Method for detecting chlorine content in coal tar

Abstract

The application discloses a detection method of the chlorine content in coal tar, which comprises the following steps: S1, weighing the coal tar sample and placing it in a crucible, installing an ignition wire, putting it into an oxygen bomb with Na2CO3 solution, screwing the oxygen bomb, and filling oxygen into the oxygen bomb; S2, burning the oxygen bomb by electrifying, completely burning the coal tar sample, then immersing the oxygen bomb into cold water for cooling and slightly shaking; S3, slowly releasing the gas in the cooled oxygen bomb to normal pressure, then opening the oxygen bomb, washing the inner wall of the oxygen bomb and the crucible with deionized water, and then transferring the solution in the oxygen bomb into a beaker; S4, potential titration, adding nitric acid into the beaker to adjust the solution to pH 3-4.5, then adding ethanol, and titrating with a silver nitrate standard solution to the reaction end point, and recording the volume of the consumed silver nitrate standard solution, so as to obtain the chlorine content in the coal tar. The application can meet the detection requirement of trace chlorine in the coal tar, and the whole process is simple, fast and high in accuracy.

Description

Technical Field

[0001] This invention relates to the field of coal tar detection technology, and specifically to a method for detecting the chlorine content in coal tar. Background Technology

[0002] In addition to macroelements such as carbon, hydrogen, oxygen, nitrogen, and sulfur, coal tar also contains trace amounts of chlorine and some metallic elements. Chlorine includes organic chlorine in the form of chlorinated hydrocarbons and inorganic chlorine in the form of ammonium chloride, sodium chloride, etc. All of these chlorines can cause serious corrosion to production equipment. Therefore, determining the chlorine content in coal tar is of great significance for coal tar processing.

[0003] Currently, there is no unified standard for the detection method of chlorine content in coal tar; relevant literature records methods such as microcoulometric method, ion chromatography, and X-ray fluorescence spectrometry, each of which has its own advantages and disadvantages.

[0004] Chinese patent application CN201310245102.5 proposes a method for separating and determining trace amounts of chlorine in tar, employing high-temperature fusion-ion chromatography to determine the chlorine content in tar: a layer of sodium carbonate is spread on the surface of the tar, the tar is ignited, and after complete ashing, the sample is cooled to room temperature, the residual ash is washed with deionized water, filtered, and diluted to volume. The chlorine content in the solution is then determined using ion chromatography. Wang Baofeng, Liao Hongqiang, et al. published a method in [Coal Chemical Industry] for determining the chlorine content in blended coal, coke, and tar using ion chromatography. This method involves covering 1g of sample with 8g of sodium carbonate, igniting at 680℃ for 3h, dissolving in deionized water, filtering, and diluting to volume in a 1000mL volumetric flask. Chloride ions are then determined using ion chromatography. This method is cumbersome, time-consuming, has incomplete hydrogen chloride absorption, high blank values, and numerous interfering peaks, and requires high precision in chromatographic columns and analytical conditions.

[0005] Liu Ying, Lü Ming, et al. published an article in "Ansteel Technology" on the optimization and practice of a method for determining chlorine content in coal tar. The method uses a high-temperature pyrolysis-microcoulometric method to determine the chlorine content in coal tar: the sample is injected into a quartz boat using a microsyringe, and then carried into the pyrolysis tube by a sampler. The sample is oxidized and burned at 1000℃, converting organic chlorine into chloride ions, which are then determined using microcoulometrics. Although this method has high sensitivity, it suffers from problems such as long titration cell equilibration time, baseline drift, and easy carbon buildup in the pyrolysis tube.

[0006] Hu Guomao published a paper in "Inner Mongolia Petroleum and Chemical Industry" on the determination of total chlorine content in coal tar using single-wavelength dispersive X-ray fluorescence spectrometry. The method involves placing 1 mL of sample into a sample cup, inserting it into the instrument's autosampler, and automatically determining the chlorine content using a standard curve method. While this method is simple to operate and requires no sample pretreatment, it suffers from difficulties in matching standards and samples, significant matrix effects, and expensive instruments, resulting in high testing costs. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a method for detecting chlorine content in coal tar. The method employs an oxygen bomb combustion-potential titration method to determine the chlorine content in coal tar, achieving a detection limit as low as 10 mg / kg, thus meeting the requirements for detecting trace amounts of chlorine in coal tar. The entire process is simple, fast, and highly accurate.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention provides a method for detecting the chlorine content in coal tar, comprising the following steps:

[0010] S1. Weigh a coal tar sample and place it in a crucible. Install the ignition wire and place it in an oxygen bomb containing Na2CO3 solution. Tighten the oxygen bomb and fill it with oxygen.

