Ethanol-modified Carbon Dioxide Research Articles

Rapid Separation of Five Cyclosporin Analogs by Supercritical Fluid Chromatography

Recently there has been a resurgence of interest in cyclic peptides due to their therapeutic advantages in terms of potency, permeability, proteolytic stability, and unique selectivity relative to traditional smaller drug molecules. Cyclosporin is a family of cyclic peptides widely used as autoimmune suppression agents. Cyclosporin analogs consist of eleven amino acids with the main difference lying at the side chain of its amino acid residues. In this study, a single step separation method was developed utilizing Supercritical Fluid Chromatography (SFC) to resolve five naturally occurring cyclosporin analogs (Cyclosporin A, B, C, D, and H) on a bare silica-packed column. The optimized method involved use of ethanol-modified carbon dioxide as mobile phase on a bare silica column at 80 °C and UV detection at 220 nm. Although column temperature and back pressure generally had insignificant effect on SFC separation, it was found in our study that increasing temperature and pressure greatly improved peak shape and resolution.

The Bitumen Upgrading of Nigerian Oil Sand by Supercritical Carbon Dioxide Modified with Alcohols

The experimental study of bitumen extraction from Nigerian oil sand by supercritical carbon dioxide was carried out using a high-pressure extractor. Fifty grams (50 g) of oil sand was placed into a 100-mL extractor at a temperature of 110 °C and pressures of 50, 60, or 65 MPa for the interaction with pure carbon dioxide or modified by the addition of 3 g of ethanol or 2-propanol in three runs to investigate the co-solvent effect on recovery. The liquid recovery of bitumen, using pure carbon dioxide, was determined to be equal to 16.3%, on average, after three runs over the entire pressure range, with a maximum of 18.5% at 50 MPa. The addition of ethanol improved liquid recovery, while the addition of 2-propanol worsened it by ∼5% (on average). The maximum liquid recovery of 24.5% after three runs, using ethanol-modified carbon dioxide, was observed at 60 MPa. The average outgassing losses obtained with the addition of co-solvents increased in the following order: pure carbon dioxide (16.1%), ethanol (19.5%), 2-propanol (24.93%). The obtained bitumen fractions were upgraded by rejection of asphaltenes and petcoke. Chromatographic analysis (gas chromatography–mass spectroscopy, coupled with total ion chromatography (GC-MS TIC)) has shown that the composition of the collected fractions after the first runs is lighter than that observed after the subsequent runs. The fuel-related physicochemical properties of the extracted bitumen fractions were calculated using Khan’s correlations based on the refractive indices. The obtained characteristics matched those observed in the published data of maltene of Athabasca bitumen.

Supercritical extraction of crude oil by methanol- and ethanol-modified carbon dioxide

The effect of ethanol and methanol cosolvents on the extraction yield and kinetics of crude oil originating from the Halfdan field of the North Sea by supercritical carbon dioxide was investigated across a pressure range of 20–60MPa under a fixed temperature of 60°C. Results inform that the pure carbon dioxide recovery varied between 43 and 77% while the recovery of the liquid phase of oil ranged between 22 and 56% across the entire pressure range. Using ethanol- and methanol-modified CO2, the total recovery yield increased significantly averaging an additional 18.2% and 19.4% respectively when compared to pure carbon dioxide. The ethanol addition improved the recovery of the liquid phase of oil averaging 9.6% while the methanol addition improved it to 7.3% across the entire pressure range.Study of the kinetics of extraction process indicated that heavier fractions were extracted faster with the ethanol- compared to the methanol-modified CO2. GC–MS TIC chromatographic analysis of the extracted oil fractions showed that the extraction of C19-C30 single carbon number groups with the addition of methanol is more dependent on pressure. Predominantly, ethanol addition was more efficient in extraction of C17-C38 single carbon number groups while methanol contributed more in extraction of C7-C9 SCN groups.

SUPERCRITICAL FLUID EXTRACTION of QUERCETIN FROM ONION SKINS

ABSTRACTSupercritical fluid extraction, with ethanol‐modified carbon dioxide, of free quercetin from onion skins (red and yellow varieties) was studied. Static mode was investigated as an extraction method, which generated a total of 0.024 g of free quercetin per kg of onion skin for the red variety, and 0.020 g per kg for the yellow variety, at 5700 psi, 40C, an average of 7.6% (molar concentration) of ethanol, and in an extraction period of 2.5 h.The modifier was found to have an important influence on free quercetin recovery. the greater the amount of ethanol collected in the trap, the greater the amount of free quercetin recovered.Identification and quantification analysis were conducted in a High Performance Liquid Chromatography system.

Removal of Trace Heavy Metals from a Natural Medicine Material by Supercritical CO2 Chelating Extraction

Removal of arsenic, mercury, lead, and copper from a natural medicine material by supercritical carbon dioxide containing a chelating ligand, diethylammonium diethyldithiocarbamate (Et2NH2DDC), was studied. The contents of As, Hg, Pb, and Cu in the natural medicine material, which was a mixed powder of six plants, were <2, 0.2, 2, and 10 μg/g, respectively. It was shown that Et2NH2DDC was an effective ligand for the extraction of the heavy metals. The effects of pressure, temperature, modifier, and time on the extraction were systematically investigated. The results showed that there were the extraction efficiency-based optimal temperatures of arsenic, lead, and copper with the order Tm,Pb < Tm,As < Tm,Cu, while the extraction efficiency of mercury decreased as the temperature increased. When the pressure or the amount of the modifier, ethanol in supercritical CO2, was increased, the extraction efficiencies of arsenic, lead, and mercury were not enhanced noticeably, while the extraction efficiency of copper increased markedly. Except for lead, the extraction efficiencies of As, Hg, and Cu increased as the extraction time extended. With the suitable pretreatment, the natural medicine material in which the content of arsenic was 4 times more than the limit of the U.S. Food and Drug Administration (FDA) could meet the standard after the extraction with Et2NH2DDC in supercritical ethanol-modified carbon dioxide.

Temperature effects for chiral separations using various bulk fluids in near‐critical mobile phases

As supercritical fluid chromatography becomes more accepted as a facile means for the separation of chiral compounds, the need for mobile phases that can readily solubilize these polar compounds grows. Prior studies suggest that HFC-134a may prove suitable due to its very high eluotropic strength compared to carbon dioxide-based mobile phases. A comparison is made between ethanol-modified carbon dioxide, HFC-134a, and decafluoropentane as to their relative eluotropic strength, selectivity, and efficiency for three chiral compounds using a Whelk O-1 chiral bonded phase. The bulk component of the mobile phase was found to have relatively little effect on chiral selectivity over the range of 5° to 95°C. Chirality 9:693–698, 1997. © 1997 Wiley-Liss, Inc.

Temperature effects for chiral separations using various bulk fluids in near-critical mobile phases

As supercritical fluid chromatography becomes more accepted as a facile means for the separation of chiral compounds, the need for mobile phases that can readily solubilize these polar compounds grows. Prior studies suggest that HFC-134a may prove suitable due to its very high eluotropic strength compared to carbon dioxide-based mobile phases. A comparison is made between ethanol-modified carbon dioxide, HFC-134a, and decafluoropentane as to their relative eluotropic strength, selectivity, and efficiency for three chiral compounds using a Whelk O-1 chiral bonded phase. The bulk component of the mobile phase was found to have relatively little effect on chiral selectivity over the range of 5° to 95°C. Chirality 9:693–698, 1997. © 1997 Wiley-Liss, Inc.