CN102706949B - Method for determination of inorganic element in fuel gas - Google Patents

Abstract

The invention provides a method for measuring inorganic elements in gas, which includes the following steps: sample collection, after the gas flows through the filter membrane, the gas is divided into two parts and flows through the cation absorbing liquid and the anion absorbing liquid; sample processing, the filter membrane is divided into two parts , a part of the filter membrane is digested with acid solution, and then added to the cation absorbing liquid, constant volume and filtered to obtain the filtrate for cation analysis; after the other part of the filter membrane is extracted with water, the extract is added to the anion absorbing liquid and then constant volume and filtered, The filtrate used for anion analysis is obtained; for sample analysis, the filtrate is subjected to capillary electrophoresis test respectively, and then the data is processed. According to the method and device provided by the present invention, the disadvantages of low efficiency, long time-consuming, high analysis cost and difficulty in popularization of the traditional sampling method are overcome, the goal of rapid detection of various inorganic elements is realized, the operation cost is low, the operation is simple, and it is convenient promote.

Description

A method for determining inorganic elements in gas

technical field

The invention belongs to the field of chemical analysis and testing, and in particular relates to a rapid determination method for inorganic elements in gas.

Background technique

Due to the influence of formation and environment, the gas often contains different concentrations of inorganic elements. These inorganic elements exist in the form of small solid particles, mist and gas. When these inorganic elements settle and adhere to or permeate on the surface of various equipment, components and materials used in the gas industry, it will cause hazards such as metal corrosion and material aging. However, there is no mature collection device and determination method for inorganic elements in gas so far.

At present, the methods of collecting inorganic elements in gas can be divided into gas-solid adsorption method and gas-liquid absorption method. Uddin et al. (Energy Fuels, 2009, 23, 4710-4716) and Ozaki et al. (Fuel, 2008, 87, 3610-3615) respectively reported the enrichment of inorganic mercury in coal-based gas by using synthetic adsorbents based on the gas-solid adsorption method And quantitative detection. However, the collection efficiency of these traditional methods is not high, and the target objects are all for individual inorganic elements. In addition, a large amount of samples and reagents need to be consumed. Commonly used methods for detecting inorganic elements include atomic absorption (Anal. .Pharm.Biomed.Anal.,2010,52,652-655; Anal.Chim.Acta,2007,584,204-209), inductively coupled plasma-mass spectrometry (Anal.Chem.,2004,76,2910-2915; J. Agric. Food Chem., 2005, 53, 5138-5143) and ion chromatography (Anal. Chem., 2003, 75, 6789-6798). These methods have played an important role in the analysis of inorganic elements, but some of their shortcomings also hinder their own application and development. The atomic absorption method cannot detect inorganic elements at the same time, and the light source needs to be replaced every time an element is detected, which is cumbersome to operate. Inductively coupled plasma-atomic emission spectrometry is not sensitive to the detection of some non-metallic elements. Inductively coupled plasma-mass spectrometry, expensive instruments, high analysis costs, is not conducive to popularization, and is not suitable for the detection of some non-metallic elements. Although ion chromatography has made outstanding contributions to the detection of non-metallic elements, its analysis time is long, the sensitivity is often not up to the detection requirements under trace conditions, and complex sample pre-enrichment steps are required. In addition, Rupp et al. (Anal.Chem., 2010, 82, 6315-6317) used gas chromatography-mass spectrometry to analyze trace amounts of Hg, AsH ₃ , PH ₃ and H ₂ Se in simulated gas, but this method is only applicable to The detection of some volatile inorganic elements cannot be detected for most inorganic elements, especially metal elements.

Contents of the invention

Aiming at the deficiencies in the prior art, the present invention provides a method for measuring inorganic elements in gas, which can not only effectively collect various inorganic elements in gas and realize rapid determination thereof, but also has high efficiency and low cost.

According to one aspect of the present invention, there is provided a method for measuring inorganic elements in gas, comprising the following steps:

Sample collection, after the gas flows through the filter membrane, it flows through the cation absorbing liquid and the anion absorbing liquid in two parts;

For sample processing, the filter membrane is divided into two parts. One part of the filter membrane is digested with acid solution, then added to the cation absorbing liquid, constant volume, and filtered to obtain the filtrate for cation analysis; the other part of the filter membrane is extracted with water, and the extract is added to After the anion absorbs the liquid, it is constant to volume and filtered to obtain the filtrate for anion analysis;

For sample analysis, the filtrates were subjected to capillary electrophoresis tests, and then the data were processed.

