A method for separating normal alkanes from a petroleum geologic sample

Abstract

The application discloses a method for separating normal alkanes from a petroleum geological sample. The method separates saturated hydrocarbon components in the petroleum geological sample by using isohexane, adsorbs normal alkanes in the saturated hydrocarbon components by using a molecular sieve, and desorbs the normal alkanes adsorbed by the molecular sieve by using dichloromethane. The method for separating normal alkanes can effectively avoid loss of low-carbon-number and low-boiling-point compounds caused by sample concentration, and can more safely, efficiently and integrally obtain normal alkanes, isomeric alkanes and naphthenes in the sample. Meanwhile, the method avoids additional organic solvent extraction operation after the molecular sieve is dissolved by using hydrogen fluoride acid, and sample loss caused by the operation.

Description

Technical Field

[0001] This invention relates to a method for separating n-alkanes from petroleum geological samples. Background Technology

[0002] Biomarker compounds (such as steranes, hopanes, and acyclic isoprene) and abiotic marker compounds (such as n-alkanes and monomethyl isoalkanes) in the saturated hydrocarbon components of petroleum geological samples have important phasing significance, especially in the study of paleosedimentary environments, paleoclimates, paleobiota, the degree of thermal evolution of organic matter, and hydrocarbon migration and accumulation.

[0003] Due to limitations in current equipment and detection capabilities, co-escape of compounds frequently occurs, thus affecting the application of molecular geochemical methods in paleoecology, paleoenvironment, and oil source correlation. Firstly, limited by chromatographic (GC) resolution, n-alkanes co-escape with other types of alkanes in some chromatographic and chromatographic-mass spectrometric (GC-MS) analyses. This not only affects compound identification but also severely distorts quantitative and semi-quantitative organic geochemical indicators, leading to incorrect judgments. Furthermore, when using chromatographic isotope ratio mass spectrometry (GC-irMS) to analyze the carbon isotopes of saturated hydrocarbon components in petroleum geological samples, the separation of different compounds is extremely poor. The isotopic values ​​of a single peak often represent a combined response to isotopes of n-alkanes, isoalkanes, and even cycloalkanes (Ellis and Fincannon, 1998; Grice et al., 2008), resulting in significant isotopic distortion. Furthermore, when detecting certain low-concentration compounds, such as samples with extremely low levels of specific biomarker compounds, even with selected ion monitoring (SIM), the instrument's detection limit remains higher than the substance's concentration, thus limiting the analysis. In full scan mode, excessively large concentration differences between compounds (such as the difference between normal alkanes and biomarker compounds) severely distort the detection of low-concentration compounds. Given these circumstances, it is necessary to separate normal alkanes from other compounds (isoalkanes and cycloalkanes) in the saturated hydrocarbon fraction of petroleum geological samples to meet analytical requirements.

[0004] Currently, methods for separating n-alkanes from saturated hydrocarbon components in petroleum geological samples can be broadly classified into two types: molecular sieve methods and urea complexation methods. In the molecular sieve technology sequence, previous methods used... Molecular sieves and SAPO-11 molecular sieve methods are used to produce low-carbon n-alkanes ( <C 14The ZSM-5 molecular sieve method suffers from low (or complete) recovery rates and significant loss of isoparaffins (such as pterane and phytane), failing to fully address the recovery issues of n-alkanes and other alkanes (isoparaffins and cycloalkanes). It places high demands on the pressure resistance of the pressurization equipment and experimental setup, and cannot perform batch sample separation operations. More importantly, after complexing n-alkanes with various molecular sieves, hydrofluoric acid is needed to dissolve and break the molecular sieves, followed by extraction of the n-alkanes using organic solvents. Existing methods for desorbing n-alkanes from molecular sieves are complex, time-consuming, and have stringent experimental environmental requirements, posing safety hazards. In the urea technology series, the recovery rates of alkanes with different carbon number ranges vary greatly due to complexation temperature, time, solvent type, and urea dosage. Additional dehydration and multiple concentration operations further complicate this method.

