Method for preparing fatty acid from fatty acid monomethyl ester

The invention relates to a method for preparing fatty acid from fatty acid monomethyl ester, which comprises the following steps: 1) in the presence of a catalyst consisting of p-toluenesulfonic acid and sulfuric acid, heating to react fatty acid monomethyl ester with water to generate fatty acid and methanol; and 2) promoting the reaction to be completed by supplementing water and removing methanol. The fatty acid can be obtained by catalyzing the hydrolysis of the fatty acid monomethyl ester under normal pressure by using a very small amount of catalyst, the reaction rate is high, the high-yield and high-purity fatty acid can be obtained, the process for preparing the fatty acid by using the fatty acid monomethyl ester is simple, the catalyst and methanol can be recycled, and the process cost is greatly reduced. 本申请涉及一种利用脂肪酸单甲酯制备脂肪酸的方法，包括如下步骤：1)在对甲苯磺酸与硫酸组成的催化剂存在下，通过加热使脂肪酸单甲酯与水反应以产生脂肪酸和甲醇；2)通过补加水和去除甲醇推动反应完成。本发明用极少量的催化剂便可在常压下催化脂肪酸单甲酯水解得到脂肪酸，反应速率快，并可得到高收率和高纯度的脂肪酸，且本发明利用脂肪酸单甲酯制备脂肪酸的工艺简单，并能回收利用催化剂和甲醇，大大降低了工艺成本。