Preparation Of Pervaporation Composite Membranes Based On Hyperbranched Ploysiloxane For Low Molecule Alcohol Removal From Water

Low molecule alcohols like n-butanol, 2,3-butanediol are renewable biofuels and important chemical body, all can be produced by fermentation. How to separate low molecule alcohols economically and effectively are significant. Pervaporation as a membrane process for liquid separation have been applied to organic solvent dehydration, dilute organics removal from water and org-org separations because of its energy-saving, no harmful effects on environment and simple operation. In the process of research on new type of pervaporation membrane, hyperbranched polymers standed out and have been studied extensively. Compared to the corresponding linear polymer, hyperbranched polymers have a lower degree of entanglement, excellent rheological, and more important, hyperbranched polymers have a large number of terminal functional groups and a lot of free-volume. As a results, the pervaporation membrane contain hyperbranched polymers generally have a higher flux. However, the application of hyperbranched polymers in pervaporation mainly focus on organic solvent dehydration and the org-org separations. Research on hyperbranched polymers applied to pervaporation for organics removal from water was few. This acticle was main to manufacture new type hyperbranched pervaporation membranes for low molecules alcohol removal from water based on hyperbranched polysiloxane.In this paper, based on highly branched structures of hyperbranched polysiloxane, different pervaporation membranes were prepared for n-butanol removal from water, and study the 2,3-butanediol removal from water using extraction and pervaporation coupling method. The details were as following: First, hyperbranched polysiloxane(HPSi O) synthesized through one-step method by AB2 monomer, and a new type multilayer composite membranes was fabricated based on HPSi O-c-PDMS-1(as a intermediate layer) and VTES-c-PDMS(as selective layer); Second, HPSi O-c-PDMS-3 composite membranes contain different HPSi O contents were fabricated and all the composite membranes were commanded to analysis the morphology and physical performance; At last, a ternary phase diagram of 2,3-butanediol/water/n-butanol solution was made through liquid-liquid extraction, selected suitable extraction for long time pervaporation separation operation successively from PVA membrane to HPSi O-c-PDMS-2 membrane, analysis the concentration of 2,3-butanediol in permeated residue to estimate the possible of 2,3-butanediol removal from water. The results were as following:(1) Successfully synthesized a high degree hyperbranched polysiloxane, and the composite membranes showed an obvious multilayer structure. With the increaseing of PDMS molecular weight in selective layer(VTES-c-PDMS layer), the permeation fluxs of multilayer composite membranes and the permeability of n-butanol decreased while the selectivity and separation factor increased. Where the membrane flux of FHPV-3 multilayer composite membranes reached 450g/(m2h), the separation factor reached 28; With the increasing of the feed temperature, the membrane flux and separation factor both increased; With the increasing of the feed concentration, the flux of.multilayer composite membranes increased while the separation factor changed slightly. On the other hand, the n-butanol concentration in penetrants reached 42wt% when the feed concentration was 2.5wt%.(2) For HPSi O-c-PDMS-3 composite membranes, when HPSi O content was less than 50wt%, distribution of HPSi O in organic matrix was form of spherical; when HPSi O content was above 50wt%, distribution of HPSi O in organic matrix was inform of chain. With the increasing of HPSi O content, the hydrophobic of composite membrane decreased, the permeability of n-butanol and the selectivity decreased while the flux of increased. When HPSi O content was 37.5wt%, the membrane flux reached 229.85g/(m2h), the separation factor reached 39.5, which the flux of membrane reached the. The form of HPSi O distribution in the membrane matrix did not influence the pervaporation performance on feed concentration and feed temperature.(3) The ternary phase diagram of 2,3-butanediol/water/n-butanol solution was successfully achieved at 24 oC through liquid-liquid extraction; The pervaporation performance of PVA and HPSi O-c-PDMS-2 membranes on temperature changes illustrated that the appropriate temperature for long time PVA membranes pervaporation was 40 oC and the appropriate temperature for HPSi O-c-PDMS-2 membranes was 50oC~60oC; When PVA membrane pervaporation for 10 h, the water concentration in permeated residue decreased from 31.27wt% to 10.85wt%, the 2,3-butanediol concentration increased from 10.56wt% to 14.09wt%, then when HPSi O-c-PDMS-2 membranes pervaporation for 48 h, the 2,3-butanediol concentration reached to 69.41wt%.