Preparation method and system of formaldehyde bottled standard gas

Abstract

The application is suitable for the technical field of gas preparation, and provides a preparation method and system of formaldehyde bottled standard gas, the preparation method of formaldehyde bottled standard gas comprises the following steps: placing solid trioxane and a catalyst in a reactor; performing vacuumizing treatment on the reactor and a transfer pipeline in steps; heating the reactor in a predetermined temperature range to make the trioxane catalytically cracked into formaldehyde gas; blowing the formaldehyde gas to a pre-saturation gas cylinder through the passivated transfer pipeline; and supplementing inert gas into the gas cylinder to obtain formaldehyde standard gas, the preparation method of formaldehyde bottled standard gas provided by the application realizes cracking conversion rate ≥ 95%, transfer efficiency ≥ 95%, and standard gas concentration stability reaches 1.6 ppb / day by optimizing the structure of the cracking reactor, i.e. three-way ball valve multi-state control, precise temperature control, segmented pressure blowing transfer and gas cylinder pre-saturation treatment, and solves the technical bottlenecks of formaldehyde adsorption loss and fast value decay in the traditional method.

Description

Technical Field

[0001] This invention belongs to the field of gas preparation technology, and in particular relates to a method and system for preparing standard formaldehyde bottled gas. Background Technology

[0002] Formaldehyde standard gas is a key reference material for environmental monitoring (such as indoor air quality testing) and instrument calibration (formaldehyde analyzers). Currently, mainstream preparation methods face three major technical bottlenecks:

[0003] Poor stability:

[0004] Formaldehyde molecules are highly polar and easily adsorbed onto the inner walls of pipelines / gas cylinders. The concentration of standard gas in traditional steel cylinders decreases by 5-8% within 30 days, which is difficult to meet the requirements for the long-term stability of standard substances.

[0005] Commercially available formaldehyde standard gas stability is only 3.5 ppb / day, and deteriorates to more than 5 ppb / day under high humidity conditions.

[0006] The transfer resulted in significant losses:

[0007] Liquid formaldehyde vaporization requires high-temperature vaporization (>150℃), and the formaldehyde adsorption rate is as high as 12-15% when the pipeline is not passivated.

[0008] Although the permeation tube method is highly accurate, the formaldehyde polymerizes due to pressure changes when transferring it to the gas cylinder, resulting in a measured transfer efficiency of ≤85%. Summary of the Invention

[0009] This invention provides a method for preparing standard formaldehyde bottled gas, aiming to solve the above-mentioned problems.

[0010] This invention is achieved as follows: a method for preparing bottled formaldehyde standard gas, comprising the following steps:

[0011] Solid trioxymethylene and a catalyst are placed in a reactor;

[0012] The reactor and transfer pipeline were vacuumed in stages.

[0013] The reactor is heated within a predetermined temperature range to catalytically decompose paraformaldehyde into formaldehyde gas.

[0014] The formaldehyde gas was passed through a passivated transfer pipeline and purged into a pre-saturated gas cylinder.

[0015] Inert gas is added to the gas cylinder to obtain formaldehyde standard gas.

[0016] Preferably, the catalyst is added at 90-110% of the mass of paraformaldehyde, the catalytic cracking temperature is 230±5℃, and the vacuum degree is ≤10. -6 hPa.

[0017] Preferably, the catalyst is a core-shell structure formed by phosphorus pentoxide (P2O5) and MOF-303. In preparation, MOF-303 is synthesized by a solvothermal method, and then MOF-303 is immersed in a phosphorus pentoxide saturated acetonitrile solution (50 g / L), stirred at 55-65℃ for 3-5 h, and vacuum dried to obtain the core-shell structure. Through the selective adsorption of water molecules by MOF-303, phosphorus pentoxide is protected from deactivation, and the mesoporous structure of the shell accelerates formaldehyde diffusion and improves the pyrolysis efficiency.

[0018] Preferably, when heating the reactor within a predetermined temperature range, ultrasonic cavitation effect is used to break up the paraformaldehyde crystals, increasing the reaction contact surface and improving the pyrolysis conversion rate.

[0019] Preferably, segmented purging control is used during gas transfer:

[0020] First, with ≤10 -6 A vacuum of hPa is used to remove residual gas from the transfer pipeline;

[0021] Purge the cylinder with high-purity nitrogen until the pressure reaches 9-11 bar.

[0022] Preferably, the pre-saturation treatment of the gas cylinder includes the following steps:

[0023] Fill the empty bottle with 10 ppm formaldehyde standard gas up to 10 bar;

[0024] Allow the gas cylinders to stand for 3 days or more. It is preferable to purchase the gas cylinders in one go based on the annual sales volume and perform saturation treatment in one go. Extending the pre-saturation time is beneficial to the stability of formaldehyde levels.

[0025] Preferably, before the gas cylinder is pre-saturated, the gas cylinder is sealed, including the following steps:

[0026] a) Inject a cholesteric liquid crystal solution containing a photoinitiator (22wt% chiral agent S811, 78wt% nematic liquid crystal E7, 0.5wt% photoinitiator TPO; the injection amount can be adjusted appropriately according to the inner surface area of ​​the gas cylinder).

