I have an analogy that I've used to teach the bare bone basics of the Biodiesel reaction to people that's based on semi trailers, semi trucks, and cement walls.
It seems to work well for people with little understanding of chemistry.
(That and I'm a visual person w/ a background in cars & diesels).
With that in mind, I'd like to present it here & then, if the pro's here are willing, have them come in & post the technical data behind the analogy (somewhat in the "the semi's do this, technically, this is what's happening" sort of thing) & we'll have somewhat of a "visual" analogy that can easily explain how the Biodiesel reaction works.
So...with that in mind...here goes.
Oils Are Like Semi Trailers Hooked To A Cement Wall.
All organic oils start life as Tri-glycerides.
Like 3 semi trailers connected to a cement wall.
Technically - 3 Fatty Acid Chains connected to a glycerol molecule
The semi trailers are the fatty acid chains
The cement wall is the glycerol molecule
They're connected to the wall with their trailer hitches
They're sitting on a hill w/ the wall at the top of the hill and the trailers pointing downward.
If they become detached from the wall they can roll away
|| = semi trailer
|| = semi trailer
|| = semi trailer
So, with that in mind....
All oils start out like the above.
3 semi's all hitched up to the wall.
Technically - The fatty acid chains are connected to the glycerin molecule with a chemical bond
Within an oil, there are several of these 3 trailer/cement wall combinations.
Get enough of them together and you've got oil.
Technically - Get enough tri-glycerides packed together and you have an organic oil.
However, like in real life, not all semi trailers are the same length.
Technically - Some oils have longer fatty acid chains than others.
Also, some have lots of cargo in them (densely packed) and some have hardly anything in them (wide open spaces).
Technically - Some oils are saturated (densely packed) while others are unsaturated (wide open spaces).
As oils age with time, water and heat, the 3 trailer/cement wall combination can change. Sometimes the trailers get knocked around by a torrential rain storm (water) or rust wears out the hitch (heat).
Technically - water, heat, and other factors can "naturally" break the chemical bond
As the storms and rust wear down the hitches, some of the trailers can break away from the wall and start rolling away.
Technically - Trailers that roll away from the wall are called Free-Fatty Acid Chains
OK, now some technical stuff..
3 Trailers Hooked To The Wall = A Tri-glyceride
2 Trailers Hooked To The Wall = A Di-glyceride
1 Trailer Hooked To The Wall = A Mono-glyceride
Back to the semi trailers...
Now we'll introduce two more items.
A Semi Tractor and a Hitch Breaker.
The semi tractor will represent Methanol
The hitch breaker will represent the catalyst
The Goal Of The Biodiesel Reaction
With everything above in mind, the goal in making Biodiesel is to unhitch the semi trailers from the cement wall and hook them up to a semi-tractor. This will leave a cement wall and a semi-tractor trailer combination.
The semi-tractor trailer combination will represent Biodiesel
Technically - A fatty acid chain connected to a methanol molecule is called a "Fatty-Acid Methyl Ester", or commonly called Biodiesel
Methanol is just one alcohol among many that can be used to make Biodiesel. Biodiesel can also be made from Ethanol and other alcohols. Methanol is the most commonly used alcohol because it works extremely well and it's relatively inexpensive in comparison to other alcohols. For the purpose of this analogy, we'll be using Methanol.
As we noted above, some trailers can be different lengths, have different amounts of cargo in them, and can weigh more than other semi trailers.
Technically - Biodiesel can have fatty acid chains of different lengths and saturations (densities). This difference can effect such things as the gel point and energy content (commonly measured in BTU's) of the biodiesel.
If a semi trailer starts out long and has lots of cargo in it, just because it gets hooked up to a semi tractor won't change the semi trailer. It'll still be relatively long and still weigh the same.
Technically - When fatty acid chains hook up with methanol, the chain length is still the same and the "saturation" of the chain (how much cargo is in the semi) typically doesn't change either.
There are way's to change the length of the semi trailer as well as how much stuff is in it.