[0005] There are currently many types of molecular sieves, such as type, type, Type ASM-5, SAPO, and Mordenite, etc. (Ellis and Fincannon, 1998; Grice et al., 2008; Invention Patent CN 103869027B). Molecular sieves are the most common, have been industrially produced for many years, and are readily available. Nevertheless, existing methods based on… The separation effect of molecular sieve-based n-alkane separation methods is still not satisfactory. Summary of the Invention

[0006] To at least partially address the aforementioned technical problems in the existing technology, embodiments of the present invention provide an efficient and convenient method for separating n-alkanes from petroleum geological samples, using isohexane, The use of molecular sieves and dichloromethane enables safer, more stable, higher recovery rates, and more convenient and faster separation operations, making the acquisition of n-alkanes, isoalkanes, and cycloalkanes more efficient and complete.

[0007] As one aspect of the present invention, a method for separating n-alkanes from petroleum geological samples is provided, the method comprising: S1. wetting a chromatography column with silica gel as the stationary phase with isohexane, and using isohexane as the eluent to perform column chromatography separation on the petroleum geological sample to obtain an eluent solution containing saturated hydrocarbon components.

[0008] By adopting the above technical solution, saturated hydrocarbon components in petroleum geological samples can be effectively separated, thus avoiding the solvent conversion caused by using n-alkanes (such as n-hexane and n-pentane) as the eluent when separating n-alkanes in petroleum geological samples using conventional methods, which would otherwise result in the loss of low carbon number and low boiling point compounds.

[0009] In one or more possible embodiments, the method further includes: S2. The molecular sieve is placed in the elution solution containing saturated hydrocarbon components obtained in S1 to pre-adsorb the n-alkanes in the elution solution containing saturated hydrocarbon components obtained in S1, thereby obtaining a solution adsorbed with n-alkanes. Molecular sieve and elution solution containing saturated hydrocarbon components after pre-adsorption.

[0010] In one or more possible embodiments, the method further includes: S3. taking the sample obtained in S2 with adsorbed n-alkane... The molecular sieve and the pre-adsorbed elution solution containing saturated hydrocarbon components were transferred to a... In a chromatography column with molecular sieves as the stationary phase, elution with isohexane yields a product containing adsorbed n-alkanes. Molecular sieves and elution products, wherein the elution products are a mixed solution of isoalkanes and cycloalkanes.

[0011] In one or more possible embodiments, the method further includes: S4. reacting the n-alkane-adsorbed material obtained in S3 with dichloromethane. Molecular sieve ultrasonic extraction was used to obtain a solution of n-alkane.

[0012] In one or more possible embodiments, the chromatography column is a quartz glass column with an inner diameter of 13 mm and a length greater than 60 mm.

[0013] It should be noted that the chromatography column of the present invention can be any size chromatography column. When different chromatography columns are selected, the amounts of the corresponding reagents in S1 to S4 can be adjusted accordingly. In any embodiment of the present invention, the chromatography column is preferably a quartz glass column with an inner diameter of 13 mm and a length greater than 60 mm, and the amounts of the corresponding reagents in S1 to S4 are also adapted accordingly.

[0014] In one or more possible embodiments, the chromatography silica gel is activated chromatography silica gel, and the activation of the chromatography silica gel includes:

[0015] The silica gel for chromatography was dried at 150°C for 12 hours under vacuum and then cooled to room temperature before use.

[0016] By adopting the above technical solution, the water adsorbed in the silica gel can be effectively removed, thereby improving the silica gel's fixation ability during the chemical separation process.

[0017] In one or more possible embodiments, the ratio of the chromatography silica gel, the petroleum geological sample, and the eluent is 2g:10mg:5ml.

[0018] It should be noted that, in this invention, based on the selection of the chromatography column specifications and the above-mentioned material usage ratio, the optimal effect of separating saturated hydrocarbon components from petroleum geological samples can be achieved.

[0019] In one or more possible embodiments, the petroleum geological sample is selected from one of black crude oil, rock extract, condensate oil, or light oil.

