The effect of phase inversion promoters on the structure and performance of polyetherimide hollow fiber membrane using in gas-liquid contacting process

Low molecular weight organic compounds were added to the spinning dope as phase inversion promoters and their effects on the structure of polyetherimide (PEI) hollow fibers as well as their performance as membrane contactor were investigated. Water, methanol, ethanol, glycerol and acetic acid were added individually to the solvent NMP to prepare a dope containing 15 wt% PEI, 4 wt% additive, 81 wt% NMP and hollow fiber membranes were fabricated via wet spinning method.The solution containing water as the additive had the lowest thermodynamic stability and highest viscosity, which yielded hollow fiber with a thin skin layer of high porosity and a sublayer with sponge-like structure. The four other polymer solutions were more stable thermodynamically and less viscous. Fast solvent/coagulant exchange yielded thick skin layers of lower porosity and sublayers of finger-like macrovoids.Among all fabricated follow fibers, adding methanol resulted in the highest absorption flux, which was ascribed to its high porosity and low tortuosity

The effect of bore fluid type on the structure and performance of polyetherimide hollow fiber membrane in gas-liquid contacting processes

The effect of bore fluid type on the structure and performance of polyetherimide hollow fiber membranes in contactor application was investigated. Water was used as phase inversion promoter in spinning dope and water and pure NMP were used as bore fluid. SEM micrographs show that the major parts of both membranes consist of spongelike structure which is related to the high viscosity of spinning dope that reduces the diffusion of coagulant (water) into membrane sublayer and decreases the rate of phase inversion. In the case of water as bore fluid (membrane #M1) there is skin layer on the inner surface of membrane and some drop-shaped voids in the structure of membrane but in the case of pure NMP as bore fluid (membrane #M2), the inner surface of membrane is skinless with big pores and there are fingerlike macrovoids, originating from the inner surface and extending to the vicinity of outer surface which is related to the penetration of bore fluid and dissolving the polymer. Furthermore, membrane #M2 has higher mean pore size and effective surface porosity. The absorption flux of both fabricated membranes was investigated in the case of liquid in lumen side (case #1) and liquid in shell side (case #2) where in case #1, membrane #M1 has higher absorption flux but in case #2, membrane #M2 has higher absorption flux. The different trend in absorption flux confirms that the surface of membrane in contact with the gas phase in a membrane contactor should be skinless with big pores to facilitates the diffusion of solute gas through membrane but the pore size on the surface of membrane in contact with the liquid phase should be adjusted to obtain high absorption flux and low wettabilit

Kinetics study of hydrazodicarbonamide synthesis reaction

In this study, the kinetics of hydrazodicarbonamide (HDCA) synthesis reaction was investigated. Hydrazodicarbonamide is prepared by reaction of urea and hydrazine in acidic medium. Synthesis of HDCA from urea and hydrazine is a two steps reaction. In the first step, semicarbazide is synthesized from the reaction of one mole of urea and one mole of hydrazine and in the second step, semicarbazide reacts with urea to produce hydrazodicarbonamide. By controlling the temperature and pH in the reaction, hydrazine concentration and the amount of produced hydrazodicarbonamide were measured and using these data, reaction rate constants were calculated. Based on this study, it was found that the semicarbazide formation reaction from hydrazine is the rate limiting step. Rate of semicarbazide synthesis is -r1 = 0.1396 [NH2NH2]0.5810 and the rate of hydrazodicarbonamide synthesis is -r2 = 0.7715 [NH2NHCONH2]0.8430

Analysis of polyetherimide/N-Methyl-2-Pyrrolidone/nonsolvent phase separation behavior

