| Due to coal-dominated energy consumption structure,the environmental contamination has become a serious problem and has attracted more and more attention.The development of coal and natural gas can not only achieve the clean and efficient use of coal,but also ease the domestic market supply and demand of natural gas contradiction.The core technology of coal to natural gas is the design of methanation reactor and the development of high efficiency catalyst.CO methanation reaction is a strong exothermic process,will lead to the active components of the catalyst sintering and carbon deposition,which seriously affect the safe and stable operation of industrial devices.Si C has good thermal stability and chemical inertness.Besides,the excellent thermal conductivity of SiC contributes to the transfer of the heat in time and inhibits the formation of the "hot spot" in the catalyst bed.In this paper,SiC support was prepared by microwave-assisted carbothermal reduction method,and loaded nickel metal for CO methanation reaction and compared with the traditional oxide Al2O3 support;in addition,the SiC-based catalyst was further modified by adding Ce additives to obtain anti-carbon and anti-sintering catalyst at high temperature to meet the requirements of high concentration CO efficient and stable operation of the methanation catalyst.The major results of this paper were summarized as follows:?1?The silicon carbide powder was prepared by microwave-assisted carbothermal reduction using nano-silica and graphite as raw materials.The optimum preparation conditions were as follows: Si/C atomic ratio is 1:1.2,microwave output power 2.5 kW,calcination temperature 11001400 °C,constant temperature time is 30 min;the crystalline phase of the prepared silicon carbide is 3C-SiC with an average grain size of about 40 nm and a specific surface area of 8.8 m2g-1;?2?10Ni/SiC and 10Ni/Al2O3 catalysts were prepared by impregnation and carried out CO methanation performance evaluation.The results showed that the low temperature reactivity of 10Ni/Al2O3 was high,the CO conversion rate was 95.6% at 320 °C,10Ni/SiC showed obvious advantages in the high temperature range of 500600 °C,CO conversion and CH4 selectivity were 94.9% and 82.3%,respectively,however the CO conversion and CH4 selectivity on 10Ni/Al2O3 were 91.9% and 80.2%,respectively.?3?The 10Ni/Al2O3,10Ni/SiC and 7Ce-10Ni/SiC were evaluated for CO methanation at 600 °C.When the space velocity increased from 15 000 mL g-1 h-1 to 60 000 mL g-1 h-1,10Ni/Al2O3 remained unchanged for the first 20 h,then the CO conversion and CH4 selectivity decreased gradually.When the reaction extended to 62 h,the reaction was forced to terminate because of blockage of reactor caused by severe carbon deposition.When the reaction on 10Ni/SiC was carried out for 100 h,the pre-pressure of the reactor increased slightly to 1.2 MPa,and the reactivity and selectivity decreased slightly.The 7Ce-10Ni/SiC showed extremely high stability during the reaction of 100 h,and the CO conversion and CH4 selectivity maintained the same level.?4?The results of 10Ni/SiC and 10Ni/Al2O3 showed that the Ni particle size on 10Ni/SiC was smaller and the degree of dispersion was higher,so it could provide more reactive sites for CO methanation reaction.The used 10Ni/Al2O3,10Ni/SiC and 7Ce-10Ni/Si C results revealed that the Ni particles showed different growth rates,the agglomeration of 7Ce-10Ni/SiC was the smallest among them,the deposition rates were 0.01935 g/h,0.00528 g/h and 0.00465 g/h,respectively.10Ni/Al2O3 displayed the largest amount of carbon deposition which is graphite carbon or graphitized carbon,and majority the formation of more carbon fiber,which led to the phenomenon of Ni was stripped.?5?The characterization results of 7Ce-10Ni/SiC showed that CeO2 was uniformly dispersed around the Ni particles,which effectively prevents the agglomeration of Ni particles,increases the Ni dispersion and enhances the force between the metal and the support.In addition,the Ce3+/Ce4+ redox electron pair increased the electron cloud density of Ni and promoted the dissociation of CO,thus accelerated the methanation reaction rate. |
PDF Full Text Request