(199b) Control of Ethanol Dehydration in the Supercritical Water Reforming of Ethanol into Hydrogen

Ethanol, a renewable resource, may be reformed non-catalytically into hydrogen by a novel process utilizing supercritical water which acts synergistically as a solvent and as a reactant. Ethanol reformed by this process does not require energy-intensive separation following fermentation or subsequent distillation. In addition this novel process produces little or no carbon build-up inside the reactor even after days of continuous operation. The principal reactions that occur are: (1) direct reformation of ethanol into hydrogen and carbon oxides, (2) pyrolytic decomposition of ethanol into hydrogen, methane, and carbon oxides, and (3) dehydration of ethanol. Dehydration of ethanol occurs as an undesired reaction in the non-catalytic reformation of ethanol to hydrogen. A preliminary series of supercritical water reformation of ethanol experiments were conducted to validate a novel 400 mL Haynes Alloy 230 tubular reactor for supercritical water reformation process. It is found that the ethanol dehydration reaction is present as a side reaction even in the water-rich mixture of the current process and its byproduct ethylene further undergoes hydrogenation reaction with the process ultimate product, hydrogen, producing ethane. Experiments were performed between 857 K and 1042 K and between 24 MPa and 32 MPa. The effects of temperature, pressure, and space time upon molar concentration of ethylene and ethane in the gaseous ambient products are discussed. The optimal process conditions that minimize this wasteful ethane formation are found and experimentally demonstrated.