| Brew it Yourself - Biodiesel |
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| Keith Addison, Journey To Forever | |||
| Friday, 29 June 2007 | |||
  There's a lot to be said for the great feeling of independence you'll get from making your own fuel. If you want to make it yourself, there are several good recipes available for making high-quality biodiesel, and they all say what we also say: some of these chemicals are dangerous, take full safety precautions, and if you burn/maim/ blind/kill yourself or anyone else, that will make us very sad, but not liable - we don't recommend anything, it's nobody's responsibility but your own. Methanol is the main or only ingredient in barbecue fuel or fondue fuel, sold in supermarkets and chain stores as "stove fuel" and used at the dinner table; it's also the main ingredient in the fuel kids use in their model aero engines. So get it in perspective, no need to be frightened. Where do I start? It's all quite simple really, thousands of people are doing it, very few of them are chemists or technicians, and there's nothing a layman can't understand, and do, and do it well. But there is quite a lot to learn. We've tried to make it easy for you. The process Vegetable oils and animal fats are triglycerides, containing glycerine. The biodiesel process turns the oils into esters, separating out the glycerine. The glycerine sinks to the bottom and the biodiesel floats on top and can be siphoned off. The process is called transesterification, which substitutes alcohol for the glycerine in a chemical reaction, using lye as a catalyst. We use methanol to make methyl esters. We'd rather use ethanol because most methanol comes from fossil fuels (though it can also be made from biomass, such as wood), while ethanol is plant-based and you can distil it yourself, but the biodiesel process is more complicated with ethanol. Ethanol (or ethyl alcohol, grain alcohol) also goes by various other well-known names, such as whisky, vodka, gin, and so on, but methanol is a deadly poison: first it blinds you, then it kills you, and it doesn't take very much of it. It takes a couple of hours, and if you can get treatment fast enough you might survive. (But don't be put off - it's easy to do this safely. Safety is built-in to everything you'll read here.) Methanol is also called methyl alcohol, wood alcohol, wood naphtha, wood spirits, methyl hydrate (or "stove fuel") - all the same thing. Methylated spirits (denatured alcohol) doesn't work; isopropyl alcohol (rubbing alcohol) also doesn't work. The lye catalyst can be either sodium hydroxide (caustic soda, NaOH) or potassium hydroxide (KOH), which is easier to use, and it can provide a potash fertilizer as a by-product. Sodium hydroxide is often easier to get and it's cheaper to use. If you use potassium hydroxide, the process is the same, but you need to use 1.4 times as much. You can get KOH from soapmakers' suppliers and from chemical suppliers. Other chemicals, such as isopropyl alcohol (isopropa-nol) for titration, are available from chemicals suppliers. CAUTION: Lye (both NaOH and KOH) is dangerous - don't get it on your skin or in your eyes, don't breathe any fumes, keep the whole process away from food, and right away from children. Lye reacts with aluminium, tin and zinc. Use glass, enamel, stainless steel or HDPE (High Density Polyethylene) containers for methoxide. Our first biodiesel We got about 60 litres of used oil from our local McDonald's. There were four 16-litre cans of it, a mix of used cooking oil and residual beef and chicken fats. Two of the tins were solidified, the other two held a gloppy semi-liquid. We warmed it up a bit on the stove and filtered it through a fine mesh filter, and then again through coffee filter papers, but it was quite clean - very little food residue was left in the filters. We'd also bought 10 litres of the cheapest new cooking oil we could find - we don't know what kind of oil it was, the tins only said "Cooking Oil" - and used this for our first experiment. It worked, but we've learnt a lot since then. Now it's easy to make high-quality biodiesel every time without fail. And we don't use open containers for processing now, and neither should you - and mix the methanol in closed containers too. Biodiesel from new oil Make your first test-batch using new oil (fresh and uncooked). Follow the instructions below, but use 1 litre of oil instead of 10 litres, and 200 ml of methanol instead of 2 litres, with 3.5 grams of lye. Check the quality of your biodiesel with this basic quality test. We used 2 litres of methanol to 10 litres of vegetable oil, and 3.5 grams of pure, granular lye (sodium hydroxide) per litre of oil - 35 grams for 10 litres. We mixed the lye with the 2 litres of methanol in a strong, heatproof glass bottle with a narrow neck to prevent splashing. It fumed and got hot, and took about 15 minutes to mix. (Use closed containers for mixing methoxide.) This mixture is sodium methoxide, an extremely powerful base which enjoys eating stuff like human flesh - take full safety precautions when working with sodium methoxide, have a source of running water handy. Meanwhile, we'd warmed the 10 litres of new oil in a steel bucket on the stove to about 40°C to thin it so it mixed better. In fact, 55°C is a better processing temperature. Don't let it get too hot or the methanol will evaporate. (Methanol boils at 64.7°C) Stirring well, we carefully added the sodium methoxide to the oil. The reaction started immediately, the mixture rapidly separating into a clear, golden liquid on top with the light brown glycerine settling out at the bottom. We kept stirring for an hour, keeping the temperature constant. Then we let it settle overnight. The next day we siphoned off 10 litres of biodiesel, leaving two litres of glycerine in the bottom of the bucket. Washing Biodiesel must be washed before use to remove soaps, excess methanol, residual lye, free glycerine and other contaminants.
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