GB794808A - Ethylene glycol purification - Google Patents

Abstract

Ethylene glycol is recovered from a mixture containing ethylene glycol and alkaline salts of terephthalic acid by a process comprising diluting the mixture with water, acidifying the diluted mixture with mineral acid to form a precipitate of solid matter, partially dehydrating the resulting precipitate-free mixture by distillation, neutralizing the partially dehydrated mixture, distilling the neutralized mixture and recovering ethylene glycol as a distillate. Suitable mineral acids are, for example, hydrochloric acid, orthophosphoric acid and sulphuric acid. The precipitated solid matter is removed from the aqueous ethylene glycol solution by decantation or by filtration in which conventional filtering agents, such as diatomaceous earth, may be used. It is desirable that the aqueous ethylene glycol solution is maintained at an acid pH value during the dehydration step. In the examples: (a) crude ethylene glycol recovered from the manufacture of ethylene glycol terephthalate polyester and containing disodium terephthalate, sodium hydroxide, acetals and solid matter is mixed with water and sufficient sulphuric acid to impart an acidic value of pH 2; the solid matter is filtered off by passing the mixture through a diatomaceous earth filter; the remaining solution is distilled until about 80 per cent of the water is distilled off and is then neutralized with caustic soda solution and the resulting mixture distilled; the second fraction of the distillate consists substantially of pure ethylene glycol; and (b) the process is carried out as in (a) except that phosphoric acid is used instead of sulphuric acid. Specification 578,079, [Group IV], is referred to.