How refrigerants work and are made

Every fridge and air conditioner relies on a liquid that boils at a carefully chosen temperature.

stations: 6
things upstream: 18
raw sources: 11
steps from the ground: 4

The short version

A refrigerant has to boil below the cold side's temperature and condense above the warm side's. Natural fluids such as ammonia and carbon dioxide skip the fluorine chemistry. Widely used HFC-134a is built in two reactors, where trichloroethylene meets hydrogen fluoride and chlorine gives way to fluorine. Distillation then pulls off hydrogen chloride and sends unreacted feed back around.

Make hydrogen fluoride

Synthetic fluids begin with fluorite, a mineral that gives off hydrogen fluoride when treated with concentrated sulfuric acid.

Goes in
Fluorspar Sulfuric acid
Swap chlorine for fluorine

Trichloroethylene, a chlorine-bearing feedstock, meets hydrogen fluoride in a first reactor. Fluorine takes the place of most of its chlorine, hydrogen chloride comes off, and the result is an intermediate called HCFC-133a.

Goes in
Chlorine
Finish in a second reactor

The intermediate takes on one more fluorine from more hydrogen fluoride, under different conditions from the first step. That gives HFC-134a. Each stage needs its own settings, which is why the job takes two reactors.
Distill and recycle

One patent combines the output of both reactors and feeds it to a distillation column. A second column recovers hydrogen chloride. Unreacted hydrogen fluoride and intermediate get topped up and returned to their reactors, which saves columns and energy over distilling after each step.
Purify the fluid

The product stream still holds small amounts of intermediate and hydrogen fluoride, so it goes to a separate purification step before it is ready to sell.
Blend or use natural fluids

Refrigerants are sometimes blended to balance properties, and a blend vaporizes across a small temperature range called glide. Ammonia, carbon dioxide and propane take none of the fluorine route above.

Goes in
Ammonia Carbon dioxide Propane

End of the lineRefrigerant Next it goes into refrigerator, air conditioner, asthma inhaler.

Worth repeating

Refrigerants of the late 1920s such as ammonia and sulfur dioxide were toxic, flammable or explosive, which sent Thomas Midgley Jr. looking for a safer fluid.
Thomas Midgley Jr. helped develop both Freon and leaded gasoline, two inventions that later did great harm to the planet.