"Chemicals Used to Control Contaminants in the Ethylene Plant"Contaminants and Impurities in Ethylene Plants Subcommittee Tutorial

"Chemicals Used to Control Contaminants in the Ethylene Plant"

Contaminants and impurities in Ethylene Plants Subcommittee Tutorial

Debby Rossana, Ph.D., Retired, Nalco Water, An Ecolab Company

Sherri Elder, Ph.D., New Page Sustainable Chemistry

During the production of ethylene, there are a number of impurities the operator of the plant has to contend with. There are contaminations in the feedstocks and recycle streams as well as a multitude of ppm levels of impurities that are made during the cracking process. And if that is not enough, there are other contaminants that form during the separation/purification process. A large proportion of the latter become foulants. Many of these various contaminants and impurities can cause serious processing problems for the ethylene producer if they are not removed. These problems may be off spec products, catalyst poisons, corrosion, foaming, emulsions and fouling.

Because of issues these impurities bring to the production of ethylene, they need to be removed or controlled in some way. This paper looks at chemical means of dealing with some of the impurities in the system. There are situations where addition of a chemical can render the impurity harmless. These would be chemicals such as neutralizers to control acids (CO2, H2S and the organic acids - acetic primarily, but also propionic acid, butyric acid and higher analogs), scavengers to remove acetaldehyde or scavengers to remove CS2. More often, however, chemicals are added to combat the problems associated with the impurity, rather than the impurity itself. These would include antifoams, filmers, emulsion breakers, dispersants and antifoulants.

Because these problems occur throughout the plant, in multiple pieces of equipment, an in-depth discussion of each area is impossible. However, a high-level look at the issues where chemical approaches can provide some benefit will be presented and this will benefit the engineer in solving processing problems.