Two Stage Base Base Recipes
By Rick Da Tech
If you find you’re having trouble making biodiesel to the quality you desire, you may want to consider the Base/Base method. This method is nothing more than splitting the mixing into two steps with a portion of the methoxide used on each step.
Since Transesterification is reversible, we need an excess of methanol to ensure complete conversion. With more methanol present than glycerine we ensure that our reaction goes the way we want. The Base/Base method is another way to improve the reaction by shifting the ratio of glycerine to methanol even further in favor of methanol and complete reaction.
There are other reasons why the base base method improves quality. Like, when we drain the glycerin from the first stage, we are also draining all the water with it. Water limits how far the conversion process can go. Also, by removing the glycerin we are removing a methanol sponge that soaks up the methanol an keeps it away from the reaction zones where it's needed.
Determine your recipe just like you would for your normal single stage recipe with whatever percentage of methanol you are using and NaOH or KOH according to your normal procedure. Mix up your methoxide and divide it into two containers. The first container containing 80% of your methoxide and the second containing the remaining 20% of your methoxide.
- Heat oil to 130F
- Add 80% container of methoxide as normal
- Mix 1 to 2 hours
- Settle for 30 minutes
- Drain glycerine
- Perform the 3/27 Test
- Add 20% container of methoxide as normal
- Mix for 1 to 2 hours
- Settle overnight
- Drain glycerine
This method was initially from the University of Iowa. However, the researchers there strongly favor the acid/base method over the base/base method. This is primarily due to the dramatically improved economics of the acid/base method in a commercial setting. The biggest advantage of this method over the acid base method is that we don’t need to use acids in the process. That means one less hazardous material to stock in our production areas.
Be sure to always perform the 3/27 Test between the first and second stages. If you are using NaOH and happen to make high conversion biodiesel in the first stage, then processing the second stage will result in a processor full of glop.
Neutral's Base Base Recipe
If your quality is acceptable and you desire to reduce your methanol consumption, you can use this recipe, developed by Neutral on Infopop, to maintain your quality while reducing the methanol used.
Here we have a different approach to building the recipe. In this case we are aiming for the minimum methanol and catalyst we can use in the first stage and still obtain a good separation. It takes at least 14% methanol to consistently achieve separation with good mixing. If you have trouble getting separation on the first stage then increase the amount of methanol you use in the first stage slightly. In order to adjust for the fact that higher titration oils may not separate every time we multiply the titration value by 1.15 for the first stage.
The second stage will not change with the titration since hopefully we have converted all the FFA to soap in the first stage, so we use the same recipe on the second stage no matter the titration.
The process will be the same as described earlier for the 80/20 method.
Both of these methods are more time consuming and make more soap than the single stage base method we normally use, but can either increase the conversion level of our fuel or reduce methanol consumption.
No Titration Two Stage
The idea, developed on the UK forum, is to use a set amount of catalyst on the first stage, measure conversion using the 3/27 test, and prepare a second stage recipe using the results of the conversion test. It would be like accidentally shorting the catalyst on a single stage process, then reprocessing using the 3/27 test to build the reprocessing recipe. This recipe eliminates the need for a titration. It does not eliminate the need to test your oil for water or to dry it before processing.
Once you know the percentage of unconverted oil in your first stage, you can build a recipe. Since we have no FFA in the second stage, we don’t need extra catalyst to neutralize it. That means we only need to adjust our base catalyst down to account for the oil already converted. So if our test resulted in 20% unconverted oil, we would multiply our base catalyst of 5g/L by 0.20 (or 20%) and by our batch size in liters for the catalyst needed for the second stage.
This method calls for using 5g of NaOH or 7g of KOH as our base (or starting) catalyst amount. So our first stage would be 80% of the total methanol and 5g per liter for catalyst.
For an example 100 Liter batch using 20% methanol with 10% fallout after the first stage:
500g of NaOH (or 700g of KOH)
20L X 0.80 = 16 liters of methanol
%fallout X base X volume = 0.10 x 5g/L x 100L = 50g of NaOH (or 70g of KOH)
20L X 0.20 = 4 liters of methanol
neutral's base/base method - infopop archive thread
No-Titration Method - Biopowered Wiki
More Biodiesel Recipes