Adnan Ripin

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

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.

CO2 reforming of CH4 over Ni/mesostructured silica nanoparticles (Ni/MSN)

The development of supported Ni-based catalysts for CO2 reforming of CH4 was studied. Ni supported on mesostructured silica nanoparticles (MSN) and MCM-41 were successfully prepared using an in situ electrochemical method. The N2 physisorption results indicated that the introduction of Ni altered markedly the surface properties of MCM-41 and MSN. The TEM, H2-TPR and IR adsorbed CO studies suggested that most of the Ni deposited on the interparticles surface of MSN have higher reducibility than Ni plugged in the pores of MCM-41. Ni/MSN showed a higher conversion of CH4 at about 92.2% compared to 82.6% for Ni/MCM-41 at 750 °C. After 600 min of the reaction, Ni/MCM-41 started to deactivate due to the formation of shell-like carbon which may block the active sites and/or surface of catalyst, as proved by TEM analyses. Contrarily, the activity of Ni/MSN was sustained for 1800 min of the reaction. The high activity of Ni/MSN was resulted from the presence of greater number of easily reducible Ni on the surface. In addition, the large number of medium-basic sites in Ni/MSN was capable to avoid the formation of shell-like carbon that deactivated the catalyst, thus increased the stability performance. The results presented herein provide new perspectives on Ni-based catalysts, particularly in the potential of MSN as the support.

Influence of multi-walled carbon nanotubes on textural and adsorption characteristics of in situ synthesized mesostructured silica.

Carbon nanotubes-mesostructured silica nanoparticles (CNT-MSN) composites were prepared by a simple one step method with various loading of CNT. Their surface properties were characterized by XRD, N2 physisorption, TEM and FTIR, while the adsorption performance of the CNT-MSN composites were evaluated on the adsorption of methylene blue (MB) while varying the pH, adsorbent dosage, initial MB concentration, and temperature. The CNTs were found to improve the physicochemical properties of the MSN and led to an enhanced adsorptivity for MB. N2 physisorption measurements revealed the development of a bimodal pore structure that increased the pore size, pore volume and surface area. Accordingly, 0.05 g L(-1) CNT-MSN was able to adsorb 524 mg g(-1) (qm) of 60 mg L(-1) MB at pH 8 and 303 K. The equilibrium data were evaluated using the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models, with the Langmuir model affording the best fit to the adsorption data. The adsorption kinetics were best described by the pseudo-first order model. These results indicate the potential of CNT-MSN composites as effective new adsorbents for dye adsorption.

Effects of Ultrasonic Waves on Vapor-Liquid Equilibrium of an Azeotropic Mixture

Abstract Azeotropic and extractive distillation techniques used to separate azeotropic mixtures are among the most challenging separation processes in the chemical industry. In this work, an innovative distillation technique which employed ultrasonic waves was proposed to intensify the conventional multi-column azeotropic distillation method into a single-column alternative. The effects of ultrasonic intensity on the vapor-liquid equilibrium (VLE) of methyl-tert-butyl-ether (MTBE)-methanol was investigated at 50, 100, 200, and 250 W/A·cm2 and at a fixed frequency of 40 kHz. Studies were also done to examine the effects of ultrasonic frequency on the VLE data at 25 and 68 kHz frequencies. It was found that ultrasonic waves at 50 W/A·cm2 intensity and 25 kHz frequency gave the highest relative volatility (α) at 2.654 and completely eliminated the MTBE-methanol azeotrope, thereby allowing highly pure MTBE to be recovered in just a single distillation column. The results revealed that ultrasonic waves had the potential to favorably manipulate α, and hence, the VLE of an azeotropic mixture.

Mathematical modeling of a single stage ultrasonically assisted distillation process.

The ability of sonication phenomena in facilitating separation of azeotropic mixtures presents a promising approach for the development of more intensified and efficient distillation systems than conventional ones. To expedite the much-needed development, a mathematical model of the system based on conservation principles, vapor-liquid equilibrium and sonochemistry was developed in this study. The model that was founded on a single stage vapor-liquid equilibrium system and enhanced with ultrasonic waves was coded using MATLAB simulator and validated with experimental data for ethanol-ethyl acetate mixture. The effects of both ultrasonic frequency and intensity on the relative volatility and azeotropic point were examined, and the optimal conditions were obtained using genetic algorithm. The experimental data validated the model with a reasonable accuracy. The results of this study revealed that the azeotropic point of the mixture can be totally eliminated with the right combination of sonication parameters and this can be utilized in facilitating design efforts towards establishing a workable ultrasonically intensified distillation system.

Composite membranes based on heteropolyacids and their applications in fuel cells

Heteropolyacids (HPAs) are a class of inorganic materials that have been widely used as additives to enhance the performance of fuel cell membranes, recently. This chapter covers the use of HPAs in the preparation of proton exchange membranes (PEM) for polymer electrolyte membrane fuel cells (PEMFCs). The fundamental aspects of HPAs and their corresponding salts in addition to various structural configurations such as Keggin, Wells–Dawson, and Lacunar are discussed. The use of HPAs for preparation of membranes for high-temperature PEMFC and direct methanol fuel cell (DMFC) based on the immobilization on various substrates including perfluorinated sulfonic acids (PFSAs), aromatic hydrocarbons, poly(vinyl alcohol) (PVA), and polybenzimidazole (PBI) are reviewed. The research challenges that need to be addressed to bring the new composite membranes to practical application are also discussed.

