Study On The Preparation,modification Of Microfiltration Carbon Membranes And Their Separation Performance For Oily Wastewater

With the rapid development of economical society and the continuous progress of industrial modernization,people are increasingly dependent on the consumption of oil and its products,bringing a rapid expansion of industrial scale related to oil extraction and processing.As a result,a large number of industrial oily wastewater is produced and discharged.Disordered discharge of oily wastewater would cause serious harm to the human’s production,living and ecological environment.Therefore,the discharge standard of oily wastewater has become more stringent.The traditional separation methods of oil-water are incapable of meeting the requirements,so it is urgent to develop new and efficient oil-water separation treatment technology.Membrane separation has attracted much attention due to its advantages of stable performance,simple operation,low energy consumption,no chemical addition and high interception effect.As the key of membrane separation technology,membrane materials have always been the research hotspot and difficulty in this field.Carbon membrane is a new type of membrane material which has developed rapidly in recent years.In addition to the advantages of conventional membranes,it has higher chemical stability,mechanical strength and separation performance,and has shown many advantages for oily wastewater treatment.However,previous studies have also found that carbon membrane is prone to be contaminated and short service time during application.Therefore,it is urgent to resolve those problems before large-scale industrial application.In this paper,microfiltration carbon membrane was prepared using phenolic resin as precursor,sodium carboxymethyl cellulose as binder and diatomite(DE)as dopant.In particular,the structure of carbon membrane was adjusted and controlled by acid/base treatment,surface coating,post-oxidation treatment and other modification methods to improve its anti-pollution performance and separation performance.The average pore size and porosity of carbon membrane were meaured by bubble-pressure and boiling methods.In addition,the thermal stability,surface functional groups,microstructure,morphology of the membranes were analyzed by thermogravimetric analysis,Fourier transform infrared spectroscopy,x-ray diffraction and scanning electron microscope,respectively.The effects of acid/base treatment way,type of acid/base treatment,acid/base treatment concentration,coating solution type,coating solution concentration,post-oxidation temperature,post-oxidation holding time and other factors on the oil-water separation performance of carbon membrane were incestigated.Furthermore,the regeneration of carbon membrane was also attempted by cleaning,the influence of regenerant type and concentration on the performance recovery of carbon membrane were investigated.Results have demonstrated that(1)Using diatomite treated by acid/base as dopant has a significant effect on the thermal stability of precursor membrane.The average pore size and porosity of the carbon membrane could be effectively improved by doping DE by acid/base or the carbon membrane treated with acid/base directly.The carbon membrane blended with DE treated by 10%NaOH has the lowest average pore size of 0.208μm and the highest porpsity of58.68%.Carbon membrane treated by 10%NaOH has the maximum permeation flux of615.479Kg/m~2h,while the carbon membrane treated by distilled water has the maximum oil rejection of 94.79%.(2)When carbon membrane is modified by surface coating,the coating agent of polyvinyl alcohol(PVA)is easier to form hydrophilic film than polyethylene glycol(PEG).With the increase of PVA concentration,the coating becomes thicker,and tends to be smoother and denser.Meanwhile,the permeation flux of carbon membrane tends to decrease,while the oil rejection tends to increase.Carbon membrane coating with 3%PVA has the maximum permeation flux of 939.474Kg/m~2h.Carbon membrane coating with 9%PVA has the maximum oil rejection of 58.47%.(3)When carbon membrane is treated by post-oxidation,proper post-oxidation temperature and holding time could improve the thermal stability of the carbon membrane,as well as the average pore size and porosity.For post-oxidized carbon membrane by 120℃with holding time of 30min,the lowest average pore size is reached at0.208μm,together with the highest porpsity of 58.51%.For post-oxidized carbon membrane by80℃with holding time of 30min,it has the maximum permeation flux of 363.158Kg/m~2h.For post-oxidized carbon membrane by 160℃with holding time of 30min,it has the maximum oil rejection of 97.57%.(4)Combine the above three modification methods,the separation effect of carbon membrane could be effectively improved under the respective optimal processing conditions.Among them,modification by PVA coating has the highest permeation flux and modification by post-oxidation has the best rejection effect.