Method for representing long-term release mechanism of volatile organic compounds in indoor material

Abstract

The invention belongs to the field of indoor environment health research, and particularly relates to a method for effectively representing a volatile organic compound (VOCs) release mechanism of an indoor material under long-term physical and chemical action. According to the method, accurate and effective characterization of the long-term release characteristic of the material is realized by simplifying a complex physical and chemical coupling problem and combining an aging test and a parameter determination experiment. The method comprises the following steps: designing a natural aging experiment to simulate an actual long-term release process of a material; extracting material samples with different aging times, and determining corresponding VOCs key parameters by utilizing an environment chamber experiment; and fitting the change of the key parameters along with time by using a single exponential function so as to characterize the long-term release characteristic of the VOCs in the material. The method is suitable for material-VOCs combined release research under different temperature and humidity conditions, and results can be used for long-term concentration prediction of indoor VOCs in a dynamic environment and further applied to reasonable material selection in building design, ventilation design in specific space and time, health risk assessment and the like.

Description

Technical Field

[0001] The invention belongs to the field of indoor environmental health, and particularly relates to an effective method capable of characterizing the long-term release mechanism of volatile organic compounds in indoor materials under the action of physical and chemical coupling. Background Art

[0002] People spend more than 85% of their lives in indoor building environments (residential and office buildings). Building materials and furniture are a continuous source of indoor volatile organic compounds (VOCs), accounting for about 90% of the total observed indoor VOCs. Indoor air pollution can cause a series of respiratory and cardiovascular diseases. In addition, some VOCs, especially benzene, toluene, ethylbenzene, xylene and formaldehyde, are carcinogenic or mutagenic. Among them, the International Agency for Research on Cancer (IARC) clearly stated that benzene and formaldehyde are classified as Class A carcinogens. A study on long-term indoor formaldehyde concentration monitoring in newly renovated homes and offices in China showed that most buildings could not be reduced to the safety limit set by GB / T 18883-2022 "Indoor Air Quality Standard" after 12 months of ventilation. In an article in 2023, the journal Nature pointed out that there is an urgent need to conduct long-term investigations on indoor air pollution, and emphasized that there is a significant gap in the current research on the impact of long-term exposure to indoor air pollutants on human health, calling on all sectors to pay attention to it. Most of the previous studies on VOCs released from building materials and furniture focused on the short-term release process, while ignoring the long-term release characteristics and their impact on indoor air quality. In addition to physical diffusion, the long-term release process of materials also includes chemical reactions such as hydrolysis, which makes the release mechanism of VOCs more complicated. In addition, temperature and humidity significantly affect the release of VOCs, among which increased temperature significantly promotes the release of VOCs. Therefore, under the combined effect of dynamic environmental factors and chemical reactions, indoor materials may still release a large amount of VOCs after long-term use. Therefore, studying the long-term release mechanism of building materials and furniture and their impact on indoor air quality has important academic significance and broad application prospects. Summary of the invention

[0003] The purpose of the present invention is to address the current lack of theoretical research and characterization methods for the long-term release characteristics of volatile organic compounds (VOCs) in indoor materials under the combined effects of physical diffusion and chemical reaction. The present invention proposes a simple and innovative characterization method for revealing the long-term release characteristics of VOCs in indoor materials.

[0004] In order to achieve the above purpose, the present invention designs a natural aging experiment for indoor materials to study the changes in VOCs release over time during use. In combination with the environmental chamber experimental system, the three key release parameters of VOCs at different aging times (initial concentration C0, diffusion coefficient D m , distribution coefficient K); the key parameters measured at each aging time node are used to comprehensively characterize the long-term VOCs release characteristics of indoor materials. It includes the following steps:

[0005] 1) Purchase experimental materials and cut them into small samples, and wrap the five surfaces of the samples that do not release VOCs with aluminum foil to achieve a one-dimensional release consistent with actual use; then place the prepared samples on a stainless steel rack for natural aging, and the rack is placed in a naturally ventilated indoor environment;

[0006] 2) In order to simulate the real indoor environment, the room used in the aging experiment was air-conditioned in summer and heated in winter, but the indoor temperature or relative humidity was not strictly controlled;

[0007] 3) The samples that were not subjected to aging experiments were used as the control group and sealed with plastic wrap and ziplock bags in the laboratory to measure the key parameters of VOCs release of the materials in their initial state;

[0008] 4) Every two to three months, regularly take multiple samples of each material for parameter measurement experiments;

[0009] 5) Before conducting the parameter measurement experiment, the sample must be sealed and stored for a certain period of time to ensure that the VOCs concentration in the material is evenly distributed;

