Batch production of micron size particles from poly(ethylene glycol) using supercritical CO2 as a processing solvent

The major advantage of using supercritical carbon dioxide (CO₂) as a solvent in polymer processing is an enhancement in the free volume of a polymer due to dissolved CO₂, which causes a considerable reduction in the viscosity. This allows spraying the polymer melt at low temperatures to produce micron size particles. We have used supercritical CO₂ as a solvent for the generation of particles from poly(ethylene glycol) (PEG) of different molecular weights. Since PEG is a hydrophilic compound, it is a most commonly used polymer for encapsulating a drug. PEG particles with different properties may allow keeping a good control over the release of the drug. It has been possible to produce particles with different size, size distribution, porosity and shape by varying various process parameters such as molecular weight, temperature, pressure and nozzle diameter. A flow and a solidification model have been applied in order to have a theoretical insight into the role of different parameters.     

Formylation with supercritical carbon dioxide over Ru/Al2O3 modified by phosphines: heterogeneous or homogeneous catalysis?

The formylation of 3-methoxypropylamine with hydrogen and “supercritical” carbon dioxide over Ru-based catalysts was studied. In this solventless process, carbon dioxide acts as both reactant and solvent. Interestingly, Ru/Al₂O₃ modified by the phosphine 1,2-bis(diphenylphosphino)ethane (dppe) showed a high formylation activity at 100% selectivity, comparable to those of the homogeneous catalysts RuCl₂(dppe)₂ and RuCl₂(PPh₃)₃. Analysis of the reaction mixture by ICP-OES and structural studies by in situ X-ray absorption spectroscopy discovered that the presence of the phosphine modifier led to the formation of a homogeneous ruthenium catalyst.     

Phase equilibria of poly(methyl methacrylate) in supercritical mixtures of carbon dioxide and chlorodifluoromethane

Phase behavior data are presented for poly(methyl methacrylate) (PMMA: M_w= 15,000, 120,000) in supercritical solvent mixtures of carbon dioxide (CO₂) and chlorodifluoromethane (HCFC-22). Experimental cloud point curves, which were the phase boundaries between single and liquid-liquid phases, were measured by using a high-pressure equilibrium apparatus equipped with a variable-volume view cell at various CO₂ compositions up to about 63 wt% (on a polymer-free basis) and at temperatures up to about 100 °C. The cloud point curves exhibited the characteristics of a lower critical solution temperature phase behavior. As the CO₂ content in the solvent mixture increased, the cloud point pressure at a fixed temperature increased significantly. Addition of CO₂ to HCFC-22 caused a lowering of the dissolving power of the mixed solvent due to the decrease of the solvent polarity. The cloud point pressure increased with increasing the molecular weight of PMMA.     

Extraction of nimbin from neem seeds using supercritical CO2 and a supercritical CO2–methanol mixture

Nimbin, a component found in neem seeds, which is reported to have several valuable medicinal properties including: anti-inflammatory, anti-pyretic, anti-fugal, antihistamine and antiseptic was extracted from neem seeds using supercritical CO₂ and CO₂ with a methanol modifier.Nimbin extraction yields using supercritical carbon dioxide were found to be approximately 85% at 308 K, 23 MPa and a CO₂ flow rate of 0.62 cm³/min for a 2-g sample of neem. An optimum extraction pressure appears to exist at ≈23 MPa and 328 K. Although extraction using a methanol modifier did improve the extraction somewhat, methanol was not found to be an effective modifier for extracting nimbin.Dynamic extraction curves were predicted using three empirical models and a theoretical model. The three empirical models were: a Langmuir gas adsorption model, a first order plus dead time (FOPDT) model and a so-called tⁿ cyclone model used to incorporate sigmoidal curves. The parameters in the empirical models were fitted to the experimental data. The Goto et al. [J. Chem. Eng. Jpn. 31 (1998) 171] theoretical model was compared to the experimental results and was found to fit the data well. The theoretical model shows that the extraction yield depends strongly on the solvent flow rate, that is, external mass transfer or equilibrium is the controlling step of this process.     

