Novel Sampling Device for Obtaining Process Near-Infrared Spectra of High-Pressure Gases

A novel sampling device for making real-time, on-line, near-infrared measurements of high-pressure gases has been constructed and tested. The design makes it possible to measure background spectra between each sample measurement. The position of a floating piston inside a cylindrical cell is controlled by the pressure differences between the sample gas and the background gas. The optical path is transverse to the cylinder axis so that the sample gas is in the beam when its pressure is highest and the background gas is in the beam when its pressure is highest. At 350 psia, a pressure difference of ∼20 psia will drive the piston to the end having the lower pressure and allow the spectrum of the higher pressure gas to be measured. Near-IR spectra of CO 2 as a function of pressure and of 15 different natural gas samples were measured and analyzed.