ABSTRACT
The.sulfur-iodine.(S-I).cycle.is.a.thermochemical.water-splitting.process.that.utilizes.thermal.energy.from.a.high-temperature.heat.source.to.produce.hydrogen.(H2).. It. is.comprised.of. three.coupled.chemical. reactions,.as.shown. in.figure.4.1..First,. the.central.low-temperature.Bunsen.reaction.(Section.I).is.employed.to.produce.two.
liquid.phases.from.sulfur.dioxide.(SO2),.iodine.(I2),.and.water.(H2O)..Under.proper. conditions,.these.two.phases.become.immiscible.and.can.be.readily.separated..The. lighter.upper.phase.is.sulfuric.acid.(H2SO4),.and.the.denser.lower.phase.is.an.aqueous.complex.of.HI,.H2O,.and.I2.(HIx)..After.separation,.the.two.liquid.phases.are.sent. to.the.two.other.sections.for.decomposition..Section.II.(H2SO4.decomposition).first. concentrates.the.sulfuric.acid.that.has.been.received.from.Section.I.and.then.decomposes.it.into.SO2,.O2,.and.H2O.at.high.temperature..The.decomposed.products.are. returned.to.Section.I.to.continue.the.S-I.cycle..In.Section.III.(HI.decomposition).HI. is.distilled.from.HIx.and.is.then.decomposed.into.H2.and.I2.at.intermediate.temperature..H2.is.separated.for.external.use.and.iodine.is.cycled.back.to.Section.I.to.support. the.Bunsen.reaction..The.key.advantages.of.the.S-I.cycle.are.that.it.has.no.effluent. and.the.reactants.are.in.easily.transportable.liquid.or.gaseous.form..All.the.chemicals.used.are.recycled,.and.the.only.required.process.inputs.are.heat.and.water.
