A system and method for preparing a certified reference material of formic acid gas in air

Abstract

The present application relates to the technical field of preparing formic acid gas standard substance, and more particularly to a system and method for preparing formic acid gas standard substance in air. The system comprises a nitrogen source, an oxygen source, a vacuum pump, a raw material container, an intermediate container, a finished product container, a first three-way valve, a second three-way valve, a catalytic cracking pipe and a catalytic oxidation pipe; the nitrogen source, the oxygen source and the vacuum pump are communicated with the first three-way valve; the raw material container is communicated with the intermediate container through the second three-way valve and the catalytic cracking pipe in sequence; the intermediate container is communicated with the finished product container through the catalytic oxidation pipe; and the first three-way valve is communicated with the second three-way valve. The present application prepares formic acid standard gas through a two-step reaction with trioxane as a raw material, avoids the quality loss in the process of preparing formic acid standard gas with fuming formic acid, and can accurately obtain the amount of formic acid standard gas.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of preparing formic acid gas standard substance, and more particularly to a system and method for preparing formic acid gas standard substance in air. BACKGROUND

[0002] Formic acid (HCOOH), also known as ant acid, is colorless and has a pungent odor, and is one of the basic organic chemical raw materials, which is widely used in pesticide, leather, dye, medicine and rubber industries. Formic acid is the most abundant organic acid in urban atmosphere, and the content of formic acid in the atmosphere is generally more abundant than that of main inorganic acids (nitric acid and hydrochloric acid). Although formic acid is one of the main factors causing atmospheric acidification, the emission and monitoring of formic acid are limited at present. In order to standardize the ecological environment monitoring work, the Ministry of Ecological Environment has recently approved the release of "Determination of Formic Acid, Acetic Acid and Oxalic Acid in Environmental Air Particulate Matter by Ion Chromatography" (HJ 1271-2022) as a national ecological environment standard, which fills the gap of formic acid monitoring standard in the atmosphere in China. At present, the quantitative detection of formic acid in gas mainly adopts ion chromatography method, and the formic acid in environmental air sample is extracted by water ultrasonic extraction, separated by ion chromatography column, and detected by suppressor conductivity detector. The method is complicated, and the error in the analysis process is large, while the method of directly analyzing formic acid in gas by using helium ionization detector gas chromatography is more simple and has higher measurement accuracy. However, there is a lack of formic acid gas standard substance at present, which cannot meet the traceability requirements of the content of formic acid in the air.

[0003] At present, the method for preparing gas standard substance from liquid is injection weighing method, that is, the liquid is injected into a stainless steel tube with a certain volume sealed by valves at both ends through a syringe, then the stainless steel tube is connected to the preparation system, the liquid in the stainless steel tube is transferred to the target gas cylinder, and then dilution gas is added. However, pure formic acid has strong volatility and water absorption, and uncontrollable mass loss will occur during the transfer process by using a syringe, and more water will be introduced, so it is difficult to accurately calculate the amount of formic acid. SUMMARY

[0004] The present application provides a system and method for preparing formic acid gas standard substance in air to overcome the problem that the amount of formic acid cannot be accurately calculated in the prior art.

[0005] To solve the above technical problems, the technical scheme adopted by the present application is: a system for preparing formic acid gas standard substance in air, comprising a nitrogen source, an oxygen source, a vacuum pump, a raw material container, an intermediate container, a finished product container, a first three-way valve, a second three-way valve, a catalytic cracking pipe and a catalytic oxidation pipe; the nitrogen source, the oxygen source and the vacuum pump are communicated with the first three-way valve; the raw material container is communicated with the intermediate container in sequence through the second three-way valve and the catalytic cracking pipe; the intermediate container is communicated with the finished product container through the catalytic oxidation pipe; and the first three-way valve is communicated with the second three-way valve.

[0006] The catalytic cracking pipe is used for cracking trioxymethylene vapor into formaldehyde; the catalytic oxidation pipe is used for oxidizing the formaldehyde into formic acid; the intermediate container is used for temporarily storing the intermediate product, so as to facilitate sampling and detection; and the oxygen source is not only used for providing oxygen to oxidize the formaldehyde into formic acid, but also can be filled into the finished product container together with the nitrogen provided by the nitrogen source, so as to form an atmosphere similar to air.

