Cross-linked membranes based on acrylated cyclodextrins and polyethylene glycol dimethacrylates for aromatic/aliphatic separation

Abstract

The cost and energy efficient separation of aromatic/aliphatic and isomeric mixtures using membranes is a great challenge for the petrochemical industry. However since these mixtures are causing strong swelling effects with most of the polymeric membrane materials, especially at elevated temperatures, cross-linking is necessary in many cases. Furthermore highly selective membranes can be reached, if the well-known ability of cyclodextrins to form host–guest interactions with specific substrates is used. Therefore in this work, cross-linked polymers based on PEG-DMA (polyethylene glycol dimethacrylate) and acrylated cyclodextrins have been prepared and investigated in pervaporation experiments using toluene/cyclohexane mixtures at 60 °C. Thereby membranes with different ratios of PEG-DMA having diverse molecular weights as well as membranes with acrylated α-cyclodextrin and acrylated β-cyclodextrin, respectively have been investigated. Also membranes without any acrylated cyclodextrins have been prepared as a reference. In this case, an aliphatic triacrylate with a similar molecular weight as the cyclodextrin acrylate has been used as a multifunctional cross-linker. The separation experiments using a toluene/cyclohexane mixture showed that especially the membranes based on PEG-DMA and acrylated β-cyclodextrins obtained high selectivities already at low aromatic concentrations in the feed, e.g. with a toluene content of 10 wt.% in the feed a selectivity of α = 14 and a permeability of 0.3 kg μm m −2 h −1 was found at 60 °C feed temperature.