Please note: This document is in DRAFT status and is presented for your perusal. Be gentle with criticism, because, like I said, it is a DRAFT. There are no pictures at the moment because Madalene’s camera recently ‘bit the big one’. However, they are forthcoming.
In the home manufacture of biodiesel one is faced with a problem. That problem is variability of ingredients. Today’s oil is not the same as yesterday’s oil, which is not the same as tomorrow’s oil. Even if they come from the same place! Methanol is methanol, lye is lye, but OIL is, well, who knows what. That is why it is important to test your oil to find out its properties, so you can make the right decisions as you make it. This is the difference between “cross your fingers and hope we don’t get glop” method and actually getting good fuel consistently.
One of the most important methods of testing your oil is titration. Titration is actually a general term for the process of testing a solution by adding small quantities of a reagent until a reaction occurs to your satisfaction, and is a very common technique in Chemistry. In biodiesel, the titration we are usually talking about is an attempt to find out how many Free Fatty Acids (FFAs) are in our oil. In general, heavily used oil will contain more FFAs, and virgin oil will contain less. However, there is no way to know until you titrate!
The reason we must know how many FFAs are in our oil is that it will determine how much catalyst (NaOH or KOH, typically) we will need in our reaction. Thats right, forget all those ‘recipes’ for biodiesel. You don’t know how much to add until you titrate! Anything else is just a wacky guess. Sometimes wacky guesses work out, but usually they don’t.
This visual guide will help you with your titration. It really is easy. In fact, it will take you longer to read this guide than it will take for you to do your titrations. Once you have your little kit set up, you’ll be able to do titrations so fast it’ll make your head spin, you can even do them on the hood of your car behind the very restaurant you are collecting your waste oil from!
As you read through the guide, do not worry if you don’t understand all the theory. I don’t know much about the chemistry of baking, but I can still make a cake from scratch by following a recipe. If you don’t get the chemistry of titration, thats OK, just follow the recipe, and you’ll be fine.
* Isopropyl Alcohol, AKA Isoproanol, AKA Rubbing Alcohol, at least 70% concentration, OR Ethanol, 190 proof or greater (denatured is OK).
* Oil to be tested
* Your alkali compound, either NaOH (lye) or KOH (Potassium hydroxide)
* An indicator, either Phenolphthalein or Phenol Red (more discussion of this later)
* Water (distilled if you want, but tap works in a pinch)
* A 1 liter bottle with tight fitting lid for your catalyst solution
* A small bottle with lid for holding your indicator solution
* A way to measure in a large amount of liquid in milliliters, such as a graduated cylinder or graduated measuring cup
* A few oral syringes from the drug store, or another method of measuring individual milliliters
* Eyedropper, pipet, or other way to dispense a liquid ‘drop by drop’
* A sensitive scale for weighing in grams, you don’t need to own one, just find one you can borrow or use one time
* Small glass jar with lid and labels removed (smaller is better, baby food jars would be great)
* A mixing tool, like a straw, glass rod, or the ever-popular chopstick
This procedure is broken into three parts, the first part is your titration setup. We will prepare your titration kit so it is ready for future titrations. It will take a little longer, but you will only need to do it the first time! Future titrations will go very quickly because you took the time to do this setup correctly. The second part is a discussion of the theory behind titration, and the reason we are bothering. The third part will be the actual titration, for future testing, that will be the part you will pay attention to. At the very end is a ‘quick version’ of all this for you to keep as a reference.
Titration Setup – First Time Only
First we will make an Alkali Solution. Our Alkali Solution is a 0.1% solution of your base of choice (again, either NaOH or KOH; use the same one you will be using in your actual batches) in water. We will make one liter of this solution, and since you only use a few milliliters per titration, that liter will last you for hundreds of titrations.
Because water weighs 1 gram per milliliter, a liter will weigh 1000 grams. If we want 0.1% of this weight to be our base, then we need to add a single gram of catalyst to a liter of water. You will need a sensitive scale to weigh out the single gram of either KOH or NaOH, then simply add to a liter of pure water in a clean, well sealable bottle, and shake to dissolve. This bottle should be well sealed, and labeled, “0.1% solution of NaOH (or KOH) in water”.
Do you really need a scale to weigh this? The short answer is yes. You need a good scale to make good biodiesel. The long answer is that you can do with a pretty cheap digital kitchen scale for your big batches, but its handy to have something that can weigh with at least a half gram accuracy for test batches. For things like making this alkali solution you need even more accuracy, probably 0.1 gram accuracy. You can get this with a decent triple-beam balance or a nicer digital scale, but since you aren’t doing this sort of precision measuring very often, you can borrow the use of a very precise scale from a jeweler friend, or a buddy at a college or high school science lab.
