Study On Removing The Organic Substance From Air Using Gas Membrane Separation

Using gas membrane technology to separate the microscale organic substance from the air is very important to the environment protection. This technology has so many advantages, such as few investment > little energy consume, convenience operation. In this paper, PVDF-SR composite membrane is prepared to remove the decahydronaphthalene (DHT) from the air. Membrane model and the experiment circuit are designed to reduce the exit concentration under 25ppm.First, the separation membrane materials are chosen from CA,PVA,PVB>PVDF and SR. From swelling experiments, the swelling degree of DHT in SR is larger than that of the other materials, such as CA> PVA, PVB, PVDR it can reach to 100%. In CA -. PVA , PVB % PVDF, the time of swelling experiments that used to come to balance is about 20 min. but after 60 min DHT in SR does not come to swelling balance as SD (swelling degree) is 0.55. In PVDF. the swelling degree is very small. At 50 癈. D (diffusion coefficient) of DHT in SR is 1.74X 10~~mrrr, S (solution coefficient) is 1.15. P (permeation coefficient) is 2.001 X 10"2mm2. Therefore. PVDF and SR are selected as support layer and separation layer, respectively.Then, the plane membrane, which using PAN, PS, PVDF as support layer (effective area is 15.9cm~, the thickness of SR is 0.45mm). are prepared to separate the DHT from air. As PVDF-SR composite membrane, (at 50癈.the entry pressure is one atm. the vacuum degree is 0.05atm. the flow rate is 1.5L min.the separating time is 2hr.) the entry concentration is 986.2ppm. however the exit concentration is down to 572.3ppm. descending degree is 41.97%. The separation factor ( a ) is 288. The capacity of unit membrane area reaches 6.996kg/nr ?day.Third, the hollow fiber, which using PVDF, PS as support layer and SR as separation layer, is prepared. From the separation results, the entry concentration increases with the rise of entry pressure and the temperature, but decreases with the increment of flow rate. The separation factor ( a) decreases with the increment of flow rate and the entry pressure, but increases with the temperature. As PS-SR composite membrane, (at 50癈.the entry pressure is one atm. the vacuum degree is lOmmHg. the flow rate is l.lnr.the separating time is Ihr.) the entry concentration is 71.2ppm. however the exit concentration is down to 39.6ppm. descending degree is 44.32%. The separation factor( a ) is 426. the capacity of unit membrane area is 14.052g/m: ?day.Last, cascade calculation is studied. As PVDF-SR composite membrane, as theentry concentration is 1231.4ppm. the exit concentration of last unit should under25ppm. If a , are both constant, then the cascade number is 7; if/? is constant.a is variable, then the exit concentration only reach 108ppm as the cascadeconnection is 14. more cascade number are needed.