A Microreactor for Hydrogen Production in Micro Fuel Cell ... - Parc

JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 13, NO. 1, FEBRUARY 2004

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A Microreactor for Hydrogen Production in Micro Fuel Cell Applications Ashish V. Pattekar and Mayuresh V. Kothare, Associate Member, IEEE

Abstract—A silicon-chip based microreactor has been successfully fabricated and tested for carrying out the reaction of methanol reforming for microscale hydrogen production. The developed microreactor in combination with a micro fuel cell is proposed as an alternative to conventional portable sources of electricity such as batteries due to its ability to provide an uninterrupted supply of electricity as long as a supply of methanol and water can be provided. The microreformer-fuel cell combination has the advantage of not requiring the tedious recharging cycles needed by conventional rechargeable lithium-ion batteries. It also offers significantly higher energy storage densities, which translates into less frequent “recharging” through the refilling of methanol fuel. The microreactor consists of a network of catalyst-packed parallel microchannels of depths ranging from 200 to with a catalyst particle filter near the outlet fabricated 400 using photolithography and deep-reactive ion etching (DRIE) on a silicon substrate. Issues related to microchannel and filter capping, on-chip heating and temperature sensing, introduction and trapping of catalyst particles in the microchannels, flow distribution, microfluidic interfacing, and thermal insulation have been addressed. Experimental runs have demonstrated a methanol to hydrogen molar conversion of at least 85% to 90% at flow rates enough to supply hydrogen to an 8- to 10-W fuel cell. [976]

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Index Terms—Fuel cell, lab-on-a-chip, micro fuel cells, microfluidics, microreactor, microreformer, system-on-chip.

I. INTRODUCTION AND LITERATURE SURVEY

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HE use of microreactors for in situ and on-demand chemical production is gaining increasing importance as the field of microreaction engineering matures from the stage of being a regarded as a theoretical concept to a technology with significant industrial applications. Various research groups have successfully developed microreactors for chemical processing applications such as partial oxidation of ammonia [29], nitration [5], phosgene synthesis [1], multiphase processing [17] and chemical detection [10]. The objective of this work is to demonstrate a working microreaction system for use as a sustained source of hydrogen fuel for proton exchange membrane (PEM) fuel cells through

Manuscript received December 13, 2002; revised September 4, 2003. This work was supported in part by the U.S. National Science Foundation (“XYZ-on-a-Chip” initiative Grant CTS-9980781) and the Pittsburgh Digital Greenhouse. Fabrication of the microreactor was performed in part at the Cornell Nanofabrication Facility (a member of the National Nanofabrication Users Network) which was supported by the National Science Foundation by Grant ECS-9731293, its users, Cornell University, and Industrial Affiliates. Subject Editor C.-J. Kim. The authors are with the Integrated Microchemical Systems Laboratory, Department of Chemical Engineering, Lehigh University, Bethlehem, PA 18015 USA (e-mail: [email protected]; [email protected]). Digital Object Identifier 10.1109/JMEMS.2004.823224

the catalytic steam reforming of methanol. A major constraint in the successful commercialization of miniature fuel cells as an alternative to conventional rechargeable batteries for supplying electricity to portable electronic devices such as laptop computers and mobile phones has been the difficulties and hazards involved in the storage and handling of hydrogen, which is used as fuel. In either compressed gas or liquid form, hydrogen presents significant explosion hazards. Also, the stored density of hydrogen in compressed or liquid form is significantly lower in comparison to storage in the form of liquid hydrocarbons such as methanol which can be reformed for generation of the gas as and when needed. Another method of hydrogen storage in the form of metal hydrides [31], [19] has been discussed in depth in the literature. However, the use of hydrides to store hydrogen suffers from several drawbacks, which include the loss of hydrogen storage capacity after repeated use (limited alloy operating life), higher weight per unit amount of hydrogen stored (hydrides have the metal weight added to the total storage cylinder weight), and difficulty in extracting all the stored hydrogen (hysterisis). Also, since a hydride cylinder is a passive storage device, a fuel cell that is being supplied with hydrogen from a hydride container may not perform properly in case of a sudden high electricity demand (e.g., using several accessories at once in a portable electronic device) as there is no way of increasing the default maximum hydrogen flow rate. In contrast, a hydrogen producing microreactor could incorporate complete integrated control systems, which would immediately boost the production rate based on fuel cell demand by increasing the reactant flow rates. The developed microreactor in combination with a micro fuel cell [15] is therefore proposed as an alternative to conventional portable sources of electricity such as batteries due to its ability to provide an uninterrupted supply of electricity as long as a supply of methanol and water can be provided. Also, the energy storage density per unit volume/weight of this system is higher than that of batteries, which translates into less frequent recharging through the refilling of methanol fuel. Though considerable work already exists in the literature on the catalytic steam reforming of methanol for production of hydrogen using conventional reactors [2], [8], [11] , [12], the use of microreactors for in situ methanol reforming is a relatively new idea [9], [16], [20], [21], [23], [24], [26], [28], [30]. Literature on the macroscale steam reforming of methanol includes analysis of the reaction thermodynamics [2] for prediction of optimum reactor temperature and feed compositions, catalyst characterization studies [11], and experimental studies on macroscale pilot reactors [12]. Results obtained in the study of methanol reforming in these conventional reactors

