Carbon Dioxide Methanol Research Articles

Characterization of five chemistries and three particle sizes of stationary phases used in supercritical fluid chromatography

Sub-2-microns particles employed as supporting phases are known to favor column efficiency. Recently a set of columns based on sub-2-microns particles for use with supercritical fluid mobile phases have been introduced by Waters. Five different stationary phase chemistries are available: BEH silica, BEH Ethyl-pyridine, XSelect CSH Fluorophenyl, HSS C18 SB and BEH Shield RP18. This paper describes the characterization of 15 stationary phases, the five different chemistries, and three particle sizes, 1.7 (or 1.8), 3.5 and 5 microns, with the same carbon dioxide–methanol mobile phase and a set of more than a hundred compounds. The interactions established in the 15 different chromatographic systems used in supercritical fluid chromatography (SFC) are assessed with linear solvation energy relationships (LSERs). The results show the good complementarity of the five column chemistries, and their comparative location inside a classification map containing today around 70 different commercial phases. Among the five different chemistries, the HSS C18 SB phase displays a rather unusual behavior in regards of classical C18 phases, as it displays significant hydrogen–bonding interactions. Besides, it appears, as expected, that the BEH Ethyl–pyridine phase has weak interactions with basic compounds. The effect of particle size was studied because smaller particles induce increased inlet and internal pressure. For compressible fluids, this pressure change modifies the fluid density, i.e. the apparent void volume and the eluting strength. These changes could modify the retention and the selectivity of compounds in the case of method transfer, by using different particle sizes, from 5 down to 1.7μm. A hierarchical cluster analysis shows that stationary phase clusters were based on the phase chemistry rather than on the particle size, meaning that method transfer from 5 to 1.7 microns can be achieved in the subcritical domain i.e. by using a weakly compressible fluid.

Separation of 9 Sulfonamide Drugs in ≈4 Min by Ultra-High Performance Supercritical Fluid Chromatography (UHPSFC): with a Feasibility Study for Detection in Milk

Nine widely used veterinary sulfonamide drugs were baseline separated (R s ≥1.5) in just over 4 min using a 3 × 100 mm, 1.8 μm RX-Sil column, with 9.2 % methanol in carbon dioxide, at 110 bar and 30 °C, with direct UV detection at 260 nm using a 3 mm, 2 μL tapered flow cell. Pressure drop was only 172 bar. Optimization was difficult due to the similarity in structures. Small changes in modifier concentration, temperature and pressure, each tended to improve the resolution of some peak pairs but degraded the resolution of others. There were four critical pairs, each responding differently to changes in conditions. Optimization was performed by plotting resolution between pairs as a function of modifier concentration first, temperature second, and outlet pressure third. Retention time was then minimized by changing flow rate. The estimated limit of quantitation (LOQ, S/N >10), for direct injections, was ≈200–400 ng/g of each, inadequate for regulatory requirements. Solid phase extraction (SPE) attempted to pre-concentrate samples spiked with sulfamethazine by ≈20:1. From water, the limit of detection (LOD) was ≈2.7 ng/mL with LOQ ≈9 ng/mL using UV at 260 nm. The LOD for milk was 6.2 ng/mL, and LOQ was 20.1 ng/mL. A better pre-concentration step or a more sensitive detector such as MS–MS is required. Even with these inadequacies, SFC was shown to be a feasible, faster, “greener” alternative to HPLC for the separation of these drugs.

Modelling of retention in analytical supercritical fluid chromatography for CO2—Methanol mobile phase

Mathematical modelling of the chromatography process requires knowledge of the isotherm model. Therefore a necessary step in calculations is estimation of the isotherm model parameters. In this study the inverse method has been successfully used to estimate the linear isotherm model parameters in supercritical fluid chromatography (SFC). Estimation was based on measured retention times of experimental band profiles. The solute was n-octadecylbenzene. The mobile phase was carbon dioxide–methanol, 95/5% (v/v), and the column was 250mm×4.6mm i.d. packed with 5-micron Luna C18(2) particles. The experiments were done for outlet pressures from 100bar to 150bar at different flow rates and different sets of experimental conditions: (1) column operated under convective air (CA); (2) column operated in still air conditions. Moreover in the latter thermal mode were considered two cases. In the first case the temperature of the oven air was different from the inlet temperature of the mobile phase. In the second case the temperature of the oven air was the same as inlet temperature of the mobile phase. The column efficiency was also analysed.

