Electrohydrolysis recycling of waste iodide salts into hydriodic acid for the chemical conversion of biomass into liquid hydrocarbons

Laboratory-scale electrohydrolysis with a bipolar membrane (EHBM) in a three-compartment Aqualytics cellstack demonstrated that waste sodium and potassium iodide salts are efficiently recycled into hydriodic acid and the corresponding base. Batch efficiencies for the acid product of 1.01–1.39 M solutions ranged from 50 to 95%. Highly efficient production is correlated with modified membranes, differential cellstack pressure, or both. Slightly higher pressure on the salt line provides reversed osmosis transfer of water through the membranes and significantly diminishes ‘back-migration’ of acid. Dilute HI solutions (1.00–1.39 M) can be distilled to afford the concentrated reagent (7.57 M) required for the reduction of biomass carbohydrates to liquid fuels. Costs estimates for recycling waste iodide salts into concentrated HI are less than $0.13/l, a cost savings of over two orders of magnitude for this reducing acid. Producing 2.5 M products by EHBM before costly concentration suggests that both acid and base costs may total about $0.16/l.