Technically - There are chemical ways to modify a fatty acid chain. Some include something called Hydrogenation; which will be discussed later
OK, back to the semi trailers, the wall, the semi-tractors, and the hitch breaker.
In order to "make Biodiesel", you have to bring in a hitch breaker to unhitch the semi-trailer from the cement wall. The trailer will then start rolling away from the wall as it becomes unhitched. The semi-tractor pulls up, hooks up to the semi trailer, and pulls away.
Technically - The catalyst breaks the bond between the fatty acid chain and the glycerol. The methanol then attaches to the fatty acid chain forming Biodiesel.
Now, our hitch breaker can only unhitch one trailer at a time and tends to like to do things evenly. He'll run from one 3 semi/cement wall combo to the other unhooking just one trailer & then heading off to another combo.
Technically - Catalyst doesn't break all the bonds on a tri-glyceride at once. It starts by breaking off one fatty acid chain first. The methanol attaches to the fatty acid chain and the process repeats. As this occurs the catalyst strips the three fatty acid chains down to 2 , then one, and then removes the last bond.
In general, tri-glycerides break down into di-glycerides first, then into mono glycerides, and then into just a glycerol molecule.
Methanol molecules only attach one at a time as well. The oils like to break down as evenly as possible, so first a large majority of the tri-glycerides convert to di-glycerides. The fatty acid chains attach to methanol and you have biodiesel.
At any given time during the reaction your "mixture" of biodiesel, mono-glycerides, di-glycerides, and tri-glycerides can vary.
You may start off with
Tri-Glycerides - 100%
Di-Glycerides - 0%
Mono-Glycerides - 0%
Biodiesel - 0%
Glycerol - 0%
And then move slowly from the top to the bottom.
Tri's turn into di's....and some biodiesel gets formed.
Di's turn into mono's...and more biodiesel gets formed.
Mono's then turn into just glycerin...and the rest of the biodiesel gets formed.
In a perfect world, all of the fatty acid chains will attach to methanol and you'll be left with just biodiesel and glycerin. But, the world isn't perfect....more on that later.
Back to the semi's
As the hitch breaker unhitches the trailers from the wall, some will naturally roll away from the wall, but, there's nothing really from keeping the trailers from rolling back into the hitches on the wall.
Technically - Even though the catalyst can break the chemical bond between the glycerin and the fatty acid chain, the fatty acid chain can still re-attach to the glycerin molecule again.
To keep the semi trailers from "rehitching" back up to the wall, we bring in LOTS of semi tractors. In fact, we will bring in almost double the amount of semi tractors to the number of trailers to be hitched to. This is to ensure that as soon as a trailer gets unhitched and starts rolling away from the wall a semi-tractor has a chance to get between the trailer and the wall and hitch up.
When everything is said and done, we'll still have some semi-tractors left over that didn't get to connect to the trailers. But that's ok, we wanted to make sure we had enough to keep up with our hitch breaker (who by the way is really quick at unhitching trailers).
Technically - We use excess methanol to "push" the chemical reaction along. In a perfect world, we'd only use enough methanol needed to connect to each fatty acid chain. However, because the fatty acid chains can re-attach to the glycerin molecule, we "over do it" with the methanol.
The majority of the excess methanol will end up in the Glycerin. Some of it will also wash out when the biodiesel is washed.
So, in summary
3 Semi Trailers hooked to a wall make up oil.
Unhitch the trailer (with a catalyst) and hook it up to a semi-tractor (methanol), and you've got Biodiesel.
To unhitch the trailers, you have to do it in an even fashion and you risk not getting all of them, so we bring in more semi's than needed.
...next time we'll discuss free-fatty acids already in the oil (trailers that came unhooked without the hitch breaker).
If any of you see a mistake in any of this, please feel free to post a correction to it.
When we're all done, I'll create a nice article with pictures similar to the one I did for the overall biodiesel reaction.
That way we'll have a nice way of explaining the reaction to people so that it's easily understood.
Graydon, I enjoyed reading your analogy.
and per your request I add a couple of observations.
The trailers and conc' blocks just set around and do nothing until the semi-tractors arrive.