[0011] S2, the oxygen bomb is ignited and burned, the coal tar sample is completely burned, and then the oxygen bomb is immersed in cold water to cool and shaken slightly;

[0012] S3. After the oxygen bomb has cooled, slowly release the gas to atmospheric pressure and then open it. Rinse the inner wall of the oxygen bomb and the crucible with deionized water. Then transfer the solution inside the oxygen bomb into a beaker.

[0013] S4, potentiometric titration: Add nitric acid to a beaker to adjust the pH to 3-4.5, then add ethanol, and titrate with silver nitrate standard solution to the reaction endpoint. Record the volume of silver nitrate standard solution consumed to obtain the chlorine content in coal tar.

[0014] Preferably, in step S1, the mass of the coal tar sample is 0.5–2 g.

[0015] Preferably, in step S1, the volume of the Na2CO3 solution is 10-15 mL;

[0016] The concentration of Na2CO3 in the Na2CO3 solution is 1% to 2%.

[0017] Preferably, in step S1, oxygen is introduced into the oxygen bomb at a pressure of 3 to 3.2 MPa for 1 to 2 minutes.

[0018] Preferably, in step S2, the cooling time of the oxygen bomb immersed in cold water is 10 to 15 minutes.

[0019] Preferably, in step S3, the slow venting time is not less than 2 minutes, and the amount of deionized water used is 20-25 mL.

[0020] Preferably, in step S4, the amount of ethanol added is 90-100 mL.

[0021] Preferably, in step S4, the concentration of the silver nitrate standard solution is 0.001 mol / L.

[0022] Preferably, in step S4, the formula for calculating the chlorine content in the coal tar is as follows:

[0023]

[0024] In the formula, ω represents the chlorine content in the coal tar sample, in ppm;

[0025] c is the concentration of the silver nitrate standard titration solution, in mol / L;

[0026] V is the volume of silver nitrate standard solution consumed in the titration, in mL;

[0027] 35.45 is the atomic weight of chlorine, in g / mol;

[0028] m is the mass of the coal tar sample, in grams.

[0029] The beneficial effects of this invention are as follows:

[0030] 1. This invention employs the oxygen bomb combustion-potential titration method. Under high pressure and oxygen-rich conditions, the sample is completely combusted, and organic chlorine is converted into hydrogen chloride. After absorption by sodium carbonate solution, chloride ions are determined by potentiometric titration. By reducing the concentration of silver nitrate standard titration solution, adding a large proportion of ethanol, and increasing the sample amount, the detection limit of chlorine content is ensured to be as low as 10 mg / kg, which fully meets the detection requirements for trace chlorine in coal tar. This method is simple and fast.

[0031] 2. This invention can easily and accurately determine the chlorine content in coal tar; the precision and accuracy have been verified, with a relative standard deviation of <5% and a spiked recovery rate of 92% to 105%. Detailed Implementation

[0032] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way.

[0033] The present invention provides a method for detecting the chlorine content in coal tar, comprising the following steps:

[0034] S1. Weigh a coal tar sample and place it in a crucible. Install the ignition wire and place it in an oxygen bomb containing Na2CO3 solution. Tighten the oxygen bomb and fill it with oxygen.

[0035] In this step, weigh 0.5–2 g of coal tar sample and place it in a crucible. Install the ignition wire and place it inside an oxygen bomb containing Na₂CO₃ solution. Then tighten the oxygen bomb and charge it with oxygen for 1–2 minutes under a pressure of 3–3.2 MPa. The volume of the Na₂CO₃ solution is 10–15 mL, and the concentration of Na₂CO₃ is 1%–2%.

[0036] This step mainly utilizes the oxygen bomb to create conditions for the complete combustion of the subsequent coal tar sample and the absorption of hydrogen chloride converted from organochlorine, thereby improving the accuracy of the detection method; Na2CO3 solution is used as the absorption liquid to absorb the hydrogen chloride converted from organochlorine after the complete combustion of the coal tar sample.

