A method for analyzing the molecular structure of Fischer-Tropsch oil based on simulated distillation and nuclear magnetic resonance

Abstract

The present invention relates to the technical field of oil product analysis, and provides a method for analyzing the molecular structure of Fischer-Tropsch oil based on the combination of simulated distillation and nuclear magnetic resonance. The present invention obtains the distillation range and simplified carbon number distribution of the Fischer-Tropsch oil sample by simulated distillation, and calculates the high-temperature simulated chain length; obtains the ratio of primary, secondary and tertiary hydrogen in the sample by nuclear magnetic hydrogen spectrum analysis, and then calculates the degree of branching; obtains the terminal methyl content, branched methyl content, normal alkane content and isoalkane content of the Fischer-Tropsch oil sample by nuclear magnetic carbon spectrum calculation, and calculates the number of branched chain nodes and the number of branches. The present invention combines simulated distillation with nuclear magnetic resonance, which can greatly enhance the accuracy and speed of analysis, and has a wide range of applications, meets the needs of oil product analysis, has strong practical application value, and solves the problem that the structure of Fischer-Tropsch oil is difficult to accurately analyze in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of oil analysis, and in particular to a method for analyzing the molecular structure of Fischer-Tropsch oil based on the combination of simulated distillation and nuclear magnetic resonance. Background Art

[0002] Although today's society is moving towards green and low-carbon development, its dependence on petroleum products is still high. However, during the processing and use of crude oil, a large amount of SO x and NO x and other toxic and harmful gases, and a certain amount of environmentally unfriendly aromatic compounds will inevitably remain in the final product oil. Fischer-Tropsch oil is a liquid hydrocarbon synthesized by the Fischer-Tropsch synthesis method using a mixture of carbon monoxide and hydrogen under catalytic conditions. The mixture of carbon monoxide and hydrogen usually comes from coal, natural gas or biomass. Due to the synthesis method of Fischer-Tropsch oil, compared with petroleum, it is a saturated straight-chain alkane without sulfur or nitrogen. Its composition is single, its physical and chemical properties are excellent, and it meets the use requirements of increasingly stringent environmental regulations. Therefore, Fischer-Tropsch oil is widely used in various industries in society. For example, new Fischer-Tropsch based lubricant base oil is prepared by hydroisomerization of Fischer-Tropsch wax. However, the composition and structure of Fischer-Tropsch based lubricant base oil are complex, among which different alkane structures, normal isomer ratio, number of branches and other factors will have a crucial impact on key indicators such as flash point, viscosity, and pour point of lubricant base oil products. In order to improve the safety of Fischer-Tropsch based lubricant base oil in use, it is very important to accurately understand its specific composition and structure.

[0003] Existing methods for analyzing oil structure primarily include gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), and mass spectrometry (MS). Because Fischer-Tropsch lubricant base oils are primarily composed of long-chain alkanes with carbon numbers ranging from 16 to 60, which have a high boiling point, using GC-MS to analyze oils presents sampling difficulties. Furthermore, Fischer-Tropsch lubricant base oils are non-polar compounds with few functional groups, making them difficult to effectively separate using liquid chromatography. Furthermore, Fischer-Tropsch oils have a complex composition, with tens of thousands of normal isomers, making it difficult to accurately analyze their composition and structure using mass spectrometry.

[0004] Therefore, it is difficult to accurately obtain the structural details of Fischer-Tropsch oil using existing analytical techniques. Summary of the Invention

[0005] In view of this, the present invention provides a method for analyzing the molecular structure of Fischer-Tropsch oil based on the combination of simulated distillation and nuclear magnetic resonance. The method provided by the present invention can obtain the structural details of Fischer-Tropsch oil with high accuracy and fast analysis speed.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] A method for analyzing the molecular structure of Fischer-Tropsch oil based on the combination of simulated distillation and nuclear magnetic resonance comprises the following steps:

[0008] The Fischer-Tropsch oil sample is subjected to simulated distillation, and a simplified carbon number distribution of the Fischer-Tropsch oil sample is obtained according to the distillation range; normal alkanes are used as standard samples, and the high-temperature simulated calculated chain length of the Fischer-Tropsch oil sample is calculated according to the simplified carbon number distribution;

[0009] The Fischer-Tropsch oil samples were analyzed by nuclear magnetic resonance using deuterated chloroform as solvent. 1 H-NMR spectra and 13 C-NMR spectrum; according to 1 H-NMR spectrum, calculating the ratio of primary, secondary and tertiary hydrogens in the Fischer-Tropsch oil sample by characteristic peak intensity or area integration; and calculating the degree of branching of the Fischer-Tropsch oil sample based on the ratio of primary, secondary and tertiary hydrogens;

[0010] Will 13 The chemical shift characteristic areas in the C-NMR spectrum are integrated and normalized to calculate the terminal methyl content, branched methyl content, normal alkane content and isoalkane content of the Fischer-Tropsch oil sample; the number of branch nodes and the number of branches of the Fischer-Tropsch oil are calculated based on the degree of branching, terminal methyl content and branched methyl content.

[0011] Preferably, the method for obtaining the simplified carbon number distribution includes: obtaining the percentage of each carbon number according to the distillation range of the Fischer-Tropsch oil sample and dividing the carbon number intervals, calculating the representative carbon number and its content according to the most depositable carbon number in each interval, and drawing the simplified carbon number distribution of the Fischer-Tropsch oil sample according to the representative carbon number and its content.

[0012] Preferably, the ratio of primary, secondary and tertiary hydrogens in the Fischer-Tropsch oil sample is calculated according to Formula 1:

[0013] Primary hydrogen: secondary hydrogen: tertiary hydrogen = A (CH3) :A (CH2) :A (CH) Formula 1;

[0014] In formula 1: A (CH3) represent 1 The chemical shifts in the H-NMR spectrum are the area-integrated counts of primary hydrogens, A (CH2) represent 1 The chemical shift in the H-NMR spectrum is the area integral count of the parahydrogen. (CH) represent 1 Chemical shifts in H-NMR spectra are area-integrated counts at tertiary hydrogen.

