Adsorptive Separation Of Ethylene And Propylene In Dry Gas By Activated Carbon

As the most important fundamental chemical raw material, ethylene is a major indicator to evaluate the level of the National Chemical industry. The dry gas in refinery plant is rich in ethylene, and can bring huge economic and social benefits if effectively utilized. One method is utilizing the dilute ethylene in dry gas to react with benzene to make styrene. However, propylene in the dry gas would participate in reaction, which not only affect the product purity, but also increase the consumption of benzene and subsequent separation cost. Therefore, the separation of ethylene and propylene is of great theoretical and practical value. In this paper, the adsorption characteristics and regeneration methods of main components in dry gas had been systematically studied, providing necessary basis for setting up the adsorption separation method of ethylene and propylene in dry gas.Adsorption isotherms of pure methane, ethylene, ethane, propylene, propane on activated carbon were measured by ASAP2050volumetric analyzer from0.60kPa to150.00kPa, at temperature of298K,313K and333K, respectively. The Langmuir model, Freundlich model Langmuir-Freundlich model and BET equation were applied to fit the component’s adsorption isotherms individually, correlation of adsorption equilibrium data by Langmuir-Freundlich showed the best fitting effect.The breakthrough curves of dry gas was determined using the dynamic apparatus under adsorption pressure of0.2MPa,0.3MPa,0.5MPa,0.7MPa,1.0MPa, and temperatures of298K,313K and333K, respectively. Accordingly, the adsorption isotherms of main components, such as methane, ethylene, ethane, propylene and propane, and the separation factor of ethylene and propylene can be obtained. The adsorption capacity of various components increased with the increase of pressure or the decrease of temperature. Under different conditions, there is a significant difference between the breakthrough time of ethylene and propylene. And the separation factor is7.0-11.2, indicating that activated carbon has excellent adsorption selectivity for ethylene and propylene. Due to the influence of too much components, adsorption capacity, content inequality and other factors, the average error of Laden Ratio Correlation (LRC) is between31.38%and48.33%, while Flory-Huggins Vacancy Solution Model (FHVSM) is between31.27%and56.56%.The regeneration effects of temperature, hydrogen purge and vacuumization on activated carbon were studied. Comparing with vacuumization, hydrogen purge is a more preferable approach. Generally, its regeneration rate can reach95%. Specifically, the maximum regeneration rate is up to98%under room atmosphere,313K, hydrogen with the velocity of1OOmL·min-1. The regeneration effect of vacuumization for weakly-adsorbed components (methane, ethylene and ethane) was much better than strongly-adsorbed components (propylene, propane), and the influence of evacuation for activated carbon regeneration was inconspicuous.The stability of activated carbon was also investigated. After5times adsorption and desorption, activated carbon adsorption capacity was slightly change(≤2.0%). It indicated that the regeneration method is feasible, and this activated carbon is of desirable stability, which can adapt to the requirements of adsorption separation of ethylene and propylene in dry gas.