[0010] 6) At the beginning of the experiment, use acetone or alcohol to clean the inner wall of the environmental chamber, and then use clean air to blow away the remaining pollutants in the chamber;

[0011] 7) Set the gas temperature and relative humidity in the environmental chamber to the required values, with the control accuracy of temperature and relative humidity being ±0.5°C and ±5% respectively;

[0012] 8) Place the single-sided release samples with the same aging time and uniform internal VOCs distribution into the environmental chamber after the purge, and seal the environmental chamber;

[0013] 9) Use online monitoring equipment to directly measure the VOCs concentration in the environmental chamber until the VOCs concentrations in the material phase and the air phase in the chamber reach equilibrium; if there is no online VOCs analysis equipment, skip step 9) and proceed directly to step 10); otherwise skip steps 10) and 11);

[0014] 10) When the VOCs concentrations in the material phase and the air phase in the chamber reach equilibrium, use a dinitrophenylhydrazone adsorption tube DNPH (for aldehydes and ketones) or a Tenax adsorption tube enax-TA (for non-aldehydes and ketones) connected to a high-precision sampling pump at the air outlet of the environmental chamber to collect gas phase VOCs to determine the gas phase equilibrium concentration C of VOCs. equ ; After sampling, open the high-pressure gas cylinder and introduce pure air into the environmental chamber. At this time, the material begins to release VOCs; then select appropriate time intervals to collect VOCs gas at the air outlet of the environmental chamber using DNPH or Tenax-TA, and end the experiment when the gas phase VOCs concentration is basically reduced to a stable level;

[0015] 11) Use high performance liquid chromatography (HPLC) or gas chromatography-mass spectrometry (GC-MS) for quantitative analysis to obtain the hourly concentration C of each VOCs in the environmental chamber. a ;

[0016] 12) Establish a physical model of the VOCs release process of indoor materials in the environmental chamber, wherein step 9) corresponds to equations (1) and (3); steps 10) and 11) correspond to equations (2) and (3):

[0017]

[0018]

[0019] In this model: C a is the gas phase VOCs concentration in the environmental chamber, μg / m 3 ; C equ is the equilibrium concentration of gas-phase VOCs in the environmental chamber, μg / m 3 ; t is the release time, s; D m is the diffusion coefficient of VOCs in the material, m 2 / s; K is the distribution coefficient of VOC in the material; A is the surface area of ​​the material, m 2 ; L is the material thickness, m; V is the volume of the environmental chamber, m 3 ; β = AL / V, which represents the ratio of the material volume to the environmental chamber volume; p n and q n About D m and K function; h m is the convective mass transfer coefficient, m 2 / s;Bi m =h m L / D m , is the mass transfer Biot number;

[0020] 13) The hourly concentration C of each VOCs obtained from the experimental test aand equilibrium concentration C equ The data is combined with equation (1) or (2), and the particle swarm coupled ant colony algorithm is used for nonlinear fitting to obtain the diffusion coefficient D of VOCs in the material at different aging times. m and the distribution coefficient K; then the initial concentration C0 is determined by combining K and formula (3);

[0021] 14) At the same temperature, the D m and K fluctuate with aging time, while C0 decreases exponentially with aging time; the C0 determined at each aging time is fitted with a single exponential function nonlinearly to determine the quantitative change law of VOCs release in the material with aging time; the research method of VOCs long-term release characteristics of the material under different temperature and humidity conditions is the same.

[0022] Features and effects of the present invention:

[0023] The present invention has significant advantages in the field of long-term release of VOCs involving complex physical diffusion and chemical reactions inside materials, solves the bottleneck problem in the prior art, and provides an effective tool for studying and controlling the impact of long-term gaseous pollutants on indoor environment and human health. The present invention designs a simple aging test and combines it with an environmental chamber test system to comprehensively characterize the long-term release characteristics of VOCs in materials. This method can also be extended to the study of long-term release of VOCs in materials under different environmental factors (temperature and relative humidity), providing a reliable basis for realizing the prediction of long-term release concentration of VOCs under dynamic environmental factors and exposure health research. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of material aging experiment in indoor environment

[0025] Figure 2 Experimental system diagram for parameter determination experiment

[0026] Figure 3 Nonlinear fitting results of formaldehyde concentration released from medium density fiberboard at different aging times

[0027] Figure 4 The nonlinear fitting results of single exponential function of C0 and aging time DETAILED DESCRIPTION

[0028] The present invention proposes a relatively simple method that can effectively characterize the long-term release mechanism of volatile organic compounds under the comprehensive physical and chemical effects of indoor materials, which is described in detail as follows in conjunction with the accompanying drawings and examples:

[0029] The schematic diagram of the aging experiment of the indoor material of the present invention is as follows Figure 1As shown. The VOCs key parameter test system in materials with different aging times consists of four parts: air intake system, temperature and humidity control system, sampling system and environmental chamber. The air intake system consists of a high-pressure gas cylinder 1 with a pressure reducing valve, a valve 2 and a mass flow controller 3; the temperature and humidity control system consists of a closed cabin filled with pure water 4, a three-way valve 5, an empty closed cabin 6, a temperature and humidity monitor 7, and a constant temperature water bath 9, which are used to adjust and control the temperature and humidity of the air inside the environmental chamber 10; the INNOVA-1214i online monitoring device is used to measure the formaldehyde concentration.

