Determination method for aromatic hydrocarbon content in high-melting-point wax

Abstract

The invention relates to a method for determining the content of aromatic hydrocarbons in high-melting-point wax. The method comprises the following steps: S102, respectively determining the first absorbance of a high-melting-point wax sample under the wavelength of 270 nm and the second absorbance of the high-melting-point wax sample under the wavelength of 285 nm by using an ultraviolet spectrophotometer under the constant-temperature condition of M DEG C; s104, under the condition that the first absorbance and the second absorbance are not higher than an absorbance threshold value, respectively calculating the alkylbenzene concentration and the naphthalene concentration of the sample based on the first linear equation and the second linear equation; wherein the first linear equation and the second linear equation are obtained by the following steps: S202, preparing an alkylbenzene standard solution and a naphthalene standard solution with known gradient concentrations, and mixing to obtain a plurality of mixed standard samples with two different component concentrations; s204, respectively measuring the first absorbance and the second absorbance of the plurality of mixed standard samples under the constant temperature condition of M DEG C by using an ultraviolet spectrophotometer; and S206, calculating to obtain a first linear equation and a second linear equation.

Description

Technical Field

[0001] The present application relates to the technical field of chemical analysis, and in particular to a method for determining the content of aromatic hydrocarbons in high melting point wax. Background Art

[0002] Aromatic hydrocarbons, also known as aromatic hydrocarbons, are an important class of organic compounds characterized by the presence of one or more benzene ring structures in the molecule. They are widely used in many fields such as plastics, dyes, solvents, drugs, rubbers and fuels, and are a class of raw materials with important chemical uses. However, in many petrochemical products, the presence of aromatic hydrocarbons not only affects key performance indicators, quality and production efficiency, but also poses a potential threat to human health, safety of use and environmental impact. Therefore, relevant departments and units have issued aromatic hydrocarbon content limit indicators and testing standards, and strictly required the aromatic hydrocarbon content in petrochemical products to ensure that the products meet specific application standards and regulatory requirements.

[0003] There are several methods for detecting aromatic content: gas chromatography, high performance liquid chromatography, solid phase extraction-gas chromatography, column chromatography, etc. The choice of method usually depends on the sample type, the type of aromatics and the experimental conditions. The relevant standards for the determination of aromatic content in China are: HS / T 50-2016 "Determination of aromatic content in hydrocarbons" uses gas chromatography-mass spectrometry and gas chromatograph equipped with FID detector; NB / SH / T 0966-2017 "Determination of aromatic content in white oil" uses ultraviolet spectrophotometry; SH / T 0693-2000 "Determination of aromatic content in gasoline (gas chromatography)" standard uses gas chromatography for detection; SH / T 0409-1992 "Determination of aromatic content in liquid paraffin (ultraviolet spectrophotometry)" uses ultraviolet spectrophotometry. Among them, gas chromatography and high performance liquid chromatography have problems such as complex operation, long extraction time and expensive instruments. The instrument used in ultraviolet spectrophotometry is cheap, the experimental conditions are easy to achieve, and it can be detected quickly, making it suitable for analyzing a large number of samples.

[0004] The current SH / T 0409-1992 "Determination of Aromatics Content in Liquid Paraffin (Ultraviolet Spectrophotometry)" standard is a domestic petrochemical industry standard, which provides a detailed process for determining the aromatics content in liquid paraffin using ultraviolet spectrophotometry. This standard applies to liquid paraffin products, including but not limited to other related wax products and quality control and analysis of white oil. However, when testing samples with a melting point higher than room temperature, this method cannot be applied because the sample is semi-solid or solid. Even if the sample is heated to a liquid and then transferred to a cuvette for measurement, it will still solidify quickly and cannot be measured.

[0005] The CN218995135U patent adds a cuvette thermostat to the UV spectrophotometer to solve the problem of solidification during the test of high melting point samples, and the sample can be kept in a liquid state at a constant temperature. When measuring, the aromatic content of the sample needs to be within the detection range. If it exceeds the detection range, the sample needs to be diluted. According to the SH / T 0409-1992 standard, isooctane is used as a dilution solvent in the prior art. Due to the blue shift of the absorbance value, volatilization or boiling of isooctane itself when heated, it cannot match the baseline calibration, resulting in inaccurate measurement results. Summary of the invention

[0006] In order to solve the problems existing in the prior art, the present application provides a method for determining the aromatic content in high melting point wax.

[0007] According to the first aspect of the present application, a method for determining the aromatic content in a high melting point wax is provided, wherein the melting point of the high melting point wax is defined as N°C, and the method comprises the following steps: S102: using an ultraviolet spectrophotometer to measure the first absorbance of the high melting point wax sample at a wavelength of 270 nm and the second absorbance at a wavelength of 285 nm at a constant temperature of M°C, wherein M≥N; S104: when the first absorbance and the second absorbance measured in S102 are not higher than the absorbance threshold, the alkylbenzene concentration and the naphthalene concentration of the sample are calculated based on the first linear equation and the second linear equation respectively; and the aromatic hydrocarbon content in the sample is calculated based on the alkylbenzene concentration and the naphthalene concentration of the sample; The first linear equation and the second linear equation are obtained by the following steps: S202: preparing alkylbenzene standard solutions and naphthalene standard solutions with known gradient concentrations, and mixing them to obtain a plurality of mixed standard samples with different concentrations of the two components; S204: using an ultraviolet spectrophotometer to respectively measure the first absorbance of the multiple mixed standard samples obtained in S202 at a wavelength of 270 nm at a constant temperature of 24° C., and respectively measure the second absorbance of the multiple mixed standard samples obtained in S202 at a wavelength of 285 nm; S206: Based on the concentration of alkylbenzenes in each mixed standard sample in S202 and the first absorbance and the second absorbance measured in S204, the first linear equation is calculated; based on the concentration of naphthalene in each mixed standard sample in S202 and the second absorbance measured in S204, the second linear equation is calculated.

