Supercritical Technology Research Articles

Preparation and Characterization of Mullite Fiber-Reinforced Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub> Aerogel Composites

Mullite fiber-reinforced Al2O3-SiO2 aerogel composite was prepared through hybrid sol-gel process, vacuum pressure impregnation technology and ethanol supercritical drying technology using aluminum chloride hexahydrate (AlCl3·6H2O), tetraethoxysilane (TEOS) and mullite fiber as raw materials. The samples were characterized by XRD, SEM, BET, Hot Disk and Universal Testing Machine. The results showed that mullite fiber-reinforced Al2O3-SiO2 aerogel composite possessed excellent heat-insulation performance, high-temperature stability and mechanical property. The thermal conductivities of composite increased from 0.0186W/mK at 150°C to 0.1198W/mK at 1200°C. The surface area of Al2O3-SiO2 aerogel increased from 589m2/g at ambient temperature to 667m2/g at 600°C, and correspondingly the pore diameter increased from 21.47nm to 27.82nm. The phase of Al2O3-SiO2 aerogel was from boemite at ambient temperature to γ-Al2O3 at 600°C, and to mullite at 1200°C. The compressive strength was 1.8MPa, when the shape variables reached 10%, the tensile strength was 0.69MPa, the bending strength was 6.4MPa.

Energy Environment Implication in Thermal Power Plant by using Supercritical Technology – Indian Scenario

In India, emissions of Green House Gases (GHGs) are increasing due to rise in energy demands to sustain economic growth. Coal is used as a dominant fuel in Indian thermal power plants but the efficiency of these is low in comparison with prevailing international standards. As such emissions of GHGs are much higher and feasible to achieve. The adoption of Clean Coal Technologies (CCTs) – like the Supercritical (SC) steam cycle – for new capacity addition in Indian thermal power plants will increase the efficiency of the Indian grid. These technologies are more environmentally and would help to meet increased energy demands. India has taken initiatives for the adoption of the technology as explained in the 11th plan of the Planning Commission. Finally, it is concluded from the study that SC and USC technology penetration would be helpful for reducing GHGs emission. The hypothetical scenarios analysis shows that up to 50% technology penetration for new capacity addition until 2027 would be helpful for reducing GHGs emission.

The super- and sub-critical effects for dielectric constant in diethyl ether.

Results of dielectric constant (ε) studies in diethyl ether for the surrounding of the gas - liquid critical point, TC - 130 K < T < TC + 50 K, are presented. The analysis recalls the physics of critical phenomena for portraying ε (T) evolution along branches of the coexistence curve, along its diameter (d(T)) and in the supercritical domain for T > TC. For the ultrasound sonicated system, the split into coexisting phases disappeared and dielectric constant approximately followed the pattern of the diameter. This may indicate the possibility of the extension of the "supercritical technology" into the ultrasound "homogenized" subcritical domain: the "strength" and the range of the precritical effect of d(T) are ca. 10× larger than for ε (T > TC).

Preparation and Characterization of Monolithic Al2O3 Aerogels

Al2O3 aerogels were obtained through sol-gel process and ethanol supercritical drying technology using anhydrous aluminium chloride (AlCl3) and propylene oxide as precursor and gelation initiator respectively. Monolithic Al2O3 aerogels with porous and large specific surface area were achieved in our studies. Morphology and properties of Al2O3 aerogels were investigated by techniques of X-ray diffraction, Nitrogen adsorption/desorption analysis, Scanning electron microscopy, and Fourier transform infrared spectroscope. The results showed that the Al2O3 aerogels possessed a porous network microstructure made up of needles or rod-shaped particles and a specific surface area of 398 m2/g at 600°C. It was transformed to θ-Al2O3 after calcined at 1200°C.

Supercritical fluid and pharmaceutical applications. Part I: Process classification

The supercritical fluid technology has been target of many pharmaceuticals investigations in particles production for almost 35 years. This is due to the great advantages it offers over others technologies currently used for the same purpose. A brief history is presented, as well the classification of supercritical technology based on the role that the supercritical fluid (carbon dioxide) performs in the process. Key words: Supercritical fluid technology, supercritical carbon dioxide, pharmaceuticals.

