mixed gas of O2 and He into the reaction chamber 12.

[0053] The water vapor generator 3 is used for supplying water vapor into the reaction chamber 12 to simulate the humidity of the early atmosphere of the earth; the water vapor generator 3 has a water vapor outlet, and the water vapor outlet of the water vapor generator 3 is connected to the water vapor inlet 122 of the reaction chamber 12.

[0054] The nitric acid refrigeration collector 4 is connected to the product outlet 123 of the reaction chamber 12 and is used for collecting the nitric acid generated by the photochemical reaction in the reaction chamber 12.

[0055] In an optional embodiment, the reaction chamber 12 adopts a stainless steel barrel which is open at one end and closed at the other end, and the internal space of the stainless steel barrel is used as a place for generating nitric acid by ultraviolet photochemical reaction. Specifically, the axial length of the stainless steel barrel is 20 cm, and the inner diameter of the stainless steel barrel is 2.5 cm; the stainless steel barrel is fixed horizontally on a horizontal operation table, that is, the axis of the stainless steel barrel is arranged horizontally, the ultraviolet light inlet and the product outlet 123 are arranged at the axial two ends of the stainless steel barrel, and the reaction gas inlet 121 and the water vapor inlet 122 are arranged on the side wall of the stainless steel barrel.

[0056] Optionally, the reaction gas inlet 121 and the water vapor inlet 122 are arranged at an angle of 90° and closer to the side wall of the stainless steel barrel on the side of the ultraviolet light inlet. In this way, the reaction gas source and the water vapor supplied into the reaction chamber 12 can be mixed more fully, and the mixed gas can be in contact with the ultraviolet light for a longer time in the reaction chamber 12, so that the reaction is more sufficient.

[0057] In order to further fully react, one end of the stainless steel barrel is opened as a UV light inlet, the diameter of the UV light inlet is 2.5 cm, the other end of the stainless steel barrel has a barrel end wall, and the product outlet 123 is arranged on the barrel end wall. Optionally, the MgF2 glass window 124 is installed on the UV light inlet of the stainless steel barrel through a sealing flange 13, and the UV light source 11 is connected with the sealing flange 13. The UV light source 11 is fixedly installed between the UV light inlet and the UV light source 11 through the MgF2 glass window 124, and the UV light emitted by the UV light source 11 is irradiated into the reaction chamber 12 through the MgF2 glass window 124, so that the UV light source can irradiate in the reaction chamber 12 without dead angle. The connection between the UV light source 11 and the reaction chamber 12 is sealed by a Teflon gasket, and a nut is manually tightened to fix it.

[0058] Further, the reaction chamber 12 is provided with a first heating device configured to control the temperature of the reaction chamber 12 at 65±0.5℃. Illustratively, the first heating device includes a first resistance wire, and the outside of the stainless steel barrel is wrapped with the resistance wire. During the reaction process, the heating temperature of the first resistance wire is controlled by adjusting the voltage to control the temperature of the reaction chamber 12 at 65±0.5℃, so as to prevent the generated nitric acid from being adsorbed on the inner wall of the stainless steel barrel under low temperature conditions.

[0059] In this embodiment, the gas supply pipeline of the reaction gas source supply system 2 includes a main gas pipe 24, a first branch gas pipe 25, a second branch gas pipe 26 and a third branch gas pipe 27. One end of the main gas pipe 24 is connected with the reaction gas inlet 121 of the reaction chamber 12, and the other end of the main gas pipe 24 is connected with the first branch gas pipe 25, the second branch gas pipe 26 and the third branch gas pipe 27 through a four-way pipe 28. x The N2 gas cylinder and the NO x gas cylinder of the first gas supply device 21 supply N2 and NO+NO2 mixed gas respectively; the second gas supply device 22 has a CO2 gas cylinder; the third gas supply device 23 has an O2 gas cylinder and a He gas cylinder which supply O2 and He respectively; the main gas pipe 24, the first branch gas pipe 25, the second branch gas pipe 26 and the third branch gas pipe 27 are all provided with a gas flow controller.

