Preparation And Characterization Of Coconut Shell-based Carbon Molecular Sieve For Air Separation

Carbon molecular sieve（CMS）is a porous carbon adsorbent with uniform pore size.It is widely used in gas separation and purification,especially pressure swing adsorption（PSA）of air for N₂ production.The ideal carbon molecular sieve for nitrogen production by air separation has a two-stage pore system,that is,a large pore as a transportation channel and a micropore for gas separation.The pore volume of the micropore is large and the pore size is equivalent to the size of the gas molecules to be separated.At present,the air separation performance of domestically produced coal-based and polymer-based CMS has basically reached foreign high-performance CMS water.However,the preparation process has problems such as high cost and serious pollution.In addition,The production process of carbon molecular sieve is complicated.It leads that there are some interdepended parameters to influence the performance of CMS.The current pressure swing adsorption evaluation methods have limitations in guiding the preparation of carbon molecular sieves,and it is difficult to characterize the pore structure of the sample during the CMS preparation process and optimize the process parameters.This paper uses coconut shell char as carbon precursor and phenol formaldehyde resin as binder to prepare CMS for air separation to produce N₂.The pressure swing adsorption method and the spontaneous liquid-gas imbibition（SLGI）method were used to characterize the samples during the carbon molecular sieve preparation process,and the changes in the pore structure of the carbonization,activation and carbon deposition samples under different conditions were analyzed.And choose the carbonization conditions as the final carbonization temperature of 800℃,the carbonization constant temperature time of 30 min;the activation conditions are the water flow rate 0.6 m L/min,the activation temperature 830℃,the activation time 120 min;the carbon deposition conditions are the benzene flow rate 0.3 m L/min,the deposition temperature 800℃,deposition time 150 min.In the PSA test,the N₂ concentration of the product gas of the prepared CMS sample reached 93.2%,and the highest O₂concentration of the desorption gas reached 32.9%.Using H₂O as the liquid probe,N₂ and SF₆ as the gas probe,spontaneous liquid-gas imbibition behaviors of the samples during the carbonization,activation and deposition stages of the CMS preparation process were investigated and then compared with PSA test data.The results show that the rates of spontaneous H₂O-N₂ imbibition and spontaneous H₂O-SF₆imbibition reflect the pore size of different samples in different molecular size ranges;the equilibrium gas displacements of N₂ and SF₆ reflect the pore volume of the samples in different molecular size ranges.Comparing with PSA,SLGI can characterize pore structure of CMS intermediate products prepared under different conditions,it is better than PSA in guiding the production of CMS.