Soapstock Acid Oil

About This Product

Soapstock acid oil is the generic acidulated residue of vegetable oil refining, sold without reference to a single crop. Sulphuric acid splits the soaps in refinery soapstock back into free fatty acids, which separate as a dark oil layer above the acid water. For a biofuel producer it is the cheapest fatty feedstock available and the one that most tests a plant. The attraction is classification: as a refining residue it counts as a waste stream under RED II and comparable schemes, earning incentives reserved for non-crop feedstocks at a fraction of virgin oil cost. The difficulty is that its composition is not fixed. Free fatty acid runs from 50 to 90 percent depending on what the source refinery was processing, with neutral oil, moisture, unsaponifiables, phosphatides and sulphate making up the balance. A pretreatment train sized for the average parcel will fail on the worst, so plants running it design around the extremes and analyse every delivery. Processing follows from the acidity. At these levels alkali transesterification is impossible, as caustic saponifies the free acids rather than catalysing, so the routes are acid esterification, pre-esterification ahead of transesterification, or hydrotreating. Residual sulphuric acid corrodes ordinary steel and the sulphur poisons hydrotreating catalysts. Bio Green Fuels supplies soapstock acid oil against a lot analysis covering free fatty acid, moisture and impurities, unsaponifiables, sulphur, sulphate and iodine value.