Membranes Propanol data

Work at the University of Dortmund (Buchaly et al 2007) has introduced membrane separation units downstream of a reactive distillation process, as illustrated in Figure 6.13. The authors studied the heterogeneously catalysed n-propyl propionate synthesis from 1-propanol and propionic acid. Experiments were carried out on a pilot scale membrane unit to examine how effective the membrane was for the dewatering of the binary 1-propanol-water mixture (see Section 6.5 on drying for other membrane dewatering data). 

Experimental. The hollow fiber membranes used for this study were Naflon 811, which Is a copolymer of polysulfonyl fluoride vinyl ether and polytetrafiuoroethylene, and sulfonated and/or quaternated derivatives of polyethylene (kindly supplied by Dr. E. Korngold from Ben Gurlon University In Israel). The aqueous alcohol solutions studied thus far are those of methanol, ethanol and 2-propanol. The separations were accomplished via the pervaporatlon process as described In Reference 9. Counter Ions were replaced In the hollow fiber by soaking the permeator for twenty four hours In 1 molar solutions of the pertinent Ions. For example, experiments were conducted with Na as a counter Ion. When this set of experiments was finished, the sodium was exchanged by Ll etc. Each data point shown In Figure 14 consists of 6 to 10 measurements taken over a time period of 8 hours. Re-runs with the various counter Ions proved that the intrinsic properties of the membrane remain unchanged and the permeability measurements are reproducible. 

The swelling of the fiber In It s different counter-Ion variations Is In accord with the mass transport data. The maxima around 20 mole X 2-propanol In the feed mixture Indicates the presence of synergism related to hydrophlllc/hydrophohlc contributions. The later results from the Isopropyl sites of the alcohol and suggests solubility of the 2-propanol In the amorphous non-lonlc regions of the membrane. 

In Fig. 6.15 are summarized the sorption isotherms of methanol, ethanol and propanol by Nafion [272,281 ], along with the data for water. It can be observed that for alcohol activity higher than 0.5 the alcohol sorption follows the order methanol > ethanol > propanol, as expected according to the size of the sorbate. At low alcohol activities the alcohol uptakes were nearly identical. The behavior of water uptake is different and could be due to the fact that in one case [272] the membrane was used without treatment, while Zhao et al. [281] performed the measurements on the expanded form. In the last case the sorption of water is higher than methanol, while for the untreated membrane more methanol is sorbed in the membrane as compared to water. The data by Jalani et al. [276] for a cast Nafion membrane, not shown in Fig. 6.15, indicates a similar behavior, with the uptake order at high activities being water tv methanol > ethanol > propanol. 

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