| China is the second largest consumer of petroleum resource in the world.The demand and consumption of petroleum have been increasing year by year in China.Petroleum sludge is a kind of solid waste generated during crude oil production,storage,transportation and refining inevitably.There are more than 5000,000 tons of petroleum sludge generated in China annually according to the statistics.As a kind of hazardous waste,petroleum sludge has been enrolled in the "National list of hazardous wastes" and non-hazardous treatment is required.On the other hand,it is of great interest to recover oil from petroleum sludge for resource utilization because of its high content of oil.As a relatively mature technology,centrifugal separation is easy to operate,clean and efficient that is suitable for engineering applications of resource utilization of petroleum sludge.However,petroleum sludge is generally considered as a water-in-oil(W/O)emulsion with high viscosity and poor fluidity.Thus,it's difficult to transport during the process of centrifugal separation.What's more,the water in petroleum sludge is stably emulsified which is hard to be removed by centrifugal separation.In order to get higher separation efficiency,it's necessary to apply pretreatment on petroleum sludge to break the W/O emulsion.A new micro-emulsion method for tempering pretreatment is proposed and studied in this paper.It can break the W/O emulsion effectively with the ultra-low interface tension.The experimental studies focus on two aspects,including viscosity reduction and removal of emulsified water.The main results and conclusions are summarized as follows:(1)The viscosity properties of petroleum sludge were analyzed and it showed that petroleum sludge was a typical non-Newtonian fluid with pseudoplastic characteristics.And the shear thinning behavior of petroleum sludge was more obvious than that of common heavy oil.The macromolecular structures formed by heavy components such as resins and asphaltenes promoted the stability of the W/O emulsion which was the fundamental reason for the high viscosity of petroleum sludge.The rheological curve of petroleum sludge was fitted by the rheological models.The fitting results showed that the P-L model was more suitable for describing the rheological behavior of Guolian sludge.(2)The effects of surfactant,micro-emulsion dosage and composition on the viscosity have been discussed.Experiments showed that the maximum viscosity reduction was achieved by using SDBS as single surfactant when the dosage was 25%.Viscosity reduction rate of more than 95%was obtained,especially 99.215%under 99 s-1.The fluidity of petroleum sludge was greatly improved.Considering both the effect of viscosity reduction and economy,SDBS and OP-10 are suitable.Viscosity reduction rate of 99.436%was obtained under 99 s-1 with the composited surfactant of OP-10 and SDBS at a ratio of 2:1,which was higher than that of using single surfactant.(3)The water content and variation of water droplet size of different layers of petroleum sludge before and after centrifugation was obtained by DSC analysis.The results indicated that the emulsified water could not settle under a certain centrifugal parameter because of stable emulsification.While the emulsified water merged together and settled into lower layer after centrifugation by pretreatment of micro-emulsion.Because the oil-water interfacial tention was reduced and the oil-water interfacial films were broken.(4)The effect of oil phase,cosurfactant and surfactants combination on dewatering were studied.The maximum dewatering efficiency of 94.60%was achieved by using kerosene as oil phase and n-butanol as cosurfactant.Surfactant combination experiment showed that a composited surfactant of CTAB and NP-10 at a ratio of 1:6 could achieve a dewatering efficiency of 95.23%.And it was higher than the efficiency by using NP-10 as single surfactant at the same condition,which was 78.94%.The interaction point was confirmed in the mixed micelle through 2D NMR NOESY experiment.This interaction resulted in a higher surface activity of the composite surfactant system and a lower oil-water interface tension,which leaded to a better demulsification effect. |
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