CN114965792A - Analysis method for rapidly detecting content of C4-C22 alkane - Google Patents
Analysis method for rapidly detecting content of C4-C22 alkane Download PDFInfo
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- 238000004458 analytical method Methods 0.000 title claims abstract description 31
- 150000001335 aliphatic alkanes Chemical class 0.000 claims abstract description 48
- 238000000034 method Methods 0.000 claims abstract description 38
- 238000004817 gas chromatography Methods 0.000 claims abstract description 23
- 238000000926 separation method Methods 0.000 claims abstract description 20
- 238000004587 chromatography analysis Methods 0.000 claims abstract description 12
- 238000009835 boiling Methods 0.000 claims abstract description 11
- 239000007789 gas Substances 0.000 claims description 27
- VLKZOEOYAKHREP-UHFFFAOYSA-N n-Hexane Chemical compound CCCCCC VLKZOEOYAKHREP-UHFFFAOYSA-N 0.000 claims description 25
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 19
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 13
- 239000001257 hydrogen Substances 0.000 claims description 13
- 229910052739 hydrogen Inorganic materials 0.000 claims description 13
- 229910052757 nitrogen Inorganic materials 0.000 claims description 9
- 239000012159 carrier gas Substances 0.000 claims description 7
- 150000002431 hydrogen Chemical class 0.000 claims description 2
- 238000002156 mixing Methods 0.000 claims description 2
- 238000002203 pretreatment Methods 0.000 claims description 2
- 238000001514 detection method Methods 0.000 abstract description 15
- 239000000523 sample Substances 0.000 description 69
- 239000002808 molecular sieve Substances 0.000 description 21
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 description 21
- 239000012188 paraffin wax Substances 0.000 description 19
- -1 C12 alkane Chemical class 0.000 description 15
- 230000000052 comparative effect Effects 0.000 description 9
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 8
- 229910052799 carbon Inorganic materials 0.000 description 8
- 238000002309 gasification Methods 0.000 description 8
- 238000013375 chromatographic separation Methods 0.000 description 7
- 230000000694 effects Effects 0.000 description 7
- 238000002347 injection Methods 0.000 description 7
- 239000007924 injection Substances 0.000 description 7
- 238000005259 measurement Methods 0.000 description 7
- 239000000243 solution Substances 0.000 description 7
- DIOQZVSQGTUSAI-UHFFFAOYSA-N decane Chemical compound CCCCCCCCCC DIOQZVSQGTUSAI-UHFFFAOYSA-N 0.000 description 6
- 238000002360 preparation method Methods 0.000 description 6
- 239000012488 sample solution Substances 0.000 description 6
- 239000012086 standard solution Substances 0.000 description 6
- 239000012535 impurity Substances 0.000 description 5
- 230000014759 maintenance of location Effects 0.000 description 5
- 238000012986 modification Methods 0.000 description 5
- 230000004048 modification Effects 0.000 description 5
- 238000010606 normalization Methods 0.000 description 4
- 229910001220 stainless steel Inorganic materials 0.000 description 4
- 239000010935 stainless steel Substances 0.000 description 4
- 239000004215 Carbon black (E152) Substances 0.000 description 3
- 150000004945 aromatic hydrocarbons Chemical class 0.000 description 3
- 238000002485 combustion reaction Methods 0.000 description 3
- 229910001873 dinitrogen Inorganic materials 0.000 description 3
- 229930195733 hydrocarbon Natural products 0.000 description 3
- 150000002430 hydrocarbons Chemical class 0.000 description 3
- 239000000178 monomer Substances 0.000 description 3
- 238000002161 passivation Methods 0.000 description 3
- 238000005070 sampling Methods 0.000 description 3
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- 239000012085 test solution Substances 0.000 description 3
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- 238000010438 heat treatment Methods 0.000 description 2
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- 239000003153 chemical reaction reagent Substances 0.000 description 1
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- 238000001035 drying Methods 0.000 description 1
- 238000010812 external standard method Methods 0.000 description 1
- 239000002737 fuel gas Substances 0.000 description 1
- 125000004435 hydrogen atom Chemical group [H]* 0.000 description 1
- 229940057995 liquid paraffin Drugs 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N2030/022—Column chromatography characterised by the kind of separation mechanism
- G01N2030/025—Gas chromatography
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Abstract
