(241d) Effects of Morphology and Dopants on the CO2 Capacity of Nanofibrous Calcium-Oxide Based Materials for Sorption-Enhanced Steam Methane Reforming

Hydrogen production is an essential component of the refining and petrochemical industries. Steam-methane reforming (SMR) is the primary method of hydrogen production in the U.S. Sorption enhanced steam-methane reforming (SE-SMR) is an attractive adaption of SMR that reduces operating temperature and down-stream processing. The primary drawbacks of SE-SMR materials are incomplete carbonation, slow carbonation kinetics, loss in activity upon cycling, and high regeneration temperature.

Nanofibrous calcium oxide, synthesized via electrospinning, was compared against calcium oxide synthesized via calcium acetate decomposition, hydrothermal synthesis with the aid of a surfactant, and natural sources. A thermogravimetric analyzer found that the sorption capacity of calcium oxide from nanofibers, from acetate, via hydrothermal, and from natural sources are 0.79, 0.70, 0.57, and 0.14 g_CO2/g_sorbant after 1 hour at 600ºC, 1 atm, and 100% CO₂. The capacity of calcium oxide nanofibers and CaO derived from natural sources were measured over repeated carbonation and calcination cycles. Both calcium oxide nanofibers and natural calcium oxide lost ~33% of their initial capacity after ten cycles. Despite that, in the SE-SMR process, the enhanced activity of calcium oxide nanofibers resulted in a breakthrough time, which was twice that of calcium oxide from natural sources. SEM, TEM, XRD, and BET were used to characterize the sorbents to identify the properties that directly influence the sorption properties such as overall capacity, kinetics, and stability.

Various metal nitrates were added to the calcium nitrate electrospinning solution, at various compositional ratios, as dopants to increase the stability of the sorbent. The dopants studied comprised of metals from Groups 2, 3, 4, 12, and 13 on the periodic table of elements. After reacting these doped-sorbents at 600^oC and 1 atm with 100% CO₂, the added metals were shown to have various effects on capacity, kinetics, and stability. XRD was used to identify how the dopants affect the crystal structure of calcium oxide, the dopant either forms a pure oxide crystal structure or it forms a mixed metal oxide. SEM was also used to identify morphological changes in the nanofibrous structures. The results demonstrate a promising opportunity for the application of doped electrospun materials in SE-SMR.