OK. I'm new to BD, and interested in acid esterification, as I suspect that most available feedstocks are high FFA.

I've read the main thread end to end in an attempt to understand the basic chemistry involved:

(---)H +(CH3)OH => (---)CH3 + H2O,

catalysed by H2SO4.

The problem, it seems, is that water inhibits this reaction by diluting the H2SO4. H2SO4 is a small fraction of the total volume present, and is easily diluted by a small amount of water. Unfortunately, water is also a reaction product. As the reaction progresses, the water produced dilutes the acid. The reaction slows, eventually coming to a halt. It is impossible, then to push the reaction to completion. This also explains why 95 or 98% H2SO4 is required. If it were possible to 'dry' the reaction, you should be able to complete the reaction.

Some people have reported here that settling, removing the water formed, then adding catalyst and Meth improves results. This is consistent with above.

My first idea was to heat the reaction to evap. the water, but no that won't work because we lose the alcohol, probably first.

How about this: Use an enclosed reactor, and use a dessicant drying agent (not in contact with the oil) to remove the water? If this worked, all the water could be removed from the oil, allowing completion of the reaction. You would then have nice, dry feedstock with little or no FFA. I was thinking of a small tray in the headspace above the liquid. Put the dessicant in the tray, and it will dry the air above the reaction without removing the CH3OH. Evaporation would remove the water from the oil. Since this will dry the reaction, it also might reduce the amount of H2SO4 needed. For large reactors, a small drain to a container outside the reactor might be necessary. I would probably use NaOH or KOH as the dessicant as its already on hand.

So, does this sound feasible? Is my understanding of the chemistry correct?

Or am I out in left field.

quote:

I've read the main thread end to end in an attempt to understand the basic chemistry involved:

(---)H +(CH3)OH => (---)CH3 + H2O,

catalysed by H2SO4.

The problem, it seems, is that water inhibits this reaction by diluting the H2SO4.

Not exactly -- the water inhibits the reaction because the reaction is just as happy to go backwards as forwards. As water builds up, the equilibrium of the reaction shifts back toward the left side, slowing the further accumulation of ester.

quote:

This also explains why 95 or 98% H2SO4 is required.

That's part of it, but it's also that concentrated H2SO4 has an additional property of "soaking up" water to some extent (it forms a hydration complex). Weaker H2SO4 would still be a fine acid, but it would already be fully in the hydrated form.

quote:

How about this: Use an enclosed reactor, and use a dessicant drying agent (not in contact with the oil) to remove the water?......Put the dessicant in the tray, and it will dry the air above the reaction without removing the CH3OH. Evaporation would remove the water from the oil. Since this will dry the reaction, it also might reduce the amount of H2SO4 needed. For large reactors, a small drain to a container outside the reactor might be necessary. I would probably use NaOH or KOH as the dessicant as its already on hand.

Great idea! The way they actually do it is to reflux the reaction mix into a condenser column filled with molecular sieve. The methanol and water go up into the column, and only the methanol drips back down. For serious drying, that's the way to go -- KOH or NaOH would be a less strong and less convenient dessicant.

People also add more catalyst for higher titrating oil to keep the reaction moving. Having a higher molar ratio of catalyst will also move the reaction at a faster pace.

This can confuse people into thinking that the sulphuric acid is a reactant and not a catalyst.
DD

it would be hard to build a reflux column that let water out and kept methanol in. methanol boils at a lower temp then water so it be a vapor at a lower temp. maybe something a distillation column where the methanol is pulled off and the vapors continue upwards. like a hydrocarbon cracking column...complex and beyond most home brewers, but might work in an industrial scale.

-dkenny

My hope is to find a way to get a more complete reaction for high titrating oils other than just loading up on catalyst. Seems like a waste to use catalyst just to soak up water, then have to use base catalyst just to consume the acid catalyst. Also, drying the process now would reduce soap formation in the base catalysed step wouldn't it?

I guess the only way to know is to try it.

What actually seems to work fine is to throw in a little more H2SO4 than usual (dkenny's formula is good) for high titrating oil, make sure the oil is bone dry before processing, use very concentrated H2SO4 (none of these drain cleaners), very dry methanol, and go with it.

You should be able to get oil titrating at, say, 12ml NaOH solution, down to 4 or so before the base step. That's good enough!

