A Research On Iron-based Oxygen Carriers In Chemical Loop For Hydrogen Production

With the growth of world economy and population, the demand for energy isincreased rapidly. Excessive use of fossil fuels not only cased serious environmentpollution, but faced the crisis for depletion. Therefore, there is an urgent need todevelop renewable energy. Hydrogen is competitive for its high combustion value,clean, renewable and other advantages.A new process of producing pure hydrogen by chemical loop is presented. In thisprocess, the iron-based oxygen carriers are easy to sinter. This paper focuses on thecycle stability of oxygen carrier.At first, the iron-based oxygen carriers are prepared with a copercipitation method,Al2O3、ZrO2、MoO3、SnO2、Cr2O3、CeO2、MgO are added respectively to modifythe oxygen carrier. Both the oxidation reaction and reduction reaction are carried outat800℃. In order to prevent the Fe2O3is reduced to Fe during the reductionreaction, the CO concentration in reducing gas (CO/CO2) is controlled at about60%.It is showed that metal oxides could prevent sintering during the reaction, so thehydrogen production of the sample adding metal oxide was higher than that of thepure iron oxide.The hydrogen productions are stable in cycling for the samplesmodified with CeO2, ZrO2and MgO. If the samples are modified with Al2O3, MoO3,Cr2O3, the hydrogen production will have a rapid decline in the previous cycles, andthen become gradual. However, the sample modified with SnO2is plummeting. Afterseven cycles, the samples by hydrogen production in descending order are: ZrO2>CeO2>MgO> SnO2> Cr2O3> MoO3> Al2O3> pure Fe2O3. The hydrogen production ofthe ZrO2modified sample is the most and its conversion rate of reaction is about80%.With the increasing of ZrO2adding amount, the hydrogen production has arapid-growing at first, subsequent the growth arrives to a platform, the appropriatedosage was5%. XRD analysis confirmed that the oxidation and reduction process ofsamples cycle between Fe3O4and FeO since the second cycles.Porous iron oxide has been synthesized with a hard template method and the stabilityis poor at high temperature. Further research needs to be done to improve itsproperties.