I am preparing catalyst from metal nitrates as a precursor. During calcination process, NOx and nitratic acid are generated as a byproduct. I am using wet scrubbing process where 10% caustic solution is counter flowed from the top of scrubber system, but the process is inefficient. Can anyone please suggest me more efficient solution which can be used in scrubbing these polluting gases?
You can use water as scrubbing solution, however for nox absorption you have to mix effulent gas with air in order to convert nox in to NO2 and to be absorbed in chilled water in a column. The chilled water and gas flow will be counter current in column. The effluent gases coming out of column can be absorbed in NaOH.
U can use reducing agents like sodium, potassium, calcium hydrosulphide with NaOH to maintain pH more than 12 to avoid H2S.
Another way in wet condition u can use ammonia solution for scrubbing NO2
Thank you gentlemen for your valuable feedback...
Mr. Ravat, I have read about several ctatalytic converters but at this stage we can not afford this. You can please share the available details to initiate in that direction as it is greener approach than others.
Mr Muthineni...your suggestion of scrubbing NOx gases in chilled water is appreciated. I am using NaOH solution at present but it could not serve the purpose. I shall try with chilled solution, that may help.
Dr. Malani...I read several articles mentioning use of reducing agent and it seems more practical. I was afraid of H2S gas generation when we use these solutions. But as you have mentioned, if I maintain pH more than 12, the issue can be resolved.
I agree that Dr. Ravat's suggestion of a catalytic solution is a greener approach.
Selecting a suitable NOx reduction catalyst to match the requirement for NOx conversion is not an issue. However there could be several process - design issues that may need to be overcome.
1) The evolution of NOx during the batch calcination will presumably be a batch process with varying levels of NOx as well as unsteady flow of vapor. This would require controlled dosages of the reductant ammonia to be fed along with the gas flow
2) Sufficient energy to heat the feed gas to the catalytic converter to an operating temperature of ~ 250 - 300C - use of waste heat if available could reduce cost of energy.
3) Further details on scale of operation,complete composition and volume flow of gas to be treated, temperature and pressure ..etc will enable a more informed response
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