[0060] In one optional embodiment, the main gas pipe 24 of the reaction gas source supply system 2 is connected with the first gas supply device 21, the second gas supply device 22 and the third gas supply device 23 through a four-way pipe 28 interface and three branch pipes, and the main gas pipe 24, the first branch gas pipe 25, the second branch gas pipe 26 and the third branch gas pipe 27 all adopt quartz capillary tubes with a diameter of 1 / 8 mm. The N2 gas cylinder and the NO xThe gas cylinder, the CO2 gas cylinder of the second gas supply device 22, the O2 gas cylinder of the third gas supply device 23 and the He gas cylinder can also be provided with a gas flow controller respectively, Figure 4 Only the first gas flow controller 251, the second gas flow controller 261 and the third gas flow controller 271 provided on the three branch pipes are shown in the figure. The gas flow controllers at different positions are used to precisely adjust the flow of different reaction gases, so as to simulate the composition of the early atmosphere of the earth.

[0061] In this embodiment, the water vapor generator 3 uses high-purity helium as a carrier gas to deliver water vapor into the reaction chamber 12. Specifically, the water vapor generator 3 includes a water tank 31 and a helium source 32. The water tank 31 contains ultrapure water, and the ultrapure water does not fill the water tank 31, that is, the volume of the ultrapure water in the water tank 31 accounts for 1 / 2-3 / 4 of the volume of the water tank 31. The water vapor outlet is arranged at the top of the water tank 31, and the water vapor outlet is connected with the water vapor inlet 122 of the reaction chamber 12 through a water vapor path 34. The bottom of the water tank 31 is provided with a helium gas inlet, and the helium gas inlet is connected with the helium source 32 through a helium gas path 33. The helium source 32 supplies helium into the water tank 31 through the helium gas path 33, and the helium flow is used to carry the water vapor into the reaction chamber 12 through the water vapor path 34. Among them, the helium gas path 33 is also provided with a gas flow controller, which is the fourth gas flow controller 331 in Figure 5 , to precisely control the flow of helium. Of course, it can be understood that a gas flow controller can also be arranged on the water vapor path 34.

[0062] In order to prevent the nitric acid generated in the reaction chamber 12 from flowing back to the water tank 31, the water vapor path 34 has a first diameter and the helium gas path 33 has a second diameter, and the first diameter is greater than the second diameter, and the first diameter is 3-5 times the second diameter. For example, the water vapor path 34 and the helium gas path 33 are both quartz capillary tubes, and the first diameter of the water vapor path 34 is 4 times the second diameter of the helium gas path 33. Specifically, the water vapor inlet 122 of the reaction chamber 12 is connected to the water tank 31 through a quartz capillary tube with a diameter of 1 / 8 mm, and the helium source 32 is connected to the water tank 31 through a quartz capillary tube with a diameter of 1 / 32 mm. The helium source 32 supplies helium into the water tank 31 through a quartz capillary tube with a smaller diameter, and the water vapor is brought into the reaction chamber 12 through a quartz capillary tube with a larger diameter, which can effectively prevent the nitric acid generated in the reaction chamber 12 from flowing back to the water tank 31. Further, the water tank 31 is provided with a second heating device configured to maintain the ultrapure water in the water tank 31 at 25-65℃. Optionally, the second heating device includes a second resistance wire which can be wound around the water tank 31, and the heating temperature of the second resistance wire is controlled by adjusting the heating voltage to control the temperature in the water tank 31 to be between 25℃ and 65℃, and the humidity of the simulated early Earth atmosphere is controlled by adjusting the He gas flow rate and the heating temperature of the water tank 31.

