Adsorption Of Trace Ethane With Potassium Hydroxide Modified Activated Carbon

It is an effective method for recycling and reusing carbon resources by purify industrial waste gas or flue gas which contain much of CO₂.Adsorption separation method was usually used to purify CO₂.Industries contain traces ethane,which is very similar to CO₂,making it more difficult to separate ethane from CO₂.Therefore,the key to obtaining high-purity CO₂ is to develop an adsorbent with good adsorption performance and high efficiency.In this paper,coconut shell activated carbon?AC?was used as the main adsorbent,and KOH was used as activator to prepare different adsorbents by impregnation method and physical grinding method.The preparation conditions of adsorbents,properties of adsorption,regeneration and selectivity of ethane were systematically studied.The main conclusions are as follow:First,a series of adsorbents were prepared by KOH impregnation method and high temperature activation of AC under N₂ atmosphere.The effects of different impregnation concentration,impregnation temperature,immersion time,activation temperature and activation time on the preparation of adsorbent were investigated.The order of the factors were as follow:activation time>immersion concentration>activation temperature>immersion time>immersion temperature.And it was got the optional preparation conditions.Ethane breakthrough capacity of the optimum adsorbent A-0.5-8 reached 357.1?g/g,which was 110%?169.6?g/g?higher than that of the blank AC.The results showed that the relationship between the specific surface area,pore volume and micropore ratio of the sample and the breakthrough amount of ethane is complicated.The micropores in the adsorbent are the main sites for ethane adsorption,and a small amount of mesopores can facilitate the diffusion of ethane molecules.Then,using physical grinding method,the effects of alkali-carbon ratio,activation temperature and activation time were investigated.The optimal conditions were as follow:alkali-carbon ratio,0.5;activation temperature,800°C;activation time,2 h.The capacity of the optimal adsorbent A-800-0.5-2 reached 482.1?g/g,which was 184%higher than that of the blank AC.The results showed that the micropore ratio is between 80%and 85%,which is more favorable for the adsorption of trace ethane.The micropore ratio is less than 80%or more than 86%the breakthrough capacity of ethane is decreased.After KOH activation,the mass fraction of O on the surface of AC-800-0.5-2 increased by 63.5%compared with AC.It is speculated that surface oxygen species may promote the adsorption of ethane.In CO₂,the ethane breakthrough capacity of A-0.5-8 and AC-800-0.5-2 are lower than that under N₂ atmosphere,because CO₂ will cause severe competitive adsorption to ethane.But the adsorption performance is more than blank sample.The ethane breakthrough adsorption amount of AC-800-0.5-2 decreased to 98.2?g/g,which was 120%higher than that of the blank sample.The regeneration and selectivity experiments were carried out.The results showed that the regeneration rates of A-0.5-8 and AC-800-0.5-2 were about 98%,which means that he adsorbents prepared by the two methods has excellent regeneration performance.Calculating selectivity among alkane,AC-800-0.5-2 was found that it has bad adsorption for methane,while has better adsorption for ethane and propane.