Method for Determining Trace Benzene Series Compounds in Fischer-Tropsch Synthesis Light Naphtha
Through the combined use of all two-dimensional gas chromatography-time-of-flight mass spectrometry technology, combined with specific heating procedures and analytical conditions, the accuracy and efficiency of trace benzene detection in Fischer-Tropsch synthesis light naphtha was solved, and efficient separation and accurate detection of components were achieved.
Patent Information
- Application Number
- CN202310165724.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-02-24
- Publication Date
- 2025-08-01
- Estimated Expiration
- 2043-02-24
AI Technical Summary
The prior art is difficult to accurately detect trace benzene in Fischer-Tropsch synthesis of light naphtha, and the traditional methods are costly and inefficient.
The combination of all two-dimensional gas chromatography-time-of-flight mass spectrometry technology is used, combined with specific heating procedures and analysis conditions, and the components in light naphtha are separated by non-polar and medium polar columns to achieve accurate detection of trace benzene.
The detection accuracy and efficiency of trace benzene is improved, the experimental time is optimized, and the accuracy and rationality of the detection results are ensured.
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Figure CN116068088B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of analytical test components, and particularly relates to a method for determining trace benzene series compounds in Fischer-Tropsch synthetic light naphtha. Background Technique
[0002] Coal-based Fischer-Tropsch synthesis is a process in which syngas produced by coal gasification is used as a raw material and converted into liquid hydrocarbon compounds under the action of a catalyst. The products have the characteristics of complete and continuous carbon number distribution, high content of straight-chain alkanes and alkenes, and no sulfur, nitrogen, and dienes. The light naphtha components in its synthesis products mainly include alkanes, alkenes, and organic oxygen-containing compounds such as alcohols, aldehydes, acids, ketones, and esters, as well as trace benzene series compounds. In order to more accurately qualitatively and quantitatively analyze the main components, it is necessary to separate and identify the trace benzene series compounds.
[0003] Currently, the methods for testing benzene series compounds include gas chromatography-mass spectrometry, chemical reaction methods, gas chromatography, etc. The chemical reaction methods are complex and the processes are cumbersome. For gas chromatography and gas chromatography-mass spectrometry methods, the peak capacity of the chromatograph is small, the chromatographic peaks overlap severely, and trace benzene series compounds cannot be detected. At the same time, when these methods are used for determination, the samples need to be pretreated, and generally solid-phase extraction technology is required for pretreatment, resulting in high costs.
[0004] For the separation and analysis of complex systems of naphtha, the biggest disadvantage of traditional one-dimensional chromatography as an analytical technique based on separation is the insufficient peak capacity, making it difficult to obtain satisfactory analysis results. The comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOFMS) coupling technology has unique advantages in the analysis of complex components. Comprehensive two-dimensional gas chromatography is a two-dimensional system that uses a modulator to connect two chromatographic columns with different separation mechanisms and independent of each other in series. This system has the advantages of high resolution, high sensitivity, high peak capacity, and short analysis time, and can measure the main components while determining the separated target components.
[0005] The research hopes to use comprehensive two-dimensional gas chromatography to detect trace benzene series compounds in Fischer-Tropsch synthetic light naphtha. However, it is found in the actual detection process that if the heating rate is too fast, the trace benzene series compounds cannot be separated and the measurement results are inaccurate. On the contrary, if the heating rate is too slow, the measurement time is long and the efficiency is low. Summary of the Invention
[0006] In view of this, it is necessary to provide a method for determining trace benzene series compounds in Fischer-Tropsch synthetic light naphtha.
[0007] The solution of the present invention to solve its technical problems is:
[0008] A method for determining trace benzene series compounds in Fischer-Tropsch synthetic light naphtha, adding Fischer-Tropsch synthetic light naphtha into comprehensive two-dimensional gas chromatography for component detection;
[0009] Among them, the specific heating program is as follows: the initial temperature is 30 - 35°C and is maintained for 15 - 25 min, then it is heated to 180 - 250°C at a rate of 1 - 5°C / min and held for 5 - 15 min.
