Process for the production of pure methylal

摘要

The invention relates to a continuous process to make and isolate methylal by reacting formaldehyde and methanol with an acid catalyst under at least partial formation of methylal and water, to form a mixture M2 comprising formaldehyde, methanol, methylal, and water, separating the said mixture M2 in a distillation column B into three distinct product streams, one being a distillate taken from the column head BH which is rich in methylal, one taken from the column bottom stream BB being almost pure water, and one taken from the side of the column B below the reaction zone which stream is rich in methanol, characterised in that the ratio of the amount of substance of methanol to the amount of substance of formaldehyde in the mixture M1 is at least 3 mol/mol, and to an apparatus to be used with this process.

主权项

1. A continuous process to make and isolate methylal which comprises
reacting in a reactor A a mixture M1 comprising formaldehyde and methanol with an acid catalyst under at least partial formation of methylal and water, to form a mixture M2 comprising formaldehyde, methanol, methylal, and water, and feeding the said mixture M2 to the side of a distillation column B to a feed point in a height corresponding to between 40% and 70% of the effective height of column B, separating the said mixture M2 in the said distillation column B which comprises a reaction zone C within the said distillation column B into three distinct product streams, one being a distillate (5) taken from the column head BH of column B which is rich in methylal, one stream (4) taken from the column bottom stream BB of column B being almost pure water, and one stream (3) taken from the side of the column B below the reaction zone C which stream is rich in methanol, optionally, feeding the product stream (5) taken from the column head BH of column B which consists almost exclusively of methylal, and further comprises a mass fraction of less than 10% of methanol to the side of a rectifying column D which is operated with a pressure which is higher than the pressure in column B, where a stream (7) comprising a mixture of methylal and methanol having a mass fraction of methylal of between 70% and 95% is recovered from the column top DH, and pure methylal is recovered as sump product stream (6) from the bottom DB of the column D, in a purity in excess of 99.5%, wherein the ratio of the amount of substance of methanol to the amount of substance of formaldehyde in the mixture M1 is at least 3 mol/mol, and the reaction of formaldehyde and methanol to form mixture M2 under at least partial formation of methylal and water is conducted in a the separate reactor A, and the mixture M2 from reactor A is fed to the side of the distillation column B to a feed point in a height corresponding to between 40% and 70% of the effective height of column B.