DTaylor,
what's your initial titration level??
making BD works best if it keep simple. the catalyst isn't just used to soak up water. it use to convert the FFA's to biodiesel. water stops the process as you know. there are means to remove this water but there more for the industrial scale not homebrew.

are you looking at homebrew scale or industrial scale?

of course the best part about BD making is there are new ideas and solutions all the time

-dkenny

quote:

Originally posted by dkenny:
it would be hard to build a reflux column that let water out and kept methanol in. methanol boils at a lower temp then water so it be a vapor at a lower temp. maybe something a distillation column where the methanol is pulled off and the vapors continue upwards. like a hydrocarbon cracking column...complex and beyond most home brewers, but might work in an industrial scale.

-dkenny

For esterification the process used is Reactive Distillation which is geared more to a continuous process rather than a batch set up. I agree probably more industrial than homebrew as it is a little complex.

DKenny-

Home brew, but I have several friends who are interested, so this might become a sort of 'co-op'

I didn't mean to say that the H2SO4 is there only to soak up water, but that the water produced is diluting the acid, and that's why more acid will drive the reaction further. This is why people calculate the quantitity of acid requried by the formula using initial and desired final titration levels. Catalyst isn't consumed in the reaction, so the reason to use more catalyst for higher titrating oils is to compensate for water production. Removing the water produced would, theoretically, get the reaction further with a constant amount of catalyst per liter of oil.

Provo-

I think that a lot of failures or poor results are due to water contamination, not excess water production. Yes, bone dry oil and good reagents will alleviate that, but some sort of drying system would be insurance against that.

Fuzznag et al-

Dessicant drying is the simplest solution I could think of for home brew scale. It would be slow, depending on evaporation to remove the water from the oil, but reactor design (increasing surface area) would help. My goal is to find a way to condition my feed stock so that the trans-esterification is as straightforward as possible.

I appreciate everyone's input on this.

DT

"if you make something foolproof, only a fool will use it"
"if you make something foolproof, then some idiot will make a better fool"

DT,
What does your feedstock currently titrate? What are you currently using for a processor?
Are you currently producing using transesterification?
The only reason that I ask these questions is that it will make it easier for dkenny and others come up with a workable plan for you.
I guess I am lucky in that our oil titrates low.
You might want to try the acid-base method and become comfortable with it and then try to refine it by adding water removal.
DD

Currently, I have access to feedstock with titrations no higher than 6-7 NaOH, but more and more people are getting into BD brewing and I expect it will get harder and harder to get good feedstock.

I've only just started making BD by base catalysed transesterification with good results. Mostly I'm trying to understand and quantify the chemistry required to convert high titrating oils at an experimental level.

My first experiments will be with acid-base method. Building a drying system is going to take some effort, and I want to have a good base-line to compare to. My goal is to be able to condition feedstock to a uniform condition before trans-esterification; I think it MIGHT be easier to put the effort into prepping the feedstock, than to deal with problems (excess soap, poor conversion, reagent consumption, etc.) after conversion.

Right now, this is a research project more than a production problem. When I have experimental data, I'll post here. Thanks guys. This is SO much more informative than JTF. But, at least, they got me interested.

DTaylor,

Have you looked into the costs of acid esterification?
if a gallon of acid costs $20. that works out to 1.89cent/ml
edit->oops math error that should be 0.52 cents/ml.

with you're oil you'll need around
7-3=4*0.2 = 0.8ml/Liter or 0.41 cents per liter not very much

other things to think about
process time - the acid stage typically takes around 12 hrs
if you're going to evaporate water and methanol its going to take a long, long, long time. this might become a bottle neck in you production
how to maintain the temps? cost to maintain the temps?
materials to make the reactor out of?

just some idle thoughts

-dkenny

This message has been edited. Last edited by: dkenny,

Cost of acid is what got me wondering about drying the process. I was thinking about being able to esterify FFA's with less catalyst. I can get significantly higher yields with acid esterification, and if I can reduce the amount of acid required for esterification (and the base required to neutralize it), I think it's worth the effort. Once I have the chemistry optimized I can design the equipment required for my desired output.

I envision a large preprocessing tank used to dry and esterify high FFA feedstock, feeding into a much smaller reactor.

I'm running some 1L baseline tests right now (no drying as of yet).

