METHOD FOR AVOIDING CORROSION

摘要

The invention relates to a method of avoiding corrosion in the separation of methylamine from a product stream ( 10 ) which is obtained in the preparation of methylamines by gas-phase reaction of methanol and ammonia and includes monomethylamine, dimethylamine, trimethylamine, ammonia and methanol as components, where ammonia is separated off by pure distillation in a first column ( 1 ), the remaining components of the product stream obtained as bottoms ( 12 ) are fed to a second column ( 2 ). Trimethylamine ( 14 ) is separated off in the second column ( 2 ) by extractive distillation with introduction of water. The further components of the product stream obtained as bottoms ( 15 ) from the second column ( 2 ) are fed to a third column ( 3 ), in which monomethylamine and dimethylamine are separated off at the top. The monomethylamine and dimethylamine are separated by distillation in a fourth column ( 4 ). To avoid corrosion alkali metal hydroxide is added to the second or third column ( 3 ).