I have made several liters of biodiesel and I want to test them for soap. I was wondering if I need to use 100 grams of unwashed bd or could I use a smaller amount? It seems to be alot especially if you do multiple titrations to confirm results. Also, where does the value 30.44 come from?

Sure, you could do less (like 10 grams). I usually modify this to work in volumes rather than weight, and I tend to do it 10 ml at a time, but in that case my results aren't easy to compare to anyone else's results so I dont' tend to talk about it online. Basically if you're just running comparisons of different batches you made, you can do solmething like 10 ml (just test the same quantity each time), but it'll be harder to translate into percentages of soap (which I never do by the way since I only compare my batches against each other rather than against any hard numbers percent-wise)
They included 100 g because it's more accurate to titrate larger samples.
Mark

quote:

Originally posted by girl mark:
Sure, you could do less (like 10 grams). I usually modify this to work in volumes rather than weight, and I tend to do it 10 ml at a time, but in that case my results aren't easy to compare to anyone else's results so I dont' tend to talk about it online. Basically if you're just running comparisons of different batches you made, you can do solmething like 10 ml (just test the same quantity each time), but it'll be harder to translate into percentages of soap (which I never do by the way since I only compare my batches against each other rather than against any hard numbers percent-wise)
They included 100 g because it's more accur ate to titrate larger samples.
Mark

GM I was looking at your "testing for oil" on CBT and it appears you are using 5 ml of Bromophenol, however it appears as .5 ml in the text below the picture. Am I seeing things

Ian

I posted this awhile back on one of the forums and no one responded, so I am giving it another try. I think I pretty much understand the calculations, but I just want some verification.

Calculations:
soap in parts per million=
(ml of .o1N HCL solution)/weight of sample*30.44

residual catalyst in parts per million=
(ml of .01N HCl)/weight of sample*561

I have been trying to figure out this soap test. The 30.44 in the ppm soap calc. is from sodium oleate. Wouldn't it be 3.044, if you are using 0.01N HCl? The AOCS method calc is ((ml HCl used)(0.1N)(304.4))/((weight of sample)(1000)). This will give you grams of soap (as sodium oleate)/gram of sample. To get ppm soap, don't divide by 1000. And if you use KOH as a catalyst, then you would use 320.56 for potassium oleate instead of 304.4.

Also, wouldn't the 561 from residual catalyst calc be 5.61 if using 0.01N HCl? The formula for this equation is ((ml HCl used)(0.1N)(56.1))/((weight of sample)(1000)). This will give you grams of KOH catalyst/gram of sample. Your equation will be different depending on your catalyst. If you us KOH as your catalyst, then you would use 56.1, NaOH = 40.0, and NaOCH3 = 54.0

I tried titrating with 0.1N HCl and I used very little, but when titrating with 0.01N HCl, I was able to adjust for the color change, which in turn give me more accurate readings.

The procedure also uses, 0.5 g crude glycerol, 5 g unwashed methyl esters, and 100 g washed methyl esters instead of 100 g samples. When testing small batches, 100 g doesn't give you much left over.

I have not tested all my samples yet, but I did test a batch that I used 6.5 g NaOH and 7.9 g NaOH. I did find that the 6.5 sample gave me 1.7 ppm soap and the 7.9 sample gave me 1.4 ppm soap.

IanTucker

I does look like it is 5ml instead of 0.5ml. The procedure I use calls to 1 ml. The indicator in the picture is very dark compared to mine too. I also use isopropyl alcohol instead of the acetone/water soln. When I added my bd to the acetone/water soln, I ended up with this cloud of precipitate that no matter how much I heated it, it would not go away, but it did not do this with the isopropyl. It dissolved very nicely.

quote:

Originally posted by dieseldan:
IanTucker

I does look like it is 5ml instead of 0.5ml. The procedure I use calls to 1 ml. The indicator in the picture is very dark compared to mine too. I also use isopropyl alcohol instead of the acetone/water soln. When I added my bd to the acetone/water soln, I ended up with this cloud of precipitate that no matter how much I heated it, it would not go away, but it did not do this with the isopropyl. It dissolved very nicely.

