Showing papers by "Mohamed Mahmoud Nasef published in 2015"

State-of-the-Art Technologies for Separation of Azeotropic Mixtures

Abstract: Azeotropic separation technologies have been classified broadly into two major categories, i.e., distillation and membrane processes. Because normal distillation has limitations for azeotropic mixtures, enhancements have been proposed that either introduce a third component serving as an entrainer in extractive and azeotropic distillation processes or apply a pressure swing distillation system. Among the membrane processes, pervaporation was reported to be most promising for azeotropic separations. More recently, an approach known as process intensification has been proposed for combining multiple processes into single units such as a dividing wall distillation column or exploiting sonication phenomena to break an azeotrope in an ultrasonic distillation system. This article reviews the state-of-the-art technologies covering all the separation techniques mentioned here. Existing techniques are appraised, and technology gaps are identified. Based on these insights, areas for further development are suggested, aiming at satisfying the process objectives by inherently safer, environmentally benign and economically more attractive techniques.

Improved methanol barrier property of Nafion hybrid membrane by incorporating nanofibrous interlayer self-immobilized with high level of phosphotungstic acid

Abstract: High level of phosphotungstic acid (PWA) was self-immobilized on electrospun nylon nanofiberous sheet to fabricate highly selective methanol barrier layer for sandwich structured proton conducting membranes. Simple tuning for the assembly conditions of central layer and thickness of outer Nafion layers allowed obtaining different composite membranes with superior methanol barrier properties (namely, P = 3.59 × 10–8 cm2 s–1) coupled with proton conductivities reaching 58.6 mS cm–1 at 30 °C. Comparable activation energy for proton transport and more than 20 times higher selectivity than Nafion 115 confirm the effectiveness of the central layer and resulting membranes for application in direct methanol fuel cells (DMFCs). When tested in DMFC single cell, the performance of hybrid membrane was far better than Nafion 115 especially at higher methanol concentrations.

Tuning N-methyl-D-glucamine density in a new radiation grafted poly(vinyl benzyl chloride)/nylon-6 fibrous boron-selective adsorbent using the response surface method

Abstract: A new adsorbent containing boron-selective groups was prepared by radiation induced grafting of vinyl benzyl chloride (VBC) onto nylon-6 fibers followed by functionalisation with N-methyl-D-glucamine (NMDG). The density of glucamine loaded in the adsorbent was tuned by optimisation of the reaction parameters such as NMDG concentration, reaction temperature, reaction time and degree of grafting using response surface methodology (RSM) employing Box–Behnken design (BBD). The optimum parameters for achieving the maximum glucamine density (1.7 mmol g−1) in the adsorbent are 10.6%, 81 °C, 47 min and 121% for the NMDG concentration, reaction temperature, reaction time and degree of grafting (DG), respectively. The deviation between the optimum experimental and predicted glucamine density is found to be 1.2% suggesting the reliability of RSM in predicting the yield and optimising the functionalisation reaction parameters. The chemical composition, morphology and structure of the NMDG-containing fibrous adsorbent were studied using Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The thermal properties were determined using differential scanning calorimetry (DSC) and the thermal stability was evaluated by thermogravimetric analysis (TGA). Considering the physico-chemical properties of the fibrous adsorbent and the preliminary results of boron adsorption, it can be suggested that this adsorbent is a promising candidate for boron removal.

High refractive index materials: A structural property comparison of sulfide- and sulfoxide-containing polyamides

Abstract: High-refractive-index polyamides (PAs) are developed by incorporation of sulfide- or sulfoxide linkages and chlorine substituents. The PAs are synthesized through the polycondensation of two novel diamine monomers, 2,2'-sulfide-bis(4-chloro-1-(4-aminophenoxy) phenyl ether (3a) and 2,2'-sulfoxide-bis(4-chloro-1-(4-aminophenoxy) phenyl ether (3b), with various aromatic diacids (a-e). The ortho-sulfide or sulfoxide units, pendant chlorine groups, and flexible ether linkages in the diamine monomers endowed the obtained PAs with excellent solubilities in organic solvents. The resulting PAs showed high thermal stability, with 10% weight loss temperatures exceeding 415°C under nitrogen and 399°C in air atmosphere. The combination of chlorine substituents, sulfide or sulfoxide linkages, and ortho-catenated structures provided polymers with high transparency along with high refractive index values of up to 1.7401 at 632.8 nm and low birefringences (<0.0075). The structure-property relationships of the analogous PAs containing sulfide or sulfoxide linkages were also studied in detail by comparing the results

Kinetic behaviour of graft copolymerisation of nitrogenous heterocyclic monomer onto EB-irradiated ETFE films

Abstract: Kinetic behaviour of graft copolymerisation of a nitrogenous heterocyclic monomer, 4-vinylpyridine (4-VP), onto electron beam irradiated poly(ethylene-co-tetra- fluoroethylene) (ETFE) films was investigated in correla- tion with reaction parameters (absorbed dose, monomer concentration and reaction temperature). This was estab- lished by determination of initial polymerisation rate (rp0), characteristic radical recombination rate (c) and delay time (t0). The orders of the dependence of the initial rate of grafting on the absorbed dose and monomer concentration were found to be 2.28 and 3.49, respectively. The effect of temperature was investigated in the range of 50-70 C and the activation energy was determined. The incorporation of poly(4-VP) grafts and the accompanied chemical changes in the grafted ETFE films were monitored using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, respectively. The results of the present study showed that a quantitative kinetic description for grafting of 4-VP onto ETFE can be established and the degree of grafting can be tuned by controlling the reaction parameters.

