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cracking byproduct to give ffa and GLYCEROL

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December 10, 2009, 06:22 PM
cracking byproduct to give ffa and GLYCEROL
Originally posted by Bunk:
Originally posted by Weldshop:
All I know about my HCl is that it says 30% balm inhibitor.

30° Baumé maybe? If so, see: What is a "degree Baumé"?


Hmm, I'll look at the label tomorrow and let you know.


1996 K2500 4x4 6.5TD
December 10, 2009, 07:25 PM

You might do better going to the hardware store and getting a gallon of muriatic acid. It is typically around 34 - 36% pure HCl. It will say on the label. It is also cheap.
December 10, 2009, 08:43 PM
I'll check it out, thanks

1996 K2500 4x4 6.5TD
December 10, 2009, 11:49 PM
Double D
Originally posted by Wayne Zschech:

Just for interest's sake, how much acid did it take to split the glyc? What was your T for oil before making it into biodiesel? When you'll neutralize tell us how much it T at.

After neutralizing, what do you estimate the level of glycerin and other contaminates to be? Is there a way of working out simply?


The batch titrated at 2ml KOH (93%).
I used 10g KOH per liter of feedstock.

I didn't titrate the glycerine byproduct. I just added a gunk of sulfuric, that didn't split at room temp so I added another gunk, and it split within a couple minutes. It should have taken around 10g. I probably out close to 20g in it if I had to guess.
I'll have to titrate it when I neutralize it.
August 11, 2010, 07:36 AM
So I have been digging around on the forum but have yet to find an actual method for this.

Is there a way to calculate how much acid of a given type and concentration to use, perhaps based on a soap type titration?
August 11, 2010, 11:38 AM
The best way to determine the recipe is to use a soap titration.

Divide the acid into two batches and test again between the two stages to verify the acid to use in the second stage.

After decanting the FFA from the glycerin, add a weak caustic like soda ash or lime to bring the pH of the glycerin back up to 7.

Run the sweet water through filters to remove the trash, adding water as needed to thin it out.

Use vacuum distillation to remove the methanol and water from the glycerin without causing it to break down.

Glycerin is a clear solid of the consistency of jello. It may take several filtering and distillation stages to get a clear gel at the end.

It works best if you leave the methanol in the glycerin till after the ffa has been split out.

The ffa must have the water removed before AE can be attempted on it.

August 13, 2010, 07:45 PM
Do a soap titration as Rick suggested. (I have not read his method but assume it's a standard titration using bromophenol, HCl, and a solvent.) Convert the amount of HCl needed into moles of monoprotic acid per gram of glycerin. Convert into gallons of (whatever acid your using) per gallon of glycerin.
August 13, 2010, 08:55 PM
I do all of mine based on mass but I've found that if you are using sulfuric as your neutralizer you will need to add 125% of the calculated amount. I am assuming this is because of the uncomplete disassociation of H2SO4. So basically if you calculate that there is 0.5mol/kg of base you need 0.5/2*1.25 moles of H2SO4/kg. The 2 because there are 2 H+ for each sulfuric molecule.
August 16, 2010, 11:12 PM
The "little bit extra" is needed to overcome the buffer capacity and get complete conversion to FFA. This may or may not be desirable depending on your glycerin buyers requests.
August 19, 2010, 07:56 PM
Well if you count H2SO4 as a buffer sure. I use HCl to titrate the required amount for complete conversion of soap to FFA. Sulfuric doesn't completely disassociate into ions though which is why I am assuming it requires more on a mole basis than HCl.
August 20, 2010, 05:55 PM
I image the buffering I've observed is from the second disassociation of hydrogen from the sulfide. Hard telling not knowing though. 25% extra does seem a bit high for buffering to be the only factor, I think some of that excess is simply there to speed up the kinetics. If your not damaging your tanks and your geting rid of the glycerol, then your doing better than most.

August 28, 2010, 11:10 PM
I am using 96% Sulfuric and have found great seperation and 3 distinct layers with FFA Gylcerin and lastly salts using between 3.25-3.5% by volume on gyclerin that is coming from bio titrated at 2 with a base of 9 so 11 g per liter of KOH. I am having a hard time getting data on our gylcerin that has already been flashed of methanol and I have a very large amount of that in storage, any suggestions on making it easier to crack? Any more than 3.5 gets suspended salts and eventually just solidifys the coctail.
August 28, 2010, 11:49 PM
You could try hot water.

