Membrane materials in the pervaporation separation of aromatic/aliphatic hydrocarbon mixtures—A review

The separation of aromatic/aliphatic hydrocarbon mixtures is a significant process in chemical industry,but challenged in some cases.Compared with conventional separation technologies,pervaporation is quite promising in terms of its economical,energy-saving,and eco-ffiendly advantages.However,this technique has not been used in industry for separating aromatic/aliphatic mixtures yet.One of the main reasons is that the separation performance of existed pervaporation membranes is unsatisfactory.Membrane material is an important factor that affects the separation performance.This review provides an overview on the advances in studying membrane materials for the pervaporation separation of aromatic/aliphatic mixtures over the past decade.Explored pristine polymers and their hybrid materials (as hybrid membranes) are summarized to highlight their nature and separation performance.We anticipate that this review could provide some guidance in the development of new materials for the aromatic/aliphatic pervaporation separation.     

芳香硝基化合物的氟化

从反应原理、催化剂的选择、副反应的发生与控制等方面综述了芳香硝基化合物直接氟化的研究进展，阐述了硝基氟化的意义及应用重要性，介绍了硝基氟化的最新研究与发展方向。     

Selective oxidation of methanol in exhaust gas containing aromatic compounds

The activity of exhaust catalysts of methanol and gasoline mixture fueled automobiles is inhibited by coexistent aromatic compounds contained in the exhaust stream. One approach to avoid this inhibition could be the utilization of a molecular-sieve effect. It seems probable that the migration of aromatic compounds, which have larger molecular sizes than that of methanol, will be blocked by these supports and methanol will selectively reach the active sites of the catalysts. Thus, we examined the simultaneous oxidation of methanol and toluene over some ion-exchanged Pt/zeolite catalysts. Experimental results showed that ion-exchanged Pt/zeolite catalysts are less affected by coexistent toluene and have a higher selectivity for methanol oxidation compared with an alumina-supported platinum catalyst, suggesting that the use of these catalysts is effective for oxidizing methanol in the exhaust stream containing aromatic compounds. Among the catalysts tested, a Pt/H-MOR catalyst was found to be the most effective for the oxidation of methanol and effectively catalyzed the reaction in the presence of toluene even at low temperature.     

Permselectivities of aromatic polyamide membranes for aqueous alcohol mixtures in pervaporation

The separation of water/alcohol mixtures was carried out using a series of fluorine-containing aromatic polyamide membranes. Aromatic polyamides were prepared by direct polycondensation of fluorine-containing diamine (2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, BAPPH) and various aromatic diacids. The separation factor toward water increased when the feed ethanol concentration was increased. The solubility of ethanol in aromatic polyamide membrane is higher than that of the water, but the diffusivity of water across the membrane is higher than that of alcohols. A separation factor of 83 and a permeation rate of 262 g/m²h with a 90 wt% feed ethanol concentration at 25 °C was obtained.     

水合肼法还原芳香硝基化合物制备芳胺的技术进展

综述了水合肼法还原芳香硝基化合物制备芳胺及其衍生物的近况,讨论了影响还原反应的主要因素和工艺条件,并展望了水合肼法制备芳胺工艺的应用前景和发展方向。     

芳香族硝基化合物废水处理现状及发展前景

从物理、化学和生化3个方面综述了芳香族硝基化合物废水处理技术的现状,介绍了最新的废水处理技术——纳米技术,并展望了含芳香族硝基化合物废水处理技术的应用前景。     

Deep desulfurization of diesel fuels: kinetic modeling of model compounds in trickle-bed

Five catalysts with different hydrodesulfurization (HDS) and hydrogenation activity were tested in HDS of fresh crude heavy atmospheric gas oil (HAGO) (1.33 wt% S), two partially hydrotreated HAGO (1100 and 115 ppm S) and two model compounds, dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (DMDBT), dissolved in model solvents and HAGO. Aromatic compounds in the liquid decreased significantly the HDS rate of 4,6-DMDBT, especially for catalysts with high hydrogenation activity. H₂S displayed a similar inhibition effect with all catalysts. These effects were extremely pronounced in HAGO where the DBT HDS rate decreased by a factor of 10 while 4,6-DMDBT – of 20 relative to paraffinic solvent. The feasibility of using a highly active hydrogenation catalyst for deep HDS of HAGO is diminished by the strong impact of aromatics.     

