Abstract
The aim of the study is to improve the performance of thin-film composite (TFC) membranes with a thin selective layer based on chitosan (CS) via different approaches by: (1) varying the concentration of the CS solution; (2) changing the porosity of substrates from polyacrylonitrile (PAN); (3) deposition of the additional ultrathin layers on the surface of the selective CS layer using interfacial polymerization and layer-by-layer assembly. The developed membranes were characterized by different methods of analyses (SEM and AFM, IR spectroscopy, measuring of water contact angles and porosity). The transport characteristics of the developed TFC membranes were studied in pervaporation separation of isopropanol/water mixtures. It was found that the application of the most porous PAN-4 substrate with combination of formation of an additional polyamide selective layer by interfacial polymerization on the surface of a dense selective CS layer with the subsequent layer-by-layer deposition of five bilayers of poly (sodium 4-styrenesulfonate)/CS polyelectrolyte pair led to the significant improvement of permeance and high selectivity for the entire concentration feed range. Thus, for TFC membrane on the PAN-4 substrate the optimal transport characteristics in pervaporation dehydration of isopropanol (12–90 wt.% water) were achieved: 0.22–1.30 kg/(m2h), 99.9 wt.% water in the permeate.
Highlights
Distillation, low temperature crystallization, adsorption and extraction are common separation methods for liquid mixtures, but these methods, as a rule, are energy-intensive, labor-intensive and have a negative impact on the environment [1,2,3]
This work is devoted to the improvement of the pervaporation isopropanol dehydration performance of thin-film composite (TFC) membranes with a thin selective layer based on chitosan by several approaches: (1) varying concentration of the CS solution; (2) varying the porosity of PAN membranes; and (3) deposition of the additional ultrathin layers on the surface of the chitosan layer by interfacial polymerization and the layer-by-layer assembly
TFC membranes with a dense selective layer based on chitosan (CS) on the surface of PAN porous substrates were prepared
Summary
Distillation, low temperature crystallization, adsorption and extraction are common separation methods for liquid mixtures, but these methods, as a rule, are energy-intensive, labor-intensive and have a negative impact on the environment [1,2,3]. The distillation method cannot separate the azeotropic mixtures of liquid substances without using the additional third agents like benzene or cyclohexane, which may cause an impurity in the product. Pervaporation is one of the most efficient membrane methods for the separation of low molecular weight liquid mixtures, which is widely used for the dehydration of alcohols and other organic substances [4,5,6,7,8,9] and characterized by high efficiency with low energy consumption, a compact equipment, environmental friendliness and the ability of the automation [10]. The low permeability and mechanical strength of pervaporation CS membranes are limiting factors for the widespread adoption of these membranes in industrial processes of alcohol dehydration
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