SynopsisThe pervaporation separation of ethanol-water mixtures was carried out through a series of ionically crosslinked polyacrylic acid ( PAA) -nylon 66 blended membranes crosslinked to varying degrees in aluminum nitrate solution. Optimum pervaporation results were obtained from crosslinked blends containing 75 wt % nylon 66 and 25 wt % PAA. The optimum crosslinking time was found to be between 30 and 40 h. The optimum operating temperatures of the pervaporation runs were found to be 2-3°C below the boiling points when the highest permeation flux reached 857.6 (g/ m2 h ) and the best separation factors (water/ethanol) were 10.1.
INTRODUCTIONThere is a growing interest in the use of pervaporation separation processes for separation of the ethanol-water system.'-6 Recently the use of ionically crosslinked blended polyacrylic acid (PAA) -nylon 6 membranes to separate ethanol-water mixtures has been reported from this laboratory.?According to the solution diffusion theory,' there are two parameters, diffusion and solubility, that affect the permeability of liquids through the polymer membrane. They can be adjusted and controlled by changing hydrophilic-hydrophobic balance properties of a membrane. Therefore, it is one of the important goals of pervaporation separation research to keep developing new membrane materials.Compared with nylon 6, nylon 66 is a little bit more hydrophobi~.~**~ For some mechanical properties, nylon 66 is a little better than nylon 6." A recent study in this laboratory found that nylon 6 is still too hydrophilic for PAAnylon blended membranes and suggested the use of nylon 66 instead of nylon 6." The subject of this investigation is to develop this new material of crosslinked PAA-nylon 66 blended membranes, test its pervaporation properties, and optimize its preparation and operating conditions over a wide range of temperatures and feed concentrations.
EXPERIMENTAL MaterialsThe nylon 66 used was obtained from Polysciences, Inc. The polyacrylic acid (PAA) was obtained from Polysciences in a 25% by weight aqueous solution
Membrane PreparationThe blended PAA-nylon 66 membranes were prepared by the wet techn i q~e .~? '~. '~ The nylon 66 was dissolved in 88 wt % formic acid at room temperature to form a 10 wt ' 3% nylon 66 solution. The nylon 66 solution and the 25 wt % PAA ( M W 90,000) aqueous solution were mixed together and blended for 24 h to form a homogeneous solution. The casting solution was cast onto a glass plate with the aid of a Gardner casting knife adjusted to an appropriate thickness. The membrane was then predried at room temperature for 10 min before drying in an oven at 55-60°C for 50 min. This was followed by crosslinking in a 10 wt % A1 ( N03)39H20 aqueous solution at room temperature for different times. It was subsequently removed from the crosslinking bath, rinsed, and immersed in deionized water for at least 30 h. Then it was put into methanol for 24 h before being put again into deionized water ready for using. The thickness of the films was measured with a digital m...
