High-Pressure Measuring Cell for Raman Spectroscopic Studies of Natural Gas

Abstract

A system for obtaining Raman spectra of gases at high pressure has been constructed. In order to ensure that a natural gas sample is totally representative, a high-pressure gas-measuring cell has been developed, built up by stainless steel fittings and a sapphire tube. The design and construction of this cell are described. A perfect pressure seal has been demonstrated up to 15.0 MPaA (MPa absolute). The cell has been successfully used to obtain Raman spectra of natural gas samples. Some of these spectra are presented and assigned. The most remarkable observation in the spectra is that it is possible to detect hydrogen sulfide at concentrations of 1–3 mg H2S/Nm3. An attempt to make a quantitative analysis of natural gas by the so-called “ratio method” is presented. In addition to this, the relative normalized differential Raman scattering cross sections for ethane and i-butane molecules at 8.0 MPaA and 10.2 MPaA have been determined.

Determination of Water Vapor Pressure Over Corrosive Chemicals Versus Temperature Using Raman Spectroscopy as Exemplified with 85.5% Phosphoric Acid

“…[18][19][20][21][22][23] Calibration spectra of internal standard gasses for quantitative determination of the water are also shown in Figure 3, for the examples of methane to the left or hydrogen to the right. The methane gas phase spectrum contains the well-known [24][25][26][27][28] ro-vib Q-branch band structure of the ν 1 (A 1 )…”

A new optical capillary cell for spectroscopic studies of geologic fluids at pressures up to 100 MPa

“…The current HPOC is similar to our previous optical cell that we used to calibrate a Raman spectrometer (Chou et al, 1990). Similarly, the optical cell designed by Hansen et al (2001a) can not be used for pressures more than 15 MPa (Hansen et al, 2001a(Hansen et al, ,b, 2002, and when compared with our HPOC, the wall thickness of their sapphire tube is quite large (6.35 mm OD X 4.43 mm ID), and the sample volume in their 39.5-mmlong tube is also several orders of magnitude larger. Also, the round and thick-walled capillary tubing in that design caused optical distortion (Stem et al, 1998) and low efficiency in collecting Raman spectra.…”

“…Several types of high-pressure optical cells (HPOC) have been used in investigations of geologic fluids, particularly those involving studies of gas hydrates, and include the diamond anvil cell (e.g. Chou et al, 1990;Sum et al, 1997;Thieu et al, 2000;Hansen et al, 2001a). Smelik and King, 1997;Nakano et al, 1999;Schicks and Erzinger, 2003;Schicks and Ripmeester, 2004), and silica or sapphire tubes (e.g.…”

Photonic bandgap fiber-enabled Raman detection of nitrogen gas

“…Typically an enhancement of 10's to 100's is achieved with multipass approach. Increasing Raman light collection efficiency by specially designed optics [4] and utilizing higher gas pressure [5] also helped to raise detected Raman signals.…”

“…Due to its ubiquitous occurrence in the atmosphere (essentially 78% nitrogen, 21% oxygen, 0.93% argon, 0.038% carbon dioxide, variable amounts of water, and trace other gases), measuring nitrogen has been largely overlooked. However, there are occasions where measurement of all inert gases including nitrogen plays an important role such as determining thermal conductivity of natural gas [5].…”