[0015] Preferably, the nuclear magnetic resonance analysis further comprises testing to obtain DEPT 90° and DEPT 135° spectra of the Fischer-Tropsch oil sample; 13 The ratio of primary, secondary, tertiary and quaternary carbon in the Fischer-Tropsch oil sample was calculated by the characteristic peak intensity or area integration of C-NMR, DEPT 90° and DEPT 135° spectra, and the ratio of primary, secondary and tertiary hydrogen was obtained according to the ratio of primary, secondary, tertiary and quaternary carbon. 13 The ratio of primary, secondary and tertiary hydrogens obtained from C-NMR, DEPT 90° and DEPT 135° spectra is 1 The ratio of primary, secondary and tertiary hydrogen obtained from H-NMR spectrum was verified;

[0016] The ratio of primary, secondary, tertiary and quaternary carbons is calculated according to Formula 2:

[0017] Primary carbon: Secondary carbon: Tertiary carbon: Quaternary carbon = A (a) :A (b) :A (c) :A (d) Formula 2;

[0018] In formula 2: A (a) represent 13 The chemical shift in the C-NMR spectrum is the area integral value of the primary carbon. (b) represent 13 The chemical shift in the C-NMR spectrum is the area integral value of the secondary carbon. (c) represent 13 The chemical shift in the C-NMR spectrum is the area integral value of the tertiary carbon. (d) represent 13 The chemical shifts in the C-NMR spectrum are the area-integrated values ​​of the quaternary carbon.

[0019] Preferably, the degree of branching is calculated according to Formula 3:

[0020]

[0021] In formula 3: B I represents the degree of branching, A (CH3) represent 1 The chemical shift in the H-NMR spectrum is the area integral value of primary hydrogen; A (CH+CH2) represent 1 The chemical shifts in the H-NMR spectrum are the total area integrated values ​​of tertiary hydrogen and secondary hydrogen.

[0022] Preferably, the terminal methyl content is calculated according to Formula 4; the branched methyl content is calculated according to Formula 5:

[0023] P t =100[I a～b / IT ] Equation 4;

[0024] P b =100[I c～d / I T ] Equation 5;

[0025] In formulas 4 and 5: P t Indicates the terminal methyl content, expressed as a percentage; P b Indicates the branched methyl content, expressed as a percentage; I a～b express 13 The area integral value of the chemical shift interval corresponding to the terminal methyl group in the C-NMR spectrum; c～d express 13 The area integral value of the chemical shift interval corresponding to the methyl group located in the branched chain in the C-NMR spectrum; T express 13 The chemical shift in the C-NMR spectrum is the area integrated value from 0 to 50.

[0026] Preferably, the number of branch nodes is calculated by Formula 6:

[0027] Number of branch nodes = 2P b / P t Formula 6.

[0028] Preferably, the normal alkane content is calculated according to Formula 7, and the isoalkane content is calculated according to Formula 8:

[0029] P N =100[3I a+ I b～c ] / I T Formula 7;

[0030] P I =P N [I a～b -I a ] / I a Formula 8;

[0031] In formulas 7 and 8: P N is the normal alkane content, expressed as a percentage, P I is the isoparaffin content, expressed as a percentage; I a for 13 The area integral value corresponding to γ-CH3 in the straight-chain alkane in the C-NMR spectrum; b～c 13 -(CH2) in C-NMR spectrum n - the corresponding area integral value; I a～b for 13The area integral value corresponding to the terminal methyl group in the C-NMR spectrum; T express 13 The chemical shift in the C-NMR spectrum is the area integrated value from 0 to 50.

[0032] Preferably, when the branching degree of the Fischer-Tropsch oil sample is less than 15% and the carbon number distribution interval is greater than 40, the calculation formulas for the terminal methyl content, the branched methyl content, the normal alkane content and the isoalkane content are as shown in Formula 4-1, Formula 5-1, Formula 7-1 and Formula 8-1:

[0033] P t =100[I 10～15.8 / I T ] Formula 4-1;

[0034] P b =100[I 15.8～22.8 +I 28 ] / I T Formula 5-1;

[0035] P N =100[3I 32 +I 29.5～30.5 ] / I T Formula 7-1;

[0036] P I =P N [I 10～15.8 -I 32 ] / I 32 Formula 8-1;

[0037] When the branching degree of the Fischer-Tropsch oil sample is greater than 15% and the carbon number distribution interval is greater than 40, the calculation formulas for the terminal methyl content, the branched methyl content, the normal alkane content and the isoalkane content are as shown in Formula 4-2, Formula 5-2, Formula 7-2 and Formula 8-2:

[0038] P t =100[I 13.8～14.6 / I T ] Formula 4-2;

[0039] P b =100[I 19.2～22.8 ] / I T Formula 5-2;

[0040] P N =100[3(I 32 +I 28 )+I 29.2～30.7 +I 37.2 ] / I T Formula 7-2;

[0041] P I =P N [I 13.8～14.3 -I 32 ] / I 32 Formula 8-2;

[0042] When the degree of branching of the Fischer-Tropsch oil sample is greater than 15%, and the carbon number distribution interval is greater than 20 and less than 40, the calculation formulas for the terminal methyl content, the branched methyl content, the normal alkane content, and the isoalkane content are as shown in Formula 4-3, Formula 5-3, Formula 7-3, and Formula 8-3:

[0043] P t =100[I 10～15.8 / I T ] Formula 4-3;

[0044] P b =100[I 15.8～23.8 +I 28 ] / I T Formula 5-3;

[0045] P N =100[3I 32 +I 29.6～30.8 ] / I T Formula 7-3;

[0046] P I =P N [I 10～15.8 -I 32 ] / I 32 Formula 8-3;

[0047] When the branching degree of the Fischer-Tropsch oil sample is greater than 15% and the carbon number distribution interval is less than 20, the calculation formulas for the terminal methyl content, the branched methyl content, the normal alkane content and the isoalkane content are as shown in Formula 4-4, Formula 5-4, Formula 7-4 and Formula 8-4:

[0048] P t =100[I 10～15.8 / I T ] Formula 4-4;

[0049] P b =100[I 15.8～21.8 +I 28 ] / I T Formula 5-4;

[0050] P N =100[3I 32 +I 29.0～31.0 ] / I T Formula 7-4;

[0051] P I =P N [I 10～15.8 -I 32 ] / I 32 Formula 8-4.

