NOVELTY - L-methionine is produced by adding liquid alkali, D,L-methionine powder, and pure water into 1st chemical reaction kettle, stirring uniformly, sealing kettle, vacuuming sealed kettle, adding acetic anhydride into chemical reaction kettle in which raw material contains D,L-methionine powder:acetic anhydride:liquid alkali of weight ratio 14-16:19-21:25, 30% hydrochloric acid, pure water, active carbon, and bio-enzyme catalyst, concentration of liquid alkali is 20%, and weight ratio refined D,L-methionine powder:acetic anhydride:liquid alkali:pure water is 14-16:19-21:25:40, and stirring.    USE - Production of L-methionine for pharmaceutical preparation, nutritional supplement, feed additive (all claimed).    ADVANTAGE - Production method is simple and environment-friendly, reaction process is short under moderate reaction condition, operation is easy, and L-methionine product quality is good.    DETAILED DESCRIPTION - L-methionine is produced by adding liquid alkali, D,L-methionine powder, and pure water into 1st chemical reaction kettle, stirring uniformly, sealing kettle, vacuuming sealed kettle, adding acetic anhydride into chemical reaction kettle in which raw material contains D,L-methionine powder:acetic anhydride:liquid alkali of weight ratio 14-16:19-21:25, 30% hydrochloric acid, pure water, active carbon, and bio-enzyme catalyst, concentration of liquid alkali is 20%, and weight ratio refined D,L-methionine powder:acetic anhydride:liquid alkali:pure water is 14-16:19-21:25:40, stirring and sending steam to interlayer in 1st chemical reaction kettle, increasing temperature, sealing under condition of mixed liquid to micro-boiling until pressure reaches 2 atm, keeping temperature, slowly stirring and reacting for 11.5-12.5 hours, slowly adding 30% hydrochloric acid to reaction liquid through pump into crystallizing kettle, stirring and mixing until pH is 6, circulating cold water into crystallizing kettle interlayer, reducing kettle liquid temperature to 0-3 degrees C, cooling and crystallizing for 8 hours, centrifuging to separate solid and liquid and obtain 1st batch of crystal, returning filtrate to concentrating tank, concentrating to one half of volume of returned filtrate, crystallizing for 8 hours to obtain 2nd batch of crystal, combining 1st and 2nd batches of crystals, adding pure water which is 5 times the weight of crystal, stirring to completely dissolve, adding proper amount of hydrochloric acid to adjust pH of solution to 4, using constant temperature system for controlling temperature of material liquid at 35-40 degrees C, adding 1-2% crystal enzymatic reaction catalyst prepared using pig kidney extract, stirring uniformly, allowing to stand for 30 hours, adding proper amount of liquid alkali to adjust pH to 5.5, naturally cooling and stirring to crystallize product, transferring L-methionine crude product into 2nd chemical reaction kettle, adding 10 times of pure water, stirring uniformly, sending steam to 2nd chemical reaction kettle, heating to 70 degrees C, adding 1-2% active carbon to L-methionine to decolor and obtain L-methionine supernatant, transferring clear liquid into refining neutralized kettle, naturally cooling water, reducing temperature to 0-3 degrees C, maintaining constant temperature for 12 hours to obtain crystalline body of L-methionine, centrifuging crystalline body of L-methionine to separate into solid and liquid, drying wet L-methionine at 44-50 degrees C for 5-6 hours, crushing dried block material, packing and storing.