[0007] Further, the first switch valve and the second switch valve are installed on the intermediate container in communication, the catalytic cracking pipe is communicated with the intermediate container through the first switch valve, and the intermediate container is communicated with the catalytic oxidation pipe through the second switch valve.

[0008] Further, the first heating member is arranged on the catalytic cracking pipe, the second heating member is arranged on the catalytic oxidation pipe, and the third heating member is arranged on the raw material container.

[0009] Further, the catalytic cracking pipe is filled with acidification glass balls, and the catalytic oxidation pipe is filled with V-Ti-O catalyst.

[0010] Further, the third switch valve is arranged on the finished product container, the finished product container is communicated with the catalytic oxidation pipe through the third switch valve, and the weighing member is arranged at the bottom of the finished product container.

[0011] The present application also provides a method for preparing formic acid gas standard substance in air by using the above system, comprising the following steps:

[0012] S1. disconnecting the raw material container containing Xmg of trioxymethylene from the second three-way valve, then vacuumizing the raw material container, weighing after vacuumizing, and recording the weight value m1 of the raw material container at this time;

[0013] S2. connecting the vacuumized raw material container with the second three-way valve again, then closing the passage connected with the raw material container of the second three-way valve, opening the remaining two passages of the second three-way valve, opening all the three passages of the first three-way valve, opening the first switch valve and the second switch valve, closing the third switch valve, and starting to vacuumize the system by opening the vacuum pump;

[0014] S3. After the system is vacuumed, the vacuum pump is closed, the nitrogen source and the oxygen source are closed, all the passages of the first three-way valve are closed, all the passages of the second three-way valve connected with the raw material container are opened, and the second switch valve is closed; the third heating element is opened to heat the raw material container to 60℃, and the first heating element is opened to heat the catalytic cracking tube;

[0015] S4. After t hours, the first heating element is closed; after the catalytic cracking tube is cooled to room temperature, all the passages of the first three-way valve are opened, the oxygen source is opened, the passages of the second three-way valve connected with the raw material container are closed; the passage of the first three-way valve connected with the oxygen source is opened, and the oxygen source is opened;

[0016] S5. The first switch valve is closed, the second heating element is opened to heat the oxidation catalytic tube to 120-140℃, then the oxygen source is opened, the oxygen flow rate of the oxygen source is kml / min, and the first switch valve, the second switch valve, and the third switch valve are opened.

[0017] S6. The second heating element, the third switch valve, and the oxygen source are closed, and the weight Ma of the product container is weighed;

[0018] S7. All the passages of the second three-way valve are opened, the vacuum pump is opened for a period of time and then closed, then the passages of the second three-way valve connected with the raw material container are closed, the nitrogen source is opened, the nitrogen flow rate of the nitrogen source is jml / min, the third switch valve is opened, mN of nitrogen is filled into the product container, the third switch valve is closed, and then the weight Mb of the product container and the weight m2 of the raw material container are weighed;

[0019] S8. The amount of substance of each component in the product container is calculated.

[0020] Further, the nitrogen flow rate jml / min: oxygen flow rate kml / min = 4:1.

[0021] Further, the step S3 is:

[0022] After the system is vacuumed, the vacuum pump is closed, the nitrogen source and the oxygen source are closed, all the passages of the first three-way valve are closed, all the passages of the second three-way valve connected with the raw material container are opened, and the second switch valve is closed; the third heating element is opened to heat the raw material container to 60℃, and the first heating element is opened to heat the catalytic cracking tube to 170-190℃.

[0023] Further, in the steps S1 and S4, X:t = 10:3.

