Sandia researchers participated in a recent collaborative effort related to a novel electrical energy storage and hydrogen production system. The process would allow utilities to store energy during off-peak production for later use, reducing the need to install additional generators to meet peak demand. The system is also targeted for large industrial users of hydrogen.

Funded by the Department of Energy Office of Power Technologies, the collaboration involved Sandia, the Western Research Institute, the State of Wyoming and the SRT Group (Miami, Fla.), which developed the proprietary process. The technology relies on the chemical reaction of bromine and hydrogen to form hydrogen bromide (HBr) and oxygen. HBr is a potentially useful intermediate for hydrogen production because its electrolysis potential is significantly lower than water and it is highly soluble in water.

The HBr ideally would be split into hydrogen and bromine during off-peak hours, using lower-cost electricity. The result is the indirect electrolysis of water into hydrogen and oxygen, using only a fraction of the electricity required for conventional electrolysis, according to the SRT Group.

The primary chemical reaction is
  CH₄ + Br₂ = 4 HBr + C(s)

HBr is electrolyzed to produce H₂ and Br₂, which is then recycled back into the process
  2 HBr + 2 e- = H₂ = Br₂

Sandia conducted an investigation of the "front end" of the bromine-based hydrogen production cycle. For the SRT Group's technology to work, one of the issues to be resolved is the efficient production of HBr from hydrocarbon precursors. Sandia researchers studied the reaction of methane and bromine at elevated temperature to determine the yield and kinetics of HBr formation. Laboratory experimentation and computational chemistry were combined to provide a preliminary description of this reaction for possible application to reactor design at a larger scale.

Researchers designed and constructed a small-scale experimental reactor consisting of a quartz helical tube heated in an electric furnace. A range of reactant ratios and reactor residence times were surveyed at temperatures ranging from 500°C to 800°C.

Their experimental data showed that conversion of methane to HBr was high (greater than 90%) at temperatures near 800°C, with soot among the reaction products. At lower temperatures, HBr conversion was significantly reduced, as was soot. Calculations of chemical equilibrium behavior and reactions kinetics for the experimental conditions were performed using the CHEMKIN package. The results indicated that high conversions to HBr can be achieved.

Contact:
Bob Bradshaw
rwbrads@sandia.gov
(925) 294-3229