Performance Investigation For Syngas Production Via Biogas From Municipal Solid Waste

With the increasing demands of energy and concerns of environment protection, the production efficiency and the use of clean energy have been particularly important and urgent. Biogas is a kind of fuel which is produced from anaerobic decomposition of organic material, it is clean and environmentally friendly. Raw biogas typically contains equal amounts of CH4 and CO2, which, if reformed properly, can provide a renewable source of hydrogen from waste. Nowadays, landfill gas accounts for 80%of the world biogas production. Landfills of municipal solid wastes, as the largest raw material of biogas now, are used to produce renewable energy.CO2 and CH4 from the landfills are ideal reactant for reforming reactions because they produce a suitable H2/CO ratio, for the Fisher-Tropsch or ethylene and dimethyl syntheses. Biogas reforming is essentially carbon dioxide reforming or dry reforming of methane. Ni-based catalysts are investigated mostly based on this reaction and may be for industrial application in the future. However, CDRM is difficult to be extensively utilized in chemical industry because it is accompanied by the heavy carbon deposition and serious metal sintering of Ni-based catalysts, leading to rapid losses in catalytic activity and stability.Therefore, preventing carbon deposition and metal sintering are of great importance for the CDRM on Ni-based catalyst.There are larger pore size, thicker pore walls as well as good thermal stability in the SBA-15 mesoporous molecular sieve. It is a good support for the catalysts. In this study, we use the Ni as the aticve component and supported with the SBA-15 to prepare the Ni-SBA-15 catalyst by impregnation way. In order to improve the catalyst performance, the Ni-Mo bimetallic catalysts were prepared, and the transition metal (Co, Zr, W), alkaline earth metals (Mg, Ca) and rare earth (La, Ce) were modified on the Ni-Mo/SBA-15 catalysts. The catalytic performance, structure, thermal stability, dispersion of nickel and carbon deposition of the modified and unmodified catalysts were comparatively investigated by many characterization techniques such as N2 sorption, H2-TPR, CO2-TPD, XRD, FT-IR,SEM and TEM analysis, etc. It was found that:The Ni/Mo/SBA-15 and Ni/Mo/M/SBA-15 catalysts were prepared by the wet-impregnation method. All the chemical reagents used in this work were from Sinopharm Chemical Reagent Co. Ltd. A weighed amount of (NH4)6Mo7O24-4H2O was placed in a beaker of 100 ml and a small amount of distilled water was added. After 30 min, the appropriate weight of support reforming of methane to synthesis gas. Before and after the stability test to maintain good mesoporous structure and pore clogging. There are no carbon deposition and pore clogging, keeping the stability of Ni-Mo/ZrO/SBA-15 catalyst for 150h, indicating that ZrO2has more special effects on the catalysts. Research findings, ZrO2 has a good oxygen exchange capacity and migration ability, and the oxygen vacancy is the body phase and the driving force of surface and surface and gas phase oxygen exchange. ZrO2 exists in the vector the aerobic space of the catalyst surface, and accelerate the exchange of surface and bulk as well as gas phase oxygen, the oxygen exchange between the different solid-phase reaction is carried out at the same time, oxygen enrichment ZrO2 poor oxygen circulation between the ZrO2 and ZrO2 between the Mo lattice oxygen exchange is very fast, to prevent the reduction of the reaction of MoO3 and MoO2. Therefore, the addition of ZrO2 to maintain the MoO3/MoO2/Mo and NiO/Ni redox dynamic equilibrium in the stability of the experimental conditions, to prevent the phase transition of Ni, Mo and its oxides, thus maintaining Ni-Mo/ZrO/SBA-15 catalyst activity and stability.Introduced in the Ni-Mo/SBA-15 catalyst with La2O3 and CeO2 formed MoxLa1-XO3 MoXCe1-XO2 solid solution, it has good storage and releasing oxygen capacity, which can improve the catalytic activity and stability. O2-lattice deformation in the solid solution can increase the migration of lattice oxygen, and the reduction caused by the lattice oxygen migration is not limited to the surface into the bulk. It also found that the easy sintering of CeO2 in the (SBA-15) was added under continuous stirring. The slurry was heated to 80 ℃ and maintained at that temperature until the water evaporated. The residue was then dried at 100 ℃ and then, added nickel nitrate Ni(NO3)2-6H2O as well as the second composition in turns in the same way. The samples after impregnation for 24 h were dried at 100 ℃ overnight and then calcined at 550 ℃ for 6 h in an air. The nominal compositions of the catalyst in terms of weight percentage. The formed catalyst powder was pressed into flakes, crushed, and sieved to 60-80 mesh for further use.3wt%Mo/12wt%Ni-/SBA-15 catalysts had a best catalytic performance under the reaction conditions. T=800 ℃, CH4:CO2=1:1 and GHSV=1.2×104 ml gcat-1h-1, over the 3wt%Mo/12wt%Ni-/SBA-15 catalyst, the CH4 conversion was up to 97%and maintained 90%for 500h and the CO2 conversion was up to 97 %and maintained 80%for 550h. The H2/CO molar ratio is stable maintains at around 0.9 after running the reaction for 550 h.SBA-15 mesoporous structure was maintained before and after the reaction, no pore clogging and carbon deposition was found in the surface of the No-Mo/SBA-15 catalysts, The Mo2C was formation on the catalysts surface after the reaction, indicating that the results of the carbon migration of Ni to Mo, which is of Mo, played the suppression of carbon deposition on the Ni-based catalysts.The Ni-Mo/SBA-15 catalyst modified with transition metal oxides (CoO, ZrO, WO) with excellent catalytic activity and stability for the carbon dioxide preparation of the heat treatment process, resulting in specific surface area decreases, and thus greatly reduce the reservoir and releasing oxygen capacity of the CeO2, due to grain grpwth and reduce the dispersion, but also makes the CeO2 and NiO and MoO3 reduce gaseous oxygen exchange capacity.Compared with Ni-Mo/SBA-15 catalyst prepared step-by-step impregnation method on Ni-Mo/MgO (CaO)/SBA-15 catalysts showed poor stability. The stability of the series of catalysts are far lower than Ni-Mo/SBA-15. The main reason for deactivation of the catalyst is zeolite by alkaline impacts.It is caused the surface area decreased and pore destruction. The exacerbated effect resulting catalyst stability greatly reduced when the second metal and alkaline earth metal were addedThe catalysts with 12 wt%Ni loading had a best catalytic performance under the reaction conditions. T=800℃, CH4:CO2=1:1 and GHSV=1.2×104 ml gcat-1h-1, over the 12 wt%Ni-SBA-15 catalyst, Both of the CH4 and CO2 conversion was 97% and are above 90% and maintained to this level for 950 h and 750h respectively, and then the CH4 conversion decreases to 86%, meanwhile, the CO2 conversion goes down to 70% after running the reaction for 1008 h, respectively. The H2/CO molar ratio is stable maintains at around 0.9 after running the reaction for 1008 h.