Extraction of bioactive components from Centella asiatica using subcritical water

Bioactive components, asiatic acid and asiaticoside, were extracted from Centella asiatica using subcritical water as an extraction solvent. Extraction yields of asiatic acid and asiaticoside were measured using high-performance liquid chromatography (HPLC) at temperatures from 100 to 250 °C and pressures from 10 to 40 MPa. As temperature or pressure increased, the extraction yield of asiatic acid and asiaticoside increased. At the optimal extraction conditions of 40 MPa and 250 °C, the extraction yield of asiatic acid was 7.8 mg/g and the extraction yield of asiaticoside was 10.0 mg/g. Extracted asiatic acid and asiaticoside could be collected from water as particles with a simple filtering process. Dynamic light scattering (DLS) was used to characterize particle size. Particles containing asiatic acid were larger (1.21 μm) than particles containing asiaticoside (0.76 μm). The extraction yields of asiatic acid and asiaticoside using subcritical water at 40 MPa and 250 °C were higher than extraction yields using conventional liquid solvent extraction with methanol or ethanol at room temperature while the subcritical water extraction yields were lower than extraction yields with methanol or ethanol at its boiling point temperature.     

Carbohydrate content and composition of product from subcritical water treatment of coconut meal

Coconut meal, a by-product from coconut milk production, was treated with subcritical water at 100–200 °C for 30–240 min in a batch-type reactor. The analysis focused on the content and constituent neutral sugar of the soluble carbohydrate in the liquid products. The carbohydrate is composed of both monosaccharides and oligosaccharides. Treatments at 100–150 °C gave a small amount of a carbohydrate (3.5–5.1 g/100 g dry coconut meal). At 175 °C, the carbohydrate content increased from 4.9 to 9.6 g/100 g dry coconut meal (p < 0.05) for 30–240 min of treatment, but the value decreased from 10.6 to 6.1 g/100 g dry coconut meal for 30–240 min of treatment at 200 °C. The soluble carbohydrate contained mannose, glucose, galactose and arabinose. A response surface methodology study indicated that 13.9 g/100 g dry coconut meal of mannose in the soluble carbohydrate could be produced at 227 °C in 3 min.     

Clean and efficient synthesis of flavanone in sub-critical water

Subcritical water (SbcW) is one of the environmentally benign medium for organic chemical reactions, especially for acid/base catalyzed reactions without using acid or base. However, problems such as low reaction rates and poor selectivity that greatly hinder the application of this attractive technique in industrially interesting processes. Synthesis of flavanones was studied in water at subcritical temperature (250 °C). SbcW was found to be a very promising solvent. The highest flavone product yield in subcritical water was 64% in 60 min at 250 °C. Any side reactions or by-products were did not observed under these conditions.     

Recovery of water-soluble compounds from Ganoderma lucidum by hydrothermal treatment

The polypore fungus Ganoderma lucidum provides bioactive compounds containing several triterpenoids and polysaccharides that are reported to posses anti-cancerous and immunomodulatory properties. In this study, we determined the optimal conditions for extracting water-soluble polysaccharide compounds present in the ground form (3-mm particle size) of G. lucidum using water in subcritical conditions at distinct temperatures by two methods: batch-type subcritical water extraction and semi-continuous-type extraction. The optimal condition where solubility is higher to recover the maximum total amount of β-glucan from G. lucidum (0.44 mg/100 g dried sample) was determined to be 473 K at 10 MPa, with a water flow rate of 1 ml/min for 130 min. For batch-type and semi-continuous-type extractions, the best solubility was obtained at 473 K having efficiencies of 78.1% and 57.4%, and the highest extracted amounts of total WSOC were 328 and 241 mg WSOC/g dry sample, respectively.     

