Synthesis and preparation of polysaccharide based membranes for the pervaporation separation of liquid mixture systems of industrial interest

Abstract

Pervaporation membrane processes have been established as an important separation unit operation in chemical engineering processes. The pervaporation process is technologically mature for the dehydration of aqueous alcohol mixtures and is expected to find further progress in the organic/organic separations and the organic or water separation from water/organic mixtures.

Various pervaporation membranes made from natural polymers such as chitosan and alginate as well as EPDM rubber have been fabricated and investigated in terms of the permeation flux and separation factor in pervaporation experiments. Dense and thin film composite membranes were extensively investigated for the separation of water from aqueous alcohol mixtures, the separation of alcohols from alcohol/toluene mixtures, the separation of methanol from methanol/MTBE mixtures, and the separation of a model aroma compound from aqueous mixtures.

Sodium alginate membranes are known to be hydrophilic and suitable for dehydration applications. However, since sodium alginate is water soluble and mechanically brittle efforts to increase the mechanical strength of the alginate membrane have been made which include the metal ion crosslinking and the insolubilization reactions.

As part of research effort to increase the mechanical strength of alginate membranes, two ply composite membranes consisting of sodium alginate and chitosan were prepared and the preparation parameters were analyzed by means of experimental design which lead to optimum membrane structure and preparation conditions.

Composite chitosan membranes were also prepared for the separation of aqueous alcohol mixtures and the pervaporation characteristics of dense and composite membranes were compared. In addition, it was shown that the coating of hydrophobic polysulfone substrate with hydrophilic polymers such as polyvinyl alcohol could enhance structural stability of the composite membrane.

The preparation and pervaporation performance study of the alginate composite membrane consisting of a chitosan layer sandwiched between the top alginate layer and polyvinylidene fluoride substrate layer were carried out for the separation of aqueous alcohol mixtures.

Chitosan membranes were chemically modified in acetic anhydride solution. Modified membranes (N-acetylated chitosan (or chitin)) were found to be much stronger than the chitosan membranes. The N-acetylation reaction made the chitosan membrane robust for the pervaporation separation of organic/organic mixtures such as alcohol/toluene while keeping its polar property.

Polyelectrolyte complex membranes with high hydrophilicity were developed from chitosan and anionic surfactants. The rheological properties of the casting solutions and also the pervaporation performance of the complex membranes for the separation of methanol/MTBE mixtures were extensively investigated. It was found that the resulting membrane thickness could be decreased because of a chain-coiling phenomenon induced by the interaction between cationic chitosan and anionic surfactant molecules.

Ethylene propylene diene monomer (EPDM) membranes were prepared to separate a model aroma compound from aqueous solution and the transport phenomenon of aroma compound was modeled based on the resistance-in-series model.