[0024] Further, the step S8 is:

[0025] The mass of the trioxane participating in the reaction is Δm = m2-m1; the mass of the oxygen in the product container is mO = Ma-Δm; the mass of the nitrogen in the product container is mN = Mb-Ma;

[0026] The amount of substance of oxygen is = [mO / M O2 -3Δm / M C3H6O3 ] × oxygen purity;

[0027] The amount of substance of nitrogen is = [(m b -m a ) / M N2 ] × nitrogen purity;

[0028] The amount of substance of formic acid is 3Δm / M C3H6O3 × trioxane purity × catalytic cracking reaction conversion rate × catalytic oxidation reaction conversion rate;

[0029] The method for detecting the cracking reaction conversion rate of trioxane is that, after step S4 and before step S5, the reaction is stopped, and the conversion rate is detected by sampling from the intermediate container; the average value of multiple measurements is the reaction conversion rate.

[0030] Compared with the prior art, the beneficial effects of the present application are:

[0031] The present application uses trioxane as a raw material to prepare formic acid standard gas through two continuous reactions, avoids the quality loss in the process of preparing formic acid standard gas by using fuming formic acid, reduces the introduction of water, and can accurately measure the conversion rate in the preparation process. By weighing the mass of the added trioxane and measuring the conversion rate of the two reactions, a more accurate mass value of the formic acid gas standard can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a schematic diagram of the overall structure of embodiment 1 of a system for preparing formic acid gas standard material in air according to the present application;

[0033] Figure 2 is a schematic diagram of the internal structure of the catalytic cracking tube in embodiment 1 of a system for preparing formic acid gas standard material in air according to the present application;

[0034] Figure 3 is a flowchart of an embodiment of a method for preparing formic acid gas standard material in air according to the present application.

[0035] In the drawing: 1, nitrogen source; 2, oxygen source; 3, vacuum pump; 4, raw material container; 5, intermediate container; 6, finished product container; 7, first three-way valve; 8, second three-way valve; 9, catalytic cracking tube; 10, catalytic oxidation tube; 11, first on-off valve; 12, second on-off valve; 13, third on-off valve; 14, first heating element; 15, second heating element; 16, third heating element; 17, weighing element; 18, flow meter; 19, acidification glass ball. DETAILED DESCRIPTION

[0036] The drawing is only used for illustrative description, and cannot be understood as a limitation to the patent; in order to better illustrate the embodiment, some components in the drawing can be omitted, enlarged or reduced, and do not represent the size of the actual product; for those skilled in the art, it is understandable that some well-known structures in the drawing and their descriptions can be omitted. The positional relationship described in the drawing is only used for illustrative description, and cannot be understood as a limitation to the patent.

[0037] The same or similar reference numerals in the drawing of the embodiment of the present application correspond to the same or similar components; in the description of the present application, it is understood that if the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "long" and "short" is based on the orientation or positional relationship shown in the drawing, it is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the positional relationship in the drawing are only used for illustrative description, and cannot be understood as a limitation to the patent, and for those skilled in the art, the specific meaning of the above terms can be understood according to the specific situation.

[0038] The technical solutions of the present application will be further described below through specific embodiments, and in conjunction with the drawings:

[0039] Embodiment 1

[0040] Reference Figure 1 and Figure 2 Embodiment 1 of the system for preparing formic acid gas standard substance in air according to the present application comprises a nitrogen source 1, an oxygen source 2, a vacuum pump 3, a raw material container 4, an intermediate container 5, a finished product container 6, a first three-way valve 7, a second three-way valve 8, a catalytic cracking tube 9 and a catalytic oxidation tube 10; the nitrogen source 1, the oxygen source 2 and the vacuum pump 3 are in communication with the first three-way valve 7; the raw material container 4 is in communication with the intermediate container 5 in sequence through the second three-way valve 8 and the catalytic cracking tube 9; the intermediate container 5 is in communication with the finished product container 6 through the catalytic oxidation tube; and the first three-way valve 7 is in communication with the second three-way valve 8.

[0041] Specifically, the nitrogen source 1 and the oxygen source 2 are nitrogen cylinders and oxygen cylinders with valves; the nitrogen source 1 and the oxygen source 2 are connected to the first three-way valve 7 through a three-way pipe, and the outlets of the nitrogen source 1 and the oxygen source 2 are each provided with a flowmeter 18, which can control the flow rate of the output gas and can also observe the real-time flow rate.

