The Study On Oxygen Carriers For Syngas Production Via Chemical-looping Of Methane

Chemical looping of methane technology can decouple the traditional gas co-feed CH₄-CO₂ reforming or CH₄-O₂ partial oxidation into two sub-reactions at different times or different spaces through the circulation of oxygen carrier and oxygen transfer.Conducive to the regulation of the reaction process:the lattice oxygen in the oxygen carrier instead of the gas phase oxygen and CH₄ reaction,can directly obtain the synthesis gas with H₂/CO ratio of2,and can avoid the use of expensive pure oxygen,when using CO₂ as an oxidant can have both CO.This thesis mainly studies the regulation of methane chemical loopimg reaction process and the optimization design of oxygen carrier.The specific work is as follows:?)BaFe₃Al₉O₁₉9 hexaaluminate oxygen carrier was synthesized by the two-step method and and its activity and cycle stability in the synthesis gas of chemical looping partial oxidation of methane?CLPOx?by changing the O₂ regeneration time were investigated.The results show that the conversion rate of CH₄ and the selectivity of CO increased significantly with the shortening of O₂ regeneration time?15?4.2min?,when the reaction temperature is900?.When the regeneration time is 4.2min,the conversion rate of CH₄ is 88%,the selectivity of CO is 88%and there is no obvious carbon deposition.The series of characterization reveals the reasons for the effect of regeneration period for performance improvement:?1?Reduction of Fe³⁺in the Al?1?,Al?2?and Al?3?sites?Fe¹,Fe²and Fe³?for activation of methane complete oxidation.?2?The increase in reduced Fe²⁺to Fe⁰responsible for the partial oxidation of CH₄.?3?un-oxidized surface Fe⁰resulted from shorter regeneration period?5 and 4.2min?acted as catalysts for dry reforming of CH₄ and CO₂ at the beginning of reaction,which also contributed to the increase of CO formation for these two samples.?)Different loadings of xwt%Pt/CeO₂?x=0,0.1,0.5,1,1.5?oxygen carriers were prepared by ammonium carbonate coprecipitation method,and its activity and cycle stability in the synthesis gas of methane chemical looping reforming?CL-POM-CO₂?were investigated.The results show that the reaction temperature is 700?,with the increase of Pt content?0?0.5?,the conversion rate of CH₄ and selectivity of synthesis gas increase obviously,and the content of Pt?0.5?1.5?is continuously increased,the performance is not significant.When the Pt mass fraction is 0.5%,the performance is optimal,the conversion rate of CH₄ is 77%,the selectivity of CO is 96%,the H₂/CO ratio is 2,the yield of synthesis gas is 4.24 mmol/g and the conversion rate of CO₂ is 97%.Revealing the structure-activity relationship between performance and structure through a series of characterization:the presence of Pt⁰in the noble metal Pt does not change the structure of the cerium base oxygen carrier,but the oxygen vacancies change significantly,which promotes the low-temperature redox activity of the cerium base oxygen carrier.When the Pt site is exposed excessively,little difference in performance during the reaction due to the sintering of some Pt particles.?)0.5wt%Ni/CeO₂ oxygen carrier was prepared by ammonium carbonate coprecipitation method,and 8.8wt%Ni/CeO₂ oxygen carrier was prepared by wet impregnation,the low temperature stability was compared with 0.5wt%Pt/CeO₂ oxygen carrier for syngas productin via methane chemical looping reforming.The results show that both Pt and Ni are beneficial to the activation of methane at a reaction temperature of 700°C,but Ni easily causes carbon deposition in methane cracking,resulting in a syngas with a H₂/CO ratio much greater than 2.In order to investigate the activation of Pt on CH₄/CO₂ as a small molecule in Pt-modified cerium base oxygen carrier,the mechanism of Pt on the chemical looping dry reforming of methceriuane was explored through series characterization:Pt is beneficial to low temperature catalysis of CO₂ cracking and syngas cogeneration.