The invention particularly relates to an analysis method for rapidly detecting the content of C4-C22 alkane, which belongs to the technical field of content analysis and comprises the following steps: pretreating alkane to be detected to reach the concentration to be detected, and obtaining a sample to be detected; carrying out gas chromatography analysis on the sample to be detected to obtain alkane content; wherein, the temperature of the sample inlet of the gas chromatographic analysis is set temperature, so that the sample to be detected is instantly gasified before entering the chromatographic column; the temperature rise procedure of the gas chromatographic analysis is step temperature rise so that components of the sample to be detected flow out at corresponding column temperatures through different boiling points to realize separation; the sample is instantly gasified before entering the chromatographic column through the sample inlet, then is rapidly and quantitatively transferred into the chromatographic column, and through the programmed temperature rise of the gradient temperature rise, the components in the sample flow out at the optimal column temperature through different boiling points, so that the separation is achieved, and the detection time is effectively shortened.
Description
Technical Field
The invention belongs to the technical field of content analysis, and particularly relates to an analysis method for rapidly detecting the content of C4-C22 alkane.
Background
The alkane detection is that an alkane sample is injected into a sample injection system of a gas phase analyzer, separation is carried out in a chromatographic column after temperature programming, and finally an electric signal is displayed in a detector so as to measure the peak area of the alkane sample.
In the prior art, the alkane analysis method is to inject a sample into a chromatographic system, the system is formed by connecting 2 double-gas-path gas chromatographs with a thermal conductivity cell detector in series, 2 chromatographic columns are arranged in a first chromatograph, one is a short chromatographic column without separation effect, and the other is a long distribution column with separation effect. The outlet of the thermal conductivity cell detector of the first instrument is connected with the inlets of two identical 5A molecular sieve chromatographic columns of the second instrument. The indirect method is used for measuring the content of the alkane, and the direct method is used for measuring the carbon distribution, wherein the non-distribution method is to measure the content of the non-normal alkane and then calculate the content of the normal alkane. Injecting the sample into a short chromatographic column without separation effect to obtain a full sample peak area, then introducing the sample into a 5A molecular sieve chromatographic column, deducting normal paraffin to obtain a non-normal paraffin peak area, comparing the non-normal paraffin peak area with the full sample peak area, calculating the mass percent of the non-normal paraffin by an external standard method, and subtracting the mass percent of the non-normal paraffin from one hundred to obtain the total normal paraffin content. The distribution method is to inject a sample into a long distribution column to obtain a full-sample chromatogram, then the sample passes through a 5A molecular sieve column to obtain a non-normal alkane distribution map, the background of the non-normal alkane distribution map is the same as that of the non-normal alkane of the full-sample chromatogram, and the net normal alkane peak area on the full-sample chromatogram can be determined from the slave plane. The relative distribution of the n-alkane monomers is calculated by a normalization method, and the percentage area of the n-alkane monomers in the sample can be obtained by combining the total content of the n-alkane monomers measured by a non-distribution method. The method has the advantages of complex operation and low utilization rate, not only causes the problems of high investment and operation cost, but also still cannot solve the problem of long detection time.
Disclosure of Invention
The application aims to provide an analysis method for rapidly detecting the content of C4-C22 alkane so as to solve the problem of long alkane detection time at present.
The embodiment of the invention provides an analysis method for rapidly detecting the content of C4-C22 alkane, which comprises the following steps:
pretreating alkane to be detected to reach the concentration to be detected, and obtaining a sample to be detected;
carrying out gas chromatography analysis on the sample to be detected to obtain alkane content;
wherein, the temperature of the sample inlet of the gas chromatographic analysis is set temperature, so that the sample to be detected is instantly gasified before entering the chromatographic column;
the temperature rise procedure of the gas chromatography is step temperature rise, so that the components of the sample to be detected flow out at the corresponding column temperature through different boiling points to realize separation.