I read your post, you are using weight instead of volume. Can you give me a quick and dirty run down (if you have time) on how you tritrate for soap using your method.
I appreciate it,

Ian

For starters, I weigh out 0.5g glycerine, 5g unwashed bd, or 100g washed bd.

This is a modified version of the AOCS method Cc 17-79, soap in oil that I got from one of Gerpen's articles. This is a two step titration where you first titrate with HCl to neutralize the free catalyst and then you continue to titrate with HCl to free the Na+ or K+ from the FAA and salt.

The procedure is:
1. Dissolve sample in 100 mL isopropyl alcohol and 2mL 1% phenolphthalein indicator (in isopropyl).
2. Titrate with 0.01N HCl until you get the phenolphthalein color change (red to clear). Designate the titrant volume as "A".
3. Add 1mL 0.4% bromophenol blue indicator (in water).
4. Titrate with 0.01N HCl until the color changes from blue to yellow. Designate this volume as "B".

Here are the equations.

(A x (conc. of HCl) x (MW of catalyst))/(1000 x (weight of sample)) = grams of catalyst/gram of sample

(B x (conc. of HCl) x (MW of soap))/(1000 x (weight of sample)) = grams of soap/gram of sample

The MW of NaOH = 40.0, KOH = 56.1, NaOCH3 = 54.0
MW of sodium oleate = 304.4, potassium oleate = 320.56

When the level of catalyst and soap are small, it is a good idea to use blank samples. Just prepare a second sample without glycerine, BD unwashed, or BD washed. Titrate the blank at the same time as the sample and subtract the quantities for the blank from the numbers from the sample.

I screwed up in a previos post.

quote:

To get ppm soap, don't divide by 1000

To get ppm, you need to multiply by one million.

OK, I need help.

I weighed out 100g of unwashed biodiesel. I added 100mL of IsoHEET. I added 5mL of Bromophenol Blue (I know, it should have been .5mL). Then I decided to cut it in half incase I messed up, so I added another 100mL of IsoHEET, mixed, and separated into two equal amounts.
I added 7mL of .01N HCL, got bored because it was going so slow and started using .1N HCL. After 5mL of .1N it completely cleared. So it should have titrated at something less than 57mL of .01N HCL.
Using:
soap in parts per million=
(ml of .o1N HCL solution)/weight of sample*30.44

I get 57/(50g*30.44) = .03745 ppm soap.

There is no way that is right.

When I use Diesel Dan's method in the above post:

quote:

(B x (conc. of HCl) x (MW of soap))/(1000 x (weight of sample)) = grams of soap/gram of sample
The MW of NaOH = 40.0

I get:
(57*.01*40)/(1000*50) = .000456
Even if I multiply this times 1 million I only end up with 456 ppm soap.

Is that a good number?

Could 3 days of 100g of biodiesel sitting in a mason jar with 100ml of IsoHEET have brought the soap down? I was expecting something like 1500 ppm.

-Jim

I did them again, twice, much more slowly this time. It still took 4mL and 4.25mL, respectively. These times I used 10g of biodiesel.

Using:
soap in parts per million=
(ml of .o1N HCL solution)/weight of sample*30.44

I get 4/(10g*30.44) = .0131 ppm soap.

There is still no way that is right.

When I use Diesel Dan's method in the above post:

quote:

(B x (conc. of HCl) x (MW of soap))/(1000 x (weight of sample)) = grams of soap/gram of sample
The MW of NaOH = 40.0

I get:
(4*.01*40)/(1000*10) = .00016
Even if I multiply this times 1 million I only end up with 160 ppm soap.

Is that a good number? That seems awfully low.

-Jim

quote:

Originally posted by Jim D:
Using:
soap in parts per million=
(ml of .o1N HCL solution)/weight of sample*30.44

I get 4/(10g*30.44) = .0131 ppm soap.

If all I need now is to multiply it by 1 million then I end up with 1310ppm soap. That seems like it is in the ballpark, but that is doing math to get the expected answer. I want to do the math and let the answer be the answer.

