Separation Of Aromatic Compounds Research Articles

Multipolar/polarizable molecular dynamics simulations of Liquid–Liquid extraction of benzene from hydrocarbons using ionic liquids

Separation of aromatic compounds from aromatic/aliphatic mixtures using various solvents has been a field of intense studies. One possibility for this separation is liquid–liquid extraction using room temperature ionic liquids (ILs) as solvent. Computational simulations using classical molecular dynamics (MD) calculations provide a viable approach to investigate these processes. Due to the highly charged nature of the solvent, an accurate force field is needed to accurately describe the inter–molecular interactions between the different mixture components. Here, we present the use of the multipolar/polarizable force field AMOEBA to explore the capacity of 1,3-dimethylimidazolium tetrafluorobrorate, [DMIM][BF4], and ethyl-methylimidazolium tetrafluorobrorate, [EMIM][BF4], to extract benzene from a mixture of benzene-dodecane. Our results indicate that [DMIM][BF4] exhibits a better capacity of extracting benzene than [EMIM][BF4]. Detailed structural and selectivity/distribution ratio analysis are provided based on our simulations to gain further insights on the different systems.

Preparation of a poly(1, 6-hexylene dimethacrylate) conventional size high performance liquid chromatographic monolithic column for separation of small molecules

A porous monolithic column was prepared by in situ free-radical polymerization in a stainless steel column (4.6 mm i.d. × 100 mm). The polymerization reacted using 1,6-hexylene dimethacrylate as single crosslinking monomer, methanol and 1-dodecanol as the binary porogens and 2,2-azobisisobutyronitrile asinitiator. During the column preparation process, the ratio of monomer to porogen was optimized to obtain the best column. The chemical groups and morphology of monolithic column were characterized by the Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. Furthermore, the influence of mobile phase composition and flow rate on the separation of aromatic compounds was investigated.The results showed that the poly(1,6-hexylene dimethacrylate) monolithic column had high mechanical stability at flow rate of 4 mL/min. Phenol, 1-naphthol, biphenyl and phenanthrene were easily separated on the prepared monolithic column using acetonitrile/water (58/42, v/v) as mobile phase at flow rate of 2 mL/min. The relative standard deviation of run-to-run and column-to-column of the retention times for the four standard compounds were <0.3% and 3.3%, respectively. Three kinds of small molecules (phenols, aromatic hydrocarbons, aromatic acids) were successfully separated on the poly(1,6-hexylene dimethacrylate) monolithic column. The possible chromatogramphic retention mechanism on poly(1,6-hexylene dimethacrylate) monolithic column was determined as hydrophobic interaction and dipole-dipole interaction. The conventional size poly(1,6-hexylene dimethacrylate) monolithic column has potential to separate small molecule compounds rapidly by high performance liquid chromatography.

Synthesis of Large-Pore Silica Microspheres Using Dodecylamine as a Catalyst, Template and Porogen Agent

This paper reports a strategy combing a modified Stober method and a post-hydrothermal treatment for the fabricating of silica microspheres with large pores. Dodecylamine (DDA), used as a catalyst, template and porogen agent, plays an important role in controlling both the particle morphology and the pore expansion. By adjusting the concentration of DDA (20, 40 and 80 mmol/L) and the temperature of hydrothermal treatment (80–140 °C), the pore size ranging from 3.5 to 16 nm could be obtained. The synthesized sub-2 µm silica spheres were modified with dimethyloctadecylchlorosilane (C18) and successfully applied for the separation of aromatic compounds in high-performance liquid chromatography (HPLC). The silica may be a good candidate as HPLC packing materials.

Separation of aromatic components from light cycle oil by solvent extraction

ABSTRACTTo improve the versatility of light cycle oil (LCO), separation of aromatic compounds from LCO by solvent extraction was investigated. LCO was analyzed to identify 35 components: 19 aromatics and 16 alkanes. The batch liquid–liquid equilibrium extraction of LCO was performed using furfural, sulfolane, and methanol as extraction solvents. In each solvent, the aromatics present in LCO were selectively extracted relative to the alkanes. The separation selectivities of aromatics relative to alkanes were larger in sulfolane than in the other solvents. Among the aromatic components, di- and tricyclic compounds were selectively extracted relative to the monocyclic ones.

