Showing papers in "Journal of Supercritical Fluids in 2014"

Supercritical fluid extraction of vegetable matrices: Applications, trends and future perspectives of a convincing green technology

Abstract: Along more than a decade, R&D on supercritical fluid extraction (SFE) of vegetable matrices has been increasingly reported in the literature. Aiming at portraying the current state of this field and its evolution in terms of raw materials, products, modes of operation, optimization, modeling techniques, and closeness to industrial application, a large compilation of almost 600 essays from 2000 to 2013 has been deeply analyzed in order to unveil those indicators and their trends. Furthermore, strengths and weaknesses are identified, and some remarks that may drive upcoming research are provided. Globally, more than 300 species are reported in the literature, with prevalence of the extraction of seeds (28% of works) and leaves (17%). The main families of extracted compounds, cosolvents and operating conditions adopted are critically examined, being possible to conclude that researchers investigate many times working regions far from the optimum due to practical limitations or absence of experimental optimization. Current phenomenological, statistical and semi-empirical approaches are reviewed, along with scale-up studies, and economic analysis. In the whole, the most comprehensive picture over SFE of vegetable matrices is provided in this review, highlighting pertinent aspects and opportunities that may further consolidate the convincing route of this technology for the next years.

Extraction of phenolic compounds and anthocyanins from blueberry (Vaccinium myrtillus L.) residues using supercritical CO2 and pressurized liquids

Abstract: This work explored the potential of subcritical liquids and supercritical carbon dioxide (CO2) in the recovery of extracts containing phenolic compounds, antioxidants and anthocyanins from residues of blueberry (Vaccinium myrtillus L.) processing. Supercritical CO2 and pressurized liquids are alternatives to the use of toxic organic solvents or extraction methods that apply high temperatures. Blueberry is the fruit with the highest antioxidant and polyphenol content, which is present in both peel and pulp. In the extraction with pressurized liquids (PLE), water, ethanol and acetone were used at different proportions, with temperature, pressure and solvent flow rate kept constant at 40 °C, 20 MPa and 10 ml/min, respectively. The extracts were analyzed and the highest antioxidant activities and phenolic contents were found in the extracts obtained with pure ethanol and ethanol + water. The highest concentrations of anthocyanins were recovered with acidified water as solvent. In supercritical fluid extraction (SFE) with CO2, water, acidified water, and ethanol were used as modifiers, and the best condition for all functional components evaluated was SFE with 90% CO2, 5% water, and 5% ethanol. Sixteen anthocyanins were identified and quantified by ultra performance liquid chromatography (UPLC).

Extraction of antioxidant compounds from blackberry (Rubus sp.) bagasse using supercritical CO2 assisted by ultrasound

Abstract: Supercritical carbon dioxide extraction (SFE) was performed to recover bioactive components from blackberry ( Rubus sp.) industrial residues. Ultrasound was applied during the extractions in order to enhance rate and yield. Moreover, water and ethanol at different proportions were used as cosolvents to improve the extraction of polar compounds from the residues. The extraction global yields were measured at all performed conditions (pressure, temperature, ultrasound power and cosolvent). The extracts were evaluated in terms of their antioxidant activity, measured using two methods, phenolic content, monomeric anthocyanins, and anthocyanin profile. The application of ultrasound in SFE helped increasing the extraction rate at the beginning of the process, which could be observed on the extraction curves at 15 MPa, the lowest pressure applied. Scanning electron microscopy (FESEM) was used to analyze the blackberry bagasse undergoing SFE with and without ultrasounds and showed that ultrasound disturbs the cell walls, enhancing the release of the extractable compounds. The extracts have shown high antioxidant activity and phenolic contents when obtained at higher temperatures. Regarding anthocyanins, the use of water as cosolvent resulted in a significant increase. Four major anthocyanins were identified and quantified by ultra performance liquid chromatography (UPLC).

Astaxanthin extraction from Haematococcus pluvialis using CO2-expanded ethanol

Abstract: The authors want to thank Spanish Projects AGL2011-29857-C03-01 and CONSOLIDER INGENIO 2010 CSD2007-00063 FUN-C-FOOD (Ministerio de Economia y Competitividad) and the European project MIRACLES (KBBE.2013.3.2-02: The CO2 algae biorefinery). Fabian A. Reyes would like to thank CONICYT-Chile for supporting his fellowship in CIAL-CSIC, Spain.

