Concentration Of Hydrochloric Acid By Batch Salt Distillation

Hydrochloric acid is a commonly used chemical product, in washing production of iron and steel, electroplating and steel structure, as well as in chemical pharmaceuticals and rare earth processing. These processes discharge huge amount of waste hydrochloric acid with low concentration. Since hydrochloric acid forms the highest azeotrope during distillation, which contains HCl 20.2 wt.%, and the azeotropic point is 108.6℃,it can not be separated by common distillation to obtain the hydrochloric acid whose concentration is higher than the azeotropic composition 20.2 wt.%.This paper studied the concentration of hydrochloric acid by using batch salt distillation.Firstly, the effect of different amount of magnesium chloride on vapor-liquid equilibrium of hydrochloric acid-water system was studied in this paper, correlated using the improved Chen-NRTL equation. The experimental results showed that the azeotropic composition of hydrochloric acid-water system decreased as the increase of the amount of magnesium chloride.Secondly, this paper studied the concentration of hydrochloric acid by using batch salt distillation. Take the hydrochloric acid of low concentration as an example, at first, the paper investigated the effect of different amount of magnesium chloride only in the still and different reflux ratio on the concentration of overhead hydrochloric acid. The results showed that when the mass concentration of magnesium chloride in the still is 0.25g/ml, the highest concentration of overhead hydrochloric acid is 24%, and the concentration of overhead hydrochloric grows lower as the time passed. Then, the paper conducted the experiment of batch salt distillation to concentrate hydrochloric acid. The experimental results showed that when the mass concentration of magnesium chloride in the still is 0.25g/ml and the velocity of adding salts at reflux liquid is 0.5g/min, the highest concentration of overhead hydrochloric acid is 28.8%, and the volatile HCl from the top of the column can be collected as products.At last, this paper added absorption device on the top of the column to absorb the volatile HCl produced during the batch distillation. The experimental results showed that the overhead volatile HCl increased as the increase of the amount of magnesium chloride and the increase of reflux ratio.