[0042] In the embodiment, the intermediate container 5 is provided with a first switch valve 11 and a second switch valve 12, the catalytic cracking tube 9 is connected to the intermediate container 5 through the first switch valve 11, and the intermediate container 5 is connected to the catalytic oxidation tube 10 through the second switch valve 12. The intermediate container 5 is a tubular structure with both ends penetrating through, and the first switch valve 11 and the second switch valve 12 are respectively installed at the two ends of the intermediate container 5.

[0043] In the embodiment, the catalytic cracking tube 9 is provided with a first heating element 14, the catalytic oxidation tube 10 is provided with a second heating element 15, and the raw material container 4 is provided with a third heating element 16.

[0044] Specifically, the first heating element 14, the second heating element 15 and the third heating element 16 are all electric heating wires, the first heating element 14 is wound on the outer wall of the catalytic cracking tube 9, the second heating element 15 is wound on the outer wall of the catalytic oxidation tube 10, and the third heating element 16 is wound on the outer wall of the raw material container 4, so that the catalytic cracking tube 9 and the catalytic oxidation tube 10 can be quickly heated. The catalytic oxidation tube 10 is a 1 / 8 inch or 1 / 4 inch diameter stainless steel tube, and in the embodiment, a 1 / 8 inch diameter stainless steel tube is preferred. The catalytic cracking tube 9 is a 1 / 8 inch or 1 / 4 inch diameter stainless steel tube, and in the embodiment, a 1 / 8 inch diameter stainless steel tube is preferred.

[0045] In the embodiment, the catalytic cracking tube 9 is filled with acidified glass balls 19, and the catalytic oxidation tube 10 is filled with V-Ti-O catalyst. Specifically, the acidified glass balls 19 in the catalytic cracking tube 9 are glass balls soaked in phosphoric acid and then dried.

[0046] In the embodiment, the finished product container 6 is provided with a third switch valve 13, the finished product container 6 is connected to the catalytic oxidation tube 10 through the third switch valve 13, and the bottom of the finished product container 6 is provided with a weighing element 17. Specifically, the weighing element 17 is an electronic balance.

[0047] In the embodiment, the nitrogen source 1, the oxygen source 2, the vacuum pump 3, the raw material container 4, the intermediate container 5, the finished product container 6, the first three-way valve 7, the second three-way valve 8, the catalytic cracking tube 9 and the catalytic oxidation tube 10 are all connected through glass pipes. The inner walls of the raw material container 4, the intermediate container 5, the finished product container 6, the catalytic cracking tube 9, the catalytic oxidation tube 10 and the glass pipes connecting the components are all silanized.

[0048] Example 2

[0049] Referring to Figure 3 , this embodiment is a method for preparing a standard air of formic acid gas using the system in Example 1, comprising the following steps:

[0050] S1. disconnect the raw material container 4 containing 10 mg of trioxane from the second three-way valve 8, then vacuumize the raw material container 4, weigh after vacuumization, and record the weight value m1 of the raw material container 4 at this time;

[0051] S2. connect the vacuumized raw material container 4 to the second three-way valve 8 again, then close the passage connecting the second three-way valve 8 to the raw material container 4, open the remaining two passages of the second three-way valve 8, open all three passages of the first three-way valve 7; open the first switch valve 11 and the second switch valve 12, close the third switch valve 13, and start vacuumizing the system by opening the vacuum pump 3;

[0052] S3. after completing the vacuumization of the system, close the vacuum pump 3, close the nitrogen source 1 and the oxygen source 2, close all three passages of the first three-way valve 7, open all passages connecting the second three-way valve 8 to the raw material container 4, and close the second switch valve 12; open the first heating element 14 to heat the catalytic cracking tube 9 to 180℃; open the third heating element 16 to heat the raw material container 4 to 60℃;

