A method for detecting 17 elements in coal pitch by inductively coupled plasma atomic emission spectrometry

Abstract

This invention provides a method for determining 17 elements in coal tar pitch using inductively coupled plasma optical emission spectrometry (ICP-OES), comprising the following three steps: 1) ashing; 2) acidification; and 3) instrumental testing. This invention utilizes a novel high-purity quartz ashing dish with a spout, eliminating the need for expensive platinum dishes compared to existing testing standards. It also overcomes the problem of commonly used laboratory ashing dishes easily introducing impurities such as calcium, magnesium, and aluminum (the main components of ashing dishes and glazes). Furthermore, it reduces the number of main steps, simplifies the process, and improves digestion efficiency by optimizing the ratio of various acids in the digestion system. Based on inductively coupled plasma optical emission spectrometry (ICP-OES), this invention achieves the simultaneous detection of 17 elements in coal tar pitch, and compared to existing technologies, it can also detect lithium and silicon.

Description

Technical Field

[0001] This invention belongs to the field of detection and analysis technology of impurity element content in organic compounds, specifically involving a method for detecting 17 elements in coal tar pitch using inductively coupled plasma optical emission spectrometry (ICP-OES). Background Technology

[0002] Prebaked anodes are a typical example of carbon anode materials used in aluminum electrolysis. They are consumable anode materials produced in electrolytic cells. Raw materials for producing prebaked anodes include coal tar pitch and petroleum coke. Petroleum coke is calcined to obtain calcined coke, which is then mixed with recycled anode residues, fine powder, and other materials, along with coal tar pitch binder. Through various processes, the prebaked anode product is obtained. During aluminum electrolysis, as the prebaked anode material is slowly consumed, carbon slag or ash enters the electrolytic cell, affecting the electrolyte composition and the elemental content in the molten aluminum. Furthermore, excessively high impurity element content increases the electrochemical consumption of the anode. Therefore, the detection of impurity element content in aluminum anode materials is an important physicochemical testing item.

[0003] Coal tar pitch is the residue after coal tar distillation. It has no fixed melting point and contains trace amounts of impurities such as vanadium, iron, nickel, and sodium. Domestically, the ash content of coal tar pitch is generally required to be less than 0.3%, while the ash content of petroleum coke is typically required to be less than 0.5%. Therefore, the overall impurity content of coal tar pitch is lower than that of petroleum coke. Although the impurity content in coal tar pitch is low, this indicator is quite important for the reactivity of the anode with carbon dioxide and air. This is because the portion of the anode product that reacts preferentially with carbon dioxide and air is the binder matrix, i.e., the coal tar pitch portion. As an important binder for prebaked anodes, the impurity content of coal tar pitch is a key factor to consider in both the domestic market and in import / export coal tar pitch transactions.

[0004] Currently, there are few standards and literature on the detection of impurity elements in coal tar pitch, with only one industry standard: SN / T2493-2010 "Detection of Calcium, Iron, Sodium, Nickel, Silicon, Titanium and Vanadium in Coal Tar Pitch - Inductively Coupled Plasma Atomic Emission Spectrometry". Since coal tar pitch and petroleum coke have similar chemical compositions, the detection of impurity elements in coal tar pitch can refer to the relevant detection standards for petroleum coke. Looking at the detection standards for impurity elements in petroleum coke, the main detection methods are atomic absorption spectrometry (AAS), X-ray fluorescence analysis (XRF), and inductively coupled plasma atomic emission spectrometry (ICP-OES). The characteristics of atomic absorption spectrometry (AAS) are: a different cathode lamp is required for each element tested, and multi-element testing cannot be performed simultaneously. The characteristics of X-ray fluorescence analysis (XRF) are: simultaneous determination of multiple elements, but the instruments (approximately 1-2 million RMB), supporting equipment, and standard materials are expensive, making it difficult to meet resource requirements. The characteristics of inductively coupled plasma atomic emission spectrometry (ICP-OES) are: a wide dynamic linear range, good stability, low interference, and the ability to rapidly determine multiple elements simultaneously, with low-cost supporting equipment and standard materials. There are relevant domestic, international, and industry standards and references for the detection of impurity elements in petroleum coke using ICP-OES. A review of these standards reveals that the testing principles and operational procedures are largely consistent with SN / T 2493-2010 "Detection of Calcium, Iron, Sodium, Nickel, Silicon, Titanium and Vanadium in Coal Tar Pitch - Inductively Coupled Plasma Atomic Emission Spectrometry," and basically refer to the standard ISO 14435-2005 "Determination of Trace Metals in Petroleum Coke by Inductively Coupled Plasma Atomic Emission Spectrometry for Carbon Materials for Aluminum Production." The testing procedure is as follows: the sample is ashed in a platinum dish at 700℃±10℃, then fused with alkali and leached with acid, followed by ICP-OES analysis. This method requires a 100... The method involves using a 1 mL platinum dish, platinum tongs, and a lithium borate mixed flux. Platinum dishes are expensive, and the lithium borate mixed flux is also costly. If a laboratory tests more than one sample at a time, it needs to purchase two more platinum dishes, which is difficult for ordinary laboratories to obtain. Furthermore, the method has complicated testing steps, is prone to contamination, is prone to failure, and has high testing costs, long cycles, low efficiency, and cannot determine the element Li.