1057-7157/04$20.00 © 2004 IEEE

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Fig. 2.

Integration of on-chip heater and temperature sensor.

Fig. 3.

SEM image of platinum temperature sensor.

Fig. 1. Microchannel device fabrication.

form a good background for the development of microreactors for this purpose. Silicon is considered a good material for fabrication of microreactors due to the high strength of the Si-Si bonds which results in the chemical inertness and thermal stability of silicon. Well-established silicon micromachining techniques commonly used in the microelectronics industry facilitate easy fabrication of microchannels and other desired features on silicon substrates, making silicon an excellent choice for microreactor fabrication. In Sections II–V, we discuss the theoretical and experimental issues in the development of a prototype silicon chip based microreformer. We have previously published our preliminary work related to the fabrication and experimental operation of a prototype microreformer [26]. The current paper presents a significantly improved design in the form of a network of 1000 parallel microchannels of cross section 400 packed with copper/zinc oxide (Cu/ZnO) catalyst particles of appropriate size. The configuration of the network itself is such that the reactor chip provides the required conversion at the desired net flow rate while ensuring equal residence times in all parallel microchannels. The catalyst particles are trapped in the microchannels by a filter [4] near the microreformer outlet, formed using deep-reactive ion etching (DRIE) of silicon. On-chip platinum lines meandering along the microchannels serve as heaters and temperature sensors compatible with

commercially available temperature controllers and are used to maintain the temperature while carrying out experimental runs of the microreformer [22]. II. THE METHANOL REFORMING PROCESS Methanol reforming refers to the chemical reaction between and water vapor for the production methanol gas. This process is typically carried out in of hydrogen

PATTEKAR AND KOTHARE: HYDROGEN PRODUCTION IN MICRO FUEL CELL APPLICATIONS

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in a separate water-gas shift reactor or by oxidation to (reaction 4) after separating the hydrogen from the product gases using a selective membrane (e.g., made of palladium) [14]. The and the excess water vapor are subsequently generated the only by-products of the process and can be safely vented to the atmosphere (4) Typical residence times (contact times between the reacting gases and the catalyst) for sufficient conversion of methanol to hydrogen are known to be of the order of about 500 to 700 milliseconds [13]. The reforming reactions are endothermic in the production, i.e., a certain amount of heat energy direction of has to be supplied to the system for carrying out the reactions. per mole of converted reacThe values of the heat load , and for reactions (1), tant are (2) and (3) respectively, with the ’ ’ sign representing an endothermic reaction and the ’ ’ sign representing an exothermic reaction. From the above discussion, it can be seen that several reaction engineering issues need to be considered in the design of the proposed microchannel reformer. These include overall flow rate and pressure drop considerations, minimum residence times for good conversion at the desired flow rate, optimum operating yield, and energy temperature and pressure for maximum requirements during the microreactor operation for maintaining the operating temperature. The method of fabrication of the microreactor using conventional silicon-processing techniques is described in Section III followed by detailed theoretical analysis of the design to illustrate some of the reaction engineering principles described in Section IV. Results from the operation of the fabricated microreactor are presented in Section V.

Fig. 4. Mask layout for channel network and filter.