Chemical recycling of carbon fiber reinforced plastic using supercritical methanol

Abstract: Advanced chemical recycling of carbon fiber reinforced plastic (CFRP) was developed using supercritical methanol. In this method, the thermosetting epoxy resin in CFRP was converted to a thermoplastic resin by the selective decomposition of the bridged structure by supercritical methanol at 270 °C and 8 MPa for 90 min and the resin dissolved in supercritical methanol. On the other hand, the carbon fiber was fully recovered from CFRP without the plastic component and it had no thermal damage. The bridged structure in the epoxy resin could be formed again by adding a cross-linker to the recovered thermoplastic resin and the thermosetting resin was reproduced. This was the first attempt on the recycling of thermosetting epoxy resin. However, in order to maintain the strength of the recycled epoxy resin to that of virgin epoxy resin, the proper ratio of the recovered thermoplastic resin to virgin epoxy resin was determined. The recovered carbon fiber from CFRP maintained the shape of the plain fabric and the reduction of the tensile strength was less than 9% compared with the virgin one. The recovered carbon fiber could be used to make a recycled CFRP with epoxy resin and cross-linker, the strength of which was close to that of virgin CFRP.

Exploiting microalgae as a source of essential fatty acids by supercritical fluid extraction of lipids: Comparison between Scenedesmus obliquus, Chlorella protothecoides and Nannochloropsis salina

Abstract: Supercritical CO2 extraction from microalgae is applied with the aim of obtaining an oil rich in α-linolenic (ALA) essential fatty acid and with a low ω6:ω3 ratio. The maximum extraction yield is obtained at 60 °C and 30 MPa with 0.4 kg/h of CO2 and 5% of co-solvent (ethanol). When the effect of pressure, temperature and density on the supercritical extraction yield and solubility are studied, the thermodynamic cross-over is found at a pressure close to 30 MPa, while the extraction cross-over occurs at around 25 MPa. The experimental solubility data are correlated by literature empirical models. Mathematical models developed by Sovova are applied to describe the experimental extraction curves. Soxhlet extraction of lipids is also carried out, obtaining a similar fatty acids profile but proving to be less selective than SCCO2 method. Among the three species of microalgae examined, results show that Scenedesmus obliquus oil is richer in ω-3 fatty acids and ALA than Chlorella protothecoides and Nannochloropsis salina lipids. The effect of the extraction parameters on ALA content and the fatty acid profile is also analysed, concluding that the ω-3 percentage is favoured by lower temperatures, lower pressures and shorter extraction times.

Supercritical carbon dioxide extraction of microalgae lipid: Process optimization and laboratory scale-up

Abstract: Supercritical carbon dioxide (SC-CO 2 ) extraction of lipid from Scenedesmus sp. for biodiesel production was investigated and compared to conventional extraction methods. The effect of biomass pre-treatment prior to extraction and extracting conditions, namely pressure in the range of 200–500 bar, temperatures in the range of 35–65 °C and CO 2 flow rate in the range of 1.38–4.02 g min −1 , on SC-CO 2 extraction yield and quality of lipid were investigated. Three levels full factorial design of experiments and response surface methodology was used to model the system. A second order polynomial model was developed and used to predict the optimum conditions. Scaling up to a laboratory larger scale was also tested. The results indicated that SC-CO 2 extraction was superior to other extraction techniques, but exhibited significant variations in yield with changes in operating parameters. In the developed model, it was found that the linear and quadratic terms of the temperature, as well as the interaction with pressure had a significant effect on lipid yield; whereas, their effect on lipid quality was insignificant. The best operating conditions, in the tested range, were 53 °C, 500 bar and 1.9 g min −1 , in which lipid extraction yield of 7.41% (dry weight basis) was obtained. Negligible differences were observed when the fatty acid composition of SC-CO 2 extracted lipid was compared to that extracted by the conventional methods. At the optimum conditions, SC-CO 2 extraction was successfully scaled-up by eight-folds and the extracted lipid yield dropped by 16%.