[0052] Preferably, after obtaining the normal alkane content and the isoalkane content, the method further includes calculating the average alkyl chain length of the Fischer-Tropsch oil sample according to the normal alkane content and the isoalkane content, and verifying the high-temperature simulation calculated chain length according to the calculated average alkyl chain length; the average alkyl chain length is calculated according to Formula 9 to Formula 10:

[0053] C P =P N +P I Formula 9;

[0054] L=2(C P / P t ) Equation 10;

[0055] In formulas 9 and 10: C p represents the sum of normal paraffin and isoparaffin contents; L represents the average alkyl chain length.

[0056] The present invention provides a method for analyzing the molecular structure of Fischer-Tropsch oil based on the combination of simulated distillation and nuclear magnetic resonance, comprising the following steps: performing simulated distillation on a Fischer-Tropsch oil sample to obtain a simplified carbon number distribution of the Fischer-Tropsch oil sample according to the distillation range; using normal alkanes as standard samples, calculating the high-temperature simulated calculated chain length of the Fischer-Tropsch oil sample according to the simplified carbon number distribution; performing nuclear magnetic resonance analysis using deuterated chloroform as a solvent to obtain the high-temperature simulated calculated chain length of the Fischer-Tropsch oil sample. 1 H-NMR spectra and 13 C-NMR spectrum; according to 1 The ratio of primary, secondary and tertiary hydrogens in the Fischer-Tropsch oil sample is calculated by H-NMR spectrum through characteristic peak intensity or area integration; the degree of branching of the Fischer-Tropsch oil sample is calculated based on the ratio of primary, secondary and tertiary hydrogens; 13 The chemical shift characteristic regions in the C-NMR spectrum are integrated and normalized to calculate the terminal methyl content, branched methyl content, normal alkane content, and isoalkane content of the Fischer-Tropsch oil sample; the number of branched nodes and the number of branches of the Fischer-Tropsch oil are calculated based on the degree of branching, terminal methyl content, and branched methyl content. In the art, simulated distillation alone cannot analyze the structural details of mixed hydrocarbons, and the peaks of the Fischer-Tropsch oil nuclear magnetic resonance spectrum are complex and difficult to distinguish. The present invention combines two commonly used methods to greatly enhance the accuracy and speed of analysis and greatly reduce the workload of analysts and testers.

[0057] The method provided by the present invention is suitable for analyzing oil products produced by the Fischer-Tropsch process, including long-chain oil products (C10 ~C 60 ) and Fischer-Tropsch base oil lubricants made from hydrogenated isomerization of Fischer-Tropsch wax are friendly to the detection of high-boiling point substances (boiling point is above 520°C), have a wide range of applications, and the process meets the needs of oil analysis. It has strong practical application value, can greatly reduce the labor intensity of analysts and testers, and solves the problem that the structure of Fischer-Tropsch oil is difficult to accurately analyze in the existing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 A flow chart of the method for analyzing the molecular structure of Fischer-Tropsch oil provided by the present invention;

[0059] Figure 2 This is the distillation diagram of oil sample 2;

[0060] Figure 3 is the carbon number distribution diagram of oil sample 2;

[0061] Figure 4 For oil sample 2 1 H-NMR spectrum;

[0062] Figure 5 For oil sample 2 13 C-NMR spectrum;

[0063] Figure 6 DEPT 90° spectrum of oil sample 2;

[0064] Figure 7 DEPT 135° spectrum of oil sample 2;

[0065] Figure 8 This is the distillation diagram of oil sample 1;

[0066] Figure 9 is the carbon number distribution diagram of oil sample 1;

[0067] Figure 10 For oil sample 1 1 H-NMR spectrum;

[0068] Figure 11 For oil sample 1 13 C-NMR spectrum;

[0069] Figure 12 DEPT 90° spectrum of oil sample 1;

[0070] Figure 13 DEPT 135° spectrum of oil sample 1;

[0071] Figure 14 This is the distillation diagram of oil sample 3;

[0072] Figure 15 is the carbon number distribution diagram of oil sample 3;

[0073] Figure 16 For oil sample 3 1 H-NMR spectrum;

[0074] Figure 17 For oil sample 3 13 C-NMR spectrum;

[0075] Figure 18 DEPT 90° spectrum of oil sample 3;

[0076] Figure 19 DEPT 135° spectrum of oil sample 3;

[0077] Figure 20 For oil sample 4 1 H-NMR spectrum;

[0078] Figure 21 For oil sample 4 13 C-NMR spectrum;

[0079] Figure 22 DEPT 90° spectrum of oil sample 4;

[0080] Figure 23 This is the DEPT 135° spectrum of oil sample 4. DETAILED DESCRIPTION

[0081] The present invention provides a method for analyzing the molecular structure of Fischer-Tropsch oil based on the combination of simulated distillation and nuclear magnetic resonance, comprising the following steps:

[0082] The Fischer-Tropsch oil sample is subjected to simulated distillation, and a simplified carbon number distribution of the Fischer-Tropsch oil sample is obtained according to the distillation range; normal alkanes are used as standard samples, and the high-temperature simulated calculated chain length of the Fischer-Tropsch oil sample is calculated according to the simplified carbon number distribution;

[0083] The Fischer-Tropsch oil samples were analyzed by nuclear magnetic resonance using deuterated chloroform as solvent. 1 H-NMR spectra and 13 C-NMR spectrum; according to 1 H-NMR spectrum, calculating the ratio of primary, secondary and tertiary hydrogens in the Fischer-Tropsch oil sample by characteristic peak intensity or area integration; and calculating the degree of branching of the Fischer-Tropsch oil sample based on the ratio of primary, secondary and tertiary hydrogens;

[0084] Will 13 The chemical shift characteristic areas in the C-NMR spectrum are integrated and normalized to calculate the terminal methyl content, branched methyl content, normal alkane content and isoalkane content of the Fischer-Tropsch oil sample; the number of branch nodes and the number of branches of the Fischer-Tropsch oil are calculated based on the degree of branching, terminal methyl content and branched methyl content.

