GB669671A - Production of gaseous hydrogen chloride from an aqueous solution thereof - Google Patents

Abstract

Gaseous hydrogen chloride is produced from an aqueous solution thereof containing a higher percentage of hydrogen chloride than an azeotropic mixture of the same by feeding the solution into the upper portion of a fractionating column wherein it is contacted with ascending steam which is <PICT:0669671/III/1> introduced or generated at the lower portion of the column and with an aqueous solution of a hygroscopic salt which is introduced at an intermediate portion of the column. The column 3 is constructed, e.g. of impervious carbon or graphite, reinforced resins, stoneware, or glass enamelled material and comprises a top packed section 5, a top open section 4, an intermediate packed section 6, an intermediate open section 7, a bottom packed section 8 and a reservoir 9 for effluent salt solution. Hydrogen chloride solution is fed into section 4 and falls via a distributer plate 10 into section 6 where hydrogen chloride gas is stripped out by ascending steam fed via a pipe 32 into a vapour space 11 above reservoir 9. The resultant substantially constant boiling point mixture drips through a perforated plate 12 onto a distributer plate 13 where it is mixed with a concentrated solution of a hygroscopic salt (e.g. calcium lithium, zinc, magnesium or ferric chloride) fed through a pipe 14 and as a result hydrogen chloride gas is salted out. The resultant salt and hydrogen chloride solution falls down section 8 where hydrogen chloride gas is stripped out by ascending steam and the diluted salt solution from reservoir 9 is withdrawn and recycled to the column via a neutralizing tank 16 and an evaporator 20. Hydrogen chloride gas and moisture are withdrawn from the top of the column via a pipe 23 and pass through a water-cooled condenser 24, a refrigerated after-cooler 25 and a mist separator 26 the condensed acid from which is fed back to the column via reflux lines 27 and 28. The column may be operated at sub- or super-atmospheric pressures, the preferred range being 10-60 p.s.i. absolute. If desired the steam introduced via pipe 52 may be steam from the evaporator 20. Alternatively steam may be generated within the column by placing heating surfaces, e.g. of tantalum, in the bottom of the column. U.S.A. Specification 2,357,095 is referred to.