Study On The Threatment Of High Salinity Brine With Osmotic Membrane Distillation

Zero discharge of high salinity brine is an inevitable requirement for environment sustainable development.How to treat high-salt brine and meet the requirement of "zero discharge" is one of the most important and urgent issues at home and abroad.As a new membrane separation technology,membrane distillation,driven by the vapor pressure difference on both sides of the membrane,has the characteristics of low energy consumption,high rejection and low operating pressure.It is expected to be applied to concentrate high saline water,meet the petrochemical industry,metallurgy field waste-water reduction,recycling and zero emissions request.In this paper,the feasibility of concentrating high salinity brine by osmosis membrane distillation(OMD)was discussed.The effects of the type of osmotic agents,cross-flow velocity,membrane surface orientation,and feed temperature on membrane distillation separation performance were studied.The concentrating performance of concentrating chlorine alkali anode dilute brine by OMD is also compared with direct contact membrane distillation(DCMD)processes.The effect of membrane orientation on the water flux was tested.Firstly,the influences of the type of osmotic agents and hydrodynamic conditions on the membrane distillation separation performance for concentrating high salinity brine with OMD were investigated.A significant enhancement in water flux and overall mass transfer coefficient could be achieved when an osmotic agent was used compared to a direct membrane distillation configuration,and the salt rejection of three osmotic agents shows above 99.9%.The percentage increase in flux is notably greater with higher feed concentrations.With the increase of cross flow velocity on both sides of the membrane,the permeate fluxes increase and the effects of polarizations reduce for all the systems.Using a mathematical approach,this improvement in water flux was found to be mainly caused by the temperature polarization occurred on the permeate side of the membrane.OMD is characterized by shorter concentration time and less energy consumption when concentrating the diluted brine in the chlor-alkali industry as compared to DCMD processes.This work illustrates that OMD is a promising process for effective and efficient concentration of highly saline brine.In addition,the effects of membrane orientation and feed temperature on membrane distillation separation performance were investigated,and the membrane properties were characterized respectively.Asymmetric membrane had higher liquid entry pressure(LEP)than symmetric membrane,which could effectively reduce the risk of membrane wetting.The water flux of the symmetric membrane is almost unchanged,but the water flux and overall mass transfer coefficient of the asymmetric membrane in the membrane active layer faced the feed solution mode are higher than in the membrane active layer faced the osmotic agent mode.The higher water flux of the membrane active layer faced the feed solution mode was obtained as compared to the membrane active layer faced the osmotic agent mode,indicating that the diffusion of water vapor paly a dominant role in the membrane active layer.While the water flux increased with the increase of the membrane pore size and the feed temperature,the overall mass transfer coefficient decreased with the increase of the feed temperature.It has also been found that the temperature polarization of the membrane active layer faced the feed solution mode is less than the temperature polarization of the membrane active layer faced the osmotic agent mode.The concentrative concentration polarization of the membrane active layer faced the feed solution mode is more severe than the concentrative concentration polarization of the membrane active layer faced the osmotic agent mode.The dilutive concentration polarization of the membrane active layer faced the feed solution mode has less adverse effect on the performance of membrane distillation than the dilutive concentration polarization of the membrane active layer faced the osmotic agent mode.