September 24, 2010, 05:45 PM
Greasy Greek
Glad to see your on hear MaineBioMatt, I was going to forward this discussion to you.
June 01, 2012, 08:40 AM
Originally posted by Weldshop:
commercial biodiesel plants apparently involving glycerin post-processing, and presumably sulfuric acid.

I dont know why they wouldnt just use HCl, It's cheaper, lighter, safer and cracks glyc into all 3 products.

Mixing and bringing the ph to ~5 seems to give a fine split.

I realize this thread is quite old but rather than begin a new thread I decided to post here.

Hard and fast numbers are difficult (if not impossible) to generate in terms of "cracking" the byproduct due to multiple factors and what I'm about to share here is unique to this particular sample of byproduct so please do not assume this will work for your byproduct.

Working off the pH value given by Weldshop of ~5 since this was an observable result he was getting at a known pH value, I decided to perform a little bench test based on his info. The following will set the stage:

Using one liter of byproduct where the oil's original titration was ~ 3.5 KOH for a total of 11.28g/L KOH; using ACS grade HCl (34-38%) to lower pH to ~5; I added HCl in 1mL increments and recorded the pH level each mL of acid was able to bring the byproduct to. I used a calibrated pH meter/electrode with an attached ATC (automatic temp compensator) on a magnetic stir/heat plate. I had to raise the temp of the byproduct to between 30-33C and maintain for reasons of viscosity of the product at ambient temps. I'm uncertain as to the water content of the byproduct but I'm assuming it should be relatively low due to my having dried the oil before the original conversion; however, I'm sure that the "cracking" procedure itself created some water. I will list each mL of HCl added and its resulting effect on pH. Original pH of the byproduct was ~10.6.

1mL - 9.39 11mL - 7.94 21mL - 7.50 31mL - 7.18 41mL - 6.94 51mL - 6.59
2mL - 9.02 12mL - 7.88 22mL - 7.47 32mL - 7.16 42mL - 6.91 52mL - 6.54
3mL - 8.80 13mL - 7.83 23mL - 7.43 33mL - 7.13 43mL - 6.89 53mL - 6.47
4mL - 8.69 14mL - 7.78 24mL - 7.40 34mL - 7.11 44mL - 6.86 54mL - 6.41
5mL - 8.52 15mL - 7.73 25mL - 7.37 35mL - 7.09 45mL - 6.83 55mL - 6.34
6mL - 8.39 16mL - 7.69 26mL - 7.34 36mL - 7.06 46mL - 6.80 56mL - 6.27
7mL - 8.29 17mL - 7.65 27mL - 7.30 37mL - 7.04 47mL - 6.77 57mL - 6.20
8mL - 8.18 18mL - 7.61 28mL - 7.27 38mL - 7.02 48mL - 6.73 58mL - 6.13
9mL - 8.09 19mL - 7.57 29mL - 7.24 39mL - 7.00 49mL - 6.69 59mL - 6.05
10mL - 8.01 20mL - 7.53 30mL - 7.21 40mL - 6.97 50mL - 6.64 60mL - 5.98

61mL - 5.90
62mL - 5.81
63mL - 5.72
64mL - 5.62
65mL - 5.52
66mL - 5.42
67mL - 5.30
68mL - 5.16
68.5mL - 5.10
69mL - 5.03

Unlike Weldshop, I did not get a split into all 3 products, rather 2. I'm missing the salt layer. The reaction sat overnight. I attained the initial split into gly and ffa rather quickly, but the bottom salt layer has yet to form. Does anyone have any thoughts? Should I allow more time to sit? Should the pH have been taken even lower? In which layer would the salts most likely reside, the gly or ffa? Thanks for any input and I hope the results I've given here can at least point anyone who might be interested in this process to "find their way." Cheers!
June 01, 2012, 08:42 AM
Sorry....that pH value "table" did not turn out as planned. Sorry it's all jammed together
March 12, 2013, 06:40 AM

We have started a new thread looking at the possibility of making triacetin from glycerol. An obvious problem is the initial purification of the glycerol. The ffas are a particular problem. Perhaps some of you who have some experience would have a look at the thread and have some ideas on the subject.