(530g) Liquid-Fed Plastic Pyrolysis Pilot Plant: Effect of Reactor Volume on Product Yields

Plastic waste is a global environmental challenge because of poor end-of-life practices. Chemical deconstruction methods such as pyrolysis can convert waste plastic into useful chemical products, providing an incentive for plastic to be recycled instead of ending up in landfills or the environment. In this study, a unique plastic pyrolysis pilot plant was used for fast pyrolysis (1-5 seconds vapor residence time) of HDPE at 600 °C. A dissolution pre-treatment step dissolved the 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 at constant feed rate 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 seconds 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, showing that the pilot plant system can be “tuned” to produce the desired pyrolysis product.