[0020] In one or more possible embodiments, in S2, the... The molecular sieve is placed in the elution solution containing saturated hydrocarbon components obtained in S1 to pre-adsorb the n-alkanes in the elution solution containing saturated hydrocarbon components obtained in S1, thereby obtaining a solution adsorbed with n-alkanes. Molecular sieves and pre-adsorbed elution solutions containing saturated hydrocarbon components include:

[0021] In a vacuum, Molecular sieves were dried at 150℃ for 12 hours and then cooled to room temperature to obtain activated molecular sieves. Molecular sieves;

[0022] Activated The molecular sieve was placed in the elution solution containing saturated hydrocarbon components obtained in S1, ultrasonically vibrated for 20 min, and then refrigerated for 12 h to pre-adsorb the n-alkanes in the elution solution containing saturated hydrocarbon components obtained in S1, thus obtaining a product with adsorbed n-alkanes. Molecular sieve and elution solution containing saturated hydrocarbon components after pre-adsorption.

[0023] By adopting the above technical solution, on the one hand, it can improve the performance of the project. Molecular sieve activation can effectively remove adsorbed water from the molecular sieve, thereby improving its fixation capacity during adsorption; on the other hand, it can also be activated under refrigeration conditions. Molecular sieves can stably adsorb n-alkanes from saturated hydrocarbon components to the maximum extent.

[0024] In one or more possible embodiments, in S2:

[0025] When the petroleum geological sample is black crude oil or rock extract, The amount of molecular sieve used is 4 mg;

[0026] When the petroleum geological sample is condensate oil or light oil, The amount of molecular sieve used is 6 mg.

[0027] To further adapt to the specifications of the chromatography column selected in this invention, the usage of some materials has been further optimized, such as:

[0028] In one or more possible embodiments, S3, in the chromatography column, the activated The amount of molecular sieve used is 2g.

[0029] By adopting the above technical solution, the activated state is controlled in S3. The amount of molecular sieve used is 2g, which can completely adsorb n-alkanes in saturated hydrocarbon components.

[0030] In one or more possible embodiments, S4, the amount of dichloromethane used is 20 ml.

[0031] By adopting the above technical solution, in S4, dichloromethane is selected to extract the molecular sieve adsorbed with n-alkanes. The strong polarity of dichloromethane can be used to completely desorb the n-alkanes adsorbed on the molecular sieve. At the same time, the reagent (i.e., dichloromethane) has a low boiling point and a fast subsequent volatilization and concentration rate. Compared with the use of hydrofluoric acid in the prior art, it is safe and easy to obtain.

[0032] In one or more possible embodiments, dichloromethane is used to treat the S3 sample containing adsorbed n-alkane. When performing ultrasonic extraction with molecular sieves, the extraction time for each extraction should be controlled at 30 minutes at room temperature, and this step needs to be repeated three times.

[0033] By adopting the above technical solution, on the one hand, by controlling the extraction time of a single extraction, it is possible to effectively prevent the increase in pressure inside the sample bottle caused by excessively high temperature in the ultrasonic cell; on the other hand, multiple extractions can completely desorb and adsorb n-alkanes.

[0034] The beneficial effects of the above-mentioned technical solutions provided in the embodiments of this application include at least the following:

[0035] This invention is based on This type of molecular sieve, from the separation of group components to the desorption of n-alkanes, uses reagents that are completely different from those of previous methods, reducing experimental procedures, simplifying operation, making it safer and more convenient, with higher recovery rates and stronger repeatability.

[0036] This invention uses isohexane to separate saturated hydrocarbon components from petroleum geological samples, effectively avoiding the loss of low-carbon and low-boiling-point compounds during sample concentration. This invention... After molecular sieves adsorb n-alkanes from saturated hydrocarbon components, dichloromethane is used to desorb the adsorbed n-alkanes from the molecular sieves, which can obtain the n-alkanes in the sample more safely, efficiently and completely. At the same time, it avoids the additional organic solvent extraction operation after dissolving the molecular sieve with hydrofluoric acid, as well as the sample loss that occurs as a result.

[0037] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained in accordance with the structures particularly pointed out in the description, claims and drawings. Attached Figure Description

[0038] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0039] Figure 1 This is a gas chromatogram of the saturated hydrocarbon component in Example 1 of the present invention;

[0040] Figure 2 This is a gas chromatogram of the mixed components of isoalkanes and cycloalkanes in Example 1 of the present invention;

[0041] Figure 3 This is a gas chromatogram of the n-alkanes in Example 1 of the present invention;

[0042] In the figure, the vertical axis represents relative abundance (%), and the horizontal axis represents time (min). Detailed Implementation

[0043] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0044] In the description of this invention, it should be noted that the terms "comprising", "including", "having", "containing", etc., are all open-ended terms, meaning that they include but are not limited to.