Bio-oil production from oil palm biomass via subcritical and supercritical hydrothermal liquefaction

Abstract: This paper presents the studies on the liquefaction of three types of oil palm biomass; empty fruit bunch (EFB), palm mesocarp fiber (PMF) and palm kernel shell (PKS) using water at subcritical and supercritical conditions. The effect of temperature (330, 360, 390 °C) and pressure (25, 30, 35 MPa) on bio-oil yields were investigated in the liquefaction process using a Inconel batch reactor. The optimum liquefaction condition of the three types of biomass was found to be at supercritical condition of water i.e. at 390 °C and 25 MPa, with PKS yielding the maximum bio-oil yield of 38.53 wt%, followed by EFB and PMF, with optimum yields of 37.39 wt% and 34.32 wt%, respectively. The chemical compositions of the bio-oils produced at optimum condition were analyzed using GC–MS and phenolic compounds constituted the major portion of the bio-oils, with other minor compounds present such as alcohols, ketones, aromatic hydrocarbons and esters.

Optimization of the supercritical fluid coextraction of oil and diterpenes from spent coffee grounds using experimental design and response surface methodology

Abstract: The reported work aimed at the optimization of operating conditions of the supercritical fluid extraction (SFE) of spent coffee grounds (SCG) using pure or modified CO 2 , with particular emphasis on oil enrichment with diterpenes like kahweol, cafestol and 16- O -methylcafestol. The analysis comprised the application of Box–Behnken design of experiments and response surface methodology, and involved three operating variables: pressure (140–190 bar), temperature (40–70 °C) and cosolvent (ethanol) addition (0–5 wt.%). The best conditions to maximize total extraction yield are 190 bar/55 °C/5 wt.% EtOH, leading to 11.97% (g oil /100 g SCG ). In terms of the concentration of diterpenic compounds in the supercritical extracts, the best operating conditions are 140 bar/40 °C/0 wt.% EtOH, providing 102.90 mg g −1 oil . The measurement of extraction curves near optimized conditions (140 bar/55 °C/0 wt.% EtOH and 190 bar/55 °C/0 wt.% EtOH) confirmed the trends of the statistical analysis and revealed that SFE enhances diterpenes concentration by 212–410% at the expenses of reducing the extraction yield between 39% and 79% in comparison to n -hexane extraction.

Supercritical fluid extraction of spent coffee grounds: Measurement of extraction curves, oil characterization and economic analysis

Abstract: This work addresses scientific and techno-economic aspects of supercritical fluid extraction (SFE) of spent coffee grounds which are of interest under the biorefinery context. Soxhlet experiments were carried out and SFE curves were measured at 190 bar and 40 °C/55 °C. The extracts were characterized by GC-FID, and the triacylglycerides profiles were almost constant along an extraction curve, and similar to the n-hexane Soxhlet results: linoleic and palmitic acids content in both extracts are 44.5 and 37.5% (wt.), respectively. The oil solubility, intraparticle diffusion, convective mass transfer coefficient, and oil removal flux (this one estimated for infinite dilution) were calculated and discussed in detail in the ranges of operating conditions under analysis. It was concluded that solubility is the chief parameter behind the distinct cumulative extraction curves, and that all experiments are subjected to equivalent mass transfer resistances. An economic analysis involving cost of manufacturing (COM) and net income calculations were performed for distinct operating conditions and unit arrangements. The optima results were obtained for an arrangement of 3 beds of 1 m3, extraction time of 2.0 h, 300 bar, 50 °C and 30 kg CO 2 k g SCG − 1 h − 1 . Under these conditions production can reach 454 ton year−1, a cost of manufacturing (COM) around 2.4 M€, and process net income of 56.6 M€. A sensitivity analysis varying the unit capacity, extraction time and precipitation pressure (extract vessel), showed the process economics to remain viable.

Obtaining sugars from coconut husk, defatted grape seed, and pressed palm fiber by hydrolysis with subcritical water

Abstract: In this work, three residues from the food industry (coconut husk, defatted grape seed and pressed palm fiber) were subjected to subcritical water hydrolysis with the aim of producing fermentable sugars. Hydrolysis kinetics were determined using a semi-batch unit equipped with a 50 mL reactor. The process was conducted at 208 °C and 257 °C for 30 min, with water flow rate of 33 mL/min and under 20 MPa. The liquefaction degree of the raw materials increased with temperature. The total reducing sugars recovered also increased with temperature. Maximum total reducing sugars recovered for coconut husk, defatted grape seed and pressed palm fiber using SWH were 11.7%, 6.4% and 11.9% from total raw material, respectively. Coconut husk presented the highest amount of monosaccharides (3.4%), followed by pressed palm fiber (2.4%) and defatted grape seeds (0.7%). On the other hand, the degradation products that are also fermentation inhibitors increased with temperature as well. Each raw material presented a different monosaccharides and inhibitors profile, which indicates that SWH should be evaluated and optimized individually for each case.

