Pretreatment method of oil sample and measurement method of trace elements in oil sample

Abstract

The present invention discloses a method for measuring trace elements in a pre-treatment of an oil sample and an oil sample. The oil sample is a carbon fiber precursor oil; the pre-treatment method of the oil sample comprises the following steps: a sample of a set mass is subjected to carbonization treatment to obtain a product after carbonization treatment; the product after carbonization treatment is heated to an ashing treatment temperature for ashing treatment to obtain a product after ashing treatment; wherein, if the oil sample is a low-silicon or silicon-free carbon fiber precursor oil, the ashing treatment temperature is 500-600°C; if the oil sample is a carbon fiber precursor oil with a silicon content greater than 500ug / g, the ashing treatment temperature is 600-650°C; the product after ashing treatment is dissolved, then constant volume is carried out, and a clear and bright sample solution is obtained. The present invention adopts a dry digestion method to pre-treat the oil sample to meet the detection requirements of the ICP-OES method; the operating steps are simple, accurate and reproducible.

Description

Technical Field

[0001] The invention relates to a method for pre-treating an oil sample for carbon fiber production and measuring the content of trace elements such as metal ions in the sample by adopting an ICP-OES method, and belongs to the field of detecting the content of trace elements in oils. Background Art

[0002] Currently, carbon fiber precursor (also known as carbon fiber precursor, referred to as "precursor") requires immersion oiling with one or more oils during production. This reduces friction during production, improves antistatic properties and bundled properties, prevents fuzzing due to static electricity during subsequent pre-oxidation, and improves carbonization processability. This oil is called a carbon fiber precursor oil.

[0003] Carbon fiber precursor oils are generally categorized as silicone-containing and silicone-free. While the formulations and performance of these oils vary from manufacturer to manufacturer, their primary functions remain essentially the same. As a coating material on the precursor surface, the type and content of metal ions and other trace elements in the oil directly impact the type and content of metal ions in the precursor and carbon fiber ash, and thus the antioxidant and ablation resistance of the precursor and carbon fiber. Therefore, measuring the content of these trace elements in the oil is crucial.

[0004] Currently, most carbon fiber precursor oils are white emulsion-type organic oils, which require pretreatment before further measurement of trace element content such as metal ions using ICP-OES. However, to date, no relevant pretreatment standards or methods for carbon fiber precursor oils have been found in China. Summary of the Invention

[0005] In order to overcome the above-mentioned shortcomings, the present invention provides a pretreatment method for an oil sample and a method for measuring trace elements in an oil sample. The main purpose is to propose a method for pretreating a carbon fiber precursor oil sample so that the sample solution obtained after pretreatment meets the testing requirements of the ICP-OES method.

[0006] Based on the premise that there are no relevant standards to refer to, the present invention proposes a dry digestion scheme to pre-treat the oil sample according to the characteristics of the carbon fiber precursor oil to obtain a clear and bright sample solution that meets the measurement requirements of the ICP-OES method. Then, the ICP-OES method can be used to measure the content of trace elements in the carbon fiber precursor oil.

[0007] This invention improves upon conventional dry digestion. Targeting the characteristics of carbon fiber precursor oils, extensive research has determined the appropriate chemicals, dosage and timing of dosing, digestion temperature and steps, and dissolution methods. While successfully addressing sample pretreatment issues, this method crucially enables rapid and complete sample decomposition while minimizing the use of acid. Finally, combined with inductively coupled plasma emission spectrometry (ICP), it enables rapid and accurate detection of various trace element contents in the oil, providing essential data for the research and development of precursor and carbon fiber production processes. In summary, this invention primarily addresses the measurement of trace element content in carbon fiber precursor oils and proposes a practical method. Users can apply this method directly or make minor adjustments based on the specific characteristics of their own products, filling a significant gap in the industry.

