Para-xylene adsorption separation process using nano-zeolite Ba-X

The liquid phase adsorption process was studied on nano-zeolite Ba-X for separating para-xylene from a feed mixture containing all C₈ aromatics. Nano-zeolite Ba-X with different ratios of SiO₂/Al₂O₃ was synthesized through hydrothermal process and ion-exchanged with barium. The product was characterized by X-ray diffraction, scanning electron microscopy (SEM), nitrogen adsorption and in situ Fourier transform infrared (FTIR) spectroscopy. The adsorption process was carried out in a breakthrough system at temperature range of 120–160 °C under 4–7 atm pressure. The influence of nano-zeolite water content on the separation process was studied. The optimization of adsorption process was also investigated by changing the operation conditions. The adsorption isotherm for all C₈ aromatic isomers and also desorbents indicated the typical Langmuir type. The selectivity factor of adsorbent for para-xylene and the adsorption capacity at saturation of the different adsorbate samples with each component from C₈ aromatic mixture were determined. It was observed that the selectivity of para-xylene increased by barium ion-exchange of cationic sites in nano-zeolite X and the adsorbent selectivity for para-xylene relative to each of meta-xylene, ortho-xylene and ethyl-benzene under the optimum conditions was found to be 7.191, 2.819 and 3.745, in the order given. It was also studied the influence of desorbent type on its selectivity for para-xylene compared to each isomer from the C₈ aromatic mixture.     

碳八芳烃异构体分离技术评述

介绍了碳八芳烃异构体工业分离技术的现状、对二甲苯分离技术的新发展。评述了择形催化生产对二甲苯的技术、利用结晶处理高浓度对二甲苯原料、变压吸附低成本浓缩对二甲苯技术、分子筛膜分离对二甲苯等。     

Influence of the Type of Reducing Agent (H2, CO, C3H6 and C3H8) on the Reduction of Stored NOX in a Pt/BaO/Al2O3 Model Catalyst

In this investigation, a comparative study for a NO _X storage catalytic system was performed focusing on the parameters that affect the reduction by using different reductants (H₂, CO, C₃H₆ and C₃H₈) and different temperatures (350, 250 and 150 °C), for a Pt/BaO/Al₂O₃ catalyst. Transient experiments show that H₂ and CO are highly efficient reductants compared to C₃H₆ which is somewhat less efficient. H₂ shows a significant reduction effect at relatively low temperature (150 °C) but with a low storage capacity. We find that C₃H₈does not show any NO _X reduction ability for NO _X stored in Pt/BaO/Al₂O₃ at any of the temperatures. The formation of ammonia and nitrous oxide is also discussed.     

Electrochemical quartz crystal microbalance studies of thin-solid films of higher fullerenes: C76, C78 and C84

Thin-solid films of higher fullerenes, viz. C₇₆, C₇₈ and C₈₄, were prepared by the drop coating technique and characterized by simultaneous cyclic voltammetry and piezoelectric microgravimetry with the use of an electrochemical quartz crystal microbalance. Properties of the films were compared with those reported earlier for the C₆₀ and C₇₀ thin-solid films. The effect of nature of the counter cation on electrochemical properties of the films has been probed by employing acetonitrile solutions of two different 0.1 M supporting electrolytes, namely tetra(n-butyl)ammonium (TBA⁺) hexafluorophosphate and potassium hexafluorophosphate. Stability of the films with respect to dissolution depends on the fullerene oxidation state as well as on the nature of both the fullerene in the film and the counter cation in the supporting electrolyte. The TBA⁺ counter cation ingress to the film for compensation of the negative charge of the reduced fullerene is accompanied by the acetonitrile solvent intake. The number of acetonitrile molecules per TBA⁺ counter cation entering the film is higher the higher the fullerene. Also, the Langmuir films of higher fullerenes were prepared at the air-water interface and the film morphology was characterized by the Brewster angle microscopy.     

