Biodiesel Glycerin – Can you really make soap out of it?

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.

If you are like the rest of us that make biodiesel, your biodiesel glycerin (BDG) may be piling up adding to the proverbial “glycerin lake”.

I’m sure at one point or another you thought to yourself, “What the heck am I going to do with all this glycerin”?!

The Answer? Make Soap!

You may be thinking or have heard “You can’t make soap from glycerin, that’s impossible!” And technically, that is true — pure glycerin cannot be made into soap. However, glycerin is the byproduct of soap making and is present in most “all natural” soaps.

So, What gives? Why can we use our BDG to make soap?
In reality BDG is not pure glycerin. It has what I like to call “Saponifiable Elements” left over from the biodiesel production process. These saponifiable elements are simply ingredients in the BDG that can participate in saponification or, put another way, there’s stuff in the glycerin that can be turned into soap!

These ingredients may include Mono-glycerides, Di-glycerides, Unreacted Oil and/or biodiesel. In addition to saponifiable elements, BDG already contains soaps that were created during the biodiesel production process.

You can see this in the following photo.

These are biodiesel glycerin samples from several different biodiesel batches that have had the saponifiable ingredients separated from the glycerin. The top layer is everything that can be turned into soap and the bottom layer is the glycerin. As you can see, not all BDG is the same.

So if you think about it, in a way, our BDG is already soap. You can think of it as just a really bad batch of soap, one that is undersaponified and unbalanced. It needs to be “Re-Batched”.

During the process of rebatching your BDG into soap, you might also want to think about adding other ingredients to add lather or hardness to better balance the soap you make. In the next section, we’ll show you how!

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 first thing required before reacting your BDG into soap is to work out something called a saponification value (SAP) value. This will tell you how much sodium hydroxide (NaOH) or potassium hydroxide (KOH) you will need to fully saponify your BDG.

A SAP value is important for a number of reasons. First and foremost, it keeps you from making caustic hot soap which can range from a minor irritant to just plain dangerous. Secondly, it will ensure that all of the ingredients in the BDG are reacted into soap, otherwise you can end up with a soap that feels oily and cleans poorly. Finally the SAP value will take the guess work out of the process and allow you to make consistent soaps, batch after batch.

By having a SAP value your BDG is now just another ingredient in the soap making process. You can use it to formulate recipes with other ingredients or even perform some advanced soapmaking techniques such as superfatting your bar soap or creating fully transparent liquid soap.

If you have ever made bar soap from BDG you may have found that it can be fairly soft unless the oil you used to make your biodiesel came from saturated oils such as coconut, lard, tallow or hydrogenated vegetable oil. Also, both bar and liquid BDG soaps can benefit from adding ingredients to help them lather better. Some may say that lather is just eye candy for cleaning but that is not totally true. It’s true that our BDG soaps clean extremely well out of the box, but with extra lather they can actually perform better too. This is because the bubbles formed by the lather have a lifting effect on the dirt and make it easier to wash away during the cleaning process.

This is where balancing your soap comes in. By adding other whole oils or fatty acids you can add the missing properties to your BDG soaps to create the desired soap you want to create. For hardening bar soaps you might think about using coconut oil, palm kernel oil, lard, tallow, stearic acid and/or palmitic acid. To add lather to both your bar and liquid soaps you might think about using coconut oil, palm kernel oil, castor oil, myristic acid and/or lauric acid.

To assist in the BDG soaping process and to make it a bit easier to make quality BDG soaps you can use the KNC SAP process outlined on my blog. Another tool you can use is the KNC Soap Calculator which will help you formulate a balanced recipe for your BDG that will give you a nice firm bar soap and/or bar and liquid soap with tons of lather. To get you started we have several basic BDG soap recipes on our website along with tons of useful information to make your BDG soaping a success!

We also have published a great book, called Making Biodiesel Soaps that covers the ins & outs of making great soaps from biodiesel glycerin. We even offer a Biodiesel Glycerin Soap Making Kit to help you get started! We’ve had several people use our book and kits to get started and some have even created successful small business selling the soaps they make!

So, what are you waiting for? Now’s a great time to start getting rid of that “glycerin lake” sitting out back & turning it into not only something worthwhile to clean with but possibly even a marketable product!

Happy soaping! 🙂

About Utah Biodiesel Supply

Utah Biodiesel Supply is an industry leader in offering innovative ways to empower our customers to produce Biodiesel. From free online instructional videos on how to get started making this great renewable fuel to promotional items to help our customers proclaim their energy independence, Utah Biodiesel Supply has it covered. With the widest selection available of Biodiesel equipment, supplies, and promotional items, you're sure to learn something new about Biodiesel every time you visit.

6 comments on “Biodiesel Glycerin – Can you really make soap out of it?

  1. I just finished making my first batch of BioDiesel. I told my wife that the byproducts could be made into soap. How do you remove the methanol from the BDG before processing?

  2. Great question. One of the easiest ways is to get a big pot, take it outside & away from everything, use a portable electric burner or camp stove (again away from EVERYTHING), and slowly heat it up while stirring to about 200-250 deg. F. Keep stirring until the bubbles quit coming up.

    There’s a really good example here:
    example 1

    and here:
    example 2

    The other way is to put it under vacuum and use a methanol recovery still to get it all out. There’s plans for how to build one here:
    Dehydrator Plans

  3. hello this is santhi
    I purchased your book(making bio diesel soaps).This book heaps me so much.I would like to know how can we make hybrid soaps(making bar soap from potassium based bio glycerin).please reply as soon as possible .I am not able to find out this thing in book.
    thank you sir

  4. HI
    My daughter (age 11) has to do science project (in south africa )and we decided to use the topic : from frying pan to the bath tub! The main goal is to proof that one can make soap(greener product) from used oil i.e biodiesel. Any comments suggestion on this topic will be appreciated.
    Regards from South Africa

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