If you are going to do an acid/base process, and you also want to do a glycerol prerinse, should it be done after the acid step? I would think the glycerol would remove the water produced by the acid process, along with other crud.
Sorry if this is a common question that has been asked and answered before.
not sure if this has been asked before.
I know I never tried this before.
I could how this might help..
the excess caustic in the glycerin would neutralize the acid. help remove some of the water..maybe all of it?
you might need to tweak the amount of methanol in base stage..
sound to me like you should try a sample and let us know how it works..1 done with the gyl wash and one without. both from the same oil.
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acid esterification followed by glycerine prewash works well. The other way around doesn't work as well because the remaining soap (any that doesn't fully settle) messes up your sulfuric acid catalyst. Titration more or less takes care of that, but the formula should vary a little from the standard DKenny one I think.
Trying to answer that question next month in some experiments I'm doing.
The reason I want to do glycerine pretreatment before esterification is because :
a) I acidify the byproduct of biodiesel
production, which is glycerine/soap/biodiesel- and can then esterify the resulting FFA/biodiesel that I recover. It's really easy to esterify that product. I was doing this as part of something I was jokingly calling the 'base ackwards method'.
b) Glycerine pretreatment is unparalleled in removing water. The problem is that it doens't work well with really high_FFA oils because of separation issues.
c)I think there are ways around all of this which would still give you the benefits of both techniques.
Thanks for the replies.
I will be giving this a try when the weather warms up and I can vent my shop again. (Current temps are around - 20 to - 30 C these days)
Will report back.
Happy New year!
Funny, base-ackwards ... ha ha. I've been calling it back-slopping.
The theory seems sounds, acid esterify to the point that almost all FFA has been esterified.
Titration after esterification should correlate pretty closely with total acid you added assuming a high conversion (about 1.4 @ 1ml/L).
Then choose to use extra lye/methylate to neutralize and react OR .....
Add caustic glycerol from last batch to neutralize remaining acid, remove water and soap. Settle and remove glycerol.
Now you should be able to transesterfy with the minimum amount of catalyst.
Well kinda, doesn't always work out.
I didn't neutralize the glycerol cocktail from the previous batch like you did. I was hoping to use the left over caustic in the cocktail to neutralize the acid in an attempt to reduce the amount of sodium methylate required.
The reaction didn't go the way I had hoped. The oil was pretty bad, started with a Na titration of 21 and reduced it down to 5.9.
I still consider 5.9 to be on the soapy side of production. But after days of "waiting it out" I re-tirated at 4.2.
I decided to add the glycerol anyways in an attempt to neutralize the acid and perhaps do a little bit of a caustic strip. In which I was hoping that the glycerol settling would remove much of the soap that I would produce.
When I do the acid stage I use 13% methanol by volume. Saving the 7% for transesterfication.
I was hoping that when I added my glycerol cocktail that I would have not only the 13% methanol in solution from acid eserification but also the previous 7-8% methanol excess from the last batch. I figured that the acid/FFA would be neutralized and that the now weak amount of catalyst remaining would start the transesterifation in the precense of nearly 20% methanol. However the equilibrium is shifted to the right due to the abundance of glycerol.
My hope was not to get good yeilds, but to simply "recover some methanol from the previous batches glycerol through a pre-reaction".
Basically I wanted glycerol going into the reaction that contained about 40% methanol to come out of the reactor with about 20% methanol.
Well when I drained the reactor initially the glycerol was really really runny (expected) since it had so much methanol in the reactor.
Methanol really does prefer the glycerol phase, so I tried not to drain *all* the glycerol in hopes to have some methanol remaining.
Upon re-titrating, expecting to have a 0.1 or something I came back with 3.9. Not exactly the drop I was expecting.
This was the first time I tried this, perhaps next time I'll try Dr. Pepper bottles instead of 330 gallon batches
Either way the batch turned out ok, I ended up using the same amount of methlyate I would have used without the procedure. Either way I still believe it has hope.
The SunBreak BioStudio, LLC
How about using any glycerol removed during the acid stage only, and using that in the next batch of acid esterfication? Effectively resuing the acid and methanol, while removing water. Hmmm, I may have to try that on the next one.
how in the world are you going to remove that water by doing this? the "glycerol" from the first stage is mostly water, if your'e getting it to settle down low (as opposed to float).
Mine first stage glycerol sinks. What percentage of the glycerol content from the first stage would you guess is water? And what are the limitations of water removal with glycerol in terms of overall percentages...say start at 1 percent and it will remove an additional X percent total volume
Not sure if I totally understand your questions.
First of all, if you're talking about glycerine pretreatment with caustic-containing glycerine, it works really well for removing water. I don't have my notes but I got water content routinely down to 75 PPM as measured by a Karl Fischer instrument (and can't recall, a year later, how high it was to begin with). However, I THINK that most heated settling, at least at Piedmont Biofuels Coop, gets water content down to 2000 PPM. Maybe someone with a Sandy Brae tester can chime in and tell us what they're getting as far as heated settling water content, which is relevant cause it's the easiest way to remove water in general.
1- the stuff that sinks at the end of an acid esterification step is full of water. It is not glycerine unless you're using a really weird catalyst (not just acid) or have an extremely long processing time, probably on the order of days and days.
2-the reaction is sensitive to water. So, if you're trying to re-use acid and methanol that's in that 'bottoms' layer, it's going to inhibit the reaction. We generally try to remove as much water as possible.
3- What I've done with that layer is to put it into some glyceirne that's going to be methanol-recovered. It adds some amount of water to that batch of glycerine. I'm not too worried about that, compared to the effect of water on esterification.
4- if you want to pull water out of oil for esterification, using glycerine pretreatment (with caustic glycerine, not acid-water-methanol) may or may not work- in high-FFA oils, there can be problems doing this over a KOH homebrew titration of about 10 or 12, so the oils that are most in need of drying out via glycerine pretreatment are the ones least likely to work well in that situation.
5- there's a long thread that I think (I didn't check recently) makes my point #4 point here. Pages 4 and 5 have my input and summary of what I think happened when the guy tried to combine glycerine pretreatment with acid esterification:
Thanks again GM. That boy had quite a mess on his hands. I was under the impression that the glcerine from the acid stage could be used the same way as glycerine from the base stage. I knew it contained water and salts, but wasnt aware that it contained more water than anything else.
Im definately not a chemist.
hi all i am interested in this esterification stage glycerol pretreatment i know it uses caustic glycerol from a base stage but i dont know the volumes, i have just finished the first stage acid on 80l of lard that titrated at 9.5 KOH math was 9.5-3=6.5x0.2=1.3ml/L H2S04 80x1.3=104 rounded it up to 110ml h2so4 in 10L methanol after 10 hrs titrated at 2.25 so i added 4l caustic glycerol run the pump for 30min then left it for 6hrs then drawn off 4l from the bottom. i think i should of took only half 2l like d kenny method for 14+ titration does anyone know how much to add and remove , what i removed was strong in methanol vapours thank you all andy
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