HOW CAN CHLORIDE EVAPORATE??? 1

[devaxrayz]

our plant bottom section of distillation column was contaminated by chloride (Cl-). This chloride come from sea water leakage outside distillation system to the feed (liquid). The concentration accumulate at this bottom section reach 250 ppm.

As i know chloride is in form of ion and it can not be evaporate. But from our lab analysis, we found that the top product (our pure product) is also contaminated by it.

How can this chloride ion get into our top distillation product?? is it carried over by the vapour (entrainment) from the bottom section?? or can it form a volatile compound such as HCl and than evaporate??

Chloride fastly promoted corrosion like pitting corrosion, doesn't it?? So should we shutdown the plant and do cleaning program for the equipment??

 

[hacksaw]

you are getting products of reaction (chlorination).

 

[25362]

What are the operating temperatures and pressures ?

 

[25362]

Although it appears strange, there are chlorides that boil at relatively low temperatures. For example, FeCl₃ melts at 304^oC and boils at 316^oC at atmospheric pressure. The solid undergoes sublimation at lower temperatures and pressures. The CRC Handbook tells us that the solid at 246<sup>o[/sup}C has a vapour pressure of 20 mm Hg. Petroleum re

Besides, some chlorides (e.g., magnesium chloride) decompose at temperatures above 177oC to form volatile HCl in the presence of moisture.

Thus, chlorides may appear in distillation overheads.</sup>

 

[25362]

It seems there is one truncated para. The intention was to say that petroleum refineries find chlorides as such in the distillates and overheads of vacuum towers.

 

[devaxrayz]

25362:
nice response.

we have our discussion here and i guess the cl- was carried by the vapour (entrainment) instead forming other compound such as HCl.

So my guess is: HE leakage, sea water contain Cl- mixed with distillation feed, accumulate in bottom section.

Then the bottom liquid was evaporated in reboiler, the vapour caried away liquid droplet (as entrainment) which contain disolved Cl- to the top of column. So the distillate was contaminated by Cl-

since we can not observe this mechanism, i'm still not sure about this. I need more opinion.

Thanx

dev

 

[25362]

Can you be more explicit on the operating conditions and the kind of operation under review ?

 

[devaxrayz]

it was a mixture of methanol (85% w/w) and water distillation
bottom temperature 112 C
bottom pressure 1.7 barg

top temperature 84 C

feed contaminated by Cl- entered from middle of tower (tray 33 of 85)

as i mentioned Cl- source is sea water leakage so it also contain (in bottom) other constituent such as possessed by sea water.

thanx

dev

 

[25362]

Although your theory of entrainment as well as of a possible foaming effect caused by solids and dissolved air and other trace contaminants in the feed, are all plausible, I, on the other hand, am rather inclined to believe that some chlorides, in particular MgCl[sub[2[/sub] at the bottom temperatures, hydrolise and convert to HCl, which will find its way to the column overhead.