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Microstructured reactors for hydrogen production

Abstract

Small scale hydrogen production by partial oxidation (POX) and oxidative steam reforming (OSR) have been studied over Rh-impregnated microchannel Fecralloy reactors and alumina foams. Trying to establish whether metallic microchannel reactors have special advantages for hydrogen production via catalytic POX or OSR with respect to activity, selectivity and stability was of special interest. The microchannel Fecralloy reactors were oxidised at 1000 deg C to form a {alpha}-Al2O3 layer in the channels in order to enhance the surface area prior to impregnation. Kr-BET measurements showed that the specific surface area after oxidation was approximately 10 times higher than the calculated geometric surface area. Approximately 1 mg Rh was deposited in the channels by impregnation with an aqueous solution of RhCl3. Annular pieces (15 mm o.d.,4 mm i.d., 14 mm length) of extruded {alpha}-Al2O3 foams were impregnated with aqueous solutions of Rh(NO3)3 to obtain 0.01, 0.05 and 0.1 wt.% loadings, as predicted by solution uptake. ICP-AES analyses showed that the actual Rh loadings probably were higher, 0.025, 0.077 and 0.169 wt.% respectively. One of the microchannel Fecralloy reactors and all Al2O3 foams were equipped with a channel to allow for temperature measurement inside the catalytic system. Temperature profiles obtained along the reactor  More>>
Authors:
Publication Date:
Jul 01, 2005
Product Type:
Thesis/Dissertation
Report Number:
NEI-NO-1580
Reference Number:
RN06007353; TVI: 0523
Resource Relation:
Other Information: TH: Thesis (Dr Ing); 4 papers, 40 figs., 299 refs., 12 tabs
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 42 ENGINEERING; EVALUATED DATA; EXPERIMENTAL DATA; COMPARATIVE EVALUATIONS; HYDROGEN; PRODUCTION; CHEMICAL REACTORS; MICROSTRUCTURE; PARTIAL OXIDATION PROCESSES; STEAM REFORMER PROCESSES; RHENIUM; INORGANIC COMPOUNDS; ALUMINIUM OXIDES; RHENIUM CHLORIDES; NITRATES; DESIGN; PERFORMANCE TESTING; PHYSICAL CHEMISTRY; CHEMICAL ENGINEERING; CARBON OXIDES; FOAMS; CATALYSIS; SYNTHESIS GAS; CHEMICAL REACTIONS
OSTI ID:
20675224
Research Organizations:
Norges teknisk-naturvitenskapelige universitet, Trondheim (Norway)
Country of Origin:
Norway
Language:
English
Other Identifying Numbers:
Other: ISBN 82-471-7146-5; TRN: NO0505555
Availability:
Commercial reproduction prohibited; OSTI as DE20675224
Submitting Site:
NW
Size:
vp.
Announcement Date:
Dec 29, 2005

Citation Formats

Aartun, Ingrid. Microstructured reactors for hydrogen production. Norway: N. p., 2005. Web.
Aartun, Ingrid. Microstructured reactors for hydrogen production. Norway.
Aartun, Ingrid. 2005. "Microstructured reactors for hydrogen production." Norway.
@misc{etde_20675224,
title = {Microstructured reactors for hydrogen production}
author = {Aartun, Ingrid}
abstractNote = {Small scale hydrogen production by partial oxidation (POX) and oxidative steam reforming (OSR) have been studied over Rh-impregnated microchannel Fecralloy reactors and alumina foams. Trying to establish whether metallic microchannel reactors have special advantages for hydrogen production via catalytic POX or OSR with respect to activity, selectivity and stability was of special interest. The microchannel Fecralloy reactors were oxidised at 1000 deg C to form a {alpha}-Al2O3 layer in the channels in order to enhance the surface area prior to impregnation. Kr-BET measurements showed that the specific surface area after oxidation was approximately 10 times higher than the calculated geometric surface area. Approximately 1 mg Rh was deposited in the channels by impregnation with an aqueous solution of RhCl3. Annular pieces (15 mm o.d.,4 mm i.d., 14 mm length) of extruded {alpha}-Al2O3 foams were impregnated with aqueous solutions of Rh(NO3)3 to obtain 0.01, 0.05 and 0.1 wt.% loadings, as predicted by solution uptake. ICP-AES analyses showed that the actual Rh loadings probably were higher, 0.025, 0.077 and 0.169 wt.% respectively. One of the microchannel Fecralloy reactors and all Al2O3 foams were equipped with a channel to allow for temperature measurement inside the catalytic system. Temperature profiles obtained along the reactor axes show that the metallic microchannel reactor is able to minimize temperature gradients as compared to the alumina foams. At sufficiently high furnace temperature, the gas phase in front of the Rh/Al2O3/Frecralloy microchannel reactor and the 0.025 wt.% Rh/Al2O3 foams ignites. Gas phase ignition leads to lower syngas selectivity and higher selectivity to total oxidation products and hydrocarbon by-products. Before ignition of the gas phase the hydrogen selectivity is increased in OSR as compared to POX, the main contribution being the water-gas shift reaction. After gas phase ignition, increased formation of hydrocarbon by-products upon steam addition leads to a decrease in CO selectivity without any significant change in the hydrogen selectivity. The Rh/foams of the lowest loadings (0.025 wt.%) yield the highest maximum catalyst temperatures and also display higher propane conversion than the 0.077 wt.% and 0.169 wt.% Rh/Al2O3 for both POX and OSR. However, the oxygen conversion does not reach completion and the hydrogen selectivity is lower, compared to the higher loadings. These effects of loading could be ascribed to differences in particle composition and structure. TPR suggested that a part of the Rh is present as a less reducible phase on the 0.025 wt.% Rh/Al2O3 foams as compared to the higher loadings. The Rh/Al2O3/Fecralloy microchannel reactor and the 0.025 wt.% Rh/Al2O3 foams were subjected to experiments with changing residence time. Changing the residence time interval corresponding to 1000 - 2000 Nml/min reactant flow has little influence on conversion and selectivity over the foams but lowering the residence time below 10 ms (flows higher than 1000 Nml/min) for the Rh/Al2O3/Fecralloy reactor increases the synthesis gas (H2 and CO) selectivity during both POX and OSR. This probably due to quenching of the gas phase reactions at high linear gas velocity and suggests that direct formation of hydrogen and CO is part of the reaction scheme. Microchannel reactors thus have potential for isolating kinetic effects and minimising gas phase contributions. The Rh/Al2O3 foams show significant deactivation upon a few temperature cycles under reactant exposure, strongest with steam present in the reactant mixture. FE-SEM analyses confirm that Rh sinter into larger particles upon exposure to reaction conditions, more pronounced when steam is fed. No deactivation is observed for the Rh/Al2O3/Fecralloy microchannel monoliths despite repeated temperature cycling under POX and OSR reactant exposure. In fact the selectivity to synthesis gas increases upon time. (Author)}
place = {Norway}
year = {2005}
month = {Jul}
}