The National Hydrogen Association Annual Hydrogen Conference and Expo 2006 saw the presentation of a number of papers exploring different aspects of using biofuels—primarily ethanol and biodiesel—as feedstock for hydrogen production.
Biofuels are attractive to hydrogen producers for a variety of reasons: they are renewable; as liquids they are easily transported; and there is reduced net CO2 emitted to the atmosphere in their processing compared to fossil fuel feedstocks.
Furthermore, a lower-grade biofuel works just fine as an input for hydrogen production. The significant amount of water in low-quality ethanol can be used in the steam reforming reaction, for example. One of the methods proposed at the conference use “crude” ethanol—the ethanol mixture that has been produced by fermentation, but not yet distilled.
|Effect of Temperature and Steam-To-Carbon Ratio on the Equilibrium Product Gas Distribution from the Steam Reforming of Ethanol.|
Steam Reforming of Ethanol at Elevated Pressure for Distributed Hydrogen Production. Distributed hydrogen production facilities will need to store and transport hydrogen at pressures in excess of 5,000 psig. This is typically achieved by compressing the product hydrogen, and the compression process consumes 18% to 32% of the lower heating value of the hydrogen produced, a significant parasitic load on the overall process efficiency.
This project, undertaken by Argonne National Laboratory, investigates the option of steam reforming ethanol at elevated pressures, since this pathway almost eliminates the cost of compression by feeding a pressurized liquid stream into the reformer.
The research team investigated the use of two catalysts, a commercially-available nickel catalyst and an in-house developed Rhodium catalyst. The latter (a 4wt%RhLaAl2O3 catalyst) produced higher yields than the nickel with efficiencies of approximately 89% at a steam to coal ration of 1.5.
Funding has been cut for the project, but the team hopes to regain it to continue the work.
Generation of SynGas from Ethanol. This was one of two papers presented by Etudes Chimiques et Physiques, a small French R&D company working with low-temperature high-voltage discharge (GlidArc) to assist the partial oxidation (POX) of ethanol with atmospheric air.
According to ECP, the feed conversion is total, with no soot, coke or tars produced. Hydrogen constitutes about 30 vol.% of the syngas at the optimum conditions, produced with 80% thermal efficiency. The electric power for the GlidArc represents less than 1% of the heating value of the reformate.
ECP also applies its technology to biodiesel (the second paper). Preliminary tests in France achieved 1 kg/hour of H2 from 9 kg/h of biodiesel.
Hydrogen Production by Catalytic Reforming of Crude Ethanol over a Commercial Catalyst in Packed bed Tubular Reactor and Packed Bed Membrane Reactor. This paper, from HTC Purenergy, described the use of crude ethanol (i.e., pre-distillation) as an input into a packed bed tubular reactor.
All the oxygenated hydrocarbons in crude ethanol can be reformed completely to hydrogen and carbon dioxide, the latter which can be separated by membrane technology.
By the company’s analysis, the use of crude ethanol reforming delivers 2.2 times the end energy as using the same volume of ethanol in an internal combustion engine. Their logic is as follows. One liter of fuel-grade ethanol (after distillation) is equivalent to 8.33 liters of crude ethanol (pre-distillation).
After taking one-liter of fuel-grade ethanol into a Carnot engine with 20% efficiency, the end thermal energy is 4,391 KJ.
By contrast, reforming 8.33 liters of crude ethanol with 85% conversion, and applying that in a 50%-efficient fuel cell, yields chemical energy of 9,850 KJ.
Low temperature Biofuel Reformation by Alkaline Enhancement. This poster session by Energy Conversion Devices describes the use of an alkaline material to reduce the temperature of operation for the conversion of ethanol and methanol as low as 110º C.
Hydrogen production from biodiesel fuel in a microchannel steam reformer. This poster session from Innovatek described its work with the reforming of B100 in microchannel reactors. At 500º C, there was complete conversion of the B100 to a reformate consisting of 62% hydrogen, 23% CO2, 10% methane and less than 5% CO.
Compared with ultra low-sulfur diesel, the biodiesel produced slightly higher hydrogen concentration and lower methane concentration in the reformate stream at the same steam to carbon ratio.
Progress report: High-pressure distributed ethanol reforming