[0045] Existing methods for separating n-alkanes from petroleum geological samples typically use n-hexane and / or n-pentane to dissolve the saturated hydrocarbon components. However, after dissolving the saturated hydrocarbon components with these two organic solvents, subsequent extraction of n-alkanes involves solvent conversion, i.e., from n-hexane and / or n-pentane to isooctane. This complicates the separation process. Furthermore, isooctane has a high boiling point and volatilizes slowly at room temperature and pressure. Even under negative pressure, its addition leads to significant losses of low-boiling-point, low-carbon-number n-alkanes and isoalkanes (such as pterane and phytane). After solvent conversion, molecular sieves are added to the saturated hydrocarbon components dissolved in isooctane for adsorption. After adsorption, the remaining liquid phase is a mixed solution of isoalkanes and cycloalkanes. This mixed solution needs to be volatilized and concentrated before instrumental testing. Practice has shown that low-boiling-point compounds (palmitane, phytane, and isoalkanes with fewer than 18 carbon atoms) in the samples are significantly lost during volatilization, interfering with subsequent quantitative, semi-quantitative, and isotopic analyses of isoalkanes and cycloalkanes.

[0046] In the current technology for obtaining n-alkanes, it is common to use strong corrosive acids (e.g., hydrofluoric acid, hydrochloric acid) to dissolve the stationary phase (molecular sieve), and organic solvents to perform multiple extractions and separations of the acid solution. Because of the involvement of highly corrosive substances, the risk factor of the separation operation is increased, and hydrofluoric acid reagent is not easy to store and obtain in the laboratory, thus making the separation operation difficult to implement.

[0047] Since the existing technology did not meet the inventor's expectations, the inventor conducted further research and development and came up with this invention.

[0048] This invention employs isohexane to separate saturated hydrocarbon components from petroleum geological samples, effectively avoiding the loss of low-carbon and low-boiling-point compounds during solvent conversion and concentration. This invention also utilizes... Molecular sieves adsorb n-alkanes from saturated hydrocarbon components, and then dichloromethane is used to desorb the n-alkanes adsorbed by the molecular sieves. This method avoids the use of highly corrosive acids and can obtain n-alkanes from the sample more safely, efficiently, and completely, avoiding the loss of isoalkanes and cycloalkanes.

[0049] The present invention will be further described below with reference to specific embodiments. The scope of protection of the present invention is not limited to the following embodiments. Unless otherwise stated, the materials involved in the embodiments are all conventional commercially available products.

[0050] Example 1

[0051] This embodiment separates n-alkanes from rock extracts, and the steps are as follows:

[0052] S1. Activate 35-70 mesh silica gel at 150°C for 12 hours and cool to room temperature; fill 2g of activated silica gel into quartz glass chromatography column I (the specifications of chromatography column I are an inner diameter of 13mm and a length greater than 60mm), and wet the silica gel (i.e., the stationary phase) with isohexane.

[0053] S2. Transfer 10 mg of rock extract sample to chromatography column I, add 5 mL of isohexane for elution, and obtain an elution solution containing saturated hydrocarbon components.

[0054] S3. 60-80 mesh The molecular sieve was activated at 150℃ for 12 hours, then cooled to room temperature for later use.

[0055] S4, Take the activated product prepared in S3 4 mg of molecular sieve was placed in the elution solution containing saturated hydrocarbon components obtained by S2, ultrasonically vibrated for 20 min, and refrigerated (5℃) for 12 h. This was used to pre-adsorb n-alkanes from the elution solution containing saturated hydrocarbon components obtained by S2, yielding a solution adsorbed with n-alkanes. Molecular sieve and elution solution containing saturated hydrocarbon components after pre-adsorption;

[0056] S5, take the activated product obtained from S3. 2g of molecular sieve was packed into quartz glass chromatography column II;

[0057] S6, the adsorbed n-alkane obtained in S4 The molecular sieve and the pre-adsorbed eluent containing saturated hydrocarbon components were transferred into chromatography column II prepared by S5, and 5 mL of isohexane was added for elution to obtain a solution adsorbed with n-alkanes. Molecular sieves and elution products (wherein, the elution products are a mixed solution of isoalkanes and cycloalkanes);

[0058] S7. Use 20 mL of dichloromethane to treat the n-alkane adsorbed in S6. Molecular sieve ultrasonic extraction was performed for 20 minutes, and the process was repeated three times. The solutions obtained from the three extractions were then mixed to obtain a n-alkane solution.

