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Titrating Oil (Testing for free fatty acids in restaraunt fryer oil)
by Maria "Mark" Alovert of Local B100
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Titration is an indirect test for free fatty acids (FFA) in waste restaurant fryer oil.
Each titration only takes about 30 seconds (after you've made your initial bottle of reference tester solution), although it looks terribly complicated 'on paper'. Titration is done by reacting a small sample of free fatty acid (which happens to be in a ml of waste oil) with a measured amount of lye, and using pH to tell us when the FFA is all used up.
Why We Titrate
We do a titration to find out how much free fatty acid is present and to find out how much to compensate for it by adding more lye so there's some left for the desired biodiesel reaction.
How To Titrate
How To Use The Information
We know that we can compensate for the fact that the free fatty acid will consume some of our lye, by adding a specific amount of lye to 'sacrifice' to the soap-making side reaction that the FFA forces on us.
The way this particular titration is written, every 1 ml titration result (ie the acid number) will tell us to add an extra 1 gram of lye for each liter of oil/ffa you're using to make biodiesel to compensate for the side reaction caused by the FFA.
Step 1: Make Reference Tester Solution- (do this only the first time)
Every 1 ml of this solution will now contain 1/1000 of a gram of lye- an amount too small to weigh. The water makes it possible to measure such tiny amounts of lye however.
Step 2- Perform a blank titration:
Realistically, you may not always need to do this, but it's good to know that your alcohol isnt' a variable in your titration results.
Step 3: Measuring Oil Sample:
Measure an exact 1 ml of oil with an oral syringe, into a jar (or beaker) with about 10 ml of isopropyl alcohol (such as Heet brand (red bottle) gas line antifreeze from an auto parts store) . Measure the oil with a different syringe than the isopropyl. The amount of oil is very crucial , but the isopropyl isn't.
You can measure right into the same liquids as you did the blank titration on. The liquid will be yellow after you've added the oil.
In this photo we're using an odd measuring technique- we've sucked up an 'air bubble' into the syringe. This makes it easier to see what we're measuring. In any graduated device (syringe, pipette, etc) you should read the bottom of the curve of liquid.
Also, never fill your syringe or pipette with only 1 ml and then try to squirt all of it out- it's impossible to measure an accurate mililiter this way. Fill it to 2 or 3 ml and then drop the level down by 1 ml so your measurement is more accurate.
If you haven't done a blank titration first, now's the time to add about 5 drops of phenolpthaleine or phenol red pH indicator (from pool supply store). Swirl the jar to dissolve everything. It will be murky yellow in color.
If you're working with solid oils or in very cold weather, please warm
the oil before dissolving- you don't want it to form big bubbles of oil
as shown on the left. You will keep swirling while doing the next few
steps to keep these blobs from forming.
To the right is some oil that is properly suspended in the isopropyl:
Step 4: Add And Measure Lye/Water Solution:
Phenol red and phenolpthaleine will stay pink for different amounts of time- the phenol red will usually turn yellow after a minute, but the phenolpthaleine will stay purple.
Now, wipe out the beaker and do this again. Try to get the same result more than once in a row- it's easy to make mistakes when measuring such small quantities of liquids. You can throw the liquids down the drain- they're fairly benign.
Step 5: Calculate:
Each 1 ml of lye/water corresponds to 1 extra gram of lye you'll need to add when making your liter batch, just to eliminate the free fatty acids in that oil. If your oil takes more than 4 ml of lye or 5 ml of KOH, don't use it until you gain more experience. 'Average' restaurant oil will require about 3 ml on the titration, and really bad fast food grease can take 10 or so, which is completely unusable with NaOH catalyst.
