Method for Determining Contents of Target Components in a Gas Mixture by Raman Spectroscopy

Abstract

The present invention provides a method for determining the contents of target components in a gas mixture by Raman spectroscopy, comprising performing Raman spectroscopic detection on the gas mixture to obtain a Raman spectrum; selecting one characteristic peak from the Raman spectrum as the reference peak, and its corresponding component serves as the reference component, and normalizing the characteristic peaks in the Raman spectrum relative to the reference peak to obtain the relative Raman peak heights of various characteristic peaks; determining the peak positions of the characteristic peaks of various target components in the Raman spectrum of the gas mixture in combination with the Raman spectra of the pure target components; determining the molar ratios or volume ratios of the target components to the reference component in the gas mixture based on the relative Raman peak heights of the target components and regression coefficient(s) obtained from a training sample set of the gas mixture; and determining the molar fractions or volume fractions of various target components in the gas mixture based on the molar ratios or volume ratios of the target components to the reference component.

Description

Method for Determining Contents of Target Components in a Gas Mixture by Raman SpectroscopyTechnical FieldThe present invention relates to a method for determining the contents of target components in a gas mixture by Raman spectroscopy, and particularly to a method for determining the contents of various target components in an ethylene cracking gas mixture by Raman spectroscopy.Background ArtAnalysis of raw organic materials in production plants, including ethylene, propylene, and butadiene, especially effluent gases from ethylene cracking furnaces, is very important. The gas-phase material (cracking gas) at the outlet of an ethylene cracking furnace mainly contains light fractions such as H₂, CH₄, C₂H₆, C₂H₄, C₃H₈, C₃H₆, and C₄H₈. Measuring the concentrations of these components allows operators to determine the cracking depth and the product distribution inside the furnace, which supports optimization of the process parameters of the cracking reaction.Gas chromatography (GC) is one of the common methods for analyzing the composition of a gas mixture. For example, for analysis of the cracking gas composition in an ethylene cracking furnace, a multi-dimensional gas chromatograph is mainly used. Through a switching system with multiple columns and multiple valves, using various techniques such as cutting, back-flushing, and capillary columns, different components in the sample gas are separately detected on different paths and different detectors (e.g., a flame ionization detector FID detects hydrocarbon content in the gas mixture, and a thermal conductivity detector TCD detects H₂ content and N₂ content in the gas mixture), so as to obtain analysis results of multiple components in the cracking gas, such as from H₂ to toluene. Its advantage is that the analysis results are comprehensive and rich in information, but the interval time between two injections (i.e., the time required for sample analysis and instrument preparation for the next injection) is usually about 20 minutes, or even 30 minutes or longer. In addition, on-line chromatographic detection and analysis also have disadvantages such as complex systems, numerous auxiliary devices, and high on-site maintenance workload, which limit its widespread application.Due to the increased output of cracking furnaces and the diversity of cracking raw materials, the maximization of production benefits requires increasingly faster detection and analysis speeds for specific production indicators such as cracking depth, in order to adjust process parameters and optimize product distribution timely. In recent years, spectroscopic methods such as near-infrared and Raman spectroscopy have been increasingly applied to the rapid detection and analysis of cracking raw materials and liquid-phase products. Laser Raman spectroscopy technology is a molecular structure characterization technology based on the Raman scattering effect, which can achieve non-destructive and rapid analysis of samples. Moreover, the spectral detection system has a simple structure, low maintenance cost, and easy operation, so it has been widely used in fields such as petroleum refining, chemicals, and pharmaceuticals.However, currently, for the technology of analyzing the composition of a gas mixture by laser Raman spectroscopy, due to problems such as low gas molecular density, small scattering cross-sections, and weak Raman spectra, it is difficult to use this technology in the analysis of a gas mixture with many components. In particular, for a process gas mixture, such as ethylene cracking gas, which has an approximately atmospheric pressure, a weak Raman signal, many components, and severe signal interference, it is difficult to obtain fast and accurate analysis results.In summary, the current methods for detecting and analyzing a gas mixture have problems such as slow speed and / or poor accuracy of results, thus failing to achieve rapid and accurate detection and analysis of a gas mixture, especially a gas mixture with many components, such as ethylene cracking gas mixtures.Summary of the InventionWith respect to the technical problems of slow speed and / or poor accuracy of results in the detection and analysis methods of a gas mixture in the prior art, the present invention provides a method for determining the contents of target components in a gas mixture by Raman spectroscopy, which can achieve rapid and accurate detection and analysis of a gas mixture (such as an ethylene cracking gas mixture).To achieve the above objectives, in a first aspect, the present invention provides a method for determining the contents of target components in a gas mixture by Raman spectroscopy, comprising1) performing Raman spectroscopic detection on the gas mixture to obtain a Raman spectrum;2) selecting one characteristic peak from the Raman spectrum as the reference peak, and its corresponding component serves as the reference component, and normalizing the characteristic peaks of various target components in the Raman spectrum relative to the reference peak to obtain the relative Raman peak heights of various characteristic peaks;3) determining the peak positions of the characteristic peaks of various target components in the Raman spectrum of the above gas mixture, in combination with the Raman spectra of the pure target components;4) determining the molar ratios or volume ratios of the target components to the reference component in the gas mixture, based on the relative Raman peak heights of the characteristic peaks at the specific peak positions of the target components obtained in steps 2) and 3) and one or more, preferably one or two, regression coefficient(s) obtained from a training sample set of the gas mixture; and5) determining the molar fractions or volume fractions of various target components in the gas mixture, based on the molar ratios or volume ratios of the target components to the reference component obtained in step 4).In a second aspect, the present invention provides a Raman spectroscopic analysis apparatus, comprising a processor and a memory, wherein the memory stores at least one computer program, and when executed by the processor, the at least one computer program causes the processor to perform the method for determining the contents of target components in a gas mixture by Raman spectroscopy according to the first aspect.In a third aspect, the present invention provides a computer-readable storage medium, which stores at least one program instruction, and causes the computer to perform the method for determining the contents of target components in a gas mixture by Raman spectroscopy according to the first aspect when executed by a processor.In a fourth aspect, the present invention further provides a computer program product, comprising at least one program instruction, which, when executed by a processor, causes the processor to perform the method for determining the contents of target components in a gas mixture by Raman spectroscopy according to the first aspect.In a fifth aspect, the present invention provides an on-line detection and analysis system for a gas mixture based on Raman spectroscopy, comprising a sampling unit, a Raman spectroscopic detection unit, and the Raman spectroscopic analysis apparatus according to the second aspect;wherein the sampling unit is respectively connected to the outlet pipeline of the reactor and to the Raman spectroscopic detection unit, wherein the Raman spectroscopic detection unit is used for detecting the gas mixture collected by the sampling unit to obtain a Raman spectrum of the gas mixture; the Raman spectroscopic detection unit is also connected to the Raman spectroscopic analysis apparatus, wherein the Raman spectroscopic analysis apparatus is used for analyzing the Raman spectrum of the gas mixture to obtain the molar fractions or volume fractions of various target components in the gas mixture.The method according to the present invention can achieve at least the following technical effects:(1) The Raman spectroscopic analysis method and the on-line detection system for the content of each component in a gas mixture according to the present invention can achieve rapid and accurate quantitative analysis of a process gas mixture (such as an ethylene cracking gas mixture);(2) The Raman spectroscopic analysis method for the content of each component in a gas mixture according to the present invention determines the contents of various components based on the relative Raman peak heights of various components. The model structure is simple and has strong adaptability, and can be applied to on-line real-time analysis of the composition of cracking gas obtained from different reactions.Brief Description of DrawingsFigure 1 is a flowchart illustrating an embodiment of the method for determining the contents of target components in a gas mixture by Raman spectroscopy according to the present invention;Figure 2 is an original Raman spectrum of an untreated ethylene cracking gas mixture detected by an embodiment of the method for determining the contents of target components in a gas mixture by Raman spectroscopy according to the present invention;Figure 3 is a Raman spectrum obtained after target background subtraction and baseline correction of Figure 2;Figure 4 is a Raman spectrum obtained after target background subtraction and baseline correction and normalization processing of Figure 3;Figure 5 is a schematic structural diagram of an embodiment of the Raman spectroscopic analysis apparatus according to the present invention;Figure 6 is a hardware architecture diagram of an embodiment of the on-line detection and analysis system of an ethylene cracking gas mixture based on Raman spectroscopy according to the present invention;Figure 7 is a working principle diagram of an embodiment of the on-line detection and analysis system of an ethylene cracking gas mixture based on Raman spectroscopy according to the present invention;Figure 8 is a comparison of the volume fraction values of four target components (H₂, methane, ethylene, propylene) determined by an embodiment of the method for determining the contents of target components in a gas mixture by Raman spectroscopy according to the present invention with the volume fraction values of the four target components (H₂, methane, ethylene, propylene) determined by gas chromatography.Detailed DescriptionThe embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The following embodiments serve illustrative purposes only and shall not be construed as limitations to the technical scope of the present invention.It should be noted that, without conflict, the features in the distinct technical solutions of the present invention can be combined with each other.In this disclosure, it should also be noted that, unless otherwise clearly specified and limited, the terms such as "installation," "connection," should be interpreted broadly. For example, it may be fixedly installed or connected, or detachably installed or connected; it may be directly installed or connected, or indirectly installed or connected; it may be a wired connection or a wireless connection. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the context of this disclosure.Any specific numerical value disclosed herein (including the endpoints of numerical ranges) is not limited to an exact value of the numerical value, but should be understood to also encompass values close to the exact value, such as all possible numerical values within ±5% of the exact value. Furthermore, for the disclosed numerical ranges, one or more new numerical range(s) can be obtained by arbitrarily combining the endpoint values, an endpoint value with a specific point value within the range, and the various specific point values, and these new numerical ranges should also be considered as specifically disclosed herein.Unless otherwise defined, the terms used herein have the same meanings as commonly understood by those skilled in the art. If a term is defined herein and its definition differs from the common understanding in the art, the definition herein shall prevail.The expressions "comprise" or "include" used herein should be interpreted as including all specifically mentioned features as well as optional, additional, unspecified features. As used herein, the use of the term "comprise" also discloses options where no other features beyond the specifically mentioned features are present, such as the expressions "consist essentially of..." and "consist of...".In the context of this application, the term "one or more" has the same meaning as "at least one" and can therefore be used interchangeably.In a first aspect, as shown in Figure 1, the present invention provides a method for determining the contents of target components in a gas mixture by Raman spectroscopy, comprising1) performing Raman spectroscopic detection on the gas mixture to obtain a Raman spectrum;2) selecting one characteristic peak from the Raman spectrum as the reference peak, and its corresponding component serves as the reference component, and normalizing the characteristic peaks of various target components in the Raman spectrum relative to the reference peak to obtain the relative Raman peak heights of various characteristic peaks;3) determining the peak positions of the characteristic peaks of various target components in the Raman spectrum of the gas mixture in combination with the Raman spectra of the pure target components;4) determining the molar ratios or volume ratios of the target components to the reference component in the gas mixture based on the relative Raman peak heights of the characteristic peaks at the specific peak positions of the target components obtained in steps 2) and 3) and one or more, preferably one or two, regression coefficient(s) obtained from a training sample set of the gas mixture; and5) determining the molar fractions or volume fractions of various target components in the gas mixture based on the molar ratios or volume ratios of the target components to the reference component obtained in step 4).In the context of this application, the "target component" includes the reference component and other components in addition to the reference component whose contents in the gas mixture need to be determined.Preferably, when a target component includes more than one characteristic peak in the Raman spectrum of the gas mixture, one characteristic peak is selected and its relative Raman peak height is used in step 4) for determining the molar ratios or volume ratios of the target components to the reference component.In the context of this application, the "gas mixture" refers to a product mixture containing more than one gas produced by a certain reaction, preferably a cracking reaction, particularly a hydrocarbon steam cracking reaction. For example, the reaction raw material for preparing the gas mixture can be a product obtained from processing crude oil, for example, it can be ethane, propane, topped oil, raffinate oil, naphtha, kerosene, diesel oil, and / or hydrogenated tail oil. The "steam cracking" refers to a process in which petroleum hydrocarbons or petroleum fractions (such as naphtha) undergo molecular fracture and / or a dehydrogenation reaction at a high temperature (e.g., above 750°C) in the presence of steam and usually without using a catalyst.The term "cracking reaction" refers to a chemical change process that converts a compound with a higher molecular weight into one or more compound(s) with lower molecular weights through thermal energy. According to the present invention, the cracking reaction may or may not use a catalyst. Preferably, the cracking reaction is a cracking reaction carried out at a temperature ranging from 700°C to 1000°C without using a catalyst.According to the present invention, the "gas mixture" may be an on-line detection gas mixture and / or a process gas mixture collected at the outlet of a continuous reactor. Current methods for analyzing the contents of the components in a gas mixture by Raman spectroscopy usually require pressurizing the gas to be detected to enhance the signal to obtain accurate analysis results, but pressurization requires additional equipment and operations and may cause liquefaction of the gas to be detected, resulting in inaccurate analysis results. The method for analyzing the contents of the components in a gas mixture according to the present invention can be used to analyze Raman spectra obtained from detection of gases at normal temperature and normal pressure, and is therefore more suitable for the analysis of on-line detection gas mixtures and / or process gas mixtures. The "continuous reactor" refers to a reactor into which reactants enter in a continuous manner and where reactions are carried out under stable reaction conditions inside the reactor. Typically, reactants enter and leave the reactor at a constant rate, and the material concentrations do not change over time.Preferably, the gas mixture is a process gas mixture and / or an on-line detection gas mixture. Preferably, the "process gas mixture and / or on-line detection gas mixture" is not a finished gas product, but a product gas mixture collected at the outlet of a continuous reactor, preferably a continuous cracking reactor, especially a steam cracking reactor.The "Raman spectrum" may be a Raman spectrum detected by any type of spectrometer commonly used in the field of chemistry and chemical engineering. For example, the Raman spectrum can be obtained using a spectrometer (Ocean Optics QE Pro).The "reference peak" refers to a characteristic peak in the Raman spectrum whose relative Raman intensity is set to 1 through normalization processing. Correspondingly, the "normalization processing" refers to a process of setting the reference peak to a relative Raman intensity of 1 and adjusting the relative intensities of other characteristic peaks in the Raman spectrum accordingly.Since Raman spectroscopic detection generates fingerprint peaks, each component in the mixture may generate multiple characteristic peaks with different intensities and peak positions. This increases the difficulty of determining the contents of various components in the mixture. Therefore, accurately selecting the reference peak is particularly important, and accurately selecting the reference peak can effectively improve the accuracy of the analysis results of the contents of various components in the mixture.The "Raman spectra of the pure target components" refers to the Raman spectra obtained by separately detecting each pure target component and optionally balance gas(es). Preferably, an inert gas, such as N₂, is used as the balance gas during the test. In practical analysis, by separately detecting the Raman spectrum of each pure target component, the characteristic peak positions of various target components in the Raman spectrum of the gas mixture can be obtained. The characteristic peaks refer to the unique Raman scattering peaks of each substance, which correspond to specific vibrational modes of the molecule.Optionally, before selecting the characteristic peaks of the target components based on the Raman spectra of the pure target components and using them to calculate their molar ratios or volume ratios relative to the reference component, i.e., between steps 3) and 4), an optimization step 3') for the relative Raman peak heights of the characteristic peaks is included.Specifically, for step 3'), in order to overcome or at least mitigate the influence of coexisting substances on the relative Raman peak heights of the target components, the relative Raman peak height(s) of one or more characteristic peak(s) obtained by normalization in step 2) can subtract the relative Raman peak height of a reference peak at a reference point within 50 cm⁻¹, preferably within 30 cm⁻¹, of the respective peak position to obtain the optimized relative Raman peak height(s) of that characteristic peak(s).For example, the gas mixture contains 3-20 target components. For each target component, a characteristic peak is selected and its relative Raman peak height is used to calculate its molar ratio or volume ratio relative to the reference component. The step 3') which optimizes the relative Raman peak heights as described above can be performed for a portion or all of the target components, for example, from 1 to 3, such as 1, 2, or 3 target components. For example, the gas mixture contains from 5 to 15 target components. For each target component, a characteristic peak is selected and its relative Raman peak height is used to calculate its molar ratio or volume ratio relative to the reference component. The optimization step 3') as described above can be performed for a portion or all of the target components, for example, from 1 to 5 or from 2 to 4, such as 1, 2, 3, 4, or 5 target components. For example, the gas mixture contains from 7 to 20 or from 7 to 15 target components. For each target component, a characteristic peak is selected and its relative Raman peak height is used to calculate its molar ratio or volume ratio relative to the reference component. The step 3') which optimizes the relative Raman peak heights as described above can be performed for a portion or all of the target components, for example, from 1 to 7, from 2 to 6, or from 3 to 5, such as 1, 2, 3, 4, 5, 6, or 7 target components.For example, if the characteristic peak of target component A at 1200 cm⁻¹ is selected to calculate its molar ratio or volume ratio relative to the reference component, its original relative Raman peak height is a, and there is a reference peak with a relative Raman peak height of b at a reference point within the range of 1150 cm⁻¹ to 1250 cm⁻¹ (e.g., at 1220 cm⁻¹). For optimization, the optimized relative Raman peak height a' can be obtained by subtracting the relative Raman peak height b of the reference point from the original relative Raman peak height a of the characteristic peak.According to the present invention, the "normal temperature" refers to 10°C to 40°C, preferably 15°C to 35°C; the "normal pressure" refers to an absolute pressure of 0.1 MPa to 0.15 MPa.Regarding step 4), the one or more regression coefficient(s) can be determined according to any common chemometric method or statistical regression model. For example, the regression coefficient(s) can be determined using the least squares method, such as the least squares method in Matlab.Preferably, the training sample set of the gas mixture includes Raman spectra of the gas mixture and the molar ratios or volume ratios of the target components to the reference component in the gas mixture.Preferably, the molar ratios or volume ratios of the target components to the reference component in the gas mixture of the training sample