Flocculation Mechanism Of Dithiocarbamate And Performance In Treating Produced Water From Polymer Flooding

Produced water from polymer flooding is difficult to be treated for its high viscosity and emulsified characteristics owing to containing amount of residual polymer(HPAM).The water quality after treatment by conditional process used in the oilfields couldn't reach the standards for being injected into the stratum.The treatment of wastewater containing HPAM has been an important problem.Developing flocculants that could effectively separate oil and suspended substances(SS) from the polymer solution is an economic and applicable method at present.Dithiocarbamate flocculants were synthesized with amine-terminated polyoxypropane-ether compounds.The products were analyzed by infrared spectra and element composition.Flocculation activity of DTC agents in treating the kaolite suspensions were investigated,combining with analysis of zeta potential and scanning electron microscope to elucidate flocculation mechanisms.Then flocculating performance on removing oil from simulated polymer flooding produced water was studied.The effect of DTC's dosage,the concentrations of ferrous ions and HPAM(0, 200,500 and 900 mg/L),pH(4.5～9.5) and minearal ions were investigated, respectively.Finally DTC's flocculation performance on actually produced water from polymer flooding in Shengli Oilfield was evaluated.The results confirmed that there were no flocs growing up when DTC agent was dosed alone.Containing dithiocarbamic groups(CSS),DTC agent coordinated with ferrous ions in the wastewater through which the flocs formed.The net capturing and sweeping of flocs was identified to be the main flocculation mechanism.On treating simulated samples,high concentrations of HPAM decreased chelating rates between DTC and Fe²⁺ and flocs growing,and oil removal.Fe³⁺ couldn't chelate with DTC in the flocculated process since it coordinated with oxygen atom easily.Oil removal effect was better under the condition of neutrality partial to weak acidity due to that Fe²⁺ would be oxided rapidly at basic condition.On treating the actual polymer flooding produced water,20mg/L dosage of DTC was able to decrease the oil concentrations below the 10mg/L combined with Fe²⁺.PDA analyzer showed that the flocs formed and grew up rapidly,the final size being big.