The Research Of Carbon-based Composites For Ship’s Oily Water Treatment

Due to increasingly stringent emission regulations and limited space in engine room on board ships,adsorption separation technique,which takes the advantages of simple structure,good separation effect and limited space,is suitable for the treatment of ship’s oily water,and the development of composite adsorbent with low-cost and large ad/absorption capacity is the key to its on board applications.In this paper,a new composite adsorbent,which is composed of expanded graphite and activated carbon,was prepared by one-step impregnation chemical activation method.Researches undertaken are as follows:(1)Optimization of process parameters for the development of the activated carbon suitable for emulsified oil adsorption.Phenolic resin was selected as carbon source and KOH was as activating agent.Single factor optimization method was employed to evaluate the influence of the mass ratio of KOH to phenolic resin,activation temperature and heating duration of the expanded graphite on adsorption capacity of emulsified oil on the sample,and optimum processing parameters for synthesis of the activated carbon was further determined via the orthogonal test.It shows that,while the mass ratio,heating temperature and heating duration were respectively set as 4.5,650℃,and 2h,the prepared sample,which has a specific surface area1402m~2/g and meso-pore ratio 76.4%,can have an adsorption capacity about 71.1mg/g for emulsified oil.(2)The influence of the packing density of the formed expanded graphite on its mechanical strength was studied.Result shows that the as-prepared expanded graphite samples have the largest expansion volume where the heating temperature and duration for expansion were respectively about 900℃and 25s.The monolith of the expanded graphite was formed by mechanical method and then undergone the mechanical-strength measurement.It shows that the mass loss rate of the formed expanded graphite decreases in its density,and a high mechanical strength of the sample can be obtained while the prepared expanded graphite is in density about0.03g/cm~3 with a mass loss rate about around 7%.(3)Adsorption characteristics of the oily water on the composite adsorbent were evaluated by adsorption experiments performed by varying the density of the shaped expanded graphite,the flow rate of the oily water and the height of the adsorbent column.It seems that,within the flow rate of the oily water 0.38mL/s-0.46mL/s,while the density of shaped expanded graphite is0.03g/cm~3 and the height of adsorption column is selected as 20mm,the oil content of the treated water from the composite adsorbent is less than 10ppm,which can meet the discharge standard required by IMO.Moreover,results from the comparison tests show that the performance for the treatment of the emulsified oily water of the composite adsorbent is much better than that of the filter CYSC-0.5 currently used on board marine oily water separator,which brings about a processing capacity about 0.447L/cm~3 and 0.275L/cm~3 respectively for the composite adsorbent and the filter.(4)Mechanical strength test of the composite adsorbent and structure analysis of the composite adsorbent.By introduction of activated carbon into the space of the expanded graphite,it shows that the strength of the composite adsorbent has significantly been enhanced by the increment of compression resistance and crushing resistance.SEM images show that the expanded graphite mostly consist of meso-pores and macro-pores,and the main ingredient of the filter CYSC-0.5 is polypropylene fiber.Results also reveals that,the introduction of activated carbon has no effect on the structure of the expanded graphite,but it enriches the pore structure of the composite adsorbent and accordingly improves the"catching capability"of the composite adsorbent for the emulsified oil.(5)Analysis of adsorption equilibrium of emulsified oil on the composite adsorbent.Within temperature range 293-308K,the adsorption characteristic of the emulsified oil on the composite adsorbent can be fairy be described by Lagergren quasi-secondary adsorption rate model,which suggests that the duration for adsorption equilibrium is less than 15 minutes with an adsorption equilibrium capacity about 67.2 mg/g.Results from model studies on the isotherms show that Tempkin equation can predict the adsorption data with a higher accuracy,with a temperature dependence of saturated adsorption capacity 115.34-170.65mg/g.Moreover,it shows that the adsorption enthalpy of the emulsified oil on the composite is about-41kJ/mol,which suggests that the adsorption is a physical one accompanying with an exothermic process.