Low-Temperature Steam Reforming of Natural Gas after LPG-Enrichment with MFI Membranes

Abstract

Low-temperature hydrogen production from natural gas via steam reforming requires novel processing concepts as well as stable catalysts. A process using zeolite membranes of the type MFI (Mobile FIve) was used to enrich natural gas with liquefied petroleum gas (LPG) alkanes (in particular, propane and n-butane), in order to improve the hydrogen production from this mixture at a reduced temperature. For this purpose, a catalyst precursor based on Rh single-sites (1 mol% Rh) on alumina was transformed in situ to a Rh1/Al2O3 catalyst possessing better performance capabilities compared with commercial catalysts. A wet raw natural gas (57.6 vol% CH4) was fully reformed at 650 °C, with 1 bar absolute pressure over the Rh1/Al2O3 at a steam to carbon ratio S/C = 4, yielding 74.7% H2. However, at 350 °C only 21 vol% H2 was obtained under these conditions. The second mixture, enriched with LPG, was obtained from the raw gas after the membrane process and contained only 25.2 vol% CH4. From this second mixture, 47 vol% H2 was generated at 350 °C after steam reforming over the Rh1/Al2O3 catalyst at S/C = 4. At S/C = 1 conversion was suppressed for both gas mixtures. Single alkane reforming of C2–C4 showed different sensitivity for side reactions, e.g., methanation between 350 and 650 °C. These results contribute to ongoing research in the field of low-temperature hydrogen release from natural gas alkanes for fuel cell applications as well as for pre-reforming processes.