Anodic thiocyanation of mono- and disubstituted aromatic compounds

The in situ and environmentally friendly thiocyanation (no use of toxic oxidizing agents) electrochemical thiocyanation of aromatic compounds involving various derivatives of anisole and aniline to afford aromatic thiocyanates have been studied in organic acidic media. The initial electrochemical step involves anodic oxidation of thiocyanate anion to its radical (SCN), followed by dimerization to thiocyanogen (SCN)₂. The latter is polarized by the acidic solvent and attacks the aromatic nucleus of the substrate to afford the corresponding thiocyanate derivative. The sole thiocyanate products obtained in each case shows high regio-selectivity (no ortho isomer was observed) for the monosubstituted aromatics and high isomer-selectivity (no isothiocyanate isomer was detected) for both mono- and disubstituted aromatics.     

Functionalized metal‐organic polyhedra hybrid membranes for aromatic hydrocarbons recovery

Pervaporation membranes are potentially useful in the separation of aromatic/aliphatic mixtures. Wherein, the membrane material plays a key role. Herein, a series of functionalized metal‐organic polyhedra (MOPs)/hyperbranched polymer hybrid membranes are molecularly designed and fabricated for the recovery of aromatic hydrocarbons. The isostructural MOP molecules with different functional groups are uniform in shape/size and soluble in solvents, which enable them to disperse well and be compatible in/with the polymer. Pervaporation results demonstrated significant improvements of these membranes in separation performances. Particularly, the membrane with MOP‐SO₃Na_nH_m showed the separation factor of 8.03 and the permeation flux of 528 g/m²h for the recovery of toluene from its 50 wt % n‐heptane mixture, and those values are 8.4 and 540 g/m²h for benzene/cyclohexane mixture. We propose that the selectivity of these membranes is affected primarily by the polarity of functional groups in MOPs, which were further explained by the adsorption experiments and molecular simulations. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3706–3716, 2016     

Synthesis and characterization of aromatic/aliphatic co-polyureas

In the present work, a series of aromatic/aliphatic co-polyureas have been synthesized from 4,4-diphenylmethane diisocyanate (MDI), m-phenylene diamine (m-PDA), and 1,6-diaminohexane (HDA) in DMAc by a two-stage solution polymerization route. Characterizations of the polyurea products have been carried out by ¹H-nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopic techniques. Thermal properties of the polyurea samples have been investigated by differential scanning calorimetry and thermogravimetric analysis. The mechanical properties of the polyurea samples have been measured. The results show that the polyurea samples with the expected structure have been synthesized. The results of DSC analysis show the glass transition temperatures of the co-polyurea samples decrease with the increase of HDA content, and fit the Fox equation well. TGA data of the polyurea samples indicate that thermal stability of the aromatic polyurea is better than that of the co-polyureas. The thermal degradation activation energies of the co-polyureas are ∼60–70 kJ/mol. The results of mechanical measurement show that the initial modulus and tensile strength of the co-polyurea samples decrease with the increase of HDA content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The sources of polycyclic aromatic compounds in diesel engine emissions

The application of a radiotracer technique to investigate the sources of polycyclic aromatic hydrocarbons (PAH) in diesel exhaust emissions is described. In separate experiments, ¹⁴C radiolabelled naphthalene, fluorene, fluoranthene and pyrene were each added to diesel fuel which was combusted in a 2L direct injection Perkins Prima diesel engine run at steady state under a series of speed (1000-3200 rpm) and load (20-80 N m) conditions. Each PAH was recovered in the exhaust emissions, using a novel sampling system, and its specific activity used to reveal the extent of its survival and pyrosynthesis of the PAH from other fuel fragments. Survival of the PAH varied from below detection limit for fluoranthene at low speed and load to 1.25% for fluorene at high speed and low load. For mid-speed and mid-load conditions, a linear relationship was observed between the extent to which individual PAH survived combustion and the energy level of the lowest unoccupied molecular orbital (LUMO) of the molecule calculated from Hückel molecular orbital theory. LUMO is an indirect parameter related to gas phase oxidation rates of PAH. Linearity was not so apparent at other speeds and loads. Resynthesis of the PAH varied from less than 0.1% for pyrene at mid-speed and mid-load to 4.93% for naphthalene at high-speed and high-load. Probable mechanisms for the production of some of the pyrosynthetic PAH were discussed.     