[0010] Preferably, the modulation period is 1 - 5 s; the ionization source voltage is 70 - 90 eV; the ion source temperature is 200 - 250°C; the frequency is 100 Hz, and the period is 1 - 5 s.
[0011] Preferably, the specific heating program is as follows: the initial temperature is 30 - 35°C and is maintained for 15 - 25 min, then it is heated to 180 - 250°C at a rate of 1.5 - 2°C / min and held for 5 - 15 min.
[0012] Preferably, the modulation period is 5 s; the ionization source voltage is 90 eV; the ion source temperature is 250°C; the frequency is 100 Hz, and the period is 1 - 5 s.
[0013] Preferably, the specific heating program is as follows: the initial temperature is 35°C and is maintained for 15 min, then it is heated to 200°C at a rate of 4.7 - 5°C / min and held for 10 min, and then heated to 220°C at a rate of 2°C / min and held for 15 min, with the temperature error within 0.3°C, the modulation period is 3 s; and it is held for 5 min.
[0014] Preferably, the ionization source voltage is 70 eV; the ion source temperature is 250°C; the frequency is 100 Hz, the mass range is 33 - 450 amu, and the period is 4 s.
[0015] Preferably, the analysis conditions of comprehensive two-dimensional gas chromatography: the model of the first-dimensional column is HP - PONA, and the parameters are 50 m * 0.25 mm * 0.5 μm; the model of the second-dimensional column is MS, and the parameters are 2 m * 0.10 mm * 0.25 μm.
[0016] Preferably, the carrier gas flow rate is 0.5 - 2.0 mL·min-1, the split ratio is 100 - 200; the inlet temperature: 200 - 250°C, and the injection volume is 0.1 - 0.5 μL.
[0017] Preferably, the analysis conditions of time-of-flight mass spectrometry in comprehensive two-dimensional gas chromatography are: the mass acquisition range is 33 - 450 amu, the transfer line temperature is 200 - 250°C, the acquisition frequency is 100 - 120 full spectra / s, the ion source temperature is 200 - 220°C, and the detector voltage is 1250 - 1500 V.
[0018] Preferably, the components of Fischer - Tropsch synthetic light naphtha are: the alkane content is 20 - 40%, the alkene content is 40 - 70%, the oxygenate content is 1 - 5%, and the benzene series content is 0 - 1%.
[0019] Beneficial effects: The method for determining trace benzene series compounds in Fischer-Tropsch synthetic light naphtha of the present invention uses a linear programmed temperature rising method, and the components of trace benzene series compounds in light naphtha are determined in the preferred range of 1-5 °C / min. At the same time, a non-polar column and a medium polar column in comprehensive two-dimensional gas chromatography-time of flight mass spectrometry are used to separate naphtha according to boiling point in one dimension and polarity in the second dimension, realizing the separation of trace components in Fischer-Tropsch synthetic light naphtha, improving the accuracy of detection results, reasonably solving the problem of long detection time in the experimental process, and reasonably optimizing the time required for the experiment. Brief Description of the Drawings
[0020] Figure 1 It is the determination result of all components of Fischer-Tropsch naphtha in the method for determining trace benzene series compounds in Fischer-Tropsch synthetic light naphtha of the present invention. Detailed Embodiments
[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.
[0022] A method for determining trace benzene series compounds in Fischer-Tropsch synthetic light naphtha. Add Fischer-Tropsch synthetic light naphtha into comprehensive two-dimensional gas chromatography for component detection;
[0023] The specific temperature rising program is as follows: the initial temperature is 30-35 °C and is maintained for 15-25 min, and then it is raised to 180-250 °C at 1-5 °C / min and maintained for 5-15 min.
