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What is the purpose of acid esterification?
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I have not used acid esterification, but want to try because I have accumulated oil with a high concentration of FFA. I have read and studied a lot of threads and posts, but I have a couple of nagging questions.

1) What is the purpose of esterification? Is it to: convert FFA directly to methyl esters (ME) to increase the ME yield of the oil; strip FFA from triglycerides (TG) to make the subsequent base catalyzed transeseterification reaction more efficient;, or both?

2) If the purpose of acid esterification is to convert FFA to ME, then why would the methanol NOT be left in the TG for the following base reaction? ME is soluble in methanol, and since the total volume of ME produced by acid esterification, as a percent of remaining TG and methanol will be very low, then removing the methanol will, in effect, remove the ME.

3) If the purpose of acid esterification is to strip FFA from TG, then why bother to acidify the reaction. TG is relatively insoluble in methanol and FFA are soluble in methanol. Will "rinsing" the TG/FFA feed stock with methanol just strip the FFA from the TG? This would leave a, relatively, FFA free feedstock.

As you can see I am very confused about this process and would really like to learn more before I start experimenting.

Any insights would be most appreciated.
 
Location: Illinois | Registered: February 21, 2006Reply With QuoteReport This Post
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It's been a while since I've posted on here, but I'll do my best to answer your question. I have done 4 years of work with biodiesel and worked out a good method for the acid esterification.

1: The purpose of the acid esterification step is to convert as much FFA as possible into Methyl Esters to reduce the amount of OH- needed for the reaction which ultimately reduces your cost. This step also helps eliminate any FFA's that would cause the production of soap.

2: When carrying out this reaction with high FFA content oil,I always add the amount of acid that is needed + 1/2 of the amount of Methanol for the reaction. (the other half is added during the base step) I never get rid of the methanol before the base step. There is simply no need to. If your oil is a high FFA content, you can generally expect a little more than 50% to be converted to Methyl esters which is due to an equilibrium issue.

3: A FFA cannot be attached to a glyceride molecule. You must be referring to mono and di-glycerides. These molecules are generally converted in the same way that tri-glycerides are converted; during the base catalyzed step. Short answer, washing the feedstock will do nothing for you other than cause you trouble.


Here is my recipe for the acid esterification method:

Use 1/2 of the total volume of methanol that would be used for the normal reaction.

Mix this with the correct amount of 95%+ sulfuric acid (1mL sulfuric acid to 1 L oil) and heat to ~150'F for approximately 2 hours.

The amount of base must be adjusted to compensate for the addition of the acid which must be neutralized.

Add the base to the other half of methanol then add to the reaction. React for about 2 hours at 150'F.

This has worked for me numerous times and generally get a 90%+ yield. I have done analytical analysis on the small scale (1L) and rough analysis on the large scale (80L) and I am very pleased with this method.

Hope this helped some. If any further explanation is needed I can be emailed at richard.chemist@gmail.com

I don't get the chance to check this forum much.

Thanks,

Richard
 
Location: Fayetteville, AR | Registered: February 24, 2007Reply With QuoteReport This Post
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1) yes it can but the process so very slow. and yes the trans is then more efficient.

2) is its left over and available. however the process of esterification produces water!!!. just what we don't want. the amount of water depends on how bad is the oil.( high titrating = bad). i'm not sure I know the answer to the 2nd part,

3) this is recently proposed but Graham laming who then did just that. it does leave the question of what/how to process the methanol ladened with FFA.

it seems if the titration is between 14-18+KOH drain is a good idea between the acid and base stages. the amount to drain is around 1/2 the methanol quantity used in the acid stage.
if the titration is less than 14KOH then draining is not required, but yield will be slightly lower oil that just need the base processing. this is due to the water created in the acid stage.

if too much methanol is used during the acid stage the methanol/acid/water mixed will float on top of the oil. hard for home brewers to drain without a special processor setup.

if too little acid is used during the acid stage the oil will require a 2nd acid stage. except for really bad oil which will require a second stage anyway.