Synthesis and properties of aromatic ether phosphine oxide containing oligomeric phthalonitrile resins with improved oxidative stability

A series of multiple aromatic ether-linked phthalonitrile resins containing an aromatic ether phosphine oxide group in the backbone have been synthesized and characterized. The oligomeric phthalonitrile monomers were prepared from the reaction of an excess amount of either bisphenol A or resorcinol with bis(4-fluorophenyl)phenylphosphine oxide in the presence of K₂CO₃ in a N,N-dimethylformamide/toluene solvent mixture, followed by reacting with 4-nitrophthalonitrile in a two-step, one-pot reaction. Rheometric measurements and thermogravimetric analysis of the cured resins showed that the oligomeric phthalonitrile resins maintained good structural integrity upon heating to elevated temperatures and exhibited excellent thermal properties. When subjected to long-term oxidative exposures, the phosphorus-containing phthalonitriles showed superior performance and less oxidative damage compared to other aromatic-containing phthalonitrile resins. Scanning electron spectroscopy studies showed the formation of microcracks during the oxidative aging at elevated temperatures.     

Poly(9,9-dihexylfluorene) derivatives containing electron-transporting aromatic triazole segments: Synthesis, optical and electrochemical properties

We prepared three new poly(9,9-dihexylfluorene) derivatives (P1–P3) containing kinked aromatic triazole (triphenyl-1,2,4-triazole derivative) via Suzuki coupling polymerization. These copolymers were soluble in common organic solvents and showed high decomposition temperatures (T_d = 416–454 °C). The optical and electrochemical properties of P1–P3 were compared with poly(9,9-dihexylfluorene) (PFO) and P4 and P5 in which the linkages of the aromatic triazole were different. After introducing the triazole units, absorption spectra showed blue shift (388 nm → 372 nm) due to reduced conjugation, but PL spectra remained almost unchanged (417–418 nm). The linkages of triazole with fluorene segments in P1–P5 were different: (1) fluorene segments linked with triazole through a kinked angle (P1 and P2), (2) triazole as a branch unit (P3) and as terminal groups (P4), (3) fluorene segments linked with triazole in a linear way (P5). As estimated from semi-empirical MNDO calculation, two twisted conformations (ca. 90° each) exist between triazole core and fluorene groups. These kinked conformation and twisted structure increased the PL efficiency (Φ_PL = 0.60–0.73, Φ_PL = 0.58 for PFO) and partially inhibited annealing-induced excimer formation. From cyclic voltammetric results, P1–P3 exhibited better electron affinity (LUMO: −2.75 to −2.82 eV) than PFO (LUMO: −2.52 eV).     

Carbonization and liquid-crystal (mesophase) development. Part 3. Co-carbonization of aromatic and heterocyclic compounds containing oxygen, nitrogen and sulphur

A detailed investigation is reported of the effects upon size and shape of anisotropic mesophase structures in resultant semi-cokes of co-carbonizing eighteen oxygen-, nitrogen- or sulphur-containing compounds with fluorene, carbazole and acenaphthylene. Carbonizations were carried out under pressures of 130 to 320 MN m⁻² to a maximum heat-treatment temperature of 873 K, the mesophases being examined by optical and scanning electron microscopy. Additions of phthalimide, phthalic anhydride or pyromellitic dianhydride to fluorene and carbazole caused development of anisotropic carbon where none was formed on carbonization of the single compounds, or enhanced existing mesophase growth processes. Improvements in mesophase growth result in improved graphitizability of the semi-coke. Of the oxygen-containing compounds, the polycyclics with quinone groupings, or monocyclic molecules with several functional oxygen groupings, assist the growth of anisotropy. Phenol severely retards mesophase growth. Reasons are advanced which incorporate mechanisms of liquid-crystal formation. The implication for coal carbonization is that as the oxygen content in coals, on coalification, becomes increasingly attached to aromatic systems, then the oxygen in prime coking coals may actually enhance the growth of the mesophase during its carbonization. Nitrogen- and sulphur-containing compounds on co-carbonization with acenaphthylene at nitrogen or sulphur contents greater than 3% by weight may cause deterioration of mesophase growth. Such compounds do not significantly affect the carbonization of prime coking coals, but may contribute to the smallness of anisotropic structures in the carbons from coals of lower rank.     

Purification of hydrocarbons from aromatic sulfur compounds by supercritical carbon dioxide extraction

Supercritical carbon dioxide extraction to purify samples of model hydrocarbons (tetralin, decalin, and tetradecane) containing various aromatic sulfur compounds (benzothiophene, dibenzothiophene, and 4,6-dimethydibenzothiophene) was studied. The influence of extraction temperature and pressure was investigated for the extraction from a tetralin-dibenzothiophene system in the range of 293-353 K and 8-15 MPa, and it was found that the amount of tetralin extracted increased with an increase in carbon dioxide density, while the separation factor decreased with an increase in carbon dioxide density. High recovery and high separation factor values for the tetralin-dibenzothiophene system were obtained under 10 MPa at 313 K. Higher separation factor was obtained for tetralin than decalin and tetradecane, containing 4,6-dimethyldibenzothiophene than that containing dibenzothiophene.     

