Study On New Catalysts And Kinetics For Sulfur-resistant Methanation

Due to the lack of oil and a sharp increase of natural gas consumption in recent years, more attention has been paid on producing substitute natural gases from coal gradually in China. And CO methanation is a key process in producing substitute natural gases from coal. Thus developing effective methanation catalysts is an important work in coal-based natural gas process.In this study, a facile hydrothermal method was used to produce unsupported MoS2 catalyst. The influence of hydrothermal temperature, calcination temperature and additives on the methanation performance of MoS2 was investigated and the results indicated that the optimal hydrothermal temperature and calcination temperature are 220 oC and 400 oC respectively. Citric acid was used as an additive and it had a double-edged effect toward CO methanation performance, which means that citric acid played a negative effect on the catalytic activity of Mo S2 toward sulfur-resistant methanation in the presence of hydroxylamine hydrochloride. However when hydroxylamine hydrochloride was not used in the above procedure, the CO methanation performance turned out to be better. Sodium silicate was used as an additive and it had an effect toward the MoS2 structure, which is irregular nanoparticle. This may be associated with the template effect of H4SiMo12O40. But too much sodium silicate can make MoS2 nanoparticles encased by silica species. As a result, the methanation performance declines. CTAB was used as an additive and it had an effect toward the MoS2 structure, which is regular nanowire. CTAB preferentially adsorbs on the surface that parallels to MoS2(100) crystal plane, resulting in MoS2 preferentially growing on(100) direction, finally MoS2 nanowires form.One-step co-precipitation method was used to prepare MoO3/ZrO2 catalysts for sulfur resistant methanation process. These catalysts exhibited high CO methanation activity. The CO conversion of 25%MoO3/ZrO2 catalyst can reach up to 90 %, close to its equilibrium conversion. The saturated monolayer coverage of ZrO2 is 25 wt.% MoO3, where MoO3 particles was highly dispersed on ZrO2 support. When MoO3 loading was larger than its saturated monolayer coverage, ZrMo2O8 was formed, which makes the methanation activity decreased.Meanwhile, the macro-kinetics was investigated on sufur-resistant 5%CoO-15%MoO3/25%CeO2-Al2O3 methanation catalyst. The obtained kinetics can successfully predict the methanation of syngas with some amount of H2 O, CO2 or CH4 added in the feed gas, and the reaction under different pressures. The obtained kinetics can provide basis for the methanation process optimization and reactor design in large scale.