Method for analyzing hydrocarbon composition of PAO base oil

Abstract

The invention provides a method for analyzing the hydrocarbon composition of PAO base oil, which comprises the following steps: uniformly mixing PAO base oil and carbon disulfide in a mass ratio of 1: (80-110) at 60-100 DEG C by using a constant-temperature oscillator to obtain an on-machine sample; carrying out full scanning on the loading sample by adopting a gas chromatograph-mass spectrometer to obtain a characteristic ion current spectrum of each component, and determining the carbon number range of each component; and by taking mixed n-alkanes which can contain the carbon number range as a standard substance, detecting and analyzing the on-machine sample by adopting a gas chromatograph, and calculating by adopting an area normalization method to obtain the content of hydrocarbon components with various carbon numbers in the PAO base oil. The specific organic solvent carbon disulfide is added and is oscillated and uniformly mixed at a specific temperature, so that the viscosity of the PAO base oil sample is quickly reduced, the interference of high viscosity is eliminated, and the stable and uniform properties of the sample are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of oil product detection, and in particular to a method for analyzing the composition of PAO base oil hydrocarbons. Background Art

[0002] Class IV lubricant base oil, namely poly alpha olefin (PAO), is currently the best performing synthetic lubricant base oil with high viscosity index, low volatility, low fluidity, good shear stability and excellent high temperature oxidation resistance. It is internationally recognized as an ideal base oil for preparing high-end and special lubricants. Compared with traditional mineral lubricant base oils (Class I, II, and III base oils), PAO base oil has low evaporation loss and good stability. It can be used as internal combustion engine oil, gear oil, hydraulic oil, refrigeration oil, automatic transmission fluid, high viscosity aviation lubricant, CNC machine tool oil, air compressor oil, long life lubricant, transformer oil, insulating oil, high voltage switch oil, metalworking fluid, etc. in cold and extremely cold regions. It is not only widely used in automobiles, industry, and civil applications, but also the main source of high-end lubricant base oils used in aviation, aerospace, military and other industries.

[0003] According to the viscosity grade, PAO base oil can be divided into three levels: low viscosity, medium viscosity and high viscosity. Low viscosity includes: PAO2, PAO2.5 / 3, PAO4, PAO5, PAO6, PAO8, PAO9, PAO10, etc.; medium viscosity mainly includes PAO16, PAO20, PAO25, PAO40, etc.; high viscosity includes: PAO100, PAO150, PAO1000, etc. Among them, low viscosity PAO base oil products have become the best performing synthetic lubricant base oils at present due to their good viscosity-temperature performance, suitable high temperature viscosity, excellent low temperature fluidity, thermal oxidation stability and other characteristics.

[0004] The analysis and detection of the hydrocarbon composition of PAO base oil is a necessary method for calculating the conversion rate and degree of polymerization of the product, which has an important impact on the control of product performance and is an important means of controlling the quality of base oil. However, there are few methods for analyzing the hydrocarbon composition of low-viscosity PAO base oil in the prior art. Gas chromatography is fast, simple and direct, which can improve the efficiency of product analysis and the accuracy of sample measurement results in process production. It is an important means of controlling the quality of PAO base oil and plays an important role in ensuring the smooth operation of the production process.

[0005] CN111272900A discloses a gas chromatography analysis method for detecting the content of 3-chloro-2,2-dimethyl-1-propanol, which includes the configuration of the analysis sample, the analysis conditions of the gas chromatography, and the qualitative and quantitative methods, and the quantitative method used is the internal standard method. CN111521715A discloses a method for detecting total petroleum hydrocarbons C10-C40 in soil and sediments, in which the total petroleum hydrocarbons C10-C40 in the soil and sediments are extracted, purified online, concentrated, and fixed to volume, and then detected by a gas chromatograph with a hydrogen flame ionization detector, and qualitatively determined according to the retention time window, and quantitatively determined by the external standard method. CN104569247A discloses a detection method for determining alkane compounds using gas chromatography, which mainly includes sample collection and analysis and determination steps. After setting appropriate determination conditions, the method can also detect aromatic hydrocarbon compounds, halogenated hydrocarbon compounds and alcohol compounds at the same time.

