Abstract
For the detection of deep-sea natural gas hydrates, it is very important to accurately detect the 13CO2/12CO2 isotope ratio of dissolved gas in seawater. In this paper, a 13CO2/12CO2 isotope ratio sensor is investigated, which uses a tunable diode laser absorption spectroscopy (TDLAS) technique at 4.3 μm. The proposed sensor consists of a mid-infrared interband cascade laser (ICL) operating in continuous wave mode, a long optical path multi-pass gas cell (MPGC) of 24 m, and a mid-infrared mercury cadmium telluride (MCT) detector. Aiming at the problem of the strong absorption intensity of the two absorption lines of 13CO2 and 12CO2 being affected by temperature, a high-precision temperature control system for the MPGC was fabricated. Five different concentrations of CO2 gas were configured to calibrate the sensor, and the response linearity could reach 0.9992 for 12CO2 and 0.9996 for 13CO2. The data show that the carbon isotope measurement precision was assessed to be 0.0139‰ when the integration time was 92 s and the optical path length was 24 m. The sensor is combined with a gas–liquid separator to detect the 13CO2/12CO2 isotope ratio of CO2 gas extracted from water. Results validate the reported sensor system’s potential application in deep-sea natural gas hydrate exploration.
Highlights
Natural gas hydrates (NGHs) are formed on the seabed under low-temperature and high-pressure conditions [1]
Compared to state-of-the-art studies, this paper presents the following: (a) a high-precision detection method for CO2 isotopes applied for deep-sea NGHs, (b) a linear optical structure combined with a multi-pass gas cell (MPGC) to overcome the challenges of a physically compact requirement for NGH exploration, (c) a high-precision temperature control system for the MPGC to improve the measurement precision of carbon isotopes, (d) a compact cylinder cell placed between the interband cascade laser (ICL) and MPGC to remove the interference from CO2 in the environment and to improve the measurement accuracy, and (e) a prototype using a mid-infrared absorption spectroscope capable of
We reported the design and performance of a 13 CO2 /12 CO2 isotope ratio sensor based on the tunable diode laser absorption spectroscopy (TDLAS) technique
Summary
Natural gas hydrates (NGHs) are formed on the seabed under low-temperature and high-pressure conditions [1]. In 2018, a vertical cavity surface emitting laser was utilized by Ghetti et al in the detection of CO2 isotopic ratio collected from exhaled small samples of CO2 (0.1 L) with a resolution of about 0.2% [16] These instruments achieved good carbon isotope detection performance, they cannot meet the requirement of deep-sea natural gas hydrate exploration (δ13 C of ~0.01%). Compared to state-of-the-art studies, this paper presents the following: (a) a high-precision detection method for CO2 isotopes applied for deep-sea NGHs, (b) a linear optical structure combined with a multi-pass gas cell (MPGC) to overcome the challenges of a physically compact requirement for NGH exploration, (c) a high-precision temperature control system for the MPGC to improve the measurement precision of carbon isotopes, (d) a compact cylinder cell placed between the interband cascade laser (ICL) and MPGC to remove the interference from CO2 in the environment and to improve the measurement accuracy, and (e) a prototype using a mid-infrared absorption spectroscope capable of CO2 isotope detection in indoor experiments.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