III. FABRICATION PROCEDURE A. Microchannel Device Fabrication

Fig. 5. SEM images of the microchannels and catalyst filter.

the presence of metal oxide catalysts at temperatures ranging from 195 to 260 [2]. The chemical reactions taking place during the reforming process are outlined as follows: (1) (2) (3) Reaction (1) is the main reforming reaction which gives the stoichiometric conversion of methanol to hydrogen. It can be regarded as the overall effect of reactions of methanol decomposition (2) and the water-gas shift reaction (3), the relative kinetics of which determine the amount of intermediate product carbon monoxide (CO) formed in the process. Proper control of methanol to water feed ratios and reformer operating temperature and pressure conditions [2] can be used to minimize the amount of CO formed in the process, especially as higher CO formation lowers the hydrogen production rate and CO also acts as a poison for the fuel cell catalyst. Typically the either unconverted CO is converted to carbon dioxide

to 400 and Microchannels of depth ranging from 200 width of 1000 are fabricated in 1000 thick silicon substrates using photolithography followed by DRIE. A photorethickness (Shipley 1045, single/dual sist coating of up to 10 coat) is used as the etch mask for DRIE [see Fig. 1(a)]. A filter for trapping catalyst particles is also fabricated downstream near the microchannel outlet using DRIE. The filter obtained after the etching process is in the form of several 80- -thick parapart oriented parallel to the direction allel walls spaced 20 in which the fluid will flow in the channels during actual device operation. The channel side of the processed silicon wafer is subsequently aligned and anodically bonded to a pyrex wafer (thickness 1.8 mm) with mechanically drilled holes at precise positions corresponding to the inlet and outlet of the channels [see Fig. 1(b)] to obtain microchannel conduits enclosed between the silicon and glass surfaces [see Fig. 1(c)]. Teflon (PTFE) capillaries are then bonded to the inlet/outlet holes in the pyrex wafer for carrying out the microfluidic interfacing [see Fig. 1(d)]. The diameter of the hole in the pyrex wafer (1.75 mm) is slightly larger than the outer diameter

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Fig. 6. Geometry model of the channel network in FEMLAB.

of the teflon capillary (1.68 mm) used in the interconnection to ensure that the capillary can be passed freely through the hole without excessive clearance. Specific details regarding the capillary bonding process and analysis/testing and strength characterization of the interconnect are given elsewhere [25]. Finally, a water-based suspension of catalyst particles (size –70 ) is passed through the microchannel derange 50 vice. The catalyst particles of desired size range are obtained by grinding and sieving commercially available catalyst pellets (Süd-Chemie G-66B Cu/ZnO low-temperature shift (LTS) catalyst). On passing the suspension, the catalyst particles get trapped in the microchannels due to the presence of the filter near the outlet which allows only particles smaller than 20 to pass through. This results in the formation of a micropacked bed of catalyst particles in which the reaction can be carried out during the microreactor operation. After the catalyst bed formation step the device appears as schematically represented in Fig. 1(e). B. Integration of On-Chip Heaters and Temperature Sensors As discussed earlier, the microreactor has to be maintained at about 195–260 during operation. Integrated on-chip heaters and temperature sensors are used for this purpose. The heaters and sensors are in the form of platinum metal lines patterned with proper alignment on the backside of the substrate (see Fig. 2) after the microchannel etching step of Fig. 1(a). The temperature sensor is a platinum resistance-temperature device (RTD) with a linear temperature v/s resistance characteristic.

TABLE I PARAMETERS USED IN NUMERICAL ANALYSIS

The heater is a platinum line meandering along the microchannels (also on the backside of the substrate). The metal lines are laid out inside trenches etched using DRIE [see Fig. 2(a)] to avoid raised metal deposits on the silicon surface which might interfere with the backside anodic bonding step used for electrical and thermal insulation of the device. is used as a passivation layer for electrical Sputtered insulation between the heater/RTD lines and the silicon subPlatinum layer is patterned by strate [Fig. 2(b)]. The lift-off of the photoresist [Fig. 2(c)]. Thus a single patterned photoresist layer serves as both an etch mask for the etching of trenches and as the medium for lift-off of the oxide and metal. The final device, complete with the micropacked bed, capillary interfacing, heater/temperature sensors and backside anodically bonded pyrex wafer is shown schematically in Fig. 2(d). The pyrex wafer bonded on the heater/sensor side has holes drilled at locations corresponding to bonding pads of the