Hydrogen as a remedy for the detrimental effect of aromatic and cyclic compounds on the HC-SCR over Ag/alumina

The effect of hydrogen on the selective catalytic reduction of NO_x with n-octane, methylcyclohexane and toluene over a 2 wt.% Ag/Al₂O₃ was investigated. Diesel fuels contain, in addition to straight hydrocarbons, varying amounts of cyclic and aromatic compounds, which have a detrimental effect on the Ag/Al₂O₃ catalyst activity. The results showed that the NO to N₂ conversion was significantly promoted, independent of the nature (straight, cyclic or aromatic) of the hydrocarbon, in the presence of 1 vol.% H₂. The role of hydrogen is connected to a faster oxidation of the hydrocarbons and to enhanced formation of amines, which react with activated NO to form N₂.     

Determination of retention factors of aromatic compounds by gradient-elution reverse-phase high performance liquid chromatography

The retention mechanism of solutes under gradient conditions has been studied. Separation of a mixture of seven aromatic compounds in the two binary mobile phase, water/methanol and water/acetonitrile, was considered as an example. Retention factors were experimentally correlated by mobile phase composition. In this work, gradientdeviation time was newly introduced to compensate for ideal steep band along a column and experimentally determined by a linear equation form. An analytical expression in terms of the calculated retention factor and peak width was presented to predict the elution profile under gradient conditions. The calculated elution profile considered by the gradient-deviation time was closer to experimental data, and this mathematical model showed the feasibility of a predictive tool under gradient conditions.     

Pervaporation of Water/Ethanol Mixtures by an Aromatic Polyetherimide Membrane

Abstract

The pervaporation of water/ethanol mixtures through an aromatic polyetherimide membrane was attempted. The membrane was laboratory prepared using the solution casting technique. The sorption characteristics in relation to pervaporation were also studied. It was found that the preferential sorption was altered when the liquid composition was changed, whereas the water component permeated through the membrane preferentially over the whole range of feed mixture compositions. The experimental results were analyzed in terms of sorption ratio and permeation ratio to characterize nonideality of sorption and pervaporation. The effects of some operating parameters, including temperature, feed concentration, and permeate pressure, on the pervaporation performance were also investigated.     

Pervaporation Separation of Water/Ethanol Mixtures through Polycarbonate/Cobalt(III) Acetylacetonate Membranes

ABSTRACT

In the present work, cobalt(III) acetylacetonate [Co(acac)₃] was added to polycarbonate (PC) to improve its performance on pervaporation separation of water/ethanol mixtures. By adding 3 wt% of Co(acac)₃ the resulting PC/Co(acac)₃ complex membrane possessed a permeation rate similar to a pure polycarbonate membrane, but the separation factor (water/ethanol) was about three times higher. The stability of the complex membrane was tested, and it was found that, after being immersed in an aqueous ethanol solution for 72 hours, the complex membrane was still stable. In addition, the effects of the added amount of Co(acac)₃ and the feed composition on pervaporation performance are presented in this work, and the mechanism of the improvement in pervaporation performance is briefly discussed.     

Efficient separation scheme for binary mixture of CO2 and H2S using aromatic components

Separating a mixture of CO₂ and H₂S into two products through distillation is both difficult and complicated because of similar relative volatility between the two gasses, particularly when a CO₂ concentration exceeds 80%. Therefore, the separation process can involve many separating stages. However, adding a solvent (agent) to the distillation column during the separation process makes this procedure easier.

In this study, different solvents (ethylbenzene, o-xylene, m-xylene, and toluene) and operating conditions (temperature, pressure, and reflux ratio) for separating CO₂ from H₂S have been simulated through distillation using Aspen HYSYS software. Furthermore, four different aromatic compounds (solvents) for different concentrations (from 0 to 40 mol%) have been evaluated to increase the CO₂/H₂S relative volatility, reducing the quantity of the solvent required and energy consumption.

m-xylene was found to be the best solvent for separating CO₂ from H₂S because of the significant effect on relative volatility, the low quantity required for high CO₂ recovery, and the low energy for generating the solvent.