Graft Modification Of Ceramic Membranes And Its Application In Membrane Distillation

At present, shortage of freshwater resources of China is increasingly serious, the membrane distillation has the advantages of simple operation, high efficiency separation, as well as lower operating temperatures, which can make use of solar energy and industrial waste heat and other cheap energy, it is expected to become an effective way to solve the problem of shortage of freshwater resources.Membrane distillation is a new membrane separation technology, which is based on a hydrophobic porous membranes on both sides of the vapor pressure gradient. It is attracted widespread attention in the field of seawater and brackish water desalination, water volatile solute removal, wastewater treatment. Despite the many advantages of membrane distillation technology, but the properties of the membrane materials limite membrane distillation widely used. Thus, the production of high performance membrane distillation membranes, to enable them to long-term stable and efficient operation and access to a large flux, which is urgently needed to solve to realize the wide range of industrial applications of membrane distillation technology.Membrane distillation use hydrophobic microporous membranes, in which the most commonly used are organic membranes, Mainly of organic membranes are polypropylene (PP), polytetrafluoroe thylene (PTFE) and polyvinylidene fluoride (PVDF). Compared with the organic membranes material, ceramic membranes have better thermal stability and chemical stability, but because it does not have a hydrophobic, it can not be used directly for membrane distillation.Based on our previous work, hydrophobic Al2O3 ceramic membranes were prepared through surface graft modification with dimethyldichlorosilane as a modifying agent, in order to broaden the sources of hydrophobic membrane materials. And then the modified membranes are applied to separate the aqueous solution of sodium chloride.Results show that the modifying agent is successfully grafted on the membrane surface; the modified membranes have a very good hydrophobic characteristic; and no significant changes are observed in surface morphologies and pore sizes of the membranes before and after grafting. The LEP of the modified membranes was measured to be 0.11MPa. And then applied to air gap membrane distillation of NaC1 solutions.Membrane distillation results show that permeate fluxes increase with the increases in solution temperature and flow rate, but decrease with the increase in solution concentration; the solution temperature is the major factor affecting the membrane distillation; the modifying ceramic membranes have good effect of NaCl rejection. Research results demonstrate that the prepared ceramic membranes modified with the dimethyldichlorosilane can be sufficiently used in the membrane distillation of NaCl solutions.Based on air gap membrane distillation sodium chloride solution experiment, take added turbulence promoter in the membrane tube and two-phase flow strengthening measures, discuss the performance of membrane distillation strengthening effect. Results show that, take cylindrical type turbulence promoter, wound turbulence promoter and spiral turbulence promoter could improve the flux, Strengthening effect order of the strength is spiral turbulence promoter, wound turbulence promoter and cylindrical turbulence promoter; After take the measure of wo-phase flow, flux increased by 12% to 44%.