[0085] The present invention simulates distillation of a Fischer-Tropsch oil sample and obtains the carbon number distribution of the Fischer-Tropsch oil sample based on the distillation range. In the present invention, the Fischer-Tropsch oil is preferably a long-chain oil product prepared by the Fischer-Tropsch process or a Fischer-Tropsch base oil lubricant prepared by hydroisomerization of Fischer-Tropsch wax; the carbon chain length of the long-chain oil product is preferably 10 to 60; the boiling point of the Fischer-Tropsch oil is above 520°C; the present invention has no special requirements for the simulated distillation method, and methods well known to those skilled in the art can be used.

[0086] In the present invention, the carbon number distribution of the Fischer-Tropsch oil sample is preferably a simplified carbon number distribution; the method for obtaining the simplified carbon number distribution preferably includes: obtaining the percentage of each carbon number according to the distillation range of the Fischer-Tropsch oil sample and dividing the carbon number intervals, calculating the representative carbon number and its content according to the most depositable carbon number in each interval, and drawing the simplified carbon number distribution of the Fischer-Tropsch oil sample according to the representative carbon number and its content.

[0087] After obtaining the carbon number distribution, the present invention uses normal alkanes as standard samples and calculates the high-temperature simulated chain length of the Fischer-Tropsch oil sample based on the simplified carbon number distribution. In the present invention, the normal alkane standard sample is preferably a normal alkane with a carbon number less than 100. In a specific embodiment of the present invention, it is preferred to directly use the standard sample provided by the manufacturer for the simulated distillation gas chromatograph. The high-temperature simulated chain length calculation method is shown in Formula 11:

[0088] L'=(N1×C1+N2×C2+N3×C3+……N n ×C n ) / 100 Formula 11;

[0089] In formula 11, N represents the carbon number in the carbon number distribution, and C represents the percentage of alkanes with carbon number N.

[0090] The high-temperature simulated chain length calculated by simulated distillation can be compared with the calculation results obtained by subsequent nuclear magnetic resonance testing to verify each other.

[0091] The present invention uses deuterated chloroform as solvent to perform nuclear magnetic resonance analysis to obtain the Fischer-Tropsch oil sample. 1 H-NMR spectra and 13 C-NMR spectrum; according to 1 The ratio of primary, secondary and tertiary hydrogen in the Fischer-Tropsch oil sample can be calculated by integrating the characteristic peak intensity or area from the H-NMR spectrum.

[0092] In the present invention, the ratio of primary, secondary and tertiary hydrogens in the Fischer-Tropsch oil sample is preferably calculated according to Formula 1:

[0093] Primary hydrogen: secondary hydrogen: tertiary hydrogen = A (CH3) :A (CH2) :A (CH) Formula 1;

[0094] In formula 1: A (CH3) represent 1 The chemical shift in the H-NMR spectrum is the area integral value of primary hydrogen, A (CH2) represent 1 The chemical shift in the H-NMR spectrum is the area integral value of the parahydrogen. (CH) represent 1 The chemical shifts in the H-NMR spectra are the area-integrated values ​​at the tertiary hydrogen sites.

[0095] In the present invention, the nuclear magnetic resonance analysis also includes testing to obtain DEPT 90° and DEPT135° spectra of the Fischer-Tropsch oil sample; according to 13 The ratio of primary, secondary, tertiary and quaternary carbon in the Fischer-Tropsch oil sample was calculated by C-NMR, DEPT 90° and DEPT 135° spectra through characteristic peak intensity or area integration, and the ratio of primary, secondary and tertiary hydrogen was obtained according to the ratio of primary, secondary, tertiary and quaternary carbon. 13 The ratio of primary, secondary and tertiary hydrogens obtained from C-NMR, DEPT 90° and DEPT 135° spectra is 1 The ratio of primary, secondary and tertiary hydrogens was verified by H-NMR spectra; the regions of primary, secondary and tertiary carbons were determined by DEPT 90° and DEPT 135° spectra, and then 13 Integration was performed on the C-NMR spectrum.

[0096] In the present invention, the ratio of primary, secondary, tertiary and quaternary carbons is preferably calculated according to Formula 2:

[0097] Primary carbon: Secondary carbon: Tertiary carbon: Quaternary carbon = A (a) :A (b) :A (c) :A (d) Formula 2;

[0098] In formula 2: A (a) represent 13 The chemical shift in the C-NMR spectrum is the area integral value of the primary carbon. (b) represent 13 The chemical shift in the C-NMR spectrum is the area integral value of the secondary carbon. (c) represent 13 The chemical shift in the C-NMR spectrum is the area integral value of the tertiary carbon. (d) represent 13 The chemical shifts in the C-NMR spectrum are the area-integrated values ​​of the quaternary carbon.

[0099] In the present invention, the degree of branching is preferably calculated according to Formula 3:

[0100]

[0101] In formula 3: B I represents the degree of branching, A (CH3) represent 1 The chemical shift in the H-NMR spectrum is the area integral value of primary hydrogen; A (CH+CH2) represent 1 The chemical shifts in the H-NMR spectrum are the total area integrated values ​​of tertiary hydrogen and secondary hydrogen.