[0030] A method for determining the long-term release characteristics of formaldehyde in a commonly used medium density board in this example comprises the following steps:

[0031] 1) Purchase medium density fiberboard raw materials and cut them into small samples, each with a geometric surface area of ​​approximately 11 cm × 11 cm. Wrap the five non-formaldehyde-releasing surfaces of the samples with aluminum foil to achieve a one-dimensional release consistent with actual use. Place the prepared samples on a stainless steel rack for natural aging. The rack is placed in a naturally ventilated 9m 2 In indoor environment;

[0032] 2) In order to simulate the real indoor environment, the room used in the aging experiment was air-conditioned in summer and heated in winter, but the indoor temperature or relative humidity was not strictly controlled;

[0033] 3) The samples that were not subjected to the aging experiment were used as the control group and sealed with plastic wrap and ziplock bags in the laboratory to measure the key parameters of formaldehyde release of the materials in their initial state;

[0034] 4) Randomly select 5 MDF samples for parameter determination experiments on the 93rd, 155th, 208th, 277th, 337th and 417th days of the aging experiment;

[0035] 5) Before conducting the parameter determination experiment, the sample must be sealed and stored for 2 months to ensure that the VOCs concentration in the material is evenly distributed;

[0036] 6) At the beginning of the experiment, use acetone or alcohol to clean the inner wall of the environmental chamber, and then use clean air to blow away the remaining pollutants in the chamber;

[0037] 7) Set the gas temperature and relative humidity in the environmental chamber to 25°C and 50%, and the control accuracy of temperature and relative humidity are ±0.5°C and ±5%, respectively;

[0038] 8) Place the single-sided release samples with the same aging time and uniform formaldehyde distribution in the environmental chamber after the purge, and seal the environmental chamber;

[0039] 9) Use the online monitoring device INNOVA-1214i to directly measure the hourly formaldehyde concentration C in the environmental chamber a Until the formaldehyde concentration in the cabin material phase and the air phase reaches equilibrium C equ ;

[0040] 10) Establish a physical model of the formaldehyde release process of indoor materials in the environmental chamber:

[0041]

[0042] In this model: C a is the concentration of gaseous formaldehyde in the environmental chamber, μg / m 3 ; C equ is the equilibrium concentration of gaseous formaldehyde in the environmental chamber, μg / m 3 ; t is the release time, s; D m is the diffusion coefficient of formaldehyde in medium density fiberboard, m 2 / s; K is the distribution coefficient of formaldehyde in medium density board; A is the release surface area of ​​medium density board, m 2 ; L is the thickness of the medium density board, m; V is the volume of the environmental chamber, m 3 ; β = AL / V, which represents the ratio of the volume of the MDF to the volume of the environmental chamber; p n About D m and K function; h m is the convective mass transfer coefficient, m 2 / s;Bi m =h m L / D m , is the mass transfer Biot number;

[0043] 11) The hourly concentration of formaldehyde obtained by the experimental test C a and equilibrium concentration C equ The data is combined with equation (1) or (2), and the particle swarm coupled ant colony algorithm is used for nonlinear fitting to obtain the diffusion coefficient D of VOCs in the material at different aging times. m and distribution coefficient K; then combine K and formula (3) to calculate and determine the initial concentration C0; the fitting results are as follows Figure 3 As shown;

[0044] 12) At 25°C, the D value of formaldehyde in medium density board m and K fluctuate with aging time, with average values ​​of 2.18×10 -10 m 2 / s and 6.90×10 2 ; C0 shows an exponential downward trend with aging time; the C0 determined at each aging time is fitted with a single exponential function nonlinearly to determine the quantitative change law of VOCs release in the material with aging time. The results are as follows Figure 4 shown.

