Ultrasound-assisted Supercritical CO2 Research Articles

Programming and validation of a novel green procedure for the production of essential oil from Lavandula angustifolia

Lavandula angustifolia (lavender) essential oil (LEO) is extremely popular and beneficial. In the present study, LEO was extracted with green ultrasound-assisted supercritical CO2 (UscCO2) and other classical methodologies. The highest yield of LEO (5.32 % (w/w)) was achieved with the UscCO2 process, followed by hexane extraction (4.32%), scCO2 extraction (3.94 %) and hydrodistillation (HD; 3.69 %). The contents of two dominant aromatic ingredients, linalool (29.93 %) and linalyl acetate (35.08 %), obtained by the UscCO2 procedure were also the highest. Remarkably, the linalyl acetate content in UscCO2-derived LEO was nearly triple that in LEO extracted via HD (12.33 %). The novel UscCO2 technique not only provided the highest LEO quality but also revealed the highest extraction efficiency under mild extraction parameters. The dynamic solubility of LEO in the UscCO2 and scCO2 procedures was further determined to confirm the kinetic efficacy. The dynamic solubility was simulated with three density-based models, which provided excellent agreement with the experimental results. The approximate heat of vaporization, total heat of solution and heat of solvation obtained from UscCO2 dynamic extraction of LEO were significantly lower than those obtained from the scCO2 procedure. The kinetic and thermal effects of ultrasonic energy substantially contributed to the excellent performance of UscCO2.

Combination of supercritical CO2 and ultrasound for flavonoids extraction from Cosmos sulphureus: Optimization, kinetics, characterization and antioxidant capacity

A hyphenated technique using ultrasound-assisted supercritical CO2 extraction (UASCE) was developed to obtain flavonoids from Cosmos sulphureus. The highest total flavonoids content (TFC) achieved at 25 MPa pressure, 55 °C temperature, 10% cosolvent concentration, and 0.21 W/mL ultrasound energy density. UASCE improved TFC and antioxidant capacity of the extract, reduced extraction duration and extraction pressure, saved electric energy consumption and usages of CO2 and organic solvent, when compared with conventional extraction techniques. Furthermore, a high correlation between TFC and antioxidant capacity of the extract was found. HPLC analysis indicated that ultrasound effectively improved the individual concentrations of these flavonoids in extracts. Moreover, the kinetics study implied that the employed Sovová models were in good agreement with the experimental kinetic profiles. In conclusion, UASCE is a sustainable and efficient production technology in food and dietary supplement industries. Furthermore, Cosmos sulphureus can be considered as an attractive feedstock for natural flavonoids production.

Supercritical carbon dioxide extraction of Cosmos sulphureus seed oil with ultrasound assistance

A hybrid procedure using ultrasound-assisted supercritical CO2 extraction (UASCE) was developed to recover Cosmos sulphureus seed oil (CSSO). Optimization of CSSO extraction was executed by the Taguchi approach. The maximum oil yield (193.1 ± 4.4 mg/g, dry mass) was obtained at 75 dynamic extraction time, 25 MPa pressure, 55 ℃ temperature, 0.5 g/min CO2 flow rate, and 0.2 W/mL ultrasound energy density (UED). Scanning electron micrograph (SEM) revealed that a remarkable porous and loose microstructure was observed in UASCE-treated sample, this may have positive effects on oil release. CSSO acquired by UASCE had higher global yield and higher contents of unsaturated fatty acids, tocopherols, sterols, phenols, and exhibited better physicochemical characteristics, antioxidant activity and oxidation and thermal stability compared to CSSO acquired by traditional techniques. Furthermore, the kinetics study highlighted that the employed Sovová models fitted well with the extraction kinetics behaviors. The extraction transport primarily contributed from convective mechanisms during the UASCE process and ultrasound clearly increased mass transfer coefficients and abridged the characteristic extraction periods. Consequently, UASCE can be considered a high-performance and sustainable technique for plant oil extraction in food and dietary supplement industries. Cosmos sulphureus is a potential good source of edible oil due to its excellent nutritional properties.