Hydrolysis of sugarcane bagasse in subcritical water

In this work, a subcritical water process was used for the hydrolysis of sugarcane bagasse with the aim of producing fermentable sugars. Hydrolysis kinetics was determined using a semi-batch unit equipped with a 50 mL reactor. Different sample loads (2 and 11 g), flow-rates (11, 22, 33, 44 and 55 mL/min) and temperatures (213, 251 and 290 °C) were evaluated, while maintaining constant pressure (20 MPa). The liquefaction degree of the sugarcane bagasse was not affected by water flow rate and increased with temperature; the maximum liquefaction degree was 95% for hydrolysis at 251 °C and 33 mL/min. The total reducing sugars recovered increased with flow rate up to 23%. The hydrolysis process was completed faster at higher temperatures, requiring 16 min. Maximum monosaccharides + cellobiose + cellotriose yield was 5.6% at 213 °C and 33 mL/min. Approximately 60% of the sugars recovered were in the oligomeric form.     

Extraction of protocatechuic acid from Scutellaria barbata D. Don using supercritical carbon dioxide

The use of supercritical carbon dioxide (SC⿿CO₂), with water as a modifier, was evaluated in this study as a method to extract protocatechuic acid (PA) from Scutellaria barbata D. Don. The highest extraction yield of PA, 64.094 ± 2.756 μg/g of dry plant, was achieved at 75 °C and 27.5 MPa, with the addition of 15.6% (v/v) water as a modifier. The mean particle size was 0.355 mm, the CO₂ flow rate was 2.2 mL/min (STP) and the dynamic extraction time was 100 min. At pressures of 16.2⿿30.0 MPa and temperatures of 45⿿75 °C, the mole fraction solubilities of PA in SC⿿CO₂ ranged from 2.829 ÿ 10^⿿7 to 9.631 ÿ 10^⿿7. The solubility data for PA fit well in the Chrastil model. It is evident that the SC⿿CO₂ extraction uses less solvent, saves both energy and time and is an environmentally friendly extract technology that can be used in the food, cosmetic and pharmaceutical industries.     

Subcritical water extraction of steviol glycosides from Stevia rebaudiana leaves and characterization of the raffinate phase

The objectives of this work were to obtain steviol glycosides of S. rebaudiana leaves, possessing natural and noncaloric sweetener properties, using subcritical water extraction; to assess optimum extraction conditions; to determine biological activities of Stevia extracts and to characterize the raffinate phase. A Box–“Bhenken” statistical design was used to evaluate the effects of various values of temperature (100–150 °C), time (30–60 min) and flow rate (2–6 ml/min) at a pressure of 230 bar applying a solid/liquid ratio of 1:10 (m:v). The most effective parameter was temperature (p < 0.005). Optimum extraction conditions were elicited as 125 °C, 45 min, 4 ml/min flow rate which yielded 38.67 mg/g stevioside and 35.68 mg/g rebaudioside A. The total phenolic, flavonoid contents and DPPH free radical scavenging activity were found as 48.63 mg gallic acid/g extract, 29.81 mg quercetin/g extract and 92.50%, respectively. After extraction, total chlorophyll, carotenoid contents and dietary fibers were quantified as 31.91 mg/100 g, 5.71 mg/100 g and 4.98% in the raffinate phase. Hence, both extract and raffinate phases of S. rebaudiana leaves can be utilized as sources of natural sweeteners, fibers and coloring agents in the industry.     

Remediation of soil contaminated with lubricating oil by extraction using subcritical water

The remediation of lubricating oil contaminated soil was investigated by extraction using subcritical water. The effects of temperature and time on extraction efficiency were studied by performing eight individual extractions and varying the subcritical water temperature (200, 225, 250, and 275 °C) and extraction time (90, 120, 180, and 240 min) in a dynamic mode. Also, a comparison was carried out of the feasibility of two operational modes, namely, dynamic and static-dynamic mode. Of the 25,088 mg/kg of lubricating oil as the total petroleum hydrocarbon (TPH) concentration in untreated soil, the residual concentration was found to be ∼500 and 235 mg/kg for after 120 min extraction in a lab-scale apparatus and 150 min extraction in a 30-fold scale-up experiment, respectively, at 275 °C in static-dynamic mode. The result of this study showed the significant effect of the static-dynamic mode on extraction efficiency. The time and volume of water needed for the static-dynamic mode were much lower than those needed for the dynamic mode. These results are of practical interest in developing the subcritical water extraction technology for extraction of lubricating oil and, in a broad sense, petroleum hydrocarbons contaminated soil.     

