Patent ID: 7309403

Claim:
A method of avoiding corrosion of a distillation plant for the separation of methylamines from a product stream which is obtained in the preparation of methylamines by gas-phase reaction of methanol and ammonia and which comprises monomethylamine, dimethylamine, trimethylamine, ammonia and methanol as components, wherein the separation comprises the steps of; distilling the product stream in a first distillation column to separate off ammonia, feeding the remaining components of the product stream obtained as bottoms to a second column, carrying out an extractive distillation with introduction of water to separate off trimethylamine in the second column, feeding the further components of the product stream obtained as bottoms from the second column as feed to a third column, separating off monomethylamine and trimethylamine in the third column, and separating the monomethylamine and dimethylamine by distillation in a fourth column, wherein alkali metal hydroxide is added to the second or third column to prevent corrosion in the distillation plant.