Development and improvement of quantitative composition analysis methods for species relevant to gas industry with benchtop NMR spectroscopy

RWTH Publications (RWTH Aachen)

Abstract

High-pressure Nuclear Magnetic Resonance (NMR) spectroscopy has long been used to study complex molecular systems such as natural gas (NG), but high-field instruments remain costly and inaccessible for routine applications. This thesis presents improved and novel methodologies that enhance the robustness, accuracy, and affordability of benchtop ¹H NMR spectroscopy for the quantitative analysis of complex NG mixtures under high pressure. A previously introduced approach combining high-pressure benchtop NMR with indirect hard modeling (IHM) was improved to boost the accuracy for the composition analysis of hydrocarbon mixtures at up to 200 bar. Key innovations include a high-performance pressure tube and quality control (QC) parameters to ensure reproducibility. The method successfully handled complex spectra influenced by triethylene glycol (TEG), a common NG contaminant used in NG dehydration units, enabling quantification of both TEG and its spectral impact. In addition, a rapid lineshape analysis (LSA) technique was used for determining trace water content in glycol-water mixtures, achieving detection limits as low as 0.05 wt%, in excellent agreement with the Karl Fischer method. Finally, a novel flow-cell for dynamic, high-pressure NMR measurements up to 245 bar was designed using low-cost PEEK components. This setup enabled automated, in-field-compatible analysis of hydrogen-enriched NG and facilitated the estimation of non-hydrogen-bearing gases using data-driven calibration strategies. The outcomes of this work demonstrate that benchtop NMR can serve as a powerful alternative, offering reliable, low-cost compositional analysis for industrial and research environments, particularly within the energy sector.

Authors 1

1. Sergio Alejandro Ortiz Restrepo corresponding Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen