Why not to make....................... SOAP!
Maybe rancid oils are not good to make those superfatted cold process soaps but if you use the "good old" method, you can still get a good soap for washing stuffs
You need to slowly heat the oil to boiling point, in this way you will make a first "rectification" of volatile bad smelling compounds (if it smells, it flies) cool down
Then you make the saponification in salty water (30% brine) with extra water and extra lye (water
il 3:1 and 20% extra lye) all cold at first, adding the water-salt-lye solution little by little
then gently heating to boiling for a couple of hour at least, mixing well whit a whisk.
the soap will came up, while impurities remains in the water and remaining volatile bad smelling compounds flies away
then you take out the soap and repeatedly wash in new saturated brine 2 or 3 times brine:soap 1:1 until it is no more alkaline.
the process is a little bit more tricky maybe but gives you a pure soap, whitout glyceryn, something like the one used for washing machine powder