[0006] In summary, it can be seen that the pre-treatment technology in the existing technology is cumbersome and cannot solve the problem of high viscosity of PAO base oil; in addition, the quantitative methods of external and internal standards are relatively complex, inconvenient to operate, and cannot meet the requirements of rapid analysis and detection. Summary of the invention

[0007] In order to solve the above technical problems, the object of the present invention is to provide a method for analyzing the hydrocarbon composition of PAO base oil, so as to analyze the hydrocarbon composition of PAO base oil quickly, efficiently and accurately.

[0008] To achieve the above object, the present invention provides a method for analyzing the hydrocarbon composition of a PAO base oil, comprising the following steps:

[0009] (1) Pretreatment: PAO base oil and carbon disulfide are mixed uniformly at a mass ratio of 1:80-110 at 60-100°C using a constant temperature oscillator to obtain a sample for use on the machine;

[0010] (2) Detection and analysis: A gas chromatograph-mass spectrometer is used to perform a full scan on the sample to obtain a characteristic ion current spectrum of each component, determine the carbon number range of the component and characterize each component; a mixed normal alkane that can contain the carbon number range is used as a standard, and a gas chromatograph is used to detect and analyze the sample, and the content of hydrocarbon components of each carbon number in the PAO base oil is calculated by using an area normalization method;

[0011] Among them, the gas chromatography column used in the gas chromatography-mass spectrometer and the gas chromatograph is a temperature-resistant non-polar stainless steel column, the filler of which is polyborocarbosilane, and the chromatographic detection temperature is 420-440°C;

[0012] The mass spectrometry detection temperature of the gas chromatography-mass spectrometry instrument is 380-410°C.

[0013] The viscosity of PAO base oil is relatively high. During the process of analyzing its hydrocarbon composition, the viscosity of the sample will affect the selection of the analysis method, which is not conducive to the analysis of sample performance and composition. The present invention adds a suitable organic solvent, carbon disulfide, to the PAO base oil sample and mixes the two uniformly under continuous heating to quickly reduce the viscosity of the PAO base oil sample, avoid sample cracking and adsorption, reduce column load, eliminate interference from high viscosity, and ensure that the sample properties are stable and uniform, so as to achieve the conditions for analysis using a gas chromatograph.

[0014] When selecting an organic solvent, according to the principle of like dissolves like, many organic reagents can be used as solvents. However, the PAO base oil sample is a complex sample with high viscosity, wide distillation range, and numerous components. If the organic solvent is similar to the composition in the sample, it may affect the separation of the PAO sample components on the gas chromatography column. If the elution time of the organic solvent is close to that of the component, it will interfere with the quantitative analysis results of the component. The specific organic solvent carbon disulfide selected by the present invention not only helps to reduce the viscosity of the sample, but also ensures that all components in the sample are completely discharged to achieve complete separation, avoid sample decomposition, and ensure that the solvent does not interfere with the normal quantitative analysis results of the components in the sample. After screening, it was finally determined to use carbon disulfide (CS2). 2 ) is used as a solvent for diluting samples for analytical tests. Carbon disulfide can dissolve the samples very well, and the hydrogen flame ionization detector has a weak response to carbon disulfide, which will not affect the composition and content of the samples.

[0015] The present invention also controls the mixing of the PAO base oil and carbon disulfide at a specific temperature, and can avoid the volatilization or conversion of light components in the sample while reducing the viscosity of the PAO base oil, thereby ensuring the objectivity and accuracy of the analysis method.