[0045] The principle of the present invention is as follows: the natural aging experiment comprehensively considers the potential physical and chemical mechanisms that affect the long-term release characteristics of VOCs in indoor materials, including the diffusion of VOCs inside the material and its release to the indoor environment, the adsorption and secondary release of VOCs, and the hydrolysis reaction inside the material; the indoor materials after different aging times are placed in an environmental chamber for testing, and combined with the mass transfer model, a particle swarm coupled ant colony algorithm is used to perform a global search inversion to obtain the key parameters in the model that characterize the release of VOCs in the material at different aging times; the release parameters at all aging times are comprehensively considered to further determine the theoretical relationship between the characteristic parameters and time of the long-term release process of VOCs in indoor materials.

Claims

1. A method for characterizing the long-term release mechanism of volatile organic compounds in indoor materials, comprising the following steps: 1) Purchase experimental materials and cut them into small samples, and wrap the five surfaces of the samples that do not release volatile organic compounds (VOCs) with aluminum foil to achieve a one-dimensional release consistent with actual use; then place the prepared samples on a stainless steel bracket for natural aging, and the bracket is placed in a naturally ventilated indoor environment; 2) In order to simulate the real indoor environment, the room used in the aging experiment was air-conditioned in summer and heated in winter, but the indoor temperature or relative humidity was not strictly controlled; 3) The samples that were not subjected to aging experiments were used as the control group and sealed with plastic wrap and ziplock bags in the laboratory to measure the key parameters of VOCs release of the materials in their initial state; 4) Every two to three months, regularly take multiple samples of each material for parameter measurement experiments; 5) Before conducting the parameter measurement experiment, the sample must be sealed and stored for a certain period of time to ensure that the VOCs concentration in the material is evenly distributed; 6) At the beginning of the experiment, use acetone or alcohol to clean the inner wall of the environmental chamber, and then use clean air to blow away the remaining pollutants in the chamber; 7) Set the gas temperature and relative humidity in the environmental chamber to the required values, with the control accuracy of temperature and relative humidity being ±0.5°C and ±5% respectively; 8) Place the single-sided release samples with the same aging time and uniform internal VOCs distribution into the environmental chamber after the purge, and seal the environmental chamber; 9) Use online monitoring equipment to directly measure the VOCs concentration in the environmental chamber until the VOCs concentration in the material phase and the air phase in the chamber reaches equilibrium; If there is no online VOCs analysis equipment, skip step 9) and proceed directly to step 10); otherwise skip steps 10) and 11); 10) When the VOCs concentrations in the material phase and the air phase in the chamber reach equilibrium, use a dinitrophenylhydrazone adsorption tube DNPH (for aldehydes and ketones) or a Tenax-TA adsorption tube (for non-aldehydes and ketones) connected to a high-precision sampling pump at the air outlet of the environmental chamber to collect gas-phase VOCs to determine the gas-phase equilibrium concentration C of VOCs. equ ; After sampling, open the high-pressure gas cylinder and introduce pure air into the environmental chamber. At this time, the material begins to release VOCs; then select appropriate time intervals to collect VOCs gas at the air outlet of the environmental chamber using DNPH or Tenax-TA, and end the experiment when the gas phase VOCs concentration is basically reduced to a stable level; 11) Use high performance liquid chromatography (HPLC) or gas chromatography-mass spectrometry (GC-MS) for quantitative analysis to obtain the hourly concentration C of each VOCs in the environmental chamber. a ; 12) Establish a physical model of the VOCs release process of indoor materials in the environmental chamber, wherein step 9) corresponds to equations (1) and (3); steps 10) and 11) correspond to equations (2) and (3): In this model: C a is the gas phase VOCs concentration in the environmental chamber, μg / m 3 ; C equ is the equilibrium concentration of gas-phase VOCs in the environmental chamber, μg / m 3 ; t is the release time, s; D m is the diffusion coefficient of VOCs in the material, m 2 / s; K is the distribution coefficient of VOC in the material; A is the surface area of ​​the material, m 2 ; L is the material thickness, m; V is the volume of the environmental chamber, m 3 ; β = AL / V, which represents the ratio of the material volume to the environmental chamber volume; p n and q n About D m and K function; h m is the convective mass transfer coefficient, m 2 / s;Bi m =h m L / D m , is the mass transfer Biot number; 13) The hourly concentration C of each VOCs obtained from the experimental test a (t) and equilibrium concentration C equ The data is combined with equation (1) or (2), and the particle swarm coupled ant colony algorithm is used for nonlinear fitting to obtain the diffusion coefficient D of VOCs in the material at different aging times. m and the distribution coefficient K; then the initial concentration C0 is determined by combining K and formula (3); 14) At the same temperature, the D m and K fluctuate with aging time, while C0 decreases exponentially with aging time; The C0 determined at each aging time was subjected to a single exponential function nonlinear fitting to determine the quantitative change pattern of VOCs release in the material with aging time; the research method for the long-term release characteristics of VOCs of the material under different temperature and humidity conditions was the same.

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