Performance Of Adsorbing And Recoverying The Gasoline Vapor By Carbonaceous Adsorbents

In the process of petroleum products loading,unloading,storage,transportation,or distribution,a great deal of the petroleum vapor are evaporated and emitted from the tanks to air and will bring on serious petroleum loss and harm to environment.So it is of the first magnitude to take measures to recover gasoline vapors.With a long history,adsorption has been widely used in separation.Adsorbent is vital in this method.Activated carbon,a commonly used adsorbent,still has some disadvantages,such as low adsorption capacity, poor wearing quality and high temperature in fixed bed,which restrict the application of adsorption in gasoline recovery.In this thesis,activated carbon and activated carbon fiber were used as adsorbents.In order to find out the reason for the problem,the operating conditions,such as the inlet concentration of gasoline vapor and the size of the fixed bed on adsorption capacity and the effect of the vacuum degree and desorbing time on desorption capacity,were also analyzed.Besides,the influence of pore structure and surface functional groups on the adsorbing behavior was also studied by using H₂ or H₂O modified activated carbon as adsorbent.The results and achievements are summarized as follows:(1) When activated carbon was used as adsorbent,high inlet concentration could cause high adsorption capacity,while the breakthrough time is shortened and the rise of temperature of the fixed bed is extremely high.Large fix bed is benefit to the increase of the adsorption capacity as well as the extension of breakthrough time with moderate rise in temperature of the fixed bed.Gasoline vapor could be desorbed better when the vacuum degree is lower and the desorbing time is longer.But the operating cost should be taken into consideration,which is related to the desorbing time.(2) The adsorption capacity for activated carbon depends on its volume of pore with diameter between 1 and 2nm and the oxygen-contained group on the surface of activated carbon.Compared to pre-modified activated carbon,the breakthrough adsorption capacity of gasoline vapors on the H₂O modified activated carbon was improved by 47.5%because of its larger mesopore volume.Besides,the breakthrough adsorption capacity of gasoline on the H₂ modified activated carbon was improved by 23.9%because of reduction of oxygen-contained group on the surface of activated carbon. (3) Adsorption capacity of activated carbon fiber is much higher than that of activated carbon.At the same time,the temperature rise of activated carbon fiber bed,which is 4.7℃,is lower than that of activated carbon bed,which is 20℃.For activated carbon fiber,the adsorption rate is high and the breakthrough time is short,while the inlet concentration it can deal is limited.So,compared to activated carbon,activated carbon fiber should be given priority in daily use,for example,cleaning indoor air.Activated carbon is adapted to be used in petrol station or platform to recovery gasoline vapor.