[0063] In one optional embodiment, the nitric acid freezing collector 4 includes a cold source container 41 and a collection tube 42, the top of the cold source container 41 is open, the cold source container 41 contains a freezing liquid, the top of the collection tube 42 is provided with a product supply tube 421 extending to the bottom of the collection tube 42, the upper side wall of the collection tube 42 is provided with a product discharge tube 422 as an outlet for reaction products; the product outlet 123 of the reaction chamber 12 is connected to the collection tube 42 of the nitric acid freezing collector 4 through a stainless steel tube with an outer diameter of 3 mm and an inner diameter of 2 mm. Optionally, the top wall and the bottom wall of the collection tube 42 are both concave arc surfaces, the product supply tube 421 passes through the top wall and the outer wall of the product supply tube 421 is sealingly connected to the top wall; the top of the product supply tube 421 extends upwardly and is provided with a reduced diameter section 423, the inner diameter of the reduced diameter section 423 is smaller than the inner diameter of the main body of the product supply tube 421; the tube opening of the reduced diameter section 423 is connected to the product outlet 123 of the reaction chamber 12 through a stainless steel tube with an outer diameter of 3 mm and an inner diameter of 2 mm; the bottom opening of the product supply tube 421 serves as an inlet for the product to enter the collection tube 42, and the bottom opening of the product supply tube 421 is located below the product discharge tube 422 and above the liquid level of the freezing liquid.

[0064] In the freezing collection of the nitric acid generated in the reaction, the lower part of the collection tube 42 is placed in the refrigerant in the cold source container 41, and the bottom opening of the product supply tube 421 is located above the liquid level of the refrigerant, without directly contacting the low-temperature refrigerant. Moreover, since the top of the product supply tube 421 is provided with a reduced section 423 with a smaller diameter, the nitric acid and water vapor in the mixed gas after the reaction are not easily frozen into ice at the reduced section, but are more conducive to being condensed into liquid at the reduced section. The condensed liquid drops to the bottom of the collection tube 42 or flows along the wall of the collection tube 42 to the bottom of the collection tube 42, and then is frozen into solid by the low-temperature refrigerant. Therefore, the collection tube 42 with such a structure will not be blocked by ice.

[0065] In an alternative embodiment, the cooling temperature of the refrigerant in the cold source container 41 is -50±5°C. For example, the refrigerant can be prepared from liquid nitrogen and alcohol, and the nitric acid generated in the chemical reaction is collected by using the refrigerant at -50±5°C.

[0066] In order to prevent the quartz collection tube 42 from being frozen when collecting nitric acid, the distance between the bottom of the collection tube 42 and the bottom of the cold source container 41 is not less than 2 cm, preferably 2-4 cm, and the bottom opening of the product supply tube 421 is located 4 cm above the liquid level of the refrigerant. Alternatively, the bottom of the collection tube 42 is located 2-3 cm below the liquid level of the refrigerant.

[0067] In an alternative embodiment, the cold source container 41 and the collection tube 42 of the nitric acid freezing collector 4 are both quartz glass tubes. For example, the inner diameter of the cold source container 41 is 3 cm, and the height is 20 cm; the outer diameter of the collection tube 42 is 18 mm, and the inner diameter is 15 mm; the outer diameter of the product supply tube 421 is 12 mm, and the inner diameter is 9 mm; and the outer diameter of the product discharge tube 422 is 6.4 mm.

[0068] In an alternative embodiment, the outer diameter of the reduced section 423 at the top of the product supply tube 421 is 6.4 mm, and the product supply tube 421 is sealingly connected with the stainless steel tube by using a manual quick connector with an inner diameter of 6.4 mm. Specifically, one end of the manual quick connector is sealingly connected with the reduced section 423 at the top of the product supply tube 421 through an O-shaped rubber sealing ring, and the other end of the manual quick connector is sealingly connected with the stainless steel tube by using a circular rubber pad, and the stainless steel tube is directly connected with the rubber pad for sealing connection.

[0069] The embodiment also provides a method for preparing nitric acid by simulating the photochemical reaction of the early atmosphere of the earth, which uses the experimental device described above in the embodiment and comprises the following steps:

[0070] Step 1: System impurity removal pretreatment, using high-purity N2gas to continuously purge the reaction chamber 12 and supplying high-purity He gas to the ultrapure water (MQ water) in the water tank 31 to remove impurity pollution that may exist in the reaction chamber 12 and dissolved trace O2 in the ultrapure water.