-dkenny


'84 bluebird school bus, DD8.2L turbo( 4/2011, the bus tranny has died..Frown 8.23.11 bus driven to scrap yard Frown )
2006 Jeep Liberty CRD Smile - the wife's
99 dodge 2500 5.9l 24v..-mine Smile
everything run B100 when its warm enough Smile
 
Location: RTP, North Carolina | Registered: December 15, 2004Reply With QuoteReport This Post
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Richard,

Thanks for your excellent response. It is most informative.

As far as the following is concerned:

quote:
Originally posted by analyticalchemist:


3: A FFA cannot be attached to a glyceride molecule. You must be referring to mono and di-glycerides. These molecules are generally converted in the same way that tri-glycerides are converted; during the base catalyzed step. Short answer, washing the feedstock will do nothing for you other than cause you trouble.


I was wondering if the FFA are more soluble in methanol (no acid) than triglycerides. If so, then can the methanol be used to just "strip" the FFA from the TG feed stock. I see this as a solubility issue, not an esterification or transesteridication question.
 
Location: Illinois | Registered: February 21, 2006Reply With QuoteReport This Post
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quote:
Originally posted by dkenny:

3) this is recently proposed but Graham laming who then did just that. it does leave the question of what/how to process the methanol ladened with FFA.


If the FFA can be stripped from the TG with methanol only, then could acid be added to the FFA/Methanol mixture at a later date?
 
Location: Illinois | Registered: February 21, 2006Reply With QuoteReport This Post
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producer,that would be the theory, but how to process the methanol/FFA?

analyticalchemist,
about your answer to #3. washing the feedstock with methanol will remove the FFA. no conversion they'll just be FFA disolved in methanol. this principle is used during titration.

about your recipe
should we vary the amount of acid? depending on the titration of the oil. we vary the amount of caustic base on titration. so why not the acid?

doesn't the titration tell how much to adjust the amount caustic for the base stage. how does the titration know if is measuring H2SO4 or FFA ?

-dkenny


'84 bluebird school bus, DD8.2L turbo( 4/2011, the bus tranny has died..Frown 8.23.11 bus driven to scrap yard Frown )
2006 Jeep Liberty CRD Smile - the wife's
99 dodge 2500 5.9l 24v..-mine Smile
everything run B100 when its warm enough Smile
 
Location: RTP, North Carolina | Registered: December 15, 2004Reply With QuoteReport This Post



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dkenny,

To answer your question "about your recipe
should we vary the amount of acid? depending on the titration of the oil. we vary the amount of caustic base on titration. so why not the acid?


You can vary the amount of acid depending on the amount of titrant that was used to titrate the sample. However, you need to calculate the point at which it is no longer beneficial (economically) to add more acid. Also, Some people will disagree with me, but I have found that the acid stage will not get rid of ALL of the FFA. There is a point where it reaches an equilibrium and will no longer esterify any FFA's. I find that generally after 1.5 or so mL per liter of oil, the process is much less cost efficient due to the amount of lye needed to neutralize the excess acid.

Hope this helps.

Richard
 
Location: Fayetteville, AR | Registered: February 24, 2007Reply With QuoteReport This Post
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analyticalchemist, you said:

quote:
Originally posted by analyticalchemist:
dkenny,

To answer your question "about your recipe
should we vary the amount of acid? depending on the titration of the oil. we vary the amount of caustic base on titration. so why not the acid?
. . . .
Richard


We vary the amount of caustic based on the titration because the caustic is consumed in relation to the amount of caustic.

Is the acid consumed during esterification, or is it just diluted as the concentration of the byproduct, water, increases?
 
Location: Illinois | Registered: February 21, 2006Reply With QuoteReport This Post
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analyticalchemist,
the process stops because of the water created during the process. if this water is removed then the process will continue. however, water and methanol don't separate...

I have done a couple of batches where the process stopped at 7 (KOH homebrew). after letting the batch sit for 12 hrs and draining the water/acidic/methanol the titration dropped to 3.

The other thing I have read but I don't argee with is the need for the 'extra' caustic to neutralize the excess acid. what excess acid? even on the batches that started at 27 ( and drained) the ending titration was 3. I used the same amount of KOH as if the oil was initially 3.


One thing I don't understand is why some batches end lower than 3? some end at 1.5KOH this is below the theoretical minimum. one theory is the acid oil react..