[0027] b) Rotate the gas cylinder (20-40 rpm, 20-40 min) to ensure the solution evenly covers the inner wall;

[0028] c) Curing with ultraviolet light (8-12 min) to form a liquid crystal photonic crystal film (thickness 10-30 μm, pitch 0.40-0.50 nm).

[0029] An electrode interface can be integrated at the gas cylinder valve to connect to an external electric field controller (0-10V adjustable). When formaldehyde needs to be released, a voltage is applied (the voltage V can be set to target concentration × 0.1, e.g., 1V corresponds to 10ppm of standard gas release). The liquid crystal lattice spacing (0.1-10nm) is adjusted to control the formaldehyde release rate, and the cylinder valve is opened to release the standard gas.

[0030] It needs to be explained that after a liquid crystal photonic crystal film is formed on the inner wall of the gas cylinder, formaldehyde standard gas is then filled into the cylinder, initiating self-assembly. When left to stand, formaldehyde molecules spontaneously embed into the liquid crystal spiral cavity, achieving molecular-level encapsulation, forming a periodic superstructure, increasing the formaldehyde diffusion barrier, reducing the decay rate, and improving the service life.

[0031] Preferably, the method for calculating the mass of inert gas added during the step of adding inert gas to the gas cylinder is as follows:

[0032] Prepare two sets of reactors, one for the experimental reaction and the other for weighing the reference.

[0033] After the reactor is evacuated, the mass of the reference and the reactor are weighed alternately, and the difference m0 between the reference and the reactor is recorded until the range of 6 consecutive sets of experimental data is ≤0.00005g.

[0034] Then weigh the gas cylinder and let its mass be M0;

[0035] After purging, the reactor was removed, and the mass of the reference and the reactor was weighed alternately. The difference between the reference and the reactor was recorded as m1 until the range of 6 consecutive experimental data was ≤0.00005g. The actual mass of paraformaldehyde transferred was m=m0-m1. The mass of nitrogen required was calculated as M based on the mass of paraformaldehyde added m and the concentration of the formaldehyde standard to be prepared.

[0036] Then weigh the gas cylinder and let its mass be M1. The mass of nitrogen added during purging is M2 = M1 - M0 - m. Therefore, the mass of nitrogen added is M - M2.

[0037] This invention also provides a system for realizing a method for preparing standard formaldehyde bottled gas, comprising:

[0038] A reactor used to catalyze the cracking of solid paraformaldehyde into formaldehyde gas;

[0039] A transfer system is used to transfer formaldehyde gas from the reactor to a pre-saturated gas cylinder;

[0040] The temperature control system is used to control the catalytic cracking temperature and the transfer temperature;

[0041] The storage system is used to store formaldehyde standard gas, preferably using pre-saturated PW gas cylinders (+W21.8 to 1 / 4 connector) to minimize the instability of the value caused by formaldehyde adsorption in the cylinder.

[0042] The vacuum system performs vacuuming treatment on the reactor and transfer pipelines in stages.

[0043] Preferably, the reactor includes a three-way ball valve and a pipeline connected to the three-way ball valve, preferably a 1 / 4-inch pipeline. The three-way ball valve has ports A, B, and C. The pipeline is connected to port A, and paraformaldehyde, a catalyst, and silane silica wool are sequentially added into the pipeline towards port A. By optimizing the reactor structure, pyrolysis time, catalytic conditions, and other factors, the amount of formaldehyde can be accurately measured, and the concentration of the formaldehyde standard gas generated can be calculated.

[0044] Preferably, the transfer system includes a passivated transfer pipeline and a gas distribution device. The transfer pipeline connects port B to the gas cylinder, and the gas distribution device is used to purge formaldehyde gas into the gas cylinder via the transfer pipeline. The transfer pipeline contains a catalyst and silane-based silica wool. Preferably, the phosphorus pentoxide in the transfer pipeline has two adjacent sections, and the outer sides of the two adjacent phosphorus pentoxide sections are lined with silane-based silica wool. Passivation treatment of the transfer pipeline reduces the adsorption loss of formaldehyde in the transfer system. The transfer efficiency of formaldehyde gas can be improved by optimizing the purging method, for example, purging at a flow rate of ≤1 L / min in the initial stage; when the gas cylinder pressure reaches 5-7 bar, switching to a flow rate of ≤0.5 L / min to purge to the target pressure of 9-11 bar.

[0045] Preferably, the temperature control system includes a heating belt, heat-insulating aluminum foil, and a temperature control module. The heating belt is connected to the temperature control module. The pipeline and the transfer pipeline are respectively wrapped with heating belt and heat-insulating aluminum foil. The catalytic cracking temperature and the transfer temperature are set by the temperature control module to ensure catalytic and transfer efficiency.

[0046] Preferably, the vacuum system employs a high-vacuum molecular pump assembly, comprising a mechanical pump and a molecular pump.

[0047] Preferably, the system for preparing standard formaldehyde bottled gas further includes an ultrasonic system for generating ultrasonic cavitation to break up paraformaldehyde crystals. The ultrasonic system includes a piezoelectric ceramic ultrasonic transducer (frequency 40±2kHz, power density 1.5W / cm³). 2 It is wrapped around the outside of the pipeline and arranged at intervals (5mm) with the heating belt. Preferably, the ultrasonic wave is turned on only during the heating stage (100-180℃) to prevent trioxymethylene from splashing. The amplitude increases linearly with the temperature (20%→100%).

