QUICK-START CATALYZED METHANOL PARTIAL OXIDATION mFOFUVIER*

n m S. Ahmed and R. Kumar

Argonne National Laboratory 9700 South Cass Avenue Argonne, Illinois 60439

to be presented at The 1995 Automotive Technology Development Contractors' Coordination Meeting

Dearborn, MI October 23-27,1995

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof. nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsi- bility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Refer- ence herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom- mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

The submitted manuscript has been authored by a contractor of the U. S. Government under contract No. W-31-109-ENG-38. Accordingly, the U. S. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U. S. Government purposes.

"This research was supported by the U. S . Department of Energy, Electric and Hybrid Propulsion Systems Division, Office of Transportation Technologies, under contract number W-3 1-109-ENG-38.

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QUICK-START CATALYZED METHANOL PARTIAL OXIDATIQN REFORMER

S. Ahmed and R. Kumar Electrochemical Technology Program

Argonne National Laboratory

Methanol is an attractive alternative fuel for fuel-cell-powered ve--Aes because of easy handling and vehicle refueling, and because it has a sufficiently high fuel energy density. For low- temperature fuel cells, the methanol must be converted (reformed) before use to a hydrogen-rich gas mixture. The reformer for this operation must be efficient, compact, and light-weight. It should be capable of a rapid start and be dynamically responsive, Le., able to supply varying amounts of hydrogen as the demand changes during the drive cycle. The catalytic methanol partial oxidation reformer that is described in this paper offers all the requisite attributes for use in transportation fuel cell systems.

The partial oxidation of methanol produces hydrogen, and carbon oxides. A small amount of

CH,OH(Z) + 0, -.+ H2 + CO, + CO water fed in with the methanol converts most of the carbon monoxide to additional hydrogen and carbon dioxide. Being an exothermic reaction, partial oxidation offers the advantage that it generates heat, which allows the reactor to warm up to reaction conditions rapidly. Once reaction temperature has been reached, it can be maintained by controlling the amount of oxygen (air) fed into the reactor. Thereafter, the varying hydrogen demand (load) can be met by changing the feed rates while maintaining the proportions of methanol, air, and water. Conducting the above reactions in a catalyzed process achieves the desired results at lower temperatures, and with greater selectivity (by suppressing undesirable side reactions), than is the case with uncatalyzed, high-temperature partial oxidation reforming of methanol.

The bench-scale prototype methanol reformer (5-1 0 kW equivalent) developed at Argonne is a cylindrical reactor loaded with copper zinc oxide catalyst. Liquid methanol, along with a small amount of water, is injected as a fine spray into a flowing air stream, past an igniter (which serves to vaporize and ignite a small fraction of the methanol) onto the catalyst bed where the partial oxidation reaction takes place.

The catalyst for the partial oxidation process is in the oxide form, ready for use as received, and does not need to be protected from exposure to air. The steam reforming process also uses the copper zinc oxide catalyst, but for that process the catalyst is active only in its reduced state. Reduction of the catalyst is slow (to prevent its overheating), and is carried out in situ. Once reduced, the catalyst must be protected from exposure to air thereafter, even when the reformer is shut down and at room temperature. Thus, the partial oxidation process design, operation, and maintenance are significantly simplified as a result of the catalyst being active in the oxide form.

Tests were conducted on a 5-cm diameter, 0.8-L reactor with the catalyst in pellet form, supported on cordierite honeycomb disks. Start-up studies with this prototype reformer showed hydrogen production in less than 25 seconds and hydrogen concentration in the reformate increased to more than 30% in less than 100 seconds. It is anticipated that even shorter start-up times will be achieved with the help of a systematic start-up protocol that provides the optimum feed proportions as a fhction of the temperature distribution in the catalyst bed. The reformer was operated at various steady-state conditions with methanol feed rates in the range 30-55 ml/min. The air feed rate was varied such that the oxygedmethanol molar ratio varied between 0.25-0.3 1; the water feed rate was held at -1 5% by volume of the combined methanol and water. These experiments were conducted over a number of days and included numerous stadstop cycles. The product gas fiom the reformer contained approximately 50% hydrogen and less than 5% (typically 3%) carbon monoxide, the balance being carbon dioxide and nitrogen.