[0024] When measuring components, take 2 mL of Fischer-Tropsch synthetic light naphtha, and use a pipette gun to add Fischer-Tropsch synthetic light naphtha into comprehensive two-dimensional gas chromatography for component detection. During the experiment, the temperature is adjusted linearly. The initial temperature is adjusted to 30-35 °C and maintained for 15-25 min, then it is raised to 180-250 °C at 1-5 °C / min and maintained for 5-15 min, improving the accurate qualitative determination of benzene series compounds, and separating alkanes, alkenes, oxides, and benzene series compounds into different regions respectively to obtain the distribution of all components.
[0025] Further, the modulation period is 1-5 s; the ionization source voltage is 70-90 eV; the ion source temperature is 200-250 °C; the frequency is 100 Hz, and the period is 1-5 s.
[0026] Further, the specific temperature rising program is as follows: the initial temperature is 30-35 °C and is maintained for 15-25 min, and then it is raised to 180-250 °C at 1.5-2 °C / min and maintained for 5-15 min.
[0027] Further, the modulation period is 5 s; the ionization source voltage is 90 eV; the ion source temperature is 250 °C; the frequency is 100 Hz, and the period is 1 - 5 s.
[0028] Further, the specific temperature rising program is as follows: the initial temperature of 35 °C is maintained for 15 min, then it is heated to 200 °C at a rate of 4.7 °C - 5 °C / min and held for 10 min, and then heated to 220 °C at a rate of 2 °C / min and held for 15 min. The temperature error is within 0.3 °C, the modulation period is 3 s; and it is held for 5 min.
[0029] Under the two-stage temperature change, the content of trace benzene series in Fischer-Tropsch synthetic light naphtha can be detected, making the result more accurate. On the two-dimensional chromatogram, as the retention time extends, the molecular polarity of the eluted substances increases. The top several groups of pink, blue, orange, etc. are aldehydes, ketones, alcohols, esters, acids and other oxides as well as benzene series. At the same time, with the increase of the temperature gradient, the data accuracy is higher and the recovery rate of the added standard for measuring all components is more accurate.
[0030] Further, the ionization source voltage is 70 eV; the ion source temperature is 250 °C; the frequency is 100 Hz, the mass range is 33 - 450 amu, and the period is 4 s.
[0031] Further, the analysis conditions of the comprehensive two-dimensional gas chromatography: the model of the first-dimensional column chromatographic column is HP-PONA, and the parameters are 50 m * 0.25 mm * 0.5 μm; the model of the second-dimensional column chromatographic column is MS, and the parameters are 2 m * 0.10 mm * 0.25 μm.
[0032] During the process of detecting components in Fischer-Tropsch synthetic light naphtha, the non-polar column and the medium-polar column are used to separate the naphtha according to the boiling point in one dimension and the polarity in the second dimension, facilitating the detection of components.
[0033] Further, the carrier gas flow rate is 0.5 - 2.0 mL·min-1, the split ratio is 100 - 200; the inlet temperature: 200 - 250 °C, and the injection volume is 0.1 - 0.5 μL.
[0034] Further, the analysis conditions of the time-of-flight mass spectrometry in the comprehensive two-dimensional gas chromatography are: the mass acquisition range is 33 - 450 amu, the transfer line temperature is 200 - 250 °C, the acquisition frequency is 100 - 120 full spectra / s, the ion source temperature is 200 - 220 °C, and the detector voltage is 1250 - 1500 V.
[0035] Further, the components of Fischer-Tropsch synthetic light naphtha are: the alkane content is 20 - 40%, the alkene content is 40 - 70%, the oxygenate content is 1 - 5%, and the benzene series content is 0 - 1%.
[0036] The experimental results are related to the components of Fischer-Tropsch synthesis light naphtha. Identifying the components of Fischer-Tropsch synthesis light naphtha is equivalent to reducing a variable and ensuring the accuracy of the experimental results.
[0037] The present invention will be further described below by way of examples, but the present invention is not limited thereto.