[0053] S4. after 3 hours, close the first heating element 14; after the catalytic cracking tube 9 cools to room temperature, open all passages of the first three-way valve 7, open the oxygen source 2, close the passages connecting the second three-way valve 8 to the raw material container 4; open the passage connecting the first three-way valve 7 to the oxygen source 2, and open the oxygen source 2 for 25 minutes;

[0054] S5. after 5 minutes, close the first switch valve 11 and the oxygen source 2, open the second heating element 15 to heat the oxidation catalytic tube to 130℃, then open the oxygen source 2 to make the oxygen flow rate of the oxygen source 2 be 20 ml / min, and open the first switch valve 11, the second switch valve 12, and the third switch valve 13;

[0055] S6. after 1 hour, close the second heating element 15, the third switch valve 13, and the oxygen source 2, and weigh the weight Ma of the finished product container 6;

[0056] S7. open all passages of the second three-way valve 8, open the vacuum pump 3 for 10 minutes, then close the vacuum pump 3, close the passage connecting the second three-way valve 8 to the raw material container 4, open the nitrogen source 1, open the third switch valve 13, fill the finished product container 6 with mN mass of nitrogen, then close the third switch valve 13, weigh the weight Mb of the finished product container 6 and the weight m2 of the raw material container 4;

[0057] S8. Calculate the amount of substance of each component in finished container 6;

[0058] The mass of trioxymethylene participating in the reaction is Δm = m2 - m1; the mass of oxygen in the finished product container 6 is mO = Ma - Δm; the mass of nitrogen in the finished product container 6 is mN = Mb - Ma;

[0059] Amount of oxygen = [mO / M O2 -3Δm / M C3H6O3 × Oxygen purity;

[0060] Amount of nitrogen gas = [(m b -m a ) / M N2 [×Nitrogen purity;]

[0061] Formic acid amount = 3Δm / M C3H6O3 × Trioxymethylene purity × Catalytic cracking reaction conversion rate × Catalytic oxidation reaction conversion rate;

[0062] The method for detecting the conversion rate of paraformaldehyde cracking reaction is as follows: after step S4 and before step S5, the reaction is stopped, and a sample is taken from the intermediate container 5 for testing. The average conversion rate of multiple measurements is the reaction conversion rate.

[0063] Example 3

[0064] Reference Figure 3 This embodiment is another embodiment of the method for preparing formic acid gas standard material in air using the system in Example 1, and includes the following steps:

[0065] S1. Separate the raw material container 4 containing 20mg of trioxymethylene from the second three-way valve 8, then evacuate the raw material container 4, weigh it after evacuation, and record the weight value m1 of the raw material container 4 at this time.

[0066] S2. Reconnect the vacuumed raw material container 4 to the second three-way valve 8, then close the passage connecting the second three-way valve 8 to the raw material container 4, open the remaining two passages of the second three-way valve 8, and open all three passages of the first three-way valve 7; open the first switch valve 11 and the second switch valve 12, close the third switch valve 13, and start the vacuum pump 3 to begin evacuating the system.

[0067] S3. After completing the system vacuuming, turn off vacuum pump 3, turn off nitrogen source 1 and oxygen source 2, close all three passages of the first three-way valve 7, open all passages of the second three-way valve 8 connected to the raw material container 4, and close the second switch valve 12; turn on the first heating element 14 to heat the catalytic cracking tube 9 to 190°C; turn on the third heating element 16 to heat the raw material container 4 to 60°C.

[0068] S4. After 6 hours, the first heating element 14 is turned off; the catalytic cracking tube 9 is cooled to room temperature, all the passages of the first three-way valve 7 are opened, the oxygen source 2 is turned on, the passage of the second three-way valve 8 connected to the raw material container 4 is closed; the passage of the first three-way valve 7 connected to the oxygen source 2 is opened, and the oxygen source 2 is turned on for 25 minutes;

[0069] S5. After 5 minutes, the first switch valve 11 is turned off, the second heating element 15 is turned on to heat the oxidation catalytic tube to 140℃, then the oxygen source 2 is turned on, the oxygen flow rate of the oxygen source 2 is 20ml / min, and the first switch valve 11, the second switch valve 12 and the third switch valve 13 are turned on.

