Ethylene is the most commonly produced petrochemical product. The bulk of annual commercial ethylene production is based on thermal cracking of hydrocarbon feedstocks with steam. Usual raw materials for pyrolysis are refinery gas, liquid petroleum gas (LPG), natural gas liquids (NGL), naphtha or gas oil. The production of ethylene is a very complex process, including cracking, cooling, compression and separation steps. Fouling and corrosion are observed in almost all process parts and can cause significant production losses. This article focuses on chemical treatment concepts for very powerful corrosion control programmes and protection of ethylene plant components.
Figure 1 illustrates the common application areas where corrosion inhibitor programmes can be applied in the hot section. Similarly affected by corrosion are the depentaniser overhead system of the gasoline hydrogenation unit (GHU) and the hydrocarbon fractionation section (cold section).
Primary cracking reaction products are ethylene, propene, acetylene, methane and hydrogen. Secondary cracking reaction products are C4 to C7 hydrocarbons and heavier products. The cracked gas may also include corrosive species such as oxygen, oxygenates, C02, H2S, phenols and organic acids (i.e. formic, acetic and propionic acid). Well established chemical treatment concepts for corrosion control include oxygen scavengers, alkalising amines, filming amines (FFAs) or combinations of them.