Application Of Natural Polymer Materials In Separation Of Caprolactam-water System By Pervaporation Membrane

Pervaporation (PV) as a novel separation technology, compared with other traditional methods, has far more effective characters due to high selectivity, simplicity, low energy consumption, environmental-friendly cleaning and breaking through the limits of vapor-liquid equilibrium. The study is based on seperation of solution mixied withε-Caprolactam(CPL) and water, CPL from the HPO technology introduced by Baling Petrochemical Co. Ltd. (SINOPEC, China) from DSM Corporation (Dutch).s-Caprolactam (CPL), as the monomer of nylon-6, is an important organic chemical material. Since CPL is a very heat sensitive substance and has lower volatility than water. A small trace of water and other impurities will affect the production of fiber and resin.Thus, dehydration of CPL is a demanding profession. Traditional separation techniques, crystallization under a reduced pressure distillation through triple-effect evaporation sets, is often widely adopted by chemical industry in manufacture of CPL. But disadvantages, such as large consumption of steam pressure, low heat transfer coefficient and the pollutants into the second phase, make researchers look for a new or alternative technology to improve the dehydration process in CPL aqueous solution.As it is well known that a suitable membrane material is the most important technologic process in PV. And then, with as simply treated as possible, people can achieve the best effect of pervaporation. In addition, worsening environmental problems led to an increasing tendency to find the nontoxic, environmental-friendly macromolecule materails. In this dissertation, several materials were discussed.KGM and chitosan(CS) as the main membrane materials, combined with Poly (vinyl alcohol) (PVA) and Poly(acrylic acid)(PAA), which were also nontoxic, environmental-friendly, cross-linked by Glutaraldehyde, were layed on the (PAN) ultrafiltration membrane chosen as supported substrate layer. Following the methods above, KGM crosslinked membranes, KGM-PVA/PAN, KGM-CS/PAN, CS-PVA/PAN and CS-PAA/PAN were prepared to the separation of CPL/water mixtures. The membranes were characterized by FT-IR, XRD, TGA, DTG, DSC and SEM to analyze the relationships between the structures and characteristics of polymer membranes and swelling behavior and separation performances.On KGM crosslinked membranes, effects of crosslinking agents loading, feed temperature, feed composition in PV performances, were investigated. The experimental results indicated that with the crosslinking agents loading in the membranes rising, the degree of swelling (D.S) decreased, but the thermal stability of polymer membranes increased. Through evaluating the pervaporation performance, we came to a conclusion that with the increase of crosslinker content, permeation flux decreased and separation factor increased. Temperature of mixtures increasd, flux of membranes increased and the separation factor reduces; CPL concentration in the mixtures increase would also reduced the flux and increased separation factor. The experimental results also showed that the temperature dependence of the pervaporation flux agreed well with the Arrhenius relationship and activation energy ((?)E) is also calculated to verify the nature of the hydrophilic membrane.The law of KGM-PVA cross-linked blend membranes in the CPL/water system by pervaporation is as follows:to some extent, the more KGM content in the membrane, the more swelling and flux, but the lower separation factor; The law was different in KGM-CS crosslinked blend membranes to that of KGM-PVA blend membranes: content of CS in membrane increasing maked the flux reduce first and then increase, separation factor was increase first and them remained basically unchanged; The law of CS-PVA cross-linked blend membranes are more complex:as CS content increased in membranes, the changes of flux first increased and then decreased, the separation factor is just the opposite; CS-PAA blend membranes in pervaporation experiments show the characteristics as follows:with the increase of the content of PAA in membranes, membrane flux was higher and separation factor was lower. When liquid temperature and water content in liquid components increased, permeation flux of three groups of membranes concerned above increased and the separation factor of them decreased. The classical solution- diffusion model was chosen as transport model to evaluation the pervaporation performance of the membranes, which were used in our study, for separation of caprolactam - water system:a) through simulating transport coefficients in the model, with the temperature and water content increased, the water transport coefficients were increasing. The results of total activation energy simulated in the model had shown that with the change of ratio in composition or the ratio of crosslinking agents, the change in the trend of activation energy is often not single, and the more single component content, the more activation energy. It is confirmed that multi-component membrane is more conducive to the further penetration than one-component membrane. b)It was shown that with the increase of temperature and CPL content, CPL transport coefficients were increasing but the water transport coefficients didn't change much, resulting that selectivity of membrane changed as the liquid temperature and composition change significantly. The simulation of different membranes in this study proved that the data used in this article of several pervaporation membranes were in line with the classical solution - diffusion model and the results would have a certain guiding significance for description of the membrane structure and choices of pervaporation conditions in industrial applications of pervaporation separation of caprolactam-water system.