Study On Tri-reforming Of Methane Over Ni/γ-Al₂O₃Monolithic Catalyst

Tri-reforming of methane is a process which uses CH₄, CO₂, O₂and H₂O toproduce for syngas. It can not only deal with industrial waste gas to reduce CO₂emissions, but also can get syngas for methanol, dimethyl ether and other downstreamproducts. TRM has the advantages of high process efficiency, lower carbon depositionon the catalyst, appropriate n（H₂）/n（CO） of syngas at1.5².Compared with traditionalgranular catalysts, monolithic catalysts have the advantages of low pressure drop acrossa reactor, high efficiency of mass transfer. They are suitable to the process which needsto be working at high space velocity. In this paper, a series of monolithic catalysts wereprepared and tested, which has cordierite monoliths as first carrier, γ-alumina as secondcarrier and Ni as activity component.Firstly, a detailed thermodynamic analysis of TRM for syngas production isperformed using the equilibrium constant method. The effects of temperature, pressureand feed gas on the reforming process are studied. The calculation results show that thereaction temperature is conducive to positive TRM reaction, the conversion rate of CH₄and CO₂increase with the rise of reaction temperature.Increasing reaction pressure willinhibit the reaction forward because of the increase of reaction volume in TRM.With theincrease of the content of O₂, the conversion rate of CH₄rise while CO₂decrease, boththe yields of H₂and CO decrease, and the value of n（H₂）/n（CO） almost keep the same.The increase of water vapor content is conducvie to positive the reaction of streamreforming of methane, the conversion rate of CH₄and yield of H₂increase, and thevalue of n（H₂）/n（CO） also increase.Secondly, the factors affecting the properties of Ni based monolithic catalysts forTRM were optimized. The experiment results show that it has good coating effect whilecoupling agent is5%in solid content-nitric acid concentration is10%and couplingagent is10%-nitric acid concentration is8%. It performances better in TRM when theroasting temperature of catalyst is about650℃and Ni loading is about10wt%. Thecatalysts keep the activity after working50h continuously.Finally, the effects of reaction conditions in TRM are studied on10wt%Ni/γ-Al₂O₃-650℃monolithic catalyst. The results show that reaction temperature canpromote CH₄and CO₂conversion rates, and the conversion rates become stable whenthe temperature reaches up to850℃. The conversion rates of CH₄and CO₂reduce first and then flatten later as GHSV increases from30000h-1to150000h-1, while thevariation tendency of n（H₂）/n（CO） is on the contrary. Although an excess of O₂canmake CH₄conversion rate higher, CO₂conversion rate will fall. And the content of O₂can not adjust the value of n（H₂）/n（CO）. Meanwhile, the content of H₂O should not betoo much. Although it can increase the value of n（H₂）/n（CO）, CO₂conversion rate willalso drop.