Abstract
Sodium alginate (NaAlg) based membranes were prepared using a solution technique, crosslinked with poly(styrene sulfonic acid-co-maleic acid) (PSSA-co-MA). Subsequently, the membranes were modified by the incorporation of 0, 10, 20, 30 and 40% w/w of titanium dioxide with respect to sodium alginate. The membranes thus obtained were designated as M, M-1, M-2, M-3 and M-4, respectively. An equilibrium swelling experiment was performed using different compositions of the water and isopropanol mixtures. Subsequently, we used a pervaporation cell fitted with each membrane in order to evaluate the extent of the pervaporation dehydration of isopropanol. Among the membranes studied, the membranes containing 40 mass% of titanium dioxide exhibited the highest separation factor(α) of 24,092, with a flux(J) of 18.61 × 10−2 kg/m2∙h at 30 °C for 10 mass% w/w of water in the feed. The total flux and the flux of water were found to overlap with each other, indicating that these membranes can be effectively used to break the azeotropic point of water–isopropanol mixtures. The results clearly indicate that these nanocomposite membranes exhibit an excellent performance in the dehydration of isopropanol. The activation energy values obtained for the water permeation were significantly lower than those of the isopropanol permeation, underlining that these membranes have a high separation ability for the water–isopropanol system. The estimated activation energies for total permeation (EP) and total diffusion (ED) values ranged between 10.60 kJ∙mol−1 and 3.96 kJ∙mol−1, and 10.76 kJ∙mol−1 and 4.29 kJ∙mol−1, respectively. The negative change in the enthalpy values for all the membranes indicates that sorption was mainly dominated by Langmuir’s mode of sorption.
Highlights
Pervaporation has emerged as an alternative to classical distillation processes for the dehydration of alcohols
TiO2, demonstrated an excellent performance in membrane fouling mitigation and enhancement of flux owing to their superhydrophilic characters upon irradiation with UV light [23,24,25,26], During the process of UV irradiation, a complex and not fully understood process leads to the reduction of the Ti(IV) state to the Ti(III) state by the photo activated electrons, and the holes oxidize the O2− ions
We have found some matrix appears to exhibit enhanced interactions with the titanium dioxide particles, and this may serve evidence that the sodium alginate matrix appears to exhibit enhanced interactions with the titanium to increase the effective level of the crosslinking which would act to reduce the degree of swelling
Summary
Pervaporation has emerged as an alternative to classical distillation processes for the dehydration of alcohols. TiO2 , demonstrated an excellent performance in membrane fouling mitigation and enhancement of flux owing to their superhydrophilic characters upon irradiation with UV light [23,24,25,26], During the process of UV irradiation, a complex and not fully understood process leads to the reduction of the Ti(IV) state to the Ti(III) state by the photo activated electrons, and the holes oxidize the O2− ions This leads to a new surface containing absorbed -OH groups, rendering the surface hydrophilic [27]. It is reported that titanium dioxide can be used in aggressive conditions because of its high chemical and thermal stability [29] Based on this background information, we have set out to develop membranes for pervaporation by incorporating different levels of TiO2 into a sodium alginate matrix, which was further crosslinked with PSSA-co-MA. The results were discussed in terms of the pervaporation separation efficiency of the membranes
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