Effect of Spinneret Dimension on Structure and Performance of Polyetherimide Hollow Fiber Membrane in Membrane Contactor

In hollow fiber membrane fabrication process, a number of parameters such as dope compositions and flow rate, bore fluid type and flow rate, air gap etc. affect on the structure and characteristics of membrane. One of effective parameters is the dimension of spinneret and in this study; the effects of this parameter on the properties of polyetherimide (PEI) hollow fiber membrane and its performance in membrane contactor were studied. A polymer solution was used for fabrication of two PEI membranes at the same fabrication conditions while the dimension of spinneret was different. Through the addition of water as the nonsolvent additive to the polymer solution, the thermodynamic stability of the solution decreased and upon the enhancement in the phase inversion process, the effects of chain reorientation or chain relaxation on the structure of hollow fiber membrane were minimized. The fabricated membranes were characterized by different tests and their performance in membrane contractor and in CO2 absorption test was evaluated in two cases: 1- distilled water in lumen side and pure CO2 in shell side, 2- distilled water in shell side and pure CO2 in lumen side. The results show that smaller dimension of spinneret enhances the properties of membrane such as 250% increase in mean pore size and 300% increase in gas permeation rate. In addition, the smaller dimension of the spinneret makes more pores in the structure of membrane that can be related to the shorter diffusion length of the coagulant. Furthermore, the CO2 absorption flux improves by 150%

Thin film polyamide membranes containing modified manganese dioxide nanotubes for removal of sodium and copper ions

Hypothesis: Today, with the development of different industries and the disposal of untreated wastewaters, environmental pollution and pollution of water resources are increasing very rapidly. Membrane technology is an advanced and hopeful way to treat water and wastewater. Nanofiltration technology is widely used in water treatment and desalination of seawater. Methods: The performance of thin film polyamide membranes containing unmodified and modified manganese dioxide nanotubes was investigated. After hydrothermal synthesis of manganese dioxide nanotubes, the inner surface of the nanotubes was modified with polydopamine, and then, their performance in thin film polyamide membranes (in terms of monovalent/divalent ions rejection and permeation flux) was investigated. Findings: Unmodified and modified nanotubes were characterized by Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) and X-ray diffraction analysis (XRD). In addition, the morphology and structure of the thin film membranes were investigated by FESEM test and the performance of the membranes was studied in terms of permeation flux, contact angle and rejection of sodium and copper ions. The maximum pure water flux, 18.6 L/m2h, was obtained for the membrane containing 0.10 %wt modified nanotube, an increase of 21.88% compared to the neat membrane. Creation of tiny pores on the surface of the membranes through hydrophilic nanotubes resulted in higher flux while there are extra routes through the nanotubes for water permeation. The maximum rejection of sodium ion (97.02%) for the membrane containing 0.2 %wt modified nanotubes could be related to the stacking of the nanotubes and more spatial hindrance, reduction in the diameter of the nanotube due to the coating and permeation of water through the nanotubes

Development of high performance surface modified polyetherimide hollow fiber membrane for gas-liquid contacting processes

Low wettability is a vital characteristic for the membrane used in membrane contactor. Blending surface modifying macromolecule (SMM) in spinning dope is an interesting method to enhance the hydrophobicity of membrane and in this research, the effect of SMM on the properties and structure of polyetherimide (PEI) hollow fiber membrane in terms of mean pore size, liquid entry pressure of water (LEPw), membrane porosity and contact angle was investigated and compared with the properties of the PEI membrane without SMM. Furthermore the performance of PEI surface modified membrane in contactor applications in terms of CO2 absorption with distilled water was evaluated and compared with the absorption flux of PEI membrane without SMM and also, with the absorption flux of commercial and in-house made hydrophobic membranes which shows superior performance of surface modified PEI membrane e.g. in case of water in lumen side and pure CO2 in shell side of contactor and at Vliquid=0.5ms-1, the absorption flux of PEI surface modified membrane is 2.94×10-3molm-2s-1 which is 114% higher than PEI without SMM and 73% higher than commercial membrane contactor, Celgard MiniModule® 0.75X5

Porous polyethersulfone hollow fiber membrane in gas-liquid contacting processes

Porous polyethersulfone hollow fiber membranes were fabricated via dry-wet phase inversion method with the polymer concentration in the spinning dope either 13wt% or 15wt%. The fabricated hollow fiber membranes were characterized by different test methods and the performance of membranes in contactor applications was tested by CO2 absorption. The mean pore size, effective surface porosity and membrane porosity decreased while the membrane density and Liquid Entry Pressure (LEPw) increased as polymer concentration increased. The CO2 absorption flux of the fabricated membranes was measured in two cases; i.e. when the absorbent, distilled water, was in the lumen side or in the shell side. The CO2 flux for the membrane, fabricated from 13wt% PES solution, was compared with some commercial and in-house made membranes. The former membrane had 111% higher flux than a commercial PTFE membrane