Foaming of PCL/clay nanocomposites with supercritical CO2 mixtures: The effect of nanocomposite fabrication route on the clay dispersion and the final porous structure

Supercritical fluids have been established as alternative foaming agents in various polymers as well as nanocomposite systems. Most recently, supercritical carbon dioxide (scCO₂) has also been used in some studies as a medium of clay dispersion in the polymer matrix providing a solvent-free fabrication route for nanocomposites. In this work, this latter route was followed for the development of porous poly(ɿ-caprolactone) (PCL)/clay nanocomposites after pressure quench. Similarly, PCL/clay nanocomposites were also prepared using the solvent casting and melt blending methods and were then processed with scCO₂ with the batch foaming technique (isothermal pressure quench) to produce their porous counterparts. Poor clay dispersion and non-uniform porous structures were observed when pure CO₂ was used as a dispersion medium for nanocomposite preparation and as a blowing agent, respectively. On the contrary, polymer intercalation and more uniform cell structures were produced when CO₂⿿ethanol mixtures were used as blowing agents.     

Phase behaviour of l-lactic acid based polymers of low molecular weight in supercritical carbon dioxide at high pressures

The results of investigations of phase behaviour in the systems l-lactic acid based polymers + carbon dioxide at high pressures are presented. The measurements have been performed in wide temperature and composition ranges. Two samples of the polymer differing in molecular weight (M_n: 1080 and 3990 g/mol) have been investigated. Both samples of the polymer were characterized with the gel permeation chromatography and NMR spectroscopy. The influence of the structure of the polymer on the solubility in supercritical carbon dioxide has been discussed. The results obtained suggest that the solubility of low molecular weight l-lactic acid based polymers in supercritical carbon dioxide is not controlled by its size, but to a large extent by the character of its terminal groups. The phase behaviour in the system l-lactic acid + carbon dioxide has been also investigated and the results were compared with those for the systems composed of l-lactic acid based polymers and carbon dioxide.     

Synthesis of vicinal diamines via Zn–H2O–CO2-induced reduction of aromatic imines in supercritical carbon dioxide

Zn–H₂O–CO₂ is a good reducing reagent for the reduction of imines in supercritical carbon dioxide (scCO₂). They provide the corresponding vicinal diamines in moderate to good yields. The results showed that carbon dioxide plays an important role as both solvent and reagent.     

Rapid Hydrogenation of Aromatic Nitro Compounds in Supercritical Carbon Dioxide: Mechanistic Implications via Experimental and Theoretical Investigations

An exceptionally rapid hydrogenation of nitrobenzene to aniline [TOF=252,000 h⁻¹] over palladium containing MCM‐41 (Pd/MCM‐41) with excellent yield of >99% can be achieved in supercritical carbon dioxide at 50 °C and a hydrogen pressure of 2.5 MPa. It has been observed that this promising method preferred a single phase between liquid substrate and carbon dioxide‐hydrogen system. The ascendancy of the supercritical carbon dioxide medium is established in comparison with the conventional organic solvent and solvent‐less conditions. Changes in the reaction parameters such as carbon dioxide and hydrogen pressure, temperature and the reaction time do not affect the selectivity. A combined experimental and theoretical study has elucidated the mechanism under the studied reaction condition because experimental observations revealed a direct conversion of nitrobenzene to aniline. However, density functional theory (DFT) calculation shows that the direct conversion is energetically unfavourable; hence, a stepwise mechanism has been proposed. Theoretical predictions and experimental observations suggested that the rate‐limiting step of nitrobenzene conversion is different from that of the liquid phase hydrogenation. This catalytic process can also be successfully extended to the hydrogenation of other aromatic nitro compounds with different substituents. Easy separation of the liquid product from catalyst and the use of an environmentally friendly solvent make this procedure a viable and an attractive green chemical process.     

Formation of deagglomerated PLGA particles and PLGA-coated ultra fine powders by rapid expansion of supercritical solution with ethanol cosolvent

Rapid expansion of supercritical solution (RESS) was used for preparing polymer particles and polymer coating of ultra fine powders. The polymer of pharmaceutical interest was Poly(lactic-co-glycolic acid) (PLGA with PLA: PGA ratio of 85: 15 and MW of 50,000–75,000) and the simulated core particles were 1.4-μm SiO₂ and 70-nm TiO₂ particles. The supercritical solution was prepared by dissolving PLGA in supercritical carbon dioxide with ethanol as a cosolvent. Supercritical solution of CO₂-PLGA was sprayed through capillary nozzles to ambient conditions, resulting in formation of submicron PLGA particles. Similarly, rapid expansion of supercritical solution of CO₂-PLGA suspended with the core particles could provide solvent evaporation and deposition of submicron PLGA particles on the surface of the core particles, resulting in the formation of coating films on dispersed particles of SiO₂ and agglomerates of TiO₂. The influences of the core particle size, spray nozzle diameter as well as powder-to-polymer weight ratio were also investigated and discussed with respect to the coating performance.     