Optimization of enzymatic biodiesel synthesis using RSM in high pressure carbon dioxide and its scale up

Enzymatic synthesis of biodiesel by the transesterification of canola oil and methanol in high pressure carbon dioxide [HPCO(2): near-critical and supercritical carbon dioxide (NcCO(2) and ScCO(2))] was optimized using response surface methodology (RSM). RSM based on 5-level-5-factor central composite rotatable design (CCRD) was used to evaluate the effects of temperature, pressure, enzyme loading, substrate molar ratio, and time on the conversion to biodiesel by transesterification. Finally, batch reactions for biodiesel synthesis were preformed in a 100 mL and 7 L high-pressure stirred batch reactors.

Review and advances of direct methanol fuel cells (DMFCs) part I: Design, fabrication, and testing with high concentration methanol solutions

A review of the experimental studies on passive and semi-passive direct methanol fuel cells (DMFCs) is conducted, with an emphasis on high concentration methanol and pure methanol. Key issues such as methanol transport, water management, oxygen transport, and carbon dioxide release in the DMFC are analyzed in detail. The design and fabrication, development approaches, challenges and opportunities on DMFCs passively fed with high concentration methanol are discussed. The advances of DMFC stacks and prototype developments are presented. Several unresolved issues and challenges in DMFCs are identified and reviewed in detail.

Experimental measurements and predictions of density, viscosity, and carbon dioxide solubility in methanol, ethanol, and 1-propanol

The solubilities of carbon dioxide in different alcohols, methanol, ethanol, and 1-propanol, were measured at two different temperatures (303.2 and 323.2)K and pressures up to 6MPa. The experimental data of saturated alcohol density and viscosity were also reported at each temperature and pressure. The solubility data shows that the solubility of carbon dioxide in alcohol increases with pressure and decreases with temperatures in the studied pressure and temperature ranges. The higher dissolution of carbon dioxide in alcohols resulted in increase in the saturated liquid densities and decrease in saturated liquid viscosities. The experimental solubility as well as saturated liquid density data were predicted with two cubic equations of state (EOS), Peng–Robinson (PR) and Soave–Redlich–Kwong (SRK). The modeling results demonstrated that both equations of state correlated the solubility data well over the studied pressure and temperature ranges. However, the saturated liquid densities calculated with the SRK EOS were much better than those of PR EOS.

Characterization and use of hydrophilic interaction liquid chromatography type stationary phases in supercritical fluid chromatography

All stationary phase chemistries are useful to achiral packed-column supercritical fluid chromatography (pSFC), but the majority of recent applications are based on polar stationary phases of the type used in normal-phase HPLC. Some manufacturers have recently introduced pSFC-tailored stationary phases, while others simply advocate the use of selected HPLC columns among their brands for SFC use. Indeed, any column developed for HPLC use can be used with supercritical fluids. Besides, hydrophilic interaction liquid chromatography (HILIC) is facing an increasing interest. Consequently, a number of HILIC-devoted stationary phases are now commercialized by most column manufacturers. As HILIC stationary phases are polar, their possible use in pSFC seems obvious, although literature examples are not numerous. However, whether they provide acceptable peak shapes in SFC conditions is a serious concern for them to find applicability. Indeed, columns optimized for HILIC mobile phases may not be optimum for SFC mobile phases. We present the characterization of eleven HILIC-type stationary phases used with carbon dioxide–methanol mobile phases in the isocratic mode. The columns are compared in terms of their retention and separation characteristics assessed by the solvation parameter model, and based on peak shapes. For this purpose, hundred and forty-six low molecular weight molecules, comprising neutral, basic and acidic compounds, were eluted on each column. Data analysis is carried out with hierarchical cluster analysis and principal component analysis in order to define three clusters of columns with similar selectivity: the first cluster comprises neutral stationary phases like amide and diol phases; the second one comprises basic stationary phases like aminopropyl-bonded silica; the last cluster comprises bare silica stationary phases. Sample applications with three different test mixtures relevant to pharmaceutical applications (barbiturates, benzodiazepines and propionic acids) are presented to assess the complementarity of some selected columns.

