Polymer and red oil formation in caustic wash tower of olefin plants: mechanism and affecting’s factors

Pyrolysis of liquid and gaseous feedstocks for ethylene production is achieved in steam cracking units. The cracked gases contain carbon dioxide and hydrogen sulfide that must be removed from the cracked gas. Hydrogen sulfide is a catalyst poison for hydrogenation reactors. Carbon dioxide can freeze at low temperatures in heat exchangers and fractionation equipment. It can also be absorbed into ethylene, effecting the product quality and further processing. These acid gases are scrubbed with caustic solution (NaOH) in caustic wash towers. The caustic tower (caustic scrubber) is typically integrated upstream of the last crack gas compressor stage. Caustic Tower operation is a key factor to the achievement of on-specification ethylene and propylene production. The tight limit on the allowable contaminant content levels driven by polymer producers necessitates close scrutiny and evaluation of the operation and performance of the Caustic Tower System. Acid gases are created during the thermal cracking of any given steam-cracker feedstock. The preferred choice for removing these acid gases from the cracked gas is by absorption using dilute caustic soda. The Absorber, or Caustic Tower, is designed and operated to remove these acid gases; namely carbon dioxide (CO۲) and hydrogen sulfide (H۲S) and to a lesser extent some of the weaker acid gases such as mercaptans (R-SH). This paper provides an overview of what the Caustic Tower process is, the acid gas and caustic concentrations and reactions of the process, and the key operating parameters. Caustic Tower fouling like red oil and factors involved with its presence are described. Fundamentals of Caustic Tower controls and monitoring are provided to aid in the improvement of performance. In this study, however, we discussed the problems related to the spent caustic system from the beginning to neutralization in an olefin plant. With an increased understanding of the factors affecting the formation and increasing this material, we tried to eliminate or control it. Also, by recovering it, the profit increased, and pollution effluents could be reduced at the plant.

کلیدواژه ها:

Caustic wash Tower(CWT) ، red-oil ، Free radical polymerization ، Aldol condensation ، Diels-Alder reaction