Oxygen Transfer Material Research Articles

Production of hydrogen by unmixed steam reforming of methane

Unmixed steam reforming is an alternative method of catalytic steam reforming that uses separate air and fuel–steam feeds, producing a reformate high in H 2 content using a single reactor and a variety of fuels. It claims insensitivity to carbon formation and can operate autothermally. The high H 2 content is achieved by in situ N 2 separation from the air using an oxygen transfer material (OTM), and by CO 2 capture using a solid sorbent. The OTM and CO 2 sorbent are regenerated during the fuel–steam feed and the air feed, respectively, within the same reactor. This paper describes the steps taken to choose a suitable CO 2 -sorbent material for this process when using methane fuel with the help of microreactor tests, and the study of the carbonation efficiency and regeneration ability of the materials tested. Elemental balances from bench scale experiments using the best OTM in the absence of the CO 2 sorbent allow identifying the sequence of the chemical reaction mechanism. The effect of reactor temperature between 600 and 800 ∘ C on the process outputs is investigated. Temperatures of 600 and 800 ∘ C under the fuel–steam feed were each found to offer a different set of desirable outputs. Two stages during the fuel–steam feed were characterised by a different set of global reactions, an initial stage where the OTM is reduced directly by methane, and indirectly by hydrogen produced by methane thermal decomposition, in the second stage, steam reforming takes over once sufficient OTM has been reduced. The implications of these stages on the process desirable outputs such as efficiency of reactants conversion, reformate gas quality, and transient effects are discussed.

Unmixed steam reforming of methane and sunflower oil: A single-reactor process for [formula omitted]-rich gas

Initial tests results are presented for the novel process of hydrogen production called unmixed steam reforming (USR) using methane and sunflower oil fuels. The USR process relies on two mass transfer materials which operate on a two-step cycle: an oxygen transfer material (OTM) which provides the heat necessary for the steam reforming reaction, and a CO 2 sorbent which shifts the water gas reaction yielding a H 2 -rich reformate gas. A shortlist of Ni-based OTMs and a natural dolomite were tested during bench-scale investigation and optimisation stages following micro-reactor tests. Under near-isothermal conditions, we show the sequence via which the main reactions occurred. We unexpectedly found that thermal decomposition of the fuel played a significant role in the early H 2 production concurrent with coking conditions, by causing the OTM to initially reduce. The direct OTM reduction from the fuel via the unmixed combustion reaction then took over to a point where the steam reforming reaction could begin. Most importantly, carbon lay-down (coking) during the fuel/steam flow did not lower gradually the process efficiency, as it was shown to completely oxidise under the cyclic feeds of air and fuel/steam flows of the USR process. Both methane and sunflower oil were shown to be suitable fuels for the USR process.

Oxygen transfer and catalytic properties of nickel iron oxides for steam reforming of methane

Nickel iron oxide (NiFe 2O 4) has been tested as a combined catalyst precursor and oxygen transfer material for improved conversion of methane into syngas. Thermogravimetric measurements with simultaneous gas analysis have demonstrated the superior behavior of nickel iron oxide compared to iron oxide. The enhanced catalytic activity is attributed to the generation of fresh nickel surfaces in the course of the reduction of the metal oxide. This allows for a periodic in situ generation of fresh, catalytically active nickel.

04/02469 Renewable energy investment opportunities inMauritius — an investor's perspective: Palanichamy, C. et al. Renewable Energy, 2004, 29, (5), 703–716

This study considers the feasibility of using highly oxygenated and volatile pyrolysis oils from biomass wastes as sustainable liquid fuels for conversion to a hydrogen-rich syngas using the chemical looping reforming process in a packed bed. Pine oil and palm empty fruit bunches oil- ‘EFB’- were investigated with a Ni/Al2O3 catalyst doubling as oxygen transfer material (OTM). The effect of molar steam to carbon ratio (S/C) and weight hourly space velocity were investigated at 600 °C and atmospheric pressure on the fuel and steam conversion, the H2 yield and the H- and C-products distribution. With a downward fuel feed configuration and using a H2-reduced catalyst, maximum averaged fuel conversions of ∼97% for pine oil and 89% for EFB oil were achieved at S/C ratios of 2.3 and 2.6 respectively (on a water-free oil basis). This produced H2 with a yield efficiency of approximately 60% for pine oil and 80% for EFB oil notwithstanding equilibrium limitations, and with little CH4 by-product. Both oils exhibited very similar outputs with varying S/C. Upon a short number of cycles, i.e. starting from an oil-reduced catalyst, the fuel conversion dropped slightly but the steam conversion was constant, resulting in a slow decrease in H2 yield. Despite their high level of oxygen content, the pyrolysis oils were shown to maintain close to 90% reduction of the oxidised catalyst upon repeated cycles, but the rate of reduction decreased with cycling.