| Melt Spinning Stretching (MS-S) is an economic, convenient, cleaning method to prepare membranes. Usually semi-crystal polyolefin materials are suitable to be made into membrane by this process. In China, the research and development (R&D) on the preparation of polyolefin with MS-S method have been carrying out earlier, and the polypropylene (PP) microporous hollow fibre membranes (HFM) can be scale-up produced. However, compare with oversea advanced products, the comprehensive properties of domestic PP membranes are not good enough to fit the market demand. At the same time, the research and development of polyethylene (PE) hollow fibre membranes hardly carry over, because of the limitation of relative control and mechanic techniques. In this paper, basing on prior work, we study the process of PP hollow fiber membrane in order to develop the properties of this kind of membranes. Besides polypropylene, poly(4-methyl- 1 -pentene) (PMP) was also chosen as membrane materials in view of its excellent oxygen/nitrogen separation properties. To develop the application filed of polyolefin membranes, the separation performances of GIL or L/L membrane contactor based on PP HFM were study systematically.The optimization of the preparation of the PP hollow fiber membraneA model for describing the formation of melt-spun hollow fiber by differential equations is created. The model was calculated with numerical method. The simulation results fit the experimental data well. It is found that According to these results, the spinning process can be optimized.An improved method is achieved for the preparation of PP microporous hollow fiber membrane with high gas (water) flux. Besides materials, low spinneret temperature (Tm + 2050 CC). large draw ratio (2000-4000) and direct-hot-stretching temperature (TR + 40-I 00 0C) areconsidered the key factors.The gas flux of the improved membrane is 9.0 X 1 02cm3/cm2.s.cmHg, 2.5 times of that of the unimproved membrane (3.4 X 1 02cm3/cm2.s.cmHg). The water flux of the membrane increases from 48.OL.m2.hr' to 86.OL.m2hf~. The microprous membrane fouling caused by tap water is comprehensively discussed. The mechanism of membrane fouling by tap water can be- Iv -described with filtration-cake theory. The water flux resistance of membranes are 4.7 X lO'2m' (improved) and 8.4 X lO'2m' respectively.The separation and recovery of ammonia from mixed gas or waterWe briefly discussed the properties of the PP HFM contactor for removal gaseous ammonia directly from mixed gas in ammonia manufactory in order to find an economic way to substitute conventional soft-water washing absorption technology. The hollow fiber membrane (HFM)32contactor has very high elimination (99.9%) under optimum operation conditions. 5.1 Nm /(m .h) gas treatment ability can be achieved, as outlet and inlet ammonia concentration axe O.O2gINm3 and 2O.Og/Nm~ respectively and gas stay-time in contactor is only O.04s when acid supply around the membrane is sufficient. The results of industrial tests indicated that this technology could be used to eliminate mixed gas containing ammonia and replace conventional soft-water washing and absorption techniques.Recent research indicated that hydrophobic microporous hollow fiber membrane Contactor could be used to separate volatile contaminants from wastewater efficiently. The factors that influence the effect of separation of NH3/1120 are investigated carefully. The modules assembled with this PP hollow fiber membrane have good performances for separation of NH3/H20. It is found that the structure properties of PPHFM have little effect on the removal efficiency, and the feed side dominates the resistance of mass transfer. The overall mass transfer coefficient (K) only is dependent on the flux of ammonia solution and independent on the pressure and concentration of ammonia solution. Concentration of absorbing acid influence slightly on the overall transfer coefficients K while the absorbent supply is sufficient. Under this condit...
|
PDF Full Text Request