Scaling factors, hydrogen production

The suitability of a cycle for hydrogen production depends upon the overall thermal efficiency and operational feasibility. A highly endothermic reaction step is required in a cycle to achieve effective heat-to-chemical energy conversion. For efficient mass and momentum transfer a fluid based system is preferred [96] and, ultimately, for large-scale hydrogen production other factors such as environmental effects and cost effectiveness must also be considered. 

With respect to a large-scale hydrogen production, nuclear power can play a significant role if used as a provider of electricity in the electrolysis process or as a provider of high-temperature heat in fossil fuel conversion. An introductory option would be the use of cheap surplus electricity. Production of hydrogen as a bulk energy carrier is by a factor of about 2 too expensive compared with the today s commercial business of natural gas and oil, however, the trend to include external effects into the energy cost may help to achieve economic attractiveness [2]. 

Table 3.7 Hydrogen production methods environmental, economic and scaling factors.

A technical process was developed by Lonza for the Ir-catalyzed hydrogenation of an intermediate of dextromethorphan (Fig. 34.9) which was carried out on a > 100-kg scale [70]. Important success factors were ligand fine tuning and the use of a biphasic system chemoselectivity with respect to C=C hydrogenation was high, but catalyst productivity rather low for an economical technical application. Satoh et al. reported up to 90% ee for the hydrogenation of an intermediate of the antibiotic levofloxacin using Ir-diphosphine complexes. Best results were obtained with bppm and a modified diop in the presence of bismuth iodide at low temperature [71]. 

SPE electrolysers are at present available at a scale of 0.5-10 Nm3 hydrogen per hour at an output pressure up to 200 bar. The available systems operate at a rather poor overall efficiency, 50-70% [44, 48], The projected price level of these systems, at industrial production level, is at least a factor of 3-5 too high. 

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