Nonsolvent Induced Phase Separation (NIPS) is among the most well-known methods for membrane fabrication in which the phase separation behavior of the polymer solution is one factor that governs the structure of the membrane ultimately obtained. In this study, phase separation behavior of the polyetherimide (PEI)-casting dope was investigated for different types of coagulants and nonsolvent additives. Cloud point data were obtained by the titration method on the ternary polyetherimide/solvent/coagulant diagramfrom a limited number of experiments. The whole cloud point curves were then drawn by calculation using the fitting parameters based on the linearized cloud point relation (LCP). In the first part, water, methanol, ethanol, glycerol, and acetic acid were used as the coagulants for the PEI/NMP solution. The cloud point curves obtained for the above coagulants indicated that water has the strongest coagulation power among them. In the second part, methanol, ethanol, glycerol, and acetic acid were used as nonsolvent additives to NMP in different (nonsolvent additive/NMP) mass ratios. The latter (NMP+nonsolvent additive) mixtures were then used as the solvents to prepare PEI/(NMP+nonsolvent additive) solutions. The cloud point data obtained for the above solutions using water as a coagulant indicated that the cloud point curves shift toward the polymer/solution axis as the (nonsolvent additive/NMP) mass ratio increase

A porous polyethersulfone hollow fiber membrane in a gas humidification process

A porous polyethersulfone hollow fiber membrane was fabricated via a dry-wet phase inversion process. The membrane was characterized by measuring the pore size, porosity and LEPw. Scanning electron microscopy (SEM) revealed the presence of finger-like macrovoids in the cross-section of the membrane, which contributed to the reduction of tortuosity. The fabricated membrane was further applied in gas humidification. It was found that the water flux was increased by an increase in the gas and liquid flow rates and temperature but reduced by an increase in gas pressure. The water flux of the fabricated membrane exhibited a gas humidification performance superior to a commercial humidifier, e.g. it has 380% higher water flux than the Perma Pure®1 model PH-60T-24SS at Tliquid = 40 °C

Effect of polymer concentration on the structure and performance of polyetherimide hollow fiber membranes

In this paper, polyetherimide (PEI) hollow fiber membranes were used in gas-liquid contacting process. Porous polyetherimide hollow fiber membranes were fabricated via wet phase inversion method. The polymer concentration in dope solution varied from 10 to 15. wt%. Water was used as internal and external coagulant. Gas permeation test using helium as test gas, liquid entry pressure of water (LEPw) test and scanning electron microscopy (SEM) were used for membrane characterization. The mean pore size, effective surface porosity and void fraction of membranes decreased as the polymer concentration increased, while LEPw and membrane density increased.CO2 absorption rate of fabricated membranes were measured in a gas-liquid hollow fiber membrane contactor system using distilled water as absorbent and the results showed that CO2 absorption rate of membranes increases as polymer concentration decreases. In addition, CO2 absorption rate of hollow fiber membranes in which polyetherimide concentration was between 10 and 12wt%, was higher than commercial PVDF hollow fiber membranes

Experimental study on the performance and long-term stability of PVDF/montmorillonite hollow fiber mixed matrix membranes for CO2 separation process

Porous asymmetric polyvinylidene fluoride (PVDF)/montmorillonite (MMT) hollow fiber mixed matrix membranes (MMMs) with different nano-clay loadings were prepared via wet phase inversion technique and was used for membrane contactor. The fabricated MMMs were characterized in terms of morphology, structure, gas permeability, wetting resistance and mechanical stability. From morphology point of view, the fabricated membranes had a finger-like/sponge-like structure in the middle layer with a very porous thin outer skin layer and an inner skinless sponge-like structure. Atomic force microscopy (AFM) revealed an increase in surface roughness with increasing MMT loading. From gas permeation test, the surface porosity of the MMMs was higher than the plain PVDF membrane and the mean pore size of the membranes was small (34-22nm) and decreased slightly at 5wt.% MMT loading. A significant improvement in LEPw and hydrophobicity caused the prepared MMMs to show high wetting resistances. Mechanical stability test of membranes demonstrated an increase in stress at break and collapsing pressure with a slight loss in elongation with clay loading. CO2 absorption tests with water as absorbent showed that the absorption rate of the MMMs was higher than the plain membrane and increased with MMT loading. For example, at MMT loading of 5wt.% and absorbent flow rate of 0.5ms-1, the absorption flux was 1.89×10-3molm-2s-1 that was 48.7% higher than the plain PVDF membrane. Moreover, the absorption rate of the best fabricated MMM was higher than the commercial PVDF membrane. A long-term contactor test of this membrane over 350h showed that wetting did not take place and the absorption flux remained almost constant. It was concluded that, due to the higher surface hydrophobicity, wetting resistance and performance, MMMs can be a promising candidate to be used in contactor applications