Please note that the titration should be done with the same catalyst you're going to use- if you're using Red devil Lye to make your fuel, use that to make your lye/water mixture, and if you're using KOH, use a gram of that KOH to make water/KOH mixture instead
Step 6: Working With Batches Larger Than 1 Liter:
if titration showed 2 ml, that translates to 2 extra grams for each liter of oil I"m reacting to make biodiesel. If i'm reacting 90 liters of oil I do the following math:
90 liters oil x (5 grams NaOH + 2)
90 x 7 = 630 grams NaOH needed to make biodiesel with this oil
90 liter processor, KOH catalyst, and titration which showed 3.8 ml for that oil:
90 x (7 grams KOH plus 3.8 ml)=
90 x 10.8= 972 grams of KOH for this particular oil
To confuse matters further, KOH comes in a variety of purities. You want an 85% or higher I think. However for beginners I recommend just buying the 99% pure from Traditional Tanners, www.braintan.com. Later on you can adjust your KOH levels to compensate for impurities (ie if you've got 90% pure KOH use 10% more of it). Do not adjust the results of the titration! the titration will automatically reflect the impurity level for you. Realistically I dont think all of this is a very big deal, though
Step 7: The Shopping List For The Titration:
1 bottle of phenol red indicator or phenolpthalein . You can get phenol red at the hardware store if they sell swimming pool supplies. Phenolpthalein is at laboratory supply houses or science educational suppliers like www.enasco.com
1 bottle of distilled water
an empty bottle to store 1 liter of the .1% NaOH solution in
a container of NaOH or KOH- Red Devil Lye from hardware store or KOH from braintan.com
isopropyl alcohol- at least 70% isopropyl rubbing alcohol or 99% in the form of red bottle IsoHeet from auto parts stores
three oral syringes- sold at drug stores- graduated in ml.
several small jars- one to use as the titration 'beaker', one for a sample of oil, and one for handling the .1% NaOH solution so you can dip a syringe into it without contaminating the whole bottle. If using IsoHeet add another one so that you can use the syringe in spite of the IsoHeet's small bottle mouth.
a rag to wipe out the 'beaker' between titrations.
a scale- triple beam is versatile, but something smaller from eBay or smoke shops or pawn shops or science supply houses works fine. There are a few at www.b100supply.com and www.biodieselwarehouse.com. In the meantime you can assemble this homemade scale for temporary use
The biodiesel industry tends to use a lot more (for the catalyst, not the 'titration')- 1% by weight or about 9 grams per liter. The more catalyst you use, the better the quality of the biodiesel (see next month's Energy Self-Sufficiency Newsletter article, which will be about quality testing) up to a point, but the tradeoff is that more catalyst causes more soap to be produced. So many homebrew recipes recommend 3.5 grams per liter for NaOH or 4.9 grams per liter for KOH, which is a tradeoff to reduce soap formation. Catalyst is not the only factor which influences quality, so people get away with successes and failures using both amounts. Generally if I am working with high-ffa oil (over 4 ml on an NaOH titration, or thereabouts) which is more likely to make 'glop', or if I"m working with oil that tested high in water and which I have not dewatered (see the webpage on testing for water in oil) then I begin to think about compromising and use a smaller quantity of 'base' catalyst (ie closer to that 3.5 grams NaOH that others may recommend). I'm not sure yet whether this really helps. If you can keep your titration measurements accurate, though, you'll reduce the variables and make it easier to troubleshoot any problems you may encounter.
Biodiesel-O-Matic spreadsheet and online biodiesel calculators:
Click here to download the Localb100.com Collaborative Biodiesel Tutorial project's 'Biodiesel-o-Matic spreadsheet', by Eric Henry
Click here for Rick da Tech's online version at kitchen-biodiesel.com. Rick also has a second calculator, designed for those who want to use Red Devil Lye cans, and allows you to vary the oil level based on the titration results, so as to let you use full cans of Red Devil Lye: here
Improving Accuracy of Measurements:
You can also make improvements by measuring more than 1 gram of alkali for your initial lye/water or KOH/water solution. It can be done in a variety of ways but I recommend just using 3 liters of distilled water and measuring 3 grams of lye or KOH.
Others recommend adding 10 grams lye to 1 liter of water to make a stock solution, then measuring out 100 ml of stock, and diluting it into a working dilution with 900 ml of water.
More about this titration:
The Collaborative Biodiesel Tutorial 'visual guide to titration' by Sam Ley
The 'chopstick titration method' by 'Tilly from Paradise'
If you have any questions, feel free to ask them by clicking here
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