Activated Carbon Was Prepared By Coal And The Effect Of Surface Modification On Methane Adsorption

Physical and chemical structure of coal is very complex, so makes it extremely difficult for researching the behavior of coal methane adsorption. Due to the special physical and chemical structure of deformed coal, there is a biggish difference in adsorption performance between it and undeformed coal. Coal-based active carbon and coal have similar microstructure, their pore and surface chemical properties are relatively close, so it can be used to explore the adsorption behavior of coal methane adsorption as a simple model. To modify with active carbon from coal under appropriate conditions to change surface pore structure and the composition of surface functional groups, the purpose is to cause the change of methane adsorption behavior.In this paper, taking KOH as the activating agent, the undeformed coal and paragentic deformed coal was made of activated carbon by using chemical activation method. And on this basis, modifing the active carbon from coal by using HNO3 oxidized and H2SO4-(NH4)2S2O8 oxidized. Then we got the surface physical and chemical characteristics of coal and the series of coal-based active carbons:The results of mercury displacement test show that the open pore is the main type of undeformed coal, deformed coal has flask hole and the pore connectivity is poor.(1) The nitrogen adsorption isotherms of coal samples belong to the second type,this proves that deformed coal and undeformed coal contain the rounde hole system continuously, And submicroscopic porosity as the main contributor for increasing specific area is developed in deformed coal. The nitrogen adsorption isotherms of the series of coal-based active carbons belong to the first type. The results of specific area determination showed that the closed pores in coal was knocked through by HNO3oxidized; Since H2SO4-(NH4)2S2O8 oxidized has strong oxidizing property, the hole wall of coal-based active carbons was burned excessively, then the part of the microporous structure collapsed or blocked, and leaded to micropore volume, specific area and total pore volume were reduced.(2) The determination results of FT-IR showed that the number of oxygen-containing functional groups of coal-based active carbons has increased noticeably after the modification, main functional groups: Carbonyl, Carboxyl andLactone. The results of Boehm titration and XPS warrant the conclusion of FT-IR, their order is: Carboxyl > Lactone base > Phenolic hydroxyl group. Because of the micro fracture and pore structure in deformed coal(P8D) is development, activating agent extensively contacts with deformed coal surface, so it led to the reaction more fully and the acid oxygen-containing functional groups on the surface of deformed coal was dissipated overmuch. Also for the same reason, the surface of deformed-coal-based active carbon was added more acidic functional groups.The methane adsorption experimental of coal and coal-based active carbons has been investigated. Coal-based active carbons from coal deformed is always keep the characteristics which micropores are development and specific surface area is large in the process of reform of activated carbon and subsequent acidification treatment.Therefore, we maintain that the surface area and pore structure have a fundamental impact on methane adsorption. It is decided that the methane adsorption capacity is strong when micropores are development and specific surface area is large.Acid modified has an obviously inhibition for adsorption active of coal-based active carbons. HNO3 oxidized has an effect on sparse hole, reaming on the series of coal-based active carbon. Specific surface area and pore volume has a significant increased after modified. But the methane adsorption capacity is decrease.The reason why the methane adsorption capacity of the series of coal-based active carbons is also decreased after H2SO4-(NH4)2S2O8 oxidized is that the hole wall of active carbon from coal were corroded due to the strong oxidizing of H2SO4-(NH4)2S2O8 oxidized. The surface content of oxygen containing functional groups was increased as well as specific surface area and pore volume was decreased. Both of side have the strongly inhibition for methane adsorption.Thus, the acidic liquid not only to make the activated carbon pore structure is reformed, but affects the changes of surface types and volume of oxygen containing functional groups of activated carbon. The change has an inhibition for methane adsorption. And it’s stronger than pore structure increase on methane adsorption capacity.Coal and coal-based active carbons have some similarities on the surface structure and chemical properties. Making coal-based active carbons as a coal simplified model,it can be applied to the coal of structure complex. To study surface pore structure of coal and oxygen containing functional groups have a guiding significance on methane adsorption active.