(501b) A Modeling and Experimental Study of CO2-Selective Water-Gas-Shift Membrane Reactor for Fuel Cells

Improving water gas shift (WGS) reaction for hydrogen purification is of particular interest to the application of fuel cells. As a reversible and exothermic reaction, the conventional WGS reactor is not efficient, resulting in a high concentration of unconverted CO (about 1%) in the H2 product and a bulky, heavy reactor. For CO cleanup, current known approaches include methanation and preferential oxidation. But, both consume a significant amount of hydrogen and add additional steps. However, using a CO2-selective membrane reactor shifts the WGS reaction towards the product side, which enhances the conversion of CO and increases the purity of the H2 product at high pressure. In addition, air can be used as the sweep gas to remove the permeate, CO2, on the low-pressure side of the membrane to achieve a high driving force for the separation. This presentation will report on a modeling and experimental study of the membrane reactor.

In the modeling study, a one-dimensional non-isothermal model was developed to simulate the reaction and transport process in a hollow-fiber type membrane reactor with countercurrent gas flows. The reaction rate equation for the Cu/ZnO catalyst from literature was incorporated into the model. The synthesis gases with different CO concentrations from autothermal reforming of gasoline with air were used as the feed gas, while heated air was used as the sweep gas. The modeling results showed that the exit CO concentration of less than 10 ppm was achievable. The effects of several important system parameters including inlet feed temperature, inlet sweep temperature, feed-side pressure, feed inlet CO concentration, and catalyst activity were investigated. In the experiments, a rectangular flat-sheet membrane reactor using the commercial Cu/ZnO catalyst was set up. The gas mixture with the composition of an autothermal reforming syngas (1% CO, 45% H2, 17% CO2, and 37% N2) was used as the feed gas, and Ar or air was used as the sweep gas (using Ar for the ease of GC analysis). By varying the feed flow rate, the performance of the reactor was investigated. The experimental data agreed well with the modeling results based on the same geometrical dimensions of the reactor. A CO concentration of less than 10 ppm and a H2 concentration of greater than 52% (on the dry basis) were achieved.