[0038] Example 1
[0039] Take 2 ml of Fischer-Tropsch synthesis light naphtha and put it into a chromatographic vial, and directly conduct the determination by comprehensive two-dimensional gas chromatography. The analysis conditions of the comprehensive two-dimensional gas chromatography are adjusted as follows: the carrier gas flow rate is 1.0 mL·min-1, and the split ratio is 200. The inlet temperature: 250 °C, and the injection volume is 0.2 μL. The model of the first-dimensional column chromatographic column is HP-PONA, and the parameters are 50 m * 0.25 mm * 0.5 μm; the model of the second-dimensional column chromatographic column is MS, and the parameters are 2 m * 0.10 mm * 0.25 μm. The specific temperature rising program: the initial temperature is 30 °C, rising to 200 °C at a rate of 5 °C / min, and the modulation period is 3 s. Hold for 10 min. The ionization source voltage is 70 eV; the ion source temperature is 250 °C; the frequency is 100 Hz, the mass range is 33 - 450 amu, and the period is 4 s.
[0040] After the test, qualitative analysis is carried out by using the Chroma TOF data processing software and the NIST 05 spectral library. In the data processing method, the parameters are set at a certain first-dimensional peak width (generally set as 4 times the modulation period) and second-dimensional peak width (generally 0.1 s). By comparing the mass spectrometry diagrams, the fragments of the peaks with a similarity greater than 700 are combined to calculate the peak area.
[0041] Table 1 Determination results of benzene series compounds in Fischer-Tropsch synthesis light naphtha
[0042] Name R.T.(s) Similarity Formula CAS Quant Masses Ethylbenzene 2136,2.100 889 C8H10 100-41-4 91 o-Xylene 2190,2.070 923 C8H10 95-47-6 91 p-Xylene 2196,2.060 886 C8H10 106-42-3 91 Propyl-Benzene 2694,2.030 897 C9H12 103-65-1 91
[0043] In Fischer-Tropsch synthesis light naphtha, taking S / N≥100 as the standard, and by comparing with the NIST spectral library, taking the similarity greater than 800 as the standard, a total of 5 benzene series compounds are identified. The too fast temperature rising rate causes some benzene series compounds not to be separated.
[0044] Example 2
[0045] Take 2 ml of Fischer-Tropsch synthesis light naphtha and put it into a chromatographic vial, and directly conduct the determination by comprehensive two-dimensional gas chromatography. The analysis conditions of the comprehensive two-dimensional gas chromatography are adjusted as follows: the carrier gas flow rate is 1.0 mL·min-1, and the split ratio is 200. The inlet temperature: 250 °C, and the injection volume is 0.2 μL. The model of the first-dimensional column chromatographic column is HP-PONA, and the parameters are 50 m * 0.25 mm * 0.5 μm; the model of the second-dimensional column chromatographic column is MS, with parameters of 2m * 0.10 mm * 0.25 μm. Specific temperature rising program: initial temperature 35°C, hold for 15 min, rise to 200°C at a rate of 2°C / min, temperature error within 0.3°C, modulation period 3 s. Hold for 5 min. Ionization source voltage 70 eV; ion source temperature 250°C; frequency 100 Hz, mass range 33 - 450 amu, period 4 s.
[0046] After the test, qualitative analysis was carried out using the NIST 05 spectral library through Chroma TOF data processing software. In the data processing method, the parameters were set at a certain one-dimensional peak width (generally set to 4 times the modulation period) and two-dimensional peak width (generally 0.1 s). By comparing the mass spectrometry diagrams, the fragments of the peaks with a similarity above 700 were combined to calculate the peak area.
