ABSTRACT
Conventional, fossil, liquid hydrocarbon fuels will continue to cover a major portion oftheever-increasingworldenergyrequirementsfortheforeseeablefuture,basically duetotheirdemandintransportationandtheexistingrelevantextensiveinfrastructure.Inthisperspective,thedirectuseofnonfossil,syntheticliquidfuels(SLFs) attractsalotofinterest.Currently,thetermsynthetic fuel (synfuel)referstoaliquid fuel produced at commercial scale from low-energy-content carbonaceous sources, suchascoal,naturalgas,oilshale,tarsand,andotherbiomass,thatareupgradedat theexpenseofadditionalenergy,alsoobtainedfromthecombustionoffossilfuels. Thetermsgastoliquid(GTL)andcoaltoliquid(CTL)refertoprocessestoconvert naturalgas(orothergaseoushydrocarbons)andcoal,respectively,intolonger-chain liquid hydrocarbons such as gasoline or diesel fuel. Syngas is a gas mixture that containsvaryingamountsofCOandH2 whose exothermic conversion to fuel and otherproductshasbeencommerciallypracticedsincealongtimeago,forexample, viatheFischer-Tropsch(FT)technology,andwhichcanbealsousedasasourceof purehydrogenandcarbonmonoxide[1,2].Thus,infact,hydrogenandsyngasare thebasicrawmaterialstoproduceSLFsandchemicalsviaindustriallyavailable processes. These procedures can be rendered more attractive and environmentally friendlierwhencombinedwitharenewableenergysource,suchassolarenergy. Indeed,itisgenerallyacceptedthatonlysolar-driventechnologiesofferapermanent solutiontobothoilindependenceandclimatechangeduetotheunmatchedmagnitudeandavailabilityofsolarresource[3].Whensolarenergyisemployedforthe production of the raw materials for the synthesis of such synthetic fuels, the latter arecharacterizedwiththetermsolar fuels.Inthebroadsense,thistermcancontain inadditiontosolar hydrogensyntheticliquidhydrocarbonsandalcoholsproduced fromreactionsbetweenH2 and CO that have originated from solar-aided dissociationprocessesaswellasmetalpowdersobtainedbysolarthermalreduction(TR)of metal oxides [4].
