Study On Deoiling Process And Surface Behavior Of Surfactants In Oily Sludge

Oily sludge is a kind of hazardous waste with complex composition and rich oil resources.Failure to adopt appropriate methods to deal with it will not only cause serious environmental pollution,but also lead to a large amount of waste of petroleum.The effective treatment of oily sludge has become a urgent matter due to the strength of environmental protection has been increasing year by year.Treatment of oily sludge by using surfactant is an effective method.However,the choice of surfactant mostly based on deoiling rate in current researches,and the deoiling process has not been studied in depth.In this study,the landing sludge of Liaohe oilfield was treated as the object of treatment.Several kinds of treatment agents were screened out according to the indexes of solid residual oil rate,liquid turbidity and oil content after treatment.The selected treatment agents were compounded,and the effects of different influencing factors on the deoiling efficiency of the compound surfactant system were explored.The changes of solid and oil phases before and after treatment were analyzed,and the deoiling process was explored by investigating the surface behavior in different surfactant systems.The analysis of oil,water,solid three-phase showed that the oil content in the sludge was 31.4%,which means high recycling value.The four components of crude oil from sludge was analyzed,the result showed that content of colloid and asphaltene was 41.07%.The analysis results of particle size and solid phase composition showed that the composition of the sludge was complex and the particle size was thin,which makes it difficult to treat.Various surfactants and alkaline was used to wash oily sludge at the same conditions,and the residual oil fraction and liquid phase properties was investigated.The results showed that rhamnolipid,OP-10 and sodium silicate had better deoiling efficiency.When the mass ratio of sodium silicate,rhamnolipid and OP-10 was 6:2:1,the best deoiling effect was obtained,and the solid residual oil rate was reduced to 4.43%.The effects of the three agents on oil-water interfacial tension were investigated by interfacial tensiometer.It was found that a single agent can effectively reduce oil-water interfacial tension,but the compound surfactant has a stronger ability to reduce oil-water interfacial tension,which may be one of the reasons for its better deoiling effect.On the basis of the above compounding ratio,the optimum deoiling conditions were determined through experiments.The results showed that the concentration was 2%,the time was 40min,the agent-sludge ratio was 4:1,and the temperature was 60?,which had higher deoiling efficiency and the cost was relatively low,the residual oil was reduced to 0.71%under this condition.The treated oily sludge was observed by microscope and SEM,the results showed that the oil-containing substance on the surface of solid phase was significantly reduced after the treatment.Meanwhile,the particle size decreased and the solid became looser.The analysis results of the infrared spectroscopy and thermogravimetric and four components of rude oil showed that the surfactants were more capable of removing light components from oil,and the residues in the solid were mainly heavy components such as asphaltene.The determination of contact angle showed that the surfactant obviously improved the hydrophilicity of the sludge,and the lower the residual oil rate,the stronger the hydrophilicity.The sodium silicate solution has little effect on the surface wettability of the sludge,and the contact angle of the solution on the surface of the sludge is always greater than 120°;while the rhamnolipid and OP-10 can wet the surface of the sludge,and the solution is in the sludge.The equilibrium contact angles of the surfaces are approximately 20° and 10°,respectively.Surfactant compounding enhances the adsorption capacity of rhamnolipid on the surface of the sludge,resulting in an increase in the negative charge of the sludge surface,but its wetting ability to the sludge is similar to that of a single rhamnolipid solution.The solution is on the surface of the sludge.The static equilibrium contact angle is approximately 24°.The wetting model can better describe the wetting ability of the surfactant.The results show that the surfactant with strong wetting ability has a lower equilibrium contact angle and the contact coefficient attenuation coefficient is larger.The wetting of the surfactant on the surface of the sludge reduces the adhesion of the crude oil on the surface of the solid phase.Different surfactant systems have different efficiency in reducing the work of adhesion.Among them,the synergistic effect of the surfactant on the adhesion work is the highest,at 100 mg/L can significantly reduce the adhesion of crude oil.Comprehensive analysis can be concluded that the wetting ability of the compound surfactant on the surface of the sludge is not significantly weaker than that of the single surfactant.When the concentration is low,the adhesion work of the crude oil can be significantly reduced,and the crude oil is more easily peeled off from the solid surface;The compound surfactant has lower interfacial tension,higher solubilization ability for the stripped crude oil,and promotes the transfer of crude oil from the solid phase to the liquid phase;the addition of sodium silicate to the surfactant system has the ability to reduce the interfacial tension.At the same time,it enhances the electrostatic repulsion of the surface of crude oil and sludge,and the difficulty of re-adsorbing the stripped crude oil on the surface of the solid phase increases.