Process for reducing the formation of coke when used plastics are used in the refinery

摘要

Thermally pretreated used plastics or mixtures of used plastics can be recycled together with petroleum distillates in refinery plants, such as crackers, visbreakers and hydrogenation plants. A disadvantage is the formation of coke, which occurs even at low temperatures and results in a shortening of the operating times. The process according to the invention is based on thermal degradation of the plastic content in the extruder without addition of the active gases, a progressive temperature profile up to a maximum of 475 DEG C being set in 2/3 of the effective extruder length and a degressive temperature profile up to from 300 to 380 DEG C being set in the final 1/3 of the effective extruder length, and a coke-reducing additive known per se being metered in at the end of the extruder head or before a downstream static mixer in an amount whose concentration after the subsequent mixing-in of the pretreated used plastic content in amounts of up to 20% by weight into the refinery stream is between 10 and 200 ppm in the total feedstock for the petroleum processing step. The pretreatment of the used plastics can be carried out either as an integral step in the refinery plants or externally.