Process for purification of crude glyceride oil compositions

A process for purification of crude glyceride oil compositions comprising:

• (A) diluting a crude glyceride oil composition containing gum material and wax as main components of impurities, with an organic solvent,
• (B) bringing the diluted crude glyceride oil composition into contact with a semipermeable membrane having a molecular weight cut-off value of 10,000-20,000, comprising polyimide consisting essentially of a repeating unit represented by the general formula:
• ##STR5## wherein R.sup.1 represents a divalent organic group, under pressure to obtain a semipermeable membrane permeable liquid in which the gum material in the glyceride oil after removal of said organic solvent is 100 ppm or less, and subjecting the semipermeable membrane permeable liquid to acid treatment by adding at least one kind of acid or salt thereof selected from the group consisting of oxalic acid, citric acid, acetic acid, glacial acetic acid, phosphoric acid, sodium phosphate, sodium polyphosphate and sulfuric acid, wherein the amount of the acid added is 0.001 to 0.5% by weight based on the weight of the glyceride oil,
• (C) carrying out bleaching of the glyceride oil obtained from said semipermeable membrane permeable liquid with at least one kind of an adsorbent selected from the group consisting of clay, activated clay, activated carbon and bone black, wherein the adsorption treatment is carried out by dispersing the adsorbant in the degummed oil and heating to a temperature of 80.degree. to 120.degree. C. for five to sixty minutes with stirring under a reduced pressure of 1 to 200 mm Hg abs, and then
• (D) carrying out deodorizing to obtain a purified glyceride oil wherein the deodorizing is carried out by stripping the glyceride oil with sparge steam in an amount of 2 to 20% by weight based on the weight of the glyceride oil at a temperature of 240.degree. to 270.degree. C. under a reduced pressure of 1 to 10 mm Hg abs,
• wherein the cut-off value is a minimum molecular weight of a polyethylene glycol having a removal rate of at least 95%, as measured using toluene solutions of polyethylene-glycols having different average molecular weights at a temperature of 25.degree. C. and a pressure of 3 kg/cm.sup.2.