Hydrogen Production via Steam Reforming of Methane with Simultaneous CO2 Capture over CaO−Ca12Al14O33

Abstract

Two processes to produce hydrogen via steam reforming are compared in a laboratory fixed bed reactor: conventional steam reforming with a nickel-based catalyst and sorbent-enhanced steam reforming with a mixture of a nickel-based catalyst and CaO−Ca12Al14O33 sorbent. A preliminary thermodynamic study was performed to determine the operating window of the sorption enhanced reforming at atmospheric pressure. Operating temperatures less than 650 °C are required to take advantage of the favorable thermodynamics due to the in situ capture of CO2, while maximum gain in methane conversion between the two process options is attained for a steam to methane molar ratio of around 3. Under these conditions, CaO−Ca12Al14O33 (85:15 wt) synthesized using calcium acetate as a CaO precursor acted as an effective CO2 sorbent, reducing by 67% the amount of total CO2 that would have been emitted in conventional steam reforming. Due to CO2 capture, the methane steam reforming equilibrium shifted to higher hydrogen purities. Hydrogen concentrations higher than 92%, on a dry basis, were achieved at 650 °C, 1 atm of pressure, and a steam to methane molar ratio of 3.4, as opposed to 77% produced under the same conditions via the conventional steam reforming. The experimental reactor was operated batchwise and with cyclic alternation between reforming/sorption conditions and higher-temperature conditions to regenerate the sorbent. The performance of the material is deemed adequate as a moderate loss (ca. 15%) in sorption capacity after 13 consecutive cycles was observed.