Ultrasound-assisted regioselective ring opening of epoxides with nitrogen heterocycles using pyrrolidonium and imidazolium-based acidic ionic liquids

Abstract: Imidazolium and N-methyl-2-pyrrolidonium ionic liquids under ultrasound irradiation were developed as a green and expeditious approach for C--alkylation and N-alkylation of the nitrogen heterocycles including indoles and imidazoles with aliphatic and aromatic epoxides. Ionic liquids were used with a dual role of catalyst and solvent. The highest yield (85 %) was obtained with N-methyl-2-pyrrolidonium dihydrogen phosphate [H-NMP]H2PO4 as a pyrrolidonium ionic liquid under ultrasound at 50 kHz, with a reaction time of 60 min and reaction temperature of 60 °C. The combination of ionic liquids and ultrasonic irradiation was found to be an effective, green and eco-friendly method for alkylation of indoles and imidazoles.

Separation of Azeotropic Mixture Using Multi-stage Ultrasound-Assisted Flash Distillation

Abstract: A mathematical model for an ultrasound-assisted vapor liquid equilibrium (VLE) system developed in Aspen Custom Modeler is exported to Aspen Plus flowsheeting environment to form a block in the software library to represent a single stage flash separation unit. The block is then arranged in series to mimic an ultrasonically intensified distillation process. As a case study, an ethanol/ethyl acetate separation process is examined. The results show that a 99 mol% ethyl acetate recovery is established when a series of 27 flash VLE devices are used. The system is also evaluated for other minimum boiling azeotropic mixtures, and consistent results are obtained, thus revealing the potentials of ultrasound-assisted system as an alternative strategy for azeotropic mixture separations.

Preparation and characterization of poly(3-hydroxybutyric acid)/poly(vinyl acetate) blend films

Abstract: Modification of poly(3-hydroxybutyric acid) (PHB) films by blending with poly(vinyl acetate) (PVAc) was investigated. The variation effect of poly(vinyl acetate) proportions in PHB/PVAc blend on the chemical structure, thermal stability, melting and phase morphology and crystallization behaviour were studied. The structure was characterized by Fourier transform infrared, thermogravimetric analysis, X-ray Diffraction (XRD) and field emission scanning electron microscopy. The properties of poly(3-hydroxybutyric acid) were found to be improved by blending with poly(vinyl acetate) and the level of improvement is a function of the proportion of poly(vinyl acetate) in the blend. The thermal stability for the blending was more stable than the pure polymers. The TGA results of the prepared polymers showed three-step decomposition assigned to the thermal degradation of poly(3-hydroxybutyric acid) hard and poly(vinyl acetate). For the XRD, the crystallization rate was decreased by blending poly(3-hydroxybutyric acid) with poly(vinyl acetate).

Preparation and characterization of poly(1-vinyl imidazole)-graft-etfe/phosphoric acid proton conducting membranes

Abstract: Proton conducting membranes obtained by radiation-induced grafting (RIG) of 1-vinylimidazole (1-VIm) onto poly(ethylene- co -tetraflouroethene) (ETFE) films followed by phosphoric acid (PA) doping was prepared. The effect of grafting parameters on the grafted basic moiety was studied. The level of PA doping was controlled by manipulation of reaction parameters. The obtained membranes were investigated with Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), differential scanning calorimeter (DSC) and DC impedance spectroscopy. The obtained membranes proved to have less-water dependent proton conductivity with a value of 140 mS/cm at 120 o C and 17 % RH% at acid doping level of of 6.54 mmol/repeat unit. The membranes have potential for application in high temperature polymer electrolyte membrane fuel cell (PEMFC).

Kinetics of Radiation-Induced Graft Copolymerization of Vinylbenzyl Chloride onto Nylon Fibers

Abstract: The graft copolymerization of vinylbenzyl chloride (VBC) onto nylon-6 fiber was investigated by the pre-irradiation method using electron beam. The effects of grafting parameters, monomer concentration, absorbed dose and reaction temperature were investigated. The empirical kinetic rate equation dGo/dt=k[M]^0.86*[D]^1.06 was used to describe grafting of VBC onto nylon-6. The overall activation energy for graft copolymerization of VBC was found to be 22.6 kJ/mol. The results revealed that the grafting kinetic was controlled by the amounts of trapped radicals and monomer molecules. Fourier transform infrared (FT-IR) was used to provide evidence for the formation of grafted copolymers.

Aspen Plus Simulation of Ultrasound Assisted Distillation for Separating Azeotropic Mixture

Abstract: Earlier works have proved the potentials of altering the vapor liquid equilibrium of azeotropic mixture by sonication phenomena. In this work a mathematical model of a single stage vapor-liquid equilibrium system developed in Aspen Custom Modeler is exported to Aspen Plus to represent one stage of ultrasonic flash distillation (USF). The USF modules are connected serially to mimic a distillation process. As a case study, the separation of ethanol-ethyl acetate mixture is considered. The final targeted composition of 99 mole % of ethyl acetate was achieved when 27 USF modules were used despite the fact that the mixture form azeotrope at 55 mole % ethyl acetate. The results reinforced the anticipated potentials of sonication phenomena in intensifying distillation process to overcome azeotropes, and provide useful insights for the development of a pilot-scaled facility that is currently under development.