Liquid–Liquid Equilibria Data for Ethylbenzene or p-Xylene with Alkane and 1-Butylpyridinium Nitrate Ionic Liquid at 298.15 K

Liquid–liquid equilibrium data (LLE) for the mixtures of ionic liquid (IL) + alkane + aromatic {1-butylpyridinium nitrate, [BPy][NO3] (1) + heptane, octane, or decane (2) + ethylbenzene (3)} and {[BPy][NO3] (1) + heptane, octane, or decane (2) + p-xylene (3)} at T = 298.15 K and P = 89 Kpa were measured. The degree of reliability of the experimental LLE data was examined by using the Othmer-Tobias and Hand correlation. For the six studied ternary mixtures, the separation factor and distribution ratio of aromatic hydrocarbons derived from LLE data and were applied to determine if [BPy][NO3] can be used as dearomatization solvent. The separation of aromatic compounds with similar molecular weight (ethylbenzene and p-xylene) from alkanes demonstrates that p-xylene can be separated more easily from alkanes. The triangular phase diagrams for all studied systems were sketched, and the tie lines were compared with the NRTL model.

Separation of Aromatic Compounds from Hydrocarbon Mixtures by Vapor Permeation Using Liquid Membranes with Ionic Liquids

Separation of Aromatic Compounds from Hydrocarbon Mixtures by Vapor Permeation Using Liquid Membranes with Ionic Liquids

In English

Aromatic compounds are organic contaminants in aqueous streams of various industries. Even at low concentration, benzene and its derivatives are toxic agents. Silicas are promising materials for benzene and phenol adsorption from water mixtures due to their unique physical and chemical properties. In this research, we realized sol-gel synthesis of β-cyclodextrin-MCM 41 silica using β-cyclodextrin-containing silane and tetraethyl orthosilicate as silica sources in the presence of ionic template (cetyltrimethylammonium bromide). β-Cyclodextrin-silane was prepared by modification of (3 aminopropyl)triethoxysilane with oligosaccharide activated by N,N'-carbonyldiimidazole. The successful incorporation of β-cyclodextrin moieties in silica is verified by means of FT-IR spectroscopy and quantitative chemical analysis. Obtained β-cyclodextrin-MCM 41 silica was characterized by X-ray diffraction, transmission electron microscopy, and low-temperature adsorption-desorption of nitrogen. On the basis of analysis, β-cyclodextrin-MCM 41 silica is well-ordered mesoporous material with high surface area (about 800 m 2 g –1 ) and sufficient oligosaccharide group loading (up to 0.022 µmol m –2 ). Adsorption of benzene and phenol from aqueous solutions on β-cyclodextrin-MCM 41 silica was studied as the function of time and equilibrium concentration. Greater specificity of aromatic compounds adsorption for β-cyclodextrin-MCM-41 silica in comparison with MCM-41 was demonstrated. Moreover, the higher adsorption performance of β cyclodextrin MCM 41 silica towards benzene and their adsorptive affinity to phenol can be useful in the separation of aromatic compounds. The proposed synthesis approach may be applicable for obtaining of ordered β-cyclodextrin-containing functional materials with high affinity to aromatic compounds of suitable geometry for water treatment.

SEPARATION OF AROMATIC INTERMEDIATES OF BIOLOGICAL INTEREST USING EMULSION LIQUID MEMBRANES

Established applications of emulsion liquid membranes (ELM) refer to refining in hydrocarbons and hydrometallurgical processing, rehabilitation of poisoned patients. In this work we investigated the separation of aromatic compounds of biological interest, more often encountered as intermediates in dyes and drugs industry: aniline, nitrobenzene, ortho and para-toluidine, using emulsion liquid membranes. The experimental results showed that in the case of basic substances separation the main physicochemical characteristics which have to be considered are alkalinity and water solubility. Thus, for the liquid emulsion membranes operation it is preferred to have a basicity as high as possible and a solubility as low as possible.

High-performance liquid chromatography separation of small molecules on a porous poly (trimethylol propane triacrylate-co-N-isopropylacrylamide-co-ethylene dimethacrylate) monolithic column

A porous monolith was prepared by in situ free-radical polymerization using N-isopropylacrylamide (NIPAAm) and trimethylol propane triacrylate (TMPTA) as functional monomers, ethylene dimethacrylate (EDMA) as crosslinking agent. The chemical group of the monolith was assayed by a Fourier transform infrared spectroscopy (FT-IR) method and the morphology of optimized monolithic column was characterized by scanning electron microscopy (SEM). The mechanical strength and permeability have been studied in detail as well. The run-to-run and column-to-column reproducibility of the retention times were less than 0.9% and 3.0%, respectively. Furthermore, the influence of temperature and mobile phase composition on the separation of aromatic compounds was investigated. The results indicated that poly (trimethylol propane triacrylate-co-N-isopropylacrylamide-co-ethylenedimethacrylate) (TMPTA-co-NIPAAm-co-EDMA) monolithic column not only had high porosity and strong rigidity, but also was a promising tool for analyzing small molecule compounds with a short analysis time by controlling the column temperature.