Extraction of mangiferin from Mahkota Dewa (Phaleria macrocarpa) using subcritical water

A pharmacological active component, mangiferin, was extracted from Mahkota Dewa using subcritical water extraction. The subcritical water extractions were carried out at temperatures ranging 323–423 K, pressures ranging 0.7–4.0 MPa, and extraction times ranging 1–7 h. Extraction yield of mangiferin was measured using high-performance liquid chromatography (HPLC). The extraction yield was strongly dependent on the temperature while weakly dependent on the extraction pressure. As the extraction temperature increased, the extraction mangiferin yield increased, possibly resulting from the decrease in polarity of subcritical water at higher temperature. At an optimal extraction condition of 373 K, 4.0 MPa and extraction time of 5 h, the extraction yield of mangiferin was 21.7 mg/g. This value was close to the extraction yield with methanol (25.0 mg/g) and higher than those with water (18.6 mg/g) or ethanol (13.2 mg/g) at their boiling points.     

A bioactivity based comparison of Echinacea purpurea extracts obtained by various processes

Echinacea species is provided as dietary supplements for various infectious and immune related disorders and has a potential role in cancer prevention. The aim of this study was to optimize the extraction of total flavonoids using different extraction methods and investigate the cytotoxic effects on various cancer cell lines (CaCo-2, MCF-7, A549, U87MG, and HeLa) and VERO (African green monkey) as a non-cancerous cell line. Box-Behnken statistical design was used to evaluate the effect of pressure (100–200 bar), temperature (40–80 °C) and ethanol as co-solvent (6–20 wt%) at a flow rate of 15 g/min for 60 min in supercritical CO₂ extraction and the effect of temperature (60–100 °C), time (5–15 min) and power (300–900 W) in microwave-assisted extraction. Optimum extraction conditions were elicited as 300 bar, 80 °C and 13% co-solvent yielding 0.472 mg rutin equivalent total flavonoids/g extract in SC-CO₂ extraction, whereas 60 °C, 10 min and 300 W yielded the highest (0.202 mg rutin equivalent) total flavonoids in microwave-assisted extraction. Additional trials with subcritical water (0.022 mg/g) and Soxhlet extraction with methanol (0.238 mg/g) yielded lower flavonoid contents. The exposures upto 50 μg/ml of extracts revealed no significant inhibition on the proliferation of both tested cancer cells and healthy VERO cells.     

Kinetics of high temperature conversion of furfuryl alcohol in water

The kinetics of furfuryl alcohol conversion to 4-hydroxycyclopent-2-enone (4-HCP), polymers and levulinic acid (LA) in water was investigated in batch reactors at temperatures 110–200 °C. These acid catalyzed reactions are at high temperatures catalyzed by hydrogen ions formed by autodissociation of water. At temperatures 180–200 °C and reaction times 5–10 min more than 50 mol% yields of 4-HCP were achieved. A kinetic model which describes experimental data was developed. The values of the apparent activation energies of the main reaction and the side reactions are very similar, what means that the selectivity of 4-HCP formation is independent on the temperature. It indicates, that is attractive to perform furfuryl alcohol transformation to 4-HCP at high temperatures without changing the selectivity.     

Chemical conversion of wood by treatment in a semi-batch reactor with subcritical water

Sugi (Cryptomeria japonica D. Don) wood meal was extracted with subcritical water in a semi-batch reactor. About 70–90% by weight of the sugi wood meal was converted into water-soluble compounds. The main components of the water-soluble compounds were monosaccharides and oligosaccharides, as a result of hydrolysis of cellulose and hemicellulose. White precipitates appeared in the solution after settling for 48 h. X-ray diffractometry clearly showed that precipitates had crystallized into cellulose II. High yield of total saccharides (including the precipitates) was obtained at 310–320 °C, 25 MPa and 65 g min⁻¹ water flow rate from a wood meal charge of 2.0 g, while the decomposition reaction was completed within about 20 min. Moreover, the yield increased to more than 60% when the wood meal was pretreated for improved wettability. It is shown that saccharides can be produced from sugi wood powder quickly and effectively by treatment in subcritical water.     

