Moving from lab to the scale upThis is a featured page


The following is from Keith the best web site on Biofuel



Moving on to bigger things

When you're confident that you can get good results every time, even using oil from different sources, then it's time to scale up the process to provide your fuel needs. Now that you have a feel for the process and know what to expect, you'll have a much better idea of what sort of processor you want than if you'd started off building the processor (as many do) rather than learning the process first.
    "Understanding of the process is vital to operate the plant." -- Prof. P.V. Pannir Selvam, Technology Center, Department of Chemical Engineering, Universidade Federal do Rio Grande do Norte (UFRN), Brazil, Biofuel mailing list, 15 Apr 2007
See Biodiesel processors.

However, one-litre test batches are not just something for beginners. It's a basic technique you'll always use. Many experienced biodiesel makers do test batches with each batch of oil. Many not only titrate the oil every time to calculate the right amount of lye to use, they also do "bracket" tests in sequence, followed by wash tests. You learn a lot that way, your fuel gets better, life gets easier.

In fact life is already easier -- people who start off making 40-gallon batches often never learn the accuracy and discipline that comes from making one-litre test batches first. Their fuel quality suffers for it, and when they encounter that inevitable "problem batch", they suffer for it too.

But if you've followed the instructions here carefully, you'll be familiar with all the variables, you'll have good methodology, and you'll be in a much better position to trouble-shoot a problem batch successfully.

Keep a Biodiesel Journal -- make notes, keep records. Get some small glass jars and keep samples of all your batches, clearly labelled and cross-referenced to the notes in your journal. You won't regret it.

When scaling up from small test-batches to a full-sized processor, be aware that the process will probably need some adjusting. All the various processing methods use averages and approximations because processors vary so widely. Blenders especially agitate much faster than any full-scale processor, a real processor will probably take longer to achieve the same result. Use the fuel quality tests to fine-tune it to your particular processor. See Scaling up.

Removing the water

Water in the oil will interfere with the lye, especially if you use too much lye, and you'll end up with jelly. Test first for water content -- heat half a litre or so of the oil in a saucepan on the stove and monitor the temperature with a thermometer. If there's water in it it will start to "snap, crackle and pop" by 50 deg C (120 deg F) or so. If it's still not crackling by 60 deg C (140 deg F) there's no need to dewater it.

See Mike Pelly's recommendations: Removing the water.

Here's another way, from Aleks Kac -- it uses less energy and doesn't risk forming more Free Fatty Acids (see below) by overheating. Heat the oil to 60 deg C (140 deg F), maintain the temperature for 15 minutes and then pour the oil into a settling tank. Let it settle for at least 24 hours. Make sure you never empty the settling vessel more than 90%.

Here's what Biofuel mailing list member Dale Scroggins says about water removal:
    Water in vegetable oil can exist as free water, which will eventually settle to the bottom of a vessel; as suspended droplets, which may settle if the oil is heated, or the droplets are coalesced; and as water in solution with other impurities in the oil. Free water is the easiest to remove. The droplets are removed most efficiently by coalescing and draining. Suspended droplets that cannot be coalesced and water in solution are more problematic.

    Boiling off the water is more difficult than it appears on the surface. Colligative properties of solutions (and some mixtures) can make removal of the last traces of water almost impossible. Water mixed with oil will not boil at the same temperature and pressure as pure water. As water is removed, more heat or lower pressure will be required to remove more water. If the oil contains salts or semi-soluble fatty acids, distillation is even more difficult.

    As the percentage of water in the solution decreases (its molar fraction) its vapor pressure will continue to drop. Lowering pressure in the system alone may be insufficient to sustain vaporization when the solution becomes concentrated (the molar fraction of the solute greatly exceeds that of the solvent). Results will vary depending upon the nature of the water-soluble impurities in the oil. Few solutions are ideal, in terms of Raoult's law, and in used vegetable oil, there is no way to know what solutes are in the oil.
The important thing is how well-used, or overused, the oil is. Titration will tell you that. The higher the titration result, the more water it's likely to contain, and the more difficult it will probably be to remove the water.

Start with heating to 60 deg C and settling, as Aleks Kac recommends, and if that doesn't give satisfactory results, try boiling it off, as Mike Pelly recommends. Then try processing small test batches of a litre or less first. If you still have difficulties, try to find better-quality oil.

Washing

Biodiesel must be washed before use to remove soaps, excess methanol, residual lye, free glycerine and other contaminants. Some people (fewer and fewer of them) say washing isn't necessary, arguing that the small amounts of contaminants cause no engine damage.

Read what the Fuel Injection Equipment (FIE) Manufacturers (Delphi, Stanadyne, Denso, Bosch) have to say about these contaminants:
Summary -- html
Full document -- Acrobat file, 104kb

See also: Determining the Influence of Contaminants on Biodiesel Properties, Jon H. Van Gerpen et al., Iowa State University, July 31, 1996 -- 12,000-word report on contaminants and their effects. Acrobat file, 2.1Mb:
http://www.biodiesel.org/resources/reportsdatabase/reports/gen/gen014.pdf

Myth:
    > I did notice that a lot of the chemistry in the book was wrong.
    > His main argument seemed to be against losing the energy in
    > the methanol that was washed out.

    The "energy" does you no good if your particular thermodynamic cycle can't take advantage of it. What is the cetane rating of methanol?
    -- Ken Provost, Biofuel mailing list, "Re: washing?"
Quite so. The cetane rating of methanol is only 3, very low. Low cetane-number fuel in a diesel causes ignition delay and makes the engine knock. The high-speed diesel engines in cars and trucks are designed to use fuels with cetane numbers of about 50. The US biodiesel standard specifies a cetane number higher than 47, the EU standard specifies higher than 51. The methanol in unwashed biodiesel doesn't "make a great fuel anyway". It's also very corrosive. The EU biodiesel standard specifies less than 0.2% methanol content.

Quality biodiesel is well-washed biodiesel. Filtering it is no use, and letting it settle for a few weeks won't help much either. Anyway washing the fuel is easy.

See Washing


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