KOH for titration

[Eddie Biofuels Forum Newbie Find all posts View Profile Close Eddie]

Hi all, thanks firstly for the excellent info, it has cleared up a lot of my problems.. just a quick question tho, when using KOH for titration fluid, should i increase the amount by 1.4? the info i have read on titration always says use 1 gram of NaOH, so do i use the same amount of KOH?
thanks

[darren leonadas Senior Member Find all posts View Profile Close darren leonadas]

Re: KOH for titration

A Standard solution is "a standard solution". I believe 1g of catalyst to 1 litre of distilled water is your standard solution for titration. Messing with the maths will give you different results.
Correct me if i'm wrong, Tilly, Terry syd, Tony WA, ??

[Terry Syd Senior Member Find all posts View Profile Close Terry Syd]

Re: KOH for titration

The titrating fluid is made with 1 gram per litre, no matter whether you use NaOH or KOH.

The base for NaOH is 5 grams and 7 grams for KOH (that's the extra 1.4 multiplication part).

Here is the part that throws people. If you use 90% pure, then you have to add another 10% - for the base only. (ie: 5.5 NaOH or 7.7 KOH)

However, the titrating fluid is correcting as it goes. If it takes more fluid to get a change in color, because it is less pure, then that is reflected in the additional KOH you have to use.

You must however use the same KOH in the titrating solution as you will use in your conversion reaction.

[Matt Senior Member Find all posts View Profile Close Matt]

Re: KOH for titration

A standard solution is 1g in 1 litre of either, however if you tirate with NaOH then you have to multiply it by 1.4 before adding it to your base of 7 for KOH and then allow for purity ie divide by .9 for 90%.

If you start with KOH titration solution just add the amount to 7 and allow for purity, that's it

Matt
I'm confused myself now so don't ask too much more!

[Eddie Biofuels Forum Newbie Find all posts View Profile Close Eddie]

Re: KOH for titration

thanks all, ill go ahead with some test batches and see how it all goes.
ive been scouting around for some used oil supplies today, i didnt realise what a hot commodity it is, lot harder to get hold of a good supply than i thought. hah..

[Bill Biofuels Forum Newbie Find all posts View Profile Close Bill]

Re: KOH for titration

It is all based on atomic weights.
Na (sodium) is 23 awu (or atomic weight units)
K (potassium) is 39 awu
H (hydrogen is 1
O (oxygen) is 16

The hydroxide (OH) is one unit of 17 awu and is a discrete ionic group and is the one of importance. It is the catalyst. It has a negative charge. The sodium and potassiums are each singley positively charged and are just counter-ions. They only contribute to the weight.

So
Potassium hydroxide (KOH) weighs 39 + 16 + 1 = 56 awu
Sodium hydroxide (NaOH) weighs 23 + 16 + 1 = 40 awu.

To get the same weight of hydroxide (17 awu) you either need either 56 awu of potassium hydroxide or 40 awu of sodium hydroxide.

You can now replace the awu with lbs, grams or tonnes, it doesn't matter. It is still the same equivalence for the hydroxide ion.

56 grams of potassium hydroxide will give 17 grams of hydroxide.
40 grams of sodium hydroxide will give 17 grams of hydroxide.

It is the hydroxide that reacts with the free fatty acids (FFA). This tells you how much extra catalyst you need to add ( ie consumed by the free fatty acid and converting it to soap) before you have start having catalyst left over to make the biodiesel.

[hdj80 Senior Member Find all posts View Profile Close hdj80]

Re: KOH for titration

Blimmin heck Bill.

Well if you use KOH can you titrate with NaOH. I'd say YES!
Am I right or wrong?

[Bill Biofuels Forum Newbie Find all posts View Profile Close Bill]

Re: KOH for titration

Sure can, if you know the purity of your KOH.

Otherwise, as pointed out by another poster, use KOH for both.

I am not dure whether this will help but try this.

The general mix is for every 100g of oil you need 1g KOH and 20g methanol. You also have to add extra KOH to neutralise the FFA.

So:
Using a 10mL plastic syringe, add 10mL (approximately 10g) of oil to 60mL isopropanol. This makes a yellow solution. Heat under the hot tap if you need to melt and dissolve the oil.

Add three drops of phenolphthalein solution (make by adding 1g phenolphthalein in 100mL isopropanol, heat until dissolved and store in a brown bottle away from light).

Make up a 0.1 molar solution of KOH (5.6g in 1L). You can titrate the FFA using another 10mL syringe for the KOH solution. Titrate from a yellow to a red. The red is the endpoint. Don't go past it.

Let us say you had a 10mL FFA titration against the 10g of oil. 10mL of 0.1M KOH is 5.6g/1000mL x 10mL = 0.056g KOH to neutralise the FFA for every 10g oil.

Therefore for every 10g of oil you would need:

0.056g KOH to neutralise the FFA
0.10g KOH to act as a catalyst
2.0g methanol to turn the oil into biodiesel. 1.0g is consumed in the reaction. 1.0g is in excess to drive the reaction towards completion.

I wouldn't be too fussed about the accuracy. If you have 90% KOH purity, then your 0.10g KOH flakes contains 0.09g KOH and that 0.09g probably works just as well as 0.10g but a little slower.

But is is important to get rid of the FFA otherwise if you are not careful and you have really hard boiled second hand oil, it can consume all of your catalyst and you won't make biodiesel.

[Terry Syd Senior Member Find all posts View Profile Close Terry Syd]

Re: KOH for titration

HDJ80, yes you can titrate with the NaOH, but then you have to compensate by multiplying the NaOH titration by 1.4 in order to use the KOH. Also, this assumes that the NaOH and KOH are the same purity.

If you have to error, error on the too much KOH side. You won't get a gel like you might with NaOH, you might loose a tad biodiesel to soap, but you ensure that you get a good conversion.