Comparative Study of Two Different Hydrogen Redistribution Strategies along a Fluidized-Bed Hydrogen Permselective Membrane Reactor for Methanol Synthesis

Abstract

In this work, two different hydrogen redistribution strategies along a bubbling fluidized-bed hydrogen permselective membrane reactor have been compared. In the first strategy, fresh synthesis gas flows in the tube side of the fluidized-bed membrane reactor in cocurrent mode with reacting material in the shell side, so that more hydrogen is provided in the first segments of the reactor. In the second strategy, fresh synthesis gas flows in the tube side of the fluidized-bed membrane reactor in countercurrent mode with reacting material in the shell side, so that more hydrogen is provided in the last segments of the reactor. A dynamic two-phase theory in the bubbling regime of fluidization was developed to model and compare two strategies from different points of view. Comparison between cocurrent and countercurrent modes of operation shows that the reactor in the countercurrent configuration operates with higher conversion of methanol, longer catalyst life, and higher carbon dioxide removal, whereas the reactor in the cocurrent configuration operates with higher carbon monoxide removal, lower water production, and higher hydrogen permeation rate. Enhancement of the carbon dioxide removal in countercurrent mode and the carbon monoxide removal in cocurrent mode causes a lower environmental impact. The lower water production rate in cocurrent mode reduces catalyst recrystallization.