Abstract
Hydrogen production from renewable sources is gaining increasing importance for application as fuel, in particular with high efficiency and low impact devices such as fuel cells. In addition, the possibility to produce more sustainable hydrogen for industrial application is also of interest for fundamental industrial processes, such as ammonia and methanol synthesis. Catalytic processes are used in most options for the production of hydrogen from renewable sources. Catalysts are directly involved in the main transformation, as in the case of reforming and of electro-/photo-catalytic water splitting, or in the upgrade and refining of the main reaction products, as in the case of tar reforming. In every case, for the main processes that reached a sufficiently mature development stage, attempts of process design, economic and environmental impact assessment are presented, on one hand to finalise the demonstration of the technology, on the other hand to highlight the challenges and bottlenecks. Selected examples are described, highlighting whenever possible the role of catalysis and the open issues, e.g. for the H2 production from reforming, aqueous phase reforming, biomass pyrolysis and gasification, photo- and electro-catalytic processes, enzymatic catalysis. The case history of hydrogen production from bioethanol for use in fuel cells is detailed from the point of view of process design and techno-economic validation. Examples of steady state or dynamic simulation of a centralised or distributed H2 production unit are presented to demonstrate the feasibility of this technology, that appears as one of the nearest to market. The economic feasibility seems demonstrated when producing hydrogen starting from diluted bioethanol.
Highlights
Hydrogen is the most abundant element in the universe and raised particular interest in recent times due to its high energy content per unit mass: its enthalpy of combustion is − 286 kJ/mol
The latter can be used as substrate for steam reforming, but challenges are related to the optimisation of the catalytic materials for this application, which are currently based on Ni as active phase
Co and Cu-based catalysts were developed for this application [70,71,72,73,74,75] and based on detailed kinetic modelling [76, 77] two different plants were simulated: (1) a small scale fuel processor coupled with a fuel cell for residential size Combined Heat & Power (CHP) [78,79,80,81,82,83] and (2) an industrial scale plant for centralised hydrogen production, with economic assessment [63, 64]
Summary
Hydrogen is the most abundant element in the universe and raised particular interest in recent times due to its high energy content per unit mass: its enthalpy of combustion is − 286 kJ/mol. The production of electric energy via a fuel cell on board or for distributed CHP options, looks more suited to small- and micro-scale applications In both cases the use of diluted bioethanol has been explored as a less expensive feedstock than fuel-grade ethanol. Moving a step further on this route, it is observed that the water condensation (to purify the reformate) and the hydrogen reaction with air (in the fuel cell) release heat at temperatures below the foreseen pinch-points of the reforming process: one approximately at the boiling point of the hydroalcoholic feed (cold feed—hot products exchange), and the other at the catalyst activation temperature (reacting mixture—combustion gases exchange) These subpinch heat loads are aligned with the typical sanitary water temperatures in civilian buildings, allowing to design a CHP system suited for micro-scale distributed use
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