Hydrogen production from renewables: from catalyst to process design

Hydrogen production from renewables: from catalyst to process design Ilenia Rossetti Università degli Studi di Milano, Dipartimento di Chimica e-mail: ilenia.rossetti@unimi.it H2 has been proposed in the recent past as a promising energy vector. It may be either used as fuel in internal combustion engines or, better, used in fuel cells for heat and power cogeneration (CHP). Growing interest has been focused on different ways to obtain it from renewable sources. Among the possible options, we have explored the possibility to produce H2 conveniently from bioethanol and glycerol by adapting the steam reforming process to these new renewable raw materials. The research activity started from the development and characterization of catalysts for the reaction. Ni, Co and Cu based catalysts, including some bi-metallic formulations, have been tested. An innovative preparation method, flame pyrolysis, has been compared to more conventional ones, such as precipitation and impregnation. We have particularly focused our attention on catalyst resistance to deactivation by sintering and coking. Both aspects have been improved by using the FP preparation method, leading to high thermal resistance and to a strong metal support interaction. Besides stabilizing the metal at high temperature, the latter feature helped increasing metal dispersion, with a consistent decrease of the coking rate. After the definition of suitable materials, it is compulsory to understand the economic feasibility of the process. To this aim we developed a demonstrative project for cogeneration with residential size (5kWelectrical + 5 kWthermal). Parallel to the experimental evaluation of the performance of this integrated unit, constituted by 6 reactors for H2 production and purification and a fuel cell with the mentioned size, we performed process simulation and design to optimize the process conditions. This required the definition of a suitable kinetic model to be implemented in the process simulation. Kinetic modeling was at first carried out on the basis of literature data, and further on the basis of original kinetic data collected on the best performing catalyst developed in this work. Finally, we explored the possibility to use diluted bioethanol solutions (<90 vol%), which are intrinsically less expensive feedstock than dehydrated ethanol (99 vol%). Different purification options have been tested in order to decrease the cost of bioethanol production. The coupling of the bioethanol purification section with the CHP unit confirmed the cost effectiveness of the use of diluted bioethanol streams for hydrogen production and conversion. Finally, the effect of possible impurities remained in the bioethanol stream has been experimentally evaluated on real bioethanol batches, differently purified, depending on the catalyst formulation and on reaction temperature.