set are obtained by measuring the contents of various target components in the gas mixture using gas chromatography.When the gas mixture is a process gas mixture and / or an on-line detection gas mixture, the regression coefficient(s) are preferably determined by the following steps:i) collecting gas mixture samples at the outlet of a continuous reactor at two or more time points;ii) performing Raman spectroscopic detection and gas chromatographic detection, respectively, on the gas mixture samples collected at the same time point, wherein the relative Raman peak heights of the target components relative to the reference component are obtained from the detected Raman spectra, and the molar ratios or volume ratios of the target components to the reference component are obtained by gas chromatographic detection, wherein the corresponding sets of said relative Raman peak heights and said molar ratios or volume ratios obtained at each time point form a training sample set; andiii) using the training sample set in combination with a statistical regression model to establish the relationship between the relative Raman peak heights and the molar ratios or volume ratios described in step ii), thereby obtaining the regression coefficient(s).According to the present invention, the detection time of the gas mixture in the gas chromatograph can be determined according to the number and types of target components in the gas mixture and the elution times of these target components when detected using the gas chromatograph. For example, if the target components elute earlier when detected using gas chromatography, the gas chromatographic detection time can be appropriately shortened, i.e., it is sufficient that all target components whose contents are to be determined have eluted, without waiting for all components to elute.Preferably, the gas mixture samples are collected at 5 or more time points, preferably 10 or more time points, more preferably 15 or more time points, even more preferably 20 or more time points. For example, the gas mixture samples are collected at 5 to 50 time points, preferably 10 to 40 time points, more preferably 15 to 35 time points, even more preferably 20 to 30 time points.In some embodiments, two gas mixture samples are collected simultaneously for Raman spectroscopic detection and gas chromatographic detection, respectively. In some embodiments, the collected gas mixture sample is first subjected to Raman spectroscopic detection and then to gas chromatographic detection.Preferably, the relative Raman peak heights of the target components in step ii) are obtained from the detected Raman spectra according to steps 2) and 3) above. Specifically, a characteristic peak is selected from the Raman spectrum as a reference peak, preferably a characteristic peak at the same peak position as in step 2), and its corresponding component serves as the reference component, and the characteristic peaks of various target components in the Raman spectrum are normalized relative to the reference peak to obtain the relative Raman peak heights of various characteristic peaks. When a target component includes more than one characteristic peak in the Raman spectrum of the gas mixture, one characteristic peak (preferably a characteristic peak at the same peak position as in step 4)) is selected and its relative Raman peak height is used in the step of determining the regression coefficient(s).For step ii), in order to obtain the molar ratios or volume ratios of the target components to the reference component in the gas mixture of the training sample set, for example, the molar fractions or volume fractions of various target components in the gas mixture can first be measured using gas chromatography, and then the molar ratios or volume ratios of the target components to the reference component in the gas mixture can be calculated.Since the regression coefficient(s) used in the method for determining the contents of various components in a gas mixture according to the present invention are obtained based on a training sample set of the gas mixture (rather than one or two components therein) and the molar ratios or volume ratios in the training sample set are obtained using gas chromatography, the influence of other components in the gas mixture than the target components on the Raman spectrum is fully considered. Therefore, by means of the regression coefficient(s) of the present invention, the contents of various target components in the gas mixture can be obtained more accurately.Once the regression coefficient(s) used in the method for determining the content of various components in a gas mixture according to the present invention are obtained using the training sample set, the regression coefficient(s) can be repeatedly used subsequently to quickly and accurately determine the molar ratios or volume ratios of the target components to the reference component in similar gas mixtures, and then quickly and accurately obtain the molar fractions or volume fractions of various target components in the gas mixture. For large-scale production processes (e.g., with an annual output of over 100,000 tons) where the reaction raw materials remain basically the same and the reaction types and conditions are similar for a long period (e.g., one year or longer), quickly and accurately adjusting the process parameters for the contents of the primary components in the on-line detection gas mixture can effectively increase the yields of the target components (e.g., ethylene).Preferably, the method according to the present invention includes, between steps 1) and 2), a step 1') of performing background subtraction and baseline correction on the original Raman spectrum of the gas mixture.The "background subtraction" refers to removing the influence of factors such as background other than the feed components on the Raman spectrum, thereby improving the accuracy and reliability of the Raman spectral data. The "baseline correction" refers to the process of adjusting the baseline of the feed component peaks to zero. The "background subtraction" and "baseline correction" can be performed using any conventional method and standards existing in instrument analysis-related software.Figure 2 shows an original Raman spectrum obtained by detecting a gas mixture using a Raman spectrometer (Ocean Optics QE Pro). The original Raman spectrum in Figure 2 is subjected to background subtraction and baseline correction to obtain Figure 3, where P0, P1, and P2 are the characteristic peaks of N₂, ethylene, and H₂, respectively. Normalization using the P1 peak as the reference peak yields Figure 4. It can be seen that by introducing background subtraction and baseline correction techniques into the method according to the present invention, and using a characteristic peak of the reference component as a reference for normalizing various characteristic peaks in the Raman spectrum, the repeatability of the Raman spectrum can be greatly improved, and the influence of pressure fluctuations of the gas mixture and changes in spectral detection conditions (such as laser power) on the Raman spectrum can be significantly reduced.According to the present invention, the gas mixture comprises organic gas(es) and / or inorganic gas(es).Preferably, the gas mixture comprises 2 or more, preferably 3 or more, more preferably 5 or more, even more preferably 7 or more organic gases. For example, the gas mixture comprises from 2 to 20, or from 3 to 20, or from 5 to 15, or from 7 to 10 organic gases.More preferably, the organic gas is a gas composed of carbon and hydrogen elements and optionally having unsaturated bonds, wherein the organic gas preferably has one to seven carbon atoms, more preferably one to four carbon atoms, even more preferably one to three carbon atoms.Preferably, the gas mixture comprises at least one organic gas composed of carbon and hydrogen elements and having unsaturated bond(s).By means of the method for determining the contents of target components in a gas mixture by Raman spectroscopy according to the present invention, the contents of various components in a process gas mixture and / or an on-line detection gas mixture that is present at normal temperature and normal pressure and contains multiple (e.g., 5 or more, or even 7 or more) organic gases can be accurately obtained.Preferably, the gas mixture contains n target components, where n is an integer greater than or equal to 2, preferably greater than or equal to 3, more preferably greater than or equal to 5, preferably less than or equal to 50, more preferably less than or equal to 30, even more preferably less than or equal to 20. Their molar fractions or volume fractions are cj (j = 1, …, n), and their Raman peak heights are Pj (j = 1, …, n). According to the principles of Raman spectroscopy, for different components in the same mixture, the ratio of the Raman peak height of the j-th component to that of the reference component should be proportional to their molar fractions or volume fractions, and is independent of the detection conditions and the feed gas pressure. Thus, the following equation can be obtained: (1)in Equation (1), Pj is the Raman peak height of the j-th component in the gas mixture, P1 is the Raman peak height of the reference component in the gas mixture, Kj is the Raman intensity factor of the j-th component in the gas mixture, K1 is the Raman intensity factor of the reference component in the gas mixture (it is usually assumed that the Raman intensity factor of the reference component is 1), cj is the molar fraction or volume fraction of the j-th component in the gas mixture, and c1 is the molar fraction or volume fraction of the reference component in the gas mixture, where j=1 corresponds to the reference component.For the normalized spectrum of any gas mixture, the characteristic peak height (i.e., relative Raman peak height) P1 of the reference component is set to be 1. From Equation (1), the following Equation (2) can be obtained: (j = 1, ..., n) (2)wherein zj is the molar ratio or volume ratio of the j-th component to the reference component in the gas mixture, cj is the molar fraction or volume fraction of the j-th component in the gas mixture, c1 is the molar fraction or volume fraction of the reference component in the gas mixture, Pj is the relative Raman peak height of the j-th component in the gas mixture, and kj is the regression coefficient of the j-th component in the gas mixture, where j=1 corresponds to the reference component.Equation (2) is more suitable for the gas mixtures with fewer components (e.g., consisting of only 5 or fewer gases and containing 2 or fewer organic gases, and where the peaks of various components are relatively distinct).To improve the calculation accuracy of the analysis model, Equation (2) can be further extended to:zj = kj0 +kj1Pj, (j = 1,…, n) (3)wherein zj is the molar ratio or volume ratio of the j-th component to the reference component in the gas mixture, Pj is the relative Raman peak height of the j-th component in the gas mixture, kj0 is the first regression coefficient of the j-th component in the gas mixture, and kj1 is the second regression coefficient of the j-th component in the gas mixture, where j=1 corresponds to the reference component.The regression coefficients kj, kj0, and kj1 in Equations (2) and (3) are preferably determined through steps i), ii), and iii) described above.Preferably, for any gas mixture of unknown composition, which contains n target components, where n is an integer greater than or equal to 2, preferably greater than or equal to 3, more preferably greater than or equal to 5, preferably less than or equal to 50, more preferably less than or equal to 30, even more preferably less than or equal to 20, the sum of the molar fractions or volume fractions of these n target components is 1, i.e.: (4)wherein z1=1, thus equation (4) can be further extended to: (5)Therefore, the molar fractions or volume fractions of various target components in the gas mixture are