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Base/Base Two Stage Processing
by: AndrewM

Introduction

For home biodiesel production, the 2-Stage Base/Base Process is now considered an established way to boost conversion rates compared to Single Stage Base Processing. Increased interest in higher conversion rates is partly the result of new feedback coming from conversion tests like Warnquist (3/27) and to a lesser extent, pHlip. Also, some homebrewers have vehicles with modern fuel injection systems which are thought to be more sensitive to small variations in fuel quality. Some homebrewers simply want to make the highest quality fuel possible, while others are interested in reducing methanol consumption.

Why Use 2 Stage Base/Base Process?

Conversion testing performed by homebrewers, as well as testing done by academics, has shown that the 2-Stage Base/Base Process can increase conversion rates significantly over a single stage process with all other variables left constant. If conversion is already high, the 2-stage process allows for a reduction in methanol use, while maintaining high quality output.

This method, compared to single stage, results in significantly higher conversion rates, using the same amount of methanol and catalyst. Or, similar levels of conversion are reached, using significantly less excess methanol than with single stage. This method has successfully produced fuel that passes the Warnquist (3/27) test with methanol volumes as low as 14.5% of the starting oil. Typically, homebrewers use between 16 and 20% methanol when using this method.

More testing would be helpful to quantify the improved conversion of oil (triclycerides or TRI) into biodiesel (fatty acid methyl ester or FAME) and to establish the 2-Stage Base/Base method’s limits in homebrewing. Research quantifying the increase in soap production would also be helpful, so that homebrewers can make informed choices about which method suits them best.

Chemistry Theory of The 2 Stage Base/Base Process

Theoretically, using two stages allows the reaction to proceed forward more completely due the kinetics involved in the equilibrium reactions that produce FAME from TRI. At the end of stage one of the 2-stage reaction, we remove as much glycerol as possible. Glycerol removal reduces the likelihood that glycerol will react with the FAME and convert back into monoglyceride and methanol. The glycerol removal is called “retracting the limiting product.” This is a well-known and useful method of driving a chemical equilibrium reaction forward towards the desired end product. The practice has had a place in the science around biodiesel research and production since the 1940’s.

In this discussion, I am leaving out the side reaction involving soap production.

At the end of stage one of the reaction, the following constituents are present in equilibrium with each other: Methanol (M), Triglycerides (Tri), Diglycerides (Di). Monogycerides (Mono), Glycerol (G) and Fatty Acid Methyl Ester (FAME). See the below reactions performed in the presence of an alkaline catalyst (NaOH or KOH).

Tri + M <-> Di + FAME

Di + M <-> Mono + FAME

Mono + <-> G + FAME

By removing glycerol from the reaction vessel and re-starting the reaction with more methanol and catalyst, we cause the system to reestablish a new equilibrium point. This new equilibrium point is much farther to the right, due to the greatly reduced quantity of glycerol. This results in more complete conversion of triglycericdes to fatty acid methyl esters, along with a corresponding reduction in the intermediate products, diglycerides and monoglycerides.

Methodology for the 2-Stage Base/Base Process

This discussion of the 2-Stage Base/Base Process assumes that you are already familiar with the basic Single Stage Process.

Researchers at the University of Iowa pioneered the development of 80/20 - 90/10 version of the 2-Stage Base/Base Process. The 80/20 - 90/10 recipe was adapted by backyard brewers and became the 80/20 - 80/20 version. 80/20 - 80/20 is essentially a shortcut that is used to avoid having to make the calculations (algebra) to determine how much catalyst to put into each of the two batchs of methoxide. More testing is needed to determine the benefits of one over the other.

Before you begin, you will need to choose which of two versions of the 2-Stage Base/ Base Process you plan to use. Choose either the 80/20 80/20 version (easier) or the 80/20 90/10 version, (originally used by academics who developed the two stage process). In these two versions, the first pair of numbers indicates the percentage of the total methanol for the first stage/second stage and the second pair of numbers indicates the percentage of the total catalyst for the first stage/second stage. The only difference between the two versions is the percentage of total catalyst placed into each of the two carboys of methanol to make the methoxide.

You will also need to decide how much methanol you will use in total, as a percentage of the oil you plan to start with.

The 2-Stage Base/ Base Process begins just like a single stage process, except that you add methoxide in two stages, and stop in the middle to remove the glycerol layer.

