CN115479880A - A method for measuring the permeability coefficient of high-density polyethylene film when blocking volatile organic compounds - Google Patents

Abstract

The invention provides a method for measuring the permeability coefficient when a high-density polyethylene (HDPE) film blocks volatile organic compounds, and belongs to the technical field of risk control and evaluation of organic polluted sites. Based on the existing testing methods of permeability coefficient and permeation rate of high-density polyethylene film, which are only suitable for the determination of water vapor or a single volatile organic compound, it is impossible to measure multiple volatile organic compounds at the same time. Method for Determination of Permeability Coefficient of High Density Polyethylene Films Barrier to Volatile Organic Compounds by Simulator and GC‑MS Tests. This method is highly innovative and widely applicable, and can simultaneously measure the permeability coefficient of various volatile organic compounds permeating high-density polyethylene membranes, providing technical reference for the screening and evaluation of HDPE membrane barrier repair technology for organically polluted sites.

Description

Determination of Permeability Coefficient of a High Density Polyethylene Film in Barrier of Volatile Organic Compounds method

technical field

The invention belongs to the technical field of risk control and evaluation of organic polluted sites, and in particular relates to a method for measuring the permeability coefficient of high-density polyethylene film blocking volatile organic compounds in organic polluted sites.

Background technique

Volatile organic compounds (VOCs) are easily inhaled by the human body through the air, and when they reach a certain amount, they will cause serious consequences such as damage to the human liver, kidneys, brain and nervous system. Therefore, it is very important to block the exposure route of VOCs through risk control technology. Barrier landfill technology blocks the migration and diffusion of pollutants in the soil by laying a barrier layer, isolates the polluted soil from the surrounding environment, and avoids the contact of pollutants with the human body and the harm to the human body and the surrounding environment caused by the migration of precipitation or groundwater. One of the main risk management techniques. Due to the advantages of short treatment period and low treatment cost, barrier landfill technology has been developed in my country for more than ten years and has been applied in nearly a thousand projects. Methods to block the exposure pathways of volatile organic compounds include laying barrier layers, foam covering, etc.

High-density polyethylene (HDPE) film is a common barrier material. Composite liner composed of HDPE film and soil cushion is often used in organic pollution sites and organic and heavy metal compound pollution sites. However, literature (Edil T B.A review ofaqueous-phase VOC transport in modern landfill liners[J].Waste Management,2003,23(7):561-571. and Feng Shijin, Peng Mingqing, Chen Zhanglong, et al. Pollutants in composite liners One-dimensional transient diffusion-convection migration law research [J]. Geotechnical Engineering Journal, 2022, 44(5): 799-809.) shows that VOCs can pass through HDPE membrane at a relatively fast speed. Therefore, it is very important to study the effect of VOCs passing through HDPE film.

Test methods for the permeability of plastic films and sheets include the cup weight gain and weight loss method, electrolytic sensor method, infrared detector method, humidity sensor method and differential pressure method. The cup weight gain and weight loss method uses the water vapor pressure difference on both sides of the membrane to measure the water vapor quality passing through the sample in the moisture permeable cup for a certain period of time, so as to calculate the water vapor transmission rate and water vapor transmission coefficient. Among them, the weight-increasing method means that the overall quality of the moisture-permeable cup gradually increases, and the weight-loss method means that the overall quality of the moisture-permeable cup gradually decreases. In the electrolytic sensor method, water vapor passes through the sample from the wet chamber into the dry chamber, is carried by the carrier gas into the electrolytic cell, is quantitatively absorbed by the phosphorus pentoxide on the electrode surface, and is electrolyzed into oxygen and hydrogen. According to the numerical calculation of the electrolytic current Get the water vapor transmission rate. In the infrared detector method, water vapor passes through the sample from the high-humidity chamber and enters the low-humidity chamber, and is carried by the carrier gas to the infrared detector to generate an electrical signal. The water vapor transmission rate of the sample is calculated according to the output electrical signal. In the humidity sensor method, water vapor passes through the sample from a high-humidity chamber with saturated water vapor into a low-humidity chamber, and the relative humidity and penetration time of the low-humidity chamber are measured with a humidity sensor to calculate the water vapor transmission rate of the sample. At present, the cup weight gain and weight loss method, electrolytic sensor method, infrared detector method, and humidity sensor method are only suitable for the measurement and calculation of the permeability coefficient or transmittance of water vapor permeating HDPE membranes, and cannot measure the permeation rate of volatile organic compounds. Permeability coefficient of HDPE membrane.