Synthesis of alkali-metal-doped C60 nanotubes

C₆₀ nanotubes have been synthesized by a solution-solution method. After degassing in a dynamic vacuum, the C₆₀ nanotubes doped with alkali metals by means of vapor evaporation method. Different temperatures have been studied to evaporate the alkali metals for the doping experiments. Raman spectrum was further employed to analyze the doping concentration of the obtained samples. It was found that all three alkali metals (Li, Na and K) used can be efficiently doped into the C₆₀ nanotubes, forming A_xC₆₀ nanotubes. The doping concentration of Li, Na changed from low to high level, depending on the experiment temperatures, while K doping always gave saturated doping. The melt points, the ionic sizes and vapor pressures of alkali metals were thought to affect the final doping results.     

Similarity and differences in the oxidative dehydrogenation of C2–C4 alkanes over nano-sized VOx species using N2O and O2

The effect of O₂ and N₂O on alkane reactivity and olefin selectivity in the oxidative dehydrogenation of ethane, propane, n-butane, and iso-butane over highly dispersed VO_x species (0.79 V/nm²) supported on MCM-41 has been systematically investigated. For all the reactions studied, olefin selectivity was significantly improved upon replacing O₂ with N₂O. This is due to suppressing CO_x formation in the presence of N₂O. The most significant improving effect of N₂O was observed for iso-butane dehydrogenation: S(iso-butene) was ca. 67% at X(iso-butane) of 25%.Possible origins of the superior performance of N₂O were derived from transient experiments using ¹⁸O₂ traces. ¹⁸O¹⁶O species were detected in ¹⁸O₂ and ¹⁸O₂–C₃H₈ transient experiments indicating reversible oxygen chemisorption. In the presence of alkanes, the isotopic heteroexchange of O₂ strongly increased. Based on the distribution of labeled oxygen in CO_x and in O₂ as well as on the increased CO_x formation in sequential O₂–C₃H₈ experiments, it is suggested that non-lattice oxygen species (possibly of a bi-atomic nature) originating from O₂ are non-selective ones and responsible for CO_x formation. These species are not formed from N₂O.     

Synthesis and solid-state studies of self-assembled C60 microtubes

C₆₀ microtubes were fabricated by a modified solution evaporation method, evaporating a solution of C₆₀ in toluene in an atmosphere of m-xylene at room temperature. The C₆₀ microtubes have outer diameters ranging from 2 to 8 μm. IR spectra, TG analysis and X-ray diffraction showed a solvated structure for the as-grown C₆₀ microtubes. Through a gentle heat-treatment in vacuum, pure C₆₀ microtubes with single crystalline fcc structure were obtained after the elimination of solvents. It is suggested that the C₆₀ microtubes form through self-assembly from several individual C₆₀ nanorods.     

Deposition of C60, C70 and C84 fullerene molecules, in benzene via a change of the fluid state, from a gas–liquid two phase region to the critical point

We dissolve C₆₀, C₇₀ or C₈₄ molecules in benzene and change the fluid state from a gas–liquid two-phase region (25.0 °C) to the critical point (289.0 °C) and from the critical point to the original state (25.0 °C) along the gas–liquid coexistence curve. We find that particle-like and whisker-like nano/micro clusters, which are composed of C₆₀ molecules, deposit on the surface of a silicon substrate placed vertically in C₆₀/benzene solution during the temperature change, whereas no appreciable clusters are detected on the silicon substrate in either C₇₀/benzene or C₈₄/benzene solutions. The clusters, in which fcc lattice structures are formed by C₆₀ molecules, remain stable in the solution. The present result suggests that C₆₀ molecules can be separated and extracted from a mixture of C₆₀, C₇₀ and C₈₄ molecules dissolved in benzene.     

The intercalation of C60-containing PEO into layered MnPS3

This paper reports the synthesis and magnetism of a new polymer-inorganic intercalation nanocomposite based on a C₆₀-containing poly(ethylene oxide) (C₆₀-PEO) into layered MnPS₃, which is characterized by XRD, IR and thermal analyses. The lattice expansion (Δd) of the intercalation nanocomposite is about 9.3 Å indicating the successful intercalation. And the charge balance is maintained by K⁺ ions coordinating with PEO chain of C₆₀-PEO polymer, which come from the pre-intercalation compound Mn_1−xPS₃[K_2x(H₂O)_y]. Magnetic measurements indicate that the intercalation nanocomposite (C₆₀-PEO/MnPS₃) exhibits a magnetic phase transition from paramagnetism to ferrimagnetism at about 40 K. And the distinctive hysteresis of M-H relationship further confirms that it is a low temperature ferrimagnetic nanocomposite.     