[0005] In Wang Jinrong et al.'s "Determination of 16 Elements in High-Purity Petroleum Coke and High-Purity Coal Tar Ash by ICP-AES", the ashing temperature (700℃) in SN / T 2493-2010 is referenced for ashing. However, this method requires weighing 200g of the original sample, has a long ashing time, high energy consumption, and generates significant pollution. After ashing, the ash content needs to be calculated before subsequent elemental tests can be performed. Furthermore, this method cannot test for Si.

[0006] Because coal tar pitch and petroleum coke have significantly different physicochemical properties—for example, the softening point of coal tar pitch is typically 35℃-120℃, while petroleum coke is formed by coking at high temperatures (approximately 500℃-550℃) and is relatively stable—the ash temperature of coal tar pitch can be lowered compared to petroleum coke, thus reducing energy consumption.

[0007] Since coal tar pitch that has undergone various pretreatments has a very low ash content, usually less than 0.3%, the acid dissolution method can effectively decompose the sample, making it unnecessary to use the costly and cumbersome lithium borate alkaline fusion method.

[0008] To meet the demands of the coal tar pitch testing market, there is an urgent need in this field to develop a low-cost, high-efficiency method for the simultaneous determination of multiple elements in coal tar pitch. Summary of the Invention

[0009] To address the above problems, this invention develops a method for determining 17 elements in coal tar pitch using inductively coupled plasma optical emission spectrometry (ICP-OES), characterized by the following three steps: 1) Ashing; 2) Acidification; 3) On-machine testing.

[0010] In one specific embodiment, the ashing is performed using a high-purity quartz dish with a spout.

[0011] In one specific embodiment, the acidification process employs a digestion system comprising hydrochloric acid, nitric acid, and hydrofluoric acid.

[0012] In one specific embodiment, the volume ratio of hydrochloric acid, nitric acid, and hydrofluoric acid in the digestion system is 3:1:1.

[0013] In one specific embodiment, the following three steps are adopted: 1) Ashing: A certain amount of coal tar pitch sample is placed in a high-purity quartz dish with a spout. The quartz dish is placed in a muffle furnace at room temperature. The temperature is raised to 150℃ in 1 hour and held for 30 minutes. The temperature is raised to 300℃ in 1 hour and held for 30 minutes. Then the temperature is raised to 500℃ in 1 hour and burned at 500℃ until no carbon particles are left. The sample is then cooled to room temperature.

[0014] 2) Acidification: Cover the top of the quartz dish with a PTFE watch glass to prevent dust from being introduced. Moisten the ash with a little water, add hydrochloric acid and nitric acid in a volume ratio of 3:1, transfer all the ash to a PTFE beaker and heat on a hot plate until no ash is visible to the naked eye. Heat to near dryness, cool to room temperature, add hydrofluoric acid of equal volume to nitric acid and a small amount of ultrapure water, heat at ≤60℃ for 2 hours, and after cooling, transfer all the liquid to a plastic volumetric flask, dilute to the mark with ultrapure water, and shake well for later use.

[0015] 3) On-machine testing: Multiple elements were determined using a matrix-matched standard solution on an inductively coupled plasma atomic emission spectrometer.

