# CuSO4 in SO2/SO3 gas sampling in Sulphuric Acid Production

What role does $$\ce{CuSO4}$$ has in the gas sampling of an $$\ce{SO2/SO3}$$ gas mix in a catalytic converter for sulphuric acid production?

To give you a little context: We take gas samples from the beds of the catalytic converter to determine the efficiency of the catalyst. We use "cartridges" that we make with glass tubes filled with $$\ce{CuSO4}$$. The $$\ce{CuSO4}$$ (lab grade) comes in crystal version as a pentahydrate. We heat it for around $$\pu{30 minutes}$$ at $$\pu{105 ^\circ C}$$ and then we use it to make the cartridges. The cartridges are placed between the sampling point and the sampling bag (made of Teflon). This is a process that has been made since many years but nobody here is able to tell me why. The answer they give me is that the cartridges are used to "remove" the $$\ce{SO3}$$ from the sample but I can't see how that could happen. My theory is that because anhydrous $$\ce{CuSO4}$$ is hygroscopic (I've read it's been used as a desiccant) it may be used to avoid the formation of $$\ce{H2SO4}$$ that could damage the gas analyzer (a SICK S700). I've really googled it but can´t find the answer. Hope someone could enlighten me in the subject.

• Where do you install your cartridges? I suppose you are oxidizing a gaseous current of SO2 + O2 over a catalyst (either vanadium oxide or platinum). SO2 is oxidized in SO3, and this gaseous current is dissolved into somewhat diluted sulfuric acid. Where do you put your cartridges in this setup ? Does the gas go through your cartridges ? Before or after catalytic oxidation? – Maurice Nov 23 '19 at 21:34
• That's exactly the process as you describe it. We use the cartridges on sampling points after and before each bed. The gas passes through the cartridges and ends in the sampling bag. The gas analyzer measures %SO2 and %O2 v/v and with this data we determine the conversion to SO3 un each bead and of the full reactor. – Ed Corso Nov 24 '19 at 21:32