“…All these facts are in good agreement with the results given in Petrov et al. 22 Thus, we can conclude that changes in the CH 4 spectra leads to both changes in the calculated values of its concentration (approximately –0.3% between the data obtained from the analysis of the syngas spectra obtained at 25 bar and at 1 bar), and increases the SD of its concentrations. Obviously, since the calculated values for all components of the mixture are normalized to 100%, change in the concentration of one of them (e.g., CH 4 , as in our case) leads to a proportional change in the concentrations of the remaining components.…”
Section: Resultssupporting
confidence: 92%
“…1 where ΔiN is the error due to the shot noise of Raman peak, ΔiS is the error caused by change in the spectrum of i th component in the analyzed mixture compared to its reference spectrum, ΔO is the error caused by an incorrect determination of other components' concentrations in the mixture, because relative concentrations are determined. The data presented show that for, e.g., CH 4 , the effect of pressure and environment on band contours results in measurement errors ΔCH4S several times higher than the errors caused by deviations of the signal intensities ΔCH4N and for, e.g., H 2 , whose change of spectral characteristics is negligible, 22 the main error is Δ O due to deviations of calculated concentrations of CH 4 , CO, and CO 2 . Figure 3.Residuals after applying the contour fit method to syngas spectra (25 bar and 1 bar) using reference spectra (25 bar).…”
Section: Resultsmentioning
confidence: 80%
“…and for, e.g., H 2 , whose change of spectral characteristics is negligible, 22 the main error is Á O due to deviations of calculated concentrations of CH 4 , CO, and CO 2 .…”
Section: Chmentioning
confidence: 98%
“…21 Previously, we studied changes in the Raman spectra of CO-CO 2 -H 2 -CH 4 mixtures as a function of pressure and molecular environment. 22 It was found that among the main components of syngas, the most significant changes are observed in the methane Raman spectrum and they can lead to additional errors in concentration determination. The main purposes of this work are to confirm these assumptions experimentally and to evaluate the effect of exposure time and pressure on the minimum detectable concentration and measurement errors.…”
“…All these facts are in good agreement with the results given in Petrov et al. 22 Thus, we can conclude that changes in the CH 4 spectra leads to both changes in the calculated values of its concentration (approximately –0.3% between the data obtained from the analysis of the syngas spectra obtained at 25 bar and at 1 bar), and increases the SD of its concentrations. Obviously, since the calculated values for all components of the mixture are normalized to 100%, change in the concentration of one of them (e.g., CH 4 , as in our case) leads to a proportional change in the concentrations of the remaining components.…”
Section: Resultssupporting
confidence: 92%
“…1 where ΔiN is the error due to the shot noise of Raman peak, ΔiS is the error caused by change in the spectrum of i th component in the analyzed mixture compared to its reference spectrum, ΔO is the error caused by an incorrect determination of other components' concentrations in the mixture, because relative concentrations are determined. The data presented show that for, e.g., CH 4 , the effect of pressure and environment on band contours results in measurement errors ΔCH4S several times higher than the errors caused by deviations of the signal intensities ΔCH4N and for, e.g., H 2 , whose change of spectral characteristics is negligible, 22 the main error is Δ O due to deviations of calculated concentrations of CH 4 , CO, and CO 2 . Figure 3.Residuals after applying the contour fit method to syngas spectra (25 bar and 1 bar) using reference spectra (25 bar).…”
Section: Resultsmentioning
confidence: 80%
“…and for, e.g., H 2 , whose change of spectral characteristics is negligible, 22 the main error is Á O due to deviations of calculated concentrations of CH 4 , CO, and CO 2 .…”
Section: Chmentioning
confidence: 98%
“…21 Previously, we studied changes in the Raman spectra of CO-CO 2 -H 2 -CH 4 mixtures as a function of pressure and molecular environment. 22 It was found that among the main components of syngas, the most significant changes are observed in the methane Raman spectrum and they can lead to additional errors in concentration determination. The main purposes of this work are to confirm these assumptions experimentally and to evaluate the effect of exposure time and pressure on the minimum detectable concentration and measurement errors.…”
“…The sensitivity of Raman spectroscopy covers a wide concentration range, down to very low concentration, 1,2 even to sub-ppm levels 3,4 . Raman spectroscopy has been widely used for gas analysis in various domains of investigation such as monitoring of polluted air 5 or automobile exhaust gases, 1 fuel gas analysis, [6][7][8] diagnosis and monitoring of disease states by human breath analysis, 3,4,9 controlling and monitoring of fruit ripening, 10 analyzing of gas bubbles appearing as defects inside industrial glasses to optimize production process. 11 Other applications can also be found in the field of environmental gas sensing, e.g.…”
Quantitative analysis of gases by Raman spectroscopy is based on relative Raman scattering cross-sections (RRSCS) and the evolution of different spectral parameters (peak position, peak area, peak intensity, etc.). However, most of the calibration data were established at low pressure (low density) and without evaluating the effect of the composition. Using these data may lead to considerable errors, especially when applied to gas mixtures at high pressure as found in natural fluid inclusions. The aim of this study is to reevaluate the RRSCS of CO2 and to establish new calibration data based on the variation of CO2 Fermi diad splitting as a function of pressure (density) and composition over a pressure range of 5 to 600 bars at 22 and 32 °C. A high-pressure optical cell system (HPOC) and a heating-cooling stage were used for Raman in-situ analyses at controlled PTX conditions. Our experimental results show that the RRSCS of CO2 varies slightly with pressure but can be considered constant over the studied pressure range. It can be used to measure the proportion of CO2 in gas mixtures with an uncertainty of about ± 0.5 mol%. Different polynomial equations were provided to calculate pressure and density of CO2-N2 gas mixtures with an uncertainty of ± 20 bar or 0.01 g.cm −3. A comparison of PVTX properties of natural CO2-N2 fluid inclusions hosted in quartz from the Central Alps (Switzerland) obtained by Raman measurement and as derived from phase transition temperatures by microthermometry experiments shows comparable values. ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Detailed uncertainty calculations and the coefficients of regression polynomial equations 3, 4 and 5 (PDF)
The in situ analysis of natural gas is one of the most promising applications of Raman spectroscopy. It is necessary to take into account the pressure effect on the spectrum of methane to improve the accuracy of this technique. This study aimed to develop and verify two methods for simulating the ν2 Raman band of methane at any spectral resolution and pressure. The first method was based on the use of the spectroscopic parameters of each single line (position, intensity, broadening, and shift coefficient). The second one was based on the use of the spectral profiles, each of which replaces a group of lines. The data required for the implementation of each method are presented in this work. A comparison of the calculated and measured spectra with a resolution of ~0.5 and ~7 cm−1 was performed. It was shown that the differences do not exceed 5% for each method in the range of 1–60 atm.
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