I an acquaintance of mine is making ethyl esters in Congo and failed on
his first attempt. I think he just used too much NaOH. He has some very
good questions that I thought I'd post here for comments. Enjoy . . .
Questions:
1. We produced soap rather than bio-diesel. Question is why?
- because the oil still has too much water even though it had been
heated until the foaming stopped?
- because we used too much NaOH?
- because the ethanol has absorbed water in storage? unlikely I think.
2. The little bit of moisture that the NaOH absorbs in transfer is
unlikely to add more than 0.2 g H2O to the ethanol. That would raise
the water % only about 0.1%, in other words from 0.3% to 0.4%. This is
still within the less-than-0.5% tolerance.
3. What effect if any does the elevated free fatty acids have on the
reaction? Leif, you say that FFAs (and water) are the enemies of
transesterification. I assume that they originate from the fatty acid
chains that are split off from the glycerine, hence the term "free",
but that they are further degraded making them unusable for adding the
methyl or
ethyl elements for the esters. How are the FFAs different from the
newly split off TRANS-fatty acids at the beginning of the
transesterification reaction?
MARSAVCO says that peasant produced palm oil tends to have 20-30% FFAs
because of natural oil decomposition ( due to delay between harvest and
oil extraction, delayed sterilisation of the oil, all water not
removed, and oil contaminated by bacteria that promote decomposition.)
This is the oil we are using, though it has been filtered and the water
has been removed. If FFA's are a significant barrier, can we come up
with a simple way to separate them from the tri-glycerides before
starting transesterification?
4. Looking at the diagram descriptions of transesterification and
saponification from the Pelly description it appears that the
difference between the two is what gets attached to the fatty acid
chain. Transesterification appears to add the methyl or ethyl part of
the alcohol (without the hydroxide portion) to the fatty acid chain.
Saponification
appears to add oxygen and Na to the fatty acid chain. When alcohol is
in the mix what favors the alcohol element bonding over the oxygen-Na
bonding? Obviously water tips the balance, but what is the mechanism?
Does having an excess of catalyst also tip the balance in favor of soap?
5. It looks like sodium methylate and sodium ethylate are solutions of
sodium ions and alcohol minus the H from the OH group. Does the H shed
by the alcohol and the OH from NaOH form water, resulting in an aqueous
solution of Na+ and CH3O- or CH3CH2O-? If this is the case, water is
already present in the reaction in a certain concentration. Does a
further increase in the water concentration eventually tip the reaction
from alcohol + fatty acid chain to Na + fatty acid chain? If so, at
what point and
why?
----------------------------------------------------
Here's the lab procedure/observations:
Maybe I should wait for the first success, but feel an obligation to
share
the failures as well. Hopefully we have gotten all the mistakes out of
the
way in this first try. We were all a bit nervous about this.
We followed the general outline of Mike Pelly's method, increasing the
amount of ethanol to 30% rather than 20% by volume. We know we made at
least
one big mistake: 50% more NaOH than the cookbook called for. I'm not
sure
if this explains the soap result or not. We are using what we think is
virtually dry oil and alcohol with <0.4% water. Below is the
description of
procedure and observations. We welcome everyone's comments and
suggestions.
Titration procedure & determination of NaOH amount:
1. Made up titration solution from 400 ml filtered rainwater and 0.4
gram
NaOH.
2. Mix 10 ml isopropyl alcohol (70%) + 1 ml palm oil; on rereading the
Pelly description this should be 99%+ pure (even though the picture
shows a
similar drug store brand rubbing alcohol bottle.) We plan to use 10 ml
99%
ethanol next time.
note: that palm oil and rubbing alcohol don't mix very well; best that
we
got was an emulsion of tiny oil bubbles. Raises question: What are we
measuring the concentration of FFAs? do the FFAs dissolve in the
alcohol
solution, leaving a pure tri-glyceride/di-glyceride/mono-glyceride oil
fraction?
3. add 3 drops phenophthalein indicator
4. using 3 ml plastic pipette, determine that 24 drops of 0.1% NaOH =
1 ml
5. titration
Titration #1 -- 253 drops before solution stays pink for at
least 10
seconds
Titration #2 -- 265 drops before solution stays pink for at
least 10
seconds
avg = 259 drops = 259/24 ml = 10.8 ml 0.1% NaOH solution
necessary to
raise oil solution to 8-9 pH.
equivalent of 10.8 x .001 g NaOH / ml palm oil sample = 0.0108
g /
ml =
10.8 g/liter
according to Mike Pelly's description, this is the amount of
NaOH
needed
to neutralise the FFA
6. Calculation of NaOH amount --
adding 3.6 g/liter to catalyze the transesterification reaction, need a
total of 14.4 g NaOH/liter palm oil
we are using 400 ml oil for test batch, so need 0.4 liter X 14.4 g
NaOH =
5.8g NaOH / 400 ml palm oil
Mixing NaOH + Etoh Solution:
30% Etoh = 120 ml per batch;
Ethanol is absolut 99.3% by analysis, containing 0.1% methanol and
0.3% H2O
according to the label.
Amount of NaOH = 5.8 g / 400 ml oil
Calculations for concentration :
5.8 g / 120 ml Etoh = 0.04833 g/ml
For 400 ml Etoh -- 0.04833 X 400 = 19.3 g
We made up mixture of 400 ml Etoh + 28.7 g NaOH (BIG mistake
calculating,
don't know how.)
This works out to about 49% more NaOH than we should have have had.
NaOH added to ethanol held in a 500 ml conical flask
Mixture stirred vigorously for 20 minutes on magnetic stirring
machine; all
NaOH beads dissolved.