[0016] The present invention also optimizes the type of gas chromatography column, injection method and detection temperature accordingly. There are many heavy hydrocarbon components in PAO base oil. In order to ensure that all components are fully gasified and flowed out, the present invention controls a higher detection temperature and selects a non-polar, high-temperature resistant large-diameter stainless steel capillary chromatographic column. The chromatographic column also has a higher separation efficiency for hydrocarbon components; at the same time, in order to ensure the accuracy of the quantitative analysis results of light components in the sample, cold column head injection is adopted in the injection method, which avoids the temperature being too high during sample injection, and the light components being cracked or gasified too quickly to affect the quantitative analysis results.

[0017] According to a specific embodiment of the present invention, preferably, in the pre-treatment step, the mass ratio of PAO base oil to carbon disulfide is 1:90-110.

[0018] According to a specific embodiment of the present invention, preferably, in the pre-treatment step, the PAO base oil is mixed with carbon disulfide at 70-80°C.

[0019] According to a specific embodiment of the present invention, preferably, in the pre-treatment step, the oscillation frequency of the constant temperature oscillator is 70-110 times / min, and the oscillation time is 20-40 min.

[0020] According to a specific embodiment of the present invention, preferably, the oscillation frequency of the constant temperature oscillator is 80-100 times / min, and the oscillation time is 20-30 min.

[0021] The present invention pre-treats the sample by adopting a micro-oscillator that can continuously heat at a constant temperature and cool rapidly. The continuous constant temperature heating oscillation can quickly reduce the viscosity of the sample, eliminate the interference of high viscosity, and ensure that the properties of the sample are stable and uniform; the rapid cooling is to avoid the decomposition or transformation of light components in the sample under long-term heating. In addition, rapid cooling to room temperature can shorten the sample pre-treatment time and meet the requirements of rapid analysis.

[0022] According to a specific embodiment of the present invention, preferably, the specification of the heat-resistant non-polar stainless steel chromatographic column is 10m×530μm×0.15μm, and the maximum use temperature of the heat-resistant non-polar stainless steel chromatographic column under programmed temperature is 450°C, and the maximum use temperature under constant temperature mode is 430°C;

[0023] According to a specific embodiment of the present invention, preferably, the model of the temperature-resistant non-polar stainless steel chromatographic column is MXT-1, produced by Ruisi Taikang Technology (Beijing) Co., Ltd.

[0024] According to a specific embodiment of the present invention, preferably, the chromatographic detection temperature is 430-440°C.

[0025] According to a specific embodiment of the present invention, preferably, the chromatographic conditions of the gas chromatography-mass spectrometer further include the following parameters:

[0026] Heating program: initial temperature 35-50℃, hold for 5-8min, program temperature rise 2-6℃ / min, final temperature 380-410℃, hold for 15-25min;

[0027] Carrier gas: high-purity helium, purity 99.999%;

[0028] Carrier gas flow rate: 4.0-6.0mL / min;

[0029] Injection volume: 0.1-1.0 μL;

[0030] Inlet temperature: 180-220℃;

[0031] Injection mode: split;

[0032] Split ratio: 5:1;

[0033] The mass spectrometry conditions of the gas chromatography-mass spectrometer also include the following parameters:

[0034] Ionization method: electron impact (EI);

[0035] Electron energy: 70eV;

[0036] Ion source temperature: 310-330℃;

[0037] Quadrupole temperature: 220-250°C;

[0038] Scan mode: full scan.

[0039] According to a specific embodiment of the present invention, preferably, the chromatographic conditions of the gas chromatograph also include the following parameters:

[0040] Heating program: initial temperature 35-60℃, hold for 0-5min, program temperature rise 6-10℃ / min, final temperature 420-440℃, hold for 15-25min;

[0041] Carrier gas: high purity nitrogen;

[0042] Carrier gas flow rate: 4.0-6.0mL / min;

[0043] Injection volume: 0.1-1.0 μL;

[0044] Inlet temperature: Track column temperature;

[0045] Injection mode: cold on-column injection;

[0046] Split ratio: no split;

[0047] Hydrogen flow rate: 30-40mL / min;

[0048] Air flow rate: 300-400mL / min;

[0049] Septum purge flow rate: 2.0-3.0mL / min.

