4% dilute salt, acid-purified to 8%
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There’s a question: for 4% dilute salt solution that needs to be concentrated to 8% acidity, can evaporation be used for concentration? Is it water that evaporates away, or water plus HCl? Through distillation, is it salt, acid, or water that remains at the bottom of the tower? It’s quite confusing I did some simulations; using the PR equation, the product at the top of the tower is HCl, while using the NRTL equation it’s water. Could someone please give me some advice? Thank you so much!
This post was last edited by Du Xiaoping on 2015-6-25 15:28: Water and HCL. During the PVC production process, waste acid is generated. To reduce the amount of waste acid produced, many companies have installed acid-salt separation units that extract the HCl gas from the waste acid and heat it using steam. According to the instructions for this device, what is produced as a result of the analysis is HCL; of course, some water will also evaporate along with it. It is best to evaporate and then cool, resulting in HCL.
Our factory installed a salt acid separation unit a few years ago, but... it was never put into use and ended up as scrap metal in a building; tens of millions were wasted. I wonder if it was ever successful or operated properly
I agree with you; in recent years, hydrochloric acid has been very cheap, almost given away for free. HCL isn’t that expensive either. The process of extracting hydrochloric acid from it requires steam, electricity, and labor, so the cost of the resulting HCL isn’t low. Moreover, the equipment often develops leaks, which is why many manufacturers choose not to use it even though they have it. Of course, salt acid resolution devices are not complex, and there are many companies that have succeeded in developing them.
Such a dilute salt acid. Concentrating by distillation is not cost-effective, and the corrosion resistance of the equipment also needs to be taken into account. It’s better to find another method of concentration.
Genuine salt acid is cheap; acid produced as a by-product in industry is even cheaper. The acid generated as a by-product in the production of chlorinated paraffins has its concentration increased through cyclic absorption. I’m not sure if this method will work for your situation.
I just want to use distillation; simulation calculations can be easily carried out since the concentration isn’t very high. Thank you!
The reflux ratio is very low. Well, we are indeed considering the materials for the tower and its internal components. Ugh, this is frustrating
You mean that the salt and acid will be at the top of the tower? Well, since my concentration is relatively low, I think it’s better to evaporate the water first; once a certain concentration is reached, both the top and bottom of the tower will contain a salt-acid mixture in an azeotropic state. I’m not sure if that’s correct
This post was last edited by qugd on 2015-7-2 at 10:39. The concentration of salt acid in your system is too low; at the top of the tower there is an even weaker salt acid solution, while at the bottom there is an azeotropic salt acid mixture. Because the proportion of water is too high and its heat capacity is large, distillation is very costly. Increasing it from 4% to 8% may seem like not much of a change based on the numbers, but in reality, it involves using 2 tons of dilute acid for every 1 ton of water, which results in high energy consumption. Moreover, the 1 ton of water that is evaporated also contains a significant amount of acid components. If the proportion of water is reduced first using other physical methods, without affecting the evaporation of salts and acids, this will improve efficiency, but it may be more difficult to find materials suitable for such equipment.