[0008] In one embodiment of the present application, it further includes S103: when the absorbance measured in S102 is higher than the absorbance threshold, diluting the sample, and repeating S102 after dilution.

[0009] In one embodiment of the present application, the dilution solvent used in S103 is the same as the solvent used to prepare the alkylbenzene standard solution and the naphthalene standard solution in S202.

[0010] In one embodiment of the present application, the dilution solvent used in S103 is any one of cyclohexane, n-heptane, and petroleum ether.

[0011] In one embodiment of the present application, the S104 includes: based on the alkylbenzene concentration and naphthalene concentration of the sample, and the mass concentration of the diluted sample in the S103, respectively calculating the alkylbenzene content and the naphthalene content in the sample; adding the alkylbenzene content and the naphthalene content to obtain the aromatics content in the sample.

[0012] In one embodiment of the present application, the absorbance threshold is no higher than 1.5.

[0013] In one embodiment of the present application, at least three mixed standard samples are obtained by mixing in S202.

[0014] In one embodiment of the present application, the first linear equation is: 270nm-285nm =a1X1+b1, where A 270nm-285nm is the difference between the first absorbance and the second absorbance, X1 is the concentration of alkylbenzenes, and a1 and b1 are the parameters of the first linear equation calculated in S206.

[0015] In one embodiment of the present application, the second linear equation is: 285nm =a2X2+b2, where A 285nm is the second absorbance, X2 is the naphthalene concentration, and a2 and b2 are the parameters of the second linear equation calculated in S206.

[0016] In one embodiment of the present application, the ultraviolet spectrophotometer used in S102 and S204 is provided with a cuvette thermostat.

[0017] A beneficial effect of the present application is that, by measuring the absorbance using an ultraviolet spectrophotometer under a constant temperature condition higher than the melting point of the sample, it is ensured that the high melting point wax sample can remain in a liquid state during the measurement process. The present application provides a method for accurately measuring the aromatic content in high melting point wax, which does not require cumbersome separation, nor does it require the use of high-cost instruments and equipment. It only requires the use of low-cost, easy-to-operate ultraviolet spectrophotometry to complete a large number of sample analyses, with fast detection speed and easy experimental conditions. In addition, the present method obtains an accurate linear equation by specifically establishing a standard curve under non-room temperature conditions. The present method eliminates the blue shift of the absorbance value, volatilization or boiling, which affect the accurate detection of the content when the detection is performed under a constant temperature state, so that the accuracy of the determination is high.

[0018] Other features and advantages of the present application will become apparent from the following detailed description of exemplary embodiments of the present application with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the application and, together with the description, serve to explain the principles of the application.

[0020] Figure 1 is a graph showing the absorbance variation of different solvents at different temperatures when the ultraviolet wavelengths are 270 nm and 285 nm in Example 1 of the present application; Figure 2 is a linear equation diagram between the concentration (X1) of alkylbenzene substances in the mixed standard sample and the absorbance in Example 3 of the present application; Figure 3 is a linear equation diagram between the concentration (X2) of naphthalene substances in the mixed standard sample and the absorbance in Example 3 of the present application; Figure 4 is a linear equation diagram between the concentration (X1) of alkylbenzene substances in the mixed standard sample and the absorbance in Example 4 of the present application; Figure 5 is a linear equation diagram between the concentration (X2) of naphthalene substances in the mixed standard sample and the absorbance in Example 4 of the present application; Figure 6 is a linear equation diagram between the concentration (X1) of alkylbenzene substances in the mixed standard sample and the absorbance in Example 5 of the present application; Figure 7 It is a linear equation diagram between the concentration (X2) of naphthalene substances in the mixed standard sample and the absorbance in Example 5 of the present application. DETAILED DESCRIPTION

[0021] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application.

[0022] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present application, its application, or uses.

[0023] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered as part of the specification.

[0024] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0025] In this document, “upper”, “lower”, “front”, “back”, “left”, “right”, etc. are only used to indicate the relative position relationship between related parts, rather than to limit the absolute positions of these related parts.

[0026] In this article, "first", "second", etc. are only used to distinguish each other, and do not indicate the importance and order, or the premise of each other's existence.

[0027] In this document, “equal”, “same”, etc. are not strictly limited in a mathematical and / or geometric sense, but also include errors that can be understood by those skilled in the art and are allowed in manufacturing or use.

[0028] The present application provides a method for determining the aromatic content in high-melting-point wax, and defines the melting point of high-melting-point wax as N°C. It is understood that N°C is at least a temperature higher than room temperature, and high-melting-point wax generally refers to a type of wax with a melting point above 60°C, which has a higher melting point and better stability, such as high-melting-point Fischer-Tropsch wax, which generally has a melting point between 85°C and 120°C. The SH / T 0409-1992 "Determination of Aromatic Content in Liquid Paraffin (Ultraviolet Spectrophotometry)" standard is only applicable to low-melting-point paraffins that can remain liquid without heating, and the melting point of high-melting-point wax exceeds the applicable scope of this standard.