[0008] The present invention provides a method for pre-treating an oil sample, which uses a dry digestion method to pre-treat the oil sample, wherein the oil sample is a carbon fiber precursor oil; the method comprises the following steps:

[0009] (1) Carbonization treatment step: Carbonizing a sample of a set mass to obtain a carbonized product;

[0010] (2) Ashing treatment step: heating the carbonized product to an ashing treatment temperature for ashing treatment to obtain an ashing product; wherein, if the oil sample is a low-silicon carbon fiber precursor oil with a silicon content of not more than 500ug / g or a carbon fiber precursor oil without silicon, the ashing treatment temperature is 500-600°C, and the ashing treatment time is 6-8h; if the oil sample is a carbon fiber precursor oil with a silicon content of more than 500ug / g, the ashing treatment temperature is 600-650°C, and the ashing treatment time is 6-8h;

[0011] (3) Dissolution and volume determination step: The product after the ashing treatment is dissolved, and after all the solution is dissolved, the volume is determined to obtain a sample solution.

[0012] Preferably, before the carbonization step, the method further comprises:

[0013] Sampling and adding test sample steps: shake the oil sample, take a sample from the oil sample, and drop the sample to the bottom of the container, and ensure that the sample does not drop or splash onto the side wall of the container;

[0014] Preferably, the sample is taken from the middle of the oil sample;

[0015] Preferably, the container is a quartz beaker;

[0016] Preferably, before the sampling and adding steps, the container needs to be pre-treated, specifically: first soaking the container in nitric acid, then ultrasonically cleaning the container with ultrapure water, and finally calcining the container to constant weight;

[0017] Preferably, at least two parallel samples are taken for each oil sample.

[0018] Preferably, in the carbonization treatment step: adding an auxiliary agent concentrated sulfuric acid to the container containing the sample, then heating it to the carbonization treatment temperature, and performing carbonization treatment at the carbonization treatment temperature until the sample completely turns black, no bubbles are emitted, and no white smoke is emitted; wherein the carbonization treatment temperature is 195-205°C.

[0019] Preferably, in the carbonization step, the mass of each sample is 1.0000-1.2000 g. Preferably, the amount of concentrated sulfuric acid added as an auxiliary agent does not exceed 0.5 mL; further preferably, the amount of concentrated sulfuric acid added as an auxiliary agent is 0.5 mL; preferably, the volume concentration of concentrated sulfuric acid is 95-98%.

[0020] Preferably, the ashing step is performed in a muffle furnace.

[0021] Preferably, the heating rate in the ashing step is 4-6°C / min, preferably 5°C / min.

[0022] Preferably, in the dissolving and volume setting step, nitric acid and hydrofluoric acid are used to dissolve the product after the ashing treatment.

[0023] Preferably, in the dissolving and volume setting step: concentrated nitric acid is added to the container containing the product after the ashing treatment for dissolving treatment, and then the dissolved solution is transferred to a centrifuge tube; the container is rinsed with dilute nitric acid several times, and the rinsing solution is transferred to the centrifuge tube; concentrated hydrofluoric acid is added to the centrifuge tube, and the centrifuge tube is shaken. After all the solution is dissolved, the volume is fixed to 20-25 mL with dilute nitric acid to obtain a sample solution; preferably, the concentrated nitric acid and hydrofluoric acid are of high purity or above, preferably UPS electronic grade standard acid; preferably, when the mass of each sample is 1.0000-1.2000 g: the amount of the concentrated nitric acid used is 1.0-3.0 mL; the amount of the concentrated hydrofluoric acid used is 1-2 mL; preferably, the volume concentration of the dilute nitric acid is 2-5%; preferably, the total amount of dilute nitric acid used to rinse the container is 3-8 mL.

[0024] The present invention also provides a method for measuring trace elements in the above oil sample, which comprises the following steps:

[0025] 1) Pre-treating the oil sample using any of the methods described above to obtain a sample solution;

[0026] 2) Using an inductively coupled plasma emission spectrometer (ICP) to measure the sample solution, the content of trace elements in the oil sample is measured.

