This article is written by Rick Knicely from the Knice-N-Clean Soap Company. He’s the author of Making Biodiesel Soaps and is a leading expert on producing high quality, commercial grade soaps from biodiesel glycerin.
Improving Bar Soaps Made From Biodiesel Glycerin
– by Rick Knicely
Have you ever wondered how your biodiesel production process can affect the soap you make from the remaining biodiesel glycerin (BDG)?
If you have high titration oils you might be thinking about acid esterification to lower the titration of your oil and give you a higher yield of biodiesel. Well if you are a soaper this can also help you make better bar soap!
The BDG obtained after biodiesel production is a soup of byproducts and leftovers. These include methanol, biodiesel, soap and glycerin and may include mono-glycerides, di-glycerides, excess caustic and water.
NOTE: The methanol must be removed from your BDG prior to using it to make soap that will come into contact with a person or animal.
The biodiesel, di-glycerides and mono-glycerides can all be turned into soaps. I like to call these “saponifiable elements” within the BDG. When you create a SAP value for your BDG you are working out what percentage of the BDG is saponifiable. From that you work out how much caustic it will take to turn the saponifiables into soaps. So if you were to add up all of the soaps and compare that to how much glycerin there is you can work out what’s called the “Glycerin Ratio”.
The glycerin ratio of BDG can be all over the map, but typically with oil that titrates from 3 to 6, the ratio is 30%-50% soaps and the rest is glycerin. When the titration of your oil starts to climb so does the percentage of soaps that end up in the BDG.
If you are using lard, tallow, coconut oil, palm kernel oil or palm oil this can be a good thing because your soap will end up hard right out of the box. However, if you are like most of the rest of us and are using oils like soy, canola, corn or any other unsaturated oil, the excess soaps can cause your bars to be soft and rubbery. So you can see why it might be a good idea to lower your glycerin ratio as much as possible.
So why do these oils make for a soft rubbery bar of soap?
It has to do with the fatty acid makeup of the oils. When you are talking about making soap from oils there are 7 main fatty acids. Stearic Acid, Palmetic Acid, Myristic Acid, Lauric acid, Oleic Acid, Linoleic Acid and Ricinoleic Acid.
Stearic Acid, palmetic acid, lauric acid and myristic acid are all saturated fatty acids and will make a hard bar of soap. Oleic acid is an unsaturated fatty acid and will make a softer bar of soap that can get a bit harder with time. Ricinoleic acid is also an unsaturated fatty acid that will make a softer bar of soap. Linoleic is a polyunsaturated fatty acid which makes for a very soft bar of soap.
So let’s have a look at the fatty acid profile of the most common unsaturated oils that we like to use to make our biodiesel from. These “soft” properties are also reflected in the biodiesel produced from these oils making biodiesel that has a lower cloud point.
Unsaturated Oils Used In Biodiesel Production
You can see that all of these oils are really high in the “soft” soap fatty acids and really low in the “hard” soap fatty acids.
So when you use acid esterification to lower the titration of your oil you are also lowering the percentage of soaps in the glycerin ratio of your BDG.
The soap will be a bit harder “out of the box” but can still benefit from adding some hardening ingredients. However the amount you will need to use will be significanly less than if you had not used acid esterifcation to lower the titration of your oil.
The trick to a super bar of soap is balancing the recipe. The bar should be nice and hard with both quick and long lasting lather and some conditioning properties. The linoleic and oleic acids are great fatty acids for conditioning but not so good for lather or hardness. But it still needs something to make it harder and give it a nice lather.
What ingredients can help with that?
Saturated oils high in myristic acid or lauric acid will add the quick lather you are used to and oils high in stearic acid or palmetic acid will add hardness and long lasting lather.
So lets have a look at some of the saturated fats or oils that can help to add hardness and lather to your BDG soaps.
Saturated Oil Used To Improve BDG Bar Soaps
|Palm Kernel Oil
You can see that these ingredients are really high in the fatty acids that help add lather and harden bar soaps.
Stearic acid, palmetic acid, myristic acid and lauric acid are all available in flakes and can be used in addition to or in place of the saturated oils to better tailor your recipe.
If you think about it our BDG is really just a bad batch of soap. One that is poorly saponified and unbalanced. The SAP value takes care of saponification. And by lowering the glycerin ratio and adding a percentage of saturated fats, oils and/or fatty acids you can balance the BDG soap recipe and make a super bar of soap!
Give It A Try!
Want to give some of these great suggestions a try? The Knice-n-Clean Soap Company offers a wide variety of the different soap making additives mentioned above right on their website! Click here to see their great selection!
While there, be sure to check out all their great soap making recipes for making various kinds of unique biodiesel glycerin soaps. You can also build your own custom soap recipe using their cool soap recipe calculator!
Learn more about making biodiesel glycerin soaps in Ricks e-book, Making Biodiesel Soaps, available right on our website!