[0048] Preferably, the three-way ball valve has three operating states:

[0049] State 1: Port A is connected to Port B, and Port B is connected to the vacuum system;

[0050] State 2: Port B is connected to Port C. Port B is connected to the gas cylinder, and Port C is connected to the gas distribution device.

[0051] State 3: Closed state, ports A, B, and C are not connected to each other.

[0052] Compared with the prior art, the embodiments of this application have the following main advantages:

[0053] The method for preparing bottled formaldehyde standard gas provided by this invention achieves a pyrolysis conversion rate of ≥95%, a transfer efficiency of ≥95%, and a standard gas concentration stability of 1.6 ppb / day by optimizing the structure of the pyrolysis reactor, namely, multi-state control of the three-way ball valve, precise temperature control, segmented pressure purging and transfer, and pre-saturation treatment of the gas cylinder. This solves the technical bottleneck of formaldehyde adsorption loss and rapid decay in traditional methods. Attached Figure Description

[0054] Figure 1 This is a flowchart of a method for preparing standard formaldehyde bottled gas provided by the present invention.

[0055] Figure 2 This is a schematic diagram of the system for preparing standard formaldehyde bottled gas provided by the present invention.

[0056] Figure 3 This is a schematic diagram of the working state of the three-way ball valve in the system for realizing the method of preparing standard gas for formaldehyde bottled according to the present invention. Detailed Implementation

[0057] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein in the specification of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the terms "comprising" and "having," and any variations thereof, in the specification, claims, and foregoing drawings of this application are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the specification, claims, or foregoing drawings of this application are used to distinguish different objects, not to describe a particular order.

[0058] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0059] Example 1

[0060] This invention provides a method for preparing bottled formaldehyde standard gas, such as... Figure 1 As shown, it includes the following steps:

[0061] Solid trioxymethylene and a catalyst are placed in a reactor;

[0062] The reactor and transfer pipeline were vacuumed in stages.

[0063] The reactor is heated within a predetermined temperature range to catalytically decompose paraformaldehyde into formaldehyde gas.

[0064] The formaldehyde gas is passed through a passivated transfer pipeline and purged into a pre-saturated gas cylinder. In this embodiment, silanization passivation treatment is used to reduce adsorption.

[0065] Inert gas is added to the gas cylinder to obtain formaldehyde standard gas.

[0066] The catalyst is added at 90% of the mass of paraformaldehyde, the catalytic cracking temperature is 225℃, and the vacuum degree is ≤10. -6 hPa, the catalyst is phosphorus pentoxide (P2O5) and MOF-303 forming a core-shell structure. In preparation, MOF-303 is synthesized by a solvothermal method, and then MOF-303 is immersed in a phosphorus pentoxide saturated acetonitrile solution (50 g / L), stirred at 55 °C for 3 h, and vacuum dried to obtain the core-shell structure.

[0067] In this embodiment, segmented purging control is used during gas transfer:

[0068] First, with ≤10 -6 A vacuum of hPa is used to remove residual gas from the transfer pipeline;

[0069] High-purity nitrogen gas is introduced to purge until the cylinder pressure reaches 9 bar. The transfer efficiency of formaldehyde gas can be improved by optimizing the purging method, such as purging at a flow rate of ≤1 L / min in the initial stage; when the cylinder pressure reaches 5 bar, the flow rate is switched to ≤0.5 L / min to purge until the target pressure of 9 bar is reached.

[0070] Preferably, the pre-saturation treatment of the gas cylinder includes the following steps:

[0071] Fill the empty bottle with 10 ppm formaldehyde standard gas up to 10 bar;

[0072] Allow the gas cylinders to stand for 3 days or more. It is preferable to purchase the gas cylinders in one go based on the annual sales volume and perform saturation treatment in one go. Extending the pre-saturation time is beneficial to the stability of formaldehyde levels.

[0073] In this embodiment, the method for calculating the mass of inert gas added during the step of adding inert gas to the gas cylinder is as follows:

[0074] Prepare two sets of reactors, one for the experimental reaction and the other for weighing the reference.

[0075] After the reactor is evacuated, the mass of the reference and the reactor are weighed alternately, and the difference m0 between the reference and the reactor is recorded until the range of 6 consecutive sets of experimental data is ≤0.00005g.

[0076] Then weigh the gas cylinder and let its mass be M0;

[0077] After purging, the reactor was removed, and the mass of the reference and the reactor was weighed alternately. The difference between the reference and the reactor was recorded as m1 until the range of 6 consecutive experimental data was ≤0.00005g. The actual mass of paraformaldehyde transferred was m=m0-m1. The mass of nitrogen required was calculated as M based on the mass of paraformaldehyde added m and the concentration of the formaldehyde standard to be prepared.

[0078] Then weigh the gas cylinder and let its mass be M1. The mass of nitrogen added during purging is M2 = M1 - M0 - m. Therefore, the mass of nitrogen added is M - M2.

[0079] Example 2

[0080] This invention provides a method for preparing bottled formaldehyde standard gas, such as... Figure 1 As shown, it includes the following steps:

[0081] Solid trioxymethylene and a catalyst are placed in a reactor;

[0082] The reactor and transfer pipeline were vacuumed in stages.

