Chemical Looping Oxidative Dehydrogenation of Ethylbenzene in a 10 kg/Day Fixed-Bed Demonstration Unit: Long-Term Performance and Process-Economic Implications

Abstract Chemical looping oxidative dehydrogenation (CL-ODH) has the potential to intensify styrene production by coupling ethylbenzene dehydrogenation with selective combustion of coproduct hydrogen using lattice oxygen of a mixed oxide-based oxygen carrier, but its scale-up behavior and catalyst durability remain uncertain. Here, we report catalyst optimization, design, and operation of an integrated fixed-bed demonstration unit with an ethylbenzene feed capacity of 10 kg/day, or approximately 5 kilowatts thermal (kWth), and an experimentally informed process-economic analysis. During lab-scale catalyst optimization, lanthanum substitution and alkali-molybdate promotion suppressed unselective oxidation in model dehydrogenation and selective hydrogen combustion (SHC) formulations. A 0.5 wt % K2MoO4-promoted industrial KFeOx-based dehydrogenation (DH) catalyst was selected for long-term operation for the purpose of an initial evaluation of the scalability of the process and the feasibility of using an established industrial DH catalyst in the CL-ODH processing scheme. The demonstration unit was operated for 1000 h over 1900 redox cycles at 575–625 °C. After an initial break-in period, ethylbenzene conversion decreased from 90.1% to 88.5%; however, styrene selectivity declined during extended cycling, resulting in an end-of-run (EOR) single-pass styrene yield of approximately 78% under the reference conditions. In situ addition of potassium precursors such as KOH, with or without a high-temperature oxidation treatment, recovered 4.1–5.1% of styrene yield on an absolute basis. Long-term operation also revealed issues such as an increasing reactor pressure drop resulting from agglomeration of the promoted industrial DH catalyst, identifying mechanical stability of the promoted commercial dehydrogenation catalyst as a scale-up risk, which can be resolved from advanced CL-ODH catalyst formulations. Process modeling projected start-of-run emissions of approximately 0.40 tonne of CO2 per tonne of styrene, compared with 0.72 tonne of CO2 per tonne for conventional dehydrogenation, while economic competitiveness is strongly affected by carbon loss to CO2 and coke, natural gas price, and the assumed value of avoided emissions. These results demonstrate important future directions for CL-ODH scale-up while highlighting its potential to achieve both favorable economics and lower CO2 emissions, especially in regions with high energy prices and/or strong incentives for CO2 emission reduction.