[0050] According to a specific embodiment of the present invention, more preferably, the chromatographic conditions of the gas chromatograph include the following parameters:

[0051] Heating program: initial temperature 45-50℃, hold for 0-2min, program temperature rise 8-10℃ / min, final temperature 430-440℃, hold for 18-20min;

[0052] Carrier gas: high-purity nitrogen, purity 99.999%;

[0053] Carrier gas flow rate: 4.5-5.0mL / min;

[0054] Injection volume: 0.2-0.5 μL;

[0055] Inlet temperature: Track column temperature;

[0056] Injection mode: cold on-column injection;

[0057] Split ratio: no split;

[0058] Detector temperature: 430-440°C;

[0059] Hydrogen flow rate: 38-40mL / min;

[0060] Air flow rate: 380-400mL / min;

[0061] Septum purge flow rate: 2.8-3.0mL / min.

[0062] According to a specific embodiment of the present invention, preferably, the gas chromatograph-mass spectrometer is an Agilent 7890-5975 gas chromatograph-mass spectrometer.

[0063] According to a specific embodiment of the present invention, preferably, the PAO base oil is polymerized from monomers with the same carbon number. In this case, when the content of C10 hydrocarbons, C20 hydrocarbons, C30 hydrocarbons, C40 hydrocarbons, C50 hydrocarbons, and C60 hydrocarbons is obtained by the analysis method of the present invention, the content of monomer hydrocarbons, dimer hydrocarbons, trimer hydrocarbons, tetramer hydrocarbons, pentamer hydrocarbons, and hexamer hydrocarbons in the PAO base oil can be determined.

[0064] The present invention adopts the area normalization method for quantification, and the method is as follows:

[0065] The content of each component in the sample i , calculated by mass fraction as follows:

[0066]

[0067] Where: i —The content of component i in the sample measured, in % (mass fraction);

[0068] A i —The measured peak area of ​​component i.

[0069] It should be noted that when processing the data, the organic solvent carbon disulfide should be deducted before calculating the results. The results of the raw material monomer (C10), dimer hydrocarbon (C20), trimer hydrocarbon (C30), tetramer hydrocarbon (C40), pentamer hydrocarbon (C50), and hexamer hydrocarbon (C60) are the contents of multiple components i, ω i The accumulated value of .

[0070] According to the structural characteristics of low-viscosity PAO base oil, the theoretical correction factor has basically the same response value on the hydrogen flame ionization detector, so the area normalization method can be used for quantitative analysis, which is accurate and easy to operate. In the present invention, the qualitative analysis of the sample composition adopts a technical means combining standard sample and mass spectrometry, and the qualitative result is more accurate.

[0071] The technical solution provided by the present invention has the following beneficial effects:

[0072] The present invention provides a technology for pre-treating samples using a micro-oscillator with continuous heating and rapid cooling, which can quickly reduce the viscosity of the samples, eliminate the interference of high viscosity, and ensure that the properties of the samples are stable and uniform; gas chromatography is used for analysis, and area normalization method is used for quantification; and mass spectrometry is used for qualitative analysis.

[0073] The present invention provides a method for analyzing the hydrocarbon composition of a PAO base oil based on the product characteristics of a PAO base oil. By adding a specific organic solvent, carbon disulfide, and mixing uniformly under specific pretreatment conditions, the viscosity of a PAO base oil sample is quickly reduced, interference from high viscosity is eliminated, and stable and uniform properties of the sample are ensured. At the same time, the present invention controls the detection temperature, optimizes the injection method, ensures that light components in the sample will not be cracked, and heavy components can be completely vaporized and flowed out, and selects a specific high-temperature resistant non-polar large-diameter stainless steel chromatographic column, thereby improving the accuracy and stability of the detection and analysis method.

