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Sustainability is a topic that is becoming more and more important in energy production systems. Due to new energy policies, hydrogen is receiving increasing attention as a carbon-free energy carrier embedded in hybrid renewable energy systems (HRES). This paper presents a sustainability analysis of the HRES operation involving electrolytic hydrogen production and conversion to methane through Power-to-Methane (PtM). The analysis is based on day-ahead (DA) scheduling to accomplish the minimum HRES operating cost by comparing two PtM models: A simple rigid model with constant input/output efficiency without hydrogen storage and a linearised electrolyser and methane model with hydrogen storage. The subsequent analysis is conducted by adding heat and gas accumulators in the linearised PtM model to evaluate the added flexibility of these components. Based on the optimal DA programming solution, the three PtM representations are compared based on their respective operating costs and carbon dioxide emissions. The outcomes show that hydrogen into the HRES via a PtM process is not a direct sign of sustainability and that the environmental impact depends on the electricity source provided by the electrolyser. Therefore, this paper highlights that the growth of RES and the integration of PtM should go in synergy and deducting that a more accurate model is required to understand the potential of PtM.

To date there is no consensus about the most appropriate analytical method for measuring carbon nanotubes (CNTs), hampering the assessment and limiting the comparison of data. The goal of this study is to develop an approach for the assessment of the level and nature of inhalable multi-wall CNTs (MWCNTs) in an actual workplace setting by optimizing and evaluating existing analytical methods. In a company commercially producing MWCNTs, personal breathing zone samples were collected for the inhalable size fraction with IOM samplers; which were analyzed with carbon analysis, inductively coupled plasma mass spectrometry (ICP-MS) and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX). Analytical methods were optimized for carbon analysis and SEM/EDX. More specifically, methods were applied and evaluated for background correction using carbon analyses and SEM/EDX, CNT structure count with SEM/EDX and subsequent mass conversion based on both carbon analyses and SEM/EDX. A moderate-to-high concordance correlation coefficient (RC) between carbon analyses and SEM/EDX was observed [RC = 0.81, 95% confidence interval (CI): 0.59-0.92] with an absolute mean difference of 59 µg m-3. A low RC between carbon analyses and ICP-MS (RC = 0.41, 95% CI: 0.07-0.67) with an absolute mean difference of 570 µg m-3 was observed. The large absolute difference between EC and metals is due to the presence of non-embedded inhalable catalyst particles, as a result of which MWCNT concentrations were overestimated. Combining carbon analysis and SEM/EDX is the most suitable for quantitative exposure assessment of MWCNTs in an actual workplace situation.

To date there is no consensus about the most appropriate analytical method for measuring carbon nanotubes (CNTs), hampering the assessment and limiting the comparison of data. The goal of this study is to develop an approach for the assessment of the level and nature of inhalable multi-wall CNTs (MWCNTs) in an actual workplace setting by optimizing and evaluating existing analytical methods. In a company commercially producing MWCNTs, personal breathing zone samples were collected for the inhalable size fraction with IOM samplers; which were analyzed with carbon analysis, inductively coupled plasma mass spectrometry (ICP-MS) and scanning electron microscopy/ energy dispersive X-ray spectroscopy (SEM/EDX). Analytical methods were optimized for carbon analysis and SEM/EDX. More specifically, methods were applied and evaluated for background correction using carbon analyses and SEM/EDX, CNT structure count with SEM/EDX and subsequent mass conversion based on both carbon analyses and SEM/EDX. A moderate-to-high concordance correlation coefficient (RC) between carbon analyses and SEM/EDX was observed [RC = 0.81, 95% confidence interval (CI): 0.59-0.92] with an absolute mean difference of 59 μg m-3. A low RC between carbon analyses and ICP-MS (RC = 0.41, 95% CI: 0.07-0.67) with an absolute mean difference of 570 μg m-3 was observed. The large absolute difference between EC and metals is due to the presence of non-embedded inhalable catalyst particles, as a result of which MWCNT concentrations were over- estimated. Combining carbon analysis and SEM/EDX is the most suitable for quantitative exposure assessment of MWCNTs in an actual workplace situation. © The Author 2017. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.