In the above method, the filter membrane is used to collect the inorganic elements in the gas. The filter membrane is made of high molecular polymer material. Wherein, the filter membrane is preferably a polytetrafluoroethylene membrane.

In the above method, the cation absorbing liquid is an acid liquid, which is used to absorb cations in the gas. Wherein the cation absorbing liquid is preferably a boric acid solution. In a specific embodiment, the concentration of the boric acid solution is 10-50mmol/L.

In the above method, the anion absorbing liquid is lye, which is used to absorb anions in the gas. Wherein the anion absorbing liquid is preferably a sodium hydroxide solution. In a specific embodiment, the concentration of the sodium hydroxide solution is 10-50 mmol/L.

In the above method, the acid solution is a strong acid, which is used to digest the filter membrane. The acid solution is preferably pure nitric acid. In a specific embodiment, in the sample processing step, in order to speed up the digestion and extraction, methods such as microwave assistance can be adopted.

In a specific embodiment of the above method, in the sample processing step, the filtering step may adopt membrane filtration, such as 0.45 μm membrane filtration.

In the above method, in the sample analysis step, the sample injection method during the capillary electrophoresis test is column end field amplification sample injection and ultraviolet light source detection. In a specific embodiment, when detecting cations, the sample injection method is the column end field amplification sample injection method. First, water is injected under a pressure of 0.5 psi for 5 seconds, and then the sample is injected under a voltage of 10 kV for 10 seconds. In another specific embodiment, when detecting anions, the sample injection method is a column end field amplification sample injection method. First, water is injected under a pressure of 0.5 psi for 10 seconds, and then a sample is injected under a voltage of -5 kV for 10 seconds.

In a specific embodiment of the above method, in step 3), when detecting cations, the separation voltage is 20kV, and the ultraviolet detection wavelength is 214nm, wherein the mobile phase: 10mmol/L imidazole, 1mmol/L 18-crown ether -6, 10% (v/v) methanol, acetic acid to adjust the pH to 3.5.

In another specific embodiment of the above method, in step 3), when detecting anions, the separation voltage is -10kV, and the ultraviolet detection wavelength is 254nm, wherein the mobile phase: 40mmol/L potassium chromate, 0.5mmol/ L cetyltrimethylammonium bromide, 20mmol/L tris, and acetic acid to adjust the pH to 9.1.

The above method also includes the drawing of blank control test and standard curve, and the concentration of inorganic elements contained in the gas is obtained through data processing.

The blank control test refers to that no sample is collected, the anion and cation absorption liquid is placed for the same time as the actual sampling, and then the anion and cation absorption liquid is fixed to volume and filtered, and the obtained filtrate is subjected to capillary electrophoresis test to obtain the data of the blank sample. .

The standard curve includes the drawing of a positive ion standard curve and the drawing of an anion standard curve. The processed sample solution is analyzed by capillary electrophoresis, and the detected components can be divided into two categories: cations and anions. Cations include, for example, ammonium ions, potassium ions, calcium ions, sodium ions, manganese ions, zinc ions, barium ions, aluminum ions, lead ions, and the like. Anions such as chloride ions, nitrite ions, nitrate ions, sulfate ions and monohydrogen phosphate ions, etc.

The drawing of the standard curve includes: the drawing of the negative ion standard curve and the drawing of the positive ion standard curve. Configure a series of standard mixed solutions containing anions and cations contained in gas, and then use capillary electrophoresis to measure, and draw a standard curve with concentration versus peak area. In a specific embodiment, the drawing of the cation standard curve includes: preparing a mixture containing ammonium ion, potassium ion, calcium ion, sodium ion, manganese ion, zinc ion, barium ion, aluminum ion and lead ion concentration of 10 , 25, 50, 75, 100, 200, 500, 750, 1000ng/mL standard series mixed solution, then measure the standard series according to the operating conditions of the instrument, repeat the measurement for each concentration 3 times, and draw the standard curve with the concentration versus peak area. In another specific embodiment, the drawing of the anion standard curve includes: preparing a mixture containing chloride ion, nitrite ion, nitrate ion, sulfate ion and monohydrogen phosphate ion concentration of 10, 25, 50, 75, 150, 250, 400ng/mL standard series mixed solutions. The standard series were determined according to the operating conditions of the instrument, each concentration was measured three times, and the standard curve was drawn with the concentration versus peak area.