[0029] The method provided by the present disclosure comprises the following steps: S102: Using an ultraviolet spectrophotometer, respectively measure the first absorbance of the high melting point wax sample at a wavelength of 270 nm and the second absorbance at a wavelength of 285 nm under a constant temperature condition of M°C, wherein M≥N.

[0030] Specifically, since M℃ is greater than the melting point (N℃) of the high melting point wax, the high melting point wax sample to be tested can be completely dissolved into a liquid state under the constant temperature condition of M℃. The first absorbance and the second absorbance of the wax liquid at wavelengths of 270nm and 285nm are measured by an ultraviolet spectrophotometer, respectively, so that the first absorbance and the second absorbance are used to calculate the aromatic hydrocarbon content in the sample in the subsequent steps.

[0031] S104: When the first absorbance and the second absorbance measured in S102 are not higher than the absorbance threshold, the alkylbenzene concentration and the naphthalene concentration of the sample are calculated based on the first linear equation and the second linear equation respectively; and the aromatic hydrocarbon content in the sample is calculated based on the alkylbenzene concentration and the naphthalene concentration of the sample.

[0032] Specifically, the aromatic substances contained in the high melting point wax basically include alkylbenzene substances and naphthalene substances. Therefore, in order to determine the aromatic content in the high melting point wax, it is only necessary to determine the alkylbenzene content and the naphthalene content in the high melting point wax respectively, and then add the alkylbenzene content and the naphthalene content to obtain the aromatic content in the sample.

[0033] The Lambert-Beer law describes the relationship between the strength of a substance's absorption of light of a certain wavelength and the concentration of the absorbing substance and the thickness of its liquid layer. According to the Lambert-Beer law: in a multi-component mixture, if the absorption properties of each component do not affect each other, there is an additive property between the absorbances. Furthermore, according to the requirements for calculating the aromatic content by dual wavelengths, alkylbenzenes have basically no absorption at a wavelength of 285nm, but have a certain absorption at a wavelength of 270nm; naphthalene has a certain absorption at both 270nm and 285nm wavelengths, so the alkylbenzene content and naphthalene content can be quantitatively determined separately according to the degree of spectral overlap between them.

[0034] It should be noted that the absorbance data can be trusted only when the first absorbance and the second absorbance measured in S102 are not higher than the absorbance threshold. If they exceed the absorbance threshold, it means that the value exceeds the confidence interval, the current absorbance data does not conform to the linear equation, and the sample needs to be diluted to reduce its absorbance to a level not higher than the absorbance threshold.

[0035] In one embodiment of the present application, the method further includes S103: when the absorbance measured in S102 is higher than the absorbance threshold, diluting the sample, and repeating S102 after dilution. It can be understood that the actual reason why the absorbance measured in S102 is too high is that the concentration of aromatic hydrocarbons in the sample is too high. As long as it is diluted, the concentration of aromatic hydrocarbons in the sample can be reduced, thereby reducing the first absorbance and the second absorbance.

[0036] The single dilution multiple depends on the actual content of the sample. If the dilution multiple is too small, the dilution effect is poor and multiple dilutions are required to make the sample meet the experimental requirements. If the dilution multiple is too large, the absorbance may drop to too low a level after a single dilution, which may adversely affect the accuracy of calculating the aromatic hydrocarbon content.

[0037] After one dilution, S102 needs to be repeated, that is, the first absorbance of the high melting point wax sample at a wavelength of 270nm and the second absorbance at a wavelength of 285nm are measured again using the ultraviolet spectrophotometer under the constant temperature condition of M℃. After the second measurement, if the first absorbance and the second absorbance are still higher than the absorbance threshold, S103 needs to be performed again, that is, the sample is diluted again; if the first absorbance and the second absorbance are no longer higher than the absorbance threshold, S104 can be performed, that is, the first absorbance and the second absorbance measured this time are used to calculate the content of aromatic hydrocarbons.

[0038] In one embodiment of the present application, the absorbance threshold is not higher than 1.5. The present application has found through experiments that setting the absorbance threshold to 1.5 can ensure the accuracy of the calculation of the aromatic content. When the absorbance is not higher than 1.5, there is a good linear relationship between the horizontal and vertical coordinates of the first linear equation and the second linear equation; and when the absorbance is higher than 1.5, due to nonlinear effects, impurity interference, and instrument detection limitations, it is easy to deviate from the established linear range of the standard curve. At this time, the alkylbenzene concentration and naphthalene concentration calculated based on the first absorbance and the second absorbance will have a large deviation from the actual concentration, and the accuracy is significantly reduced.

[0039] In one embodiment of the present application, the dilution solvent used in S103 is any one of cyclohexane, n-heptane, and petroleum ether. Compared with the dilution solvent isooctane used in the prior art, the solvent effect of cyclohexane, n-heptane, and petroleum ether is lower. Under the condition of temperature change (within the boiling point range), the ultraviolet absorbance of the above four substances is less deviated, and the absorbance value is stable. Therefore, the present application selects any one of cyclohexane, n-heptane, and petroleum ether as the solvent for diluting the sample, thereby avoiding the influence of heating on the solvent, avoiding the deviation of the measurement result, and improving the accuracy of the measurement result.