shown as follows: (6)wherein cj is the molar fraction or volume fraction of the j-th component in the gas mixture, zj is the molar ratio or volume ratio of the j-th component to the reference component in the gas mixture, and zi is the molar ratio or volume ratio of the i-th component to the reference component in the gas mixture, where j=1 corresponds to the reference component.By means of the above regression coefficient(s) of the present invention and the above Equations (2) or (3), particularly Equation (3), and Equation (6) for determining the molar ratios or volume ratios of the target components in the gas mixture, the molar fractions or volume fractions of various target components in the gas mixture, particularly an on-line detection gas mixture or a process gas mixture, can be obtained simply, quickly, and accurately.Preferably, the gas mixture is an ethylene cracking gas mixture containing ethylene obtained through a cracking reaction, preferably a steam cracking reaction. Furthermore, the gas mixture may also be a cracking gas mixture containing other hydrocarbons such as propylene obtained through a cracking reaction.The terms "ethylene cracking gas" or "ethylene cracking gas mixture" can be used interchangeably in the context of this application and refer to a mixture containing ethylene produced by cracking a certain raw material. Such a mixture is preferably a process gas mixture and / or an on-line detection gas mixture.Preferably, the content of ethylene in the target components of the "ethylene cracking gas" or "ethylene cracking gas mixture" is 15% by weight or more, preferably 20% by weight or more, more preferably 30% by weight or more, for example, 15% by weight to 70% by weight, or 20% by weight to 60% by weight, or 30% by weight to 50% by weight, relative to the total weight of the target components of the ethylene cracking gas or ethylene cracking gas mixture.Preferably, the ethylene cracking gas mixture comprises hydrogen, methane, ethane, ethylene, acetylene, propane, propylene, propyne, and optionally butene and / or butadiene.Preferably, the reference component of the ethylene cracking gas mixture is ethylene.Preferably, the characteristic peak of ethylene located near 1345 cm⁻¹ is used as the reference peak.According to the context of the present invention, the expression "near 1345 cm⁻¹" means 1345 cm⁻¹ ± 10 cm⁻¹, preferably 1345 cm⁻¹ ± 5 cm⁻¹, more preferably 1345 cm⁻¹ ± 2 cm⁻¹.By selecting the characteristic peak of ethylene located near 1345 cm⁻¹ as the reference peak, the accuracy of the analysis results for the content of each component in the ethylene cracking gas mixture can be effectively improved.When the gas mixture is an ethylene cracking gas mixture that is an on-line detection gas or a process gas, and hydrogen, methane, ethane, ethylene, acetylene, propane, propylene, and propyne account for 80% or more by volume of the contents of the target components in the gas mixture, in order to obtain the regression coefficient(s) of the present invention, the analysis cycle of the target components of the gas mixture by the gas chromatograph can be approximately 15 minutes (a TCD detector and an FID detector can be used), wherein the "analysis cycle" generally includes program heating time, elution time, and program cooling time.Optionally, before the ethylene cracking gas mixture is subjected to Raman spectroscopic detection, some direct Raman signal enhancement measures can be implemented from a hardware perspective, including: increasing the laser power, increasing the collection angle of the Raman scattered light, reducing the optical signal transmission loss, improving the detection sensitivity of the spectrometer while reducing the detection noise level (e.g., using CCD cooling), and appropriately increasing integration time of the spectrometer (e.g., setting integration time of the spectrometer to a range from 30 s to 90 s). The introduction of these measures can further enhance the on-line Raman spectroscopic detection signal of the ethylene cracking gas mixture.Preferably, the Raman spectroscopic detection is performed under the following conditions: a laser power of greater than or equal to 1 W, preferably 1 W to 3 W; and / or a spectral line width of less than or equal to 0.2 nm, preferably less than or equal to 0.15 nm; and / or a spectral integration time of 30 s to 90 s, preferably 50 s to 70 s, more preferably 45 s to 60 s. Such detection conditions can address the problem of low pressure of the ethylene cracking gas mixture, which affects the detection accuracy.Furthermore, the Raman spectroscopic detection can be performed under conditions of a spectral range of 300 to 3100 cm⁻¹ and / or a spectral resolution of no greater than 10 cm⁻¹, preferably no greater than 8 cm⁻¹, more preferably no greater than 6 cm⁻¹, thereby ensuring that the Raman spectrometer is applicable to the detection of process gas mixtures and / or on-line detection gas mixtures, and ensuring the stability of the Raman spectrometer under on-line operating conditions. At the same time, the spectral range can ensure coverage of the Raman characteristic spectral regions of the target components in the ethylene cracking gas mixture, and the spectral resolution can ensure the accuracy of the spectral measurement.The Raman spectroscopic detection can use a charge-coupled device (CCD) detector. To reduce the noise level of the detector while improving the signal-to-noise ratio, a highly sensitive Raman spectrometer can be selected. The detector of such a Raman spectrometer can be a back-illuminated CCD area array detector equipped with a semiconductor cooler (also known as a thermoelectric cooler, abbreviated as TEC), wherein the cooling temperature is typically lower than or equal to -15°C.Based on the above hardware selection and parameter design, the Raman spectroscopic detection signal is improved, the noise level is reduced, and engineering implementation and application are relatively convenient.For the analysis of the contents in the ethylene cracking gas mixture according to the method of the present invention, the molar fractions or volume fractions of various target components in the gas mixture can be obtained in about 1 minute or less. Compared with gas chromatography, the Raman detection method of the present invention can significantly shorten the detection and analysis time and obtain molar fractions or volume fractions of various target components with accuracy comparable to gas chromatography.Furthermore, the implementation environment for performing Raman detection and analysis of the gas mixture according to the method of the present invention can include a terminal and a server, and the method can be executed on the terminal or the server. The terminal and the server can be connected for communication to enable the transmission and exchange of information.The terminal can be any electronic product that interacts with a user through one or more method(s) such as a keyboard, touchpad, touch screen, and voice interaction, such as a PC (Personal Computer), PPC (Pocket Personal Computer), and tablet computer.The server can be a single server, a server cluster composed of multiple servers, or a cloud server that provides basic cloud computing services such as cloud services, cloud databases, cloud computing, cloud functions, cloud storage, network services, cloud communications, middleware services, domain name services, security services, CDN (Content Delivery Network), as well as big data and artificial intelligence platforms.In a second aspect, the present invention further provides a Raman spectroscopic analysis apparatus. As shown in Figure 5, the Raman spectroscopic analysis apparatus may include a processor 201 and a memory 202. The memory stores at least one computer program. When executed by the processor, the at least one computer program causes the processor to execute the method for determining the contents of target components in a gas mixture by Raman spectroscopy according to the first aspect.In addition, the Raman spectroscopic analysis apparatus may also contain components for implementing various functions of the apparatus, including wired or wireless network interfaces, keyboards, and input / output interfaces, in order to input and output data.In a third aspect, the present invention further provides a computer-readable storage medium, which stores at least one program instruction, and causes the processor to execute the method for determining the contents of target components in a gas mixture by Raman spectroscopy according to the first aspect when executed by a processor.In a fourth aspect, the present invention further provides a computer program product, comprising at least one program instruction, which, when executed by a processor, causes the processor to execute the method for determining the contents of target components in a gas mixture by Raman spectroscopy according to the first aspect.The computer program product including computer-executable instructions can be stored in the computer-readable storage medium. All or part of the steps in the method according to the first aspect of the present invention can be defined by the computer-executable instructions included in the computer program product stored in the computer-readable storage medium, and executed by a processor executing the computer-executable instructions to implement the method for determining the contents of target components in a gas mixture by Raman spectroscopy according to the first aspect. The computer-readable storage medium includes tangible, non-transitory machine-readable storage media and may also include high-speed random access memory, such as dynamic random access memory (DRAM), static random access memory (SRAM), double data rate synchronous dynamic random access memory (DDR RAM), or other random-access solid-state memory devices, and may include non-volatile memory, such as one or more magnetic disk storage device(s) (such as internal hard disks and removable disks), magneto-optical disk storage devices, optical disk storage devices, flash memory devices, semiconductor memory devices (such as erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM)), compact disc read-only memory (CD-ROM), digital versatile disc read-only memory (DVD-ROM) disks, or other non-volatile solid-state storage devices.In a fifth aspect, the present invention provides an on-line detection and analysis system of a gas mixture based on Raman spectroscopy, comprising a sampling unit, a Raman spectroscopic detection unit, and the Raman spectroscopic analysis apparatus according to the second aspect;wherein the sampling unit is connected to the outlet pipeline of the reactor and to the Raman spectroscopic detection unit respectively, wherein the Raman spectroscopic detection unit is used for detecting the gas mixture collected by the sampling unit to obtain a Raman spectrum of the gas mixture; the Raman spectroscopic detection unit is also connected to the Raman spectroscopic analysis apparatus, wherein the Raman spectroscopic analysis apparatus is used for analyzing the Raman spectrum of the gas mixture to obtain the molar fractions or volume fractions of various target components in the gas mixture.In some embodiments, the sampling unit and the Raman spectroscopic detection unit are arranged separately. In this case, when the sampling unit includes a Raman probe, the Raman probe and the Raman spectroscopic detection unit are arranged separately. In some embodiments, at least a portion of the sampling unit is integrated with the Raman spectroscopic detection unit into a Raman spectrometer. In this case, when the sampling unit includes a Raman probe, the Raman probe can be integrated with the Raman spectroscopic detection unit into the Raman spectrometer.In one embodiment, as shown in Figure 6, one end of the Raman spectrometer is connected to the on-line sampling device via a dedicated Raman optical fiber so that the target can be subjected to Raman spectroscopic