Biodiesel & Alternative-Fuel Tanks
Tank selection for biodiesel and alternative-fuel production and storage: which materials handle the process temperatures, chemical compatibility with methanol, catalyst (KOH/NaOH) and glycerin, flammable-storage code considerations, and where polyethylene fits.
Biodiesel and other alternative-fuel processes need a range of storage and process vessels, not one tank. A typical setup includes raw feedstock storage, final product storage, reaction tanks, water-wash tanks, neutralization tanks, and wastewater treatment tanks. Choosing the right material for each comes down to the chemicals it will see and the temperature it runs at.
Material by Temperature
- Polyethylene — the preferred, lowest-cost choice for the low-temperature side of the process, service up to about 140°F.
- Fiberglass (FRP) — handles higher process temperatures, up to roughly 180°F.
- Stainless or carbon steel — for service above 180°F, where plastics and FRP are past their range.
Polyethylene tanks resist all aspects of the low-temperature (up to 140°F) biodiesel manufacturing process, which is why poly is so common for reaction, wash, and storage vessels on smaller and mid-size systems. Plastic tanks also cut cost and simplify installation compared with steel at these temperatures.
The Process, in Brief
Biodiesel is most often made by a base-catalyzed reaction. The catalyst splits the oil (feedstock) into glycerin and biodiesel. The catalyst is typically a potassium hydroxide (KOH) or sodium hydroxide (NaOH) and methanol solution. The oil-and-catalyst mixture is held just above the boiling point of the alcohol to speed the reaction, with reaction times commonly running from two hours up. After the glycerin and biodiesel phases separate, the excess alcohol is recovered.
Chemical Compatibility Notes
- Methanol — compatible with polyethylene in this service. Cross-reference the Chemical Resistance Chart for your exact concentration and temperature.
- KOH / NaOH (the catalyst) — sodium hydroxide and potassium hydroxide are well within polyethylene's range at process temperature.
- Glycerin — the co-product, compatible with poly.
- Always confirm the specific chemical, concentration, and temperature against the resistance data before committing to a material, and check gasket and fitting materials separately from the tank shell.
Flammable Storage & Code
- Methanol is flammable. Contact your local fire officials about permit restrictions on methanol storage before you build out.
- Glycerin can also draw fire-official review depending on how much residual methanol it carries and the sophistication of your process.
- For flammable-liquid storage, UL-142 covers aboveground steel tanks fit for service with Class I flammables. Match the vessel rating to the code requirement for the fluid it holds.
Standards & Sizing
Polyethylene upright storage tanks are covered by ASTM D1998. Cone-bottom and closed-top vertical poly tanks are common on biodiesel skids for full drainage between batches. Tell us your process temperatures, the chemicals in each vessel, and your capacities, and we will help you match materials tank by tank. Contact us or request a quote to plan a biodiesel or alternative-fuel system.
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