Preparation Of Activated Carbon Derived From Pitch And The Performance For CH₄/N₂ Adsorptive Separation

Activated carbon is a kind of inorganic porous material mainly composed of carbon,which consists of graphite crystallite-based amorphous carbon and small amount of ash.Rich oxygen-containing functional groups,high specific surface area and micropore content,adjustable pore size and stable chemical properties make activated carbon suitable for application of adsorption.Since CH₄ and N₂ in coalbed methane are similar in physical and chemical properties,the separation of CH₄ and N₂ has always been a difficult point in the field of gas adsorption.The preparation of adsorbents with high efficiency of CH₄/N₂adsorption separation is the key to solving this problem.In this work,the chemical activation method is adopted,with asphalt as the main carbon source,hawthorn branches,polyacrylamide and melamine are added to adjust the pore structure and surface properties of the pitch-based activated carbon,thereby improving the adsorption and separation performance of CH₄/N₂.The effects of carbon source composition,activation temperature and ratio of carbon source to activation agent on pore structure,surface properties and CH₄/N₂ adsorption separation performance of pitch-based activated carbon a investigated systematically.The surface properties and pore structure of activated carbon are characterized by infrared spectroscopy,elemental analysis,scanning electron microscopy,273 K-CO₂ adsorption and 77 K nitrogen adsorption/desorption.The specific content and conclusions are as follows:?1?Pitch-based activated carbons are prepared by chemical activation method with pitch as carbon source and KOH as activation agent.The effects of the ratio of asphalt to KOH and activation time on the surface properties,pore structure and separation of CH₄/N₂ are studied.The results show that the pitch-based activated carbon is mainly microporous,and with the increase of KOH content and the increase of activation temperature,the specific surface area and microporous content of activated carbon increase,the content of surface oxygen-containing functional groups decreases,and The adsorption amount of CH₄ and N₂ on activated carbon increases and the CH₄/N₂ separation ratio decreases.The increase of micropore volume of activated carbon,especially below 1.1nm,is beneficial to the increase of adsorption capacity of activated carbon on CH₄ and N₂.The surface oxygen content?oxygen functional group?of activated carbon and V_{0.45 nm-0.57 nm} increase are favorable for the ioprovement of CH₄/N₂.When the ratio of pitch to KOH is 2:1 and the activation temperature is 700°C,the adsorption amount of CH₄ on activated carbon?298 K and 100 kPa?reaches 28.5 m³/g,and the separation ratio is 3.4.?2?Series of composite activated carbons are prepared with different carbon source such as hawthorn branches,pitch and KOH as activation agent.The influence of the proportion of carbon source type,composite carbon source on surface properties,pore structure and CH₄/N₂ adsorption separation performance are investigated.The results show that when the ratio of asphalt to hawthorn branches is 1:1,the specific surface area and micropore volume of activated carbon reach a maximum.Compared with activated carbon prepared by single carbon source,the composite activated carbon has high specific surface area and micropore volume,and the surface functional group content is slightly higher than that of single carbon source activated carbon,and its adsorption and separation effect on CH₄/N₂ is better.Activated carbon prepared by mixed carbon source has a high CH₄ adsorption capacity of 35.1 cm³/g and the CH₄/N₂ separation ratio reaches 3.5 at 298 K and 100 kPa.?3?Polyacrylamide and melamine as organic carbon sources mix with pitch,and K₂CO₃ and KOH are used as activation agent respectively to prepare composite activated carbon.The effects of different organic carbon sources on the surface properties,pore structure and adsorption and separation properties of CH₄/N₂ are investigated.When activation temperature is 600°C,the adsorption amount of CH₄ and N₂ decreases with the decreases of V_{0.45 nm-1.00 nm} on activated carbons,the selectivity of CH₄/N₂ is consistent with V_{0.45 nm-0.57 nm}/V_{0.45 nm-1.00 nm},the adsorption amount and selectivity to CH₄ and CH₄/N₂ are 19.8 cm³/g and 3.9?298 K and 100 kPa?,respectively.