Synthesis Of The Oxygen Adsorbent And Simulation And Experiment Study For Air Separation By The Dual-reflux Pressure Swing Adsorption

In this paper,the NaK-LSX molecular sieve with high crystallinity and purity is synthesized in sodium-potassium system by seeding growth method and hydrothermal synthesis.Then,the NaK-LSX molecular sieve is sequentially exchanged by Na⁺and Li⁺.Finally,the N₂ adsorption capacity and the N₂/O₂ separation factor of the synthesized zeolite were measured.The NaK-LSX zeolite is obtained under the optimization conditions,in which the ratio of SiO₂/Al₂O₃,?Na₂O+K₂O?/SiO₂,H₂O/?Na₂O+K₂O?and Na₂O/?Na₂O+K₂O?is 1.9,2.94,11.92 and 0.76 repectively.The optimal Na⁺ion-exchange conditions are as follows:exchange with a 1M NaCl solution at 90?,the ratio of Na/K is 1.5,this exchange is carried out 3times and each time is 3h.Followed by,the best Li⁺ion-exchange conditions are as follows:exchange with a 2M LiCl solution at 0.2MPa and 130?,this exchange is carried out4times,3h for each time,the ratio of Li/Na is 4.The ratio of sesbania and binder is 1%and 5%.The activation maintains 4h under the temperature of 450?.The N₂/O₂separation factor is 5.2 at ambient temperature and 0.1Mpa.The dual pressure swing adsorption?DR-PSA?could produce two high purity and recovery product gases simultaneously.It is especially suitable for applications where two high purity product gases are required at the same time.In this article,the DR-PSA process is applied to the field of air separation.The N₂/O₂ adsorption quantity on LiLSX zeolite is measured by the adsorption equilibrium measurements.Then,the data is fitted to obtain adsorption isotherm parameters by Extended Langmuir equation and is applied to simulate of DR-PSA process.A two-bed experimental apparatus is designed to verify the feasibility of the process and the reliability of the mathematical model.In order to obtain the optimal operating condition,a series of runs are carried out to investigate the effects of feed or light reflux step time,heavy reflux flow rate,feed flow rate and the lowest vacuum pressure?P_L?on the performance of DR-PSA process.Experimental and simulation results show:the purity of O₂ in light product stream could be enriched to 99.1%with a recovery of 98.0%,while the purity of N₂ in heavy product stream could be concentrated to 99.0%with a recovery of 99.3%under the optimal condition,in which values of t_FE/LR,Q_HR,Q_LR,Q_F,P_L,Q_HP,Q_LP are 60s,0.300m³/h,0.025m³/h,0.300m³/h,0.4bar,0.238m³/h and 0.062m³/h,respectively and the productivity is0.553mol/kg/h/O₂?In addition,a binary mixture gas?79%N₂/21%O₂?is used to simulate the actual air in the previous basis research,ignoring the influence of argon in the air.When the feed gas is 78%N₂/21%O₂/1%Ar,the purity of O₂ in the light product gas is reduced from 99.1%to 94.85%,and the recovery of 93.34%,while the purity of N₂ is concentrated to 98.15%with a recovery of 99.83%under the optimal condition that is obtained in the previous study.