Estimating hydrogen sulfide solubility in ionic liquids using a machine learning approach

Abstract: For the design and development of new processes of gas sweetening using ionic liquids (ILs), as promising candidates for amine solutions, an amazing model to predict the solubility of acid gases is of great importance. In this direction, in the current study, the capability of artificial neural networks (ANNs) trained with back propagation (BP) and particle swarm optimization (PSO), to correlate the solubility of H 2 S in 11different ILs have been investigated. Different structures of three-layer feed forward neural network using acentric factor ( ω ), critical temperature ( T c ), critical pressure ( P c ) of ILs accompanied by pressure ( P ) and temperature ( T ), as input parameters, were examined and an optimized architecture has been proposed as 5–9–1.Implementation of these models for 465 experimental data points collected from the literature shows coefficient of determination ( R 2 ) of 0.99218 and mean squared error (MSE) of 0.00025 from experimental values for PSO-ANN predicted solubilities while the values of R 2 = 0.95151 and MSE = 0.00335 were obtained for BP-ANN model. Therefore, through PSO training algorithm we are able to attain significantly better results than with BP training procedure based on the statistical criteria.

Near critical and supercritical impregnation and kinetic release of thymol in LLDPE films used for food packaging

Abstract: The impregnation of organic compounds in polymeric materials using supercritical carbon dioxide (scCO2) is a well-known technique, which is currently used in drug/polymer formulation. In this work, near critical and supercritical impregnation of thymol in linear low-density polyethylene (LLDPE) films was done in order to develop a new technique for preparation of active polymers to be used as food packages. The properties of thymol as a natural antimicrobial and antioxidant agent have motivated this study about the assessment of its migration from the polymer to different food simulant. Impregnation assays of thymol in LLDPE films were done in a high-pressure cell, where pure thymol was solubilized in supercritical carbon dioxide at 313 K and pressures varying from 7 to 12 MPa. This procedure allowed the preparation of plastic films with thymol concentrations ranged between 5100 and 13,200 ppm. Migration tests showed that the pressure applied during the impregnation procedure is a key parameter that affects the content of the active compound into the polymer, since thymol solubility in scCO2 and absorption phenomena in the polymer increased with the pressure. The correlation between experimental data and a phenomenological transfer model allowed the estimation of the diffusion coefficient of thymol in LLDPE, which was ranged from 7.5 × 10−13 to 3.0 × 10−12 m2 s−1.

Extraction of curcuminoids from deflavored turmeric (Curcuma longa L.) using pressurized liquids: Process integration and economic evaluation

Abstract: Pressurized liquid extraction (PLE) of curcuminoids from deflavored turmeric rhizomes was optimized. The rhizomes were initially deflavored by extraction with supercritical CO2. Immediately after SFE, PLE process was performed using ethanol as the solvent and a static extraction time of 20 min, and the independent variables were the temperature (333–353 K) and pressure (10–35 MPa). The results indicate that the optimum extraction temperature and pressure were 333 K and 10 MPa, respectively. PLE required three and six times less extraction time than low-pressure solvent extraction and Soxhlet extraction, respectively, to produce similar extraction yields. The cost of manufacturing (COM) decreased from US$ 94.92 kg−1 to US$ 88.26 kg−1 when the capacity of the two-extractor system increased from 0.05 m3 to 0.5 m3 and from US$ 94.92 kg−1 to US$ 17.86 kg−1 when the cost of the raw materials decreased from US$ 7.91 kg−1 to US$ 0.85 kg−1 for a two 0.05 m3 extractor system.

