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I have a potential problem in that I need to reliably remove ozone from a stream of ionized gases, mostly air. The flow rate is quite low, less than 400 sccm. I was thinking of something catalytic, maybe platinum mesh? There may well be a related need to remove any $\ce{NO_x}$ created. I am open to suggestions — it's mainly a health and safety issue if it vents into the air.

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Ozonolysis is a synthetic procedure deploying diluted ozone as a reagent. This reaction may be relevant in the context of your question, because i) during the reaction, the gas typically is bubbled across a solution (and you have some exhaust to deal with), and ii) even more importantly, after the reaction, the organic products are to be isolated safely, too.

Here, I would like to suggest to use what is otherwise described as reductive workup. Ozone, which may dissolve in solvents, hereby is quenched (deactivated) by a material which in turn is oxidized by ozone. Because ozone is a powerful oxidizer, the deactivation is performed while keeping the concentration of ozone entering the quench solution low, and simultaneously keeping the temperature of this solution low, too.

The provision of the flux of 400 mL/min only partly describes your problem. It neither states the concentration of ozone in this input, nor the regime of this input -- it may be in batches, it could be a contiously working line. With these uncertainties in hand, bubbling the ozone-containing gas input into an aqueous solution of sodium hydrogensulfite (with "i", $\ce{NaHSO3}$) seems both simple to setup, manage, and scale. The reaction basically will yield sodium sulfate ($\ce{Na2SO4}$).

As an example, Ragan et al. published about an Ozonolysis at large industrial scale I hereby refer to. For about 19 h, their recation was running at low temperature with a constant flow of 15-20 L/min, 4-5 wt% $\ce{O3}$ in air bubbled across their reaction vessel. After completion of reaction, their workup reported was pouring the reaction solution slowly (over 30 min) to a prechilled quench solution of 3.0 kg $\ce{NaHSO3}$ in 6 L water at 0 degC. Only then they allowed the mixture to warm slowly to room temperature.

Depending on the conditions in your example, maybe you do not need to cool your sulfite solution as much, yet monitoring the temperature of the stirred quench solution is recommended. With the parameters missing in your question, the minimal quantity of bisulfite you need might be estimated. Equally, there are KI/starch indicator stripes, which may be used to check if the concentration of oxidizing ozone still is significant; if present, they will change from colourless to dark blue (ref, example).

Literature reference: Ragan et al., Safe Execution of a Large-Scale Ozonolysis: Preparation of the Bisulfite Adduct of 2-Hydroxyindan-2-carboxaldehyde and Its Utility in a Reductive Amination, Organic Process Research & Development 2003, 7, 155−160 (DOI: 10.1021/op0202235).

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