Do test batches first. That's better. Adding sulfuric acid to methanol, spatters. It splatters concentrated mineral acid around. It's an exothermic reaction, it gets hot. That's a lot of acid to try to add to methanol. I suppose the alcohol would boil. I'd say it's not safe to try to add that much of those two chemicals together. I have not added concentrated sulfuric acid to potassium soap, but in theory, like muriatic acid added to soap the inorganic salt formed and free fatty acids were released. I think it would be safest to add the acid to the soap. Concentrated sulfuric acid reacts with double bonds in fatty acids. H2SO4 turns some fatty acids brownish, that's evidence a reaction occurred. I expect it would be safer to add the acid to the soap with mixing if possible. Your soap is thick, mixing would be difficult especially since methanol vapor is emminating from your soap. Breating enough methanol vapor can cause things like permanent blindness and death. You said you did the Muriatic acid on soap experiment, this is about the same thing but with stronger acid. Removing water from the free fatty acid product may be required. That's energy expensive. Be careful, concentrated sulfuric acid is dangerous if not handled properly.
I found a news story using key words chicago glycerin sulfuric acid explosion on a google search, complete with photographs. Two workers mixed glycerin and sulfuric acid "improperly", then it exploded. 21 people were hurt or something like that. It was pretty big. As I wrote sulfuric acid plus methanol reacts violently, exothermically (it gets hot). Glycerine is like 3 methanol molecules lined up side by side, that also react exothermically. In your soap you've got some glycerine, but maybe not much, since you removed glycerine. Any way; Sulfuric acid reacts with potassium soap to form potassium sulfate an inorganic salt plus free fatty acids. If the free fatty acids need drying then do so. I suppose it would be impractical to filter out the inorganic salt from the free fatty acids. The dry free fatty acids could be reacted with anhydrous methanol and a catalytic amount of concentrated sulfuric acid to form the fatty acid methyl esters (biodiesel) along with monos, di-s and triglycerides that weren't in on making the soap from the first wet transesterification attempt. The Fisher esterification of free fatty acids reacting with methanol make the esters (biodiesel) plus some water. So there might be too much water present to do a base processing step without first drying the reaction liquid. So the soap is reacted to make free fatty acids. The free fatty acids might need to be dried. The dried free fatty acids are reacted with anhydrous methanol with sulfuric acid as a catalyst to produce biodiesel plus water. But a further base transesterification step is probably needed to turn the triglycerides and diglycerides and monoglycerides that remain into biodiesel. And the base transesterification step needs to also be bone dry to work well. Not 100% of the initial vegetable oil was made into soap, there was some soap in some vegetable oil. More than two steps.
Oh don't worry, I treat the sulphuric like nitro glycerine, the high concentration I have, if you put a drop or two on a paper towel, it will cause it to basically turn to black ash with no flame. An invisible droplet will ruin a pair of jeans. I've been handling this stuff for 10 years and it still scares the hell out of me, which causes a healthy respect which leads to extreme caution.
Location: West Michigan | Registered: April 26, 2006
cooper_farm; Are you saying that citric acid will react with potassium soap to produce the free fatty acids? If that's not what you're saying, what do you mean by use citric acid, sounds interesting as a possible alternative to sulfuric acid. Thanks