Catalytic depolymerisation and conversion of Kraft lignin into liquid products using near-critical water

Abstract: A high-pressure pilot plant was developed to study the conversion of LignoBoost Kraft lignin into bio-oil and chemicals in near-critical water (350◦C, 25 MPa). The conversion takes place in a continuous fixed-bed catalytic reactor (500 cm3) filled with ZrO2 pellets. Lignin (mass fraction of approximately 5.5%) is dispersed in an aqueous solution containing K2CO3(from 0.4% to 2.2%) and phenol (approximately 4.1%).The feed flow rate is 1 kg/h (reactor residence time 11 min) and the reaction mixture is recirculated internally at a rate of approximately 10 kg/h. The products consist of an aqueous phase, containing phenolic chemicals, and a bio-oil, showing an increased heat value (32 MJ/kg) with respect to the lignin feed. The 1-ring aromatic compounds produced in the process are mainly anisoles, alkylphenols, guaiacols and catechols: their overall yield increases from 17% to 27% (dry lignin basis) as K2CO3 is increased.

Silk fibroin aerogels for drug delivery applications

Abstract: Silk fibroin (SF) is a natural protein, derived from the Bombyx mori silkworm. Silk fibroin based porous materials are being extensively investigated for biomedical applications, due to their biocompatibility and biodegradability. The results presented here demonstrate the potential of SF aerogels as drug delivery devices for the extended release of ibuprofen, a candidate drug. SF aerogels are loaded with of ibuprofen using supercritical carbon dioxide (scCO2) at 40 °C and 100 bar. Differential scanning calorimetry of the ibuprofen-loaded SF aerogels indicates that the ibuprofen is amorphous. Scanning electron microscopy and nitrogen adsorption/desorption analysis are used to investigate the morphology and textural properties. Phosphate buffer solution (PBS) soaking studies, at 37 °C and pH 7.4, reveal that SF aerogels do not swell nor exhibit any weight loss for up to 6 h, the lifetime of the release measurements performed in the present study. In vitro ibuprofen release in PBS, at 37 °C and pH 7.4, occurs over a 6-h period when the ibuprofen is loaded in SF aerogel discs that are 1.4 cm in diameter and 0.85 cm in height. In contrast, the dissolution of the same amount of pure ibuprofen occurs in 15 min. Furthermore, the release of ibuprofen from these SF aerogel discs are modeled using the Ritger–Peppas model which indicates that ibuprofen release follows Fickian diffusion.

Supercritical carbon dioxide extraction of lithium-ion battery electrolytes

Abstract: Two different separator materials (polyethylene fleece – Freudenberg 2190 and porous glass fiber – Whatman ® GF/D) and two different lithium-ion battery electrolytes have been investigated regarding their behavior in an autoclave extraction with supercritical helium head pressure carbon dioxide (sc HHPCO 2 ). Mixtures of dimethyl carbonate (DMC)/ethylene carbonate (EC) and ethylmethyl carbonate (EMC)/EC, each with 1 mol/L LiPF 6 were used. In addition to these proof of principle experiments, the developed extraction method was further applied to real battery samples. Commercial 18650 cells (after formation and aging) were opened and the jelly roll was extracted with sc HHPCO 2 . Extracts were analyzed with gas and ion chromatography (GC, IC). Recovery rates and extract compositions strongly depend on the material of which the electrolyte is extracted. Further structure determination of electrolyte aging products was performed with different ionization modes in GC–mass spectrometry (GC–MS) experiments. Diethyl carbonate (DEC), dimethyl-2,5-dioxahexane dicarboxylate (DMDOHC), ethylmethyl-2,5-dioxahexane dicarboxylate (EMDOHC) and diethyl-2,5-dioxahexane dicarboxylate (DEDOHC) are aging products of electrolyte degradation which were successfully extracted and identified. Their concentrations correlate with solid electrolyte interphase (SEI) growth on the negative electrode which was investigated with scanning electron microscopy (SEM).

Supercritical CO2 extraction of oil from seeds of six grape cultivars: Modeling of mass transfer kinetics and evaluation of lipid profiles and tocol contents

Abstract: The current study focuses on the recovery of grape seed oil by supercritical CO2 extraction. Grape seeds from six grape cultivars were extracted in two subsequent harvesting years, and the resulting oils were characterized for the relative amount of: (a) lipid classes; (b) lipid acyl chains; and (c) tocopherols and tocotrienols. Comparative extractions were performed by utilizing n-hexane as solvent and by mechanical pressure. A well-established modeling approach was applied to evaluate the mass transfer parameters affecting the kinetics of supercritical CO2 extraction: with these parameters, process scale-up can be addressed. The results reported in this study testify the potentiality of grape seed oil as a source of unsaturated fatty acids and tocols. Moreover, they offer a clear picture of the similarities and differences among oils from different grape cultivars and obtained through different extraction techniques.