Alternatively, you can do this little trick. Weigh out 10 grams of your alkali, and dissolve in a liter of water. Now, take 100mL of that solution (which is a 1% solution), and add 900mL of pure water to top it up to 1L of 0.1% solution. Sure you wasted 9g of catalyst, but in the big picture, that doesn’t matter, and you’ve got a fairly precise solution, without having a very precise scale.
Now that you have your Alkali Solution you need your Indicator Solution. There are two options here, pre-made solutions (easy), or making your own solution. The easiest by far is to go to your local Pool and Hot Tub supply store and buy a bottle of Phenol Red, a clear liquid used for testing your pool to make sure it won’t give all the kids chemical burns.
A more accurate (but less available) indicator is Phenolphthalein (fee-nole-thay-lean). You can buy Phenolphthalein from local chemistry supply houses and many online chemistry stores. It is not hazardous and fairly cheap, but you may have to order it. There are two ways to get it, solid, and solution. Try to buy the pre-made solution, look for 0.1% Phenolphthalein in 100% Ethanol or 50% Ethanol. Both are fairly common, and will work for our purpose, though they have a shelf life of around 1 year.
You will have solid Phenolphthalein if you are incredibly frugal, use a LOT of indicator, or just happened to run across some at a chemistry lab garage sale (like me). Solid is great because it keeps forever and is very cheap per use. However, it is a pain, because you need to repeat the process you used to make the Catalyst Solution. Simply weigh out 1 gram of the solid, mix with 500mL of Ethanol, and top up to 1L with pure water to produce a 0.1% solution in 50% Ethanol. If you have a super-precise scale, weigh out 0.1 grams of solid, mix with 50mL ethanol, and top up with 50mL of water. This means less to toss when your year of shelf-life runs out. Label your bottle well, and enjoy.
Titration – The Theory
Now that your setup is done, lets take a moment to discuss why we are bothering with this big ugly mess, and what is really happening. Then we’ll actually do it.
Your oil is not just one chemical, it is a mixture of hundreds of chemicals, all of which will affect the final product. What we are doing when we titrate is measuring the amount of one such chemical, Free Fatty Acids. These little buggers will turn into soap during your actual reaction (which is OK, if controlled), and if left unneutralized can cause washing problems, or even potential engine problems down the road. What we need to do when adding an alkali to our actual batch of fuel is to add enough alkali to serve as a catalyst in the reaction PLUS enough to neutralize the FFAs, without adding so much catalyst that soap production gets out of hand. The first part, the amount used to catalyze (complete) the reaction is fixed at about 5 grams per liter for NaOH and 7 grams per liter for KOH. There is some discussion about what those values should be, but you can be sure that they are the same for all oil. The second part we figure out by measuring the amount of FFAs in our oil by slowly adding our alkali to the oil (which is acidic, thanks to the FFAs). Since acids and bases cancel each other out, we just keep adding alkali until the acids are all used up. If we keep track of how much alkali it took to do that, we know how much to add to our actual batch.
Our Indicator Solutions are special chemicals that turn color when there are base molecules (actually OH- ions) around that aren’t hooked up to anything. When it turns color in our titration that means that our FFAs are done being neutralized, and that there are now ‘extra’ alkali molecules hanging around. In a water-based solution, this would mean a pH greater than 7. However, is titrating as simple as looking for a pH of 7? NO! A pH measurement is only meaningful in a water-based solution, which this is not. pH strips and electronic pH meters will be, at best, very difficult to properly interpret, or at worst, outright liars if used in this situation.
Our chemical indicators change color at a pH of 8.5 to 10 (though phenolphthalein changes over a tighter range, making it slightly more accurate). However, used in the oil setting, they aren’t really measuring pH, they are measuring ‘extra alkali molecules’. Since FFAs are a weak acid and our alkali compounds are strong bases, you need to have more molecules that it would seem to take to neutralize the FFAs, because not all of the FFA molecules have broken their ionic bonds (released their H+ ion) and become truly acidic. So to neutralize all of the FFA molecules, you must have a solution with ‘extra’ alkali molecules that will hang around and wait for the lazy FFA molecules to break their ionic bonds so they can be neutralized. The point at which there is enough alkali to neutralize all the FFAs (even the ‘lazy’ ones that haven’t become acids yet) is called the equilibrium point, and is a tricky point, because it will appear to be basic (in this case, a pH of about 9 in an aqueous solution). That equilibrium point happens at about the same point that phenolphthalein turns purple, and fairly close to the same point that phenol red turns red, which is why we are using them for titrating instead of regular pH strips or electronic pH meters.
Do you need to understand all that theory? NO, though it may help. The point I want to make though is that there is a chemical reason we have chosen these chemical indicators in favor of other measurement methods. There is method to our madness!