detection. The other end of the Raman spectrometer is connected to a remote monitoring PC via a communication optical fiber to obtain the Raman analysis results of various target components in the gas mixture.In one embodiment, the on-line sampling device (such as the 1# on-site sampling unit in Figure 6) is directly installed on the reaction device, including a gas sampler and a gas Raman probe. When the material flow rate of the reaction device is low and it is a batch reaction device, its own quenching and three-stage water-cooled separation and recovery system is already sufficient to meet the subsequent on-line analysis requirements. Therefore, the on-line gas sampler of the reaction device is installed behind the three-stage water cooling, and the material temperature is close to normal temperature. The sampler allows the gas mixture to pass through a filtration reflux section and a cooling dehydration section, retaining solid particles, heavy components, and moisture within the process pipeline, extracting the light components, and sending them uniformly to the Raman probe at a certain flow rate. The purified gas mixture is mainly composed of H₂ and C₁-C₄ hydrocarbons. The Raman probe connected to the sampler is connected to the Raman spectrometer using a dedicated Raman optical fiber.In one embodiment, the working principle of the on-line Raman spectroscopic detection and analysis apparatus is shown in Figure 7. The monochromatic excitation light emitted by the laser irradiates the target sample in the sampling tube (also called a flow cell) through a dedicated optical fiber and the Raman probe. The excited Raman scattered light is collected by the Raman probe and transmitted to the spectrometer through the dedicated optical fiber for dispersion and analog-to-digital conversion. Finally, the Raman spectral data is transmitted to a computer for preprocessing and analytical model calculation to obtain the corresponding component content or other indicators of the target sample.The Raman spectrometer can adopt a positive pressure explosion-proof form. The key components of the on-line detection and analysis system include: a laser (e.g., a 532 nm laser), a Raman spectrometer, a programmable logic controller, and an embedded PC, wherein the embedded PC can be configured with a control software for each optical component, a Raman spectrum preprocessing software, and a quantitative analysis software for gas mixture components.The present application can include the following technical solutions:Item 1. A method for analysis of the contents in a gas mixture by Raman spectroscopy, comprisingsplitting the gas mixture into n key components, and selecting one component from the n key components as a reference component;performing a spectral signal processing on the original Raman spectrum of the gas mixture to obtain a normalized spectrum of the gas mixture;determining the relative Raman peak heights of the n key components based on the normalized spectrum of the gas mixture;determining the molar ratios of n-1 key components relative to the reference component, based on the relative Raman peak heights of the n-1 key components and regression coefficient(s);determining the molar fractions of the n key components respectively, based on the molar ratios of the n-1 key components relative to the reference component.Item 2. The method for analysis of the contents in a gas mixture by Raman spectroscopy according to Item 1, wherein the performing spectral signal processing on the original Raman spectrum of the gas mixture to obtain a normalized spectrum of the gas mixture comprises:performing background subtraction and baseline correction on the original Raman spectrum of the gas mixture to obtain a corrected Raman spectrum;using the independent characteristic peak of the reference component as the spectral normalization reference peak, and normalizing the corrected Raman spectrum to obtain the normalized spectrum of the gas mixture.Item 3. The method for analysis of the contents in a gas mixture by Raman spectroscopy according to Item 1, wherein the determining the relative Raman peak heights of the n key components based on the normalized spectrum of the gas mixture comprises:determining the relatively independent characteristic spectral peaks of the n key components of the gas mixture in combination with the Raman spectra of pure component sample gases;determining the relative Raman peak heights of the n key components of the gas mixture in the normalized spectrum of the gas mixture according to the relatively independent characteristic spectral peaks of the n key components of the gas mixture.Item 4. The method for analysis of the contents in a gas mixture by Raman spectroscopy according to Item 1, wherein the molar ratios of the n-1 key components relative to the reference component are calculated by the following equation:where zj(t) is the molar ratio of the j-th component of the gas mixture relative to the reference component, Pj(t) is the relative Raman peak height of the j-th component in the gas mixture, kj0is the first regression coefficient of the j-th component of the gas mixture, and kj1 is the second regression coefficient of the j-th component of the gas mixture.Item 5. The method for analysis of the contents in a gas mixture by Raman spectroscopy according to Item 4, further comprisingdetermining the first and second regression coefficients of the n-1 key components of the gas mixture according to a training sample set of the gas mixture;wherein the training sample set of the gas mixture comprises: the normalized spectrum of the gas mixture and the molar ratios or volume concentration ratios of the n-1 key components of the gas mixture relative to the reference component.Item 6. The method for analysis of the contents in a gas mixture by Raman spectroscopy according to Item 5, wherein the determining the first and second regression coefficients of the n-1 key components of the gas mixture according to the training sample set of the gas mixture comprises:determining the molar ratios of the n-1 key components of the gas mixture relative to the reference component according to the training sample set of the gas mixture;determining the relative Raman peak heights of the n-1 key components according to the normalized spectrum of the gas mixture and the characteristic peak positions of the n-1 key components;determining the first and second regression coefficients of the n-1 key components of the gas mixture respectively according to the molar ratios of the n-1 key components relative to the reference component and the relative Raman peak heights of the n-1 key components, in combination with a statistical regression model.Item 7. The method for analysis of the contents in a gas mixture by Raman spectroscopy according to Item 1, wherein the molar fractions of the n components are calculated by the following equations:,;where cj is the molar fraction of the j-th component in the gas mixture, zj is the molar ratio of the j-th component relative to the reference component in the gas mixture, j=1, 2, ... n.Item 8. A method for on-line detection of ethylene cracking gas based on Raman spectroscopy, comprisingdetecting the ethylene cracking gas using a Raman spectrometer to obtain the original Raman spectrum of the ethylene cracking gas;determining the molar fractions of various key components of the ethylene cracking gas according to the original Raman spectrum of the ethylene cracking gas, using the method for analysis of the contents in the gas mixture by Raman spectroscopy according to any one of Items 1 to 7;wherein the key components of the ethylene cracking gas include: hydrogen, methane, ethane, ethylene, acetylene, propane, propylene, propyne, and other components, where the other components are C4 olefins or butadiene, and the reference component of the ethylene cracking gas is ethylene.Item 9. The method for on-line detection of ethylene cracking gas based on Raman spectroscopy according to Item 8, further comprising: using the independent Raman peak of ethylene located near 1345 cm⁻¹ as the spectral normalized reference peak.Item 10. The method for on-line detection of ethylene cracking gas based on Raman spectroscopy according to Item 8, further comprising: before detecting the ethylene cracking gas, configuring the laser power of the Raman spectrometer to be greater than or equal to 1 W, the line width to be less than or equal to 0.1 nm, and the spectral integration time to be set to a range from 30 s to 90 s.Item 11. A Raman analysis apparatus, comprising a processor and a memory, the memory stores at least one computer program, and the at least one computer program is loaded and executed by one or more of the processor(s), causing the processor to execute the method for analysis of the contents in the gas mixture by Raman spectroscopy according to any one of Items 1 to 7.Item 12. A computer-readable storage medium, wherein the computer-readable storage medium stores at least one program code, and the program code is loaded and executed by a processor, causing the computer to execute the method for analysis of the contents in the gas mixture by Raman spectroscopy according to any one of Items 1 to 7.Item 13. A system for detecting ethylene cracking gas on-line based on Raman spectroscopy, comprising a sampling unit, a Raman spectrometer, and the Raman analysis apparatus according to Item 11;wherein one end of the sampling unit is connected to the outlet pipeline of the ethylene cracking furnace, and the other end of the sampling unit is connected to the Raman spectrometer, the Raman spectrometer is used for detecting the sample gas extracted by the sampling unit to obtain the original Raman spectrum of the ethylene cracking gas, and the Raman analysis apparatus is connected to the Raman spectrometer for analyzing the original Raman spectrum of the ethylene cracking gas to obtain the molar fractions of various key components of the ethylene cracking gas.ExampleThe following example will further illustrate the method of the present application with reference to the drawings, but does not limit the present application accordingly.I) Apparatus and Raw MaterialsThe following apparatuses and raw materials were used during the implementation of this example:Cracking apparatus: CBL reaction apparatus designed and developed by China Petroleum & Chemical Corporation;Laser: Laser MGL-N-532-3W available from Changchun New Industries Optoelectronics Tech. Co., Ltd., spectral line width ≤ 0.15 nm, power 2.3 W;Raman probe: RPB-532-N-FF available from Jiangyin Yunxiang Optoelectronic Technology Co., Ltd.;Optical fiber: commercially available, applicable to 532 nm laser;Raman spectrometer: Ocean Optics QE Pro, with a detector of a back-illuminated CCD area array detector equipped with TEC;Gas chromatograph: Agilent 7890A, Column: Agilent HP-5A molecular sieve column (for H₂ and CH₄) and Agilent HP-PLOT Al₂O₃ column (for other hydrocarbon gases), Detector: Agilent thermal conductivity detector TCD (for detecting H₂) and Agilent flame ionization detector FID (for detecting hydrocarbon gases);15 standard gas samples: purchased from Dalian Date Gas Co., Ltd., each using N₂ as the balance gas and the remainder being pure substances with the following volume percentages: methane 90.04%, ethane 90.14%, ethylene 90.80%, acetylene 1.00%, propylene 49.62%, propane 50.30%, propyne 1.01%, propadiene 1.01%, 1,3-butadiene 9.80%, 1-butene 9.72%, isobutene 10.32%, cis-2-butene 10.00%, trans-2-butene 9.97%, n-butane 9.97%, isobutane 9.64%;Reaction raw material: naphtha, with a density (d₄²⁰) at 20°C of 0.6826 g / cm³, and distillation properties as shown in Table 1:Table 1: Naphtha Distillation Properties Distillation cuts under normal pressureTemperaturesInitial boiling point36.6℃5wt%54.9℃10wt%58.3℃20wt%62.7℃30wt%66.1℃40wt%69.3℃50wt%72.1℃60wt%75.1℃70wt%78.2℃80wt%82.0℃90wt%88.2℃Final boiling point104.5℃Note: The initial boiling point meant the temperature at which the first drop of raw material distills, and