Solar-Thermal Processing of Methane to Produce Hydrogen and Syngas

Abstract

A solar-thermal aerosol flow reactor has been constructed, installed, and tested with the High-Flux Solar Furnace (HFSF) at the National Renewable Energy Laboratory (NREL). Experiments were successfully carried out for the dissociation of methane to produce hydrogen and carbon black and for the dry reforming of methane with carbon dioxide to form syngas (hydrogen and carbon monoxide). Approximately 90% dissociation of methane was achieved in a 25-mm diameter quartz reaction tube illuminated with a solar flux of 2400 kW/m2 (or suns). The carbon black produced was amorphous and had a particle size of 20 to 40 nm. Approximately 70% conversion was achieved for dry reforming using a solar flux of 2000 kW/m2. The experimental results for both processes are very encouraging and support further work to address the technical issues and to develop the processes.

Methane Activation by Heterogeneous Catalysis

“…In order to achieve a net CO 2 conversion, the heat of reaction must not be created by burning fossil fuels. Instead solar-thermal reactors are an interesting development [24] and could be used in the future. Aside from environmental aspects, methane dry reforming is of general interest to the chemical industry because it delivers a lower H 2 =CO ratio than steam reforming which is desirable, e.g.…”

Experimental analysis of direct thermal methane cracking

“…In the solar field, very high sunlight concentration factors (about 3000) are needed to reach temperatures over 1500 K [3,[22][23][24][25][26]. There are already some designs and experimental set-ups that could be useful for long-term generation of H 2 [27].…”

Production of hydrogen by thermal methane splitting in a nozzle-type laboratory-scale solar reactor

“…1, that was obtained from Gemini software [7] (software for thermodynamic equilibrium calculation developed by Thermodata), shows that methane decomposition is complete at about 1300 K. However, the reaction is not kinetically favorable [8,9], and a higher temperature is required to obtain high methane to hydrogen conversion rates and high-quality CB. Dahl et al [10] obtained exactly the same equilibrium products than that shown in Fig. 1, and they found that trace products at 1500 K include acetylene, ethylene, butylene, propylene, ethane at quantities less than 1 × 10 −3 moles for 1 mole of methane fed.…”

“…The reaction is kinetically hindered and the residence time (t r ) of the reactant in the high-temperature reacting zone (for a nozzle type b, i.e. 10 mm diameter and 10 mm cavity length, and a global flow rate of 1.1 L n / min, t r is about 40 ms at normal conditions and 8 ms at 1500 K, 1 atm) is not high enough to reach significant conversion [10]. Tables 2 and 3 list the results obtained with a 2 m-diameter concentrator and the corresponding operating conditions.…”

“…The indirect heating concept requires high-temperature material with drastic specifications, and the direct heating concept may lead to severe problems of optical window breakage due to possible carbon deposition. Tubular and vortex-type solar reactors have been tested by others [5,10,[14][15][16][17][18], they used either direct or indirect heating of the reactant by concentrated solar energy. In the experiment of Dahl et al [5,10,18], an Ar/CH 4 mixture is decomposed in an indirect solar heating reactor composed of concentric vertical graphite tubes.…”