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Influence of the conditions for reforming HDPE pyrolysis volatiles on the catalyst deactivation by coke

Barbarias, Itsaso, Artetxe, Maite, Lopez, Gartzen, Arregi, Aitor, Bilbao, Javier, Olazar, Martin
Fuel processing technology 2018 v.171 pp. 100-109
catalysts, fluidized beds, gasification, hydrogen, nickel, polyethylene, pyrolysis, steam, temperature
Pyrolysis of high density polyethylene (HDPE) has been carried out in a conical spouted bed reactor (500°C) and the volatiles have been reformed in-line over a Ni commercial catalyst in a fluidized bed reactor. The evolution of reaction indices (conversion, H2 yield and other gaseous product yields) with time on stream has been studied under the following operating conditions: temperature, 600–700°C; space-time, 8.3–20.8gcatmingHDPE−1, and steam/plastic ratio, 3–5. High initial conversion (>94.5%) and H2 yields (>76.7%) are attained under all the operating conditions studied, with HDPE conversion and H2 yield increasing when the three variables are increased, which is explained by the enhancement of the reforming reaction. However, a significant effect of operating conditions on catalyst stability has been observed. Thus, an increase in temperature, space-time and steam/plastic ratio decreases catalyst deactivation as a consequence of a lower rate of coke deposition on the catalyst due to both a lower C5+ coke precursor amount in the reaction medium and a higher gasification rate of the coke deposited.