[0102] get 13 After the C-NMR spectrum, the present invention will 13 The chemical shift characteristic regions in the C-NMR spectrum were integrated and normalized to calculate the terminal methyl content, branched methyl content, normal alkane content, and isoalkane content of the Fischer-Tropsch oil sample.

[0103] In the present invention, the terminal methyl content is preferably calculated according to Formula 4; the branched methyl content is preferably calculated according to Formula 5:

[0104] P t =100[I a～b / I T ] Equation 4;

[0105] P b =100[I c～d / I T ] Equation 5;

[0106] In formulas 4 and 5: P t Indicates the terminal methyl content, expressed as a percentage; P b Indicates the branched methyl content, expressed as a percentage; I a～b express 13 The area integral value of the chemical shift interval corresponding to the terminal methyl group in the C-NMR spectrum; c～d express 13 The area integral value of the chemical shift interval corresponding to the methyl group located in the branched chain in the C-NMR spectrum; T express 13 The chemical shift in the C-NMR spectrum is the area integral value from 0 to 50. c～d The subscripts c to d in the 13 The chemical shifts corresponding to all methyl groups located in the side chains in the C-NMR spectrum are not necessarily continuous and need to be determined according to the 13 C-NMR spectrum, for example, when the branching degree of the Fischer-Tropsch oil sample is less than 15% and the carbon number distribution interval is greater than 40, I 15.8～22.8 and I 28 The chemical shifts are all branched methyl groups, so they need to be calculated when performing area integration; other chemical shifts (including I a , Ib～c , I a～b The above situation also applies when determining (etc.), and will not be described in detail later.

[0107] In the present invention, the number of branch nodes is preferably calculated by Formula 6:

[0108] Number of branch nodes = 2P b / P t Formula 6.

[0109] In the present invention, the normal alkane content is preferably calculated according to Formula 7, and the isoalkane content is preferably calculated according to Formula 8:

[0110] P N =100[3I a+ I b～c ] / I T Formula 7;

[0111] P I =P N [I a～b -I a ] / I a Formula 8;

[0112] In formulas 7 and 8: P N is the normal alkane content, expressed as a percentage, P I is the isoparaffin content, expressed as a percentage; I a for 13 The area integral value corresponding to γ-CH3 in the straight-chain alkane in the C-NMR spectrum; b～c for 13 -(CH2) in C-NMR spectrum n - the corresponding area integral value; I a～b for 13 The area integral value corresponding to the terminal methyl group in the C-NMR spectrum; T express 13 The chemical shift in the C-NMR spectrum is the area integrated value from 0 to 50.

[0113] In the present invention, the I a～b , I c～d , I a , I b～c The chemical shift region (i.e., the values ​​of a~b, c~d, a and b~c) is preferably determined by ChemDraw simulation. The present invention determines the detailed P values ​​of the Fischer-Tropsch oil sample under the following four conditions through a large number of ChemDraw simulations. t 、P b 、P N 、P I The calculation formula is as follows:

[0114] In a specific embodiment of the present invention, different chemical shift regions are selected according to the degree of branching and carbon number distribution range of the Fischer-Tropsch oil sample. Specifically, when the degree of branching of the Fischer-Tropsch oil sample is less than 15% and the carbon number distribution range is greater than 40, the calculation formulas for the terminal methyl content, the branched methyl content, the normal alkane content and the isoalkane content are as shown in Formula 4-1, Formula 5-1, Formula 7-1 and Formula 8-1:

[0115] P t =100[I 10～15.8 / I T ] Formula 4-1;

[0116] P b =100[I 15.8～22.8 +I 28 ] / I T Formula 5-1;

[0117] P N =100[3I 32 +I 29.5～30.5 ] / I T Formula 7-1;

[0118] P I =P N [I 10～15.8 -I 32 ] / I 32 Formula 8-1;

[0119] When the branching degree of the Fischer-Tropsch oil sample is greater than 15% and the carbon number distribution interval is greater than 40, the calculation formulas for the terminal methyl content, the branched methyl content, the normal alkane content and the isoalkane content are as shown in Formula 4-2, Formula 5-2, Formula 7-2 and Formula 8-2:

[0120] P t =100[I 13.8～14.6 / I T ] Formula 4-2;

[0121] P b =100[I 19.2～22.8 ] / I T Formula 5-2;

[0122] P N =100[3(I 32 +I 28 )+I 29.2～30.7 +I 37.2 ] / I T Formula 7-2;

[0123] P I =P N[I 13.8～14.3 -I 32 ] / I 32 Formula 8-2;

[0124] When the degree of branching of the Fischer-Tropsch oil sample is greater than 15%, and the carbon number distribution interval is greater than 20 and less than 40, the calculation formulas for the terminal methyl content, the branched methyl content, the normal alkane content, and the isoalkane content are as shown in Formula 4-3, Formula 5-3, Formula 7-3, and Formula 8-3:

[0125] P t =100[I 10～15.8 / I T ] Formula 4-3;

[0126] P b =100[I 15.8～23.8 +I 28 ] / I T Formula 5-3;

[0127] P N =100[3I 32 +I 29.6～30.8 ] / I T Formula 7-3;

[0128] P I =P N [I 10～15.8 -I 32 ] / I 32 Formula 8-3;

[0129] When the branching degree of the Fischer-Tropsch oil sample is greater than 15% and the carbon number distribution interval is less than 20, the calculation formulas for the terminal methyl content, the branched methyl content, the normal alkane content and the isoalkane content are as shown in Formula 4-4, Formula 5-4, Formula 7-4 and Formula 8-4:

[0130] P t =100[I 10～15.8 / I T ] Formula 4-4;

[0131] P b =100[I 15.8～21.8 +I 28 ] / I T Formula 5-4;

[0132] P N =100[3I 32 +I 29.0～31.0 ] / I T Formula 7-4;

[0133] P I =P N [I10～15.8 -I 32 ] / I 32 Formula 8-4.