Valorization of chia (Salvia hispanica) seed cake by means of supercritical fluid extraction

Chia (Salvia hispanica) seed is a source of natural antioxidants and essential fatty acids. The present study evaluated the oil extraction from chia seed cake, a residue from chia seed oil extraction by cold pressing. Extraction conditions (pressure, temperature, solvent) and its effects in the quality of the extracts were studied. The re-use of an agroindustrial residue (chia seed cake) for obtaining extracts rich in bioactive compounds (high added value), mainly using the supercritical technology, is a novelty. Published studies on this subject have not been found. Supercritical fluid extraction (SFE) was performed at pressures from 150 to 300bar and temperatures of 40–50°C, using CO2 as solvent or CO2 added to ethanol (EtOH) or ethyl acetate (EtOAc) as cosolvents at 2.5–7.5% w/w of the total CO2 mass. Extracts obtained by SFE were compared to extracts obtained by low-pressure techniques (LPE), using hexane, EtOH, and EtOAc as solvents. All extracts were evaluated as antioxidant content (ABTS and DPPH methods), total phenolics content (TPC), fatty acids profile (GC-FID) and in vitro antimicrobial activity analysis. SFE assays using pure CO2 reached yields up to 10.6±0.2% at 300bar and 50°C. SFE with 7.5% of EtOH increased the process yield and TPC of the extract. LPE techniques using EtOH and EtOAc produced extracts with the best TPC values (50±3 and 79±2mg CAE/gextract, respectively) and EC50 values (760±19 and 621±11μg/mL, respectively). GC-FID confirmed the high content of linoleic and α-linolenic acids (∼80% together), and the presence of palmitic, stearic and oleic acids, in minor amounts for all of the extract samples evaluated. It was noted that chia seed cake extracts presented the same quality that whole chia seed extracts, studied by other authors. Extracts obtained by different techniques also showed weak antimicrobial activity against B. cereus. The economic evaluation indicated SFE of chia seed cake is a profitable way to reuse this agroindustrial waste.

Development Features of Supercritical (Ultra-Supercritical) Technology in the World and Experiences We Can Learn

The development and technical characteristics in different stages of supercritical (ultra-Supercritical) technology abroad are introduced in this paper. At the same time, according to the development trend of supercritical (ultra-supercritical) technology, the corresponding revelations are given in this paper. That is: It is an inevitable choice to develop supercritical (ultra-supercritical) technology if we want to improve the thermal efficiency and heat efficiency.

Carotenoids Functionality, Sources, and Processing by Supercritical Technology: A Review

Carotenoid is a group of pigments naturally present in vegetal raw materials that have biological properties. These pigments have been used mainly in food, pharmaceutical, and cosmetic industries. Currently, the industrial production is executed through chemical synthesis, but natural alternatives of carotenoid production/attainment are in development. The carotenoid extraction occurs generally with vegetal oil and organic solvents, but supercritical technology is an alternative technique to the recovery of these compounds, presenting many advantages when compared to conventional process. Brazil has an ample diversity of vegetal sources inadequately investigated and, then, a major development of optimization and validation of carotenoid production/attainment methods is necessary, so that the benefits of these pigments can be delivered to the consumer.

Inhalable curcumin formulations by supercritical technology

Inhalable dry formulations for pulmonary delivery of curcumin have been produced by supercritical antisolvent micronization. The antioxidant curcumin was co-processed with hydroxypropyl-beta-cyclodextrin (HP-β-CD) and polyvinylpyrrolidone (PVP) to form binary and ternary composites with enhanced flow-ability for pulmonary delivery. The micronization process adopted was the atomized rapid injection solvent extraction (ARISE) system, and was operated at 95bar and at temperatures of 25°C and 40°C. The products were evaluated in terms of morphology, composition, crystallinity and aerodynamic particle size distributions. A synergistic effect of the excipients on the aerodynamic properties of micronized curcumin formulations has been found. The fine particle fraction (FPF) of curcumin in ARISE-processed powders was as high as 61% in ternary systems, whilst untreated curcumin had a FPF of 10% and micronized binary systems had FPF below 40%. The process produced yields of about 80%, demonstrating significant potential for further development of curcumin formulations for pulmonary administration.

Supercritical CO&lt;sub&gt;2&lt;/sub&gt; Extraction of γ-Linolenic Acid from &lt;i&gt;Spirulina platensis&lt;/i&gt;

Arthrospira (Spirulina) platensis contains large quantities of γ-linolenic acid (GLA). GLA is an essential omega-6 unsaturated fatty acid made in the human body from linoleic acid. It can be metabolized to various important eicosanoids such as prostaglandins, thromboxanes, leukotrienes, prostacyclins, and lipoxins. The aim of this study was to investigate the optimal extraction parameters of GLA from A. platensis using supercritical CO2 technology. Results showed that operating temperatures and pressures were important factors in the extraction of GLA. A maximum GLA yield of 161.98 μg/g could be obtained at a pressure of 30 MPa, a temperature of 60°C, and a CO2 flow rate of 6 mL/min. Conversely, only a yield of 104.16 μg/g could be obtained at a pressure of 10 MPa, a temperature of 40°C, and a CO2 flow rate of 6 mL/min. The correlation between pressure and yield could be explained by an increase in collision rates between CO2 molecules and carrier affinity under a high pressure. Therefore, an operating temperature between 50 and 60°C and a pressure of 30 MPa should be used to maximize the yield of GLA from A. platensis using supercritical CO2 technology.

