# Is there a T-V or P-V chart relating LiBr temperatures for recovery?

I'm working on a project and would like to consider a LiBr solution to be used as a desiccant. I don't know however the temperature of air vs pressure to recover it. I was thinking of using a nozzle/diffuser and room temperature air to recover it's desiccant properties, but I'm not sure that this is possible.

Without some fancy equipment to measure the salt concentration in the solution, a simple saturated solution of lithium bromide would have some relative humidity which would be a function of temperature. I looked quickly for some relative humidity table of lithium bromide and found the following reference which has an equation that can be used for calculating the relative humidity ($RH_{sat}$) over a saturated solution of lithium bromide as a function of the temperature in Celsius ($T_C$).

"Humidity Fixed Points of Binary Saturated Aqueous Solutions" JOURNAL OF RESEARCH of the National Bureau of Standards, Vol. 81A, No.1, January-February 1977, Lewis Greenspan (pdf link)

$RH_{sat} = 7.75437 - 0.0654994T_C + 0.420737\times10^{-3}T_C^2$

Some values for $RH_{sat}$ are:

• 7.75 % at 0 C
• 5.41 % at 100 C

So as long as some solid lithium bromide remained then the solution would be saturated. If all the lithium bromide dissolves, then you'd simply boil the solution to regenerate it. Lithium bromide is about twice as soluble in a boiling solution (somewhat over 100 C) as at room temp (20 C). So boil down to some starting volume of solution or until you see solid lithium bromide in the boiling solution. When the solution cools to room temperature about half the lithium bromide will crystallize out regenerating the saturated desiccant solution.

If you do want to boil this to regenerate then be sure and use some boiling stones. The solution would seem likely to bump.