[0016] In one specific embodiment, the following three steps are adopted: 1) Ashing: Weigh 5 grams (accurate to 0.0001 grams) of coal tar pitch and place it in a high-purity quartz dish with a spout. Place the quartz dish in a muffle furnace at room temperature, raise the temperature to 150°C for 1 hour, hold for 30 minutes, raise the temperature to 300°C for 1 hour, hold for 30 minutes, raise the temperature to 500°C for another hour, and calcine at 500°C until no carbon particles remain. Cool to room temperature. 2) Acidification: Cover the top of the quartz dish with a 10cm diameter PTFE watch glass to prevent dust from being introduced. Moisten the ash with a little water, add 2mL of analytical grade nitric acid and 6mL of analytical grade hydrochloric acid, and transfer all the ash to a 250mL PTFE beaker. Heat on a hot plate to digest, and do not exceed 260℃. Digest until no ash is visible to the naked eye, heat to near dryness, cool to room temperature, add 2mL of hydrofluoric acid and a small amount of ultrapure water, heat at ≤60℃, digest for 2 hours, and after cooling, transfer all the liquid to a 100mL plastic volumetric flask, dilute to the mark with ultrapure water, and shake well for later use. 3) On-machine testing: Multiple elements were determined using a matrix-matched standard solution on an inductively coupled plasma atomic emission spectrometer.

[0017] This invention also provides a method for determining 17 elements in coal tar pitch using inductively coupled plasma optical emission spectrometry (ICP-OES), and its application in the simultaneous determination of multiple elements in coal tar pitch.

[0018] This invention develops a method for directly weighing coal tar pitch samples for ashing treatment, transferring the ash without loss to a polytetrafluoroethylene beaker for acidification treatment, and then directly performing elemental analysis using ICP-OES after acidification treatment.

[0019] The beneficial effects of this invention are as follows: 1. The detection method of this invention is low in cost, low in energy consumption, and generates minimal pollution. ① Compared to existing detection standards, it does not require the use of expensive platinum dishes. ② The sample weight is small (5-10 grams), reducing environmental pollution caused by the ashing process. ③ The ashing temperature is low: the ashing temperature of existing detection standards and references is around 700℃, while the ashing temperature of the detection method of this invention is around 500℃.

[0020] 2. This invention overcomes the shortcomings of commonly used laboratory ashing dishes by employing a novel high-purity quartz ashing dish with a spout, which easily introduces impurities such as calcium, magnesium, and aluminum (the main components of ashing dishes and glazes), thus avoiding the significant impact of ash loss on results during ash transfer. The high-purity quartz used in this invention has the following advantages: a. High purity: Ordinary high-purity quartz has a purity of ≥99.9% (3N) and low impurity elements.

[0021] b. Extremely high thermal stability: extremely low coefficient of thermal expansion (approximately 5.5 × 10⁻⁶). -7 ( / ℃), with excellent thermal shock resistance, and can withstand drastic temperature changes.

[0022] c. Excellent chemical stability: Extremely resistant to acids (except hydrofluoric acid and hot phosphoric acid), and resistant to most chemical substances. Does not react with most metals and acidic gases at high temperatures.

[0023] d. High mechanical strength and low viscosity: high purity, few internal defects, and high intrinsic strength.

[0024] 3. The detection method of this invention is simple and efficient. Existing testing standards mainly involve the following steps: ashing → alkali fusion → acidification → instrumental measurement. The detection method of this invention mainly involves the following steps: ashing → acidification → instrumental measurement. This invention reduces the main steps, simplifies the process, and improves digestion efficiency by optimizing the ratio of various acids in the digestion system.

[0025] 4. This invention can simultaneously detect 17 elements in coal tar pitch, and compared with existing technologies, it can detect lithium and silicon. Attached Figure Description

[0026] Figure 1 This is a high-purity quartz ashing dish with a spout used in this invention. Quartz ashing dish dimensions: bottom diameter: approximately 75mm; top diameter: approximately 85mm; height: approximately 35mm; the angle between the bottom and the dish wall is approximately 110°, with a smooth, rounded connection. Detailed Implementation

[0027] Example 1: Simultaneous determination of 17 elements in coal tar pitch Instruments and reagents 5100 Inductively Coupled Plasma Emission Spectrometer (Agilent Technologies, USA), equipped with a hydrofluoric acid resistant sample introduction system.

[0028] 31 element standard solutions (Al, Ca, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb, Ti, V, Zn, Si) (Steel Research Institute NACK, NCS149174), 100 μg / mL.