[0027] The aforementioned method for measuring trace elements in oil samples requires the preparation of a blank sample. This preparation involves performing the carbonization, ashing, and dissolution steps without adding a sample to obtain a blank sample. Because trace elements may be introduced during each step, the blank sample is used to remove trace elements introduced during each operation, thereby subtracting the background from the sample processing.

[0028] Beneficial effects of the present invention:

[0029] (1) Based on the premise that there are no relevant standards to refer to, this invention proposes a dry digestion scheme to pre-treat the oil sample according to the characteristics of carbon fiber precursor oil, so as to obtain a clear and bright sample solution that meets the measurement requirements of the ICP-OES method, and then the content of trace elements in the carbon fiber precursor oil can be measured by the ICP-OES method.

[0030] (2) The pretreatment method for the oil sample provided in the embodiment of the present invention includes carbonizing, ashing, and dissolving and fixing the sample to obtain a sample solution. During the ashing process, different ashing temperatures and times are used for oil samples with low silicon content or no silicon content and oil samples with high silicon content, so that the oil sample can be completely ashed without burning.

[0031] (3) In the carbonization step, the amount of concentrated sulfuric acid added as an auxiliary agent is selected so that the subsequent ashing process will not cause dead burning, resulting in insolubility, or incomplete ashing or excessively long ashing time;

[0032] (4) The solution of the present invention provides the minimum amount of two acids used to dissolve the product after ashing treatment, so as to protect the matrix tube of the ICP instrument to the greatest extent and reduce the detection cost.

[0033] (5) The present invention has made improvements based on the conventional dry digestion. Based on the characteristics of carbon fiber precursor oil, a large amount of research has been conducted to determine which drugs to use, the dosage of drugs and the timing of adding drugs, the digestion temperature and steps, the dissolution method, etc., and on the premise of successfully solving the sample pretreatment problem, the most critical thing is that the sample can be quickly and completely decomposed using this method, and the amount of acid used is small. Finally, combined with inductively coupled plasma emission spectrometry (ICP), it can quickly and accurately detect the content of various trace elements in the oil, providing basic data support for the production and research and development of precursor production processes and carbon fiber production processes. In short, the present invention mainly studies the method for measuring the trace element content of carbon fiber precursor oil and proposes a practical method. According to the ideas given by this method, users can directly use it or make minor adjustments according to the characteristics of their own products to perform measurements, filling the gap in the industry. DETAILED DESCRIPTION

[0034] To further illustrate the technical means and effects employed by the present invention to achieve its intended objectives, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention is provided in conjunction with the following embodiments. In the following description, different references to "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0035] The inventors of this application have studied the thermal decomposition properties of several carbon fiber precursor oils commonly used by carbon fiber companies (existing carbon fiber precursor oils have the following characteristics: milky white liquid appearance, pH 3-11, and active ingredient content of 20-45wt%). They have designed experimental methods based on their thermal properties and, after experimental verification, have provided a sample pretreatment method for the oils to meet the testing requirements of the ICP-OES method. The specific solution is as follows:

[0036] A method for pre-treating an oil sample, wherein the oil sample is a carbon fiber precursor oil, using a dry digestion method to pre-treat the oil sample; the method comprises the following steps:

[0037] Sampling and adding test sample steps: shake the oil sample thoroughly, use a plastic dropper to take a small amount of sample from the middle of the oil sample and add it dropwise to the middle of the bottom of a 50mL quartz beaker. When adding the sample, be careful not to add the sample dropwise to the side wall of the container or splash onto the side wall of the container.

[0038] In addition, before the sampling and adding steps, the quartz beaker used should be soaked in nitric acid, ultrasonically cleaned with ultrapure water, and burned to constant weight.

[0039] The appropriate sampling amount for each pre-treated oil sample is 1.0-1.2 g, accurate to 0.0001 g.