Solubilities of four macrolide antibiotics in supercritical carbon dioxide and their correlations using semi-empirical models

Accurate experimental determination of a solid drug’s solubility in supercritical fluids and its correlation is crucially important to the development of supercritical technologies for the pharmaceutical industry. In the present work, the solubilities of azithromycin, erythromycin, clindamycin and clarithromycin in supercritical carbon dioxide were measured at temperatures ranging from (308 to 348) K and pressures from (12.2 to 35.5) MPa using a static method. The mole fraction solubilities ranged from 2.7×10−5 to 11.46×10−5. The crossover region was observed for azithromycin, clarithromycin, clindamycin and erythromycin from 13.8 to 14.0MPa, 15.0 to 15.2MPa, 14.8 to 15.2MPa and 16.8 to 17.1MPa, respectively. Solubility data were correlated using four semi-empirical density-based models (Chrastil, Kumar, Johnston, Bartle and Mendez-Santiago and Teja models). The average absolute relative deviations ranged from 1.7 to 7.4; 2.07 to 8.1; 7.21 to 10.37 and from 5.13 to 9.44 for Chrastil, Bartle, K–J and M–T models, respectively. The results showed that by using three temperature-independent parameters these models can be applied for satisfactory solubility predictions at different pressures and temperatures. A comparison among the four models revealed that the K–J and Chrastil models gave much better correlation of the solubilities in comparison with other models. Using the correlation results, the heat of drug–CO2 solvation and that of drug vaporization was separately approximated in the range of −13.56 to −23.12 and 33.07–47.65kJmol−1. The correlation results showed good agreement with the experimental data.

Techno-economic evaluation of the extraction of turmeric (Curcuma longa L.) oil and ar-turmerone using supercritical carbon dioxide

Extracting volatile compounds using supercritical carbon dioxide (scCO2) is one of the most interesting applications of supercritical technology because of the high solubility of these substances in CO2. Supercritical carbon dioxide extraction (SFE) has been applied for obtaining extracts from several vegetable matrices, including turmeric (Curcuma longa L.), due to its valuable volatile oil. However, a techno-economic evaluation of turmeric oil and ar-turmerone extraction has not yet been performed. Therefore, the effects of temperature, pressure and process time on the extract yield, relative ar-turmerone yield and manufacturing cost were evaluated in this work. Turmeric rhizomes were ground, sieved and placed in contact with scCO2 flowing at 8.4×10−3kg/min in a laboratory scale SFE unit. Major compounds in the extracts were identified and quantified by gas chromatography. The manufacturing cost (COM) of the extracts was estimated using a model cost developed in the simulator SuperPro Designer 8.5®. Using SFE led to high yields of extract and ar-turmerone. Fast extraction combined with relatively low solvent consumption were observed. Yields of 6.4% and 1.02% of extract and ar-turmerone, respectively, were obtained at 333K and 25MPa for a solvent mass to feed mass ratio of 1.31. For these conditions, the lowest manufacturing cost (COM=US$ 178.8/kg extract) was estimated for a unit containing two 0.005-m3 extractors.

Application Present Status of Supercritical Water Oxidation Technology in Industrial Wastewater Treatment

Supercritical Water Oxidation (SCWO) is a unique environmentally safe technology being widely used in industrial wastewater treatment for its remarkable superiority of removes organic matters efficiently. Characteristics of supercritical water, fundamental principle and flow sheet of SCWO were introduced. Meanwhile, application situations of SCWO in different fields of industrial wastewater treatment were presented in detail, the existing problems in its application were pointed out. At last the prospect for the development of SCWO was also proposed.