[0040] In one embodiment of the present application, S104 includes: based on the alkylbenzene concentration and naphthalene concentration of the sample, and the mass concentration of the diluted sample in S103, respectively calculating the alkylbenzene content and naphthalene content in the sample. Specifically, alkylbenzene content = alkylbenzene concentration / diluted sample mass concentration; naphthalene content = naphthalene concentration / diluted sample mass concentration. The present application is based on the first absorbance and the second absorbance measured in S102, and substitutes them into the first linear equation and the second linear equation to calculate the alkylbenzene concentration and naphthalene concentration in the sample, and based on the mass concentration of the diluted sample in S103, calculate the alkylbenzene content and naphthalene content, and then add the alkylbenzene content and the naphthalene content to obtain the aromatics content in the sample.

[0041] The first linear equation and the second linear equation are obtained by the following steps: S202: preparing alkylbenzene standard solutions and naphthalene standard solutions with known gradient concentrations, and mixing them to obtain a plurality of mixed standard samples with different concentrations of the two components.

[0042] Specifically, multiple alkylbenzene standard solutions with different concentrations and gradient differences, and multiple naphthalene standard solutions with different concentrations and gradient differences can be configured. Alkylbenzene standard solutions and naphthalene standard solutions of different concentrations are mixed to obtain multiple mixed standard samples, and the concentrations of the two components in each mixed standard sample are different and all known, so as to facilitate the subsequent calculation of the first linear equation and the second linear equation. It should be noted that when preparing mixed standard samples, it is necessary to ensure that the concentration of a single substance in each standard sample (i.e., the concentration of alkylbenzenes or the concentration of naphthalene) has obvious gradient differences, so that differentiated points can be taken when establishing a standard curve; in addition, standard solutions of different concentrations can be freely arranged and combined, and it is only necessary to ensure that the concentrations of the same substance in each mixed standard sample are different.

[0043] In one embodiment of the present application, at least three mixed standard samples are mixed in S202. It is understandable that the more the number of mixed standard samples, the more accurate the standard curve established, and the more accurate the first linear equation and the second linear equation calculated. The number of mixed standard samples is at least three, preferably five, and more preferably seven, and more mixed standard samples can also be prepared to further improve the accuracy of the linear equation.

[0044] In one embodiment of the present application, the solvent used for configuring alkylbenzene standard solution and naphthalene standard solution in S202 is the same as the dilution solvent used in S103, i.e., any one of cyclohexane, normal heptane, and petroleum ether is used as the solvent used for configuring the standard solution. It is understandable that the standard solution configured by S202 is used to set up a standard curve, so it is necessary to eliminate the factors affecting the accuracy of absorbance as soon as possible, as previously mentioned, the solvent effect of cyclohexane, normal heptane, and petroleum ether is relatively low, and its absorbance is relatively not susceptible to temperature. Further, the solvent identical with the dilution solvent of S103 is used to control the variable to the greatest extent, so as to eliminate the influence of the solvent on absorbance as much as possible, and it is ensured that the availability and accuracy of setting up a standard curve are achieved.

[0045] S204: Using an ultraviolet spectrophotometer, respectively measure the first absorbance of the multiple mixed standard samples obtained in S202 at a wavelength of 270 nm at a constant temperature of 24° C., and respectively measure the second absorbance of the multiple mixed standard samples obtained in S202 at a wavelength of 285 nm.

[0046] Specifically, the mixed standard sample is heated and maintained at M°C, and the absorbance of each mixed standard sample at wavelengths of 270 nm and 285 nm is measured at this temperature, thereby constructing an environment consistent with the sample measurement (i.e., S102), eliminating the measurement deviation caused by temperature differences and ensuring the accuracy of the established curve.

[0047] S206: Based on the concentration of alkylbenzenes in each mixed standard sample in S202 and the first absorbance and the second absorbance measured in S204, a first linear equation is calculated; based on the concentration of naphthalene in each mixed standard sample in S202 and the second absorbance measured in S204, a second linear equation is calculated.

[0048] Since the concentrations of alkylbenzenes and naphthalenes in each mixed standard sample in S202 are known values, and the first absorbance and the second absorbance measured in S204 can correspond to the aforementioned concentrations, respectively, based on the mapping relationship, the first linear equation and the second linear equation can be calculated, respectively, as follows: The first linear equation is: 270nm-285nm =a1X1+b1, where A 270nm-285nm is the difference between the first absorbance and the second absorbance, X1 is the concentration of alkylbenzenes, a1 and b1 are the parameters of the first linear equation calculated in S206; The second linear equation is: 285nm =a2X2+b2, where A 285nm is the second absorbance, X2 is the naphthalene concentration, and a2 and b2 are the parameters of the second linear equation calculated in S206.

[0049] Since alkylbenzenes have basically no absorption at a wavelength of 285nm, but have a certain absorption at a wavelength of 270nm, and naphthalene has a certain absorption at both wavelengths of 270nm and 285nm, it can be seen that the substance corresponding to the second absorbance measured at a wavelength of 285nm is naphthalene. Therefore, the second linear equation can be calculated based on the second absorbance and the concentration of naphthalene in the mixed standard sample, and the parameters a2 and b2 can be calculated. The substances corresponding to the first absorbance measured at a wavelength of 270nm include naphthalene and alkylbenzenes. In order to obtain the absorbance corresponding to a single substance of alkylbenzene, it is necessary to make a difference between the first absorbance and the second absorbance. The substance corresponding to the obtained absorbance difference is alkylbenzene. Therefore, it is necessary to calculate the first linear equation based on the difference between the first absorbance and the second absorbance, and the concentration of alkylbenzene in the mixed standard sample, and the parameters a1 and b1 can be calculated.