Correction needed for next experiment:
assume that we used 120 ml of the 400ml mixture, leaving 280 ml
with
0.07175 g/ml
This means the current solution contains the equivalent of
20.09 g
NaOH
Concentrated wanted = 0.04833 g NaOH/ml
20.09 g / 0.04833 g/ml = 416 ml ethanol
conclusion: need to add 136 ml ethanol to bring NaOH
concentration
down to
0.04833 g/ml
Mixing the sodium ethoxide and palm oil
Palm oil was heated to about 55C before mixing.
120 ml of sodium ethoxide was poured into 400 ml of oil held in a round
1000 ml flask with a long neck.
The "solution" was agitated. Attempt made to use a magnetic stirring
machine failed (even when solution transfered to conical flask)
Finally settled on swirling the solution in the flask, changing
direction
frequently.
Continued for 25 minutes.
Observations on the sodium ethylate (ethoxide) - palm oil reaction.
As soon as the sodium ethylate was poured into the oil, several large
white
blobs formed in a matter of a few seconds and remained through all
subsequent agitation. The mixture quickly clouded up with a tendency to
form small transluscent gel-like curds suspended in the general
solution.
No visible separation of fractions, except for the large white blobs.
Just
a general dirty yellow-brown opaque liquid, thinning when kept at 50C,
and
thickening when cooled.
After 40 minutes of cooling the mixture was a sloppy gelatin
consistency.
I put the flask in a boiling water bath. The mixture melted to an
opaque
amber liquid (though the largest white blobs persisted.) Heated
mixture to
75C. Picture no. 1 shows dark amber liquid with a few white blobs and
congealing substances at the bottom of the flask. As the mixture cooled
below 65C, it began to solidify (picture no. 2).
Noticing that a very thin layer of clear light tan, oil-like substance
floated above the thickening goo, I decided to put it through another
round
of heating in a boiling water bath. The results were surprising, at
least
to me. The mixture melted more slowly. And when it did melt it
produced a
lot of foam. After 15 minutes the melted mixture (at 90-95C)
threatened to
foam up out of the flask. The flask was removed from the water bath,
part
of the contents poured into a 500 ml conical flask, the rest poured
into a
bowl.
The cooling mixture quickly solidified this time. Added water to the
mixture in the flask and shook it up. Found that the solidifying
mixture
dissolved in water and was slippery, soapy. Continued agitation
produced
foam on the surface and a cream colored emulsion (picture no. 3).
Within 20
minutes this mixture separated into four fractions: foam, a few
globules of
oil-like substance floating on the mixture surface, the butterscotch
colored
emulsion layer, and a darker liquid at the bottom of the flask that
looked
like soapy water (picture no. 4).
Conclusions / Questions:
1. We produced soap rather than bio-diesel. Question is why?
because the oil still has too much water even though it had
been
heated
until the foaming stopped?
because we used too much NaOH?
because the ethanol has absorbed water in storage? unlikely I
think.
2. The little bit of moisture that the NaOH absorbs in transfer is
unlikely to add more than 0.2 g H2O to the ethanol. That would raise
the
water % only about 0.1%, in other words from 0.3% to 0.4%. This is
still
within the less-than-0.5% tolerance.
3. What effect if any does the elevated free fatty acids have on the
reaction? Leif, you say that FFAs (and water) are the enemies of
transesterification. I assume that they originate from the fatty acid
chains that are split off from the glycerine, hence the term "free", but
that they are further degraded making them unusable for adding the
methyl or
ethyl elements for the esters. How are the FFAs different from the
newly
split off TRANS-fatty acids at the beginning of the transesterification
reaction?
MARSAVCO says that peasant produced palm oil tends to have 20-30% FFAs
because of natural oil decomposition ( due to delay between harvest and
oil
extraction, delayed sterilisation of the oil, all water not removed,
and oil
contaminated by bacteria that promote decomposition.) This is the oil
we
are using, though it has been filtered and the water has been removed.
If
FFA's are a significant barrier, can we come up with a simple way to
separate them from the tri-glycerides before starting
transesterification?
4. Looking at the diagram descriptions of transesterification and
saponification from the Pelly description it appears that the difference
between the two is what gets attached to the fatty acid chain.
Transesterification appears to add the methyl or ethyl part of the
alcohol
(without the hydroxide portion) to the fatty acid chain. Saponification
appears to add oxygen and Na to the fatty acid chain. When alcohol is
in
the mix what favors the alcohol element bonding over the oxygen-Na
bonding?
Obviously water tips the balance, but what is the mechanism? Does
having an
excess of catalyst also tip the balance in favor of soap?
5. It looks like sodium methylate and sodium ethylate are solutions of
sodium ions and alcohol minus the H from the OH group. Does the H shed
by
the alcohol and the OH from NaOH form water, resulting in an aqueous
solution of Na+ and CH3O- or CH3CH2O-? If this is the case, water is
already present in the reaction in a certain concentration. Does a
further
increase in the water concentration eventually tip the reaction from
alcohol
+ fatty acid chain to Na + fatty acid chain? If so, at what point and
why?
Next week at the Lusekele Biodiesel club --
1. Titrate 1ml of commercial vegetable oil to compare results
2. Correct the concentration of NaOH in the ethoxide and retry the
Pelly
method.
3. Consider trying the acid-base two-stage alternative proposed by
Kac,
increasing the alcohol to 30%.
Appreciate any input anyone can give. Our internet access is very
limited
but e-mail connections pretty good if a little slow. If you come across
useful info, please forward to us.
Biofuel at Journey to Forever:
http://journeytoforever.org/biofuel.html
Biofuels list archives:
http://infoarchive.net/sgroup/biofuel/
Please do NOT send Unsubscribe messages to the list address.
To unsubscribe, send an email to:
[EMAIL PROTECTED]
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/biofuel/
<*> To unsubscribe from this group, send an email to:
[EMAIL PROTECTED]
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
