Experimental and DFT investigation of reactivity in the near-azeotropic R1233zd(E)/R1336mzz(E) mixture

Year: 2026

Authors: Doninelli M., Speziani M., Alessandri I., Di Marcoberardino G.

Autors Affiliation: Univ Brescia, Dipartimento Ingn Meccan Industriale, via Branze 38, I-25123 Brescia, Italy; Univ Brescia, Dipartimento Ingn Informaz, via Branze 38, I-25123 Brescia, Italy; INSTM Natl Consortium Mat Sci & Technol, UdR Brescia, via Branze 38, I-25123 Brescia, Italy; CNR INO, UdR Brescia, via Branze 45, I-25123 Brescia, Italy.

Abstract: Halogenated olefin refrigerants and their mixtures are increasingly considered as low-GWP working fluids for high-temperature heat pumps and organic Rankine cycles. However, their unsaturated nature raises chemical stability concerns that conventional assessment methods may fail to capture. This work demonstrates that the standard static-isochoric thermal stability test – while effective for pure components, yielding safe-use temperatures of 200 degrees C for R1233zd(E) and 350 degrees C for R1336mzz(E) – fails to detect polymerisation pathways through pressure monitoring alone, as no non-condensable gases are produced. Using the near-azeotropic R1233zd(E)/R1336mzz(E) mixture as a case study, polymerisation is shown to occur at 110 degrees C – conditions relevant to ORC and HTHP applications – with liquid and solid reaction products observed in dedicated aging experiments at saturation pressure (below 15 bar), and independently during bubble point measurements at higher pressures. Density Functional Theory simulations reveal energetically favourable chaingrowth reaction pathways that explain this behaviour, and combined Raman spectroscopy and ATR-FTIR characterisation of the solid products identifies functional groups consistent with a fluorinated oligomeric structure, in agreement with the DFT-predicted mechanism. These findings establish a multi-method framework – combining standard stability testing, DFT simulations, and spectroscopic analysis – as essential for the reliable chemical assessment of olefin-containing refrigerant mixtures, and raise concerns regarding the suitability of the R1233zd(E)/R1336mzz(E) mixture as a working fluid under the investigated conditions.

Journal/Review: INTERNATIONAL JOURNAL OF REFRIGERATION-REVUE INTERNATIONALE DU FROID

Volume: 192      Pages from: 107116-1  to: 107116-14

More Information: The research is funded by the project COFFEE under the National Recovery and Resilience Plan (PNRR) , Mission 4 Component 2 Investment 1.3, Project title Network 4 Energy Sustainable Transition – NEST funded by the European Union – NextGenerationEU (Project Code PE0000021) , Cascade call of the Spoke 5 Energy Conversion.
KeyWords: R1233zd(E); R1336mzz(E); Thermal stability; Polymerisation; Density functional theory; Raman spectroscopy
DOI: 10.1016/j.ijrefrig.2026.107116