Formula for base line tests:

1L dry WVO, titrates at ~7.5g/L NaOH.
Dissolve 1.1 ml H2SO4 in 100ml meth.
Heat oil to 55C, add acid/alcohol sol'n.
React for 24 hours.

(According to the formula, this should reach an end titration of 2. I intentionally chose a lower endpoint than normally possible)

My first test batch reached titration of 3-3.5 after 12 hours (didn't expect titration this low, was adding titrant in .5ml increments.) Final numbers tonight.

If I did the math right (boy, Chem101 was a long time ago), the amount of H2SO4 I used (1.1ml, about 2.02g) would require .85 g NaOH to neutralize. Does this sound right?

The drying test aparatus will have a large surface area and shallow depth to facilitate evaporation. I'll use the same formula, and see if a lower titration is achieved. If this works, the next test would be to reduce the catalyst and see if I can get to the same titration, and how long it takes.

quote:

If I did the math right (boy, Chem101 was a long time ago), the amount of H2SO4 I used (1.1ml, about 2.02g) would require .85 g NaOH to neutralize. Does this sound right?

Let's see....assuming 96% conc. H2SO4 (s.g. 1.8), 1.1ml weighs 1.98g, of which 96%, or 1.90, is H2SO4. With a molecular weight of 98, 1.90g is .0194 moles of H2SO4. Since there's two hydrogens per molecule, you'll need .0388 moles of NaOH to neutralize.

.0388 moles of NaOH (molecular weight 40) is 1.55g.

DTaylor,

uh..you don't get to choose the end point its 3 ...sometimes it'll end lower but without consistency.

so for you sample you used 0.2ml too much acid. so much for cost. at 1.1ml/per you using 0.5 cents per liter..or $0.5 per 100 liters..not very much money.

if you really want to fine tune my method..and there is fine tuning to be done. work out the amount of methanol needed based on titration to ensure the methanol/water/acid mix settles to the bottom. then draining should be done all the time and will result is a titration drop. the Acid is mostly removed. I typically see a 4 ml koh drop in titration when I drain.

I have never worried about the amount of base need to neutralize the acid left in the mix. The titration tells you this number. that's why its 3..if the extra acid was gone it would be lower!
so forget the concept of extra base to neutralize the acid.

you evaporation will not work you're not removing the acid only the water and methanol.

-dkenny

Titrating 7.5 and acid esterifying? The question you must ask is why? Wash your oil with glycerol. Simmpler and safer. I acid esterify but the oil usually titrates about 80. I try to get it down to 10 and then glycerol wash. Titration of 7.5, that is luxury! How do you treat a headache? Smash your finger with a hammer? No, take an asprin. Try the easy, safe route. I just gotta shake my head.

quote:

Originally posted by funnyfidel:
Titrating 7.5 and acid esterifying? The question you must ask is why? Wash your oil with glycerol. Simmpler and safer. I acid esterify but the oil usually titrates about 80. I try to get it down to 10 and then glycerol wash. Titration of 7.5, that is luxury! How do you treat a headache? Smash your finger with a hammer? No, take an asprin. Try the easy, safe route. I just gotta shake my head.

I'm using KOH. There must be a curve, not a hard step, but I find that if my oil titrates above about 7 the loss in yield seems higher than I'd like. For example, my last base-base process started with oil at 7.6, and my yield from 52g oil was about 38g, or 73%. The oil was very dry going in. I may not be settling long enough between reaction stages, but when my oil was titrating in the 3-4 range, I would have yields up around 90% consistently.

I am hoping that acid-base processing will bring back my yield. Will glycerine prewash do the same?

I am not sure where the number came from. But people say that you lose about 3% in yield for every ml of titration. A brief look at your yield numbers does support this.
DD

quote:

Originally posted by Dandy Don:
I am not sure where the number came from. But people say that you lose about 3% in yield for every ml of titration. A brief look at your yield numbers does support this.
DD

Since my numbers are anecdotal only, I would be more inclined to believe yours. But maybe I'm just being hopeful??? I'd love to hear the source, or some corroboration.

quote:

Originally posted by greiswig:
I am hoping that acid-base processing will bring back my yield. Will glycerine prewash do the same?

Yes, how much are you processing? I would gladly sacrifice a bit of oil to avoid working with sulphuric.