(142c) Sorption-Enhanced Reaction Processes: Steam Methane Reforming Combined with in-Situ Co2 Removal for Increased Hydrogen Production

Eduardo L. G. Oliveira, Carlos A. Grande and Alírio E. Rodrigues ^*

LSRE ? Laboratory of Separation and Reaction Engineering, Department of Chemical Engineering, Faculty of Engineering, University of Porto. Rua Dr. Roberto Frias (4200-465), Porto, Portugal.

New global policies on energy production are leading to stringent process optimisation and development. Attending to reduce the emission of greenhouse gases, new processes and new fuels are under research. Hydrogen is envisioned as the fuel of the future. Actually, almost 80% of hydrogen consumed worldwide is produced by Steam Methane Reforming (MSR).

The most important reactions in the MSR are:

                                                  (1)

                                                                (2)

                                               (3)

All these reactions are reversible and the overall scheme results endothermic. As can be noted from the reaction scheme, this reaction is thermodynamically limited and requires very high temperatures to obtain reasonable methane conversions, increasing energy demands of the process and also capital cost. The removal of products from the reaction media (removal of hydrogen and/or carbon dioxide) can displace the equilibrium to obtain higher amounts of hydrogen.

The removal of hydrogen is being studied through the use of membrane-aided reformers, where H₂ is removed from the media shifting equilibrium and at the same time obtaining a purified stream. The second route for enhance hydrogen production by equilibrium shifting is the removal of CO₂ from the reaction media.

In our group we have been studying CO₂ adsorption at high temperatures using hydrotalcites. An example of the amount adsorbed of CO₂ at 673K in hydrotalcite (Condea) measured by breakthrough curves is shown in Figure 1. The removal of carbon dioxide from the reaction media has two advantages: it displaces reaction equilibrium resulting in higher yields of hydrogen and also produces a stream with less CO (undesirable by-product for fuel cells). This work reports experimental data of a large-pore Ni-based catalyst (see SEM picture in Figure 2) combined with high temperature adsorption data of CO₂ in hydrotalcite. The combination of MSR reaction ? CO₂ adsorption (SERP concept) is also presented.

Figure 1. Adsorption of CO₂ on hydrotalcite at 673K: breakthrough curves (adsorption / desorption cycles) and pure component equilibrium.

Figure 2. SEM picture of large pore Ni-based catalyst used for steam methane reforming.