Preparation and retention mechanism study of graphene and graphene oxide bonded silica microspheres as stationary phases for high performance liquid chromatography

Graphene oxide (GO) bonded stationary phase for high performance liquid chromatography (HPLC) was fabricated by coating GO sheets onto aminosilica microspheres via covalent coupling. Graphene (G) functionalized HPLC stationary phase was then prepared through hydrazine reduction of GO bonded silica (GO@SiO2) composite, which was the first example of using graphene as stationary-phase component for HPLC. Effective separations of the tested neutral and polar compounds on both GO@SiO2 and graphene bonded silica (G@SiO2) columns were achieved under the optimal experimental conditions. Compared with commercial C18 column, the different chromatographic performances of GO and graphene bonded columns were ascribed to their unique retention mechanisms. The polyaromatic scaffold of GO and graphene gives π–π stacking property and hydrophobic effect, and other retention mechanisms, such as π–π electron-donor–acceptor (EDA) interaction for the separation of nitroaromatic compounds and hydrogen bonding for hydroxyl and amino compounds, may also be taken into consideration. Experimental results indicated that the mixed-mode retention mechanism can facilitate the separation of analytes with similar hydrophobicity, which is a unique property compared with C18 column. Additionally, G@SiO2 showed higher affinity to aromatic analytes in contrast with GO@SiO2 and its retention mechanism was not consistent with the typical reversed phase behavior. The separation of aromatic compounds on G@SiO2 column relies primarily on the π–π stacking interaction and then the hydrophobicity, while the two interactions have equal shares on GO@SiO2 column.

A novel sorbent for chromatographic separations: A silica matrix modified with non-covalently bonded tetrakis(β-cyclodextrin)-porphyrin conjugates

We prepared new phases for LC that consisted of silica modified with non-covalently bonded tetrakis(β-cyclodextrin)-porphyrin (where cyclodextrin is CD) conjugates. The effects of the porphyrin core, type of spacer and β-CD moieties on the behaviours of the modified phases for the separation of aromatic compounds (benzene, toluene, ethylbenzene, propylbenzene, butylbenzene, pentylbenzene, o-terphenyl, triphenylene, phenol and caffeine) and fluorinated aromatic compounds (pentafluorobenzonitrile, pentafluoronitrobenzene and hexafluorobenzene) were studied using the Tanaka test. The results indicate that the non-covalent substitution of silica with CD-based macromolecules that have a porphyrin core can be a very effective method for preparing novel sorbents with specific chromatographic properties for applications in LC.

Recent advances in preparation of novel chromatographic stationary phases with carbon nanotubes

Carbon nanotubes (CNTs) as a new functional material have attracted the interest of scientists and engineers in analytical chemistry, due to their excellent physical, chemical and mechanical properties. The preparation of chromatographic stationary phases with CNTs has been performed by packing method or in situ catalytic chemical vapor deposition. The deposition of CNTs on a chromatographic solid matrix (e. g. silica micro-particles or organic polymer microspheres) was carried out to generate a packing material for high performance liquid chromatography. Capillary monolithic columns for liquid chromatography were also prepared by embedding CNTs in polymer monolithic columns. Columns with CNTs have the unique advantages in the separation of aromatic compounds for the tr electron system of CNTs. Herein, the recent applications of CNTs in the preparation of chromatographic stationary phases are reviewed, including gas chromatography and liquid chromatography. The future developments in this field are also prospected.

Effect of the Chain Length on the Aromatic Ring in the Separation of Aromatic Compounds from Methylcyclohexane Using the Ionic Liquid 1-Ethyl-3-methylpyridinium Ethylsulfate

Liquid−liquid equilibrium (LLE) data for the ternary systems methylcyclohexane + benzene + 1-ethyl-3-methylpyridinium ethylsulfate, methylcyclohexane + toluene + 1-ethyl-3-methylpyridinium ethylsulfate, and methylcyclohexane + ethylbenzene + 1-ethyl-3-methylpyridinium ethylsulfate are reported under atmospheric pressure and at T = 298.15 K. The selectivity, the percent removal of aromatic compound, and the distribution coefficient were calculated from the LLE data, and the influence of the presence of radicals in the benzene ring were analyzed. The reliability of the experimental LLE data was ascertained using the Othmer−Tobias and Hand equations. The nonrandom two-liquid (NRTL) model was used to correlate the experimental data for the ternary systems. A search of the literature has indicated that data for the mixtures presented here have not been reported previously.

