An oil mercaptan sulfur standard solution and a preparation method thereof

Abstract

The oil mercaptan sulfur standard solution comprises n-dodecanethiol and isooctane, the content of hydrogen sulfide in the n-dodecanethiol is less than 3 μg / g, more preferably less than 1 μg / g; the purity of the isooctane is greater than 99.5 wt%, more preferably greater than 99.9 wt%, and the change range of the mercaptan sulfur concentration in the standard solution within 12 months is limited to 2%, more preferably less than 1%. The oil mercaptan sulfur standard solution uses isooctane as a solvent, which is closer to the molecular structure of light fuel but can ensure the singleness of the structure and the quality stability; n-dodecanethiol is used as the source of mercaptan sulfur, which ensures the high content and singleness of the mercaptan sulfur, and the change range of the mercaptan sulfur concentration in the obtained standard solution within 1 year is less than 2%.

Description

Technical Field

[0001] This invention belongs to the field of analytical chemistry, specifically relating to a standard solution of thiol sulfur in oil for determining the thiol sulfur content in oil products and its preparation method. Background Technology

[0002] Light hydrocarbons, including liquefied petroleum gas (LPG), gasoline, aviation fuel, and diesel, are mixtures of alkanes, alkenes, and aromatics. Both light hydrocarbon feedstocks and their derivatives contain a certain amount of non-hydrocarbon compounds with heteroatoms such as sulfur, nitrogen, and oxygen. Sulfur-containing compounds have the greatest impact on fuel performance and are therefore the subject of extensive research. When used as fuel products, sulfur content must not only meet product standards but also requirements related to sulfur speciation. Different forms of sulfides have varying effects on the metal corrosion resistance of products, and therefore require different detection methods. Existing methods for detecting sulfides in petroleum products include the burner method, microcoulometric method (coulometric method), ultraviolet fluorescence method, and X-ray spectroscopy.

[0003] Thiols are a class of non-aromatic compounds containing a thiol functional group (-SH). Thiol sulfur is the sulfur atom in a thiol, and it is one of the sulfur-containing compounds in petroleum products. Catalytic hydrogenation of thiols can achieve desulfurization, producing the corresponding hydrocarbons. Hydrodesulfurization in petroleum refining is based on this reaction. Thiols are generally found in hydrocarbons, have an unpleasant odor, and can worsen the stability of petroleum products. During combustion, they are converted into toxic and corrosive sulfur dioxide and sulfur trioxide, which are harmful to the elastic materials of fuel systems and corrode the metal components of fuel systems, affecting the lifespan of related machinery. Emissions into the atmosphere also pollute the air and contribute to acid rain. Therefore, controlling the thiol content in petroleum products is extremely important. The national standard for automotive gasoline, GB17930-2016, specifies that the thiol sulfur content should not exceed 0.001%, and the detection method is the GB / T1792 potentiometric titration method.

[0004] Currently, there are no standard substances for thiol sulfur in oil products. Therefore, it is necessary to develop and prepare a standard solution for thiol sulfur in oil products to fill the gap in the corresponding standard substances. This is of great significance for the detection of thiol sulfur content in light oil fractions and the traceability of related instruments. Summary of the Invention

[0005] This invention discloses a standard solution of thiol sulfur in oil products, comprising n-dodecyl mercaptan and isooctane, wherein the hydrogen sulfide content in the n-dodecyl mercaptan is less than 3 μg / g, more preferably less than 1 μg / g; and the purity of the isooctane is greater than 99.5 wt%, more preferably greater than 99.9 wt%.

[0006] The concentration of thiol sulfur in the standard solution is 10-20 μg / g, more preferably 15-16 μg / g.

[0007] The variation in the concentration of thiol sulfur in the standard solution within 12 months is limited to 2%, more preferably less than 1%.

[0008] The n-dodecyl mercaptan needs to undergo hydrogen sulfide content testing and removal treatment before use, including the following steps: (1) Dissolve lead acetate in water to prepare an aqueous solution of lead acetate, and use the aqueous solution of lead acetate to make test paper; (2) Use the test paper to quickly test n-dodecyl mercaptan. If the test paper turns brown or black, hydrogen sulfide removal treatment is required. If the test paper does not change color, hydrogen sulfide removal treatment is not required. (3) Prepare sodium bicarbonate solution. Add sodium bicarbonate solution to n-dodecyl mercaptan and react for 10-30 min. Separate the liquid and liquid phases. The oil phase obtained is n-dodecyl mercaptan treated with hydrogen sulfide removal. (4) Test the hydrogen sulfide concentration in n-dodecyl mercaptan again using the test paper. If the test paper still changes color, repeat steps (3) and (4) until the test paper does not change color.