-dkenny


'84 bluebird school bus, DD8.2L turbo( 4/2011, the bus tranny has died..Frown 8.23.11 bus driven to scrap yard Frown )
2006 Jeep Liberty CRD Smile - the wife's
99 dodge 2500 5.9l 24v..-mine Smile
everything run B100 when its warm enough Smile
 
Location: RTP, North Carolina | Registered: December 15, 2004Reply With QuoteReport This Post
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The definition of a catalyst is speeding up the reaction without being consumed. If you add acid to your reaction....you must compensate for it to neutralize it. If you don't, you will not be able to get complete conversion of your triglycerides to FAME's.

I've used this method and done numerous studies on it. I can assure you that it will work.
 
Location: Fayetteville, AR | Registered: February 24, 2007Reply With QuoteReport This Post
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analyticalchemist,

quote:
The definition of a catalyst is speeding up the reaction without being consumed.


Hi. Can you please provide access to your studies?

In the case of Base Transesterification, as I understand it, the catalyst is consumed. It is consumed by the soap-making side reaction.


Andrew

http://biodieselcommunity.org
03 Dodge 2500 B100 homebrew
79 Rabbit B100 homebrew
 
Location: Northern California | Registered: February 27, 2006Reply With QuoteReport This Post
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I agree that the process works. without a doubt.
but the titration indicates an acid level. correct? so how does it know the difference between H2S04 and FFA ? I don't think it can tell the difference. so the titration done before the base stage adjusts for the H2S04 left in the mix. therefore, no additional adjustments are needed.

we just disagree on the amount of acid needed. through many batches I determined that the amount of acid ( H2S04) needs to vary with the titration. the extra acid in my method pushes the process further without the need of a 2nd acid stage in most cases.

here are some examples
initial titration of 7. I use 0.8ml of acid per liter much lower than all other methods.

at 13 titration I use 2 ml per liter. the same as most people

at 27 titration I use 4.8 ml per liter. more than twice most people but ending titration if the starting is less than 14 is almost always 3 or less in a single stage of acid without draining. for the cases where the titration is over 18, initially the titration lowered to 7 before draining and 3 after draining.

none of this was done with lab samples but 60 gallon batches of WVO.

-dkenny


'84 bluebird school bus, DD8.2L turbo( 4/2011, the bus tranny has died..Frown 8.23.11 bus driven to scrap yard Frown )
2006 Jeep Liberty CRD Smile - the wife's
99 dodge 2500 5.9l 24v..-mine Smile
everything run B100 when its warm enough Smile
 
Location: RTP, North Carolina | Registered: December 15, 2004Reply With QuoteReport This Post



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The amount of acid used to catalyze the acid esterification reaction increases with the amount of FFA present. The amount of methanol required also increases with the amount of FFA present.

When the FFA is converted to FAME, water is produced. Generally, the esterification reaction is much more tolerant of water and will not 'hang-up' until about 3% wt of water present. The base catalyzed transesterification reaction, on the other hand, will 'hang-up' at about 1% wt of water.

Depending on the amount of FFA available, there could be too much water produced to allow for a very efficient base catalyzed conversion to FAME.

Keep in mind that solubility (and lack thereof) of methanol, water, TG, ester, glycerol, acid and base tends to control the abillity to convert FFA and TG to the desired products.

This is ultimately the challenge presented by lower cost (so called) high FFA feedstocks.
 
Location: Nova Scotia, Canada | Registered: July 17, 2005Reply With QuoteReport This Post
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so now we need to figure out a way to determine the amount of methanol base on titration. it should use the minimum amount needed for the acid stage but enough for the acid stage to complete. after the acid stage the watet/methanol/acid mix should sink to the bottom for easy draining.

just some early morning thoughts


-dkenny


'84 bluebird school bus, DD8.2L turbo( 4/2011, the bus tranny has died..Frown 8.23.11 bus driven to scrap yard Frown )
2006 Jeep Liberty CRD Smile - the wife's
99 dodge 2500 5.9l 24v..-mine Smile
everything run B100 when its warm enough Smile
 