[0050] In one embodiment of the present application, the ultraviolet spectrophotometer used in S102 and S204 is provided with a cuvette thermostat. Specifically, the cuvette thermostat includes: a thermostat component, a temperature control component and a power supply. The thermostat component includes a cuvette tank and a heating element embedded in the wall of the cuvette tank. A pair of windows that are parallel to each other and corresponding in position are independently provided on the two side walls of the cuvette tank. By appropriately heating the cuvette and its contents, the sample to be tested reaches and remains at M°C, and the cuvette thermostat can be arranged inside the ultraviolet spectrophotometer to keep the temperature above the melting point during the measurement process, thereby avoiding the problem of inaccurate absorbance measurement caused by partial solidification of solidified and semi-solidified wax and wax products at room temperature. The present application provides a cuvette thermostat on an ultraviolet spectrophotometer, thereby enabling detection of solidified and semi-solidified wax samples at room temperature outside the applicable scope of the standard without any impact on the instrument and performance by simply replacing components inside the ultraviolet spectrophotometer.

[0051] Example 1: Selecting a dilution solvent 1. Experimental equipment and reagents Equipment: UV spectrophotometer equipped with a cuvette thermostat (brand: Shimadzu UV-2600), cuvette, volumetric flask, beaker, pipette.

[0052] Reagents: isooctane (brand: Aladdin), cyclohexane (brand: Myrel), petroleum ether (brand: Jindong Tianzheng), n-heptane (brand: Aladdin), naphthalene standards (naphthalene, 1-methylnaphthalene, 2,6-dimethylnaphthalene; brand: McLean), alkylbenzene standards (dodecylbenzene, tetradecylbenzene; brand: Aladdin).

[0053] 2. Experimental methods On the UV spectrophotometer, using a blank cuvette as a control, spectral scanning in the range of 200nm-400nm was performed on isooctane, cyclohexane, petroleum ether and n-heptane, respectively. The sample cell equipped with a constant temperature device tank was set to gradient heating at different temperatures: 30℃, 50℃, 70℃, 90℃ and 120℃. When the set temperature was stably reached for 1 minute, scanning detection was carried out, and the absorbance at wavelengths of 270nm and 285nm was recorded.

[0054] 3. Experimental results and analysis Table 1: Absorbance values ​​of various solvents at different temperatures

[0055] Table 2: Average absorbance changes of each solvent

[0056] The results shown in Table 1 are records of absorbance values ​​of four solvents, namely, isooctane, cyclohexane, petroleum ether and n-heptane, when heated to 30°C, 50°C, 70°C, 90°C and 120°C, respectively. Table 2 is based on the results shown in Table 1 and calculates the mean absorbance change of the four solvents, that is, the average decrease in absorbance when the temperature increases by 10°C. Figure 1 Shown is the absorbance variation trend of the above solvents at different temperatures.

[0057] It can be seen that the absorbance variation mean of the solvent isooctane used in the SH / T 0409-1992 standard is relatively large, the ultraviolet absorbance shift is relatively large when the temperature rises (within the boiling point range), the absorbance value is not stable enough, and the negative impact on the baseline calibration operation is relatively large. Therefore, isooctane is not suitable as a diluent solvent in the determination method of the aromatic hydrocarbon content in the high melting point wax provided in this application.

[0058] The mean absorbance change of cyclohexane, petroleum ether, and normal heptane is very small, the ultraviolet absorbance deviation is small when the temperature rises (within the boiling point range), the absorbance value is relatively stable, and the negative impact on the baseline calibration operation is smaller. Therefore, any one of cyclohexane, petroleum ether, and normal heptane can be selected as the dilution solvent of this application. In the subsequent examples, petroleum ether is selected as the dilution solvent and as the control reference solution.

[0059] Example 2: Preparation of standard solution and mixed standard sample 1. Preparation and determination of naphthalene standard solution Petroleum ether was used as the diluent solvent and mixed with naphthalene standards such as naphthalene, 1-methylnaphthalene, and 2,6-dimethylnaphthalene to prepare 7 naphthalene standard solutions with gradient concentrations. The concentrations of the 7 naphthalene standard solutions were: 0.01561, 0.01254, 0.006317, 0.003171, 0.009439, 0.01866, and 0.02318 (unit: mg / ml).

[0060] Using petroleum ether as the reference solution on an ultraviolet spectrophotometer, the absorbance values ​​of seven naphthalene standard solutions at wavelengths of 270nm and 285nm were measured respectively. The results are as follows: Table 3: Absorbance measurement results of naphthalene standard solution

[0061] According to the data results in Table 3, the concentration X of the naphthalene standard solution can be obtained. N and absorbance A 285nm The linear equation between is: 285nm = 27.836X N +0.0033, correlation coefficient R 2 =0.9945 (>99%). It can be seen that there is a good linear relationship between the absorbance and concentration of the naphthalene standard solution at 285nm, and the naphthalene concentration can be calculated based on the absorbance at 285nm.

[0062] In addition, the absorbance value of the naphthalene standard solution at 270nm is 270nm And the same with the concentration X N There is a good linear relationship, concentration X N and absorbance A 270nm The linear equation between is: 270nm = 33.508X N +0.364, correlation coefficient R 2 =0.9907 (>99%), which shows that the measurement results are consistent with the rule that "naphthalene has certain absorption at wavelengths of 270nm and 285nm".

[0063] 2. Preparation and determination of alkylbenzene standard solution Petroleum ether was used as a diluent solvent and mixed with alkylbenzenes such as undecylbenzene and tetradecylbenzene to prepare 7 gradient concentration alkylbenzene standard solutions. The concentrations of the 7 alkylbenzene standard solutions were: 0.03342, 0.1658, 0.2637, 0.3283, 0.6440, 1.2404, 1.7941 (unit: mg / ml).

