Final report on EURAMET.QM-S6/1195: Bilateral comparison of liquefied hydrocarbon mixtures in constant pressure (piston) cylinders

Abstract

Traceable liquid hydrocarbon mixtures are required in order to underpin measurements of the composition and other physical properties of LPG (liquefied petroleum gas) and LNG (liquefied natural gas), thus meeting the needs of an increasingly large European industrial market.The development of traceable liquid hydrocarbon standards by National Measurement Institutes (NMIs) was still at a relatively early stage at the time this comparison was proposed in 2011. NPL and VSL, who were the only NMIs active in this area, had developed methods for the preparation and analysis of such standards in constant pressure (piston) cylinders, but neither laboratory had Calibration and Measurement Capabilities (CMCs) for these mixtures.This report presents the results of EURAMET 1195, the first comparison of liquid hydrocarbon mixtures between NMIs, which assessed the preparation and analytical capabilities of NPL and VSL for these mixtures. The comparison operated between August 2011 and January 2012. Each laboratory prepared a liquid hydrocarbon standard with nominally the same composition and these standards were exchanged for analysis.The results of the comparison show a good agreement between the laboratories' results and the comparison reference values for the six components with amount fractions greater than 1.0 cmol/mol (propane, propene, iso-butene, n-butane, iso-butane and 1-butene). Measurement of the three components with lower amount fractions (1,3-butadiene, iso-pentane and n-pentane) proved more challenging. In all but one case, the differences from the comparison reference values for these three components were greater than the expanded measurement uncertainty.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by EURAMET, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Advances in metrology for energy-containing gases and emerging demands

“…After a bilateral comparison between NPL and VSL (Euramet.QM-S6) [99], the CCQM-GAWG organised a key comparison coordinated by NPL. After applying a correction for the stability of these mixtures (caused by hydrocarbons migrating from the compartment containing the liquid mixture to that containing helium), the vast majority of the results agreed within the respective uncertainties with the KCRV.…”

Development of a Novel Leak-Free Constant-Pressure Cylinder for Certified Reference Materials of Liquid Hydrocarbon Mixtures

“…International comparison studies have been designed to assess the preparative and analytical capabilities of liquid hydrocarbon mixture standards developed in PCPCs; 3,4 piston does not guarantee a perfect seal. 3 In this study, we developed a novel leak-free bellows-type constant-pressure cylinder (BCPC) for liquid hydrocarbon mixture standards. In contrast to the PCPC that separates two chambers with a piston, the BCPC has a bellows-type liquid chamber (without a seal between the two chambers) that is completely separated from the gas chamber containing the pressurizing helium.…”

“…As a result, PCPCs are widely used to develop accurate and traceable standards for liquid hydrocarbon mixtures. International comparison studies have been designed to assess the preparative and analytical capabilities of liquid hydrocarbon mixture standards developed in PCPCs; , however, the composition of liquid hydrocarbon mixtures in a PCPC might change with time, given that the piston does not guarantee a perfect seal . In this study, we developed a novel leak-free bellows-type constant-pressure cylinder (BCPC) for liquid hydrocarbon mixture standards.…”