Extraction of toluene, o-xylene from heptane and benzyl alcohol from toluene with aqueous cyclodextrins

The separation of aromatic compounds (toluene and o-xylene) from heptane and of benzyl alcohol from toluene with aqueous solutions of cyclodextrins has been experimentally investigated, because cyclodextrins and its derivatives can selectively incorporate several organic compounds, whereas the separation of the aqueous solution of complexed cyclodextrins from the organic feed is simple. Cyclodextrins are not soluble in organic liquids, but cyclodextrin derivatives are highly soluble in water. Hydroxypropyl-β-cyclodextrins with different degrees of substitution and methylated β-cyclodextrin were selected for the extraction of toluene and o-xylene from heptane. Hydroxypropyl-β-cyclodextrin (two different substitution degrees) and hydroxypropyl-α-cyclodextrin were selected for the extraction of benzyl alcohol from toluene. The liquid–liquid distribution experiments were carried out at room temperature. Toluene and o-xylene form 1:1 complexes with different cyclodextrins and heptane can form 1:1 to 1:3 complexes. Benzyl alcohol forms 1:3 complexes with hydroxypropylated cyclodextrins. The models developed describe the experimental data reasonably well, considering the large deviations in the analyses. Aqueous cyclodextrin solutions are not feasible for the separation of aromatic components from aliphatic hydrocarbons, due to low distribution ratios of toluene (0.05) and o-xylene (0.023) between the aqueous and organic phase. With high distribution ratios of benzyl alcohol, between 0.3 and 2.2 depending on the CD concentration (at a solvent-to-feed ratio of 1) and a benzyl alcohol/toluene selectivity of at least 100, aqueous hydroxypropylated cyclodextrin solutions have sufficient potential for extracting benzyl alcohol from toluene.

Reversed-Phase Electrochromatography with a Monolithic Microcolumn Prepared in a 2.2-mm-Inner Diameter Fused-Silica Tube

Capillary electrochromatography possesses advantages of high separation efficiency and velocity, but it also has its disadvantages due to its small inner diameter, such as poor detection sensitivity, low sample capacity, and some trouble in its column preparation. To overcome these shortcomings, a monolithic microcolumn with a surface area larger than 200 m2/g was prepared by sol-gel polycondensation of tetraethoxysilane-hydrochloric acid-poly(ethylene glycol) and filling with fine quartz sand in a 2.2-mm-i.d. fused-silica tube. The prepared microcolumn was used in the separation of aromatic compounds by reversed-phase electrochromatography. Some factors that affected electroosmotic flow were explored, such as electric field strength, buffer concentration, and buffer pH. Acetonitrile concentration in the mobile phase was investigated for phenol, benzene, and naphthalene separation. The separation results were satisfying with the electrochromatographic microcolumns. The detection limits of phenol, benzene, and naphthalene were 0.07, 0.26, and 0.04 mg/L, respectively.

Monolithic columns with mixed modes of reversed-phase and anion-exchange stationary phase for capillary electrochromatography

A capillary electrochromatography (CEC) monolithic column with mixed modes of reversed-phase and anion-exchange stationary phases was prepared by in situ polymerization of 2-(methacryloxy)ethyltrimethylammonium methyl sulfate (MEAMS) and ethylene dimethacrylate (EDMA) in a binary porogenic solvent consisting 1-propanol and 1,4-butanediol. The ammonium groups on the surface of the stationary phase generate an electroosmotic flow (EOF) from cathode to anode, and serve as a strong anion-exchange stationary phase at the same time. The EOF of the stationary phase can be determined by the amount of MEAMS monomer in reaction mixtures during the polymerization. The monolithic stationary phases exhibited reversed-phase chromatographic behavior toward neutral solutes. For charged solutes, hydrophobic as well as electrostatic interaction/repulsion with the monoliths was observed. Separations of aromatic compounds and basic compounds on the prepared column were performed under the mode of CEC. Peak tailing of basic compounds was avoided and the efficient separation of aromatic acids was achieved using neutral mobile phase due to the same direction of EOF and electrophorestic mobility of negatively charged solutes.

