Feasibility Study on Power Generation from Waste Plastics with Partial Precombustion Carbon Capture and Conversion

Abstract

The feasibility of upcycling waste plastics into concurrent production of carbon nanotubes (CNTs) and of a hydrogen-enriched gaseous hydrocarbon stream was shown to be possible in a continuous steady-state steady-flow process. The feedstock was post-consumer (waste) low-density polyethylene (LDPE), which was pyrolyticaly gasified at 800°C, in a flow of nitrogen carrier gas. The evolving gaseous hydrocarbon pyrolyzates were first used as carbon growth agents for CNTs in a reactor, a process that lowered their carbon content and increased their hydrogen content. Thereafter, the unreacted hydrocarbon pyrolyzates and the generated hydrogen were mixed with air and burned. This conversion of solid waste plastics to gaseous fuels allowed thorough mixing with air and, upon ignition, the formation of environmentally benign fuel-lean premixed flames for subsequent power generation purposes. The CNT generation in the reactor took place by chemical vapor deposition (CVD) on untreated stainless steel mesh substrates, which also served as catalysts. Provisions were made for automatic motion and replenishment of the substrate/catalyst for continuous CNT production. The reactor was specifically designed to have a cold-wall configuration, where only the catalyst substrate was heated to a temperature of 800°C, in an otherwise unheated chamber. This cold-wall reactor has significantly lower energy consumption than conventional hot-wall reactors of similar dimensions and throughput. This work is part of an overall study that aims at illustrating the upcycling of common recycled post-consumer plastics simultaneously to gaseous fuels and value-added nanomaterials. Its specific goal was to produce the latter in a newly designed low energy input reactor.