Liquid-fed waste plastic pyrolysis pilot plant: Effect of reactor volume on product yields

Abstract

A unique waste plastic pyrolysis pilot plant was used for fast pyrolysis (1–5 s vapor residence time) of HDPE at 600 °C. A dissolution pre-treatment step dissolved the high-density polyethylene (HDPE) in recycled pyrolysis wax to create a liquid feed to the pyrolysis reactor, avoiding clogging and bridging of the plastic particles that is common in alternative feeding strategies. Three different reactor volumes were tested to determine the effect of residence time on product distribution. Pyrolysis products were cooled through a series of two condenser to separate the products into three groups: a heavy, waxy product (> C15), a lighter liquid product (C6-C15), and a gaseous product (C1-C6). GC/MS analysis was used to characterize the composition of each product. Multiphysics modeling was conducted to estimate the residence time in the reactor and compare the pilot plant results to previously published micropyrolysis research. It was found that residence time had a significant effect on product distribution, with an increase from 1 to 4.5 s of residence time causing a 9 wt% drop in wax (C20-C30) production and a 11 wt% increase in light oil (C5-C10) production. The trends for product distribution as a function of residence time were found to be consistent between both the pilot plant and micropyrolysis systems, demonstrating that the pilot plant system can be “tuned” to produce the desired pyrolysis product.