Method for detecting hydrocarbon in compressed gas

Abstract

The invention relates to a method for detecting hydrocarbon in compressed gas, a gas chromatograph and a thermal desorption instrument are combined for detection, and experimental consumables used during detection comprise an adsorption tube and a chromatographic column; the method comprises the following steps: preparing a hydrocarbon solution with known concentration as a stock solution, designing an experiment by taking the sample adding volume of the stock solution as an independent variable to obtain a regression analysis equation, and calculating the hydrocarbon content according to a quantitative formula Xm = V * C * VC. According to the invention, a direct sample introduction method for detecting hydrocarbon in compressed gas is innovated, the enrichment characteristic of the adsorption tube is utilized, online configuration before direct sample introduction is avoided, the sample detection is more maneuverable, and the device is very suitable for the characteristics of serving multiple clients by a laboratory platform, and the uncertainty loss of an air bag sampling mode is avoided. The sampling device is small in sampling size and convenient to transport; and the compound fixed by the adsorbent is difficult to lose or escape in the natural environment.

Description

Technical Field

[0001] The invention relates to a method for detecting hydrocarbons in compressed gas, belonging to the technical field of medical compressed gas detection. Background Art

[0002] The process gases used in the production and inspection of medical devices are high-pressure gases. These gases can directly or indirectly come into contact with sterile, implantable medical devices during processes such as purging and initial product packaging. The use of uncontrolled compressed gases in production activities can directly or indirectly contaminate medical devices, impacting their safety during clinical use. Relevant requirements for compressed gas control are outlined in documents such as the industry standard YY / T 0033-2000, "Management Specification for the Production of Sterile Medical Devices," the national standard GB 50457-2019, "Design Specification for Cleanrooms in the Pharmaceutical Industry," and the GMP regulation, "Good Manufacturing Practice for Medical Devices."

[0003] The main pollutants in compressed gas systems are particulate matter, microorganisms, moisture and oil.

[0004] Currently, compressed gas is usually tested for single items such as particulate matter, microorganisms, moisture, and oil. For example, for particulate matter detection, an online particle detector is generally used, such as the "A Method for Testing the Cleanliness of Compressed Air Pipelines on Offshore Oil Platforms" disclosed in Publication (Announcement) No. CN104316564B and the "A Test Method for Detecting Microorganisms in Compressed Gas" disclosed in Publication (Announcement) No. CN106324052B; these patents all include detection of particulate matter, microorganisms, moisture, and oil.

[0005] After extensive searching, no method for detecting hydrocarbons in compressed gas has been found. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the present invention provides a method for detecting hydrocarbons in compressed gas. The specific technical solution is as follows:

[0007] A method for detecting hydrocarbons in compressed gas is performed by combining a gas chromatograph and a thermal desorber. The experimental consumables used in the detection include adsorption tubes and chromatographic columns. The experimental steps are as follows:

[0008] Step 1: Collect a fixed volume of compressed gas as a sample using an adsorption tube. During the sampling phase, screen the adsorption tube to determine the working flow rate of the adsorption tube, the total sample volume, and the operating parameters of the gas chromatograph and the thermal desorber.

[0009] Step 2: Prepare a hydrocarbon solution of known concentration as a stock solution, use the volume of the stock solution as the independent variable, design an experiment, and obtain the regression analysis equation:

[0010] y = k*V + d, y is the peak area detected by the adsorption tube, V is the volume of hydrocarbons in the sample / stock solution, and k and d are constants;

[0011] The regression equation uses a stock solution with a known hydrocarbon concentration to determine the functional relationship between the peak area y detected in the adsorption tube and the sample volume V of the hydrocarbon in the stock solution. Once the functional relationship is determined, in actual application, the sample volume V of the hydrocarbon in the sample can be calculated by measuring the peak area y detected in the adsorption tube using a sample collected by the adsorption tube (in this case, the hydrocarbon concentration in the sample is unknown, and although the actual injection volume is known, the sample volume of the hydrocarbon is unknown).

[0012] Step 3: According to the quantitative formula Xm=V×C×V C Calculate hydrocarbon content;

[0013] Xm is the hydrocarbon content, mg / m 3 ; C is the concentration of the stock solution, mg / μL; V C is the volume coefficient, V C =1000 / actual volume of sample.

[0014] As a further improvement, when the sample is prepared by a compression system, the total peak area detected in the sample is y0, and the background peak area of ​​the environment in which the compression system is located is y1, y=y0-y1.

[0015] As a further improvement, when the sample is from a pre-filled container, the total peak area detected in the sample is y0, and y=y0.

[0016] As a further improvement, the actual volume of the sample is equal to the product of the working flow of the adsorption tube and the sampling time.