[0074] The analytical method of the invention has the advantages of being rapid, simple, highly accurate and good in repeatability. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 This is a typical gas chromatogram of the hydrocarbon composition of the PAO base oil obtained in Example 1;

[0076] Figure 1 In the figure, 1 represents the carbon disulfide solvent, 2 represents the raw material monomer (carbon 10), 3 represents the dimer (carbon 20), 4 represents the trimer (carbon 30), 5 represents the tetramer (carbon 40), 6 represents the pentamer (carbon 50), and 7 represents the hexamer (carbon 60).

[0077] Figure 2 The gas chromatogram of the hydrocarbon composition of the PAO base oil obtained in Comparative Example 1;

[0078] Figure 2 In the figure, 1 represents carbon disulfide solvent, 2 represents raw material monomer and solvent cyclohexane, 3 represents dimer (C 20), 4 represents trimer (C 30), 5 represents tetramer (C 40), and 6 represents pentamer (C 50).

[0079] Figure 3 The gas chromatogram of the hydrocarbon composition of the PAO base oil obtained in Comparative Example 2;

[0080] Figure 3 In the figure, 1 represents the carbon disulfide solvent, 2 represents the raw material monomer (carbon 10), 3 represents the dimer (carbon 20), 4 represents the trimer (carbon 30), 5 represents the tetramer (carbon 40), and 6 represents the pentamer (carbon 50). DETAILED DESCRIPTION

[0081] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0082] The reagents and instruments used in the specific embodiments of the present invention are as follows:

[0083] Carbon disulfide: water-sealed analytical grade;

[0084] Normal alkane standard: a mixed standard sample containing positive carbon 5 to positive carbon 100, with a purity greater than 96.0%;

[0085] Analytical balance: 0.1 mg;

[0086] Miniature constant temperature speed regulating multi-purpose oscillator;

[0087] Gas chromatograph: 7980A, Agilent, equipped with hydrogen flame detector and G4513A autosampler;

[0088] Gas chromatograph-mass spectrometer: Agilent 7890-5975, Agilent, equipped with hydrogen flame detector and G4513A autosampler;

[0089] Chromatographic column: high temperature resistant non-polar large-diameter stainless steel chromatographic column, model MXT-1, Ruisi Taikang Technology (Beijing) Co., Ltd., specification 10m×0.53mm×0.15μm;

[0090] Example 1

[0091] This embodiment provides a method for analyzing the hydrocarbon composition of a PAO base oil, which is as follows:

[0092] S1. Configure the sample on the machine:

[0093] Take 0.02 g of the PAO base oil sample to be tested, place it in a 2 mL volumetric flask, add 2 mL of carbon disulfide to make up the volume; place the volumetric flask in a micro constant temperature oscillator for oscillation, the operating temperature is 70 ° C, the oscillation frequency is 80 times / min, the oscillation time is 20 min, and the solution to be tested after oscillation is quickly cooled to obtain the sample for the machine.

[0094] S2. Gas chromatography-mass spectrometry detection:

[0095] The sample solution obtained in S1 is injected into a gas chromatography-mass spectrometer for detection, and the carbon number range and qualitative results of each hydrocarbon component of the PAO base oil are obtained by scanning in a full scan mode;

[0096] Among them, the conditions of gas chromatography-mass spectrometry are:

[0097] Chromatographic column: high temperature resistant non-polar large-diameter stainless steel chromatographic column, model MXT-1, Ruisi Taikang Technology (Beijing) Co., Ltd., specification 10m×0.53mm×0.15μm;

[0098] Heating program: initial temperature 35°C, hold for 5 min, program temperature rise 5°C / min, final temperature 410°C, hold for 15 min;

[0099] Carrier gas: high-purity helium (purity 99.999%);

[0100] Carrier gas flow rate: 4.5 mL / min;

[0101] Injection volume: 0.2 μL;

[0102] Inlet temperature: 200°C;

[0103] Injection mode: split;

[0104] Split ratio: 5:1;

[0105] Ionization method: electron impact (EI);

[0106] Electron energy: 70eV;

[0107] Ion source temperature: 330°C;

[0108] Quadrupole temperature: 250°C;

[0109] Scan mode: full scan.