-Jim

According the formula,
soap in parts per million=
(ml of .o1N HCL solution)/weight of sample*30.44

You should have calculated 4/10*30.44, but this will not give you ppm. You will have to use 3044 instead, which will give you 4/10*3044=1218.

I know how you feel. I was having a heck of a time figuring out the soap test. The method I have came from Gerpen's modified AOCS method Cc 17-79, so I am pretty sure the results I get are the correct results. Good luck.

Question - could a pH meter be used for this test in place of an indicator solution? If so, what is the range of pH that would expect at the end point?

Okay, did some looking:
Bromophenol blue (CAS #: 115-39-9): from pH 3.0 (yellow) to pH 4.6 (blue)

So, hopefully to answer my own question, if i use this method and add 0.01N HCL when the pH reaches 3.0, I should stop and record the final addition amount of the HCL solution, correct?

Thanks!

Wes

ok, another thought. There is a test to determine the saponification number. This can be done with a meter with a little bit of software. Can this number (the saponification number) be used to convert to ppm?

thanks

There is a procedure that measures the acid value using a pH meter, so it is probably possible. (acid value, or industrial titration, is used to determine %ffa (%ffa = 1/2 AV)) The procedure to determine the acid value by electrometric titration is as follows:
1. Standardize the standard alkali (KOH) by electrometric titration of pure potassium acid phthalate. (I don't know what you would standardize the HCl with.)
2. weigh sample
3. add 125 ml solvent mixture (isopropyl alcohol and toluene) (I use only isopropyl for my solvent)
4. place electrode half immersed in solution. Start stirrer and operate to give a vigorous agitation. Immerse the tip of the burette tip 1 cm below the surface of the sample.
5. Titrate with alkali. After each addition, wait till the meter reading is essentially constant, record burette and meter reading graphically. Limit increments of alkali so the changes in meter readings are 0.5 pH units (0.03 volts) or less; when inflections in titration curve occur, add alkali in 0.05 ml portions.
6. Perform blank using 125 ml solvent mixture.

I titrate using indicator solutions. It seems to be so much easier.

As for the saponification number, the “saponification number” is used as an indicator of fatty acid chain length in triglycerides. The value is a measurement of the ml of KOH required to complete the hydrolysis of one gram of fat or oil. This is similar to the acid value test, neutralizing the positive end of a ffa with OH. When we perform the soap test, we are taking HCl to split the soap molecules into ffa and salt. When the pH reaches about 4.6, where the brophenol blue changes color, indicates that all the soap has been split.

Thank you very much. That should give me a great start.

dieseldan,
I'm having a heck of a time trying to do the soap test using your instructions.
I'm trying to test unwashed bd.
I added 5g bd to 100ml isopropyl but no matter how much phenolphthalein I add it won't turn red.
Did I misunderstand something in your instructions?
thanks

quote:

but no matter how much phenolphthalein I add it won't turn red

That means that there is no free catalyst in the sample. You start out with the weighed sample in isopropyl and add the phenolphthalein. If it turns pink, titrate with HCl till it clears (it will have a tint from the bd, so it won't be clear like water). Once the sample is clear, add your bromophenol blue. If that turns blue, then there is soap, titrate till it turns yellow. If the sample is yellow after adding the bromophenol blue, then you are done and no soap is present. Hope this helps.

I think I printed something (I though it was in this article but apparently not- sorry!!!) saying that I couldnt' get the phenolpthaleine test to work most of the time either. I think it was written for the biodiesel industry where they use much more catalyst than we do, so there's more left over to neutralise than we have. They use 1% by weight plus titration NaOH or KOH- so about 9 grams NaOH instead of our homebrew customary 5. Try a test batch with 9 grams perliter plus titration and then see if the phenolpthaleine instructions make sense on the unwashed fuel...

Mark

I use 5 g/L + titration. I have never found unreacted catalyst in the bd, but I do find it in the glycerine. I found it during base/base, acid/base/base reactions, and bd made from glop. I have also found it with this one WVO I get. It is practically VO; titrated like VO and hardly any water. I will try the 9 g/L + titration to see the outcome.