Vegetable Glycerin vs. (Synthetic?) Glycerin

Okay, I've gone and confused myself through over-researching things once again.

I started to notice vegetable glycerin as ingredients in soaps. I thought glycerin was a product of rendering animal fats. And now I'm curious.

So I started trying to figure out what different types of glycerin is available and why each type is used. Searching the forums I found a post that said most glycerin is from synthetics and that vegetable glycerin use was more hypoallergenic.

So, instead of just learning about soaps I'm not stuck on this tangent of confusion.

- What types of glycerin are there?
- Why / how are they considered different?
- What is everyone using in these uber lather 'squirt of glycerin' recipes / methods I keep reading?

I feel like I need Tyler Durden to teach me how to make soap from scratch at this point... but I don't want to join a Fight Club. ;)

Thanks.

I don't know about anyone else, but I'm using Vegetable Glycerine.

Glycerine can be produced from any fat, animal or vegetable. It is produced when soaps are made by saponification of fats, but in many cases it is not separated and remains in the soap. It is also a byproduct of biodiesel production via transesterification. In this case, it must be separated from the fatty acid methyl ester produced.

It is a relatively simple chemical

C-OH
|
C-OH
|
C-OH

It can be synthesized starting with propylene and chlorine, but with the current production of biodiesel in the world, glycerine is in surplus and this process is not economically viable. Regardless of its source - animal fat, vegetable fat, synthetic production - it is the same chemical and in its pure state you will not be able to differentiate it based on source. Since biodiesel production is currently the primary source of glycerine, and since most biodiesel is produced from vegetable fats, most of the glycerine available today is vegetable in origin. But as shown above, this really does not matter.