Preparation of poly(L-lactic acid) submicron particles in aerosol solvent extraction system using supercritical carbon dioxide

The aerosol solvent extraction system process (ASES), which is one of the supercritical anti solvent processes (SAS), was used to produce poly(L-lactic acid) (PLLA) into the submicron particles. Dichloromethane (DCM, CH₂Cl₂) and carbon dioxide were selected as a solvent and as an antisolvent for PLLA, respectively. The objective of this study was to investigate the effect of the various process parameters such as temperature, pressure, and solution concentration on PLLA particles. With increasing temperature and pressure, particle size was increased. Also, higher PLLA concentration led to larger particle size and broader particle size distribution. A scanning electron microscope (SEM) was used to observe the morphology and size of PLLA particles recrystallized by ASES process. The mean particle size and its distribution of processed particles were measured by using a laser diffraction particle size analyzer (PSA).     

Extraction of Furfural with Carbon Dioxide

Abstract

A new approach to separate furfural from aqueous waste has been investigated. Recovery of furfural and acetic acid from aqueous effluents of a paper mill has successfully been applied on an industrial scale since 1981.

The process is based on the extraction of furfural and acetic acid by the solvent trooctylphosphineoxide (TOPO). Common extraction of both substances may cause the formation of resin residues. Improvement was expected by selective extraction of furfural with chlorinated hydrocarbons, but ecological reasons stopped further development of this project.

The current investigation is centered in the evaluation of extraction of furfural by supercritical carbon dioxide. The influence of temperature and pressure on the extraction properties has been worked out. The investigation has considered the multi-component system furfural-acetic acid-water-carbon dioxide. Solubility of furfural in liquid and supercritical carbon dioxide has been measured, and equilibrium data for the ternary system furfural-water-CO₂ as well as for the quaternary system furfuralacetic acid-water-CO₂ have been determined. A high-pressure extraction column has been used for evaluation of mass transfer rates.     

Polymeric microparticles prepared by supercritical antisolvent precipitation

This work has as main objective the development of a model process to obtain microparticles of an acrylate-methacrylate copolymer (Eudragit L100^® and Eudragit EPO^®) using supercritical carbon dioxide (SC-CO₂) as antisolvent (GAS). After studying the behaviour of the copolymers in SC-CO₂ at different operation conditions (pressure, temperature and presence of ethanol (EtOH)), efforts were invested in the optimization of Eudragit EPO^® precipitation from an organic solution using carbon dioxide as antisolvent in batch mode. After loading the precipitation vessel with a fixed quantity of the copolymer dissolution, the SC-CO₂ has been added until the pressure of operation has been reached. Three process parameters, namely, solution nature, presence of surfactants and organic solvent removal step, have been evaluated. Microparticles with mean diameter from about 2 to 12 μm are obtained.     

Effects of supercritical carbon dioxide on waste banana peels for heavy metal removal

The effects of supercritical carbon dioxide (CO₂) on waste banana peels for copper adsorption were evaluated. Supercritical CO₂ was employed both in a solvent extraction for antioxidant compound recovery and in an emerging biomass treatment to increase the subsequent heavy metal-removal step; the latter is termed “explosion with supercritical CO₂”. This lignocellulosic biomass was analyzed before and after being subjected to both processes by scanning electron microscopy and X-ray patterning. Thermal gravimetric and differential scanning calorimetry analyses were performed to understand the different effects of supercritical carbon dioxide employed in these two processes on banana peels. The explosion with supercritical CO₂ process resulted in a more pronounced effect on the vegetable structure. Nevertheless, no increase in the copper-removal capacity was achieved. The adsorption studies showed similar behaviors for fresh and extracted samples, demonstrating that banana peels previously extracted with supercritical CO₂ retained their adsorption capacity for subsequent heavy metal removal.     

Supercritical Fluid Extraction Coupled with Solvent-Less Spray Collection Mode for Rapid Separation of Indirubin and Tryptanthrin from Folium Isatidis

Supercritical carbon dioxide modified with acetonitrile and water for the extraction of indirubin and tryptanthrin from Folium Isatidis and the collection of these two bioactive ingredients by a spray mode are presented in this study. Two pumps, one for the addition of the modifier and the other for the transportation of CO₂, were used for supercritical fluid extraction (SFE). This is a fast and environmentally-friendly approach for the production of herbal medicine. Compared to conventional solvent extraction, the yield of bioactive indirubin and tryptanthrin by this SFE process was approximately the same, but with a shorter process time and better protection of the environment.     

