Method of preparing bio-polyols from epoxidized fatty acid esters

A method of preparing bio-polyols from epoxidized fatty acid esters comprising steps of:

• replacing amphoteric compound by using alkyl sulfonic acid, wherein the alkyl sulfonic acid are synthesized with Brønsted strong acid to produce Brønsted acid IL, a molar ratio of the alkyl sulfonic acid and the Brønsted strong acid is within 1.0 to 1.5;
• mixing the epoxidized fatty acid esters and the Brønsted acid IL at a predetermined ratio, adding alcohols for using as ring-opening reagent, thus producing reaction solution, wherein the reaction solution is heated within a temperature of 30° C. to 100° C. for 1 to 24 hours to cause ring-opening hydroxylation, wherein a molar ratio of the alcohols and the epoxidized fatty acid esters is within 4 to 20, and a molar ratio of the Brønsted acid IL and the epoxidized fatty acid esters is within 0.01 to 0.15;
• and
• extracting and layering the reaction solution by using deionized water to acquire upper-layer solution and lower-layer solution, wherein the lower-layer solution consists of ionic liquid which is concentrated and dried to recycle reusable ionic liquid, and the upper-layer solution consists of bio-polyols which are extracted by using the deionized water and alkaline water and then dehydrated.