Abstract
For the first time, the effect of the side-chain in polyalkylmethylsiloxane towards pervaporative removal of methyl tert-butyl ether (MTBE) from water was studied. The noticeable enhancement of separation factor during the pervaporation of 1 wt.% MTBE solution in water through the dense film (40–50 µm) can be achieved by substitution of a methyl group (separation factor 111) for heptyl (161), octyl (169) or decyl (180) one in polyalkylmethylsiloxane. Composite membrane with the selective layer (~8 µm) made of polydecylmethylsiloxane (M10) on top of microfiltration support (MFFK membrane) demonstrated MTBE/water separation factor of 310, which was 72% greater than for the dense film (180). A high separation factor together with an overall flux of 0.82 kg·m−2·h−1 allowed this M10/MFFK composite membrane to outperform the commercial composite membranes. The analysis of the concentration polarization modulus and the boundary layer thickness revealed that the feed flow velocity should be gradually increased from 5 cm·s−1 for an initial solution (1 wt.% of MTBE in water) to 13 cm·s−1 for a depleted solution (0.2 wt.% of MTBE in water) to overcome the concentration polarization phenomena in case of composite membrane M10/MFFK (Texp = 50 °C).
Highlights
Methyl tert-butyl ether (MTBE) is used as an additive to increase the octane number of gasoline, which allows to improve the antiknock properties of the fuel and to reduce the concentration of CO in exhaust gases as well as the cost of gasoline production [1,2]
The polyalkylmethylsiloxanes demonstrate greater affinity to organic components over the water molecules and showed high selectivity in pervaporative recovery of organics from aqueous solutions since the sorption selectivity plays a major role in the overall selectivity of pervaporation process [38,39,40]
The polymers with long side alkyl chain became more favorable for the comparison of MTBE with PDMS because of the drop of the distance parameter for the MTBE-polymer from 3.6 down to 2.6 MPa1/2
Summary
Methyl tert-butyl ether (MTBE) is used as an additive to increase the octane number of gasoline, which allows to improve the antiknock properties of the fuel and to reduce the concentration of CO in exhaust gases as well as the cost of gasoline production [1,2]. As a result of leakage during storage and transportation of both MTBE and gasoline, there is a serious threat of groundwater pollution [3,4,5]. MTBE is the second most frequently detected compound in coastal and groundwater [6]. Due to the problem of groundwater pollution with MTBE, its use was limited in the European Union and almost completely prohibited in the USA and Canada in the 2000s. Despite these limitations, the global production of MTBE was about 12 million tons per year in 2011 [9]
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