Soapstock

Soapstock is a byproduct generated during the refining of edible oils and fats. It is a viscous, dark brown to black material that consists primarily of free fatty acids, phospholipids, gums, pigments, and other impurities removed from the crude oil. The process of refining typically involves alkali treatment, where a caustic solution is added to the crude oil to neutralize free fatty acids and remove other undesirable components. This neutralization reaction creates soap molecules, which then emulsify with the impurities and oil, forming soapstock.

The composition of soapstock can vary depending on the type of oil being refined and the specific refining process used. For instance, soybean oil soapstock will differ in composition from palm oil soapstock. Historically, soapstock was often considered waste material and disposed of. However, due to its fatty acid content, it has found several industrial applications.

Soapstock can be further processed to recover valuable components. Acidulation, a process where acid is added to break down the soaps, allows for the separation of fatty acids. These recovered fatty acids can then be utilized in various industries. Applications include their use in the production of animal feed, as a component in the manufacture of soaps and detergents, and as a feedstock for biodiesel production. In some cases, soapstock is also used as a raw material in the production of lubricants and asphalt. The economic viability of these applications depends on the market price of the recovered components and the cost of processing the soapstock.