Study On Preparation Of Coal Based Activated Carbon By Low Ratio KOH And Its Application On Coalbed Methane Separation

Nowadays,the development and application of coalbed methane become one of the new research hotspots.Activated carbon is an adsorbent with developed pore structure and high storage capacity which is widely used in energy storage,gas separation and catalyzing chemical reaction,etc.In view of the structure characteristics and price advantage of coal based activated carbon,the investigation of coal based activated carbon with high specific surface area and its application in coalbed methane separation has significant meaning in theories and industry application.In this study,activated carbon was prepared from coal by KOH impregnation method,the influences of preparation conditions and activating agent on the properties of activated carbon were investigated;the effects of activated carbon on the separation of simulated coalbed methane were researched;and the growth and catalytic mechanism of coal-based carbon nanotubes which were founded in prepared activated carbonwas preliminarily discussed.The main results and conclusions were as follows:1.Shenmu coal was a kind of high quality raw material for preparing activated carbon with high specific surface area;the properties of activated carbon were influenced by the granularity and the coal type of raw material.When the carbonization temperature increased from 400? to 600?,the average pore diameter of JC(Jincheng)activated carbon decreased from 41.3nm to 12.71nm,the average pore diameter of SM(Shenmu)activated carbon gradually increased from 3.17nm to 7.14nm.When the temperature rose,the JC coke formed more micropores which resulting in the reduction of the average pore size.Relatively,the carbonization reaction of SM coal under the same condition has been basically completed,when the temperature rose,the ignition loss of carbon skeleton increased,causing average pore size larger;with the temperature of activation increased,the specific surface area of JC activated carbon first increased then decreased,and the best activation temperature is 850?;with the increase of the activation time,the specific surface area of TX(Taixi)activated carbon increased,and the main proportion of pore was micropore.2.The optimized conditions of preparing activated carbon using Shenmu coal by impregnation method were:carbonization temperature 450?,carbonization time 60min,activation temperature 825?,activation time 60 min.The specific surface area of granular activated carbon under the optimal conditions was 764.76 m2/g.3.Micropore volume of activated carbon had important influence on specific surface area.The Average pore size was mainly influenced by micropore volume,porosity and pore size distribution,while the influence of specific surface area and pore volume were negligible..When adding 10%Ni(NO3)2 to raw coal,the optimal carbonization temperature decreased from 500? to 450?,the maximum specific surface area increased from 590.83 m2/g to 690.72 m2/g,the number of micropores increased,at the same time,the micropore diameter increased slightly,and the micropore volume and total volume all increased,while the pore structure and type did not change.4.Ni(N03)2 promoted the K-carbon elimination reaction,which generated more tartaric acid potassium hydrate.In alkaline environment,the great amount of OH-which were produced by KOH ionization had strong reducibility.It combined with Ni2+in Ni(N03)2 to generate Ni(OH)2.One part of Ni(OH)2 turned into NiO after high temperature dehydration,another part of Ni(OH)2 dissolved in KOH and generated K4[Ni(OH)6],which became K4Ni03 after dehydration.The elemental K and elemental Ni were formed by the oxidizing reaction between K4Ni03 and C.5.Within the pressure range of 0 to 0.5 MPa,activated carbon adsorption saturation prolonged when adsorption pressure increased,which illustrated that the higher pressure was benefit to the separation of CH4 by activated carbon.For different activated carbon with similar specific surface area,the higher the average pore diameter and the total volume,the smaller the impact of stress on the separation.Activated carbon with different specific surface area may have the same adsorption capacity,which demonstrated that the specific surface area was not the only factor that influenced the adsorption properties of activated carbon,the pore size and the volume were also important factors.6.The van der Waals force between CH4 molecular and adsorptive sites enhanced with increasing pressure.At the beginning of the adsorption,the concentration of CH4 decreased rapidly,as the process proceed,the surfaces were covered by CH4 molecules gradually,the surface free energy of activated carbon reduced,and the concentration of CH4 increased slowly.7?When the CH4 content in the feed gas was 10%,the fraction of coverage of CH4 molecules on the surface of activated carbon was low,both the decrease and increase process of CH4 concentration were slow,and the adsorption curve presented as "V" type.When CH4 content was 20%,the concentration of CH4 decreased rapidly at first,and then increased rapidly after a short stay at a minimum value,the adsorption curve shown like a groove.When CH4 content was 60%,the number of CH4 molecular filling the adsorption sites increased,van der Waals force enhanced meanwhile,which made the adsorption finished immediately,the adsorption process soon reached the minimum value,and increasing concentration process was relatively slow,the curve shown as "V"type.8?Carbon nanotube was discovered in the study,thus this part was added in.Multiwalled carbon nanotubes were formed during the preparation of activated carbon,the carbon were from the coal source..The longth of carbon nanotube was from several micrometers to tens of micrometers,the diameter was about 100nm,the thickness of tube-wall was 20nm,the number of plies was 60,carbon nanotube was coated with columnar catalyst,the degree of graphitization of carbon nanotubewas high and the crystal shape was regular.The catalyst elements was Fe,but it was hard to explain the growth mechanism of carbon nanotubes from raw materials without Fe element,thus the catalytic mechanism needed further discussion.9?The "stair style" growth mechanism of carbon nanotube was proposed.Gaseous carbon atoms dissolve in molten catalyst particles and precipitate into solid graphene sheet.Carbon nanotube grown from outside to inside and from bottom to top,thus formed a certain height difference between outer and inner layer,which looked like layers of the "stair" from the cross-section drawn.