(450b) Molten Salt Chemical Looping Catalysis for Reactive Separation of HBr in a Halogen Based Natural Gas to Liquids Process

Halogen based conversion of methane to liquid fuels is improved by using molten salts for hydrogen halide reactive separation and regeneration. Molten bromide salts are used in a chemical looping process to selectively convert hydrogen bromide to molecular bromine in the presence of hydrocarbons. The process involves two steps: oxygen reacts with NiBr₂ that is dissolved in molten KBr-LiBr and forms bromine and NiO particles; the slurry is then pumped to another reactor where HBr reacts with the NiO to re-form the NiBr₂ and water, which closes the salt chemical looping cycle. Sixty-eight metal oxides/bromides were considered, and NiO-NiBr₂ was the only material that cycled at 500 °C with reasonable thermodynamics and kinetics.

In contrast to solid-based chemical looping systems, the liquid bromide salt was found to be cycleable without attrition or deactivation. Further, selectivity to hydrogen bromide oxidation over hydrocarbon oxidation was very high when mixtures of olefins and hydrogen bromide were bubbled through the oxide-salt slurry. This was justified by the fact that hydrogen bromide is soluble in the melt whereas hydrocarbons did not dissolve.

In addition, a process model that makes use of reactive separation of hydrogen bromide from hydrocarbons using molten salt-based chemical looping is presented as a potentially lower cost alternative to a process model using conventional separations in bromine-base methane conversion. The heat exchange duties and separations in corrosive and non-corrosive environments were compared using the two models.