Investigation On The Adsorption Mecanism And Application Of Carbon Nanotubes In Oily Wastewater Treatment

Aiming at the problem of oily wastewater treatment,different sources of petroleum products were used as adsorbate.The adsorption capacity of multi-walled carbon nanotubes?MWCNTs?on these adsorbates were investigated.The adsorption kinetics and the adsorption equilibrium behavior of MWCNTs were observed.Dynamic adsorption experiments were carried out using simulate the oily wastewater at the end,and flow rate of wastewater on adsorption and treatment efficiency of MWCNTs on oily wastewater was also analyzed to get some basic rules of oily wastewater treated by MWCNTs.Compared with activated carbon and walnut shell,MWCNTs show high adsorption capacity.For kerosene and diesel 1^#,adsorption capacity on MWCNTs were 13 times and 12times of walnut shells and activated carbon.Oil adsorbed on MWCNTs and walnut shells were desorbed through vacuum filtration and the desorbrd adsorbents were recycled for adsorption.With the increase of number of recycles,the adsorption capacities and desorption rate for MWCNTs and walnut shells are both reduced and eventually stabilized.The desorption rate of walnut shell is more than twice of MWCNTs.When the two kinds adsorbents used together,with the increase of mass ratio between MWCNTs and walnut shells,adsorption capacities of different oils increased and desorption rate decreased.It was found that stratified filling was better than mixing of the two kinds of adsorbents.Whatever the filling manner or the ratio between the two kinds of adsorbents,the adsorption capacity of the three kinds of oils are all in the order of kerosene<diesel 1^#<diesel 2^#,while the desorption rate is kerosene>diesel 1^#>diesel 2^#.For the system studied,MWCNTs have faster adsorption rate,and the adsorption equilibrium can be reached in about 60 min.All the experimental data can be accurately represented by a pseudo second-order kinetic model.The increasing of operating temperature is beneficial to increase the adsorption rate.In the range of 288 K-318 K,the value of activation energy suggests that physisorption dominates the adsorption of diesel 1^#and diesel2^#onto MWCNTs.Under 288 K,298 K and 308 K,adsorption process was consisted of external surface adsorption,internal diffusion in large interstitial pores and in small interstitial pores between the tubes for diesel 1^#and diesel 2^#on MWCNTs.Under 318 K,the process shows two stages,i.e.surface adsorption and intraparticle diffusion stages.Initial adsorption behavior was found in the adsorption process of diesel oil onto MWCNTs.Under different temperatures,the adsorption for diesel 1^#and diesel 2^#on MWCNTs were all accord with Freundlich model,belonging to favorable adsorption process.The rise of temperature is favorable for the adsorption process.The adsorption process for the two kinds of diesel onto MWCNTs was endothermic and spontaneous.With the increase of adsorption capacity,isosteric adsorption enthalpy?H decreases gradually.And under the same adsorption capacity,adsorption enthalpy of diesel 2^#was a little bigger than diesel 1^#.Consistent with the results of kinetic studies,the value of?H and?G suggest that physisorption dominates the adsorption of diesel 1^#and diesel 2^#onto MWCNTs.Through dynamic experiments,it was found that carbon nanotubes had good recycle performance,with steady adsorption capacities of 6.7 g?g^-1 for four times of reuses.