Application of a carbon membrane reactor for dehydrogenation reactions

This research tests a membrane reactor, equipped with a molecular-sieve carbon membrane, using isobutane dehydrogenation on a chromia alumina catalyst as a model reaction. Most pores of the carbon membrane employed are 6– in size and previous independent transport studies show that the permeability ratio of hydrogen to isobutene is larger than 100. These features make the membrane an excellent highly selective low-cost candidate for application in a membrane reactor. The novelty of this study is in the proposed application at relatively high temperatures (450°C and 500°C); only a few studies have tested carbon membrane reactors.Two types of operation modes were studied, using either nitrogen as a sweeping gas in counter current flow or using vacuum as a driving force for membrane transport. As expected, higher conversions were achieved with decreasing feed flow rate. The conversion achieved in the counter-current flow operation method was higher than in all other modes achieving a maximum of 85% at 500°C. While this result is much higher than in the corresponding PFR, the obtained improvement is a result of nitrogen transport and dilution. The conversions obtained in the vacuum mode show modest gains above the ones received in the PFR (40% vs. 30% at 500°C). These results were compared with simulations that used the experimentally determined transport parameters.