(675f) Advances in the Use of Electrochemical Oxidative Dehydrogenation to Convert Natural Gas Liquids to Value Added Chemicals

The U.S. has seen tremendous growth of natural gas liquids (NGLs) supply over recent years, due to the development of unconventional resources. The processing of natural gas into pipeline-quality dry natural gas is complex/costly and involves several processes to remove oil, water, acid gases, and NGLs. NGL recovery is a capital and energy intensive process utilizing cryogenic distillation requiring stages of compression/expansion with high degrees of heat integration. Natural gas processors reject C₂H₆ at the separation facility sending it to the natural gas pipeline for sale. Although C₂H₆ rejection is useful in eliminating the costs associated with cryogenic separation, it has limited applicability and results in overall revenue loss as ethane typically sells at a small premium in comparison to natural gas.

Ohio University (OHIO), via U.S. Department of Energy’s National Energy Technology Laboratory (NETL) DE-FE0031709 award, is developing a modular technology that simultaneously separates NGLs from shale gas and converts these NGLs to olefin building blocks. The modularity of the technology provides turn-key integration either at the well or further downstream as a distributed chemicals platform for stranded shale gas. Specifically, OHIO is developing an oxidative dehydrogenation (ODH) technology based on a solid oxide fuel cell platform, with a solid electrolyte (membrane) that separates the fuel from oxygen and heterogeneous electro-catalysts that facilitate olefin generation. The reactions below describe the anodic and cathodic reactions based on ethane (other NGLs would follow a similar mechanism) as well as overall ODH and thermal cracking reactions and associated thermodynamics.

Anode: C₂H₆ + O^2- → C₂H₄ + H₂O +2e^-

Cathode: 1/2O₂ + 2e^- → O^2-

Overall ODH: C₂H₆ + 1/2O₂ → C₂H₄ + H₂O ΔH°_reaction = -103.7kJ/mol

Thermal Cracking: C₂H₆ → C₂H₄ + H₂ ΔH°_reaction = 143.9kJ/mol

This specific approach provides significant advantages in comparison to similar oxidative dehydrogenation technologies including scalability and electricity as a process by-product, while offering higher thermal efficiency than thermal cracking – the state-of-the-art dehydrogenation technique at scale.

Prior development efforts at OHIO have shown electrode choice and fabrication technique significantly affect the SOFC’s performance as screen-printed perovskites with rare-earth and alkali-earth chemistries were initially tested. The alkali-earth chemistries showed promising alkane conversion and olefin yield but would require additional improvements for industrially relevant figures of merit. Recent development efforts have prioritized catalyst infiltration as an electrode fabrication technique, thus leveraging enhanced catalytic surface area, lower sintering temperatures and improved triple-phase boundary sites. The results of this fabrication technique including materials characterization and catalyst performance for electrogenerative ODH will be presented at the meeting.