[0029] Hydrochloric acid and nitric acid were of superior purity, and hydrofluoric acid was of analytical purity; the laboratory water met the requirements of GB / T 6892 Class I water.

[0030] Instrument operating conditions The operating parameters of the inductively coupled plasma atomic emission spectrometer are shown in Table 1.

[0031] Table 1 ICP-OES Operating Parameters Preparation of standard solution series Table 2. Mass concentration (mg / L) of each element in the standard solution series of Al, Cu, Fe, etc. Table 3. Mass concentrations (mg / L) of the Si standard solution series The testing steps are as follows: 1. Ashing The operating steps are as follows: Weigh 5 grams (accurate to 0.0001 grams) of coal tar pitch into a quartz ashing dish, place the quartz ashing dish in a muffle furnace at room temperature, raise the temperature to 150°C for 1 hour, hold for 30 minutes, raise the temperature to 300°C for 1 hour, hold for 30 minutes, and then raise the temperature to 500°C for 1 hour. At this temperature, calcine until no carbon particles are present, and then cool to room temperature.

[0032] 2. Acidification Taking into account the total acid volume used for digestion, the hydrolysis of metal ions, and the acidity of the test solution, this method selects a total acid volume of 10.0 mL, which can ensure complete digestion of the sample and maintain a low acidity and stability of metal ions in the test solution.

[0033] The operating steps are as follows: Cover the top of the quartz ashing dish with a 10cm diameter PTFE watch glass to prevent dust from being introduced. Moisten the ash with a small amount of water. Add 2mL of analytical grade nitric acid and 6mL of analytical grade hydrochloric acid to the quartz ashing dish. Transfer all the ash to a 250mL PTFE beaker and heat on a hot plate for digestion. The temperature should not exceed 260℃. Digest until no ash is visible to the naked eye. Heat to near dryness and cool to room temperature. Add 2mL of hydrofluoric acid and a small amount of ultrapure water to digest the siliceous compounds. The heating temperature should not exceed 60℃. Digest for 2 hours. After cooling, transfer all the liquid to a 100mL plastic volumetric flask and dilute to the mark with ultrapure water. Shake well. If necessary, dilute the test solution according to the working curve range. Perform a sample blank test along with the sample.

[0034] 3. On-machine measurement Based on the instrument's recommended initial elemental analysis lines, select 2-4 spectral lines for each element. Scan the standard solution and sample solution according to the selected instrument operating parameters. Based on the spectrum displayed on the computer, eliminate interfering spectral lines and retain those with good waveforms, low interference, low background, and high intensity. Select appropriate background points and observe the linearity of the calibration curve and the spiked recovery results. Taking all factors into consideration, the recommended analytical spectral lines for Al, Ca, Cr, Cu, Co, Fe, Mg, Mn, Ni, Pb, Ti, V, Zn, Li, K, Na, and Si are shown in Table 4.

[0035] Typically, coal tar pitch has an ash content of less than 0.3%, and the ash content of a 5g sample is less than 0.015g. The mass ratio in a 100mL solution is very low. Moreover, the ash mainly consists of various oxides, and the composition is complex, with no single component as the main component. Therefore, matrix interference need not be considered.

[0036] A series of standard solutions were measured according to the selected instrument operating parameters. A calibration curve was plotted with the mass concentration of the analyte on the x-axis and its corresponding emission intensity on the y-axis. The sample blank solution was tested 11 times consecutively under the same conditions, and the standard deviation was calculated. Three times the standard deviation was taken as the method detection limit, as shown in Table 4.

[0037] Table 4. Analytical spectra, calibration curves, and method detection limits for 17 elements including Al, Cu, and Fe. Table 5 Spike recoveries of 17 elements including Al, Cu, and Fe Comparative Example 1 The difference from Example 1 is that the digestion system used in the acidification step is 10.0 mL hydrochloric acid-hydrofluoric acid (4:1, volume ratio).

[0038] Comparative Example 2 The difference from Example 1 is that the digestion system used in the acidification step is 10.0 mL nitric acid-hydrofluoric acid (4:1, volume ratio).

[0039] Comparative Example 3 The difference from Example 1 is that in the acidification step, the digestion system uses 10.0 mL of hydrochloric acid alone.

[0040] Comparative Example 4 The difference from Example 1 is that 10.0 mL of nitric acid was used alone in the digestion system during the acidification step.

