Regarding the issue of oxygen injection into styrene storage tanks
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Styrene uses p-tert-butylcatechol as a polymerization inhibitor; it is an oxygen-demanding type of inhibitor. It is generally agreed that oxygen – actually air, as direct injection of oxygen is not feasible – needs to be introduced into the storage tank. However, as for the exact method of doing this, I searched online and found two main approaches. I would like to ask everyone which one is more scientific. The first method is gas-phase oxygen injection using an oxygen-poor nitrogen blanket, which involves injecting a portion of air (probably instrument air, which is clean) into the nitrogen blanket; as a result, the oxygen in the gas phase of the storage tank gradually moves into the liquid phase. The second method is liquid-phase oxygen injection; it is said that gas-phase oxygen injection is not effective, as the inhibitor cannot reach the desired location, and oxygen promotes the polymerization of styrene in the gas phase. One theory is that the level gauge uses a blow-out type level gauge, with nitrogen being injected at the top and connected to a gas-phase nitrogen seal space, while air is injected at the bottom to directly enter the liquid phase. Personally, I think the second explanation seems more scientific. But I don’t have much experience in this area, so I would like to ask everyone: in actual work, which method is better? Is there any that is actually used?
The safe limit value (LOC) for the oxygen content in styrene material is 9.0% (V); therefore, it is relatively ‘safe’ to inject oxygen-poor nitrogen with an oxygen content of 4–6% (V), prepared by mixing a small amount of instrument air with nitrogen, into the styrene storage tank. Generally, it is sufficient to inject this oxygen-poor nitrogen gas for polymer inhibition into the return line of the storage tank discharge pump ； Large storage tanks can also be equipped with an air injection distribution ring near the bottom of the tank.