Supercritical CO2 extraction of total flavonoids from Iberis amara assisted by ultrasound

Iberis amara is used in herbal medicine where it has been shown to have heterogeneous pharmacological effects. In this study, ultrasound-assisted supercritical CO2 extraction (UASCE) of total flavonoids from Iberis amara was optimized. The maximal total flavonoids content (TFC) was achieved at 25 MPa pressure, 46 °C temperature, 0.34 W/mL ultrasonic energy density, which was 18% higher than that obtained with traditional supercritical CO2 extraction. Furthermore, kinetics study showed that ultrasound primarily improves the extraction rate during constant extraction rate period. High correlation (r = 0.78) exists between TFC and antioxidant activity of extracts. Moreover, HPLC analysis revealed that ultrasound introduction can effectively increase the individual concentrations of interested flavonoids (rutin, kaempferol, quercetin, catechin) in extracts in the range from 16.8% to 45.1%. In conclusion, this study suggests that UASCE is a feasible combined technique to produce flavonoids from Iberis amara on an industrial level as well as for analytical purposes.

Preparation of graphene/PMMA composites with assistance of ultrasonic wave under supercritical CO2 conditions

The two-dimensional material graphene has many excellent physicochemical properties such as large specific surface area, high electron migration rate, good chemical properties, good thermal conductivity, high elastic modulus and mechanical strength that make it very valuable for theoretical research and application in the preparation of graphene/polymer composites. In this paper, the effects of ultrasonic intensity and reaction time on the molecular weight and yield of PMMA under supercritical CO2 conditions were investigated. It was found that there are threshold and optimal values of ultrasonic intensity for initiating the reaction in supercritical CO2 system. The threshold value is 150 W/cm2 and the optimal ultrasonic intensity value is 225 W/cm2. There is also an optimal value of ultrasonic initiation time for ultrasonic initiation polymerization. Combining the reaction yield and the molecular weight of the product, 2 h of ultrasonic initiation is a suitable initiation reaction time. Based on the synthesis of PMMA by ultrasonic excitation, the preparation of Graphene/PMMA composites by ultrasound assistance was also investigated. The TG and DTG characterization of PMMA and complex materials prepared by ultrasonic excitation showed that the radicals generated by ultrasonic excitation were uniformly distributed and did not generate unsaturated double bonded polymers. The electrical conductivity of the Graphene/PMMA composites prepared by ultrasonic excitation at a graphene content of 1 wt% increased to 1.13 × 10-1 S/cm, which is better than that of the Graphene/PMMA prepared by in situ polymerization. This may be attributed to the ultrasound-assisted supercritical CO2 fluid action that resulted in a more uniform distribution of Graphene mixed with PMMA in the prepared composites. Therefore, it is of important practical significance for the preparation of Graphene/PMMA composites by ultrasound-induced polymerization.

A laboratory study on extracting active ingredients from scrophularia striata boiss using ultrasound-assisted supercritical fluid extraction technique

ABSTRACT The aim of this study was adopted survey a novel method with the frequencies of 37 and 80 kHz and the power of 50–310 W in the supercritical extraction system to extracting ingredients from Scrophularia striata Boiss plant which include analgesics, bacteria, depression and infectious agents, using ultrasound-assisted supercritical CO2 fluid extraction (USC CO2) or supercritical CO2 fluid extraction (SC CO2) techniques at frequencies of 37 and 80 kHz, temperature of 45, 55 and 65 °C, and pressures of 150, 180, 210 bar. The ultrasonic technique is underpinned by the formation of high-frequency ultrasonic waves that can generate cavities. Such cavities cause disturbances in the cell walls of solid matrix, which facilitate the solvent penetration and mass transfer and thus increase the extraction yield. According to the results indicated a 24-percent increase in yield for the USC CO2 extraction technique at a frequency of 37 kHz, optimal pressure of 180 bar, and temperature of 65 °C, in comparison to the SC CO2 technique. Such an increase is acceptable given that the USC CO2 technique is relatively inexpensive and pro-environmental.