[0017] Beneficial effects of the present invention:

[0018] The present invention innovates the direct injection method for detecting hydrocarbons in compressed gas, utilizes the enrichment characteristics of the adsorption tube, avoids the online configuration before direct injection, and makes the detection of samples more flexible, which is very suitable for the characteristics of laboratory platforms serving multiple customers.

[0019] Compared with the air bag sampling method, the present invention can enrich the hydrocarbons in the compressed gas being measured by utilizing the adsorption characteristics of the adsorbent when using the adsorption method, thereby avoiding the uncertainty loss of the air bag sampling method.

[0020] The pre-treatment process of the adsorption tube is programmed, which solves the problem of large errors in the test results caused by temperature changes in the detection environment or the sample transportation environment. Compared with the sampling method of the gas transfer method, the sampling volume of the present invention is small and easy to transport. In addition, the compounds fixed by the adsorbent are unlikely to be lost or escaped in the natural environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Repeated sampling and analysis results at different temperatures for the same adsorption tube;

[0022] Figure 2 This is the relationship between the desorption time and desorption efficiency of the adsorption tube;

[0023] Figure 3 This is a graph showing the difference in adsorption efficiency of different types of adsorption tubes under the same sampling conditions;

[0024] Figure 4 This is a parallel comparison chart of the desorption efficiency of different types of adsorption tubes for the measured substances;

[0025] Figure 5 It is a peak area graph corresponding to the stock solution of known concentration and different injection volumes;

[0026] Figure 6 It is a relationship diagram of the known concentration of stock solution and different injection volumes;

[0027] Figure 7 This is the sampling result S1 of the computer room environment;

[0028] Figure 8 It is the sampling result S0 of the compression system. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0030] Example 1

[0031] The method for detecting hydrocarbons in compressed gas mainly comprises a gas chromatograph and a thermal desorber as the main instruments and equipment, and mainly comprises an adsorption tube and a chromatographic column as the main experimental consumables.

[0032] The experimental process is as follows:

[0033] The first step is to use an adsorption tube to collect a fixed volume of compressed gas. During the sampling phase, the operating flow rate and total sample volume of the adsorption tube should be controlled according to the performance of the adsorption tube and the concentration of pollutants in the sample. Overloading the operating flow rate will reduce the adsorption efficiency of the adsorption tube and affect the accuracy of the quantitative results. Controlling the total sample volume is to avoid overflow in the adsorption tube, which would affect the accuracy of the quantitative results. The adsorbent in the adsorption tube is usually activated carbon powder or an equivalent synthetic adsorption material.

[0034] After a large number of experiments, the inventors found that the indicators that affect adsorption performance are shown in Table 1:

[0035] Table 1

[0036]

[0037] The “inflection point” is a certain flow rate state, above which the adsorption efficiency begins to decrease.

[0038] Based on the above variable factors, the empirical formula for the adsorption capacity of the adsorption tube is derived as follows:

[0039] q=C S ×V S ×t s ×C t ×η×λ;

[0040] q is the adsorption capacity of the adsorption tube (㎎);

[0041] C S is the substance concentration of the sample (mg / L);

[0042] V S is the sampling rate of the sample (ml / min);

[0043] t s is the sampling time of the sample (s);

[0044] C t It is the temperature factor that affects adsorption in the adsorption tube;

[0045] η is the adsorption efficiency of the adsorbent (%);

[0046] λ is the regeneration coefficient of the adsorption tube (%);

[0047] Among them, C t =R t / R0;

[0048] R t is the adsorption efficiency of the adsorption tube at t℃ (%);

[0049] R0 is the adsorption efficiency of the adsorption tube at the reference temperature (%);

[0050] Where η=(y A -y B ) / y A ;

[0051] y A is the concentration of the substance (e.g., hydrocarbon) upstream of the adsorption bed (the location where the adsorbent is packed in the adsorption tube) (mg / L);

[0052] y B is the concentration of the substance downstream of the adsorption bed (mg / L);

[0053] Where λ = n z / n0;

[0054] n z is the adsorption amount of the adsorption tube for the zth time (㎎), where z is the number;

[0055] n0 is the first adsorption dose of the adsorption tube (㎎).

[0056] like Figure 1 As shown in the figure, the adsorption amount of the substance when the adsorption tube is reused under different temperature conditions is measured multiple times, and the detection amount is expressed as the peak area detected by the gas chromatograph. Figure 1 The detection amount in the figure refers to the influence of the adsorption tube on the substance being measured, and the figure shows the peak area of ​​the chromatogram.

[0057] pass Figure 1 It can be seen that the data trend of repeated measurements of an adsorption tube at different temperatures.