Optionally, the set temperature is 275 ℃ to 300 ℃.
Optionally, the gradient temperature rise includes an initial section, a temperature rise section and a temperature drop section, the temperature of the initial section is 120 ℃, the heat preservation time of the initial section is 0.5min, the temperature rise rate of the temperature rise section is 10 ℃/min, the end point temperature of the temperature rise section is 300 ℃, the retention time of the end point temperature of the temperature rise section is 7min, the end point temperature of the temperature drop section is 100 ℃, and the retention time of the end point temperature of the temperature drop section is 5 min.
Optionally, the pre-treatment of the alkane to be detected specifically includes mixing the alkane to be detected and n-hexane.
Optionally, the volume ratio of the alkane to be detected to the n-hexane is 3: 97.
optionally, the sample feeding mode of the gas chromatography is forward sample feeding.
Optionally, the carrier gas for gas chromatography is nitrogen, and the flow rate of the nitrogen is 30mL/min-40 mL/min; the gas for gas chromatographic analysis is hydrogen, and the flow rate of the hydrogen is 30mL/min-40 mL/min; the combustion-supporting gas of the gas chromatographic analysis is air, and the flow rate of the air is 350mL/min-400 mL/min.
Optionally, the detector temperature for gas chromatography is 300 ℃ to 320 ℃.
Optionally, the gas chromatography split ratio is 10: 1.
optionally, the column flow rate for the gas chromatography is 1.0 mL/min.
One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:
according to the analysis method for rapidly detecting the content of the C4-C22 alkane, provided by the embodiment of the invention, a sample is instantly gasified before entering a chromatographic column through an injection port, then is rapidly and quantitatively transferred into the chromatographic column, and through the programmed temperature rise of gradient temperature rise, components in the sample flow out at the optimal column temperature through different boiling points, so that the separation is achieved, and the detection time is effectively shortened.
The foregoing description is only an overview of the technical solutions of the present invention, and the embodiments of the present invention are described below in order to make the technical means of the present invention more clearly understood and to make the above and other objects, features, and advantages of the present invention more clearly understandable.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
Fig. 1 is a flow chart of a method provided by an embodiment of the invention.
Detailed Description
The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.
Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
In order to solve the technical problems, the general idea of the embodiment of the application is as follows:
according to an exemplary embodiment of the present invention, there is provided an analytical method for rapidly detecting the content of C4-C22 alkane, the method including:
the device adopted by the whole method comprises: the system comprises a gas path system, a sample introduction system, a programmed temperature separation system, a detection and temperature control system and a recording system, wherein the gas path system comprises a gas source, a purification drying tube and a carrier gas flow rate control and gasification device; the sample injection system comprises a sample injector, a gasification chamber and a heating system, wherein the sample injector generally adopts a micro-injector and adopts a front sample injection port for sample injection; the gasification chamber is made of stainless steel pipes, and heating wires are arranged outside the pipes; the temperature programmed separation system comprises a column chamber, a chromatographic column and a temperature control component. The chromatographic column is a capillary column Agilent HP-PONA 19091S-001,50m 0.200mm 0.50 μm or the same type chromatographic column; the detection system comprises a detector, specifically, the detector is an FID detector; the temperature control system comprises the temperature of the gasification chamber, the temperature of the chromatographic column and the temperature of the detector.
S1, pretreating alkane to be detected to reach a concentration to be detected, and obtaining a sample to be detected;
in some embodiments, the pretreatment includes dilution of the sample with n-hexane to 3 → 100(V → V). N-hexane was chromatographically pure, and specifically, 3 volumes of the sample was mixed with 97 volumes of n-hexane in the dilution procedure.
The reason why the concentration of the sample to be measured is controlled to be 3% is that the chromatographic separation effect is better due to the decrease in the concentration of the sample, and the possibility of the resulting system contamination can be reduced to a lower level.