Development and validation of an ultrasound-assisted supercritical carbon-dioxide procedure for the production of essential oils from Perilla frutescens

Four different isolation techniques, the ultrasound-assisted supercritical CO2 (UscCO2) extraction, traditional supercritical CO2 (TscCO2) extraction, steam distillation (STD) and heat-reflux extraction (HRE), were utilized to isolate volatile oils from the purple leaves of P. frutescens. The highest yield of volatile oils obtained by the UscCO2 procedure was 1.62% (weight of extracted oil/dry weight of plant material), which was 13.7, 30.2 and 72.2% higher than the oil yields obtained by TscCO2 extraction, STD and HRE, respectively. In addition, the content of perillaldehyde (49.76%, w/w) obtained by the UscCO2 process was approximately 1.09, 1.43 and 1.23 times higher than the contents obtained by STD, HRE and TscCO2 extraction, respectively. Moreover, the theoretical solubility of volatile oils in supercritical solvent was evaluated with the dynamic extraction method and then correlated with the Chrastil, Bartle and Kumar and Johnston models, with average absolute relative deviations (AARDs) of 0.71%, 0.74% and 3.56%, respectively.

Ultrasound-assisted supercritical CO2 extraction of cucurbitacin E from Iberis amara seeds

Cucurbitacin E (CuE) is an active compound with heterogeneous biological activity and is abundant in Iberis amara seeds. To extract CuE from the seeds, a novel procedure using ultrasound-assisted supercritical CO2 extraction (UASCE) was exploited in this study. The Taguchi design method was adopted for optimizing the experimental conditions of UASCE using L25 (56) orthogonal array. The highest CuE yield (8.61 ± 0.06 mg/g, dry mass) for UASCE was achieved at 60 min dynamic extraction time, 25 MPa pressure, 50 °C, 2 mL/min CO2 flow rate, 12% co-solvent concentration, and 200 W ultrasonic power. The obtained results revealed that UASCE improved the CuE yield by 26.1% and decreased extraction duration by 34.8% as well as reduced the usage amount of CO2 by 52% compared with orthodox supercritical CO2 extraction. Furthermore, the kinetics study demonstrated that the adopted Sovová models fitted well with the experimental extraction curves. The convective mechanism plays a prominent role in UASCE process and mass transfer coefficients increased with the amplification of ultrasonic power. This hybrid technique can be considered as an efficient and promising extraction procedure to obtain CuE from Iberis amara seeds in industrial scale.

Kinetics and mass transfer considerations for an ultrasound-assisted supercritical CO2 procedure to produce extracts enriched in flavonoids from Scutellaria barbata

Six bioactive flavonoids were isolated from Scutellaria barbata D. Don through heat-reflux, ultrasound-assisted, conventional supercritical CO2 and ultrasound-assisted supercritical CO2 (USC-CO2) extractions using different extraction schemes and parameters. The USC-CO2 extraction method produced higher yields of six flavonoids that were 28.09–29.31, 24.64–27.74 and 18.63–19.03% higher than those of heat-reflux, ultrasound-assisted and conventional supercritical CO2 extractions, respectively, with time durations that were lower by factors of 2.29, 1.14 and 2 than those of the three other extraction techniques and with less-harsh operating conditions. Therefore, the current procedure is a promising technique for the extraction of various bioactive constituents from a wide variety of raw matrixes. Furthermore, a second-order kinetic model and a mass transfer model based on Fick’s second law were successfully correlated with the overall USC-CO2 dynamic extraction of S. barbata D. Don. The results obtained from the second-order kinetic model indicated that the energy barrier in the USC-CO2 procedure was lower than that in the traditional extraction techniques. In addition, the mass transfer model revealed that incrementing the operation temperature from 32 to 52 °C at constant pressure might effectively enhance the mass transfer and diffusion in the current procedure and that the current procedure is dominated by intraparticle diffusion. These results provide very helpful information for the design and development of an efficient procedure to extract bioactive flavonoids from a wide variety of matrixes for future applications in industrial extraction processes.

