High-efficiency and high-precision analysis method for detailed hydrocarbon content in needle coke raw material

Abstract

The invention belongs to the technical field of chemical analysis and testing, and particularly relates to a high-efficiency and high-precision analysis method for the content of detailed hydrocarbons in a needle coke raw material, and the method comprises four parts of sample pretreatment and asphaltene separation, chromatographic column separation, mass spectrometry and data processing. By adopting the analysis method disclosed by the invention, the separation efficiency of four components is obviously improved; the cost of consumables is reduced by more than 40%; the total yield of the finally obtained four components and the asphaltene separation efficiency both reach 98%, the mass spectrometry RSD is smaller than 2%, the precise analysis requirement of the high-end needle coke raw material is met, meanwhile, the anti-interference capacity is enhanced, and the analysis error caused by asphaltene adsorption in a traditional method is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical analysis and testing, and particularly relates to a high-efficiency and high-precision analysis method for detailed hydrocarbon content in needle coke raw materials. Background Art

[0002] In the needle coke production process, accurate analysis of the detailed hydrocarbon composition of needle coke feedstocks such as heavy oil, FCC slurry oil, and aromatic-rich oil is crucial. These feedstocks primarily consist of four components: saturates, aromatics, resins, and asphaltenes. Accurate analysis of total aromatics content, as well as tri- and tetra-ring aromatics, is crucial for determining feedstock properties, optimizing production processes, and improving product quality.

[0003] For example, suitable aromatics can promote the formation of a highly ordered layered structure in needle coke, improving its structural properties. The three-ring and four-ring aromatics (such as phenanthrene and anthracene) in FCC slurry have the characteristics of short side chains, moderate molecular weight (200-300Da), and strong planarity. During the carbonization process, these molecules form a wide-area mesophase liquid crystal through π-π stacking, and then arrange into a more regular structure, which is the key structural feature of needle coke. At the same time, the regularly arranged aromatic layers can reduce the coefficient of thermal expansion (CTE) of needle coke to less than 1.0×10 -6 / °C, forming highly graphitized microcrystals, reducing the resistivity of needle coke and improving its conductivity. Furthermore, increasing the content of three- and four-ring aromatics can improve process economics and significantly increase the yield of needle coke.

[0004] However, traditional specifications lack analytical standards for these raw materials, and existing methods have the following problems: First, the asphaltene content in raw materials such as heavy oil and FCC slurry is high (>5%). Traditional methods use asphaltene because it is insoluble in n-heptane, which can lead to blockage of sieve plates or adsorption columns; second, in the extraction column, asphaltene undergoes irreversible adsorption and cannot be completely eluted, resulting in a yield of less than 90%, making further analysis impossible; third, existing methods have low separation efficiency, poor mass spectrometry data stability, and high analysis costs, making it difficult to meet the quality control needs of high-end needle coke raw materials. Summary of the Invention

[0005] The purpose of the present invention is to provide an efficient and high-precision analysis method for detailed hydrocarbon content in needle coke raw materials, so as to solve the problems of low separation efficiency of high-asphalt samples, poor stability of mass spectrometry data and high analysis cost.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: An efficient and high-precision analysis method for detailed hydrocarbon content in needle coke raw materials comprises the following steps: (1) Sample pretreatment and asphaltene separation: The needle coke raw material was mixed with n-hexane, heated to reflux, and then subjected to gradient sedimentation to separate the asphaltene; (2) Chromatographic column separation: Use activated porous silica gel packed column for chromatographic separation, and use n-hexane, n-hexane-dichloromethane mixed solvent, and dichloromethane-ethanol mixed solvent for segmented elution in turn to achieve separation of saturated fractions, aromatic fractions, and colloids; (3) Mass spectrometry analysis: The separated saturated fraction and aromatic fraction were diluted with n-hexane and dichloromethane, respectively. After ultrasonic treatment, they were analyzed by gas chromatography-mass spectrometry. Parameters such as ionization voltage, split ratio, helium flow rate, solvent delay time, and scanning range were set. (4) Data processing: Based on the summation of the characteristic ion peak group intensities and combined with the inverse coefficient correction, quantitative analysis of alkanes and polycyclic aromatic hydrocarbons is achieved.