C2H2 gas sensor based on Ni-doped ZnO electrospun nanofibers

Pure and Ni-doped ZnO nanofibers were synthesized using the electrospinning method. The morphology, crystal structure and optical properties of the nanofibers were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL) spectroscopy, respectively. It is found that Ni doping does not change the morphology and crystal structures of the nanofibers, and the ultraviolet emissions of ZnO nanofibers present red shift with increasing Ni doping concentration. C₂H₂ sensing properties of the sensors based on the nanofibers were investigated. The results show that the C₂H₂ sensing properties of ZnO nanofibers are effectively improved by Ni doping, and 5 at% Ni-doped ZnO nanofibers exhibit a maximum sensitivity to C₂H₂ gas.     

Synthesis of Buckminsterfullerene C60 functionalised core cross-linked star polymers

Buckminsterfullerene C₆₀ core functionalised core cross-linked star (CCS) polymers have been prepared for the first time, using atom transfer radical polymerisation and the arms-first approach. A simple and efficient method is presented which allows the construction of star polymers consisting of a large number of arms and multiple units of C₆₀ per core, far in excess of that obtained previously. The C₆₀ CCS polymers were characterised by gel permeation chromatography (GPC), UV-vis spectroscopy and cyclic voltammetry (CV). GPC revealed that the C₆₀ CCS polymers possess weight average molecular weights (M_w) ranging from 172-411 kDa and up to 30 arms per macromolecule. The average number of molecules of C₆₀ per CCS polymer core was found to be dependent on the C₆₀/PMMA ratio employed and was determined by UV-vis spectroscopy to range up to 6.2. CV revealed that, like pristine C₆₀, the C₆₀ CCS polymers possessed three reversible one electron reductions. However, the reduction potentials were positively shifted, implying that the electron affinity of these macromolecules is higher than pristine C₆₀.     

Effect of Ti5Si3 on wear properties of Ti3Si(Al)C2

Near-fully dense Ti₃Si(Al)C₂/Ti₅Si₃ composites were synthesized by in situ hot pressing/solid–liquid reaction process under a pressure of 30 MPa in a flowing Ar atmosphere at 1580 °C for 60 min. Compared to monolithic Ti₃Si(Al)C₂, Ti₃Si(Al)C₂/Ti₅Si₃ composites exhibit higher hardness and improved wear resistance, but a slight loss in flexural strength (about 26% lower than Ti₃Si(Al)C₂ matrix). In addition, Ti₃Si(Al)C₂/Ti₅Si₃ composites maintain a high fracture toughness (K_IC = 5.69–6.79 MPa m^1/2). The Ti₃Si(Al)C₂/30 vol.%Ti₅Si₃ composite shows the highest Vickers hardness (68% higher than that of Ti₃Si(Al)C₂) and best wear resistance (the wear resistance increases by 2 orders of magnitude). The improved properties are mainly ascribed to the contribution of hard Ti₅Si₃ particles, and the strength degradation is mainly due to the lower Young's modulus and strength of Ti₅Si₃.     

Transalkylation and disproportionation of toluene and C9 aromatics over zeolite beta

Transalkylation and disproportionation (TADP) of toluene and C₉ aromatics from a commercial stream have been studied over a zeolite possessing a three-dimensional, 12-membered ring pore system. The study encompassed the effect of C₉ aromatics content in feed on TADP. Formation of xylenes was maximum with a feed containing 50 50 toluene and C₉ aromatics. In order to understand the role of different C₉ aromatics in TADP, experiments using individual C₉ aromatics with and without toluene mixture as feed were carried out. An interesting observation of these experiments was that ethyltoluenes produced xylenes through disproportionation of toluene generated from their deethylation. The total yield of xylenes was much less than that obtained from trimethyl benzenes. A reaction scheme accounting all the reactions taking place during TADP is proposed.     

