2,3,3,3-Tetrafluoropropene, or HFO-1234yf, is a hydrofluoroolefin (HFO) with the formula CH2=CFCF3. This colorless gas has been proposed as a replacement for R-134a as a refrigerant in automobile air conditioners.
HFO-1234yf is the first in a new class of refrigerants acquiring a global warming potential (GWP) rating one 335th that of R-134a (and only 4 times higher than carbon dioxide, which can also be used as a refrigerant but which has properties significantly different from those of R134a, especially requiring operation at around 5 times higher pressure) and an atmospheric lifetime of about 400 times shorter.
HFO-1234yf was developed to meet the European directive 2006/40/EC that went into effect in 2011 requiring that all new car platforms for sale in Europe use a refrigerant in its AC system with a GWP below 150.
HFO-1234yf, which has a 100-year GWP of 4, could be used as a "near drop-in replacement" for R-134a, the current product used in automobile AC systems, which has a 100-year GWP of 1430. This means that automakers would not have to make significant modifications in assembly lines or in vehicle system designs to accommodate the product. HFO-1234yf has the lowest switching cost for automakers among the currently proposed alternatives, although the initial cost of the product is much higher than that of R-134a. The product could be handled in repair shops in the same way as R-134a, although it would require different, specialized equipment to perform the service. One of the reasons for that is the mild flammability of HFO-1234yf. Another issue affecting the compatibility between HFO-1234yf and R-134a-based systems is the choice of lubricating oil. The current lubricating oil is showing signs of damage to plastic and aluminium, and issues with health, including mouth dryness, rashes, and sore throat, among other effects.
Shortly after confirmation from automakers that HFO-1234yf would be adopted as a replacement of R-134a automotive air-conditioning refrigerant, Honeywell and DuPont announced jointly built a manufacturing facility in Changshu, Jiangsu Province, China to produce HFO-1234yf. In addition, Honeywell is building a new plant in Geismar, Louisiana, USA to produce the new refrigerant as well. Although others claim to be able to make and sell HFO-1234yf, Honeywell and DuPont hold most or all of the patents registered for HFO-1234yf.
On July 23, 2010, General Motors announced that it will introduce HFO-1234yf in 2013 Chevrolet, Buick, GMC, and Cadillac models in the U.S.
Although the product is classified slightly flammable by ASHRAE, several years of testing by SAE proved that the product could not be ignited under conditions normally experienced by a vehicle. In addition several independent authorities evaluated the safety of the product in vehicles and some of them concluded that it was as safe to use as R-134a, the product in use in cars today. In the atmosphere, HFO-1234yf degrades to trifluoroacetic acid, which is a mildly phytotoxic strong organic acid with no known biodegradation mechanism in water. In case of fire it releases highly corrosive and toxic hydrogen fluoride and the highly toxic gas carbonyl fluoride.
In December 2012, Mercedes-Benz showed that the substance ignited when researchers sprayed it and A/C compressor oil onto a car's hot engine. A senior Daimler engineer who ran the tests, stated "We were frozen in shock, I am not going to deny it. We needed a day to comprehend what we had just seen." Combustion occurred in more than two thirds of simulated head-on collisions. The engineers also noticed etching on the windshield caused by the corrosive gases. BMW, and VW-Audi agreed with Mercedes and left the SAE R-1234yf CRP Team, stating that the performed tests are not sufficient to fully judge the safety of their vehicles. The German automakers have been leaning towards carbon dioxide refrigerant, which may be safer for both passengers and the environment.
Following Mercedes claims that the new refrigerant could be ignited, Germany's Kraftfahrt-Bundesamt (Federal Motor Transport Authority) conducted its own tests. The Authority concluded that while the substance was potentially more hazardous than previously used R-134a, it did not comprise a serious danger. However the German automakers disagree with their findings, and test procedures. Following other independent and in house testing, General Motors still plans to transition all new models to the new refrigerant by 2018. Chrysler announced that they would continue the transition to R1234yf as well. Japanese automakers are also making the transition to R1234yf, Honda and Subaru have begun to introduce the new refrigerant already with the 2017 models.
Typical methods for producing HFO-1234yf start with 1,2,3,3,3-pentafluoropropene. Hydrogenation of this alkene gives 1,2,3,3,3-pentafluoropropane, which upon heating with an Al-based catalyst undergoes dehydrofluorination: CF3CFHCFH2 → CF3CF=CH2 + HF