Studies On Nitrogen-preferred Adsorbent

Our county is rich in coalbed methane, and it is important to exploit and utilize the resource. But concentrating coalbed methane is a tough job. Adsorption is the most economical and reasonable method to separate methane and nitrogen. Most adsorbents used for this purpose are methane-prefered adsorbents. Nitrogen-prefered adsorbent was studied in this thesis in order to separate methane and nitrogen effectively.First, resin was used as raw material and modified with Mo-compounds. Adsorption resin H103, anion exchange resin D301 and cation exchange resin D072 were modified with (NH4)6Mo7O24, Mo7O246- and MoO22+ respectively. There is an obvious difference between nitrogen and methane in their adsorption capabilities on adsorption resin H103 modified, and the adsorbed amount of methane on this adsorbent is much more than that of nitrogen, therefore, this kind of resin could be employed for separation of nitrogen and methane via its high methane selectivity. However, all this kind of resins is not nitrogen-prefered adsorbent.In addition to resins, type-B silica gel with BET surface area of 377 m2/g was chosen and modified with (NH4)6Mo7O24,H3PO4?12MoO3·30H2O,MoO3,NH4NO3 and molybdenum blue. According to the characterization of the adsorbents, the BET surface area of adsorbents modified is lower than that of original silica gel since part of the pores was blocked after modification.Adsorption isotherms of nitrogen and methane on these adsorbents were measured at room temperature. According to these isotherms, modification with (NH4)6Mo7O24 with equal weight of (NH4)6Mo7O24 and silica gel showed particular effect, and the adsorbed amount of methane and nitrogen on the adsorbent are nearly same. Compared with others, the adsorption selectivity for nitrogen of this adsorbent is improved considerably. It might be due to the change of the potential field of the microcosmic structure of the adsorbent caused by Mo- and NH4+. This change prohibits the adsorption of methane and promotes the adsorption of nitrogen. Breakthrough curves of a mixture of nitrogen and methane also indicates that the adsorption selectivity for nitrogen is improved on the adsorbent, and further research is suggested.