Vapor-liquid equilibrium of ethanol/ethyl acetate mixture in ultrasonic intensified environment

A vapor-liquid equilibrium (VLE) study was conducted on ethanol/ethylacetate mixture as a preliminary step towards developing an ultrasonic-assisted distillation process for separating azeotropic mixtures. The influence of ultrasonic intensity and frequency on the vapor-liquid equilibrium (VLE) of the mixture was examined using a combination of four ultrasonic intensities in range of 100–400W/cm2 and three frequencies ranging from 25–68 kHz. The sonication was found to have significant impacts on the VLE of the system as it alters both the relative volatility and azeotrope point, with preference to lower frequency operation. A maximum relative volatility of 2.32 was obtained at an intensity of 300 W/cm2 and a frequency of 25 kHz coupled with complete elimination of ethanol-ethyl acetate azeotrope. Results from this work were also congruent with some experimental and theoretical works presented in the literature. These findings set a good beginning towards the development of an ultrasonic assisted distillation that is currently in progress.

Flammability Assessments of Sonication Process in Organic Mixture

The prospect of sonication phenomenon in facilitating separation of azeotropic mixtures calls for more detailed study towards developing an intensified distillation system. One important element that require in depth consideration is safety since ultrasound is a potential ignition source with a low threshold value of 1 mW/mm2. In this study, the aim is to investigate the potential of fire hazards that may be introduced by sonication when used in the environment of flammable organic liquid. Simulation study in MATLAB programming environment is carried out based on a mathematical model developed using first principle. Simulations of bubble conditions covering its whole life cycle regimes are carried out and validated with experimental works. Evaluation is made for an extreme condition where the ultrasonic waves are focused directed towards a stainless steel target material immersed in ethanol-water mixture. As sonication occurs, bubbles form slowly by rectified diffusion process with radius of 6 μm, and move toward the metal target. The experimental results revealed that cavitation bubbles filled with explosive vapor are not ignited. This is consistent with the simulation study where the maximum energy released during the bubble collapse is found to be small, which is 0.19267 pJ compared to minimum ignition energy of the liquid at 0.23 mJ. This concludes that the focused ultrasound wave in organic liquid does not trigger ignition, thus suggesting the ultrasonic distillation system is potentially.

Electrooxidation of nitrite ions on gold/polyaniline/carbon paste electrode

Nitrite ions can penetrate from fertilizers into underground water and consequently contaminate the water and food sources. A facile two-step electrochemical method was used to fabricate gold/polyaniline/carbon paste electrode (Au/PAni/CPE) for nitrite sensing. The Au/PAni/CPE was visualized and characterized by scanning electron microscopy, energy-dispersed X-ray spectroscopy, X-ray diffraction and electrochemical methods. The electrocatalytic activity of bare CPE, PAni/CPE and Au/PAni/CPE toward the electrooxidation of nitrite was examined and compared via cyclic voltammetry. To obtain the optimal condition for fabrication of the electrode, the number of cycles in cyclic voltammetry for synthesis of polyaniline and the deposition time in potentiostatic deposition of gold were optimized with respect to the electrooxidation of nitrite. In a phosphate buffer solution (PBS, pH 7.0), the peak current was linear to the concentration of nitrite in the range from 3.8×10-5 M to 1.0×10-3 M with a detection limit of 2.5×10-5 M. The interference effect on the nitrite detection was also studied. The proposed method was also employed for the determination of nitrite in rain and lake water samples.

A simulation of claus process via aspen hysys for sulfur recovery

Abstract In refineries, due to the environmental pollutions, sulfur content in petroleum need be reduced. The incineration process is used for sulfur recovery system which is not friendly process to the environment and needs high temperature. This actual process exhaust high amount of SO2 from the incinerator stack to the environment. The Claus process is the best method to recover sulfur from acid gases that contain hydrogen sulfide. The particular reaction for sulfur removal from sour gas is hydrogen sulfide (H2S) sulfur dioxide (SO2) reformation (2H2S+O2=S2+2H2O). The aim of this study is to get a simulation that is suitable for the characterization of sulfur recovery units. The experimental design for this study was collected from a petroleum refinery located in Iran. This experimental relation supports us to gather with definite consistency that is normally not available online for such process. Aspen HYSYS v8.8 software was used to simulate the Claus process by reactors and component splitters. The result shows the complete conversion of sour gas to product. The simulation protects the environmental impact by SO2 emission. This behavior can be reproduced by this HYSYS design very well. It was found that the BURNAIR feed composition and molar flow is the only factors which can affect the hydrogen sulfide conversion. The sulfur mole fraction increased only in the range of 0.94 to 0.98 by increasing N2 from 0.7 to 0.9.