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First off - this project is still in the early planning stages. The basic scope is that a plant want's to switch from using conc. sulphuric acid (~98%) in its process (nitration) to oleum.

I questioned why they would do this and their reasoning is supply shortage of sulphuric acid causing downtimes. Apparently an alternative supplier is not possible and they want to use oleum to supplement their shortfalls.

I'm conducting a high-level review of this idea. From my brief assessment it would seem that in most cases sulphuric acid and oleum are interchangeable, and, in cases where equipment is designed for compatibility with sulphuric acid it should also be compatible with oleum.

Some of the points that have I have flagged so far...

storage tanks -- material compatibility seems fine, but generation of fumes (SO3) may not be compatible with the scrubbing system

pumps/handling -- oleum (depending on concentration) can have significantly different viscosity and freezing points which in the local climate might cause issues.

nitration -- nitration reaction kinetics would likely be affected when switching to oleum...this would require labscale investigation and cannot be predicted accurately. The presence of dissolved SO3 might affect the reaction?

reconcentration -- there is currently a system in place designed to reconcentrate spent sulphuric acid (vacuum distillation), what changes would be required to re-concentrate oleum

It would be appreciated if anyone with experience could contribute other concerns or comment on the above.

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  • $\begingroup$ Do you need to change the process at all? Oleum used for transportation of sulphuric acid because it is less corrosive (no free water content) and depending on the SO3 content it can be solid rather than liquid at room temperature. Just dilute it with water to convert back to sulphuric acid. $\endgroup$ – alephzero Mar 18 '20 at 21:33
  • $\begingroup$ @alephzero This is by all means true. There are other things that need to be considered such as the release of SO3 gases and excessive heat of dilution when mixing with water $\endgroup$ – SimpleJack Mar 20 '20 at 6:40

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