Oxidative Fast Pyrolysis of High-Density Polyethylene on a Spent Fluid Catalytic Cracking Catalyst in a Fountain Confined Conical Spouted Bed Reactor

Abstract

The oxidative fast pyrolysis of plastics was studied in a conical spouted bed reactor with a fountain confiner and draft tube. An inexpensive fluid catalytic cracking (FCC) spent catalyst was proposed for in situ catalytic cracking in order to narrow the product distribution obtained in thermal pyrolysis. Suitable equivalence ratio (ER) values required to attain autothermal operation were assessed in this study, i.e., 0.0, 0.1, and 0.2. The experiments were carried out in continuous regime at 550 °C and using a space-time of 15 g catalyst min g HDPE −1. The influence of an oxygen presence in the pyrolysis reactor was analyzed in detail, with special focus on product yields and their compositions. Operation under oxidative pyrolysis conditions remarkably improved the FCC catalyst performance, as it enhanced the production of gaseous products, especially light olefins, whose yields increased from 18% under conventional pyrolysis (ER = 0) to 30% under oxidative conditions (ER = 0.1 and 0.2). Thus, conventional catalytic pyrolysis led mainly to the gasoline fraction, whereas light olefins were the prevailing products in oxidative pyrolysis. Moreover, the oxygen presence in the pyrolysis reactor contributed to reducing the heavy oil fraction yield by 46%. The proposed strategy is of great relevance for the development of this process, given that, on one hand, oxygen cofeeding allows solving the heat supply to the reactor, and on the other hand, product distribution and reactor throughput are improved.

ACS Sustainable Chemistry & Engineering Virtual Special Issue: Thermal and Catalytical Chemical Conversions of Plastic Wastes for Sustainable Production of Energy, Fuels, and Chemicals

“…Lee et al also utilized sea shell waste-derived catalysts for thermo-catalytic conversion of biodegradable straw to recover monomers (e.g., lactic acid), which is about 130 times higher than noncatalytic conversion. Orozco et al investigated oxidative fast pyrolysis of plastics using a conical spouted bed reactor with a fountain confiner and draft tube and found that the yield of light olefins increases from 18% for conventional pyrolysis (equivalence ratio = 0) to 30% for oxidation conditions (equivalence ratio = 0.1 and 0.2). Fan et al reported the effect of iron-based microwave adsorbents (Fe, Fe 3 O 4 , and FeS 2 ) on polystyrene plastics.…”