[0134] In the above formulas 4-1 to 8-4, IT represents 13 The chemical shift in the C-NMR spectrum is the area integral count at 0 to 50, and the number in the subscript of I represents 13 The range of chemical shift values ​​in C-NMR spectra

[0135] In the present invention, the isomerization degree and reaction site of the reaction during the preparation of Fischer-Tropsch oil can be obtained based on the terminal methyl content and the branched methyl content; the size of the branching degree can indicate the amount of branched methyl groups generated by isomerization, which can reflect the degree of isomerization reaction.

[0136] In the present invention, after obtaining the normal alkane content and the isoalkane content, the average alkyl chain length of the Fischer-Tropsch oil sample is calculated based on the normal alkane content and the isoalkane content, and the high-temperature simulation calculated chain length is verified based on the calculated average alkyl chain length (the error between the two calculation results is less than 5%, which is considered to meet the analytical calculation requirements); the average alkyl chain length is calculated according to Formula 9 to Formula 10:

[0137] C P =P N +P I Formula 9;

[0138] L=2(C P / P t ) Equation 10;

[0139] In formulas 9 and 10: C p represents the sum of normal paraffin and isoparaffin contents; L represents the average alkyl chain length.

[0140] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0141] Example 1

[0142] Four oil samples were tested and recorded as Oil Sample 1, Oil Sample 2, Oil Sample 3 and Oil Sample 4, among which Oil Sample 1 was Fischer-Tropsch wax raw material, Oil Sample 2 was Fischer-Tropsch based lubricant base oil made by hydrogenation and isomerization of Fischer-Tropsch wax, Oil Sample 3 was a refined and cut oil sample of Fischer-Tropsch based lubricant base oil, and Oil Sample 4 was an isomerized and cut oil sample of Fischer-Tropsch based lubricant base oil.

[0143] The following is the specific analysis process of oil sample 2:

[0144] according to Figure 1 The structural details of oil sample 2 are analyzed as follows:

[0145] (1) Perform simulated distillation on oil sample 2 to obtain a distillation range diagram, such as Figure 2 As shown, according to the distillation diagram, we can analyze and obtain a simplified carbon number distribution diagram, as shown in Figure 3 shown.

[0146] according to Figure 2 The carbon number distribution in the oil is used to calculate the high temperature simulation chain length L' of oil sample 2 according to formula 11:

[0147] L'=(N1*C1+N2*C2+N3*C3+……N n *C n ) / 100 Formula 11

[0148] After calculation, the actual average chain length of this sample is 30.4.

[0149] (2) Place oil sample 2 in a nuclear magnetic resonance tube and perform nuclear magnetic resonance testing using deuterated chloroform as solvent to obtain 1 H-NMR spectrum, 13 C-NMR spectrum, DEPT 90° and DEPT 135° spectra, the results are as follows Figures 4 to 7 As shown, according to Figure 4 Calculate the proportion of hydrogen at each level, according to Figures 5-7 The proportion of carbon at each level is calculated, and then the proportion of hydrogen at each level is calculated based on the proportion of carbon at each level. The two are verified, and the calculation results are as follows;

[0150] Primary hydrogen: secondary hydrogen: tertiary hydrogen = A (CH3) :A (CH2) :A (CH) =5.52:10.95:1

[0151] Where A (CH3) represent 1 The chemical shift in the H-NMR spectrum is the area integral count of primary hydrogen, the chemical shift value is 0.8~1.0, and the integral result is 5.52; A (CH2) represent 1 The chemical shift in the H-NMR spectrum is the area integral count of the parahydrogen, the chemical shift value is 1.2 to 1.45, and the integral result is 10.95; A (CH) represent 1 The chemical shift in the H-NMR spectrum is the area integral count at the tertiary hydrogen, the chemical shift value is 1.0-1.2, and the integral result is 1.

[0152] Primary carbon: Secondary carbon: Tertiary carbon = A (a):A (b) :A (c) =1.38:5.22:1

[0153] Where A (a) represent 13 The chemical shift in the C-NMR spectrum is the area integral of the primary carbon, the chemical shift value ranges from 10 to 21, and the integral result is 1.38; A (b) represent 13 The chemical shift in the C-NMR spectrum is the area integral of the secondary carbon, the chemical shift values ​​are 22-31 and 36-40, and the integral result is 5.22; A (c) represent 13 The chemical shift in the C-NMR spectrum is the area integral of the tertiary carbon, with a chemical shift value of 31 to 35, and an integral result of 1. The tertiary carbon content in oil sample 2 is extremely small and can be ignored.

[0154] The hydrogen ratio of each level calculated based on the carbon ratio of each level is:

[0155] Primary hydrogen: secondary hydrogen: tertiary hydrogen = 4.14:10.44:1

[0156] (3) Calculate the degree of branching (B) based on the ratio of primary, secondary and tertiary hydrogens. I ):

[0157]

[0158] Where A (CH3) represent 1 The chemical shift in the H-NMR spectrum is the area integral count of primary hydrogen, the chemical shift value is 0.8~1.0, and the integral result is 5.52; A (CH+CH2) represent 1 The chemical shifts in the H-NMR spectrum are the area-integrated counts of the tertiary and secondary hydrogen atoms, with a chemical shift range of 1.0 to 2.0, resulting in an integral of 13.14. The degree of branching indicates the number of branched methyl groups formed by isomerization and reflects the extent of the isomerization reaction.

[0159] The branching degree of oil sample 2 was calculated to be 28.01%.

[0160] (4) According to Figure 2 、 Figure 3 The carbon number distribution and the calculated branching degree are used to select the terminal methyl content (P t ) and the content of branched methyl groups (P b ) is calculated as follows.

[0161] P t =100[I 13.8～14.6 / I T ]

[0162] P b =100[I 19.2～22.8 ] / I T

[0163] Where I T represents the area integral counts at chemical shifts from 0 to 50, I 13.8～14.6 represents the area integrated counts at chemical shifts of 13.8 to 14.6, I 13.8～14.6 and I 19.2～22.8 The integration results are shown in Table 1; the terminal methyl group and the branched methyl group content can show the isomerization degree and reaction site of the reaction.