[0064] Using petroleum ether as the reference solution on an ultraviolet spectrophotometer, the absorbance values ​​of seven alkylbenzene standard solutions at wavelengths of 270nm and 285nm were measured respectively. The results are as follows: Table 4: Absorbance measurement results of alkylbenzene standard solutions

[0065] According to the data results in Table 4, the absorbance A of the alkylbenzene standard solution at 280nm 285nm The values ​​are all between 0.009 and 0.007, and are stable and close to 0. In addition, the absorbance value A of the alkylbenzene standard solution at 270nm 270nm And its concentration X W There is a good linear relationship, A 270nm = 0.5416X W +0.3291, correlation coefficient R 2 =0.9974 (>99%), which shows that the measurement results are consistent with the rule that "alkylbenzenes have basically no absorption at a wavelength of 285nm, but have a certain absorption at a wavelength of 270nm".

[0066] 3. Configuration of mixed standard samples According to the above operation of preparing standard solution, the above-mentioned naphthalene and alkylbenzene standards were weighed and mixed to prepare 7 mixed standard samples with known component concentrations. The comparison table of component concentrations of the 7 mixed standard samples is shown in Table 5.

[0067] Table 5: Comparison table of concentrations of mixed standard components

[0068] Example 3: Determination of aromatic content in wax sample with a melting point of 70°C 1. Establish a standard curve at 80°C The melting point of the wax sample to be tested in this embodiment is 70° C., so under the condition of 80° C., the sample can be fully dissolved into liquid to ensure the accuracy of the measurement. First, the 7 mixed standard samples prepared in Example 2 are used to establish a standard curve under the condition of 80° C.

[0069] Specifically, the absorbance values ​​of the seven mixed standard samples prepared in Example 2 at wavelengths of 270 nm and 285 nm were measured on an ultraviolet spectrophotometer with a blank cuvette as a control, wherein the sample pool equipped with a thermostat was subjected to a gradient heating setting at 80° C., and scanning detection was performed after the set temperature was stably reached for 1 min.

[0070] Table 6: Absorbance measurement results of mixed standard sample (80℃)

[0071] According to the determination results shown in Table 6, the concentration X1 and absorbance A of alkylbenzenes in the mixed standard sample at 80°C can be obtained. 270nm , A 285nm The linear equation between is: 270nm - 285nm = 1.8172X1+ 0.2486, R 2 = 0.9961, corresponding to the linear equation diagram as follows Figure 2 In addition, since X1=W1*C1, where W1 is the alkylbenzene content of the sample in this embodiment (%), and C1 is the mass concentration of the diluted sample in this embodiment (mg / ml), it can be deduced that the calculation formula for the alkylbenzene content at 80°C is: .

[0072] According to the determination results shown in Table 6, the concentration X2 and absorbance A of naphthalene in the mixed standard sample at 80°C can be obtained. 285nm The linear equation between is: 285nm = 30.956X2- 0.0261, R 2 = 0.9959, corresponding to the linear equation diagram as follows Figure 3 In addition, since X2=W2*C1, where W2 is the naphthalene content of the sample in this embodiment (%), and C1 is the mass concentration of the diluted sample in this embodiment (mg / ml), it can be deduced that the calculation formula for the naphthalene content at 80°C is: .

[0073] 2. Test the sample and calculate the aromatic content 2.1 Experimental methods: Petroleum ether is added to a pair of 1 cm cuvettes as a reference and placed in a UV spectrophotometer for background correction scanning in the 200-350 nm wavelength range. The sample pool equipped with a constant temperature device tank is set to gradient heating at 80°C. When the set temperature is reached, a high melting point wax sample (or wax sample dilution) is placed in the other pair of cuvettes, and the constant temperature is continued for ten minutes, and then its absorbance at wavelengths of 270nm and 285nm is measured.

[0074] If the absorbance value is less than or equal to 1.5, the aromatic content can be directly calculated based on the standard curve; if the value is greater than 1.5, it needs to be further diluted with petroleum ether as a diluent, and then tested again until the absorbance is vertically less than or equal to 1.5. In this embodiment, the mass concentration of the diluted sample C1 = 0.4606 mg / ml.

[0075] The samples were measured twice.

[0076] 2.2 Experimental results: Table 7: Test results of sample 3 of Example 3

[0077] According to Table 7, the aromatic hydrocarbon content in the sample finally measured in this embodiment is 0.2118%, and the percentage difference between the results of the two measurements is only 1.65%, which is less than 3%. It can be seen that the method provided in this application has high stability and good repeatability.

[0078] Example 4: Determination of aromatic content in wax sample with a melting point of 85°C 1. Establish a standard curve at 90°C The melting point of the wax sample to be tested in this embodiment is 85° C., so under the condition of 90° C., the sample can be fully dissolved into liquid to ensure the accuracy of the measurement. First, the 7 mixed standard samples prepared in Example 2 are used to establish a standard curve under the condition of 90° C.

[0079] Specifically, the absorbance values ​​of the seven mixed standard samples prepared in Example 2 at wavelengths of 270 nm and 285 nm were measured on an ultraviolet spectrophotometer with a blank cuvette as a control, wherein the sample cell equipped with a thermostat was subjected to a gradient heating setting at 90° C., and scanning detection was performed after the set temperature was stably reached for 1 min.