[0071] Before formally starting the reaction, the N2gas cylinder of the first gas supply device 21 is independently supplied with gas, high-purity N2gas is continuously purged for more than 24 hours to remove possible impurity gas pollution; at the same time, the helium source 32 of the water vapor generator 3 continuously supplies high-purity He gas to the MQ water in the water tank 31 to remove possible dissolved O2 in the MQ water, preventing trace O2 and other impurity gases from participating in the reaction during the formal experiment and adversely affecting the experimental results. In this step, the nitric acid freezing collector 4 does not perform freezing enrichment, that is, the collection tube 42 of the nitric acid freezing collector 4 is not placed in the refrigerant in the refrigerant container 41.

[0072] Step 2: After completing the system impurity removal pretreatment, according to the data of the early Earth atmosphere composition, the reaction gas source is used to supply the required gas components to the reaction chamber 12, and the water vapor generator 3 is used to supply water vapor to the reaction chamber 12; after the flow rates of the various gases are stabilized, the ultraviolet light source 11 is turned on, and the collection tube 42 of the nitric acid freezing collector 4 is placed in the refrigerant in the refrigerant container 41 to freeze collect the generated HNO3.

[0073] Specifically, the first gas supply device 21 supplies a mixture of NO x and N2 to the reaction chamber 12 at a predetermined concentration and flow rate, and the flow rate is kept constant at 100 mL / min; the concentration of NO x in the mixture of NO x and N2 supplied to the reaction chamber 12 is 5 ppm; the second gas supply device 22 supplies CO2 to the reaction chamber 12 at a predetermined concentration and flow rate, and the flow rate is kept constant at 0.5 mL / min; the third gas supply device 23 provides pure O2 or a mixture of O2 and He to the reaction chamber 12 at a predetermined concentration and flow rate, and the flow rate of the pure O2 or the mixture of O2 and He varies with the concentration of oxygen in the reaction chamber 12 set by the experiment. The flow rate of the helium gas used in the water vapor generator 3 is 2.2 mL / min and remains unchanged. In this step, the flow rates of each gas of the three gas supply devices and the water vapor generator 3 are adjusted separately, starting from a low flow rate and adjusting the flow rates of different gases in order from small to large, so as to accurately control the flow rates of various gases; after the flow rates on all gas paths are stabilized, the ultraviolet light source 11 is turned on to perform ultraviolet photochemical reaction. The ultraviolet light source 11 is a L11798 type vacuum ultraviolet light source produced by Japan Hamamatsu Photonics Co., Ltd., with wavelengths mainly at 125 nm and 160 nm, as shown in Figure 7 .

[0074] According to the research results of the predecessors on the composition of the early earth atmosphere, the first gas supply device 21, the second gas supply device 22 and the third gas supply device 23, the water vapor generator 3 use pure N2, CO2, O2, He gas, water vapor and trace NO x The configuration simulates the composition of the early Earth atmosphere, and the concentration of each gas component is adjusted by a gas flow controller. Among them, the water vapor generator 3 uses helium as a carrier gas through ultrapure water heated to 25℃~65℃, and carries water vapor into the reaction chamber 12. The first gas supply device 21 supplies the pre-configured 5.0ppm NO x N2+NO x Mixed gas (NO x Mainly NO, NO2 content of about 0.1ppm) is supplied to the reaction chamber 12. During the entire simulation experiment, N2+NO x The flow rate of gas remains unchanged at 100 mL / min, and the flow rate of water vapor also remains basically unchanged at 2.2 mL / min. It is only necessary to control the helium flow rate unchanged.

[0075] In step 2 of this embodiment, in each experiment, other parameters remain unchanged, and the third gas supply device 23 is adjusted to supply a mixture of O2 and He with different O2 concentrations, or to supply pure O2 gas, to the reaction chamber 12 to obtain nitric acid test results prepared with different O2 concentrations. That is, by changing the flow rate of oxygen or the mixture of oxygen and helium supplied to the reaction chamber 12, a series of experiments are carried out. During this series of experiments, the NO x The flow rates of the N2 mixed gas, CO2, and helium carrier gas transporting water vapor remain unchanged, while only the flow rate of the oxygen or oxygen and helium mixture is varied. This allows the proportions of different gas components in the reaction chamber 12 to vary with the added oxygen concentration during each experimental process. The flow rate of the oxygen or oxygen and helium mixture supplied to the reaction chamber 12 can be set to a linearly increasing gradient. By controlling the oxygen content in the reaction chamber 12 from low to high, multiple simulation experiments are conducted to investigate whether nitric acid can be generated under different oxygen concentrations in the early Earth's atmosphere, whether the generated nitric acid has an oxygen isotope anomaly, and what factors control the oxygen isotope anomaly. Finally, based on the oxygen isotope anomaly of atmospheric nitrate, the evolution of trace oxygen content in the atmosphere during different historical periods is inferred.

