Simultaneous quantification of aliphatic and aromatic hydrocarbons in produced water analysis using mobile¹H NMR

Abstract

Legislated environmental limits regarding the hydrocarbon content of discharge water from offshore oil and gas are becoming progressively more stringent. This is helping stimulate the development of analytical methods that are both robust and reliable whilst being able to quantify oil in water content at the ppm level of detection. Previously, in Wagner (2016 Meas. Sci. Technol. 27 105501), we showed how such a measurement requirement of total oil content could be met by the application of mobile benchtop NMR. Here, we extend this non-optical measurement platform to enable separate quantification of the aromatic and aliphatic oil content of the discharge water; the aromatic content is of increasing interest on account of its much greater toxicity. Our revised method deploys a two solvent measurement protocol whilst retaining the self-calibration characteristic of the original approach. This new methodology was successfully validated using water contaminated with a variety of aromatic and aliphatic hydrocarbons. The uncertainty related to the NMR measurements was shown to be comparable to that of sample preparation; results were also successfully validated against gas chromatography and infrared measurements.

Mid-IR sensing platform for trace analysis in aqueous solutions based on a germanium-on-silicon waveguide chip with a mesoporous silica coating for analyte enrichment

“…Quantum cascade laser (QCL) light is coupled from the chip back-side into the waveguide making use of grating couplers and monolithically integrated microlenses. By this means a limit of detection (LOD) for aromatic hydrocarbons sufficiently low to meet the regulation requirements (∼1 ppm for industry, sub-ppm for drinking water) [7,8] can be reached. Here first measurements of toluene in water reveal a detection limit of 7 ppm, limited by the noise of the used laser spectrometer.…”

Solid-Phase Extraction Nuclear Magnetic Resonance (SPE-NMR): Prototype Design, Development, and Automation

“…It is also applied in the laboratory for hydrate formation and oil field emulsions characterization, for example. − Proton ( 1 H) NMR can detect all compounds with hydrogen atoms in their structure and, as a result, can theoretically measure the total hydrocarbon contamination of produced water. Furthermore, NMR techniques are readily made self-calibrating through the inclusion of reference compounds, require no optical window, and allow for quantitative separate analysis of aromatic and aliphatic hydrocarbon content. , Conventional high-field NMR spectrometers (typically employing superconducting magnets) will provide both enhanced sensitivity and compound spectral resolution for such OiW monitoring. Their complexity, size, and cost, however, effectively preclude them from any realistic field application. , Recent advancements in NMR technology have, however, produced benchtop low-field permanent magnets with increased sensitivity and magnetic field homogeneity.…”

“…Their complexity, size, and cost, however, effectively preclude them from any realistic field application. , Recent advancements in NMR technology have, however, produced benchtop low-field permanent magnets with increased sensitivity and magnetic field homogeneity. These are mobile, significantly cheaper than conventional high magnetic field systems, and generally more robust to environmental conditions, all of which make them more suitable for field applications. , A major traditional limitation of all NMR has been comparatively poor sensitivity with ppm of OiW levels being considerably below any practical detection limit; the application of solid-phase extraction (SPE) as a sample preparation technique for NMR has, however, allowed for quantitative OiW monitoring at this ppm level. , …”

“…We have recently developed a custom-made SPE-aided NMR system and conducted a successful lab-based manual proof-of-concept evaluation of the combined system for the measurements of OiW content in produced water. , This utilizes chemically bonded silica sorbents to concentrate the ppm oil contamination of produced water to NMR detectable levels. A hydrogen-free solvent (perchloroethylene (PCE)) was used for elution purposes; this contained 0.5–3 wt % of chloroform (CHCl 3 ) and/or hexamethyldisiloxane (HMDSO), which acted as internal calibration references that do not overwhelm the contaminant NMR signal while allowing for quantification of both OiW aliphatic and aromatic content.…”

“…A schematic illustration of the SPE process stages, as applied in this study, is shown in Figure . These stages are a loading step during which the contaminants of interest (all hydrocarbon contaminants in this case) are adsorbed into the sorbent material in the cartridge, an air flushing step where the sample liquid is flushed out from the sorbent, and finally an elution solvent extraction step where the adsorbates (hydrocarbons) are extracted using the relevant solvent …”