Caustic Tower Red Oil – How to Effectively Mitigate the Oil Soluble Aldol Polymers

The formation of “red oil,” (long chain aldol polymers) in the caustic tower continues to be a recurring problem that can impact the efficiency of acid gas removal and lead to fouling and emulsions in the spent caustic recovery system. A key reason this is a recurring problem is the inherent limitations of controlling the aldol polymerization reactions using inhibitors that work in the aqueous phase with no activity in higher molecular weight polymers that are insoluble in caustic. Over time, even small upsets in matching the water phase inhibitor with demand can cumulatively lead to deposit accumulation of red oil over the long run-length of best-in-class ethylene plants. This can impact efficiency and ease of operation. Red oil deposits can accumulate and potentially increase the risk of not being able to meet efficiency and run-length targets. This paper reviews the chemistry of aldol polymerization and explains the limitation of using chemistry that works only in the aqueous phase. Case histories are presented to demonstrate the power of inhibitor chemistry that works in both oil and water phases. These concepts are timely as plants increase run-length targets and for those trying to recover from upsets in control using chemistry that is only active in the water phase.