Waseem, I agree with your method.

If the gas exiting the flask is saturated with water, the pressure of the water vapour will be the saturation vapour pressure (p_bath) that can be easily determined by Antoine law. Then, fixing the temperature of the reactor, the saturation vapour pressure in the reactor is set (p_reactor), and your Relative Humidity is p_bath/p_reactor. Note that the molar ratio and the water vapour pressure will be the same.

Moreover, I would suggest to use at least 2 conical flasks to ensure a full saturation of the gas with water vapour.

However, if in any point of your piping, between the bath and the reactor, you have a cold spot, you will have accumulation of acidic (H2SO3 !) liquid water in it. And the RH will be determined by the temperature of this cold spot.

Best regards

Thanks a lot Sebastien for your time.

Noted your suggestions.

sometimes with this method for Lower RH, i get low values of temperature of waterbath like 5 c or 7c but I put ice cubes in water bath while monitoring the temperature.

To take out the affect of absorption of water from my calculations, I currently make the water saturated with SO2 (outlet conc of SO2 from gas analyzer equals inlet conc with no adsorbent in the reactor). However, when I put in the adsorbent, there is some SO2 gas in the system and it may affect the readings of analyzer. So I purge out that with nitrogen gas directly to the reactor disconnecting the waterbath. I hope I can get the precise adsorption capacity of my adsorbent following this procedure.

Any more suggestions and recommendations are welcomed.

Cheers!