Preliminary data on the transient response is promising. During step changes in the feed rates, the reactor was found to be very responsive. The product compositions showed slight variations with the changes in processing rates, but for only brief periods, and quickly returned to the levels that prevailed before the step change.

Thus, the catalyzed methanol partial oxidation reformer offers the hardware features of small size, low weight, and the absence of moving parts; the operational features of rapid start, dynamic response, and ease of control; and the system-level features of a simple design resulting from fewer unit operations (e.g., no pre-vaporization of liquid feeds, no recycle loops, no indirect heat transfer) and no need to protect the catalyst from exposure to air.

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Quick-Start Catalyzed Methanol Partial Oxidation Reformer

Shabbir Ahrned and Romesh Kumar Electrochemical Technology Program

Argonne National Laboratory

1995 Automotive Technology Development Contractors Coordnation Meeting, Dearborn, MI, October 23-27, 1995

Requirements for Reformers in Fuel Cell Systems for Light-Duty Vehicles

@Rapid start - low thermal mass - low operating temperature - direct heat transfer

Dynamic response I - direct heat transfer I - absence of recycle loops I

- fast reactions - simple construction

Compact and lightweight

Efficient I - minimum energy loss

Argonne Electrochemical Technology Program

Partial Oxidation Reforming is Perceived to Have Two Significant Drawbacks

1. Hydrogen concentration in the reformate is lower than that from steam reforming

2. Fuel cell system efficiencies may be lower than with steam reforming

Argonne Electrochemical Technology Program

Hydrogen Concentration in the Reformate Increases as the Oxygen is Decreased

010 0.1 012 0.3 0.4 C Oxygen-to-Methanol Molar Ratio

5

Argonne Electrochemical Technology Program

Efficiency of Partial Oxidation Reformed Methanol Systems is Sensitive to Fuel Utilization in the Fuel Cell Stack

SR

Oxygen-to-Methanol Ratio E I "h 20 m 65 70 75 80 85 90 !

Electrochemical Fuel Utilization, % 5

Argonne Electrochemical Technolob Program

Our Catalytic Partial Oxidation Reformer Provides all the Reauisite Attributes

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0

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Rapid start (less than 100 s)

Direct liquid feed injection

Compact reactor (no indirect heat exchange)

Simple reactodfuel cell system design

Good dynamic response (at least 40% instantaneous turn-down)

Argonne Electrochemical Technology Program

Schematic of the Methanol Partial Oxidation Reformer

Methanol + -[Nozzle

Products

Reactor: cylindrical

Catalyst: copper zinc oxide - honeycomb, 64 channels/cm2 - pellets

Nozzle: 20-micron droplets

Igniter: Nichrome wire coil

Argonne Electrochemical Technolob Program

Significant Hydrogen is Produced in Less Than 100 Seconds from Start-up

0

o 25 i o 75 100 12s is0 17s 2 0 Time, s

Argonne Electrochemical Technology Program

Steady-State Operation Yields 50% Hydrogen, Less Than 5% Carbon Monoxide

0 10 20 30 40

Cumulative Time, h Argonne Electrochemical Technolob Program

Summary of the Salient Features of the Methanol Partial Oxidation Reformer

Hardware features - small size, low weight - no moving parts

Operational features - rapid start - dynamically responsive - easy to control

- no recycle loops - no need to sequester catalyst

0 System-level features

Argonne Electrochemical Technology Program

In Conclusion

We have built and tested a 5-10 kW size reformer

Operates with direct injection of liquid methanol

Product contains 50% hydrogen, <5% carbon monoxide and no methane

Argonne Electrochemical Techno logy Program

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