the final boiling point meant the temperature at which the last drop of raw material distills.II) Preparing the training sample set and determining regression coefficientsIt was known that steam cracking at a temperature ranging from 750°C to 1000°C could produce a cracking gas mixture containing the following primary components: H₂, methane, ethane, ethylene, acetylene, propane, propylene, propyne, and some C4+ organic gases. The sum of the contents of these components in the cracking gas mixture was approximately equal to 100%, wherein the C4+ organic gases were mainly C4 olefins and dienes. The above 15 standard gas samples were separately detected using a Raman spectrometer to obtain Raman spectra containing characteristic peaks of one of the 15 gases and N₂. Since the peak position of N₂ was known at 2331 cm⁻¹, the characteristic peak positions of these 15 gases in the Raman spectra could be determined. Since Raman spectroscopic detection generated fingerprint peaks, organic gases typically generated multiple characteristic peaks with different intensities and peak positions. Here, one characteristic peak was selected for each of the above primary components and listed in Table 2.Table 2: Characteristic peak positions of the primary components in the cracking gas mixtureComponentsC2H4H2CH4C2H6C2H2C3H8C3H6C3H4C4+characteristic peak positions(cm-1)134558629212904197586691921421655The naphtha reaction raw material was fed into the CBL cracking apparatus at a flow rate of 3 kg / h. The temperature of the cracking apparatus was raised. When the temperature stabilized at 800°C, two portions of the cracking gas mixture were collected at the outlet of the cracking apparatus after being cooled to room temperature by cooling water. One portion of the collected cracking gas mixture sample was irradiated using a laser through an optical fiber and a Raman probe to generate Raman signals, which were then transmitted via the Raman probe and optical fiber to the Raman spectrometer for Raman spectroscopic detection, wherein the spectral integration time was set to 50 seconds. The other portion of the collected cracking gas mixture sample was subjected to gas chromatographic detection using a gas chromatograph to obtain component data within an analysis period of 15 minutes.The obtained Raman spectrum of the cracking gas mixture was subjected to background subtraction and baseline correction. The independent characteristic peak of ethylene at 1345 cm⁻¹ was used as the reference peak, ethylene as the reference component, and various characteristic peaks in the Raman spectrum were normalized to obtain a processed Raman spectrum. Then, using the characteristic peak positions of the pure substances shown in Table 2, the characteristic peak positions of the target components in the detected Raman spectrum of the cracking gas mixture were determined, and the corresponding original relative Raman peak heights were obtained. Then, the original relative Raman peak heights of CH₄, C₂H₆, C₂H₂, C₃H₈, C₃H₄, and C4+ subtracted the relative Raman peak heights of their respective reference peak positions shown in Table 3 to obtain their respective optimized relative Raman peak heights (not shown).Table 3: Reference peak positions of the primary components in the cracking gas mixtureComponentsH2CH4C2H6C2H4C2H2C3H8C3H6C3H4C4+Reference peak positions(cm-1)-29072875-1988876-21531632In addition, the volume fractions of various primary components in the cracking gas mixture were obtained through the gas chromatographic detection, and then their volume ratios relative to the reference component ethylene were obtained. Thus, a first set of data of the training sample set was obtained, including the relative Raman peak heights of various primary components and their volume ratios relative to the reference component ethylene.The above operation was repeated twice at a temperature of 800°C to obtain the second and third sets of data of the training sample set. The temperature of the cracking apparatus was further raised, and for every 10°C rise in temperature, three sets of data were obtained using the above method, until the temperature reached 880°C, where the last three sets of data were obtained using the above method, resulting in a total of 27 sets of data of the training sample set.The regression coefficients kj1 and kj0 for the primary components in the cracking gas mixture, shown in Table 4, were obtained by fitting the 27 sets of data from the training sample set using the least squares algorithm.Table 4: Regression coefficients of the primary components in the cracking gas mixtureComponentsC2H4(j=1)H2(j=2)CH4(j=3)C2H6(j=4)C2H2(j=5)C3H8(j=6)C3H6(j=7)C3H4(j=8)C4+(j=9)Characteristic peak gain (kj1)1.01.0080.54730.63270.61630.50772.3640.45571.0291Intercept (kj0)00.0120.0126-0.0123-0.00030.0043-0.0200.00270.1086The obtained regression coefficients kj1 and kj0 for each primary component were used in the subsequent determination of the volume fractions of the corresponding primary components in the on-line cracking gas mixture collected at the outlet of the naphtha cracking reaction apparatus.III) Raman spectroscopic and gas chromatographic detection of the target cracking gas mixtureThe naphtha reaction raw material was continuously fed into the CBL cracking apparatus at a flow rate of 3 kg / h. The temperature of the cracking apparatus was raised. When the temperature was stabilized at a temperature ranging from 820°C to 850°C and the reaction had been running for 39 minutes, two portions of the cracking gas mixture were collected at the outlet of the cracking apparatus after being cooled to room temperature by cooling water. One portion of the cracking gas mixture sample was irradiated using a laser through an optical fiber and a Raman probe to generate Raman signals, which were then transmitted via the Raman probe and optical fiber to the Raman spectrometer for Raman spectroscopic detection, wherein the spectral integration time was set to 50 s, thereby obtaining the first set of data for the target cracking gas mixture. The other portion of the cracking gas mixture sample was subjected to gas chromatographic detection using a gas chromatograph to obtain component data within an analysis period of 15 minutes. The obtained volume fractions of the primary components in the cracking gas mixture were used for comparison with the results obtained by Raman spectroscopy of the present invention.The above operation was repeated at the reaction run time points of 57 min, 70 min, 78 min, 94 min, 102 min, 162 min, 172 min, 191 min, 205 min, 225 min, and 237 min to obtain the 2nd to 12th sets of data for the target cracking gas mixture.IV) Processing the Raman spectra of the target cracking gas mixture and obtaining relative Raman peak heightsThe 12 sets of Raman spectra were respectively subjected to background subtraction, baseline correction, and normalization to obtain their original relative Raman peak heights. Then, for the 12 sets of data, the relative Raman peak heights of the reference peak positions shown in Table 3 were subtracted from the original relative Raman peak heights of each primary component to obtain their respective optimized relative Raman peak heights. The optimized relative Raman peak heights are listed in Table 5, where the independent characteristic peak of ethylene at 1345 cm⁻¹ was used as the reference peak, and ethylene was used as the reference component.Table 5: Optimized relative Raman peak heights of the primary components in the cracking gas mixtureReaction run time (min)C2H4H2CH4C2H6C2H2C3H8C3H6C3H4C4+3910.2190.9150.2370.0090.0130.1900.0080.2405710.2130.9670.2390.0090.0160.2000.0220.2647010.2301.0300.2270.0150.0130.1870.0180.2337810.2291.0150.2230.0170.0140.1880.0140.2349410.2511.0880.2100.0220.0220.1760.0150.19110210.2531.0910.2110.0200.0200.1760.0170.18816210.2581.0910.2100.0200.0270.1750.0180.18217210.2611.0970.2100.0210.0180.1740.0230.18119110.2411.0250.2220.0160.0110.1840.0230.21920510.2411.0250.2220.0160.0200.1880.0110.22822510.2240.9570.2350.0110.0060.2000.0230.26123710.2240.9690.2380.0090.0090.2000.0130.271V) Calculating the volume fractions of the primary components in the target cracking gas mixtureFor n=9 primary components, i.e., H₂, methane, ethane, ethylene, acetylene, propane, propylene, propyne, and C4+ organic gases, their respective regression coefficients kj1 and kj0 shown in Table 4 and their respective optimized relative Raman peak heights shown in Table 5 were incorporated into Equations (3) and (6) as shown below to obtain the volume fraction of each primary component in the cracking gas mixture.zj = kj0 +kj1Pj, (j = 1,…, 9) (3)where zj is the molar ratio or volume ratio of the j-th component to the reference component in the target cracking gas mixture, Pj is the relative Raman peak height of the j-th component in the target cracking gas mixture, kj0 is the first regression coefficient of the j-th component in the target cracking gas mixture, and kj1 is the second regression coefficient of the j-th component in the target cracking gas mixture, where j=1 corresponds to ethylene. (j = 1, ..., 9) (6) where cj is the molar fraction or volume fraction of the j-th component in the target cracking gas mixture, zj is the molar ratio or volume ratio of the j-th component to the reference component in the target cracking gas mixture, and zi is the molar ratio or volume ratio of the i-th component to the reference component in the target cracking gas mixture, where j=1 corresponds to ethylene. The calculated volume fractions of the primary components are listed in Table 6, and the volume fractions detected using the gas chromatograph are also listed in Table 6 for comparison with the analysis results of Raman spectroscopy of the present invention.Table 6: Volume fraction results of the four primary components in the cracking gas mixture obtained by Raman spectroscopy of the present invention and the gas chromatography method out of the present inventionReaction run time (min)C2H4 volume fractionH2 volume fractionCH4 volume fractionC3H6 volume fractionGC valueRS valueGC valueRS valueGC valueRS valueGC valueRS value3937.3437.158.318.6319.2919.0816.1915.975736.3636.098.298.1819.4319.5616.3116.337036.2436.329.058.8720.7020.9415.4715.317836.1836.429.088.8620.8120.7015.5715.499436.9336.5710.039.7022.4922.2414.1914.5110236.9236.598.929.7822.7722.3114.5214.5016236.5536.599.689.9522.6122.3114.0514.4017236.7136.559.9010.0722.5622.4114.1714.3419136.3736.529.269.3220.5820.9515.2215.1420536.6636.299.249.2420.8320.8115.1315.4122536.0636.128.618.5919.3619.3816.1616.3923735.9435.958.818.5519.2519.5216.0216.25Note: GC value meant a value obtained from gas chromatography, RS value meant a value obtained from Raman spectroscopyFor a more direct comparison, the volume fraction results of the four key components H₂, CH₄, C₂H₄, and C₃H₆ in Table 6 were plotted in Figure 8. It can be seen from the data in Table 6 and Figure 8 that the volume fractions of the four key components in the cracking gas mixture obtained by Raman spectroscopy of the present invention are basically the same or very similar to those obtained by the gas chromatography method, thus proving that Raman spectroscopy of the present invention can accurately obtain the content of each component in the on-line gas mixture. However, due to the long detection time of the gas chromatography method, obtaining the volume fractions of a set of primary components by gas chromatography requires an analysis period of 15 minutes or longer, while obtaining a set of primary component volume fractions by Raman spectroscopy of the present invention only takes about 1 minute. Therefore, compared with gas chromatography, Raman spectroscopy of the present invention can achieve results with comparable accuracy significantly faster.For large-scale production processes (e.g., with an annual output of over 100,000 tons) where the reaction raw materials remain basically the same and the reaction types and conditions are similar for a long period (e.g., one year or longer), since Raman spectroscopy of the present invention can quickly and accurately obtain the content of each key component in the on-line detection gas mixture, and thus quickly and accurately adjust the process parameters of the on-line reaction, the yields of the key components (e.g., ethylene) can be effectively improved.Within the scope of the technical concept of the present invention, various modifications can be made to the above technical solutions of the present invention, and these modifications all fall within the protection scope of the present invention.It should be additionally noted that the various specific technical features described in the above embodiments can be combined in any suitable manner, provided they are not contradictory.Furthermore, various different embodiments of the present invention can also be combined arbitrarily, as long as they do not violate the spirit of the present invention, and they should also be regarded as the disclosures of the present invention. CLAIMS1. A method for determining the contents of target components in a gas mixture by Raman spectroscopy, comprising1) performing Raman spectroscopic detection on the gas mixture to obtain a Raman spectrum;2) selecting one characteristic peak from the Raman spectrum as the reference peak, and its corresponding component serves as the reference component, and normalizing the characteristic peaks of various target components in the Raman spectrum relative to the reference peak to obtain the relative Raman peak heights of various characteristic peaks;3) determining the peak positions of the characteristic peaks of various target components in the Raman spectrum of the above gas mixture, in combination with the Raman spectra of the pure target components;4) determining the molar ratios or volume ratios of the target components to the reference component in the gas mixture, based on the relative Raman peak heights of the characteristic peaks at the specific peak positions of the target components obtained in steps 2) and 3) and one or more, preferably one or two, regression coefficient(s) obtained from a training sample set of the gas mixture; and5) determining the molar fractions or volume fractions of various target components in the gas mixture, based on the molar ratios or volume ratios of the target components to the reference component obtained in step 4).2. The method according to claim 1, wherein the gas mixture is a process gas mixture and / or an on-line detection gas mixture collected at the outlet of a continuous reactor.3. The method according to claim 1 or 2, comprising, between steps 3) and 4), a step 3') of using the relative Raman peak height(s) of one or more characteristic peak(s) obtained by normalization in step 2) to subtract the relative Raman peak height of a reference peak at a reference point within 50 cm⁻¹, preferably within 30 cm⁻¹, of the respective peak position to obtain the optimized relative Raman peak height(s) of said characteristic peak(s).4. The method according to any one of the preceding claims, wherein the training sample set of the gas mixture includes Raman spectra of the gas mixture and the molar ratios or volume ratios of the target components to the reference component in the gas mixture.5. The method according to claim 4, wherein the molar ratios or volume ratios of the target components to the reference component in the gas mixture of the training sample set are obtained by measuring the contents of various target components in the gas mixture using gas chromatography.6. The method according to any one of claims 2 to 5, wherein the regression coefficient(s) are determined by the following steps:i) collecting gas mixture samples at the outlet of a continuous reactor at two or more time points, preferably 5 or more time points, more preferably 10 or more time points, even more preferably 15 or more time points;ii) performing Raman spectroscopic detection and gas chromatographic detection on the gas mixture samples collected at the same time point respectively, wherein the relative Raman peak heights of the target components are obtained from the detected Raman spectra, preferably according to steps 2) and 3), and the molar ratios or volume ratios of the target components to the reference component are obtained by gas chromatograph, wherein the corresponding sets of said relative Raman peak heights and said molar ratios or volume ratios obtained at various time points form a training sample set; andiii) using the training sample set in combination with a statistical regression model to establish the relationship between the relative Raman peak heights and the molar ratios or volume ratios described in step ii), thereby obtaining the regression coefficient(s).7. The method according to any one of the preceding claims, comprising, between steps 1) and 2), a step 1') of performing background subtraction and baseline correction on the Raman spectrum of the gas mixture.8. The method according to any one of the preceding claims, wherein, in step 1), the gas mixture subjected to the Raman spectroscopic detection is a gas mixture at normal temperature and normal pressure.9. The method according to any one of the preceding claims, wherein the gas mixture comprises 2 or more, preferably 3 or more, more preferably 5 or more, even more preferably 7 or more organic gases, for example, from 2 to 20, or from 3 to 20, or from 5 to 15, or from 7 to 10 organic gases,preferably, the organic gas is a gas composed of carbon and hydrogen elements and optionally having unsaturated bond(s), wherein the organic gas preferably has one to seven carbon atoms, more preferably one to four carbon atoms, even more preferably one to three carbon atoms.10. The method according to any one of the preceding claims, wherein the gas mixture contains n target components (n is an integer greater than or equal to 2, preferably greater than or equal to 3, more preferably greater than or equal to 5), and the molar ratios or volume ratios of the target components to the reference component in the gas mixture in step 4) are calculated by the following Equation (2):zj = kjPj , (j = 1, …, n), (2)where zj is the molar ratio or volume ratio of the j-th component to the reference component in the gas mixture, Pj is the relative Raman peak height of the j-th component in the gas mixture, and kj is the regression coefficient of the j-th component in the gas mixture, where j=1 corresponds to the reference component.11. The method according to any one of the preceding claims, wherein the gas mixture contains n target components (n is an integer greater than or equal to 2, preferably greater than or equal to 3, more preferably greater than or equal to 5), and the molar ratios or volume ratios of the target components to the reference component in the gas mixture in step 4) are calculated by the following Equation (3):zj = kj0 +kj1Pj, (j = 1, …, n), (3)where zj is the molar ratio or volume ratio of the j-th component to the reference component in the gas mixture, Pj is the relative Raman peak height of the j-th component in the gas mixture, kj0 is the first regression coefficient of the j-th component in the gas mixture, and kj1 is the second regression coefficient of the j-th component in the gas mixture, where j=1 corresponds to the reference component.12. The method according to any one of the preceding claims, wherein the gas mixture contains n target components (n is an integer greater than or equal to 2, preferably greater than or equal to 3, more preferably greater than or equal to 5), and the molar fractions or volume fractions in step 5) are calculated by the following Equations (4) and (6): (4), (6);where cj is the molar fraction or volume fraction of the j-th component in the gas mixture, zj is the molar ratio or volume ratio of the j-th component to the reference component in the gas mixture, j = 1, ..., n, where j=1 corresponds to the reference component.13. The method according to any one of the preceding claims, wherein the gas mixture is an ethylene cracking gas mixture containing ethylene, obtained through a cracking reaction, preferably a steam cracking reaction.14. The method according to claim 13, wherein the ethylene cracking gas mixture comprises hydrogen, methane, ethane, ethylene, acetylene, propane, propylene, propyne, and optionally butene and / or butadiene, and the reference component of the ethylene cracking gas mixture is preferably ethylene.15. The method according to claim 13 or 14, wherein the characteristic peak of ethylene located near 1345 cm⁻¹ is used as the reference peak.16. The method according to any one of claims 13 to 15, wherein the Raman spectroscopic detection is performed under the following conditions: a laser power of greater than or equal to 1 W, preferably 1 W to 3 W; and / or a spectral line width of less than or equal to 0.2 nm, preferably less than or equal to 0.15 nm; and / or a spectral integration time of 30 s to 90 s, preferably 50 s to 70 s, more preferably 45 s to 60 s.17. A Raman spectroscopic analysis apparatus, comprising a processor and a memory, wherein the memory stores at least one computer program, which causes the processor to execute the method for determining the contents of target components in a gas mixture by Raman spectroscopy according to any one of claims 1 to 16 when executed by the processor.18. A computer-readable storage medium, storing at least one program instruction, which causes the computer to execute the method for determining the contents of target components in a gas mixture by Raman spectroscopy according to any one of claims 1 to 16 when executed by a processor.19. A computer program product, comprising at least one program instruction, which causes a processor to execute the method for determining the contents of target components in a gas mixture by Raman spectroscopy according to any one of claims 1 to 16 when executed by the processor.20. An on-line detection and analysis system of a gas mixture based on Raman spectroscopy, comprising a sampling unit, a Raman spectroscopic detection unit, and the Raman spectroscopic analysis apparatus according to claim 17;wherein the sampling unit is connected to the outlet pipeline of the reactor and to the Raman spectroscopic detection unit respectively, wherein the Raman spectroscopic detection unit is used for performing Raman spectroscopic detection on the gas mixture collected by the sampling unit to obtain a Raman spectrum of the gas mixture; the Raman spectroscopic detection unit is also connected to the Raman spectroscopic analysis apparatus, wherein the Raman spectroscopic analysis apparatus is used for analyzing the Raman spectrum of the gas mixture to obtain the molar fractions or volume fractions of various target components in the gas mixture. ABSTRACTThe present invention provides a method for determining the contents of target components in a gas mixture by Raman spectroscopy, comprising performing Raman spectroscopic detection on the gas mixture to obtain a Raman spectrum; selecting one characteristic peak from the Raman spectrum as the reference peak, and its corresponding component serves as the reference component, and normalizing the characteristic peaks in the Raman spectrum relative to the reference peak to obtain the relative Raman peak heights of various characteristic peaks; determining the peak positions of the characteristic peaks of various target components in the Raman spectrum of the gas mixture in combination with the Raman spectra of the pure target components; determining the molar ratios or volume ratios of the target components to the reference component in the gas mixture based on the relative Raman peak heights of the target components and regression coefficient(s) obtained from a training sample set of the gas mixture; and determining the molar fractions or volume fractions of various target components in the gas mixture based on the molar ratios or volume ratios of the target components to the reference component. 