However, before the tractors arrive, a group of "hookers" jump into the tractors. One hooker will team up with a small group of tractors. It is the hookers job to 1) reach out from the tractor and unhook the the trailer from the conc' blocks; 2)hold onto the, now unhooked, trailer until...; 3) he hooks the trailer to a tractor from the group of tractors that he started with, and 4); leaves the newly connected tractor and trailer and rejoins his group of unconnected tractors.
[Mixing a small amount of catalyst (hookers) with a large amount of methanol (tractors) speeds the reaction.]
Now these hookers are funny. The hookers union requires them to immediately leave their tractor group and permanently attach themselves to any free trailers that may have broken from the trailers and blocks before the tractors arrived. It is up to the yard manager to manage the situation by either 1) ensuring that no free trailers are present when the tractors arrive (this is possible, but very impractical), or 2) assign a few "sacrificial hookers" to ride with the tractors into the trailer area. Once the "sacrificial hookers" have hooked up with a trailer, then the rest of the operation can proceed as planned.
If you assigned more "sacrificial hookers" than needed for the number of free trailers, then the extra "sacrificial hookers" will just stay joined with a group of tractors and do their regular duties.
However, if you under-calculated the number of free trailers, then all of the "sacrificial hookers" and some of the regular hookers will hook to a free trailer. The problem with this is after hooking to the free trailers, there may not be enough regular hookers left to perform the normal operation.
[When calculating the amount of catalyst two factors must be considered. 1) the base amount and, 2) the titration amount. At the start of the reaction any FFA present will immediately react with the catalyst to form soap. That catalyst is then no longer available to the main reaction].
On another point about the hookers. They are lazy. As the operation of breaking the trailers free from the concrete and hooking to a tractor proceeds, a lot of "free" concrete blocks start to appear. The hookers have a tendency to just jump onto a free concrete block, and try to avoid any further work. However, by keeping the activity level high and making the tractors work very very close to the trailers still connected to concrete blocks, then a hooker can be shook loose and made to unhook and hook tractors to a few more trailers.
[At the end of the reaction most of the catalyst winds up in the glycerol. Higher mixing intensity, higher operating temperatures, and longer reaction times may be needed to achieve good conversion.]
The final point about the hookers. If you set up your yard operations so that you only provide one tractor for each trailer, then problems arise at the end of the operation. Near the end of the reaction there are so few tractors left to attach to the few trailers still connected to the concrete blocks that the hookers will actually "unhook" a tractor from a trailer and "re-hook" the trailer to a concrete block. You could try to remove the free concrete blocks as soon as the last trailer is unhooked, but you would also remove some of the lazy hookers that are still needed to complete the reaction.
[Excess methanol is needed to drive the reaction to completion. Continual removal of the glycerol during the reaction results in less conversion per Dr. Van Gerpen's grad student in an Iowa state thesis.]
Graydon, this is sophomoric, but somewhat fun.
I think the chemistry is simpler to understand!
Yep, I'm with Bob... Chemistry complicated... Analogy more complicated...
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lol. I thought it was just me.
One problem with using the semi analogy is that not everyone understands trucking terminolog, or is familiar with trucks. So you're replacing one thing people have difficulty visualising, with another. I admire the effort however.
I posted this in another thread. It's about the simplest (and thus incomplete) description I can give of what you do when you make biodiesel. It was done mostly to try and highlight the difference between transesterification, and simply removing a contaminant in the oil (or blending something into it).
I've edited it slightly.
In the oil molecule, the three pieces that break off to form biodiesel, are long chains of atoms. Each chain is connected at one end to a central molecule, which is much smaller.
There are many different oil molecules.
What makes the oil molecules different from each other is the particular chains that are attatched to the central molecule, the size and shape of these chains can vary.
What makes the various vegetable oils (canola, sunflower etc) different from each other, is which types of oil molecules they contain, and in what ratio.
The central molecule is the part that becomes the glycerol molecule after the reaction. This part is ALWAYS the same, regardless of the oil molecule.