In the differential pressure method, the sample divides the reaction chamber into two parts, one of which is filled with 10 ⁵ Pa test gas as a high-pressure chamber, and the other part is evacuated to near zero by a vacuum pump as a low-pressure chamber. The pressure change is measured by the pressure measuring devices connected to both sides of the high-pressure chamber and the low-pressure chamber respectively, and the permeation time is recorded, so that the gas permeation amount and gas permeability coefficient can be calculated. The pressure difference method uses the pressure difference between the high-pressure chamber and the low-pressure chamber filled with the test gas to measure the gas permeation rate and gas permeability coefficient of the test gas, which can be used for volatile organic compounds. However, the differential pressure method requires a professional air permeability tester. This method is highly specialized, narrowly adaptable, and each test is only suitable for the determination of one gas permeation rate and permeability coefficient.

The invention proposes a method for measuring the permeability coefficient of the high-density polyethylene film blocking volatile organic compounds based on a high-density polyethylene film blocking simulation device and GC-MS testing. The determination method includes high-density polyethylene film barrier simulation device and GC-MS testing equipment. The high-density polyethylene film barrier simulation device is composed of two reactors. Add the mixed solution of volatile organic compounds to No. 1 reactor and seal it with HDPE film. Put the sealed No. 1 reactor into No. 2 reactor and let it stand at constant temperature. , to vaporize the volatile organic compounds and permeate the HDPE membrane through molecular diffusion into the No. 2 reactor. The amount of volatile organic compounds in the reactor was measured by gas chromatography-mass spectrometry, and the permeability coefficient was calculated. This method is highly innovative and widely applicable, and can simultaneously measure the permeability coefficients of various volatile organic compounds permeating HDPE membranes, providing technical reference for the screening and evaluation of HDPE membrane barrier repair technologies for organically polluted sites.

Contents of the invention

The purpose of the invention is to provide a method for measuring the permeability coefficient when the high-density polyethylene film blocks volatile organic compounds.

Technical scheme of the present invention:

A method for measuring the permeability coefficient when high-density polyethylene film blocks volatile organic compounds, by adding a mixed solution of volatile organic compounds into the No. 1 reactor and sealing it with an HDPE film barrier layer, and putting the sealed No. Keep the reactor at a constant temperature to vaporize the volatile organic compounds and enter the No. 2 reactor through molecular diffusion through the HDPE membrane, and measure the amount of volatile organic compounds in the No. 2 reactor by gas chromatography-mass spectrometry to calculate the permeability coefficient; Specific steps are as follows:

S1: Establish a device for volatile organic compounds to permeate HDPE membrane;

S11: Select No. 1 reactor, add HDPE film barrier layer to No. 1 reactor, and add an appropriate amount of volatile organic compound solution to No. 1 reactor, and seal it;

S12: select the No. 2 reactor, put the No. 1 reactor vertically into the No. 2 reactor, seal the No. 2 reactor, and let it stand for a period of time to measure the amount of volatile organic compounds in the No. 2 reactor;

During the standing period, the volatile organic compounds in the No. 1 reactor were transformed from liquid to gaseous, and finally reached a gas-liquid equilibrium state in the No. 1 reactor; at the same time, the volatile organic compounds in the air of the No. 1 reactor permeated through molecular diffusion The HDPE film enters the No. 2 reactor; the measurement time period of the No. 2 reactor should be selected after the volatile organic compounds in the No. 1 reactor reach the gas-liquid equilibrium state, and the time period during which the mass of the volatile organic compounds in the No. 2 reactor increases uniformly;

S2: Determination of the quality of volatile organic compounds permeating the barrier layer of HDPE film;

S21: Determination of the mass of volatile organic compounds passing through the HDPE film barrier layer of No. 1 reactor into No. 2 reactor by gas chromatography-mass spectrometry;

S211: Set test parameters according to the chromatographic-mass spectrometry-related detection standards of the volatile organic phase;

S212: Measure the mass Δm of volatile organic compounds entering the No. 2 reactor through the HDPE film barrier layer in different time periods according to the determined test parameters and standard curve;

S3: Calculate the permeability coefficient of volatile organic compounds permeating the barrier layer of HDPE film;

S31: Measure and calculate the area A of the HDPE membrane barrier layer permeating organic matter, and record the permeation time t;

