| In recent years, air pollution and water pollution problems are spreading to major cities of the world and become more serious than before, such as PM2.5(commonly known as haze) and oil leakage. PM2.5 particle size is small in size and rich in a large number of toxic and harmful substances, which have a great influence on human health and environmental quality. Oily sewage sources are very extensive, such as petrochemical, mining, machinery processing, leather, textile,food and other industries, and the emission is large, if directly discharged into the water, the ecological balance of natural would be destroyed. However, traditional air filtration technology has the problems of low efficiency and short service life. Nanofibrous membranes have the advantages of large surface area, high porosity, simple production process. As a consequence,membranes with a certain thickness have attracted much attention in the field of filtration due to their high efficiency. However, due to the disadvantages of high pressure drop, low yield, poor performance and lack in theoretical research, the application of nanofibrous membranes is limited.This paper mainly focuses on the above issues. Firstly, the method of preparing high efficiency and low resistance air filter material by using single needle spinning device and structured receiving template is studied. PAN is served as the spinning material on account of its facile electrospinning process, uniform fiber fineness, homogeneous and fluffy structure. Bulged bubble structure, embossed paper structure and plane structure(aluminum foil) were employed as receiving template to study the effect of templates structure, spinning time and modified structure on the nanofibrous membrane filtration performance. Results showed that when using bulged bubble as a receiver with spinning time of 8-10 h, nanofibrous membranes have low density and high quality factor with the average diameter of 3.5 μm. Therefore pressure drop of PAN nanofibrous membrane declined from 151.7 mm H2 O dropped to 28.7 mm H2 O and filtration efficiency from 97.32% drop to 95.55% when receiving template changed from aluminum foil to bulged bubble. In addition, adding fine yarns on a bulged bubble gap can effectively improve the uniformity of the PAN nanofiber membranes. As a result, the filtration efficiency was improved to96.33% while filtration resistance fell from 287 Pa to 247 Pa.Secondly, industrial production of nano air filter membrane is studied in this paper. Using the three-dimensional free surface electrostatic spinning device with output of 20-25 g/h was used for eletrospinning with PAN as spinning material to study the effect of distance, voltage, solution volume, receiving drum speed, traverse speed, temperature and humidity, pore size parameters on the filtration properties of nanofibrous membrane. Since high efficiency and low resistance membranes is both required to prepare masks and filters. Their characteristics of filtration performance, air permeability, moisture-penetrability, strength, diameter and pore size distribution was studied. The research results indicated on the condition that the quantity of solution of about the 50~60ml, roller speed of about 30~40 r/s, traversing speed of 800 cm/Min, voltage of 60-68 KV, distance of 15 cm, average pore size of 2 ~ 3 μm. Nanofibrous membranes’ filtration efficiency could achieved 95~99.56% with filtration resistance of 100~250 Pa, air permeability of300 L·m-2·s-1, moisture permeability of 9.6~13m2·Pa·w-1, strength of 50~80 N, fiber diameter of50~300 nm and pore size of 0 to 3 μm, which could satisfy American Standard(NOISH), EU standards(EN143) China standard GB2626-2006.Then, the mechanism of high efficiency and low pressure drop PAN nanofibrous membranes was analyzed. The effects of solution properties, nano fiber orientation and Na Cl aerosol flow velocity on the membrane filtration performance were investigated respectively. The mechanism of electrostatic effect, inertial deposition, gravity sedimentation, diffusion effect and intercept effect were analyzed. The mathematical models of unsteady filtration efficiency and pressure drop are established, and the results are compared with the experimental results. The results showed that the viscosity of PAN solution of 1200 CP is a optimal condition of the spinning solution, and the speed has little effect on the performance of the filter, but properties of products. The filtration efficiency decreases while pressure drop increases with the increase of Na Cl flow velocity. The main filtration mechanism of the high filtration efficiency of the nanofibrous membrane is the inertial deposition, diffusion effect and interception effect. The fitting formula for the filtration efficiency of the nanofibrous membrane is as follows:η( )-=dtcbta)exp(exp-100. The fitting formula for the pressure drop of the nanofibrous membrane is as follows: V.Finally, in order to expand the application field of nanofibrous membranes, the preparation technology and application of high strength nanofibrous membranes are studied in this paper. By comparing with several common water processing materials, this paper finds out the advantages and disadvantages of nanofibrous materials. Then methods of changing film thickness, addingNa Cl, changing the receiving roller speed, hot rolling and flat heat bonding to improve film strength were studied in this paper. Membranes with high strength were used for waste water filtration. The results showed that, hot rolling and flat heat bonding prepared electrospun membrane/nonwovens composite membrane has a strength of 50 ~ 60 N, which is about 60 times of films without treated; the intensity, elongation at break of 50% to 75%, and tenacity is 10 to 20 times more than films without treated, which shows that they are effective ways to improve the nanofibrous film strength. And hot plate bonding membrane’s emulsification oil interception rate is as high as 98.56%, which is higher than that of PVDF commercial ultrafiltration of 97%. Also pure water flux of hot plate bonding membranes is about 4004 L/(m2·h)with water contact angle of about 50 to 70°, indicated that the plating bonding enhanced nanofibrous membranes have great application potential in water treatment. |
PDF Full Text Request