In the above method, by measuring the processed actual sample and the blank control sample, after subtracting the peak area of the blank control from the measured peak area of the sample, the concentration values of each element are obtained in the corresponding standard curve, so as to realize the detection of the inorganic elements in the gas. Quantitative analysis is carried out to obtain the content of various inorganic elements in the gas. The calculation formula is as follows:

Convert sample volume to standard sample volume:

$V_o=V\×\frac{273}{273+t}\×\frac{P}{101.3}$ Formula 1)

In the formula:

V ₀ —standard sampling volume, the unit is L;

V—sample volume, unit is L;

t—sampling point temperature, unit is ℃;

P—the pressure of the sampling point, in kPa.

Calculate the content of inorganic elements in gas:

$C=\frac{(C_i-C_0)\×V_i}{V_o}$ Formula (2)

In the formula:

C—the content of inorganic elements in the gas, the unit is μg/m ³ ;

C _i —sample concentration value, unit is ng/mL;

C ₀ —concentration value of blank sample, unit is ng/mL;

V _i - constant volume of the sample solution, in mL;

V ₀ —standard sampling volume, the unit is L;

According to another aspect of the present invention, a device for determining inorganic elements in fuel gas is provided, including a double-flow path gas-liquid absorption device and a capillary electrophoresis instrument, wherein the double-flow path gas-liquid absorption device includes: a filter device containing a filter membrane; The anion absorption bottle connected with the device; the cation absorption bottle connected with the filter device.

In the above device, the filter device containing a filter membrane is used to collect the inorganic elements in the gas. In a specific embodiment, a filter head of polytetrafluoroethylene membrane is installed in the membrane filtration device.

In the above device, the gas inlet of the anion and cation absorption bottle has a quartz sieve plate. In a specific embodiment, the thickness of the quartz sieve plate in the anion and cation absorption bottle is 5 mm. The anion and cation absorption bottle can also be connected with a gas flow device to control and measure the gas flow.

According to the method and device provided by the present invention, the disadvantages of low efficiency, long time consumption, high analysis cost and difficulty in popularization of the traditional sampling method are overcome, and the goal of rapid detection of various inorganic elements is realized. According to the method and device provided by the present invention, the operating cost is low, the operation is simple, and it is easy to popularize. It provides a reliable and easy-to-implement new method for the effective collection and rapid detection of inorganic elements in gas, which can meet the requirements of inorganic elements in gas. The needs of element detection and research can also be used for real-time monitoring of the content of inorganic elements in gas.

Description of drawings

Figure 1 shows a schematic diagram according to an embodiment of the present invention;

Fig. 2 has shown the standard cationic capillary electrophoresis separation chromatogram according to an embodiment of the present invention;

Fig. 3 shows a standard anion capillary electrophoresis separation chromatogram according to an embodiment of the present invention.

Detailed ways

The present invention will be further described below in conjunction with specific examples.

Fig. 1 shows a schematic diagram according to an embodiment of the present invention. The gas coming out of the gas delivery pipeline 1 passes through the flange 2 and the rear 3 of the pressure reducing valve, enters the double-flow path gas-liquid absorption device, and then is discharged from the absorption device. The dual-channel gas-liquid absorption device mainly includes a filter head 4 containing a polytetrafluoroethylene membrane 5 , a cation absorption bottle 6 , an anion absorption bottle 7 and a flow meter 11 . The gas entering the double-flow path gas-liquid absorption device flows through the filter head 4 containing the polytetrafluoroethylene membrane 5 and is divided into two streams. One stream of gas passes through the cation absorbing bottle 6 and the flow meter 11 and is discharged, and the other stream passes through the anion absorbing bottle. 7 and flow meter 11 after discharge. The bottom of the cation absorbing bottle 6 is covered with a quartz sieve plate 8, and gas enters from the bottom of the cation absorbing bottle 6, and flows out from the top of the cation absorbing bottle 6 after passing through the cation absorbing liquid 9. The bottom of the anion absorbing bottle 7 is also covered with a quartz sieve plate 8, and gas enters from the bottom of the anion absorbing bottle 7, and flows out from the top of the anion absorbing bottle 7 after being absorbed by the anion absorbing liquid 10.

