(218b) Neutralizer Selection for Control of Acid Corrosion in Ethylene Plants

During the production of ethylene, many contaminants are formed and distributed throughout the system. These contaminants are usually classified into Organic and Inorganic. Organic foulants are the result of complex chemical reactions and may contain Sulfur, nitrogen, oxygen. Oxygen containing materials are often further oxidized to organic acids.

The cracked gas stream going overhead in the Primary fractionator will contain both organic and inorganic acids that will condense in the overhead exchangers. The aqueous pH of the condensed water will be low, resulting in corrosion in the overhead condensing system. Corrosion is generally most severe at the dew point. The acidic species found in the overhead vapor are present in the water as it condenses, thus lowering the pH. This will result in a general corrosion attack, possibly with some localized pitting of the exchanger tubes and pipe walls.

Preventing corrosion in the overhead system will be based on controlling the aqueous pH above 5 at dew point conditions. An organic neutralizing amine is water-soluble and will therefore be present in the water droplets at the initial dew point. The reaction will form salts that will be washed through the system in the condensed water. Improper neutralizer choice and/or application can result in serious corrosion problems. An example showing the use of a simulation method using Ionic Equilibria Modeling is discussed in this paper. The Ionic Equilibria Model is used to carry out a rigorous electrolyte simulation resulting in neutralizing amine selection and application guidelines.