[0007] Furthermore, the heating reflux time in step (1) is 1-1.2 h.

[0008] Furthermore, the settling time in step (1) is 1 hour, and the filter residue is washed three times with 40-45°C n-hexane.

[0009] Furthermore, the activation conditions of the porous silica gel in step (2) are as follows: the pore size is 50-100Å, the specific surface area is greater than 300m 2 / g of silica gel was placed in an oven at 120℃ for activation for 4 hours, cooled, added with 2% distilled water, shaken and allowed to stand for 12 hours.

[0010] Furthermore, in step (2), the volume ratio of the n-hexane-dichloromethane mixed solvent is 3:1, the volume ratio of the n-hexane-dichloromethane mixed solvent is 1:1, and the elution flow rate is 2 mL / min.

[0011] Furthermore, in step (3), the saturated fraction is diluted 30 times with n-hexane, and the aromatic fraction is diluted 30 times with dichloromethane; specifically, n-hexane is used as the solvent to dilute the saturated fraction at a liquid-to-solid ratio of 30 mL / g; and dichloromethane is used as the solvent to dissolve the aromatic fraction at a liquid-to-solid ratio of 30 mL / g.

[0012] Furthermore, the parameters of the gas chromatography-mass spectrometry instrument in step (3) are: ionization voltage 70 eV, split ratio 50:1, carrier gas is helium, column flow rate is 1.2 mL / min, and injection volume is 1 μL.

[0013] Furthermore, the characteristic ion peak group includes ∑71, ∑69, ∑109, ∑128, ∑178, and ∑202, and the error of the inverse descent coefficient correction is less than 1.5%.

[0014] The beneficial effects of the present invention are as follows: (1) Improved separation efficiency: The method of the present invention improves the separation efficiency of the four components by 20%, shortens the analysis cycle by 30%, and significantly improves the detection efficiency compared with traditional methods.

[0015] (2) Reduced costs: Domestic activated porous silica gel was used to replace expensive prefabricated separation columns, reducing consumables costs by more than 40%.

[0016] (3) Improved analysis accuracy: Using the method of the present invention, the final total yield of the four components is as high as 98%, the asphaltene separation efficiency is as high as 98%, and the mass spectrometry RSD is less than 2% (repeated determination), which meets the requirements for precise analysis of high-end needle coke raw materials.

[0017] (4) Enhanced anti-interference ability: The n-hexane precipitation method completely removes asphaltene, avoids column clogging, and solves the analytical errors caused by asphaltene adsorption in traditional methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the analytical method of the present invention; DETAILED DESCRIPTION

[0019] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0020] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The embodiments cannot be described one by one here, but the embodiments of the present invention are not limited to the following embodiments.

[0021] Example 1: A method for analyzing the detailed hydrocarbon content in needle coke raw materials with high efficiency and high precision, comprising the following steps: Step 1: Sample pretreatment and asphaltene separation Weighing and dissolving: Accurately weigh 1.0 g of FCC slurry sample, add 50 mL of n-hexane, and heat under reflux for 1 h.

[0022] Gradient sedimentation: After standing for 1 h, filter using medium-speed quantitative filter paper and wash the filter residue three times with 40°C n-hexane to ensure complete transfer of soluble matter.

[0023] Asphaltene recovery: The filter residue was dissolved in trichloroethylene under reflux, evaporated to dryness and weighed to calculate the asphaltene content.

[0024] Step 2: Chromatographic column separation Porous silica gel activation: Use activated porous silica gel filling column. The porous silica gel activation method is as follows: Place silica gel with a pore size of 50-100Å in a 120℃ oven for 4 hours, cool it down, add 2% distilled water, shake it well and let it stand for 12 hours to obtain a specific surface area of ​​300m 2 / g of activated silica gel and then loaded into the packed column.

[0025] Column packing and elution: (1) Saturated fraction: elute with n-hexane (flow rate 2 mL / min) and collect the eluate.