Methanol electrocatalytic oxidation on highly dispersed platinum–ruthenium/graphene catalysts prepared in supercritical carbon dioxide–methanol solution

An effective, simple, low temperature and environmentally benign supercritical fluid (SCF) route is presented for preparing graphene-supported metal nanoparticles. With the assistance of supercritical carbon dioxide (SC CO2), ultrafine PtRu nanoparticles with an average size of 2.87 nm were very uniformly distributed on the surfaces of functionalized graphene sheets (FGSs) by the reduction of a mixture of H2PtCl6 and RuCl3 precursors. The catalytic property of the as-prepared composites for methanol oxidation was investigated by cyclic voltammetry and chronoamperometry. In comparison with their carbon black (Vulcan XC-72) counterparts, the PtRu/FGSs composites showed considerably improved catalytic activity and stability for methanol oxidation. The high surface area of graphene and even distribution of ultrafine bimetallic particles are vital for the superior electrocatalytic performance of the PtRu/FGSs composites. The findings suggest that highly efficient graphene-supported metallic electrocatalysts can be fabricated by the supercritical fluid method and graphene as a favorable electrocatalytic carrier, which has promising potential application in direct methanol fuel cells.

Characterization of sample preparation of Prozac® capsules using enhanced fluidity liquid extraction

Enhanced Fluidity Liquid Extraction (EFLE) using carbon dioxide–methanol mixtures as the mobile phase is explored for its ability to extract Fluoxetine-Hydrochloride, the active pharmaceutical ingredient in Prozac® capsules. Optimum conditions for extracting the pure compound were found using a 50% carbon dioxide–50% methanol mobile phase. Co-extraction and/or interference from common excipients such as starch, lactose, and micro-crystalline cellulose was not observed. However, mannitol excipient was found to significantly reduce the EFLE extraction efficiency of Fluoxetine-Hydrochloride. Employing an extraction temperature of 80 °C, a pressure of 375 atm, and a flow rate of 3.5 mL min−1, produced an extraction recovery of Fluoxetine-Hydrochloride from Prozac® capsules of 99 ± 2% in just 3 minutes using only about 5 mL of total methanol. When a static modifier mode was employed under similar conditions, it was found that only 400 μL of methanol added to the vessel prior to extraction with pure carbon dioxide resulted in a Fluoxetine-Hydrochloride recovery of 98 ± 8% after only 5 minutes. In contrast to EFLE results, Fluoxetine-Hydrochloride extractions performed using pure room temperature methanol were 3 to 5 times longer and produced extracts that contained significant amounts of starch excipient that was also co-extracted from the Prozac® capsules. These findings indicate that EFLE may be a useful alternative sample preparation method for Fluoxetine-Hydrochloride, and possibly other pharmaceuticals, that can greatly reduce time and solvent usage in the process.

Selective hydrogenation of styrene oxide to 2-phenyl ethanol over polyurea supported Pd–Cu catalyst in supercritical carbon dioxide

2-Phenyl ethanol (2-PEA) is an important chemical which finds several applications in perfumes, deodorants, soaps and detergents. It is prepared by different polluting and dangerous routes. The current work is concerned with production of 2-PEA by hydrogenation of styrene oxide using polyurea encapsulated catalysts (EnCat) in methanol and supercritical carbon dioxide (scCO 2). Bimetallic Pd–Cu catalyst encapsulated with polyurea, Pd–Cu EnCat, is the best catalyst. The epoxide ring in styrene oxide is selectively hydrogenated to give 2-PEA in scCO 2 without formation of any isomerization or deoxygenated products, which are formed in methanol. A complete conversion of styrene oxide with 100% selectivity to 2-PEA was obtained without addition of any promoter. Effects of various parameters were studied and a bifunctional site Langmuir–Hinshelwood–Hougen–Watson kinetic model was found to be in good agreement with the experimental data. The process is clean and green.

Compact apparatus for rapid measurement of high-pressure phase equilibria of carbon dioxide expanded liquids

A new apparatus based on a synthetic method was developed for phase equilibrium measurements. The characteristic features of the apparatus are its light weight (ca. 288 g), variable-volume with a free piston, position sensing device for the piston, precise pressure and temperature control, and a window for visual observation. The inner volume of the cell can vary from 2.5 to 8.8 cm 3. The cell was constructed from titanium so that the composition of the sample can be determined by direct weighing of the cell. The apparatus was designed for temperatures up to 473 K and pressures up to 25 MPa. To confirm the reliability of the apparatus, vapor–liquid equilibria of the carbon dioxide–methanol system were measured. The estimated uncertainties of temperature, pressure, and composition of carbon dioxide were less than ±0.05 K, ±0.02 MPa, ±0.20 wt%, respectively. Bubble-point pressures obtained in this work agreed well with the literature data. Bubble-point pressure data for carbon dioxide with acetone, methyl ethyl ketone (MEK), and methyl isobutyl ketone (MIBE) were measured at temperatures ranging from 313 to 353 K, and could be correlated well with the Peng–Robinson equation of state. The P– x diagrams at a given temperature for acetone, MEK, and MIBK binaries with carbon dioxide were found to be practically identical.