[0059] In the embodiments of the present invention, it is necessary to explain the following:

[0060] In S1, the amount of silica gel used here is the optimal amount determined after multiple experiments to achieve the precise separation of saturated hydrocarbon components. When the mesh size of the silica gel and / or the specifications of the chromatography column change, the amount of silica gel used also changes accordingly to achieve the effect of separating saturated hydrocarbon components from the geological sample.

[0061] In S2, an elution solution containing saturated hydrocarbon components is obtained. The reason is that this embodiment was carried out under the illumination of a fluorescent lamp. The inventors observed that the fluorescent components (i.e., aromatic hydrocarbon components) remained at the bottom of the chromatography column and had not yet flowed into the above elution solution. Therefore, it is believed that the final elution solution obtained is an elution solution containing saturated hydrocarbon components.

[0062] In S4, here The amount of molecular sieve used was determined after multiple experiments. Molecular sieves can stably adsorb n-alkanes from saturated hydrocarbon components to the maximum extent; when When the mesh size of the molecular sieve changes, The amount of molecular sieve used also changes accordingly to achieve the optimal effect of adsorbing n-alkanes from saturated hydrocarbon components.

[0063] In S5, here The amount of molecular sieve used was determined after multiple experiments. Molecular sieves can further completely adsorb the remaining n-alkanes in the eluent containing saturated hydrocarbon components after pre-adsorption; when When the mesh size of the molecular sieve and / or the specifications of the chromatography column change, The amount of molecular sieve used also changes accordingly in order to achieve efficient and complete adsorption of n-alkanes from saturated hydrocarbon components.

[0064] The inventors concentrated the mixed solution of isoalkanes and cycloalkanes obtained in S6 and the n-alkanes solution obtained in S7 to 0.5 mL, and then injected them into a gas chromatograph for component analysis, repeating the process three times. The testing equipment and conditions were as follows: Agilent 7890A gas chromatograph, flame ionization detector (FID, detector temperature 310℃), HP-5 column (60 m × 0.25 mm, thickness 0.25 μm), temperature program starting at 50℃ and holding for 10 min, then increasing to 70℃ at a rate of 4℃ / min, followed by increasing to 310℃ at a rate of 8℃ / min (holding for 40 min). The carrier gas was 99.999% nitrogen at a flow rate of 1 mL / min, the injection mode was splitless injection of 1 μL, and the injection port temperature was 310℃.

[0065] Analysis results as follows Figures 1-3 As shown in Table 1 below.

[0066] Table 1: Comparison of repeatability results of the method for separating n-alkanes in Example 1

[0067]

[0068] From the above results, we can conclude that:

[0069] Before performing the separation of n-alkanes, the gas chromatograms of the saturated hydrocarbon components were combined. Figure 1 Let's look at the sample: the carbon number range of the n-alkanes is C. 12 –C 33 The most prominent isoalkanes are pristane and phytane, while monomethyl isoalkanes are present in very low amounts. The cycloalkanes series are C16-26-3 ... 27 –C 29 Predominantly steranes, with C 27 The content of steranes is extremely high, and no other types of cycloalkanes were found. Specifically, the pristane / phytane ratio is 0.02, and the C1 ratio is [not specified]. 27 - / C 29 -Steane = 14.42. The re-identification of the above compounds can be confirmed by standard co-injection and gas chromatography-mass spectrometry analysis.

