The present invention discloses a method for separating and extracting 
isostearic acid from 
monomer acid. The present invention relates to a method for separating and extracting 
isostearic acid, in particular to a novel method for separating and extracting 
isostearic acid from 
monomer acid. The present invention provides a method for separating and extracting isostearic acid from 
monomer acid, which is suitable for use in commercial production. The method is characterized in: esterify the byproduct (monomer acid) obtain in production of 
dimer acid through bleaching earth catalytication process under 
medium pressure without catalyst to obtain monomer acid ester, treat by 
catalytic hydrogenation under 
medium pressure, and filter to obtain hydrogenised monomer acid ester; envelope with carbamide, filter, separate, and wash with water to obtain crude product of isostearic acid ester; perform molecular 
distillation to obtain refined isostearic acid ester, and then perform 
hydrolysis to obtain isostearic acid. Compared to the separation and extraction technique in the prior art, the present invention has the following advantages: the acidity and 
viscosity are low during hydrogenisation, and therefore the service life of catalyst is long, no 
nickel soap will be formed, and the 
corrosion to equipment is reduced; the product can be enveloped and separated by carbamide more easily; the 
distillation can be performed at a lower temperature; the 
iodine value of final product is low, the color is light, and the purity is high.