[0083] The reactor is heated within a predetermined temperature range to catalytically decompose paraformaldehyde into formaldehyde gas.

[0084] The formaldehyde gas is passed through a passivated transfer pipeline and purged into a pre-saturated gas cylinder. In this embodiment, silanization passivation treatment is used to reduce adsorption.

[0085] Inert gas is added to the gas cylinder to obtain formaldehyde standard gas.

[0086] The catalyst is added at 95% of the mass of paraformaldehyde, the catalytic cracking temperature is 228℃, and the vacuum degree is ≤10. -6 hPa, the catalyst is phosphorus pentoxide (P2O5) and MOF-303 forming a core-shell structure. In preparation, MOF-303 is synthesized by a solvothermal method, and then MOF-303 is immersed in a phosphorus pentoxide saturated acetonitrile solution (50 g / L), stirred at 58°C for 3.5 h, and vacuum dried to obtain the core-shell structure.

[0087] In this embodiment, segmented purging control is used during gas transfer:

[0088] First, with ≤10-6 A vacuum of hPa is used to remove residual gas from the transfer pipeline;

[0089] High-purity nitrogen gas is introduced to purge until the cylinder pressure reaches 9.5 bar. The transfer efficiency of formaldehyde gas can be improved by optimizing the purging method, such as purging at a flow rate of ≤1 L / min in the initial stage; when the cylinder pressure reaches 5.5 bar, the flow rate is switched to ≤0.5 L / min to purge until the target pressure of 9.5 bar is reached.

[0090] Preferably, the pre-saturation treatment of the gas cylinder includes the following steps:

[0091] Fill the empty bottle with 10 ppm formaldehyde standard gas up to 10 bar;

[0092] Allow the gas cylinders to stand for 3 days or more. It is preferable to purchase the gas cylinders in one go based on the annual sales volume and perform saturation treatment in one go. Extending the pre-saturation time is beneficial to the stability of formaldehyde levels.

[0093] In this embodiment, the method for calculating the mass of inert gas added during the step of adding inert gas to the gas cylinder is as follows:

[0094] Prepare two sets of reactors, one for the experimental reaction and the other for weighing the reference.

[0095] After the reactor is evacuated, the mass of the reference and the reactor are weighed alternately, and the difference m0 between the reference and the reactor is recorded until the range of 6 consecutive sets of experimental data is ≤0.00005g.

[0096] Then weigh the gas cylinder and let its mass be M0;

[0097] After purging, the reactor was removed, and the mass of the reference and the reactor was weighed alternately. The difference between the reference and the reactor was recorded as m1 until the range of 6 consecutive experimental data was ≤0.00005g. The actual mass of paraformaldehyde transferred was m=m0-m1. The mass of nitrogen required was calculated as M based on the mass of paraformaldehyde added m and the concentration of the formaldehyde standard to be prepared.

[0098] Then weigh the gas cylinder and let its mass be M1. The mass of nitrogen added during purging is M2 = M1 - M0 - m. Therefore, the mass of nitrogen added is M - M2.

[0099] Example 3

[0100] This invention provides a method for preparing bottled formaldehyde standard gas, such as... Figure 1 As shown, it includes the following steps:

[0101] Solid trioxymethylene and a catalyst are placed in a reactor;

[0102] The reactor and transfer pipeline were vacuumed in stages.

[0103] The reactor is heated within a predetermined temperature range to catalytically decompose paraformaldehyde into formaldehyde gas.

[0104] The formaldehyde gas is passed through a passivated transfer pipeline and purged into a pre-saturated gas cylinder. In this embodiment, silanization passivation treatment is used to reduce adsorption.

[0105] Inert gas is added to the gas cylinder to obtain formaldehyde standard gas.

[0106] The catalyst is added at 100% of the mass of paraformaldehyde, the catalytic cracking temperature is 230℃, and the vacuum degree is ≤10. -6 hPa, the catalyst is phosphorus pentoxide (P2O5) and MOF-303 forming a core-shell structure. In preparation, MOF-303 is synthesized by a solvothermal method, and then MOF-303 is immersed in a phosphorus pentoxide saturated acetonitrile solution (50 g / L), stirred at 60°C for 4 h, and vacuum dried to obtain the core-shell structure.

[0107] In this embodiment, segmented purging control is used during gas transfer:

[0108] First, with ≤10 -6 A vacuum of hPa is used to remove residual gas from the transfer pipeline;

[0109] High-purity nitrogen gas is introduced to purge until the cylinder pressure reaches 10 bar. The transfer efficiency of formaldehyde gas can be improved by optimizing the purging method, such as purging at a flow rate of ≤1 L / min in the initial stage; when the cylinder pressure reaches 6 bar, the flow rate is switched to ≤0.5 L / min to purge until the target pressure of 10 bar is reached.

[0110] Preferably, the pre-saturation treatment of the gas cylinder includes the following steps:

[0111] Fill the empty bottle with 10 ppm formaldehyde standard gas up to 10 bar;

[0112] Allow the gas cylinders to stand for 3 days or more. It is preferable to purchase the gas cylinders in one go based on the annual sales volume and perform saturation treatment in one go. Extending the pre-saturation time is beneficial to the stability of formaldehyde levels.

