Caustic Stripping with Soda Ash

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This method was posted on the infopop forum by uniquewater in September of 2006. It is a variant on caustic stripping with lye. The WVO in the pictures was lowered from a KOH titration of 10ml down to 1ml!

Caustic stripping using Soda Ash is somewhat safer than using NaOH due to it being a weaker base. Yield does not seem to be greatly reduced using this technique, but there have not been any reports of people using it on very high titration oils. Soda Ash can be purchased from any chemical company you get KOH or NaOH. If not check your pool supply store, it’s a pH increaser and it costs about half as much as NaOH per pound. It’s single disadvantage seems to be difficulty in filtering out the soap. What follows is a paraphrase from the infopop thread that explains the technique starting with titrating to determine how much soda ash to use.

The Steps

  1. Titrate WVO and calculate recipe
  2. Add Soda Ash to water
  3. Add water/soda ash to oil and mix
  4. Add salt water to speed separation
  5. Filter out soap

Titration

Prepare a stock solution of Soda Ash (SA) and Water at:
1g SA into 1L H2O
Add 5 drops Phenol red to approximately 10ml of 91% Isopropanol.
Then dissolve 1ml of WVO to solution.
Titrate Phenol red/alcohol solution with Stock Solution of SA/Water.

The Recipe

1 liter of filtered WVO
500 ml of water x grams of Soda Ash = the number of ml found in the titration

Mixing

Before Picture

Dissolve the soda ash into the water then add to the filtered WVO and mix.

This will create a white "Creamy WVO" which will be broken by adding a saturated salt-water solution.

After Mixing

Separating soap from WVO

Mix a 10%-20% solution of salt water solution.
Mix 3:1 ratio of Creamy WVO to Salt water.
Allow solution to separate for at least One Hour (the longer the better).

Separation Results

After Settling Picture

Top Layer: WVO

Middle Layer: Soap

Bottom Layer: Salt water

Decant or Filter

The WVO layer will yield LESS FFAs and may have residual water/soap.
Mix again with 3:1 ratio of WVO to salt water to rid any excess water/soap.
Remove WVO layer for Biodiesel production by a combination of decanting and filtering. Check for water content before processing the WVO.

Optional method for improved soap removal

When adding salt water to creamy WVO a bubbler can be used.
Drop bubbler to bottom salt-water layer and bubble for at least One hour.
This will push soap to the TOP to be skimmed.

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