S32: Calculate the partial pressures of the pollutants in Reactor No. 1 and Reactor No. 2 according to the mass of volatile organic compounds permeating the barrier layer of the HDPE film into Reactor No. 2, and calculate the pressure difference Δp;

S321: Measurement and calculation of the partial pressure p ₁ of volatile organic compounds in No. 1 reactor: replace the HDPE film barrier layer in the bottle cap of No. The internal volatile organic compounds reach gas-liquid equilibrium, that is, the concentration in the gas phase no longer increases; measure the amount of volatile organic compounds in the gas phase of No. 1 reactor after equilibrium, and calculate the partial pressure p ₁ of various volatile organic compounds;

S322: Measurement and calculation of the partial pressure _p2 of the volatile organic compounds in the No. 2 reactor: according to the amount of the volatile organic compounds in the No. 2 reactor, calculate the partial pressure p2 of various volatile organic compounds in the No. 2 reactor according to formula ( ₂ );

Calculation formula: P·V＝n·R·T (2)

Among them, P is the partial pressure p ₂ of the volatile organic compounds in the No. 2 reactor, the unit is pa; V is the volume of the No. 2 reactor minus the No. 1 reactor, and the unit is m ³ ; n is the volatile organic compound in the No. 2 reactor The amount of substance in , unit mol; R is the molar gas constant, unit J/(mol K); T is the temperature during standing, unit K;

S33: Calculate the permeability coefficient Pv according to formula (1) according to the mass of volatile organic compounds Δm, unit g, the area A of HDPE membrane permeating organic matter, unit m ² , the reaction time t, unit h, and the pressure difference Δp, unit pa. g/(m2 ^· h·pa);

Calculation formula:

For the No. 1 reactor above, select a glass bottle with a volume of 1-5mL and an open cap, and cut the HDPE film to a size suitable for the cap; insert the cut HDPE film into the cap of Reactor No. 1, and pass it through the silicone ring. enhance its tightness.

For the No. 2 reactor, select a glass bottle with a volume of 20-40 mL and a lid, and place the sealed No. 1 reactor vertically in the No. 2 reactor.

Beneficial effects of the present invention: by adding the mixed solution of volatile organic compounds into No. 1 reactor and sealing it with HDPE film, putting the sealed No. 1 reactor into No. Molecular diffusion permeates the HDPE membrane into the No. 2 reactor, and the method of measuring the amount of volatile organic compounds in the reactor by gas chromatography-mass spectrometry calculates the permeability coefficient. The method is widely applicable and can simultaneously measure the permeability coefficient of various volatile organic compounds permeating HDPE membrane. The permeability coefficient of volatile organic compounds determined by this invention patent can provide a reference for the barrier effect of using high-density polyethylene film as a barrier material in organically polluted sites.

Description of drawings

Figure 1 is a schematic diagram of the experiment.

detailed description

The specific implementation manners of the present invention will be further described below in conjunction with the accompanying drawings and technical solutions.

Example 1

Determination of the permeability coefficient of 23 kinds of volatile organic compounds in the basic items of "Soil Environmental Quality Construction Land Soil Pollution Risk Management and Control Standards"

S1: Establish a device for volatile organic compounds to permeate HDPE membrane;

In step S1, the method for establishing the device for volatile organic compounds to permeate the HDPE membrane comprises the following steps:

S11: Select No. 1 reactor, add a high-density polyethylene film barrier layer to No. 1 reactor, and add volatile organic compound solution to No. 1 reactor, and seal it;

S111: Select a chromatographic vial with a volume of 1.5 mL as the No. 1 reactor, and cut a 0.5 mm thick high-density polyethylene film to a size suitable for the cap. Use a vernier caliper to measure the inner diameter of the cap of the chromatographic vial to be 0.88cm, and the diameter of the cap mouth to be 0.66cm;

S112: Insert the cut high-density polyethylene film into the bottle cap of No. 1 reactor, and enhance its sealing performance with a silicone pad. From top to bottom, there are bottle cap, silicone ring, and high-density polyethylene film. Among them, the thickness of the annular silicone pad is 0.5mm, the diameter of the outer ring is 0.88cm, and the diameter of the inner ring is 0.66cm;

S113: Select 23 kinds of volatile organic compounds in the basic items of "Soil Environmental Quality Construction Land Soil Pollution Risk Management and Control Standard GB36600-2018". Prepare a standard mixed solution of volatile organic compounds with a concentration of 200 μg/mL and a solvent of methanol. Take 100μL of the standard mixed solution and add it to a 1.5mL chromatographic vial.