[0113] In this embodiment, the method for calculating the mass of inert gas added during the step of adding inert gas to the gas cylinder is as follows:

[0114] Prepare two sets of reactors, one for the experimental reaction and the other for weighing the reference.

[0115] After the reactor is evacuated, the mass of the reference and the reactor are weighed alternately, and the difference m0 between the reference and the reactor is recorded until the range of 6 consecutive sets of experimental data is ≤0.00005g.

[0116] Then weigh the gas cylinder and let its mass be M0;

[0117] After purging, the reactor was removed, and the mass of the reference and the reactor was weighed alternately. The difference between the reference and the reactor was recorded as m1 until the range of 6 consecutive experimental data was ≤0.00005g. The actual mass of paraformaldehyde transferred was m=m0-m1. The mass of nitrogen required was calculated as M based on the mass of paraformaldehyde added m and the concentration of the formaldehyde standard to be prepared.

[0118] Then weigh the gas cylinder and let its mass be M1. The mass of nitrogen added during purging is M2 = M1 - M0 - m. Therefore, the mass of nitrogen added is M - M2.

[0119] Example 4

[0120] This invention provides a method for preparing bottled formaldehyde standard gas, such as... Figure 1 As shown, it includes the following steps:

[0121] Solid trioxymethylene and a catalyst are placed in a reactor;

[0122] The reactor and transfer pipeline were vacuumed in stages.

[0123] The reactor is heated within a predetermined temperature range to catalytically decompose paraformaldehyde into formaldehyde gas.

[0124] The formaldehyde gas is passed through a passivated transfer pipeline and purged into a pre-saturated gas cylinder. In this embodiment, silanization passivation treatment is used to reduce adsorption.

[0125] Inert gas is added to the gas cylinder to obtain formaldehyde standard gas.

[0126] The catalyst is added at 105% of the mass of paraformaldehyde, the catalytic cracking temperature is 232℃, and the vacuum degree is ≤10. -6 hPa, the catalyst is phosphorus pentoxide (P2O5) and MOF-303 forming a core-shell structure. In preparation, MOF-303 is synthesized by a solvothermal method, and then MOF-303 is immersed in a phosphorus pentoxide saturated acetonitrile solution (50 g / L), stirred at 62 °C for 4.5 h, and vacuum dried to obtain the core-shell structure.

[0127] In this embodiment, segmented purging control is used during gas transfer:

[0128] First, with ≤10 -6 A vacuum of hPa is used to remove residual gas from the transfer pipeline;

[0129] High-purity nitrogen gas is introduced to purge until the cylinder pressure reaches 10.5 bar. The transfer efficiency of formaldehyde gas can be improved by optimizing the purging method, such as purging at a flow rate of ≤1 L / min in the initial stage; when the cylinder pressure reaches 6.5 bar, the flow rate is switched to ≤0.5 L / min to purge until the target pressure of 10.5 bar is reached.

[0130] Preferably, the pre-saturation treatment of the gas cylinder includes the following steps:

[0131] Fill the empty bottle with 10 ppm formaldehyde standard gas up to 10 bar;

[0132] Allow the gas cylinders to stand for 3 days or more. It is preferable to purchase the gas cylinders in one go based on the annual sales volume and perform saturation treatment in one go. Extending the pre-saturation time is beneficial to the stability of formaldehyde levels.

[0133] In this embodiment, the method for calculating the mass of inert gas added during the step of adding inert gas to the gas cylinder is as follows:

[0134] Prepare two sets of reactors, one for the experimental reaction and the other for weighing the reference.

[0135] After the reactor is evacuated, the mass of the reference and the reactor are weighed alternately, and the difference m0 between the reference and the reactor is recorded until the range of 6 consecutive sets of experimental data is ≤0.00005g.

[0136] Then weigh the gas cylinder and let its mass be M0;

[0137] After purging, the reactor was removed, and the mass of the reference and the reactor was weighed alternately. The difference between the reference and the reactor was recorded as m1 until the range of 6 consecutive experimental data was ≤0.00005g. The actual mass of paraformaldehyde transferred was m=m0-m1. The mass of nitrogen required was calculated as M based on the mass of paraformaldehyde added m and the concentration of the formaldehyde standard to be prepared.

[0138] Then weigh the gas cylinder and let its mass be M1. The mass of nitrogen added during purging is M2 = M1 - M0 - m. Therefore, the mass of nitrogen added is M - M2.

[0139] Example 5

[0140] This invention provides a method for preparing bottled formaldehyde standard gas, such as... Figure 1 As shown, it includes the following steps:

[0141] Solid trioxymethylene and a catalyst are placed in a reactor;

[0142] The reactor and transfer pipeline were vacuumed in stages.

[0143] The reactor is heated within a predetermined temperature range to catalytically decompose paraformaldehyde into formaldehyde gas.

[0144] The formaldehyde gas is passed through a passivated transfer pipeline and purged into a pre-saturated gas cylinder. In this embodiment, silanization passivation treatment is used to reduce adsorption.

[0145] Inert gas is added to the gas cylinder to obtain formaldehyde standard gas.

