Quality of KOH and NaOH - what is minimum and effects?

[RogueRose]

I have seen that some people use food grade lye and others say that technical grade is fine. I'm not sure that food grade is always of a higher % but I think that it does contain less harmful "extras" / pollutants. Some places sell KOH that is 96-98% and others sell 86-90%. IDK what % the NaOH usually is, I especially notice the difference in the KOH though.

I've noticed that the lye used for biodiesel is usually of the lower % and they say that it is fine to use for soap as well, IDK if that is just a ploy to sell more product or what.

I would think that if you had 86% KOH you would need more (weight wise) to make the soap than you would if you had 96%. I'm also wondering what the remaining 14% is in the lye.

Anyone have any input on this?

 

[DeeAnna]

CriTI'm not sure that food grade is always of a higher % but I think that it does contain less harmful "extras" / pollutants.

Food grade will have a tiny bit lower level of metallic impurities, but otherwise there is no great difference. Not enough IMO to warrant paying more for food grade when using it for soap. Others swear by food grade, but honestly, food grade and non-food grade all come out of the same factories. If it makes you feel better to use food grade, use it. Otherwise....

Some places sell KOH that is 96-98% and others sell 86-90%. IDK what % the NaOH usually is, I especially notice the difference in the KOH though.

To get the minimum % as provided by the manufacturer, read the certificate of analysis (COA) or ask the supplier for that info if it's not provided otherwise. Bear in mind that lye, especially NaOH, is not going to remain at that minimum purity when you start to use it. Every time you open the bottle, the NaOH is going to react with CO2 and water in the air. Again, if it makes you feel better to buy higher purity lye, then buy it. Otherwise....

I've noticed that the lye used for biodiesel is usually of the lower % and they say that it is fine to use for soap as well, IDK if that is just a ploy to sell more product or what.

No it's not a ploy, unless you want it to be. If you're shopping for best price, do the math to see what the cost is per pound (or kilogram) of NaOH or KOH on a 100% pure basis, delivered, from various suppliers. If you're shopping for good customer service and/or variety of products, then the biodiesel guys will be at a disadvantage, since they may only be selling lye and nothing else that appeals to soapers.

I would think that if you had 86% KOH you would need more (weight wise) to make the soap than you would if you had 96%.

Yes. That is why you want to always compare costs on a 100% pure basis. Edit: And calculate recipes taking the purity into account.

I'm also wondering what the remaining 14% is in the lye.

Read the COA. You should see things like sodium carbonate (Na2CO3), salt (NaCl), trace metals, etc.