Integrally skinned polysulfone hollow fiber membranes for pervaporation

Abstract

SYNOPSISFrom polysulfone as polymer, integrally skinned hollow fiber membranes with a defectfree top layer have been spun. The spinning process described here differs from the traditional dry-wet spinning process where the fiber enters the coagulation bath after passing a certain air gap. In the present process, a specially designed tripple orifice spinneret has been used that allows spinning without contact with the air. This spinneret makes it possible to use two different nonsolvents subsequently. During the contact time with the first nonsolvent, the polymer concentration in the top layer is enhanced, after which the second coagulation bath causes further phase separation and solidification of the ultimate hollow fiber membrane. Top layers o f f 1 pm have been obtained, supported by a porous sublayer. The effect of spinning parameters that might influence the membrane structure and, therefore, the membrane properties, are studied by scanning electron microscopy and pervaporation experiments, using a mixture of 80 wt % acetic acid and 20 wt % water at a temperature of 70°C. Higher fluxes as a result of a lower resistance in the substructure could be obtained by adding glycerol to the spinning dope, by decreasing the polymer concentration, and by adding a certain amount of solvent to the bore liquid. Other parameters studied are the type of the solvent in the spinning dope and the type of the first nonsolvent.

Characterization of morphology controlled polyethersulfone hollow fiber membranes by the addition of polyethylene glycol to the dope and bore liquid solution

“…Polysulfone (PSF) and polyethersulfone (PES) have been used by many researchers [1][2][3][4][5][6][7] in the preparation of hollow fiber membranes as membrane forming normally a homogeneous solution, which is forced to phase separate by changing its composition when immersed in a nonsolvent bath. Kinetic processes play a key role in this transition.…”

“…Most hollow fiber membranes are prepared by the so-called dry-wet spinning process and only few have been prepared by a wet-wet or dual bath spinning process [4][5][6]. The wet-wet spinning process can be very well applied for controlling the shell side surface structure.…”

“…When a weak nonsolvent is applied, like e.g. glycerol completely dense skin layers can be obtained supported by a porous sub-structure, which make the membrane suitable for gas separation [4,6] and pervaporation [5]. Here, the diffusion of solvent out of the nascent fiber is much higher than the diffusion of nonsolvent into the nascent fiber.…”

“…When the solvent concentration in the coagulation bath is higher than in the nascent fiber solvent might even diffuse into the nascent fiber, diluting the polymer concentration prior to phase separation. Proper application of the wet-wet spinning process requires a triple-layer spinneret; the bore liquid composition controls the inside structure, while the outside liquid composition controls the structure of the shell side [5][6][7].…”

Preparation of asymmetric chitosan hollow fiber membrane and its pervaporation performance for dimethyl carbonate/methanol mixtures

“…Some polymer materials have been used in the preparation of integrally skinned asymmetric hollow fiber membranes for pervaporation, such as polysulfone, poly (vinylidene fluoride), polyimide, and so on. [17][18][19][20] Different from these materials, chitosan is a highly crystalline and strongly hydrophilic material. Both phase inversion process and drying process are important to obtain integrally skinned asymmetric chitosan hollow fiber membranes (CHFMs).…”