Polyethylene waste co-processing in fluid catalytic cracking plants

Abstract

Plastics pollution is an overwhelming environmental problem that must be solved as soon as possible. Refining processes such as the Fluidized Catalytic Cracking (FCC) process with a global capacity of 14 million barrels per day, may help to solve it in the short term, as many scientists have already pointed out. Just by co-processing 5 wt % polyethylene waste in those units, 37 million tons per year of polyethylene could be eliminated from landfills and transformed into valuable fuels. However, refiners must be completely sure that processing polyethylene in their FCC plants will not cause any deleterious effects. That is the purpose of this paper.

Low density polyethylene waste was transformed into valuable hydrocarbons by co-processing in proportions of 5 and 10 wt % with heavy gasoil in an FCC pilot plant which operates as industrial FCC plants do. Polyethylene was completely converted mainly into naphtha and liquified petroleum gas; at 510 °C polyethylene was converted into naphtha (46 %), LPG (20 %), light cyclic oil (9 %), heavy cyclic oil (15 %), coke (6 %) and dry gas (4 %); at 530 °C, the order and proportions changed significantly, naphtha (43 %), LPG (35 %), heavy cyclic oil (0 %), light cyclic oil (2 %), coke (8 %) and dry gas (12 %); LPG olefinicity and naphtha research octane number increased slightly. No catalyst circulation problems nor clogging or plugging were observed. However, at the highest experimental reaction temperature (530 °C), dry gas yield increased to more than 4 wt %, this could be a problem for most of industrial plants since it may overload the wet gas compressor.