A method of cleaning a cold box of an exchanger includes performing a methanol pre-flush of the system and inspecting filters in a filtration unit. The method includes adding toluene reformate to circulation tank and circulating the toluene reformate. The method includes analyzing the circulating toluene reformate for sulfur content. The method includes starting a circulating pump and resuming circulation in a bottom to top flow. The method includes reversing circulation flow path to a top to bottom flow. The method includes returning the circulation flow path to the bottom to top flow and circulating the toluene reformate. The method includes starting the circulation pump and resuming circulation of the toluene reformate in the bottom to top flow path until sulfur levels are stable. The method includes emptying the toluene reformate from the system and flushing the system. The method includes performing a methanol post wash and dedusting the system.