[0037] S2, the oxygen bomb is ignited and burned, the coal tar sample is completely burned, and then the oxygen bomb is immersed in cold water to cool and shaken slightly;

[0038] In this step, the coal tar sample is completely combusted under high pressure and oxygen-enriched conditions. Combustion converts the organic chlorine compounds in the coal tar into hydrogen chloride. The generated hydrogen chloride is then absorbed by a Na₂CO₃ solution. The reaction between Na₂CO₃ and hydrogen chloride is as follows:

[0039] Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂

[0040] In the above process, the oxygen bomb is immersed in cold water for 10 to 15 minutes to cool down; during the cooling process, the oxygen bomb is gently shaken to accelerate the absorption of hydrogen chloride by the Na2CO3 solution.

[0041] S3. After the oxygen bomb has cooled, slowly release the gas to atmospheric pressure and then open it. Rinse the inner wall of the oxygen bomb and the crucible with deionized water. Then transfer the solution inside the oxygen bomb into a beaker.

[0042] In this step, the cooled oxygen bomb is slowly and evenly released to atmospheric pressure for at least 2 minutes. After that, the oxygen bomb is opened and the inner wall of the oxygen bomb and the crucible are rinsed with 20-25 mL of deionized water. Then, the solution inside the oxygen bomb is transferred to a beaker.

[0043] S4, potentiometric titration: Add nitric acid to a beaker to adjust the pH to 3-4.5, then add ethanol, and titrate with silver nitrate standard solution to the reaction endpoint. Record the volume of silver nitrate standard solution consumed to obtain the chlorine content in coal tar.

[0044] In this step, first add a few drops of nitric acid to the beaker to adjust the pH to 3-4.5 (e.g., 3.5-4.5), then add 90-100 mL of ethanol, and then titrate with a 0.001 mol / L silver nitrate standard solution to the reaction endpoint, and record the volume of silver nitrate standard solution consumed, thereby obtaining the chlorine content in coal tar.

[0045] The reaction endpoint described above can be determined by the potential change during the titration process.

[0046] The formula for calculating the chlorine content in coal tar is as follows:

[0047]

[0048] In the formula, ω represents the chlorine content in the coal tar sample, in ppm;

[0049] c is the concentration of the silver nitrate standard titration solution, in mol / L;

[0050] V is the volume of silver nitrate standard solution consumed in the titration, in mL;

[0051] 35.45 is the atomic weight of chlorine, in g / mol;

[0052] m is the mass of the coal tar sample, in grams.

[0053] The method for detecting chlorine content in coal tar of the present invention will be further described below with specific examples.

[0054] Example 1

[0055] The method for detecting chlorine content in coal tar in this embodiment is as follows:

[0056] Weigh 1.9025g of coal tar sample and place it in a crucible. Install the ignition wire, then place it into an oxygen bomb containing 10mL of 1% Na2CO3 solution. Tighten the oxygen bomb and charge it with oxygen for 1 minute at 3MPa. After the coal tar sample is completely burned, immerse the oxygen bomb in cold water for 10 minutes and gently shake it. Then, slowly and evenly release the gas from the cooled oxygen bomb to atmospheric pressure over 3 minutes. Open the oxygen bomb and rinse the inner wall of the oxygen bomb and the crucible with approximately 20mL of deionized water. Transfer the solution from the oxygen bomb to a beaker. Add a few drops of nitric acid to adjust the pH of the test solution to 3.5, add approximately 90mL of ethanol, and perform potentiometric titration of the absorbent solution in an ethanol-water system using 0.0010mol / L silver nitrate standard solution. After titrating to the reaction endpoint, record the volume of silver nitrate standard solution consumed (1.05mL). Calculate the chlorine content in the coal tar using the formula: 19.6ppm.

[0057] Example 2

[0058] The method for detecting chlorine content in coal tar in this embodiment is as follows:

[0059] Weigh 1.0212 g of coal tar sample and place it in a crucible. Install the ignition wire, then place it into an oxygen bomb containing 10 mL of 1% Na₂CO₃ solution. Tighten the oxygen bomb and charge it with oxygen for 1 min at 3 MPa. After the coal tar sample is completely burned, immerse the oxygen bomb in cold water for 10 min and gently shake it. Then, slowly and evenly release the gas from the cooled oxygen bomb to atmospheric pressure over 3 min. Open the oxygen bomb and rinse the inner wall of the oxygen bomb and the crucible with approximately 20 mL of deionized water. Transfer the solution from the oxygen bomb to a beaker. Add a few drops of nitric acid to adjust the pH of the test solution to 4. Add approximately 90 mL of ethanol. Titrate the absorbent solution in an ethanol-water system with 0.0010 mol / L silver nitrate standard solution using potentiometric titration. After titrating to the reaction endpoint, record the volume of silver nitrate standard solution consumed (2.18 mL). Calculate the chlorine content in the coal tar using the formula: 75.7 ppm.