Economic analysis of a plant for biodiesel production from waste cooking oil via enzymatic transesterification using supercritical carbon dioxide

Abstract: Enzymatic transesterification is becoming a commercially competitive route to biodiesel. Supercritical CO2 (scCO2) is well established as a solvent for extraction processes. Here we analyze the economy of a scCO2-based, enzymatic process, for the production of biodiesel from waste cooking sunflower oil (WCO). The conversion of WCO to fatty acid ethyl esters (FAEE) catalyzed by immobilized lipase from Thermomyces lanuginosus (Lipozyme TL IM), and downstream separation to recover biodiesel conforming to the EN14214 norm, were studied in a pilot plant unit. The data generated was used to design an envisaged industrial plant, for which an energy balance was carried out. Investment and production costs were estimated for the conversion of 8000 tonWCO/year. This led to biodiesel costs of 1.64€/L and 0.75€/L (for a WCO price of 0.25€/kg; enzyme prices of 800€/kg and 8€/kg, respectively), which already reflect the ca. 10% impact of glycerol sales.

Extraction of phenolic compounds from pitanga (Eugenia uniflora L.) leaves by sequential extraction in fixed bed extractor using supercritical CO2, ethanol and water as solvents

Abstract: With the goal of maximizing the extraction yield of phenolic compounds from pitanga leaves (Eugenia uniflora L.), a sequential extraction in fixed bed was carried out in three steps at 60 °C and 400 bar, using supercritical CO2 (non-polar) as solvent in a first step, followed by ethanol (polarity: 5.2) and water (polarity: 9.0) in a second and third steps, respectively. All extracts were evaluated for global extraction yield, concentration and yield of both polyphenols and total flavonoids and antioxidant activity by DPPH method (in terms of EC50). The nature of the solvent significantly influenced the process, since the extraction yield increased with solvent polarity. The aqueous extracts presented higher global extraction yield (22%), followed by ethanolic (16%) and supercritical extracts (5%). The study pointed out that the sequential extraction process is the most effective in terms of global extraction yield and yield of polyphenols and total flavonoids, because it produced the more concentrated extracts on phenolic compounds, since the supercritical ethanolic extract presented the highest phenolics content (240.5 mg GAE/g extract) and antioxidant capacity (EC50 = 9.15 μg/mL). The most volatile fraction from the supercritical extract, which is similar to the essential oils obtained by steam distillation or hydrodistillation, presented as major compounds the germacrenos D and B + bicyclogermacrene (40.75%), selina-1,3,7(11)-trien-8-one + selina-1,3,7(11)-trien-8-one epoxide (27.7%) and trans-caryophyllene (14.18%).

Optimization of subcritical water extraction of antioxidants from Coriandrum sativum seeds by response surface methodology

Abstract: Subcritical water extraction (SWE) of antioxidants from Coriandrum sativum seeds (CSS) was optimized by simultaneous maximization of the total phenolics (TP) and total flavonoids (TF) yield and antioxidant activity, using IC 50 value. Box–Behnken experimental design (BBD) on three levels and three variables was used for optimization together with response surface methodology (RSM). Influence of temperature (100–200 °C), pressure (30–90 bar) and extraction time (10–30 min) on each response was investigated. Experimentally obtained values were fitted to a second-order polynomial model and multiple regression. Analysis of variance (ANOVA) was used to evaluate model fitness and determine optimal conditions. Moreover, three-dimensional surface plots were generated from employed mathematical model. The optimal SWE conditions obtained in simultaneous optimization were temperature of 200 °C, pressure of 30 bar and extraction time of 28.3 min, while obtained values of TP and TF yields and IC 50 value at this experimental point would be 2.5452 g GAE/100 g CSS, 0.6311 g CE/100 g CSS and 0.01372 mg/ml, respectively. Moreover, good and moderate linear correlation was observed between antioxidant activity (IC 50 value) and total phenolics content ( R 2 = 0.965), and total flavonoids content ( R 2 = 0.709) which indicated that these groups of compounds are responsible for antioxidant activity of C. sativum extracts.