Prepare for the reaction:

Heat your oil

Titrate your oil

Measure your catalyst

Mix you catalyst into the methanol for both stages

Be sure your stage 1 catalyst is 100% dissolved,

Then:

Add 80% of your methoxide.

Run the processor for 1-2 hours.

Just before turning off the pump, take a small sample. Observe how fast your glycerol is separating from your partially reacted biodiesel. Once glycerol has separated, wait several more minutes. Normally, the total time needed for glycerol separation is 15 to 30 minutes.

Drain off glycerol layer that has separated in your reactor.

Separate biodiesel from mixed layer and return this to the processor by sucking it in the oil intake line. Close the valve on the bottom of your reactor and suck the separated fuel back into your reactor using your pump.

Add the remaining 20% of the total methoxide.

Run the processor for 1-3 more hours.

Settle over night.

Drain the remaining glycerol. (Often about 20-25 % of the total glycerol)

Wash and dry as usual.

The variation in run times will depend on your mixing, temperature, and the methanol percentage used. At around 18% methanol, 1 hour per stage is often sufficient, although this will depend on your equipment and starting temperature. Longer run times seem to increase conversion. See example batches with 80/20 80/20 and 80/20 90/10 below.

Amount of Methanol, Catalyst & Mixing Time

This process is considered an intermediate to advanced technique. This is technique is not suggested for your first batch. The amount of methanol and catalyst can be varied, and will depend on your required level of conversion, degree of mixing, and the inherent trade offs between cost, ease of washing, and time available to process. Another method of determining methanol and catalyst amounts (neutral’s method) for stages 1 and 2 is discussed here. It may be beneficial, particularly when working with high FFA feedstock.

Conclusion

The 2 Stage Base/Base Process gives homebrewers an additional tool that facilitates high conversion rates and reduces the total glyceride content of their finished product. Using the 2 Stage Base/Base Process does add some time and additional steps to the procedure when compared to the single stage base process. But those homebrewers who use it, love the consistent output of highly converted fuel.

Example Batches

The following are examples of batches made with the 80/20 - 80/20 version and the 80/20 – 90/10 version.

80/20 – 80/20 Example.

In this example, 18% methanol was used and 7 was the base # for KOH.

132 liters (34.9 gallons) oil which titrates at 1.5 ml KOH.

23.8 liters (6.3 gallons) methanol

1225 grams of KOH, using 7 as base # (90% purity)

*Divide Methanol into carboy 1 (80%) 19 liters (5 us gal) and carboy 2 (20%) 4.75 liters (1.25 us gal)

*Divide KOH into batch 1 (80%) 980g and batch 2 (20%) 245g.

Add Batch 1 KOH to Carboy 1 and Batch 2 KOH to carboy 2.

Mix until dissolved

Add carboy 1 methoxide to processor

Run 1 hr or more.

Stop the reactor mixing and wait 20-30 minutes for the layers to separate.

Take out stage one glycerol layer.

Add the remaining carboy 2 methoxide.

Run 1 hr or more.

Let stand overnight or for at least 8 hrs.

Remove the second stage glycerol layer.

*If you have a large enough tank to do so, make the methoxide in one batch. In which case, use 19 liters (5 us gal) in stage one, and the rest in stage two.

80/20 – 90/10 Example.

In this example, 18% methanol was used and 7 was the base # for KOH.

132 liters (34.9 gallons) oil which titrates at 1.5 ml KOH.

23.8 liters (6.3 gallons) methanol

1225 grams of KOH, using 7 as base # (90% purity)

Divide Methanol into carboy 1 (80%) 19 liters (5 us gal) and carboy 2 (20%) 4.75 liters (1.25 us gal)

Divide KOH into batch 1 (90%) 1103g and batch 2 (10%) 123g.

Add Batch 1 KOH to Carboy 1 and Batch 2 KOH to carboy 2.

Mix until dissolved

Add carboy 1 methoxide to processor

Run 1 hr or more.

Stop the reactor mixing and wait 20-30 minutes for the layers to separate.

Take out stage one glycerol layer.

Add the remaining carboy 2 methoxide.

Run 1 hr or more.

Let stand overnight or for at least 8 hrs.

Remove the second stage glycerol layer.


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