S2, carrying out gas chromatography analysis on the sample to be detected to obtain alkane content; wherein, the temperature of the sample inlet of the gas chromatographic analysis is set temperature, so that the sample to be detected is instantly gasified before entering the chromatographic column; the temperature rise procedure of the gas chromatography is step temperature rise, so that the components of the sample to be detected flow out at the corresponding column temperature through different boiling points to realize separation.
In some embodiments, the carrier gas for gas chromatography is nitrogen with a flow rate of 30-40ml/min, the fuel gas for gas chromatography is hydrogen with a flow rate of 30-40ml/min, the combustion-supporting gas for gas chromatography is air with a flow rate of 350-400 ml/min; the purity of the gas source is 99.99%.
The reason for controlling the nitrogen flow to be 30-40ml/min is that the detector has high sensitivity and good stability under the condition, the waste of resources can be caused by overlarge flow value, and the influence on the sensitivity of the detector can be caused by overlarge post dead volume caused by undersize.
The reason for controlling the hydrogen flow to be 30-40ml/min is that the detector has high sensitivity and good stability under the condition, the waste of resources is caused by overlarge flow, and the flame cannot be ignited due to undersize flow.
The reason for controlling the air flow to be 350-400ml/min is to ensure that the hydrogen is completely combusted, and if the air flow is too large, the resources are wasted, and if the air flow is too small, the baseline instability can be caused.
In some embodiments, the column flow rate for gas chromatography is 1.0mL/min and the split ratio for gas chromatography is 10: 1.
The column efficiency can be higher by controlling the flow rate of the column to be 1.0 mL/min; the control of the split ratio to be 10:1 can prevent the sample introduction overload from causing poor peak shape.
In some embodiments, the temperature of the vaporization chamber is 275-; the detector temperature is 300-320 ℃.
The reason for controlling the temperature of the gasification chamber to be 275 ℃ and 300 ℃ is that under the condition, the separation and peak shape of the components C4-C22 reach the optimal condition, the temperature is excessively high, so that the front part of the stationary phase of the column is peeled off or decomposed, the baseline is unstable, ghost peaks are caused, and the excessively low temperature causes the front peak.
The mechanism that components in a sample can flow out at the optimal column temperature through different boiling points by adopting gradient temperature rise is that the separation degree of the components with low boiling points is ensured by using lower temperature, and the components with slightly higher boiling points are ensured to be completely discharged as far as possible by gradually raising the temperature.
The programmed temperature has the advantages of improving separation, narrowing peaks, reducing detection limit, saving time and the like.
The analytical method for rapidly detecting the content of C4-C22 alkane according to the present invention will be described in detail below with reference to examples, comparative examples and experimental data.
Example 1
The method for rapidly determining the content of the C4-C22 alkane in the embodiment takes C12 alkane as an example, and is determined according to the following steps:
(1) preparation of test solution
3.0ml of the sample solution was aspirated into a 100.0ml volumetric flask into which about 30ml of n-hexane had been added, and was shaken up after the volume had been made up to the mark.
(2) Preparation of control solutions
3.0ml of the standard solution was taken up into a 100.0ml volumetric flask into which about 30ml of n-hexane had been added, and was shaken up after the volume had been made up to the mark.
(3) Measurement by gas chromatography
The chromatographic conditions were as follows:
a chromatographic column: agilent HP-PONA 19091S-001,50m × 0.200mm × 0.50 μm or the same type of chromatographic column
A detector: FID detector sampling mode: front sample introduction
Carrier gas: nitrogen gas; nitrogen flow rate: 30ml/min
Gas combustion: hydrogen gas; hydrogen flow rate: 40ml/min
Combustion-supporting gas: air; air flow rate: 400ml/min
Temperature of a front sample inlet: detector temperature at 290 ℃: 320 deg.C
The split ratio is as follows: 10:1
Column flow rate: 1.0ml/min
Column temperature: gradient temperature rise
| -- | Speed/min | Numerical value of DEG C | Retention time (min) | Run time (min) |
| Initial | - | 120 | 0.5 | 0.5 |
| First order procedure | 10 | 300 | 7 | 25.5 |
| After operation | - | 100 | 5 | - |
And respectively injecting a sample solution to be tested and a standard solution, and finally calculating the area percentage content of C12 alkane.
