Acta Photonica Sinica, Volume. 52, Issue 9, 0930001(2023)

Process Gas Detection of C2H2 Preparation by CH4 Cracking Based on Hollow Core Fiber Enhanced Raman Spectroscopy

Fu WAN1、*, Rui WANG1, Weiping KONG1, Qiang LIU1, Hongcheng SUN1, Mingyong WANG2, and Weigen CHEN1
Author Affiliations
  • 1State Key Laboratory of Power Transmission Equipment Technology,School of Electrical Engineering,Chongqing University,Chongqing 400044,China
  • 2Sinopec Chongqing Svw Chemical Co.,Ltd.,Chongqing 401254,China
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    In the chemical industry, accurate measurement of the components and amounts of gas products in the C2H2 preparation by CH4 cracking is critical for monitoring reaction progress and assuring the quality of C2H2 production. The partial oxidation technique of creating acetylene from natural gas (mostly methane) is essentially an incomplete combustion of methane involving oxidation, cracking, water-gas shift, and acetylene breakdown processes. H2, CO, CO2, C2H2, C2H6, and C2H4 are the most important intermediate products.Gas chromatography-mass spectrometry, nano-sensor techniques, infrared spectroscopy, and other approaches are commonly used to identify process gases. The detection time of gas chromatography and mass spectrometry is long, and it is difficult to miniaturize the equipment, so there are some limitations when using these method; the nano-sensor method detects a single component, and cross-sensitivity problems will occur between different gas components; infrared spectroscopy can not detect multi-component gas mixtures, and it can not realize the detection of homonuclear diatomic gases. Raman spectroscopy is a technique for directly determining the characteristics and concentrations of substances. Raman spectroscopy directly measures the features and concentrations of substances by using spherical Raman scattered light of various frequencies generated by substances under laser irradiation. Any inert gas with several components can be detected and studied at the same time. Raman spectroscopy detection is limited in gases due to the narrow Raman scattering cross section and moderate Raman scattering impact. This makes identifying the process gases utilized in CH4 cracking to produce C2H2 challenging. The invention of hollow-core fiber has enabled the creation of a novel medium for the interaction of gas and laser. In the hollow-core fiber, both a gas chamber for testing and a light transmission medium can be employed. It can extend the time the laser interacts with the gas and increase the collection efficiency of spherical Raman light, both of which will boost the gas Raman signal.A gas fiber-enhanced Raman spectroscopy detection system based on hollow-core anti-resonant fiber is conceived and built in this article. To considerably filter out the silicon noise created by the hollow-core fiber, the CCD noise reduction and small-aperture cooperative noise reduction methods are developed, which enhanced the signal-to-noise ratio by roughly 6 times. Under the following conditions, the Raman spectra of the principal gases generated during the cracking of CH4 to make C2H2 are detected: laser power of 200 mW, coupling efficiency of 95%, pressure of 1 bar, and integration duration of 60 s. Each gas has many Raman shift spectral peaks, peak attribution, and Raman spectral intensity calculated. In order to obtain higher sensitivity and more accurate analysis, typical Raman spectral peaks for each gas are recognized based on the idea of relatively independent peaks and high peak intensities. H2, CO, CO2, CH4, C2H2, C2H6, and C2H4 have characteristic Raman spectral peaks of 595, 2 142, 1 389, 2 917, 1 974, 2 957, and 1 342 cm-1, respectively. The limit of detection for H2, CO, CO2, CH4, C2H2, C2H6, and C2H4 are calculated to be 6.3, 26.6, 1.2, 2.2, 4.2, 3.9, and 9.1 L/L?bar, respectively. The Raman spectra of each separate gas are analyzed, and a quantitative analytical model between the gas concentration and the intensity of the distinguishing Raman peaks is constructed. The calculated R2 is greater than 0.999.In order to confirm the detection performance of the developed hollow-core fiber-enhanced Raman spectroscopy platform for real samples, the components and contents of the gases in the process of C2H2 preparation by CH4 cracking in a process line of Sinopec Chongqing Svw Chemical Co., Ltd. are examined. The Raman spectral peaks of the seven gases are clearly discernible, and individual Raman peaks of each gas exist fully separately, with no evidence of a cross-over phenomenon. From the intensity of the characteristic Raman spectral peaks of each gas and the obtained linear quantitative analysis curves, the concentrations of H2, CO, CO2, CH4, C2H2, C2H6 and C2H4 in the gas mixture are calculated to be 560 588.51 μL/L, 230 678.21 μL/L, 33 107.65 μL/L, 56 086.77 μL/L, 77 945.56 μL/L, 1 307.19 μL/L and 1 823.55 μL/L, respectively, proving that the process gases meet the quality requirements (H2: 548 993.78 μL/L, CO: 236 006.59 μL/L, CO2: 34 362.33 μL/L, CH4: 58 064.38 μL/L, C2H2: 75 506.62 μL/L, C2H6: 1 372.30 μL/L, C2H4: 1 917.75 μL/L), the concentrations of each gas are in accordance with the calibration values of the chromatograph with an error of about 2.11%~4.95%. The application of this method allows for greater control over the manufacture of C2H2 via CH4 cracking.

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    Fu WAN, Rui WANG, Weiping KONG, Qiang LIU, Hongcheng SUN, Mingyong WANG, Weigen CHEN. Process Gas Detection of C2H2 Preparation by CH4 Cracking Based on Hollow Core Fiber Enhanced Raman Spectroscopy[J]. Acta Photonica Sinica, 2023, 52(9): 0930001

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    Paper Information

    Category:

    Received: Apr. 14, 2023

    Accepted: May. 18, 2023

    Published Online: Oct. 24, 2023

    The Author Email: WAN Fu (fu.wan@hotmail.com)

    DOI:10.3788/gzxb20235209.0930001

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