Preparation Of Cellulose-based Microporous Carbon Based On The Separation And Enrichment Of CH₄ From Low-concentration Coalbed Methane

Guizhou Province is rich in coal-bed methane resources,but most of the extracted CH₄concentration is less than 30%,which cannot be used directly,and most of it is discharged.The key to improving the utilization of low-concentration coalbed methane CH₄ is to separate CH₄from the CH₄/N₂ mixture.In industry,activated carbon has become the main adsorbent for the separation of CH₄/N₂ due to its advantages such as large specific surface area,developed pore structure,simple preparation and low cost.According to the theory of adsorption potential,adsorbents with a pore size distribution of 0.38-1.50 nm are most conducive to CH₄ adsorption.However,the preparation of activated carbon has the problems of difficult to control the pore size distribution and less micropore volume.In response to this problem,the paper is based on:1)under the action of mechanical ball milling,the high temperature and high pressure generated by the local collision of the carbon precursor and the sphere can accelerate the diffusion of the activator into the raw material,so that the activator is more uniformly dispersed in the carbon precursor;2)at high temperature,The uniformly dispersed small molecular size K vapor in the precursor can diffuse into the carbon material,distorting the carbon layer,adding more defects,and forming more extremely narrow micropores;the principle of potassium-containing compounds(KOH/KMn O₄,C₆H₅K₃O₇,CH₄N₂O/C₆H₅K₃O₇)are activators,the hydrothermal carbon formed after hydrothermal carbonization of cellulose is the carbon source,and activated carbon is prepared by mechanochemical activation.The precursor was characterized by TG-IR and XRD to study its activation process,and the prepared activated carbon was characterized by N₂adsorption/desorption isotherm,SEM,XPS,XRD,FT-IR,etc.,to study its pore structure and surface chemistry Properties,using static capacity method and dynamic penetration method to evaluate the performance of the prepared activated carbon for low-concentration coalbed methane CH₄ adsorption and separation.The main results are as follows:1.The mechanical force coupling KOH/KMn O₄ chemical activation method to prepare microporous carbon and its adsorption and separation performance for CH₄/N₂.The effects of milling time and KOH/KMn O₄ addition ratio on the microporous carbon pore structure and CH₄/N₂ adsorption and separation performance were studied.The results show that the carbon material prepared by the ball milling method can effectively increase its micropore volume(Vmic)and form a narrower ultramicropore distribution(the most probable pore size is 0.42/0.46 nm).With the increase of the milling time and the addition of KMn O₄,the Vmic of the carbon material AC_X-QT(x=30,60,90 min;T=0.2,0.4,0.6)first increased and then decreased.When the milling time is 60min and the KMn O₄ addition amount is 0.4(HTC:KOH:KMn O₄ is 1:1:0.4),the Vmic of the carbon material AC_0.4-Q60 is the largest,which is 0.63 cm³/g.The microporous carbon AC_0.2-Q60with a Vmic of 0.55 cm³/g showed the highest static adsorption capacity of CH₄(3.22 mmol/g,273 K,1 bar,the same below),and the selectivity of CH₄/N₂(0.2/0.8)was 7.82.This is because AC_0.4-Q60 contains too many oxygen-containing functional groups on the surface,which reduces the interaction force(dispersion force)with CH4 molecules,making AC_0.2-Q60 CH₄ static adsorption with moderate pore structure and surface oxygen content The highest capacity.In addition,when the simulated coalbed methane passes through the adsorption column filled with AC_0.2-Q60,the CH4 concentration can be increased from 20%to 35.77%(CH₄/N₂/O₂=20%/64%/16%,10 ml/min,298 K,1 bar,the same below),and still has excellent CH₄ adsorption stability after six adsorption/desorption cycles.2.C₆H₅K₃O₇ activation method to prepare microporous carbon and its CH₄/N₂ adsorption and separation research.The effects of activation conditions on the pore structure of microporous carbon and the adsorption and separation performance of CH₄/N₂ were studied.The results show that the Vmic of the carbon material ACQK_1-800-1 is 0.46 cm3/g and the most probable pore size is0.42 under the optimal process conditions(activation temperature is 800?,activation time is 1h,HTC:C₆H₅K₃O₇ is 1:1).nm,its static adsorption capacity for CH₄ is 2.57 mmol/g.ACQK_1-800-1was subjected to dynamic mixed gas penetration experiments under different adsorption conditions(raw material flow rate,concentration,adsorption temperature,adsorption pressure).The results show that ACQK_1-800-1 can be separated well under any conditions.The CH₄/N₂mixture has a much higher adsorption capacity for CH₄ than N₂,but the separation effect is best at low flow rate,low concentration,low temperature and high pressure.When the simulated coalbed methane passes through the adsorption column filled with ACQK_1-800-1,the CH₄ concentration can be increased from 20%to 32.61%,and it still has excellent CH₄ adsorption stability after six adsorption/desorption cycles.3.C₆H₅K₃O₇/CH₄N₂O activation method to prepare microporous carbon and its adsorption and separation performance for CH₄/N₂.The effects of the addition of C₆H₅K₃O₇ and CH₄N₂O on the pore structure of microporous carbon and the performance of CH₄/N₂ adsorption and separation were studied.The results showed that the N element was successfully doped into the carbon skeleton.With the increase of the addition of C₆H₅K₃O₇,the Vmic of the carbon material ACK_XN₁(X is the content of C₆H₅K₃O₇ added)increases first and then decreases,and the content of N element gradually decreases.When the addition of C₆H₅K₃O₇ is 2(HTC:C₆H₅K₃O₇:CH₄N₂O is 1:2:1)The Vmic of the carbon material ACK₂N₁ is the largest,0.78 cm³/g,C/N is 35.98,showing the highest static adsorption capacity of CH₄(3.00 mmol/g),and the selectivity of CH₄/N₂(0.2/0.8)is 6.47.With the increase of the addition of CH₄N₂O,the Vmic for preparing carbon material ACK₁N_Y(Y is the content of CH₄N₂O)first increases and then decreases,and the content of N element gradually increases.When the addition of CH₄N₂O is 2(HTC:C₆H₅K₃O₇:CH₄N₂O is 1:1:2).The V_mic of the carbon material ACK₁N₂ is the largest,0.53cm³/g,showing the highest static adsorption capacity of CH₄(2.84 mmol/g).When the simulated coalbed methane passes through the adsorption column filled with ACK₂N₁ with the highest CH₄adsorption capacity,the CH₄ concentration can be increased from 20%to 34.58%,and it still has excellent CH₄ adsorption stability after six adsorption/desorption cycles.