Recovery of silicon from silicon sludge using supercritical water

In this paper, we propose a new methodology for recovering silicon from silicon sludge using supercritical water in a semi-batch reactor. Silicon sludge is the waste discharged from the silicon ingot cutting process and consists of cutting oil, cooling water, and silicon particles. The oil contained in silicon sludge was removed completely within several minutes by supercritical water elutriation at 400 or 500 °C and 25 MPa. The recovery percentage of silicon was only 70% at 400 °C owing to silicon dissolution. However, the recovery percentage was greater at a higher temperature (95% at 500 °C) because silicon dissolution was suppressed owing to the low ion product of water at higher temperatures. The silicon recovered at 500 °C and 25 MPa was approximately 99.2% pure. Contamination by oxidation was negligible because an oxide film did not grow on the silicon surface during the supercritical water treatment. We conclude that high-purity silicon can be recovered efficiently by supercritical water elutriation using a semi-batch reactor and that the methodology is promising for recovery of silicon from silicon sludge.     

Integrated supercritical fluid extraction and subcritical water hydrolysis for the recovery of bioactive compounds from pressed palm fiber

Pressed palm fiber (PPF), a residue obtained from palm oil industry, is a source of bioactive compounds, such as carotenoids, which are used as food additives. It also has cellulose and hemicellulose that can be used to yield fermentable sugars for the production of second generation ethanol. Supercritical fluid extraction (SFE) of pressed palm fiber provides an oil rich in carotenoids while subcritical water hydrolysis (SubWH) produces hydrolysates with high amounts of fermentable sugars. In this work, the effects of pressure (15–30 MPa) and temperature (318 and 328 K) on SFE of carotenoids were investigated. The SFE extract with highest carotenoid content was obtained at 318 K and 15 MPa (2.3% d.b., 0.81 mg β-carotene/g extract). After the extraction, the influence of process temperature (423–633 K), pressure (15 and 25 MPa), solvent:feed ratio (120 and 240), and residence time (1.25–5 min) on SubWH of the extraction residue was studied. At the temperature of 523 K, the highest total reducing sugar yield (11–23 g glucose/100 g carbohydrate) and the highest biomass conversion (40–97%) were obtained for any pressure and solvent:feed ratio. The highest selectivity for saccharide formation was found at 423 K (20–59 mol glucose/mol furfural equivalent). Optimal conditions for high saccharide formation and low sugar degradation product in subcritical hydrolysis were obtained at 523 K, 15 MPa, solvent:feed ratio of 120, residence time of 2.5 min with a total reducing sugar yield of 22.9 g glucose/100 g carbohydrate and a conversion of 84.9%.     

Direct and indirect power ultrasound assisted pre-osmotic treatments in convective drying of guava slices

Application of ultrasound to osmotic dehydration of guava slices via indirect sonication using an ultrasonic bath system and direct sonication using an ultrasonic probe system was studied. Pre-treatments were designed in three osmotic solution concentrations of 0, 35, and 70 °Brix at indirect ultrasonic bath power from 0 to 2.5 kW for immersion times ranging for 20–60 min and direct ultrasonic probe amplitudes from 0 to 35% for immersion times of 6–20 min. The calculated ultrasound intensities from calorimetric ultrasound power dissipated indicated that direct sonication was more intensive than indirect sonication. The general linear model (GLM) showed that ultrasound input (power and amplitude), osmotic solution concentrations, and immersion time increased the water loss, solid gain, and total colour change of guava slices significantly with P < 0.0005. Indirect sonication in osmotic solutions contributed to high water loss and solid gain with acceptable total colour change than direct sonication. Applying ultrasound pre-osmotic treatment in 70 °Brix prior to hot-air drying reduced the drying time by 33%, increased the effective diffusivity by 35%, and decreased the total colour change by 38%. A remarkable decrease of hardness to 4.2 N obtained was also comparable to the fresh guava at 4.8 N.     

