Efficiency And Membrane Fouling Control In ASP Flooding Oilfield Wastewater Treated By Polytetrafluoroethylene(PTFE) Membrane

The ASP compound flooding technique is a chemical flooding technique,which uses alkali,surfactant and polymer as flooding agents.During the process of using the ternary compound flooding technique,a large number of alkali,surfactants and polymers remain in the oilfield wastewater.Compared with other types of oilfield wastewater,ASP flooding oilfield wastewater has high contents of polymers,oil and suspended solid,high pH,temperature as well as salinity.The traditional method(coagulation-precipitation(gas float)-filtration)of treating ASP flooding oilfield wastewater was inefficient,however,membrane separation technology can not directly implement the oil-water separation through the demulsification process with its unique advantages.However,the high pH values(10-13)of the ASP flooding oil-field wastewater exceed the tolerance ranges of most membranes,such as polyvinylidene fluoride(PVDF),polysulfone(PSF),polyether sulfone(PES),which are susceptible to be chemically damaged.Polytetrafluoroethylene(PTFE)is characterized by the resistances to acid,alkali,high temperature,microbial attack,oxidation,oil and compression,so it can be used to treat the ASP flooding oilfield wastewater.This study set up the pilot system to treat the ASP flooding oilfield wastewater by PTFE membrane,and optimized the operational parameters of the system;investigated the efficiency during the treatment process of ASP flooding oilfield,and the effects of interactions among the main pollutants on the pollutants removal;analyzed the constituents of membrane pollutants and studied the adsorption fouling rules of the main pollutants on PTFE membrane.Besides,the pattern of membrane pollution was also determined by mathematical simulation;based on the analysis of PTFE membrane pollution mechanisms,then the membrane cleaning method was established.This study provides a new approach to solve the problem of the treatment of ASP flooding oilfield wastewater.This research optimized the operational parameters during the treatment process of ASP oilfield wastewater by PTFE membrane in the pilot system.The results showed that optimal operating parameters were: permeate flux 10 L/m2·h,backwashing cycle 60 min,backwashing flux 90 L/m2·h and intensity of gas washing 10 m3/m2·h.The removal efficiencies of oil,APAM?TOC?turbidity and SS were 74.82%-83.6%,95.8%-98.25%,81.56%-91.47%,84.25%-91.74%,88.42%-98.95%,respectively.A terminal filtration device was also utilized to treat the synthetic wastewater to study the effects of the interactions among different pollutants on the removal efficiency.The results indicated that the ions and surfactants decreased the removal efficiencies of the APAM and oil.However,the oil increased the removal efficiencies of APAM and surfactants.Moreover,APAM enlarged the removal efficiencies of oil and surfactants.This study analyzed the membrane pollutant ingredients,the effects of the interactions among contaminants on membrane fouling and the patterns of the membrane fouling.The results showed that both of the organic and inorganic fouling appeared on the PTFE membrane surface during the treatment process of ASP flooding oilfield wastewater;the resistance of membrane pore blocking(7.696 ± 0.22×1011 m-1)was much greater than that of cake layer(2.716 ± 0.13×1011 m-1),which indicated that membrane pore blocking was the main fouling form when PTFE membrane was contaminated by organic pollutants.The classic "cake" model was used to simulate the decay processes.The results showed that the models with good adaptation were complete blocking,standard blocking and rapid blocking when PTFE membrane was used to filtrate oil,APAM and ASP flooding oilfield wastewater,respectively.Moreover,the adsorption mechanisms of the oil and APAM were determined based on the adsorption thermodynamics and adsorption kinetics on PTFE membrane.The results indicated that the adsorption isotherms of oil and APAM belonged to Temkin model and Langmuir model,respectively.Both of the adsorption processes belong to the physical adsorption,in which hydrogen bonding was the main physical adsorption force.Differently,the adsorption of oil on PTFE membrane was an exothermic process,while the adsorption of APAM on PTFE membrane was an endothermic process.The equilibrium adsorption time of oil and APAM on PTFE membrane were approximately 16 h and 20 h,respectively.The pseudo-first order kinetic model had the highest degree of fit for the oil and APAM adsorption processes.The membrane cleaning method was established based on the fouling mechanisms when PTFE membrane was used to treat the ASP oilfield wastewater.On the basis of single factor experiments,Design-Expert software was used to do the regression analysis of the experimental results.The quadratic multinomial regression model was achieved,in which the flux recovery rate was the response value.The best condition was achieved for membrane cleaning by calculating the extreme value: NaOH 1 %,NaClO 0.72 %,HCl 0.65 %,soaking time 3.35 h;temperature 40.06 ?.Accordingly,the practical permeation flux was 99.34% under this condition.The microanalysis of SEM-EDX,AFM and FTIR proved that the cleaning condition was effective.