Location: RTP, North Carolina | Registered: December 15, 2004Reply With QuoteReport This Post
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quote:

we just disagree on the amount of acid needed. through many batches I determined that the amount of acid ( H2S04) needs to vary with the titration. the extra acid in my method pushes the process further without the need of a 2nd acid stage in most cases.

here are some examples
initial titration of 7. I use 0.8ml of acid per liter much lower than all other methods.

at 13 titration I use 2 ml per liter. the same as most people

at 27 titration I use 4.8 ml per liter. more than twice most people but ending titration if the starting is less than 14 is almost always 3 or less in a single stage of acid without draining. for the cases where the titration is over 18, initially the titration lowered to 7 before draining and 3 after draining.

none of this was done with lab samples but 60 gallon batches of WVO.

-dkenny

dkenny,
Do you drain off the accumulated water and if so do you find that the volume of water recovered depends on the initial titration value? By definition the catalyst in a reaction isn't destroyed and the amount of catalyst should only effect the bulk reaction rate not the final values.
So if you might find that if you fixed the amount of acid the higher titration oil (greater initial % FFA's) would take longer to reach a given endpoint assuming of course you can remove the accumulating water.
Another possible complication is that you would expect the acid to be quite soluble in any water phase (much more so than the oil phase) so if the water was allowed to settle during the reaction (a good thing) the actual acid catalyst concentration in the oil phase may be much lower that at the start. Your additional acid would have the effect of compensating for this decrease.
Just something to think about.
 
Registered: March 23, 2004Reply With QuoteReport This Post
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Rick G,
no I don't drain unless the initial titration is above 18. I have found that if its above 18 drain cause a sudden drop in titration. to me this shows that the acid likes the water/methanol better than the oil/ME.

removing the water during the processing is more complicated for a home brewer.

when I do drain the amount is pretty consistant with 1/2 the amount of methanol used for the acid stage.

recently I tried draining on a batch that started at 7 but the results weren't the same. meaning no drop in titration after draining. I suspect the water/acid/methanol layer floated. this would indicate that too much methanol was used. more stuff to research... now if I can get a bunch of oil that titrate from 7 to 10 or so.


-dkenny


'84 bluebird school bus, DD8.2L turbo( 4/2011, the bus tranny has died..Frown 8.23.11 bus driven to scrap yard Frown )
2006 Jeep Liberty CRD Smile - the wife's
99 dodge 2500 5.9l 24v..-mine Smile
everything run B100 when its warm enough Smile
 
Location: RTP, North Carolina | Registered: December 15, 2004Reply With QuoteReport This Post
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I can assure you that even in the base catalyzed method the catalyst (the base) is NOT consumed!!!

The methanol is consumed! The lye isn't. The lye settles mainly to the glycerine...check the pH of the glycerine..it's basic!!! Yes, a small amount is used in the production of soap, but isn't that what we are trying to aviod with the acid catalyzed method...why else would we do it!?! This method also should ELIMINATE the need to titrate a sample at all! That is also the reason you want to wash the fuel is because minute amounts of the lye is still in the fuel and can cause damage to your vehicles fuel system.


The acid catalyzed method works like this:

The acid is added to the system in order to convert FFA to FAME. The FFA must have methanol present in order to be able to convert to the FAME. After the acid catalyzed portion of the reaction is complete, the acid that was added in order for this reaction to happen must be neutralized! If it is not, then the lye will react with the strong acid (sulfuric) to produce water + salt. (the product of any strong acid + strong base reaction) For example:

If you have a 100 Liter batch of WVO that titrates at lets say 14 mL KOH. You can add 1 mL of sulfuric acid for each liter of oil that you have to convert. This would mean that you would add 100 mL of sulfuric acid. At this time, I would also add 1/2 of the amount of methanol for the reaction.

for a 100 liter batch of WVO, 20 L of methanol should be used, so I would add 10 L at this time.

Heat the reaction for about an hour with the acid. During this hour the Acid Esterification of the FFA takes place if and only if there is a methoxy group present for the conversion to work. (this comes from the methanol) Here is the link to this reaction mechanism:

http://www.chemguide.co.uk/physical/catalysis/esterify.html

After this has taken place...you STILL have the acid that you added to cause this reaction to happen. (the catalyst)

Now, what is in your mixture is:

WVO
FAME
Methanol
Sulfuric acid

You want to convert the WVO (mono, di, and triglycerides) into FAME now. This is done with the base catalyzed method. (the second step of acid esterification reaction for the production of biodiesel)

You should now add the methoxide mixture which is:

The other half of your methanol (10 liters) along with the amount of lye needed for the reaction. 3.5g NaOH per liter of WVO or 4.9g KOH per liter WVO.

