Study On Mechanism Of Blocking Polyether To Strengthen Dusting Process Of High Stability Oily Wastewater

With the application of polymer flooding technology in Bohai oilfield, a lot of oily wastewater is generated correspondingly. The HPAM existed in the water thereby the stability of oily wastewater is strong, which leads to much difficult to remove oil in wastewater. Currently, the most effectively used method for treating oily wastewater is adding cationic polymer. It can easily reduce the stability of oil drop by electrostatic charge neutralization. But the flocs of cationic polymer are very viscous; these viscous flocs could lower the efficiency of treatment and induce the paralysis of wastewater treatment system. It has found that using nonionic block polyether to deal with this kind of oily wastewater can not only avoid the generation of oil sludge but also remove the oil in water efficiently through previous studies. However, its mechanism is not clear, so the optimization of demulsifiers and application in field are restricted. Aiming at this problem, the mechanism of demulsification process by block polyether for treating high stability oily wastewater is studied.At first, this paper measured the basic properties of SZ36-1CEPK oily wastewater, its PH=6.8, oil content is4724mg/L, the solid content is80mg/L, polymer concentration is282mg/L, the median particle size is5.1μm, the alkane carbon number of crude oil in wastewater is9.2. The emulsified oily wastewater has a high stability. The properties of block polyether which have a good performance for treating wastewater as follows:the molar ratio of EO to PO is close to0.75in its molecular structure; the working temperature of block polyether is more than cloud point temperature and less than the PIT. The cloud point is less than30℃(too small), or greater than40℃(too high) for the other block polyether with no performance.Thermodynamic experimental results show that the block polyether diffusion from water phase to interface is a spontaneous process and controlled by entropy. The entropy change of this process can reflect the replacement ability to natural surface-active substances and the change ability to interface film tightness of block polyether molecular. The entropy change of DMEA1231in diffusion process had the maximum value which is614J/K·mol, namely the bigger entropy change, the better performance.Macro flocculation kinetics experiments show that the flocculating rate of cationic polymer is3to5times than that of block polyether. For DMEA1231, the optimum processing conditions are:temperature is55℃, stirring is200rpm. Micro flocculation kinetics experiments show that the coalescence rate of oil droplet treated by block polyether is significantly greater than the effect of cationic polymer. But the temperature has a great influence on block polyether than cationic flocculant. With different from cationic flocculant, block polyether achieve demulsification by droplets coalescence and have no influence on aggregation of oil droplet.Zeta potential determination results showed that the cationic flocculant can effectively destroy double electrode layer and oil removal was achieved by electrostatic neutralization. However, the electrical of wastewater did not change after joining block polyether. It suggested the difference mechanism of cationic flocculant and block polymer. Block polyether can significantly reduce the interface expansion modulus. With the temperature increasing, the PO chain can transfer the active substance into oil phase therefore the expansion modulus decreasing. At55℃, the interface expansion modulus was minimum value, which consistent with PIT and flocculation kinetics. Coalescence-Flocculation was the process of demulsification by block polyether. Droplets coalescence was the key step and controlled by phase inversion. Different factors on the interface expansion modulus experiment results show that interface expansion modulus decreasing with the dosage of block polyether. Also the polymer concentration and molecular weight can increase the interface expansion modulus.According to phase transition temperature of DMEA1231and composition analysis results, the HLD value of DMEA1231-O/W emulsion system was calculated to study the mechanism of demulsification process by DMEA1231for treating high stability oily wastewater. When the temperature is55℃, the HLD value is0.886. The phase inversion of emulsion occurred by DMEA1231inducing near the PIT(55℃). The stability of emulsion in this condition is lowest.