Methanol quality and its effects on the fuel-cell reformer off-gas composition

Abstract

Previous research articles that deal with methanol-steam reforming with Cu/ZnO/Al?O? catalyst do not take into account the quality of methanol used and the effect that it would have on catalyst performance and the off-gas composition as a result. This study focuses on three methanol qualities, and qualifies and quantifies the change in the off-gas composition over a period of 30 hours of operation using each methanol quality. In order to achieve this aim, the problem statement is as follows: The full impact of various methanol fuel qualities on the operation of the reformer and subsequently the composition of the off-gases which is not commonly known nor addressed in literature. The addressing of the problem statement was approached by three experiments on a methanol steam reformer filled with catalyst similar to commercial Cu/ZnO/Al?O?. Each experiment analysed the off-gas condensate, as well as the analysis of gas samples and catalyst in 10 hour intervals. A fuel qualifying experimental facility was designed and built which delivered the respective methanol-water mixture qualities into an evaporator after which it was reformed into hydrogen, carbon dioxide, and carbon monoxide while condensing the unreformed methanol and water. The experimental facility was evaluated according to the design outcomes and requirements stipulated by the design criteria. The catalyst was manufactured using methods described by various articles. Condensate samples confirmed that lower methanol quality decreased the maximum methanol conversion and lifespan of the catalyst when compared to that of the higher methanol quality. An increase in acidity of the condensate was observed due to chloride compounds which were presented faster when reforming lower quality methanol. The gas samples indicated that the methanol quality did not significantly affect the stoichiometric concentrations of hydrogen and carbon dioxide. The carbon monoxide concentration was highest during the first 10 hours while reforming all methanol qualities and converged to about 0.3mol% for all methanol qualities. No hydrogen sulphide was detected in the reformer outlet stream. The analysed catalyst samples revealed signs of sintering while reforming by a change in pore size, roughing and coarser catalytic surface texture, and indications of cleavage and brittle fracture when compared to fresh catalyst. Sintering was independent of methanol quality and the lower methanol qualities did not drastically alter the catalyst topology. The catalyst exposed to lower quality methanol presented an increased amount of chloride impurities chemisorbed to the catalyst compared to the catalyst exposed to higher quality methanol as well as an increased penetration depth into the catalyst pellet. There was no carbon deposition detected from any of the methanol qualities.