Measuring [NaOH] in a working vacuum evaporator. 1

[Okie2]

How can the concentration of NaOH, in water solution, be measured while the solution is in a vacuum evaporator? The goal is to take the concentration to say 28% to cause the precipitation of a crystalline material.

My list of potentials include pH, Conductivity, Density and Viscosity.

I also suspect it might be beneficial to remove a stream of the solution and filter the precipitate on a "continual" basis, as there will be approximately 10% solids when the endpoint is reached. If the stream is removed, the concentration measurement might be simplified.

I would appreciate any comments.

 

[Compositepro]

The simplest and most robust would be density measurement. There are many commercial instruments. One method is to use differential pressure measurement between two points at different elevations. The sense lines are purged with a tiny flow of pure water.

 

[Okie2]

Thank you for your help. I didn't realize the density measurement could be made without removing a sample from the evaporator but it makes sense since the pressure of the system has no effect on it's mass.

I agree with your comment of simple and robust. Those features are very important.

 

[danw2]

I like the simplicity of DP. Calibrate it with plain water. Nice.

K-Patents sells a process refractometer for density measurement in adqueous solution (optical refractive Index).