Improvement Of The Quality Of Gasoline And Its Additives By Pervaporation

Pervaporation, as a novel separation technology, has outstanding technical advantages and favorable promising application prospects in the separation of organic-organic mixtures. Separation performance of pervaporation process mainly depends on the property of the target membranes. Therefore, selecting an appropriate material with excellent separation performance constitutes an important issue in pervaporation research. Methyl tert-butyl ether (MTBE) is an important additive for gasoline. An azeotrope of methanol and MTBE would be formed in the producing process of MTBE, so methanol needs to be eliminated from the mixture of methanol and MTBE to improve the purity of MTBE, but traditional distillation won't meet the requirment. Sulfur in the gasoline makes the products of combustion of gasoline harmful to the environment and human, so it is necessary to get rid of the sulfur from the gasoline. Herein, the mixture of methanol/MTBE and the mixture of n-octane/thiophene(model gasoline) were selected as the objective mixtures for separation by pervaporation. According to the principle of solubility parameters, membrane materials were selected for the separation. Cellulose acetate (CA) and poly (N-vinyl-2-pyrrolidone) (PVP) blend membranes were fabricated for the separation of methanol/methyl tert-butyl ether (MTBE) mixtures, and good pervaporation performance were achieved. Fumed silica was filled in the polydimethylsiloxane followed by crosslinking with ethyl orthosilicate to form the active layer of the PDMS/polysulfone(PS) composite membranes.The pervaporation performance of silica-filled membrane was inproved compared to the unfilled membrane. The membrane composition and pervaporation conditions were investigated and optimized.The structure, morphology and physiochemical properties of the membranes were characterized and analysed by FT-IR, XRD, SEM, TGA, DSC and universal testing machine. The factional free volume and free volume cavity size of ailica-filled PDMS membranes were tested by the PALS.For the pervaporation separation of methanol/MTBE mixture by CA-PVP blend membranes, the effect of membrane composition and operation conditions including the feed concentration, feed flow rate and operating temperature on the pervaporation performance were systematically investigated. The sorption and swelling behavior of membranes were also studied. For the feed containing 20 wt% methanol, the membrane CA-PVP-15, containing 15 wt% PVP, exhibited the best performance with the flux of 430 g/(m2h) and the separation factor of 411 at 313 K.For the pervaporation separation of n-octane/thiophene by silica-filled PDMS/PS composite membranes, the effect of silica content in the membranes, as well as the operation conditions including the feed concentration, feed flow rate and operating temperature on the pervaporation performance were studied. The PDMS/PS membrane filled with 1.0 wt% silica showed the best performance for the feed containing 1300 ppm thiophene at 303 K with the flux of 2.08 kg/(m2h) and the sulfur enrichment factor of 4.69.