| Oilfield produced water is the main by-product in the process of oil exploitation.Once it enters the food chain,it will damage the ecological environment and endanger human health.Therefore,from the perspective of environmental protection and water conservation,oilfield produced water will be deeply treated to meet the discharge or reuse standards.As a kind of membrane treatment technology,inorganic ceramic membrane has been widely used in the field of oilfield produced water treatment because of its high mechanical strength,good chemical stability and not easy to be eroded by microorganisms.The problem of membrane pollution mechanism in the process of production of tablet ceramic film is determined by using the tablet ceramic film processing oilfield to determine the main pollutant and filter the optimal condition of the return injection standard,and use the interface theory of internal theory to explore the membrane pollution behavior and micromechanism of the ceramic membrane,and reveal the process and micromechanism of the film pollution process and the main pollutants in the oil field.The cleaning agents and cleaning methods are selected,and the same cleaning method is used to clean the membrane under different working conditions to reveal the influence mechanism of operating conditions on membrane pollution,so as to provide experience for the further application of ceramic membrane technology in the field of oilfield produced water reinjection regeneration.The research on permeability characteristics and critical flux of flat ceramic membrane shows that under the experimental conditions,the water flux increased with the increase of membrane pressure and the critical flux of oilfield produced water treated by flat ceramic membrane is 50 L/(m~2·h).The optimization control and membrane fouling mechanism of flat ceramic membrane for oilfield produced water treatment were studied.Four main operating factors affecting the flux of flat ceramic membrane were investigated.Taking the average membrane flux as the response value,four factors and three-level orthogonal experiments of initial membrane flux,filtration time,backwash time and aeration intensity were constructed.The experimental results show that the significance of the four factors on the average membrane flux is as follows:initial membrane flux>backwash time>filtration time>aeration intensity.The optimal operation conditions of flat ceramic membrane for oilfield produced water treatment are initial membrane flux of 80 L/(m~2·h),filtration time of 10min,backwashing time of 30s,aeration intensity of 3L/min.The average membrane flux is the largest under this condition,which is 27.82 L/(m~2·h).By comparing EDS element analysis and FTIR analysis of raw water and polluted layer,it is concluded that the organic pollutants of flat ceramic membrane are mainly amines or amides,hydrocarbons,carboxylic acids,aromatics and alcohols,and inorganic salt ions such as Si,Fe,Ca,Mg,Ba are also important components of membrane pollution.Analysis of membrane fouling resistance based on Darcy's law shows that resistance and gel layer resistance are the main drag factors in the process of flat ceramic membrane filtration,accounting for about 70%of total resistance.The interfacial thermodynamics of the flat ceramic membrane in the process of treating the oil field produced water membrane pollution was carried out.Pure oil solution,Na Cl oil solution and mixed electrolyte oil solution were prepared.The flux of ceramic membrane in these three kinds of oil solutions was measured with time.Combined with XDLVO theory,the thermodynamic mechanism of membrane fouling interface in these three kinds of oil solutions was explored.The thermodynamic study on the interface of flat ceramic membrane shows that at the initial stage of membrane fouling,the total interaction energy between the membrane and the oil droplet interface decreases gradually with the increase of the distance between the two interfaces,and finally changes from attraction to repulsion.The total interaction energy between oil layer and oil drop is mutual attraction,and the total interaction energy decreases with the increase of the distance between oil layer and oil drop.Salinity has a certain effect on the zeta potential of crude oil.Due to the electrostatic shielding of salt ions,the zeta potential of three solutions is reduced,in order:pure oil solution>Na Cl Solution>mixed electrolyte solution,resulting in the decrease of EL interaction in three oil solutions in turn,and because the composition of oil layer and oil drop is the same,the EL interaction in the three solutions can be shown as mutually exclusive.High efficiency membrane cleaning technology for oilfield produced water treatment by flat ceramic membrane was developed.The cleaning effect of cleaning agent type,concentration of cleaning agent and cleaning method on the polluted membrane was investigated.The optimal cleaning conditions recommended in the test were:2%sodium hydroxide for 2h+2%nitric acid for 1h.The flux recovery rate can reach more than 90%after using the cleaning cycle to clean the contaminated membrane.Under the optimal cleaning mode,the polluted membrane under different working conditions was cleaned,and the cleaning times of the polluted film were multiple linear return with SPSS analysis software.The results show that clear water flux,backwashing time and initial membrane flux have significant effects on the cleaning times.The scanning electron microscope(SEM)analysis of the new membrane,the contaminated membrane without any cleaning,the contaminated membrane after physical cleaning and the contaminated membrane after several times of chemical cleaning,as well as the infrared spectrum analysis of sodium hydroxide cleaning solution and nitric acid cleaning solution show that the surface morphology and element composition of the membrane after chemical cleaning are similar to those of the new membrane,and the cleaned pollutants are mainly inorganic carbonate and nitrate.The contact angle analysis shows that the cleaning condition can improve the hydrophilicity of the membrane. |
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