Selective Adsorption And Separation Of Mixture Gases Using Synthetic Porous Carbons

Physical adsorption is a critical separation method due to its low energy consumption,no corrosion and easy operation.One of the key points to the widespread use of adsorptive separation method is the development of highly efficient adsorbents.Porous carbons are widely used in gas separation and storage due to their developed pore structure,high specific surface area and well electrical and thermal conductivity.However,conventional porous carbons commonly show disordered structures,and uneven pore size distributions owing to the uncertained precursors.Therefore,precisely regulating the pore structure and surface chemistry of carbon materials to meet the requirements of specific gas adsorption and separation still has great challenges.This paper has carried out the following work around the preparation of efficient porous carbon adsorbents and investigated their gas adsorption and separation performances,the main conclusions are as follows:(1)For most of porous carbon adsorbents,there are weak adsorption interactions and low selectivity for low-eoncentration CO2 separation,and there is usually a "trade-off"phenomenon for the adsorption capacity and selectivity.Herein,macroporous/microporous nitrogen-rich(6.1 wt%)monolithic carbons were investigated.The effect of pore structure and surface chemistry of porous carbons on the separation of low-concentration of CO2 was investigated.The results show that the rich nitrogen species(such as pyrrolic-N and pyridine-N)in the porous carbons have strong affinity for weakly acidic CO2 moleculars,combined with the macropore structure,high specific surface area and suitable pore size,they can effectively increase the adsorption capacity and selectivity of the porous carbons.The equilibrium adsorption capacity is up to 6.5 and 4.0 mmol·g-l,respectively,at 1 bar/0? and 25?.The results of dynamic breakthrough show that the porous carbons have excellent adsorption separation performance(SCO2/N2 = 454;SCO2/CH4=11)for the mixtures of CO2/N2 and CO2/CH4 under ambient temperature and pressure conditions and porous carbons have excellent cyclic regeneration performance and moisture-resistance performance.(2)For the traditional porous carbons,the adsorption of CO2 relies solely on physical adsorption,the adsorption interaction is weak.The adsorption performance of CO2 decreases with the increase of adsorption temperature,and the adsorption capacity and selectivity are usually low.Herein,in order to improve the adsorption performance of porous carbon adsorbents under elevated temperature conditions.Laponite was introduced in phenolic resin by the interfacial assembled principle based on the organic-inorganic hybrid method and principle of complementarity.Weakly polar carbon composites were prepared after carbonizition and activattion,which overcome the limitation of single-component carbon materials for the physicochemical properties.These weakly polar porous carbon adsorbents with hierarchical structure can significantly increase adsorption performances of COZ under elevated temperature eonditions.The equilibrium adsorption results show that adsorption capacity of CO2 is 1.7 mmol·g-1 at 70? and 1 bar.Subsequently,the carbon composites were applied to the adsorption separation of low-concentration COZ,high CO2/n2 selectivity factor(114.3)is achieved at 70 C.This high selectivity is attributed to the synergistic effect of pore structure and surface functionalization of carbon composites.High specific surface area,suitable pore size,strong affinity between CO2 and carbon skeletons coupled uniform mesopores(7 nm)promote CO2 adsorption and accelerate the breakthrough of N2 at elevated temperatures.(3)For porous carbon materials,micropores are the main places for gas molecules storage and sieving,and furtherly,the porous carbon materials which are rich in micropores on the mesoporous carbon wall,high adsorption force is obtained.By changing the physical activation time of carbon composites,regulating the pore structure of carbon composites and controlling the surface polarity of carbon skeleton,the research work was further extended to the study of low carbon hydrocarbon separation and CH4/N2 separation.The results show that this series of porous carbons can efficiently separate C1-C3 hydrocarbons by equilibrium effect.Under ambient temperature and pressure conditions,the C2H4 dynamic adsorption capacity is 1.4 mnol·g-1.The dynamic selectivity factor of C2H4/CH4 is 25.The C2H6 dynamic adsorption capacity is 1.7 mmol·g-l,the dynamic selectivity factor of C2H6/CH4 is 90.The largest C3H6 and C3H8 absorption capacities are 3.1 mmol·g-1 and 3.2 mmol·g-1,respectively,and selectivity factors are 217(C3H6/CH4)and 227(C3Hs/CH4),respectively.In addition,these adsorbents also exhibit good adsorption capacity and separation selectivity in the separation of a CH4/N2 mixture which is extremely difficult to separate.The CH4 dynamic adsorption capacity is 0.92 mmol·g-l,and the CH4/N2 separation selectivity factor is 26.3 under ambient temperature and pressure conditions.It is much higher than the performance of the reported porous adsorbents.