Systems and methods for processing mixed plastic waste

A system for processing a mixed plastic waste, the system comprising:

• a first reactive screw extruder having an inlet to receive a mixed plastic waste with a plurality of plastic polymers and an outlet, the first reactive screw extruder being configured to heat the mixed plastic waste to a temperature sufficient to cause initial dechlorination of any chlorine-containing polymers in the plurality of plastic polymers;
• a first extrusion product stream connected to and in fluid communication with the outlet of the first reactive screw extruder to receive a first extrusion product therefrom, the first extrusion product stream including the mixed plastic waste;
• a second reactive screw extruder having an inlet to receive the first extrusion product stream and an outlet, the second reactive screw extruder being configured to heat the mixed plastic waste of the first extrusion product stream to a temperature sufficient to cause initial depolymerization of a portion of the plurality of plastic polymers;
• a second extrusion product stream connected to and in fluid communication with the outlet of the second reactive screw extruder to receive a second extrusion product therefrom;
• a first separation unit having an inlet connected to and in fluid communication with the second extrusion product stream and an outlet, the first separation unit configured to separate the second extrusion product stream into a solids material and a separated extrusion product, the solids material being purged from the first separation unit through a purge stream;
• a separated extrusion product stream connected to and in fluid communication between the outlet of the first separation unit and a first inlet of a junction to enable flow of the separated extrusion product from the first separation unit to the junction, the junction having a second inlet to receive a process solvent and a reaction catalyst therethrough, the junction configured to mix the separated extrusion product, the process solvent, and the reaction catalyst to define a process feed stream, the process solvent being one or more of a carbon black oil, a heavy cat cycle oil, a vacuum gas oil or any hydrocarbon with a boiling point ranging from about 300° C. to about 565° C.;
• a multi-tray reactive distillation column having a feed stream inlet to receive the process feed stream from the junction;
• a plurality of side streams connected to and in fluid communication with the multi-tray reactive distillation column, at least one of the plurality of side streams arranged to draw naphtha from the multi-tray reactive distillation column;
• a bottoms stream connected to and in fluid communication with the multi-tray reactive distillation column proximate to a bottom portion thereof, the bottoms stream containing the process solvent, unreacted plastic polymers, the reaction catalyst, and coke;
• a second separation unit connected to and in fluid communication with the bottoms stream, the second separation unit configured to separate at least a portion of the coke and the reaction catalyst from the bottoms stream;
• and
• a recycle stream connected to and in fluid communication between the second separation unit and the second inlet of the junction to return at least a portion of the process solvent and unreacted plastic polymers in the bottoms stream to the junction.

A method of processing a mixed plastic waste, the method comprising:

• introducing a mixed plastic waste with a plurality of plastic polymers into a first reactive screw extruder;
• operating the first reactive screw extruder at a temperature sufficient to cause initial dechlorination of any chlorine-containing polymers in the plurality of plastic polymers, the temperature ranging from about 300° ° C. to about 350° ° C.;
• passing the mixed plastic waste to a second reactive screw extruder;
• adding a hydrogen donor solvent, or gaseous hydrogen with a transition metal catalyst, to the second reactive screw extruder with the mixed plastic waste therein;
• operating the second reactive screw extruder at a temperature sufficient to cause initial depolymerization of a portion of the plurality of plastic polymers in the mixed plastic waste, the temperature ranging from about 400° C. and about 450° C.;
• providing a residence time of the mixed plastic waste within the second reactive screw extruder to allow a transfer of hydrogen from the gaseous hydrogen or hydrogen donor solvent to free radical compounds created during the initial depolymerization of the portion of the plurality of plastic polymers in the mixed plastic waste to produce an extrusion product;
• separating a solids material from the extrusion product exiting the second reactive screw extruder to provide a purified extrusion product;
• mixing the purified extrusion product with a process solvent and a reaction catalyst to define a process feed stream, the process solvent being one or more of a carbon black oil, a heavy cat cycle oil, a vacuum oil, or any hydrocarbon boiling in the range from about 300° C. to about 565° C.;
• passing the process feed stream to a reactive distillation column, the process feed stream being fed onto a tray of the reactive distillation column;
• operating the reactive distillation column to facilitate depolymerization of at least another portion of the plurality of plastic polymers in the presence of the reaction catalyst;
• removing a distillate from the reactive distillation column via one or more distillate side streams connected to the reactive distillation column, the distillate being at least naphtha;
• removing a flow of the process solvent, unreacted plastic polymers, reaction catalyst and coke via a bottoms stream connected to a bottom end portion of the reactive distillation column;
• separating at least a portion of the reaction catalyst and coke from the bottoms stream;
• returning at least a portion of the process solvent and the unreacted plastic polymers in the bottoms stream to mix with extrusion product in the process feed stream, thereby circulating process solvent through the reactive distillation column and between an outlet and an inlet thereof;
• and
• adding make-up process solvent to the circulating process solvent.