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

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 degrees C and using a space-time of 15 gcatalyst min gHDPE -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. ; This work was carried out with financial support from Spain's ministries of Science, Innovation and Universities RTI2018-101678-BI00 (MCIU/AEI/FEDER, UE) and RTI2018-098283-JI00 (MCIU/AEI/FEDER, UE) and Science and Innovation PID2019-107357RB-I00 (MCI/AEI/FEDER, UE) and TED2021-132056B-I00 (MCI/AEI/FEDER, UE), the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 823745, and the Basque Government IT1645-22.