[0026] (2) Aromatic fraction: Switch to a mixture of n-hexane and dichloromethane in a volume ratio of 3:1 as the aromatic fraction eluent and collect until the eluent becomes colorless.

[0027] (3) Gel: Elute with a mixture of dichloromethane and ethanol (volume ratio 1:1), evaporate to dryness, and weigh.

[0028] (4) Four components: Get the four component contents of the sample.

[0029] Step 3: Mass spectrometry analysis Sample preparation: The saturated fraction was diluted 30 times with n-hexane, and the aromatic fraction was diluted 30 times with dichloromethane; specifically, n-hexane was used as the solvent to dilute the saturated fraction at a liquid-to-solid ratio of 30 mL / g; and dichloromethane was used as the solvent to dissolve the aromatic fraction at a liquid-to-solid ratio of 30 mL / g.

[0030] Instrument parameters: Agilent 8890-5977B GC-MS system was used, with an ionization voltage of 70 eV, an ion source temperature of 250°C, a transfer line temperature of 340°C, a split ratio of 50:1, helium as carrier gas, a column flow rate of 1.2 mL / min, an injection volume of 1 μL, a solvent delay of 3 min, elimination of solvent interference, and a scan range of m / z 50–700, covering the characteristic peaks of C16–C32 hydrocarbons.

[0031] Data analysis: By matching the NIST mass spectrum library and combining it with a custom inversion coefficient table (C16~C32), the contents of paraffins, monocyclic aromatic hydrocarbons, pentacyclic aromatic hydrocarbons, and polycyclic aromatic hydrocarbons are calculated.

[0032] Step 4: Result Verification Precision test: RSD of repeated measurements by the same operator is less than 2%, and RSD between laboratories is less than 5%.

[0033] Recovery verification: The experiment showed that the total recovery of the four components was 98.3%, and the asphaltene separation efficiency was 99.5%.

[0034] Example 2: A high-efficiency and high-precision analysis method for detailed hydrocarbon content in needle coke raw materials comprises the following steps: Step 1: Sample pretreatment and asphaltene separation Weighing and dissolving: Accurately weigh 1.0 g of FCC slurry sample, add 60 mL of n-hexane, and heat under reflux for 1.2 h.

[0035] Gradient sedimentation: After standing for 1 h, filter using medium-speed quantitative filter paper and wash the filter residue three times with 42°C n-hexane to ensure complete transfer of soluble matter.

[0036] Asphaltene recovery: The filter residue was dissolved in trichloroethylene under reflux, evaporated to dryness and weighed to calculate the asphaltene content.

[0037] Step 2: Chromatographic column separation Porous silica gel activation: Use activated porous silica gel filling column. The porous silica gel activation method is as follows: Place silica gel with a pore size of 50-100Å in a 130℃ oven for 4.5 hours, cool it down, add 2% distilled water, shake it well and let it stand for 14 hours to obtain a specific surface area of ​​300m 2 / g of activated silica gel and then loaded into the packed column.

[0038] Column packing and elution: (1) Saturated fraction: elute with n-hexane (flow rate 2 mL / min) and collect the eluate.

[0039] (2) Aromatic fraction: Switch to a mixture of n-hexane and dichloromethane in a volume ratio of 4:1 as the aromatic fraction eluent and collect until the eluent becomes colorless.

[0040] (3) Gel: Elute with a mixture of dichloromethane and ethanol (volume ratio 1.5:1), evaporate to dryness, and weigh.

[0041] (4) Four components: Get the four component contents of the sample.

[0042] Step 3: Mass spectrometry analysis Sample preparation: The saturated fraction was diluted 30 times with n-hexane, and the aromatic fraction was diluted 30 times with dichloromethane; specifically, n-hexane was used as the solvent and the saturated fraction was diluted at a liquid-to-solid ratio of 30 mL / g; at the same time, dichloromethane was used as the solvent and the aromatic fraction was dissolved at a liquid-to-solid ratio of 30 mL / g.