[0146] The catalyst is added at 110% of the mass of paraformaldehyde, the catalytic cracking temperature is 235℃, and the vacuum degree is ≤10. -6 hPa, the catalyst is phosphorus pentoxide (P2O5) and MOF-303 forming a core-shell structure. In preparation, MOF-303 is synthesized by a solvothermal method, and then MOF-303 is immersed in a phosphorus pentoxide saturated acetonitrile solution (50 g / L), stirred at 65°C for 5 h, and vacuum dried to obtain the core-shell structure.

[0147] In this embodiment, segmented purging control is used during gas transfer:

[0148] First, with ≤10 -6 A vacuum of hPa is used to remove residual gas from the transfer pipeline;

[0149] High-purity nitrogen gas is introduced to purge until the cylinder pressure reaches 11 bar. The transfer efficiency of formaldehyde gas can be improved by optimizing the purging method, such as purging at a flow rate of ≤1 L / min in the initial stage; when the cylinder pressure reaches 7 bar, the flow rate is switched to ≤0.5 L / min to purge until the target pressure of 11 bar is reached.

[0150] Preferably, the pre-saturation treatment of the gas cylinder includes the following steps:

[0151] Fill the empty bottle with 10 ppm formaldehyde standard gas up to 10 bar;

[0152] Allow the gas cylinders to stand for 3 days or more. It is preferable to purchase the gas cylinders in one go based on the annual sales volume and perform saturation treatment in one go. Extending the pre-saturation time is beneficial to the stability of formaldehyde levels.

[0153] In this embodiment, the method for calculating the mass of inert gas added during the step of adding inert gas to the gas cylinder is as follows:

[0154] Prepare two sets of reactors, one for the experimental reaction and the other for weighing the reference.

[0155] After the reactor is evacuated, the mass of the reference and the reactor are weighed alternately, and the difference m0 between the reference and the reactor is recorded until the range of 6 consecutive sets of experimental data is ≤0.00005g.

[0156] Then weigh the gas cylinder and let its mass be M0;

[0157] After purging, the reactor was removed, and the mass of the reference and the reactor was weighed alternately. The difference between the reference and the reactor was recorded as m1 until the range of 6 consecutive experimental data was ≤0.00005g. The actual mass of paraformaldehyde transferred was m=m0-m1. The mass of nitrogen required was calculated as M based on the mass of paraformaldehyde added m and the concentration of the formaldehyde standard to be prepared.

[0158] Then weigh the gas cylinder and let its mass be M1. The mass of nitrogen added during purging is M2 = M1 - M0 - m. Therefore, the mass of nitrogen added is M - M2.

[0159] Example 6

[0160] This invention provides a system for implementing the formaldehyde bottled standard gas preparation method described in Examples 1-5, such as... Figures 2-3 As shown, it includes:

[0161] A reactor used to catalyze the cracking of solid paraformaldehyde into formaldehyde gas;

[0162] A transfer system is used to transfer formaldehyde gas from the reactor to a pre-saturated gas cylinder;

[0163] The temperature control system is used to control the catalytic cracking temperature and the transfer temperature;

[0164] The storage system is used to store formaldehyde standard gas, preferably using pre-saturated PW gas cylinders (+W21.8 to 1 / 4 connector) to minimize the instability of the value caused by formaldehyde adsorption in the cylinder.

[0165] The vacuum system performs vacuuming treatment on the reactor and transfer pipelines in stages.

[0166] The reactor includes a three-way ball valve and a pipeline connected to the three-way ball valve, preferably a 1 / 4-inch pipeline. The three-way ball valve has ports A, B, and C. The pipeline is connected to port A, and paraformaldehyde, a catalyst, and silane silica wool are sequentially added into the pipeline towards port A. By optimizing the reactor structure, pyrolysis time, catalytic conditions, and other factors, the amount of formaldehyde can be accurately measured, and the concentration of the formaldehyde standard gas generated can be calculated.

[0167] Furthermore, the transfer system includes a passivated transfer pipeline and a gas distribution device. The transfer pipeline connects to port B and the gas cylinder. The gas distribution device is used to purge formaldehyde gas into the gas cylinder through the transfer pipeline. The transfer pipeline contains a catalyst and silane silica cotton. Preferably, the phosphorus pentoxide in the transfer pipeline has two adjacent sections, and the outer sides of the two adjacent phosphorus pentoxide sections are lined with silane silica cotton. By passivating the transfer pipeline, the adsorption loss of formaldehyde in the transfer system is reduced.

[0168] Furthermore, the temperature control system includes a heating belt, heat-insulating aluminum foil, and a temperature control module. The heating belt is connected to the temperature control module. The pipeline and transfer pipeline are respectively wrapped with heating belt and heat-insulating aluminum foil. The catalytic cracking temperature and transfer temperature are set by the temperature control module to ensure catalytic and transfer efficiency.

[0169] Preferably, the vacuum system employs a high-vacuum molecular pump assembly, including a mechanical pump and a molecular pump.

[0170] In this embodiment, the three-way ball valve has three operating states:

[0171] State 1: Port A is connected to Port B, and Port B is connected to the vacuum system;

[0172] State 2: Port B is connected to Port C. Port B is connected to the gas cylinder, and Port C is connected to the gas distribution device.

[0173] State 3: Closed state, ports A, B, and C are not connected to each other.

