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How to Do Biodiesel Titrations

In my three part series called Introduction to Biodiesel, I explained what biodiesel is, and how it is made, stored, and used. You’ll find links to it in the resources section below, as well as links for some of the supplies you will need. In this post, I will explain what you need to know about titrating oil, a very important step in the production process.

A certain amount of catalyst is required to complete the reaction that converts the oil to biodiesel. Oil develops acidity as a result of the cooking process. Some of the catalyst, which is a base, will be consumed to neutralize the acid leaving an insufficient amount of catalyst to carry out the reaction. The purpose of the titration is to determine how much additional catalyst to use to neutralize the acidity of the oil.

Safety Precautions
The catalysts are strong bases and should be treated carefully. They will burn your skin, so wear gloves and safety glasses while handling the catalyst.

Make the Titration Solution
First we need to make a titration solution which must contain a known about of catalyst. Our titration solution needs to be made from the same catalyst that we use for our process. In my case, I now use potassium hydroxide so that’s what I make my solution from. The titration solution is 0.1% KOH in distilled water, and it needs to be accurate. Some people describe a method where you make a 10% solution, then dilute it 90% twice to get to the 0.1 %. That is supposed to be more accurate. I purchased a scale that is accurate to 0.01 grams. I measure exactly 1 gram of KOH and dissolve it in 1000ml of distilled water. Once it is thoroughly dissolved and mixed, I fill my titration solution bottle and throw the rest away.

1.00 Gram KOH

1.00 Gram KOH

Most experts say you should make a new titration solution about every 90 days to avoid it “going bad.” I’m not sure how it would go bad if it is stored in a properly sealed container. Maybe the concern is that the water will evaporate. As I’ll describe in a future post, my processing method allows some margin for error in the titration. I have had good results keeping my solution for up to a year, but if you want to be extra safe make a new solution every 90 days. Whatever you decide, keep it sealed very tightly and label it with the date you made it.

Perform the Titration
Begin with 10 ml of isopropyl alcohol in a small, clean beaker. The measurement is not critical so just get close to the 10ml. I use a 50 ml beaker and a small stir bar on the stir plate. You can also do this without the stir plate simply by manually swirling it. Add about 5 drops of your indicator solution. I use phenolpthaleine which turns pink when the pH changes from acidic to basic.

Isopropyl Alcohol, pH Indicator, 0.1% KOH Solution

Isopropyl Alcohol, pH Indicator, 0.1% KOH Solution

Next is the optional step of neutralizing any acid in the isopropyl alcohol. As I’ve mentioned before, my reaction process allows for an extra margin for error so I don’t usually perform this step. Basically you add your indicator solution slowly one drop at a time until you get a slight color change to pink. This means you have neutralized any acid in the alcohol and it is now close to a pH of 7.0.

10 ml Isopropyl Alcohol with 5 Drops pH Indicator

10 ml Isopropyl Alcohol with 5 Drops pH Indicator

Next you add exactly 1.0 ml of oil to the alcohol. This measurement is more important so you should use a small, clean syringe with 0.1 ml graduations. Note that I take the sample of oil from the processor after all the oil is filtered and loaded into the processor, and the mixing/heating has begun. This ensures that you get more uniform samples. During your first test batches, you’ll be dealing with smaller amounts of oil. Add the 1.0 ml oil sample to the beaker of isopropyl alcohol and indicator solution and swirl it if you aren’t using a stir plate. The acid in the oil will lower the pH of the mixture so you should not see any more pink if you did the optional step.

Exactly 1.0 ml Oil Sample

Exactly 1.0 ml Oil Sample

Now fill a clean syringe with titration solution. For this step I use a 3.0 ml syringe. Note you starting amount in the syringe. Add titration solution 1 drop at a time slowly until you begin to get a color change to pink. At this point the pink will likely go away in about 5 seconds or less. If it does, add another drop. Continue this process until the pink doesn’t go away for up to 30 seconds. You have now neutralized all the acid in your oil. The critical number you’re looking for is how much titration solution you used. Note the amount left in the syringe and record the amount used to the nearest 0.1 ml.

Color Change

Color Change

If you’re new to the process or your oil source is not certain, perform 3 titrations and take the average. I have found that my oil source is so good that my titration value rarely varies significantly. I usually only do 1 titration unless the first value is way off my expected value. A rule of thumb is that anything higher than 3.0 is not very good oil. I consistently get values around 1.2-1.5 for my oil source which is very good. That doesn’t mean you can’t use oil with a high titration value, but consider looking for a better source in the future if you do.

The titration is done. Record the values and get your average. You will use this number in the next step of the process to measure out your catalyst and mix your methoxide. The titration result in milliliters equals how many grams of catalyst in addition to the base amount you will use per liter of oil. You can find more about this in my 3 part series. I will also describe the next steps in more detail in a future post.

Notes about supplies
I wanted to mention some things about the supplies you’ll need and where to get them. I like to buy things on Amazon because it is fast and easy. When you’re starting out, you’ll want smaller quantities of some of the supplies.

For example if you aren’t sure if biodiesel is for you, you probably won’t want to buy a case of 100 syringes. So I included a link on Amazon for 5 of the 1.0 ml syringes. Once I started processing regularly, I found I was going through a lot of syringes. You have to use brand new clean syringes every time you process and these costs can add up. Early on I tried to clean and reuse them, but that didn’t go so well. Now I buy my syringes by the case.

I also started out doing titrations without a stir plate, but eventually I acquired a couple of them used and they really make some of the steps easier. Just be careful making big investments until you’re sure you want to get into biodiesel seriously.

Below in the resources section, I have included Amazon links for some of the supplies you’ll need to start out small.

Conclusion
Making biodiesel at home isn’t for everyone. There are important things to consider about safety, health, and the impact on your vehicle. So do your research and consider them carefully. If you are still interested and want to learn more, please join me next time as we explore the process further on our journey to self-sufficiency.

Resources for this post:
My previous introduction to biodiesel:
Part 1 – What is biodiesel and what supplies do you need
Part 2 – How the process works and safety considerations.
Part 3 – How to store it and how to use it.
Small scale with 0.01 gram accuracy
Phenolpthaleine pH indicator solution
Magnetic Stir Plate
12mm stir bar
1.0 ml syringe 10 for about $5
50 ml beaker

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