[0043] Instrument parameters: Agilent 8890-5977B GC-MS system was used, with an ionization voltage of 70 eV, an ion source temperature of 250°C, a transfer line temperature of 350°C, a split ratio of 55:1, helium as carrier gas, a column flow rate of 1.2 mL / min, an injection volume of 1 μL, a solvent delay of 3 min, elimination of solvent interference, and a scan range of m / z 50–700, covering the characteristic peaks of C16–C32 hydrocarbons.

[0044] Data analysis: By matching the NIST mass spectrum library and combining it with a custom inversion coefficient table (C16~C32), the contents of paraffins, monocyclic aromatic hydrocarbons, pentacyclic aromatic hydrocarbons, and polycyclic aromatic hydrocarbons are calculated.

[0045] Step 4: Result Verification Precision test: RSD of repeated measurements by the same operator is less than 2%, and RSD between laboratories is less than 5%.

[0046] Recovery verification: The experiment showed that the total recovery of the four components was 98%, and the asphaltene separation efficiency was 99.2%.

[0047] Example 3 A high-efficiency and high-precision analysis method for detailed hydrocarbon content in needle coke raw material comprises the following steps: Step 1: Sample pretreatment and asphaltene separation Weighing and dissolving: Accurately weigh 1.0 g of FCC slurry oil sample, add 55 mL of n-hexane, and heat to reflux for 1.1 h.

[0048] Gradient sedimentation: After standing for 1 h, filter using medium-speed quantitative filter paper and wash the filter residue three times with 45°C n-hexane to ensure complete transfer of soluble matter.

[0049] Asphaltene recovery: The filter residue was dissolved in trichloroethylene under reflux, evaporated to dryness and weighed to calculate the asphaltene content.

[0050] Step 2: Chromatographic column separation Porous silica gel activation: Use activated porous silica gel filling column. The porous silica gel activation method is as follows: Place silica gel with a pore size of 50-100Å in a 125℃ oven for 4.2 hours, add 2% distilled water after cooling, shake well and let it stand for 15 hours to obtain a specific surface area of ​​300m 2 / g of activated silica gel and then loaded into the packed column.

[0051] Column packing and elution: (1) Saturated fraction: elute with n-hexane (flow rate 2 mL / min) and collect the eluate.

[0052] (2) Aromatic fraction: Switch to a mixture of n-hexane and dichloromethane in a volume ratio of 3.5:1 as the aromatic fraction eluent and collect until the eluent becomes colorless.

[0053] (3) Gel: Elute with a mixture of dichloromethane and ethanol (volume ratio 1.2:1), evaporate to dryness, and weigh.

[0054] (4) Four components: Get the four component contents of the sample.

[0055] Step 3: Mass spectrometry analysis Sample preparation: The saturated fraction was diluted 30 times with n-hexane, and the aromatic fraction was diluted 30 times with dichloromethane; specifically, n-hexane was used as the solvent and the saturated fraction was diluted at a liquid-to-solid ratio of 30 mL / g; at the same time, dichloromethane was used as the solvent and the aromatic fraction was dissolved at a liquid-to-solid ratio of 30 mL / g.

[0056] Instrument parameters: The GC-MS system was Agilent 8890-5977B, with an ionization voltage of 70 eV, an ion source temperature of 250°C, a transfer line temperature of 350°C, a split ratio of 53:1, helium as carrier gas, a column flow rate of 1.2 mL / min, an injection volume of 1 μL, a solvent delay of 3 min, and elimination of solvent interference. The scan range was m / z 50–700, covering the characteristic peaks of C16–C32 hydrocarbons.

[0057] Data analysis: By matching the NIST mass spectrum library and combining it with a custom inversion coefficient table (C16~C32), the contents of paraffins, monocyclic aromatic hydrocarbons, pentacyclic aromatic hydrocarbons, and polycyclic aromatic hydrocarbons are calculated.

[0058] Step 4: Result Verification Precision test: RSD of repeated measurements by the same operator is less than 2%, and RSD between laboratories is less than 5%.