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heater and sensor lines. It also has larger metal pads patterned on the exposed (nonbonded) side which are connected to the heater/sensor bonding pads by ultrasonically bonded aluminum wire for electrical interfacing to the temperature controller. Scanning electron microscope (SEM) images of the fabricated RTD are shown in Fig. 3. A detailed view showing the trench in which the metal line is deposited is also shown in the figure.

ible fluids (6) [6] are used to model gas flow through the geomis the permeability etry, where is the fluid velocity vector, of the porous medium, denotes the pressure, denotes the fluid viscosity, and is the fluid density

IV. MICROREACTOR DESIGN

The gas is modeled as a compressible fluid in accordance with the ideal gas law, where denotes the volume occupied by moles of the gas at temperature :

A. Configuration of the Channel Network The single channel device described in Section III was for illustrative purposes only, the actual microreactor consists of a network of precisely oriented parallel microchannels for carrying out the reforming reaction since a simple single channel design proves to be inadequate from the point of view of the operating requirements on a typical microreformer. For example, design constraints such as the minimum hydrogen production rate based on fuel cell demand, the maximum pressure drop that can be provided using the microfluidic interface and pumping system and the minimum time that the reacting gases should spend in contact with the catalyst particles to ensure sufficient methanol to hydrogen conversion require a minimum total cross section of the flow conduit. At the same time, to ensure uniform catalyst utilization across the entire reactor chip and uniform fast heat transfer rates for proper dynamic operation of the microreactor, the flow has to be distributed uniformly across the chip area. The microchannel network design (photolithography mask layout) used in the actual fabrication to satisfy these constraints is shown in Fig. 4. The shaded regions shown in the figure are the regions where the mask allows light to pass through during the exposure step. The design consists of seven . The catalyst parallel microchannels, each of width 1000 particle filter is also shown in the figure. Since a positive photoresist is used in the processing as an etch mask for subsequent etching (DRIE) of the patterned silicon substrate, the shaded regions in Fig. 4 are regions where the photoresist is exposed and the substrate is subsequently etched to form the channel network and the filter. SEM images of the microchannels and the filter are shown in Fig. 5. Locations of inlet and outlet holes drilled in the capping pyrex wafer for the microfluidic interfacing are marked in Fig. 4. The inlet and outlet are strategically positioned in the network so that the net length traveled by the reacting gas mixture across any alternate parallel path is the same. Thus when the microchannel network is packed with the catalyst particles and the gas flow is started during operation, the gas will see an approximately equal resistance to flow across any parallel flow path, leading to uniform flow distribution across the entire chip area. The objective behind this design is to ensure equal residence times across parallel paths and ensure equal conversion and utilization of catalyst across the entire reactor chip. B. Flow Modeling and Simulation Rigorous modeling and simulation of gas flow through the microchannel network was carried out to verify that the flow distribution is indeed uniform. Darcy’s law for flow through porous media (5) [18] and the continuity equation for compress-

(5) (6)

(7) where as

is the universal gas constant. This can also be written (8)

denotes the gas molecular weight. Equations (5), (6) where and (8) can be combined into a single governing equation describing the flow of the gas mixture through the packed bed of catalyst particles (9) FEMLAB [7], a MATLAB-based generic 3-D geometry modeling software for finite-element analysis of coupled partial differential equations was used for numerical integration of the governing equation to solve for the pressure profile across the chip cross section for a given boundary condition of inlet pressure with the outlet being at atmospheric pressure. A geometry model of the channel network created in FEMLAB for the analysis is shown in Fig. 6. The axes dimensions are all marked in meters. It can be seen from the figure that the active region of the microreactor (the area with catalyst packed microchannels) is about 4 cm 4 cm in size. The silicon substrate is 1 mm thick and the top and bottom capping pyrex wafers are 1.85 mm thick as in the actual fabricated device. ) properties Values of gas mixture (1:1 molar used in the numerical analand porous bed permeability ysis for visualizing the flow distribution are outlined in Table I along with values of the other parameters used in the simulais calculated at the reactor tion. The gas mixture viscosity operating temperature of 463 K (190 ) using mixing rules [27]. The porous bed permeability is calculated for a packing randomly packed spherical particles based on the of 50 Kozeny-Carman equation [18]: (10) which when combined with (5) gives (11) and bed porosity where particle diameter for the case when where refers to the hydraulic diameter of the flow channel [18].