[0060] Example 3

[0061] The method for detecting chlorine content in coal tar in this embodiment is as follows:

[0062] Weigh 0.5021 g of coal tar sample and place it in a crucible. Install the ignition wire, then place it into an oxygen bomb containing 10 mL of 1% Na₂CO₃ solution. Tighten the oxygen bomb and charge it with oxygen for 1 min at 3 MPa. After the coal tar sample is completely burned, immerse the oxygen bomb in cold water for 10 min and gently shake it. Then, slowly and evenly release the gas from the cooled oxygen bomb to atmospheric pressure over 3 min. Open the oxygen bomb and rinse the inner wall of the oxygen bomb and the crucible with approximately 20 mL of deionized water. Transfer the solution from the oxygen bomb to a beaker. Add a few drops of nitric acid to adjust the pH of the test solution to 4.5, add approximately 90 mL of ethanol, and perform potentiometric titration of the absorbent solution in an ethanol-water system using 0.0010 mol / L silver nitrate standard solution. After titrating to the reaction endpoint, record the volume of silver nitrate standard solution consumed as 4.96 mL. Calculate the chlorine content in the coal tar using the formula: 350 ppm.

[0063] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for detecting chlorine content in coal tar, characterized in that, Includes the following steps: S1. Weigh a coal tar sample and place it in a crucible. Install the ignition wire and place it in an oxygen bomb containing Na2CO3 solution. Tighten the oxygen bomb and fill it with oxygen. S2, the oxygen bomb is ignited and burned, the coal tar sample is completely burned, and then the oxygen bomb is immersed in cold water to cool and shaken slightly; S3. After the oxygen bomb has cooled, slowly release the gas to atmospheric pressure and then open it. Rinse the inner wall of the oxygen bomb and the crucible with deionized water. Then transfer the solution inside the oxygen bomb into a beaker. S4, potentiometric titration: Add nitric acid to a beaker to adjust the pH to 3-4.5, then add ethanol, and titrate with silver nitrate standard solution to the reaction endpoint. Record the volume of silver nitrate standard solution consumed to obtain the chlorine content in coal tar.

2. The method for detecting chlorine content in coal tar as described in claim 1, characterized in that, In step S1, the mass of the coal tar sample is 0.5 to 2 g.

3. The method for detecting chlorine content in coal tar as described in claim 1, characterized in that, In step S1, the volume of the Na2CO3 solution is 10-15 mL; The concentration of Na2CO3 in the Na2CO3 solution is 1% to 2%.

4. The method for detecting chlorine content in coal tar as described in claim 1, characterized in that, In step S1, oxygen is introduced into the oxygen bomb at a pressure of 3 to 3.2 MPa for 1 to 2 minutes.

5. The method for detecting chlorine content in coal tar as described in claim 1, characterized in that, In step S2, the oxygen bomb is immersed in cold water for 10 to 15 minutes to cool down.

6. The method for detecting chlorine content in coal tar as described in claim 1, characterized in that, In step S3, the slow venting time is no less than 2 minutes, and the amount of deionized water used is 20-25 mL.

7. The method for detecting chlorine content in coal tar as described in claim 1, characterized in that, In step S4, the amount of ethanol added is 90-100 mL.

8. The method for detecting chlorine content in coal tar as described in claim 1, characterized in that, In step S4, the concentration of the silver nitrate standard solution is 0.001 mol / L.

9. The method for detecting chlorine content in coal tar as described in claim 1, characterized in that, In step S4, the formula for calculating the chlorine content in the coal tar is as follows: In the formula, ω represents the chlorine content in the coal tar sample, in ppm; c represents the concentration of the silver nitrate standard titration solution, in mol / L; V is the volume of silver nitrate standard solution consumed in the titration, in mL; 35.45 is the atomic weight of chlorine, g / mol; m is the mass of the coal tar sample, g. m is the mass of the coal tar sample, in grams.

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