[0110] S3. Prepare standard samples:

[0111] Weigh 0.02 g of normal alkane standard (a mixed standard sample containing positive carbon 5 to positive carbon 100, with a purity greater than 96.0%) and place it in a 2 mL volumetric flask, add 2 mL of carbon disulfide to make up the volume, place the volumetric flask in a micro constant temperature oscillator and oscillate at a temperature of 70°C, an oscillation frequency of 80 times / min, and an oscillation time of 20 min. After oscillation, the test solution is quickly cooled to obtain a standard sample solution.

[0112] S4. Gas chromatography detection:

[0113] The standard sample solution obtained in S3 is injected into a gas chromatograph for chromatographic detection to determine the retention time of normal alkanes from carbon 5 to carbon 100 for qualitative analysis;

[0114] The sample solution obtained in S1 is injected into a gas chromatograph for chromatographic detection, and the content of each hydrocarbon component of the PAO base oil is measured by preliminary qualitative analysis using retention time and quantitative analysis using area normalization method;

[0115] Among them, the chromatographic conditions of the gas chromatograph are:

[0116] Chromatographic column: high temperature resistant non-polar large-diameter stainless steel chromatographic column, model MXT-1, Ruisi Taikang Technology (Beijing) Co., Ltd., specification 10m×0.53mm×0.15μm;

[0117] Heating program: initial temperature 50°C, hold for 0 min, program temperature rise 9°C / min, final temperature 440°C, hold for 18 min;

[0118] Carrier gas: high purity nitrogen;

[0119] Carrier gas flow rate: 5.0 mL / min;

[0120] Injection volume: 0.2 μL;

[0121] Inlet temperature: Track column temperature;

[0122] Injection mode: cold on-column injection;

[0123] Split ratio: no split;

[0124] Detector temperature: 440°C;

[0125] Hydrogen flow rate: 40mL / min;

[0126] Air flow rate: 400mL / min;

[0127] Septum purge flow rate: 3 mL / min.

[0128] Figure 1 This is a typical gas chromatogram of the hydrocarbon composition of the PAO base oil obtained in Example 1.

[0129] Example 2

[0130] This embodiment provides a method for analyzing the hydrocarbon composition of a PAO base oil, which is the same as that of Embodiment 1, except that: in the sample preparation process in S1, the temperature used in the micro-constant temperature oscillator is 80° C., the oscillation frequency is 100 times / min, the oscillation time is 30 min, and the solution to be tested is rapidly cooled after oscillation, and the detection temperature is 430° C.

[0131] Example 3

[0132] This embodiment provides a method for analyzing the hydrocarbon composition of a PAO base oil, which is the same as that of Embodiment 1, except that: in the sample preparation process in S1, the temperature used in the micro-constant temperature oscillator is 75° C., the oscillation frequency is 90 times / min, the oscillation time is 25 min, and the solution to be tested is rapidly cooled after oscillation.

[0133] Comparative Example 1

[0134] This comparative example provides a method for analyzing the hydrocarbon composition of a PAO base oil, which is the same as that of Example 1, except that the carbon disulfide in Example 1 is replaced by a mixture of cyclohexane and carbon disulfide in a mass ratio of 1:1.

[0135] Figure 2 This is the gas chromatogram of the PAO base oil hydrocarbon composition obtained in Comparative Example 1.

[0136] Comparative Example 2

[0137] This comparative example provides a method for analyzing the hydrocarbon composition of a PAO base oil, which is the same as Example 1, except that the chromatographic detection temperature is 390° C., and the gas chromatographic column is a DB1ht chromatographic column with a specification of 10 m×530 μm×0.17 μm.

[0138] Figure 3 This is the gas chromatogram of the PAO base oil hydrocarbon composition obtained in Comparative Example 2.

[0139] Experimental example

[0140] This experiment is used to verify the methodology of Example 1 above.

