Ethyl Mercaptan in BBQ Propane

[BradC]

G'day all,

Among other things I picked up an old 2.5HP window A/C that was short on refrigerant from Ebay (.99c) to cut up and experiment with.

The first thing I did was to recover the R22, braze on some service valves and charge it up with propane. When the propane went in it *stank* of Ethyl Mercaptan.

I checked the MSDS from the supplier and it's supposed to be >95% propane with ethyl mercaptan and a few trace hydrocarbons. Checking the PT in the bottle it looks pretty close.

Now the oddity.

I ran the A/C for about 30 minutes playing with different charge levels and then left it for 2 weeks. When I went to recover the gas today I noticed the smell of ethyl mercaptan had completely gone. The only noticeable odour was the mineral oil.

Now, the reason I made this observation was I've seen a number of web pages where people have either charged splits, or DX heat pumps with ducted heads with BBQ propane. Most of them have made the assertion that if it leaked they'd know about it from the smell.

To follow this further I whipped up a 50/50 mix of propane and isobutane and put it in my car A/C. Drove around for a couple of hours (the unit was originally R12 and "retrofitted" with 134a). Not only was the cooling *far* better, but again when I checked the gas there was *no* smell.

Something in the refrigeration process is removing or breaking down the Ethyl Mercaptan.

Just a heads up.

[xxargs]

Etymercaptan are one of worlds most strongest bad-smelling odour and typical dose in BBQ-propane is 8 - 12 ml each 1000 kg of propane and this enough to make so strong smell of 'gas' leak as you want to leave the rom/area fast as possible depend scaring of exposion on few seconds if level reach 1/5 of LEL (LEL = Lowest explosion level).

LEL for propan is ~40 gram per m^3 air and 1/5 LEL set for propan/butan to 8 gram/m^3, and propan on LEL level (2 percent volume in air) burns very slowly and need almost a pilot flame helping to continue burning and even if rise concentration to optmimum (stochiometric around 7 volyme percent i air) is flame speed is maximum 0.38 m/s.

Cooking gas from coal and distrubed in grid has big amount of carbon dioxide and hydrogen and this gas have around 1.1 m/s i flame speed and result with blended gas with air in explosion in houses is much, much worse destroying force compare to explosion with perfect stochiometric blended propan/air. And we still not talking on acetylene in welding equipment on explosions force - this gas can detonate with 2000 m/s i flame speed !!!

Etymer captan itself is very simular to ethyl alcohol but replace oxygene atom with sulfur atom and most of dryers absorb gladly ethyl alcohol and I thinking does same thing on etymercaptan - is why bad smelling gone over time in AC-equipment.

Amount of etymercaptan in BBQ-propane is very little - around 6-10 gram on 1000 kg give around 6-10 ppm by weigth. and 8 gram blended propane with etymercaptan on 1200 gram air (~1 m^3 air ) give ~0.005 ppm etymercaptan by weigt in air and still smell badly at hell.

---

If you fill gasoline in your car, you put out almost 100-150 gram of propan, butan, pentan and simular high flamability gas in same explosion level as propan on the street and possibly going under the car and hit the hot catalysator if fuelstation not have gas return system.

Pure propan itself need 460 -490 degree C for self ignite and in practical not ignite from red-hot equipmet as glowing catalysator, but gas from gasoline can self ignite from 250 degree C hot surface depend of heavier CH-chain more easly broke down, steam/gas from gasoline is easier to ignite compare to propane and flame speed in stochiometric blend is almost same as propan around 0.4 m/s.

Millions people fill fuel in the the car every day over 50 year and most year of them without gas returning system in fuel station, and if we passing same risk level as ***** guy tell us HC have, we should have at least ten serious explosion on each fuel-station every day...

If some one put in etymercatan in same amount in gasoline as propane - i think every fuel station needs close down by rules depend of 'smelling gas' hundred of meter around station and every gasoline car also smells 'gas' and forbidden to use...

[NoNickName]

Unfortunately BBQ propane also contains relevant quantities of water, that now pollute your system.

[Koopy]

Moisture mixing with refrigerant becomes acidic. What happens when moisture mixes with propane. Does it become acidic or can it coexist with out consequence

[NoNickName]

The oil becomes acidic and metals oxidise. Refrigerants are insensitive to moisture.

[xxargs]

Propane itself not react with water, mostly oil react with water.

Water in propane is easy to remove with filter dryer compare to other unwanted gases as etane, metane and butane.

Propane itself not absorb so much water compare to R134a, R22, R410a, R407C etc. Propane is very simular to R12 in this case.