Preparation And Properties Research Of Pore-Size Controllable Carbon Membrane

Carbon membrane, a kind of inorganic membrane, is prepared by the pyrolytic carbonization of substance which contains carbon. It has high temperature-resistant, acid and alkali-resistant properties and high performances of mechanical intensity, osmosis, selectivity and sorption. In addition, its surface and microstructure can be modified and improved. Since 1980s, carbon membrane has been rapidly developed abroad. Carbon membrane for micro-filtration has been reported in commercial application, while carbon membrane for gas separation is still in the laboratory scale.Currently, the cost of carbon membrane is relatively high which limits its application in extensive subassembly and industrialized manufacture. Therefore one of the main research fields in carbon membrane is to find a membrane raw material. This material should be feasible, cheap, and have good sorption property. Lignin is a kind of natural resource next to than fiber in amount exists in nature. As thebyproducts of wood hydrolysate and paper making industry, it used to pollute environment because it hasn't been fully used. Considering future environment and resources, it is essential to pay more attention to the exploiture of lignin.This paper introduced the preparation process and basic performance of carbon membranes which were synthesized by using lignin as one of raw materials and pore-forming agent. Firstly, some basic properties of lignin such as surface energy were researched. The experiment showed the surface energy of lignin was about 21-22 mJ/m~2. It indicated that lignin was a low surface energy substance. Secondly, the dissolution behavior of lignin was studied. Using granularity instrument and SEM, we knew that lignin was swollen in HC1. The external shape of lignin was modified markedly in HC1 which was changed from rotundity to rectangle. And FTIR showed the structure of lignin in HC1.Lignin- phenol-formaldehyde resins were prepared by using phenol, formaldehyde and lignin with a content of 8 14 20 . Then the resins were coated on the glass board and furtherly pyrolyzed in a flowing nitrogen atmosphere. Thus the carbon membranes were obtained.From the analysis of carbon membrane micro-structure by using SEM, we can observe that the carbon membranes had apparent pore size of micro-nanometer. Therefore it meant that lignin maybe act as a pore-forming agent in the carbon membranes. For example, when thelignin content was 6%, the micro-size of pore shifted from 1.1 to 2.6um and the nano-size ranges from 120 to 320nm. The pore size was closely related with lignin content. So it probably also meant that the pore structure of carbon membrane may be controlled by adjusting the lignin content. The membrane adsorption ability and thickness was increasing with the increase of lignin content. In addition, the lignin content also had effluence to electric resistance of membrane. Through CP/MAS I3C NMR spectrum we can find that carbon membranes still had a feature of phenol-formaldehyde resin. So the carbon membranes had a possibility to be improved by prolonging carbonization time.