[0141] (1) Repeatability verification

[0142] The degree of closeness between independent results obtained by correctly and normally operating the same test sample in the same method under the same test conditions and within a short time interval is equal to or less than the absolute difference between two single test results obtained under the above conditions (confidence level is 95%).

[0143] The experiment was carried out according to the method of Example 1, and the repeatability analysis results are shown in Table 1.

[0144] Table 1 Repeatability analysis results

[0145] Serial number Raw material monomer, % Dimer, % Trimer, % Tetramer, % Pentamer, % Hexamer, % 1 1.621 11.565 61.801 17.138 6.814 1.061 2 1.628 11.492 61.717 17.184 6.885 1.094 3 1.639 11.456 61.797 17.174 6.863 1.071 4 1.660 11.523 61.884 17.037 6.793 1.103 5 1.645 11.51 61.837 17.078 6.831 1.099 6 1.656 11.529 61.842 17.088 6.799 1.086 average 1.642 11.513 61.813 17.117 6.831 1.086 Standard Deviation 0.015 0.037 0.057 0.058 0.037 0.017 RSD(%) 0.90 0.30 0.10 0.30 0.50 1.50

[0146] (2) Reproducibility verification

[0147] The degree of closeness between the individual test results obtained by the same method for the same test sample under different test conditions (different operators, different instruments, different laboratories) and the correct and normal operation. Its value is equal to or less than the absolute difference between the two single test results obtained under the above conditions (confidence level is 95%).

[0148] The experiment was carried out according to the method of Example 1, and the PAO base oil on-machine sample solution was measured under different conditions, and the precision was calculated according to GB / T 6379.2-2004. The precision analysis results are shown in Table 2.

[0149] Table 2 Precision analysis results

[0150]

[0151]

[0152] (3) Accuracy verification

[0153] Take the sample from the machine and conduct a spike test by adding hexadecane to the sample. The spike recovery results are shown in Table 3.

[0154] Table 3 Determination of spike recovery

[0155]

[0156] From Table 1, Table 2, Table 3 and Figure 1 The results show that the analytical method of the present invention can completely separate the components in the PAO base oil sample with good separation, and can accurately determine the content of each component, and the method has high accuracy.

[0157] The gas chromatograms and methodological verification results obtained in Examples 2 and 3 are equivalent to those in Example 1.

[0158] Figure 2 The gas chromatogram of the PAO base oil hydrocarbon composition obtained in Comparative Example 1. Figure 2 It can be seen that the monomer and solvent cyclohexane in the sample both peak at position 2, thus affecting the determination of the monomer content. Therefore, using a mixed solvent of cyclohexane and carbon disulfide or cyclohexane alone as a solvent is not suitable for the present invention.

[0159] Figure 3 The gas chromatogram of the hydrocarbon composition of the PAO base oil obtained in Comparative Example 2. Figure 3 It can be seen that when using the DB1ht column to separate samples, due to the limitation of the maximum operating temperature of the column, the sample detection temperature is 390°C. Due to the low temperature, the sample components are not completely eluted.

Claims

1. A method for analyzing the hydrocarbon composition of a PAO base oil, comprising the following steps: (1) Pretreatment: PAO base oil and carbon disulfide are mixed uniformly at a mass ratio of 1:80-110 at 60-100°C using a constant temperature oscillator to obtain a sample for use on the machine; (2) Detection and analysis: A gas chromatography-mass spectrometer is used to perform a full scan of the sample to obtain the characteristic ion current spectrum of each component, determine the carbon number range of the component and qualitatively analyze each component; Using a mixed normal alkane that can contain the carbon number range as a standard, using a gas chromatograph to detect and analyze the sample on the machine, and using an area normalization method to calculate the content of hydrocarbon components of each carbon number in the PAO base oil; Among them, the gas chromatography column used in the gas chromatography-mass spectrometer and the gas chromatograph is a temperature-resistant non-polar stainless steel column, the filler of which is polyborocarbosilane, and the chromatographic detection temperature is 420-440°C; The mass spectrometry detection temperature of the gas chromatography-mass spectrometry instrument is 380-410°C.