The detection results of the samples and the samples are shown in table 1, the average value of the content of C12 alkane in the sample 1 is 99.76%, the average value of the content of C12 alkane in the sample 2 is 99.76%, and the average value of the content of C12 alkane in the present embodiment is 99.76%.
Table 1:
example 2
The method for rapidly determining the content of the C4-C22 alkane in the embodiment takes C12 alkane as an example, and is determined according to the following steps:
(1) preparation of test solution
3.0ml of the sample solution was aspirated into a 100.0ml volumetric flask into which about 30ml of n-hexane had been added, and shaken up after the volume had been brought to the mark.
(2) Preparation of control solutions
3.0ml of the standard solution was taken up into a 100.0ml volumetric flask into which about 30ml of n-hexane had been added, and was shaken up after the volume had been made up to the mark.
(3) Measurement by gas chromatography
The chromatographic conditions were as follows:
and (3) chromatographic column: agilent HP-PONA 19091S-001,50m × 0.200mm × 0.50 μm or the same type of chromatographic column
A detector: FID detector sampling mode: front sample introduction
Carrier gas: nitrogen gas; nitrogen flow rate: 30ml/min
Gas combustion: hydrogen gas; hydrogen flow rate: 40ml/min
Combustion-supporting gas: air; air flow rate: 400ml/min
Front injection port temperature: detector temperature at 290 ℃: 320 deg.C
The split ratio is as follows: 10:1
Column flow rate: 1.0ml/min
Column temperature: gradient temperature rise
| -- | Speed/min | Numerical value of DEG C | Retention time (min) | Run time (min) |
| Initial | - | 120 | 0.5 | 0.5 |
| First order procedure | 10 | 300 | 7 | 25.5 |
| After operation | - | 100 | 5 | - |
And respectively injecting a sample solution to be tested and a standard solution, and finally calculating the area percentage content of C12 alkane.
The detection results of the samples and the samples are shown in table 2, the average value of the content of C12 alkane in the sample 1 is 99.68%, the average value of the content of C12 alkane in the sample 2 is 99.71%, and the average value of the content of C12 alkane in the present embodiment is 99.70%.
Table 2:
example 3
The method for rapidly determining the content of the C4-C22 alkane in the embodiment takes C12 alkane as an example, and is determined according to the following steps:
(1) preparation of test solution
3.0ml of the sample solution was aspirated into a 100.0ml volumetric flask into which about 30ml of n-hexane had been added, and was shaken up after the volume had been made up to the mark.
(2) Preparation of control solutions
3.0ml of the standard solution was taken up into a 100.0ml volumetric flask into which about 30ml of n-hexane had been added, and was shaken up after the volume had been made up to the mark.
(3) Measurement by gas chromatography
The chromatographic conditions were as follows:
a chromatographic column: agilent HP-PONA 19091S-001,50m × 0.200mm × 0.50 μm or the same type of chromatographic column
A detector: FID detector sampling mode: front sample introduction
Carrier gas: nitrogen gas; nitrogen flow rate: 30ml/min
Gas combustion: hydrogen gas; hydrogen flow rate: 40ml/min
Combustion-supporting gas: air; air flow rate: 400ml/min
Front injection port temperature: detector temperature at 290 ℃: 320 deg.C
The split ratio is as follows: 10:1
Column flow rate: 1.0ml/min
Column temperature: gradient temperature rise
| -- | Speed/min | Numerical value of DEG C | Retention time (min) | Run time (min) |
| Initial | - | 120 | 0.5 | 0.5 |
| First order procedure | 10 | 300 | 7 | 25.5 |
| After operation | - | 100 | 5 | - |
And respectively injecting a sample solution to be tested and a standard solution, and finally calculating the area percentage content of C12 alkane.
