Bioethanol-Based Fuel Processor
Development of a Bioethanol Steam Reforming Fuel Processor Producing 5m3 of Syngas per Hour for Fuel-Cell-Based Power Plants
Tech Area / Field
- CHE-IND/Industrial Chemistry and Chemical Process Engineering/Chemistry
- ENV-APC/Air Pollution and Control/Environment
3 Approved without Funding
TATA Science and Technical Center, Russia, N. Novgorod reg., Sarov
- Boreskov Institute of Catalysis, Russia, Novosibirsk reg., Akademgorodok
- Nissan Motor Co., Ltd., Japan, Tokyo\nUniversita di Messina, Italy, Messina\nInstitute of Solid State Physics, Latvia, Riga\nUniversité de Poitiers / Laboratoire de Catalyse en Chimie Organique, France, Poitiers\nUniversity of Central Florida / Interdisciplinary Studies, USA, MA, Westford\nUniversity of Miami / Clean Energy Research Institute, USA, FL, Coral Gables\nAustin Peay State University, USA, TN, Clarksville\nN-GHY S.A. Fuel Processors for Fuel Cells, France, Albi\nNanotech Industries, USA, CA, Daily City\nUniversity of Ontario Institute of Technology, Canada, ON, Oshawa
Project summaryBioethanol is a 12-14-percent water solution of ethyl alcohol produced by biochemical conversion of woodworking and agricultural wastes. As distinct from natural gas and oil refinement products, bioethanol is a renewable fuel available in almost unlimited amount, and its use does not fall under international agreements on the reduction of greenhouse emissions. Bioethanol can therefore be considered one of the most promising kinds of fuel to produce hydrogen-containing syngas for fuel cell power plants [1-6]. Existing solutions in this direction show that catalytic steam reforming is the most promising ways to produce syngas from bioethanol. The complexity of this process is attributed to its endothermic nature and possible carbon deposition as a result of by-reactions. Thermodynamic calculations suggest that in order to suppress the carbon deposition, the mole ratio of water to ethanol should be no less than 2, and the reaction temperature should be 700-800°C. The presence of abundant water in bioethanol provides such a ratio.
Bioethanol steam reforming can be performed on applied cobalt, rhodium, nickel and copper-nickel catalysts with the formation of СН4, Н2, СО, СО2, acetaldehyde and ethylene according to the following reactions (carbonization not included).
By choosing appropriate catalysts and conditions for this process, one can almost completely preclude the formation of acetaldehyde and ethylene, and to achieve the content of methane in dry syngas of no more than 1 % vol. The resulting syngas can be used as a fuel for high-temperature solid-oxide fuel cells. As applied to the development of self-contained power plants, however, a more promising solution today is to use high-temperature polymer-exchange membrane fuel cells (HT PEMFC) working at a temperature of 160-180°C. In order to use syngas produced by bioethanol steam reforming as a fuel for HT PEMFCs, one needs to bring the content of CO in dry syngas at least down to 1 % vol. This can only be done by CO steam reforming in a separate reactor at lower temperatures (200-300°C).
This project deals in particular with HT PEMFCs as the most practicable fuel cell, on the basis of which an efficient power plant can be built. This implies that the fuel processor being developed should comprise two catalytic reactors: one for bioethanol steam reforming and another for CO steam reforming. As applied to high-temperature fuel cells that can be sensitive to the quality of hydrogen-containing fuel, the fuel processor being developed can additionally be equipped with a fine cleaning reactor to produce syngas with CO content around 10 ppm. As literature data show, it is rather difficult to reduce the CO content from 1 % vol. to 10 ppm (by selective catalytic oxidation or methanation of CO), and if HT PEMFCs are used, the fuel processor will have a by far less sophisticated design if this step is excluded.
Thus, bioethanol as a renewable feed stock can enable fuel production (syngas, hydrogen) for all major fuel cell types. However, wide use of bioethanol for fuel cell-based power plants is limited by the unresolved matter of developing an efficient and inexpensive catalyst for bioethanol steam reforming with a long service life and new types of heat-integrated compact fuel processors. The complexity of developing the latter is associated with the necessity of evaporating large quantities of liquid and efficient heat supply to the region where the endothermic reaction takes place.
Our preliminary data indicate that catalysts containing rhodium and cobalt are most promising as applied to the development of long service-life catalysts for bioethanol steam reforming. The service life of such catalysts achieved during the preliminary investigations was no less than 1000 hours. Taking into account specific features of bioethanol steam reforming, along with activity and stability, the catalysts should possess heat conductivity of about 1-5 W/m/K that can be achieved on metal substrates. Our previous experience shows that it is reasonable to make such catalysts using twill-woven heat-conducting metal grid substrates and a special process of physical and chemical substrate treatment to develop the surface with subsequent formation of a catalytically active layer on it.
To effectively supply heat to the region of endothermic reaction, it is suggested that the principle of thermal conjugation should be used for the processes of bioethanol steam reforming and ethanol oxidation. A thermally conjugated reactor will be a device consisting of flat channels containing the catalyst of bioethanol steam reforming on a reinforced heat-conducting substrate inside. Heat will be generated by catalytic oxidation of alcohol contained in bioethanol either on the surface of the catalyst in the space between the channels, or in a starting heater. In the latter case, heat for bioethanol steam reforming will be supplied to the space between the channels in the form of hot oxidation products.
CO steam reforming reactor development will rest upon the experience in making catalytic devices with controlled longitudinal temperature profile that will help us make the reactor as compact and as efficient as possible.
Before we design and make a demo fuel processor, we will perform numerical simulations and optimization of the key process components and quantitative assessment of the fuel processor efficiency.
Thus, major project tasks can be outlined as follows: development of catalysts for bioethanol steam reforming and oxidation of ethyl alcohol resistant to deactivation and having a service life on the order of 2000-3000 hours on the basis of heat-conducting grid or porous metal substrates; development of a process flow for the fuel processor and making a compact heat-integrated demo sample of the fuel processor on the basis of the catalysts made for bioethanol steam reforming with an output of 5 m3/h of syngas with methane and CO content about 1 % vol.
The technical approach proposed in the Project rests upon the development of new types of heat conducting and heat resistant catalysts of regular structure on grid substrates to enable 100-percent bioethanol reforming to CO, H2, CH4 and CO2 without acetaldehyde and unsaturated hydrocarbons in reaction products and with methane content not exceeding 1-2 %. The catalysts shall be capable of ensuring a service life of 2000-3000 hours. This will be achieved by making catalysts on the basis of active components containing Rh compounds and oxides of transition metals.
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