[0058] In the second step, a thermal desorber is used to release the compounds enriched in the adsorption tube. During the desorption process, the instrument parameters that need to be controlled are shown in Table 2:

[0059] Table 2 Thermal desorption system parameters

[0060]

[0061] After research, it was found that the indicators affecting the desorption performance are shown in Table 3:

[0062] Table 3

[0063]

[0064] Pre-purge uses the sample carrier gas to replace the interfering gas in the adsorption tube at room temperature. By controlling the time and flow of the pre-purge and the total volume of the replacement gas, it should be ensured that at least the lumen of the adsorption tube is fully cleaned and replaced.

[0065] Adsorption tube analysis uses high temperature to activate the adsorbent in the adsorption tube. The temperature is greater than the boiling point of the substance (such as hydrocarbons), causing it to separate from the adsorbent and be blown away from the adsorption tube by the carrier gas. Although time is not the primary factor affecting adsorption tube analysis, it is the key to ensuring sufficient activation and release of the adsorption tube.

[0066] The cold trap works in two stages. The first stage is low temperature, temporarily storing the desorbed substances (such as hydrocarbons) in the cold trap. The temperature value is selected according to the inert temperature of the chemical substance. The second stage is high temperature, which reactivates the substances (such as hydrocarbons) temporarily stored in the cold trap and enters the analysis workstation with the help of carrier gas. High temperature is not conducive to the residue of substances and purifies the cold trap.

[0067] Carrier gas provides pneumatic source for the workstation.

[0068] The third step is to use gas chromatography to analyze the substances (such as hydrocarbons) desorbed from the adsorption tube. During the analysis stage, the instrument parameters that need to be controlled are shown in Table 4:

[0069] Table 4 Gas chromatography system parameters

[0070]

[0071] The fourth step is to screen the best adsorption tube. The technical difference between different types of adsorption tubes is the built-in adsorbent components. Taking hydrocarbons as the adsorption object, the relative adsorption amount and relative desorption amount of the adsorption tube are verified as evaluation indicators. The peak area of ​​the first desorption substance of the adsorption tube is the largest, which proves that the adsorption efficiency of this type of adsorption tube for the target substance (such as hydrocarbons) is the best; the peak area of ​​the second desorption substance of the adsorption tube is the smallest, which proves that the desorption efficiency of this type of adsorption tube for the target substance (such as hydrocarbons) is better. See the data analysis case. Figure 3 、 4 .

[0072] Figure 3 The curves of different colors represent different types of adsorption tubes. Figure 4 The curves of different colors represent different types of adsorption tubes.

[0073] Figure 3 It is the difference in adsorption efficiency of different types of adsorption tubes under the same sampling and analysis conditions. The larger the peak area, the more suitable the model is. It is a screening technology method. Figure 4 It is a retest of the residual amount after desorption of the adsorption tube. The smaller the peak area, the more suitable the model. The final selection of the adsorption tube model is based on Figure 3 Maximum peak sum Figure 4 The minimum peak meets the requirements at the same time, indicating that the selected adsorption tube is beneficial for capture and desorption.

[0074] Example 2

[0075] Technical application of Example 1

[0076] 1. Establishing the linear relationship of quantitative solution

[0077] The injection volume (sample volume) of the stock solution (prepared hydrocarbon solution of known concentration) is used as the independent variable. The designed experimental procedure is used to analyze the peak area detected by the dependent variable (external standard substance, such as stock solution) to obtain a linear regression equation of a linear relationship. The analysis results are as follows: Figure 5 、 Figure 6 As shown, Figure 5 yes Figure 6 The corresponding peak area detection results of the data curve. Figure 5 The eight different curves represent the peak area response results of eight different injection volumes.

[0078] Figure 5 The test results obtained R 2 =0.9999 linear regression analysis equation, linear relationship see Figure 6 ,exist Figure 6 In the table, the sample volume refers to the sample volume of the stock solution, and the peak area on the ordinate refers to the peak area detected by the stock solution.

[0079] 2. Quantitative Calculation

[0080] The regression equation obtained using the stock solution takes the detected peak area (y) of the adsorption tube as the independent variable. When the sampled compressed gas (sample) is prepared by a compression system (used to prepare compressed air), the total peak area (y0) detected in the sample is the sum of the substances in the compression system (such as hydrocarbons) and the substances in the environmental background (such as hydrocarbons). The background peak area (y1) of the environment in which the compression system is located can be deducted as the background value, that is, the reported value of the independent variable is y=y0-y1; when the sample is a pre-filled container for standby use, the background value (background peak area y1) can be regarded as zero, and the total peak area y0 detected in the sample is the reported value, that is, the reported value of the independent variable y=y0.

[0081] The quantitative formula is: Xm=V×C×V C ;

[0082] Xm is the hydrocarbon content, mg / m 3 V is the volume of the substance (e.g., hydrocarbon) sampled, in μL. Here, to obtain the correlation function for the sample volume of hydrocarbons, if a stock solution with a known hydrocarbon concentration is used, this represents the sample volume of the stock solution; if a sample with an unknown hydrocarbon concentration is used, this represents the sample volume of the sample. C is the concentration of the stock solution, in mg / μL; V C is the volume coefficient, V C=1000 / (actual volume of sample).