[0076] If too little HNO3 solid material is collected in the collection tube 42, it will be difficult to obtain accurate test results. Therefore, in this embodiment, the reaction time for each set of experiments is set to 4-6 hours, so that after the frozen HNO3 solid material collected in the collection tube 42 is thawed, about 1 mL of HNO3 solution can be obtained.

[0077] After the reaction is completed, the HNO3-containing solution collected in the collection tube 42 of the nitric acid refrigeration collector 4 is all transferred to a capped sample tube and diluted and then sealed and stored in the refrigerator.

[0078] Specifically, the collection tube 42 is taken out of the refrigerant of the cold source container 41, the HNO3-containing solid in the collection tube 42 is thawed at room temperature, the HNO3-containing solid in the collection tube 42 is warmed and melted to obtain about 1 mL of HNO3-containing solution (such as 0.8-1.2 mL); then, the HNO3-containing solution collected in the collection tube 42 is all transferred to a capped sample tube, the refrigeration collector is washed 3 times with MQ water to avoid residual contamination, and the HNO3-containing washing solution is transferred to the sample tube, and finally the HNO3 solution is diluted to 2-2.5 mL, sealed and stored in the refrigerator for testing the nitrogen and oxygen isotopes of nitric acid.

[0079] According to the above steps, the simulation experiment results are shown in Table 1:

[0080] Table 1 Simulation experiment data results

[0081]

[0082] After the preparation of nitric acid, the content and δ 15 N, δ 17 O, δ 18 O and △ 17 O values are shown in Table 1. The experimental results show that the △ 17 O value of nitric acid has an overall increasing trend with the oxygen concentration, and when the oxygen concentration increases from 0 to 5.1%, the △ 17 O value of nitric acid is between 0.3‰ and 1.1‰, and the maximum value is only 1.1‰; when the oxygen concentration increases to 5.4%, the △ 17 O value of nitric acid increases to 4.7‰, and the △ 17 O value of nitric acid continues to increase with the further increase of the oxygen concentration, such as when the oxygen concentration increases to 8.1‰ and 11.2‰, the △ 17 O value of nitric acid increases to 10.1‰ and 14.02‰, respectively, which shows that the generated nitric acid has an oxygen isotope anomaly, and the △ 17 O value of the nitric acid produced by the ultraviolet photochemical reaction is closely related to the atmospheric oxygen concentration.

[0083] Compared with the prior art, the experimental device and method for preparing nitric acid by simulating the photochemical reaction of the early atmosphere of the earth provided by the embodiment can achieve the following beneficial effects:

[0084] 1. The application can irradiate the N2, H2O, CO2, trace O2 and NOx The early atmosphere of the Earth, the process of simulating the photochemical reaction of the early atmosphere of the Earth, can produce HNO3 with significant oxygen isotope non-mass fractionation effect, thereby proving that the photochemical reaction in the early anoxic atmosphere of the Earth can generate nitric acid, and the oxygen isotope non-mass fractionation of the generated nitric acid is closely related to the oxygen concentration, and then the non-mass fractionation effect of the nitrate trioxide isotope in the early sedimentary formation (such as Proterozoic moraine and other sediments) can be used to trace the oxygen source in the early atmosphere of the Earth, and important experimental basis is provided for the oxygen concentration increasing event in the early Proterozoic atmosphere of the Earth, which has important significance for the related research on the early climate change of the Earth.

[0085] 2、The experimental device of the present application has simple structure and is easy to operate, and the experimental process does not need complex manual operation, thereby improving the experimental efficiency, and the generated nitric acid is efficiently recovered by the nitric acid freezing collector, the experiment does not generate toxic gas, and the environment is not polluted, which is green and environmentally friendly.