[0164] Calculation showed that the terminal methyl content of oil sample 2 was 6.83% and the branched methyl content was 15.22%.

[0165] (5) According to Figure 2 、 Figure 3 The carbon number distribution and the calculated degree of branching are used to select the normal alkane carbon content (P N ), isoparaffin carbon content (P I ) is calculated as follows:

[0166] P N =100[3(I 32 +I 28 )+I 29.3～30.7 +I 37.2 ] / I T

[0167] P I =P N [I 13.8～14.6 -I 32 ] / I 32

[0168] Calculation showed that the normal hydrocarbon content of oil sample 2 was 51.13% and the isohydrocarbon content was 49.12%.

[0169] (6) The number of branch nodes is calculated by the following formula:

[0170] Number of branch nodes = 2P b / P t

[0171] After calculation, the number of branch nodes of oil sample 2 is 4.46.

[0172] (7) Calculation of average alkyl chain length A uniform chain length can be selected to replace the entire oil for structural analysis. The average alkyl chain length L is calculated by the following formula:

[0173] C P =P N +P I

[0174] L=2(C P / P t )

[0175] After calculation, the average alkyl chain length of oil sample 2 is 29.4, which is within 3.28% of the actual average chain length of 30.4, meeting the requirements of analysis and calculation.

[0176] The analysis and calculation results of oil sample 2 in this example are summarized in Table 1.

[0177] Table 1 Detailed analysis results of the structure of Fischer-Tropsch lubricant base oil

[0178]

[0179]

[0180] The analysis process of oil samples 1, 3 and 4 was similar to that of oil sample 2, except that different P was selected based on the carbon number distribution and branching degree. t 、P b 、P N 、P I The calculation formula is as follows. Among them, the distillation diagram of oil sample 1 is as follows Figure 8 As shown, the simplified carbon number distribution diagram is as follows Figure 9 As shown, 1 H-NMR spectrum, 13 C-NMR spectrum, DEPT 90° and DEPT 135° spectra are as follows Figures 10-13 As shown; the distillation diagram of oil sample 3 is as follows Figure 14 As shown, the simplified carbon number distribution diagram is as follows Figure 15 As shown, 1 H-NMR spectrum, 13 C-NMR spectrum, DEPT 90° and DEPT 135° spectra are as follows Figures 16-19 As shown in the figure, the distillation range of oil sample 4 is 20℃, the theoretical carbon number interval is less than 5, and the 1 H-NMR spectrum, 13 C-NMR spectrum, DEPT 90° and DEPT 135° spectra are as follows Figures 20-23 shown.

[0181] The formula selection for different oil samples is shown in Table 2:

[0182] Table 2 Structural formula selection for different oil sample types

[0183]

[0184]

[0185] The analysis results of oil samples 1, 3, and 4 are shown in Table 3.

[0186] Table 3 Analysis results of oil samples 1, 3 and 4

[0187]

[0188] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for analyzing the molecular structure of Fischer-Tropsch oil based on the combination of simulated distillation and nuclear magnetic resonance, characterized in that: The following steps are involved: The Fischer-Tropsch oil sample is subjected to simulated distillation, and a simplified carbon number distribution of the Fischer-Tropsch oil sample is obtained according to the distillation range; normal alkanes are used as standard samples, and the high-temperature simulated calculated chain length of the Fischer-Tropsch oil sample is calculated according to the simplified carbon number distribution; The Fischer-Tropsch oil samples were analyzed by nuclear magnetic resonance using deuterated chloroform as solvent. 1 H-NMR spectra and 13 C-NMR spectrum; according to 1 H-NMR spectrum, calculating the ratio of primary, secondary and tertiary hydrogens in the Fischer-Tropsch oil sample by characteristic peak intensity or area integration; and calculating the degree of branching of the Fischer-Tropsch oil sample based on the ratio of primary, secondary and tertiary hydrogens; Will 13 The chemical shift characteristic areas in the C-NMR spectrum are integrated and normalized to calculate the terminal methyl content, branched methyl content, normal alkane content and isoalkane content of the Fischer-Tropsch oil sample; the number of branch nodes and the number of branches of the Fischer-Tropsch oil are calculated based on the degree of branching, terminal methyl content and branched methyl content.

2. The method according to claim 1, characterized in that The method for obtaining the simplified carbon number distribution includes: obtaining the percentage of each carbon number according to the distillation range of the Fischer-Tropsch oil sample and dividing the carbon number intervals, calculating the representative carbon number and its content according to the maximum depositable carbon number in each interval, and drawing the simplified carbon number distribution of the Fischer-Tropsch oil sample according to the representative carbon number and its content.

3. The method according to claim 1, characterized in that The ratio of primary, secondary and tertiary hydrogens in the Fischer-Tropsch oil sample is calculated according to Formula 1: In formula 1: represent 1 The chemical shift in the H-NMR spectrum is the area integral value of primary hydrogen. represent 1 The chemical shift in the H-NMR spectrum is the area integral value of the parahydrogen. (CH) represent 1 The chemical shifts in the H-NMR spectra are the area-integrated values ​​at the tertiary hydrogen sites.