Claims

1. A method for determining the content of a target component in a gas mixture by Raman spectroscopy, wherein the method comprises: 1) Performing Raman spectroscopy detection on the gas mixture to obtain a Raman spectrogram; 2) Selecting a characteristic peak from the Raman spectrogram as a reference peak, and the corresponding component as a reference component, and normalizing the characteristic peaks of each target component in the Raman spectrogram with respect to the reference peak to obtain the relative Raman peak height of each characteristic peak; 3) Combining the Raman spectrogram of the pure target component to determine the peak positions of the characteristic peaks of each target component in the Raman spectrogram of the gas mixture; 4) Determining the molar ratio or volume ratio of the target component to the reference component in the gas mixture based on the relative Raman peak height of the characteristic peak at the specific peak position of the target component obtained in steps 2) and 3) and one or more, preferably one or two regression coefficients obtained from the training sample set of the gas mixture; and 5) Determining the molar fraction or volume fraction of each target component in the gas mixture based on the molar ratio or volume ratio of the target component to the reference component obtained in step 4).

2. The method according to claim 1, wherein the gas mixture is a process gas mixture collected at the outlet of a continuous reactor and / or an on-line detection gas mixture.

3. The method according to claim 1 or 2, wherein between steps 3) and 4), it includes step 3') of obtaining the optimized relative Raman peak height of the characteristic peak by subtracting the relative Raman peak height of the reference peak at a reference point within 50 cm, preferably within 30 cm, near the respective peak positions from the relative Raman peak height of one or more characteristic peaks obtained by the normalization process in step 2). -1 Therein, the reference point is within 50 cm, preferably within 30 cm -1 from the relative Raman peak height of the reference peak at the reference point to obtain the optimized relative Raman peak height of the characteristic peak).

4. The method according to any one of the preceding claims, wherein the training sample set of the gas mixture comprises the Raman spectrogram of the gas mixture and the molar ratio or volume ratio of the target component to the reference component in the gas mixture.

5. The method according to claim 4, wherein the molar ratio or volume ratio of the target component to the reference component in the gas mixture of the training sample set is obtained by measuring the content of each target component in the gas mixture by gas chromatography.

6. The method according to any one of claims 2 to 5, wherein the regression coefficient is determined by the following steps: i) Collecting gas mixture samples at the outlet of a continuous reactor at two or more time points, preferably 5 or more time points, more preferably 10 or more time points, still more preferably 15 or more time points; ii) Performing Raman spectroscopy detection and gas chromatography detection on the gas mixture samples collected at the same time point respectively, wherein the relative Raman peak height of the target component is obtained from the measured Raman spectrogram and preferably according to the methods of steps 2) and 3), and the molar ratio or volume ratio of the target component to the reference component is obtained by gas chromatography detection, and the corresponding relative Raman peak heights and the molar ratio or volume ratio obtained at each time point form a training sample set; and iii) Using this training sample set and combining a statistical regression model to establish the relationship between the relative Raman peak height and the molar ratio or volume ratio described in step ii), thereby obtaining the regression coefficient.

7. The method according to any one of the preceding claims, wherein the method includes a step 1') of background subtraction and baseline correction for the Raman spectrogram of the gas mixture between steps 1) and 2).

8. The method according to any one of the preceding claims, wherein In step 1), the gas mixture for Raman spectroscopy detection is a gas mixture at normal temperature and pressure.

9. The method according to any one of the preceding claims, wherein the gas mixture comprises two or more, preferably three or more, more preferably five or more, still more preferably seven or more organic gases, such as 2 to 20, or 3 to 20, or 5 to 15, or 7 to 10 organic gases. Preferably, the organic gas is a gas composed of carbon and hydrogen elements and optionally having unsaturated bonds, wherein the organic gas preferably has one to seven carbon atoms, more preferably one to four carbon atoms, still more preferably one to three carbon atoms.

10. The method according to any one of the preceding claims, wherein the gas mixture comprises n target components (n is an integer greater than or equal to 2, preferably greater than or equal to 3, more preferably greater than or equal to 5), and the molar ratio or volume ratio of the target components to the reference component in the gas mixture in step 4) is obtained by calculating with the following formula (2): z j = k j P j , (j = 1, …, n) (2) Among them, z j is the molar ratio or volume ratio of the j-th component in the gas mixture to the reference component, P j is the relative Raman peak height of the j-th component in the gas mixture, k j is the regression coefficient of the j-th component in the gas mixture, where j = 1 corresponds to the reference component.

11. The method according to any one of the preceding claims, wherein the gas mixture comprises n target components (n is an integer greater than or equal to 2, preferably greater than or equal to 3, more preferably greater than or equal to 5), and the molar ratio or volume ratio of the target components to the reference component in the gas mixture in step 4) is obtained by calculation using the following formula (3): z j = k j0 + k j1 P j , (j = 1, …, n) (3) Among them, z j is the molar ratio or volume ratio of the j-th component in the gas mixture to the reference component, P j is the relative Raman peak height of the j-th component in the gas mixture, k j0 is the first regression coefficient of the j-th component in the gas mixture, k j1 is the second regression coefficient of the j-th component in the gas mixture, where j = 1 corresponds to the reference component.

12. The method according to any one of the preceding claims, wherein the gas mixture comprises n target components (n is an integer greater than or equal to 2, preferably greater than or equal to 3, more preferably greater than or equal to 5), and the mole fraction or volume fraction in step 5) is obtained by calculation using the following formulas (4) and (6): c1 + c2 + … + c n = 1 (4), Among them, c j is the mole fraction or volume fraction of the j-th component in the gas mixture, z j is the molar ratio or volume ratio of the j-th component in the gas mixture to the reference component, j = 1, …, n, where j = 1 corresponds to the reference component.

13. The method according to any one of the preceding claims, wherein the gas mixture is an ethylene cracking gas mixture containing ethylene obtained by a cracking reaction, preferably a steam cracking reaction.

14. The method according to claim 13, wherein the ethylene cracking gas mixture comprises hydrogen, methane, ethane, ethylene, acetylene, propane, propylene, propyne and optionally butene and / or butadiene, and the reference component of the ethylene cracking gas mixture is preferably ethylene.

15. The method according to claim 13 or 14, wherein the characteristic peak of ethylene located near 1345 cm -1 is used as the reference peak.

16. The method according to any one of claims 13 to 15, wherein the Raman spectroscopy detection is carried out under the following conditions: the laser power is greater than or equal to 1 W, preferably 1 W to 3 W; and / or the spectral line width is less than or equal to 0.2 nm, preferably less than or equal to 0.15 nm; and / or the spectral integration time is 30 s to 90 s, preferably 50 s to 70 s, more preferably 45 s to 60 s.

17. A Raman spectroscopy analysis device, comprising a processor and a memory, wherein at least one computer program is stored in the memory, and when the at least one computer program is executed by the processor, the processor executes the method for determining the content of the target component in the gas mixture by Raman spectroscopy according to any one of claims 1 to 16.

18. A computer-readable storage medium, wherein at least one program instruction is stored, and when the program instruction is executed by a processor, the processor executes the method for determining the content of the target component in the gas mixture by Raman spectroscopy according to any one of claims 1 to 16.

19. A computer program product, comprising at least one program instruction, and when the program instruction is executed by a processor, the processor executes the method for determining the content of the target component in the gas mixture by Raman spectroscopy according to any one of claims 1 to 16.

20. An on-line detection and analysis system for a gas mixture based on Raman spectroscopy, comprising a sampling unit, a Raman spectroscopy detection unit and the Raman spectroscopy analysis device according to claim 17; The sampling unit is respectively connected to the outlet pipeline of the reactor and to the Raman spectroscopy detection unit, wherein the Raman spectroscopy detection unit is used to perform Raman spectroscopy detection on the gas mixture collected by the sampling unit to obtain a Raman spectrogram of the gas mixture; the Raman spectroscopy detection unit is also connected to the Raman spectroscopy analysis device, wherein the Raman spectroscopy analysis device is used to analyze the Raman spectrogram of the gas mixture to obtain the mole fraction or volume fraction of each target component in the gas mixture.

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