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(555a) Chemical Looping for Modular Conversion of Rejected Ethane to Liquid Fuels: Feasibility and Economics

Neal, L. - Presenter, North Carolina State University
Li, F., North Carolina State University
Ethane has transport challenges for shale-producers at geographically isolated locations; it is not easily liquefied for transport, and dedicated ethane pipeline capacity is limited. This leads to frequent ethane rejection, where ethane is dumped back into natural gas for transport in pipelines. Furthermore, the concentrations of ethane in wet-gas exceeds natural gas pipeline specifications, leading to potential flaring. We have proposed a transportable, modular scale, ethane to liquids (ETL) technology enabled by low-temperature (<750 ËšC) chemical looping oxidative dehydrogenation of ethane (CL-ODH). In CL-ODH, a redox catalyst selectively donates lattice oxygen to convert ethane to ethylene and water. By use of automated valve switching, air is introduced to the reactor, in a separate step, to regenerate the depleted redox catalyst. The exothermic air regeneration generates heat - allowing for the system to be operated in an autothermal mode. This saves significant amounts of energy compared to traditional steam cracking, which requires high temperature furnaces (>1000 °C). The low-temperature operation of and use of parallel packed beds in CL-ODH makes it well suited for modular (and consequently lower-cost) implementation. Although ethylene is valuable, separation and transport at geographically isolated facilities is difficult. In ETL, the ethylene-rich product generated by CL-ODH is compressed and oligomerized to energy-dense, transportable liquid fuels.

The mature oligomerization technology in the proposed ETL system is well studied, but there are several technical and economic concerns to address for CL-ODH. Additional study is needed to assess the performance and lifespan of the redox catalyst, and in-depth techno-economic analysis of the CL-ODH-based ETL is needed to further increase confidence. In this work we present experimental, process modeling, and techno-economic analysis (TEA) of the CL-ODH-based ETL system. Longer-term, 500+ hr. laboratory testing demonstrates the excellent performance of the catalysts and gives high confidence in their long-term durability and activity. The ASPEN-based process modeling and TEA indicate the potential for profitable operation at typical gasoline prices. The process economics are shown to be capital driven, giving rise to nonobvious considerations for recycle. Furthermore, the conditions under which electrical cogeneration is viable are explored.