4. The method according to claim 1, wherein The nuclear magnetic resonance analysis also includes testing to obtain DEPT 90° and DEPT 135° spectra of the Fischer-Tropsch oil sample; 13 The ratio of primary, secondary, tertiary and quaternary carbon in the Fischer-Tropsch oil sample was calculated by C-NMR, DEPT 90° and DEPT 135° spectra through characteristic peak intensity or area integration, and the ratio of primary, secondary and tertiary hydrogen was obtained according to the ratio of primary, secondary, tertiary and quaternary carbon. 13 The ratio of primary, secondary and tertiary hydrogens obtained from C-NMR, DEPT 90° and DEPT 135° spectra is 1 The ratio of primary, secondary and tertiary hydrogen obtained from H-NMR spectrum was verified; The ratio of primary, secondary, tertiary and quaternary carbons is calculated according to Formula 2: Primary carbon: Secondary carbon: Tertiary carbon: Quaternary carbon = A (a) :A (b) :A (c) :A (d) Formula 2; In formula 2: A (a) represent 13 The chemical shift in the C-NMR spectrum is the area integral value of the primary carbon. (b) represent 13 The chemical shift in the C-NMR spectrum is the area integral value of the secondary carbon. (c) represent 13 The chemical shift in the C-NMR spectrum is the area integral value of the tertiary carbon. (d) represent 13 The chemical shifts in the C-NMR spectrum are the area-integrated values ​​of the quaternary carbon.

5. The method according to claim 1, wherein The degree of branching is calculated according to Formula 3: In formula 3: B I represents the degree of branching, represent 1 The chemical shifts in the H-NMR spectra are the area-integrated values ​​of primary hydrogen; represent 1 The chemical shifts in the H-NMR spectrum are the total area integrated values ​​of tertiary hydrogen and secondary hydrogen.

6. The method according to claim 1, characterized in that The terminal methyl content is calculated according to Formula 4; the branched methyl content is calculated according to Formula 5: P t =100[I a～b / I T ] Formula 4; P b =100[I c～d / I T ] Formula 5; In formulas 4 and 5: P t Indicates the terminal methyl content, expressed as a percentage; P b Indicates the branched methyl content, expressed as a percentage; I a～b express 13 The area integral value of the chemical shift interval corresponding to the terminal methyl group in the C-NMR spectrum; c～d express 13 The area integral value of the chemical shift interval corresponding to the methyl group located in the branched chain in the C-NMR spectrum; T express 13 The chemical shift in the C-NMR spectrum is the area integrated value from 0 to 50.

7. The method according to claim 6, characterized in that The number of branch nodes is calculated by Formula 6: Number of branch nodes = 2P b / P t Formula 6.

8. The method according to claim 1, characterized in that The normal alkane content is calculated according to Formula 7, and the isoalkane content is calculated according to Formula 8: P N = 100[3I a+ I b～c ] / I T Formula 7; P I = P N [I a～b - I a / I a Equation 8; In formulas 7 and 8: P N is the normal alkane content, expressed as a percentage, P I is the isoparaffin content, expressed as a percentage; I a for 13 The area integral value corresponding to γ-CH3 in the straight-chain alkane in the C-NMR spectrum; b～c 13 -(CH2) in C-NMR spectrum n - the corresponding area integral value; I a～b for 13 The area integral value corresponding to the terminal methyl group in the C-NMR spectrum; T express 13 The chemical shift in the C-NMR spectrum is the area integrated value from 0 to 50.

9. The method according to claim 1, 6 or 8, characterized in that When the branching degree of the Fischer-Tropsch oil sample is less than 15% and the carbon number distribution interval is greater than 40, the calculation formulas for the terminal methyl content, the branched methyl content, the normal alkane content and the isoalkane content are as shown in Formula 4-1, Formula 5-1, Formula 7-1 and Formula 8-1: P t = 100[I 10～15.8 / I T ] Formula 4-1; P b =100[I 15.8～22.8 +I 28 ] / I T Formula 5-1; P N = 100[3I 32 +I 29.5～30.5 ] / I T Formula 7-1; P I = P N [I 10～15.8 - I 32 / I 32 Equation 8-1; When the branching degree of the Fischer-Tropsch oil sample is greater than 15% and the carbon number distribution interval is greater than 40, the calculation formulas for the terminal methyl content, the branched methyl content, the normal alkane content and the isoalkane content are as shown in Formula 4-2, Formula 5-2, Formula 7-2 and Formula 8-2: P t =100[I 13.8～14.6 / I T ] Formula 4-2; P b = 100[I 19.2～22,8 ] / I T Formula 5-2; P N = 100[3(I 32 + I 28 ) + I 29.2～30.7 + I 37.2 / I T Equation 7-2; P I = P N [I 13.8～14.6 - I 32 / I 32 Equation 8-2; When the degree of branching of the Fischer-Tropsch oil sample is greater than 15%, and the carbon number distribution interval is greater than 20 and less than 40, the calculation formulas for the terminal methyl content, the branched methyl content, the normal alkane content, and the isoalkane content are as shown in Formula 4-3, Formula 5-3, Formula 7-3, and Formula 8-3: P t =100[I 10～15.8 / I T ] Formula 4-3; P b =100[I 15.8～23.8 +I 28 ] / I T Formula 5-3; P N = 100[3I 32 +I 29.6～30.8 ] / I T Formula 7-3; P I = P N [I 10～15.8 I 32 / I 32 Equation 8-3; When the branching degree of the Fischer-Tropsch oil sample is greater than 15% and the carbon number distribution interval is less than 20, the calculation formulas for the terminal methyl content, the branched methyl content, the normal alkane content and the isoalkane content are as shown in Formula 4-4, Formula 5-4, Formula 7-4 and Formula 8-4: P t =100[I 10～15.8 / I T ] Formula 4-4; P b =100[I 15.8～21.8 +I 28 ] / I T Formula 5-4; P N = 100[3I 32 +I 29.0～31.0 ] / I T Formula 7-4; P I = P N [I 10～15.8 - I 32 / I 32 Equation 8-4.

10. The method according to claim 9, characterized in that After obtaining the normal alkane content and the isoalkane content, the method further includes calculating the average alkyl chain length of the Fischer-Tropsch oil sample based on the normal alkane content and the isoalkane content, and verifying the high-temperature simulation calculated chain length based on the calculated average alkyl chain length; the average alkyl chain length is calculated according to Formula 9 to Formula 10: C P =P N +P I Formula 9; L=2(C P / P t ) Equation 10; In formulas 9 and 10: C p represents the sum of normal paraffin and isoparaffin contents; L represents the average alkyl chain length.

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