Porous PES and PEI hollow fiber membranes in a gas-liquid contacting process-A comparative study

Porous polyetherimide (PEI) and polyethersulfone (PES) hollow fiber membranes were spun under the same spinning conditions and the fabricated membranes were characterized using various analytical methods. The membranes were then subjected to gas–liquid contactor experiments. While the PEI casing solution was thermodynamically less stable, the PES casting solution was less viscous which resulted in a more porous membrane structure. The mean pore size and effective surface porosity obtained by the gas permeation test showed superior properties of the PES membrane. Both PEI and PES membranes had sufficiently high LEPw values even though both polymers were known to be relatively hydrophilic, most likely due to their small pore sizes. The absorption flux of the PES membrane was 4.4×10-3 mol m-2 s-1 at the liquid flow velocity Vliquid of 1.8 m s-1, which was 267% higher than that of the PEI membrane (1.2×10-3 mol m-2 s-1) due to the larger pore size and smaller tortuosity of the PES membrane

A review on the effect of proton exchange membranes in microbial fuel cells

Microorganisms in microbial fuel cells (MFC) liberate electrons while the electron donors are consumed. In the anaerobic anode compartment, substrates such as carbohydrates are utilized and as a result bioelectricity is produced in the MFC. MFCs may be utilized as electricity generators in small devices such as biosensors. MFCs still face practical barriers such as low generated power and current density. Recently, a great deal of attention has been given to MFCs due to their ability to operate at mild conditions and using different biodegradable substrates as fuel. The MFC consists of anode and cathode compartments. Active microorganisms are actively catabolized to carbon sources, therefore generating bioelectricity. The produced electron is transmitted to the anode surface but the generated protons must pass through the proton exchange membrane (PEM) in order to reach the cathode compartment. PEM as a key factor affecting electricity generation in MFCs has been investigated here and its importance fully discussed

Characterization of partial pore wetting in hollow fiber gas absorption membrane contactors: an EDX analysis approach

In this work a novel method to evaluate the partial pore wetting of gas absorption membranes is proposed. The method consists of two approaches, one by energy-dispersive X-ray spectrometry (EDX), and the other by calculating the mass transfer resistances from the gas and liquid phase in the pore, using the parameter obtained by He gas permeation experiments. For this purpose, hollow fibers were spun from polyetherimide (PEI) and polyethersulfone (PES). As well, the lumen of a PEI hollow fiber was coated with silicone rubber. The hollow fibers were then characterized by He gas permeation experiments, critical entry pressure of water (CEPw), contact angle, scanning electron microscopy (SEM) and EDX. The hollow fibers were then subjected to CO2 gas absorption using aqueous NaCl solution as absorbent. After drying the hollow fiber was subjected to the EDX analysis. The cross-sectional profile of Na and Cl content in the hollow fiber revealed that the pores of the PES hollow fibers were partially wetted, particularly at the pore inlet. Calculation of mass transfer resistances, on the other hand, revealed that the resistance came from gas phase in most hollow fibers, except for the PES hollow fiber where the liquid phase contribution was significant. Silicone rubber coating of the PEI hollow fiber increased the surface hydrophobicity and reduced the pore wetting considerably. Thus, it was concluded that the proposed method can be used as a powerful tool to investigate the pore wetting for many membrane contactor applications

Porous polyethersulfone hollow fiber membrane in CO2 separation process via membrane contactor - the effect of nonsolvent additives

A membrane contactor (MC) is used for natural gas sweetening and wastewater treatment with a membrane that is acting as a separating barrier between two phases, usually liquid and gas. The performance of membrane is governed by parameters such as pore size, porosity, tortuosity and surface hydrophobicity, which can be controlled by a number of methods. Addition of nonsolvents to spinning solution is known to be one of such methods. In this study, the effects of low molecular weight additives as phase inversion promoters on the morphology of polyethersulfone hollow fiber membranes and their performance in gas-liquid MC processes were investigated. It was found that among the six nonsolvent additives under study, addition of water resulted in the highest CO2 flux, by decreasing the thermodynamic stability of polymer solution and maintaining high solvent-nonsolvent exchange rate