Rendered tallow (beef or mutton) and lard (pork) make excellent biodiesel when they are clean, dry and not rancid, but the fuel clouds at 12-16°C for tallow and 8-12°C for lard, so it gels in cold weather and suits warm climates or blending with vegetable-oil biodiesel. Animal fat is also food, soap stock and lamp fuel, so it competes with those uses in lean times.
Part of Biodiesel Production
Animal fat as a biodiesel feedstock: beef and mutton tallow and pork lard, rendered, filtered and reacted like vegetable oil.
Solid Fat Makes Solid-Prone Fuel
Tallow and lard are solid at room temperature, because their fatty-acid chains are more saturated than a vegetable oil’s. The same chains give a higher melting point to the biodiesel made from them. The parent’s cold-weather table puts the cloud point (where wax crystals first appear) at 12-16°C for tallow and 8-12°C for lard, against 0-2°C for sunflower and soybean and -3 to 0°C for rapeseed (Cold Weather Performance; the figures are the parent’s and are not sourced to a standard). The parent suggests blending 50/50 with vegetable-oil biodiesel.
What You Need
- Raw fat trimmed and rendered (the same rendering as for lamp fuel; see Rendering Fat for Lamp Fuel)
- Filtering cloth and a warm room for filtering while liquid
- A titration kit (Oil Preparation & Titration), because rancid fat has free fatty acid
- A reaction vessel that holds 55-60°C so the fat stays liquid
Method
Step 1: Render and strain. Melt gently, strain through cloth while hot and let it settle; pour off the water and skim impurities.
Step 2: Check it is fresh. Rancid fat has a high acid number and wastes lye, and rancid smell is the sign (Free Fatty Acid Problem).
Step 3: Titrate and react as for any oil, with the oil kept at 55-60°C so it is liquid when the methoxide goes in. Fat that sets as it cools will cloud the reaction; reheat if it does.
Step 4: Store fuel warm in cold weather, or blend it down before storing.
What The Fat Was Worth Before
Fat is food at 9 kcal per gram, so a litre of rendered fat (about 0.9 kg) is about 8,100 kcal of food. It is also the structural fat in hard soap (Fat Selection), candle and lamp fuel and leather dressing. The corpus’s soap guide notes that animal fat for soap competes with nutrition in lean times (Plant Oils); fuel adds a further competitor. The corpus has no sourced per-animal fat yield, so plan from what your own slaughter actually renders.
Common Mistakes
- Not keeping the fat liquid. A lump of cold fat in the vessel does not react and plugs the drain.
- Using high-FFA, old fat without testing. It makes soap.
- Forgetting the cold. Biodiesel from lard in a winter tank sets and plugs filters.
Hot fat and hot methanol
Rendering and reacting use heated fat; methoxide and heated fat in the same room means a burn and vapour hazard. Keep the methanol vessel sealed and outdoors, heat in a water bath rather than over a flame, and see Methanol Hazards.
What’s Next
- Learn next: Cold Weather Performance, for the cloud points and blending
- Combine with: Waste Cooking Oil, the vegetable-oil partner for a blend