Fig. 14.

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Results from microreactor operation: Hydrogen production rate.

which point the hydrogen production rate steadily rose till a major portion of the reactor exit gas was hydrogen. In order to avoid problems of liquid condensation in the mass-spectrometer inlet capillary and to determine the exact methanol conversion rate, the unreacted methanol and water were collected by a to condense substantially condensing unit (operating at 0 all of the unreacted methanol and water) connected between the reactor outlet and the gas analyzer. Fig. 14 shows the results from a typical reaction run of the microreactor in the form of a plot of the variation of hydrogen production rate with time as the temperature of the device is raised from the catalyst activation range of below 175 to the microreactor operating temperature . Data collection was started toward the end of the of 200 catalyst activation phase, about 10 min before the temperature of the hotplate was raised to the operating value of 200 . Argon at constant flow rate of 1.5 SLPM (standard liters per minute) was used as a carrier gas to measure the hydrogen production rate in the microreactor, as discussed earlier. A plot of the mole fractions of the different components of the reacted gas (after condensing and separating the unreacted methanol and water) measured using the mass spectrometer for the microreactor is shown in Fig. 15 operating temperature range of 190–200 (Argon-free basis). The composition values were obtained after proper calibration of the gas analyzer using a standard mixture of known composition, with consideration of individual species fragmentation patterns inside the mass-spectrometer ion-trap. It can be seen that soon after the temperature is set to , the hydrogen production steadily rises to a value of 200 about 71.91 SCCM (Standard cubic centimeters per minute). , hydrogen forms At operating temperatures of 190–200 about 70% of the reactor exit gases (water and methanol free basis). For the experimental run shown, the temperature of the

microreactor was maintained at desired levels by placing it on a hotplate due to ease of practical handling. The use of on-chip heating was demonstrated in a separate heating experiment in which the microreactor was maintained at temperatures of up to 250 using a controller directly connected to the platinum heating lines patterned on the microreactor chip as per Fig. 9. for the reaction During the steady-state operation at 200 was passed run shown, 2.5 ml of 1:1.5 molar through the microreactor at a flow rate of 5 cc/h of the liquid mixture. The liquid mixture inside the syringe pump prior to feeding into the microreactor was maintained at the room temperature of 20 , resulting in the feed liquid specific gravity of 0.9067 gm/cc. This translates into a methanol feed rate of 2.46 gm/h (0.076 875 mol/h) and a total methanol feed of 1.23 gm. On the exit side, all methanol and water was condensed and collected as liquid before the gases were mixed with 1.5 SLPM of argon and sent to the mass spectrometer for analysis. The net amount of liquid thus collected was 0.7 mL, . with a measured specific gravity of 0.9643 gm/cc at 20 Using methanol-water mixture specific gravity data [27], this by weight. mixture was found to contain 21.53% Thus the total amount of unreacted methanol collected at the microreactor exit for this run was 0.1453 gm. The methanol for this run can be calculated as shown conversion in (17) (17) The net hydrogen production rate for this run was 0.1764 mol/h. From the point of view of fuel cell requirement, a 20-W fuel cell operating at 80% efficiency needs a hydrogen flow rate of 0.372 mol/h. Thus the above reaction run provides

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Fig. 15.


Results from microreactor operation: Microreactor exit gas composition.

TABLE III FLOW RATES OF VARIOUS SPECIES AT MICROREACTOR INLET AND OUTLET

Work is currently in progress to determine the optimum operating conditions for maximum hydrogen production at a given methanol flow rate. Improved catalysts are also being tested to allow for higher throughput rates in a given reactor volume (size). VI. CONCLUSION

enough hydrogen for generating 9.48 W of power in the fuel cell. Table III lists the total flow rates of various species at microreactor inlet and outlet and can be used to verify the overall mass balance in the system. It was observed that for reaction runs in which the molar methanol to water feed concentrations were more than 1:1.5, at the microreactor exhaust was the amount of CO and less than that expected from stoichiometry (1). Based on thermodynamic considerations [2], the microreactor was operating within the region of possible carbon deposition inside the reaction chamber, which would lead to lower than stoichiometric at the reactor outlet. Carbon decomposition of CO and position is undesirable as it will lead to catalyst deactivation over time. However, this can be avoided by either using a high water-to-methanol feed ratio (excess water) such as for the run shown in Figs. 14 and 15 (higher net storage volume for given amount of stored methanol) or by carrying out the reaction at higher operating temperatures (requiring better thermal isolation to avoid higher heat loss).

