| Summary: |
Wide attention is currently focused upon fuel cells as sources of electrical power that offer environmental compatibility and reliable and quiet operation. Portugal has the only Iberia company producing and commercialising fuel cells (PEMFC- Polymer Electrolyte Membrane Fuel Cell), the SRE. The hydrogen logistics for fuelling the fuel cells operating in Portugal is challenging.
Hydrogen has a very low energy density per normal volume and storage and transportation strategies have to be developed. One possibility is using metallic hydrides but the maximum storage capacity is still very low, around 0.5 kWh/kg. Liquid hydrocarbons have much higher energy content, e.g. methanol does have 6.3 kWh/kg. It is then apparent why steam reforming becomes so attractive.
The research in methanol and ethanol steam reforming exploded starting in 2004, with the number of papers per year more than duplicating.
Methanol has been the most frequent choice mainly because it can operate at moderate temperatures (around 250°C).
The off-gas of a methanol steam-reforming unit is roughly 75% hydrogen and 25% carbon dioxide with small amounts of carbon monoxide. To reduce the carbon monoxide levels (which poisons the PEMFC catalyst) several approaches can be followed, but perhaps the most interesting one is simple to use more efficient catalysts and lower the reactor's temperature (the CO formation is an endothermic reaction).
This year, a Japanese group reported a catalyst that is one order of magnitude more active than the traditional CuO/ZnO/Al2O3 catalyst, even at
230°C. This opens the doors for doing the steam reforming of methanol at temperatures around 200°C. Furthermore, if the catalyst is microchannel supported its efficiency becomes even higher.
The present project aims ultimately to combine in a single reactor a steam reforming unit and a PEMFC, operating at around 200°C or less. For that it will be studied: i) the micro-supported methanol steam-reforming with  |
Summary
Wide attention is currently focused upon fuel cells as sources of electrical power that offer environmental compatibility and reliable and quiet operation. Portugal has the only Iberia company producing and commercialising fuel cells (PEMFC- Polymer Electrolyte Membrane Fuel Cell), the SRE. The hydrogen logistics for fuelling the fuel cells operating in Portugal is challenging.
Hydrogen has a very low energy density per normal volume and storage and transportation strategies have to be developed. One possibility is using metallic hydrides but the maximum storage capacity is still very low, around 0.5 kWh/kg. Liquid hydrocarbons have much higher energy content, e.g. methanol does have 6.3 kWh/kg. It is then apparent why steam reforming becomes so attractive.
The research in methanol and ethanol steam reforming exploded starting in 2004, with the number of papers per year more than duplicating.
Methanol has been the most frequent choice mainly because it can operate at moderate temperatures (around 250°C).
The off-gas of a methanol steam-reforming unit is roughly 75% hydrogen and 25% carbon dioxide with small amounts of carbon monoxide. To reduce the carbon monoxide levels (which poisons the PEMFC catalyst) several approaches can be followed, but perhaps the most interesting one is simple to use more efficient catalysts and lower the reactor's temperature (the CO formation is an endothermic reaction).
This year, a Japanese group reported a catalyst that is one order of magnitude more active than the traditional CuO/ZnO/Al2O3 catalyst, even at
230°C. This opens the doors for doing the steam reforming of methanol at temperatures around 200°C. Furthermore, if the catalyst is microchannel supported its efficiency becomes even higher.
The present project aims ultimately to combine in a single reactor a steam reforming unit and a PEMFC, operating at around 200°C or less. For that it will be studied: i) the micro-supported methanol steam-reforming with at least two steam reforming catalysts, steady and unsteady state operation; ii) the use of a metallic and a carbon molecular sieve membranes to improve the reactor's methanol conversion and to purify the hydrogen stream produced; iii) the integration of the steam reforming unit with a PEMFC.
Indeed, Basile et al. found that the use of a catalytic membrane reactor improves the methanol conversion for all operating conditions.
These authors used a Pd/Ag membrane. However, our group has a strong experience with Carbon Molecular Sieve Membranes which are stable at 200°C in a reducing atmosphere and far more permeable and cheaper.
Materials are being developed for PEMFC to operate at 200°C. The steam reforming reaction is endothermic and the necessary heat can be supplied by the PEMFC, which operates exothermally. Combining the two units will originate a high efficient reactor.
This project will benefit from the recently established link with IMM (Germany), who will supply the micro-channel supported catalysts. The longrun collaboration with GKSS (Germany), expert in high temperature PEMFC, and the collaboration with the fuel cell Portuguese company SRE. |