[0083] Example 3

[0084] Application case of embodiment 2

[0085] Evaluate the gaseous oil content in the compressed air in a compressed air system.

[0086] Step 1: Sampling

[0087] According to the designed test parameters, the compressed air in the compression system and the air in the machine room environment were sampled at 0.2 L / min (working flow rate). The sampling time was 4 hours and the sampling volume of each adsorption tube was 48 L.

[0088] Step 2: Analysis

[0089] The two adsorption tubes were analyzed by the gas chromatography according to the second step of Example 1. The output gas chromatographic peak area results are shown in Table 5:

[0090] Table 5

[0091] <![CDATA[y1 of the computer room environment]]> <![CDATA[y0 of the compression system]]> 1499.7 2208.6

[0092] The y1 of the computer room environment in Table 5 is based on Figure 7 We get the y0 of the compression system according to Figure 8 get.

[0093] Step 3: Calculation

[0094] according to Figure 6 The obtained regression analysis equation is: y=796.19V+14.561. The peak area y=y0-y1 is substituted into the formula as the independent variable to calculate the volume V of the dependent variable.

[0095]

[0096] The concentration of the stock solution is known, C = 0.0017 mg / μL;

[0097] The adsorption tube was sampled at 0.2 L / min for 4 hours. The actual sampling volume of each sample (actual sample volume) was 0.2 L / min × 240 min = 48 L, which was converted to m 3 Volume coefficient of unit, V C =1000 / 48;

[0098] Step 4. Conclusion

[0099] Substitute the above three known factors into the quantitative formula, Xm=V×C×V C=0.87×0.0017×1000 / 48=0.031, the hydrocarbon content in the compressed air in the tested compression system is 0.031 mg / m 3 .

[0100] In the above embodiments, the technical advantages of the present invention are as follows:

[0101] The present invention innovates the direct sampling method for oil content detection in compressed gas, utilizes the enrichment characteristics of the adsorption tube, avoids the online configuration before direct sampling, and makes the detection of samples more flexible, which is very suitable for the characteristics of laboratory platforms serving multiple customers.

[0102] Compared to air bag sampling, which requires using air bags to transfer sample gas from the field to the laboratory and then extracting a portion of the sample through the top of the gas phase workstation, the air bag is affected by ambient temperature fluctuations during the sample transfer process, and the test substances in the sample may aggregate and settle or be adsorbed by the inner surface of the air bag, resulting in deviations in the test results. The adsorption method of the present invention can enrich the hydrocarbons in the test gas by utilizing the adsorption properties of the adsorbent, avoiding the uncertainty loss of air bag sampling.

[0103] The pre-treatment process of the adsorption tube is programmed, which solves the problem of large errors in the test results caused by temperature changes in the detection environment or the sample transportation environment. Compared with the sampling method of the gas transfer method, the sampling volume of the present invention is small and easy to transport. In addition, the compounds fixed by the adsorbent are unlikely to be lost or escaped in the natural environment.

[0104] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for detecting hydrocarbons in compressed gas, It is characterized in that The test was carried out by combining a gas chromatograph and a thermal desorber. The experimental consumables used in the test included adsorption tubes and chromatographic columns. The test steps are as follows: Step 1: Collect a quantitative volume of compressed gas as a sample using an adsorption tube. During the sampling stage, screen the adsorption tube to determine the working flow rate of the adsorption tube, the total volume of the sample, and the working parameters of the gas chromatograph and the thermal desorber; Step 2: Prepare a hydrocarbon solution of known concentration as a stock solution, take the volume of the stock solution as the independent variable, design an experiment, and obtain the regression analysis equation: y=k*V+d, y is the peak area y detected by the adsorption tube, V is the volume of hydrocarbons added in the sample / stock solution, k and d are constants; Step 3: According to the quantitative formula Xm = V × C × V C Calculate hydrocarbon content; Xm is the hydrocarbon content, mg / m 3 ; C is the concentration of the stock solution, mg / μL; V C is the volume factor, V C =1000 / actual volume of sample.

2. A method for detecting hydrocarbons in compressed gas according to claim 1, Features: When the sample is prepared by a compression system, the total peak area detected in the sample is y 0 , the background peak area of ​​the compression system environment is y 1 , y=y 0 -y 1 .

3. A method for detecting hydrocarbons in compressed gas according to claim 1, Features: When the sample is a pre-filled container, the total peak area detected in the sample is y 0 , y=y 0 .

4. A method for detecting hydrocarbons in compressed gas according to claim 1, Features: The actual volume of the sample is equal to the product of the working flow rate of the adsorption tube and the sampling time.

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