Study On Air-gap Membrane Distillation By Using PTFE Hollow Fiber Membrane

With the acceleration of urbanization process and the growth of the population,the problem of water pollution has become increasingly prominent. Membrane distillation is one of a new, easy to operate, can take advantage of industrial low-grade heat source membrane separation technology, but during to its high energy consumption and low thermal efficiency, the industrialization process is always hindered. The multi-effect membrane distillation technique is based on membrane distillation and added an internal heat recovery device, so that you can improve the internal steam heat utilization and reduce the problem of energy loss.This study uses self-made polytetrafluoroethylene（PTFE） hollow fiber membrane wires as hot membrane, and the solid pipe as cool membrane. The PTFE membrane and solid pipe are intertwined with 1:6 ratio to make the air-gap membrane module, and with water gained-output-ratio（GOR）, membrane water permeate flux（J）,rejection（R） as a measure to study the effects of hot feed temperature T1, cool feed temperature T4, feed flow rate Q, feed concentration on membrane application performance. The main contents and conclusions are as follows:（1） Making 2 wt% NaCl as a feed solution, the experiment is tested in a single component. The results show that the permeate flux and GOR increased with the increase of hot feed temperature T1. With the increase of cool feed temperature and the decrease of feed flow rate, The results show that permeate flux decreased but GOR increased. With the increase of feed flow rate, the permeate flux increased but GOR decreased. But the rejection rate has been stabled at 99.9%, and during the test,the water GOR could reach 2.861, the water permeate flux could reach 6.144·m-2·h-1.（2） Making 2 wt% NaCl as a feed solution, the experiment is tested in adual-component,drawing the same impact conclusion. But during the dual-component testing, the water GOR could reach only 1.798 highly, and the water permeate flux is only 3.888·m-2·h-1 highly, is less than the single component. So it is obvious that the single multi-effect membrane distillation performance is superior than multivessel membrane.（3） Making the reverse osmosis（RO） brine generated in electroplating wastewater as a feed solution, do the concentrated experiment. The results show that when the hot feed temperature T1, cool feed temperature T4, feed flow rate Q are 80℃,30℃, 40L·h-1, the water water COD can be concentrated form 760 mg·L-1 to6000mg·L-1, the electrical conductivity can be concentrated form 37000 μs·cm-1 to300000μs·cm-1, the water permeate flux could reach 3.160·m-2·h-1. And during the enrichment process, the membrane operation performance is very stable, the electrical conductivity of permeate water could be less than 50 μs·cm-1, and the COD is less than 10 mg·L-1.（4） Concentrating 3 wt% H₂SO₄ as a feed solution, the experiment is tested in a dual-component. The results show that when the hot feed temperature T1, cool feed temperature T4, feed flow rate Q are 80℃, 30℃, 40L·h-1, the H₂SO₄ solution can be concentrated from 3 wt% to 20 wt%, the water permeate flux could reach2.780L·m-2·h-1, the electrical conductivity of permeate water is 150μs·cm-1. In the stability tests, the membranes work 300 h of continuous operation, the water permeate flux could maintain at 2.938L·m-2·h-1 above, the electrical conductivity of permeate water could be less than 46 μs·cm-1.