Before understanding how alkali refining works, let’s first learn about what vegetable oil is. Vegetable oil, also known as base oil, carrier oil, or medium oil, contains no additives or preservatives and is extracted by cold pressing (extraction below 70°C). Common vegetable oils include: jojoba oil, sweet almond oil, grape seed oil, rosehip oil, argan oil, wheat germ oil, olive oil, etc.

Alkali Refining

The main purpose of alkali refining is to remove impurities from the oil, including free fatty acids, unsaponifiables, and residual phospholipids. The free fatty acids here are mostly high molecular weight fatty acids and unsaturated fatty acids, which are unstable factors in oil. Through the combination of free radicals, non-cyclic dimer mixtures can be formed. Free radicals can also undergo addition reactions with unsaturated double bonds, producing cyclic or non-cyclic compounds. The method of alkali refining is to add a certain amount of sodium hydroxide to the heated oil. Sodium hydroxide reacts with the free fatty acids in the oil to form sodium salts and water. The reaction formula is as follows:

RCOOH + NaOH → RCOONa + H2O

The sodium salts generated in the neutralization reaction are called sodium soaps (RCOONa), commonly known as soapstock, which are gelatinous precipitates that are not easily soluble in oil. Soapstock has strong adsorption capacity; it can adsorb proteins, mucilage, pigments, and other impurities in the oil. Then, methods such as adding hot water, standing, and centrifugal separation are used to separate the soapstock, water, and other impurities.