[0070] S6. After 1 hour, the second heating element 15, the third switch valve 13 and the oxygen source 2 are turned off, and the weight Ma of the product container 6 is measured;

[0071] S7. All the passages of the second three-way valve 8 are opened, the vacuum pump 3 is turned on for 10 minutes, then the vacuum pump 3 is turned off, the passage of the second three-way valve 8 connected to the raw material container 4 is closed, the nitrogen source 1 is turned on, the nitrogen flow rate of the nitrogen source 1 is 80ml / min, the third switch valve 13 is turned on, the product container 6 is filled with mN mass of nitrogen, then the third switch valve 13 is turned off, the weight Mb of the product container 6 and the weight m2 of the raw material container 4 are measured;

[0072] S8. The amount of substance of each component in the product container 6 is calculated;

[0073] The mass of trioxymethylene participating in the reaction Δm = m2-m1; the mass of oxygen in the product container 6 mO = Ma-Δm; the mass of nitrogen in the product container 6 mN = Mb-Ma;

[0074] The amount of substance of oxygen = [mO / M O2 -3Δm / M C3H6O3 ]×oxygen purity;

[0075] The amount of substance of nitrogen = [(m b -m a ) / M N2 ]×nitrogen purity;

[0076] The amount of substance of formic acid = 3Δm / M C3H6O3 ×trioxymethylene purity×catalytic cracking reaction conversion rate×catalytic oxidation reaction conversion rate;

[0077] The method for detecting the conversion rate of trioxymethylene cracking reaction is as follows: after step S4 and before step S5, the reaction is stopped, the sample is taken from the intermediate container 5 for detection, and the average value of multiple measurements is the reaction conversion rate.

[0078] Obviously, the above embodiments of the present application are merely exemplary but not intended to limit the embodiments of the present application. Based on the above description, any other variations or changes can be made by those skilled in the art without departing from the spirit and principles of the present application. It is not necessary to list all the embodiments here. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application shall fall within the scope of the claims of the present application.

Claims

1. A system for preparing a formic acid gas standard in air, characterized by, The utility model relates to a kind of nitrogen source (1), oxygen source (2), vacuum pump (3), raw material container (4), intermediate container (5), finished product container (6), first three-way valve (7), second three-way valve (8), catalytic cracking pipe (9) and catalytic oxidation pipe (10);The nitrogen source (1), oxygen source (2) and vacuum pump (3) are communicated with first three-way valve (7);The raw material container (4) is sequentially communicated with intermediate container (5) by second three-way valve (8), catalytic cracking pipe (9);The intermediate container (5) is communicated with finished product container (6) by catalytic oxidation pipe line;The first three-way valve (7) is communicated with second three-way valve (8);The raw material container (4) is equipped with trioxymethylene;First heating part (14) is equipped on the catalytic cracking pipe (9), second heating part (15) is equipped on the catalytic oxidation pipe (10), and third heating part (16) is equipped on the raw material container (4);The catalytic cracking pipe (9) is filled with acidification glass ball (19);The catalytic oxidation pipe (10) is filled with V-Ti-O catalyst;Finished product container (6) bottom is equipped with weighing element (17).

2. The system for preparing a formic acid gas standard in air according to claim 1, wherein, First switch valve (11) and second switch valve (12) are installed on the intermediate container (5) and are communicated, the catalytic cracking pipe (9) is communicated with intermediate container (5) by first switch valve (11), and the intermediate container (5) is communicated with catalytic oxidation pipe (10) by second switch valve (12).

3. The system for preparing a formic acid gas standard in air according to claim 2, wherein, Third switch valve (13) is equipped on the finished product container (6), and the finished product container (6) is communicated with catalytic oxidation pipe (10) by third switch valve (13).

