Channel steam reforming

II.C.4 Novel Catalytic Fuel Processing Using Micro-Channel Steam Reforming and Advanced Separations Technology... 

Hao, Y, Du, X, Yang, L, Shen, Y, Yang, Y. Numerical simulation of configuration and catalyst-layer effects on micro-channel steam reforming of methanol. InL J. Hydrog. Energy 2011 36 15611-15621. 

The catalytic combustor provides heat for the endothermic reforming reaction and the vaporization of liquid fuel. The endothermic reforming reaction is carried out in a parallel flow-type micro-channel of the reformer unit. It is well known that the methanol steam reforming reaction for hydrogen production over the Cu/ZnO/AbOs catalyst involves the following reactions [10]. Eq. (1) is the algebraic summation of Eqs. (2) and (3). 

The steam reformer is a serpentine channel with a channel width of 1000 fim and depth of 230 fim (Figure 15). Four reformers were fabricated per single 100 mm silicon wafer polished on both sides. In the procedure employed to fabricate the reactors, plasma enhanced chemical vapor deposition (PECVD) was used to deposit silicon nitride, an etch stop for a silicon wet etch later in the process, on both sides of the wafer. Next, the desired pattern was transferred to the back of the wafer using photolithography, and the silicon nitride was plasma etched. Potassium hydroxide was then used to etch the exposed silicon to the desired depth. Copper, approximately 33 nm thick, which was used as the reforming catalyst, was then deposited by sputter deposition. The reactor inlet was made by etching a 1 mm hole into the end... 

Methanol Steam Reforming 1 [MSR 1] Electrically Heated Serpentine Channel Chip-like Reactor... 

Reuse et al. [24] applied a reactor carrying micro structured plates for methanol steam reforming over commercial copper-based low-temperature water-gas shift catalyst from Sud-Chemie. The reactor took up 20 plates made of FeCrAl alloy of size 20 mm x 20 mm x 0.2 mm. The channel size was 200 pm x 100 pm (Figure 2.5). The catalyst was conditioned by oxygen and hydrogen treatment. 

Development of Catalyst Coatings for Methanol Steam Reforming in Micro Channels... 

Figure 2.10 Carbon dioxide yield from methanol steam reforming vs. temperature at a constant residence time of 125 ms and different channel geometries, from Pfeifer etal. [22] (by courtesy of Springer Verlag).

Kolb et al. [52] applied small externally heated sandwich-type reactors for catalyst screening for propane steam reforming. Two plates of 2 mm thickness were attached to each other and bonded by laser welding. The reactors where 41 mm long and 10 mm wide carrying 14 channels each, which were 25 mm long, 500 pm wide and 250 pm deep on each plate, thus resulting in a total channel cross-section of 500 pm x 500 pm when mounted. 

Two reaction mechanisms for partial propane oxidation exist in the literature. One of them proposes that the reaction starts with catalytic combustion followed by reactions of a lower rate, namely steam reforming, C02 reforming and water-gas shift [54], Aartun et al. [55] investigated both reactions. The other mechanism proposes that the partial oxidation reaction occurs directly at very short residence times [56], which are easier to achieve in the micro channels. 

An early application of a combined steam reformer/catalytic combustor on the meso scale was realized by Polman et al. [101]. They fabricated a reactor similar to an automotive metallic monolith with channel dimensions in the millimeter range (Figure 2.65). The plates were connected by diffusion bonding and the catalyst was introduced by wash coating. The reactor was operated at temperatures between 550 and 700 °C 99.98% conversion was achieved for the combustion reaction and 97% for the steam reforming side. A volume of < 1.5 dm3 per kW electrical power output of the reformer alone was regarded as feasible at that time, but not yet realized. 

Von Hippel et al. [104] patented a special reactor head, which allows for a distribution of the two gas flows through each individual channel. Even at a 1 200 °C monolith temperature the heads did not heat up to more than 200 °C, hence silicone rubber was applied for sealing the heads. This concept was applied for coupling methane combustion and steam reforming in separate flow paths [105],... 

Figure 2.68 Results from numerical calculations for combustion-assisted methane steam reforming, (a) Outlet conversion dependence on channel half-height (b) wall temperature as a function of dimensionless reactor length. Calculation results determined at constant inlet velocity [108]...

Reuse et al. [68] combined endothermic methanol steam reforming with exothermic methanol combustion. The reactor consisted of a stack of 40 foils, 20 dedicated to each reaction (see Figure 2.77). The total length of the foils was 78 mm and their thickness was 200 pm. The foils carried 34 S-shaped channels each with a length of 30 mm, a depth of 100 pm and a width of 310 pm. A special plate in the center of the stack allowed for temperature measurements. The plates were made of FeCrAlloy and an a-alumina film 5 pm thick was generated on their surface by temperature treatment at 1000 °C for 5 h to improve the adherence of the catalyst coatings (see Section 2.10.7). 

A total of206 mg [119] of commercial Cu/Zn catalyst from SiidChemie (G-66MR) ground to the nanometer range was coated into the channel system at 5 pm thickness to promote the steam reforming reaction. A cobalt oxide catalyst was prepared by impregnating the corundum layer (see above) with cobalt nitrate and calcining at 350 °C for 2 h 434 mg [119] of the CoO catalyst were applied for the combustion reaction (see Section 2.5). 

Bravo et al. [29] dealt with the coating of a commercial CuO/ZnO catalyst on quartz and fused-silica capillaries for future application in micro channels. The catalyst was mixed with boehmite as binder and water at a mass ratio of44 11 100. The boehmite was treated with hydrochloric or nitric acid before. The capillaries were pretreated with a hot sulfuric acid/solid oxidation step before coating. The capillaries were filled with the catalyst/binder suspension and then cleared with air. In this way, catalyst coatings up to 25 pm thick were obtained. The coatings were applied to methanol steam reforming (see Section 2.4.1). 

Pfeifer et al. [45] deposited CuO/ZnO and PdO/ZnO nanoparticles on micro channels by wash coating. A stable dispersion of the nanoparticles was achieved when polymers such as hydroxylpropylcellulose were added to the solvent 2-propa-nol. The wash coating was performed on both single micro structured foils and stacked foils (post-coating, see Figure 2.97). These coatings were applied to methanol steam reforming [22]. 

G. P., Datye, A., Wall coating of a CuO/ Zn0/Al203 methanol steam reforming catalyst for micro channel reformers, Chem. Eng.J. 2004, 101, 113-121. 

Men, Y., Gnaser, H., Zapf, R., Kolb, G., Hessel, V., Ziegler, C., Parallel screening of Cu/Ce02/y-Al203 for steam reforming of methanol in a 10 channel micro-reactor, Catal. Commun. 2004, submitted for publication. 

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