Potential of ion mobility spectrometry versus FT-MIR and GC-MS to study the evolution of a heat transfer fluid after its heating process in a thermosolar plant

• A lab-scale reactor was used to produce degraded HTF samples reproducing conditions in a thermosolar plant.
• New methods have been developed to analyze HTF by IMS techniques.
• A global response was obtained using UV-IMS to distinguish between raw and degraded HTF samples.
• Benzene and phenol were identified in HTF degraded samples by GC-3H-IMS.
• Results obtained with IMS instruments were comparable with FT-MIR and GC-MS.

Heat transfer fluid (HTF) is commonly used in heat transfer industrial processes such as those performed in thermosolar plants. Although HTF is thermally stable, the high temperatures used in such plants (around 400 °C) and overheating in continuous cycles can alter its composition. The potential changes in its initial composition (biphenyl and diphenyl ether), and the likely production of new compounds, such as benzene and phenol, require using fast-response portable instruments for on-site quality control at thermosolar plants. In this work, the degradation profile of HTF heated for a variable time was for the first time characterized by using two different ion mobility spectrometry (IMS) instruments. The simple one used a UV lamp as ionization source (UV-IMS), whereas the other included a chromatographic column coupled to a tritium source (GC-3H-IMS). Other analytical techniques such as Fourier transform-mid infrared spectroscopy (FT-MIR) and gas chromatography–mass spectrometry (GC-MS) were also used for the same purpose. Based on the results, both IMS instruments can be useful for online quality control of HTF in a thermosolar plant. Thus, the UV-IMS instrument can be used for screening purposes and the GC-3H-IMS instrument for selective detection of benzene and phenol as degradation products.