Example 1

1. Sample collection:

The gas is collected by using a double-flow path gas-liquid absorption device, and the diameter of the filter membrane is 45mm. At a flow rate of 400mL/min, collect for 90min. The cation absorption bottle contains 6mL of 50mmol/L boric acid solution (used to absorb soluble cations in gas). The anion absorption bottle contains 6mL of 50mmol/L sodium hydroxide solution (used to absorb soluble anions in gas).

2. Sample treatment: Divide the collected sample filter membrane into two halves, cut one half into pieces, add 6 mL of analytically pure nitric acid, and put it into a microwave instrument for microwave-assisted digestion. Pour the digested solution into a polytetrafluoroethylene bottle, add the sample containing 50mmol/L boric acid absorption solution, mix well and make up to volume (12ml), and filter it through a 0.45μm membrane for inorganic cation analysis; cut the other half After crushing, add 6mL double-distilled water and put it into a microwave instrument for microwave-assisted extraction. The extracted solution was poured into a polytetrafluoroethylene bottle, and the sample filled with 50mmol/L sodium hydroxide absorption solution was added, mixed to a constant volume (12ml), and filtered through a 0.45μm membrane for analysis of inorganic anions.

3. Sample analysis:

3.1 Drawing of standard curve

Standard cation curve: the preparation contains ammonium ions, potassium ions, calcium ions, sodium ions, manganese ions, zinc ions, barium ions, aluminum ions and lead ions at concentrations of 10, 25, 50, 75, 100, 200, 500, 750, 1000ng/mL standard series mixed solution. The analysis instrument adopts P/ACE MDQ capillary electrophoresis instrument from Beckman Company of the United States, and the chromatographic conditions are: use a fused quartz capillary with no coating on the inner surface, 60cm in length (of which the effective length is 50cm), and the inner diameter is 75μm; the mobile phase is 10mmol/L Imidazole, 1mmol/L 18-crown-6, 10% (v/v) methanol, acetic acid to adjust the pH to 3.5; the separation voltage was 20kV; the column temperature was 25°C; the UV detection wavelength was 214nm; Sampling method, that is, water is injected under 0.5psi pressure for 5s, and then sample is injected under 10kV voltage for 10s. The determination was repeated 3 times for each concentration. A standard curve was drawn with concentration versus peak area. Table 1 is the test results of the standard cationic solution. The capillary electrophoresis chromatogram of the standard mixture with a concentration of 200ng/mL is shown in Figure 2.

Table 1 Cationic standard solution linear equation and detection limit

Anion standard curve: Prepare a series of standard mixed solutions containing chloride ion, nitrite ion, nitrate ion, sulfate ion and monohydrogen phosphate ion concentration of 10, 25, 50, 75, 150, 250, 400ng/mL . The analysis instrument adopts the P/ACE MDQ capillary electrophoresis instrument of Beckman Company of the United States. The chromatographic conditions are: use a fused quartz capillary with no coating on the inner surface, the length is 60cm (the effective length is 50cm), the inner diameter is 75μm; the mobile phase is 40mmol/L Potassium chromate, 0.5mmol/L cetyltrimethylammonium bromide, 20mmol/L trishydroxymethylaminomethane, acetic acid to adjust the pH to 9.1; the separation voltage is -10kV; the column temperature is 25°C; the UV detection wavelength 254nm; using the column end field amplification sample injection method, that is, first inject water at 0.5psi pressure for 10s, and then inject samples at -5kV voltage for 10s. Each concentration was measured three times, and a standard curve was drawn with concentration versus peak area. Table 2 is the detection result of standard anion solution. The capillary electrophoresis chromatogram of the standard mixture with a concentration of 200ng/mL is shown in Figure 3.

Table 2 Anion standard solution linear equation and detection limit

3.2 Blank control experiment

Place the double-channel gas-liquid absorption device without filter membrane in the air for 90 minutes. Wherein, 6 mL of 50 mmol/L boric acid solution is contained in the cation absorption bottle, and 6 mL of 50 mmol/L sodium hydroxide solution is contained in the anion absorption bottle. The liquids in the anion and cation absorption bottles were fixed to volume (12ml), filtered through a 0.45μm membrane, and then subjected to capillary electrophoresis tests. The test conditions were the same as those when drawing the standard anion and cation curves. The anion and cation blank samples of the blank control experiment were measured 3 times.

3.3 Determination of samples

Determination of cations: the test conditions are the same as the test conditions when drawing the standard cation curve, and the measurement is repeated 3 times. Determination of anions: the test conditions are the same as the test conditions when drawing the standard anion curve, and the determination is repeated 3 times.

3.4 Data processing

After subtracting the corresponding blank control anion and cation peak areas from the measured anion and cation sample peak areas, the element concentration values in each sample were obtained from the corresponding standard curve, and then calculated according to the formulas (1) and (2) for each inorganic element content. Table 3 and Table 4 are the test results of inorganic elements in actual samples. The recovery rate of each inorganic ion was between 89% and 106%, meeting the laboratory analysis requirements.

Table 3 Determination results of inorganic elements in actual gas samples (1)

—Indicates not detected.

Table 4 Determination results of inorganic elements in actual gas samples (2)

It can be seen from Table 3 and Table 4 that, according to the method and device provided by the present invention, the contents of various inorganic elements contained in the gas can be effectively determined.

It should be noted that the above-mentioned embodiments are only used to explain the present invention, and do not constitute any limitation to the present invention. The invention has been described with reference to typical embodiments, but the words which have been used therein are words of description and explanation rather than words of limitation. The present invention can be modified within the scope of the claims of the present invention as prescribed, and the present invention can be revised without departing from the scope and spirit of the present invention. Although the invention described therein refers to specific methods, materials and examples, it is not intended that the invention be limited to the specific examples disclosed therein, but rather, the invention extends to all other methods and applications having the same function.

Claims (10)

1. a method of measuring inorganic elements in combustion gas, comprises the following steps:

Sample collection, gas-flow is after filter membrane, and minute two parts flow through kation absorption liquid and negative ion absorption liquid;

Sample preparation, filter membrane is divided into two parts, and a part of filter membrane is cleared up by acid solution, then adds after kation absorption liquid, and constant volume, filtration, obtain the filtrate for cation analysis; By after another part filter membrane water extraction, extract adds constant volume and filtration after negative ion absorption liquid, obtains the filtrate for anion analysis;

Sample analysis, carries out respectively Capillary Electrophoresis test by described filtrate, then data is processed;

Wherein, the filtering membrane that described filter membrane is macromolecular material, described kation absorption liquid is acid solution, and described negative ion absorption liquid is alkali lye, and the acid solution that described filter membrane is cleared up use is strong acid.

2. method according to claim 1, is characterized in that, described filter membrane is poly tetrafluoroethylene.

3. method according to claim 1, is characterized in that, described kation absorption liquid is BAS, and the concentration of described BAS is 10～50mmol/L.

4. method according to claim 1, is characterized in that, described negative ion absorption liquid is sodium hydroxide solution, and the concentration of described sodium hydroxide solution is 10～50mmol/L.

5. method according to claim 1, is characterized in that, the acid solution that described filter membrane is cleared up use is pure nitric acid.

6. method according to claim 1, is characterized in that, input mode during described Capillary Electrophoresis test is styletable electrical field magnified injection, and ultraviolet source detects.

7. according to the method described in any one in claim 1～6, it is characterized in that, in described sample analysis step, when kation is detected, separation voltage is 20kV, and it is 214nm that ultraviolet detects wavelength, mobile phase wherein: 10mmol/L imidazoles, 1mmol/L18-crown ether-6,10%(v/v) methyl alcohol, it is 3.5 that acetic acid is adjusted pH.

8. according to the method described in any one in claim 1～6, it is characterized in that, in described sample analysis step, when negative ion is detected, separation voltage is-10kV that it is 254nm that ultraviolet detects wavelength, mobile phase wherein: 40mmol/L potassium chromate, 0.5mmol/L cetyl trimethyl ammonium bromide, 20mmol/L trishydroxymethylaminomethane, it is 9.1 that acetic acid is adjusted pH.

9. utilize in claim 1-8 method described in any one to measure a device for inorganic elements in combustion gas, comprise dual flow path Gas-Liquid Absorption device and capillary electrophoresis apparatus, wherein dual flow path Gas-Liquid Absorption device comprises: filtration unit; The negative ion absorption bottle being connected with filtration unit; The kation absorption bottle being connected with filtration unit.

10. device according to claim 9, is characterized in that, the gas feed of described negative ion absorption bottle and kation absorption bottle has quartzy sieve plate.