Non-oxidative dehydrogenation of light alkanes using ceramic membranes: A technological and techno-economic assessment

This dissertation presents a technological and techno-economic assessment of applying ceramic proton-conducting membranes in the non-oxidative dehydrogenation (NODH) of light alkanes. Ligh alkane NODH generates light olefins, which are widely used in the production of plastics. However, alkane NODH is limited by thermodynamic equilibrium, which restricts olefin yields (ca. 30-40%), even at elevated temperatures (500-700 ᵒC). Ceramic membranes can be used to increase olefin yields for a given temperature, which thereby potentially allows for a drastic reduction in energy intensity and carbon footprint of industrial processes for the production of plastics. The first aim of this dissertation is to identify technological hurdles that need to be overcome to substantiate membrane industrialization for this application. Results indicate that the rate and mechanism of the alkane NODH reaction strongly differ with gas phase composition. Besides, the stability of the applied alumina-supported PtSn dehydrogenation catalyst reduces in more olefin rich and hydrogen poor atmospheres. It is further known that ceramic membranes function optimally in the presence of steam, implying that the used PtSn catalyst will be exposed to moistened atmospheres in membrane reactors. This work demonstrates that cofeeding steam deteriorates the stability of the PtSn catalyst, meaning that Sn free catalyst compositions are preferred in membrane reactors. Alternatively, the Pt catalyst can be deposited directly onto the ceramic membrane material to optimize the mass transfer from catalyst to membrane. However, this dissertation shows that the olefin selectivity and catalyst stability of Pt supported onto ceramic membranes are considerably worse as compared to alumina-supported Pt. For this reason, the dehydrogenation catalyst needs to be physically separated from the ceramic membrane in membrane reactors for this application. The second aim of this dissertation is to assess the techno-economic viability of membrane-assisted light alkane NODH. The results indicate that the capital investment and profitability of membrane-driven alkane NODH is similar to conventional olefin production technologies. However, the targeted savings in carbon emissions are only attained when fully renewable electricity is utilized. Furthermore, green electrification of conventional olefin production processes leads to a similar reduction in carbon footprint as commercialization of membrane-assisted alkane NODH.