Infusion of graphene in natural rubber matrix to prepare conductive rubber by ultrasound-assisted supercritical CO2 method

In recent years, graphene has become the most popular conductive filler in conductive polymers which can be used in many practical applications. A proper selection of the mixing method is the decisive factor to maximize the excellent conductivity of graphene in a polymer matrix. In this work, ultrasound-assisted supercritical CO2 (scCO2) method was used for the first time to prepare graphene infiltrated conductive natural rubber (NR). Many interesting phenomena were discovered. First, it was found that NR was fully swollen after an ultrasound-assisted scCO2 penetration and a following rapid decompression process. The degree of expansion of NR in scCO2 was even larger than in toluene. Secondly, ultrasound-assisted scCO2 method coupled with a rapid decompression process successfully inserted graphene particles in the swollen NR to prepare conductive NR/graphene materials. The impacts of the decompression method, vulcanization degree, and ultrasonication duration on graphene infusion were studied and analyzed. Under an optimal condition, the surface conductivity of as-prepared unvulcanized graphene/NR film or vulcanized film with a low graphene loading fraction (0.34 vol%) could reach to 0.2 S/m or 0.02 S/m, respectively, taking a leading position in the reported graphene/NR composites. Our conductive NR was shown to be satisfactory as a strain sensor for the measurement of fine movements of human body such as heartbeat, finger bending, and vocalization. Since only scCO2, one of the most environmentally benign solvents, was used in the whole process, this routine is not only efficient but also environmentally friendly. We believe this method is versatile and can be applied to many other polymers that can be swollen in scCO2.

Development and characterization of a green procedure for apigenin extraction from Scutellaria barbata D. Don

This study compared the use of ultrasound-assisted supercritical CO2 (USC-CO2) extraction to obtain apigenin-rich extracts from Scutellaria barbata D. Don with that of conventional supercritical CO2 (SC-CO2) extraction and heat-reflux extraction (HRE), conducted in parallel. This green procedure yielded 20.1% and 31.6% more apigenin than conventional SC-CO2 extraction and HRE, respectively. Moreover, the extraction time required by the USC-CO2 procedure, which used milder conditions, was approximately 1.9 times and 2.4 times shorter than that required by conventional SC-CO2 extraction and HRE, respectively. Furthermore, the theoretical solubility of apigenin in the supercritical fluid system was obtained from the USC-CO2 dynamic extraction curves and was in good agreement with the calculated values for the three empirical density-based models. The second-order kinetics model was further applied to evaluate the kinetics of USC-CO2 extraction. The results demonstrated that the selected model allowed the evaluation of the extraction rate and extent of USC-CO2 extraction.

Ultrasound coupled with supercritical carbon dioxide for exfoliation of graphene: Simulation and experiment

Ultrasound coupled with supercritical CO2 has become an important method for exfoliation of graphene, but behind which a peeling mechanism is unclear. In this work, CFD simulation and experiment were both investigated to elucidate the mechanism and the effects of the process parameters on the exfoliation yield. The experiments and the CFD simulation were conducted under pressure ranging from 8MPa to 16MPa, the ultrasonic power ranging from 12W to 240W and the frequency of 20kHz. The numerical analysis of fluid flow patterns and pressure distributions revealed that the fluid shear stress and the periodical pressure fluctuation generated by ultrasound were primary factors in exfoliating graphene. The distribution of the fluid shear stress decided the effective exfoliation area, which, in turn, affected the yield. The effective area increased from 5.339cm3 to 8.074cm3 with increasing ultrasonic power from 12W to 240W, corresponding to the yield increasing from 5.2% to 21.5%. The pressure fluctuation would cause the expansion of the interlayers of graphite. The degree of the expansion increased with the increase of the operating pressure but decreased beyond 12MPa. Thus, the maximum yield was obtained at 12MPa. The cavitation might be generated by ultrasound in supercritical CO2. But it is too weak to exfoliate graphite into graphene. These results provide a strategy in optimizing and scaling up the ultrasound-assisted supercritical CO2 technique for producing graphene.

Production of graphene quantum dots by ultrasound-assisted exfoliation in supercritical CO2/H2O medium