4. A method for preparing a gas standard of formic acid in air using the system of claim 3, wherein It includes the following steps: S1.trioxymethylene is separated from the raw material container (4) with Xmg of trioxymethylene in the raw material container (4) and second three-way valve (8), then the raw material container (4) is vacuumized, is weighed after vacuumizing, and the weight value m1 of the raw material container (4) at this time is recorded; S2.the raw material container (4) after vacuumizing is communicated with second three-way valve (8) again, then the path that second three-way valve (8) is connected with raw material container (4) is closed, the remaining two paths of second three-way valve (8) are opened, and the three paths of first three-way valve (7) are all opened;First switch valve (11) and second switch valve (12) are opened, third switch valve (13) is closed, and vacuum pump (3) is started to system vacuumizing; S3.after completing the vacuumizing of system, vacuum pump (3) is closed, nitrogen source (1) and oxygen source (2) are closed, the three paths of first three-way valve (7) are all closed, the path that second three-way valve (8) is connected with raw material container (4) is all opened, and second switch valve (12) is closed;Third heating part (16) is opened to heat raw material container (4) to 60 DEG C, and first heating part (14) is opened to heat catalytic cracking pipe (9); S4. t hours later, the first heating element (14) is closed; after the catalytic cracking tube (9) is cooled to room temperature, all the passages of the first three-way valve (7) are opened, the oxygen source (2) is opened, and the passage of the second three-way valve (8) connected to the raw material container (4) is closed; the passage of the first three-way valve (7) connected to the oxygen source (2) is opened, and the oxygen source (2) is opened; S5. The first switch valve (11) is closed, the second heating element (15) is opened to heat the oxidation catalytic tube to 120~140℃, then the oxygen source (2) is opened, the oxygen flow rate of the oxygen source (2) is kml / min, and then the first switch valve (11), the second switch valve (12) and the third switch valve (13) are opened; S6. The second heating element (15), the third switch valve (13) and the oxygen source (2) are closed, and the weight Ma of the product container (6) is measured; S7. All the passages of the second three-way valve (8) are opened, the vacuum pump (3) is opened for a period of time and then closed, then the passage of the second three-way valve (8) connected to the raw material container (4) is closed, the nitrogen source (1) is opened, the nitrogen flow rate of the nitrogen source (1) is jml / min, the third switch valve (13) is opened, mN mass of nitrogen is filled into the product container (6), then the third switch valve (13) is closed, and the weight Mb of the product container (6) and the weight m2 of the raw material container (4) are measured; S8. The amount of substance of each component in the product container (6) is calculated.

5. The method for preparing a formic acid gas standard in air according to claim 4, characterized in that, The nitrogen flow rate jml / min: oxygen flow rate kml / min = 4:

1.

6. The method for preparing a formic acid gas standard in air according to claim 4, characterized in that, The step S3 is: After the system is vacuumized, the vacuum pump (3) is closed, the nitrogen source (1) and the oxygen source (2) are closed, all the passages of the first three-way valve (7) are closed, the passage of the second three-way valve (8) connected to the raw material container (4) is opened, and the second switch valve (12) is closed; the third heating element (16) is opened to heat the raw material container (4) to 60℃, and the first heating element (14) is opened to heat the catalytic cracking tube (9) to 170~190℃.

7. The method for preparing a formic acid gas standard in air according to claim 4, characterized in that, In the steps S1 and S4, X:t = 10:

3.

8. The method for preparing a formic acid gas standard in air according to claim 4, characterized in that, The step S8 is: The mass of trioxane participating in the reaction is Δm = m2-m1; the mass of oxygen in the product container (6) is mO = Ma-Δm; and the mass of nitrogen in the product container (6) is mN = Mb-Ma; Amount of substance of oxygen = [m0 / M O2 - 3Δm / M C3H6O3 ] x oxygen purity; Amount of substance of nitrogen = [ (Mb - Ma) / M N2 ] x purity of nitrogen; Molar amount of formic acid substance = 3Δm / M C3H6O3 x trimethylolpropane purity x catalytic cleavage reaction conversion x catalytic oxidation reaction conversion; The method for detecting the conversion rate of the trioxane cracking reaction is as follows: after the step S4 and before the step S5, the reaction is stopped, a sample is taken from the intermediate container (5) for detection, and the average value of the conversion rate measured multiple times is the reaction conversion rate.

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