[0009] The concentration of lead acetate in step (1) is 1-10 wt%, more preferably 3-6 wt%; the test paper is dried in an inert atmosphere at a temperature of 30-50°C and a pressure of 0.01-0.05 MPa.

[0010] The water used in steps (1) and (3) is ultrapure water with a resistivity higher than 18 MΩ·cm, and more preferably a resistivity greater than 20 MΩ·cm.

[0011] The concentration of sodium bicarbonate in step (3) is 1-10 wt%, more preferably 3-6 wt%.

[0012] The volume ratio of sodium bicarbonate and n-dodecyl mercaptan in step (3) is 1:1.5-3, more preferably 1:2-2.5.

[0013] Unless otherwise specified, all concentrations mentioned in this invention refer to mass concentrations.

[0014] The present invention has the following beneficial effects: Using isooctane as a solvent provides a molecular structure closer to that of light fuel oil while ensuring structural uniformity and quality stability. Dodecyl mercaptan, a liquid with a slight odor, low volatility, and readily soluble in organic solvents, exhibits typical characteristics of thiols. Using dodecyl mercaptan as the source of thiol sulfur ensures high thiol sulfur content and a single source. A purifying agent is used to remove hydrogen sulfide, which affects detection, and it is easily separated (using a separatory funnel). The resulting standard solution shows a thiol sulfur concentration variation of less than 2% within one year. Detailed Implementation

[0015] The present invention will now be described in further detail with reference to specific embodiments.

[0016] Example 1 I. Preparation of Reagents Solvent: Use isooctane (brand: Fisher, model O296-4) organic reagent with a purity greater than 99% (mass fraction) as solvent; Solute: n-dodecyl mercaptan reagent with a mass fraction greater than 98% (brand: Maclean Reagent, catalog number D806874) was used as the solute; Preparation of detection and purification agents: Dissolve lead acetate [(CH3COO)2Pb·3H2O] in water to prepare a 5% (w / w) aqueous solution. Immerse test paper in the lead acetate solution until saturated, then dry to prepare test paper. Dissolve (50±1) g of sodium bicarbonate (NaHCO3) in water and dilute to 1 L in a volumetric flask to prepare a sodium bicarbonate aqueous solution.

[0017] Ultrapure water: Water with a resistivity higher than 18 MΩ·cm.

[0018] II. Detect and clean the process (ensure that the solvent and solute do not contain hydrogen sulfide) 1. Hydrogen sulfide detection: Take a small amount of isooctane or n-dodecyl mercaptan and insert a small piece of test paper. If the test paper turns brown or black, it indicates the presence of hydrogen sulfide, which needs to be removed. If there is no color change, it means the sample does not contain hydrogen sulfide and can be prepared directly.

[0019] 2. Removal of hydrogen sulfide: (1) Pour the isooctane or n-dodecyl mercaptan containing hydrogen sulfide quantitatively into a separatory funnel; (2) Add sodium bicarbonate solution equivalent to half the sample volume and shake vigorously; (3) Let it stand to separate the two phases, release and discard the aqueous phase after separation; (4) Use fresh test paper to test isooctane or n-dodecyl mercaptan again, and continue the removal process until the solvent and solute do not contain hydrogen sulfide. Transfer the solvent and solute that meet the requirements to brown bottles and store them in the dark.

[0020] III. Preparation and Value Setting Process 1. At an ambient temperature of 20°C, accurately transfer the required amount of isooctane into a 250 mL volumetric flask, make up to volume, add 25.51 mg of n-dodecyl mercaptan, and let stand at 25°C for 24 hours in the dark. 2. Determination was performed using a gas chromatograph manufactured by Agilent Technologies under the following conditions: capillary column (60m × 320μm × 0.5μm); detector: FID; carrier gas: high-purity nitrogen, flow rate 0.6 L / min; hydrogen fuel gas flow rate 30 mL / min, air flow rate 400 mL / min; injection port temperature: 300℃; detector temperature: 300℃; column temperature: 210℃; injection volume: 1.0 μL; split ratio: 10:1. A solution with serial number NIM-RM3099 manufactured by the National Institute of Metrology of China was used as a standard. The prepared thiol sulfur standard solution was injected into the gas chromatograph using an automated injection system for detection. The concentration of the solution was obtained based on the measured response value. The determined thiol sulfur was 15.7 μg / g.

[0021] IV. Stability and Uniformity Examination The homogeneity of the aforementioned prepared standard solutions was investigated. According to JJF1343-2012 "General Principles and Statistical Principles for Determining Standard Reference Values", the sampled samples should be sufficiently representative of the population. Six 20 mL samples were randomly selected from the front, middle and back of the dispensing order, and the homogeneity of the standard solutions was observed three times.