In this research, three kinds of graphene quantum dots (GQDs)—pristine graphene quantum dots (PGQDs), expanded graphene quantum dots (EGQDs) and graphene oxide quantum dots (GOQDs)—were produced from natural graphite, expanded graphite, and oxide graphite respectively in an ultrasound-assisted supercritical CO2 (scCO2)/H2O system. The effects of aqueous solution content ratio, system pressure, and ultrasonic power on the yields of different kinds of GQDs were investigated. According to these experiment results, the combination of the intense knocking force generated from high-pressure acoustic cavitation in a scCO2/H2O system and the superior penetration ability of scCO2 was considered to be the key to the successful exfoliation of such tiny pieces from bulk graphite. An interesting result was found that, contrary to common experience, the yield of PGQDs from natural graphite was much higher than that of GOQDs from graphite oxide. Based on the experimental analysis, the larger interlayer resistance of natural graphite, which hindered the insertion of scCO2 molecules, and the hydrophobic property of natural graphite surface, which made the planar more susceptible to the attack of ultrasonic collapsing bubbles, were deduced to be the two main reasons for this result. The differences in characteristics among the three kinds of GQDs were also studied and compared in this research. In our opinion, this low-cost and time-saving method may provide an alternative green route for the production of various kinds of GQDs, especially PGQDs.

Ultrasound-assisted supercritical CO2 treatment in continuous regime: Application in Saccharomyces cerevisiae inactivation

Laboratory continuous regime equipment was designed and built for supercritical CO2 microbial inactivation assisted by high power ultrasound (SC-CO2-HPU). Apple juice, previously inoculated with 1–10 × 107 CFU/ml of Saccharomyces cerevisiae, was treated in the equipment at different juice residence times (3.06–9.2 min), temperatures (31–41 °C) and pressures (100–300 bars). Inactivation ratios were fitted to a hybrid (boolean-real) model in order to study the effect of the process variables. The maximum inactivation achieved by the system was 7.8 log-cycles. The hybrid model demonstrated that HPU has a significant effect on inactivation after shorter residence times. A multi-objective optimization performed with the hybrid model showed that 6.8 log cycles of inactivation could be obtained after a minimum residence time (3.1 min) with HPU application, whereas under the same conditions but without HPU, the inactivation would be 4.3 log-cycles. Therefore, the ultrasound assisted continuous system has shown a great potential for microbial inactivation using SC-CO2 under mild process conditions.

Inkjet Printing Patterns of Highly Conductive Pristine Graphene on Flexible Substrates

Highly conductive pristine graphene electrodes were fabricated by inkjet printing using ethyl cellulose-stabilized ink prepared from pristine graphene. Pristine graphene was generated by exfoliation from graphite using ultrasound-assisted supercritical CO2. The ink, at concentrations up to 1 mg/mL, was stable for more than 9 months and had compatible fluidic characteristics for efficient and reliable inkjet printing. The inkjet printing patterns of the graphene on diverse substrates were uniform and continuous. After 30 printing passes and annealing at 300 °C for 30 min, the printed films developed a high conductivity of 9.24 × 103 S/m. The resistivity of the printed electrodes on the flexible substrates increased by less than 5% after 1000 bending cycles and by 5.3% under a folding angle of 180°. The presented exfoliated pristine graphene and the corresponding efficient methods for formulating the ink and fabricating conductive electrodes are expected to have high potential in applications involving graphene-based flexible electronic devices.

Inactivation kinetics and cell morphology of E. coli and S. cerevisiae treated with ultrasound-assisted supercritical CO2

The inactivation kinetics of Escherichia coli (E. coli) and Saccharomyces cerevisiae (S. cerevisiae) cells in apple juice subjected to supercritical carbon dioxide (SC-CO2) assisted by high power ultrasound (HPU) at different pressures (100–350bar, 36°C) and temperatures (31–41°C, 225bar) were studied. On average, shorter process times were required to achieve the total inactivation of S. cerevisiae (2–6min) in apple juice than E. coli (7min). The inactivation kinetics of E. coli and S. cerevisiae were satisfactorily described by the Peleg Type A and the Weibull model, respectively, considering temperature and pressure as model parameters. Transmission electron microscopy (TEM) and light microscopy (LM) techniques were used to study the cellular changes of SC-CO2 (350bar, 36°C, 5min) and SC-CO2+HPU (350bar, 36°C, 5min, 40W) treated cells. TEM and LM images revealed that 5min of SC-CO2 treatment generated minor morphological modifications, although no inactivation of the cells was obtained. However, 5min of SC-CO2+HPU treatment totally inactivated the population of both microorganisms. SC-CO2+HPU produced the degradation of the internal cell content and the disruption of the cell wall and plasmalemma, which prevented the possible regrowth of the cells during refrigerated storage.