Concentration of dilute hydrochloric acid
Thread Content
I have received various batches containing waste acid solutions, namely 2.5% hydrochloric acid solutions; the amount of such solutions is only about 2 cubic meters, but when mixed with 70 cubic meters of water, the pH value drops to around 4. In my opinion, concentration can be considered as a reference; it may contain a small amount of HCL, but definitely some of the acid will remain in the solution. Relevant experiments were conducted, and it was found that after concentration, the pH value of the condensed liquid was 7, while the pH value of the remaining liquid increased slightly; 250 ML was concentrated to 150 ML. Have I been wrong to consider hydrochloric acid to be a volatile acid?
The normal pressure azeotrope of the HCl/H2O binary system is at 109 °C with a HCl mass fraction of 20.2%. Therefore, for dilute acids with a concentration below 20%, the HCl concentration in the vapor at atmospheric pressure will be well below 20.2%, with H2O being the main component. The hydrochloric acid commonly referred to is a volatile acid, generally meaning an acid with a concentration higher than that of the azeotropic mixture, such as 31% industrial hydrochloric acid. However, even with 15% dilute acid, assuming that the vapor evaporated contains only a few percent HCl, it still has a strong pungent odor in the air, and inhaling it can cause severe damage to the respiratory system. Therefore, from the perspective of the degree of hazard, it is not excessive to call it a volatile acid. 98% concentrated sulfuric acid will not behave like this.
The azeotrope temperature is 108.2°C. According to your analysis, if it is concentrated to below 15% and evaporated at temperatures below 108°C, the majority of the resulting substance will be water. As required by the factory, we are able to carry out this concentration process!
20% azeotropy; generally, at 15%, about 1-3% evaporates