[0059] Recovery verification: The experiment showed that the total recovery of the four components was 97.5%, and the asphaltene separation efficiency was 98.8%.

[0060] Comparative Example 1 Compared with Example 1, the difference is: Step 1: Sample pretreatment and asphaltene separation Weighing and dissolving: Accurately weigh 1.0 g of FCC slurry sample, add 50 mL of n-heptane, and heat under reflux for 1 h.

[0061] Gradient sedimentation: After standing for 1 h, filter using medium-speed quantitative filter paper and wash the filter residue three times with 80°C n-heptane to ensure complete transfer of soluble matter.

[0062] Asphaltene recovery: The filter residue was dissolved in trichloroethylene under reflux, evaporated to dryness and weighed to calculate the asphaltene content.

[0063] The n-hexane in step 2 and step 3 was replaced by n-heptane, and other parameters and operations were the same as those in Example 1.

[0064] Comparative Example 2 Compared with Example 1, the difference is: Step 2: Chromatographic column separation Alumina activation: Use activated alumina filling column. The alumina activation method is as follows: Place silica gel with a pore size of 50-100Å in a 120℃ oven for 4 hours, add 2% distilled water after cooling, shake well and let it stand for 12 hours to obtain a specific surface area of ​​150m 2 / g activated alumina was then loaded into a packed column. Other parameters and operations were the same as in Example 1.

[0065] Comparative Example 3 The GB / T 511-2010 standard method was used without using dynamic reflux and asphaltenes were directly precipitated with n-heptane.

[0066] Comparative Example 4 Compared with Example 1, the difference is that: Step 3: in mass spectrometry analysis, the split ratio is 30:1; other parameters and operations are the same as in Example 1.

[0067] Comparison of the analytical results of the embodiments and comparative examples of the present invention The asphaltene separation efficiency, the total yield of the four components, and the chromatographic column clogging rate in Examples 1-3 and Comparative Examples 1-6 were recorded respectively. The results are shown in Table 1.

[0068] Table 1 Group Asphaltene separation efficiency Total yield of four components Chromatography column plugging rate Example 1 99.5% 98.3% 0% Example 2 99.2% 98% 0% Example 3 98.8% 97.5% 0% Comparative Example 1 86% 85% 14% Comparative Example 2 86.5% 85.2% 12% Comparative Example 3 84.0% 85.3% 30% Comparative Example 4 99.2% 98.2% 0% The analytical accuracy data of Examples 1-3 and Comparative Examples 1-6 were recorded respectively. The results are shown in Table 2.

[0069] Table 2 Group Repeatability RSD (%) Inter-laboratory RSD (%) Example 1 1.6 3.8 Example 2 1.8 4.0 Example 3 1.7 4.2 Comparative Example 1 1.8 4.5 Comparative Example 2 3.5 6.8 Comparative Example 3 7.5 12.3 Comparative Example 4 1.7 4.0 As can be seen from the data in Table 1, the asphaltene separation efficiencies in Examples 1-3 reached 99.5%, 99.2%, and 98.8%, respectively, with an average separation efficiency exceeding 99%, indicating that the dynamic reflux treatment with n-hexane can completely remove asphaltene and avoid its interference with subsequent analysis.

[0070] The total yields of the four components in Examples 1-3 were 98.3%, 98%, and 97.5%, respectively, with an average of 97.93%, which was about 15% higher than that of the traditional method (total yield of 85.3% in Comparative Example 3), further demonstrating the high efficiency of the method of the present invention in component recovery; the RSDs (relative standard deviations) of repeated measurements in Examples 1-3 were 1.6%, 1.8%, and 1.7%, respectively, meeting the stringent repeatability requirements of high-end analysis; the inter-laboratory RSD was 3.8%-4.2%, indicating that the method has good cross-laboratory applicability and high data reliability.

[0071] In Comparative Example 1, replacing n-hexane with n-heptane reduced asphaltene separation efficiency to 86%, the total four-component recovery to 85%, and the column clogging rate to 14%. In Comparative Example 3, which did not utilize dynamic reflux, the clogging rate reached 30%, and the total recovery was only 85.3%, demonstrating that dynamic reflux can enhance asphaltene separation and improve component recovery.