[0080] Table 8: Absorbance measurement results of mixed standard sample (90℃)

[0081] According to the determination results shown in Table 8, the concentration X1 and absorbance A of alkylbenzenes in the mixed standard sample at 90°C can be obtained. 270nm , A 285nm The linear equation between is: 270nm - 285nm = 1.8155X1+ 0.2478, R 2 = 0.9978, corresponding to the linear equation diagram as follows Figure 4 In addition, since X1=W3*C2, where W3 is the alkylbenzene content of the sample in this embodiment (%), and C2 is the mass concentration of the diluted sample in this embodiment (mg / ml), it can be deduced that the calculation formula for the alkylbenzene content at 90°C is: .

[0082] According to the determination results shown in Table 8, the concentration X2 and absorbance A of naphthalene in the mixed standard sample at 90°C can be obtained. 285nm The linear equation between is: 285nm = 30.846X2- 0.0272, R 2 = 0.9953, corresponding to the linear equation diagram as follows Figure 5 In addition, since X2=W4*C2, where W4 is the naphthalene content of the sample in this embodiment (%), and C2 is the mass concentration of the diluted sample in this embodiment (mg / ml), it can be deduced that the calculation formula for the naphthalene content at 90°C is: .

[0083] 2. Test the sample and calculate the aromatic content 2.1 Experimental methods: Petroleum ether is added to a pair of 1 cm cuvettes as a reference and placed in a UV spectrophotometer for background correction scanning in the wavelength range of 200-350 nm. The sample pool equipped with a constant temperature device tank is set to gradient heating at 90°C. When the set temperature is reached, a high melting point wax sample (or wax sample dilution) is placed in the other pair of cuvettes, and the constant temperature is continued for ten minutes, and then its absorbance at wavelengths of 270 nm and 285 nm is measured.

[0084] If the absorbance value is less than or equal to 1.5, the aromatic content can be directly calculated based on the standard curve; if the value is greater than 1.5, it needs to be further diluted with petroleum ether as a diluent, and then tested again until the absorbance is vertically less than or equal to 1.5. In this embodiment, the mass concentration of the diluted sample C2 = 0.2720 mg / ml.

[0085] The samples were measured twice.

[0086] 2.2 Experimental results: Table 9: Test results of sample 4 of Example 4

[0087] According to Table 9, the aromatic hydrocarbon content in the sample finally measured in this embodiment is 0.8425%, and the percentage difference between the results of the two measurements is only 0.68%, which is less than 3%. It can be seen that the method provided in this application has high stability and good repeatability.

[0088] Example 5: Determination of aromatic content in wax sample with a melting point of 110°C 1. Establish a standard curve at 120°C The melting point of the wax sample to be tested in this embodiment is 110° C., so under the condition of 120° C., the sample can be fully dissolved into liquid to ensure the accuracy of the measurement. First, the 7 mixed standard samples prepared in Example 2 are used to establish a standard curve under the condition of 120° C.

[0089] Specifically, the absorbance values ​​of the seven mixed standard samples prepared in Example 2 at wavelengths of 270 nm and 285 nm were measured on an ultraviolet spectrophotometer with a blank cuvette as a control, wherein the sample pool equipped with a thermostat was subjected to a gradient heating setting at 120° C., and scanning detection was performed after the set temperature was stably reached for 1 min.

[0090] Table 10: Absorbance measurement results of mixed standard sample (120℃)

[0091] According to the determination results shown in Table 10, the concentration X1 and absorbance A of alkylbenzenes in the mixed standard sample at 120°C can be obtained. 270nm , A 285nm The linear equation between is: 270nm - 285nm = 1.8106X1+ 0.2485, R 2 = 0.9993, corresponding to the linear equation diagram as follows Figure 6 In addition, since X1=W5*C3, where W5 is the alkylbenzene content of the sample in this embodiment (%), and C3 is the mass concentration of the diluted sample in this embodiment (mg / ml), it can be deduced that the calculation formula for the alkylbenzene content at 120°C is: .

[0092] According to the determination results shown in Table 7, the concentration X2 and absorbance A of naphthalene in the mixed standard sample at 120°C can be obtained. 285nm The linear equation between is: 285nm = 30.764X2- 0.0329, R 2 = 0.9948, corresponding to the linear equation diagram as follows Figure 7 In addition, since X2=W6*C3, where W6 is the naphthalene content of the sample in this embodiment (%), and C3 is the mass concentration of the diluted sample in this embodiment (mg / ml), it can be deduced that the calculation formula for the naphthalene content at 120°C is: .

[0093] 2. Test the sample and calculate the aromatic content 2.1 Experimental methods: Petroleum ether is added to a pair of 1 cm cuvettes as a reference and placed in a UV spectrophotometer for background correction scanning in the wavelength range of 200-350 nm. The sample pool equipped with a constant temperature device tank is set to gradient heating at 120°C. When the set temperature is reached, a high melting point wax sample (or wax sample dilution) is placed in the other pair of cuvettes, and the constant temperature is continued for ten minutes, and then its absorbance at wavelengths of 270 nm and 285 nm is measured.

[0094] If the absorbance value is less than or equal to 1.5, the aromatic content can be directly calculated based on the standard curve; if the value is greater than 1.5, it is necessary to further dilute with petroleum ether as a diluent and then test again until the absorbance is vertically less than or equal to 1.5. In this embodiment, the mass concentration of the diluted sample C3 = 0.315.

[0095] The samples were measured twice.