Water and ethanol as co-solvent in supercritical fluid extraction of proanthocyanidins from grape marc: A comparison and a proposal

Abstract: Supercritical carbon dioxide (SC-CO 2 ) extraction of grape marc was studied using water (W) and ethanol (EtOH) as co-solvent at 15% (w/w), 100 and 200 MPa, and 313.15, 323.15 and 333.15 K to analyze their influence upon total phenols of the extracts. The overall extraction curves were determined and suggested 10 MPa and 313.15 K as the best operating conditions for SC-CO 2 + 15%W extraction, and 10 MPa and 333.15 K for SC-CO 2 + 15% EtOH. The phenolic yields obtained were 63.4 g/kg of extract for SC-CO 2 + 15% W and 38.8 g/kg of extract for SC-CO 2 + 15% EtOH. An alternative method combining Sc-CO 2 + 15% W extraction, followed by SC-CO 2 + 15% EtOH was tested. This procedure provided the best results allowing to obtain the highest phenolic yield (68.0 g/kg of extract), phenol content (733.6 mg GAE/100 g DM), proanthocyanidins concentration (572.8 mg catechin/100 g DM) and antioxidant activity (2649.6 mg α-tocopherol/100 g DM). SC-CO 2 methods were compared with methanol extraction.

Hydrolysis of sugarcane bagasse in subcritical water

Abstract: 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 56% at 213 °C and 33 mL/min Approximately 60% of the sugars recovered were in the oligomeric form

Extraction of proanthocyanidins from grape marc by supercritical fluid extraction using CO2 as solvent and ethanol–water mixture as co-solvent

Abstract: The extraction of phenolic compounds from grape marc using supercritical CO2 containing 15% ethanol–water mixture (57%, v/v) (EtW) as co-solvent, at 8, 10, 20 and 30 MPa/313.15 K suggested 8 MPa as the most suitable pressure. At 8 MPa/313.15 K, different co-solvent percentages (15, 10, 7.5%) at CO2 flow rate of 6 and 4 kg/h were investigated for proanthocyanidins (PAs) the extraction. The highest extraction yields were obtained at 4 kg/h CO2–7.5% EtW flow rate ( 2600 mg GAE 100 g DM − 1 ) and 6 kg/h CO2–10% EtW ( 2527 mg GAE 100 g DM − 1 ). At 6 kg/h CO2–10% EtW flow rate the amounts of monomeric ( 188 mg catechin 100 g DM − 1 ) and oligomeric ( 154 mg catechin 100 g DM − 1 ) fractions of PAs, as well as their antioxidant activity ( 809 and 546 mg α -tocopheroll 100 g DM − 1 ) were higher than at 4 kg/h CO2–7.5% EtW-flow rate. SC-CO2 methods were compared with conventional methanol extraction.

Extraction of bioactive compounds from peach palm pulp (Bactris gasipaes) using supercritical CO2

Abstract: a b s t r a c t Natural compounds with biological activity have recently attracted special interest in the agro-industry as sources of additives in nutraceutical food production and pharmaceutical industries. Herein, we evalu- ated extracts obtained from peach palm fruit (Bactris gasipaes) using supercritical carbon dioxide, in terms of yield, total phenolic content, total flavonoids, total carotenoids, and antioxidant activity by -carotene bleaching method. Extractions were performed at 40, 50, and 60 ◦C and 100, 200, and 300 bar; addition- ally, Soxhlet (with petroleum ether) and methanol extraction were conducted. The results showed that supercritical CO2 allows obtaining extracts rich in carotenoids and, although it presents lower yield than conventional extraction (SOX), supercritical CO2 represents a technique with greater advantages. The best operation condition for supercritical extraction was 300 bar-40 ◦

The synergy of supercritical CO2 and supercritical N2 in foaming of polystyrene for cell nucleation

