Soapstock Acid Oil

About This Product

Soapstock acid oil is recovered from the chemical refining of crude vegetable oils. When a refinery neutralises crude oil with caustic soda, the free fatty acids become sodium soaps, which are centrifuged off together with entrained neutral oil, phospholipids and water. That wet, alkaline soapstock is then acidulated, usually with sulphuric acid, which turns the soaps back into free fatty acids; the oily layer separated from the acid water is sold as acid oil. This product covers acid oil from mixed or unspecified vegetable-oil soapstocks, as distinct from single-source soybean, rapeseed or sunflower acid oils. Because FFA typically runs at 50–80 %, soapstock acid oil cannot go straight into an alkaline biodiesel reactor. FAME producers esterify it with methanol over an acid catalyst, or glycerolyse it, and may distil the resulting ester to reach EN 14214. HVO and SAF producers can accept the high acidity, but acid oil tends to carry phosphorus, sodium from residual soap and sulphate, all of which must be removed in pretreatment ahead of the hydrotreating catalyst. Many buyers blend acid oil into a wider feed slate rather than running it neat. Acid oil is usually traded on total fatty matter (TFM), commonly 90–95 % or more, with an MIU maximum often in the 3–5 % range and FFA reported. Sulphur deserves particular attention: incomplete washing leaves residual sulphuric acid and sulphate, which can push sulphur from tens to hundreds of mg/kg. Iodine value depends on the refinery's crude slate, so a mixed-source lot may vary from one delivery to the next. Phosphorus, metals, chloride and, for HVO, nitrogen are added as the route requires; polyethylene is rarely an issue with refinery residues. Acid oils are not named in Annex IX of the Renewable Energy Directive. Under RED III they are discussed in some markets as processing residues and in others as co-products, their treatment varies between Member States and voluntary schemes, and some aviation and national schemes restrict them. Buyers should confirm the classification their authority will accept, and the scope of the certificate behind the lot, with their certification body. For mixed-source material, traceability should identify the refinery or refineries that produced the soapstock and support the buyer's mass-balance entries. Acid oil is dark, acidic and mildly corrosive. Stainless steel or suitably lined ISO tanks are preferred, and flexitank providers should confirm that the liner and valve are compatible with a high-FFA, possibly acidic cargo. It usually remains pumpable at moderate temperatures but thickens in cold weather, so gentle heating may be needed for discharge. Bulk parcels move as MARPOL Annex II cargoes, with vessel type and previous-cargo rules to check. In an enquiry, give your TFM basis, maximum MIU, sulphur and phosphorus limits, the pretreatment you run, whether mixed-source material is acceptable or a single source oil is required, the volume, packaging and delivery terms, and the sustainability documentation you need.