Experimental and Theoretical Study on Thermal Stability of Mixture R1234ze(E)/R32 in Organic Rankine Cycle

The use of Organic Rankine Cycle (ORC) for renewable energy utilization and industrial waste heat recovery is currently attracting growing attention. The working fluids in ORC may face thermally decompose during the working process. The thermal stability and pyrolysis mechanism of R1234ze(E)/R32 mixtures was studied by ReaxFF-MD simulations and DFT calculation. The experimental results indicated that the pyrolysis temperature range is 230 degrees C-250 degrees C for R1234ze(E), 270 degrees C-290 degrees C for R32 and 230 degrees C-250 degrees C for R1234ze(E)/R32 mixtures. The cleavage of C-H, C-C bond is the main decomposition pathway of pure R32, R1234ze(E), respectively. The decomposition rate of R32 is significantly slower than that of R1234ze(E). In the mixture R1234ze(E)/R32, R1234ze(E) can significantly promote the decomposition of R32, while R32 has a slight inhibitory effect on the decomposition of R1234ze(E). The CF3 radicals generated by the decomposition of R1234ze(E) significantly reduced the energy barrier of R32 decomposition and promoted the decomposition rate of R32. The H and F radical in the system is more inclined to react with R32 than R1234ze(E) due to their lower energy barrier. The increase of the pressure and mass ratio of R1234ze(E) in the mixture system has a great promoting effect on the pyrolysis of the mixtures.