[0086] The above specific embodiments further specifically describe the purposes, technical solutions and beneficial effects of the present application, and it should be understood that the above description is only a specific embodiment of the present application, and is not used to limit the protection scope of the present application, and any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. An experimental device for simulating photochemical reactions in the early Earth's atmosphere to produce nitric acid, characterized in that: include: The ultraviolet light photochemical reaction system includes an ultraviolet light source and a reaction chamber, wherein the reaction chamber has an ultraviolet light inlet, a reaction gas inlet, a water vapor inlet, and a product outlet; an ultraviolet light-transmissive MgF2 glass window is sealed and installed at the ultraviolet light inlet, and the ultraviolet light source is arranged outside the MgF2 glass window to provide ultraviolet light required for the reaction into the reaction chamber through the MgF2 glass window; a reaction gas source supply system, connected to the reaction gas inlet, for supplying gas required for the ultraviolet photochemical reaction to generate nitric acid into the reaction chamber to simulate the composition of the early Earth's atmosphere; a water vapor generator for providing water vapor to the reaction chamber to simulate the humidity of the early Earth's atmosphere; the water vapor generator has a water vapor outlet, and the water vapor outlet of the water vapor generator is connected to the water vapor inlet; A nitric acid freezing collector is connected to the product outlet and is used to collect nitric acid generated by the photochemical reaction in the reaction chamber.

2. The experimental device for preparing nitric acid by simulating photochemical reactions in the early Earth atmosphere according to claim 1, characterized in that: The reaction gas source supply system includes a gas supply pipeline, the outlet end of the gas supply pipeline is connected to the reaction gas inlet, and the inlet end of the gas supply pipeline is provided with a first gas supply device, a second gas supply device and a third gas supply device; The first gas supply device is used to provide NO to the reaction chamber. x a second gas supply device for providing CO2 to the reaction chamber; a third gas supply device for providing pure O2 or a mixture of O2 and He to the reaction chamber.

3. The experimental device for preparing nitric acid by simulating photochemical reactions in the early Earth atmosphere according to claim 2, characterized in that: The gas supply pipeline includes a main gas pipe, a first branch gas pipe, a second branch gas pipe and a third branch gas pipe; one end of the main gas pipe is connected to the reaction gas inlet, and the other end is connected to the first branch gas pipe, the second branch gas pipe and the third branch gas pipe through a four-way connection; The first gas supply device has an independent gas supply of N2 gas cylinder and NO x gas cylinders; the second gas supply device has a CO2 gas cylinder; the third gas supply device has an O2 gas cylinder and a He gas cylinder with independent gas supply; The main air pipe, the first branch air pipe, the second branch air pipe and the third branch air pipe are all provided with a gas flow controller.

4. The experimental device for preparing nitric acid by simulating photochemical reactions in the early Earth atmosphere according to claim 1, characterized in that: The reaction chamber adopts a stainless steel barrel with one end open and the other end closed. The opening at one end of the stainless steel barrel serves as an ultraviolet light inlet. The axial length of the stainless steel barrel is 20 cm and the inner diameter is 2.5 cm.

5. The experimental device for preparing nitric acid by simulating photochemical reactions in the early Earth atmosphere according to claim 4, characterized in that: The axis of the stainless steel barrel is arranged horizontally, the ultraviolet light inlet and the product outlet are arranged at the axial ends of the stainless steel barrel, and the reaction gas inlet and the water vapor inlet are arranged on the side wall of the stainless steel barrel.

6. The experimental device for preparing nitric acid by simulating photochemical reactions in the early Earth atmosphere according to claim 1, characterized in that: The water vapor generator includes a water tank and a helium source. The water tank is filled with ultrapure water. The water vapor outlet is provided at the top of the water tank. A helium inlet is provided at the bottom of the water tank. The helium inlet is connected to the helium source through a helium path. The water vapor outlet is connected to the water vapor inlet through a water vapor path.

7. The experimental device for preparing nitric acid by simulating photochemical reactions in the early Earth atmosphere according to claim 6, characterized in that: The water vapor path and the helium path both use quartz capillaries. The water vapor path has a first diameter, the helium path has a second diameter, and the first diameter is 3-5 times the second diameter.

