Alamin Idris

Effects of Phase Separation Behavior on Morphology and Performance of Polycarbonate Membranes

The phase separation behavior of bisphenol-A-polycarbonate (PC), dissolved in N-methyl-2-pyrrolidone and dichloromethane solvents in coagulant water, was studied by the cloud point method. The respective cloud point data were determined by titration against water at room temperature and the characteristic binodal curves for the ternary systems were plotted. Further, the physical properties such as viscosity, refractive index, and density of the solution were measured. The critical polymer concentrations were determined from the viscosity measurements. PC/NMP and PC/DCM membranes were fabricated by the dry-wet phase inversion technique and characterized for their morphology, structure, and thermal stability using field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis, respectively. The membranes’ performances were tested for their permeance to CO2, CH4, and N2 gases at 24 ± 0.5 °C with varying feed pressures from 2 to 10 bar. The PC/DCM membranes appeared to be asymmetric dense membrane types with appreciable thermal stability, whereas the PC/NMP membranes were observed to be asymmetric with porous structures exhibiting 4.18% and 9.17% decrease in the initial and maximum degradation temperatures, respectively. The ideal CO2/N2 and CO2/CH4 selectivities of the PC/NMP membrane decreased with the increase in feed pressures, while for the PC/DCM membrane, the average ideal CO2/N2 and CO2/CH4 selectivities were found to be 25.1 ± 0.8 and 21.1 ± 0.6, respectively. Therefore, the PC/DCM membranes with dense morphologies are appropriate for gas separation applications.

Swelling mechanism of urea cross-linked starch–lignin films in water

ABSTRACT Coating fertilizer particles with thin films is a possibility to control fertilizer release rates. It is observed that novel urea cross-linked starch–lignin composite thin films, prepared by solution casting, swell on coming into contact with water due to the increase in volume by water uptake by diffusion. The effect of lignin content, varied from 0% to 20% in steps of 5% at three different temperatures (25°C, 35°C and 45°C), on swelling of the film was investigated. By gravimetric analysis, the equilibrium water uptake and diffusion coefficient decrease with lignin content, indicating that the addition of lignin increases the hydrophobicity of the films. When temperature increases, the diffusion coefficient and the amount of water absorbed tend to increase. Assuming that swelling of the thin film is by water uptake by diffusion, the diffusion coefficient is estimated. The estimated diffusion coefficient decreases from 4.3 to 2.1 × 10−7 cm2/s at 25°C, from 5.3 to 2.9 × 10−7 cm2/s at 35°C and from 6.2 to 3.8 × 10−7 cm2/s at 45°C depending on the lignin content. Activation energy for the increase in diffusion coefficient with temperature is observed to be 16.55 kJ/mol. An empirical model of water uptake as a function of percentage of lignin and temperature was also developed based on Fick’s law.

Modeling of CO2 Capture by Amine Solution (MDEA) in Hollow Fiber Membranes

The absorption of carbon dioxide is investigated in a hollow fiber membrane contactor, a two dimensional model is suggested to predict the CO2 removal efficiency. The continuity equation consisting of convection and diffusion terms is applied in both shell and tube sides, and only diffusion is considered in axial and radical directions through the membrane. All equations are solved numerically by COMSOL software and the numerical method is on the basis of Finite Element Method (FEM). Amine solution is chosen as an absorbent to remove CO2 in different operating conditions such as gas and liquid flow rate. The result of this modeling was compared with experimental data taken from literature and good agreement was observed. The simulation results revealed that methyldiethanolamine (MDEA) was an efficient absorbent. The suggested model is recommended to predict CO2 concentration in a hollow fiber membrane contactor.

Phase Behavior and Ternary Diagram Construction for Membrane Forming Polycarbonate Solutions

Cloud points at different polymer concentrations were obtained by the simple titration method and compared with the numerically calculated theoretical binodal curves for Polycarbonate/Dimethylacetamide/Water (PC/DMAc/Water) and Polycarbonate/N-Methyl-2-pyrrolidone/Water (PC/NMP/Water). The interaction parameters for solvent polymer and nonsolvent polymer were obtained from Hansens solubility parameters. The cloud points determined were found to be in close agreement with the theoretical binodal curve calculated. Coagulation values for different solvents such as Dichloromethane (DCM), Dimethylacetamide (DMAc), N-Methyl-2-pyrrolidone (NMP) and Tetrahydrofuran (THF) were also determined and the results were plotted in a ternary diagram to realize the effect of interaction parameters on the coagulation values. The higher the mutual affinity of solvent to polymer (low χ23), the faster is the liquid-liquid demixing rate to occur. For DCM solvent, fastest demixing rate was exhibited and lowest for the THF.