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Molten Salt Cerium-based Oxygen Carrier Partial Oxidation Of Methane To Syngas In The Pilot Study

Posted on:2008-12-15Degree:MasterType:Thesis
Country:ChinaCandidate:Y G WeiFull Text:PDF
GTID:2191360212986514Subject:Non-ferrous metallurgy
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With the development of the world economy, the oil will dry up increasingly in the world, and the abundant natural gas will become the most promising substitute of oil. The prospecting making known, the natural gas reserves reach 43 trillion steres in our country, which is 10% in the total natural gas reserves of the world. We can see from the existent technology of the natural gas transform, the routs of methane transform include two kinds: direct transform and indirect transform. The large-scale applications mainly centralized in the methane indirect transform at present, and in the methane indirect transform preparation syngas is the important part. The technologies of the steam reforming of methane, the carbon dioxide of methane, partial oxidation of methane, unite reforming of methane, and self-thermal reforming are included in the preparation technologies of syngas which have been industrialization or being developed currently. Although the technology of the steam reforming of methane has been industrialization, it had some deficiencies for highly energy consumption and ratio of H2/CO.The conventional technology of partial oxidation of methane to syngas has overcome the deficiencies of SRM, while it needs to consume pure oxygen and add the production cost. In order to solve these contradictions, a novel technology of production syngas, partial oxidation of methane to syngas using lattice oxygen in molten salt has been brought forward by our research group. In the technology methane is oxidized by lattice oxygen in metal oxides which can change their valences, through the technology the production cost can be reduced, at the same time, the heat- point existed in the catalyst bed and blast and so on in the conventional technology can be avoidedFerric oxide, perovskite-type oxides and rare earth metal oxides as the oxygen carriers are beforehand researched for partial oxidation of methane to syngas, and finally CeO2 is used as active component of oxygen carrier. A series of ceria-based oxygen carriers are prepared by incipient wetness impregnation, and are experimented for partial oxidation of methane to syngas in molten salt (1: 1 weight ratio of Na2CO3 and K2CO3) .The ΔrG, ΔrH and logK in some most possiblereactions are calculated in theory based the principle of the minimal Gibbs free energy change by using HSC Chemistry 5.1 produced by Outokump. Charts of equilibrium compositions of CH4 and CeO2 at different reaction amounts were drown by the same software. When the methane is excessive the carbon has the higher ratio at the high temperature area, at the same time, the unreacted methane occurs pyrogenation. Although the amount of CO has some increase with temperature, the increasing speed is slow, and the amount of H2 has a sharp increase when temperature increasing, so the H2/CO ratio is more than 2.If the CeO2 is excessive, the amounts of carbon, H2O and CO2 have obvious decrease, and the amounts CO and H2 continuously increase with the temperature, the results show that the higher temperature is favorable for production synthesis gas with appropriate H2/CO ratio.Using the γ-Al2O.3 which has a bigger BET surface, heat-stability and resistance smash capability as a carrier, The 5%, 10% , 20% , 30% , 40% CeO2 carried y-Al2O3 are prepared by incipient wetness impregnation;The oxygen carriers were characterized by means of XRD, SEM, TG, O2-TPD and H2-TPR, etc... The circulation performances of oxygen carriers are investigated by TG experiment; In the quartz tube reactor the three space velocities of 0.462×105, 0.924×105, 1.386×105 h-1 are experimented from 750 to 900℃, respectively. The results show that the space speed of 0.924×105 h-1 and the temperature of 850 to 900'C are suitable for making syngas; When the oxygen carrier is used in circulation some agglomerations are found, which result in a little decrease of methane conversion and CO selectivity. The pure and different mass of CeO2 carried γ-Al2O3 as oxygen carriers are investigated in molten salt.When the temperature is higher than 865℃, the 10% CeO2/γ-Al2O3 catalyst has the higher methane conversion, H2 and CO selectivity, which are 79% , 96% å'Œ 97% at tiptop, respectively; When temperature is 870℃ the H2/CO ratio reaches 2, and it is close to the theory value. These experimentations indicate that the partial oxidation of methane to syngas using lattice oxygen of CeO2 in molten salt is feasible; the activity of oxygen carriers could be improved by carried γ-Al2O3, but the amount of CeO2 has a optimal value and the reaction temperature also has a optimal range.The technology of partial oxidation of methane to syngas using lattice oxygen in molten salt is a good energy utilization and practicality new method. There aresome aspects which need to in-depth investigation for instance the design of reactor, the performances optimization of oxygen carriers and the reaction mechanism.
Keywords/Search Tags:molten salts, oxygen carriers, cerium oxide, partial oxidation, syngas
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