Separation of Polycyclic Aromatic Compounds from Model Gasoline by Magnetic Alumina Sorbent Based on π-Complexation

Magnetic alumina sorbent was used in the separation of aromatic compounds from gasoline by a π-complexation mechanism. Magnetic alumina sorbents can effectively adsorb polycyclic aromatics and polycyclic aromatic sulfur compounds from model gasoline, and the amounts adsorbed were up to 0.12 mmol·(g of sorbent)-1. The interactions between various aromatics and sorbents of different acidities were studied. The results showed that the amounts adsorbed are related to the capability of forming π-complexation interactions, and the magnetic alumina sorbent used was found to have the following order of adsorptive ability for aromatics: pyrene > naphthalene > DBT ≈ fluorene. Al3+ and its oxide are Lewis π-acids, and aromatic compounds are Lewis π-bases; thus, they can form π-complexes with each other. The π-complexation was verified by fluorescence spectrum. The quenching of the fluorescence of pyrene by Al3+ was due to partial π-electron transfer from pyrene to the cation according to Lewis theory and fluorescen...

Thermodynamic Modeling and Experimental Studies of Dearomatization Process from a Complex Petroleum Fraction

Experimental studies and thermodynamic modeling for the separation of aromatic compounds from a complex mixture of hydrocarbons have been carried out. The sample used in this work is the main material for producing lubricating oils, and the solvent used for extraction of aromatic components is a new selective solvent which has unique specifications in comparison with conventional solvents such as furfural. This modeling is based on the method of Ruzicka for making model molecules. The parameters required for modeling were obtained, and then liquid–liquid equilibrium calculations were done and compared with the experimental data. These calculations were also carried out using published parameters for the vapor–liquid equilibria of the components involved in the mixture. The results have been compared with the previous calculations as well as with the experimental data, and good agreement was found.

Spherical Clay Conglomerates: A Novel Stationary Phase for Solid-Phase Extraction and “Reversed-Phase” Liquid Chromatography

A new solid phase is presented to be used for the solid-phase extraction (SPE) of organic compounds from aqueous solutions and as a stationary phase for the separation of organic compounds in "reversed-phase" HPLC. The material consists of spherical clay conglomerates (SCCs) in the size ranges of 2-5, 5-10, and 10-20 μm. SCCs are especially well suited for the extraction and separation of aromatic compounds with electron-withdrawing substituents, because of the formation of specific electron donor-acceptor (EDA) complexes of such compounds with natural clay minerals. A series of nitroaromatic compounds (NACs), e.g., nitrophenols, and nitrotoluenes, served as probe substances for the characterization of the SPE with SCCs online coupled to a C18-HPLC-DAD system. Breakthrough volumes were > 1 L and method detection limits (MDLs) < 100 ng/L for compounds with moderate to high affinity towards clay minerals. The performance of the material is hardly affected by matrix effects and because of its excellent physical properties, i.e., regenerability and pressure-resistance, it meets the requirements for fully automated routine trace analysis of several primary pollutants, such as 6-methyl-2,4-dinitrophenol (DNOC) or 2,4,6-trinitrotoluene (TNT), in various natural waters. Offline SPE with SCCs was superior or equivalent to commercial SPE products for analysis of such compounds. Finally, SCCs are shown to be well suited as a stationary phase in reversed-phase HPLC. This opens a wide range of applications, e.g., as an easy and fast separation technique that is orthogonal to C18 reversed-phase HPLC.

Separation of Aromatic Compounds Using Retrograde Crystallization in Supercritical Fluid.

We measured the solubilities of pure solids of anthracene, fluorene, acridine, and binary solid mixtures of phenanthrene+anthracene, fluorene+acridine in supercritical CO2 to determine the appropriate conditions for purification of polycyclic aromatics or heterocyclic compounds using a retrograde crystallization technique. Moreover we attempted to separate specific compounds from these two solid mixtures. As a result, it was found that (1) the crossover region of 2 kinds of solid mixtures in supercritical CO2 was sufficiently wide to isolate the solid component from the mixture; (2) the Peng-Robinson equation of state gave good predictions for solubilities of pure solids but gave poor predictions for those of the solid mixtures in supercritical CO2; and (3) phenanthrene, fluorene and acridine of high purity were separated from the solid mixtures, but anthracene was not as its amount predicted from the solubility data was very small.