Pervaporation dehydration membranes based on chemically modified poly(ether ether ketone).

摘要

Polymer hydrophilicity used to be practiced as a criterion for selecting materials for making pervaporation dehydration membranes. A new approach is proposed in this thesis: hydrophobic polymers can be selected as membrane materials since they are extremely stable in aqueous solutions, and the affinity of the hydrophobic polymer for water can be obtained by chemical modification.; Hydrophilicity is controllably imparted to the selected hydrophobic poly (ether ether ketone) (PEEK) by sulfonation treatment. Two environments (the hydrophilic environment and the hydrophobic one) are assumed to be present in the sulfonated PEEK membrane due to the big difference in local polarity of the membrane. Water dissolves only in the hydrophilic environment, forming the so-called water clusters with sulfonic groups in the centers as cores. Sorption experiments confirm the presence of the two environments and the fact that the polar organic solvents (e.g. isopropanol) also overwhelmingly dissolve in the hydrophilic environment (the clusters).; A novel transport mechanism is proposed. Both water and isopropanol jump from one cluster to another, and the jump probability is governed by the relative concentration of the species in a cluster, and the total concentration difference between two adjacent clusters acts as the driving force for both the species. The sharing of the concentration difference of one species by the other as a part of its mass transport driving force forms the basis for coupled transport, which is observed in the pervaporation dehydration of isopropanol.; Membrane relaxation is encountered in the pervaporation dehydration of ethylene glycol, which can be facilitated by heat treatment of the membrane. The separation performance of the fully relaxed membrane agrees with the modified Brun's model by ignoring the plasticizing effect of ethylene glycol. Diffusion selectivity is also rigorously derived based on this modified model, which interprets why a swollen membrane shows a reduced mobility selectivity. The local diffusion selectivity is also simulated, revealing that only a very thin layer of the membrane adjacent to its downstream surface is responsible for the selective diffusion.; A rectangular thin channel column is developed for measuring the partition and diffusion coefficients of some selected small solvents in flat sheet membranes using inverse gas chromatography (IGC). A new IGC mathematical model based on this novel column is formulated using moment analysis. Reliable partition and diffusion coefficients (at infinite dilution) of the solvents in both the sulfonated PEEK and cellulose diacetate membranes are estimated.; A method for preparing composite membranes with integrated skin is developed. The active skin layer of the composite membrane is fused into its support by using a cosolvent, and the obtained composite membrane looks more like a single matrix than a composite structure. The composite membrane shows better separation performance than its homogeneous counterpart due to presence of this integrated layer, which acts not only as reinforcement for the upper skin layer but also as a barrier layer for the transport of the permeating species. The excellent structural stability and consistent separating performance of the composite membrane is demonstrated in the long-term (∼40 h) dehydration of ethylene glycol in batch operation.