[0040] Carbonization treatment step: carbonizing a sample of a set mass to obtain a carbonized product.

[0041] The specific steps are as follows: evenly add 0.5 mL of concentrated sulfuric acid to the beaker with the sample, place it on a hot plate at 200±5°C for heating and carbonization, until the sample completely turns black, no bubbles appear, and no white smoke is emitted.

[0042] In addition, take a 50mL quartz beaker without any sample, add 0.5mL concentrated sulfuric acid into it, and place it on the hot plate at the same time as the pre-treated sample to carbonize until it turns completely black and no white smoke is emitted, which serves as a blank sample.

[0043] At least two parallel samples should be taken for each pre-treated oil sample.

[0044] Ashing treatment steps: Place the carbonized sample in a muffle furnace, heat it at 500-650°C, and keep it in ashing for 6-8 hours.

[0045] In this step, the ashing temperature should be selected based on whether the sample contains silicon or how much silicon it contains. Low-silicon carbon fiber precursor oil samples with a silicon content of no more than 500ug / g or carbon fiber precursor oil samples without silicon can be ashed at 500-600°C, otherwise dead sintering is likely to occur. Oil samples with a silicon content greater than 500ug / g need to be ashed at 600-650°C to ensure complete decomposition of the ash sample.

[0046] In the ashing step, the blank sample is also ashed.

[0047] Dissolving and volume setting step: dissolving the product after the ashing treatment, and setting the volume after all the solution is dissolved to obtain a sample solution.

[0048] This step specifically involves dissolving the ashing product with a small amount of concentrated nitric acid (approximately 1.0-3.0 mL). Transfer the solution to a 20-50 mL plastic centrifuge tube. Rinse the quartz beaker two to three times with a small amount of 2-5% dilute nitric acid and transfer it to the plastic centrifuge tube. Add 1-2 mL of concentrated hydrofluoric acid to the tube, cover, and shake. Once the solution is completely dissolved and clear, dilute it to 20-25 mL with 2% dilute nitric acid, shake well, and set aside. Next, measure the trace element content of the resulting sample solution using ICP.

[0049] The concentrated nitric acid and hydrofluoric acid used are of superior purity or above, preferably UPS grade or above.

[0050] Wherein, in the dissolving and volume setting step: the blank sample is also dissolved and volume set.

[0051] Regarding the above technical solution, it should be noted that:

[0052] (1) About carbon fiber precursor oil: It is a milky white aqueous emulsion, mainly composed of 50% water and a large amount of nano-scale epoxy resin particles, surfactants, emulsion stabilizing agents, etc. It takes 7-8 hours to dry to constant weight at a normal temperature of about 80°C. If the drying temperature is too high, splashing will generally occur in the early stage of drying, resulting in a decrease in the effective ingredients detected.

[0053] (2) Conventional dry digestion methods: First, heat the sample on a hot plate to dehydrate and carbonize it, then dissolve it after ashification. Different acids are used to dissolve the sample, and the dosage varies depending on the sample. Generally, hydrochloric acid and nitric acid are more commonly used. These digestion methods are commonly used in industries such as food, medicine, and soil.

[0054] For carbon fiber precursor oil, this method seems too broad and not very applicable. Further research is needed to propose specific, feasible and standardized methods.

[0055] (3) The present invention is characterized by:

[0056] First, carbon fiber precursor oil is a white emulsion-type organic oil, which requires pretreatment before further measurement of trace element content such as metal ions using ICP-OES. However, to date, no relevant pretreatment standards or methods for oils have been found in China, and a simple, rapid, and accurate detection method is needed.

[0057] The present invention is based on the premise that there are no relevant standards to refer to. According to the characteristics of carbon fiber precursor oil, it is the first time to propose a dry digestion scheme to pre-treat the oil.