[0041] Comparative Example 5 The difference from Example 1 is that the digestion system in the acidification step uses 10.0 mL of hydrofluoric acid alone.

[0042] Comparative Example 6 The difference from Example 1 is that 10.0 mL of aqua regia was used alone in the digestion system during the acidification step.

[0043] When the samples were digested using the digestion systems of Comparative Examples 3-6, the dissolution was incomplete. When the samples were digested using the digestion systems of Comparative Examples 1-2, complete digestion required a longer time. For example, the experimental data listed in Table 6.

[0044] Table 6 Comparison of digestion effects of different digestion systems This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. After reading this specification, those skilled in the art can make non-creative adjustments to the dosage of each component, preparation parameters, and construction process according to actual application needs. However, as long as these adjustments are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A method for determining 17 elements in coal tar pitch using inductively coupled plasma optical emission spectrometry (ICP-OES), characterized in that, The following three steps are used: 1) Ashing; 2) Acidification; 3) On-machine testing.

2. The method for determining 17 elements in coal tar pitch as described in claim 1, characterized in that, The ashing process uses a high-purity quartz dish with a spout.

3. The method for determining 17 elements in coal tar pitch as described in claim 1, characterized in that, The digestion system used for acidification includes hydrochloric acid, nitric acid, and hydrofluoric acid.

4. The method for determining 17 elements in coal tar pitch as described in claim 3, characterized in that, The volume ratio of hydrochloric acid, nitric acid, and hydrofluoric acid in the digestion system is 3:1:

1.

5. The method for determining 17 elements in coal tar pitch as described in claim 1, characterized in that, The following three steps are used: 1) Ashing: A certain amount of coal tar pitch sample is placed in a high-purity quartz dish with a spout. The quartz dish is placed in a muffle furnace at room temperature. The temperature is raised to 150℃ in 1 hour and held for 30 minutes. The temperature is raised to 300℃ in 1 hour and held for 30 minutes. The temperature is raised to 500℃ in another hour and burned at 500℃ until no carbon particles are left. The sample is then cooled to room temperature. 2) Acidification: Cover the top of the quartz dish with a PTFE watch glass to prevent dust from being introduced. Moisten the ash with a little water, add hydrochloric acid and nitric acid in a volume ratio of 3:1, transfer all the ash to a PTFE beaker and heat on a hot plate until no ash is visible to the naked eye. Heat to near dryness, cool to room temperature, add hydrofluoric acid of equal volume to nitric acid and a small amount of ultrapure water, heat at ≤60℃ for 2 hours, and after cooling, transfer all the liquid to a plastic volumetric flask, dilute to the mark with ultrapure water, and shake well for later use. 3) On-machine testing: Multiple elements were determined using a matrix-matched standard solution on an inductively coupled plasma atomic emission spectrometer.

6. The method for determining 17 elements in coal tar pitch as described in claim 1, characterized in that, The following three steps are used: 1) Ashing: Weigh 5 grams (accurate to 0.0001 grams) of coal tar pitch and place it in a high-purity quartz dish with a spout. Place the quartz dish in a muffle furnace at room temperature, raise the temperature to 150°C for 1 hour, hold for 30 minutes, raise the temperature to 300°C for 1 hour, hold for 30 minutes, and then raise the temperature to 500°C for another hour. Burn the dish at 500°C until no carbon particles remain, and then cool to room temperature. 2) Acidification: Cover the top of the quartz dish with a 10cm diameter PTFE watch glass to prevent dust from being introduced. Moisten the ash with a little water, add 2mL of analytical grade nitric acid and 6mL of analytical grade hydrochloric acid, and transfer all the ash to a 250mL PTFE beaker. Heat on a hot plate to digest, and do not exceed 260℃. Digest until no ash is visible to the naked eye, heat to near dryness, cool to room temperature, add 2mL of hydrofluoric acid and a small amount of ultrapure water, heat at ≤60℃, digest for 2 hours, and after cooling, transfer all the liquid to a 100mL plastic volumetric flask, dilute to the mark with ultrapure water, and shake well for later use. 3) On-machine testing: Multiple elements were determined using a matrix-matched standard solution on an inductively coupled plasma atomic emission spectrometer.

7. The method for determining 17 elements in coal tar pitch as described in claims 1-5 is applied to the simultaneous determination of multiple elements in coal tar pitch.

Images