Titration – The Actual Process
To begin your titration choose a small, clean, preferably glass vessel. Baby food jars work nicely. Add to this jar 10mL of your isopropyl alcohol (rubbing alcohol) or ethanol. Use a graduated cylinder, or just suck up and dispense the appropriate amount with a clean oral syringe, remembering that 1mL = 1cc. This is a neutral carrier for our titration.
Add to this three drops of your Indicator Solution. Now you are ready to titrate! Or are you? The alcohol we are using as a carrier is supposed to be neutral, but many alcohols degrade over time producing some acidic byproducts. In order to get a truly clean slate for our titration we start with what is called a blank titration. Simply add your Alkali Solution drop by single drop to your jar while swirling or mixing. After each drop, thoroughly mix and check for color change. If it is still perfectly clear, add another drop. Do this until your solution shows any sign of color change, even after a thorough mixing. Once you see consistent color change, stop adding Alkali Solution. Now your neutral carrier really is neutral, and we are ready to titrate.
Use your oral syringe to get 1mL of your oil, and add it to your jar. If your oil is solid at room temperature, you may need to heat it slightly until it liquifies. A good technique for grabbing a single tiny milliliter with a clumsy syringe is to pull a bit of air into the syringe, then suck up more than 1mL of oil. Hold the syringe perfectly vertical and suck oil until the oil level reaches one of the graduations (it doesn’t matter which one). The air space at the top will help you see the oil level in the syringe. Then, dispense 1mL of oil into your jar by lowering the plunger until the oil level moves to the next CC graduation, meaning you’ve dispensed a single mL. Then squirt the excess oil back into the oil container.
Mix well! If your oil is very solid, or re-solidifies in the the titration jar, heat the jar for 5 to 10 seconds in the microwave. Do not allow it to boil, just warm it up to keep your oil liquified.
Once the jar’s contents have been well mixed, suck 5 to 10 CCs of Alkali Solution into a syringe (you can reuse syringes, but keep oil syringes separate from catalyst syringes). Make sure you know how much solution you have sucked up, and try to make it a whole number. Then, while mixing the titration jar, add alkali solution a drop at a time to the jar, keeping track of how many milliliters you are adding. After each addition, make sure the jar’s contents are well mixed, and check for consistent color change. If there is no change, add another drop, and check again. What you want is a consistent color change to purple or red that, even if subtle, lasts through even a vigorous mixing. This means you’ve added enough alkali!
Write down the amount of alkali solution you added; that number is your titration value.
Now, do it again. Yes, again. Because this is a sensitive process subject to lots of human error, do your titration a second and third times, starting from a clean jar each time. Do this until you get a consistent titration value each time. It may take a few shots to get a consistent reading your first time, but even many seasoned biodieselers titrate at least twice ‘just to be sure’. To paraphrase a time-honored carpenter’s saying, “Titrate twice, react once!”
Once you have a consistent value for your titration, you are done! The number you get is equal to the number of grams per liter of alkali compound you will need to add to your final batch in addition to the base quantity to catalyze the reaction. For NaOH, take your titration value + 5, and add that many grams of NaOH per liter of oil to your actual batch. For KOH, take your titration value + 7 and add that many grams of KOH per liter of oil to your batch. The beauty of this method is that once you have a titration value, you don’t need to do any other calculations, you already know how many grams per liter you need.
One exception is if you titrated with an NaOH solution and are using KOH as the catalyst in your actual reaction, or vice versa. But all is not lost, you just have to do one last calculation.
* If you titrated with NaOH and are using KOH in your actual batch, take your titration value and multiply by 1.4. Add 7 and you have the number of KOH grams per liter you will need.
* If you titrated with KOH and are using NaOH in your actual batch, take your titration value and multiply by .714. Add 5 and you have the number of NaOH grams per liter you will need.
Now that you know how many grams of catalyst you need per liter of oil, do a test batch! A one liter test batch is the only way to tell if your titration worked properly, or if there are other problems with your oil that you should troubleshoot before working with an entire batch of oil. If something isn’t right, you’d rather make 1 liter of glop than 50 gallons of glop. Don’t ask me how I know.
Titration – Quick Reference
* Add 10mL isopropyl alcohol to container
* Add 3 drops of indicator
* Mix well, and add 0.1% alkali solution drop by drop until color change is detected
* Add 1mL of your oil
* Gently heat mixture if necessary
* Add alkali solution one drop at a time, keeping track of how much you add, stop when you get a consistent color change
* The number of milliliters you added is your titration value, and is equal to the number of grams of catalyst you will need to add to your base reaction amounts (5g for NaOH and 7g for KOH) per liter of oil.
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