[0174] In summary, the operational procedure for preparing bottled formaldehyde standard gas in this invention is as follows:

[0175] 1. Pre-saturation of gas cylinders: Select 10-liter PW gas cylinders, fill them with 10ppm 10bar formaldehyde standard gas and pre-saturate for more than 3 days; PW cylinders can be purchased according to annual sales volume and saturated in one go. Extending the pre-saturation time is beneficial to the stability of formaldehyde levels.

[0176] II. Experimental Procedure

[0177] 1. Reactor Assembly: The reactor mainly consists of a three-way ball valve and a 1 / 4-inch pipeline connected to port A. Two reactors need to be prepared before the reaction; one set is used as the experimental reaction apparatus, and the other as a weighing reference. Add silane-based silica cotton, 0.019 g of paraformaldehyde, and approximately 0.02 g of phosphorus pentoxide to the pipeline at port A. Phosphorus pentoxide readily absorbs moisture from the air in this step, therefore, the operation must be performed in a glove box. Figure 3 As shown, adjust the three-way ball valve to state 1 (i.e., AB connected). Connect the B end to the high-vacuum molecular pump assembly (including a mechanical pump and a molecular pump). After the mechanical pump evacuates, switch to the molecular pump to evacuate for about 30 seconds (note that during this process, paraformaldehyde will continue to sublimate, and the vacuum level cannot reach 10). -6 hPa, prolonged waiting will cause loss of trioxymethylene); then adjust the three-way ball valve to state 2 (i.e., BC connected state).

[0178] 2. Weigh the reference and reactor alternately, and record the difference m0 between the reference and reactor values ​​until the range of six consecutive sets of experimental data is ≤0.00005g.

[0179] 3. Weigh the gas cylinder (+W21.8 to 1 / 4 connector) to a mass M0, then proceed according to... Figure 2 As shown, P2O5 and silane-based silica cotton are added between the gas cylinder and reactor B port.

[0180] 4. Connect the reactor's C port to a high-vacuum molecular pump assembly (including a mechanical pump and a molecular pump), and evacuate the pipeline to 10... - 6 hPa, adjust the three-way ball valve to state 3 (closed).

[0181] 5. Wrap the pipeline with heating tape and insulation aluminum foil, set the heating temperature to about 230℃, and after reaching the set temperature, open the reactor (adjust to state 1, AB connected state) and the gas cylinder valve in sequence, and wait for the reaction to proceed for 5 hours.

[0182] 6. After the reaction, connect reactor port C to the gas distribution device and evacuate the pipeline to a vacuum of 10. -6 At hPa, use the needle valve of the gas distribution device to control the small flow rate of high-purity N2 to purge the pipeline. Adjust the reactor to BC connection and slowly purge high-purity N2 until the pressure inside the bottle is about 10 bar. Then close the bottle valve and stop purging (if the purging pressure is too high, the ball valve may leak, resulting in inaccurate weighing of trioxymethylene; if the purging pressure is too low, the transfer efficiency will be insufficient).

[0183] 7. Disassemble the reactor, alternately weigh the reference and the reactor, and record the difference (reference - reactor) m1 until the range of 6 consecutive experimental data sets is ≤0.00005g. The actual mass of paraformaldehyde transferred is m=m0-m1. Calculate the required mass of nitrogen M based on the mass m of added paraformaldehyde and the concentration of the formaldehyde standard gas to be prepared.

[0184] 8. Weigh the gas cylinder (+W21.8 to 1 / 4 connector) to a mass M1, and add nitrogen gas to purge the cylinder to a mass M2 = M1 - M0 - m.

[0185] 9. Nitrogen gas is added to the gas cylinder. The mass of nitrogen added = M - M2.

[0186] 10. Wait for the gas cylinder to cool down, weigh the mass of nitrogen added to the cylinder, and calculate the concentration of formaldehyde in the cylinder.

[0187] Example 7

[0188] Based on Example 3, this embodiment involves sealing the gas cylinder before pre-saturation treatment, including the following steps:

[0189] a) Inject a cholesteric liquid crystal solution containing a photoinitiator (22wt% chiral agent S811, 78wt% nematic liquid crystal E7, 0.5wt% photoinitiator TPO; the injection amount can be adjusted appropriately according to the inner surface area of ​​the gas cylinder).

[0190] b) Rotate the gas cylinder (20-40 rpm, 20-40 min, 30 rpm, 30 min in this example) to make the solution evenly cover the inner wall;

[0191] c) Ultraviolet light irradiation (8-12 min, 10 min in this example) to cure and form a liquid crystal photonic crystal film (thickness 10-30 μm, pitch 0.40-0.50 nm).

[0192] An electrode interface can be integrated at the gas cylinder valve to connect to an external electric field controller (0-10V adjustable). When formaldehyde needs to be released, a voltage is applied (the voltage V can be set to target concentration × 0.1, such as 1V corresponding to 10ppm standard gas release). The liquid crystal lattice spacing (0.1-10nm) is adjusted to control the formaldehyde release rate and open the cylinder valve to release the standard gas.

[0193] Example 8

[0194] Based on Example 6, this embodiment further includes an ultrasonic system for generating ultrasonic cavitation to break up paraformaldehyde crystals. The ultrasonic system comprises a piezoelectric ceramic ultrasonic transducer (frequency 40±2kHz, power density 1.5W / cm²). 2 It is wrapped around the outside of the pipeline and arranged at intervals (5mm) with the heating belt. Preferably, the ultrasonic wave is turned on only during the heating stage (100-180℃) to prevent trioxymethylene from splashing. The amplitude increases linearly with the temperature (20%→100%).

