A few years ago I released my first new method for base-catalysed biodiesel manufacture ( Imisides-Pyne ) using a heterogenous catalyst. Due to the cost and logistical difficulties involved in the use of a heterogenous catalyst, however, I never actually used that method and went on to develop another new method using a homogenous catalyst.
Having now used this method for a couple of years, and decided that it has no commercial value (as it will never replace the commercial acid/base process), I now release it for public consumption.
This method has two advantages over the conventional base-catalysed transesterification process:
1. It is foolproof (no titration required)
2. It proceeds at room temperature.
In principle, this differs from the conventional method in that it modifies the methoxide solution by the addition of a drying agent (calcium oxide, or Quicklime). This removes water and pulls the equilibrium to the right, thus resulting in a far higher concentration of methoxide, which speeds up the reaction kinetics such that heating is not required.
Here are the reactions:
1. MeOH + OH- ↔ MeO- + H2O
2. H2O + CaO → Ca(OH)2
Adding the two reactions together we get
3. MeOH + OH- + CaO → MeO- + Ca(OH)2
Note that reaction 1 is an equilibrium. The addition of the CaO removes the water, thus pulling the equilibrium to the right and greatly increasing the methoxide concentration. The obvious implication of this is that since you no longer need to worry about forming emulsions from water in your reaction mixture, you can add as much base catalyst as you want.
Dissolve about 10% w/v KOH in methanol – for example, 2kg KOH in 20L MeOH. Caution – depending on how quickly you add it, this may get hot enough to momentarily boil the MeOH – make sure there are no naked flames in the vicinity.
Now, add the CaO and stir vigorously for several minutes. Since this process is heterogenous (the CaO doesn’t dissolve), vigorous stirring is required to allow as much contact as possible with the water in solution. I generally stir for a good 5 minutes.
Now allow it to settle. Most of it will settle out quickly, but the fines take a lot longer. I generally allow two days for it to settle. How much CaO do you use? I generally use about two shovels full in 20L so that when it settled it was about an inch thick on the bottom.
Now just add the methoxide solution to the WVO in your normal quantities at room temperature. I generally use a mixing ratio of 100:15. Depending on how cold it is and your stirring setup you may need to heat the oil a little to thin it out enough for your stirrer to stir it adequately. The reaction is mildly exothermic and the temperature should increase by about 6°C. The reaction appears to go to completion in 10 minutes but I generally let it react for an hour. Let it settle for a day and tap off the sludge in the bottom that contains the glycerol, KOH and fatty acid salts.
After the initial reaction and settling period, a small amount of reaction products remain in the biodiesel due to residual methanol. When the methanol is removed, they fall to the bottom and may be isolated. There are probably several ways to do this, but due to the highly alkaline nature of the reaction mixture, water washing is not one of them.
I use air purification and just use a small aquarium pump to bubble air through the product for several weeks before using it (there is plenty of information around on other air washing setups). Against the biodiesel background, methanol has a characteristic acrid odour that you can quickly train yourself to recognize, and so a smell test can help work out whether the product is ready or not. The surest result, however, is if you just allow plenty of time for the MeOH to evaporate.
1. Quicklime is not easy to get your hands on, unlike hydrated lime, or Ca(OH)2 – don’t get the two mixed up. Although it’s made and used by the truckload in cement factories, since it has no common domestic use it is generally not sold in hardware stores or chemical suppliers. Ideally, you’re looking for a cement factory that has a retail shop, but they aren’t that common. For those of you in Melbourne it’s easy – just go for a drive up to the Unimin factory in Lilydale on a Saturday morning and you can buy it over the counter. For those of us here in WA, Cockburn Cement don’t retail to the public, but I found a mob up in the northern suburbs (Susac Lime) who said they could get some of the Cockburn product for me.
Note – Quicklime does not store well. It is very dry and will absorb water on storage. The best way to store it is to transfer it to a sealed container where it can be isolated from atmospheric moisture.
2. The methoxide solution is unstable (presumably due to carbonation) and must be freshly made for each batch
3. This method is not optimized. The initial recipe that I tried worked immediately so I didn’t bother experimenting with it further. It may be possible, for example, to get away with a lower concentration of KOH or less lime.
4. By publishing this method on the web it is now in the public domain, so you are free to redistribute it wherever you wish. My only request is that you ensure that my name is attached to the method.
Simple schematic for a pump and heater control with a high limit
Sensor for the biodiesel/glycerin layer
Interesting; thanks for sharing.
There's lots of talk about different types of lime here lately. Did you check out this thread? http://biodiesel.infopop.cc/ev...9605551/m/3397000933 You might have some interesting viewpoints or experience to contribute there as well.
I wasn't able to access any of the articles, but it appears that they are using hydrated lime as a heterogenous catalyst.
The reason for this is pretty easy to understand - hydrated lime is a very common industrial base and is much cheaper than NaOH. It is used in preference to NaOH in the waste management sector, not only because it's cheaper, but because it also adds weight to any settled flocs that you're trying to create.
It also has the advantages that as a heterogenous catalyst it will probably sop up some of the water that is formed (by adsorption) and also adds weight to the settling phase (glycerol).
Chemically, it wouldn't work as well as potassium carbonate (my first method) as the K2CO3 avoids the creation of water completely, but the lime would probably work well enough and would be a lot cheaper.
Heterogenous catalysis has a lot going for it - the glycerol sticks to the catalyst like glue, resulting in very fast separation - the only problem is engineering - how you get the settled catalyst/glycerol mass out of the bottom of the reactor.
But of course, they have to be heated. The room temperature method that I have presented here is so simple that you could make it in a big plastic bucket.
Now that the cold has settled here in the northern hemisphere we can think about next seasons bio batches.
1. If the methoxy is allowed to settle before adding to the reaction wouldn't most of the CaO sludge be left behind in the methoxy container? Decant the methoxy needed for the Biodiesel reaction from the top. This would leave some fines in the bio/gly but that could be drained with the glycerol via a GL1 setup.
2. Could whole batch demething be performed on the above biodiesel/glycerol/residual CaO fines mix before draining without releasing the water from the CaO into the bio?
3. Can the CaO sludge remaining in the bottom of the methoxy container be used over again?
4. Wouldn't the amount of CaO needed equal the number of moles of base used to make the methoxy?
Saint Paul, Mn.
Here is a thread on this Failed Miracle method of Dr.Egotrips.
The guy that did all the testing and wrote the report is a very close friend of mine.
If he told me little green men had landed in the back yard I wouldn't even check before going to get my camera and a gun.
No one would like to find a shortcut to the bio making process more than my mate, hence why he went to the trouble of doing the tests.
I guarantee if he can't make it work, it will take a miracle for anyone else to.
Contrary to the above, readers might be interested in the following paper which reviews recent investigations of solid catalysts and notes CaO, aka. quicklime, as a good candidate to be used ALONE in making biodiesel.
metal oxide catalysts
Also this other article
which notes how Ca(OH)2 forms a Ca-methoxide on its surface, kind of explains how a solid catalyst which does not dissolve into the methanol still has a chemical effect.
treatment of hydrated lime with methanol
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