[0058] Second, during the carbonization process, the amount of auxiliary sulfuric acid was studied under heating conditions at around 200°C. The inventors found that if the amount of auxiliary sulfuric acid exceeded 0.5 mL, the subsequent ashing process would burn and the solution would not dissolve. If the amount of auxiliary sulfuric acid was too little, problems such as incomplete ashing or excessive ashing time would easily occur.

[0059] Third, regarding the ashing process: The inventors discovered that different samples require different ashing temperatures and times. For example, some high-silicone oils require a temperature of 650°C for complete ashing, exceeding the typical ashing temperature and requiring a longer holding time. Similarly, for low-silicone oils, the maximum acceptable ashing temperature varies from sample to sample. For example, some low-silicone oils can burn samples at higher temperatures. Therefore, the method provided by this invention allows manufacturers to quickly identify the appropriate ashing temperature for testing.

[0060] Fourth, regarding the dissolution and volume determination step: While conventional samples can be dissolved with a single acid after ashing (residue), the inventors of this invention propose that the ashing product of carbon fiber precursor oil requires the addition of two acids. Furthermore, the present invention specifies the minimum dosage of the two acids required to dissolve the ashing product (residue) to maximize protection of the ICP instrument's matrix and reduce testing costs.

[0061] In summary, this invention, based on the lack of relevant standards and tailored to the characteristics of carbon fiber precursor oils, proposes a dry digestion method for pre-treatment of the oil. Furthermore, this method improves upon conventional dry digestion by, through extensive research, determining the appropriate chemicals, dosages and timing of dosing, digestion temperature and steps, and dissolution methods, specifically tailored to the oil's characteristics. This method not only successfully performs pre-treatment but also achieves rapid and complete decomposition of key samples with minimal acid usage. Finally, combined with inductively coupled plasma (ICP) optical emission spectrometry, it can quickly and accurately measure the content of various trace elements in the oil, providing fundamental data support for the development and production of precursor and even carbon fiber production processes.

[0062] In summary, the present invention mainly studies the detection method of trace element content of carbon fiber precursor oil and proposes a practical method. Users can use it directly or make minor adjustments based on the ideas given by this method and the characteristics of their own products to perform detection, filling the gap in the industry.

[0063] The present invention is further described below by means of specific embodiments:

[0064] Example 1

[0065] This example is used to pre-treat carbon fiber precursor oil sample 1# (also referred to as oil sample 1#, with a silicon content of no more than 500 μg / g). The sample solution obtained after pre-treatment is used to determine the trace element content (ICP-OES method). The specific steps include:

[0066] Preparation of quartz beaker: Soak a 50 mL quartz beaker in (1+1) nitric acid for 24 h, rinse with deionized water, sonicate with ultrapure water for 20 min, rinse again with ultrapure water, and place in a muffle furnace to burn to constant weight.

[0067] Sampling and Adding Test Samples: Place the treated quartz beaker on a scale and tar it. Thoroughly shake the #1 oil sample. Use a plastic dropper to take a small amount of sample from the center of the oil sample. Extend the dropper to the bottom of the beaker and drip the sample to the center of the bottom of the 50mL quartz beaker (ensuring that the sample does not drip onto or splash onto the side walls). Observe the balance reading while adding the sample. Weigh the first sample, 1.0006g. Repeat this process to weigh a parallel sample, 1.0003g.

[0068] Carbonization treatment steps: Evenly add 0.5 mL of concentrated sulfuric acid (98%) to each of the two sample beakers. Heat on a hot plate set at 200°C for carbonization until the sample turns completely black, stops bubbling, and stops emitting significant amounts of white smoke. The carbonized product is black with cracks and contains trace amounts of liquid.

[0069] Ashing treatment steps: Place the carbonized product in a muffle furnace and ash at 550°C for 6 hours (the heating rate to 550°C is 5°C / min); take it out when the furnace temperature drops to 100°C and cool it in a dryer.