[0047] Table 2 Determination results of benzene series compounds in Fischer-Tropsch synthetic light naphtha
[0048] Name R.T.(s) Similarity Formula CAS Quant Masses Ethylbenzene 2136,2.100 895 C8H10 100-41-4 91 o-Xylene 2190,2.070 916 C8H10 95-47-6 91 p-Xylene 2196,2.060 830 C8H10 106-42-3 91 m-Xylene 2325,2.150 939 C8H10 108-38-3 91 Propyl-Benzene 2694,2.030 857 C9H12 103-65-1 91 3-Ethyltoluene 2832,2.140 832 C9H12 620-14-4 105 4-Ethyltoluene 2736,2.040 869 C9H12 622-96-8 105 1,2,3-Trimethyl-Benzene 2913,2.080 841 C9H12 526-73-8 105
[0049] In Fischer-Tropsch synthetic light naphtha, with the standard of S / N ≥ 100 and by comparing with the NIST spectral library, with the standard of similarity greater than 800, a total of 8 benzene series compounds were identified. According to the boiling point order of ethylbenzene < o-xylene < p-xylene < m-xylene < propyl-benzene < 3-ethyltoluene < 4-ethyltoluene < 1,2,3-trimethyl-benzene, the peaks appeared in sequence.
[0050] Example 3
[0051] According to the conditions of Example 2, a standard addition recovery experiment was carried out, and the standard addition recovery rates of the target products are shown in Table 3:
[0052] Table 3 Standard addition recovery rates of target products
[0053]
[0054]
[0055] The standard addition recovery rates obtained from the experimental results were below 60%, not meeting the requirements of quantitative accuracy.
[0056] Example 4
[0057] Take 2 ml of Fischer-Tropsch synthetic light naphtha and put it into a chromatographic vial, then directly enter the comprehensive two-dimensional gas chromatography for determination. The analysis conditions of the comprehensive two-dimensional gas chromatography were adjusted as follows: carrier gas flow rate 1.0 mL·min-1, split ratio 200. Injector temperature: 250°C, injection volume 0.2 μL. The model of the one-dimensional column chromatographic column is HP-PONA, with parameters of 50 m * 0.25 mm * 0.5 μm; the model of the two-dimensional column chromatographic column is MS, with parameters of 2m * 0.10 mm * 0.25 μm. Specific temperature rising program: The initial temperature is 35°C and is maintained for 15 min, then it is heated to 200°C at a rate of 4.7°C - 5°C / min and held for 10 min, and then heated to 220°C at a rate of 2°C / min and held for 15 min. The temperature error is within 0.3°C, and the modulation period is 3 s. Hold for 5 min. Ionization source voltage: 70 eV; ion source temperature: 250°C; frequency: 100 Hz, mass range: 33 - 450 amu, period: 4 s.
[0058] After the test, qualitative analysis is carried out using the NIST 05 spectral library through the Chroma TOF data processing software. In the data processing method, the parameters are set at a certain one-dimensional peak width (generally set as 4 times the modulation period) and two-dimensional peak width (generally 0.1 s). Through the comparison of mass spectrometry diagrams, the fragments of peaks with a similarity above 700 are merged to calculate the peak area.
[0059] By gradient temperature rising, not only can the benzene series be accurately qualitatively analyzed, but also alkanes, alkenes, oxides, and benzene series can be separated respectively into different regions, obtaining the full-component distribution, as Figure 1 shown.
[0060] Comprehensive two-dimensional chromatography has a group separation effect. In addition to qualitatively analyzing the benzene series, the full-component distribution of light naphtha can also be seen. The first and second-dimensional chromatographic columns are respectively due to the different polarities of compounds, and the entire chromatogram is divided into different regions. Each zone represents a group of substances. On the one-dimensional chromatography, as the retention time extends, the boiling point of the eluted substances increases. The lowest red group is alkanes with the weakest polarity (including straight-chain and branched-chain), and the carbon number increases with the increase of retention time in the one-dimensional direction. The green group is alkenes with a relatively stronger polarity than alkanes (including straight-chain and branched-chain), and the carbon number also increases with the increase of retention time in the one-dimensional direction. Since the boiling point of normal alkenes with the same carbon number is higher than that of isoalkenes, the isoalkenes have a higher one-dimensional retention time than normal alkenes. Some compounds appear in pairs in the chromatogram, which is due to the existence of cis-trans isomerism in alkenes. On the two-dimensional chromatography, as the retention time extends, the molecular polarity of the eluted substances increases. The top several groups of pink, blue, orange, etc. are oxides such as aldehydes, ketones, alcohols, esters, acids, and benzene series. At the same time, with the gradient increase of temperature, the data accuracy is higher, and the spiked recovery rate of measuring the full components is more accurate.