The detection results of the samples and the samples are shown in table 3, the average value of the content of C12 alkane in the sample 1 is 99.71%, the average value of the content of C12 alkane in the sample 2 is 99.69%, and the average value of the content of C12 alkane in the present embodiment is 99.70%.
Table 3:
comparative example 1
This comparative example was compared using petrochemical industry standards with example 1: namely SH/T0410-92, which is measured by a method comprising the following steps:
(1) passivation of 5A molecular sieves
Several portions of aromatic hydrocarbon were continuously injected into the molecular sieve column.
The method for testing whether the molecular sieve can effectively adsorb the normal alkane is as follows: injecting 1 microliter of n-decane into the molecular sieve column, if the impurities of non-normal alkanes have obvious deviation from the known value, indicating that the molecular sieve needs to be replaced.
(2) Adjusting detector bridge flow
The bridge flow of the two chromatographs is about 170mA, under the normal operation condition, when the signals of the two detectors are matched, the non-normal hydrocarbon of the completely-removed normal alkane is injected, and if the front and rear peak areas of the molecular sieve are the same, the bridge flow is not changed later.
(3) Chromatographic separation conditions
Hydrogen flow rate: 70 ml/min;
temperature of the gasification chamber: 300 ℃;
detector temperature: 300 ℃;
column temperature: and (4) measuring the total content of the normal paraffin. The first chromatograph is at constant temperature and is selected to be 240 ℃ according to the property of a sample; and (3) measuring the carbon number distribution, wherein the first chromatograph adopts a temperature program to raise the temperature, the temperature raising rate ensures that the washing time of the high-boiling-point component is 25min, and the second chromatograph measures the total content of the normal alkane and the carbon number distribution and has a column temperature of 300 ℃.
A chromatographic column: a first stainless steel short packed column without separation function, which is 100cm long and 4mm in inner diameter, is filled with 101 white silanization supporter; the other chromatographic column is a distribution column with the length of 300cm and the inner diameter of 4mm, and is internally filled with a 60-80-mesh acid-washed chromoeorb 'p' supporter and coated with 20 percent of silicon rubber SE 30.
(4) Determination of total content of n-alkanes
Under typical operation conditions of chromatographic separation, 1 microliter of each two needles of a sample and a standard sample are injected into a short chromatographic column, and the total content of the normal alkane is calculated according to an area normalization method.
(5) Calculation of analysis results
The alkane content was calculated as area percent.
The results of the measurements and calculations performed in steps (1), (2), (3), (4) and (5) are shown in table 2, the average of the C12 paraffin content in sample 1 is 99.70%, the average of the C12 paraffin content in sample 2 is 99.70%, and the average of the results shows that the C12 paraffin content in this embodiment is 99.70%.
Table 4:
comparative example 2
This comparative example was compared using petrochemical industry standards and example 2: namely SH/T0410-92 in the method for measuring normal paraffin content and carbon number distribution (gas chromatography) in standard liquid paraffin and raw materials in petrochemical industry of the people's republic of China, the method is characterized in that:
(1) passivation of 5A molecular sieves
Several portions of aromatic hydrocarbon were continuously injected into the molecular sieve column.
The method for testing whether the molecular sieve can effectively adsorb the normal alkane is as follows: injecting 1 microliter of n-decane into the molecular sieve column, if the impurities of non-normal alkanes have obvious deviation from the known value, indicating that the molecular sieve needs to be replaced.
(2) Adjusting detector bridge flow
The bridge flow of the two chromatographs is about 170mA, under the normal operation condition, when the signals of the two detectors are matched, the non-normal hydrocarbon of the completely-removed normal alkane is injected, and if the front and rear peak areas of the molecular sieve are the same, the bridge flow is not changed later.