[0070] Following the separation operation, gas chromatograms of the isoalkane and cycloalkane components were combined. Figure 2 The types and distribution of compounds are basically consistent with the distribution of isoalkanes and cycloalkanes before the separation operation, mainly consisting of acyclic isoprene and regular steranes. The acyclic isoprene is mainly pterane and phytane, while the regular steranes range from C1 to C2. 27 –C 29 Between these values, the content of hopane compounds was extremely low. In three repeated experiments, the standard deviation of the relative content of each compound was mostly below 2%, indicating stable results.

[0071] After the separation operation, the gas chromatograms of the separated n-alkanes were analyzed. Figure 3 Let's look at it: the carbon number distribution range of n-alkanes is in the C... 12 –C 33 Between these measurements, the relative abundance and distribution characteristics of each n-alkanes were basically consistent with those of the n-alkanes in the saturated hydrocarbon fraction before separation. In the three repeated experiments, the standard deviation of the relative content of each compound was mostly below 3%, indicating stable results.

[0072] As a comparative example of the present invention, "isooctane dissolution of isoalkane and cycloalkane components" was used. The method of separating n-alkanes from a sample by "molecular sieve adsorption of n-alkanes and hydrofluoric acid desorption of n-alkanes" is as follows:

[0073] The first step is to activate 35-70 mesh silica gel at 150°C for 12 hours, cool it to room temperature, fill 2g of activated silica gel into a quartz chromatography column, and wet the silica gel with n-hexane (i.e., wet the stationary phase).

[0074] The second step involves taking 10 mg of rock extract from sample 698, transferring it into the chromatography column prepared in the first step, and eluting with 5 mL of n-hexane to obtain an elution solution containing saturated hydrocarbon components.

[0075] The third step involves evaporating the hexane reagent from the elution solution containing saturated hydrocarbon components in the second step at 70°C, dissolving the saturated hydrocarbon components in isooctane as a solvent, and concentrating the solution to <0.5 mL to obtain an isooctane solution containing saturated hydrocarbon components.

[0076] The fourth step is to use 60-80 mesh. The molecular sieve was activated at 150℃ for 12 hours, then cooled to room temperature for later use.

[0077] Fifth step, take 2g of the activated product prepared in step four. Molecular sieves are packed into the chromatography column;

[0078] Step 6: Transfer the isooctane solution containing saturated hydrocarbon components obtained in step 3 into the molecular sieve chromatography column prepared in step 5, and leach the chromatography column three times with 20 mL of isooctane. The resulting solution is a mixed solution of isoalkanes and cycloalkanes.

[0079] Step 7: Transfer the molecular sieve eluted in step 6, dry it with nitrogen, add 45 mL of acid solution (36%–38% HCl: 40% HF = 2:1, volume ratio), shake well, acidify the molecular sieve, and finally obtain the acid solution.

[0080] Step 8: Add 15 mL of n-hexane to the acid solution obtained in step 7 in three separate steps to extract the n-alkanes.

[0081] The solutions obtained in steps two, six, and eight were concentrated and then analyzed using equipment consistent with that used in the embodiments of the present invention. The statistical results are shown in Table 2.

[0082] Table 2: Comparison of repeatability results of experiments using the comparative method for separating n-alkanes

[0083]

[0084]

[0085] As can be seen from the test results in Table 2, compared with the present invention:

[0086] From the perspective of separation operations, the comparative method involves steps such as organic solvent conversion (isooctane), strong acid (hydrofluoric acid, hydrochloric acid) dissolution, multiple organic solvent extractions and liquid-liquid separation. This separation method is more complex, more dangerous, and requires higher operational skills from experimental equipment and personnel. In addition, hydrofluoric acid reagent is difficult to obtain, so most laboratories cannot complete the experiment.

[0087] From the perspective of separation effect, the distribution range of n-alkanes in the unseparated saturated hydrocarbon sample is within nC. 14 –nC 33Between these values, the original pristane / phytane ratio was 0.07, C 27 - / C 29 The -sterane ratio is 9.65. In the comparative example, isooctane has a high boiling point, and its addition will result in a significant loss of low-carbon n-alkanes, pteranes, and phytanes. The percentage content of alkanes with different carbon numbers varies greatly, and the relative standard deviation of the three repeated experiments is generally above 20%. This has obvious drawbacks when used for semi-quantitative analysis.