8. The experimental device for preparing nitric acid by simulating photochemical reactions in the early Earth atmosphere according to claim 7, characterized in that: The first diameter is 1 / 8 mm, and the second diameter is 1 / 32 mm.

9. The experimental device for preparing nitric acid by simulating photochemical reactions in the early Earth atmosphere according to claim 6, characterized in that: The reaction chamber is provided with a first heating device, which is configured to control the temperature in the reaction chamber to 65±0.5°C; A second heating device is provided outside the water tank and is configured to maintain the ultrapure water in the water tank at 25-65°C.

10. The experimental device for preparing nitric acid by simulating photochemical reactions in the early Earth atmosphere according to claim 1, characterized in that: The nitric acid freezing collector includes a cold source container and a collection tube. The top of the cold source container is open and filled with a freezing liquid at -50±5°C. The top of the collection tube is penetrated by a product supply tube extending to the bottom of the collection tube, and the upper side wall of the collection tube is provided with a product outlet tube; the product outlet is connected to the product supply tube through a stainless steel tube.

11. The experimental device for preparing nitric acid by simulating photochemical reactions in the early Earth atmosphere according to claim 10, characterized in that: The top of the product supply pipe is upwardly extended to be provided with a diameter-reducing section, and the inner diameter of the diameter-reducing section is smaller than the inner diameter of the product supply pipe.

12. The experimental device for preparing nitric acid by simulating photochemical reactions in the early Earth atmosphere according to claim 11, characterized in that: The distance between the bottom of the collecting tube and the bottom of the cold source container is 2-4 cm, and the bottom opening of the product supply tube is located 4 cm above the liquid level of the freezing liquid.

13. The experimental device for preparing nitric acid by simulating photochemical reactions in the early Earth atmosphere according to claim 12, characterized in that: The collecting tube and cold source container are both quartz glass tubes; the inner diameter of the cold source container is 3 cm; the outer diameter of the collecting tube is 18 mm and the inner diameter is 15 mm; the outer diameter of the product supply tube is 12 mm and the inner diameter is 9 mm; the outer diameter of the reduced diameter section is 6.4 mm; and the outer diameter of the product outlet tube is 6.4 mm.

14. A method for preparing nitric acid by simulating photochemical reactions in the early Earth atmosphere, characterized in that: An experimental device for preparing nitric acid by simulating photochemical reactions in the early Earth atmosphere according to any one of claims 1 to 13; the method comprising the following steps: According to the data of the early Earth's atmosphere composition, the reaction gas source supply system is used to supply the gas components required for the reaction into the reaction chamber, and water vapor is supplied into the reaction chamber using a water vapor generator. After the gas flow rates of each line are stable, the ultraviolet light source is turned on, and the collection tube of the nitric acid freezing collector is placed in the freezing liquid of the cold source container to freeze and collect the HNO3 generated by the reaction.

15. The method for preparing nitric acid by simulating photochemical reactions in the early Earth atmosphere according to claim 14, characterized in that: When the reaction gas source supply system is used to supply the gas components required for the reaction into the reaction chamber, the first gas supply device supplies NO into the reaction chamber according to a predetermined concentration and flow rate. x and N2 mixture at a flow rate of 100 mL / min; a second gas supply device supplies CO2 into the reaction chamber at a predetermined concentration and flow rate at a flow rate of 0.5 mL / min; a third gas supply device supplies pure O2 or a mixture of O2 and He into the reaction chamber at a predetermined concentration and flow rate; wherein the flow rate of pure O2 or the mixture of O2 and He is set according to the experimental setting of the concentration of oxygen in the reaction chamber; When water vapor is supplied into the reaction chamber using the water vapor generator, the flow rate of helium is 2.2 mL / min.

16. The method for preparing nitric acid by simulating photochemical reactions in the early Earth atmosphere according to claim 14, characterized in that: It also includes the system impurity removal pretreatment steps: Before the reaction officially starts, the reaction chamber is continuously purged with high-purity N2 gas and high-purity He gas is supplied to the ultrapure water in the water tank to remove possible impurities in the reaction chamber and trace amounts of O2 dissolved in the ultrapure water.

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