A silicon-chip based microreactor was successfully developed and tested for in-situ and on-demand production of hydrogen. A number of macroscale chemical engineering concepts were implemented at the micro scale to create a prototype chemical plant-on-a-chip. On-chip integration of various components such as heaters/sensors, reaction chambers, catalyst particle filters and microfluidic interconnectors was used for overall miniaturization as well as to ensure accurate monitoring and control of microreactor operation. Preliminary runs of the microreactor demonstrated that a single chip was sufficient to supply hydrogen to a 9.48-W fuel cell with a methanol to hydrogen conversion of 88.19%. Microreactors can be used in a number of different areas where miniature scale chemical processing is desirable, such as portable chemical analysis units, units for on-demand manufacture of minute amounts of hazardous chemicals which can be produced from less toxic reagents, and applications where it is desirable to store chemicals in the form of unreacted components due to ease and portability of storage such as the application considered in this paper. Microreactors also provide significantly higher surface area to volume ratios compared to conventional reactors and can be used to implement new reaction pathways not previously possible using conventional chemical reactors.


This study can be used as a general framework for modeling, design, and development of microscale chemical reactors and provides a good basis for proper utilization of diverse concepts from the fields of chemical and electrical engineering, MEMS design, and semiconductor processing. ACKNOWLEDGMENT The authors would like to acknowledge the help of the technical staff at the Cornell Nanofabrication Facility (CNF), especially M. Skvarla, M. Esch, J. Drumheller, and J. Clair for clarifying several issues related to the fabrication of the device. Thanks are also due to J. Zelinski (Lehigh University’s Physics Department Machine Shop) for assistance in the drilling of the pyrex wafers and to Süd-Chemie for providing the G-66B catalyst. REFERENCES [1] S. K. Ajmera, M. W. Losey, and K. F. Jensen, “Microfabricated packed-bed reactor for phosgene synthesis,” AIChE J., vol. 47, no. 7, pp. 1639–1647, July 2001. [2] J. C. Amphlett, M. J. Evans, R. A. Jones, R. F. Mann, and R. D. Weir, “Hydrogen production by the catalytic steam reforming of methanol. Part 1: The thermodynamics,” Can. J. Chem. Eng., vol. 59, pp. 720–727, 1981. [3] J. C. Amphlett, M. J. Evans, R. F. Mann, and R. D. Weir, “Hydrogen production by the catalytic steam reforming of methanol. Part 2: Kinetics of methanol decomposition using girdler G66b catalyst,” Can. J. Chem. Eng., vol. 63, pp. 605–611, 1985. [4] H. Andersson, W. van der Wijngaart, P. Enoksson, and G. Stemme, “Micromachined flow-through filter chamber for chemical reactions on beads,” Sens. Actuators B: Chem., vol. 67, pp. 203–208, 2000. [5] J. Antes, T. Tuercke, E. Marioth, K. Schmid, H. Krause, and S. Loebbecke, “Use of microreactors for nitration processes,” in Proc. 4th Int. Conf. Microreaction Technol., R. S. Wegeng, W. Ehrfeld, and I. Rinard, Eds., Atlanta, GA, Mar. 5–9, 2000, pp. 194–200. [6] R. B. Bird, W. E. Stewart, and E. N. Lightfoot, Transport Phenomena. New York: Wiley, 1960. [7] FEMLAB Reference Manual, Burlington, MA, 2001. [8] P. J. de Wild and M. J. F. M. Verhaak, “Catalytic production of hydrogen from methanol,” Catalysis Today, vol. 60, no. 1, pp. 3–10, 2000. [9] S. Fitzgerald, R. Wegeng, A. Tonkovich, Y. Wang, H. Freeman, J. Marco, G. Roberts, and D. VanderWeil, “A compact steam reforming reactor for use in an automotive fuel processor,” in Proc. 4th Int. Conf. Microreaction Technol., R. S. Wegeng, W. Ehrfeld, and I. Rinard, Eds., Atlanta, GA, Mar. 5–9, 2000, pp. 358–363. [10] T. Floyd, K. Jensen, and M. Schmidt, “Toward integration of chemical detection for liquid phase microchannel reactors,” in Proc. 4th Int. Conf. Microreaction Technol., R. S. Wegeng, W. Ehrfeld, and I. Rinard, Eds., Atlanta, GA, Mar. 5-9, 2000, pp. 461–466. [11] R. O. Idem and N. N. Bakhshi, “Production of hydrogen from methanol. 1. Catalyst characterization studies,” Ind. Eng. Chem. Res., vol. 33, no. 9, pp. 2047–2055, 1994. , “Production of hydrogen from methanol. 2. Experimental [12] studies,” Ind. Eng. Chem. Res., vol. 33, no. 9, pp. 2056–2065, 1994. [13] , “Kinetic modeling of the production of hydrogen from the methanol-steam reforming process over Mn-promoted coprecipitated Cu-Al catalyst,” Chem. Eng. Sci., vol. 51, no. 14, pp. 3697–3708, 1996. [14] S. V. Karnik, M. K. Hatalis, and M. V. Kothare, “Toward a palladium micro-membrane for the water gas shift reaction: Microfabrication approach and hydrogen purification results,” J. Microelectromech. Syst., vol. 12, pp. 93–100, Feb. 2003. [15] S. Kelley, G. Deluga, and W. Smyrl, “Miniature fuel cells fabricated on silicon substrates,” AIChE J., vol. 48, pp. 1071–1082, 2002. [16] M. V. Kothare and A. V. Pattekar, “Fuel processing microreactors for hydrogen production by methanol reforming,” in The Knowledge Foundation’s 5th Int. Small Fuel Cells 2003: Small Fuel Cells for Portable Power Applications, New Orleans, LA, May 7–9, 2003. [17] M. W. Losey, M. A. Schmidt, and K. F. Jensen, “Microfabricated multiphase packed-bed reactors: Characterization of mass transfer and reactions,” Ind. Eng., Chem. Res., vol. 40, no. 12, pp. 2555–2562, 2001.