S12: select the No. 2 reactor, put the No. 1 reactor into the No. 2 reactor, seal the No. 2 reactor, and let it stand for a period of time;

S121: Select a purge and trap bottle with a volume of 40mL as the No. 2 reactor, place the sealed No. 1 reactor vertically upwards in the No. 2 reactor, and place it in a 30°C artificial climate box after sealing.

S2: Determination of the quality of volatile organic compounds permeating the HDPE membrane;

S21: Measure the mass of volatile organic compounds passing through the HDPE film barrier layer of the No. 1 reactor and entering the No. 2 reactor by gas chromatography-mass spectrometry.

S211: Set test parameters according to the characteristics of 23 kinds of volatile organic compounds and "Determination of Volatile Organic Compounds in Soil and Sediments Headspace/Gas Chromatography-Mass Spectrometry HJ 642-2013";

S212: According to the determined test parameters, measure the mass Δm of volatile organic compounds passing through the HDPE film barrier layer into the No. 2 reactor within 1h-188h, the unit is g, and take 8 time points between 21h-188h.

In this experiment, Δm is the interval in which the mass increases uniformly. When standing for 21 hours, the gas-liquid phase in reactor No. 1 has reached equilibrium, and the amount of volatile organic compounds in reactor No. 2 has no longer increased uniformly after 188 hours. A linear fit was performed on the eight time points sampled to ensure a uniform increase in mass over this interval.

S3: Calculate the permeability coefficient of volatile organic compounds permeating the HDPE membrane.

S31: Measure and calculate the area A of the HDPE membrane permeating the organic matter to be 3.42*10 ^-5 m ² ; record the reaction time t in h;

S32: According to the quality of the volatile organic compounds entering the No. 2 reactor according to the penetration of the HDPE film barrier layer, calculate the pressure of the pollutants in the No. 1 reactor and the No. 2 reactor respectively, and calculate the pressure difference Δp, unit pa;

S321: Measurement and calculation _of pressure p1 inside the membrane: replace the high-density polyethylene membrane and silica gel ring in the No. The volatile organic compounds in the vial reached gas-liquid equilibrium. The equilibrium state has been reached at 21h in the experiment. Use a 250 μl manual injection needle to quickly inject 200 μl of gas into the gas chromatograph inlet to measure the amount of volatile organic compounds. Calculate the partial pressure p ₁ of various volatile organic compounds in the No. 1 reactor according to the mass according to formula (2).

Calculation formula: P·V＝n·R·T (2)

Wherein, P is the partial pressure p ₁ (unit: pa) of the volatile organic compound in the No. 1 reactor, V is the volume of the No. 1 reactor, 0.0015m ³ , and n is the substance of the volatile organic compound in the No. 1 reactor The amount (unit: mol), R is the molar gas constant, 8.31J/(mol·K), T is the temperature during standing, 303.15K.

S322: Calculation of external pressure p ₂ of the membrane: calculate the partial pressure p ₂ of various volatile organic compounds in the No. 2 reactor according to formula (2) according to the amount of volatile organic compounds in the No. 2 reactor.

S33: Calculate the permeability coefficient Pv according to the formula (1) according to the mass Δm of the volatile organic matter, the area A of the HDPE membrane permeating the organic matter, the reaction time t, and the pressure difference Δp, and the unit is g/(m ² ·h·pa).

Calculation formula:

Calculate the permeability coefficient Pv. The abscissa is the product of the area A of the high-density polyethylene membrane permeating organic matter, the permeation time t, and the pressure difference Δp inside and outside the membrane, and the mass m is the ordinate. Linear fitting is performed with Origin, and the intercept is set to 0. The slope obtained by fitting is the permeability coefficient Pv. The permeability coefficients and R2 values of ²³ VOCs are shown in Table 1.

