How to make Ethane Refrigerant (R170)

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In this video I'll show how to make Ethane gas (C2H6), also known as refrigerant R170. This is the slightly heavier cousin of Ethylene or "Ethene" which is C2H4 (Refrigerant R1150). Ethane has a boiling point of -88C compared to Ethylene's -104C.

The main motivation behind synthesizing Ethane was to have a refrigerant for the second stage of a cascade vapor compression system that could still reach ultra-low temperatures, but without as high of a pressure demand. Assuming a heat exchanger temperature of -20C on the first stage of a cascade system, it would take 25.3 bar or 352 psi to condense Ethylene, whereas Ethane would only require 14.2 bar or 191 psi. This means that a small system using the relatively weak reciprocating compressors from a mini-fridge or tabletop ice-maker could use Ethane for a second stage, whereas Ethylene would typically require a rotary compressor to handle the higher pressure.

Industrially, Ethane is produced from crude oil or by hydrogenation of Ethylene. The hydrogenation reaction occurs by passing Ethane and Hydrogen over a high temperature nickel catalyst. In theory this process could be done by an amateur/hobbyist, but there's actually a simpler method - electrolysis.

When an acetate solution undergoes electrolysis with a platinum anode (whether acetic acid, or some acetate salt), the acetate ions break up into Carbon Dioxide (CO2) and Ethane (C2H6), in a process known as Kolbe electrolysis. This is actually a pretty complicated process that involves a lot of organic chemistry that I don't understand - but it works.

In this video, I'll use Sodium Acetate as my electrolyte. Theoretically, straight Acetic Acid (or vinegar) can be used, but its electrical conductivity is extremely low, so Sodium Acetate is a better option. Over time, as the acetate ions are consumed, the Sodium Acetate becomes Sodium Carbonate, causing the solution to become basic (pH over 7.0). Once this happens, the Kolbe electrolysis process stops, and regular alkaline water electrolysis occurs, producing oxygen gas at the anode.

For this reason, the electrolyte needs to be made with a generous excess of acetic acid, and the reaction should be stopped if the cell pH goes above around 6-7. Since the gas output contains CO2, it has to be scrubbed with Calcium Hydroxide in order to extract the pure Ethane. I also included a dessicant canister in line with my scrubber, since the gas has a significant amount of moisture in it.

To demonstrate its refrigeration properties, I compressed my Ethane into a ~100cc pipe in an ice bath to force it to liquify, then discharged it through a valve. When the liquid Ethane is brought down to 1 atmosphere, it flashes to vapor and drops its temperature to -88C.

One additional advantage of Ethane over Ethylene is that it can be stored in liquid state at room temperature, since its critical point is 32C. At 25C, liquid Ethane has a pressure of 41.9 bar or 593 psi, so it could easily be stored in a tank meant for CO2 or Nitrous Oxide, which have much higher pressures in their liquid state at room temperature.

Link to Ethylene Synthesis video:
   • Making Ethylene (Refrigerant R1150)  

Music Used:
Kevin MacLeod - Bossa Antigua
Kevin MacLeod - Lobby Time
Kevin MacLeod - Groove Groove
Kevin MacLeod - George Street Shuffle
Kevin MacLeod - Hard Boiled