Abstract: This study examines the foaming behaviour of polystyrene (PS) blown with supercritical CO 2 –N 2 blends. This is achieved by observing their foaming processes in situ using a visualization system within a high-temperature/high-pressure view-cell. Through analyzing the cell nucleation and growth processes, the foaming mechanisms of PS blown with supercritical CO 2 –N 2 blends have been studied. It was observed that the 75% CO 2 –25% N 2 blend yielded the highest cell densities over a wide processing temperature window, which indicates the high nucleating power of supercritical N 2 and the high foam expanding ability of supercritical CO 2 would produce synergistic effects with that ratio in batch foaming. Also, the presence of supercritical CO 2 increased the solubility of supercritical N 2 in PS, so the concentration of dissolved supercritical N 2 was higher than the prediction by the simple mixing rule. The additional supercritical N 2 further increased the cell nucleation performance. These results provide valuable directions to identify the optimal supercritical CO 2 –N 2 composition for the foaming of PS to replace the hazardous blowing agents which are commonly used despite their high flammability or ozone depleting characteristics.

Hydrothermal liquefaction of wheat straw in hot compressed water and subcritical water–alcohol mixtures

Abstract: Hydrothermal liquefaction of lignocellulosic biomass (wheat straw) into bio-oil has been investigated under subcritical conditions (temperature up to 350 °C, pressure up to 200 bar) in water and water–alcohol mixtures using ethanol and isopropanol in a continuously operated tubular reactor. The effect of different reaction parameters such as temperature, pressure and water–alcohol ratio on the biomass conversion, cracking products yield and the higher heating value (HHV) of the received bio-oil was studied. The water–ethanol mixture was found to be a very reactive medium showing a complete biomass conversion and >30 wt% yield of high caloric oil (HCO). A maximum HHV of 28 MJ/kg for HCO was achieved. In addition, Ru (5 wt%) on H-Beta support was used as catalyst in a run with hydrogen in the feed showing deeper deoxygenation of reaction intermediates and highest HHV of the product oil (30 MJ/kg). This work demonstrated the usability of water–ethanol mixtures for an effective depolymerization of lignocellulosic biomass to bio-oils under subcritical reaction conditions with more than doubled HHV compared to the feedstock, in particular using a catalyst and the presence of hydrogen for further deoxygenation.

Control of number of graphene layers using ultrasound in supercritical CO2 and their application in lithium-ion batteries

Abstract: This study reports a novel strategy using ultrasound in supercritical CO2 for exfoliating graphite directly into single and few-layer graphene sheets. The mutually complementary characterizations of the as-exfoliated samples via atomic force microscopy, transmission electron microscopy and Raman spectroscopy indicate that the ultrasonic power greatly affects the number of layers and the lateral size of the graphene. Single-layer graphene with a lateral size of 50–100 nm and two-layer graphene with a lateral size of 0.5–10 μm are obtained using an ultrasonic power of 300 and 120 W, respectively. As-exfoliated graphene sheets heighten the electrochemical performance of LiFePO4 cathode materials, demonstrating graphene's remarkable electrical conductivity. The specific capacity of the LiFePO4/graphene composite cathode achieves 160 mAh/g and displays stable cycling for more than 15 cycles. This technique will enable cost-effective mass production of graphene sheets with good quality, and the as-exfoliated graphene will find wide applications, including lithium-ion batteries.

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

Abstract: 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%.

Removal of contaminants from polluted drilling mud using supercritical carbon dioxide extraction

Abstract: Liquid drilling fluid is often called drilling mud is heavy, viscous fluid mixtures use to carry rock cuttings to the surface and lubricate and cool the drill bit. During carrying cuttings they contaminated which not only reduce their functionality but also make them a hazardous and dangerous wastes which cannot be discharged anywhere without treatment. Due to this fact, in the present study, supercritical extraction process was used to remove contaminants from the drilling mud. Regarding this, effect of different parameters including extraction temperature (313–338 K) and pressure (100–200 bar), flow rate of CO2 (0.05–0.36 cm3/s) and static time (20–130 min) on the removal of contaminations from drilling mud was examined using the design of experiment of changing one factor at a time. The obtained results revealed that the optimum operational conditions that lead to the highest removal degree of contaminations are temperature and pressure of 333 K and 180 bar, respectively, flow rate of lower than 0.1 cm3/s and the static time of 110 min. In addition, to examine the effect of the supercritical extraction on the crystalline structure modification and removal contaminations X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were performed which confirmed the successful removal of contaminations from the drilling mud without significant crystalline modification.