[0070] Dissolution and volume adjustment steps: Dissolve the ashing product with 1 mL of concentrated nitric acid. Transfer the solution to a 50 mL plastic centrifuge tube. Rinse the quartz beaker 2-3 times with 2% nitric acid (approximately 1 mL each time) and transfer it to the plastic centrifuge tube. Then, add 1 mL of concentrated hydrofluoric acid to the centrifuge tube. Cover the tube and shake. Once the solution is completely dissolved and clear, dilute it to 25 mL with 2% dilute nitric acid. Shake well and set aside. Both concentrated nitric acid and hydrofluoric acid should be UPS grade or higher.

[0071] In addition, the carbonization treatment step, the ashing treatment step, and the dissolution and volume determination step were performed without adding a sample to obtain a blank sample.

[0072] Among them, after pretreatment, the 1# oil sample changed from a white emulsion to a clear and transparent solution.

[0073] ICP detection steps: The working conditions of ICP (inductively coupled plasma emission spectrometer) were set as follows: power was set to 1500 W; observation height was set to 12 mm; peristaltic pump speed was set to 45 r / min; auxiliary was set to 0.5 L / min; nebulizer was set to 0.6 L / min; injection and cleaning time was set to 30 s; the spectral lines were selected as follows: K, 766.491 nm; Na, 589.592 nm; Ca, 422.673 nm; Mg, 285.213 nm, Fe, 238.204 nm, Si, 212.412 nm and / or

[0074] A standard curve was drawn with the mass concentration of the measured element in the standard mixed solution in mg / L as the abscissa and the emission intensity as the ordinate. The correlation coefficient of the standard curve was greater than 0.999.

[0075] The measurement results are shown in Table 1:

[0076] Table 1 Trace element test results in 1# oil sample (unit: μg / g)

[0077] element K Ca Na Mg Fe Si Sample 1 0.90 1.11 2.11 0.12 2.16 468.2 Sample 2 0.99 1.01 2.26 0.13 2.20 465.5 average value 0.95 1.06 2.19 0.13 2.18 466.9

[0078] Example 2

[0079] This example is used to pre-treat carbon fiber precursor oil sample 2# (also called 2# oil sample, with a silicon content greater than 650 μg / g). The sample solution obtained after pre-treatment is used to determine the trace element content (ICP-OES method). The specific steps include:

[0080] Preparation of quartz beaker: same as in Example 1.

[0081] Sampling and adding test sample steps: The same method and steps as in Example 1 were used to weigh two samples of the 2# oil sample. The masses of the two samples were 1.0004 g and 1.0008 g, respectively.

[0082] Carbonization treatment step: the same as in Example 1. The product after carbonization treatment has a black appearance with slight cracks and contains flowable liquid.

[0083] Ashing treatment steps: the carbonized product is placed in a muffle furnace and heated at 650°C, kept warm and ashed for 6 hours, taken out when the furnace temperature drops to 100°C, and cooled in a dryer.

[0084] Dissolution and volume adjustment steps: same as Example 1.

[0085] Under the condition that no sample is added, the carbonization treatment step, the ashing treatment step, and the dissolution and volume determination step are carried out to obtain a blank sample.

[0086] Among them, after pretreatment, the 2# oil sample changed from a white emulsion to a clear and transparent solution.

[0087] ICP detection steps: same as Example 1.

[0088] The measurement results are shown in Table 2:

[0089] Table 2 Trace element test results in 2# oil sample (unit: μg / g)

[0090] element K Ca Na Mg Fe Si Sample 1 0.97 1.81 2.45 0.11 0.06 699.1 Sample 2 1.00 1.95 2.60 0.11 0.21 701.2 average value 0.99 1.88 2.53 0.11 0.14 700.2

[0091] Example 3

[0092] This example is used to pre-treat carbon fiber precursor oil sample 3# (also referred to as 3# oil sample, with a silicon content of approximately 500-600 μg / g). The sample solution obtained after pre-treatment is used to determine the trace element content (ICP-OES method). The specific steps include:

[0093] Preparation of quartz beaker: same as in Example 1.

