1.  Green hydrogen production via low-temperature alkane cracking

    (The following distinguishes renewable and green energy.  Renewable energy does not entail consumption of fossil fuels, for example wind, solar, hydro, biofuels, etc. In contrast green energy does not entail emission of CO2, for example wind, solar, hydro, and carbon-based fuels with carbon capture and sequestration (CCS).  In particular biofuels are renewable but without CCS are not green as understood here.)

    Hydrogen can be captured as an otherwise unwanted byproduct of various industrial processes.  Even if those processes are not themselves green, using such hydrogen instead of discarding it could arguably be considered green.

    Hydrogen can also be manufactured intentionally by steam reforming of methane, with oxides of carbon (CO and CO2) as byproducts.  Typically these are emitted to the atmosphere, making this method not green.

    Another commonly considered method is electrolysis of water producing hydrogen and oxygen.  This method is thermodynamically unfavorable, particularly at room temperature but less so at higher temperatures.  When the electricity comes directly from a solar panel the resulting hydrogen is clearly green.  However the 22% efficiency of solar panels in combination with the thermodynamic inefficiency of electrolysis makes this method expensive relative to the other uses to which the electricity could be put.

    Although fossil fuels are not renewable, they are still plentiful today and are projected to remain so for many decades to come, making them of considerable interest for the foreseeable future.  Natural gas (largely methane, CH4), propane (largely C3H8), gasoline (largely iso-octane, C8H18), and other alkanes (CnH{2n+2}) are refined from fossil fuels and and their principal constituent elements are carbon and hydrogen.  Hydrogen produced by removing and sequestering the carbon is green hydrogen as understood here.  Understood as a chemical reaction, this process can be expressed as the reversible reaction CnH{2n+2} <=> nC + (n+1)H2, for example CH4 <=> C + 2H2 in the case of methane.

    A straightforward implementation of this process is thermolysis or heat cracking carried out in the absence of other chemicals, especially avoiding oxygen!   In the case of methane, at 500 C and atmospheric pressure an equilibrium is reached in which half the methane has separated into hydrogen and carbon.  By 1000 C essentially all of the CH4 has been “cracked”.

    A problem with this method of producing hydrogen is that at these high temperatures the carbon tends to form carbon nanotubes that stick to the furnace orifices, eventually clogging them.  Carbon nanotubes are notoriously strong, greatly complicating cleaning them out.  Recently teams at IASS in Germany and KIT in Sweden have bubbled methane through molten tin at temperatures of 1000 C and above, with the carbon nanotubes collecting at the surface as an easily removed scum.  While this method seems very promising technically, its economics are unlikely to become clear for several years.

    We are therefore interested in alternative approaches to removing the carbon from alkanes that does not involve molten metals.  We are currently exploring methods that avoid production of nanotubes, in particular at low temperatures and low pressures.

  2. Home hydrogen

    Currently there are no practical methods of producing hydrogen at home.  As one application of the foregoing project, we would like to make a prototype of a 34″ tall device that sits on the ground directly beside the Toyota Mirai’s fuel receptacle and pumps purified hydrogen into it.

    Since natural gas is more prevalent than either propane or gasoline in typical suburban residences, and moreover is 25% hydrogen by weight, the feedstock for this device would be natural gas.   The electricity needed for the prototype can come from the house mains initially.  A more elaborate model would have a small rechargeable battery and a fuel cell powered by the generated hydrogen; alternatively it could draw its power from the Mirai’s 12 volt DC 10A power outlet.

    The pumping pressure could be anywhere from 20 to 70 MPa.   20 MPa would suffice for a range of 90 miles, 35 MPa for 155 miles, and 70 MPa for the Mirai’s EPA-rated 312 miles.

  3. Fast US crossing in an Electric Vehicle

    The record for an electric vehicle crossing the US from Los Angeles to New York, 3011 miles, is 58 hours and 55 minutes.  This included 12 hours and 48 minutes of charging time.   A fuel cell vehicle could easily shave ten hours off the recharging time.  The obstacle is the lack of infrastructure.

    Continuous production of hydrogen from a readily obtainable alkane would permit much faster refueling at either fast-fill CNG stations, purchase of bottled propane, or refilling a gasoline tank.  The tradeoffs between these alkanes need to be explored.

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