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Team Argentina:
Hydrogen production from bio ethanol

Booth Number:
H78/5

Miguel Angel Laborde (57) Pio Aguirre (48) Betina Schönbrod (26) University of Buenos Aires, Department of Chemical Engineering Buenos Aires, Argentina

Miguel Angel Laborde	Pio Aguirre	Betina Schönbrod

Hydrogen catalytic production and purification from bioethanol
Laboratorio de Procesos Catalíticos
Facultad de Ingeniería
Universidad de Buenos Aires
Pabellón de Industrias, Ciudad Universitaria, 1428 Buenos Aires
Argentina
INGAR, Instituto de Ingeniería y Diseño (CONICET-UTN)
Avellaneda 3657, 3000 Santa Fe
Argentina
Correspondence to: Miguel A. Laborde
TE/FAX: 54-11-45763240/1
e-mail: miguel@di.fcen.uba.ar

Introduction
There exist several routes for hydrogen production from primary fuels. The clean and non-contaminant feature of H2 as a fuel will depend on the process and raw material employed for its production as well as the source of energy required for this process. If it is obtained from hydrocarbons, carbon oxides are generated regardless the technology used; thus, the quality of clean fuel is only true when the raw material is biomass, which consumes CO2 during its production (growth). Ethanol is a renewable, non-toxic and easy to manipulate source, and has therefore excellent chances to replace fossil fuels.

The new application of H2 as a raw material for fuel cells for mobile sources (PEM) requires that the anode inlet gas has a CO concentration lower than 10 20 ppm. Otherwise, the anode is poisoned and the cell efficiency abruptly drops. Hence, if H2 is produced from hydrocarbons or alcohols, purification is required in order to reduce the CO levels to fuel cell requirements.

The Catalytic Processes Laboratory, in cooperation with INGAR, both from Argentina, has developed a catalytic system to produce fuel grade green H2.

Process
The system developed in Argentina consists of three catalytic reactors connected in series and operating at atmospheric pressure, as it can be seen in Figure 1.

Figure 1. Reactors scheme

The first reactor, the ethanol steam reformer, contains a nickel based catalyst; it is fed with a mixture of ethanol and water, previously vaporized. Considering that the reaction is endothermic, the reactor must be heated and energy is consumed. Working at temperatures lower than 700ºC, the feed is converted to a gaseous mixture containing hydrogen, carbon monoxide, carbon dioxide and methane. A dry gas mean composition of this mixture, is: H2 70%, CO: 8.6%, CO2: 15.7%, CH4: 5.4%. It must be noted that this mixture can be used in chemical and petrochemical industries to obtain different chemicals products that nowadays are obtained from oil.

A purification of this effluent is required in order to reduce the CO levels to PEM fuel-cell requirements. So far, the most technologically feasible purification sequence consists of a water gas shift converter (WGS) and a latter step to eliminate or reduce the remaining CO by selective or preferential oxidation (COPROX).

In the water-gas shift reactor, containing a copper based catalyst and operating at temperatures lower than 250ºC, CO concentration is reduced at 2% producing additional H2. A typical dry gas composition of the effluent is: H2: 76.4%, CO: 1.2%; CO2: 17.4% and CH4: 5%. As this reaction is slightly exothermic, an adiabatic reactor can be used. The WGS reactor is expected to have the largest volume, since this reactor operates close to equilibrium conditions. The effluent can be used to feed the high temperature fuel-cells (solid oxide, phosphoric acid and molten carbonate) without further treatments.

In the COPROX reactor, the WGSR effluent is mixed with air (or O2) and CO remaining is oxidized to CO2. In this reactor the oxidation of H2 also occurs. Then a highly selective catalyst must be employed in order to reduce the hydrogen oxidation as much as possible. The COPROX reactor operates with a CuO-CeO2 catalyst at temperatures lower than 250ºC. As both reactions as highly exothermic, a temperature control must be performed. At the outlet of this reactor CO concentration must be lower than 20 ppm.

Process synthesis and design tasks of fuel processor were made applying process integration techniques, to achieve a satisfactory global efficiency of the system.

Heat exchanged between the reformer outlet streams, hot streams and the feed cold stream should be maximized. Higher reformer temperatures diminish the processor efficiencies.

Water-to-fuel ratio fed to the reformer is a critical decision variable. Water excess must be evaporated and re-heated consuming additional fuel in the reformer. Shaft power is necessary in air compression to feed fuel cell system. It can be supplied by expanding the post combustion gases in an expander within the integrated system.

Units to be installed in vehicles require specific designs for small size process units.

A model-based reactor optimization permits to obtain optimal design.

Modeling the combustion chamber coupled to the reformer allowed optimizing the design variables to reduce the equipment volume (0.04 L/kW).

The WGS reactor unit (0.62 L/kW) has the largest volume. The heterogeneous model used allows computing the optimal reactor length and diameter and the optimal catalyst particle diameter.

The COPROX (0.02 L/kW) reactor requires catalysts with high CO selectivity to reduce the oxidation of H2.

Maximum efficiency, and minimum operation and investments cost in the entire system are required. Proper integration among heat and power sinks and sources must include the fuel processor and the cell.

Considering fuel processor for 1kW fuel cell, the main energy consumers are the reformer feed heating-evaporating-reheating (0.72 kW ), the endothermic reformer reaction (0.37 kW), the compression of air to feed reformer heater, COPROX and the cell (0,16 kW), and the cell cooling system which involve a water radiator with a fan cooler .

The reformer reactor heat must be supplied by burning external fuel and the anode outlet stream that contain a hydrogen fraction close to 30% (dry base) due to partial utilization in the cell. Less hydrogen flow from the anode stream implies more additional fuel to compensate the energy needs. Figure 2 shows the process integration.

A fraction of the cathode outlet stream can be added as oxygen source to the air combustion in the reformer section. Less oxygen utilization in the cell require more air (oxygen) to be blow, and more energy used. Summarizing: new catalitic systems and a new integrated process were developed achieving stable operation and high efficiencies.