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 thre e-compartment Aqualytics cellstack demonstrated that waste sodium and potas sium iodide salts are efficiently recycled into hydriodic acid and the corr esponding base. Batch efficiencies for the acid product of 1.01-1.39 M solu tions ranged from 50 to 95%, Highly efficient production is cor related wit h modified membranes, differential cellstack pressure, or both. Slightly hi gher 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 concentr ated reagent (7.57 M) required for the reduction of biomass carbohydrates t o liquid fuels. Costs estimates for recycling waste iodide salts into conce ntrated HI are less than $0.13/1, a cost savings of over two orders of magn itude for this reducing acid. Producing 2.5 M products by EHBM before costl y concentration suggests that both acid and base costs may total about $0.1 6/1. (C) 2000 Elsevier Science B.V. All rights reserved.