Pyrolysis mechanisms of low-GWP working fluid R1243zf in ORC systems: An experimental and simulation study

The thermal stability and pyrolysis mechanisms of R1243zf were systematically investigated using experimental methods, ReaxFF molecular dynamic (RMD) simulations, and Density Functional Theory (DFT) calculations. Experimental results indicate that the initial pyrolysis temperature of R1243zf is observed between 180 °C and 200 °C. Hydrogen fluoride (HF) is identified as the dominant gaseous decomposition product, accompanied by the formation of dark brown liquid substances. These liquid residues were determined to be primarily olefinic compounds by Gas Chromatography-Mass Spectrometry (GC-MS) analysis. RMD simulations reveal that C–C bond cleavage is established as the primary initial decomposition pathway, generating CF3 and C2H3 radicals. HF is subsequently formed through chain reactions. Furthermore, DFT calculations demonstrate that C–C bond rupture exhibits the lowest Gibbs free energy barrier (399.16 kJ mol−1), while HF formation is dominated by reactions between F radicals and adjacent H atoms, with energy barriers of 35.79–36.58 kJ mol−1. Kinetic analysis demonstrates that HF possesses the lowest apparent activation energy among the three main gaseous products. It is demonstrated that the thermal stability of R1243zf is significantly reduced above 200 °C, rendering it unsuitable for medium-high temperature Organic Rankine Cycle (ORC) applications. The findings provide a theoretical basis for the thermal stability evaluation of HFO working fluids and the optimization of ORC systems.