Preparation of curcumin-EC sustained-release composite particles by supercritical CO2 anti-solvent technology

Curcumin-ethyl-cellulose (EC) sustained-release composite particles were prepared by using supercritical CO2 anti-solvent technology. With drug loading and yield of inclusion complex as evaluation indexes, on the basis of single factor tests, orthogonal experimental design was used to optimize the preparation process of curcumin-EC sustained-release composite particles. The experiments such as drug loading, yield, particle size distribution, electron microscope analysis (SEM) , infrared spectrum (IR), differential scanning calorimetry (DSC) and in vitro dissolution were used to analyze the optimal process combination. The orthogonal experimental optimization process conditions were set as follows: crystallization temperature 45 degrees C, crystallization pressure 10 MPa, curcumin concentration 8 g x L(-1), solvent flow rate 0.9 mL x min(-1), and CO2 velocity 4 L x min(-1). Under the optimal conditions, the average drug loading and yield of curcumin-EC sustained-release composite particles were 33.01% and 83.97%, and the average particle size of the particles was 20.632 μm. IR and DSC analysis showed that curcumin might complex with EC. The experiments of in vitro dissolution showed that curcumin-EC composite particles had good sustained-release effect. Curcumin-EC sustained-release composite particles can be prepared by supercritical CO2 anti-solvent technology.

Supercritical and Superheated Technologies: Future of Biodiesel Production

Supercritical and Superheated Technologies: Future of Biodiesel Production

The Frenkel line and supercritical technologies

At present, supercritical technologies use fluids (for example, CO2, H2O) at temperatures and pressures close to critical. It is not currently clear how important critical fluctuations are for dissolution processes and chemical reactions in supercritical fluids. At the same time, our recent work has shown that qualitative changes in the system behavior occurred also at temperatures and pressures much higher than critical. This paper briefly summarizes the latest results of the search and study of the parameters P and T of the changes of dynamic types in supercritical fluids. It turned out that this region of parameters corresponded to a narrow band, namely, the “Frenkel line.” Reaching this line with increasing temperature corresponds to the disappearance of shear excitations in the liquid at all frequencies. The Frenkel line can be considered as a boundary between the liquid and the dense gas at extremely high pressures far from the critical point. Recently, a simple and mathematically rigorous method for finding the Frenkel line was proposed based on analysis of the autocorrelation function of particle velocities. We suggest using the data of the Frenkel line parameters for actual fluids to move supercritical technologies into the region of extremely high pressures exceeding critical ones by tens and hundreds of times.

The application of supercritical drying in the synthesis of silica-based materials

The supercritical drying technology applied in the synthesis of materials based on pure silica, such as aerogel, mesoporous silica glass, optical quartz glass, and noble opal is described. The parameters of supercritical drying for the case of silica material synthesis in ethanol and methanol are optimized.

Development of life cycle water-demand coefficients for coal-based power generation technologies

This paper aims to develop benchmark coefficients for water consumption and water withdrawals over the full life cycle of coal-based power generation. This study considered not only all of the unit operations involved in the full electricity generation life cycle but also compared different coal-based power generating technologies. Overall this study develops the life cycle water footprint for 36 different coal-based electricity generation pathways. Power generation pathways involving new technologies of integrated gasification combined cycle (IGCC) or ultra supercritical technology with coal transportation by conventional means and using dry cooling systems have the least complete life cycle water-demand coefficients of about 1L/kWh. Sensitivity analysis is conducted to study the impact of power plant performance and coal transportation on the water demand coefficients. The consumption coefficient over life cycle of ultra supercritical or IGCC power plants are 0.12L/kWh higher when conventional transportation of coal is replaced by coal-log pipeline. Similarly, if the conventional transportation of coal is replaced by its transportation in the form of a slurry through a pipeline, the consumption coefficient of a subcritical power plant increases by 0.52L/kWh.

ChemInform Abstract: Perspectives and Advances of Microalgal Biodiesel Production with Supercritical Fluid Technology

AbstractReview: 110 refs.

Encapsulation of Food Compounds Using Supercritical Technologies: Applications of Supercritical Carbon Dioxide as an Antisolvent

The application of supercritical technologies as an alternative to conventional methods for encapsulating food compounds is an area of research that can lead to significant innovations in various segments of industrial food processing. The existing supercritical techniques are classified as follows according to the function of the supercritical fluid used in the process: solvent; antisolvent; cosolvent or solute; nebulization compound; extractor and antisolvent techniques. Supercritical carbon dioxide (scCO2) is the substance most widely used for obtaining micro/nanoparticles due to its unique characteristics, and among the existing encapsulation supercritical techniques, those using scCO2 as the antisolvent are more likely to be successful because food compounds are generally less soluble or even insoluble in scCO2. In this context, this review presents and discusses the applications of supercritical processes using scCO2 as the antisolvent for the encapsulation of substances of interest to the food industry.