Table 1 Permeability coefficient (unit: g/(m ² ·h·pa)) and R ² value of 23 kinds of VOCs

Claims (3)

1. a kind of assay method of permeability coefficient when high-density polyethylene film cuts off volatile organic matter, it is characterized in that, by adding volatile organic compound mixed solution in No. 1 reactor and sealing with high-density polyethylene HDPE film barrier layer, sealing The final No. 1 reactor was placed in No. 2 reactor and kept at a constant temperature, so that the volatile organic compounds were vaporized and penetrated into the HDPE membrane through molecular diffusion into No. 2 reactor, and the volatile organic compounds in No. 2 reactor were determined by gas chromatography-mass spectrometry. The method for calculating the amount of sexual organic matter, calculates the permeability coefficient; the specific steps are as follows: S1: Establish a device for volatile organic compounds to permeate HDPE membrane; S11: Select No. 1 reactor, add HDPE film barrier layer to No. 1 reactor, and add an appropriate amount of volatile organic compound solution to No. 1 reactor, and seal it; S12: select the No. 2 reactor, put the No. 1 reactor vertically into the No. 2 reactor, seal the No. 2 reactor, and let it stand for a period of time to measure the amount of volatile organic compounds in the No. 2 reactor; During the standing period, the volatile organic compounds in the No. 1 reactor were transformed from liquid to gaseous, and finally reached a gas-liquid equilibrium state in the No. 1 reactor; at the same time, the volatile organic compounds in the air of the No. 1 reactor permeated through molecular diffusion The HDPE film enters the No. 2 reactor; the measurement time period of the No. 2 reactor should be selected after the volatile organic compounds in the No. 1 reactor reach the gas-liquid equilibrium state, and the time period during which the mass of the volatile organic compounds in the No. 2 reactor increases uniformly; S2: Determination of the quality of volatile organic compounds permeating the barrier layer of HDPE film; S21: Determination of the mass of volatile organic compounds passing through the HDPE film barrier layer of No. 1 reactor into No. 2 reactor by gas chromatography-mass spectrometry; S211: Set test parameters according to the gas chromatography-mass spectrometry detection standard of volatile organic compounds; S212: Measure the mass Δm of volatile organic compounds entering the No. 2 reactor through the HDPE film barrier layer in different time periods according to the determined test parameters and standard curve; S3: Calculate the permeability coefficient of volatile organic compounds permeating the barrier layer of HDPE film; S31: Measure and calculate the area A of the HDPE membrane barrier layer permeating organic matter, and record the permeation time t; S32: Calculate the partial pressures of the pollutants in Reactor No. 1 and Reactor No. 2 according to the mass of volatile organic compounds permeating the barrier layer of the HDPE film into Reactor No. 2, and calculate the pressure difference Δp; S321: Measurement and calculation of the partial pressure p ₁ of volatile organic compounds in No. 1 reactor: Replace the HDPE film barrier layer in the cap of No. 1 reactor with a silicone-polytetrafluoro composite gasket with excellent sealing performance and impermeability. Make the volatile organic compounds in No. 1 reactor reach gas-liquid equilibrium, that is, the concentration in the gas phase no longer increases; measure the amount of volatile organic compounds in the gas phase of No. 1 reactor after equilibrium, and calculate the partial pressure p ₁ of various volatile organic compounds; S322: Measurement and calculation of the partial pressure _p2 of the volatile organic compounds in the No. 2 reactor: according to the amount of the volatile organic compounds in the No. 2 reactor, calculate the partial pressure p2 of various volatile organic compounds in the No. 2 reactor according to formula ( ₂ ); Calculation formula: P·V＝n·R·T (2) Among them, P is the partial pressure p ₂ of the volatile organic compounds in the No. 2 reactor, the unit is pa; V is the volume of the No. 2 reactor minus the No. 1 reactor, and the unit is m ³ ; n is the volatile organic compound in the No. 2 reactor The amount of substance in , unit mol; R is the molar gas constant, unit J/(mol K); T is the temperature during standing, unit K; S33: Calculate the permeability coefficient Pv according to formula (1) according to the mass of volatile organic compounds Δm, unit g, the area A of HDPE membrane permeating organic matter, unit m ² , the reaction time t, unit h, and the pressure difference Δp, unit pa. g/(m2 ^· h·pa); Calculation formula:

2. the assay method of permeability coefficient when high-density polyethylene film according to claim 1 cuts off volatile organic matter, it is characterized in that, No. 1 reactor chooses volume and is 1-5mL, has the glass bottle of opening cap, HDPE film Cut to fit the size of the bottle cap; put the cut HDPE membrane into the open bottle cap of Reactor 1, and enhance its sealing with a silicone ring. 3. the assay method of permeability coefficient when high-density polyethylene film according to claim 1 cuts off volatile organic matter, it is characterized in that, No. 2 reactor chooses volume to be the glass bottle of 20-40mL, good sealing performance lid, put The sealed No. 1 reactor was vertically placed in the No. 2 reactor.

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