[0094] Sampling and adding test sample steps: The same method and steps as in Example 1 were used to weigh two samples of the 3# oil sample. The masses of the two samples were 1.0001 g and 1.0005 g, respectively.

[0095] Carbonization treatment step: the same as in Example 1. The product after carbonization treatment is a black flowable liquid.

[0096] Ashing treatment steps: same as Example 2.

[0097] Dissolution and volume adjustment step: dissolve the ashing product with 1.5 mL of concentrated nitric acid, and the rest is the same as in Example 1.

[0098] Under the condition that no sample is added, the carbonization treatment step, the ashing treatment step, and the dissolution and volume determination step are carried out to obtain a blank sample.

[0099] Among them, after pretreatment, the 3# oil sample changed from a white emulsion to a clear and transparent solution.

[0100] ICP detection steps: same as Example 1.

[0101] The measurement results are shown in Table 3:

[0102] Table 3 Trace element test results in 3# oil sample (unit: μg / g)

[0103] element K Ca Na Mg Fe Si Sample 1 0.66 0.84 2.11 0.14 1.76 550.3 Sample 2 0.82 0.90 2.05 0.13 2.00 552.7 average value 0.74 0.87 2.08 0.14 1.88 551.5

[0104] Example 4

[0105] This example is used to pre-treat carbon fiber precursor oil sample 4# (also referred to as 4# oil sample, with a silicon content of 500-550 μg / g). The sample solution obtained after pre-treatment is used to determine the trace element content (ICP-OES method). The specific steps include:

[0106] Preparation of quartz beaker: same as in Example 1.

[0107] Sampling and adding test sample steps: The same method and steps as in Example 1 were used to weigh two samples of the 4# oil sample. The masses of the two samples were 1.0003 g and 1.0008 g, respectively.

[0108] Carbonization treatment step: the same as in Example 1. The morphology of the product after carbonization treatment is black with cracks, with a little flowable liquid in it.

[0109] Ashing treatment steps: same as Example 2.

[0110] Dissolution and volume adjustment step: dissolve the ashing product with 2 mL of concentrated nitric acid, and the rest is the same as in Example 1.

[0111] Under the condition that no sample is added, the carbonization treatment step, the ashing treatment step, and the dissolution and volume determination step are carried out to obtain a blank sample.

[0112] Among them, after pretreatment, the 4# oil sample changed from a white emulsion to a clear and transparent solution.

[0113] ICP detection steps: same as Example 1.

[0114] The measurement results are shown in Table 4:

[0115] Table 4 Trace element test results in 4# oil sample (unit: μg / g)

[0116] element K Ca Na Mg Fe Si Sample 1 0.83 1.36 2.65 0.17 2.21 500.8 Sample 2 0.93 1.25 2.52 0.15 2.40 502.6 average value 0.88 1.31 2.59 0.16 2.31 501.7

[0117] Comparative Example

[0118] Samples were taken from 1# sample, 2# sample, 3# sample, and 4# sample, and 1 mL of sulfuric acid was added during the carbonization process. The morphology of the products after carbonization is compared as follows:

[0119] When 0.5 mL of sulfuric acid was added to the sample during carbonization treatment, the sample was completely carbonized and basically semi-dry, with some samples still in a fluid state;

[0120] After the sample was carbonized by adding 1.0 mL of sulfuric acid, the morphology of the product was significantly more fluid than that of the sample added with 0.5 mL of sulfuric acid; however, after the sample added with excess sulfuric acid was ashed, the low-silicon sample was easily overburned and became black coke-like, while the high-silicon sample became white crystals after ashing. Both states indicate that the sample was dead-burned, and even if more nitric acid and hydrofluoric acid were added subsequently, the sample could not be completely dissolved.

[0121] In summary, the solution of the embodiment of the present invention can produce a clear and bright sample solution, which can be used to analyze the trace element content in the sample using an inductively coupled plasma optical emission spectrometer. The oil sample pretreatment method of the embodiment of the present invention has the advantages of simple operation steps, high accuracy and reproducibility.

[0122] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiment based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for pre-treating an oil sample, wherein the oil sample is a carbon fiber precursor oil; characterized in that: The oil samples were pretreated by dry digestion method; The oil sample pretreatment method comprises the following steps: (1) Carbonization treatment step: Carbonizing a sample of a set mass to obtain a carbonized product; In this step, concentrated sulfuric acid as an auxiliary agent is added to a container containing the sample, and then the container is heated to a carbonization treatment temperature. Carbonization treatment is performed at the carbonization treatment temperature until the sample completely turns black, no bubbles are emitted, and no white smoke is emitted. The carbonization treatment temperature is 195-205°C. In the carbonization treatment step, the mass of each sample is 1.0000-1.2000 g; the amount of concentrated sulfuric acid added as an auxiliary agent does not exceed 0.5 mL; and the volume concentration of concentrated sulfuric acid is 95-98%; (2) Ashing treatment step: heating the carbonized product to an ashing treatment temperature for ashing treatment to obtain an ashing product; wherein, if the oil sample is a low-silicon carbon fiber precursor oil with a silicon content of not more than 500ug / g or a carbon fiber precursor oil without silicon, the ashing treatment temperature is 500-600°C, and the ashing treatment time is 6-8h; if the oil sample is a carbon fiber precursor oil with a silicon content of more than 500ug / g, the ashing treatment temperature is 600-650°C, and the ashing treatment time is 6-8h; (3) Dissolving and fixing the volume: dissolving the product after the ashing treatment, fixing the volume after all the solution is dissolved, and obtaining a sample solution; In this step, nitric acid and hydrofluoric acid are used to dissolve the product after the ashing treatment. The specific operation is as follows: concentrated nitric acid is added to a container containing the product after the ashing treatment for dissolution, and then the dissolved solution is transferred to a centrifuge tube; the container is rinsed with dilute nitric acid for multiple times, and the rinse solution is transferred to the centrifuge tube; concentrated hydrofluoric acid is added to the centrifuge tube, and the centrifuge tube is shaken. After all the solution is dissolved, the volume is adjusted to 20-25 mL with dilute nitric acid to obtain a sample solution.

2. The method for pre-treating an oil sample according to claim 1, wherein: Before the carbonization step, the method further comprises: Sampling and adding test sample steps: shake the oil sample, take a sample from the oil sample, add the sample to the bottom of the container, and ensure that the sample does not drop or splash onto the side wall of the container.

3. The method for pre-treating an oil sample according to claim 2, wherein: Before the sampling and adding steps, the container needs to be pre-treated, specifically: first soaking the container in nitric acid, then ultrasonically cleaning the container with ultrapure water, and finally calcining the container to constant weight; The container is a quartz beaker; sampling is taken from the middle of the oil sample; at least two parallel samples are taken for each oil sample.

4. The method for pre-treating an oil sample according to claim 1, wherein: The ashing step is carried out in a muffle furnace; the heating rate in the ashing step is 4-6°C / min.

5. The method for pre-treating an oil sample according to claim 1, wherein: The concentrated nitric acid and hydrofluoric acid are of high purity or above; when the mass of each sample is 1.0000-1.2000 g: the amount of the concentrated nitric acid used is 1.0-3.0 mL; the amount of the concentrated hydrofluoric acid used is 1-2 mL; the volume concentration of the dilute nitric acid is 2-5%; and the total amount of dilute nitric acid used to rinse the container is 3-8 mL.

6. A method for measuring trace elements in an oil sample, comprising treating the oil sample with the pretreatment method according to any one of claims 1 to 5, wherein: The sample solution obtained after the pretreatment is used; and then the sample solution is measured using an inductively coupled plasma emission spectrometer ICP to measure the content of trace elements in the oil sample.