HOWEVER!, at this point, you must add enough base in excess to neutralize the acid that you added before. If you don't, the base that you add will neutralize this acid first and you can still achieve a complete reaction, but it will take much longer. (the catalyst speeds up the reaction without being used up) In theory, you don't have to add the base at all, but it would take weeks for the reaction to occur.

You will need to figure out the molar ratio of sulfuric acid to lye that you are using in order to add the correct amount.

I hope this clears up some of the questions that you all had about my reaction. Also, as for my research materials, I have some papers that myself and fellow researchers have written that I would be glad to share with you all. I will see if I can get them uploaded to a website where they can be downloaded for your viewing pleasure.

Thanks,

Richard A. Smart
University of Arkansas
Department of Chemistry and Biochemistry
rxs14@uark.edu
 
Location: Fayetteville, AR | Registered: February 24, 2007Reply With QuoteReport This Post
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analyticalchemist,
its know that the acid process create water..
so the mix during the acid stage should be
wvo
FAME
sulfuric acid
methanol
water - this stops the process.

doesn't the water created stop the process..but using more acid will push the process further?

most home brewers use 5g NaOH or 7+ g KOH for the base not 3.5 and 4.9...

also something must be neutralizing the acid..during the acid stage.
a couple of weeks ago I tried a simple experiment..I put 1 ml H2SO4 in 1 liter of water. usning 0.1% KOH solution I wanted to see how many mls would be need to return the solution to the starting ph. it took 3 mls..

wouldn't this imply that if I used more then 1 ml of acid per liter then the titration would be more than 3 mls? but many times I used 3 mls of acid per liter and the titration ended at 3mls

-dkenny


'84 bluebird school bus, DD8.2L turbo( 4/2011, the bus tranny has died..Frown 8.23.11 bus driven to scrap yard Frown )
2006 Jeep Liberty CRD Smile - the wife's
99 dodge 2500 5.9l 24v..-mine Smile
everything run B100 when its warm enough Smile
 
Location: RTP, North Carolina | Registered: December 15, 2004Reply With QuoteReport This Post



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Greetings,

The 'trick' with this process is to remove the water produced during the acid catalyzed esterification reaction. The water and sulfuric acid and methanol have a very strong affinity for each other and will tend to stay together. If you add enough methanol, the combined densities and minimial solubility of the methanol and oil will create a separate phase that forms on top of the oil. It is this water rich methanol/sulfuric acid phase that should be removed from the oil for further neutralization and base catalyzed conversion to FAME.

The other 'trick' is how to recover the methanol from the top phase and remove the water so that the methanol can be recycled.

My experience has been with relatively high titration values in the range of 25 - 50 mL of KOH. It could be that this approach does not work as well with lower titration value waste oils due to the small amounts of methanol and sulfuric acid being used and the ability to efficiently mix these small amounts of reagents with the waste oil.

Happy New Year!
 
Location: Nova Scotia, Canada | Registered: July 17, 2005Reply With QuoteReport This Post
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dkenny,

By using Le Chattlier's principle, in theory the reaction should push farther to the right (product) if you add more acid (if the acid was a reactant) In this case, the acid is NOT a reactant...it is the catalyst. So you will reach an equilibrium...the reaction will not push further by the addition of more acid.

Why use more NaOH or KOH than needed? 5g NaOH and 7+ KOH

For virgin oil only 3.5g NaOH is needed which equates to 4.91g KOH. I don't want to spend more than I have to in order to produce fuel...that's part of the game Wink

The purpose of the acid catalyzed method is:

1. reduce/eliminate soap production by converting FFA to FAME

2. Eliminate the need to titrate the oil which eliminates the need for excess base



-Richard
 
Location: Fayetteville, AR | Registered: February 24, 2007Reply With QuoteReport This Post
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