(256d) Development of a New Low-GWP Refrigerant Composed of HFO-1123 (trifluoroethylene)

Hydrofluorocarbon (HFC) products are widely used as a refrigerant for air-conditioning systems. Commercially available HFC refrigerants, such as HFC-410A(1), has excellent properties as a refrigerant, but their high global-warming potential (hereinafter ”GWP”(2)) is now at issue because when air-conditioners being disposed of, a large proportion of refrigerant gases stored in them is emitted to the atmosphere without chemically destroyed, which results in contributing to global warming. Therefore, refrigerants with lower GWP is strongly required globally.

In line with this trend toward restricting the use of HFC with high GWP, some manufactures of room air-conditioning systems and professional-use air-conditioning equipment have begun to adopt alternative refrigerants such as HFC-32 (GWP = 675, about one third of that of HFC-410A).

In 2014, AGC (Asahi Glass Co., Ltd.) has successfully developed a new refrigerant for air-conditioning systems that can reduce GWP further, which adopts hydrofluoroolefin(HFO)-1123 as a main component.

HFO-1123 (trifluoroethylene) is strongly attractive because its performance as a refrigerant is equivalent to that of conventional refrigerants and its GWP is extremely low (GWP = 0.3(3)). As mentioned above, having a low GWP is quite important because the refrigerant gas in air-conditioners is largely emitted to the atmosphere eventually. And having a high performance as a refrigerant is also crucial to decrease the environmental burden because the lower performance as a refrigerant means consuming more electricity when used as air-conditioners, resulting in more carbon dioxide emission.

Despite HFO-1123 being so fascinating, it has a downside. Unlike chemical materials adopted in conventional refrigerants, HFO-1123 is known to disproportionate under specific conditions and in the presence of ignition sources. The formula of disproportionation reaction is described as ”C2HF3 → 0.5CF4 + 1.5C + HF + 250 kJ/mol” (4) As shown in the formula, this disproportionation reaction is highly exothermic, which means it might cause chain reaction, resulting in both temperature and pressure soaring. For example, the chain reaction of HFO-1123 disproportionation occurred when the temperature of HFO-1123 gas was more than 100 degrees Celsius and the pressure was more than 1 MPa and the gas was ignited by a hot wire (the surface temperature of wire was about 1400 degrees Celsius and the ignition energy was 19J).

Needless to say, air-conditioners have to be a safe apparatus as well as being an environmental-friendly one, so soaring in temperature and pressure of a refrigerant gas would not be allowed even under abnormal situations, like the evolution of ignition sources such as a spark in air-conditioners. This means that a refrigerant composed only of HFO-1123 cannot be safe enough for industrial applications because the failure of air-conditioners is inevitable stochastically.

The approach we developed to prevent the chain reaction under any possible situations in air-conditioners was to design the components of a refrigerant elaborately. Concretely we investigated how the chain reaction of HFO-1123 propagates, and then found some additives that have the ability to suppress the chain reaction. In this way, we successfully developed a refrigerant composed mainly of HFO-1123, with high performance, low GWP, and high stability, that is, safe.

In this study, we have investigated thoroughly the disproportionation behaviors of HFO-1123-containing gases experimentally by using an autoclave apparatus, and revealed how the composition of gases, the temperature and the pressure of gases, and the temperature and energy of ignition sources, affect them.

We also adopted computational approach and analyzed the disproportionation reaction mechanism.

Finally we developed a method to predict if the disproportionation reaction of HFO-1123-containing gases occurs or not under a specific condition, like composition, temperature, pressure of gasses.

In our presentation, we’ll show the result of our study and how we’ve succeeded in developing HFO-1123-containing refrigerant.

(1) mixture of HFC-32 (difluoromethane) and HFC-125 (pentafluoroethane) (50/50wt%)

(2) a relative measure of how much heat a greenhouse gastraps in the atmosphere in a specific time interval (here 100 years is adopted as a time interval), expressed as a factor of carbon dioxide (whose GWP is standardized to 1)

(3) measured by AIST (National Institute of Advanced Industrial Science and Technology)

(4) Combustion, Explosion, and Shock Waves, Vol. 42, No. 2, pp. 140–143, 2006