[0061] Example 5
[0062] According to the conditions of Example 4, the spiked recovery experiment is carried out again, and the spiked recovery rates of the target products measured are shown in Table 4:
[0063] Table 4
[0064]
[0065]
[0066] The spiked recovery treatment is carried out on the naphtha sample to be measured. Take two identical samples, add a certain amount of mixed standard benzene series to one of them, and measure both under the above comprehensive two-dimensional gas chromatography conditions to obtain the measured values of the spiked sample and the measured values of the blank sample (without adding standard benzene series). The spiked recovery rate is between 90% and 105%, within the allowable standard recovery rate range of the experiment.
[0067] Example 6
[0068] Mixtures of 8 benzene series standard products with different concentrations (1 ppm, 3 ppm, 5 ppm, 7 ppm, 10 ppm) are measured under the comprehensive two-dimensional gas chromatography conditions of Example 4 to obtain a standard curve. The content of benzene series in naphtha is obtained for the target component to be measured through the standard curve.
[0069] Table 5 Determination results of benzene series content in Fischer-Tropsch synthesis light naphtha
[0070]
[0071]
[0072] The content of the naphtha sample to be measured is detected. Take two identical samples, add a certain amount of mixed standard benzene series to one of them, and measure both under the comprehensive two-dimensional gas chromatography conditions of Example 4. The content of benzene series in naphtha can be accurately obtained through calculation, and the numerical value of each data can be obtained more specifically.
[0073] The above-disclosed are only the preferred embodiments of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Those of ordinary skill in the art can understand the whole or partial processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the invention.
Claims
1. A method for determining trace benzene series compounds in Fischer-Tropsch synthesis light naphtha, characterized in that: The Fischer-Tropsch synthesis light naphtha is added to the comprehensive two-dimensional gas chromatography for component detection; Among them, the analysis conditions of comprehensive two-dimensional gas chromatography are as follows: the carrier gas flow rate is 0.5 - 2.0 mL·min -1 ; injection port temperature: 200 - 250 °C; the model of the first-dimensional column is HP-PONA, with parameters of 50 m * 0.25 mm * 0.5 μm; the model of the second-dimensional column is Rxi-17Sil MS, with parameters of 2 m * 0.10 mm * 0.25 μm; The specific temperature programming procedure is as follows: the initial temperature is 35 °C and is held for 15 min, then it is heated to 200 °C at a rate of 4.7 - 5 °C / min and held for 10 min, and then heated to 220 °C at a rate of 2 °C / min and held for 15 min. The temperature error is within 0.3 °C, and the modulation period is 3 s; The analysis conditions of the time-of-flight mass spectrometry in the comprehensive two-dimensional gas chromatography are: the mass acquisition range is 33 - 450 amu, the transfer line temperature is 200 - 250 °C, the frequency is 100 Hz, the ion source temperature is 200 - 250 °C, the detector voltage is 1250 - 1500 V, and the ionization source voltage is 70 eV; The trace benzene series compounds include ethylbenzene, o-xylene, p-xylene, m-xylene, propyl-benzene, 3-ethyltoluene, 4-ethyltoluene, and 1,2,3-trimethyl-benzene.
2. The method for determining trace benzene series compounds in Fischer-Tropsch synthesis light naphtha according to claim 1, wherein: The ion source temperature is 250 °C.
3. The method for determining trace benzene series compounds in Fischer-Tropsch synthesis light naphtha according to claim 1, characterized in that: The split ratio is 100 - 200, and the injection volume is 0.1 - 0.5 μL.
4. The method for determining trace benzene series compounds in Fischer-Tropsch synthetic light naphtha according to claim 1, wherein: The content of benzene series compounds in the Fischer-Tropsch synthesis light naphtha is 0% - 1%.