2. The method for analyzing the hydrocarbon composition of the PAO base oil according to claim 1, in, In the pretreatment step, the mass ratio of PAO base oil to carbon disulfide is 1:90-110.

3. The method for analyzing the hydrocarbon composition of the PAO base oil according to claim 1, in, The PAO base oil and carbon disulfide are mixed by shaking at 70-80°C.

4. The method for analyzing the hydrocarbon composition of the PAO base oil according to claim 1, in, In the pretreatment step, the oscillation frequency of the constant temperature oscillator is 70-110 times / min, and the oscillation time is 20-40min; Preferably, the constant temperature oscillator has an oscillation frequency of 80-100 times / min and an oscillation duration of 20-30 min.

5. The method for analyzing the hydrocarbon composition of the PAO base oil according to claim 1, in, The specifications of the heat-resistant non-polar stainless steel chromatographic column are 10m×530μm×0.15μm; the maximum operating temperature of the heat-resistant non-polar stainless steel chromatographic column under programmed temperature rise is 450°C, and the maximum operating temperature under constant temperature mode is 430°C.

6. The method for analyzing the hydrocarbon composition of the PAO base oil according to claim 1, in, The model of the temperature-resistant non-polar stainless steel chromatographic column is MXT-1, produced by Ruisi Taikang Technology (Beijing) Co., Ltd.

7. The method for analyzing the hydrocarbon composition of the PAO base oil according to claim 1, in, The chromatographic conditions of the gas chromatography-mass spectrometry also include the following parameters: Heating program: initial temperature 35-50℃, hold for 5-8min, program temperature rise 2-6℃ / min, final temperature 380-410℃, hold for 15-25min; Carrier gas: high-purity helium, purity 99.999%; Carrier gas flow rate: 4.0-6.0mL / min; Injection volume: 0.1-1.0 μL; Inlet temperature: 180-220℃; Injection mode: split; Split ratio: 5:1; The mass spectrometry conditions of the gas chromatography-mass spectrometer also include the following parameters: Ionization method: electron bombardment; Electron energy: 70eV; Ion source temperature: 310-330℃; Quadrupole temperature: 220-250°C; Scan mode: full scan.

8. The method for analyzing the hydrocarbon composition of the PAO base oil according to claim 1, in, The chromatographic conditions of the gas chromatograph also include the following parameters: Heating program: initial temperature 35-60℃, hold for 0-5min, program temperature rise 6-10℃ / min, final temperature 420-440℃, hold for 15-25min; Carrier gas: high purity nitrogen; Carrier gas flow rate: 4.0-6.0mL / min; Injection volume: 0.1-1.0 μL; Inlet temperature: Track column temperature; Injection mode: cold on-column injection; Split ratio: no split; Hydrogen flow rate: 30-40mL / min; Air flow rate: 300-400mL / min; Septum purge flow rate: 2.0-3.0mL / min.

9. The method for analyzing the hydrocarbon composition of the PAO base oil according to claim 8, in, The chromatographic conditions of the gas chromatograph include the following parameters: Heating program: initial temperature 45-50℃, hold for 0-2min, program temperature rise 8-10℃ / min, final temperature 430-440℃, hold for 18-20min; Carrier gas: high purity nitrogen; Carrier gas flow rate: 4.5-5.0mL / min; Injection volume: 0.2-0.5 μL; Inlet temperature: Track column temperature; Injection mode: cold on-column injection; Split ratio: no split; Detector temperature: 430-440°C; Hydrogen flow rate: 38-40mL / min; Air flow rate: 380-400mL / min; Septum purge flow rate: 2.8-3.0mL / min.

10. The method for analyzing the hydrocarbon composition of the PAO base oil according to claim 1, in, The gas chromatograph-mass spectrometer was Agilent 7890-5975 gas chromatograph-mass spectrometer.

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