(3) Chromatographic separation conditions
Hydrogen flow rate: 70 ml/min;
temperature of the gasification chamber: 300 ℃;
detector temperature: 300 ℃;
column temperature: and (4) measuring the total content of the normal paraffin. The first chromatograph is at a constant temperature, and is selected to be 240 ℃ according to the properties of the sample; and (3) measuring the carbon number distribution, wherein the first chromatograph adopts a temperature program to raise the temperature, the temperature raising rate ensures that the washing time of the high-boiling-point component is 25min, and the second chromatograph measures the total content of the normal alkane and the carbon number distribution and has a column temperature of 300 ℃.
A chromatographic column: a first stainless steel short packed column without separation function, which is 100cm long and 4mm in inner diameter, is filled with 101 white silanization supporter; the other chromatographic column is a distribution column with the length of 300cm and the inner diameter of 4mm, and is internally filled with a 60-80-mesh acid-washed chromoeorb 'p' supporter and coated with 20 percent of silicon rubber SE 30.
(4) Determination of total content of n-alkanes
Under typical operation conditions of chromatographic separation, 1 microliter of each two needles of a sample and a standard sample are injected into a short chromatographic column, and the total content of the normal alkane is calculated according to an area normalization method.
(5) Calculation of analysis results
The alkane content was calculated as area percent.
The results of the measurements and calculations performed in steps (1), (2), (3), (4) and (5) are shown in table 4, the average of the C12 paraffin content in sample 1 is 99.70%, the average of the C12 paraffin content in sample 2 is 99.70%, and the average of the results shows that the C12 paraffin content in this embodiment is 99.70%.
Table 5:
comparative example 3
This comparative example was compared using petrochemical industry standards and example 3: namely SH/T0410-92, which is measured by a method comprising the following steps:
(1) passivation of 5A molecular sieves
Several portions of aromatic hydrocarbon were continuously injected into the molecular sieve column.
The method for testing whether the molecular sieve can effectively adsorb the normal alkane is as follows: injecting 1 microliter of n-decane into the molecular sieve column, if the impurities of non-normal alkanes have obvious deviation from the known value, indicating that the molecular sieve needs to be replaced.
(2) Adjusting detector bridge flow
The bridge flow of the two chromatographs is about 170mA, under the normal operation condition, when the signals of the two detectors are matched, the non-normal hydrocarbon of the completely-removed normal alkane is injected, and if the front and rear peak areas of the molecular sieve are the same, the bridge flow is not changed later.
(3) Chromatographic separation conditions
Hydrogen flow rate: 70 ml/min;
temperature of the gasification chamber: 300 ℃;
detector temperature: 300 ℃;
column temperature: and (4) measuring the total content of the normal paraffin. The first chromatograph is at a constant temperature, and is selected to be 240 ℃ according to the properties of the sample; and (3) measuring the carbon number distribution, wherein the first chromatograph adopts a temperature program to raise the temperature, the temperature raising rate ensures that the washing time of the high-boiling-point component is 25min, and the second chromatograph measures the total content of the normal alkane and the carbon number distribution and has a column temperature of 300 ℃.
A chromatographic column: a first stainless steel short packed column without separation function, which is 100cm long and 4mm in inner diameter, is filled with 101 white silanization supporter; the other chromatographic column is a distribution column with the length of 300cm and the inner diameter of 4mm, and is internally filled with a 60-80-mesh acid-washed chromoeorb 'p' supporter and coated with 20 percent of silicon rubber SE 30.
(4) Determination of total content of n-alkanes
Under typical operation conditions of chromatographic separation, 1 microliter of each two needles of a sample and a standard sample are injected into a short chromatographic column, and the total content of the normal alkane is calculated according to an area normalization method.
(5) Calculation of analysis results
The alkane content was calculated as area percent.
The results of the measurements and calculations performed in steps (1), (2), (3), (4) and (5) show in table 6, the average C12 paraffin content in sample 1 is 99.64%, the average C12 paraffin content in sample 2 is 99.65%, and the average C12 paraffin content in this embodiment is 99.65%.
Table 6:
the summary tables of the measurement results of the methods for rapidly measuring the alkane content in examples 1 to 3 are shown in table 7.