[0195] Comparative Example 1: Compared with Example 3, only P2O5 catalyst (without MOF-303 core-shell structure) was used to verify the deactivation prevention effect of the core-shell catalyst.

[0196] Comparative Example 2: Compared with Example 3, the gas cylinder was not pre-saturated to verify the adsorption inhibition effect on the inner wall.

[0197] Comparative Example 3: Compared with Example 3, the transfer pipeline was not passivated, and the adsorption inhibition effect of the transfer pipeline was verified.

[0198] Comparative Example 4: Simulating commercially available processes: liquid formaldehyde vaporization + ordinary steel cylinders, comprehensively comparing the shortcomings of traditional methods.

[0199] Comparative Example 5: Using a standard two-way valve (without a three-way ball valve for multi-state control), the accuracy of vacuum sealing and reaction control was verified.

[0200] The methods and products of Examples 1-5, Examples 7-8, and Comparative Examples 1-5 were tested for pyrolysis conversion rate, transfer efficiency, initial concentration, and 30-day decay rate. The test results are shown in Table 1 below:

[0201] Table 1 Test Item Results Table

[0202]

[0203] The results above show that the preparation method of the present invention has high pyrolysis conversion rate, high transfer efficiency, low attenuation rate, and good stability.

[0204] It should be noted that, for the sake of simplicity, the foregoing embodiments are all described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0205] It should be understood that the disclosed apparatus can be implemented in other ways, as illustrated in the embodiments provided in this application. For example, the apparatus embodiments described above are merely illustrative; the division of units described above is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or communication connections shown or discussed may be through some interfaces; the indirect coupling or communication connections between devices or units may be telecommunications or other forms.

[0206] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0207] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on these embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still combine, add, delete, or otherwise adjust the features of the various embodiments of the present invention according to the circumstances without conflict or creative effort, thereby obtaining different technical solutions that do not fundamentally depart from the concept of the present invention. These technical solutions also fall within the scope of protection of the present invention.

Claims

1. A method for preparing a formaldehyde bottled standard gas, characterized by, The application relates to a method for preparing a formaldehyde standard gas. The method comprises the following steps: putting solid trioxane and a catalyst into a reactor, wherein the reactor comprises a three-way ball valve with three ports A, B and C; vacuumizing the reactor and a transfer pipeline in steps by switching the three-way ball valve, wherein the switching comprises the following states: state 1: the port A is communicated with the port B, and the port B is connected with a vacuumizing system; state 2: the port B is communicated with the port C, the port B is connected with a gas cylinder, and the port C is connected with a gas distribution device; and state 3: closed state, the ports A, B and C are not communicated with each other; heating the reactor in a predetermined temperature range to make the trioxane catalytically cracked into formaldehyde gas; blowing the formaldehyde gas through a passivated transfer pipeline to a pre-saturation gas cylinder; The catalyst is added at 90-110% of the mass of paraformaldehyde, the catalytic cracking temperature is 230±5℃, and the vacuum degree is ≤10. -6 hPa, the catalyst is phosphorus pentoxide and MOF-303 forming a core-shell structure. In preparation, MOF-303 is synthesized by solvothermal method, and then MOF-303 is immersed in phosphorus pentoxide saturated acetonitrile solution, stirred at 55-65℃ for 3-5h, and vacuum dried to obtain the core-shell structure. adding inert gas into the gas cylinder to obtain the formaldehyde standard gas; First, ≤10 -6 hPa vacuum degree to remove residual gas transfer line; adopting sectional blowing control during gas transfer:

2. The method for preparing a formaldehyde bottle standard gas according to claim 1, wherein blowing high-purity nitrogen into the gas cylinder until the pressure of the gas cylinder is 9-11 bar. The pre-saturation treatment of the gas cylinder comprises the following steps: filling 10 ppm of the formaldehyde standard gas into the empty gas cylinder until the pressure of the gas cylinder is 10 bar; 3. The method for preparing a formaldehyde bottle standard gas according to claim 1, wherein standing for more than 3 days. The calculation method of the added mass of the inert gas in the step of adding inert gas into the gas cylinder is as follows: preparing two sets of reactors, one set is used for experimental reaction, and the other set is used for weighing reference; after vacuumizing the reactor, alternately weighing the mass of the reference and the reactor, recording the difference m0 between the reference and the reactor, and until the range of the continuous 6 groups of experimental data is less than or equal to 0.00005g; then weighing the mass of the gas cylinder as M0; after blowing, the reactor is removed, the mass of the reference and the reactor is alternately weighed, the difference m1 between the reference and the reactor is recorded, and until the range of the continuous 6 groups of experimental data is less than or equal to 0.00005g, the mass of the actually transferred trioxane is m=m0-m1, the mass of the required nitrogen is calculated according to the mass m of the added trioxane and the concentration of the formaldehyde standard to be prepared; then weighing the mass of the gas cylinder as M1, blowing and adding the mass M2 of nitrogen M2=M1-M0-m, and then the mass of the added nitrogen is M-M2.

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