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In my lab we have a stainless steel separator for liquid products of one of our hi-pressure catalytic testing assembly. It is a steel cylinder with two short pipes and one another short pipe with a valve. The problem is, the separator cannot be disassembled and washed. It accumulated organic residues for unknown time, presumably years (it happened before it moved into our responsibility). Some residues were washed with acetone and other solvents, but we want it much cleaner.

Personally, I would love to threat it repeatedly with a strong oxidizer, but I'm afraid that stainless steel might disagree. Also, heating above 200-300 Celsius unfortunately is out of question.

The residue is from Fischer-Tropsch synthesis, so it probably consists of heavy hydrocarbons and possybly some oxygenates and products of their reactions.

Any suggestions?

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  • $\begingroup$ Rather depends on the nature of the organic residues. Strong aq hydroxide soln? $\endgroup$
    – Waylander
    Commented Nov 8, 2017 at 20:16
  • $\begingroup$ Maybe sth that passivates steel? $\endgroup$
    – Mithoron
    Commented Nov 8, 2017 at 21:47
  • $\begingroup$ @Waylander Added the infor $\endgroup$
    – permeakra
    Commented Nov 9, 2017 at 4:30

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First try commercial cleaning solutions such as Alconox or Pierce RBS-35, with ultrasonic agitation (if you can sneak a transducer into the reactor).

Second, an oxidizer such as Godax Labs' Nochromix might work, but test it on an unimportant part of the reactor to see if it safe and effective. Read and understand its safety data sheet before use.

A last choice is chromic acid, $\ce{H2CrO4}$, which in some concentrations does not damage some types of stainless steel. N.B. Chromic acid is toxic, carcinogenic and harmful to the environment. With chlorides, it can produce toxic and volatile chromyl chloride. In high concentration it can cause ignition of materials. Check a material safety data sheet before trying it! Also prepare to dispose of this as hazardous waste. Even if the reference states it is safe for the particular steel in use, try it on an unimportant area... perhaps with some of the organic "gunk", to see if the gunk is removed and the reactor is unharmed.

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