Influence of a C12A7 mineral-based accelerator on the strength and durability of shotcrete

This study analyzed the long-term strength and durability of shotcrete when a C₁₂A₇-based accelerator is added to the mixture. Since an accelerator with a high alkali content causes a remarkable decrease in the long-term strength of shotcrete and is toxic to humans, this study evaluated the setting time, compressive strength, and resistance to permeability and repeated freeze-thaw cycles of an amorphous C₁₂A₇-based accelerator. The results showed that the C₁₂A₇ accelerator set quickly by forming a web structure from its initial setting state due to the presence of ettringite. In addition, the ettringite, with its characteristic acicular crystals, proved resistant to permeability and repeated freeze-thaw cycles. Ettringite has a structure that encouraged a smooth hydration reaction, maintaining the voids at the surface of the cement particles and resulting in the observed initial strength and decrease in the reduction of the long-term strength.     

Carbothermal synthesis, spectral and magnetic characterization and Li-cyclability of the Mo-cluster compounds, LiYMo3O8 and Mn2Mo3O8

The molybdenum cluster compounds, LiYMo₃O₈ and Mn₂Mo₃O₈ are prepared by the carbothermal reduction method and characterized by various techniques. The FT-IR at ambient temperature (RT), and Raman spectra at various temperatures (78-450 K) are reported for the first time and results are interpreted. Magnetic studies on Mn₂Mo₃O₈ in the temperature range, 10-350 K confirm that it is ferrimagnetic, with T_C = 39 K. Magnetic hysteresis and magnetization data at various fields and temperatures are presented. The Li-cyclability is investigated by galvanostatic cycling in the voltage range, 0.005-3.0 V vs. Li at 30 mA/g (0.08 C). LiYMo₃O₈ shows a total first-discharge capacity of 305 ±5 mAh/g whereas the first-charge capacity is only 180 mAh/g at RT. However, both values increased systematically with an increase in the cycle number and yielded a reversible capacity of 385 ±5 mAh/g at the end of 120th cycle. At 50 °C, the reversible capacity is 418 ±5 mAh/g at the 60th cycle. The coulombic efficiency ranges from 94% to 98%. The Li-cyclability behavior of Mn₂Mo₃O₈ is entirely different from that of LiYMo₃O₈. The total first-discharge and charge capacities are 710 ± 5 and 565 ±5 mAh/g, but drastic capacity-fading occurs during cycling. The reversible capacity at the end of 50th cycle is only 205 ±5 mAh/g. Plausible reaction mechanisms are proposed and discussed based on the galavanostatic cycling, cyclic voltammetry, ex situ XRD, ex situ TEM and impedance spectral data.     

Exergy analysis of C2 recovery plants refrigeration cycles

This paper provides an exergy analysis of the multistage refrigeration cycle used for Ethane and heavier hydrocarbons (C₂⁺) recovery plant. The behavior of an industrial refrigeration cycle with propane refrigerant has been investigated by the exergy method. The equations of exergy destruction and exergetic efficiency for the main cycle components such as evaporators, condensers, compressors, and expansion valves are developed. The relations for the total exergy destruction in the cycle and the cycle exergetic efficiency are obtained. An ethane recovery unit with its refrigeration cycle has been simulated to prepare the exergy analysis. Using a typical actual work input value; the exergetic efficiency of the refrigeration cycle is determined to be 43.45% indicating a great potential for improvements. The simulation results reveal that the exergetic efficiencies of the heat exchanger and expansion sections get the lowest rank among the other compartments of refrigeration cycle. Refrigeration calculations have been carried out through the analysis of temperature-entropy (T-S) and pressure-enthalpy (P-H) diagrams where coefficient of performance (COP) was obtained as 1.87. The novelty of this article includes the effect and sensitivity analysis of pressure drop and temperature on the exergy efficiency and coefficient of performance of the cycle.     