[0088] In summary, this invention is based on The method utilizes completely different reagents from previous methods, including molecular sieves, isohexane, and dichloromethane, from the separation of group components to the desorption of n-alkanes. This not only reduces experimental procedures and simplifies operations, making the method safer, more convenient, with higher recovery rates and stronger reproducibility, but also makes the acquisition of n-alkanes, isoalkanes, and cycloalkanes more efficient and complete.

[0089] Although the invention has been described in considerable detail and particularly with regard to several of the described embodiments, it is not intended to limit itself to any of these details or embodiments or any particular embodiment, thereby effectively covering the intended scope of the invention. Furthermore, the invention has been described above with respect to embodiments foreseeable by the inventors in order to provide a useful description, and non-substantial modifications to the invention that have not yet been foreseen may still represent equivalent modifications.

[0090] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0091] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for separating n-alkanes from petroleum geological samples, characterized in that, include: S1. Wet a chromatography column with silica gel as the stationary phase with isohexane and use isohexane as the eluent to perform column chromatography separation on petroleum geological samples to obtain an eluent containing saturated hydrocarbon components. S2. Place the 5Å molecular sieve in the elution solution containing saturated hydrocarbon components obtained in S1, sonicate for 20 min, and refrigerate for 12 h to pre-adsorb the n-alkanes in the elution solution containing saturated hydrocarbon components obtained in S1, and obtain the 5Å molecular sieve adsorbed with n-alkanes and the elution solution containing saturated hydrocarbon components after pre-adsorption. S3. The 5Å molecular sieve with adsorbed n-alkanes obtained in S2 and the elution solution containing saturated hydrocarbon components after pre-adsorption are transferred into a chromatography column with 5Å molecular sieve as the stationary phase and isohexane as the eluent to obtain the 5Å molecular sieve with adsorbed n-alkanes and the elution product, wherein the elution product is a mixed solution of isoalkanes and cycloalkanes. S4. The 5Å molecular sieve containing n-alkane obtained in S3 is ultrasonically extracted with dichloromethane to obtain a n-alkane solution.

2. The method for separating n-alkanes from petroleum geological samples as described in claim 1, characterized in that, The chromatography column is a quartz glass column with an inner diameter of 13 mm and a length greater than 60 mm.

3. The method for separating n-alkanes from petroleum geological samples as described in claim 1, characterized in that, The silica gel used in chromatography is activated silica gel, and the activation of the silica gel includes: The silica gel for chromatography was dried at 150°C for 12 hours under vacuum and then cooled to room temperature before use.

4. The method for separating n-alkanes from petroleum geological samples as described in claim 1, characterized in that, The ratio of the silica gel for chromatography, the petroleum geological sample, and the eluent is 2g:10mg:5ml.

5. The method for separating n-alkanes from petroleum geological samples as described in claim 1, characterized in that, The petroleum geological samples are selected from one of the following: black crude oil, rock extracts, condensate oil, or light oil.

6. The method for separating n-alkanes from petroleum geological samples as described in claim 1, characterized in that, In step S2, the 5Å molecular sieve is placed in the elution solution containing saturated hydrocarbon components obtained in step S1 to pre-adsorb the n-alkanes in the elution solution containing saturated hydrocarbon components obtained in step S1, resulting in a 5Å molecular sieve adsorbed with n-alkanes and a pre-adsorbed elution solution containing saturated hydrocarbon components, comprising: Under vacuum, the 5Å molecular sieve was dried at 150°C for 12 hours and then cooled to room temperature to obtain the activated 5Å molecular sieve. The activated 5Å molecular sieve was placed in the elution solution containing saturated hydrocarbon components obtained in S1, ultrasonically vibrated for 20 min, and refrigerated for 12 h to pre-adsorb the n-alkanes in the elution solution containing saturated hydrocarbon components obtained in S1, thus obtaining the 5Å molecular sieve with adsorbed n-alkanes and the elution solution containing saturated hydrocarbon components after pre-adsorption.

7. The method for separating n-alkanes from petroleum geological samples according to claim 1, characterized in that, In S2: When the petroleum geological sample is black crude oil or rock extract, the amount of 5Å molecular sieve used is 4 mg; When the petroleum geological sample is condensate oil or light oil, the amount of 5Å molecular sieve used is 6 mg.

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