The Preparation And Evaluation Of Coconut Shell-based Carbon Molecular Sieves For Air Separation By PSA

Carbon molecular sieves?CMS?is a microporous carbonaceous adsorbent with gas separation.It is an important part of the gas separation by pressure swing adsorption?PSA?technology.At present,the technology of air separation by PSA is becoming more and more mature,but the quality of gas production depends largely on the performance of CMS used in PSA.The performance of CMS prepared by using raw materials such as coal and phenolic resin in China is close to that of foreign commercial CMS.However,there are still problems such as high cost and high pollution in the preparation process of CMS.At the same time,there is no simple,fast and effective method to evaluate the pore structure change of CMS and to guide the optimization of process parameters during the preparation process.Therefore,it is of great significance to use coconut shell as raw material and to find effective and rapid evaluation methods to prepare CMS with great performance.In this paper,the coconut shell char was used as raw material,and the preparation of CMS was carried out by molding,carbonization,activation and final pore adjustment.The reaction during the carbonization and activation process was analyzed,and the reasons for the formation of the pore structure in the product were briefly discussed.At the same time,the effects of various reaction conditions on the pore structure change of the product were analyzed by PSA and spontaneous liquid-gas imbibition.The suitable carbonization conditions were as follows:heating rate 10°C/min,carbonization final temperature 800°C,constant temperature time 30min.The suitable activation conditions were water flow rate 0.80 ml/min,activation temperature 830°C,and activation time 150 min.The intermediate prepared by the carbonization and activation conditions is subjected to two-step pore structure adjustment.Performing preliminary deposition of the sample using a higher concentration of benzene in the first step of pore adjustment.A CMS with 94.96%N₂ in PSA was obtained by the low concentration benzene deposition in the second step of pore adjustment.A CMS with 96.15%N₂ in PSA was prepared by slow release agent and benzene deposition.The over-deposited sample was subjected to pore adjustment using a reactivation method to obtain a CMS with96.82%N₂ in PSA.The air separation performance of different commercial CMS and laboratory-made CMS was analyzed and compared by using PSA device.The evaluation method of PSA was improved by combining the analysis of the pressurization time,N₂ concentration in gas production,the highest O₂ concentration in desorption gas,the desorption gas volume,the N₂recovery rate and the bulk density.The gas desorption behavior of CMS with different air separation performance was preliminarily investigated after adsorbing air,N₂ and O₂respectively.It is found that CMS with different properties have great differences in gas desorption behavior.Based on the phenomenon,a method and device for evaluating the gas separation performance of microporous materials are proposed,which is expected to lay the foundation for subsequent research.