New perfluorinated rhodium–BINAP catalysts and hydrogenation of styrene in supercritical CO 2

New perfluorinated BINAP ligands and their cationic rhodium complexes have been synthesized and characterized. The catalysts have been tested in homogeneous hydrogenation of the styrene in both methanol and supercritical carbon dioxide (scCO 2). The selective hydrogenations of the styrene in scCO 2 were carried out under the same reaction conditions of 343.15 K temperature and 120 bar CO 2 pressure after 3 h (molar ratio of substrate to catalyst = 500). While all catalysts showed 100% conversion in methanol, same activity was not carried out in scCO 2. (R)-6, 6′ -diperflorooktil-2, 2′ -bis(diphenylphosphino)-1, 1′ -binaphtyl-[Rh(COD)]BArF was showed the highest conversion (96.4%) in scCO 2. Furthermore, methanol was used as co-solvent in the supercritical media in hydrogenation of styrene for the perfluorinated catalysts, which were inactive in scCO 2. Addition of methanol in scCO 2 has rather increased the conversion.

Methanol assisted selective formation of 1,2-glycerol carbonate from glycerol and carbon dioxide using nBu 2SnO as a catalyst

Selectively 1,2-glycerol carbonate was obtained from glycerol and carbon dioxide in methanol using 1 mol% n Bu 2SnO (dibutyltin(IV)oxide, 1) as a catalyst. The reaction attained equilibrium in 4 h and the yield of 1,2-glycerol carbonate obtained was as high as 35%. We observed the rate of the reaction depends on the amount of the catalyst and methanol used. During the reaction we could trap the intermediates and identify it by 13C NMR, IR and mass spectrum of the reaction mixture. The reaction proceeds upon activation of 1 by methanol forming dibutyltindimethoxide followed by dibutyltinglycerate, which undergoes CO 2 insertion to produce non-isolable 7-membered tin–glycerolcarbonato complex that finally yield glycerol carbonate. Catalyst 1 was found to be successful even with 1,2-propanediol and ethylene glycol yielding the corresponding cyclic carbonate.

Hydrodesulfurization of dibenzothiophene using CoMo/Al-HMS nanocatalyst synthesized by supercritical deposition

The developed CoMo/Al-HMS nanocatalyst (3.4 wt% Co and 9.4 wt% Mo) via supercritical methanol–carbon dioxide deposition was characterized by different techniques (adsorption–desorption of nitrogen, oxygen chemisorption, XRD, TPR, TEM and EDAX) and tested in the hydrodesulfurization of dibenzothiophene. The results indicated that supercritical impregnation of Co and Mo into support has a positive effect on the catalyst activity. The higher catalyst performance is attributed to higher and more uniform dispersed deposition of the catalytic metals on the support with increased active surface area. The results of hydrodesulfurization of dibenzothiophene demonstrated enhanced activity for the new catalyst in terms of increased conversion, selectivity and rate constant. Furthermore, addition of aromatics in the feed showed less inhibition effect of CoMo/Al-HMS nanocatalyst with respect to the commercial catalyst.

Preparation and Characterization of a Calcium Carbonate Aerogel

We report on a facile method for the preparation of a calcium carbonate aerogel consisting of aggregated secondary vaterite particles with an approximate average diameter of 50 nm. It was synthesized via a sol‐gel process by reacting calcium oxide with carbon dioxide in methanol and subsequent supercritical drying of the alcogel with carbon dioxide. The resulting monolith was opaque, brittle and had overall dimensions of 6 × 2 × 1 cm. It was characterized by X‐ray powder diffraction, nitrogen adsorption method (BET), and scanning electron microscopy.