[0096] 2.2 Experimental results: Table 11: Test results of sample 5 of Example 5

[0097] According to Table 11, the aromatic hydrocarbon content in the sample finally measured in this embodiment is 0.06734%, and the percentage difference between the results of the two measurements is only 2.91%, which is less than 3%. It can be seen that the method provided in this application has high stability and good repeatability.

[0098] Example 6: Recovery test The samples in Examples 3, 4 and 5 were taken respectively, and a certain amount of aromatic standard substances (including naphthalene and dodecylbenzene) were added respectively. The aromatic content of the new samples with the aromatic standard substances added was determined again by the same method under respective temperature conditions.

[0099] Table 12: Recovery rate determination results

[0100] It can be seen from Table 12 that the aromatic hydrocarbon content in the new sample measured by the method of the present application is compared with the original content of the sample and the recovery rate is calculated to be between 97.1% and 105.5%. The result is within an acceptable range. It can be seen that the method provided by the present application is accurate, reliable, and has strong repeatability and stability.

[0101] Example 7: Comparative Experiment of Gas Chromatography-Mass Spectrometry Gas chromatography-mass spectrometry (GC-MS) is a technique that combines gas chromatograph (GC) and mass spectrometer (MS) through an appropriate interface and uses powerful computer technology for combined analysis. This technique can simultaneously utilize the ability of gas chromatograph to efficiently separate complex mixtures and the ability of mass spectrometer to accurately identify compounds, thereby achieving qualitative and quantitative analysis of compounds in complex samples.

[0102] In this example, the accurate aromatic content in the samples of Examples 3, 4 and 5 was determined by gas chromatography-mass spectrometry, and the determination results were compared with the aromatic content results obtained by the method of the present application, thereby verifying the accuracy of the method of the present application.

[0103] Table 13: Recovery rate determination results

[0104] As shown in Table 13, the ratio between the aromatic content measured by the method of the present application and the result measured by the gas chromatography-mass spectrometry method is between 100-104%, the difference in the measurement results is very small, and there is no significant difference between the two methods. Therefore, the measurement method for the determination of the aromatic content in the high melting point wax provided by the present application has high measurement accuracy and can be used for the ultraviolet method determination of the aromatic content in the high melting point wax.

[0105] The embodiments of the present application have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein. The scope of the present application is defined by the appended claims.

Claims

1. A method for determining the content of aromatic hydrocarbons in high melting point wax, characterized in that: The melting point of the high melting point wax is defined as N°C, and the method comprises the following steps: S102: using an ultraviolet spectrophotometer to measure the first absorbance of the high melting point wax sample at a wavelength of 270 nm and the second absorbance at a wavelength of 285 nm at a constant temperature of M°C, wherein M≥N; S104: when the first absorbance and the second absorbance measured in S102 are not higher than the absorbance threshold, the alkylbenzene concentration and the naphthalene concentration of the sample are calculated based on the first linear equation and the second linear equation respectively; and the aromatic hydrocarbon content in the sample is calculated based on the alkylbenzene concentration and the naphthalene concentration of the sample; The first linear equation and the second linear equation are obtained by the following steps: S202: preparing alkylbenzene standard solutions and naphthalene standard solutions with known gradient concentrations, and mixing them to obtain a plurality of mixed standard samples with different concentrations of the two components; S204: using an ultraviolet spectrophotometer to respectively measure the first absorbance of the multiple mixed standard samples obtained in S202 at a wavelength of 270 nm at a constant temperature of 24° C., and respectively measure the second absorbance of the multiple mixed standard samples obtained in S202 at a wavelength of 285 nm; S206: Based on the concentration of alkylbenzenes in each mixed standard sample in S202 and the first absorbance and the second absorbance measured in S204, the first linear equation is calculated; based on the concentration of naphthalene in each mixed standard sample in S202 and the second absorbance measured in S204, the second linear equation is calculated.

2. The method according to claim 1, characterized in that The method further includes S103: when the absorbance measured in S102 is higher than the absorbance threshold, diluting the sample, and repeating S102 after dilution.

3. The method according to claim 2, characterized in that The dilution solvent used in S103 is the same as the solvent used to prepare the alkylbenzene standard solution and the naphthalene standard solution in S202.

4. The method according to any one of claims 2 or 3, characterized in that: The dilution solvent used in S103 is any one of cyclohexane, n-heptane and petroleum ether.

5. The method according to claim 2, characterized in that: The S104 includes: based on the alkylbenzene concentration and naphthalene concentration of the sample and the mass concentration of the diluted sample in S103, respectively calculating the alkylbenzene content and naphthalene content in the sample; and adding the alkylbenzene content and the naphthalene content to obtain the aromatics content in the sample.

6. The method according to any one of claims 1 or 2, characterized in that: The absorbance threshold is no higher than 1.

5.

7. The method according to claim 1, characterized in that At least three mixed standard samples are obtained by mixing in S202.

8. The method according to claim 1, characterized in that The first linear equation is: 270nm-285nm =a1X1+b1, where A 270nm-285nm is the difference between the first absorbance and the second absorbance, X1 is the concentration of alkylbenzenes, and a1 and b1 are the parameters of the first linear equation calculated in S206.

9. The method according to claim 1, characterized in that: The second linear equation is: 285nm =a2X2+b2, where A 285nm is the second absorbance, X2 is the naphthalene concentration, and a2 and b2 are the parameters of the second linear equation calculated in S206.

10. The method according to claim 1, characterized in that The ultraviolet spectrophotometer used in S102 and S204 is provided with a cuvette constant temperature device.

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