High rate performance of highly dispersed C60 on activated carbon capacitor

Fullerene-activated carbon composite electrodes were prepared and their charge/discharge characteristics were studied for use in a high power electric double-layer capacitor. The capacitance of the C₆₀-loaded activated carbon fiber (ACF) electrodes became greater than that of the unloaded ACF at charge/discharge current densities above 50 mA/cm². In order to obtain a highly dispersed C₆₀-loaded electrode, an ultrasonic treatment was performed. The size of the C₆₀ agglomerate decreased from 1-2 to 0.1 μm or less, and the capacitance of the C₆₀-loaded ACF electrodes increased with an increase in the ultrasonic treatment time. A higher capacitance of 172 F/g was obtained at 50 mA/cm² on a 1 wt% C₆₀-loaded electrode with ultrasonic treatment, and the C₆₀-loaded ACF electrode also showed a higher cycle performance.     

Enantioanalysis of S-deprenyl using enantioselective, potentiometric membrane electrodes based on C60 derivatives

Enantioselective, potentiometric membrane electrodes based on (1,2-methanofullerene C₆₀)-61-carboxylic acid, diethyl (1,2-methanofullerene C₆₀)-61-61-dicarboxylate and tert-butyl (1,2-methanofullerene C₆₀)-61-carboxylic acid were proposed for the enantioanalysis of S-deprenyl in pharmaceutical compounds. Molecular modeling calculations were performed to prove the reliability of the proposed electrodes. The different characteristics involved in this analysis were explained, namely (i) the stability of each molecule using total energy, hardness and dipole moment, and (ii) the explanation of the mechanism of interaction using intermolecular forces (moderate hydrogen bond interactions), atomic charges and electrostatic potential. Electronic structures as well as molecular interaction have been investigated using Hartree-Fock theory, 3-21G(*) basis set. Stability and feasibility of all the generated structures were supported by their respective energy minima and fundamental frequencies.     

Electrochemical properties of nanostructured Li1.2V3O8 in aqueous LiNO3 solution

The amorphous hydrated precursor of Li_1.2V₃O₈ was synthesized by soft chemistry method, and then heat-treated in air at several temperatures within the range 200–400 °C. The heat-treatment changed its morphological, structural and charging/discharging performance. The product obtained upon the treatment at 300 °C, consisting of uniform, rod-shaped particles, 100–150 nm in diameter and 300–800 nm in length, displayed the best electrochemical performance in aqueous LiNO₃ solution. Its initial discharge capacity amounted to 136.8 mAh g⁻¹ at a rate of C/5, which upon 50 charging/discharging cycles decreased for only 12%.     

Grafting of poly(ethylene oxide) onto C60 fullerene using macroazo initiators

In order to improve the solubility of C₆₀ fullerene in conventional solvents, grafting of hydrophilic poly(ethylene oxide) (PEO) by utilizing the radical-trapping nature of C₆₀ fullerene was investigated. Macroazo initiators containing a poly(ethylene oxide) unit, known as Azo-PEO, were prepared at various molecular weights by the reaction of 4,4′-azobis(4-cyanopentanoyl chloride) with poly(ethylene glycol) methyl ether. PEO radicals formed by thermal decomposition of Azo-PEO were successfully trapped by C₆₀ fullerene to give PEO-grafted C₆₀ fullerene. Their structures were confirmed by FT-IR spectroscopy, size exclusion chromatography, UV-vis spectroscopy, and differential scanning calorimetry. When Azo-PEO with low-molecular weight was reacted with C₆₀ fullerene, a bis-adduct, C₆₀-(PEO)₂, and a tetrakis-adduct, C₆₀-(PEO)₄, were formed. In contrast, in reactions with Azo-PEO of higher molecular weight, only the bis-adduct was formed, and no formation of the tetrakis-adduct was observed. The structure of bis-adduct was found to be 1,4-type. The solubility of C₆₀ fullerene in water, THF, methanol, and other conventional organic solvents was remarkably improved by grafting of PEO. In addition, the thermal stability of PEO was dramatically increased by grafting onto C₆₀ fullerene.