Browsing by Author "Brewer, Paul J."

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    Characterization of Fourier transform infrared, cavity ring-down spectroscopy, and optical feedback cavity-enhanced absorption spectroscopy instruments for the analysis of ammonia in biogas and biomethane
    (American Chemical Society, 2022-10-27) Culleton, Lucy P.; di Meane, Elena Amico; Ward, Michael K. M.; Ferracci, Valerio; Persijn, Stefan; Holmqvist, Albin; Arrhenius, Karine; Murugan, Arul; Brewer, Paul J.
    Novel traceable analytical methods and reference gas standards were developed for the detection of trace-level ammonia in biogas and biomethane. This work focused on an ammonia amount fraction at an upper limit level of 10 mg m–3 (corresponding to approximately 14 μmol mol–1) specified in EN 16723-1:2016. The application of spectroscopic analytical methods, such as Fourier transform infrared spectroscopy, cavity ring-down spectroscopy, and optical feedback cavity-enhanced absorption spectroscopy, was investigated. These techniques all exhibited the necessary ammonia sensitivity at the required 14 μmol mol–1 amount fraction. A 29-month stability study of reference gas mixtures of 10 μmol mol–1 ammonia in methane and synthetic biogas is also reported.
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    Investigation of cylinder pre-treatments for the stability of ammonia gas reference materials
    (Springer, 2022-07-14) di Meane, Elena Amico; Brown, Richard J. C.; Brewer, Paul J.; Ferracci, Valerio; van Wijk, Janneke I. T.
    This report describes work to evaluate the performance of different commercial and proprietary cylinder treatments in improving the stability of ammonia reference materials in high pressure cylinders. Gas mixtures of 100 µmol/mol and 10 µmol/mol ammonia in nitrogen were prepared gravimetrically at both NPL and VSL. Comparative measurements at each amount-of-substance fraction were used to assess which passivation technique minimised the loss of ammonia upon preparation. The results indicate little difference between the commercial treatments, except at lower amount-of-substance fractions (10 μmol/mol). The variation observed in performance might be explained by the different abilities of the various treatments to prevent the adsorption of ammonia molecules on the internal surfaces of the cylinder, although the role of residual water on the cylinder surface in reacting with ammonia is unclear.
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    Production and stability of low amount fraction of formaldehyde in hydrogen gas standards
    (Elsevier, 2018-03-03) Bacquart, Thomas; Perkins, Mark; Ferracci, Valerio; Martin, Nicholas A.; Resner, Kate; Ward, Michael K. M.; Cassidy, Nathan; Hook, Joshua B.; Brewer, Paul J.; Irvine, John T. C.; Connor, Paul A.; Murugan, Arul
    Formaldehyde is an intermediate of the steam methane reforming process for hydrogen production. According to International Standard ISO 14687-2 the amount fraction level of formaldehyde present in hydrogen supplied to fuel cell electric vehicles (FCEV) must not exceed 10 nmol mol−1. The development of formaldehyde standards in hydrogen is crucial to validate the analytical results and ensure measurement reliability for the FCEV industry. NPL demonstrated that these standards can be gravimetrically prepared and validated at 10 μmol mol−1 with a shelf-life of 8 weeks (stability uncertainty <10%; k = 1), but that formaldehyde degrades into methanol and dimethoxymethane, as measured by FTIR, GC-MS and SIFT-MS. The degradation kinetics is more rapid than predicted by thermodynamics, this may be due to the internal gas cylinder surface acting as a catalyst. The identification of by-products (methanol and dimethoxymethane) requires further investigation to establish any potential undesirable impacts to the FCEV.