[0022] Table 1 The analysis of variance results showed that F(6,18) = 2.08 < F0.05(6,18) = 3.11, indicating that the homogeneity of the standard material met the requirements.

[0023] Long-term stability should be assessed periodically over a relatively long period under specified storage conditions to examine the ability of the reference material to maintain its characteristic values ​​within the specified range. Sampling should be conducted according to a principle of starting with denser samples and gradually decreasing the density. One sample should be taken at intervals of 0, 1, 2, 4, 6, and 12 months after preparation, and measurements should be performed three times each time. The instruments and detection methods used in the aforementioned determination process should be used to examine the solution, and the measurement results are shown in Table 2.

[0024] Table 2 1 16.56 16.40 16.05 15.95 15.83 15.63 2 16.10 16.85 15.86 15.86 15.60 15.52 3 15.76 16.33 16.11 15.77 15.57 15.80 average value 16.14 16.53 16.01 15.86 15.67 15.65 The mercaptan sulfur standard solution in the oil did not show a significant upward or downward trend, indicating that the sample was stable during the observation period. The mercaptan sulfur standard solution in the oil of this invention exhibits good stability.

[0025] The above embodiments are merely illustrative of the present invention, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following examples are conventional means well known to those skilled in the art: the materials, reagents, etc. used are all commercially available.

[0026] verify The prepared standard solution was verified using a thiol sulfur analyzer. The ambient temperature was 22℃ and the relative humidity was 40%RH. The instrument was a microcomputer thiol sulfur analyzer manufactured by Taizhou Shengtuo Precision Instrument Co., Ltd., model TLS-2000.

[0027] 2. The test results (μg / g) were 14.82, 14.83, 14.82, 14.82, 14.85, 14.82, and 14.84.

Claims

1. A standard solution of thiol sulfur in petroleum products, comprising n-dodecyl mercaptan and isooctane, wherein the hydrogen sulfide content in the n-dodecyl mercaptan is less than 3 μg / g; the purity of the isooctane is greater than 99.5 wt%; the concentration of thiol sulfur in the standard solution is 10-20 μg / g; and the variation range of the concentration of thiol sulfur in the standard solution within 12 months is limited to 2%. The n-dodecyl mercaptan needs to undergo hydrogen sulfide content testing and removal treatment before use, including the following steps: (1) Prepare an aqueous solution of lead acetate and use the aqueous solution of lead acetate to prepare test paper; (2) Use the test paper to perform a rapid test on n-dodecyl mercaptan. If the test paper turns brown or black, hydrogen sulfide removal treatment is required. If the test paper does not change color, hydrogen sulfide removal treatment is not required. (3) Prepare sodium bicarbonate solution. Add sodium bicarbonate solution to n-dodecyl mercaptan, react for 10-30 min and then separate the liquid. The oil phase obtained is n-dodecyl mercaptan treated with hydrogen sulfide removal. (4) Test the hydrogen sulfide concentration in n-dodecyl mercaptan again using the test paper. If the test paper still changes color, repeat steps (3) and (4) until the test paper does not change color. The concentration of the lead acetate aqueous solution in step (1) is 1-10 wt%; the test paper is dried under an inert atmosphere at a temperature of 30-50°C and a pressure of 0.01-0.05 MPa. The water used in steps (1) and (3) is ultrapure water with a resistivity higher than 18 MΩ·cm; The concentration of the sodium bicarbonate solution in step (3) is 1-10 wt%; the volume ratio of sodium bicarbonate to n-dodecyl mercaptan in step (3) is 1:1.5-3.

2. The standard solution according to claim 1, characterized in that... The hydrogen sulfide content in the n-dodecyl mercaptan is less than 1 μg / g; the purity of the isooctane is greater than 99.9 wt%.

3. The standard solution according to claim 1, characterized in that... The concentration of thiol sulfur in the standard solution is 15-16 μg / g.

4. The standard solution according to claim 1, characterized in that... The concentration of thiols in the standard solution varied by less than 1% over 12 months.

5. The standard solution according to claim 1, characterized in that... The concentration of the lead acetate aqueous solution in step (1) is 3-6 wt%.

6. The standard solution according to claim 1, characterized in that... The resistivity of the water used in steps (1) and (3) is higher than 20 MΩ·cm.

7. The standard solution according to claim 1, characterized in that... The concentration of the sodium bicarbonate solution in step (3) is 3-6 wt%.

8. The standard solution according to claim 1, characterized in that... The volume ratio of sodium bicarbonate solution to n-dodecyl mercaptan in step (3) is 1:2-2.5.

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