PaulG

Thanks for the info.

"Most standards for BD quote a figure for Neutral No. this seems to range from <0.5 to <0.8 mgKOH/g.
This I guess would be to test the capacity you mentioned more than the acidity of the BD as I had assumed."

Yes. This test is measuring the amount of FFA in the BD. It is the equivalent of the free fatty acid test used in the food industry. FFA% is approximately half mg KOH per g.

"All the batches of BD in the above investigation were washed until a clear wash water with a pH of 7 was obtained."

I assume that the wash water started off alkaline and came down to 7 as the soap was washed out. It does not seem possible at this point that merely adding some isopropanol and testing again can give a pH of 5.5 unless the isopropanol is acidic. This seems to confirm the previous observation.

My view is that it should be better to stop the washing at about pH 7.5. Alkalinity does not harm steel. This would provide a buffer against any FFA left or arising in the BD and have the bonus of reducing the washing effort required. I have no experimental evidence to support this view however.

"The figures below give yield volumes of raw BD as a % of origional WAF volume.

4.2g/L 72%
4.7g/L 99%
5.2g/L 98%
5.7g/L* 95%
6.3g/L 95%
6.8g/L 92.5%
7.3g/L 84.5%
7.8g/L 66%
8.3g/L 61%"

It seems that forcing the reaction with excess NaOH lowers yield. There may be another factor here however: were you using NaOH dissolved in water? If so, as you added more NaOH the amount of water added was also increased. This may have exaggerated the losses at high levels of NaOH.

If you used NaOH in water it would be interesting to compare yields using dry NaOH. Its not that hard to dissolve NaOH in methanol. Looking forward to hearing more of the story.

[This message was edited by neutral on 31 March 2002 at 08:51 AM.]

[This message was edited by neutral on 31 March 2002 at 08:53 AM.]

Neutral,
the yield figures quoted give the ammount of LIQUID BD obtained. Reduction in yield was caused by the development of jelly above the BD/glycerine interface. This test was performed quite some time ago before I realised that the jelly could be avoided by removing the glycerine early.

Intend to compare BD from methoxides made from
a). methanol + sodium
b). methanol + solid NaOH
c). methanol + conc aqueous NaOH.
testing yet to be arranged.

My conc aqueous NaOH technique seems to be too controversial for a lot of people, tests should answer questions.
One participant on another group stated that there was no way BD could be made using conc aqueous NaOH and that he had a doctorate in chemistry sitting besides him who was of the same opinion. I guess this means that my truck is one of those rare vehicles that is capable of running on liquid soap with a cleaner exhaust than when on distillate.
That batch of my BD under test through BAA was made using conc aqueous NaOH.
pH tests on water and isopropanol will be high on list when I am back in lab.

"Stop washing at pH 7.5"
Couldn't be any worse than running unwashed BD.
Have you had any experience with using ion exchange resin to "wash" raw BD? Methanol would have to be stripped off first and raw BD filtered.

Some of my "acidity" tests seem a bit too close to the limit.
Neutrality figure in the standards <0.5 to <0.8 mgKOH/g.
This equates to 0.26 to 0.42mgNaOH/g.
1ml of 0.1% NaOH contains 1mg NaOH
8 drops at 16 drops per ml gives a figure equivalent to 0.95mgKOH/g.
Wouldn't take much acidity in the IPA to produce that result.

Regards,
Squarepeg.

PaulG

"figures quoted give the ammount of LIQUID BD obtained. Reduction in yield was caused by the development of jelly above the BD/glycerine interface."

The jelly is very diffuse and holds a lot of good BD. It is the soap which gives it its structure, so water washing will release a lot of BD and enable the true yield to be observed.

"Intend to compare BD from methoxides made from
a). methanol + sodium
b). methanol + solid NaOH
c). methanol + conc aqueous NaOH.
testing yet to be arranged."

Looking forward to this.

"Have you had any experience with using ion exchange resin to "wash" raw BD?"

No. I think it would take a lot of resin to do any good, and water is cheap and works well.

"Some of my "acidity" tests seem a bit too close to the limit, [<0.5 to <0.8 mgKOH/g]."

Yes. Since you used the right amount of NaOH the FFA left must be extrememly small. Your calculation shows that the figure you got is impossible, again confirming your IPA is acidic.