Direct in situ supercritical fluid extraction of neodymium ion from its oxide using thenoyl tri fluoro acetone–tri butyl phosphate–methanol in carbon dioxide

A novel process has been developed for the direct extraction of heavy metal ions from their oxides using ligand assisted supercritical carbon dioxide (SC CO 2) without and with a cosolvent. A systematic investigation has been carried out to ascertain the mechanism of direct in situ supercritical fluid extraction, which involves three essential steps, namely ionisation, complexation and extraction. The present work involves direct extraction of metal ions from their oxides using neodymium (Nd) as candidate metal utilizing a synergy of thenoyl tri fluoroacetone (TTA) and tri butyl phosphate (TBP). The mechanism has been established by analysing the conversion of neodymium oxide to Nd 3+ and metal complex. By the reaction with carbonic acid, the metal oxide is converted into metal cation. SC CO 2 facilitates tautomerisation and dissolution of TTA required for the chelation. Addition of methanol to SC CO 2 enhances the formation of metal complex which is being extracted in the SC fluid phase. Effects of process parameters have been evaluated on the performance of the process to ascertain the optimum conditions.

Investigation of retention behavior of drug molecules in supercritical fluid chromatography using linear solvation energy relationships

In this study, the retention behaviors of pharmaceutical and drug-like compounds in supercritical fluid chromatography (SFC) with polar stationary phases were evaluated using linear solvation energy relationships (LSERs). We used more than 200 compounds, including mono-, di-substituted benzenes, and other marketed drugs with a wide range of solvation descriptors. The dominant contribution to positive retention was the hydrogen bond donor acidity of the solutes, particularly for pyridine and amino columns. That factor is determined by the difference in basicity between the mobile and stationary phases. Another significant contributor to retention behavior was the hydrogen bond acceptor basicity of the solutes made particularly for diol and amino columns. The hydrogen bond donating ability is small for cyano and pyridine stationary phases (or should be zero) since those two phases lack hydrogen bond donor groups. The LSER results showed that the SFC retention behavior of compounds using carbon dioxide–methanol with polar stationary phases was close to that reported for normal phase LC using hexane–methanol. As expected, mobile phases containing high percentages of modifier resulted in decreased retention times for most compounds. A greater knowledge of the nature of solute/stationary phase and solute/mobile phase allows a more rapid and efficient choice in high-throughput screening of compound libraries.

Novel Copper-Zinc Oxide Arrayed Nanoatalysts for Hydrogen Production Applications

We report a simple and effective wet chemical technique for facile synthesis of large-scale and arrayed copper-zinc oxide nanostructures in regard to high performance of hydrogen production. The zinc oxide arrays as support were grown by a template-free aqueous route and subsequently the copper catalysts were impregnated on zinc oxide surface at low temperature by means of spontaneous reduction to form the hierarchical core-shell type nanostructures. Systematic analyses were employed to examine morphological, component, and structural characterizations of arrayed copper-zinc oxide nanostructures. In particular, these nanocomposites exhibited high methanol conversion, hydrogen production, and carbon dioxide selectivity at lower reaction temperature in comparison with the conventional catalysts. As shown above, our work here could open up new possibilities for the preparation of core-shell type copper-zinc oxide nanocomposites in micro reformed hydrogen fuel cell (μRHFC) devices applications.

PS-HQ: More convenient in situ polymeric cocatalyst for the PdCl 2-catalyzed acetalization in supercritical carbon dioxide

Polystyrene-supported hydroquinone (PS-HQ) is presented as an in situ polymeric cocatalyst to replace polystyrene-supported benzoquinone (PS-BQ) in the PdCl 2-catalyzed acetalization of methyl acrylate with methanol in supercritical carbon dioxide (scCO 2) under oxygen atmosphere. Due to deletion of H 2O 2 oxidation step, PS-HQ is more convenient and relatively inexpensive.

PdCl2/PS-Phenol Co-catalyzed Acetalization of Methyl Acrylate with Methanol in Supercritical Carbon Dioxide

Abstract PdCl 2 /polystyrene-supported phenol (PS-phenol) was presented as a cocatalyst for the acetalization of methyl acrylate with methanol in supercritical carbon dioxide under oxygen atmosphere. After methyl acrylate was completely converted, the highest yield and selectivity for methyl 3,3-dimethoxypropanoate were 97.7% and 100%, respectively. Compared with small molecular acidic co-catalysts, the separation of PS-phenol from the reaction system by simple filtration made the recycling of precious palladium practical and convenient.