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[18] W. L. McCabe, J. C. Smith, and P. Harriot, Unit Operations of Chemical Engineering, fifth ed. New York: McGraw-Hill, 1993, ch. 7. [19] A. Ming, J. Wu, and Q. Wang, “The hydrogen storage properties and the mechanism of the hydriding process of some multi-component magnesium-base hydrogen storage alloys,” Int. J. Hydrogen Energy, vol. 20, p. 141, 1995. [20] A. V. Pattekar and M. V. Kothare, “Microreactor and method of use to produce hydrogen by methanol reforming,” US Patent docket number LUNX-101USP, Dec. 2002. , “Design and fabrication of a microreactor for hydrogen produc[21] tion by catalytic methanol reforming,” in 2002 AIChE Ann. Meeting, Indianapolis, IN, Nov. 3–6, 2002. , “Modeling, design and control of silicon based microchemical [22] systems,” in 2002 AIChE Annual Meet., Indianapolis, IN, Nov. 3–6, 2002. , “Fuel processing microreactors for hydrogen production in micro [23] fuel cell applications,” in 7th Int. Conf. Microreaction Technology (IMRET 7), Lausanne, Switzerland, Sept. 7–10, 2003. , “Miniature fuel processors and fuel cells for portable power: In[24] dustry trends and potential applications,” in 2003 AIChE Ann. Meeting, San Francisco, CA, Nov. 16–21, 2003. , “Novel microfluidic interconnectors for high temperature and [25] a pressure applications,” J. Micromechan. Microeng., vol. 13, pp. 337–345, 2003. [26] A. V. Pattekar, M. V. Kothare, S. V. Karnik, and M. K. Hatalis, “A microreactor for in-situ hydrogen production by catalytic methanol reforming,” in Proc. 5th Int. Conf. Microreaction Technol. (IMRET 5), Strasbourg, France, May 27–30, 2001. [27] R. Perry and D. Green, Chemical Engineer’s Handbook, sixth ed. New York: McGraw-Hill, 1984, ch. 3. [28] P. Pfeifer, M. Fichtner, K. Schubert, M. A. Liauw, and G. Emig, “Microstructured catalysts for methanol-steam reforming,” in The 3rd Int. Conf. Microreaction Technol., Frankfurt, Germany, Apr. 18–21, 1999. [29] R. Srinivasan, I.-M. Hsing, P. E. Berger, M. P. Harold, J. F. Ryley, J. J. Lerou, K. F. Jensen, and M. A. Schmidt, “Micromachined chemical reactors for heterogeneously catalyzed partial oxidation reaction,” AIChE J., vol. 43, no. 11, pp. 3059–3069, Nov. 1997. [30] A. Y. Tonkovich, J. L. Zilka, M. J. LaMont, Y. Wang, and R. S. Wegeng, “Microchannel reactors for fuel processing applications. I. Water gas shift reaction,” Chem. Eng. Sci., vol. 54, pp. 2947–2951, 1999. [31] S. Tony, V. Rangelova, and N. Nikolay, “Nanocrystallization and hydrogen storage in rapidly solidified Mg-Ni-Re alloys,” J. Alloys and Compounds, vol. 334, p. 219, 2002.