[0072] The analytical method of the present invention achieves efficient and high-precision analysis of hydrocarbon content in needle coke feedstock through asphaltenes separation using dynamic n-hexane reflux, fractionated elution using an activated porous silica gel chromatography column, and GC-MS coupled with characteristic ion peak group correction. It outperforms traditional methods in key metrics such as separation efficiency, yield, and precision. This method provides a precise means of raw material analysis for needle coke production, optimizes mesophase liquid crystal formation conditions, and facilitates the preparation of highly graphitized microcrystalline needle coke, demonstrating significant industrial application value.

[0073] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A high-efficiency and high-precision analysis method for detailed hydrocarbon content in needle coke raw materials, characterized in that: The following steps are involved: (1) Sample pretreatment and asphaltene separation: The needle coke raw material was mixed with n-hexane, heated to reflux, and then subjected to gradient sedimentation to separate the asphaltene; (2) Chromatographic column separation: Use activated porous silica gel packed column for chromatographic separation, and use n-hexane, n-hexane-dichloromethane mixed solvent, and dichloromethane-ethanol mixed solvent for segmented elution in turn to achieve separation of saturated fractions, aromatic fractions, and colloids; (3) Mass spectrometry analysis: The separated saturated fraction and aromatic fraction were diluted and dissolved with n-hexane and dichloromethane, respectively, and analyzed by gas chromatography-mass spectrometry. Parameters such as ionization voltage, split ratio, helium flow rate, solvent delay time, and scanning range were set; (4) Data processing: Based on the summation of the characteristic ion peak group intensities and combined with the inverse coefficient correction, quantitative analysis of alkanes and polycyclic aromatic hydrocarbons is achieved.

2. The method for analyzing the detailed hydrocarbon content in needle coke raw material according to claim 1, characterized in that: The heating reflux time in step (1) is 1-1.2 h.

3. The method for analyzing the detailed hydrocarbon content in needle coke raw material according to claim 1, characterized in that: The settling time in step (1) is 1 hour, and the filter residue is washed three times with 40°C n-hexane.

4. The method for analyzing the detailed hydrocarbon content in needle coke raw material according to claim 1, characterized in that: The activation conditions of the porous silica gel in step (2) are as follows: the pore size is 50-100Å, the specific surface area is greater than 300m 2 / g of silica gel was placed in an oven at 120℃ for activation for 4 hours, cooled, added with 2% distilled water, shaken and allowed to stand for 12 hours.

5. The method for analyzing the detailed hydrocarbon content in needle coke raw material according to claim 1, characterized in that: In step (2), the volume ratio of the n-hexane-dichloromethane mixed solvent is 3:1, the volume ratio of the n-hexane-dichloromethane mixed solvent is 1:1, and the elution flow rate is 2 mL / min.

6. The method for analyzing the detailed hydrocarbon content in needle coke raw material according to claim 1, characterized in that: In step (3), the saturated fraction is diluted 30 times with n-hexane, and the aromatic fraction is diluted 30 times with dichloromethane; specifically, n-hexane is used as the solvent and the saturated fraction is diluted at a liquid-to-solid ratio of 30 mL / g; and dichloromethane is used as the solvent and the aromatic fraction is dissolved at a liquid-to-solid ratio of 30 mL / g.

7. The method for analyzing the detailed hydrocarbon content in needle coke raw material according to claim 1, characterized in that: The parameters of the gas chromatography-mass spectrometry instrument in step (3) are: ionization voltage 70 eV, split ratio 50:1, carrier gas is helium, column flow rate is 1.2 mL / min, and injection volume is 1 μL.

8. The method for analyzing the detailed hydrocarbon content in needle coke raw material according to claim 1, characterized in that: The characteristic ion peak group includes ∑71, ∑69, ∑109, ∑128, ∑178, and ∑202, and the error of the inverse-decreasing coefficient correction is less than 1.5%.

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