The invention discloses a method for preparing
methionine and recovering a by-product-
carbon dioxide. The method comprises the steps that a
methionine salt and
carbonate mixed solution obtained by hydrolyzing methylmercapto-ethyl
hydantoin with alkali is filtered through a microporous membrane, and then filtrate is delivered to a bipolar membrane
electrodialysis system to be subjected to
electrodialysis treatment, so that acid liquor A and alkali liquor A are obtained; the alkali liquor A is treated continuously and cyclically, and the acid liquor A is subjected to gas-liquid separation, so that gaseous
carbon dioxide and acid liquor B are obtained; the acid liquor B is delivered back into the bipolar membrane
electrodialysis system to be subjected to cyclic treatment till the pH value of the acid liquor B is 3.8-4.5, the reaction is completed, a
methionine solution is prepared, and the methionine is prepared through concentration and
crystallization of the methionine solution; the gaseous
carbon dioxide is introduced into an
absorption cell, and carbon dioxide on the upper portion of the
absorption cell absorbs
mother liquor, is subjected to
membrane distillation and concentration and then is circulated back to the
absorption cell;
carbonate crystals are grown at the bottom of the absorption
cell and guided out from the bottom of the absorption
cell; and
carbonate is recovered through
solid-liquid separation. According to the method for preparing the methionine and recovering the by-product-carbon dioxide, the gaseous carbon dioxide is recycled, so that carbon emission is reduced, and
energy resources are saved through the
membrane distillation technique.