Ashish V. Pattekar received the B.Tech. degree in chemical engineering from the Indian Institute of Technology (IIT), Bombay, in 1999. Prior to joining IIT Bombay, he was ranked overall first in the Junior College (H.S.C.) examination of Nashik Divisional Board comprising three districts and more than 100 000 students. He was a recipient of the Maharashtra State and National Merit Scholarships (India) and the Mafatlal Industries Limited Scholarship for academic and cocurricular excellence, covering his entire undergraduate tuition expenses. He joined Lehigh University, Bethlehem, PA, in August 1999 where he is currently pursuing the Doctoral degree in chemical engineering. His technical research interests include micro power systems, miniature fuel cell and fuel reforming systems, microchemical systems and microelectromechanical system (MEMS) design and fabrication, and evolutionary programming for optimization. He is currently working on the development of integrated microchemical systems for fuel processing in micro fuel cell applications as part of his Ph.D. thesis and has several publications in this area along with two pending U.S. patent applications. Mr. Pattekar received the Leonard A. Wenzel Award for best performance in his Ph.D. Qualifying Examination in 2000. He has been the President of the Chemical Engineering Graduate Students’ Association (ChEGA) at Lehigh University (2001–2002). He was recently listed in the Who’s Who Among Students in American Universities and Colleges (2003). He is the recipient of Lehigh University’s Engineering Ingenuity Award for Excellence in Graduate Research and Scholarship (2003).

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Mayuresh V. Kothare (S’96–A’97) received the B.Tech. degree in chemical engineering from the Indian Institute of Technology (IIT), Bombay, in 1991, the M.S. and Ph.D. degrees in 1995 and 1997, respectively, both in chemical engineering from the California Institute of Technology, Pasadena. He is currently an Associate Professor of chemical engineering at Lehigh University, Bethlehem, PA, and codirector of the Chemical Process Modeling and Control Research Center. In recognition of his research at Lehigh University, he was appointed a P. C. Rossin Assistant Professor (2001–2003) and a Frank Hook Assistant Professor (2002–2003). From 1995 to 1996, he was a Research Assistant with ETH and was a visiting scholar with City College New York (January–June 1997) and Purdue University (June 1996). He joined the Chemical Engineering Department, Lehigh University, in July 1998 after a one-year Postdoctoral appointment with Mobil Oil Corporation. His technical interests are in the areas of microchemical systems, microreformers, control and dynamical systems, and convex optimization techniques in robust and optimal receding horizon control. Dr. Kothare is the recipient of the Ted Peterson Student Paper Award from the CAST division of the AIChE, the ACS Petroleum Research Fund Young Investigator Grant, and the CAREER Award for Young Investigators from the U.S. National Science Foundation. He received the Alfred Nobel Robinson Award (2002) “for outstanding contributions in service of the university and unusual promise of professional accomplishments.” In 2002, he was recognized as an Outstanding Reviewer of Automatica. He is an Associate Editor of the IEEE TRANSACTIONS ON AUTOMATIC CONTROL and the IEEE Control Systems Society’s Conference Editorial Board.