Catalyst For One-step Production Of Synthetic Natural Gas (SNG) From Coal

Natural gas is a kind of cleaner energy with high calorific value. Compared withcoal, natural gas will produce less greenhouse gas and ultrafine particles. In China,energy supplying structure is characterized by rich coal, insufficient oil andnatural gas, whose energy consumption depends on coal. Coal catalytic methanationhas been an important strategic choice. One-Step coal-based synthetic natural gas isreferred to various chemical reactions occur in one reactor, including coal pyrolysisreaction, char gasification, and methanation reaction. The released heat ofmethanation reaction meets the demand of gasification reaction, achieving heatbalance in such process. Coal catalytic methanation needs less equipment, investmentand low energy consumption, thus it has been a new research field. In this thesis, aninvestigation into catalyst was carried out for one-step production of synthetic naturalgas from coal in a fixed bed reactor using steam as the gasification medium.Firstly, K-Fe double active component methanation catalyst was prepared withimmersion method. The effects of active component content and coals on methanation,as well as the effect of different catalyst on coal pyrolysis process, were demonstrated.It shows that15%KOH showed significantly excellent activity, the proper Fe contentcould promote the methanation of CO and H2. The final yield was affected by volatile,ash content, sulphur content, and so on. When the temperature was lower than600℃,the content of CH4released from coal pyrolysis process increased with thetemperature. When the temperature was higher than600℃,CH4content keptconstant. However, low content of Fe favours the release of CH4gas in the coalpyrolysis process, however high content of Fe suppressed CH4generating.Secondly, K-Fe double active component catalyst was modified with theadditives added. With the addition of calcium promoter, the combination of activecomponent and minerals in coal was prevented, and the sulfur in coal could be fixedeffectively. In multi-cycle experiments, the CH4yield remained stable. In particular,K15Fe10Mo5showed better methane selectivity than K15Fe10Ca5. K15Fe10Ca5increased methane selectivity for absorbing CO2. By contrast, K15Fe10Mo5reactedwith H2S released from coal tar to generat MoS2, adding the methanation activecenter.Shenmu coal char methanation is catalyzed by K15Fe10Ca5fitted by thehomogeneous reaction model, retract model, and modified random pore model. The methanation mechanism of Shenmu-coal with K15Fe10Ca5was modelled by thehomogeneous reaction model, suggesting that interfacial reaction is the control step.The catalysis of the alkali metals, transition metals, and alkaline earth metal, as wellas the relationship between the catalytic effect coefficient and temperature have beenstudied. Alkali metals catalyst showed better effect in the high temperature range. Thecoefficient effects of transition metal and alkaline earth metal catalysis have a slightchange.The effects of reaction temperature, reaction time, pressure, and water coal ratioon methanation have been investigated. A new feed method were designed, and theprocess technology was optimized. Furthermore, some highly active materials wereformed due to the interaction of active components at high temperature, methanationreaction could be promoted with the appropriate content of Fe. CH4yield reached themaximum value when the coal-water ratio was1:1and pressure at2MPa. As expected,staged feed method could further improved the methane production rate.