TABLE 7
As can be seen from Table 7, the alkane contents detected by the methods of examples 1 to 3 are generally higher than those detected by the methods of comparative examples 1 to 3 according to the petrochemical industry standards, and are closer to the true values, and the deviation of the alkane contents detected by the two methods is 0.03%, so that the standard deviation requirement is met. And the petrochemical industry standard detection of the alkanes adopted in the comparative examples 1 to 3 is complex in operation, large in operation error and long in time consumption.
One or more technical solutions in the embodiments of the present invention at least have the following technical effects or advantages:
(1) according to the method provided by the embodiment of the invention, different column temperatures are formulated according to different boiling points of related substances in a mixture, the related substances are quickly separated after a temperature raising program is determined, and the analysis time is shortened and the energy consumption is reduced on the premise that the peak areas of impurities reach the detection limit, the impurities are mutually separated and the separation degree meets the requirement;
(2) according to the method provided by the embodiment of the invention, the sample is instantly gasified before entering the chromatographic column through the sample inlet, and then is rapidly and quantitatively transferred into the chromatographic column. Through temperature programming, components in the sample flow out at the optimal column temperature through different boiling points, so that separation is achieved, the detection time is shortened, the analysis time of the sample is about 30min, the detection time is greatly shortened, and the energy consumption of 1/3 is reduced.
Finally, it should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (10)
1. An analysis method for rapidly detecting the content of C4-C22 alkane, which is characterized by comprising the following steps:
pretreating alkane to be detected to reach the concentration to be detected, and obtaining a sample to be detected;
carrying out gas chromatography analysis on the sample to be detected to obtain alkane content;
wherein, the temperature of the sample inlet of the gas chromatographic analysis is set temperature, so that the sample to be detected is instantly gasified before entering the chromatographic column;
the temperature rise procedure of the gas chromatography is step temperature rise, so that the components of the sample to be detected flow out at the corresponding column temperature through different boiling points to realize separation.
2. The analytical method for rapidly detecting the content of C4-C22 alkane according to claim 1, wherein the set temperature is 275 ℃ to 300 ℃.
3. The analytical method for rapidly detecting the content of C4-C22 alkanes according to claim 1, wherein the gradient temperature rise comprises an initial section, a temperature rise section and a temperature drop section, the temperature of the initial section is 120 ℃, the holding time of the initial section is 0.5min, the temperature rise rate of the temperature rise section is 10 ℃/min, the end temperature of the temperature rise section is 300 ℃, the holding time of the end temperature of the temperature rise section is 7min, the end temperature of the temperature drop section is 100 ℃, and the holding time of the end temperature of the temperature drop section is 5 min.
4. The analytical method for rapidly detecting the content of C4-C22 alkanes according to claim 1, wherein the pre-treatment of the alkanes to be detected specifically comprises mixing the alkanes to be detected with n-hexane.
5. The analytical method for rapidly detecting the content of C4-C22 alkanes according to claim 4, wherein the volume ratio of the alkanes to be detected to n-hexane is 3: 97.
6. the analytical method for rapidly detecting the content of C4-C22 alkane according to claim 1, wherein the sample introduction manner of the gas chromatography is forward sample introduction.
7. The analytical method for rapidly detecting the content of C4-C22 alkane in claim 1, wherein the carrier gas for the gas chromatographic analysis is nitrogen, and the flow rate of the nitrogen is 30-40 mL/min; the gas for gas chromatographic analysis is hydrogen, and the flow rate of the hydrogen is 30mL/min-40 mL/min; the combustion-supporting gas of the gas chromatographic analysis is air, and the flow rate of the air is 350mL/min-400 mL/min.
8. The analytical method for rapidly detecting the content of C4-C22 alkane in claim 1, wherein the detector temperature of the gas chromatography is 300-320 ℃.
9. The analytical method for rapidly detecting the content of C4-C22 alkane in claim 1, wherein the split ratio of the gas chromatographic analysis is 10: 1.
10. the analytical method for rapidly detecting the content of C4-C22 alkane in claim 1, wherein the column flow rate of the gas chromatographic analysis is 1.0 mL/min.
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