From supercritical carbon dioxide to gas expanded liquids in extraction and chromatography of lipids

Analytical‐scale extraction and chromatography of oils, fats and other liposoluble compounds can be achieved by using supercritical carbon dioxide as a solvent. Since the 90's when supercritical fluid chromatography (SFC) was a hot topic, this technology has developed into a robust, modern analytical technique that uses any proportions of compressed CO₂ mixed with an organic solvent. Supercritical fluid extraction (SFE) on the other hand is only recently starting to reform in a similar way, towards the use of more robust extraction system and enabling mixing of compressed CO₂ with larger proportions of organic solvents. In this Feature article, the development of SFC and SFE into what options we have today is described, including the latest trend of using CO₂‐expanded liquid (CXL) as extraction solvent for lipids.     

Fractionation of Gluten Lipids with Supercritical Carbon Dioxide

Gluten lipids are of two kinds, polar and nonpolar. Both groups consist of a large number of lipids. Gluten lipids can be extracted by conventional solvents as ethanol but also by supercritical carbon dioxide. The high density and the good mass transport properties make the supercritical fluid an excellent solvent. Ethanol extracted gluten lipids have been fractionated with supercritical CO₂ at different pressures and constant temperature. The extract contains triglycerides and free fatty acids, and a more concentrated fraction of polar lipids is left in the extraction vessel. While both polar and nonpolar lipids are soluble in ethanol, only nonpolar lipids are dissolved by supercritical CO₂. An addition of a small amount of ethanol to the CO₂, can, however, increase the solubility of the polar lipids.     

Modeling and optimization of process parameters for supercritical CO2 extraction of Argemone mexicana (L.) seed oil

This research article deals with the determination of optimal conditions of extraction parameters (e.g. temperature (60–100?°C), pressure (200–350?bar), particle size (0.5–1.0?mm), flow rate-CO₂ (5–15?g/min), and the % of co-solvent (0.0–10% of flow rate-CO₂) resulting to the optimal cumulative extraction yield during the supercritical fluid extraction of Argemone mexicana (L.) seed oil with and without a modifier (ethanol) using a supercritical carbon dioxide as solvent. A “five-factors-three-levels” Box-Behnken design under the response surface methodology was used to show independent and interactive effects of extraction parameters. A mathematical regression model was expressed properly by a quadratic second-order polynomial equation. The maximum oil yield (42.86%) from A. mexicana seeds was obtained with the optimal conditions (85?°C, 305?bar, 0.75?mm, 11?g/min, and 9% of flow rate-CO₂) of extraction parameters. The fatty acids analysis of the seed oil was done using gas chromatography and found its suitability as bio-fuel.     

Role of tungsten in promoting selective reduction of NO with CO over Ir/WO3–SiO2 catalysts

Catalytic hydrogenation of naphthalene to decalin was studied over a carbon-supported rhodium catalyst in supercritical carbon dioxide solvent at 333 K, and the results were compared with those in an organic solvent. cis-, trans-Decalin and tetralin were formed from the beginning of the reaction in supercritical carbon dioxide. Higher concentration of hydrogen in carbon dioxide solvent and on the active site, and also the suppression of desorption of partially hydrogenated tetralin molecules from the active site would be responsible for higher selectivity to cis-decalin in supercritical carbon dioxide than that in an organic solvent.     

Supercritical Carbon Dioxide for the Removal of Hydrocarbons from Contaminated Soil

Abstract

Soil material contaminated with hydrocarbons can be cleaned by supercritical water extraction. Due to the high critical data of supercritical water (Tc = 647 K, P _c = 22.1 MPa), supercritical carbon dioxide (T _c = 304 K, P _c = 7.3 MPa) was investigated as an alternative solvent. The amount of hydrocarbons removed from weathered contaminated soil material with supercritical carbon dioxide was less than 21%.     

Synthesis of new perfluorinated binaphthyl Mn(III) complexes and epoxidation of styrene in supercritical carbon dioxide

In this article, new perfluorinated binaphthyl Mn(III) complexes have been synthesized by template effect. The synthesized complexes were characterized by elemental analysis, FT-IR, LC/MS, UV–vis spectroscopy. After the solubility of the catalysts in scCO₂ was observed through the high pressure reactor, catalytic activities of the catalysts have been tested in homogeneous asymmetric epoxidation of styrene in both dichloromethane (organic solvent) and supercritical carbon dioxide (scCO₂). In order to determine and compare to complexes, the effect of synthesized catalysts to conversion and selectivity was investigated. Reaction parameters such as; reaction time, solvent type and position of substituents were also assessed during the analysis.