A diglyceride, is an oil molecule that has only two chains attatched, as one chain has been removed.
A monoglyceride only has one chain remaining (2 have been removed).
A free fatty acid is a chain that is floating around on it's own (that has had an oxygen and a hydrogen attatched to the end where the central molecule was previously.)
An ester (biodiesel molecule) is one of the chains that has broken off, with an alcohol molecule added where the central molecule used to be.
Some of the best laymans terms I've seen!
Ok, you guys seem to have great imaginations...
How about water in WVO, and making soap?
(Can't wait for this analogy!)
Water is like a little gang of trailer thieves (more water - more thieves). If thieves get close to the trailer-concrete block connections, then the thieves will work to break the connection. They work fairly slowly. Given enough thieves or enough time, then they can steel a lot of trailers.
As we learned earlier, a hooker always jumps onto a free trailer and claims it as his own.
This frees up the thieves and they start on another trailer-concrete block connection.
[Water in the reaction causes hydrolysis to occur. Water and heat work to break a FFA from its glycerol backbone. The FFA combines with catalyst to form soap while the water is released to hydrolyze more FFA.]
Bear with us...once the analogies are complete, it'll look better as I'll put it into a visual diagram.
Trailers work nice also later on because they make explaining saturation, hydrogenation, and other issues a little easier as well.
Once I have the visuals put together it'll also help quite a bit too.
Thanks for sharing...this is great stuff.
Thanks as well for the info.
That was GREAT producer!
But you just killed my visual on the "hookers".
Graydon, when you make up the visual presentation, do you think you could find a place for Producers hookers? I've always liked hookers and would really like to see a few more of them associated with biodiesel. Besides, they fit in so well with the whole truck idea! But please make them the young and cute kind, not the old skanky yard lizzard type you see in so many truck stops!
I've noticed the price of hookers coming down lately, whew!
That was hilarious!
If the hookers do all our work for us, does that make us pimps?
That's one of the funniest replys I've seen in this forum..
I'm laughing to hard to type.
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Truckers do love hookers.
Don't forget to add something abouT mixing energy.
Some mixing is like a NASCAR Race. Lots of cars racing around a track with small position changes as car pass and are passed.
(Swirl type mixing in a tank. Ok, but not great)
Mixing should be like a multicar car pileup. Cars "T-boneing" each other, some shooting down into the infield, others hitting the outside wall and bouncing back onto the traffic, while others go ballistic and hurtle through the air and come crashing down on other cars.
Ideally, mixing should look be like a "bumper car" ride from the carnival. Each car endlessly crashing violently into anything it gets near.
Now, if you let the hookers drive, you may have a winning analogy..........or not.
I can see a cartoon or animated short film coming together! I can hear the pneumatic brakes, diesel engines revving, and trucker horns. Instead of "Optimus Prime" (transformers), the main guy could be "Optimum Triglyceride."
Remember the cartoon from school in government class: "I'm just a bill... sittin' here on Capital Hill."?
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It OK. Welcome to the forums. You are now among friends.
Man that was funny...
Here is a question. If most of the hookers are tossed away and end up on skid row. Why cant the be taken back and used again?
[if most of the catalyst ends up in the glycerol, why cant we get it back. And why is the glycerol not caustic? And why when making soap do we need to add more catalyst?]
I really "get" the process and understand that the catalyst is just that... something that is used for the reaction but is not part of the end product (unless you are making soap, when I would guess its not a catalyst because it ends up as part of the soap).
What I don't seem to get is where is the catalyst in the glycerol mixture of soap, methanol, chicken parts, glycerol, and catalyst? And again... If there is (I believe and know there is) so much catalyst why more to turn it to soap? I would think you would actually need more oils to use the glycerin to make soap. (but I know you have to use the catalyst... because, I make soap)...
Anyway, Man the above is funny! I can't wait to see it done up like a pixar production!
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Oh man, now THAT analogy (NASCAR) wins the prize in my book! I'm a rabid NASCAR fan!
That was just awesome!!
Home of the Semi turned hooker turned NASCAR race analogy
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