Recovery of nickel from spent catalyst from palm oil hydrogenation process using acidic solutions

In this study, recovery of nickel from spent catalyst from palm oil hydrogenation process is carried out via extractive leaching process using sulfuric and hydrochloric acids. The effects of acid concentration, solid-liquid ratio, temperature and digestion time on the recovery (acid dissolution) process are investigated. It is found that sulfuric acid is the better leaching solution as compared to hydrochloric acid for recovery (dissolution) of nickel from the spent catalyst. Results from speciation modelling using VMINTEQ further imply that nickel can form sulfate complexes which are more stable than chloride complexes at concentrations higher than 1 M. The optimum conditions for maximum recovery at 85% are achieved at 67% sulfuric acid concentration, digestion time of 140 min, solid-to-liquid ratio of 1:14 and reaction temperature of 80 °C. At solution temperatures higher than 80 °C, the percentage nickel extraction is reduced. The optimization study presented here is useful for spent catalyst generators in the palm oil industry intending to recover valuable metals which may assist in reducing palm oil processing costs.     

Thermo-mechanical characterization of a silica-alumina refractory concrete based on calcined algerian kaolin

The aim of this work is to study the thermo-mechanical behaviour (bending and compressive tests, creep and thermal shock resistance) of a refractory concrete based on local kaolin grogs and aluminous cement. Strength tests revealed a behaviour that is almost linear elastic for temperatures up to 800 °C and visco-plastic at 900 °C. A crack bridging strengthening process was observed at 800 °C. The creep tests were carried out at different temperatures between 1000 and 1150 °C using stresses in the range (0.75–2.76 MPa). The stress exponent was about 1.255. Microscopic observations suggested an intergranular creep mechanism.A water quenching test was used for estimating the thermal shock resistance of the material. The tested samples supported 80 cycles of standardized cyclic thermal shock without failure. Ultrasonic measurements were applied in order to evaluate the of ultrasonic velocity changes after these thermal shock tests. Strength degradation of the samples was evaluated using two models based on ultrasonic velocity changes during test and compared with the experimental values.     

Synthetic methods in phase equilibria: A new apparatus and error analysis of the method

A new apparatus for the study of high-pressure phase equilibria using a synthetic method is described. The apparatus was especially developed for the study of solubilities of gases in condensed phases, at temperatures ranging from 243 K to 353 K and pressures up to 20 MPa. The quality of the equipment was confirmed through several tests, including measurements along the three phase co-existence line for the system ethane + methanol, the study of the solubility of methane in water, and of carbon dioxide in water.An analysis regarding the application of the synthetic isothermal method in the study of gas solubilities was performed, in order to evaluate the influence of common assumptions and of various experimental aspects on the final solubility results. The analysis revealed that the largest influence on the precision of the solubility results is related to the ratio between the volumes of the two phases in equilibrium. Experiments with small volume of the vapour phase are less susceptible to the influence of other sources of errors, resulting in a higher precision of the final results.     

Extraction of essential oils from Bunium persicum Boiss. using superheated water

A comparative study of superheated water extraction (SWE) with two conventional volatile isolation methods including hydrodistillation and Soxhlet extraction was performed on Bunium persicum Boiss. Influence of operating conditions such as temperatures from 100 to 150 °C, mean particle size from 0.5 to 1.0 mm and flow rates from 2 to 4 mL/min on the extraction process was investigated. The experiments were carried out using a laboratory-built apparatus. Separation and identification of the components were carried out by GC-FID and GC/MS. The optimum extraction efficiency for SWE was determined at 125 °C, 4 mL/min and 0.5 mm. At these operating conditions, the extraction efficiency was lower than hydrodistillation and Soxhlet extraction methods, but SWE was quicker and with respect to the valuable oxygenated components, it was more selective.