Research On Ni-based Catalysts For Methanation Of Coal Syngas

Coal is the main primary energy in China, which is chiefly distributed in thewestern traffic underserved areas. Long-distances transportation of coal in our countrymakes the utilization of coal face the problems of high cost, serious environmentalpollution and other produced wastage. At present, the in situ coversion of coal usinggreen and environmental technique is very important. The combination of gasificationand methanation could make the coal be transformed into natural gas and transportedby pipelines. This way could solve the above mentioned problems. Thus, this strategyis with a vital significance to our country. Through the exploration by scientists, thecoal gasification technology is now a mature technique, while the challenge is todevelop high activity and stability catalyst to realize syngas methanation with highcapacity and efficiency.In this paper, the catalyst preparation methods and influence factors of Ni content,additives of Mg, hydrothermal temperature and hydrothermal time had been carriedout. The results showed that the high mechanical strength and high activity of catalystcould be produced by co-precipitation and hydrothermal method. When the Ni contentwas20wt%, the catalyst activity was excellent. The additives of Mg could increasethe catalyst activity slightly, and be conducive to the stability of the catalyst structure.While the hydrothermal temperature and time had few effects on the catalytic activity.Compared with commercial production of N182catalyst(40wt%Ni), the catalystpreparation in the experiment needed lower content of Ni and higher activity.As to the Ni-Mg/Al2O3catalyst prepared by an approach combiningco-precipitation and hydrothermal methods, the influences of calcination andreduction on catalyst structure and performance for methanation were investigated byactivity evaluation and catalyst characterization using XRD, H2-TPR, TEM. Theresults showed that with the increase in calcination temperature the reduction of thecatalyst become more difficult because of the formation of NiAl2O4at hightemperatures, especially excess900℃. The specific surface area of the catalystdecreased from130to34m2/g corresponding to the calcinations temperature risefrom500℃to900℃. After calcination at600℃, the stability and catalytic activity ofthe catalyst first increased and then decreased with raising the reduction temperature,and the best methanation performance appeared at a reduction temperature of650℃. This is due to the differences in the reductive degrees of nickel oxides and in the grainsizes of resulting Ni. This study clarified that for good catalytic performance ofmethanation, the grain size of Ni should be small and the interaction between activemetal (Ni) and catalyst supporter (Al2O3) should be moderate.As to the condition of hard reduction of NiAl2O4, generated in high calcinationtemperature, the research of the effect of the methanation reaction activity andstability under the hign reduction temperature of1000℃was performed. Thecatalysts were characterized by XRD, H2-TPR, TEM and BET. The results revealedthat Ni grains were large and MgAl2O4spinel structure appeared for all samples. Withthe increase of calcination temperature, pore volume and specific surface areadecreasesed gradually and finally tends to be stable, while the catalyst activityreduced first the then increased. For the catalyst calcinated under800℃, thecomparison of activity and stability indicated that the NiAl2O4spinel structure couldbe reduced completely under1000℃and made the pore expanded. Thus, the Nigrains were separated from the pore canal and distributed around the surface of thecatalyst and lessened the carbon deposition quantity. The activity and stability werehigher and better accordingly.