From toxic refrigerants to modern systems: how early innovation shaped today’s industry

The development of hermetic compressors for domestic refrigerators in the early 1920s was a direct response to safety concerns related to the toxicity of the refrigerants used at that time, principally sulfur dioxide and methyl chloride. The first refrigerators on the market used open drive compressors, meaning a shaft seal leak could, and sometimes did, prove fatal.

Three research initiatives emerged to solve this problem. Fully hermetic compressors, small enough for the duty requirement and cheap enough for the market, provided one response and proved successful in a remarkably short period. Another approach was to substitute propane as the refrigerant in open drive compressors, marketed in the 1920s as “the safety refrigerant” because it was non-toxic.

The third route was perhaps the most imaginative. It involved creating a new class of chemicals selected for favourable properties such as pressure-temperature relationship, heat transfer performance and lubricant compatibility. This work was entrusted to a young research engineer named Thomas Midgley Jr.

Midgley first came across halogens while developing his anti-knock additive for gasoline engines just after the First World War. He had surmised that engine knocking was related to temperature distribution during combustion and, inspired by the red leaves of the trailing arbutus in the winter snow in Ohio, he added iodine to his fuel to give it some colour. This had a remarkably beneficial effect, but when the test was repeated with red aniline dye the benefit vanished. It turned out that it was the iodine, not the colour, that gave the benefit.

Once tetraethyl lead, known simply as “Ethyl,” had been established as the additive of choice, Midgley found that bromine provided a cleansing benefit by preventing the build-up of lead oxide on engine valves. He developed a process for extracting bromine from seawater, enabling the cost-effective manufacture of the fuel additive.

When challenged in the late 1920s to find a replacement for methyl chloride and sulfur dioxide, he turned back to the Group VII atoms, the halogens, and conducted a methodical review of all organic compounds with one, two or three carbon atoms combined with chlorine, fluorine, bromine and iodine. This quickly identified dichlorodifluoromethane as the best all-round candidate, and it was rapidly commercialised as the original “Freon.”

Now, a century later, we know that the three-way race in the 1920s between hermetics, hydrocarbons and halogenated alkanes has two winners. For all its many advantages, R-12 had one major drawback: the interaction between chlorine and polar stratospheric ozone was unknown to Midgley and his colleagues, but it ultimately caused CFCs to fall out of favour in the 1990s.

Today, most domestic refrigerators use hermetic compressors with a hydrocarbon refrigerant. The question is what we will be doing in another hundred years.